退火时间对中碳钢亚温淬火冷轧组织性能的影响

对热轧中碳钢板进行亚温淬火，随后冷轧(变形量50%)并进行不同时间退火，退火温度为550℃。通过扫描电镜(SEM)、X射线衍射(XRD)、背散射电子衍射(EBSD)对退火试样进行显微组织表征，并通过室温拉伸试验分析了双峰结构对力学性能的影响。结果表明，退火处理后的组织由铁素体和渗碳体两相构成，铁素体由细晶区/粗晶区共同组成。随着退火时间的延长，细晶峰值略有增大，但是增长并不明显，粗晶峰值晶粒呈减小趋势。随着退火时间的延长，试样的抗拉强度和屈服强度呈下降趋势，伸长率呈上升趋势，韧窝尺寸增大，深度增加，并且在大尺寸韧窝附近富集小尺寸韧窝。当退火时间为30 min时，力学性能最优。

Effect of annealing time on microstructure and mechanical properties of medium carbon steel subcritical quenched

The hot-rolled medium carbon steel was subcritical quenched, then cold rolled(deformation of 50%) and annealed at 550 ℃ for different time. The microstructure of annealed specimens was characterized by means of scanning electron microscopy(SEM), X-ray diffraction (XRD) and backscattered electron diffraction (EBSD), and the effect of bimodal structure on mechanical properties was analyzed by means of tensile experiments at room temperature. The results show that the microstructure after annealing is composed of ferrite and cementite, and the ferrite is composed of fine and coarse crystal regions. With the prolongation of time, the peak value of fine crystal increases slightly, the increase is not obvious, but the peak value of coarse crystal decreases. With the increase of annealing time, the tensile strength and yield strength of the specimens show a decreasing trend, while the elongation shows an increasing trend. The size and depth of dimples increase, and small dimples are enriched near large dimples. When the annealing time is 30 min, the mechanical properties are the best.