WCoB系硬質合金の組織と機械的特性におよぼすCr添加量の影響

概要

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Effects of Cr on the mechanical properties and phase formation of WCoB base alloys were studied using the model alloys whose compositions were Co-1.93mass%B-33.3mass%W-(0-20)mass%Cr. The new alloys consist of a WCoB type ternary boride as a hard phase and a cobalt base binder alloyed with Cr, W and other elements, both of which are formed by reaction boronizing sintering.<BR>The transverse rupture strength (TRS) of the alloys depended strongly on the microstructure, which varied significantly with Cr content. The highest TRS of 2.85GPa obtained at 15mass%Cr was attributed to the refinement and good distribution of WCoB boride. Moreover, the TRS of the alloy with 15mass%Cr still kept a value of about 1.8GPa at 1173K. The weight gain of the alloy oxidized in air at 1173K was less than that of SKD11 and close to that of SUS304.<BR>Corrosion resistance of the alloys in a non-oxidizing 10mass% HCl solution was better than those of a PM high speed steel, stainless steels such as JIS SUS 405, 440C, 316L and 304 and a tool steel JIS SKD11, and close to that of Hastelloy C. On the other hand, in an oxidizing 10mass% HNO<SUB>3</SUB> solution the alloys showed better corrosion resistance than a cemented carbide of WC-10mass%Co, a PM high speed steel and SKD11, and were almost same as stainless steels and Hastelloy C.