Effect of Welding Heat Input on Microstructure and Toughness of Heated‐Affected Zone in Steel Plate with Mg Deoxidation

Abstract

Effect of heat input on the microstructure and toughness of heat‐affected zone (HAZ) in steel plate with Mg deoxidation has been investigated through welding thermal cycle simulation method. With the heat input increasing from 100–400 kJ cm−1, the average prior‐austenite grain (PAG) size is increased from 43 to 56 and then to 173 µm, and the HAZ microstructure is changed from fine bainite lath to relative larger bainite lath and then to grain boundary ferrite (GBF) and intragranular acicular ferrite (IAF). With the heat input increasing up to 400 kJ cm−1, a great amount of IAF is nucleated by the MgO–MnS inclusions with the size about 2 µm. The Charpy impact values at −40 °C of HAZ are larger than 140 J, and excellent low temperature HAZ toughness is obtained for the 68 mm thickness steel plate with Mg deoxidation with the heat input in the range from 100–400 kJ cm−1.