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研究了热轧汽车用超细晶亚稳钢两相区温度630℃下退火时间对组织和力学性能的影响,利用SEM、TEM等方法对实验钢进行了组织结构表征,利用XRD法测量了室温组织中的残留奥氏体量,通过拉伸试验机测试了钢的单轴拉伸性能。结果表明:在630℃下退火,保温5 min后室温组织中存在50%以上的亚稳奥氏体,随着保温时间的延长,残奥含量先增加后减少,残奥含碳量逐渐降低;抗拉强度先逐渐升高然后略有降低,但都保持在1100 MPa以上,伸长率也先增加后减小;在630℃保温3 h后,断后伸长率(33.5%)和强塑积(38.3 GPa·%)获得最大值,抗拉强度达到1142 MPa,综合力学性能最佳。分析认为,热轧钢中大压下产生大量的位错、畸变和在两相区退火中奥氏体的形核与长大是实验钢获得组织超细化的原因;大量亚稳奥氏体的TRIP效应和超细晶基体共同作用实现了实验钢高强度和高塑性。
The microstructure and mechanical properties of annealed ultrafine-grained metastable steel in hot-rolled automotive two-phase zone at 630 ℃ were investigated. The microstructures of the experimental steel were characterized by SEM and TEM. The amount of retained austenite in the tissue was measured by tensile testing machine for uniaxial tensile properties of the steel. The results showed that there were more than 50% metastable austenite in the room temperature after annealing at 630 ℃ for 5 min. With the extension of holding time, the content of Paralympic increased first and then decreased, and the content of carbon in Paralympic decreased gradually. Tensile strength first increased gradually and then decreased slightly, but both kept above 1100 MPa, the elongation also increased first and then decreased; after 630 ℃ for 3 h, the elongation at break (33.5%) and the ductility (38.3 GPa ·%) obtained the maximum, the tensile strength of 1142 MPa, the best comprehensive mechanical properties. The analysis shows that a large number of dislocations occur in the hot-rolled steel under large pressure, and the deformation and the nucleation and growth of austenite during the annealing in the two-phase zone are the causes for the ultrafine microstructure of the experimental steel. A large amount of metastable austenite TRIP effect and ultrafine grained matrix to achieve high strength and high plasticity of experimental steel.