Anomaly in Dilatation on Heating of Co, ld Worked 18-8 Stainless Steel

Abstract

The phase translations on heating in 18-8 stainless steel as cold worked followed by solution-treatment were investigated mainly by differential dilatation method. Austenite was retained much more in rolled steel than in elongated, in hammered, and in wire-drawn ones. α phase formed by cold working transformed in to γ phase firstly at about 450.., and the most part of α into γ at the temperature range of 650-700.., and the retained stable α phase secondarily into γ phase at temperatures of 800-900... It is considered that the thermal stability of α phase is varied by the working method and working ratio.
Abnormal expansion was always observed at about 530.. in thermal dilatation curve of cold worked 18-8 stainless steel by any working method. Especially, this anomaly was observed clearly in rolled steel, and the amount of expansion was enlarged as rolling ratio was increased. but on the other hand, the amount of contraction at about 650.. caused by α→γ transformation became smaller. This anomaly was markedly observed when steel was rolled in the condition with large surface friction between roll and rolled steel, and when steel was rolled in the condition of smaller friction by using any lubricant, only the smaller anomaly was observed in dilatation curve as same as elongated, or hammered or drawn steel.