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采用力学性能测试、组织观察等方法研究回火温度对26CrMo钢显微组织和力学性能的影响。结果表明,26CrMo钢经540~690℃回火,随回火温度升高,显微组织中a相基体逐渐发生回复与再结晶,组织中马氏体形态逐渐消失,碳化物先在马氏体板条边界呈片状或棒状析出,逐渐演变为颗粒状弥散分布,690℃时碳化物在晶界聚集长大、球化。随回火温度升高,26CrMo钢强度逐渐降低,塑性、韧性逐渐增大;不同回火条件下,抗拉强度、屈服强度、延伸率和冲击功满足API 5DP标准中各级别钻杆要求。随回火温度升高,26CrMo钢总冲击功、起裂功和裂纹扩展功均逐渐增大,裂纹扩展功是起裂功的3倍以上,且两者比值变化不明显,表现出良好的抗裂纹扩展能力。不同回火温度下冲击性能的变化与其强度、塑性变化密切相关,冲击韧性好坏主要由塑性大小决定。
The effects of tempering temperature on the microstructure and mechanical properties of 26CrMo steel were studied by mechanical properties testing and microstructure observation. The results show that the martensite morphology gradually disappears in 26CrMo steel after being tempered at 540-690 ℃ with the increase of tempering temperature. The phase a matrix gradually recovers and recrystallizes in the microstructure. Slab boundaries were flake or rod-like precipitation, and gradually evolved into a granular dispersion, carbides at 690 ℃ aggregation in the grain boundary growth, spheroidization. With the increase of tempering temperature, the strength of 26CrMo steel gradually decreases and the plasticity and toughness increase gradually. Under different tempering conditions, the tensile strength, yield strength, elongation and impact energy meet the drill pipe requirements of API 5DP standards. With the increase of tempering temperature, the total impact energy, crack initiation work and crack extension work of 26CrMo steel increase gradually, and the work of crack propagation is more than 3 times of that of crack initiation work, and the ratio of the two is not obvious and shows good resistance Crack expansion ability. The impact of different tempering temperature changes with the strength and plasticity changes are closely related to the impact toughness is mainly determined by the size of the plastic.