Nickel is the main alloying element in austenitic stainless steel. Its main function is one million and stabilizes austenite, which gives the steel a complete austenite structure, so that the steel has good strength and plasticity, toughness fit, and Excellent cold, hot workability and cold formability as well as welding, low temperature and non-magnetic properties, while improving the thermodynamic stability of austenitic stainless steel, making it not only than the same chromium, molybdenum content of ferrite, martensite, etc. Stainless steels have better properties of rust and oxidation resistant media, and the stability of the surface film is improved, so that the steel has more excellent resistance to some reducing media.
Nickel is an element that is strongly one million and stabilizes austenite and enlarges the austenite phase. To obtain a single austenitic structure, the minimum nickel content required for steel containing 0.1% carbon and 18% chromium is approximately 8%, this is the basic score of the most famous 18-8 chromium-nickel austenitic stainless steel. In the austenitic stainless steel, with the increase of nickel content, the residual ferrite can be completely eliminated, and the formation of σ phase is significantly reduced. At the same time, the martensite transalkylation temperature is lowered, and even the λ→M phase transition may not occur, but the increase of the nickel content reduces the solubility of carbon in the austenitic stainless steel, thereby increasing the tendency of carbide precipitation.
The effect of nickel on the mechanical properties of austenitic stainless steels, especially chromium-nano-negative stainless steels, is mainly determined by the influence of nickel on the austenite stability. Within the range of nickel content in which martensite transformation may occur in steel, With the increase of nickel content, the strength of steel decreases, the sheet plasticity increases, and the toughness (including extremely low temperature toughness) of chromium-nickel austenitic stainless steel with stable austenitic structure is very good, so it can be used as low temperature steel, which is well known. The chromium-manganese austenitic stainless steel with stable austenitic structure, the addition of nickel can further improve its toughness. Nickel can also significantly reduce the cold work hardening tendency of austenitic stainless steel, mainly due to the increased austenite stability and reduction. It also eliminates the martensite transformation during cold working, and the cold work hardening effect of austenite itself is not obvious. The effect of cold working hardening tendency of stainless steel, nickel reduces the cold work hardening rate of austenitic stainless steel, and lowers the room temperature and low temperature of steel. The strength and the effect of plasticity determine that the increase of nickel content is beneficial to the cold forming properties of austenitic stainless steel. The increase of nickel content can also reduce or even eliminate 18-8. 17-14-2 type chrome-nickel 9-clamp) δ ferrite in austenitic stainless steel to improve its hot workability, however, the reduction of δ ferrite is detrimental to the weldability of these steels, which increases welding. The tendency of hot cracked filaments, in addition, nickel can also significantly improve the hot workability of chromium manganese nitrogen (chromium manganese nickel nitrogen) austenitic stainless steel, thereby significantly increasing the steel yield.
In austenitic stainless steels, the addition of nickel and the increase in nickel content lead to an increase in the thermodynamic stability of the steel, so austenitic stainless steels have better properties of rust and oxidation resistant media, and with nickel The content is increased and the performance of the reducing medium is further improved. It is worth noting that nickel is the only important element to improve the austenitic stainless resistance to the transgranular stress corrosion of many media.
The effect of nickel on the corrosion resistance of austenitic stainless steel in various acid media needs to be pointed out that under some conditions of high temperature and high pressure water, the increase of nickel content leads to an increase in the intergranular stress corrosion sensitivity of steel and alloy, but this The adverse effects can be alleviated or suppressed due to the increase of chromium content in steel and alloy. With the increase of nickel content in magnetic austenitic stainless steel, the critical carbon content of intergranular corrosion is reduced, that is, the intergranular corrosion sensitivity of steel The increase in properties, as for the austenitic stainless steel resistance to pitting corrosion and crevice corrosion, the role of nickel is not significant, in addition, nickel also improves the high temperature oxidation resistance of austenitic stainless steel, which mainly improves the chromium oxide film with nickel The composition, structure and performance are reduced, and the higher the nickel content, the more harmful, mainly due to one million low melting point nickel sulfide at the grain boundary in the steel.
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