Modification of non-metallic inclusions with rare-earth metals in 50CrMoV13-1 steel

The potential use of the rare-earth metals in clean steel production was investigated.Reactions between the non-metallic inclusions and the rare-earth metals were investigated in a cold-work tool-steel grade (50CrMoV13-1).A rare-earth metal alloy misch metal (Ce, La, Nd, Pr) was used for the inclusion modification.Aluminium oxide non-metallic inclusions that have a negative effect on the mechanical properties usually occur in the investigated steel.The experimental melts were made in a vacuum induction furnace with different rare-earth metal additions (50, 150, 340, 950 and 2900) ppm.The laboratory cast ingots were hot forged and analysed with light and electron microscopy.It was found that misch metal additions influence the size, composition and type of the non-metallic inclusions in the steel.Most importantly, very small inclusions are formed at lower rare-earth metal additions (up to 340 ppm), but at high additions large non-metallic inclusions are formed (2900 ppm).