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采用光学显微镜、扫描电镜和透射电镜对双层卷焊钢管高温退火前后的显微组织、析出相和位错进行研究,探讨双层卷焊钢管的退火软化机理。结果表明,高温退火有效改善了双层卷焊钢管的塑性(A50>40%),降低了其屈服强度(Rp0.2<150 MPa)。退火前后基体中的析出相类型主要为尺寸0.05~2μm的TiN、Ti(CN)、TiS、Ti4C2S2、Fe3C,以晶内析出为主,分布稀疏。在退火过程中TiS向Ti4C2S2的转变消耗了铁素体基体中的间隙原子,而使基体净化,基体中析出相促进回复与再结晶和显著降低基体中的位错密度是双层卷焊钢管退火软化的根本原因。
The microstructure, precipitated phase and dislocation before and after high-temperature annealing of double-layer wound steel pipe were investigated by optical microscope, scanning electron microscope and transmission electron microscope. The annealing softening mechanism of double-layer wound steel pipe was discussed. The results show that the high temperature annealing can effectively improve the plasticity (A50> 40%) and decrease the yield strength (Rp0.2 <150 MPa). The types of precipitates in the matrix before and after annealing are mainly TiN, Ti (CN), TiS, Ti4C2S2 and Fe3C with the size of 0.05 ~ 2μm. The transformation of TiS to Ti4C2S2 during the annealing consumes interstitial atoms in the ferrite matrix, which decontaminate the matrix, precipitates in the matrix promote recovery and recrystallization, and significantly reduce the density of dislocations in the matrix. The root cause of softening.