Abstract: By experimental research and analysis, it is clear that weak adhesion between columnar grains is the main reason for continuous cast bloom crack of 37Mn gas vessel steel. Factors that affect grain cohesion are analized by means of tensile test, SEM and dilatometer equipment, as well as optical microscopy. The results show that as increase in Al content from 0.007% yo0.033%%,hot ductility of the steel at 800 ℃ predominantly reduces while the volumn effect of A-F/P phase transformation increases. Micro cracks and voids tend to nucleate at grain boundry. Concentration of Al,P,S at grain boundry is also one reason of crack formation at the same time. Improvement measures are brought forward on that basis such as reducing N content from0.0080% to (0.0040%-0.0060%), adding small amount of Cr (0.20%-0.25%) and Mo (0.05%-0.08%), as well as soft cooling the cast bloom in the range of 750-600 ℃, the phase transformation stresses and thermal stresses are reduced effectively to avoid crack formation and spreading in the continuous cast bloom of 37Mn gas vessel steel.

Key words: Al, Cr-Mo Microalloying, 37Mn Steel, Continuous Cast bloom, Crack, Improvement Measure

摘要： 通过试验研究和理论分析等手段，明确了柱状晶界面结合力弱是37Mn气瓶钢连铸坯裂纹产生的主要原因。采用拉伸试验、扫描电镜、金属膨胀仪、金相显微镜等研究设备，分析了柱状晶结合力的影响因素。研究表明，当Al含量0.007%增加至0.033%时，使800℃时钢的热塑性显著降低，同时导致A-F/P相变过程体积效应增大，柱状晶晶界位置易形成微裂纹及孔洞；同时晶界位置Al、P、S元素偏析也是形成裂纹的原因之一。在此基础上，提出了降低钢中N含量由0.0080%降至(0.0040%～0.0060%),添加微量Cr (0.20%～0.25%)、Mo (0.05%～0.08%)以及使连铸坯在750～600℃缓冷等措施，有效减轻了晶界相变应力及热应力，避免了37Mn气瓶钢连铸坯裂纹萌发和扩展。

关键词: Al, Cr-Mo微合金化；37Mn钢；连铸坯；裂纹；改进措施