Ferrite stainless steel

Ferritic stainless steel is an important class of engineering materials with a chromium content between 15% and 30% and excellent corrosion resistance, weldability and toughness. The poor mechanical and process properties of these steels limit their use in some high-stress applications.

Ferritic stainless steel can be divided into several categories according to its chromium content, including Crl7, Cr17Mo2Ti, Cr25, Cr25Mo3Ti, Cr28 and so on. Among them, Crl7 stainless steel contains low chromium and carbon content and is often used in the manufacture of applications requiring lower strength but good corrosion resistance, such as automotive trim and household appliance parts. Cr17Mo2Ti, by adding molybdenum and titanium elements, improves the resistance to chloride corrosion and work hardening, which is suitable for Marine environment and chemical equipment. Cr25 and Cr25Mo3Ti have better corrosion resistance due to their higher chromium content and are commonly used in nitric acid and food plant equipment.

The main advantage of ferritic stainless steel is its corrosion resistance. Due to the high chromium content, this type of steel can form a dense oxide film (passivation film) in various oxidation environments, effectively preventing further oxidation. This passivation ability makes ferritic stainless steel perform well in atmosphere, water, nitric acid solutions and other oxidizing media. For example, ferritic stainless steel with a chromium content of 25% is not easy to rust even under strong oxidation conditions, maintaining metal luster.

Compared with other stainless steel, ferritic stainless steel has better heat resistance, can maintain strength and oxidation resistance in high temperature environment, so it is widely used in high temperature furnace components, combustion chamber structure and other occasions. In addition, its small coefficient of thermal expansion gives it excellent dimensional stability at high temperatures, making it suitable for applications requiring precise dimensional control.

Although ferritic stainless steel has many advantages, its mechanical properties and process properties are relatively poor. Due to the characteristics of its crystal structure, the ductility and toughness of ferritic stainless steel at room temperature are not as good as that of austenitic stainless steel. Specifically, the tensile strength, yield strength and elongation of these steels are lower than that of austenitic stainless steels, limiting their application in environments subjected to high mechanical stress.

In addition, the processing properties of ferritic stainless steel are not ideal. Due to its poor thermal conductivity, ferritic stainless steel is prone to intergranular corrosion and weld cracks during welding, which requires special process measures to be taken during welding, such as preheating and post-heat treatment. At the same time, the cold working performance is also poor, the deformation resistance is large, and the work hardening rate is high, resulting in cracking and fracture in the cold working process.

The application fields of ferritic stainless steel mainly involve construction, automobile, home appliances and other industries. Typical applications include architectural decorations, automotive exhaust systems, washing equipment, etc. In these applications, the material's corrosion and heat resistance are key considerations, while mechanical strength and processability are relatively secondary. For example, in the automotive industry, ferritic stainless steel is often used to produce silencers and exhaust system components that need to operate in high-temperature exhaust gas environments for long periods of time without corrosion.

In order to improve the mechanical properties and process properties of ferritic stainless steel, it can usually be achieved by adding alloying elements and optimizing the heat treatment process. For example, adding a small amount of nickel or molybdenum can improve its strength and toughness while reducing work hardening. In addition, the use of appropriate heat treatment processes, such as annealing treatment, can refine the grain, improve the plasticity and toughness of the material, thereby enhancing its comprehensive performance.

Ferritic stainless steel has been widely used in many fields because of its excellent corrosion and heat resistance. However, its relatively low mechanical and processability limits its range of applications. Through reasonable alloy design and heat treatment process optimization, these shortcomings can be overcome to a certain extent, and the application prospect of ferritic stainless steel can be further expanded.