Residual Copper Effects on Toughness of GMAW Low-Carbon Steel

Increasing amounts of residual copper in the steel scrap stream can lead to enrichment in recycled steel products. While copper is often controlled to avoid issues during thermomechanical processing, its downstream effects on microstructure and properties after welding are less known. This work explores the effect of increased copper content, up to 0.83 wt-%, on microstructure and Charpy impact behavior of hot-rolled low-carbon steel plates welded with gas metal arc welding (GMAW). Microstructural characterization of the hot- rolled base metal and GMAW heat-affected zone (HAZ) was conducted. It was found that austenite stabilization and an increase in hardenability from copper led to a higher fraction of more brittle non-ferritic microstructural constituents in the base metal, resulting in a higher 20 ft•lb ductile- brittle transition temperature (DBTT). However, the GMAW HAZ of all the alloys primarily consisted of tempered martensite, resulting in an overall lower DBTT than that of the base metals, with little effect from copper content. This work shows that copper’s effects on microstructural evolution must be considered during thermomechanical processing and welding to ensure high toughness in low-carbon steel plate.