20CrMn钢双辊薄带振动铸轧细晶机理试验

Experimental Study on Twin-roller Strip Cast-rolling under Vibration of 20CrMn Steel

为了改善传统双辊薄带铸轧板坯中存在的缩孔、裂纹、组织不均以及晶粒粗大等缺陷,提升双辊薄带铸轧产品带坯的力学性能,提出振动铸轧新技术,以细化铸轧带坯组织晶粒度,提高其力学性能。为了确定振动铸轧过程的细晶机理,分别在1 570℃和1 530℃两种开浇温度下进行20CrMn钢双辊薄带铸轧振动与非振动工况的对比试验,并对所得带坯微观组织及力学性能进行检测和分析。微观组织观察结果表明,在铸轧过程中振动可以有效细化产品带坯晶粒,其细晶机理为在凝固阶段振动可以提升熔池区形核率并促使振动侧枝晶尖端熔断,而在轧制阶段振动可以强化塑性变形区的动态再结晶;拉伸试验结果表明振动有效地改善了铸轧板坯的力学性能,开浇温度1 570℃时,沿轧制方向振动铸轧板坯较传统铸轧板坯屈服强度、抗拉强度和伸长率分别提高了12.11%、14.57%和38.9%,垂直轧制方向分别提高了7.72%、13.23%和34.8%;开浇温度1530℃时,沿轧制方向分别提高了9.22%、14.95%和31.25%,垂直轧制方向分别提高了21.36%、27.35%和42.86%。试验表明振动铸轧较传统铸轧不仅能在凝固阶段通过振动提高形核率,细化晶粒,还能在轧制段通过振动增强动态再结晶效果,改善材料微观组织结构,从而提升其力学性能。

In order to improve the comprehensive mechanical properties of the twin-roller cast-rolling strip,the concept of vibratory cast-rolling is proposed to refine the grain size of the strip. For the purpose of verifying the grain refinement effect of the vibratory cast-rolling technology and exploring its mechanism,twin-roller strip cast-rolling comparative experiments of 20CrMn steel under the condition of vibratory and non-vibration are carried out at two casting temperatures of 1570°C and 1530°C respectively. Then the microstructure and mechanical properties of the strips obtained from the experiments are tested and analyzed. The microstructure observation result shows that the mechanical vibration can effectively refine the grain of the cast-rolling strip. The mechanism of grain refinement is that the vibration can promote the rupture of dendrite in the vibratory side so as to increase the nucleation rate in the molten pool in the solidification stage and can promote the dynamic recrystallization of the plastic deformation zone in the rolling stage. Tensile test result shows that mechanical vibration effectively improves the mechanical properties of the cast-rolling strip. At the casting temperature of 1570°C,the yield strength,tensile strength and elongation of the vibratory cast-rolling strip are respectively 12.11% ,14.57% ,38.9% higher in the rolling direction and 7.72% ,13.23% ,34.8% higher in the vertical-rolling direction than that of the conventional cast-rolling strip.At the casting temperature of 1530°C,the yield strength,tensile strength and elongation of the vibratory cast-rolling strip are respectively 9.22% ,14.95% ,31.25% higher in the rolling direction and 21.36% ,27.35% ,42.86% higher in the vertical-rolling direction than that of the conventional cast-rolling strip. The results show that vibration casting-rolling can not only increase nucleation rate and refine grain size in solidification stage,but also enhance dynamic recrystallization effect by vibration in rolling section,improve microstructure of material and enhance mechanical properties.