高铝TRIP钢的高温力学性能

利用Gleeble3500试验机研究汽车用C-Mn-Al系TRIP钢的高温力学性能,测定了零塑性温度和零强度温度,应用差示扫描量热法测定其相变区间,采用扫描电镜和光学显微镜分析了不同拉伸温度对应的断口宏观形貌及断口附近组织组成.该钢种零塑性温度和零强度温度分别为1425℃和1430℃,第Ⅰ脆性区间为1400℃~熔点,第Ⅲ脆性区间为800~925℃.第Ⅲ脆性区脆化的原因是α铁素体从γ晶界析出,试样从975℃冷却至700℃过程中,随着α铁素体析出比例的增大,断面收缩率先减小后增大.基体α铁素体比例为8.1%时(850℃),断面收缩率降至28.9%；而拉伸温度在800℃以下时,基体α铁素体比例超过16.7%,断面收缩率回升至38.5%以上.该钢种在1275.6℃时开始析出少量粗大的AlN颗粒,但对钢的热塑性没有影响.

High-temperature mechanical properties of Al-TRIP steel

The high-temperature mechanical properties of Al-TRIP steel with 0. 16% C, 1. 49% Mn and 1. 35% Al, which is applied to automobiles, were investigated by using a Gleeble3500 machine. The phase transition temperature interval was measured by differential scanning calorimetry ( DSC) . The fractographs and microstructures near the tensile fracture of the steel at different tensile temperatures were analyzed by means of a scanning electron microscope and an optical microscope. The zero ductility temperature ( ZDT) and the zero strength temperature ( ZST) of the steel were measured to be 1425℃ and 1430℃, respectively. The brittleness temperature interval Ⅰ is from 1400℃ to the melting point, and the brittleness temperature interval Ⅲ is from 800℃ to 925℃. Ferrite precipitation from austenite grain boundaries is the main cause of the presence of the brittleness temperature intervalⅢ. With specimens cooling from 975℃ to 700℃, the proportion of ferrite increases continuously, while the reduction of area (Ψ) decreases firstly and then increases. When the proportion of ferrite reaches to 8. 1% ( at 850℃) , the value ofΨdecreases to 28. 9%;but when being stretched at 800℃, the proportion of ferrite is greater than 16. 7%, and the value ofΨis more than 38. 5%. A small number of AlN particles precipitate in the steel at 1275. 6℃. These AlN particles are coarse, but they have no influence on the ductility of the steel.