engleski

Potential fatigue strength change of welds due to repair welding

The fatigue strength of welds in polycrystalline metals depends on the hardnes, the size of defects and grains in the areas of the higest stress and on the level of welding residual stress. Changes of residual stress and hardness were experimentally determined on a weld which was repaired. Besides, steel samples with the microstructure of martensite were used with the intention to assess effects of residual stresses and grain size to the fatigue strength of welds. The samples were prepared using either thermal cycle simulator or laboratory furnance and water quenching. The used methods of microstructure preparation result in different surface residual stress. Specimens for the fatigue limit measurement were prepared either defect-free or with artificial defects. Artificila surface defects were small in comparison with the size of grains. The defects were made by drilling small holes and indenting with the Vickers pyramid. The results show that tensile residual stresses and coarser grains lower the fatigue limit of steel and vice versa. Enhancement of welding residual stresses caused by repair welding leads to fatigue strength reduction of welds while hardening of weld materials leads to its increase.

artificial defect; coarse grain; fatigue crack; repair welding

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