新型耐候钢连续冷却转变曲线的测定

Continuous cooling transformation curve of a weathering steel

用膨胀法结合金相法，在gleeble1500热模拟机上测定了新型耐候钢0．14C-1．43Mn-0．69Si．0．79A1的连续冷却转变曲线（CCT曲线）。结果表明，CCT曲线上珠光体和贝氏体的转变区分开，且在珠光体和贝氏体转变区域之间不存在奥氏体亚稳区。冷却速度小于1℃／s，转变产物为铁素体和珠光体；冷却速度为1℃／s，开始出现少量粒状贝氏体；随冷却速度的增大，铁素体和珠光体含量逐渐降低，贝氏体含量逐渐增多；冷速在5～30℃／s范围内，转变产物主要为铁素体和贝氏体；冷速大于30℃／s，马氏体开始出现；冷速达到80℃／s时，贝氏体消失，转变产物为马氏体；水淬的组织全部为马氏体。奥氏体区变形使铁素体转变区向左上方移动，贝氏体转变区向左下方移动。

Continuous cooling transformation （CCT） curve of Al-Si weathering steel was obtained by measuring the dilation of specimen during cooling on Gleeble-1500 thermal mechanical simulator combining with microstructure observation. The results show that the transformation zones of pearlite and bainite are separated in the CCT diagram. And there is no metastable austenite zone between the transformation zones of pearlite and bainite. The microstructure of ferrite and pearlite is obtained at the cooling rate below 1 ℃/s. Small amount of granular bainite is observed at the cooling rate of 1 ℃/s. Volume fraction of bainite increases while the volume fractions of ferrite and pearlite decrease as the cooling rate increases. The microstructure mainly consists of ferrite and bainite when the cooling rate ranges between 5 ℃/s and 30℃/s. For the rate beyond 30℃/s, martensite begin to appear. Bainite disappears and the microstructure mainly consists of martensite when the cooling rate reachs 80℃/s. And only martensite can be obtained after water quenching. Ferritic transformation zone moves up to left and bainitic transformation zone moves down to left because of deformation of austenite at high temperature.