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2019/6/23 18:51:07 Viewers:
Effect of 1 Nickel on Microstructure

Nickel is an element that strongly stabilizes austenite and enlarges austenite phase region. In order to obtain a single austenite structure, the minimum nickel content required for steel containing 0.1% carbon and 18% chromium is about 8%. This is the basic component of the most famous 18-8 chromium-nickel austenitic stainless steel. With the increase of nickel content in austenitic stainless steel, the residual ferrite can be completely eliminated and the formation of_phase can be significantly reduced. At the same time, the temperature of martensite hydrocarbon conversion decreases, and even the transformation of lambda to M does not occur, but the increase of nickel content will reduce the solubility of carbon in austenitic stainless steel, thus increasing the tendency of carbide precipitation.

Effect of 2-Nickel on Properties

The effect of nickel on the mechanical properties of austenitic stainless steel, especially chromium-nickel austenitic stainless steel, is mainly determined by the effect of nickel on the stability of austenite. Within the range of nickel content which may occur martensitic transformation in steel, with the increase of nickel content, the strength of steel decreases and the plasticity increases, and the toughness of chromium-nickel Austenitic STAINL ) It is well known that nickel can be used as a cryogenic steel because of its excellent properties. 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 Austenite Stability increasing, reducing or even eliminating martensite transformation during cold work. At the same time, the cold work hardening effect of austenite itself is not obvious. The influence of nickel on the cold work hardening tendency of stainless steel reduces the cold work hardening rate of austenitic stainless steel and the room temperature of steel. 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 and even eliminate the delta ferrite in 18-8 and 17-14-2 chromium-nickel austenitic stainless steel, thus improving its hot working performance. However, the decrease of delta ferrite is not conducive to the weldability of these steels and will increase the inclination of welding hot crack wires. In addition, nickel can also significantly improve the hot working performance 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 the thermodynamic stability of steel. Therefore, austenitic stainless steel has better properties of stainless steel and oxidation resistance medium, and with the increase of nickel It is worth pointing out that nickel is also the only important element for austenitic stainless steel to improve its resistance 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 that under some conditions of high temperature and high pressure water, the increase of nickel content leads to intergranular stress corrosion of steels and alloys. With the increase of nickel content in austenitic stainless steel, the critical carbon content for intergranular corrosion decreases, that is, the sensitivity of steel to intergranular corrosion 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 properties of chromium oxide film by nickel, and the higher the nickel content, the more harmful it is. This is mainly due to the low melting point nickel sulfide at the grain boundary of steel. Generally speaking, simple chromium-nickel (and chromium-manganese-nitrogen) austenitic stainless steel is only used to require stainless and oxidation resistant medium Molybdenum, as an important alloying element in austenitic stainless steel, is added to steel to further expand its application range. The main function of molybdenum is to improve the reduction medium of steel.