DZ55冷拔钢管断裂原因分析与控制措施
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摘要
采用金相检验、硬度检测、扫描电镜及能谱分析、热处理试验等手段,分析了DZ55冷拔钢管在拔制过程中产生横向裂口的原因,并提出控制措施。分析认为:由于元素偏析,导致塑性低于基体的马氏体更容易在靠近内表面的Mn元素聚集区域产生,从而引起材料塑性降低,导致DZ55冷拔钢管在冷加工中出现横向裂口。采取低温浇铸,设法扩大铸坯中心等轴晶区,以减轻或消除坯料偏析,从而减少内裂口的出现;采用高温回火+缓冷的热处理工艺,可以降低DZ55钢的强度,消除其组织中的马氏体带,从而提高了材料塑性,有利于后续的冷加工。
Causes for the transverse cracks of the DZ55 cold-drawn pipe as occurrred during the drawing process are analyzed by means of metallographic examination,hardness testing,scanning electron microscopy,and energy spectrum analysis as well as heat treatment tests. Accordingly preventive measures are proposed. The analysis result identifies that owing to element segregation,it becomes easier for the martensite matrix with plasticity lower than that of the base metal to produce in the Mn-aggregation area that close to the inner surface,which leads to reduction of the plasticity of the material, and thus causes the development of the said crack during the cold drawing process.Therefore taking low temperature casting of the billet to expand the central equiaxed zone of the billet can reduce or even eliminate the segregation so as to reduce development of the inner crack. Moreover adopting the heat treatment process of hi-temperature tempering +slow-cooling can decrease strength of the DZ55 steel, and eliminate the martensite band so as to enhance plasticity of the material,which is helpful for the cold-work process as follows.
Causes for the transverse cracks of the DZ55 cold-drawn pipe as occurrred during the drawing process are analyzed by means of metallographic examination,hardness testing,scanning electron microscopy,and energy spectrum analysis as well as heat treatment tests. Accordingly preventive measures are proposed. The analysis result identifies that owing to element segregation,it becomes easier for the martensite matrix with plasticity lower than that of the base metal to produce in the Mn-aggregation area that close to the inner surface,which leads to reduction of the plasticity of the material, and thus causes the development of the said crack during the cold drawing process.Therefore taking low temperature casting of the billet to expand the central equiaxed zone of the billet can reduce or even eliminate the segregation so as to reduce development of the inner crack. Moreover adopting the heat treatment process of hi-temperature tempering +slow-cooling can decrease strength of the DZ55 steel, and eliminate the martensite band so as to enhance plasticity of the material,which is helpful for the cold-work process as follows.
引文
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[3]杨万兵.冷拔钢管横裂缺陷的产生及控制[J].钢管,1999,28(3):18-20.
[4]艾家和,董建新,张江海,等.4Cr9Si2阀门钢丝冷拔过程中脆断的失效分析[J].2001,24(5):57-58.
[5]梁龙飞.45钢棒材冷拔断裂原因分析[J].热加工工艺,2002(3):55-56.
[6]丛铁生,谢奎龙,宫延生.55钢冷拔材横向断裂原因分析[J].物理测试,1999(4):26-29.
[7]罗家华,刘楚明.42MnMo7钢冷拔厚壁管内横裂纹的去除[J].湖南冶金,2004,32(6):25-28.
[8]蔡兆镇,朱苗勇.钢凝固两相区溶质元素的微观偏析及其对连铸坯表面纵裂纹的影响[J].金属学报,2009,45(8):949-955.
[9]曹建军,陈明安.退火工艺对42MnMo7钢管性能的影响[J].国外金属热处理,2005,26(2):30-31.
[10]周勇.不同状态对42MnMo7钢显微组织与力学性能的影响[J].理化检验(物理分册),2007,43(9):439-443.
[11]崔忠圻.金属学与热处理[M].哈尔滨:机械工业出版社,2001.
[12]彭自胜.水平连铸42MnMo7钢石油管坯的质量控制[J].特殊钢,2002,23(4):42-44.
[13]赵虎田,杨伟业,郭昌贵,等.连铸管坯二冷区电磁搅拌试验[J].钢管技术,1985,14(3):49-56.
[14]王永如,李红卫,李廷举.铜管坯水平连铸过程的电磁搅拌技术[J].有色金属加工,2011,40(5):11-14.
[15]李平凡.圆坯连铸生产45Mn2钢的工艺实践[J].炼钢,2012,28(6):25-28.