Impact of Intercritical Annealing on Retained Austenite and Toughness of a 460 MPa Grade Multiphase Heavy Gauge Plate Steel

The objective of the study described here is to elucidate structure‐property relationship in a 460 MPa multiphase steel with particular emphasis on the influence of intercritical annealing process and retained austenite on mechanical properties. The study suggests that there is significant effect on comprehensive mechanical properties of heavy gauge plate (60 mm thickness) on intercritical annealing, especially the low temperature toughness is increased from 135 to 254 J at the test temperature of −40 °C. Fine retained austenite can be obtained by optimization of interrupted on‐line cooling and partitioning during intercritical annealing heat treatment. The retained austenite stabilized by enrichment with alloying elements during heat treatment replacing coarse martensite and austenite (M/A) constituent is the underlying reason for superior toughness. The study underscores that a practical approach to enhance the toughness of heavy plate is via multiphase control during thermo‐mechanical control processing (TMCP) and off line intercritical annealing.