Although chrome-nickel austenitic steels have many advantages, but due to the growing development and applications of stainless steel heat resistant steel, nickel-based heat-resistant alloys containing less than 20% of the nickel, as well as the chemical industry in the decades increasingly , while the less the amount of the nickel deposits and because they are concentrated in a few areas, therefore appear in the world within a contradiction of nickel in terms of supply and need.
So in stainless steel and many other alloys areas (such as Forging steel, tool steel, heat resistant steel, etc.), in particular, the relative lack of national resources of nickel extensively carry out the scientific section of nickel and other elements on behalf nickel research and production practice, in this regard, more researches and applications based on manganese and nitrogen instead of nickel in stainless steel and heat-resistant steel.
The role of manganese for austenite is similar with nickel. Spoken exactly, the role of manganese does not lie in the formation of austenite, but in that it reduces the critical quenching speed of the steel, to increase the stability of the austenite in cooling to suppress the decomposition of the austenite, so that the formation of high temperature austenite is maintained to the room temperature. In improving the corrosion resistance of steel, the role of manganese, such as the manganese powder content in the steel changes from 0 to 10.4%, the steel in the air with the acid corrosion resistance can not be changed obviously. Manganese in the steel stable austenite is approximately half of the nickel, i.e. 2% of the nitrogen in the steel also stable austenite, and the effect of even larger extent than nickel. For example, want to make stainless steel containing 18% chromium get austenitic structure at room temperature, low-nickel stainless steel and nickel CrMnN which use manganese and nitrogen instead of nickel has been applied in industry, and some has successfully replaced the chrome-nickel stainless steel.
In addition, stainless steel also contains a number of other elements. The same as the others and general steel is normally kept impurity elements, such as silicon, sulfur, phosphorus and the like. Also some added for some specific purpose, such as cobalt, boron, selenium, and rare earth elements and the like. From the nature of corrosion resistance of stainless steel, these elements relative to the nine elements that have been discussed are non-major aspects, but despite this, it can not be completely ignored, because they are also impact on the performance organization of stainless steel. Silicon is a element forming ferrite, is the impurity element normally kept in general stainless steel.
From the surveys by metal powder supplier, the cobalt as an alloying element is not often use in steel, this is because of the high price of cobalt, and in other respects (such as high speed steel, carbide, and cobalt-based heat resistant alloy, alnico or hard magnetic alloys, etc.) have a more important purpose. Plus cobalt as alloying elements in the normal stainless steel is not very often, commonly used stainless steel plus cobalt, is not aimed to improve corrosion resistance but is to improve the hardness, because the main purpose of this stainless steel manufacturing slicing machinery and cutting tools, scissors and scalpel blades.
The rare earth elements used in stainless steel, mainly is to improve process performance. Such as added a small amount of rare earth elements to Crl7Ti steel and Cr17Mo2Ti steel can eliminate the ingot due to hydrogen bubbles caused and reducing the cracks in the slab. Austenitic and austenitic - ferritic stainless steel plus 0.02 to 0.5% of the rare earth elements (cerium lanthanum alloy), can significantly improve the forging performance. Had a containing 19.5% chromium, 23% nickel, and molybdenum, copper, manganese austenitic steels, only the production of castings in the past due to the performance of thermal processing, plus rare earth elements can be rolled into a variety of shapes.
Source:http://www.mhcmp.com
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