INFLUENCE OF HEAT TREATMENT MODES ON THE HARDNESS AND PHYSICAL MECHANICAL PROPERTIES OF STEEL 7HNМFB FOR MANUFACTURING WOOD-CUTTING SAWS

The article covers issues related to the heat treatment of alloyed tool steels, in particular, the newly developed steel of the 7HNМFB brand, which is used for the manufacture of wood-cutting saws. It is noted that a feature of the new steel composition is a significant reduction in the content of harmful impurities of sulfur and phosphorus, which is achieved both by the smelting technology and by the introduction of calcium and rare earth elements into the steel composition. The introduction of the latter leads to a change in the quality and shape of the distribution of non-metallic inclusions, which contributes to an increase in plastic characteristics and an increase in fracture toughness. It is shown that tempering is a strengthening heat treatment, which consists in heating the steel to the temperature of polymorphic transformation of the material and subsequent cooling. The purpose of tempering alloyed steels is to obtain a martensitic structure and increase the hardness and strength of the steel. The difference between heat treatment of alloy steels and carbon steels lies in the choice of temperatures and heating speed. The purpose of the study is to determine the influence of heat treatment modes on the structure, hardness, and physical and mechanical properties of 7HNМFB steel for the manufacture of wood-cutting saws. The choice of heat treatment temperature depends on the content of alloying elements in the steel. For example, such elements as tungsten, vanadium, chromium contribute to the formation of red-resistant martensite, which is resistant to decay. The wood-cutting tool heats up in the process of cutting (the temperature in the contact zone reaches 600…800ОС) and if the steel is not red-resistant, it loses its hardness and cutting properties. Its physical and mechanical properties depend on the chemical composition of alloyed steels and the content of alloying elements, which directly affect the cutting properties of wood-cutting tools.