铌微合金化高强塑积冷轧DP780钢的I&Q&P工艺

基于亚稳奥氏体形变诱导相变理论,在实验室采用盐浴炉对800 MPa级冷轧双相钢DP780的I&Q&P(临界退火与淬火配分)工艺进行了探讨,并采用光学显微镜、扫描电镜、拉伸试验机与XRD对不同工艺下试验钢的组织性能进行了研究。结果表明,在I&Q&P工艺试验条件下,试验钢的显微组织由铁素体、马氏体与残留奥氏体组成;830 ℃退火时铁素体晶粒尺寸以＞5 μm为主,860 ℃退火下其晶粒尺寸以＜5 μm为主。830 ℃退火时试验钢的力学性能随淬火温度的变化波动较大,860 ℃退火时试验钢的力学性能随淬火温度的变化波动较小。860 ℃退火+260 ℃淬火时,试验钢的综合力学性能最佳,其抗拉强度、伸长率与强塑积分别为802 MPa、26.8%与21.5 GPa·%,钢中残留奥氏体含量高达13.89%。

I&Q&P process of Nb microalloyed cold-rolled DP780 steel with high product of strength and elongation

Based on the theory of metastable austenite deformation induced phase transformation, the I&Q&P (intercritical annealing and quenching and partitioning) process of 800 MPa grade cold-rolled DP780 steel was investigated by using salt bath furnace in the laboratory. The microstructure and mechanical properties of the tested steel under different processes were studied by means of metallographic microscope, scanning electron microscope, tensile testing machine and XRD. The results indicate that the microstructure of the tested steel is composed of ferrite, martensite and retained austenite under the I&Q&P process. The ferrite grain size is mainly larger than 5 μm at annealing temperature of 830 ℃, however, the ferrite grain size is mainly smaller than 5 μm at annealing temperature of 860 ℃. The mechanical properties of the tested steel annealed at 830 ℃ fluctuate greatly with the change of quenching temperature, conversely, the mechanical properties of the tested steel annealed at 860 ℃ vary slightly. At annealing temperature of 860 ℃ and quenching temperature of 260 ℃, the optimum comprehensive mechanical properties are obtained with tensile strength of 802 MPa, elongation of 26.8%, and product of strength and elongation of 21.5 GPa·%, and the content of retained austenite in the steel is as high as 13.89%.