APPARATUS FOR ULTRASONIC MEASUREMENT

Abstract: The sound velocity (V) of a cast iron test object is measured by ultrasonic. The sound velocity of this test object and the sound velocity (Vm) of a given metal corresponding to the test object are compared to obtain a sound velocity ratio (V/Vm). This ratio is converted to the required physical quantity (such as a graphite spheroidizing ratio, a state classification, a tensile strength, and an elongation percentage) by an empirical formula and others (530) regarding the sound velocity ratio, thus calculating the physical characteristic value of the foregoing test object. It is, therefore, possible to measure or calculate the analytical value and characteristic value of the cast iron structural state easily without any destruction.

Description: Technical Field This invention relates to an apparatus for ultrasonic measurements. More particularly, this invention relates to an apparatus with which the values of physical characteristics such as tensile strength, percent elongation and the percent spheroidicity of graphite, as well as the values of state analysis can be measured or calculated on castings such as gray cast iron, CV cast iron and spheroidal graphite cast iron by ultrasonic waves in a nondestructive manner. Background Art Both the manufacturer and the user of a machine part generally have serious concern as to whether that part is truly made of a material to specifications. This is because the use of an incorrect or defective material has high potential to lead directly to a disastrous accident due to failure of the part. Therefore, the manufacturer makes it a rule to conduct materials tests on each of the parts produced and guarantees the authenticity of an individual part by issuing a materials test performance list which certifies that it has been produced from the material to specifications. In the case of cast iron products, the materials tests to be conducted include a tensile test and a hardness test. As for spheroidal graphite iron products, an additional test is conducted to determine the percent spheroidicity of graphite. While this is generally the basic way adopted to certify the authenticity of materials, materials tests require about 3 or 4 days including the processing of test pieces and other steps, so the manufacturer has desired the development of a method that enables various materials characteristics to be estimated in a simpler and quicker way. On the side of the user, a need exists for verifying on the actual sample that the part of interest is truly made of the material to specifications. However, to prepare a test piece for materials test, the actual sample must be broken and it has been desired to develop a method by which tensile strength and other properties can satisfactorily be estimated in a nondestructive manner. As for the test to estimate the percent spheroidicity of graphite in spheroidal cast irons to be evaluated by various materials tests, an apparatus for ultrasonic measurement was developed in the early eighties that was capable of indirect determination of the percent spheroidicity of graphite using the fact that the velocity of sound (the term "sound velocity" as used herein means the speed of propagation of ultrasonic wave) varied with the shape of graphite particles. A block diagram of an apparatus that measures the sound velocity on a cast specimen by ultrasonic wave and which computes automatically the percent spheroidicity of graphite in the specimen is shown in Fig. 16. In the drawing, numeral 1 designates an ultrasonic probe, 2 is an ultrasonic flaw detector, 3 is a D/A converter circuit, 4 is a bus line, 5 is a ROM, 6 is a RAM, 7 is a keyboard (KBD), 8 is a CRT, and 9 is a microprocessor (MPU). Details of interface circuits and the like that are connected between these components are omitted from Fig. 16. Further referring to Fig. 16, numeral 51 designates a program for measuring the sound velocity, 52 is a program for computing the percent spheroidicity, 53 is a V-S conversion formula, and 54p is a main program; these programs are stored in ROM 5 and executed by MPU 9 to perform the functions they are assigned respectively. Sound velocity measuring program 51 is activated by main program 54p when it is instructed to start measurement via keyboard 7, and the ultrasonic flaw detector 2 is controlled via bus line 4 to measure the sound velocity on the specimen la. Stated more specifically, the ultrasonic wave sent from the ultrasonic probe 1 is partly reflected by the surface of the specimen la whereas the remainder propagates through the interior of the specimen la and is also reflected by its bottom. These reflected waves are detected with the ultrasonic probe 1 and upon receiving the detection signal, the ultrasonic flaw detector 2 measures the time from the point of detection of the surface reflected wave to the point of detection of the bottom reflected wave. The measured time is sent to the D/A converter circuit 3 and thence delivered to MPU 9 as a digital value. The delivered time is the time taken by the ultrasonic wave to go back and forth through the specimen la and, hence, the input digital value is divided by twice the thickness of the specimen la that is preliminarily measured and which has already been entered from the keyboard 7 and, as a result of this operation, the sound velocity on the specimen la is determined. The thus measured value of sound velocity is stored in area V in RAM 6 by means of the sound velocity measuring program 51. The program 52 for computing the percent spheroidicity is subsequently activated by the main program 54p and performs a conversion process in accordance with the V-S conversion formula 53p, thereby computing the percent spheroidicity of graphite from the value of sound velocity stored in area V. The computed percent spheroidicity of graphite is stored in area S in RAM 6. The V-S conversion formula 53p represents the relationship between the sound velocity and the percent spheroidicity of graphite for castings and it is an empirically determined conversion formula. Stated specifically, this is a regression line as constructed by plotting the results of measurement on a plurality of castings in relevant positions on a coordinate system, the horizontal axis of which may typically represent the sound velocity (V) as determined by ultrasonic measurement while the vertical axis represents the percent spheroidicity of graphite (S) as determined by direct means of measurement in accordance with the JIS (Japanese Industrial Standards)(see 53a in Fig. 17). The percent spheroidicity of graphite stored in area S which has been computed on the basis of this empirical formula is displayed on CRT 8 by the main program 54p as the result of measurement. The tensile strength of castings is measured directly by a so-called "tensile test", or a test in which the load or the like that is applied when a test piece worked to a prescribed shape breaks on a calibrated tensile tester. However, the tensile test takes time in preparing test pieces, working them, conducting the test, etc. and, hence, 3 or 4 days are necessary before the inspector knows the acceptability of the material being tested. Under the circumstances, there has been a need for a method by which the tensile strength of a cast product can be known as soon as it is produced and which enables one to be sure that the cast product has been definitely yielded from the material to specifications. The tensile strength of a cast product depends on the tensile strength of its base and the shape of fine graphite grains that are distributed in the base and, hence, the tensile strength of the cast product would be estimated by combining its hardness, which is a substitute value of the tensile strength of the base, with the percent spheroidicity of graphite which indicates the shape of graphite. On the basis of this idea, a method has been proposed that determines indirectly the tensile strength of the cast product from the value of sound velocity and its hardness. Fig. 20 is a block diagram showing an apparatus for implementing this indirect method, namely, an apparatus for ultrasonic measurement that measures the sound velocity on a cast specimen by ultrasonic wave and which computes automatically the tensile strength of the specimen from the measured value of sound velocity and the value of hardness as measured in a separate step. In Fig. 20, the constituent elements that are the same as those which are shown in Fig. 16 are identified by like numerals. In the drawing, numeral 53 refers to a classification program, 54 is a tensile strength computing program, and 55 is a main program, all of these programs being new. These programs are stored in ROM 5 and executed by MPU 9 to perform the functions they are assigned respectively. Let us describe below the operation of the apparatus shown in Fig. 20 without going into details of part of the operation that has already been explained in connection with the case shown in Fig. 16. First, the sound velocity on the specimen la is measured and stored in area V in RAM 6. Then, the percent spheroidicity of graphite is computed from the stored value of sound velocity in area V in accordance with the empirical V-S conversion formula and then stored in area S in RAM 6. Stated specifically, this V-S conversion formula is a regression line as is constructed by plotting the results of measurement on a plurality of castings in relevant positions on a coordinate system, the horizontal axis of which may typically represent the sound velocity (V) as determined by ultrasonic measurement while the vertical axis represents the percent spheroidicity of graphite (S) as determined by direct means of measurement in accordance with the JIS (see 53a in Fig. 17). When the percent spheroidicity of graphite (S) is determined, the classification program 53 is activated by the main program 55. Then, the state of castings structure is classified by the classification program 53 in accordance with the value of said percent spheroidicity of graphite (S) and a value indicating the specific type, such as gray cast iron (FC), CV graphite cast iron (FCV) or spheroidal graphite cast iron (FCD), is written into area (F). For the sake of reference, the classification according to the JIS specifications is shown in Fig. 18. In the next step, the Brinell hardness of the specimen 1a as measured with a separate hardness tester is entered via the keyboard 7 and stored in area HB. Then, the tensile strength computing program 54 is activated by the main program 55. In accordance with the formula for conversion from the product of sound velocity and hardness to tensile strength, the program 54 computes the tensile strength from the product of sound velocity (V) and Brinell hardness (HB) that have been measured on the specimen 1a. The computed tensile strength is stored in area σB' in RAM 6. It should be noted here that the above-mentioned formula for conversion to tensile strength consists of three expressions