Effect of Surface Shot Peening and Annealing Treatment on the Microstructure and Properties of Fe-30Mn-3Al-3Si TWIP Steel
Surface shot peening and annealing heat treatment were applied to the Fe-30Mn-3Al-3Si TWIP steel to achieve toughening. The effects of shot peening and shot peening combined with annealing on the microstructure of TWIP steel were analyzed by means of metallurgical microscopy, X-ray diffraction and transmission. The hardness distribution, mechanical properties and work-hardening behaviors of the original samples , shot peened and shot peened+annealed samples were analyzed by using the micro-Vickers hardness tester and universal material tes-ting machine. Results showed that the strong plastic deformation on the surface of TWIP steels was induced by shot peening, which resulted in the formation of highly deformed layer containing dislocation clusters of 60～100 nm size and transition layer containing micro and nanoscale de-formation twin structures. This nano-micron scale grain size gradient structure could significantly increase the hardness of the highly deformed layer on the surface of TWIP steels to 366 HV0.1 . Under the combined action of residual compressive stress, the yield strength of the sample in-creased to 485 MPa, which was much higher than the corresponding value of the initial sample. However, its fracture elongation was only 41.8％due to the surface roughness induced by shot peening and the nanocrystals with low plasticity in the highly deformed layer. After the an-nealing treatment, the deformed microstructure in the shot peened sample underwent recovery and recrystallization, with recrystallized grain si-zes ranging from 1 to 3 μm in the strongly deformed layer position, and the hardness also decreased to 215 HV0.1 . The yield strength of the formed micron-micron scale grain size gradient structure specimen declined to 261 MPa, but the elongation was improved to 65.3％. Besides, the grain size gradient structure was promotable to enhance the yield and tensile strength of TWIP steel, but was not favorable for the improve-ment of elongation.
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