含铌低碳钢的连续冷却转变

The effect of Nb on the low carbon steel under continuous cooling transformation

用G leeb le-1500热力模拟实验机研究了含铌低碳钢和普通低碳钢经不同变形条件下连续冷却过程的相变规律,利用热膨胀法结合金相法得到了连续冷却转变曲线,分析比较了它们的组织演变规律,测定了含铌低碳钢在不同温度和不同变形量下硬度的变化。研究结果表明,铌的加入使铁素体转变开始温度降低,使贝氏体转变温度降低,铌对贝氏体的转变产生了抑制作用.同时铌的加入扩大了产生贝氏体的冷速范围,含铌低碳钢中贝氏体的量显著增多.含铌钢在950℃变形时贝氏体板条长度和宽度比850℃变形时大。对含铌低碳钢,在冷却速度低于1℃/s时,由于生成大量的铁素体,导致了硬度降低;而冷却速度大于1℃/s时,基体中出现了贝氏体使硬度突然增加.

The continuous cooling transformation of niobium -bearing low carbon steel and plain low carbon steel under different transformation conditions were investigated by utilizing Gleeble-1500 thermomechanical simulator. The continuous cooling transformation curves were determined by thermal dilation method and metallographic method . The microstructure evolution of these steels were analyzed and compared. Hardness of the niobium - bearing low carbon steel under different strains was measured. The research results show ferrite start temperature and bainite start temperature were decreased by addition of Nb. Bainite transformation region was enlarged by addition of niobium. There is much more bainite in niobium-bearing low carbon steel. The lath of bainite deformed at 950 ℃ were larger in length and width than deformed at 850 ℃. For niobium-bearing low carbon steel the hardness become low when cooling rate was less than 1 ℃/s , which is because the formation of large amount of ferrite. When cooling rate was larger than 1 ℃/s, the hardness was increased suddenly because of the formation of baimte.