INFLUENCE OF STRESS RELIEF ANNEALING ON MECHANICAL PROPERTIES AND FATIGUE STRENGTH OF WELDED JOINTS OF THERMO-MECHANICALLY ROLLED STRUCTURAL STEEL GRADE S420MC

摘要

Due to a number of advantages characterising thermo-mechanically rolled steels, they are often used in construction of such welded structures as bridges, pressure vessels, elements of ships, pipelines, machinery parts etc. From the viewpoint of design of welded structures exposed to changing load during their operation, critical importance is attached to fatigue strength of welded joints, which is lower than that of other i.e. non-welded structural elements. This fact is caused by significant post-weld stresses which can be reduced in several ways e.g. by stress relief annealing. German design guidelines SEW 088 concerned with welding of fine-grained steels recommend stress relief annealing to be conducted within temperature range 530-580°C for between 30-150 minutes. This article contains description of impact of stress relief annealing on mechanical properties and fatigue strength of welded joints of S420MC steel belonging to a group of thermo-mechanically rolled steels. The description includes the course of tests, results of basic mechanical tests, results of measurements of internal stresses and fatigue categories for four most popular types of welded joints in their initial states and after being subject to stress relief annealing. It was determined that the process of stress relief annealing recommended by German guidelines SEW 088 does not lead to an increase in fatigue strength of S420MC steel welded joints. The test results can be useful for designers of steel structures.