EFFECTS OF LASER-SHOCK PROCESSING ON THE MICROSTRUCTURE AND SURFACE MECHANICAL-PROPERTIES OF HADFIELD MANGANESE STEEL

The effects of laser-shock processing (LSP) on the microstructure, har dness, and residual stress of Hadfield manganese (1 pet C and 14 pet M n) steels were studied. Laser-shock processing was performed using a N d:glass phosphate laser with 600 ps pulse width and up to 120 J/pulse energy at power density above 10(12) W/cm(2). The effects of cold roll ing and shot peening were also studied for comparison. Laser-shock pro cessing caused extensive formation of epsilon hexagonal close-packed ( hcp) martensite (35 vol pct), producing up to a 130 pct increase of su rface hardness. The surface hardness increase was 40 to 60 pet for the shot-peened specimen and about 60 pet for the cold-rolled specimen. T he LSP strengthening effect on Hadfield steel was attributed to the co mbined effects of the partial dislocation/stacking fault arrays and th e grain refinement due to the presence of the epsilon-hcp martensite. For the cold-rolled and shot-peened specimens, the strengthening was a result of epsilon-hcp martensite and twins with dislocation effects, respectively. Shot peening resulted in a relatively higher compressive residual stress throughout the specimen than LSP.