大直径厚壁液压支柱管纵向开裂原因分析

Analysis of Causes for Longitudinal Cracking of Large-sized Heavy-wall Hydraulic Prop Pipe

针对大直径厚壁S890钢级液压支柱管热轧后发生纵向整体贯穿性开裂的情况,通过观察检测发现断口为穿晶解理脆性断口,显微组织为贝氏体,材料的强度、屈强比和残余应力偏高,韧性差。最终分析结果表明:由于管体弯曲过大,矫直时,因咬入端摆动大引起较大塑性变形,导致开裂,然后在较高的残余应力作用下,加上材料韧性低,裂纹得以持续扩展,最终引起管体全长贯穿性开裂失效。采取降低冷却速度得到部分铁素体的钢组织,降低钢管弯曲度和残余应力再矫直等具体改正措施后生产中再未发生管体开裂现象。

According to the problem of the post-hot-rolling longitudinal over-length cracking of the large-sized heavywall S890 steel hydraulic prop pipe,relevant observation and inspections are conducted,and then the facts as follows are identified.The fracture is a transgranular cleavage brittle fracture,the microstructure is bainite,the strength,yield ratio and residual stress of the material are high,whereas its toughness is poor.The final analysis results show that because the bending of the tube is so serious,when being straightened,the violent swing of the bite end of the pipe leads to obvious plastic deformation,and occurrence of cracking,and furthermore due to the action of high residual stress and the low toughness of the material,the crack continues to expand,eventually resulting in the full-length crack failure of the tube.Accordingly,specific measures are taken to get the pipe body cracking stopped,including reducing cooling rate to get partial ferrite structure,and getting the pipe straightened after reducing its bending degree and residual stress.