部分奥氏体化和完全奥氏体化铁素体/马氏体双相钢的CCT曲线

CCT Diagram of Ferrite/Martensite Dual-phase Steel with Part Austenitizing and Complete Austenitizing

采用Formaster热膨胀仪分别测定了部分奥氏体化与完全奥氏体化冷轧热镀锌Fe-CMn-Cr-Nb-Ti系双相钢的CCT曲线,分析了连续冷却过程中的相变规律,从动力学角度分析了部分奥氏体化与完全奥氏体化试验钢CCT曲线的区别。结果表明：在冷速分别为1,3,5℃·s^-1时,部分奥氏体化试验钢的铁素体开始转变温度比完全奥氏体化试验钢的分别高36,25,44℃;与完全奥氏体化试验钢相比,部分奥氏体化试验钢的贝氏体转变在向低冷速区推移的同时,也向高冷速区推移,贝氏体转变冷速范围变宽,为1~40℃·s^-1;当冷速为1~10℃·s^-1时,部分奥氏体化试验钢的贝氏体开始转变温度要低于完全奥氏体化试验钢的,而当冷速为15~20℃·s^-1时,情况则相反;为了保证冷轧热镀锌钢的最终淬火组织为铁素体/马氏体双相组织,冷速需大于40℃·s^-1。

The complete and part austenitizing continuous cooling transform（CCT） diagrams of cold rolled hot dip galvanized dual-phase steel of Fe-C-Mn-Cr-Nb-Ti series were measured respectively by using Formaster thermal dilatometer. The phase transformation law of the dual phase steel during continuous cooling process was studied, and the difference of complete and part austenitizing CCT diagrams of the experimental steel was also analyzed from the prospective of dynamics. The results show that, when the cooling rates was 1, 3 ℃ · s^-1 and 5 ℃ · s^-1 , the ferrite starting transformation temperatures of the experimental steel with part austenitizing were higher than the ones of with complete austenitizing as 36, 25 ℃ and 44 ℃, respectively. The cooling rates range of bainite transformation of the experimental steel with part austenitizing was 1-40 ℃ · s^-1. The cooling rates range not only moved to the low cooling rates area, but also moved to the high cooling rates area, which became wider than the one of the experimental steel with complete austenitizing. When the cooling rate range was 1-10 ℃· s^-1 , the bainite transformation starting temperature of the experimental steel with part austenitizing was lower than the one of the experimental steel with complete austenitizing. While the case was the opposite when the cooling rate range was 15-20 ℃· s^-1. For the cold rolled hot dip galvanized dual-phase steel, the cooling rate should be more than 40 ℃ · s^-1 in order to obtain the final dual-phase microstructure with ferrite and martensite.