Offshore structures which are made up of high-strength low alloy (HSLA) steel experience fatigue load due to sea waves and corrosion. In the present work, the influence of environmental conditions (air and 3.5 % NaCl solution) on the strain-controlled fatigue life of High Strength Low Alloy (HSLA) steel has been determined. Low cycle fatigue experiments were conducted on HSLA steel specimens of 12 mm diameter which were prepared parallel to the rolling direction. The strain amplitude was varied in the range of 0.4 to 0.7 % for a constant test frequency of 0.3 Hz. For all the total strain amplitudes (), a significant reduction in fatigue life was observed while testing the specimens under the presence of 3.5 % NaCl solution compared to the air environment. Microscopic investigation indicates that rigorous grain boundary oxidation has happened, and it has created the grain boundary cracking and several sites for fatigue crack initiation and propagation. The presence of corrosive compounds (FeO FeOOH) was also confirmed by the X-ray diffraction patterns. In addition, mixed modes (transannular and intergranular) of fractures were observed due to the presence of 3.5 % NaCl solution.

中文翻译：

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了解环境条件对高强度低合金 (HSLA) 钢在空气和腐蚀 (3.5% NaCl) 条件下的低周疲劳行为的影响

由高强度低合金 (HSLA) 钢制成的海上结构会因海浪和腐蚀而承受疲劳载荷。在目前的工作中，已经确定了环境条件（空气和 3.5% NaCl 溶液）对高强度低合金 (HSLA) 钢应变控制疲劳寿命的影响。在平行于轧制方向制备的直径为12 mm的HSLA钢试件上进行了低周疲劳实验。对于 0.3 Hz 的恒定测试频率，应变幅度在 0.4 至 0.7 % 的范围内变化。对于所有总应变振幅 ()，与空气环境相比，在 3.5% NaCl 溶液存在下测试样本时，观察到疲劳寿命显着降低。微观观察表明，发生了严重的晶界氧化，并产生了晶界裂纹和多个疲劳裂纹萌生和扩展的部位。 X 射线衍射图也证实了腐蚀性化合物 (FeO FeOOH) 的存在。此外，由于 3.5% NaCl 溶液的存在，观察到了混合模式（跨环和沿晶）断裂。