that are selectively used depending upon the state of castings structure: conversion expression 54a for FCD, conversion expression 54b for FCV, and conversion expression 54c for FC. Stated specifically, these expressions are regression lines as constructed by plotting the results of direct measurement on a plurality of castings in relevant positions on a coordinate system, the horizontal axis of which represents the product of sound velocity and hardness (V x HB) while the vertical axis represents the tensile strength (σB) (see 54a, 54b and 54c in Fig. 19). The thusly determined tensile strength (σB') and the like are displayed on CRT 8 by the main program 55 as the result of measurement. In the case of spheroidal graphite cast iron and CV graphite cast iron, it is also necessary to know their percent elongation as a characteristic value for verifying that they are made of the material to specifications. The percent elongation of castings has heretofore been measured by a method that depends on a tensile test as conducted using test pieces having a prescribed specification geometry. However, no convenient and indirect substitute method has ever been developed. As already mentioned, the material species of cast iron can be specified by the materials characteristic values that are attained by materials tests including a tensile test and the like; among them, the percent spheroidicity of graphite and the tensile strength have been the subject of reviews on proposed alternatives that rely upon the technique of measuring the sound velocity. However, sound velocity measurement using an apparatus for ultrasonic measurement involves variations in the result of measurement due to the apparatus such as those in the characteristics of the ultrasonic probe, the ultrasonic flaw detector and D/A conversion. Further, one cannot neglect the variations in the result of measurement due to the inspector such as those in the measurement of thickness of the specimen and in adjustments like the setting of the gate to the ultrasonic flaw detector. Under these circumstances, the empirical formula on the percent spheroidicity of graphite that has been attained by a certain apparatus and inspector for ultrasonic measurement (see 53a in Fig. 14) does not necessarily agree with the empirical formula that has been attained by another apparatus and inspector for ultrasonic measurement (see 53b in Fig. 15). The sound velocity that should correspond to a cast product having 70% spheroidicity of graphite is 5.56 km/s in one case but it is 5.62 km/s in the other case and the two values differ considerably. What is more, such difference occurs frequently. Therefore, in spite of the nondestructive and convenient nature of the measurement, the result is not reliable and this causes problems. Let us make further discussion by describing the specific problems as regards the measurement of the percent spheroidicity of graphite. In the conventional method and apparatus for ultrasonic measurement, an approximate value of percent spheroidicity of graphite is computed from the sound velocity in accordance with an available empirical formula. By means of this indirect technique, the state of castings structure is analyzed in a nondestructive manner. However, the relationship between the sound velocity and the percent spheroidicity of graphite is such that one does not correlate well to the other (see Fig. 17). Hence, an approximate value of the percent spheroidicity of graphite that has been attained by the empirical formula at issue or the result of analysis on the state of castings structure contains so great errors that they are by no means suitable for practical use as substitutes for the true percent spheroidicity of graphite. Under the circumstances, inspections such as nondestructive delivery or acceptance inspection of cast products and the like that hate damage have only low reliability in the results of inspection and, even if certain troubles occur in the production process, one may often overlook the adverse effects of such troubles by failing to detect them. Similar problems occur in connection with the measurement of tensile strength on castings. A plurality of formulae exist for conversion to tensile strength (see Fig. 19) and they are derived on the basis of the results of measurement on the typical states of castings structure that belong to the respective types. Since no general-purpose expression, relation or the like that unify them have yet been established, these formulae are selectively used in accordance with the specific type of castings. Under the circumstances, a cast product of an intermediate state that is not typical is dealt with by different conversion formulae depending upon in which type the cast product is classified and this causes great variations in the computed result of measurement; hence, the conversion formulae under consideration are by no means suitable for practical use as means of warranting the product and the like. There are also problems in connection with the measurement of percent elongation on castings. These are drawbacks including the following: in the state of the art, the only method that can be adopted is by conducting a tensile test and since this involves a destructive measurement, not all products in the production lot can be inspected; since the geometry of test pieces is prescribed by specifications, several days of time and cost are taken in preparation for the measurement; since a dedicated apparatus for tensile test is necessary, no inspectors other than testing organizations and the like which have suitable apparatus are able to conduct the measurement unless they ask for help by an outsider. An object, therefore, of the present invention is to solve these problems of the prior art by realizing an apparatus for ultrasonic measurement on castings by which the values of state analysis and characteristic values (e.g. the percent spheroidicity of graphite, state classification, tensile strength and percent elongation) of cast specimens can be measured or computed with high probability in a nondestructive and convenient manner. DE-A-4130908 relates to a method and apparatus for deciding acoustic anisotropy of acoustic and isotropic material using an ultrasonic technique. The acoustic anisotropic materials are generally steels and the acoustic anisotropy of steel is generated due to the fact that the crystalline state of the steel is changed or modified according to a rolling direction when the steel is formed. The present invention, in distinction, deals with castings which are not acoustic anisotropic materials. WO-A-8801054 relates to a method and apparatus for measuring hardness of a material by a ratio of acoustic velocity of a longitudinal wave to that of a transverse wave. No such acoustic velocity ratio is utilised in the present invention however. The reference J. Krautkrämer et al: "Ultrasonic Testing of Materials" 1983 Springer-Verlag Berlin Heidelberg New York, pages 528-536 discloses independent characteristic curves for each material and does not refer to the physical characteristics of cast products which can be expressed with a single characteristic curve as disclosed herein in the present invention. Disclosure of Invention According to this invention there is provided an apparatus for ultrasonic measurement as claimed in claim 1 herein. Various embodiments of the invention are defined in the dependent claims. In the apparatus for ultrasonic measurement according to this invention which relates to the measurement to a physical characteristic of castings, an empirical formula and the like are specified on the basis of the relationship a characteristic value of a casting product has with respect to the sound velocity ratio between a steel product and said cast product. It should be mentioned here that variations in the value of measurement which depend on the apparatus or inspector have a particular tendency for each apparatus or the like. Stated specifically, even the sound velocities as measured on a cast product and a steel product by means of the same apparatus or the like have variations of the same tendency. Therefore, if the ratio between the measured values is taken, the corresponding variations will cancel each other. Hence, the sound velocity ratio between a steel product and a cast product is hardly affected by the influences due to variations in the apparatus and the like. Consequently, the empirical formula and the like that are based on the correlation between the sound velocity ratio and a characteristic value has wide range of applications and is effective even for other apparatus or the like than that which has been used in determining said empirical formula and the like. Further, the apparatus of the present invention for ultrasonic measurement of a physical characteristic of castings have the advantage that when measuring or computing a characteristic value of a cast specimen, the sound velocity in a steel product is measured separately or an already measured value of sound velocity for the steel product is entered separately as input data and, on the basis of the measured sound velocity in the specimen, the sound velocity ratio between the specimen and the steel product is computed. In this case, too, the sound velocity ratio is substantially free from variations since it is determined by the same apparatus and the like. Stated more specifically, the empirical formula and the like which are based on the relationship a characteristic value as determined by a direct method for the measurement of said characteristic value has with respect to the sound velocity ratio are free from variations and have a wide range of applications in that they can be used with any type of apparatus for ultrasonic measurement and, once said empirical formula and the like are attained, measurements that involve destruction are not necessary. Further, when measuring a physical characteristic of a cast product as an actual product, the sound velocity in the cast product is normalized by the sound velocity in the steel product to yield the sound velocity ratio and, in accordance with the empirical formula of interest, a physical characteristic value of the cast product is computed from the sound velocity ratio. In this way, the effect of variations due to the apparatus for ultrasonic measurement under consideration and the inspector can be eliminated. Therefore, the physical characteristic value is computed from the variation-free sound velocity ratio in accordance with the general-purpose formula. As a result, the effect due to similarities or dissimilarities in the apparatus for ultrasonic measurement or the inspector is so much reduced that the physical characteristic value as associated with the cast specimen can be measured or computed with high probability by means of ultrasonic measurement in a nondestructive and convenient manner. In the present invention, analysis may be performed on the basis of both the percent carbon content and the sound velocity