Effects of Rare Earth Elements (Ce, Y) on Microstructure and Mechanical Properties of P20 Die Steel

Abstract

Electroslag remelting P20 die steels with different amount of CeO2 or Y2O3 additions have been investigated by using mechanical tests and scanning electronic microscope with energy dispersive spectrometry. The microstructure of P20 die steels is tempered martensite, in which plenty of carbides precipitate along the martensite laths. With addition of rare earth Ce or Y, the matrix microstructure is refined, the quantity of carbides is decreased, and the distribution of carbides becomes more uniform. As a result of these microstructural changes, both the impact energy and tensile strength increase with increasing rare earth content. The samples obtain optimum microstructure and mechanical properties when the amount of CeO2 or Y2O3 additions reach 4 wt.%. However, over-added CeO2 or Y2O3 (>4 wt.%) results in the increase of carbides quantity and the aggregation of carbides, which reduces the impact energy and tensile strength of the samples. Present study indicates that the optimum addition of CeO2 and Y2O3 for the P20 die steels is 4 wt.%.