高周波焼入れシャフト材の捩り強度に及ぼすP,Bの影響

Abstract

The purpose of this study is to establish a method of increasing strength of shaft steels in mode I fracture associated with intergranular fracture. The effects of phosphorus and boron on the torsional strength in mode I fracture were investigated.The strength in mode I fracture of induction hardened steel was increased by the addition of boron. The beneficial effect of the addition of boron on the torsional strength was larger than that of lowering phosphorus content from 0.013% to 0.002%. In the boron bearing steel, the segregation of boron in prior austenitic grain boundary was recognized and the amount of phosphorus segregation was one half that of boron-free steel. This was because the segregation of boron and phosphorus occurred concurrently at the induction heating and boron scavenged phosphorus in prior austenitic grain boundary.It is concluded that the increasing strength by the addition of boron was due to two causes: lowering the amount of phosphorus segregation by the effect of scavenging phosphorus in grain boundary and the increase in the grain boundary strength by the unique effect of boron. The effect of the latter on the strength was larger than the former.