Determination the causes of premature destruction of sheet electrical steel

Abstract

Sheets of electrical steel are produced by hot and cold working by pressure (mainly by rolling). In this case, the load during rolling should be chosen in such a way as not to impair the electrical properties of the steels. Received two sheets of electrical steel from different production batches. One of the sheets of electrical steel is prematurely destroyed at the stage of machining parts for electrical transformers. It has been established that an increased content of phosphorus worsens the characteristics of plasticity, which can complicate the process of pressure treatment in the manufacture of sheet electrical steel. Macrostructural analysis revealed longitudinal lines due to rolling. In places of greatest deformation, perpendicular to the direction of rolling, there are cracks and chipping of the insulating layer. Microstructural analysis showed that the cracks formed in the process of rolling sheet electrical steel propagate to a depth of 1.5–2.0 µm. The presence of linear depressions in the structure of the sheet steel indicates that the critical overload has been exceeded during rolling. The increased microhardness in samples of electrical steel is explained by the increased concentration of macro- and microstructural defects formed during the rolling process. It has been established that the main reasons for the premature destruction of electrical steel sheets are an increased content of harmful impurities and incorrectly selected pressure treatment modes, leading to the formation of macrocracks.