Effect of heat treatment parameters on the microstructure and hardness of steel 45 produced by the electroslag remelting process

Modern requirements for the quality of structural steels used in the manufacture of critical machine and mechanism components necessitate the application of highly efficient metallurgical technologies capable of producing metal with a high degree of purity and structural homogeneity. One of such technologies is electroslag remelting (ESR), which is widely employed for producing high-quality ingots of structural and alloy steels. In the present study, the influence of various heat treatment regimes on the microstructure and hardness of structural steel 45 produced by the electroslag remelting process was investigated. The experimental program included normalization, quenching with cooling in water and oil followed by tempering. Metallographic examinations were carried out using optical microscopy after standard preparation of metallographic specimens and chemical etching. The hardness of the samples was determined using the Rockwell hardness test. It was established that the initial microstructure of the steel after electroslag remelting is characterized by a ferrite-pearlite structure with relatively coarse grains. Normalization leads to the formation of a fine-grained ferrite-pearlite structure with moderate hardness. Water quenching provides the maximum increase in hardness; however, it is accompanied by the development of significant internal stresses and the formation of quenching cracks. The most rational heat treatment regime was found to be oil quenching followed by high tempering, which ensures the formation of tempered martensite (tempered sorbite) and provides an optimal combination of strength and plastic properties of the material. The obtained results can be used in the development and optimization of heat treatment regimes for critical components made of steel 45 produced by the electroslag remelting method.