Medium-Carbon Free-Cutting Steel

Abstract

The paper presents theoretical and experimental studies of the formation processes of boron nitride, aluminium nitride, aluminium oxide and manganese sulphide inclusions in a free-cutting steel. Fact Sage software was used to model the behaviour of non-metallic inclusions. Formation temperatures and the amount of key inclusions in steel were calculated. Formation order of inclusions is as follows: aluminium oxide > boron nitride > manganese sulphide > aluminium nitride. The object of study was the A45AR grade steel in 1.1–1.2 kg ingots. It was melted in an induction furnace, and aluminium, nitrided ferrosilicon and ferroboron were added after deoxidation before tapping. Quality estimation included chemical composition, macro-and microstructure, the character and shape of non-metallic inclusions. The finished metal contained fine and uniformly distributed inclusions of boron nitride. Qualitative and quantitative analysis of boron nitrides distribution in metal matrix showed that they were present both as individual and complex compounds, mostly of spherical shape. The size of BN inclusions varied from 0.18 to 6.52 μm. The amount of boron added to steel did not affect the size of MnS non-metallic inclusions.