or sound velocity ratio (which are hereunder abbreviated as the "sound velocity or the like"). To this end, the state of castings structure as it relates to the percent carbon content and the sound velocity or the like is measured by a direct means or the like and the formula or means of conversion that represent the relationship between those factors is specified experimentally. By thusly performing state classification based not only on the sound velocity or the like but also on the percent carbon content, it is now possible to clearly classify the state of castings structure which has heretofore been difficult to classify, in particular, the state of castings structure as regards the morphology of graphite or the like. Then, in accordance with the list or the like which has been determined by the direct method of measurement, the state of castings structure of the specimen is evaluated on the basis of the sound velocity or the like that have been determined by ultrasonic wave and its percent carbon content. Thus, a close analysis is performed on the basis of not only the sound velocity or the like but also the percent carbon content and, therefore, in spite of its indirect nature, the analysis permits the state of castings structure to be estimated in a closer and more correct way than has heretofore been possible. Consequently, the state of castings structure that is associated with the cast specimen can be measured or analyzed with high probability by means of ultrasonic measurement in a nondestructive and convenient manner. Thus, in various embodiments of the present invention, the apparatus for ultrasonic measurement computes the tensile strength, particularly on castings, by ultrasonic measurement, and the computation of tensile strength is performed on the basis of the percent carbon content, the hardness and the sound velocity or sound velocity ratio. To perform this computation or the like, the tensile strength of the cast product of interest as it relates to the percent carbon content, the hardness and the sound velocity or the like is measured by a direct means or the like and the formula or means of conversion that represent the relationship between those factors is specified preliminarily on an experimental basis. By thusly establishing correlation to the tensile strength based not only on the sound velocity and hardness but also on the percent carbon content, the overlap between data of measurement of tensile strength will be eliminated not only for castings in a typical state but also for castings in an intermediate state and, as a result, the data to be measured can be clearly correlated to the data to be computed. In accordance with the empirical formula or the like under consideration, the tensile strength of the cast specimen is computed from the percent carbon content and the hardness of said specimen and the sound velocity or the like in it and, by so doing, the analysis, even though it is an indirect method, permits the tensile strength of the cast product to be estimated in a closer and more correct way than has heretofore been possible. Consequently, the tensile strength of the cast specimen, which is one of its characteristic values, can be measured or computed with high probability by means of ultrasonic measurement in a nondestructive and convenient manner. Thus, in other embodiments of the present invention, the apparatus for ultrasonic measurement computes the percent elongation, particularly on castings, by ultrasonic measurement, and the computation of the percent elongation of castings is performed on the basis of the percent carbon content, the hardness and the sound velocity or sound velocity ratio (or in combination of these with the percent copper content). To perform this computation or the like, the percent elongation of the cast product of interest as it relates to the percent carbon content, the hardness and the sound velocity or the like (or in combination of these with the percent copper content) is measured by a direct means or the like and the formula or means of conversion that represent the relationship between those factors is specified preliminarily on an experimental basis. By thusly establishing correlation to the percent elongation based not only on the sound velocity and hardness but also on the percent carbon content (or in combination of these with the percent copper content), the data to be measured can be clearly correlated to the data to be computed although these data have not heretofore been correlated to each other. In accordance with the empirical formula or the like under consideration, the percent elongation of the cast specimen is computed from the percent carbon content and the hardness of said specimen and the sound velocity or the like in it (or in combination of these with the percent copper content) and, by so doing, the percent elongation of the cast product can be estimated. In other words, the percent elongation of castings can be measured indirectly although this has heretofore been impossible. Consequently, the percent elongation of the cast specimen, which is one of its characteristic values, can be measured or computed with high probability by means of ultrasonic measurement in a nondestructive and convenient manner. If, in addition to the percent carbon content, the percent copper content is also included as a parameter, there is achieved a particular advantage in that even in the case where the cast product to be analyzed in a copper-containing cast iron, its percent elongation can be measured in a nondestructive and convenient manner. It should be noted here in this invention, the percent carbon content may be replaced by the carbon equivalent. It should also be noted that while the above-described empirical formula or means of conversion possesses a characteristic function, a table and a processing procedure, the concept of this characteristic function or table embraces various items such as diagrams, graphic charts, lists, approximations and so-called sequences, maps, tables, etc. that are related to computer programs; further, the concept of processing procedure embraces means of conversion such as a computing procedure, a mathematical operation, a process, address tables, etc. that use or modify such processing procedure. The percent carbon content (or its combination with the percent copper content) which is held to be necessary for the present invention is of course familiar to the manufacturer who presets the proportions of components in the casting material but usually the customer who accepts the cast product is also in the position to be knowledgeable of that factor as one of the conditions for placement of order; therefore, aside from the special case where a cast product of unknown origin has to be analyzed for research and experimental purposes, the factor under consideration will be no impediment to practical to implementation of the present invention. Measurement of the hardness of the specimen also causes no inconvenience since this can be measured with a hardness meter that is simple to operate. Brief Description of Drawings Fig. 1 is a block diagram showing the first example of the apparatus for ultrasonic measurement which features the constitution of the present invention and which computes automatically the percent spheroidicity of graphite as one of the physical characteristic values of a cast product: Fig. 2 is a block diagram showing the second example of the apparatus for ultrasonic measurement which features the constitution of the present invention and which analyzes automatically the state of castings structure; Fig. 3, relating to the second example, shows an example of the associated conversion map; Fig. 4 is a block diagram showing the third example of the apparatus for ultrasonic measurement which features the constitution of the present invention and which measures or computes automatically the tensile strength of a cast product: Fig. 5, relating to the third example, shows in graphic form the correspondence between the computed index value α' of the cast product (horizontal axis) and the measured hardness coefficient m (vertical axis); Fig. 6, relating to the third example, shows in graphic form the correspondence between the computed tensile strength σB' (horizontal axis) and the measured tensile strength σB (vertical axis); Fig. 7 is a block diagram showing the fourth example of the apparatus for ultrasonic measurement which features the constitution of the present invention and which measures or computes automatically the percent elongation of a cast product; Fig. 8, relating to the fourth example, shows in graphic form the correspondence between the computed index value α' (horizontal axis) and the product of tensile strength σB' and percent elongation ∈ (σB' x ∈) (vertical axis); Fig. 9, relating to the fourth example, shows in graphic form the correspondence between the computed percent elongation ∈' (horizontal axis) and the measured percent elongation ∈; Fig. 10 is a block diagram showing the fifth example of the apparatus for ultrasonic measurement which features the constitution of the present invention and which measures or computes automatically the percent elongation of a cast product in the case where it is a copper-containing cast iron; Fig. 11, relating to the fifth example, shows in graphic form the correspondence between the computed value (∈'/(2 x Cu)) (horizontal axis) and the measured percent elongation ∈ (vertical axis); Fig. 12, relating to the fifth example, shows in graphic form the correspondence between the computed percent elongation ∈" (horizontal axis) and the measured percent elongation ∈; Fig. 13 is a diagrammatic presentation of examples of the morphology of graphite in castings; Fig. 14 is an example of the correlationship between the sound velocity in castings and the percent spheroidicity of graphite; Fig. 15 is another example of the correlationship between the sound velocity in castings and the percent spheroidicity of graphite; Fig. 16 is a block diagram of a conventional apparatus for measuring the percent spheroidicity of graphite; Fig. 17 is yet another example of the correlationship between the sound velocity in castings and the percent spheroidicity of graphite; Fig. 18 is a chart illustrating the morphology and classification of graphite types in castings; Fig. 19 shows in graphic form the correspondence between (sound velocity x hardness) and tensile strength; and Fig. 20 is a block diagram of a conventional apparatus for measuring the tensile strength of castings. Best Mode for Carrying Out the Invention The first example of the present invention is described below in detail with reference to drawings. Fig. 1 is a block diagram showing an apparatus for implementing the method of the present invention for ultrasonic measurement of a physical characteristic of castings, namely, an apparatus for ultrasonic measurement that measures the sound velocity in a cast specimen by ultrasonic wave and which computes automatically the