Determining impurities in samples

A sample is cut from the upper region of a continuously cast ingot and rolled to compact the impurity band in a direction that was horizontal during casting.

BACKGROUND OF THE INVENTION 
The present invention relates to the making of samples for purposes of 
determining the degree of purity of metals. Within the context of this 
invention, metal includes iron as well as non-ferous metals and alloys 
thereof. It is assumed that owing to the particular metalurgical history 
these metals may contain undesirable impurities. Impurities within this 
context are essentially non-metallic phases which are deformable depending 
upon temperature. Their inclusion is presumed to impart undesirable 
properties upon the metal. It is known to inspect and test metals through 
ultrasonic processes, and the content of the impurities can be 
subsequently indicated and evaluated. Generally speaking, these tests are 
conducted within the frame of determining degrees of impurity. 
As far as iron and iron alloys are concerned, the invention finds 
particular utility in the case of steel having been processed by 
continuous casting. 
It is a general trend to increase requirements on a product, and stringent 
requirements include the one concerning purity as defined above. Aside 
from the problem of attaining the desired degree of purity, it is also a 
problem to determine the degree of purity in the first place. With 
increasing demands, it was found that standardized test methods of the 
past are no longer adequately reliable. This means that, to an increasing 
extent, failure rates of a product, either during manufacture or even on 
use, become a rather belated indicator of the degree of purity of the 
metal involved. As far as steel and metallurgical developoments generally 
are concerned, this is a very undesirable situation. Generally speaking, 
one can not expect a "feedback" between user and manufacturer, and even if 
such a feedback exists, say through complaints, a long delay could be 
expected before such feedback can be acted upon. 
It is quite obvious that on a worldwide basis, there is a demand for new 
methods which are practical, expedient, economical and reliable as far as 
inspecting the degree of purity of components is concerned, a specific 
requirement being differentiating among areas, zones and portions of the 
product; another requirement is quantification. Sectionalizing involves 
particularly sections or portions of limited length as far as continuous 
casting is concerned. It is believed that the present invention meets all 
these requirements and constitutes a significant improvement over the art. 
The following is a summary of known test methods concerning impurities. One 
method includes the extraction of sulphur, also known as the Bauman print 
method. Metallography as per a German standardized iron test sheet for 
steel 1570 . Step turning samples being another kind of test set forth 
under the number 1580. There are also known so-called blue-fracture 
samples; ultrasonic testing of plate-stock even if entirely along the 
edges, a slime extraction method, i.e. a certain residue is isolated; and 
quantitative metallography on relatively large plate stock areas such as 
areas of 200 cm.sup.2. It is beyond the scope of this discussion to detail 
a critique on these methods. Generally however, it can be said that as far 
as the present trend towards enhancing the testing degrees of impurities 
is concerned, these methods are no longer adequate. Owing to a clear lack 
of suitable pieces of equipment the problem was posed for many years that 
it was very difficult, even impossible, to determine by way of testing 
whether any particular feature used in the making and processing of steel, 
did or did not exhibit the desired result, except that much later when 
failure rates, or lack of them, became known. 
DESCRIPTION OF INVENTION 
It is an object of the present invention to provide a new and improved 
method for the manufacture of samples to be used in ultrasonic test 
operations for purposes of highly accurately determining the degree of 
purity of the metal in the sample, so that the determining can be 
immediately and directly made upon a given product. 
It is a particular object of the present invention to provide a new and 
improved method for the making of samples for ascertaining impurities in 
metals including steel, with emphasis on continuously cast steel. 
In accordance with the preferred embodiment of the present invention, it is 
suggested to cut a sample from a product, either a continuous cast one, or 
one product which has already undergone additional deformation, with the 
proviso that this sample is to have at least a ten-fold thickness of the 
minimum pre-thickness needed or desired for ultrasonic investigation, and 
that the thickness dimension of the sample runs in a plane parallel to the 
axis of casting, or the directon of main deformation of the product being 
tested, and having plane parallel cutting surfaces transversal to that 
thickness extension, and that the sample is heated as high as possible 
(non-melting being assumed) and is then deformed transversally to that 
thickness extension, down to the desired thickness needed for ultrasonic 
testing. 
The crux of the invention is to concentrate inclusions and impurities in 
particular zones so that on the one hand there is a well-defined local 
enrichment in impurities and inclusions, which then permits, on a 
statistical basis, a rather definite conclusion about the degree of 
overall purity of that product in general, including particularly, casting 
ingots, so that owing to the increase in density, the degree of purity and 
overall evaluation on a statistical basis including continuous casting and 
such, is now made possible. Thus concentrating begins with the fact that 
impurities are flushed up in a cast product. Then the pre-sample is taken 
and then impurities are concentrated what was originally (on casting) in a 
horizontal stretch until a thin vertical dimension. That sample is then 
rolled to concentrate that horizontal stretch (upsetting) in one 
direction. That direction is in casting direction in FIG. 1 and others are 
peripherally shown in FIG. 8.

