1. Effect of nitrogen on the microstructure and heat treatment of steel
① Nitrogen, similar to carbon, can dissolve in iron to form an interstitial solid solution.
② Nitrogen increases the size of the austenite phase zone in steel, which is a robust element for forming and maintaining stability in austenite.
Its impact is about 20 times greater than that of nickel and can partially replace nickel in steel.
③ Nitrogen, together with elements such as chromium, aluminum, vanadium, titanium and others that infiltrate the surface of steel, can form highly stable nitrides. These nitrides serve as surface hardening and reinforcing elements.
④ Nitrogen makes the structure of high chromium and high chromium nickel steel more compact and solid.
⑤ Excessive residual nitrogen content in steel may result in macrostructural porosity or holes in the structure.
2. Effect of nitrogen on the mechanical properties of steel
① Nitrogen has a solid solution strengthening effect and increases the hardenability of steel.
② In nitrogen-containing ferritic steel, precipitation hardening may occur as a result of the formation of ultramicroscopic nitrides during tempering, after rapid cooling or prolonged exposure to room temperature.
Nitrogen can also lead to creep aging in low carbon steels.
As the strength and hardness of steel increases, its toughness decreases and its susceptibility to notch sensitivity increases.
The brittleness of steel caused by nitrogen is comparable to that of phosphorus and has a much greater impact than phosphorus.
Nitrogen also contributes significantly to the blue embrittlement of steel.
③ The strength and impact resistance of high chromium steel and high chromium nickel steel are improved without sacrificing plasticity.
④ The creep strength and high temperature rupture strength of steel are also improved.
3. Effect of nitrogen on the physical, chemical and technological properties of steel
① The presence of nitrogen does not have a substantial impact on the corrosion resistance of stainless steel.
② If the nitrogen content exceeds 0.16% by mass, the steel's resistance to oxidation will decrease.
③ Nitrogen-containing steel has a higher hardening rate due to cold deformation.
④ Nitrogen can decrease the tendency of grain growth in high chromium ferrite steel and increase its welding capabilities.
4. Application of nitrogen to steel
① Nitrogen is commonly used as an alloying element in steel, with a content typically ranging from less than 0.3% (by mass) to a maximum of 0.6% in specific circumstances.
② It is mainly used in nitrided quenched and tempered steel, common low-alloy steel, acid-resistant stainless steel and heat-resistant and chip-free steel. Among these, heat-resistant and chip-free steel can be used to produce components for steam turbines.
