Research on Strengthening Mechanism of Microalloying Elements in Low-carbon Bainite Steels Produced with TMCP Process
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摘要: 采用金相、透射电镜（SEM）、能谱仪（EDX）等分析手段研究了TMCP工艺生产的微合金化高强钢Q690钢的组织、第二相析出物，并在此基础上分析了其强化机理。发现钢板表面组织主要为板条贝氏体、少量粒状贝氏体以及针状铁素体，心部组织主要由粒状贝氏体和多边形铁素体构成；第二相析出物主要是铌钛的碳氮化物，尺寸在20 nm左右，弥散分布在基体上，多呈方形或类方形；硼主要以酸溶硼的形式存在，明显提高了钢的淬透性。Q690钢的强化机制主要是贝氏体相变强化、细晶强化和第二相析出强化，而这都与钢中微合金化元素的作用有关。Abstract: Microstructures and second phase precipitates in microalloyed high-strength steel Q690D produced with TMCP process are analyzed by means of optical microscope(OM),transmission electron microscopy(TEM),and energy dispersive spectroscopy(EDX) in order to study the strengthening mechanism.It is found that the surface microstructure is mainly consisted of lath bainite,a small amount of granular bainite and acicular ferrite,and the central microstructure of granular bainite and polygonal ferrite.Most of the second phase precipitates are niobium and titanium carbonitride with a size of about 20nm in length,dispersively distributing in the matrix in the shape of square or quasi-square.Boron,mainly existing in the form of acid-soluble boron,remarkably increases the hardenability of the steel.Results show the strengthening mechanism is dominated by bainite transformation strengthening,fine grain strengthening and precipitation strengthening.
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