Laser cladding of high Co–Ni secondary hardening steel on 18Cr2Ni4WA steel

• High Co-Ni secondary hardening steel coating was deposited on 18Cr2Ni4WA steel by laser cladding.
• The high Co-Ni steel coating displayed higher microhardness than the 18Cr2Ni4WA steel substrate.
• Microstructure of the high Co-Ni steel coating was investigated by SEM and EDS.
• The difference of microstructures and elements compositions between coating and substrate resulted in their different microhardness.
• Microstructural transformation of the heat-affected zone was ascribed to high cooling rate during laser cladding.

Laser cladding of the high Co–Ni secondary hardening steel on the 18Cr2Ni4WA steel using the laser direct metal deposition (LDMD) technology was investigated. The hardness was measured with a Vickers indenter, and the microstructural evolution was analyzed using a SEM equipped with an EDS and X-ray diffraction. The results indicated that the wear resistance of the 18Cr2Ni4WA steel substrate could be greatly improved by the coating of laser cladded high Co–Ni secondary hardening steel. After laser cladding, the microstructure of the heat-affected zone in the 18Cr2Ni4WA steel substrate was typical martensitic structure transformed from the initial granular bainitic structure. Besides, Fe-based ferrite, martensite, lath retained austenite, and two types of precipitations dispersed in the matrix were observed in the laser cladded high Co–Ni secondary hardening steel coating. They were determined to be the needle-shaped Fe(Cr, Co, Ni)3C cementite with size of approximately 1–3 μm and rod-shaped fine-scale (less than 0.1 μm in length) M2C carbides, respectively.