The influence of plasma-arc cutting on the microstructure and hardness of high-strength steel

The application of high-strength steels during the creation of products satisfying all the modern requirements of the market is one of the most promising areas of modern engineering. The use of these steels reduces metal consumption of produced constructions due to reducing the thickness of the metal while maintaining the same structural strength, increases the service life of products thanks to increasing durability, as well as improves the reliability of the produced product. The processing of high-strength steel has a number of features associated with increased sensitivity of such steels to a thermal effect. The aim of this study is to research the influence of plasma-arc cutting on the microstructure and hardness in the heat-affected zone of high-strength steel having hardness of 500 HBW. To do that, the research of microstructure in the heat-affected zone of plasma-arc cutting of high-strength steel with 500 HBW hardness was performed. The results of research showed the presence of parts with different structures and properties in the heat-affected zone of plasma-arc cutting: decarburized layer, hardening layer, incomplete quenching layer, tempering layer, and the base metal. While moving off the boundary of the cut the cooling rate and temperature of metal are reduced. It is the cause of lowering steel hardness. The microstructure of the base metal has a needle form, and consists of strips of different orientation and size. The structure of different parts of the heat-affected zone are: hardening layer - martensite, incomplete quenching layer - martensite + ferrite, tempering layer - tempered martensite. The total length of the heat-affected zone and the length of its individual sections were also determined.