Weldability and Microstructure Evolution of Powder Metallurgy High Chromium Cast Iron/Low Carbon Steel Welded by Gas Tungsten Arc Welding

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