1. The pre-hardened AISI P20 plasti

1. The pre-hardened AISI P20 plastic die steel (original substrate)treated by LTH obtained the uniform and dense microstructure, there were no cracks, pores and other defects. Moreover, LTH had a microleveling effect on the material surface. Comparing with the originalsubstrate, the microhardness of the laser transformation hardened layerwas improved by 2–3 times, and the compressive residual stress was 4times higher than the substrate. The depth of laser transformationhardened layer increased with increase of laser liner energy. Especially,the sample with 1.8 kW 3 mm/s obtained the deepest hardened layer(770 μm) and highest microhardness (789.7 HV).