Steel with a mass fraction of more than 12% chromium, stainless steel that is free from corrosion and rust in air, water, and steam. Stainless steel is actually a general term for stainless steel and corrosion resistant steel. The invention and use of stainless steel dates back to the First World War. British scientist Henry Brellley was commissioned by the British government's military arsenal to study the improvement of weapons. At that time, the rifle guns used by the soldiers were extremely wearable, and Brillley wanted to invent an alloy steel that was not easy to wear. The stainless steel invented by Brellley obtained British patent rights in 1916 and began mass production. Since then, stainless steel accidentally discovered from garbage dumps has swept the world. Henry Brellley is also known as the father of stainless steel.
The invention of stainless steel is of great importance in the history of metallurgy, not only in the birth of a new steel, but more importantly in making 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 three basic stainless steels invented in the early 20th century, namely austenitic, martensitic and ferritic stainless steels, followed by stainless steel. The research and development has made greater progress. In the 1930s, France developed duplex stainless steel; in the mid-1930s, the United States developed precipitation hardened stainless steel, forming five basic stainless steel types. Later, stainless steels such as nickel-nickel stainless steel, high-purity ferritic stainless steel, ultra-low carbon austenitic stainless steel and maraging stainless steel were used.
First, stainless steel classification
Stainless steel according to its metallographic structure can be divided into austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, duplex stainless steel.
(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 steels have a stable austenitic structure when they contain about 18% Cr, 8% to 25% Ni, and about 0.1% C. Austenitic stainless steel is based on Cr18Ni9 iron-based alloy, and six series of austenitic stainless steels have been developed with different applications.
Austenitic stainless steel commonly used grades: (1) 1Cr17Mn6Ni15N; (2) 1Cr18Mn8Ni5N; (3) 1Cr18Ni9; (4) 1Cr18Ni9Si3; (5) 06Cr19Ni10; (6) 00Cr19Ni10; (7) 0Cr19Ni9N; (8) 0Cr19Ni10NbN; 00Cr18Ni10N; (10) 1Cr18Ni12; (11) 0Cr23Ni13; (12) 0Cr25Ni20; (13) 0Cr17Ni12Mo2; (14) 00Cr17Ni14Mo2; (15) 0Cr17Ni12Mo2N; (16) 00Cr17Ni13Mo2N; (17) 1Cr18Ni12Mo2Ti; (18) 0Cr18Ni12Mo2Ti; 1Cr18Ni12Mo3Ti; (20) 0Cr18Ni12Mo3Ti; (21) 0Cr18Ni12Mo2Cu2; (22) 00Cr18Ni14Mo2Cu2; (23) 0Cr19Ni13Mo3; (24) 00Cr19Ni13Mo3; (25) 0Cr18Ni16Mo5; (26) 1Cr18Ni9Ti; (27) 0Cr18Ni10Ti; (28) 0Cr18Ni11Nb; 0Cr18Ni13Si4;
Austenitic stainless steels contain a large amount of Ni and Cr, which makes the steel austenitic 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 conveying. Pipes, equipment parts resistant to nitric acid, etc., can also be used as the main material of the ornament. Austenitic stainless steels are generally treated by 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.
(2) 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 mainly composed of ferrite at room temperature. The chromium content is between 11% and 30%, and its corrosion resistance, toughness and weldability increase with the increase of chromium content. The resistance to chloride stress corrosion is better than other types of stainless steel. These steels generally do not contain nickel, sometimes It also contains a small amount of Mo, Ti, Nb and other elements. These steels are characterized by high thermal conductivity, small expansion coefficient, good oxidation resistance and excellent resistance to stress corrosion. They are used to make air, water vapor, water and oxidizing acids. Corroded parts. However, the mechanical properties and process performance are poor, and it is mostly used for acid-resistant structures with little stress and used as anti-oxidation steel. Parts that work at high temperatures, such as gas turbine parts, can also be made.
Second, the development of stainless steel
The development of China's stainless steel industry is relatively late. Before the founding of the People's Republic of China, before the reform and opening up, the demand for stainless steel in China was mainly based on the advanced use of industry and national defense. After the reform and opening up, the rapid development of the national economy and the significant improvement of people's living standards have stimulated the demand for stainless steel. After entering the 1990s, China's stainless steel industry entered a period of rapid development, and the growth rate of stainless steel demand was much higher than the global level. Since 1990, the global consumption of stainless steel has grown at an average annual rate of 6%. In the 10 years of the 1990s, the apparent consumption of stainless steel in China was 2.9 times the annual growth rate of the world. In the 21st century, China's stainless steel industry has grown rapidly. From the analysis of the stainless steel application industry, the automotive industry is currently the fastest growing field of stainless steel applications. 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.
Automotive industry: The use of high-strength stainless steel to make the car body structure can greatly reduce the vehicle's own weight and enhance the strength of the car body structure. The use of stainless steel as the vehicle's panels and decorative parts can reduce maintenance costs. In addition, stainless steel is also affected by the exhaust system of automobiles due to its resistance to chloride ion corrosion and heat. Nowadays, stainless steel vehicles have been used in large quantities in countries such as Japan, the United States, and Sweden. Japan has been promoting since the 1980s, and its stainless steel train vehicles have now reached 60%. The car industry is the focus of development for 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 for exterior walls of high-rise buildings, interior and exterior columns, interior and exterior decoration and components such as handrails, floors, elevator siding, doors and windows, and curtain walls. The surface-treated, colored, and coated stainless steel plate solves the problems of fingerprints and the like after the touch, and further expands the application range of the stainless steel.
Environmentally friendly industry: Industrial waste gas, garbage and sewage treatment plants 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 are required in the absorption tower, cooler, pump, valve, flue and the like. Facilities such as waste incinerators and wastewater treatments need to be made of high-performance stainless steel.
Industrial facilities: The proportion of stainless steel used in industrial facilities in developed countries can generally reach 15%-20%, and the current domestic application ratio is still small. Stainless steel is required in the fields of chemical, petrochemical, chemical fiber, paper, food, medicine, energy (nuclear power, thermal power, fuel cells). In addition, the existing imported equipment has entered the inspection period. With the improvement of the quality of domestic stainless steel products and the development of special grade products, the application of stainless steel in domestic industrial facilities will increase year by year.
Home appliance industry: In the home appliance industry, stainless steel is used in the inner cylinder of the automatic washing machine, the inner tank of the water heater, the inner casing of the microwave oven, and the inner lining of the refrigerator, and ferritic stainless steel is often used. Western Europe has a large proportion of household electric stainless steel, and Asia generally uses less than Japan's proximity to European standards. In 1999, the consumption of ferrite and martensitic stainless steel in the household appliance industry in Japan reached 28%, and austenite accounted for 12%. China's microwave ovens, refrigerators, air conditioners, televisions, etc. are already the world's competitive export products, and the domestic appliance industry is a potential market for stainless steel applications.