Influence of oxygen content in medium carbon steel on bending fatigue strength

Commercial iron alloys apart of typical chemical elements contain phosphorus, sulfur, oxygen as well as nonmetallic inclusions. These elements can form solutions in liquid metal, or they can form separate phases. The physical and chemical reactions that occur in the process of steel melting and solidification produce non-metallic compounds and phases, referred to as inclusions. Inclusions as impurities found in steel can affect its performance characteristics. The article discusses the results of a study investigating the effect of oxygen on the fatigue strength of structural steel during rotary bending. The study was performed on 7 heats produced in an industrial plant. Fourteen heats were produced in 100 ton oxygen converter. All heats were desulfurized. The heats from the converter were subjected to vacuum circulation degassing. The experimental variants were compared in view of the heat treatment options. The examination was realized by the rotatory curving machine about the frequency of pendulum cycles: 6000 periods on minute. For basis was accepted on fatigue defining endurance level 107 cycles. The level of the fatigue-inducing load was adapted to the strength properties of steel from 540 to 650 MPa. The fatigue strength of steel with tested for oxygen content in steel was determined during rotary bending. The results revealed that fatigue strength is determined by the contents of oxygen impurity spaces and tempering temperature. A reduction in the fatigue strength during rotary bending of low-carbon steel from 368 to 252 MPa was observed when the tempering temperature changed from 200 to 600oC. It was found that with an increase in the content from 0.0023%, 0.003% of the bending transfer (for all temperatures from 298 to 328 MPa) can be transferred.