Abstract: The production flowsheet of tested 280 mm x 325 mm casting bloom of steel ML20Cr is 80t top and bottom combined blowing converter-LF-CC process. The hot ductility curves of casting bloom of tested steel at 650~1200 °C are measured by Gleeble 1500 hot simulator, and the effect of adding 0.029Ti-0.0023 B on hot ductility of steel MLCr20 (/% : 0.2i〜0.22C, 0.22~0.23Si, 0.74〜0.76Mn, 0.015~0.017P, 0.002〜0.003S, 0.95〜0.96Cr, 0.034~0.036 Al, 0.0050~0.0051N) is analyzed. Results show that in 650~ 900℃ the plasticity of steel ML20Cr containing 0.029Ti-0.0023B ( reduction of area ＞70% at 750℃) is better that of steel ML20Cr un-adding Ti-B ( reduction of area ＜50% at 750°C ). The main reason is that the prior precipitated TiN decreases the effect of fine AIN in No Ⅲ brittle zone, and the B segregate at austenite grain boundary to inhibit the formation of proeutectoid ferrite thin film, in order to effectively improve the hot ductility of steel. The commercial production results show that with adding micro Ti-B tn steel ML20Cr the cracking j-ate of casting bloom decreases from 3.7% to 0.3% .

Key words: Cold Heading Steel ML20Cr, Ti-B Microalloying, 280 mm x 325 mm Casting Bloom, Hot Ductility

摘要： 试验ML20Cr钢280 mm×325 mn连铸坯的生产流程为80t顶底复哄转炉-LF-CC工艺。借助Gleeble 1500热模拟试验机测试了试验钢连铸坯的650~1200℃热塑性曲线.并分析了添加0.029Ti-0.0023B对ML20Cr钢（/%:0.21~0.22C，0.22~0.23Si，0.74~0.76Mn，0.015~0.017P，0.002~0.003S，0.95~0.96Cr，0.034~0.036A1，0.0050~0.0051N）热塑性的影响。结果表明，在650~900℃范围,含0.029Ti-0.0023B的ML20Cr钢的塑性（750℃断面收缩率＞70%）优于不加Ti-B的ML20Cr钢（750℃断面收缩率＜50%）。其主要原因TiN优先析出,降低了细小AlN析出物在第三脆性区的影响，同时B元素在奥氏体晶界偏聚，抑制先共析铁素体薄膜的形成，从而有效改善了钢的热塑性。工业生产结果表明，加微量Ti-B后ML20Cr连铸坯开裂率由3.7%降低到0.3%。

关键词: ML20Cr冷镦钢, Ti-B微合金化, 280 mmx325 mm连铸坯, 热塑性