Influence of the atmosphere corrosion on the fatigue life of welded T-joints treated by high frequency mechanical impact

Abstract

The investigation deals with the effectiveness of high frequency mechanical impact (HFMI) treatment technology to increase the corrosion resistance of a base metal and the fatigue life of as-welded T-shaped joints and after their long-time exploitation in conditions modelling moderate climate. The conditions of moderate climate were simulated by exposing the specimens in a moisture chamber of G4 at a temperature of 40°C and air humidity of 98%. The microstructure of low alloy 15KhSND steel, weld zone and heat affected zone (HAZ) before and after the HFMI treatment was investigated. The corrosion tests of the base metal were carried out during 240, 480, 720, 960, 1200 and 2400 h, respectively. After exposure the specimens were removed and their weight reduction was defined. The duration of the corrosion test of the welded joints before fatigue tests was 1200 h. Corrosion-mechanical fracture of the hardened surface layer of the base metal, weld zone and HAZ after 1200 h of exposure is observed. The fatigue tests were carried out on six series of the welded T-joints of low alloy steel: as-welded and treated by HFMI on air; as-welded and treated by HFMI states after exposing in the chamber of G4; after accumulation 2·106 cycles and exposing in the chamber G4; after accumulation 2·106 cycles, exposing in the chamber G4 and subsequent treated by HFMI. It was established by the experiment that the use of HFMI technology can significantly increase the fatigue life of the welded T-joints of steel structures.