Correlation between Weld Metal Microstructure Evolution and Welding Process Parameters of Low Alloy Ferritic Steel Weldments

Abstract

This study attempts to propose a convenient method to adjust the welding process parameters window with the aim of high volume fraction of acicular ferrite in the weld metal (WM). The samples are directly extracted from the deposition zone of two low alloy ferritic steel dissimilar welded joints (DWJs) that manufactured using different consumables, and their microstructural evolution is controlled using thermomechanical simulation technique. The results show that it is hard for the low‐alloyed WM to obtain high amount of acicular ferrite no matter how to control the cooling process, meaning that the welding consumable with only a small amount of alloying elements is not suitable for welding this DWJ. However, for the high‐alloyed WM, the acceptable window of the cooling process is determined within 10–22 °C s−1 to achieve aimed microstructure. In situ observation shows that the preexisting bainitic laths significantly reduce the growth space of acicular ferrite plates. The average lengthening rate of acicular ferrite plates is ranged from ≈5 to ≈68 μm s−1 at a cooling rate of 3 °C s−1.