Effect of Cu content and heat input on post-weld properties and microstructure of Cu-bearing steels

To investigate the effect of Cu content on the microstructure and properties of low-carbon steel welded joints under varying heat inputs, three low-carbon steels with Cu contents of 1 wt.%, 1.5 wt.%, and 2 wt.% were designed in this study. Both simulated welding thermal cycle experiments and practical welding tests were carried out. Comprehensive post-welding analysis including thorough mechanical properties and microstructural evaluation of the microstructural evolution were meticulously investigated. The findings revealed that a Cu content below 2 wt.% does not result in the clustering of rather large Cu-rich phases, which could detrimentally affect mechanical properties; instead, it leads to precipitation strengthening through the formation of fine Cu-rich precipitates. Notably, thermal simulation experiments on Steel #1 (with 1 wt.% Cu) unveiled substantial precipitation strengthening at heat inputs exceeding 150 kJ/cm. Furthermore, practical welding tests demonstrated that an increase of Cu content up to 2 wt.% led to a refinement of grain size within the weld joints, thereby enhancing the toughness of the heat-affected zone and of the overall welding performance.