0.2C-5Mn-0.5Si-2.5Al中锰钢临界退火后的微观组织及力学性能

利用热力学模拟计算、扫描电镜(SEM)、X射线衍射仪(XRD)、拉伸试验机等设备研究了不同退火工艺下0.2C-5Mn-0.5Si-2.5Al中锰TRIP钢的相变规律、微观组织及力学性能,分析了Al对相变规律及工艺与组织性能的影响规律。结果表明:添加(质量分数)2.5 %Al后,两相区显著扩大,且A₃温度明显提高,这有助于提高临界退火温度,进而加快奥氏体逆相变过程,有效地提高在较短临界时间(1、3 min)退火后的残留奥氏体含量;因2.5 %Al的添加,微观组织中出现了δ-铁素体;在临界退火温度范围内(760~880 ℃),随着退火温度的升高,屈服强度呈现略微下降趋势,而抗拉强度逐渐增加,退火1 min时伸长率及强塑积随退火温度的增加先升高后降低,而退火3 min时伸长率及强塑积随退火温度升高呈持续下降趋势;试样在760 ℃退火3 min可获得最佳的力学性能,抗拉强度为927.69 MPa,伸长率为50.12%,强塑积为46 503.00 MPa·%。

Microstructure and mechanical properties of 0 . 2 C-5 Mn-0 . 5 Si-2 . 5 Al medium manganese steel after intercritical annealing

The phase transformation, microstructure and mechanical properties of the 0.2C-5Mn-0.5Si-2.5Al medium manganese TRIP steel under different annealing processes were studied by means of CALPHAD (calculation of phase diagram) method, SEM (scanning electron microscopy), XRD (X-ray diffractometry) and tensile test. The influence of Al on the law of phase transformation, process, microstructure and properties were studied. The research results show that after the addition of 2.5 %(mass fraction)Al, the two-phase temperature region is significantly expanded, and the A₃ temperature is obviously increased, which is beneficial to increase the intercritical annealing temperature, so the austenite reverse transformation process is accelerated, the retained austenite content after intercritical annealing for short time(1, 3 min) is effectively increased. Due to the addition of 2.5 %Al, δ ferrite appears in the microstructure. In range of 760-880 ℃, with the increase of intercritical annealing temperature, the elongation shows a trend of increasing first and then decreasing, while the yield strength decreases slightly, the tensile strength continues to increase. For 1 min annealing, with the increase of intercritical annealing temperature, the elongation and the product of strength and ductility shows a trend of increasing first and then decreasing. While for 3 min annealing, with the increase of intercritical annealing temperature, the elongation and the product of strength and ductility all show a trend of continue to decrease. The optimum mechanical properties are obtained by annealing at 760 ℃ for 3 min, where the tensile strength is 927.69 MPa, the elongation is 50.12%, and the product of strength and ductility is 46 503.00 MPa·%.