percent spheroidicity of graphite in the specimen. In the diagram, numeral 1 designates an ultrasonic probe, 2 an ultrasonic flaw detector, 3 a D/A converter circuit, 4 a bus line, 5 a ROM, 6 a RAM, 7 a keyboard (KBD), 8 a CRT, and 9 is a microprocessor (MPU). Details of interface circuits and the like that are connected between these components are omitted from Fig. 1. Further referring to Fig. 1, numeral 51 designates a program for measuring the sound velocity 511 is a program for setting the sound velocity in steel, 512 is a program for normalizing the sound velocity, 523 is a program for computing the percent spheroidicity, 530 is a (V/Vm) - S conversion formula, and 550 is a main program; these programs are stored in ROM 5 and executed by MPU 9 to perform the functions they are assigned respectively. It should be noted that ultrasonic probe 1 through microprocessor 9 and sound velocity measuring program 51 have the same configurations as in the prior art and, hence, they are identified by like numerals and their explanation is not repeated. The main program 550 is an overall measurement managing program and has two selectable modes, namely, the first mode for setting the sound velocity in steel and the second mode for measuring the percent spheroidicity of graphite in castings. In response to either mode, the main program activates other programs and controls the order in which they are executed. The sound-velocity-in-steel program 511 is a sub-program for setting the sound velocity in steel which serves as a reference value. The value of sound velocity that is measured with the sound velocity measuring program 51 and which is stored in area V is transferred by the program 511 into area Vm in RAM 6, where it is set as the sound velocity in steel. The sound velocity normalizing program 512 is a sub-program for computing the sound velocity ratio. The value of sound velocity that is measured with the sound velocity measuring program 51 and which is stored in area V is divided by the sound velocity in steel which is stored as the reference value in area Vm and the thusly computed sound velocity ratio is placed by the program 512 in area (V/Vm) in RAM 6. The percent spheroidicity computing program 523 is a sub-program for computing the percent spheroidicity of graphite; it performs a conversion process in accordance with (V/Vm) - S conversion formula 530 and computes the percent spheroidicity of graphite from the value of sound velocity ratio in area (V/Vm). The thusly computed percent spheroidicity of graphite is stored in area S in RAM 6. The (V/Vm) - S conversion formula 530 is an experimentally predetermined conversion formula and represents the relationship the percent spheroidicity of graphite (S) has with respect to the sound velocity ratio between the steel and cast product ((V/Vm)). Stated more specifically, provide first a number of cast products that resemble in shape as closely as possible, and also provide at least one steel product. Then, measure the sound velocity in these cast and steel products with an apparatus for ultrasonic measurement, and compute the sound velocity ratio between the cast and steel products. Further, measure the percent spheroidicity of graphite in each cast product by a direct method in accordance with or as adapted from JIS specifications. It should be noted that in order to insure agreement in the tendency of variations, the series of destructive measurements are desirably performed with the same apparatus for ultrasonic measurement by the same inspector if this is possible at all. Since this direct measurement is time-consuming, it is recommended that another series of measurements be performed in parallel on another group of cast products and on at least one steel product by another set of apparatus for ultrasonic measurement and inspector so as to yield a large number of results of measurement. The thusly obtained large number of results of measurement are plotted in relevant positions on a coordinate system, the horizontal axis of which may typically represent the sound velocity ratio ((V/Vm)) while the vertical axis represents the percent spheroidicity of graphite (S) as measured by direct means of measurement. In this case, the sound velocity ratio as the normalized sound velocity is taken on the horizontal axis and since it is free from any effects due to the apparatus and inspector, the results of the above-mentioned series of measurement and those of another series of measurement may be presented on one graphic chart without causing any inconvenience. Hence, the distribution diagram having its statistical reliability improved as a result of plotting the results of a large number of measurements can be expressed by a regression line or approximated by a kinked line to yield the (V/Vm) - S conversion formula 530. For the same reason, the conversion formula 530 is in no way limited to a particular apparatus and once it is computed, it is applicable as such to any other types of apparatus for ultrasonic measurement. With this configuration, the process of measuring the percent spheroidicity of graphite in castings starts with measuring the sound velocity in a steel product in mode 1 (mode for setting the sound velocity in steel), followed by processing cast products successively in mode 2 (mode for measuring the percent spheroidicity of graphite in castings). Stated in detail, a steel product that is similar in shape to the cast products as closely as possible is provided as specimen la. Then, instruct the main program 550 to perform processing in mode 1. In this mode 1, the main program 550 activates the sound velocity measuring program 51 and the sound velocity in the steel product is stored in area V. Then, the sound-velocity-in-steel setting program 511 as activated by the main program 550 sets the resulting sound velocity in steel product in area Vm. In the case where the sound velocity in steel was already measured under the same conditions on the previous day or the like, the sound velocity measurement may be omitted and alternatively a predetermined value of sound velocity in steel that has been entered via keyboard 7 may be set in area Vm. In the next place, use one of the cast products as specimen la. Then, instruct the main program 550 to perform processing in mode 2. In this mode 2, the main program 550 activates the sound velocity measuring program 51 and the sound velocity in the cast product being analyzed is stored in area V. Thereafter, the main program 550 activates the sound velocity normalizing program 512 and the sound velocity ratio as computed from the sound velocity (V) in the cast product being analyzed and the sound velocity (Vm) in steel is set in area (V/Vm). Subsequently, the percent spheroidicity computing program 523 is activated and this program 523 performs a conversion process in accordance with the (V/Vm) - S conversion formula 530 and computes the percent spheroidicity of graphite (S) from the value of sound velocity ratio in area (V/Vm). The thusly computed percent spheroidicity of graphite is stored in area S in RAM 6. The reliable percent spheroidicity of graphite as computed from the normalized sound velocity ratio on the basis of the normalized empirical formula 530 is displayed on CRT 8 by the main program 550 as the result of measurement. Thus, an approximate value of the percent spheroidicity of graphite in one cast product can be measured with high reliability in a nondestructive and easy manner. Since the sound velocity in the steel product need be measured only once, each of the remaining cast products may successively be used as specimen la for subsequent measurements of the percent spheroidicity of graphite. It should be mentioned that the percent spheroidicity of graphite is given to illustrate one characteristic value in connection with the physical characteristics of castings and the operational effect of normalization by the sound velocity in steel will equally hold with other physical characteristic values of castings. The second example of the present invention is described below in detail with reference to drawings. Fig. 2 is a block diagram showing an apparatus for implementing the method of the present invention for analyzing the state of castings structure, namely, an apparatus for ultrasonic measurement that measures the sound velocity in a cast specimen by ultrasonic wave and which analyzes automatically the state of castings structure in the specimen. To explain the constituent elements that differ from those shown in Fig. 1, the percent spheroidicity computing program 523 is replaced by a state evaluating program 523p and the (V/Vm) - S conversion map 530 is replaced by a ((V/Vm), C) - S' conversion map 530; the program is stored in ROM 5 and processed for execution by MPU 9 to perform the function it is assigned. The main program 550 has both the first mode for setting the sound velocity in steel and the second mode for analyzing the state of castings structure. In response to either mode, the main program 550 activates other programs and controls the order in which they are executed. The state evaluating program 523p is a sub-program for evaluating the state of castings structure; it performs a conversion process in accordance with the ((V/Vm), C) - S' conversion map 530p and evaluates the state of castings structure on the basis of both the value of sound velocity ratio in area (V/Vm) and the value of percent carbon content in area C. The thusly evaluated state of castings structure is stored in area S' in RAM 6. The ((V/Vm), C) - S' conversion map 530p is an experimentally predetermined conversion map and represents the relationship the state of castings structure (S') has with respect to the sound velocity ratio ((V/Vm)) between the steel and cast product and to the percent carbon content of the cast product under analysis. Stated more specifically, provide first a number of cast products that resemble in shape as closely as possible but which differ in percent carbon content, and also provide at least one steel product. Then, measure the sound velocity in these cast and steel products with an apparatus for ultrasonic measurement, and compute the sound velocity ratio between the cast and steel product. Further, use a direct method in accordance with or as adapted from JIS specifications to measure the state of castings structure, for instance, to check whether the morphology of graphite grains in each cast product is like flakes, vermicular or spheroids (FC, FCV, FCD). It should be noted that in order to insure agreement in the tendency of variations, the series of destructive measurements are desirably performed with the same apparatus for ultrasonic measurement by the same inspector if this is possible at all. Since this direct measurement is time-consuming, it is recommended that another series of measurements be performed in parallel on another group of cast products and on at least one steel product by another set of apparatus for ultrasonic measurement and inspector so