Effect of Cr addition on microstructure, mechanical properties, and corrosion behavior of weld metal in weathering steel of high-speed train bogie

The effects of Cr addition on the microstructure, mechanical properties, and corrosion behavior of two weld metals containing Ti or Mo within the Ni-Cu alloys used in high-speed train bogies were investigated. The results show that Cr can increase the acicular ferrite (AF) by about 15%, reduce the primary ferrite (PF) and the ferrite with second phase aligned (FSP), and slightly increase the M-A constituents in the weld containing Ti. Cr addition scarcely alters the AF, leads to a decline in PF and an increase in FSP, and causes a substantial increase in M-A constituents from 0.4 to 2.5% in the as-welded zone containing Mo. Meanwhile, it was found that Cr addition negatively affects weld toughness in the weld containing Mo due to the increase in the proportion and size of M-A constituents and the coarsening of inclusions. Regarding the corrosion resistance, Cr addition can promote the absorption of Cr on the surface of inclusions. This is the main reason for the reduction of the initial corrosion rate of the weld containing Mo, while this effect is attenuated in the welds containing Ti. In addition, Cr addition can densify the inner and outer rust layers, thereby reducing the corrosion rate of the welding rust layer.