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针对Φ299mm×30mm规格27SiMn钢液压支柱管表面外折严重的情况,取缺陷样进行金相分析,发现裂纹附近有明显脱碳现象;将轧管使用的Φ330mm规格27SiMn钢连铸坯酸洗,发现表面存在横裂纹等缺陷,分析认为由于铝的氮化物沿着奥氏体晶界析出,发生沿晶断裂导致热塑性降低,连铸矫直点的温度未超过第Ⅲ脆性区温度而导致铸坯产生横裂纹,经环形炉加热后轧制扩展成钢管外折。测试27SiMn钢的热塑性及熔点表明:最低断面收缩率为28.0%、低塑性温度区间达到200℃。采取降低二冷区的冷却强度等措施,使连铸矫直点的温度超过920℃,避免了连铸矫直裂纹的产生,钢管外折缺陷得到有效控制。
Aiming at the serious circumvention of the outer surface of the column of Φ299mm × 30mm 27SiMn hydraulic prop tube, taking the sample of the defect for metallographic analysis, it was found that there was obvious decarburization in the vicinity of the crack; pickling of the Φ330mm gauge 27SiMn steel continuous casting tube The surface of the existence of transverse cracks and other defects, the analysis that due to the aluminum nitride along the austenite grain boundary precipitation occurred along the fracture caused by thermoplastic decreased thermoplasticity, continuous casting straightening point temperature does not exceed the temperature of the third brittle zone resulting slab Cross-crack, heated by the ring furnace rolling expanded into a steel pipe outside the fold. Testing the thermoplasticity and melting point of 27SiMn steel showed that the minimum reduction of area was 28.0% and the low plasticity temperature reached 200 ℃. Taking measures such as reducing the cooling intensity of the second cooling zone and so on, the temperature of straightening point of the continuous casting is over 920 ° C, the straightening cracks of the continuous casting are avoided and the out-folding of the steel pipe is effectively controlled.