as to yield a large number of results of measurement. The thusly obtained large number of results of measurement are plotted in a coordinate system, with the horizontal axis typically plotting the sound velocity ratio ((V/Vm)) and the vertical axis plotting the percent carbon content (C), and the state of castings structure (FC, FCV, FCD) as evaluated by a direct means of measurement is set in a coordinate position that corresponds to the sound velocity ratio and the percent carbon content at the time of measurement under consideration. If, in this case, the sound velocity ratio is plotted on the horizontal line, any effects due to the apparatus and inspector are eliminated and an even higher probability is assured than in the case where the sound velocity is merely adopted. It is recommended that the state of castings structure to be set is preferably freed of variable components by performing statistical processing such as decision making by majority, averaging, local averaging or regression analysis on the results of the largest possible number of measurements. The state of castings structure may be exemplified by the hardness coefficient (m) and the above-mentioned morphological classification of graphite grains (FC, FCV, FCD); if desired, the percent spheroidicity of graphite in accordance with specifications of the JIS (Japanese Industrial Standards) may be adopted. The adoption of the map which is based on the sound velocity and percent carbon content enables various regions to be clearly separated although they have been found to overlap partly according to the conventional classification which is based solely on the sound velocity. Further, in addition, it is possible to classify even the state of castings structure in a region intermediate between two regions FC and FCV (see region FC' in Fig. 3). With this configuration, the process of measuring the state of castings structure starts with measuring the sound velocity in a steel product in mode 1 (mode for setting the sound velocity in steel), followed by processing cast products successively in mode 2 (mode for measuring the percent spheroidicity of graphite in castings). To state in detail without caring about partial overlap with the already-described first example, a steel product that is similar in shape to the cast products as closely as possible is provided as specimen la. Then, instruct the main program 550 to perform processing in mode 1. In this mode 1, the main program 550 activates the sound velocity measuring program 51 and the sound velocity in the steel product is stored in area V. Then, the sound-velocity-in-steel setting program 511 as activated by the main program 550 sets the resulting sound velocity in steel product in area Vm. In the case where the sound velocity in steel was already measured under the same conditions on the previous day or the like, the sound velocity measurement may be omitted and alternatively a predetermined value of sound velocity in steel that has been entered via keyboard 7 may be set in area Vm. In the next place, use one of the cast products as specimen 1a. Then, instruct the main program 550 to perform processing in mode 2. In the first step of this mode 2, the percent carbon content of cast specimen 1a (which is known as one of the data for the casting operation) is entered via keyboard 7 and set in area (C). If this data entry is omitted, processing is performed on the assumption that the percent carbon content is the same as that of the previous specimen. In the subsequent second step, the main program 550 activates the sound velocity measuring program 51 and the sound velocity in the cast product being analyzed is stored in area V. Thereafter, in the third step, the main program 550 activates the sound velocity normalizing program 512 and the sound velocity ratio as computed from the sound velocity (V) in the cast product being analyzed and the sound velocity (Vm) in steel is set in area (V/Vm). Subsequently, in the fourth step, the state evaluating program 523p is activated and this program 523p performs a conversion process in accordance with the ((V/Vm), C) - S' conversion map 530p and evaluates the state of castings structure in terms of the value of the position in the map that corresponds to the value of sound velocity ratio in area (V/Vm) and the value of percent carbon content in area (C). The thusly evaluated state of castings structure is stored in area S in RAM 6. The reliable state of castings structure as evaluated by close classification with respect to the sound velocity ratio and percent carbon content on the basis of the conversion map 530p is displayed on CRT 8 by the main program 550 as the result of measurement. For instance, if heats that have been adjusted in components and the like with a view to producing spheroidal graphite cast iron having high toughness turn into CV cast iron of lower toughness or flaky cast iron as a result of delay in processing time or the like (see arrows 520f and 530g in Fig. 3), this fact and the like can be detected in a positive and nondestructive manner. Thus, the state of castings structure can be analyzed on a single cast product with high reliability in a nondestructive and easy manner. Since the sound velocity in the steel product need be measured only once, each of the remaining cast products may successively be used as specimen 1a for subsequent analyses of the state of castings structure on those products. The third example of the present invention is described below with reference to drawings. Fig. 4 is a block diagram of an apparatus for ultrasonic measurement that measures the sound velocity in a cast specimen by ultrasonic wave and which computes automatically the tensile strength of that specimen. The configuration of this apparatus is basically similar to that of the already-described second example except that the state evaluating program 523 in the second example is replaced by a new program 540 for computing the tensile strength and except for the associated parts. To explain the constituent elements that differ from those shown in Fig. 2, the tensile strength computing program 540 is a sub-program for computing the tensile strength of castings; it performs a specified conversion process to compute the tensile strength of a cast product on the basis of three values: the value of sound velocity ratio in area (V/Vm), the value of percent carbon content in area C, and the value of Brinell hardness in area HB. The thusly computed tensile strength of the cast product is stored in area σB' in RAM 6. The specified conversion process is an experimentally predetermined computing procedure and this is a procedure for computing the tensile strength (σB') of a cast product on the basis of the relationship its tensile strength (σB) has with respect to the sound velocity ratio (V/Vm) between the steel and cast product, the percent carbon content (C) of the cast product under analysis, and its Brinell hardness (HB). This computing procedure comprises mainly an α' computing procedure 540a, an m' computing procedure 540b and a σB' computing procedure 540c. In the example under discussion, these procedures are incorporated as part of the tensile strength computing program 540 and they are executed in the order written. The α' computing procedure 540a is so specified as to express the relationship the state of castings structure (FCD, FCV, FC) has with respect to the sound velocity ratio ((V/Vm)) and the percent carbon content (C). The actual process of specifying the computing procedure of interest starts with providing a number of cast products that resemble in shape as closely as possible but which differ in percent carbon content, and also providing at least one steel product. Then, measure the sound velocity in these cast and steel products with an apparatus for ultrasonic measurement, and compute the sound velocity ratio between the cast and steel products. Further, use a direct method in accordance with or as adapted from JIS specifications to measure the state of castings structure, for instance, to check whether the morphology of graphite grains in each cast product is like flakes, vermicular or spheroids (FC, FCV, FCD) or even whether they are in a state intermediate between these types. It should be noted that in order to insure agreement in the tendency of variations, the series of destructive measurements are desirably performed with the same apparatus for ultrasonic measurement by the same inspector if this is possible at all. Since this direct measurement is time-consuming, it is recommended that another series of measurements be performed in parallel on another group of cast products and at least one steel product by another set of apparatus for ultrasonic measurement and inspector so as to yield a large number of results of measurement. It is also recommended that the index value for the state of castings structure to be set is preferably one that is freed of variable components by performing statistical processing such as decision making by majority, averaging, local averaging or regression analysis on the results of the largest possible number of measurements. The α' computing procedure 540a as a specific example of the way to compute the index value proceeds as follows. First, on the basis of the sound velocity ratio ((V/Vm)) and the percent carbon content (C), the density ρ is computed by the equation: ρ = 8.435 - 0.374 x (C) Then, the graphite area factor is computed by the equation: fg = 1.095 - 0.1395 x ρ Finally, α' is computed by the equation: α' = ((V/Vm) -2 x (7.86/ρ)-1)/fg It should be noted that 7.86 in the above equation is the value that is equivalent to the specific gravity of the steel product or the castings matrix (base). The thusly computed α' is the index value for the state of castings structure that is based on the morphological classification of graphite grains in the cast product (FC, FCV, FCD) and yet it is capable of clearly identifying a state intermediate between those types (see the horizontal axis α' of Fig. 5 and the distribution of data on the measurement). The m' computing procedure 540b is a procedure for computing the hardness coefficient m' from the index value α'. The hardness coefficient m' is an estimated value of hardness coefficient m, namely (tensile strength σB/hardness HB) and it is determined from the index value α' in accordance with the relationship between index value α' and hardness coefficient m that has been verified preliminarily on an experimental basis. This relationship is shown in Fig. 5, with the index value α' plotted on the horizontal axis and the hardness coefficient m on the vertical axis. Since there is a strong correlation between α' and m in Fig. 5, the relationship under consideration can be approximated by a kinked line or the like. To give a specific example, the m' computing procedure 540b computes the hardness coefficient m' by the following criteria: in the case of α' < 3.15, computation is performed by the equation: m' = 0.3920 - 0.0512 x