According to the definition in GB/T20878-2007, stainless steel is mainly characterized by stainless steel and corrosion resistance, and the chromium content is at least 10.5%, and the carbon content is not more than 1.2%.
Stainless steel is the abbreviation of stainless and acid-resistant steel. The steel that is resistant to weak corrosive media such as air, steam, and water or has stainless steel is called stainless steel. The steel grade is called acid-resistant steel.
Due to the difference in chemical composition of the two, their corrosion resistance is different. Ordinary stainless steel is generally not resistant to chemical medium corrosion, while acid-resistant steel is generally stainless. The term “stainless steel” does not simply refer to one type of stainless steel, but to more than one hundred industrial stainless steels, each developed to perform well in its specific field of application. The key to success is to first understand the application and then determine the correct steel grade. There are usually only six steel grades associated with building construction applications. They all contain 17-22% chromium, and the better grades also contain nickel. The addition of molybdenum can further improve atmospheric corrosion, especially corrosion resistance to chloride-containing atmospheres.
Generally speaking, the hardness of stainless steel is higher than that of aluminum alloy, and the cost of stainless steel is higher than that of aluminum alloy.
Types of stainless steel
- Ferritic stainless steel
Contains 15% to 30% chromium. Its corrosion resistance, toughness and weldability increase with the increase of chromium content, and its resistance to chloride stress corrosion is better than other types of stainless steel. Crl7, Cr17Mo2Ti, Cr25, Cr25Mo3Ti, Cr28, etc. Because of the high chromium content, ferritic stainless steel has good corrosion resistance and oxidation resistance, but poor mechanical properties and process performance. This kind of steel can resist the corrosion of the atmosphere, nitric acid and brine solution, and has the characteristics of good high temperature oxidation resistance and small thermal expansion coefficient.
- Austenitic stainless steel
It contains more than 18% chromium, about 8% nickel and a small amount of molybdenum, titanium, nitrogen and other elements. It has good comprehensive performance and is resistant to corrosion by various media. The commonly used grades of austenitic stainless steel are 1Cr18Ni9, 0Cr19Ni9, etc. The Wc of 0Cr19Ni9 steel is less than 0.08%, which is marked as “0” in the steel number. This type of steel contains a large amount of Ni and Cr, which makes the steel in an austenitic state at room temperature. This type of steel has good plasticity, toughness, weldability, corrosion resistance and non-magnetic or weak magnetic properties. It has good corrosion resistance in oxidizing and reducing media. It is used to make acid-resistant equipment, such as corrosion-resistant containers and equipment. Linings, conveying pipes, nitric acid-resistant equipment parts, etc., can also be used as the main material of stainless steel watch accessories. Austenitic stainless steel is generally solution treated, that is, heating the steel to 1050-1150 °C, and then cooling it with water or air to obtain a single-phase austenite structure.
- Martensitic stainless steel
High strength, but poor plasticity and weldability. The commonly used grades of martensitic stainless steel are 1Cr13, 3Cr13, etc. Due to the high carbon content, it has high strength, hardness and wear resistance, but the corrosion resistance is slightly worse, and it is used for high mechanical properties and corrosion resistance. Some general parts are required, such as springs, turbine blades, hydraulic valves, etc. This type of steel is used after quenching and tempering. Annealing is required after forging and stamping.
- Stainless steel plates and strips for pressure equipment
Stainless steel for pressure vessels has clear requirements for its classification and code, size, shape and allowable deviation, technical requirements, test methods, inspection rules, packaging, marking and product quality certificates. The commonly used grades are 06Cr19Ni10, 022Cr17Ni12Mo2, and the digital codes are: S30408, S31603, etc. Mainly used for food machinery, pharmaceutical machinery and other sanitary equipment.
