機械構造用低炭素鋼の組織におよぼす少量のNi, Crの影響

Abstract

In the future, with the growing use of laterite are as a raw material for steelmaking, metallic impurities such as Ni and Cr will accumulate increasingly in final products. In more general case the final products may be contaminated with Ni and Cr contained in steel scrap. But there is little information on the effects of small amounts of Ni and Cr on properties of plain carbon steels which are in the greatest demand. From such a viewpoint, the authors investigated the effects of small amounts of Ni and Cr on properties of low, medium and high carbon steels.This paper is concerned with the effects of Ni and Cr on microstructural factors of low carbon ferrite plus pearlite steels. Studies were made for JIS S15C steel, and microstructural factors, such as pearlite fraction, mean ferrite path, condition for CrN-precipitation and critical cooling rate for bainite formation were investigated. Particularly, the condition for CrN-precipitation was discussed with equilibrium state in mild steel, and the free energy equations for CrN-precipitation were presented for the case that Cr and N coexist with Al and Si.