对S135钻杆钢在空气和H2S环境中进行了不同应力幅下的疲劳试验,得到了不同条件下的疲劳寿命,并应用回归分析方法得到了该钻杆钢在不同环境中的疲劳寿命公式,分析了其疲劳断裂机制.结果表明:在空气环境中,试验钢呈现明显的疲劳极限特征;在H2S环境中,相同当量应力幅下试验钢的疲劳寿命比在空气环境中的低,且在很低的当量应力幅下仍会发生断裂,不存在疲劳极限;在不同环境和不同当量应力幅下,试验钢的疲劳裂纹均萌生于试样表面或靠近表面处,裂纹源区以解理断裂为主;在空气环境中,裂纹扩展区以疲劳条带为主要特征,在H2S环境中,裂纹扩展区以解理平面和解理台阶为主要特征,在其解理平面上存在大量的二次裂纹,具有氢脆断裂的特征.
Fatigue tests under different stress amplitude were conducted on S135 drill pipe steel in air and H2S environments, and the fatigue lives under different conditions were obtained.The fatigue life formulas of the drill pipe steel in different environments were obtained by a data regression analysis method, and the fatigue fracture mechanism was analyzed.The results show that the tested steel had an obvious characteristic of fatigue limit in the air environment.The fatigue lives of tested steel in the H2S environment were lower than those in the air under the same equivalent stress amplitude, the fracture happened under relatively low equivalent stress amplitude and no fatigue limit existed.The fatigue cracks in the tested steel were all initiated at or near the surface in different environments and under different equivalent stress amplitude, and the crack initiation region exhibited mainly cleavage fracture.The crack propagation region showed a main characteristic of fatigue striations in the air while of cleavage fracture and cleavage steps in the H2S environment.On the cleavage fracture surface existed lots of second cracks, indicating a characteristic of hydrogen embrittlement fracture.
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