不同上冷床温度对螺纹钢组织性能的影响

Impact of different temperatures of deformed steel bar on cooling bed on performance of microstructure

为了研究不同上冷床温度对螺纹钢组织演化规律及性能的影响,利用拉伸试验机和扫描电子显微镜对不同上冷床温度的螺纹钢进行了力学性能检测和金相组织分析,并通过相变理论解释了发生相变的原因,探讨了上冷床温度对螺纹钢性能的影响。结果表明,为了发生相变,其体系化学驱动力减少必须克服体系弹性能的增加和形成新相引起表面能的增加。同时形变会使形变储存能ΔGD增加。从而使相变驱动力增加,进而导致相变温度上升。随着螺纹钢上冷床温度的降低(不应低于临界相变温度),表面和中心均形成铁素体和珠光体,屈服强度由435升高到440MPa,表面维氏硬度由207上升到257,这是因为随着上冷床温度降低,其表面形成越来越多的回火索氏体,抗拉强度有升有降无明显规律,而其晶粒度由10.5上升到13.5。

In order to research the impact of temperatures of steel bar on the cooling bed on the performance of deformed steel bars and the law of structure evolution,the tensile test and metallographic structure analysis of deformed steel bars with different temperatures of steel bar on the cooling bed were carried out by means of a tensile test machine and a scanning electron microscope,with reason of phase change explained by phase change theory.The impact of the temperature of steel bar on the cooling bed on the performance of deformed steel bars was discussed and explored.The results show that the occurrence of phase change is under the condition that the reduction in the chemical driving force of the system must overcome the increase in the elastic energy of the system and the increase in surface energy caused by the formation of a new phase.Besides,the deformation will increase the deformation storage energyΔGD.As a result,the phase change driving force is increased,causing a rise of the phase change temperature.When the temperature on cooling tables decreases(not lower than the critical phase change temperature),ferrite and pearlite are formed on the surface and center,the yield strength increases from 435 to 440 MPa,and the surface Vickers hardness increases from 207 to 257.As the temperature on the cooling table becomes lower,more and more tempered sorbite is formed on its surface.The tensile strength increases and decreases irregularly.And the grain size/level increases from 10.5 to 13.5 as the temperature on the cooling table decreases.