Stress induced shear band strengthen high-silicon alloy steel via LHITT between Ms and Md temperature

This study concerns that the high-silicon alloy steel treated by the laser hardening with an in-situ thermal treatment (LHITT) between Ms and Md temperature. The shear band, such as nano-twin and ε-martensite is expected to be obtained by the aid of thermal stress during laser hardening process to strengthen the steel. The in-situ thermal treatment temperature of the steel was confirmed by thermal mechanical simulator and thermodynamic model. The residual stress of the hardening layer was measured by X-ray stress analyzer. The phase structures were characterized by X-ray diffractometer (XRD), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). Moreover, the nano-hardness was evaluated by the nano-mechanical tester. The experimental results demonstrate that the stacking faults were generated by the laser thermal stress which drives high density dislocations motion on {111}γ planes. The shear band is formed by the overlapping of the stacking faults in austenite during the LHITT process. Besides, the high surface hardness (7.9 GPa) can be achieved by the LHITT. The hard points (9.5 GPa) in LHITT sample are related with the shear band as the analysis of the elastic modulus.