Development History And Grade Differentiation of Stainless Steel
01 Birth of Stainless Steel
The time span from invention to practical industrial application of stainless steel is about ten years: in 1904-1906, Guillet, a Frenchman, first conducted a pioneering basic research on the metallurgical and mechanical properties of Fe Cr Ni alloy; From 1907 to 1911, Portevin of France and Gissen of England discovered the corrosion resistance of Fe Cr and Fe Cr Ni alloys and completed Guillet's research work; In 1908-1911, German Monnartz revealed the principle of corrosion resistance of steel and put forward the concept of passivation, such as critical chromium content, the role of carbon and the influence of molybdenum.
Soon, the practical value of stainless steel was confirmed in Europe and the United States, and industrial stainless steel grades were also introduced one after another: from 1912 to 1914, Brearley invented martensitic stainless steel containing 12-13% Cr and obtained a patent; In 1911-1914, American Dant size invented ferritic stainless steel containing 14-16% Cr, 0.07% -0.15% C; German Maurer and Strauss invented 1.0% C, 15-20% Cr,<20% Ni austenitic stainless steel. Since then, the famous 18-8 stainless steel (0.1% C-18% Cr-8% Ni) has been developed on this basis.
In practical applications, high carbon austenitic stainless steel has been found to have serious intergranular corrosion problems. Later, Bain proposed the theory of chromium deficiency in intergranular corrosion and developed stabilized austenitic stainless steels containing titanium and niobium based on 18-8 stainless steel in the early 1930s, namely AISI321 and AISI347. At the same time, ferrite austenite duplex stainless steel was also invented, and the concept of ultra-low carbon (C ≤ 0.03%) stainless steel was proposed, but due to the limitations of metallurgical equipment and technology at that time, it could not be applied to industry.
02 Growth of Stainless Steel
As early as 1934, American Folog invented precipitation hardening stainless steel. In the 1940s and 1950s, martensite and semi odorite precipitation hardening stainless steel began to be used in military and civil industries. This series starts with the successful production of Stainless W by U.S. Steel. In addition, Cr-Ni-Mn-N stainless steel, also known as AISI200 series steel in the United States, was invented to save nickel element by replacing nickel with manganese.
After World War II, the development of the fertilizer and nuclear fuel industries greatly stimulated the development of stainless steel, and with the emergence of oxygen steelmaking, ultra-low carbon stainless steel began to be commercialized in 1947. In the mid-1950s, high-performance stainless steel with excellent corrosion resistance was developed. In the late 1960s, martensitic aging stainless steel, TRIP (Transformation Induced Plasticity) stainless steel, and high-purity ferritic stainless steel with C+N ≤ 150ppm appeared successively. In the past two decades, due to various localized corrosion and damage accidents, and the continuous adoption of new catalysts and processes in the chemical processing industry, specialized stainless steels such as stress corrosion resistance, pitting corrosion resistance, crevice corrosion resistance, and corrosion fatigue resistance have been developed based on existing foundations, such as duplex stainless steel, high molybdenum stainless steel, and high silicon stainless steel. In order to meet the needs of deep drawing and cold forming, specialized stainless steel varieties that are easy to form have also been developed. At present, the stainless steel series is also constantly being improved. Since the late 1960s, various refining and continuous casting equipment for producing stainless steel have reached production capacity, and the transition from titanium stabilized austenitic stainless steel to low-carbon and ultra-low carbon austenitic stainless steel has been completed worldwide. The level of stainless steel production has reached a new level.
03 Development of Stainless Steel in China
China's stainless steel industry developed relatively late, and industrial production only began in 1952. After 1949, electric arc furnaces were used to produce stainless steel in large quantities. Prior to this, Cr13 martensitic stainless steel was first produced, and after mastering the production technology, 18-8 Cr Ni austenitic steel, such as 1Cr18Ni9Ti, was produced in large quantities, starting in 1952. Subsequently, in order to develop the domestic chemical industry, production of 1Cr18Ni12Mo2Ti and 1Cr18Ni12Mo3Ti containing 2% -3% Mo began. At the same time, in order to save the precious element nickel, since 1959, we have been imitating 1Cr17Mn6Ni5N and 1Cr18Mn8Ni5N with Mn and N-substituted Ni.
In 1958, 2% -3% Mo was added to AISI204 steel to develop 1Cr18Mn10Ni5Mo3N (204+Mo), which was used in a full cycle urea production plant to replace 1Cr18Ni12Mo2Ti.
