低成本超高强度钢G31L的过冷奥氏体连续冷却转变  

Continuous cooling transformation of super cooled austenite of a low-cost ultra-high-strength steel G31L

作　　者：杨鹏[1,2] 宁静 苏杰[2] 姜庆伟[1] Yang Peng;Ning Jing;Su Jie;Jiang Qingwei(Faculty of Materials Science and Engineering,Kunming University of Science and Technology,Kunming Yunnan 650093,China;Institute for Special Steels,Central Iron and Steel Research Institute,Beijing 100081,China)

机构地区：[1]昆明理工大学材料科学与工程学院,云南昆明650093 [2]钢铁研究总院特殊钢研究所,北京100081

出　　处：《金属热处理》2020年第12期149-154,共6页Heat Treatment of Metals

摘　　要：利用Formast-FⅡ膨胀仪测定了G31L钢的热膨胀曲线,研究其在不同冷速下的组织演变及硬度变化规律,绘制出G31L钢过冷奥氏体连续冷却转变(CCT)曲线,并分析了实际大型深盲孔锻件的锻后热处理工艺可靠性。结果表明:G31L钢的Ac1=740℃、Ac3=816℃,Ms=315℃、Mf=138℃。当冷速≤0.028℃/s时,获得珠光体、铁素体、贝氏体混合组织;当冷速在0.028~0.84℃/s之间,随冷速增大,珠光体-铁素体消失,贝氏体量逐渐降低,直至转变为全马氏体组织;当冷速大于0.84℃/s时,获得全马氏体组织。实际生产的大型深盲孔锻件经915℃保温6 h后油淬至室温并进行回火处理,锻件实心头部的心部为马氏体和少量贝氏体的混合组织,头部R/2处、头部边部及尾部为全马氏体组织,且锻件的强度和塑性均满足产品质量要求。Thermal dilatometric curves of G31 L steel were measured by Formastor-FⅡdilatometer,and the microstructure evolution and hardness at different cooling rates were studied,the supercooled austenite continuous cooling transformation(CCT)curves of the G31 L steel were drawn,and the reliability of post-forging heat treatment process of real large deep blind hole forging was analyzed.The results show that the critical temperatures of the G31 L steel as follows:Ac1=740℃,Ac3=816℃,Ms=315℃,and Mf=138℃.When the cooling rate is less than or equal to 0.028℃/s,pearlite+ferrite+bainite mixed structure is obtained;when the cooling rate is 0.028-0.84℃/s,pearlite and ferrite disappear with the increase of cooling rate,and bainite decreases in content gradually until full martensite is obtained;when the cooling rate is greater than 0.84℃/s,full martensite is obtained.The large deep blind hole forgings actually produced are heat treated at915℃for 6 h and then oil quenched to room temperature and tempered.The solid head core of the forgings has a mixed structure of martensite and a small amount of bainite,while the R/2 and edge of the head and tail are all martensite,and the strength and plasticity of the forgings meet the product quality requirements.

关 键 词：CCT曲线 马氏体 超高强度钢 深盲孔锻件 

分 类 号：TG161[金属学及工艺—热处理]