There are generally five types of stainless steel, namely ferritic, martensitic, austenitic, duplex and precipitation hardening. Among them, ferritic stainless steel is widely used to make kitchen equipment, household appliances, and the automotive industry because of its good processing performance; martensitic stainless steel is mostly used to make tool steel, surgical instruments, blades, etc. after being hardened by heat treatment; the above Both types of stainless steel require that the nitrogen content in the steel be controlled as low as possible. The low-content nitrogen control process is a key technology in the manufacturing of ferritic and martensitic stainless steel.

The performance of austenitic stainless steel is very good. Because the nickel contained in the steel will cause very obvious changes in the structure and properties of the stainless steel, it can improve the corrosion resistance of the stainless steel. It also has considerable pitting corrosion resistance after adding molybdenum element. It is currently the The most commonly used type of stainless steel material, it can be used for many different purposes.

Because duplex stainless steel has two metallographic structures of ferrite and austenite, its strength is basically twice that of austenitic stainless steel. Its comprehensive corrosion resistance is also very strong, and its tendency to stress corrosion cracking is very low. , so it is widely used in offshore fields, such as seawater desalination, industrial storage and other industry equipment.

Austenitic stainless steels and duplex stainless steels both require controlled nitrogen alloying.

Today, the consumption of ferritic stainless steel in global stainless steel production is about 30-40%, and the consumption of austenitic stainless steel accounts for about 55%; since ferritic stainless steel requires that the nitrogen content be controlled as low as possible, austenitic stainless steel The higher the nitrogen content in stainless steel, the better. Therefore, nitrogen control technology has become one of the difficult problems in stainless steel manufacturing.

Since ferritic stainless steel is cheap and has a wide market demand, reducing nitrogen content is the core technology for producing austenitic stainless steel. The core technology of stainless steel plants that currently use non-vacuum smelting technology is to reduce the reaction of N2 to 2[N], that is, to achieve the goal by reducing nitrogen addition; while plants that use vacuum smelting technology allow 2[N] to react in molten steel to N2 To achieve the goal, that is, by promoting denitrification.

The current best process for controlling nitrogen in austenitic stainless steel is carried out under normal pressure conditions. Among them, non-nitrogen-controlled type, nitrogen-controlled type, and medium-nitrogen type stainless steel have all achieved industrial production. Among them, the high-nitrogen type control technology is mastered in China. It is rarely used because it needs to control the process or parameters in each link. The solid solution speed and solid solution amount of nitrogen are related to the temperature and time of the molten steel, the intensity of the molten steel stirring, the molten steel stirring medium, etc.

After analyzing the characteristics and control processes of various stainless steel nitrogen control processes, the following conclusions can be obtained.

The first is that the process of producing ultra-low nitrogen ferritic stainless steel under non-vacuum conditions is mainly to reduce the dissociation of N2 during arc melting, reduce the violent stirring of refining, and shorten the contact time between molten steel and N2 in the air.

The second point is that the technology for manufacturing ultra-low nitrogen ferritic stainless steel under vacuum conditions is mainly to control the increase of nitrogen during the alloy addition process, and then reduce the nitrogen content during decarburization under vacuum.

The third conclusion is that the nitrogen addition process of controlled nitrogen and medium nitrogen austenitic stainless steel under normal pressure conditions mainly controls the flow rate and injection time of N2 during refining.