Study on the Grain Growth in Weld-Heat Affected Zone (Report 5)

Austenite Grain Growth of Steel in Weld-Heat Affected Zone

Abstract

In this report, grain growth equation during thermal cycle, derived by the authors, was applied to the austenite grain growth during weld thermal cycles in TIG arc and submerged arc welding of steel. And then austenite grain growth phenomenon in weld-heat affected zone (HAZ) was investigated.
Main results obtained are as follows.
1) Value of austenite grain size calculated by applying grain growth equation during thermal cycle to the measured weld thermal cycles in HAZ of two-dimensional bead agreed with the measured asutenite grain size.
From this result, it became clear that austenite grain growth during weld thermal cycle could be calculated using grain growth equation during thermal cycle.
2) Austenite grain size in HAZ is influenced by weld heat input through the change in the distribution of peak temperature, heating and cooling rate. Effect of the latter factor is dominant near the fusion line and of the former one is dominant in the region away from fusion line.
3) In weld thermal cycle, 60-80% of the total amount of grain growth occurs on heating cycle. On cooling cycle, 20-40% of the total amount of grain growth occurs and grain growth is nearly completed when temperature falls down to the 90-95% of peak temperature.
4) During weld thermal cycle, grain growth rate increases rapidly as temperature rises, taking a maximumm value just before the peak temperature and decreases rapidly as temperature falls.