Si-Mn-Cr-Mo超高强钢的CCT曲线的探讨

Study of continuous cooling transition curve of Si-Mn-Cr-Mo ultra high strength steel

利用L78型淬火膨胀仪,测定了Si-Mn-Cr-Mo超高强钢以不同冷却速度连续冷却时的膨胀曲线,并结合金相-硬度法,绘制了该钢的过冷奥氏体连续冷却转变曲线（CCT曲线）。根据CCT曲线,结合光学显微镜与显微硬度分析结果,研究分析了冷却速度对相变组织演变规律的影响。结果表明,当冷却速度为0.04~0.1℃/s时,相变组织为铁素体（F）和贝氏体（B）,冷却速度为0.2~2℃/s时,相变组织为贝氏体（B）和马氏体（M）,冷却速度大于3℃/s时,相变组织为马氏体（M）;且随着冷却速度的提高,硬度值也在提高。测定结果为该钢的控制冷却工艺提供了重要的理论依据。

Based on the measurement of the different dilatometric curves of Si-Mn-Cr-Mo ultra-high strength steel during continuous cooling on the condition of different cooling rates by using L78 quenching dilatometer,and combined with the optical microstructure analysis and hardness measurement,the continuous cooling transformation（CCT）curve of undercooled austenite for the steel was obtained.The effect of cooling rate on the microstructure evolution was investigated by the CCT curve and the analysis results of the optical microscope and microhardness. The results showed that the microstructure of the tested steel consisted of ferrite（F）and bainite（B）after phase transition at the cooling rate of 0.04 ℃/s-0.1 ℃/s,the phase transition structure became into bainite（B）and martensite（M）at the cooling rate of 0.2 ℃/s-2 ℃/s,the martensite（M）was observed at the cooling rate of more than 3 ℃/s. With the increase of cooling rate,the hardness value also increased. The results provided an important theoretical basis for the controlled cooling process of the steel.