The alloyed cementite (Fe-Ni-Cr)3C: local environment, atomic magnetic moments, and magnetization from DFT calculation

Abstract

The alloying element added to carbon steel to enhance its properties also penetrates Fe3C cementite particles, altering their properties and influencing the steel product through them. This is why the impact of alloying elements on cementite has been extensively studied. Ni and Cr exhibit opposing behavior in cementite, so cementite doped with Ni and Cr is investigated using DFT calculations. The data obtained for total energy, lattice, magnetization, local magnetic moments at metal atoms, and their nearest environment are compared to experimental magnetic data for Ni and Cr-alloyed cementite. The relationship between Fe atom magnetic moments and their nearest environment is discussed in comparison between Cr and Ni doping. Decrease in magnetization with Ni and Cr content is attributed to 1) replacement of a larger Fe magnetic moment (mFe=1.9-2.0 μB) with a smaller or even negative moment (mNi=0.2-0.5 μB, mCr=-0.3 – -1.0 μB); 2) a decrease in the average Fe moment with the number of Cr atoms in the nearest environment; and 3) a strong dependence of the Curie temperature on Cr content in Cr-doped cementite.