This study deals with the fatigue strength of high-frequency mechanical impact (HFMI)-treated unprotected structural details made of mild steel S355 considering the influence of corrosive environmental conditions. The investigations are carried out on butt welded specimens with sheet thickness t = 15 mm and on transverse non-load-carrying attachment specimens with sheet thickness t = 25 mm. Two different methods were applied for the simulation of marine corrosive environment in the laboratory. Specimens first were deposited in a salt spray chamber and then tested subsequently dry at laboratory-air conditions considering the influence of corrosion on the crack initiation. Alternatively, and to cover the effects of corrosion on the crack growth, artificial seawater was used for pre-corrosion, and after a defined timespan, fatigue tests were performed simultaneously with the specimen resting in the corrosive medium. The corrosion fatigue tests were performed in as-welded and HFMI-treated conditions at a stress ratio R = 0.1 under axial tensile and 4-point bending cyclic loading. The test results are evaluated to determine the characteristic fatigue strengths for fixed slopes m = 3 and m = 5 according to IIW recommendations for the as-welded and for the HFMI-treated condition respectively. The results of the experimental investigations based on the nominal stress approach show that the fatigue strength of both specimen types could be significantly increased by the application of HFMI treatment compared to the corresponding specimens in the as-welded condition even if exposed to the investigated corrosive conditions. The comparison with the design proposals of IIW shows that for HFMI-treated butt welds, no reduction of the FAT class due to corrosion is required and the recommended FAT class is still valid. The results for the HFMI-treated transverse attachments are slightly below the design curve recommended by IIW and a proposal to consider corrosion is derived for this case. Additional numerical investigations by applying the effective notch stress (ENS) approach are performed to determine notch stress curves. It was found that for the corroded specimens in the as-welded condition, the FAT class according to IIW could not be reached and adjustments of the existing rules are necessary to consider corrosion effects. However, it can be concluded that the effective notch fatigue resistance recommended by IIW is still applicable in the case of corroded HFMI-treated structural details.

本研究考虑了腐蚀环境条件的影响，研究了由S355低碳钢制成的高频机械冲击 (HFMI) 处理的无保护结构细节的疲劳强度。该调查是对对接进行焊接与板厚试样吨 = 15毫米，横向上非负载承载附件标本板厚吨 = 25 毫米。实验室采用两种不同的方法模拟海洋腐蚀环境。样品首先放置在盐雾室中，然后考虑腐蚀对裂纹萌生的影响，然后在实验室空气条件下进行干燥测试。或者，为了覆盖腐蚀对裂纹扩展的影响，使用人造海水进行预腐蚀，在规定的时间跨度后，将试样放置在腐蚀介质中同时进行疲劳试验。 在轴向拉伸和 4 点弯曲循环载荷下，在焊接状态和 HFMI 处理条件下以应力比R = 0.1进行腐蚀疲劳试验。评估测试结果以确定固定坡度的特征疲劳强度m = 3 和m = 5 根据 IIW 对焊态和 HMI 处理条件的建议。基于名义应力方法的实验研究结果表明，即使暴露在所研究的腐蚀条件下，与焊接状态下的相应试样相比，应用 HFMI 处理也可以显着提高两种试样类型的疲劳强度. 与 IIW 设计方案的比较表明，对于 HFMI 处理的对接焊缝，不需要因腐蚀而降低 FAT 等级，推荐的 FAT 等级仍然有效。HFMI 处理的横向附件的结果略低于 IIW 推荐的设计曲线，并且针对这种情况得出了考虑腐蚀的建议。通过应用有效缺口应力 (ENS) 方法进行额外的数值研究，以确定缺口应力曲线。结果发现，对于焊接状态下的腐蚀试样，不能达到 IIW 的 FAT 等级，需要对现有规则进行调整以考虑腐蚀影响。然而，可以得出结论，IIW 推荐的有效缺口疲劳抗力仍然适用于腐蚀 HFMI 处理的结构细节。