Microstructural Studies of Composite (Cr₃C₂–NiCr) Laser Clads Developed on Preheated Substrate T91

Abstract

High cooling speed in laser cladding process yields excellent metallurgical and mechanical properties. Indeed, this attribute along with the process’s additive nature contributes significantly to the development of thermal stresses that are the major cause of any possible crack and delamination formation across the deposition. This limitation is more common for additive materials such as chromium carbide which are crack-sensitive by nature during most of the hard facing process. In the current work, A 90 wt% Cr₃C₂–10 wt% NiCr-based laser clads were developed with and without preheating the substrate T91. In the case of preheating, the substrate was preheated at 200 °C, 400 °C, and 600 °C temperature before clad deposition. Liquid dye penetration test was carried out on the developed composite clads, whereas 20 numbers of cracks per unit length were observed on without preheated substrate. The microstructure studies revealed that the preheated substrates have shown a crack-free structure as compared to those without preheating of the substrate. The clad height, heat-affected zone, and dilution rate were found reliable in the case of cladding developed at preheated temperature (200 °C) as compared to higher preheated temperature (400 °C and 600 °C). Energy-dispersive X-ray spectroscopy study cleared that the chromium-rich phases were more segregated with iron and nickel elements on the developed clad on the preheated surface as compared to the surface developed on without preheating of the substrate. The average microhardness of the developed composite laser clads with and without preheating of the substrate was 802 ± 94 HV and 878 ± 68 HV, respectively. This was found to be much higher than the substrate microhardness (439 ± 12 HV).