Influence of the phase composition and microstructure of plasma cladding Fe-Cr-Ni-C alloy coating on residual stress and crack formation

Abstract

The Fe–Cr–Ni–C alloy coatings with different phases have been prepared by plasma cladding technique on high manganese austenitic steel preheated with different temperatures. The effect of the phase composition on crack formation, residual stress, and micro-hardness of Fe–Cr–Ni–C alloy coatings was investigated by scanning electron microscopy (SEM) with energy-dispersive spectrum (EDS), micro-hardness tester, infrared thermal imager, and residual stress tester. The results show that for Fe-based coating deposited on the substrate non-preheated, the transverse and perpendicular cracks are generated after the end of cladding, which belongs to transcrystalline fracture. The Fe–Cr–Ni–C alloy coatings are composed of the solid solution of austenitic and fishbone-like eutectic carbide, which was mainly (Cr, Fe)₇C₃. As the preheating temperature of substrate is 350 °C, granular metallic carbides with the diameter 1 μm are precipitated at grain boundaries and no cracks formed. The carbide phases are mainly (Cr, Fe)₇C₃ and (Cr, Fe)₂₃C₆ in cladding coatings. With the decreased rate of cooling, carbide precipitation phase changed from metastable (Cr, Fe)₇C₃ to stable (Cr, Fe)₂₃C₆ phase. The precipitation stable carbide phase has significance to prevent the formation of cracks and improves the micro-hardness of the Fe-based coating on the substrate preheated to 350 °C. The residual stress of specimen with substrates of non-preheating and preheating 250 and 350 °C is 234.2, 267.3, and 300.6 MPa, respectively. The maximum value of micro-hardness of coating with substrates of non-preheating is 986.1 HV, which is about six times than that of substrate.