SURFACE COATED CARBO-NITRIDE TITANIUM-BASE CERMET MATERIAL FOR INSERTS OF HIGH-SPEED CUTTING TOOLS

Abstract: A surface coated TiCN-base cermet material for inserts of cutting tools, which possesses excellent wear resistance as well as excellent chipping resistance and therefore can exhibit excellent cutting performance over a long period of use when used as a cutting insert in high speed cutting of steel or the like. The cermet material consists essentially of a substrate or a TiCN-base cermet, and a hard surface layer formed over surfaces of the substrate, the hard surface layer being formed of a single layer of one compound selected from the group consisting of TiC, TiN, and TiCN, or a composite layer of at least two compounds selected from the same group, the hard surface layer having a mean thickness within a range from 0.5 to 10 micrometers. The hard surface layer has a mean grain size of not more than 0.05 micrometers.

Description: This invention relates to surface coated carbo-nitride titanium-base cermet materials for inserts of cutting tools, which are so excellent in wear resistance and chipping resistance as to exhibit excellent cutting performance when used in high speed cutting. There are generally employed cermet materials in which a substrate of a carbo-nitride base cermet (hereinafter called "TiCN-base cermet") has been subjected to chemical vapor deposition to have surfaces thereof coated with a hard surface layer formed of a single layer of one compound selected from the group consisting of carbide titanium (TiC), nitride titanium (TiN), and carbo-nitride titanium (TiCN), or a composite layer of two or more compounds selected from the same group, the hard surface layer having a mean thickness of 0.5 - 10 micrometers. In recent years, in order to attain higher production efficiency, i.e. reduce the manufacturing cost, cutting has a tendency toward higher speed. However, if the above conventional surface coated TiCN-base cermet materials are used in cutting steel or the like at a high cutting speed of 250 meters per minute or more, they show rather short tool lives owing to insufficient wear resistance and insufficient chipping resistance of the hard surface layer. It is therefore the object of the invention to provide a surface coated TiCN-base cermet material for inserts of cutting tools, which can exhibit satisfactory wear resistance as well as excellent chipping resistance even when used as cutting inserts in high speed cutting at 250 meters per minute or more. To attain the above object, the present invention provides a surface coated TiCN-base cermet material for inserts of cutting tools, consisting essentially of: (1) a substrate of a TiCN-base cermet; and (2) a hard surface layer formed over surfaces of the substrate, the hard surface layer being formed of one of a single layer of one compound selected from the group consisting of TiC, TiN, and TiCN, and a multilayer of at least two compounds selected from the same group, the hard surface layer having a mean thickness within a range from 0.05 to 10 micrometers. The cermet material according to the invention is characterized by an improvement wherein the hard surface layer has a mean grain size of not more than 0.05 micrometers. The above and other objects, features, and advantages of the invention will be more apparent from the ensuing detailed description. Under the aforestated circumstances, the present inventor has made studies in order to improve the conventional surface coated TiCN-base cermet materials for inserts of cutting tools in respect of wear resistance and chipping resistance, and he has reached the finding that if in the conventional surface coated TiCN-base cermet materials a hard surface layer is formed, by means of physical vapor deposition, over the substrate such that the hard surface layer has a finer structure having a mean grain size of 0.05 micrometers or less substantially smaller than the conventional rang of 0.1 - 0.2 micrometers, the hard surface layer has greatly enhanced wear resistance and chipping resistance so that the cermet material can exhibit excellent cutting performance over a long tool life, if it is used in high speed cutting of steel or the like at a speed of 250 meters per minute or more. The present invention is based upon the above finding, and provides a surface coated TiCN-base cermet material having the aforestated structure. Throughout the whole specification percentage is percent by weight. The substrate of the surface coated TiCN-base cermet material according to the invention may have a conventional one. For example, the substrate may be prepared from a cermet having any one of the following chemical compositions (a) - (d): (a) at least one compound selected from the group consisting of Co and Ni; 5 - 25 % at least one compound selected from the group consisting of a carbide of Mo (Mo₂C) and a carbide of W (WC): 5 - 25%; at least one compound