Study on the Grain Growth in Weld-Heat Affected Zone (Report 4)

Austenite Grain Growth during Thermal Cycle in Steels

Abstract

In this report, grain growth equation during thermal cycle, derived by the authors, was applied to the austenite grain growth of steels during thermal cycle.
At first, the formation of austenite grains during rapid heating was examined, and then the method to calculate austenite grain growth during thermal cycle was investigated using grain growth equation during thermal cycle.
Main results obtained are as follows.
1) When 0.2 and 0.35 % carbon steels (initial microstructure: ferrite-pearlite, ferrite grain size:0.01-0.04mm) heated rapidly, austenite grains are formed at 950-1050°C and grain size of the austenite formed is 0.013-0.02 mm.
2)When low alloy steels (initial microstructure:martensite, tempered martensite, prior austenite grain size: 0.020.38mm) are heated rapidly, austenite grains are formed at 950-1050°C and grain size of the austenite formed is 0.01-0.05 mm.
3)It was confirmed that austenite grain growth could be calculated by grain growth equation during thermal cycle using the results mentioned above as initial conditions.
4)In case of the normalizing or quenching and tempering conditions for practical use, austenite grain growth during thermal cycle above 1000°C can be calculated assuming that austenite grain size is zero at the finishing temperature of austenite transformation.