水平连铸球墨铸铁QT500-7等温淬火工艺的优化研究

Optimal Study on Austempering Process Parameters for Nodular Cast Iron QT500-7 Dense Bar

为了探寻水平连铸QT500-7球铁型材抗拉强度及伸长率的最优等温淬火工艺,运用正交试验方法研究了奥氏体化温度、奥氏体化时间、等温淬火温度以及等温淬火时间对等温淬火球墨铸铁型材(ADI)力学性能的影响。结果表明,影响连铸ADI抗拉强度的主要因素为等温淬火温度;影响伸长率的主要因素为等温淬火温度和等温淬火时间,其中等温淬火温度最为重要。随等温淬火温度升高,高碳奥氏体体积分数增大,铁素体体积分数减小,且铁素体和高碳奥氏体变得粗大,导致ADI抗拉强度下降,伸长率提高。连铸球铁QT500-7型材在880℃/60 min奥氏体化+280℃/150 min等温淬火后,抗拉强度可达1 580 MPa;在960℃/120 min奥氏体化+360℃/125 min等温淬火时,伸长率为11.9%。

In order to optimize the austempering process parameters of ductile cast iron QT500-7 dense bar produced by horizontal continuous casting, the effect of austenitizing temperature, austenitizing time, austempering temperature,austempering time on tensile strength and elongation of the dense bar was investigated by using traditional orthogonal test method. The results indicate that austempering temperature is the most principal factor that affect the tensile strength of the austempered ductile cast iron(ADI). Whereas, the elongation of the ADI is mainly controlled by austempering temperature and austempering time, especially by the former. With increasing austempering temperature, the volume fraction of ferrite decreases, significant coarsening of both ferrite and austenite grains occurs, consequently the tensile strength decreases and the elongation increases. The tensile strength of the ADI can be as high as 1 580 MPa after the dense bar is initially austenitized at 880 ℃ for 60 min and then quickly quenched to the 280 ℃ salt bath for 150 min and then air cooled.Whereas, when the dense bar is austenitized at 960 ℃ for 120 min and quenched into molten salt bath maintained at 360℃ for 125 min and then air cooled, the elongation of 11.9 % can be obtained.