550 MPa级海洋工程用钢板低温韧性波动原因分析  

Cause analysis of low temperature toughness fluctuation of 550 MPa steel plate for offshore engineering

作　　者：朱康峰 麻衡 宋新莉[1] 贾涓[1] 梁小凯[2] 孙新军[2] ZHU Kang-feng;MA Heng;SONG Xin-li;JIA Juan;LIANG Xiao-kai;SUN Xin-jun(The State Key Laboratory of Refractory Materials and Metallurgy,Wuhan University of Science and Technology,Wuhan 430081,Hubei,China;Engineering Steel Research Institute,Central Iron and Steel Research Institute Co.,Ltd.,Beijing 100081,China;Yinshan Section Steel Co.,Ltd.,Laiwu Steel Group,Jinan 271105,Shandong,China)

机构地区：[1]武汉科技大学省部共建耐火材料与冶金国家重点实验室,湖北武汉430081 [2]钢铁研究总院有限公司工程用钢研究院,北京100081 [3]莱芜钢铁集团银山型钢有限公司,山东济南271105

出　　处：《钢铁》2022年第10期178-187,共10页Iron and Steel

基　　金：山东省重点研发计划资助项目(2020CXGC010305)。

摘　　要：550 MPa级海洋工程用钢在低温冲击功波动较大。为了进一步探究产生低温韧性波动的原因,在不同温度(-100℃~室温)对试验钢进行冲击试验。结合光学显微镜、扫描电子显微镜、透射电镜等设备,分析冲击断口、显微组织、第二相、夹杂物。结合热力学计算等对低温韧性波动原因进行分析讨论。结果表明,试验钢强度满足等级要求,随着温度降低冲击吸收功不断降低,韧脆转变温度为-50℃左右。在-60℃下冲击功出现较大波动,出现了18 J的极低值,断口为准解理断裂,剪切断面率为8%,裂纹源处存在Ti,Nb(C,N)和MnS的复合夹杂。而在相同温度下冲击功为122 J的试验钢,剪切断面率为34%,断口发现有明显的韧窝。试验钢组织主要为回火贝氏体加极少量铁素体,贝氏体板条中存在高密度位错,晶界上有(Fe,Cr)_(3)C合金渗碳体与少量NbC和富Cu析出相。试验钢以小角度晶界为主,大角度晶界占比较低。基体中有少量(Ca,Al,Mg,Mn,S)等复合夹杂物,多呈近圆形和多边形,大小多为1~3μm,占检测到的总数量的85.87%。占比例最高的是CaS-Oxide-MnS类夹杂,为31.2%。热力学计算结果表明试验钢凝固过程中TiN先于MnS析出。晶界与晶内粗大的析出相、夹杂物、较高比例的小角度晶界与塞积的不可动位错等多种因素对低温冲击韧性产生不利影响,存在大颗粒含钛析出相是造成冲击韧性波动大的关键原因。The impact energy of 550 MPa Marine engineering steel fluctuates greatly at low temperature.In order to further explore the cause of low temperature toughness fluctuation,impact tests were carried out on the test steel at different temperatures(-100 ℃-room temperature).The impact fracture,microstructure,second phase and inclusions were analyzed with optical microscope,scanning electron microscope and transmission electron microscope.The reason of low temperature toughness fluctuation was analyzed and discussed by thermodynamics calculation.The results show that the strength of the tested steel meets the requirements of grade,the impact absorption energy decreases with decreasing temperature,and the toughness and brittleness transition temperature is about-50 ℃.At-60 ℃,the impact energy fluctuates greatly,and an extremely low value of 18 J appears.The fracture is quasi-cleavage fracture,the shear section rate is 8%,and there are compound inclusions of Ti,Nb(C,N) and MnS at the crack source.At the same temperature,the shear section of the test steel with impact energy of 122 J is 34%,and there are obvious dimples in the fracture.The microstructure of the test steel is mainly tempered bainite and very little ferrite.There are high density dislocations in bainite slat.There are(Fe,Cr)_(3)C alloy cementite and a small amount of NbC and Cu-rich precipitates on grain boundary.The test steel mainly has small Angle grain boundary,and large Angle grain boundary is relatively low.There are a small amount of(Ca,Al,Mg,Mn,S) inclusions in the matrix,which are nearly round and polygonal in size between 1-3 μm,accounting for 85.87% of the total amount detected.The highest proportion of cas-oxide-MNS inclusions was 31.2%.Thermodynamic calculation results show that TiN precipitates earlier than MnS during solidification.Many factors,such as coarse precipitated phase of grain boundary and ingrain,inclusions,high proportion of small Angle grain boundary and immobile dislocation of plugging,have adverse effects on the impact t

关 键 词：海洋工程用钢 低温韧性 第二相 夹杂物 小角度晶界 

分 类 号：P75[天文地球—海洋科学] TG142.1[一般工业技术—材料科学与工程]