铌钛微合金钢铸坯晶界铁素体形貌与晶界裂纹  

Grain boundary ferrite morphology and grain boundary crack in Nb/Ti microalloyed steel billets

作　　者：杨忠民[1] 王凯[1] 孙秀 笪光杰 YANG Zhong-min;WANG Kai;SUN Xiu;DA Guang-jie(Institute of Structural Steels,Central Iron and Steel Research Institute,Beijing 100081,China;College of Materials Science and Engineering,Hebei University of Science and Technology,Shijiazhuang 050018,Hebei,China)

机构地区：[1]钢铁研究总院工程用钢研究所,北京100081 [2]河北科技大学材料科学与工程学院,河北石家庄050018

出　　处：《钢铁》2018年第11期70-79,共10页Iron and Steel

基　　金：国家重点研发计划资助项目(2017YFB0304700)

摘　　要：为了研究铌钛微合金钢铸坯表面横裂纹产生的原因,采用金相观察、扫描电镜观察和电子背散射衍射（EBSD）等研究方法,对比分析铌钛微合金钢连铸坯和实验室铸锭的晶界铁素体微观组织特征。结果发现了两类晶界铁素体,一类是晶界一侧呈线性清晰另一侧曲折不清晰类型（称之为晶界一侧清晰型,GF-I型）;第二类是晶界两侧均为曲折不清晰类型（称之为晶界两侧不清晰型GF-II型）,在晶界铁素体中均观察到了呈链状线性分布的微孔洞。在GF-I型晶界铁素体中,微孔洞沿晶界清晰一侧呈链状一列分布;在GF-II晶界铁素体中,微孔洞呈链状分布在晶界铁素体中间部位。晶界铌钛微合金粒子的析出促进了晶界铁素体的形核,是导致晶界铁素体中的链状微孔洞形成的重要因素。由于铌钛微合金粒子沿着原奥氏体晶界析出钉扎了原奥氏体晶界,同时也钉扎了晶界铁素体的清晰一侧晶界,改变了晶界铁素体的生长方向,使GF-I型的生长方向向着曲折一侧或沿着原奥氏体晶界生长。对于GF-II型铁素体,由于析出粒子的钉扎作用,奥氏体晶界没有发生移动,铁素体是向两侧奥氏体内长大机制。晶界微孔洞是连铸坯表面横裂纹产生和扩展的原因。In order to study the causes of surface transverse cracks of Nb/Ti microalloyed steel billets,the metallographic observation,scanning electron microscopy and electron backscatter diffraction（EBSD）were used to comparative analysis of grain boundary ferrite microstructure of continuous casting billets and laboratory ingots of Nb/Ti microalloyed steel. Through microscopic observation and analysis,the grain boundary ferrite can be divided into two types according to the morphologies. One is that the side of interfaces of the grain boundary ferrite is linear and clear,and the other side is tortuous and unclear（called a clear grain interfaces on one side,GF-I type）. The second type is the tortuous and unclear types on both sides of grain boundaries（called it is non-clear on both sides of the grain interfaces,GF-II type）. In the two types of grain boundary ferrite,chain like micropores were observed. The chain linear micropores distributed along the clear interface side of grain boundary ferrite with a clear grain boundary on one side. The chain linear micropores distributed in a near the middle of grain boundary ferrite with non-clear interface on both sides. The existence of chain like micropores is due to the precipitation of Nb/Ti microalloying particles,which promoted the formation of grain boundary ferrite chain microporoes. As a result of Nb/Ti microalloying particles precipitated along the grain boundary of the prior austenite,the prior austenite grain boundary was pinned,meanwhile clear interface side of grain boundary ferrite are pinned,and changed the direction of the growth of the grain boundary ferrite. The growth direction of a clear grain boundary ferrite（GF-I type）grows toward austenite on the nucleation side and grows along grain boundaries of the prior austenite. Because of the pinning effect of precipitated particles,the austenite grain boundaries did not move,and the grain boundaries ferrite with non-clear on both sides interface（GF-II type）grew up to austenite on both sides. And

关 键 词：微合金钢 连铸坯 晶界铁素体 横裂纹 微孔洞 取向关系 

分 类 号：TG142.1[一般工业技术—材料科学与工程]