α' in the case of 3.15 ≤ α' ≤ 4.00, computation is performed by the equation: m' = 0.2306 in the case of 4.00 < α', computation is performed by the equation: m' = 0.3000 - 0.0173 x α' The hardness coefficient m' that is computed by any of these equations provides a very good estimation of the actual hardness coefficient m. The σB' computing procedure 540c is such that the tensile strength σB' as an estimated value of tensile strength σB is computed from the hardness HB and hardness coefficient m' on the basis of the formula for defining hardness coefficient m, namely, (m = σB/HB). Stated specifically, the procedure 540c computes the tensile strength σB' by the equation σB' = m' x HB The hardness coefficient m is introduced to replace the cumbersome measurement of the true percent spheroidicity of graphite by the easier way of computation or estimation on the basis of a tensile fracture test. In the example under discussion, the role of this coefficient is expanded on the basis of experimental results and from the relationship it has, the tensile strength σB' is computed in the manner described above. With this configuration, the process of measuring the tensile strength of a cast product starts with measuring the sound velocity in a steel product in mode 1 (mode for setting the sound velocity in steel), followed by processing cast products successively in mode 2 (mode for measuring the percent spheroidicity of graphite in castings). Mode 1 is entirely the same as in the previous examples and, hence, need not be described in detail. It should only be mentioned that in mode 1, the sound velocity in the steel product is set in area Vm. In the next place, use one of the cast products as specimen la. Then, instruct the main program 550 to perform processing in mode 2. In the first step of this mode 2, the percent carbon content of cast specimen 1a (which is known as one of the data for the casting operation) is entered via keyboard 7 and set in area (C). If this data entry is omitted, processing is performed on the assumption that the percent carbon content is the same as that of the previous specimen. In the subsequent second step, the main program 550 activates the sound velocity measuring program 51 and the sound velocity in the cast product being analyzed is stored in area V. If the specimen 1a is in the as-cast state, the value in area V may be left as it is. However, in a different case like the one where the specimen 1a is an annealed cast product, 130 (m/s) is added as a correction value to the value of sound velocity in area V; if the specimen 1a is a normalized cast product, 400 (m/s) may typically be added. This correction helps further improve the probability of the computed value. Thereafter, in the third step, the main program 550 activates the sound velocity normalizing program 512 and the sound velocity ratio as computed from the sound velocity (V) in the cast product being analyzed and the sound velocity (Vm) in steel is set in area (V/Vm). Subsequently, in the fourth step, th Brinell hardness of the specimen 1a as measured with a separate hardness tester is entered via keyboard 7 and set in area HB. Then, the tensile strength computing program 540 is activated by the main program 550. The tensile strength computing program 540 executes the α' computing procedure 540a, m' computing procedure 540b and σB' computing procedure 540c in that order and computes the tensile strength on the basis of the sound velocity ratio (V/Vm), percent carbon content (C) and Brinell hardness (HB) that have been measured on the specimen la. The thusly computed tensile strength is stored in area σB' in RAM 6. The fourth step is described below in detail. First, the index value α' is computed by the α' computing procedure 540a on the basis of the sound velocity ratio (V/Vm) and percent carbon content (C). It should be noted here that if C is smaller than 9.0495 - 7.1189 x (V/Vm) when computing α', the percent carbon content (C) must be replaced beforehand by the value expressed by the equation: 8.7995 - 7.1189 x (V/Vm) This condition is applicable to the case where the cast product under analysis corresponds to gray cast iron (FC), particularly to a typical example of it; this correction of C helps further improve the probability of the computed value. In the next place, the m' computing procedure 540b computes the hardness coefficient m' from the above α'. Then, except in the case of the already evaluated gray cast iron which is mentioned above, the state of castings structure is classified on the basis of the value index α' or the value of hardness coefficient m'. For example, depending upon m' and if 0.27 ≤ m', the cast product under analysis is evaluated as being made of spheroidal graphite cast iron (FCD); in the case of 0.22 ≤ m' < 0.27, it is found to be made of worm-like graphite cast iron (FCV); and if m' < 0.22, it is found to be made of flaky graphite cast iron (FCD). Finally, the tensile strength (σB') is computed from the above-mentioned hardness coefficient m' and Brinell hardness (HB) by the σB' computing procedure 540c. The correspondence between the thusly computed tensile strength (σB') and the tensile strength (σB) that was measured directly by a tensile test is shown in Fig. 6. As is clear from the Fig. 6 graph, the tensile strength of castings that was computed by means of the apparatus of the present invention for ultrasonic measurement has an extremely high probability. For instance, the estimated precision based on variance is 2.15 (kgf/mm 2 ) and this is comparable to the estimated precision 1.93 (kgf/mm 2 ) for normalized or annealed steel products, which is used extensively in designs using steels, whereas it is by far better than the estimated precision 3.41 (kgf/mm 2 ) for quenched and tempered steel products, which is also used extensively. This tensile strength (σB') as well as the state of castings structure (FCD, FCV, FC) are displayed on CRT 8 by the main program 550 as the result of measurement and analysis. This insures the following and other facts to be detected in a positive and nondestructive manner: for example, heats that have been adjusted in components and the like with a view to producing spheroidal graphite cast iron having high tensile strength or toughness turn out to be short of the intended tensile strength or, in certain cases, turn into CV cast iron or flaky cast iron of lower strength as a result of delay in processing time or the like. Thus, the tensile strength of castings can be measured or computed on a single cast product with high reliability in a nondestructive and easy manner. In addition, the sound velocity in the steel product need be measured only once and, hence, each of the remaining cast products may successively be used as specimen 1a for subsequent analyses of the state of castings structure and measurements of tensile strength on those products. The fourth example of the present invention is described below with reference to drawings. Fig. 7 is a block diagram of an apparatus for implementing the method of the present invention for measuring the percent elongation of castings, namely, an apparatus for ultrasonic measurement that measures the sound velocity in a cast specimen by ultrasonic wave and which computes automatically the percent elongation of that specimen. The configuration of this apparatus is basically similar to that of the already-described third example except that the tensile strength computing program 540 in the third example is replaced by a new program 542 for computing the percent elongation and except for the associated parts. The following explanation centers on the differences from the example shown in Fig. 4. The percent elongation computing program 542 is substantially similar to the already-described tensile strength computing program 540 as regards the basic configuration and the technical rationale; it is a sub-program that performs a specified measurement and a specified conversion process to compute the percent elongation of a cast product. Further, the specific configurations of the two programs are similar in that each has the α' computing procedure 540a, m' computing procedure 540b and σB' computing procedure 540c and that these procedures are executed in the order written. However, the program 542 differs from the tensile strength computing program 540 in that it has an additional ∈' computing procedure 540d for computing the percent elongation in the last step. Stated more specifically, the program 542 performs a specified conversion process and computes the percent elongation of a cast product on the basis of three values: the value of sound velocity ratio in area (V/Vm), the value of percent carbon content in area C, and the value of Brinell hardness in area HB. The thusly computed elongation of the cast product is stored in area ∈' in RAM 6. The specified conversion process under consideration is an experimentally predetermined computing procedure and this is a procedure for computing the percent elongation (∈') of the cast product on the basis of the relationship its percent elongation (∈) has with respect to the sound velocity ratio ((V/Vm)) between the steel and the cast product, the percent carbon content (C) of the cast product under analysis, and its Brinell hardness (HB). This computing procedure comprises mainly the α' computing procedure 540a, m' computing procedure 540b, σB' computing procedure 540c, and the ∈' computing procedure 540d, and these procedures are executed in the order written. All procedures except the ∈' computing procedure 540d have already been described above and discussion of them will not be repeated below. The ∈' computing procedure 540d is a procedure for computing the percent elongation ∈' from the index value α' and the estimated tensile strength σB'. The percent elongation ∈' is an estimated value of the actual percent elongation ∈ and it is determined from the index value α' (which has been verified preliminarily on an experimental basis) and the tensile strength σB' (which has been computed on the basis of α') in accordance with the relationship between the index value α', the tensile strength σB' and the percent elongation ∈ which has been determined in a tensile test. This relationship is shown in Fig. 8, with the index value α' being plotted on the horizontal axis and the product of tensile strength σB' and percent elongation ∈ (σB' x ∈) on the vertical axis. Since there is a strong correlation between α' and (σB' x ∈) in Fig. 8, the relationship under consideration can be approximated by a kinked line or the like. To give a specific example, the ∈' computing procedure 540d computes the percent elongation ∈' (in %) by the following criteria: if α' < 2.68, computation is performed by the equation: ∈' = (3085-1035.6 x α')/σB' if α' ≥ 2.68, computation is performed by the equation: ∈' = (676.3-137.2 x α')/σB' Obviously, if these equations are rewritten by expressing the tensile strength σB' in terms of the above-described index value α', one can readily