selected from the group consisting of a carbide of Ta (TaC) and a carbide of Nb (NbC): 1 - 30%; and TiCN: the balance; (b) at least one compound selected from the group consisting of Co and Ni; 5 - 25 % Al: 0.01 - 2 %; at least one compound selected from the group consisting of Mo₂C and WC: 5 - 25 %; at least one compound selected from the group consisting of TaC and NbC: 1 - 30%; and TiCN: the balance; (c) at least one compound selected from the group consisting of Co and Ni; 5 - 25 % at least one compound selected from the group consisting of Mo₂C and WC: 5 - 25%; at least one compound selected from the group consisting of TaC and NbC: 1 - 30%; at least one compound selected from a carbide of Zr (ZrC) and a carbide of Hf (HfC): 0.1 - 10%; and TiCN: the balance; or (d) at least one compound selected from the group consisting of Co and Ni; 5 - 25 % Al: 0.01 - 2 %; at least one compound selected from the group consisting of Mo₂C and WC: 5 - 25%; at least one compound selected from the group consisting of TaC and NbC: 1 - 30%; at least one compound selected from ZrC and HfC: 0.1 - 10%; and TiCN: the balance. The above cermet is formed by sintering under one of the following sintering conditions (i) and (ii): (i) Sintering Temperature: 1350 - 1500 °C; Atmosphere at Sintering Temperature: nitrogen; and Pressure of Atmosphere at Sintering Temperature: 1 - 10 torr(133-1333Pa);or (ii) Sintering Temperature: 1350 - 1500 °C; Atmosphere at Sintering Temperature: vacuum; and Pressure of Atmosphere at Sintering Temperature: 10⁻² torr(1,33 Pa) or less. (iii) Sintering Temperature: 1300 - 1500 °C; Atmosphere at Sintering Temperature: nitrogen or argon; and Pressure of Atmosphere at Sintering Temperature: 1 - 200 atm (10⁵-2.10⁷Pa). The chemical composition of the cermet is limited as above for the following reason: Co and Ni serve to enhance the toughness of the cermet. However, if the Co and/or Ni content is less than 5 %, desired toughness cannot be secured, whereas in excess of 25 %, the cermet has much degraded wear resistance. Therefore, the Co and/or Ni content is limited within a range from 5 to 25 %. Al may be added according to necessity, since it forms intermetallic compounds which act to strengthen the binder phase to thereby enhance the plastic deformation resistance of the cermet. However, if the Al content is less than 0.01 %, desired results cannot be obtained, whereas if the Al contend exceeds 2 %, it will degrade the toughness of the cermet. Therefore the Al content is limited within a range from 0.01 to 2 %. Mo₂C and WC may be added to improve the sinterability of the green compact and hence enhance the strength of the resulting cermet. However, if the total content of Mo₂C and WC is less than 5 %, the strength cannot be enhanced to a desired degree, while if it exceeds 25%, the hard dispersed phase will have degraded hardness and hence degraded wear resistance. This is why the total content of MoC and WC is limited within a range from 5 to 25 %. TaC and NbC may be added to improve the oxidation resistance of the cermet. However, if the total content of TaC and NbC is smaller than 1 %, the above properties cannot be improved to a desired degree, whereas even if it exceeds 30%, no further improvement cannot be obtained in the properties. Therefore, the total content of TaC anfd NbC is limited within a range from 1 to 30 %. ZrC and HfC may be added according to necessity, i.e. in a case where it is desired to further enhance the hardness of the cerment since they act to enhance the hardness of the cermet. However, if the total content of ZrC and HfC is less than 0.1 %, the hardness cannot be improved to a desired degree, whereas if the total content exceeds 10 %, the green compact will have low sinterability. Thus, the ZrC and/or HfC content is limited within a range from 1 to 10 %. In the surface coated TiCN-base cermet material according to the invention, the hard surface layer has a mean thickness within a range from 0.5 to 10 micrometers. If the mean thickness is less than 0.5 micrometers, desired wear resistance cannot be secured, whereas if the mean thickness is larger than 10 micrometers, there will be a degradation in the chipping resistance. A preferable range of the mean thickness is from 1 to 5 micrometers. In the surface coated TiCN-base cermet material according to the invention, the hard surface layer has a mean grain size of 0.05 micrometers or less. If the mean grain size is larger than 0.05 micrometers, the hard surface layer or the cermet material cannot exhibit satisfactory wear resistance and chipping resistance when the cermet material is used in high speed cutting of steed or the like at a cutting speed of 250 meters per minute or more. To secure a mean grain size of 0.05 microns or less, a physical vapor deposition method should be employed to coat the hard surface layer over the substrate of the cermet under the following coating conditions: Reaction