Effect of Heat Input on Austenite Reversion, Recrystallization, and Ensuing Impact Toughness in Simulated Intercritical Coarse‐Grained Heat Affected Zone of Medium Mn Steel

Abstract

A systematic experimental study has been conducted on the simulated intercritical coarse‐grained heat affected zone of 690 MPa grade heavy‐plate medium Mn steel by tailoring heat input of the first welding pass to obtain the influence of initial microstructure on the austenite reversion mechanism, recrystallization, and resultant impact toughness. Results reveal that prior austenite grain size significantly increases from 30 ± 11, 41 ± 14 to 54 ± 15 μm with the increasing heat input from 15, 30 to 50 kJ cm−1, which affect the nucleation site of reversed austenite, recrystallization mechanism, and final microstructure. Accordingly, impact toughness is better at the heat input of 30 kJ cm−1 (75.2 ± 0.8 J) in comparison with that of 15 kJ cm−1 (63.3 ± 13.3 J) and 50 kJ cm−1 (26.7 ± 6.5 J) at −40 °C, which is mainly ascribed to the formation of lamellar heterogeneous structures, multiplication of slip system and morphology of high‐angle grain boundaries.