Nitrogen is a common element in steel, originating from high-temperature absorption from the charge or molten steel. Nitrogen stabilizes the austenite structure and significantly improves the strength and toughness of steel after solution treatment. Nitrogen can improve the macrostructure of high-chromium and high-chromium-nickel steels, making them dense and strong. Therefore, replacing nickel with nitrogen in stainless steel and heat-resistant steels has significant economic value and development prospects. Nitrogen has a strong affinity for alloying elements such as titanium and aluminum in steel, combining with them to form highly stable nitrides. These disperse within grain boundaries and act as precipitation strengthening, inhibiting creep deformation at high temperatures and improving creep and long-term strength. Surface penetration methods such as nitriding and carbonitriding can form nitrides and cyanides on the steel surface, thereby increasing the hardness, strength, wear resistance, and corrosion resistance of the surface layer. In addition to ferritic stainless steel, almost all types of stainless steel, especially austenitic and duplex stainless steel, have been widely alloyed with nitrogen in the past decade, bringing austenitic and α+γ duplex stainless steel into the modern stainless steel era. Stainless steel includes controlled nitrogen ([N]≤0.10% or [N]＜0.12%), medium nitrogen ([N]≤0.40% or [W]＜0.50%) and high nitrogen ([N]＞0.4% or [N]≥0.50%) stainless steel, super austenitic stainless steel and super martensitic stainless steel containing low nitrogen. Although nitrogen cannot prevent the precipitation of σ phase in duplex stainless steel, it can inhibit the formation of σ phase. The addition of nitrogen to duplex stainless steel led to the emergence of second- and third-generation duplex stainless steels (super duplex and economical duplex), establishing a family of duplex stainless steels alongside the three major categories of stainless steel: martensitic, ferritic, and austenitic. Because nitrogen has extremely low solubility in ferritic stainless steel and high solubility in austenite, its beneficial effects in duplex stainless steel are primarily reflected in improving the properties of the austenitic structure.
With the rapid advancement of science and technology, more and more industries are placing higher demands on the performance of steel materials, especially those used at high temperatures. Heat-resistant steel is widely used in the manufacture of boilers, steam turbines, power machinery, industrial furnaces, and components operating at high temperatures in industries such as aviation and petrochemicals. The development of heat-resistant steel is closely linked to advances in energy and power machinery. The performance of heat-resistant steel is crucial to the success of new technologies in thermal power generation, atomic energy, aerospace, aviation, petroleum, and chemical industries, and its importance is increasing. Currently, the biggest bottleneck in improving energy efficiency in industries such as civilian nuclear power, thermal power generation, gas-fired power generation, and the petrochemical industry is the availability of metal materials, specifically the development of low-cost, high-performance heat-resistant stainless steel. Developing new heat-resistant stainless steel is not only an effective strategy for energy conservation and emission reduction, but also can alleviate the increasingly scarce nickel resources.
Tensile properties are one of the main performance indicators of metal materials. Among them, parameters such as yield and tensile strength are the most representative mechanical performance indicators of metal materials, and are also important bases for stress calculation in engineering design and mechanical design.
2507 stainless steel (UNS S32750) is a super duplex stainless steel that combines the advantages of austenite and ferrite. It has high strength, excellent corrosion resistance and good weldability and is widely used in harsh environments. The following are its core features:
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