Heat Treatment of Nitronic50 (00Cr22Ni13Mn5Mo2N) Austenitic Stainless Steel
Nitronic50 (00Cr22Ni13Mn5Mo2N) is a high-alloy austenitic stainless steel with excellent corrosion resistance in both oxidizing and reducing environments. The alloy has excellent temperature strength and high temperature oxidation resistance. Nitronic50 also has good toughness, formability and weldability. Thus, it is often used in a wide range of applications such as oil production, refining and petrochemical, power plants, offshore and marine, medical and food industry amongst others. The heat treatments used in Nitronic50 are annealing, normalizing, tempering, and solution annealing.
Annealing
Annealing is a heat treatment process used to soften metals. This process is commonly used to increase ductility, reduce the hardness of the material and improve its cold working properties. In annealing, the austenite in the Nitronic50 is transformed into either ferrite and/or martensite depending on the cooling rate after annealing. The cooling rate is usually adjusted to achieve the desired properties. During the process, oxidation and decarburization of the surface layer takes place and the residual stresses from prior cold working processes are relieved. Common annealing temperatures for Nitronic50 range between 875°C-925°C and slow cooling is encouraged in the range of 6°C-10°C per hour.
Normalizing
Normalizing is a heat treatment process used to refine the structure of the material and homogenize the mechanical properties. This process is often used when the material has been machined and the mechanical properties are not uniform across the part. Normalizing involves heating the material to a temperature range between 825°C-925°C and air cooling afterward. After this heat treatment, the material will have an austenite-martensite structure with improved ductility, toughness, and strength. The different cooling rate between normalizing and annealing can lead to different microstructures and properties in the material.
Tempering
Tempering is a heat treatment process used to refine the austenite-martensite structure of the Nitronic50. This process is used to improve the toughness, ductility, and hardness of the material. During the tempering process, the Nitronic50 is reheated to a temperature range between 650°C-750°C, and then rapidly cooled, usually with air cooling. This process can be repeated multiple times depending on the desired properties. Tempering has the best result when done after normalizing or annealing as it will allows for a more refined microstructure and better mechanical properties.
Solution Annealing
Solution annealing is a heat treatment process used to dissolve the secondary phases or carbides that may not have been dissolved by normalizing. This process is used to improve the properties of Nitronic50 such as strength, ductility, toughness and weldability. During solution annealing, the temperature for solution annealing is usually above 1050°C and cooling is done with a range of 3°C-5°C per hour. After this process, the Nitronic50 will have a fully austenitic microstructure that can help improve the formability and weldability of the material.
Conclusion
The heat treatment of Nitronic50 consists of annealing, normalizing, tempering, and solution annealing. Annealing is used to soften the material and improve its cold working properties. Normalizing is used to refine the structure of the material and homogenize the properties. Tempering is used to refine the austenite-martensite structure of the Nitronic50 and improve its toughness, ductility, and hardness. Solution annealing is used to dissolve secondary phases and carbides and improve the formability and weldability of the material. Each heat treatment has its own advantages depending on the application and requirements.
