1. Effect of nitrogen on Microstructure and heat treatment of steel
① Nitrogen, like carbon, can be dissolved in iron to form interstitial solid solution.
② Nitrogen enlarges the austenite phase zone of steel, which is a strong element for forming and stabilizing austenite.
Its effect is about 20 times that of nickel, and it can be used in steel instead of part of nickel to a certain extent.
③ Nitrogen and chromium, aluminum, vanadium, titanium and other elements infiltrating into the steel surface can form extremely stable nitrides, which become surface hardening and strengthening elements.
④ Nitrogen makes the structure of high chromium and high chromium nickel steel compact and solid.
⑤ Excessive residual nitrogen content in steel will lead to macro structure porosity or porosity.
2. Effect of nitrogen on mechanical properties of steel
① Nitrogen has a solid solution strengthening effect and can improve the hardenability of steel.
② In nitrogen-containing ferritic steel, precipitation hardening may occur due to the precipitation of ultra-microscopic nitrides during tempering after rapid cooling or staying at room temperature for a long time.
Nitrogen also causes strain aging of low-carbon steel.
With the increase of strength and hardness, the toughness of steel decreases and notch sensitivity increases.
The brittleness of steel caused by nitrogen is similar to that of phosphorus, and its effect is much greater than that of phosphorus.
Nitrogen is also the main cause of blue embrittlement in steel.
③ The strength and impact toughness of high chromium steel and high chromium nickel steel are improved without decreasing the plasticity.
④ The creep strength and high temperature rupture strength of the steel are improved.
3. Effect of nitrogen on physical, chemical and technological properties of steel
① Nitrogen has no significant effect on the corrosion resistance of stainless steel.
② When the mass fraction of nitrogen is greater than 0.16%, the oxidation resistance will deteriorate.
③ The cold deformation hardening rate of nitrogen-containing steel is higher.
④ Nitrogen can reduce the grain growth tendency of high chromium ferrite steel and improve its weldability.
4. Application of nitrogen in steel
① As an alloy element, the content of nitrogen in steel is generally less than 0.3% (mass fraction), and can be as high as 0.6% in special cases.
② It is mainly applied to nitrided quenched and tempered steel, ordinary low-alloy steel, stainless acid-resistant steel and heat-resistant non-peeling steel, of which heat-resistant non-peeling steel can be used to manufacture components of steam turbines.