Preparation of M2 high-speed steel with uniform surface hardness by preheating assisted laser cladding on Cr12MoV steel surface

The surface hardness uniformity of Cr12MoV steel, used as cold-rolling work rolls, is crucial. However, during the laser cladding process of M2 high-speed steel powder, improving the surface hardness uniformity of the cladding layer by adjusting the laser process parameters alone is very limited. Substrate preheating is mostly used to mitigate the high stress and cracking defects in the cladding layer, while its effect on improving the surface hardness uniformity of the cladding layer has been neglected. In this paper, the influence mechanism of substrate preheating on the surface hardness uniformity of the cladding layer is investigated by combining experimental and numerical simulation methods. The results show that as the substrate preheating temperature increases (from 20 to 400 °C), the temperature and residual stress differences between the front and rear halves of the cladding layer progressively decrease. The microstructure of the cladding layer transitions from a mixed distribution of columnar and equiaxed dendrites to a uniform equiaxed dendritic structure. Furthermore, the distribution trend of Cr elements between the both halves becomes more homogeneous, and the surface hardness fluctuation coefficient of the cladding layer decreases from 75.2 to 9.1. Substrate preheating can improve surface hardness uniformity by promoting microstructural uniformity through improved temperature distribution and chemical composition homogeneity during molten pool solidification. This finding facilitates the development of high-quality M2 laser cladding layers with uniform surface hardness on Cr12MoV steel and may also provide valuable insights for the development of other cladding layers.