Weld joints fatigue properties of thin carbon steel sheet treated by nitrooxidation

Abstract

Nisko ugljični čelik DC 01 (EN 10130-91) obrađen postupkom nitrooksidacije značajno je povećao mehanička svojstva kao i otpornost na atmosfersku koroziju. To je povećanje nastalo zbog postojanja površinskih nitridnih i oksidnih slojeva. Do sada su predlagani odgovarajući postupci zavarivanja za tako obrađivane čelične limove, od kojih se zavarivanje čvrstog tijela laserskim snopom (solid-state laser beam welding) smatralo najpogodnijim. Cilj je ovoga rada bio odrediti zamorna svojstva laserom zavarenih spojeva materijala obrađenog nitrooksidacijom. Provedena je i fraktografska analiza. Ispitivanja na zamor su se provodila kod opterećenja pri savijanju s frekvencijom od 20 kHz i sinusoidalnim simetričnim ciklusom. Rezultati su dokazali da se postupkom nitrooksidacije značajno poboljšavaju zamorna svojstva zavarenih spojeva.Low carbon steel DC 01 (EN 10130-91) treated by the process of nitrooxidation significantly increased its mechanical properties as well as the resistance to atmospheric corrosion. The high increase was due to the presence of the surface nitridic and oxidic layers. Previous outcomes dealt with suggesting a suitable welding method for steel sheets treated in this way, the solid-state laser beam welding being marked as the most suitable. The aim of this paper was to determine the fatigue properties of laser beam welded joints of material treated by nitrooxidation. The fractographic analysis was carried out as well. The fatigue tests were carried out under bending load with frequency of 20 kHz and sinusoidal symmetric cycle. The results proved that the process of nitrooxidation had a great positive effect on the weld joints ultimate fatigue properties