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采用光学显微镜、X射线衍射分析、透射电镜、选区电子衍射及常温与高温拉伸试验等检测手段,基于不同回火次数下P91焊接接头显微组织的演化过程研究其对力学性能的影响.结果表明,随着回火次数的增多,接头显微组织主要保留了板条马氏体位向的回火索氏体,主要相为α-Fe相和Fe-Cr相,热影响区的室温及高温强度先增大后减小.在回火一次时,弥散析出的MX(M=V/Nb,X=C/N)型碳氮化物、位错缠结及亚稳态的位错网对接头有一定的析出强化及位错强化作用,其力学性能较佳,高温抗拉强度达最大值232.66 MPa;随着回火次数进一步增多,离散分布的碳化物Cr23C6逐渐偏聚并在晶界处演化为串链状分布,使晶界脆化,强度降低,但韧性有所改善.
The mechanical properties of the P91 welded joint were studied by means of optical microscope, X-ray diffraction analysis, transmission electron microscopy, selected area electron diffraction and tensile test at room temperature and high temperature, and the effect of different tempering times on the microstructure evolution of P91 welded joints. It is indicated that with the increase of tempering times, the microstructure of the joint mainly retains martensitic oriented tempered sorbite, the main phase is α-Fe phase and Fe-Cr phase, the room temperature and the high temperature in the heat-affected zone The strength first increased and then decreased.After tempering once, the dispersed MX (M = V / Nb, X = C / N) carbonitrides, dislocation-entangled and metastable dislocation network connectors With a certain degree of precipitation strengthening and dislocation strengthening. Its mechanical properties are better, and the maximum tensile strength at high temperature reaches 232.66 MPa. With the further increase of tempering times, the discrete distributed carbides Cr23C6 gradually segregate and evolve at grain boundaries For the chain-like distribution, the grain boundary embrittlement, strength decreased, but toughness improved.