Strengthening mechanisms and tensile properties of 20Cr2Mn2Mo processed by laser shock peening and vacuum carbonitriding

The effects of laser shock peening and vacuum carbonitriding on strength and plasticity of 20Cr2Mn2Mo were investigated. Uniaxial tension tests were carried out and the microstructures were analyzed by optical microscope, scanning electron microscope, electron backscatter diffraction, and transmission electron microscope. The phase composition was characterized by X-ray diffraction. The results revealed that the yield strength and ultimate tensile strength of samples were increased by 10.63% and 4.15%, respectively, after compound treatment due to the formation of large volume fraction of grain boundaries, high-density dislocations, and second-phase particles. However, the plasticity was only decreased by 0.99%, which was benefited from gradient structures induced by laser shock peening. The improvement of strength was mainly attributed to Orowan strengthening and dislocation strengthening. The grain refinement had little influence on the improvement of strength.