The invention is first explained with reference to a particular example 
having to do with a round made by continuous casting of steel. Here it 
assumed that all inclusions of a sample of 25 kg are concentrated in a 
relatively small sample and test sheet for purposes of ultrasonic testing. 
As shown in FIG. 1a, a sample in the form of cylinder (175 diameter, 120 
axial length) is rolled flat to have the configuration of a surfboard or 
oval which is shown in FIG. 1b. The directions of rolling are transverse 
to the axis of the round as it was cast which is perpendicular to the 
plane of the drawing. The curved strand is stretched from the underside to 
the upper side U whereby reference numeral W 11 indicates the direction of 
rolling. The direction WR1 indicates subsequent stretching. An inclusion 
ribbon band 10 of impurities is predominantly located near the upper side 
U of the presample and, of course, of the entire product. These inclusions 
are upset by the rolling. The high particle density per volume remains. 
As a final result (oval FIG. 1b) clean and dirty zones are rather very 
neatly separated in this manner as a preparation for ultrasonic testing, 
which means that unnecessary "chaf" for the test is discarded. The 
inclusions are stretched as well as widened, thereby resulting in the 
sample becoming sensitized as far as ultrasonic testing is concerned. 
In spite of a sufficiently pronounced degree of deformation, the 
sheet-stock thickness (1.12 mm) of the sample is not made to drop below a 
critical level for ultrasonics. Thus, by way of example, a disc cut of a 
round at 175 mm and 120 mm axial length was flattened to the surfboard 
configuration of 875 mm length a shaft axis of 350 mm. The original 
thickness of that disc was 120 mm and is now reduced to 12 mm. 
FIG. 2 illustrates a spectrum and size distribution of the inclusions on 
this thus defined upper side (band 10) of a round in which impurities have 
been accumulated. For symbol explanation see FIG. 4. One can say that 
rolling temperature is the parameter. 
FIG. 3 is a corresponding diagram but shows the distribution near the 
"clean" underside L. Owing to these investigations conducted by the 
applicants for purposes of determining deformability of inclusions in 
steel, it was readily determined that for attaining the goal of the 
invention to use as high a rolling temperature s possible, such as 1350 
degrees centigrade. 
FIG. 4 illustrates the inclusions which originally had a more or less 
spherical configuration but which, with increasing rolling temperature, 
are stretched to an increasing extent. This is what is meant by "inclusion 
length" of the impurities. 
FIG. 5 now shows how a basically elliptically configured inclusion is 
deformed on rolling, the illustration being in a plane parallel to the 
direction of rolling. In fact, the inclusion has been destroyed, but its 
originally elliptical contour is still recognizable. 
FIG. 6, including part 6A-6F, illustrates several types of examples, i.e. 
ultrasonically tested samples of the surfboard or oval configuration; they 
have been organized in this FIG. 6 in accordance with a certain 
classification. These examples are real and the classification is 
metallurgically justifiable. For purposes of comparison, it should be 
mentioned that the Bauman print does not differentiate among these various 
cases. In a concrete case of the sample with a Class 6, the S-discharge 
was almost white, while the emulsified casting slag was obviously not 
covered by the S-discharge. The development of the test program works as 
follows. 
Samples of a castround are plane-parallel cut or burned in cylinders of 130 
mm lengths, measured in the direction of casting. The upper side of 
casting (physically) is then identified by means of certain markings left 
by certain withdrawal rollers. The underside is thus defined simply by 
being the opposite side, and is notched by a 10 mm length cut. This cut 
serves for orienting the roll. 
These round samples are now heated to a temperature of 1350 degrees, and in 
a rolling stand the following program for roll direction WRI-FIG. 1a,b is 
provided: 130, 120, 105, 80, 70 and 60 mm. Readily now this elliptically 
deformed sample is turned by 90 degrees and is stretched in the following 
passes identified above by WRII; 48, 36, 18 and 13 mm. The position of the 
notch is a good indicator about how symmetrically one did roll. The 
elliptically contoured ovals or surfborads are then sawed and partitioned. 
As far as the upper side is concerned, two 100 mm wide strips are cut from 
the apex of the ellipse. As far as the underside is concerned, it is 
sufficient to have a strip extracted just for purposes of verification, 
calibration and reference. This is sufficient in order to determined that 
in fact what is deemed upper and under side are properly so designated and 
there was no mix-up prior to rolling. The three samples are now plane 
parallel ground and cut and tested in a suitable ultrasonic test stand 
such as a HIC apparatus. 
The invention now uses the fact that in the case of curved continuous 
casting, inclusions are basically on the upper side, that is the inside of 
the curve. As far as horizontal casting is concerned, this phenomenon is 
even more pronounced; basically it is quite independent from the contour 
and cross-section of the casting. 
FIG. 7 shows the position of the inclusion band in various products that 
have been made by casting. Inclusions are predominantly found for various 
kinds of rolled products such as billets, blooms, rounds and slabs. Upon 
suitably rolling certain sections with upsetting of that portion in the 
product which predominantly contains the inclusions, one can in fact 
produce a suitable test-sheet in which the inclusions are indeed 
concentrated, and owing the particular rolling, they are in effect 
sensitized. It may be assumed that the direction of upsetting runs 
parallel to the direction of casting, but that is not essential. With 
reference to the orientation of the casting, upsetting may occur 
horizontal transverse to the cast product. 
