Investigation on carbide dispersion modified by magnesium and rare earth in high-carbon martensitic stainless steel

Abstract

Fine and uniform carbides play a beneficial role in the high hardness and wear resistance of martensitic stainless steel. This paper investigates the effect of magnesium and rare earth(RE) on the dispersion of carbides in a high-carbon martensitic stainless steel. The results show that RE-Al-O and RE-Al-O-S inclusions were generated in RE-containing steel, while Mg-Al-O+(Ca, Mn)S and MgO+CaS inclusions were in Mg-containing steel. MC, M7C3, and M23C6 types of carbides were detected in both RE-containing and Mg-containing steels, which is consistent with thermodynamic calculation. The RE-Al-O inclusion can act as heterogeneous nuclei for carbides, while Mg-containing inclusions do not promote carbide precipitation for sulfur enrichment. The three-dimensional etching test suggests that RE-containing steel has more serious network carbides and larger carbide sizes than Mg-containing steel. The carbon segregation ratio presents an “M” shape due to δ→γ phase transformation. Rare earth is easy to combine with S and weaken the inhibiting effect of carbon segregation. Thus, magnesium has a stronger inhibitory effect on carbon segregation than rare earth.