In the late 1950s to early 1960s, industrial trials began on nickel free ferritic stainless steels such as 1Cr17Ti, 1Cr17Mo2Ti, and 1Cr25Mo3Ti, and research began on high silicon stainless steel 1Cr17Ni14Si4ALTi, which is resistant to smoke and nitric acid corrosion. This steel grade is actually an a+y duplex stainless steel. Since the 1960s, due to the development needs of domestic industries such as chemical, aerospace, aviation, and atomic energy, as well as the adoption of electric furnace oxygen steelmaking technology, a large number of new steel grades, such as 17-4PH, 17-7PH, PH15-7Mo precipitation hardening stainless steel, ultra-low carbon stainless steel 00Cr18Ni10, 00Cr18Ni14Mo2, 00Cr18Ni14Mo3 containing C ≤ 0.03%, and Cr-Mn-N stainless steel 1Cr18Mn14Mo2N (A4) without Ni, have been successfully developed and put into production. Since the 1970s, in order to solve the chloride stress corrosion problem of 18-8 type Cr Ni steel in the chemical and atomic energy industries, some a+yCr Ni duplex stainless steels have been developed and officially produced and applied. The main steel grades include 1Cr21NiSTi, 00Cr26Ni6Ti, 00Cr26Ni7Mo2Ti, 00Cr18Ni5Mo3Si2 (3RE60), and 00Cr18Ni6Mo3Si2Nb. 00Cr18Ni6Mo3Si2Nb is an A+Y duplex stainless steel containing N and Nb developed to address the issue of single-phase ferrite structure in Swedish grade 3RE60 after welding, which leads to a decrease in corrosion resistance and toughness.
In the 1980s, second-generation a+y duplex stainless steel containing N was developed and replicated to solve local corrosion damage such as pitting and crevice corrosion caused by chlorides, such as 00Cr22Ni5Mo2N, 00Cr25Ni6Mo3N, and 00Cr25Ni7Mo3WCuN. This not only formed the duplex stainless steel system in China, but also deeply studied its microstructure and properties, as well as the mechanism of N in duplex stainless steel.
Since the 1970s, other important advances in the research of stainless steel materials in China have included the development of high-strength and ultra high strength martensitic aging stainless steel, which has been put into industrial trial production and application; High purity ferritic stainless steels 00Cr18Mo2, 00Cr26Mo1, and 00Cr30Mo2 with C+N ≤ 150-250ppm were smelted and mass-produced using vacuum induction furnace, vacuum electron beam furnace, and vacuum consumable furnace; High Mo and high Mo N Cr Ni austenitic stainless steels with Mo content ≥ 4.5%, such as 00Cr20Ni25Mo4.5Cu, 00Cr18Ni18Mo5 (N), 00Cr25Ni25Mo5N, have been successfully developed and applied in chemical, petrochemical, and marine development fields; 00Cr25Ni20Nb and several ultra-low carbon high silicon stainless steels have been developed to address concentrated nitric acid corrosion and solid solution intergranular corrosion.
Since the 1980s, two grades of urea grade stainless steel 00Cr18Ni14Mo2 and 00Cr25Ni22Mo2N, which are ultra-low carbon and strictly control the phosphorus content and alpha phase in steel, have been developed. Their plates, tubes, rods, forgings, and welding materials have been applied in the large and medium-sized urea industry with satisfactory results; Due to the construction and operation of external refining equipment for stainless steel smelting in some special steel plants, such as AOD (argon oxygen refining furnace), VOD (vacuum oxygen refining furnace), etc., China's stainless steel smelting technology has reached a new level. It not only makes the production of low-carbon and ultra-low carbon stainless steel easy, but also achieves significant cost reduction and efficiency improvement in stainless steel. Due to a series of drawbacks of 18-8 Cr Ni austenitic steel containing Ti, advanced industrial countries such as the United States and Japan had already achieved the transition from Ti containing stainless steel to widely used low-carbon and ultra-low carbon stainless steel as early as the 1960s. However, China only vigorously developed, produced, and applied low-carbon and ultra-low carbon stainless steel from 1985 to 1990, and made remarkable progress. For example, by the end of 1988, the production of low-carbon and ultra-low carbon 18-8 stainless steel in China had accounted for about 10% of China's stainless steel production. However, compared with advanced countries in the production and application of stainless steel (such as Japan, the United States, and other countries where Ti containing 18-8 Cr Ni steel accounts for only about 1.5% of stainless steel production), the gap is still significant. In the 1980s, China conducted research on nitrogen controlled (N0.05% -0.10%) and nitrogen alloyed (N>0.10%) Cr Ni austenitic stainless steel. Experiments have shown that N is a cost-effective alloying element in Cr Ni austenitic stainless steel and duplex stainless steel. The strengthening effect of N element can reduce the intergranular corrosion sensitivity of stainless steel, improve the corrosion resistance of stainless steel, especially the mechanism of improving the pitting corrosion resistance of stainless steel.
