The objective of this study was to find the effect of cooling rate on microstructure and hardness of steel ball. Steel samples of φ3 mm × 10 mm have been used under the different cooling experiments to study microstructure evolution. The microstructure is observed with optical microscopy and scanning electron microscope, respectively. The transformation temperature is determined by dilatometric curves. The results show that faster the cooling rate is, the lower is the starting and finishing temperatures of austenite-to-pearlite transformation. However, faster cooling rate has no effect on the starting temperature of martensite transformation. The prior austenite grain size increases rapidly with a higher temperature and almost remains invariant with a longer austenitization time. The hardness y of steel and cooling rates x accord with a relationship: y = 11.885x⁴− 131.06x³ + 443.75x²− 320.21x + 387.45.

这项研究的目的是发现冷却速率对钢球的组织和硬度的影响。在不同的冷却实验中，使用了φ3 mm×10 mm的钢样品来研究组织演变。分别用光学显微镜和扫描电子显微镜观察微观结构。转变温度通过膨胀曲线确定。结果表明，冷却速度越快，奥氏体向珠光体转变的起始和结束温度就越低。但是，更快的冷却速度对马氏体转变的起始温度没有影响。随着温度的升高，原奥氏体晶粒尺寸迅速增加，而随着奥氏体化时间的延长，原奥氏体晶粒尺寸几乎保持不变。硬度y的钢与冷却速率x符合以下关系：y  = 11.885 x ⁴ − 131.06 x ³  + 443.75 x ² − 320.21 x  + 387.45。