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通过SEM断口分析、TEM选区电子衍射及金相技术对汽轮发电机组25Cr2MoIV钢高温紧固螺栓脆化机理进行了研究。认为螺栓在高温工作条件下,晶内会出现大量与基体保持Baker Nutting关系的超微细析出物VC,使基体的硬度值由于共格强化及弥散强化而升高,而晶界不连续网状碳化物的析出,使邻近区域的合金元素贫化,造成晶界弱化是脆化失效的主要原因。经950℃高温正火加650℃回火能有效地消除脆化的微观组织因素,使材料重新具备良好的性能。
The embrittlement mechanism of the high temperature fastening bolt of 25Cr2MoIV steel for steam turbine generator was studied by SEM fracture analysis, TEM selective electron diffraction and metallographic techniques. It is considered that under the working condition of high temperature, there will be a large number of ultrafine precipitates VC in the crystal which maintains the Baker Nutting relationship with the matrix, so that the hardness value of the matrix will increase due to the coherent and dispersion strengthening while the discontinuous mesh carbonation Material precipitation, the adjacent area of alloying elements depletion, resulting in grain boundary weakening is the main reason for embrittlement failure. The 950 ℃ high temperature normalizing plus 650 ℃ tempering can effectively eliminate the embrittlement of microstructure factors, so that the material with good performance.