Influence of Marine Media on the Fatigue Strength of Butt Welded Joints of 15KhSND Steel Hardened by High-Frequency Mechanical Impacts

We study the efficiency of application of the technology of high-frequency mechanical impacts (HFMI) aimed at increasing the fatigue resistance of butt welded joints in the stage of production of steel structures or after their long-term operation under the conditions of marine climate. Corrosion defects formed in welded joints were simulated in a KST-1 chamber filled with neutral salt fog for 1200 h at a temperature of 35 ± 2°C with dispersion of a sodium-chloride solution for 15 min every 45 min of testing for 1200 h. The concentration of sodium chloride in a solution was 50 ± 5 g/dm3 and pH = 6.5–7.2. The fatigue tests were carried out for four batches of butt welded joints of 15KhSND steel: in the aswelded state, after the HFMI treatment followed by holding in the KST-1 chamber; after operation for 2∙106 stress cycles and holding in the KST-1 chamber, and after operation for 2∙106 cycles and holding in the KST-1 chamber with subsequent HFMI hardening. It is experimentally demonstrated that the application of the HFMI technology noticeably increases the fatigue life of butt welded joints in metal structures under the conditions of variable loads and marine climate.