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Stainless steel is an extremely widely used material that can be found everywhere in people's production and life. Such an alloy steel to which an element such as chromium or nickel is added requires a reduction in carbon content for the purpose of improving corrosion resistance, and a low carbon content makes it difficult to increase the strength, which also limits the application range of stainless steel as a structural material. . Is there such a stainless steel that can reduce the amount of precious metals added to save costs, increase the strength of the material to expand the application range, and have good corrosion resistance to reduce maintenance costs and improve the service life of the finished product?
The project “Basic Research on Metallurgy to Improve Steel Quality and Service Lifeâ€, which was included in the National 973 Program in 2004, was approved in 2009. The project is based on improving metallurgical quality and materials science as the guide to extend the service life of steel. For the goal. The main results are: design and development of low-nickel, high-strength, low-cost, high wear-resistance, low-magnetic or even non-magnetic resource-saving stainless steel prototype steel; smelting and continuous casting under normal pressure using existing metallurgical processes High nitrogen steel with a nitrogen content of 0.64%; research and development of economical high strength and high toughness metastable steel. These achievements are conducive to improving the international competitiveness of China's steel companies and have broad market application prospects.
In the 1970s, high-nitrogen stainless steels appeared in the world, replacing expensive and scarce nickel with inexpensive inexhaustible nitrogen, while also increasing the strength and resistance to local corrosion of stainless steel. The main factor that hinders the widespread use of nitrogen as an alloying element is the problem of nitrogen addition. The nitrogen solubility is very low at atmospheric pressure, and it is difficult to add. Because of the small amount of addition, the beneficial effect is less obvious. The general production mode of high-nitrogen steel is pressurization. Smelting requires special production equipment, which greatly increases the production cost of high nitrogen steel and limits its production.
Dr. Su Jie, deputy director of the Institute of Structural Materials at the Iron and Steel Research Institute, is the head of the “Resource-saving Stainless Steel Research†project in the “Basic Research on Metallurgy to Improve the Quality and Service Life of Steelâ€. He said: “We are always The high-nitrogen steel with a nitrogen content of 0.64% was actually smelted and continuously cast by the existing metallurgical process, and rolled into 20mm and 14mm wide plates, which indicates that the bottleneck of high-nitrogen steel smelting and hot processing has been The basic solution has aroused strong repercussions at the 2009 International Conference on High Nitrogen Steel and has a world-leading level."
The solution of theoretical problems enables researchers to develop a series of nitrogen alloyed resource-saving stainless steels that meet different industrial needs according to the needs of enterprises, so as to realize the production and application of low-cost high-performance new stainless steel.
For example, Su Jie said: "For example, nitrogen can be added to a certain degree to make stainless steel completely free of nickel. A certain proportion of people are allergic to nickel, so this nickel-free high-nitrogen steel material can be used for human body planting. Into the object, watches, glasses frames, etc. Now 'Fiyada' watch is talking to us about cooperation."
The researchers also found that carbon and nitrogen can be mixed into a metastable steel with good plasticity. “ This material can be used in the manufacture of automobile parts and train bodies. It is 20% to 40% lower than the current 301 steel . It has better mechanical properties and close corrosion resistance. The market prospect is very broad. Currently this project has been carried out. Semi-industrial experiment."
This can be done in the future. So, where is the high-nitrogen prototype steel that the research team has successfully used in the AOD furnace (a commonly used stainless steel refining equipment)?
According to the performance characteristics of high-nitrogen prototype steel, it has a corrosion resistance comparable to that of 304 stainless steel which is currently used in large quantities, and has twice the strength of 304 stainless steel, and the price is low, which is quite competitive with 304 stainless steel. The advantage is therefore that it can replace 304 stainless steel in some areas. So far, the research team has focused on the application of this prototype steel to the following aspects: wear-resistant equipment for mining and coal washing; high-strength stainless steel fasteners; high-strength construction steel; bulletproof armor. Among them, the coal mine washing screen made of prototype steel has been successfully applied in industrial production and exhibits excellent wear resistance. After cooperation with the National Standard Parts Product Quality Supervision and Inspection Center, the M12 bolts have been successfully produced and the M20 bolts are ready for further trial production. Once the trial production is successful and the corresponding technical specifications are formulated, it can widely replace the fasteners manufactured by the current 304 stainless steel, which has enormous economic benefits.
Su Jie predicts that if national standards and building codes can keep up, steel will become the most promising application direction for the high-nitrogen prototype steel market. At present, most of the buildings such as bridges in China use ordinary steel bars, and stainless steel bars are not used. Many buildings in the cold regions and coastal areas in the world use stainless steel bars. Stainless steel bars made of high-nitrogen steel have higher strength, better corrosion resistance and zero maintenance than ordinary steel bars. According to the strength grade of the prototype steel, it can replace the current grade IV steel. Its 120-year service life and zero maintenance characteristics will greatly reduce the total cost of use.
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