高クロム鋳鉄粉をプレミックスした新ロール材の開発 ＩＩＩ 炭化物化の条件とその機構

Abstract

A study has been made to reveal the preferable conditions for the variations of carbide morphology in HIP'ed roll steel pre-mixed with high chromium iron powder, and the mechanism of the variation has been discussed. High chromium gas atomized iron powder was mixed with gas atomized roll iron powder, followed by HIP'ing to a full density. The micro-hardness measurement, observation of microstructures and EPMA analysis were carried out.The results are shown below:(1) The region where high chromium iron powder existed transforms into massive carbides under the conditions where the chromium content of high chromium iron powder is 2.5% higher than that of roll iron powder, and a sufficient cementite or graphite exists in the roll iron powder.(2) The mechanism of the variation of carbide morphology is explained in terms that the carbon consisting in cementite or graphite in the roll iron powder dissolves into matrix, and then precipitates into the carbides which existed in the high chromium iron powder.(3) The type of the carbide which grows during HIP'ing depends on the chromium content of high chro-mium iron powder; cementite appears if the chromium content is less than 18%. (Cr, Fe)7C3 carbides also appears if the chromium content is more than 18%.