Mn13高锰钢连铸坯冷却过程中碳化物的析出特征

Precipitation characteristics of the carbides for Mn13 high manganese steel slab during cooling

某企业Mn13钢采用连铸工艺生产,轧制后出现批量沿中心面分层开裂的情况,且开裂比例远高于模铸坯料,初期试验证实这与坯料中心面附近粗大碳化物析出有关,因此重点研究Mn13钢连铸坯在凝固及冷却过程中碳化物的析出特征。本研究通过Thermo-calc热力学计算和实验室模拟冷却组织观察的方法研究了Mn13钢冷却过程中碳化物的析出行为,计算结果表明,在热力学平衡条件下,碳化物在847℃时开始析出,到557℃时碳化物全部析出。模拟冷却试验的组织观察结果表明,在冷却处理前(650℃以上)没有可见的碳化物析出;冷却至550℃时碳化物开始明显析出,400~550℃为碳化物析出的敏感温度区间。在生产过程中,连铸坯在400~550℃温度区间应该选择快速冷却方式避免碳化物析出。此外,现场工艺实践表明,采用合理的连铸工艺(如钢水过热度、电磁搅拌及动态轻压下工艺)也有助于改善Mn13钢铸坯中心偏析问题,减轻铸坯凝固过程中芯部的碳化物析出倾向。

After Mn13 steel was produced by continuous casting process in some enterprise,a large number of layered cracks along the central plane appeared after hot rolling,and the cracking ratio was much higher than that of die cast billet.Initial testing results have confirmed that such issue was related to coarse carbide precipitation in the center of the billets.Therefore,it is necessary to focus on the carbide precipitation characteristics of Mn13 steel continuous casting billet during solidification and cooling.In this work,the precipitation behavior of carbides was investigated through Thermo-calc thermodynamic calculation and laboratory heat-treatment simulation.The calculation results show that under the condition of thermodynamic equilibrium,carbides begin to precipitate at 847℃,and all carbides precipitate at 557℃.The results of microstructure observation show that no visible carbides precipitate from the matrix above 650℃.When the temperature is cooled to 550℃,the carbide begins to precipitate obviously.The temperature range of 400-550℃is a sensitive temperature range for carbide precipitation,therefore the continuous casting billet should be subjected to rapid cooling to avoid carbide precipitation in this temperature range.In addition,the process practice shows that the adoption of reasonable continuous casting processes(such as proper molten steel superheat,electromagnetic stirring and dynamic soft reduction processes)can also help to improve the central segregation of Mn13 steel billets and reduce the tendency of carbide precipitation in the core during the solidification process of billets.