3Cr14不锈钢表面激光熔覆S390粉末高速钢涂层的组织及回火转变特征

Microstructure and tempering transformation of 3Cr14 stainless steel surface melt-clad with laser S390 high-speed steel coating

采用同轴送粉激光熔覆技术在3Cr14不锈钢基体上熔覆一层3mm厚的S390粉末高速钢涂层,并对熔覆后的试样进行560℃×1h×3次回火热处理.分析了熔覆层热处理前后的微观组织与析出相以及熔覆层硬度的变化规律及压痕情况.结果表明:S390熔覆层组织为淬火马氏体+残余奥氏体+黑色组织+共晶莱氏体+网状碳化物,有少量的颗粒状M_3C型碳化物在晶内析出,晶界网状碳化物以VC、V_2C为主;熔合线处形成10μm的平面晶区,然后由细晶区、柱状晶区,向熔覆层中部的等轴晶过渡;回火后,部分网状碳化物被打断,M_3C型碳化物大量回熔,有细小颗粒状的富V元素的MC、M_2C类型碳化物在晶内析出;热处理后熔覆层显微硬度提高约200HV,洛氏硬度压痕周围发现明显塑性变形区,熔覆层脆性得以改善.

A layer of S390 coating of powder metallurgical high-speed steel(PMHSS)was produced on substrate of 3Cr14 stainless steel with coating thickness of3mm by means of coaxial powder feeding laser melt-cladding technique and then heat treatment of one-hour tempering at 560℃ was carried out three times for the melt-cladding sample.The microstructure,and precipitated phases of the melt-cladding coating were analyzed and further the hardness variation rule and identation condition of the coating were analyzed before and after heat treatment.The result showed that the microstructure of S390 melt-cladding layer would consist of quenched martensite,residual austenite,black microstructure,eutectic ledeburite and network carbides;A small amount of carbide particles M3C would precipitate in the grain and the grain boundary network carbides would mainly be composed of VC and V2C;a10μm plane crystal region would form at the bond line of the crystal grain and then the fine crystal region and the dendrite would transit to ward the equiaxed crystal in the middle of the melt-cladding layer.After tempering,part of the reticular carbide would be interrupted and a large amount of M3C-type carbides would dissolve back into solution.Fine and granular element V-rich MC-and M2C-type carbides would precipitate in the crystal.The microhardness of cladding layer would increase by about200HV after heat treatment,the plastic deformation zone would be found around the Rockwell hardness indentation,and the brittleness of the cladding layer would be improved.