The original substrate used was pre-hardened AISI P20 steel with the dimension of 300 × 100 × 10 mm3. The pre-hardening was processed as follows: (a) heating the specimen to 600 ℃ and keeping warm for 2 h for pre-heating; (b) heating to 850 ℃ and keeping warm for 2 hfor hardening, and then cooling in oil; (c) heating the specimen to 600℃, keeping warm for 1 h for tempering, and then cooling in air. The initial microstructure of pre-hardened AISI P20 steel (polished and etched by 4% nital) is tempered sorbite. The chemical compositions arelisted in Table 1.