以低碳复合添加微合金元素铌和钛为成分设计思路，综合运用细晶强化、相变强化和析出强化三种强化机制，在国内某厂1750mm半连续热连轧机组进行了780MPa级大梁钢的工业试制。结果表明，终轧温度需控制在780~860℃，卷取温度需控制在450~550℃。大梁钢的显微组织为贝氏体和少量的细晶铁素体，并获得了大量弥散的尺度为10nm以下的(Nb,Ti)C析出物。大梁钢的屈服强度为700MPa，抗拉强度为780MPa，伸长率为19%。大梁钢具有良好的低温冲击韧性、冷弯成形性及焊接性能。
With the component design ideas of low carbon composite added with microalloying elements Nb and Ti, and finegrain strengthening, transformation strengthening and precipitation strengthening were used, the 780MPa grade heavyduty beams steels were carried out on a domestic factory 1750mm semicontinuous hot rolling mill. The results show that the finishing temperature to control in range of 780-860℃, and coiling temperature to control in range of 450-550℃. The microstructures of steel are bainite, small amounts of finegrain ferrite, and a lot of dispersed (Nb,Ti)C precipitates with the scale of 10nm and below. The yield and tensile strengths of the steel plate are about 700MPa and 780MPa, respectively. The elongation is 19%. The steel plate have good lowtemperature impact toughness, cold bending forming and welding performance.
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