Φ350 mm ASTM4130连铸圆坯内部裂纹形成机制研究

Analysis of the characteristics of internal crack in Φ350 mm round billet of ASTM4130 continuous casting

针对莱钢？350 mm ASTM4130连铸圆坯内部裂纹的问题,采用高温力学测试、组织观察和扫面电镜等分析手段,系统分析了ASTM4130铸态组织在不同高温段的的力学性能、断口形貌和组织转变。试验结果表明,造成ASTM4130钢圆坯内部裂纹的主要原因是拉坯矫直时,铸坯凝固组织处在900-750℃第Ⅲ脆性温度区,此时钢塑性不高,钢坯矫直过程受力大,从而产生内部裂纹。根据试验研究数据,通过优化连铸冷却参数,控制铸坯表面温降不超过150℃/m,确保了进拉矫机前表面温度大于900℃,将原来拉矫系统采用的4架3点矫直改造为5机架连续矫直,合理调整每架拉矫机的工作压力为4 MPa,避免了铸坯在此温度区间承受较大的应力或变形而产生裂纹。

For analysis of internal crack problem ofASTM4130 Φ350 mm continuous casting round billet in the Special Steel Plant of Shandong Iron and Steel Company, high temperature inechanics test, microstructure observation and ana- lytical means such as scanning electron microscope were adopted. Systematic analysis of ASTM4130 as-cast organiza- tion in different high temperature mechanical properties, fracture morphology and organization transformation were con- ducted. Test results show that the main cause of internal cracks of ASTM4130 steel round billet is that the slab solidifica- tion organization is straightening at in 900-750 ℃ in the first Ⅲ brittleness temperature zone. At that time steel plastic is not high, and the steel billet straightening process force is large, this results in internal crack. According to the experi- ment data, through the optimization of continuous casting cooling parameters, slab surface temperature drop 150 ℃/m or less to ensure the slab transfered into the machine before the surface temperature 〉900℃. The 5 frames continuously straighteners replace the four 3-point straighteners used in the system. The working pressure of each tension machine was adjusted to 4MPa, which can avoid the casting billet crack by great stress or deformation in this temperature range.