The Effect and Control of Rare Earth Ce on Carbonitrides Precipitation in 441 Ferritic Stainless Steel

Abstract

This article investigates the influence of microalloying with different Ce contents on the precipitation of carbonitrides in 441 ferritic stainless steel through high-temperature thermal simulation experiments and thermodynamic calculation.The results indicate that there are two main types of carbonitrides in 441 ferritic stainless steel without rare earth Ce addition： separately precipitated carbonitrides and heteronucleated composite carbonitrides. After adding rare earth elements to the steel， Al in the nucleation oxide of carbon nitride is gradually replaced by Ce， and the modification order is Al2O3·Ti2O3→AlCeO3·Ti2O3→Ce2O3·Ti2O3. After modification， the mismatch between Ce2O3 and carbonitrides is higher， resulting in a weakened nucleation ability. This not only transforms the morphology from fully encapsulated to semi encapsulated structure， but also intensifies the precipitation of individual carbonitrides. With the addition of high content rare earth elements， CeN gradually precipitates in the steel， and the precipitation process of TiN is inhibited， reducing the precipitation area of carbonitrides and gradually spheroidizing the morphology of carbonitrides. As high content rare earth elements are added， CeN gradually precipitates in the steel The precipitation process of TiN is inhibited during this process， reducing the precipitation area of carbonitrides and gradually spheroidizing their morphology.By comparing different Ce samples， the rare earth addition amount is 0.007%， which increase the density of heterogeneous nucleation compared to the original cast carbonitrides. The density of carbonitrides increases from 66.7 number/mm2 to 74.5 number/mm2， with an average size concentration of 1-3 μm. The best effect is to refine the grain size.

Keywords

• 441 stainless steel； solidification process； rare earth； carbonitrides； rare earth inclusions