Characterization of the cladding layer by laser cladding of 9Cr18Mo powder on 3Cr14 martensitic stainless steel and the impact of martensite obtained through post heat treatment on hardness

In this study, the relationship between microstructure and hardness of the cladding layer obtained from a real laser cladding knife was investigated. It was developed for high-end knives by laser cladding of 9Cr18Mo powder on the cutting edge of 3Cr14 martensitic stainless steel. The study indicated that martensite-free matrix structure (austenite with small amount of network Cr7C3) formed after cladding was responsible for the low hardness (420 HV) of the cladding layer. To enhance the hardness, post heat treatment (PHT) and cryogenic treatment (CT) were used. The results suggested that PHT had a significant effect on hardness enhancement, and the subsequent CT could further improve the hardness. The hardness was increased to ~700 (PHT) and 760 (PHT+CT) HV respectively, which was higher than that of 3Cr14 matrix (~620 HV). The mechanism is that PHT promotes the precipitation of Cr23C6 and then reduces the Ni and Mo equivalent (Nieq and Creq) of cladding layer matrix to austenite and martensite (A+M) region, thus promoting the formation of martensite and increasing the hardness. The subsequent CT further induces martensitic transformation of retained austenite (RA) and reduces the content and size of RA, and thus further increases the hardness. [Display omitted]