Nonmetallic Inclusion in 1Cr18Ni9Ti Steel (Solution Treatment and Stabilization Treatment)
Nonmetallic inclusions (NMIs) are mineral or organic impurities that are unintentionally included in steel during production. It is well known that NMIs can have a detrimental effect on the properties of the steel and its downstream products. Therefore, it is important to identify and control nonmetallic inclusions in steel so that the steel can meet the required quality standards. The purpose of this paper is to discuss the nonmetallic inclusions in 1Cr18Ni9Ti steel (solution treatment and stabilization treatment).
1Cr18Ni9Ti steel is an austenitic stainless steel that is commonly used in high temperature applications that require good strength, ductility, and resistance to corrosion. The steel is generally produced in round billets or flat sheets which are then subjected to a solution treatment and stabilization treatment in order to obtain the desired mechanical properties. The solution treatment includes heating the steel to a temperature above the critical point and then cooling rapidly to achieve a homogeneous structure with improved mechanical properties. The stabilization treatment further increases the mechanical properties by reducing the carbide precipitation and grain growth at elevated temperatures.
It is well known that nonmetallic inclusions in 1Cr18Ni9Ti steel may be formed during melting, casting, and heat treatment. The most common nonmetallic inclusions in 1Cr18Ni9Ti steel are oxide inclusions, sulfide inclusions, and particles of other phases such as carbides, nitrides, and sulfides. These inclusions can be further subdivided into primary and secondary inclusions. The primary inclusions are formed during the steelmaking process while the secondary inclusions are formed during the processing of the steel.
Oxide inclusions typically comprise alumina, silica, calcium oxides, and iron oxides which are formed during the oxidation processes of the steelmaking process. The presence of these oxides can impair the mechanical properties of the steel and can cause surface defects. Sulfide inclusions are usually composed of sulfur, steel droplets, and a combination of silicates. These are formed during the refining of the steel and can cause brittleness and premature failure.
Particles of other phases such as carbides, nitrides, and phosphides can also form as nonmetallic inclusions in 1Cr18Ni9Ti steel. These are typically formed during the heat treatment processes and can cause grain boundary embrittlement and reduced ductility. Other nonmetallic inclusions can include metallic elements such as oxygen, carbon, nitrogen, and hydrogen. These can be introduced during the steelmaking process, typically through the addition of ferroalloy materials.
In order to minimize the adverse effects of nonmetallic inclusions on 1Cr18Ni9Ti steel, various techniques can be used. These include adjusting the steelmaking process parameters such as the oxygen content, temperature, and slag chemistry, as well as the inclusion modification techniques such as grain refinement, nitriding, and inclusion treatment. In addition, the steel can be subjected to magnetic particle inspection to detect and remove nonmetallic inclusions.
In summary, nonmetallic inclusions are an important consideration in the production of 1Cr18Ni9Ti steel. The most common types of inclusions are oxide and sulfide inclusions, as well as particles of other phases such as carbides, nitrides, and sulfides. Various techniques can be used to reduce their detrimental effects on the properties of the steel including adjusting the steelmaking process parameters and inclusion modification techniques. It is also important to provide regular in-service inspections of the steel in order to detect and remove any inclusions that may have been introduced during downstream processing.
