Classification and application fields of stainless steel

Steel with a mass fraction of chromium greater than 12%, steel that is free from corrosion and rust in air, water, and steam is called stainless steel. Stainless steel is actually a general term for stainless steel and corrosion-resistant steel. The invention and use of stainless steel go back to the time of World War I. The British scientist Henry Brelley was commissioned by the British government military arsenal to study the improvement of weapons. At that time, the rifle barrels used by soldiers were very easy to wear, and Brillley wanted to invent an alloy steel that was not easy to wear. The stainless steel invented by Brelley obtained the British patent right in 1916 and began mass production. Since then, the stainless steel accidentally discovered from the garbage dump has become popular all over the world. Henry Brelley is also known as “the father of stainless steel.
The invention of stainless steel has extremely important significance in the history of metallurgy, which is not only reflected in the birth of a new steel type, but more importantly, it has made steel more widely used. Although there are many types of stainless steels currently used, it can be said that these steels were developed on the basis of the three basic stainless steels invented in the early 20th century, namely austenitic, martensitic and ferritic stainless steels. Has made greater progress in research and development. In the 1930s, France developed duplex stainless steels; in the mid-1930s, the United States developed precipitation hardening stainless steels, forming five basic stainless steel types. Later, a variety of stainless steels suitable for various corrosive environments appeared, such as nickel-saving stainless steel, high-purity ferritic stainless steel, ultra-low carbon austenitic stainless steel, and maraging stainless steel.
1. Classification of stainless steel
Stainless steel can be divided into austenitic stainless steel, ferritic stainless steel, martensitic stainless steel and duplex stainless steel according to its metallographic structure.
(1) Austenitic stainless steel
The room temperature structure of austenitic stainless steel is austenite, which is formed by adding appropriate nickel to high chromium stainless steel.
Austenitic stainless steel has stable austenite structure only when Cr contains about 18%, Ni 8% to 25%, and C about 0.1%. Austenitic stainless steel is based on Cr18Ni9 iron-based alloy. With different uses, six series of austenitic stainless steels have been developed.
Common grades of austenitic stainless steel: (1) 1Cr17Mn6Ni15N; (2) 1Cr18Mn8Ni5N; (3) 1Cr18Ni9; (4) 1Cr18Ni9Si3; (5) 06Cr19Ni10; (6) 00Cr19Ni10; (7) 0Cr19Ni9N; (8) 0Cr19Ni10NbN; (9) 00Cr18Ni10N; (10) 1Cr18Ni12; (11) 0Cr23Ni13; (12) 0Cr25Ni20; (13) 0Cr17Ni12Mo2; (14) 00Cr17Ni14Mo2; (15) 0Cr17Ni12Mo2N; (16) 00Cr17Ni13Mo2N; (17) 1Cr18Ni12Mo2Ti; (18) 0Cr; 1Cr18Ni12Mo3Ti; (20) 0Cr18Ni12Mo3Ti; (21) 0Cr18Ni12Mo2Cu2; (22) 00Cr18Ni14Mo2Cu2; (23) 0Cr19Ni13Mo3; (24) 00Cr19Ni13Mo3; (25) 0Cr18Ni16Mo5; (26) 1Cr18Ni9Ti; (27) 0Cr18Ni; (27) 0Cr18Ni; 0Cr18Ni13Si4;
Austenitic stainless steels contain a large amount of Ni and Cr, making the steel austenite at room temperature. It 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 lining and transportation. Pipes, nitric acid-resistant equipment parts, etc., can also be used as the main material of ornaments. Austenitic stainless steel generally adopts solution treatment, that is, the steel is heated to 1050 to 1150 ° C, and then water-cooled or air-cooled to obtain a single-phase austenite structure.