obtain formulae for computing the percent elongation ∈' solely on the basis of the index value α'. The thusly computed percent elongation ∈' provides a very good estimation of the actual percent elongation ∈. With this configuration, the process of measuring the percent elongation of a cast product starts with measuring the sound velocity in a steel product in mode 1 (mode for setting the sound velocity in steel), followed by processing cast products successively in mode 2 (mode for measuring the percent elongation of castings). Again, details of the process are substantially similar to the case of the third example and explanation of the overlapping portions will not be repeated. The only difference from the third example is that the tensile strength of a cast product is not the sole factor to be computed in mode 2 and that the percent elongation (∈') which is one characteristic value of the cast product is also computed by the percent elongation computing program 542 and outputted as the result of measurement and analysis. Further discussion is made of this point. In mode 2, the percent elongation computing program 542, like the tensile strength computing program 540, executes the α' computing procedure 540a, m' computing procedure 540b and σB' computing procedure 540c in that order and computes the index value (α') and tensile strength (σB') from the sound velocity ratio (V/Vm), percent carbon content (C) and Brinell hardness (HB) which have been measured on the specimen la. Subsequently, the ∈' computing procedure computes the percent elongation (∈') from the above-mentioned index value (α') and tensile strength (σB'). The correspondence between the thusly computed percent elongation (∈') and the percent elongation (∈) that was measured directly by a tensile test is shown in Fig. 9. As is clear from the Fig. 9 graph, the percent elongation of castings that was computed by means of the apparatus of the present invention for ultrasonic measurement has a fairly high probability. This percent elongation (∈') as well as the state of castings structure (FCD, FCV, FC) are displayed on CRT 8 by the main program 550 as the result of measurement and analysis. This insures the following and other facts to be detected in a positive and nondestructive manner: for example, heats that have been adjusted in components and the like with a view to producing cast iron having high percent elongation turn out to be short of the intended percent elongation as a result of mismatch with processing or the like. Thus, the percent elongation of castings can be measured or computed on a single cast product with high reliability in a nondestructive and easy manner. In addition, the sound velocity in the steel product need be measured only once and, hence, each of the remaining cast products may successively be used as specimen 1a for subsequent analyses of the state of castings structure and measurements of percent elongation on those products. The fifth example of the present invention is described below with reference to drawings. Fig. 10 is a block diagram of an apparatus for ultrasonic measurement that is particularly advantageous for use on copper-containing cast iron. For the especial purpose of assuring enhanced tensile strength, copper is sometimes contained in castings at significant levels of about 1% and, in the case of such copper-containing cast iron, the empirical formu1a to be used differs slightly from the case just described above and it is necessary to make corrections in accordance with the percent copper content. The configuration of the apparatus under consideration is basically similar to that of the already-described fourth example except that the ∈' computing procedure in the percent elongation computing program used in the fourth example is replaced by a new procedure for computing ∈" and except for the associated parts. The following explanation centers on the differences from the example shown in Fig. 7. The percent elongation computing program 541 is substantially similar to the already-described percent elongation computing program 540 as regards the basic configuration and the technical rationale; it is a sub-program that performs a specified measurement and a specified conversion process to compute the percent elongation of a cast product. However, the program 541 differs from the percent elongation computing program 540 in that the cast product to be measured on is limited to copper-containing cast iron and that the percent elongation of the cast product is computed not from the values of sound velocity ratio in area (V/Vm), percent carbon content in area C and Brinell hardness in area HB but from the combination of these values with the percent copper content (in %). The thusly computed percent elongation of the cast product is stored in area ∈' in RAM 6. The specified conversion process under consideration is an experimentally predetermined computing procedure and this is a procedure for computing the percent elongation (∈') of the cast product on the basis of the relationship its percent elongation (∈) has with respect to the sound velocity ratio ((V/Vm)) between the steel and cast product, the percent carbon content (C) of the cast product under analysis, its Brinell hardness (HB) and its percent copper content (Cu). This computing procedure comprises mainly the already-described α' computing procedure 540a, m' computing procedure 540b and σB' computing procedure 540c, as well as the new procedure 541d for computing ∈". In the example under discussion, these procedures are incorporated as part of the percent elongation computing program 541 and they are executed in the order written. Explanation of the α' computing procedure 540a, m' computing procedure 540b and σB' computing procedure 540c is not repeated here but, as already mentioned, they compute α', m' and σB', respectively, from the sound velocity ratio ((V/Vm)), percent carbon content (C) and Brinell hardness (HB). The ∈" computing procedure 541d is a procedure by which the percent elongation ∈" as an estimated value of the actual percent elongation ∈ is computed from the index value α', estimated tensile strength σB' and percent copper content (Cu). To determine the percent elongation ∈", the percent elongation ∈' in the aforementioned example which has been computed from the index value α' and the estimated tensile strength σB' is first corrected by the percent copper content (Cu) to yield the value (∈'/(2 x Cu)) and this value (∈'/(2 x Cu)) is fitted in the relation it has with respect to the percent elongation ∈ which was determined in a tensile test. This relationship is shown in Fig. 11, with the value (∈'/(2 x Cu)) being plotted on the horizontal axis and the percent elongation ∈ on the vertical axis. Since there is a strong correlation between (∈'/(2 x Cu)) and ∈ in Fig. 11, the relationship under consideration can be approximated by a kinked line or the like. To give a specific example, the ∈" computing procedure 541d expresses the percent elongation ∈' in terms of the index value α' and the tensile strength σB' and determine ∈" from the index value α', tensile strength σB' and percent carbon content (Cu in %) by the following criteria: if α' < 2.68, computation is performed by the equation: ∈" = (0.165 x (3085-1035.6 x α')/(σB'xU)) + 2.3 if α' ≥ 2.68, computation is performed by the equation: ∈ " = (0.165 x (676.3-137.2 x α')/(σB' x U)) + 2.3 Thus, the percent elongation ∈" is computed (in %). Obviously if the equations set forth above are rewritten by expressing the tensile strength σB' in terms of the above-described index value α', one can readily obtain formulae for computing the percent elongation ∈" solely on the basis of the index value α' and the percent copper content (Cu). The thusly computed percent elongation ∈" provides a fairly good estimation of the actual percent elongation ∈ for the copper-containing cast iron (see Fig. 12). With this configuration, the process of measuring the percent elongation of a cast product starts with measuring the sound velocity in a steel product in mode 1 (mode for setting the sound velocity in steel), followed by processing cast products successively in mode 2 (mode for measuring the percent elongation of castings). Again, details of the process are substantially similar to the case of the already-described examples and explanation of the overlapping portions will not be repeated. The only difference from the already-described examples is that besides inputting the percent carbon content of the cast specimen la, its percent copper content (which is known as one of the data for the casting operation) is entered via keyboard 7 and set in area (Cu). If this data entry is omitted, processing is performed on the assumption that the percent copper content is the same as that of the previous specimen. Thereafter, the percent elongation that has been computed by the percent elongation computing program 541 is stored in area ∈" in RAM 6 and this percent elongation (∈") is displayed on CRT 8 by the main program 550 as the result of measurement and analysis. This insures the following and other facts to be detected in a simple and nondestructive manner: for example, heats that have been adjusted in components and the like by adding copper with a view to producing cast iron having high tensile strength turn out to be short of the intended percent elongation as a result of mismatch with processing or the like. Thus, the percent elongation of castings can be measured or computed on a single cast product with high reliability in a nondestructive and easy manner even if the cast product is copper-containing cast iron. It should be noted that in all of the examples discussed hereinabove, the reference value for normalizing the sound velocity is desirably taken on a steel product that is in the same state as the so-called "castings matrix (base)"; however, other metals may be used as long as consistency is insured between the operation of preparing the computing procedures and that of actual measurements. It should also be noted in the case of basing on the sound velocity rather than on the sound velocity ratio, namely, in the case where analyses or measurements are conducted on the basis of the percent carbon content, hardness and sound velocity (or in combination of these with the percent copper content), the sound-velocity-in-steel setting program 511, the sound velocity normalizing program 512, etc. are unnecessary and the above-described examples will apply as such if only the steel-related processing and the like are eliminated; hence, a detailed explanation of this alternative case is omitted. Industrial Applicability As described on the foregoing pages, the method and apparatus of the present invention for ultrasonic measurement are suitable for use on castings if one wants to determine reliable physical characteristic values (e.g. percent spheroidicity of graphite, tensile strength and percent elongation) and state analysis values in a nondestructive and simple manner.

