A modern user requires low operating costs, but also reliability from machines and technical devices. Reliability during the service life depends on the quality of construction solutions, but also largely on the quality, properties and adaptation to the working conditions used in the construction of construction materials. During the operation of technical objects, their a highly predictable wear occurs. The problem is the phenomena of premature wear and damage of elements. The causes of failure of technical facilities are usually complex and depend on many factors. They can include the human factor and the one related to the quality, selection, production and technological processes of the materials used in the construction of the facility. In real technical facilities, many premature failures are caused by material fatigue, which is related to the imperfection of the material and the morphology of non-metallic inclusions. The paper presents the change in fatigue strength for rotational bending of highpurity structural steel. In order to diversify the matrix of inclusions, the steel was hardened and tempered at temperatures from 200C to 600C. The influence of impurity diameter and arithmetic average impurities space on the fatigue strength of industrially produced steel was investigated.