The influence of the shape of weld nobs on the fatigue strength of S540Q steel

The development of weldable steels was discussed together with the methods of obtaining them. The influence of these methods on steel properties was explained. Research was performed on quenched weldable S540Q steel of high strength. Basic mechanical properties of this steel were determined. The results of a static tensile test and technological bending test were given. Next, steel sheets were welded by semi-automatic MAG method. The welds quality was examined and their future suitability was stated. Mechanical properties of the joints welded of this steel were determined. Mechanical properties of native material and welded joints were compared. Joints microstructure was examined in the weld axis, in the heat influence zone and in the native material. Fatigue tests were conducted in the cycle of nonsymmetrical tension – compression of welded joints. The analytical fatigue strength was obtained and it was compared with fatigue strength of welded joints. Tests results were elaborated with the static analysis of linear regression. Wohler diagrams were made after conducting fatigue tests. Finally, weldable joints were melted by TIG method without adding filler metal. The angle and radius of welds nobs entrance into the native material was measured. The increase of fatigue strength is related to the decrease of geometric notch on the edges of weld nobs.