Nickel is the formation of austenite of alloying elements, but the role of nickel and chromium to only be fully demonstrated. If the simple use of nickel, nickel stainless steel in the low-carbon austenitic phase to obtain pure organizations need to nickel content up to 24% (by mass) or more, in fact, need to reach 27% nickel content (mass fraction), can significantly improve the corrosion resistance of stainless steel, so there is no separate stainless steel to nickel as alloying elements. When the nickel and chromium complex, the nickel role in improving the corrosion resistance of steel can be shown significantly, such as ferritic stainless steel to add a small amount of nickel, can make the single-phase microstructure of ferrite into austenite – Organization of ferrite phase, so that you can to increase its strength by heat treatment. Further increase of nickel content, you can become a single phase of austenite, such as ω (Cr) = 18% of steel with 8% (by mass) of nickel, the availability of fully austenitic. This is widely used in chrome-nickel austenitic 18-8 stainless steel, it with high corrosion resistance and good deformation, welding, and is not magnetic.
Nickel in the role of stainless steel and chromium in the play after the Nickel is an excellent corrosion-resistant materials, is also an important steel alloying elements. Nickel in the austenitic stanless steel is the formation of the elements,such as304,316,321.but the low-carbon steel to obtain pure nickel austenite, the volume of nickel to achieve 24%; and only when 27 percent nickel steel, in some medium resistance significant changes in corrosion. Thus alone can not constitute a nickel stainless steel. But at the same time the existence of nickel and chromium in the stainless steel, the nickel-containing stainless steel but has many valuable properties. Based on the above circumstances, we can see that nickel as alloying elements in the role of stainless steel is that it allows high-chromium steel changes, so that corrosion resistance of stainless steel and certain to improve process performance.
Nickel in pure α-Fe in the maximum solubility of 25% to 30%, when the stay was still contains carbon in ferrite, the effect is not hardened by solid solution of steel intensive. Passivation of nickel to expand the scope to improve corrosion resistance, especially in non-oxidizing media (such as sulfuric acid) in the. Nickel-iron carbide formation tendency is weaker than can promote graphitization, and weakly increased the hardenability of steel on steel is not sensitive to cold shock play a role. In carbon and high carbon steel containing an effective concentration, the quenching preferred to retain austenite.
Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)
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