扩径率对X70级大变形管线钢管变形能力的影响

Effect of expanding ratio on strain capacity of X70 grade high deformability pipeline steel pipe

利用光学显微镜(OM)、电子背散射衍射(EBSD)、透射电镜(TEM)和力学性能分析手段研究了扩径率对X70级多边形铁素体+贝氏体(PF+B)组织的UOE试制管变形能力的影响。结果表明,扩径率在0.4%~1.2%范围变动时,钢管组织中的晶粒取向、有效晶粒尺寸和大、小角度晶界比例基本保持不变;随着扩径率增加,PF组织中位错密度增加,使得屈服强度和抗拉强度略有提高;钢板UOE制管后,变形能力指数由原始钢板的2.00分别下降到不同扩径率的0.78、0.61和0.56,变形能力显著下降;然而,0.4%~1.2%的扩径膨胀对钢管的变形能力影响较小;随扩径率增加,颈缩前钢管试样的应变硬化率先减小后增大,颈缩时的应变值分别为9.7%、8.6%和8.5%,扩径率为1.2%时,应变硬化率下降较快。

Effect of expanding ratio on strain capacity of the trial X70 UOE pipeline steel pipe with polygonal ferrite and bainite(PF+B)was studied by optical microscope(OM),electron backscattered diffraction(EBSD),transmission electron microscope(TEM)and tensile test.The results show that when the expanding ratio varies in the range of 0.4%-1.2%,the grain orientation,effective grain size and proportion of high and low angle grain boundaries in the microstructure of pipe remain basically unchanged.With the increase of expanding ratio,the dislocation density in PF increases,resulting in a slight increase in yield strength and tensile strength.After UOE pipe made,the strain capacity index decreases from 2.00 of the original steel plate to 0.78,0.61 and 0.56 of different expanding ratio,and the strain capacity decreases significantly.However,there is little effect on strain capacity of UOE pipe when the expanding ratio varies in the range of 0.4%-1.2%.The strain hardening rate first decreases and then increases before necking with the increase of expanding ratio,while the strain values corresponding to the necking points are 9.7%,8.6%and 8.5%respectively.The strain hardening rate decreases rapidly when the expanding ratio reaches 1.2%.