高張力鋼Wel-ten 55の連續冷却変態図と熔接変質部の組織および性質(第2報)

Abstract

In this report, in the first place, the authors constructed the continuous cooling transformation diagram in case of rapid heating maximum temperature 1100°C in the same way as Report 1. Then they considered generally on three diagrams already obtained.As the rapid heating maximum temperature becomes higher, the positions of the beginning curves of transformation and the ending curve of pearlite remove to the longer cooling time and lower temperature side, and the critical cooling times (C2' Cf', Cp' and C6') become larger. As the cooling time, from A3 point to 500°C, becomes shorter, namely, the cooling rate becomes larger, the specimens after cooling show the following tendencies: (a) the ferrite decreases and harder structure, e. g. martinsite, increases and the hardness of specimen becomes larger, (b) the absorbed energy by impact bend becomes larger with decrease of ferrite and increases of harder structures, (c) but as the cooling time becomes smaller over the certain limit, the absorbed energy becomes smaller suddenly on the contrary and the bend angle by impact and slow bend becomes also smaller suddenly. (d) the tendencies of (b) and (c) above mentioned are remarkable in case of specimens cooled from maximum temperature 1300°C.