Structure–property-correlation in laser surface alloyed AISI 304 stainless steel with WC + Ni + NiCr

The present study concerns a detailed investigation of the characteristics and properties of the alloyed zone formed in laser surface alloyed AISI 304 stainless steel with WC + Ni + NiCr (in the ratio of 70:15:15). Laser surface alloying has been carried out using a 5 kW continuous wave (CW) Nd:YAG laser (at a beam diameter of 4 mm), with the output power ranging from 1 to 3 kW and scan speed from 0.005 m/s to 0.1 m/s by simultaneous feeding of precursor powder (at a flow rate of 20 mg/s) and using Ar shroud at a gas flow rate of 5 l/min. The effect of laser power and scan speed on the characteristics of the surface alloyed layer (microstructures, phases and composition) and property (microhardness) have been investigated in details. Laser surface alloying leads to development of fine grained γ-stainless steel with the dispersion of WC, W2C, M6C and M23C6. The microhardness of the alloyed zone is significantly improved to a maximum value of 1350 VHN as compared to 220 VHN of as-received γ-stainless steel. The optimum parameters for laser processing were derived.

► Optimization of process parameters for development of WC dispersed composite with Ni + NiCr as binder.
► Development of fine grained γ-stainless steel with the dispersion of very fine carbides (WC, W2C, M6C and M23C6).
► A significantly improved microhardness of the top surface (to 700–1350 VHN) as compared to as-received matrix (220 VHN) and its correlation with microstructures.
► Detailed microstructural evolution of the alloyed zone and its correlation with process parameters.
► Graded hardness distribution is achieved when lased with a low scan speed.