硫化锰形态控制改善亚包晶钢高温塑性的试验研究

Experimental study on controlling of MnS morphology to improve hot ductility of hypo-peritectic steel

在连铸生产过程中,亚包晶钢板坯角部裂纹的发生率较高,严重影响连铸物流和质量。从连铸板坯窄面取样做不同温度下拉伸试验,并在实验室参照钢种成分控制高锰硫比、低锰硫比和低锰硫比下的微量镁处理,从铸锭取样制成高温拉伸样,做对比高温拉伸试验,测定试样在各个温度点的断面颈缩率,观察断口,进行金相分析,观察夹杂物形态。试验得出：该类钢种在800-860℃间出现低塑性,致铸坯在矫直过程中形成角部裂纹。钢种低塑性是由于MnS夹杂物降低了奥氏体晶界初生铁素体相的强度,通过控制MnS形态,特别是钢水经微量镁处理以后,MnS夹杂物得到细化和球化,有效改善了该钢种在该温度区间的高温塑性。该试验结果运用于宝钢连铸生产实践,有效控制了角裂的发生,实现热送。

In the continuous casting process,corner cracks frequently occur in hypo-peritectic steel,which seriously affects slab quality and the continuous casting logistics.Samples were taken from the narrow face of continuously cast slab and tensile tests were made at different temperatures.Based on the steel＇s chemical composition,the high ratio of Mn to S,the low ratio of Mn to S and the trace magnesium treatment at the low ratio of Mn to S were controlled in the laboratory.The high temperature tensile samples were taken from ingot and high temperature tensile experiment results were compared.The samples＇ cross necking percentage at each temperature point was measured.Fractures were inspected and metallographic analysis were made to observe the inclusion morphology.It was found that the low ductility occurred from 800℃ to 860℃ and this caused corner cracks of slab during the straightening process.It was MnS inclusion that decreased the intensity of the primary ferrite phase on austenitic grain boundaries.By controlling the MnS morphology,especially through the magnesium treatment,MnS inclusions were refined and spheroidized,which effectively improve the steel＇s high temperature ductility within the temperature range.Now the experiment results have been applied to Baosteel＇s continuous casting production.This technology effectively controls the corner cracks and helps realize the hot delivering.