冷却速度对 900 MPa 级冷轧马氏体钢组织性能的影响

以高氢冷却工艺连退生产线为基础,以 900 MPa 级冷轧马氏体超高强钢为研究对象,研究了连续冷却相变区转变规律和连退快速冷却工艺对钢的力学性能和显微组织的影响。结果表明,连续冷却相变区由先共析铁素体转变区、贝氏体转变区和马氏体转变区组成,随着冷却速度的增加,先共析铁素体含量逐渐下降,贝氏体和马氏体含量逐渐上升,当冷却速度大于 40 ℃/s 时,不再有先共析铁素体生成;当冷却速度大于 80 ℃/s 时,则完全进入马氏体转变区。随着连退快冷工艺中冷却速度的增加,钢的屈服强度、抗拉强度和屈强比逐渐增加,断后伸长率逐渐下降。当冷却速度为 50 ℃/s 时,钢的屈服强度、抗拉强度和断后伸长率就已经达到了 900 MPa 级冷轧马氏体超高强钢的力学性能要求。

Effect of cooling rate on mechanical properties and microstructure of 900 MPa grade cold rolled martensitic steel

Based on the continuous annealing production line with high hydrogen cooling process, and taking the 900 MPa grade cold rolled martensitic ultra-high strength steel as the research object, the transformation rule of the continuous cooling phase transformation zone and the effect of the rapid cooling process on the mechanical properties and microstructure of the steel were studied. The results showed that the continuous cooling transformation zone was composed of the pro-eutectoid ferrite transformation zone, bainite transformation zone and martensite transformation zone. With the increase of the cooling rate, the content of pro-eutectoid ferrite decreased gradually, while the content of bainite and martensite increased gradually. When the cooling rate was greater than 40 ℃/s, there was no pro-eutectoid ferrite transformation. When the cooling rate was greater than 80 ℃/s, it completely entered the martensite transformation zone. With the increase of the cooling rate of the rapid cooling process, the yield strength, tensile strength and yield ratio of the steel increased gradually, while the elongation decreased gradually. When the cooling rate reached 50 ℃/s, the yield strength, tensile strength and elongation of the steel met the mechanical property requirements of 900 MPa grade cold rolled martensitic ultra-high strength steel.