Laser Surface Hardening for 38CrMoAl Steel

The laser surface hardening on 38CrMoAl steel was carried out using a continuous wave CO_2 laser.The hardened depth and the hardness distribution in the cross-section of the hardened layer were tested and the microstructure in the hardened layer was observed and analyzed.The results show that the microhardness in the hardened layer reaches 850HV0.3,which is 3～4 times as high as that in the substrate.The hardened layer consists of two sub-layers including a uniform phase transformation layer and a transition layer.The corresponding microstructure in the uniform phase transformation layer is some fine dislocated lath martensite with a few retained austenite.The microstructure in transition layer is the mixture of lath martensite and undissolved ferrite.Under a proper laser power and a suitable off-focus length,both the hardened depth and width decrease with the increase of laser-scanning speed,but the hardness enhances firstly,decrease then with the increase of the laser scanning speed.The test shows that the optimal parameters for laser-hardening 38CrMoAl steel are of that the laser power is 1.8 kW,off-focus length is 48mm,scanning speed is 20mm/s.