800MPa级水电工程用钢的CCT曲线测定与分析

Determination and Analysis on Continuous Cooling Transformation (CCT) Curve of 800 MPa Grade Steel for Hydropower Project

利用膨胀法并结合金相法,采用相变仪Formast-F测定了800 MPa级水电工程用低焊接裂纹敏感性钢的临界点相变温度和连续冷却转变静态CCT曲线,并研究了冷却速度对显微组织的影响。结果表明:试验钢Ac1为675℃,Ac3为875℃,Ar1为615℃,Ar3为739℃;当冷速小于0.25℃/s时,转变产物为铁素体(F)+珠光体(P)+少量贝氏体(B);当冷速在0.25~1℃/s时,相变产物为铁素体(F)+贝氏体(B);当冷速在1~5℃/s时,转变产物为贝氏体(B);当冷速在5~20℃/s时,转变产物为贝氏体(B)+马氏体(M);当冷速大于20℃/s时,转变产物为马氏体(M)。

The phase transition temperature and static CCT curve at critical point of 800 MPa grade steel for hydropower project with low susceptivity to weld cracking are determined with phase change instrument Formast-F and the dilatation method combing with metallographic method as well as the effects of cooling rate on microstructure are studied. The results showed that the phase transition temperatures of test steel, Ac1was 675 ℃, Ac3was 875 ℃, Ar1was 615 ℃ and Ar3was 739 ℃;when the cooling rate was less than 0.25 ℃/s, the transformation products were ferrite(F) + pearlite(P) + a small amount of bainite(B);when the cooling rate was 0.25~1 ℃/s, the transformation products were ferrite(F)+ bainite(B);when the cooling rate was 1~5 ℃/s, the transformation product was bainite(B);when the cooling rate was 5~20 ℃/s, the transformation products were bainite(B)+ martensite(M);when the cooling rate was greater than 20 ℃/s, the transformation product was martensite(M).