Weldability and microstructure evolution of powder metallurgy high chromium cast iron/low carbon steel welded by gas tungsten arc welding

Powder metallurgy high chromium cast iron (PM HCCI) and low carbon steels (LCS) were welded by multi-pass manual gas tungsten arc welding (GTAW). The effects of welding current on the microstructure evolution and mechanical properties of the weld joints were systematically investigated, the microstructure evolution model of the weld joints was proposed, and the fracture mechanism of the solders was also discussed. In the results, the tensile strength of the welded joints reaches 538.1 MPa at 140 A welding current, which is 95.3% and 97.4% of the tensile strength for PM HCCI and LCS, respectively. The microhardness of the welded joints decreases from HCCI side to LCS side in the horizontal direction, whereas in the vertical direction, the microhardness distribution is of M-shape due to the secondary tempering and alloying element diffusion/segregation. The fusion zone (FZ) mainly consists of the austenite and tempered martensite at the welding current of 140 A, and there is a single austenite columnar crystals zone between FZ and LCS; while there is a HCCI columnar crystal zone between FZ and the sintered HCCI, in which the coarsen carbides with branches are distributed along the matrix’s grain boundary.