M-A岛高温回火转变产物对核电SA508-3钢冲击韧性影响机制  

Mechanism of Improving the Impact Toughness of SA508-3 Steel Used for Nuclear Power by Pre-Transformation of M-A Islands

作　　者：蒋中华[1] 杜军毅 王培[1] 郑建能 李殿中[1] 李依依 JIANG Zhonghua;DU Junyi;WANG Pei;ZHENG Jianneng;LI Dianzhong;LI Yiyi(Shenyang National Laboratory for Materials Science,Institute of Metal Research,Chinese Academy of Sciences,Shenyang 110016,China;Erzhong(Deyang)Heavy Equipment Co.,Ltd.,Deyang 618000,China)

机构地区：[1]中国科学院金属研究所沈阳材料科学国家研究中心,沈阳110016 [2]二重(德阳)重型装备有限公司,德阳618000

出　　处：《金属学报》2021年第7期891-902,共12页Acta Metallurgica Sinica

基　　金：工业强基工程项目No.TC190A4DA/35;中国科学院青年促进会项目No.Y201732;辽宁振兴人才计划项目No.XLYC1807022;沈阳材料科学国家研究中心青年人才项目No.L2019F48。

摘　　要：利用SEM、TEM、XRD和EBSD等微观分析手段,研究了核电SA508-3钢马氏体(M)-残余奥氏体(A_(R))岛(M-A岛)高温回火转变对冲击韧性的影响机制。结果表明,正火态SA508-3钢中M-A岛呈块状,以A_(R)为主。M-A岛经650℃高温回火后,转变成铁素体和M_(3)C碳化物组成的析出相聚集区。沿析出相聚集区边缘分布的粗大M_(3)C易诱发裂纹萌生而发生解理断裂,导致SA508-3钢低温冲击韧性偏低。进一步研究表明,深冷或回火预处理将M-A岛转变成过渡产物,可改善正火态SA508-3钢650℃高温回火后析出相聚集区中M_(3)C的尺寸、形态和分布,进而在一定程度上提高了SA508-3钢低温冲击韧性,其中400℃预回火处理效果最佳。这是由于,经400℃预回火后,M-A岛中A_(R)将完全转变成细小的贝氏体,其内部具有高密度板条亚结构和渗碳体,为M_(3)C在析出相聚集区内均匀析出提供形核点;同时,400℃预回火也减少了M-A岛边缘位错密度和相变残余应力,避免了650℃高温回火过程中M_(3)C在原块状M-A岛边缘形核和迅速长大,有利于M_(3)C在析出相聚集区内均匀弥散分布。SA508-3 steel is the key structural material extensively used in large components of thirdgeneration nuclear power plants.For increasing the process efficiency of nuclear power plants,extremely thick cross-sectional heavy forgings are necessary for constructing large components for these plants.Owing to thick cross sections,the as-quenched microstructure of the center of heavy forgings is typically granular bainite,composed of bainitic ferrite and martensite(M)and retained austenite(A_(R))(M-A)islands.An M-A island is an undesired microstructure that results in the SA508-3 steel having a poor lowtemperature impact toughness after conventional tempering at 650 ℃.However,it is difficult to tailor the as-quenched microstructure owing to the limited cooling rate during the quenching process.Therefore,the modification of the tempering process is a more feasible method to adjust the microstructure and improve the mechanical properties of heavy forgings.Herein,the decomposition of A_(R)within M-A islands during different transformation paths and its effect on the mechanical properties of SA508-3 steel have been investigated.The results show that clusters of ferrite and agglomerated M_(3)C carbides are formed during conventional tempering at 650 ℃.These coarse M_(3)C carbides decorate the boundary of the cluster,reducing the impact toughness of the SA508-3 steel.Accordingly,the size and distribution of these M_(3)C carbides are tentatively modified by introducing pretreatments at different temperatures before conventional tempering at 650 ℃.This modification is because,during pretreatments,A_(R)first decomposes into various transitional microstructures such as martensite,bainite,or pearlite,which further transform into clusters of ferrite and M_(3)C carbides during tempering at 650 ℃.The results show that 400 ℃ is the optimal pretempering temperature to improve the impact toughness of SA508-3 steel.Microstructural observations reveal that during tempering at 400 ℃,A_(R)completely decomposes into fine bainite

关 键 词：核电 SA508-3钢 残余奥氏体 冲击韧性 M-A岛 粒状贝氏体 

分 类 号：TG161[金属学及工艺—热处理]