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利用飞行时间法中子衍射对比研究了充氢与未充氢1250 MPa超高强度钢的拉伸变形行为与轴向晶格变形特征,并观察了断口区组织形貌与晶粒取向特征.在无加载条件下,充氢试样的轴向(110)与(200)面间距分别大于和小于未充氢试样的对应面间距,显示出四面体间隙中H原子的进入使轴向(110)面间距有所增加,同时内部应力的平衡作用使轴向(200)面间距有所减少.未充氢试样达到1250 MPa抗拉强度发生颈缩塑性断裂,而含有8.0×10-6可扩散氢的试样在分步加载至500 MPa时发生脆性断裂.中子衍射分析表明,未充氢试样在拉应力加载至500 MPa时均基本符合线弹性变形,但至700 MPa时,轴向{200}晶粒比其余取向晶粒优先显示非线弹性变形,至800 MPa时轴向{110}晶粒也出现非线弹性变形,轴向{200}晶粒优先产生微屈服现象,而轴向{211}晶粒仍然处于线弹性阶段;充氢试样在拉伸至300 MPa时,轴向{110}晶粒出现非线弹性变形,至400 MPa时轴向{200}晶粒也出现非线弹性变形,轴向{110}晶粒优先产生微屈服现象,轴向{211}晶粒仍处于线弹性阶段.断口剖面观察显示未充氢试样内形成明显的轴向<110>拉伸纤维织构,而氢脆试样内除了明显的晶界裂纹萌生,还有晶内裂纹扩展与局部晶体转动特征.基于不同取向晶粒的微屈服概念,解释了充氢导致轴向{110}晶粒优先微屈服而不是轴向{200}晶粒优先微屈服,同时以氢伴随微区塑性变形的方式发生脆性断裂.
The tensile deformation behavior and axial lattice deformation of 1250 MPa ultrahigh strength steel with or without hydrogenation were studied by means of time-neutron diffraction. The microstructure and grain orientation of the fracture region were observed. Under the unloaded conditions, the axial (110) and (200) planes of the hydrogen-filled specimens were larger and smaller than those of the uncharged specimens, respectively. ) Plane spacing increased, meanwhile the balance of internal stress reduced the axial (200) plane spacing.The necking plastic fracture occurred when the unhydrogenated specimen reached the tensile strength of 1250 MPa, but contained 8.0 × 10-6 The brittle fracture occurred when the samples diffused hydrogen at step loading of 500 MPa. The neutron diffraction analysis showed that the unhydrogenated specimens basically matched the linear elastic deformation when the tensile stress was 500 MPa, but at 700 MPa, The {200} grains preferentially exhibit nonlinear elastic deformation over the other oriented grains, and the {110} grains also exhibit nonlinear elastic deformation up to 800 MPa, with the {200} grains preferentially generating micro-yielding at 800 MPa The axial {211} grains are still in a linear elastic phase; when the hydrogen-filled specimen is stretched to 300 MPa, the {110} Nonlinear elastic deformation of the grains occurs. At 400 MPa, the {200} grains also appear nonlinear elastic deformation. The axial {110} grains give priority to micro-yielding and the {211} grains in the axial direction are still in a linear elastic phase The fracture section observation shows that the obvious axial <110> tensile fiber texture is formed in the unhydrogenated sample, while in the hydrogen embrittlement sample, in addition to the obvious grain boundary crack initiation, intracrystalline crack propagation and local crystal rotation Based on the concept of micro-yielding of grains with different orientations, it is explained that hydrogen charging results in the preferential micro-yielding of {110} grains rather than the {200} grains of micro-yielding in the axial direction, Brittle fracture.