Study of the Influence of Ladle Treatment on the Austenite Grain Size of Case-Hardening Steel Grades

For a number of case-hardening low-carbon steels (16MnCrS5, 20MnV6, 18KhGT, 25KhGT, Е470), depending on the customer’s requirements, it is necessary to obtain stable fine austenite grains during high-temperature heating and long-term holding. The stability of the austenite grain size is ensured by microalloying of steel with a minimum sufficient amount of niobium within the limits according to the customer’s specification. This paper presents studies on mastering the technology of producing case-hardening steels with a stable austenite grain size with testing of changes in the ladle treatment technology. After adjusting the technology of ladle treatment of steel, the maximum size of austenite grain in the studied samples corresponded to 3–5 points. The results of metallographic studies show that adjusting the technology of ladle treatment of steel grade 16MnCrS5 did not allow to fully achieve the set goal, that is, to obtain an austenite grain size in case-hardening steel of no larger than 5 points. Taking into account the obtained results of metallographic studies after adjusting the technology of ladle treatment and microalloying of steel with niobium, a further strategy was developed to improve the technology of production of case-hardening steel grades resistant to the growth of austenite grains during high-temperature heating and long-term holding under the conditions at the of OAO BMZ—Management Company of BMK Holding.