Study On Plasma Nitriding And Empirical Electron Theory Of 45 Steel

In order to improve the wear and corrosion resistance of 45 steel,the surface treatment was carried out by plasma nitriding process.The test variables were nitriding temperature（480℃and 520℃）and nitrogen to hydrogen flow ratio（1:3 and 3:1）.The influence of nitriding process on the microstructure and properties of 45 steel was discussed.The crystal structure of the phase after nitriding was calculated by solid and molecular empirical electron theory.The influence of crystal structure on the properties was analyzed.The mechanism provides theoretical support for the improvement of the nitriding process.The plasma nitriding test showed that when the nitriding temperature was the same,the thickness,hardness,wear resistance and corrosion resistance of the layer were higher than the ratio of nitrogen to hydrogen flow ratio of 1:3 when the ratio of nitrogen to hydrogen flow was 3:1.The mechanical properties of the former are inferior to the latter;when the nitrogen-hydrogen flow ratio is the same,the thickness,hardness,wear resistance and corrosion resistance of the layer are higher than the nitriding temperature of 480℃when the nitriding temperature is 520℃,but the mechanical properties of the former are inferior to the latter.The impact absorption energy of the four groups of nitrided samples decreased from26%to 35%of the original sample,indicating that plasma nitriding significantly increased the brittleness of the matrix;the 45 steel nitrided layer was mainly composed ofα-Fe、ε-Fe_2-3N andγ′-Fe₄N,the latter two are the new phase of nitrided layer.If the nitrogen-hydrogen flow ratio is consistent,the content ofε-Fe_2-3N in the layer is higher than 480℃at 520℃,the content ofα-Fe、γ′-Fe₄N is lower than 480℃;If the nitriding temperature is consistent,when the nitrogen-hydrogen flow ratio is 3:1,the content ofα-Fe,γ′-Fe₄N is lower than 1:3 while theε-Fe_2-3N in the layer is higher than 1:3.The theoretical calculation results show that the order of covalent electron density and atomic average bonding energy of the crystal isα-Fe<Fe₄N<Fe₃N<Fe₂N,which means that the hardness and wear resistance of the new nitrided phase are higher than the matrix.The hardness and wear resistance ofε-Fe_2-3N are higher than those ofγ′-Fe₄N crystal;The order of lattice electron density from high to low isα-Fe>Fe₄N>Fe₃N>Fe₂N,indicating the corrosion resistance of the new phase in nitrided layer is better thanα-Fe crystal,and the corrosion resistance ofε-Fe_2-3N is better thanγ′-Fe₄N;The order of plasticity factor from high to low isα-Fe>Fe₄N>Fe₃N>Fe₂N,indicating the plasticity of the new phase is worse than that of the matrix,and the plasticity ofε-Fe_2-3N is worse than that ofγ′-Fe₄N.Theoretical calculations confirmed and explained the effect of experimental partial plasma nitriding on the properties of 45 steel.Proper reduction ofε-Fe_2-3N formation is important for reducing material brittleness.Under the conditions of this test,proper reduction of plasma nitriding temperature and nitrogen to hydrogen flow ratio can protect the mechanical properties of 45 steel.