| Austenitic stainless steel is widely used in nuclear power, aerospace, and other important fields because of its stable austenitic organization, high plasticity and toughness, no ferromagnetic, good corrosion resistant performance and machining performance. However, the austenitic stainless steel modified by common nitriding process are easy to precipitate chromium nitride and hardening surface area, consume large amounts of chromium element, this process improve the hardness of the substrate surface but decreased the corrosion resistance at the same time. The stainless steel material included the γN phase composition get from the plasma nitriding treatment at low temperature (400 ℃) has a great composite properties:wear-resisting and corrosion resistance. The yn phase composition characteristic are internal stress, nitrogen super-saturation and chromium nitrogen short-range order distribution, N is one of the main alloy elements in the γN phase and the concentrations of N atom is the main component difference between γN phase stainless steel and ordinary stainless steel. The influence of N atom on the corrosion resistance of the metal substrate is very important, and also directly affect our understanding on the nature of austenitic stainless steel corrosion resistant mechanism.To this end, the paper study the effect of N atoms in austenitic stainless steel and its concentration changes (no nitrogen and placed 1～3 nitrogen atom in substrate would be write as ON～3N) on the corrosion resistance by the first principles calculation method. First, we make a contrast research between Fe(001) with no nitrogen and Fe(001) contains one nitrogen on adsorption energy and electronic structure at three different adsorption points T (top), H (hollow)and B (bridge), the results showed that the adsorption energy of O atom in three different adsorption point have obvious increase after the N atom doped in. Such as, the adsorption energy of O atom at the most stable position H increased from 6.58 eV to 11.38 eV In electronic structure, the p orbital of O atom has the largest contribution to Fe-0 band, the hybridization interval is-6 eV～5 eV, peak of 0.21 states/eV before adding nitrogen, after add nitrogen hybrid interval and peak comes to-6 eV～6 eV and 2.30 states/eV, the hybridization interval of p orbital has little changes while peak increased 10 times, orbital hybridization increasing and bonding effect significantly. Further changed the N concentration in metal substrate we found that the relationship between N concentration and the ability of O atom adsorption on metal surface is not the monotonic. When the N concentration changed from ON to 1N, the effect of the substrate on the adsorption of oxygen atoms is at a rising range and the maximum adsorption energy is 11.38 eV; N concentration changed from 1N to 2N, the effect of the substrate on the adsorption of oxygen atoms is at a stable range between 11.38 eV and 11.15 eV; At last, N concentration changed from 2N to 3N, the effect of the substrate on the adsorption of oxygen atoms is at a decline range and the minimum value is 8.99 eV. The calculation result explained the experiment phenomenon: when the concentration of nitrogen is lower than a certain critical value, the adsorption trend of metal substrate on oxygen is obviously and makes the passivation film components of the outermost layers contains more oxide; When the concentration of nitrogen exceeds a certain critical value, the adsorption trend of metal substrate on oxygen is abated, and for other ions, such as OH" can be adsorption more easily, this makes the passivation film components of the outermost layers contains more hydroxide. |
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