The structure feature of solidied surface by laser irradiating

The surface structure of the low alloying steel CrWMn after laser solidification,with a 2kW CO2 laser,was examined by optical microscopy,and scanning electron microscopy.Experimental results showed that the macroscopical solidification structure of the steel surface was heterogeneous.The structure was ① a mixture of the white structure and the black structure in the edge of the melt zone (B zone),and ② a mixture of the center of the melt zone(A zone) structure and the B zone structure.The white structure was residual austenite(HV0.2300kgf/mm2),but the black structure was tempered martensite and residual austenite(HV0.2620kgf/mm2).Finally,it is pointed out that the phenomenon is brought obout by the nature of convection movement.