Cr元素对桥梁耐候钢相变行为的影响

Effect of chromium element on bridge weathering steel phase transformation

桥梁耐候钢可在大气环境中裸露使用,其符合资源节约与环境友好型社会发展对桥梁建设提出的新要求。本文为研究不同冷却速度下桥梁耐候钢的相变过程和组织演变情况以及Cr元素对其相变规律的影响,利用热膨胀法并结合金相建立两种不同成分桥梁耐候钢的动态CCT曲线。结果表明:Cr元素降低铁素体和贝氏体相变温度,扩大贝氏体相变区域,减小铁素体晶粒尺寸和体积分数。冷却速度由0.5℃/s增加到20℃/s,桥梁耐候钢的显微组织由铁素体和珠光体向贝氏体转变,铁素体相变开始温度和贝氏体相变终止温度降低。

Bridge weathering steel can be exposed in the atmospheric environment,and the corrosion resistance is closely related to the rust layer structure formed on the steel surface. It is known that the bridge weathering steel application conforms to the new requirements of the resource saving and environment friendly society for the bridge construction. The dynamic continuous cooling transformation（ CCT） diagrams of the two different bridge weathering steels are studied by utilizing thermal expansion and optical microscope in order to understand to the effect of Cr element and cooling rate on the phase transformation of bridge weathering steels. The results of study indicate that Cr element reduces the ferrite and bainite transformation temperature,but expands the bainite transformation region. Meanwhile,Cr element refines ferrite grain size and reduces ferrite volume fraction. With the cooling rate increased by 0. 5 ℃/s to 20 ℃/s,the microstructures of bridge weathering steels are transformed from ferrite and pearlite into bainite,and the initialtemperature of ferrite transformation and final temperature of bainite transformation are lowed.