On the behaviour and growth of grains of high strength steel during high temperature deformation

Abstract

The behaviour of grains and its boundaries in HAZ, accompanied with grain-coarsening and under stress conditions which are caused by solidification of weld metal or by welding heat, is related to hot cracking and embrittlement of HAZ. Moreover, grain-boundary migration plays an important role in hot working, creep and high temperature fatigue.
In this paper, the behaviour of austenite grains and its boundaries of high strength steel during tensile deformation at high temperature around 1300°C was studied with microscope.
The main conclusions obtained in this study are as follows:
(1) Wide fluctuation of load was observed in load-elongation curves during hot tensile deformation. It was verified that its phenomenon is caused by dynamic recrystallization. The higher rate of deformation at high temperature around 1300°C and the lower rate at somewhat, lower temperature less than, 1100°C, the more easily dynamic recrystallization tends to occur.
(2) The higherr rate of deformation at 1300°C, the higher grain-boundary migration rate and the faster it was saturated.
(3) Migration of grain-boundary triple point is caused by mechnical sliding at boundary and atomicdiffusion. Consequently the triple point migrates alternately and zigzag.
(4) Dynamic recrystallized grains were observed. Its nuclei occured preferentially and accidentally at the place near boundary within a grain.