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锻造 718合金的γ -镍基体中存在大量针状和片状的δ相析出物乃是由多次焊接修复 -焊后热处理循环所引起的显微结构的主要变化。以实验室试样 ,采用 95 4℃、长达 10 0h的等温热处理 ,模拟多次焊后热处理。在上述热处理过程中 ,由于δ相对晶界的钉扎作用 ,晶粒大小不会发生明显的改变。这些热处理使得 718合金对热影响区熔析开裂的敏感性降低。这种降低乃是由δ相的溶解、碳化硼组织的偏析和晶界析出的综合作用所引起的短时高温熔析所致。回复处理 (10 10℃ ,12h)通过高于δ-相溶解度曲线的溶解作用以消除δ -相的不利影响而有效地恢复被降低了的焊接性能。这种热处理消除了δ相对晶界的钉扎作用 ,促进了自发的晶粒细化 ,增加了特殊晶界的数量。从修复焊接 718合金时发生的热影响区熔析裂纹的角度 ,讨论了δ相、晶粒尺寸和特殊晶界数量的综合影响
The large number of acicular and lamellar δ-phase precipitates in the forged 718 alloy γ-Ni matrix is the major change in the microstructure caused by multiple weld repairs-the post-weld heat treatment cycles. Laboratory samples, using 95 4 ℃, up to 10h isothermal heat treatment, simulation of multiple post-weld heat treatment. In the above heat treatment process, the grain size does not change significantly due to the pinning effect of δ on the grain boundaries. These heat treatments reduce the sensitivity of 718 alloy to melt-heat-affected zone cracking. This reduction is due to the dissolution of δ phase, boron carbide segregation and grain boundary precipitation caused by the combination of short-term high-temperature melting due. The reprocessing (10 10 ° C, 12h) effectively restored the reduced weldability by eliminating the adverse effect of the δ-phase by dissolution above the δ-phase solubility curve. This heat treatment eliminates the pinning of δ relative to the grain boundaries, promotes spontaneous grain refinement and increases the number of special grain boundaries. The combined effect of δ phase, grain size and the number of special grain boundaries is discussed from the point of view of the melt-fracture in the heat-affected zone that occurs when welding Alloy 718.