Microstructural parameters as indicators of reliability of car castings made of 20GL steel

Abstract

The complex influence of grain number, average area and grain hardness on the section of low-alloy cast steel 20GL of car castings “Side frame” and “Truck bolster” on the basis of statistical and microstructural analysis of samples obtained after open-hearth and electric arc melting and single and double heat treatment (HT), on increase of the toughness KCV-60 > 2.0. The frequency diagram of the relationship between the number of open-hearth and electric arc melts and the same level of impact toughness in 2018 with the imposition of grain microstructure and different levels of impact toughness (KCV-60 <2.0, KCV-60 ≥ 2.0 and above KCV-60 > 2.0∙102 kJ/m2). The relationship between the number of samples obtained by open-hearth melting and passed the 2nd HT, and the same level of impact strength in 2019 with the imposition of the grain microstructure from samples after the 1st and 2nd HT and different levels of impact toughness (KCV-60 < 2.0 and KCV-60 > 2.0∙102 kJ/m2). Microstructure of samples of low-alloy cast steel 20GL of car castings “Side frame” and “Truck bolster” types was studied by optical microscopy in the search for causes of falling toughness (KCV-60 <2.0). Statistical and microstructural analysis of the array of data on the size and average area of grains, their number and hardness in 20GL steel samples after single and double HT indicated different viscoplastic properties of these castings. The authors concluded that the grain size and hardness are the most important indicators of the microstructure of low-alloy steel 20GL and are unique in their effect on toughness.