(Two) ferritic stainless steel
Common grades of ferritic stainless steel: (1) 1Cr17; (2) 00Cr30Mo2; (3) 00Cr17; (4) 00Cr17; (5) 1Cr17Mo; (6) 00Cr27Mo;
Ferritic stainless steel is a stainless steel whose main structure is ferrite at room temperature. Chromium content is 11% -30%, its corrosion resistance, toughness and weldability increase with the increase of chromium content, chloride stress corrosion resistance is better than other types of stainless steel, this type of steel generally does not contain nickel, sometimes It also contains a small amount of Mo, Ti, Nb and other elements. This type of steel has the characteristics of large thermal conductivity, small expansion coefficient, good oxidation resistance, and excellent stress corrosion resistance. It is mostly used to produce atmospheric resistance, water vapor, water and oxidizing acids. Corroded parts. However, the mechanical properties and process performance are poor, and they are mostly used in acid-resistant structures with little stress and as anti-oxidation steels. It can also produce parts that work at high temperatures, such as gas turbine parts.
Second, the development of stainless steel
The development of China’s stainless steel industry is relatively late. Since the founding of the People’s Republic of China and before the reform and opening up, China’s stainless steel demand is mainly based on the cutting-edge use of industry and national defense. After the reform and opening up, the rapid development of the national economy and the marked improvement in people’s living standards have driven the demand for stainless steel. After entering the 1990s, China’s stainless steel industry has entered a period of rapid development, and the growth rate of stainless steel demand is much higher than the global level. Since 1990, the global apparent consumption of stainless steel has increased at an average annual rate of 6%. During the 10 years of the 1990s, China’s apparent consumption of stainless steel was 2.9 times the world’s average annual growth rate. Entering the 21st century, China’s stainless steel industry is growing rapidly. From the analysis of stainless steel application industry, the automotive industry is currently the fastest growing stainless steel application field. China’s home appliance industry is a potential big market for stainless steel applications. In addition, the demand for stainless steel in the construction industry, environmental protection industry, and industrial facilities has also increased year by year, specifically.
Automobile industry: The use of high-strength stainless steel to make the car body structure can greatly reduce the weight of the vehicle and enhance the strength of the car body structure. Using stainless steel as the vehicle panel and decorative parts can reduce maintenance costs. In addition, stainless steel is also used in automobile exhaust systems due to its advantages of resistance to chloride ion corrosion and heat resistance. Now, Japan, the United States, Sweden and other countries have used a lot of stainless steel vehicles. Japan began to promote in the 1980s, and currently its stainless steel train vehicles have reached 60%. The car industry is the development focus of stainless steel applications.
Construction industry: It is one of the earliest fields of stainless steel application. In terms of architectural decoration, at present, stainless steel is mainly used in the outer walls of high-rise buildings, indoor and outer column coating, handrails, floors, elevator siding, doors, windows, curtain walls and other internal and external decorations and components. The surface-treated, colored and plated stainless steel plate solves the problem of easy fingerprints after touching, and further expands the application range of stainless steel.
Environmental protection industry: Industrial waste gas, garbage and sewage treatment devices need to be made of stainless steel. In the flue gas desulfurization process, in order to resist the corrosion of sulfur dioxide, chloride ions, and iron ions, duplex stainless steel and high-grade austenitic stainless steel need to be used in absorption towers, coolers, pumps, valves, and flues. Facilities such as waste incinerators and wastewater treatment need to be made of high-performance stainless steel.
Industrial facilities: The proportion of stainless steel used in industrial facilities in developed countries is generally 15% -20%, and the current domestic application rate is still very small. Stainless steel is needed in the chemical, petrochemical, chemical fiber, paper, food, medicine, energy (nuclear power, thermal power, fuel cell) and other fields. In addition, the existing imported equipment has entered the maintenance period. With the improvement of the quality of domestic stainless steel products and the development of special brand products, the application of stainless steel in domestic industrial facilities will increase year by year.
Home appliance industry: In the home appliance industry, the large amount of stainless steel is the inner cylinder of the automatic washing machine, the inner tank of the water heater, the outer shell of the microwave oven, and the inner lining of the refrigerator. The proportion of household electric stainless steel in Western Europe is large, and Asia is generally used less than Japan, which is close to the European level. In 1999, the consumption of ferritic and martensitic stainless steels in the Japanese home appliance industry reached 28%, and austenite accounted for 12%. The microwave ovens, refrigerators, air conditioners, and televisions produced in China are already competitive export products in the world, and the domestic appliance industry is a potential market for stainless steel applications.