Nickel is the main alloy element in austenitic stainless steel. Its main function is to stabilize austenite, so that the steel can obtain a complete austenitic structure, so that the steel has a good combination of strength, plasticity and toughness, and has excellent cold and hot workability, cold formability, welding, low temperature and non-magnetic properties. At the same time, it improves the thermodynamic stability of austenitic stainless steel, so that it is not only better than ferrite with the same chromium and molybdenum content, Martensite and other stainless steels have better properties of rust resistance and oxidation resistance media, and the stability of the surface facial mask is improved, so that the steel also has better properties of resistance to some reducing media. Nickel is an element that strongly stabilizes austenite and expands austenite phase zone. In order to obtain a single austenite structure, the low nickel content required when the steel contains 0.1% carbon and 18% chromium is about 8%, which is the basic component of 18-8 chromium nickel austenitic stainless steel. In austenitic stainless steel, with the increase of nickel content, the residual ferrite can be completely eliminated and significantly reduced σ The tendency of phase formation; At the same time, the temperature of martensite hydrocarbon conversion decreases, or even does not appear λ → M phase transformation, but the increase of nickel content will reduce the solubility of carbon in austenitic stainless steel, so as to enhance the tendency of carbide precipitation.
The influence of nickel on the mechanical properties of austenitic stainless steel, especially chromium nickel negative martensitic stainless steel, is mainly determined by the influence of nickel on the stability of austenite. Within the range of nickel content in steel where martensitic transformation may occur, with the increase of nickel content, the strength of steel decreases and the plasticity increases. Chromium nickel austenitic stainless steel with stable austenite structure has excellent toughness (including ultra-low temperature toughness), so it can be used as low temperature steel, It is well known that for chromium manganese austenitic stainless steel with stable austenite structure, the addition of nickel can further improve its toughness Nickel can also significantly reduce the cold work hardening tendency of austenitic stainless steel, which is mainly due to the increased stability of austenite, which reduces or even eliminates the martensitic transformation in the cold work process. At the same time, the cold work hardening effect of austenite itself is not obvious. The influence of stainless steel cold work hardening tendency, nickel reduces the cold work hardening rate of austenitic stainless steel, reduces the room temperature and low temperature strength of steel, and improves plasticity, It is decided that the increase of nickel content is conducive to the cold working formability of austenitic stainless steel, and the increase of nickel content can also reduce or even eliminate the δ Ferrite, thereby improving its hot workability, however, δ The reduction of ferrite is unfavorable to the weldability of these steels and will increase the tendency of welding hot crack wires. In addition, nickel can also significantly improve the hot workability of chromium manganese nitrogen (chromium manganese nickel nitrogen) austenitic stainless steel, thereby significantly improving the yield of steel.
In austenitic stainless steel, the addition of nickel and the increase of nickel content lead to the increase of thermodynamic stability of steel. Therefore, austenitic stainless steel has better rust resistance and oxidation resistance medium performance, and with the increase of nickel content, the reduction resistance medium performance is further improved It is worth pointing out that nickel is also an important element to improve the stainless resistance of austenite to transgranular stress corrosion in many media. The effect of nickel on the corrosion resistance of austenitic stainless steel in various acid media needs to be pointed out. Under some conditions of high temperature and high pressure water, the increase of nickel content leads to the increase of intergranular stress corrosion sensitivity of steel and alloy, but this adverse effect will be alleviated or suppressed due to the increase of chromium content in steel and alloy With the increase of nickel content in austenitic stainless steel of magnetic card, 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, the effect of nickel is not significant. In addition, nickel also improves the high-temperature oxidation resistance of austenitic stainless steel, which is mainly due to the improvement of the composition, structure and performance of chromium oxide film by nickel, and the higher the nickel content, the more harmful it is, This is mainly due to onemillion low melting point nickel sulfide at the grain boundary in the steel.