04 Classification of Stainless Steel Grades
China
According to GB/T 221 "Method for Representing Steel Product Grades", it is represented using a combination of Chinese Pinyin letters, chemical element symbols, and Arabic numerals.
Carbon content: Generally, an Arabic numeral is used at the beginning of the grade to indicate the average carbon content (in parts per thousand); If the average carbon content is less than one thousandth, it is represented by "0"; The carbon content not exceeding 0.03% is represented by "00".
Alloy element content: When the average alloy element content is less than 1.50%, the grade only indicates the element and generally does not indicate the content; When the average content of alloying elements is 1.5% -2.49%, 2.50% -3.49%, 22.50% -23.49%, the corresponding markings are 2, 3, 23, etc.
Stainless steel for specialized purposes, with the code representing the purpose of the steel added to the top of the grade. Example: OCr18Ni9, Y1Cr17 (easy cut steel).
United States (ASTM)
There are many methods for representing steel grades in the United States, and the AISI grade representation method is commonly used for stainless steel. At present, the ASTM stainless steel standard mainly adopts two methods of designation: UNS (Unified Numbering System for Metals and Alloys) and AISI, which are listed and compared in the standard. In the future, it will gradually transition to the UNS designation series.
AISI: Represented by three Arabic numerals. The first digit represents the category, and the second and third digits represent the sequence number.
First digit category:
2: Cr Ni Mn system;
3: Cr Ni system;
4: Cr series;
5: Low Cr series;
6: Precipitation hardening system.
For example: 201, 304, 403504.
UNS: Represented by a combination of a prefix letter and 5 Arabic numerals. The prefix letter for stainless steel is S, with the first digit representing the category and the last four digits representing the sequence number. And except for the number 1 representing the category, the first three digit codes are basically represented using the AISI brand designation method.
First digit category:
1: Precipitation hardening system;
2: Cr Ni Mn system;
3: Cr Ni system;
4: Cr series;
5: Low Cr series.
The last two digits are generally "00", "03" represents ultra-low carbon, and other digits are used to indicate that the main chemical composition is the same with slight differences in individual components, or contains other special alloy elements.
Example: S20100 S30400、S30403、S30451。
Japan (JIS)
The designation method for Japanese JIS stainless steel standards is SUS+numerical numbering.
Among them, S: steel, U: purpose, S: stainless steel; The numerical numbering is basically represented by the American AISI brand designation method.
According to the AISI designation method, namely
2: Cr Ni Mn system;
3: Cr Ni system;
4: Cr series.
A unique brand in Japan, represented by a similar AISI brand followed by J1 and J2.
Example: SUS 201 SUS 304、SUS 304J1。
According to the shape, purpose, and manufacturing method of steel, when it is necessary to use a code to represent it, add the corresponding code after the grade, as follows:
B: Bar material; CB: Cold processed bar material; HP: Hot rolled steel plate; CP: Cold rolled steel plate; HS: Hot rolled steel strip; CS: Cold rolled steel strip; CSP: Steel strip for springs; WR: Wire; Y: Welding wire; W: Steel wire; WP: Steel wire for springs; WS: Steel wire for cold heading; HA: Hot rolled angle steel; CA: Cold rolled angle steel; TB: Steel pipes for boilers and heat exchangers; TPY: Welding large-diameter steel pipes for piping; TP: Steel pipes for piping; TPD: Steel pipes are generally used for piping.
For example: SUS304-B, SUS304-WR、SUS304-HP。
Germany (DIN)
There are two methods for representing stainless steel grades according to the German DIN standard:
Alphabet symbol representation method:
Steel group code:
40-Ni<2.5%, without Mo, Nb, and Ti;
41- Ni<2.5%, containing Mo, without Nb and Ti;
43- Ni ≥ 2.5%, without Mo, Nb, and Ti;
44- Ni ≥ 2.5%, containing Mo, without Nb and Ti;
45- Contains special added elements.
Example: X5CrNi18-10,1.4301; X6Cr13,1.4000。
France (NF)
French NF standard stainless steel grade designation method:
Example: Z6CN18-09.
United Kingdom (BS)
British BS standard stainless steel grade designation method:
Example: 304S31.
European Standard (EN)
The European standards EN 10027-1 and EN 10027-2 (with dual numbering for relevant countries, such as DINEN 10027-1 and DIN EN 10027-2) specify the naming system for steel, where the designation of stainless steel is the same as the German DIN standard.
There are many grades of stainless steel, and everyone has their own usage habits. This requires us to clarify the comparative relationship between different grades.