(c) With the continuous dissolution

(c) With the continuous dissolution of carbides during the heating process, more Cr atoms were precipitated out from carbides, which was the main element to improve the corrosion resistance property. The increase of Cr atom content was conductive to the balance of Cr content between the poor and rich Cr regions. Cr could also reduce the sensitive of intergranular corrosion and improve the repair ability of steel passivating film [25–27]. For the laser transformation hardened samples, the corrosion resistance property had been improved in different degrees with varied laser parameters, especially the sample with 1.8 kW 3 mm/s possessed the best corrosion resistance property. In contrast, the sample with 1.7 kW 3 mm/s possessed the worst corrosion resistance property because some of Cr atoms were still entrapped in the residual carbides. Comparing with the sample with 1.8 kW 3 mm/s and the sample with 1.8 kW 4 mm/s, both of them showed less distinct carbide particles. However, the high scanning velocity reduced the interactiontime between laser beam and material, resulting in more undissolved carbides than the sample with 1.8 kW 3 mm/s. Therefore,Cr atoms in the sample with 1.8 kW 4 mm/s played a weaker role in thepassivation film than that in the sample with 1.8 kW 3 mm/s.