Kinetics of the Formation of Austenite at Constant Temperature

Study on the Phase Transformation in Welded Joints of Duplex Stainless Steels (Report 1)

Abstract

Kinetics of the formation of austenite in Type 329J₁ duplex stainless steel at constant temperature was investigated as the first step to analyze the amount of the austenite in HAZ of this steel. Special attention has been paid to obtain quantitative data on the formation of austenite in the range of 950-1150°C, because in this range, Widmanstätten austenite which occupies the greater part of the amount of austenite in HAZ after welding precipitates from ferrite grain boundary. The volume fraction of austenite was measured metallographically using an area-analyzer.
As the rseult, it was elucidated that the formation of austenite in the range of 950-1150°C could be expressed by the Austin-Rickett's type equation with time exponent 'n' of 1. On the other hand, from the consideration of the activation energy for the growth of austenite, it was deduced that the formation of austenite was controlled by diffusion of nitrogen or carbon to austenite from ferrite matrix.