Increasing the Corrosion Fatigue Resistance of Welded Joints by High-Frequency Mechanical Peening

The cyclic life of butt- and T-welded joints in as-welded condition and after strengthening by high-frequency mechanical peening has been studied. The welded joint specimens were made from a 12 mm thick rolled sheet of commonly used weathering steels 10KhSND and 15KhSND. The fatigue tests were carried out in air and in a corrosive medium (in a 3% NaCl solution) under pulsating tension with a frequency of 5 Hz. It has been found that high-frequency mechanical peening as a method for the plastic surface deformation of the joint metal near the fatigue damage localization sites increases the cyclic life of welded joints in air by a factor of over 10. It has been confirmed that in tests in a corrosive medium, the short-time fatigue strength of welded joints both in initial and in strengthened condition decreases. It has been shown that as a result of strengthening by high-frequency peening, the corrosion fatigue resistance characteristics of butt-welded joints of 15KhSND steel are significantly improved: the cyclic life increases by a factor of 4-10 depending on the level of applied stresses, the short-time fatigue strength, based on 2 10(6) cycles, increases by 85%. It has been found experimentally that in a 3% NaCl solution, strengthening increases the cyclic life of T-welded joints of 15KhSND and 10KhSND steels by a factor of 4-10 and 3.5-4, respectively, and that the short-time fatigue strength, based on 2 10(6) cycles, increases by 114 and 80%, respectively. Most strengthened specimens failed in the base metal, far from the fusion line; the unstrengthened specimens failed only in the transition area between the weld metal and base metal.