Temperature: 550 - 700°C Voltage Applied on Substrate: -700 - -100 volts; and Pressure of Reaction Atmosphere: 5 × 10⁻³ - 5 × 10⁻⁵ torr (0,6-0,006 Pa) An example of the surface coated TiCN-base cermet material according to the invention will be given below. EXAMPLE Substrates of TiCN-base cermets formed from green compacts having respective chemical compositions shown in Table were prepared. These cermet substrates were subjected to ordinary physical vapor deposition to have their surfaces coated with hard surface layers through adjustment of the reaction temperature, the voltage applied on the substrates, and the degree of vacuum of the reaction atmosphere to respective values shown in Table so that the hard surface layers had respective chemical compositions, mean grain sizes, and mean layer thicknesses shown in Table, to obtain surface coated TiCN-base cermet materials according to the present invention (hereinafter referred to as "coated cermet materials according to the invention") Nos. 1 - 5. For the purpose of comparison, substrates of TiCN- base cermets formed from green compacts having respective chemical compositions shown in Table were prepared, and these substrates were subjected to ordinary chemical vapor deposition to have their surfaces coated with hard surface layers under coating conditions shown in Table so that the hard surface layers had respective chemical compositions, mean grain sizes and mean layer thicknesses shown in Table, to obtain conventional surface coated TiCN-base cermet materials (hereinafter referred to as "conventional coated cermet materials") Nos. 1 - 3. Then, in order to evaluate the wear resistance, the coated cermet materials according to the invention and the conventional coated cermet materials were subjected to high speed steel-continuous cutting test under the following testing conditions: Work Material : Round Bar according to SCM 415 (hardness :HB 150); Cutting Speed: 300 m per minute; Feed Rate: 0.2 mm per rev.; Depth of Cut: 1 mm; Cutting Time: 20 minutes In the above cutting test, the flank wear of each cutting insert was measured, the results of which are shown in Table. Further, in order to evaluate the chipping resistance, the above coated cermet materials were also subjected to a high speed steel-intermittent cutting test under the following testing conditions. 10 pieces of cutting inserts of each of the coated cermet materials were subjected to the test: Work Material: Square Bar according to SCM 439 (hardness :HB 250); Cutting Speed: 250 m per minute; Feed Rate: 0.15 mm per rev.; Depth of Cut: 1 mm; Cutting Time: 5 minutes The numbers of those cutting inserts which were chipped during the cutting test were measured, and the results are shown in Table. It will be learned from Table that all the coated cermet materials according to the invention Nos. 1 - 5 possess much superior wear resistance and chipping resistance to the conventional coated cermet materials Nos 1 - 3 and therefore doubtlessly they can exhibit excellent cutting ability over a very long period of use if they are used as cutting inserts in high speed cutting at 250 meters per minute or more in particular.

Claims: Surface coated TiCN-base cermet material for inserts of cutting tools, consisting essentially of : (1) a substrate of a TiCN-base cermet ; and (2) a hard surface layer formed over surfaces of said substrate, said hard surface layer being formed of one of a single layer of one compound selected from the group consisting of TiC, TiN, and TiCN, and a multilayer of at least two compounds selected from the same group, said hard surface layer having a mean thickness within a range from 0.5 to 10 micrometers, characterized in that said hard surface layer has a mean grain size of not more than 0.05 micrometers. Surface coated TiCN-base cermet material as claimed in claim 1, characterized in that said hard surface layer has been formed by a physical vapor deposition method. Method of manufacturing a surface coated TiCN-base cermet material for inserts of cutting tools, comprising the steps of : (a) preparing a substrate of a TiCN-base cermet ; and (b) coating over surfaces of said substrate a hard surface layer formed of one of a single layer of one compound selected from the groups consisting of TiC, TiN, and TiCN, and a multilayer of at least two compounds selected from the same group, by means of a physical vapor deposition, characterized by the following conditions : Reaction Temperature : 550 - 700°C ; Voltage Applied on Substrate : - 700 - -100 volts ; and Pressure of Reaction Atmosphere : 5 × 10⁻³ - 5 × 10⁻⁵ torr (0.6-0.006 Pa), whereby said hard surface layer has a mean thickness within a range from 0.5 to 10 micrometers and a mean grain size of not more than 0.05 micrometers.

Inventors: YOSHIMURA, HIRONORI C/O TOKYO SEISAKUSHO
Applicants: MITSUBISHI MATERIALS CORPORATION
Application year: 1987
Main classification: C23C14
IPC codes: C23C14, C23C30