Osamu Terada

Superplastic Behavior and Cavitation for WC-Co Cemented Carbides

Superplastic behavior and cavitation were investigated for WC-15 mass % Co cemented carbides with the WC grain sizes of 0.7 µm (A) and 5.2 µm (B), WC-10 mass % Co cemented carbide with the WC grain size of 1.5 µm (C) and WC-5 mass % Co cemented carbides with the WC grain sizes of 0.5 µm (D) and 2.5 µm (E) by tensile tests at 1473 K. WC contiguity were 0.51, 0.31, 0.27, 0.56 and 0.49, respectively. The large elongations about 200 % were obtained for the B and the C having smaller values of WC contiguity compared to the other cemented carbides. The values of cavity volume fraction for them were less for the other cemented carbides, furthermore, cavities formed at WC/WC interfaces. Therefore, it is noted that the distribution of the Co phase is important for superplasticity of the cemented carbides.

Mechanical Properties of Sintered SKH57 High Speed Steel Affected Mainly by Titanium Nitride Addition

Using reduced and carburized SKH57 powder, titanium nitride (TiN) and titanium carbide (TiC) powders, SKH57 tool steels having TiN or TiC in the amounts up to 25.27 vol% were sintered, HIP-ed and usually heat-treated. The mechanical properties such as hardness (Hv) and transverse-rupture strength were studied.It was noted that M6C, MC and TiN particles were observed in the structure of TiN added steel, being in good contrast to MC and TiC solid solution particles in TiC added one. Then, the former steel was always higher in the hardness than the latter under the same amount of additions. It was found that SKH57 having, for instance, 17.30 vol% TiN showed the hardness of 1070-1130 Hv and the strength of about 2.5 GPa.

Some Properties of WC-TiN-Co Alloy

The microstructure, mechanical properties, etc. of WC-TiN-Co alloy were studied in comparison with those of WC-TiC-Co alloy. The WC-(0-15)mass%TiN (TiC)-10 mass%Co alloys were used as specimens. It was found that the amount of β (WC-TiC S.S) phases formed in the structure was less in the TiN contained alloy under the same addition amount of TiN or TiC, leading to the higher strength and lower hardness in the TiN contained alloy. The thickness of surrounding structure formed on the TiN core became markedly thin, probably owing to the negative affinity between nitrogen and tungsten at elevated temperatures.

The Fine Structure in Nitrogen Free TiC-Mo2C-Ni Cerment

The microstructure of Mo2C or Mo2C and WC contained cermet was studied using optical microscope and SEM. It was found by SEM that extremely fine carbides which had never been observed by optical microscope, co-existed with the carbides with surrounding structure usually observed by optical microscope. Formation mechanism of the former carbides seemed to be the same as that of the latter carbides. It was demonstrated in nitrogen free cermets that, by means of decreasing the size of usually observed carbides, the structure finer than that of nitrogen contained cermets was easily obtained.

Mechanical Properties of Sintered SKH57 High Speed Steel Prepared by Using Reduced Starting Powder

By using reduced and carburized starting powder, SKH57 was vacuum-sintered, HIP-ed and then heat-treated. Then, its mechanical properties were studied as a function of sintering temperature (TS), quenching temperature (TQ), aging temperature (TA), etc. The following results were obtained. Under a suitable condition such as TS=1200°C, TQ=1170-1200°C and TA=560-590°C, the sintered alloy showed excellent properties such as 4.8-4.9GPa of TRS and 840-870 HV. The alloy commonly fractured from a small flat region (φ10-20μm) containing micropores along the former austenite grain boundaries. The micropores were considered to be caused by the reduction of a small amount of remained oxides, which took place during sintering. The strength of the alloy, therefore, was controlled by the size of flat region, but not by the primary carbide or the former austenite grain size.