低C含7.7%Ni低温钢经两相区淬火后的组织性能  

Microstructure and Mechanical Properties of a Low Carbon 7.7%Ni Steel Subjected to Intercritical Quenching

作　　者：朱绪祥 刘东升 

机构地区：[1]江苏省(沙钢)钢铁研究院,江苏张家港215625

出　　处：《钢铁》2013年第11期72-78,83,共8页Iron and Steel

摘　　要：提出了一种Ni质量分数为7.7％的低C低温用CrNi钢,研究了其经淬火＋两相区淬火＋回火（QLT）处理后的力学性能,采用扫描电镜（SEM）、透射电镜（TEM）、X射线衍射（XRD）和电子背散射衍射（EBSD）对试验钢的显微组织演化规律进行了研究.结果表明：经QLT处理的试验钢的显微组织主要为铁素体（F）＋板条马氏体（LM）＋马氏体/奥氏体组元（M/A）＋回转奥氏体（γ ＇）.随着两相区热处理温度（tL）的升高,LM的比例逐渐增加,F的比例逐渐减少,晶粒细化,大角度晶界（HAGB）比例和平均晶界角度（AGBA）大幅增加.当tL在650～680℃时,γ ＇的体积分数约为7％.-196℃下韧性（KV2）主要取决于γ ＇含量和HAGB比例两个因素.经QLT处理,试验钢的屈服强度（Rp0.2）大于530 MPa,抗拉强度（Rm）大于670 MPa,-196℃下的冲击韧性大于150J,强韧性达到了当前9Ni钢的水平.To save the cost of constructing liquefied natural gas （LNG） storage tanks, a lean steel composition （low C CrNi steel containing 7.7% mass fraction of Ni） was proposed as a substitute of the conventional 9% Ni steel. The mechanical properties of the subject steel subjected to austenitizing followed by water quenching＋lamellarizing ＋ tempering （QI.T） were tested. Microstructure evolution in the tested steel during the QLT processing was studied. The microstructures consist of mainly ferrite （F）＋lath-like martensite （LM）, martensite/austenite （M/A） constituents and reversed austenite （y＇）. With the increase of lamellarizing temperature （tL）, the fraction of LM gradually increases while that of F decreases, resulting in refined microstructure and increased fraction of large-angle grain boundaries （HAGB）. The fraction of 3＂ maintains is at approximately 7% when h. is between 650-680 ℃. It decreases with further increase of tL. The cryogenic toughness is mainly determined by y＇ content and the fraction of HAGB. Excellent mechanical properties can be achieved in the current steel processed by the QLT heat treatment showing yield strength （Rp0.2） greater than 530 MPa, tensile strength （Rm） greater than 670 MPa, Charpy impact toughness （KV2） greater than 150 J even at -196℃. The mechanical properties of the intercritically quenched steel are equivalent to those of 9 % Ni steel.

关 键 词：两相区淬火 低温韧性 回转奥氏体 大角度晶界比例 

分 类 号：TG156.3[金属学及工艺—热处理]