摘要
热轧带钢中微合金元素未完全析出的情况普遍存在。当钢中存在过饱和固溶的微合金元素时,回火处理能使其在基体中析出,并对力学性能产生影响。以Nb-Ti微合金化热轧700 MPa级汽车大梁钢为研究对象,采用SEM、EBSD、TEM和拉伸试验等手段,研究了不同回火温度对其组织和性能的影响。结果表明,与热轧态相比,试验钢在450~600℃范围内回火时,基体组织变化不明显,主要为准多边形铁素体,尺寸略微增大。当回火温度升高至700℃时,其组织向多边形铁素体转变,晶粒尺寸迅速增大,晶界密度降低,发生部分再结晶。回火过程中,热轧阶段过饱和固溶的Ti和Nb将以(Ti,Nb)C的形式析出,且回火温度越高,(Ti,Nb)C的析出孕育期越短,析出量越大,平均粒径则呈现出先减小后增大的变化规律。当回火温度为600℃时,(Ti,Nb)C的平均粒径最小,仅为5.47 nm。试验钢在450~600℃范围内回火时,其抗拉强度、屈服强度和断后伸长率均随着温度的升高而增大。当回火温度升高至700℃时,试验钢抗拉强度和屈服强度显著减小,断后伸长率增大。当回火温度为600℃时,试验钢力学性能最优。其抗拉强度、屈服强度以及断后伸长率分别达到803 MPa、755 MPa和24.6%。强化机制分析表明,试验钢屈服强度提升主要是由微合金元素Ti、Nb在回火过程中大量析出带来的沉淀强化所致。
It is common that microalloying elements are not precipitated completely in hot rolled steel.When there are oversaturated solid solution microalloying elements in steel,tempering can precipitate them in the matrix and affect the mechanical properties.The effect of tempering temperature on microstructure and properties of Nb-Ti microalloying hot rolled 700 MPa automobile beam steel was studied by means of SEM,EBSD,TEM and tensile test.The results show that when tempering at 450℃to 600℃,the matrix structure of the experimental steel is almost identical to the hot-rolled experimental steel,and it is mainly quasi-polygonal ferrite with slightly larger size.When tempering at 700℃,the microstructure of the experimental steel transforms to polygonal ferrite,the grain size increases rapidly,the grain boundary density decreases,and partial recrystallization occurs.When tempering,the oversaturated solid solution Ti and Nb in the hot rolling stage will precipitate in the form of(Ti,Nb)C.The higher the tempering temperature,the shorter the precipitation incubation period of(Ti,Nb)C and the larger the precipitation content.The average particle size will first decrease and then increase.When the tempering temperature is 600℃,the average particle size of(Ti,Nb)C is the smallest,only 5.47 nm.The tensile strength,yield strength and elongation increase with the increase of temperature when the experimental steel is tempered in the range of 450℃to 600℃.When the tempering temperature rises to 700℃,the yield strength and tensile strength of the experimental steel decrease significantly and the elongation increases.When the tempering temperature is 600℃,the mechanical properties of the experimental steel are optimal.The tensile strength,yield strength and elongation are 803 MPa,755 MPa and 24.6%,respectively.The strengthening mechanism analysis shows that the yield strength improvement of the experimental steel is mainly caused by the precipitation strengthening of microalloying elements Ti and Nb during the tempering
作者
周强
曹燕光
杨庚蔚
李昭东
万国喜
王文军
ZHOU Qiang;CAO Yanguang;YANG Gengwei;LI Zhaodong;WAN Guoxi;WANG Wenjun(The key Laboratory of Refractories and Metallurgy,Wuhan University of Science and Technology,Wuhan 430081,Hubei,China;Institute of Structural Steels,Central Iron and Steel Research Institute Co.,Ltd.,Beijing 100081,China;Technology Center,Anyang Iron and Steel Group Co.,Ltd.,Anyang 455004,Henan,China;CITIC Metal Co.,Ltd.,Beijing 100004,China)
出处
《钢铁》
CAS
CSCD
北大核心
2023年第10期102-110,共9页
Iron and Steel
基金
国家重点研发计划资助项目(2021YFB3702402)
国家自然科学基金资助项目(52204398)。
关键词
汽车大梁钢
Nb-Ti微合金化
回火温度
力学性能
强化机理
automobile bean steel
Nb-Ti microalloying
tempering temperature
mechanical property
strengthening mechanism
