晶界铁素体与第二相粒子协同诱导异型坯表面裂纹机理研究

At home and abroad, it has become the mainstream technology choice that the use of Nb micro-alloying technology to develop low-temperature H-beam. However, Nb micro-alloyed surface cracks of the blank has become a technical bottleneck in the development of varieties. Additionally, the results of observing the microstructure shows that there are grain boundary ferrite and a large number of second phase particles near the crack. In order to study the mechanism of crack initiation, the coupling model of the grain boundary ferrite, second phase particle precipitation and high temperature mechanical properties was established and further establish crack prediction model. Firstly, the precipitation kinetic model of grain boundary ferrite and second phase particles was established was used for analyzing the precipitation order and distribution regularity. Then, a multivariate linear regression model was used to establish a coupled model of the three based on temperature. And the samples from laboratory and factory were analyzed to verify and revise the coupled model. Finally, the crack-sensitive zone forecast model based on the coupled model was proposed which provided theoretical reference for solving the problem of surface cracks in casting slabs.

国内外通过采用Nb微合金化技术开发低温用H型钢已成为主流技术选择，但是Nb微合金化异型坯表面裂纹已经成为品种开发的技术瓶颈。在观察铸坯微观结构时发现裂纹附近存在晶界铁素体和大量的第二相粒子。为了深入研究异型坯表面裂纹的产生机理，本项目通过研究晶界铁素体、第二相粒子及其高温力学性能之间的关系，建立三者之间的耦合模型，进一步建立裂纹敏感区预测模型。首先建立晶界铁素体和第二相粒子的析出长大动力学模型，分析析出顺序和分布规律；然后采用多元线性回归模型，基于温度建立三者的耦合模型，并通过分析实验室和工厂样品，对模型进行验证和修正；最后，以耦合模型为基础，建立裂纹敏感区预测模型，为现场解决铸坯表面裂纹问题提供理论参考。

铌微合金钢连铸在连铸过程中极易产生角部横向裂纹，严重影响着铸坯热延展性和钢材的综合力学性能。深入研究裂纹形成机理，调整钢液成分，优化工业参数，为钢铁生产中提高铸坯综合性能提供理论支撑是十分必要的。围绕含铬铌微合金钢异型坯裂纹产生机理，借助Thermo-Calc等热力学软件开展了相关理论计算和相应实验室实验，获得了铬含量对奥氏体转变为铁素体相变过程及析出物分布规律的影响。通过电子背散射技术、电子探针、高温共聚焦及透射电镜技术分析了铬含量对铌微合金钢的第三脆性区间、宏观组织特征、微观组织特征的影响；探究了冷却速率和应变速率对含铬铌微合金钢高温相变特性的影响规律；并最终确定了铬元素的最优加入范围，以及现场工艺条件下含铬铌微合金钢铁素体/奥氏体高温相变裂纹形成机理。