3.2. Characterization of microstructureFig. 4 shows the cross-section morphologies and EDS line scanning data of laser transformation hardened layer under the laser parameters with 1.8 kW 3 mm/s. The laser transformation hardened layer could be divided into three parts: hardened zone (HZ), transition zone (TZ), heataffectedzone (AZ) as shown in Fig. 4(a). The number of carbon atomswas obviously larger within the range of 0 to 500 μm from the hardenedsurface of the sample as shown in the EDS line scanning analysis, whichillustrated that the carbon content in HZ was higher than TZ and AZ.Higher heat input in HZ made more carbon atoms dissolve into theaustenite during the heating process. It was worth noting that thefluctuation amplitude of content of Cr atoms in HZ was obviouslysmaller than other zones as shown in the EDS analysis, which meantthat the condition of poor Cr zone was improved by the continuousdissolution of carbides. Furthermore, the center of HZ was selected tobe observed using SEM because the heat in HZ was more from the laserthan the heat conduction of the metal material itself, the heat input wasthe highest in all zones, so the microstructure of HZ would be moreobvious with higher researching value.