Nickel is the main alloying element in austenitic stainless steel.
Its main role is to stabilize one million of austenite, so that the steel obtains a complete austenite structure, so that the steel has a good combination of strength and plasticity, toughness, and has Excellent hot and cold workability, cold formability, low temperature and non-magnetic properties. That's why nickel-containing ss pipe and fittings are more popular from stainless steel pipe fittings supplier
Nickel improves the thermodynamic stability of austenitic stainless steel, making it not only have better performance of stainless and oxidizing medium than ferrite, martensite and other stainless steels with the same chromium/molybdenum content, but also on the surface the stability of the membrane is improved, so that the steel also has more excellent resistance to some reducing media.
Nickel is an element that stabilizes austenite structure
In order to obtain a single austenite structure, the minimum nickel content required when steel contains 0.1% carbon and 18% chromium is about 8%, which is the basis of the most famous 18-8 chromium-nickel austenitic stainless steel Minute.
In austenitic stainless steel, with the increase of nickel content, residual ferrite can be completely eliminated, and the tendency of σ phase formation is significantly reduced; at the same time, the temperature of martensite to hydrocarbon reduction is reduced, and even the λ→M phase transition may not occur, but The increase of nickel content will reduce the solubility of carbon in austenitic stainless steel, which will increase the precipitation tendency of carbides.
The effect of nickel on the mechanical properties of austenitic stainless steel
This is determined by the influence of nickel on the stability of austenite. In the range of nickel content in which martensite transformation may occur in the steel, as the nickel content increases, the strength of the steel decreases and the sheet plasticity increases, with stable austenite.
The structure of chromium-nickel austenitic stainless steel has excellent toughness (including extremely low temperature toughness), so it can be used as low temperature steel.
In austenitic stainless steel, the addition of nickel and the increase in nickel content lead to an increase in the thermodynamic stability of the steel. Therefore, austenitic stainless steel has better performance in stainless and oxidative media, and with nickel As the content increases, the performance of the reduction-resistant medium is further improved.
It is worth pointing out that nickel is the only important element that improves the resistance of austenitic stainless to many medium-transformation stress corrosion in many media.
Effect of nickel on corrosion resistance of stainless steel austenite structure
Under high temperature and high pressure conditions, the increase in nickel content leads to increased sensitivity to intergranular stress corrosion of steel and alloys, but this adverse effect will be alleviated or suppressed due to the increase in chromium content in steel and alloys.
With the increase of nickel content in austenitic stainless steel, the critical carbon content of intergranular corrosion decreases, that is, the sensitivity of intergranular corrosion of steel increases, as for the resistance to pitting corrosion and crevice corrosion of austenitic stainless steel, nickel The effect is not significant.
In addition, nickel also improves the high-temperature oxidation resistance of austenitic stainless steels, which is mainly due to the fact that nickel improves the composition of the chromium oxide film, the structure and performance are reduced, and the higher the nickel content, the more harmful it is because of the low melting point nickel sulfide in steel caused by.