Claims: An apparatus for ultrasonic measurement which measures the velocity of propagation of ultrasonic wave in a cast specimen with a known percent carbon content or carbon equivalent and determines the state of castings structure in said specimen, characterized in that said apparatus comprises: an empirical formula means (540a) uses an empirical formula by which a first physical quantity (V/Vm) and a second physical quantity (C) are processed to determine a third physical quantity (α') that is a value from which a hardness coefficient (m') of castings can be derived, or a conversion means (530p) by which a first physical quantity and a second physical quantity as two elements are converted to a third physical quantity (α') that is a value from which a hardness coefficient (m') of castings can be derived; a reference ultrasonic wave propagation velocity generating means (550, 511) by which the velocity of propagation of ultrasonic wave as attained by ultrasonic measurement on a steel product is generated as a reference ultrasonic wave propagation velocity; a state determining means (540) which determines said third physical quantity by said empirical formula or said conversion means, provided that the velocity ratio between the velocity of propagation of ultrasonic wave in said specimen as attained by ultrasonic measurement on said specimen and said reference ultrasonic wave propagation velocity is dealt with as said first physical quantity and that said percent carbon content (or said carbon equivalent) is dealt with as an equivalent of said second physical quantity, said means determining said state of castings structure in accordance with the thusly determined third physical quantity; and wherein said empirical formula means or said conversion means possesses either a characteristic function, a table or a processing procedure that represents correlation defining said third physical quantity by said first physical quantity and said second physical quantity, said correlation being performed by measuring a plurality of samples of a certain cast product with a measuring apparatus other than the one for ultrasonic measurement. The apparatus of claim 1 wherein said empirical formula means (540a, 540b) uses said empirical formula, and wherein said empirical formula are further processed to determine said hardness coefficient (m') by said third physical quantity ( α '); and said state determining means (540) further determines the hardness coefficient by said empirical formula and outputs the thusly determined hardness coefficient instead of determining said state of castings structure. The apparatus of claim 2 wherein said state determining means (540) further determines a tensile strength (σ B') in said specimen by said hardness coefficient (m') and hardness (H) of said specimen, and outputs the thusly determined tensile strength (σ B') instead of determining said hardness coefficient. The apparatus of claim 3 wherein said empirical formula have a function in which a first variable is C as the value of said second physical quantity, a second variable is R as the value of said first physical quantity, and a third variable is H as the value of the hardness of said certain cast product and in which a first intermediate value ρ is computed by equation ρ = 8.435 - 0.374 x C, a second intermediate value fg is computed by equation fg = 1.095 - 0.1395 x ρ, a third intermediate value α' is computed by equation α' = (R -2 x (7.86/ρ)-1)/fg, a fourth intermediate value m' is computed in accordance with any one of empirical formulae m' = 0.3920 - 0.0512 x α', m' = 0.2306 and m' = 0.3000 - 0.0173 x α' which are applied selectively under specified conditions and in which the value of function to be determined is computed by equation m' x H, or some other means of conversion that is based on equations comparable to said equations, said α' is the value of said third physical quantity, and m' is the value of said fourth physical quantity. The apparatus of claim 2 wherein said empirical formula are further processed to determine the percent elongation by said third physical quantity (α'), said hardness coefficient (m') and the hardness (H) of said specimen; and said state determining means (542) further determines the percent elongation by said empirical formula and outputs the thusly determined percent elongation instead of determining said hardness coefficient (m'). The apparatus of claim 3 wherein said empirical formula are futher processed to determine the percent elongation (ε') by said third physical quantity (α') and said tensile strength (σ B'); and said state determining means (542) further determines the percent elongation by said empirical formula and outputs the thusly determined percent clongation instead of determining said tensile strength (σ B'). The apparatus of claim 1 wherein said empirical formula means (540a, 540b) uses said conversion means, and wherein said conversion means further converts said third physical quantity (α') to said hardness coefficient (m'); and said state determining means (540) further determines the hardness coefficient by said conversion means and outputs the thusly determined hardness coefficient instead of determining said state of castings structure. The apparatus of claim 7 wherein said conversion means further converts said hardness coefficient (m') and hardness (H) of said specimen as two elements to a tensile strength (σ B') in said specimen and outputs the thusly determined tensile strength (σ B') instead of determining said hardness coefficient. The apparatus of claim 5 wherein said empirical formula have a function in which a first variable is C as the value of said second physical quantity, a second variable is R as the value of said first physical quantity, and a third variable is H as the value of the hardness of said certain cast product and in which a first intermediate value ρ is computed by equation ρ = 8.435 - 0. 374 x C, a second intermediate value fg is computed by equation fg = 1.095 - 0.1395 x ρ, a third intermediate value α' is computed by equation α' = (R -2 x (7.86/ρ)-1)/fg, a fourth intermediate value m' is computed in accordance with any one of empirical formulae m' = 0.3920 - 0.0512 x α', m' = 0.2306 and m' = 0.3000 - 0.0173 x α' which are applied selectively under specified conditions, a fifth intermediate value σB' is computed by equation m' x H and in which the value of function to be determined ε' is computed in accordance with any one of empirical formulae ε' = (3085 - 1035.6 x α')/σB' and ε' = (676.3 - 137.2 x α')/σB' which are applied selectively under specified conditions, or some other means of conversion that is based on equations comparable to said equations, said α' is the value of said third physical quantity, said m' is the value of said fourth physical quantity. The apparatus of claim 5, wherein said specimen is a copper containing cast iron and said empirical formula are processed to determine said third physical quantity by said first physical quantity, said second physical quantity and the percent of said copper. The apparatus of claim 5 wherein said specimen is a copper containing cast iron and said empirical formula have a function in which a first variable is C as the value of said second physical quantity, a second variable is R as the value of said first physical quantity, a third variable is H as the value of the hardness of said certain cast product and a fourth variable is Cu as the value of the percent of said copper, and in which a first intermediate value ρ is computed by equation ρ = 8.435 - 0.374 x C, a second intermediate value fg is computed by equation fg = 1.095 - 0.1395 x ρ, a third intermediate value α' is computed by equation α' = (R -2 x (7.86/ρ) -1)/fg, a fourth intermediate value m' is computed in accordance with any one of empirical formulae m' = 0.3920 - 0.0512 x α', m' = 0.2306, and m' = 0.300 - 0.0173 X α' which are applied selectively under specified conditions, a fifth intermediate value σH' is computed by equation m' x H and in which the value of function to be determined ε" is computed in accordance with any one of empirical formulae ε" = (0.165 x (3085 - 1035.6 x α')/(σB' x Cu)) + 2.3 and ε" = (0.165 x 676.3 - 137.2 x α' ) / (σB' x Cu)) + 2.3 which are applied selectively under specified conditions, or some other means of conversion that is based on equations comparable to said equations, said α' is the value of said third physical quantity, said m' is the value of said fourth physical quantity. The apparatus of claim 1 wherein said empirical formula means (540a) uses said empirical formula being further processed to determine a density of said specimen by said second physical quantity (C), to determine a graphite area factor of said specimen by said density and to determine said third physical quantity (α') by said graphite area factor. The apparatus of claim 1 wherein said empirical formula means (540a) uses said conversion means by which said second physical quantity (C) is converted to a density of said specimen, by which said density is converted to a graphite area factor of said specimen and by which said graphite area factor is converted to said third physical quantity (α').

Inventors: KOIWA MASAICHI, KOIWA, MASAICHI
Applicants: HITACHI CONSTRUCTION MACHINERY, HITACHI CONSTRUCTION MACHINERY CO., LTD.
Application year: 1993
Main classification: G01N29
IPC codes: G01N29