In the case of narrow sides of the ingots, the direction of upsetting may 
even be vertical, which is however, mentioned here only for purposes for 
completion, because this kind of approach, though conventional, does not 
promise the largest possible effect, and may in effect exhibit certain 
undesirable results analogous to conventional edge-zone testing. 
Now from this product, suitably rolled pieces can be cut through sawing. 
The sample thickness is transverse to the plane of the drawing of FIG. 7. 
Moreover, it is assumed that a tenfold thickness reduction is desirable 
simply to enhance sensitivity as far as the detection of inclusions is 
concerned. The test-sheet, moreover, should not be thinner than 10 mm, 
which for steel is about the minimum for ultrasonic testing. It should be 
realized that for ultrasonic testing, the first millimeter thickness or so 
of a product, i.e. a surface-near region, is not really tested. As far as 
the initial thickness of a cut sample is concerned, there is no basic 
principle limit, the limit being simply given by local rolling facilities. 
Concerning FIG. 8, horizontal upsetting of the inclusion band is explained; 
particularly in the case of a round sample (having been turned by 90 
degrees); the upsetting is carried out by a roll parallel as well as 
perpendicularly to the direction of casting (FIG. 8a). The direction of 
casting is transverse to the plane of the drawing of FIG. 8a. Prior to 
rolling, side segments of the round cross-section are cut off, so that the 
no longer round glide stock can lie flat and is introduced into the 
rolling gap in a controlled fashion. Rolling was in FIG. 8a from left to 
right or vice versa and transverse to the plane of the drawing. FIG. 8b 
now shows the flat rolled piece with upsetting having occurred 
transversely to the plane of FIG. 8b irrespective of the direction of 
rolling. The ultrasonic test, to the extent it can be seen in FIG. 8, is 
indeed a verification of the applicability of this kind of roll for the 
inventive purpose. If the previous sawing is inaccurate, i.e. not exactly 
at an angle of 90 degrees to the inclusion band 10 of impurities, then the 
ultrasonic indication does reach the edge of the sheet stock. 
The invention can be used particularly to test continuous cast material of 
unknown origin, but prior to the test, one can determine what was the 
upper and what was the under side. The method which was explained above 
and once this orientation has been made, the degree of purity of the 
material can be determined. A supplier of raw products may for example, be 
assumed to have manufactured by way of a curved continuous strand or ingot 
having dimensions of 360 mm by 420 mm which are then to be changed by 
rolling into hollows of 177 mm diameter. Pickling a dS-extraction does not 
provide adequate information. 177 mm diameter material is notched 
arbitrarily on two spots of the surface, and is then rolled into a 
"surfboard", i.e. an oval. 
FIG. 9 illustrates the result of ultrasonic testing that sample. As far as 
the ellipse is concerned, one provides mathematically as retransformation 
to the round material, and that is found in FIG. 10. Now the direction and 
orientation of casting upper side and casting under side is determined. 
Folowing this, other 100 mm round samples will be processed with knowledge 
of that particular orientation, and they are then investigated and 
inspected with regard to any impurity. Actually by this method one can 
subseqently distinguish ordinary block casting from continuous casting in 
and along a curved method. It must be mentioned that after some kind of 
deformation, this distinction has normally been almost impossible. 
FIG. 11 shows how the invention is applied to a slab ingot made by 
continuous casting. It is assumed that the so-called S-sample-taking did 
not indicate any particularly poor grading. The figure shows the 
ultrasonic test results from the upper slab surface near the middle 
therein. The lower part towards the slab center was free from any 
indication. The analized sample was roughly at one half of the slabingot 
width. 
FIG. 12 shows how, in an entirely different slab ingot, the area of the 
narrow or small side was tested. Here one sees a particular layer which 
entirely free from any inclusion Both illustrated samples are then, just 
as in the case of standard rolling of round material, widening it to a 
two-fold value and stretching it to a five-fold value. For the exact 
ascertainment of distances, thickness, and so forth, particularly 
involving the inclusions band, one had to retransform mathematically from 
the sheet to the initial product. This, however, was not done in this 
case. 
The invention is also applicable to so-called thin-wall products such as 
tubes or sheets of cross-sections with a diameter of less than 100 mm, or 
with edge-length which in accordance with the slimness cannot be subject 
to upsetting in the directing of length extension as far as the sample is 
concerned, because under pressure the sample will simply buckle. 
In this case, then, the sample can be processed as follows. For example, 
several sheets are bundled and mechanically held together, or in the case 
of tubular samples, one simply inserts a suitable core, or in the case of 
thin rods, one provides a tubular sleeve. In all these cases, one 
establishes a sample which will not kink, or bend, or buckle. The 
auxiliary element will be also deformed but does not structurally combine 
with the desired product, and can simply be separated therefrom. 
The invention is not limited to the embodiments described above; but all 
changes and modifications thereof, not constituting departures fromthe 
spirit and scope of the invention, are intended to be included.