Types of Stainless Steel Grades and The methods of naming Stainless Steel.

Stainless steel material
Stainless steel is a kind of material with brightness close to mirror surface, tough and cold to the touch. It is a relatively avant-garde decorative material with excellent corrosion resistance, formability, compatibility and toughness. It is used in heavy industry and light industry. , Daily necessities industry and architectural decoration industries.
Stainless acid-resistant steel is referred to as stainless steel. It is composed of stainless steel and acid-resistant steel. In short, the steel that can resist atmospheric corrosion is called stainless steel, and the steel that can resist chemical media corrosion is called acid-resistant steel. Generally speaking, steel with chromium content of more than 12% Cr has the characteristics of stainless steel. According to the microstructure after heat treatment, stainless steel can be divided into five categories: ferritic stainless steel, martensitic stainless steel, austenitic stainless steel, Austenitic-ferritic duplex stainless steel and precipitation hardening stainless steel.

Because stainless steel has excellent corrosion resistance, formability, compatibility, and toughness in a wide temperature range, it has been widely used in heavy industry, light industry, daily necessities industry, building decoration and other industries.

Classification method
There are many classification methods for stainless steel materials, the common ones are the following, among which the classification according to the metallographic structure is the most common.
Chemical composition classification
Basically, it can be divided into two major systems: chromium series stainless steel (such as ferrite series, martensitic series) and chromium-nickel series stainless steel (such as austenitic series, abnormal series, precipitation hardening series).
Metallographic organization classification
Can be divided into austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, duplex stainless steel, precipitation hardening stainless steel.

Classified by corrosion resistance type
It can be divided into stress corrosion resistant stainless steel, pitting corrosion resistant stainless steel, and intergranular corrosion resistant stainless steel.
Classified by functional characteristics
It can be divided into free-cutting stainless steel, non-magnetic stainless steel, low-temperature stainless steel, and high-strength stainless steel.
There are nearly 100 types of stainless steel that have been included in various standards in the world, and with the advancement of technology and the development of industry and agriculture, new stainless steel grades are still increasing. For a known grade of stainless steel, the chromium equivalent [Cr] and nickel equivalent [Ni] can be calculated based on its chemical composition, and the structure and properties of the steel can be roughly estimated by using the Schaeffler-Delong stainless steel structure chart.

Matrix tissue classification
1. Ferritic stainless steel. Containing 12% 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.
2. Austenitic stainless steel. The chromium content is more than 18%, and it also contains about 8% nickel and a small amount of molybdenum, titanium, nitrogen and other elements. Good overall performance, resistant to corrosion by various media.
3. Austenitic-ferritic duplex stainless steel. It has the advantages of austenitic and ferritic stainless steel, and has superplasticity.
4. Martensitic stainless steel. High strength, but poor plasticity and weldability.

Types:
Austenitic stainless steel: stainless steel with an austenitic structure at room temperature. When the steel contains about 18% Cr, 8%-10% Ni, and about 0.1% C, it has a stable austenite structure. Austenitic chromium-nickel stainless steel includes the famous 18Cr-8Ni steel and high Cr-Ni series steel developed by adding Cr and Ni content and adding Mo, Cu, Si, Nb, Ti and other elements on this basis. Austenitic stainless steel is non-magnetic and has high toughness and plasticity, but its strength is low. It is impossible to strengthen it through phase transformation. It can only be strengthened by cold working.
Such as adding S, Ca, Se, Te and other elements, it has good machinability. In addition to resistance to oxidizing acid media corrosion, this type of steel can also be resistant to corrosion by sulfuric acid, phosphoric acid, formic acid, acetic acid, and urea if it contains elements such as Mo and Cu. If the carbon content of this type of steel is less than 0.03% or contains Ti and Ni, its resistance to intergranular corrosion can be significantly improved. High-silicon austenitic stainless steel has good corrosion resistance to nitric acid. As austenitic stainless steel has comprehensive and good comprehensive properties, it has been widely used in various industries.

Ferritic stainless steel: A stainless steel whose structure is mainly ferritic in use. The chromium content is between 11% and 30%, and it has a body-centered cubic crystal structure. This kind of steel generally does not contain nickel, and sometimes also contains a small amount of Mo, Ti, Nb and other elements. This kind 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 make atmospheric resistance. , Water vapor, water and oxidizing acid corroded parts. This type of steel has disadvantages such as poor plasticity, significantly reduced plasticity and corrosion resistance after welding, which limits its application. The application of out-of-furnace refining technology (AOD or VOD) can greatly reduce interstitial elements such as carbon and nitrogen, so this type of steel is widely used.
Austenitic-ferritic duplex stainless steel: It is a stainless steel with austenite and ferrite structure each accounting for about half. In the case of low C content, the Cr content is 18% to 28%, and the Ni content is 3% to 10%. Some steels also contain Mo, Cu, Si, Nb, Ti, N and other alloying elements. This type of steel has the characteristics of austenitic and ferritic stainless steel. Compared with ferrite, it has higher plasticity and toughness, no room temperature brittleness, and significantly improved intergranular corrosion resistance and welding performance, while still maintaining iron The 475℃ brittleness, high thermal conductivity and superplasticity of element stainless steel. Compared with austenitic stainless steel, it has high strength and significantly improved resistance to intergranular corrosion and chloride stress corrosion. Duplex stainless steel has excellent pitting corrosion resistance and is also a nickel-saving stainless steel.

Martensitic stainless steel: stainless steel whose mechanical properties can be adjusted by heat treatment. In layman’s terms, it is a kind of hardenable stainless steel. Typical grades are Cr13 type, such as 20Cr13, 30Cr13, 40Cr13, etc. After quenching, the hardness is higher, and different tempering temperatures have different strength and toughness combinations. They are mainly used for steam turbine blades, tableware, and surgical instruments. According to the difference in chemical composition, martensitic stainless steel can be divided into martensitic chromium steel and martensitic chromium-nickel steel. According to the different structure and strengthening mechanism, it can be divided into martensitic stainless steel, martensitic and semi-austenitic (or semi-martensitic) precipitation hardening stainless steel, and maraging stainless steel.
Representative steel grade, chemical composition, mechanical properties at room temperature: the representative steel grades of martensitic stainless steel are 12Cr13, 20Cr13, 30Cr13, etc., the representative steel grades of ferritic stainless steel are 10Cr17, 10Cr17Mo, etc., and the representative steel grades of austenitic stainless steel are 06Cr19Ni10(304), 022Cr19Ni10(304L), 06Cr17Ni12Mo2(316), 022Cr17Ni12Mo2(316L), 06Cr18Ni11Ti(321), 06Cr18Ni11Nb(347), etc. The representative steel number of duplex stainless steel is 00Cr26Ni7Mo2Ti and so on.

Stainless Steel Grade Name and Density:
China
Japan
USA
Korea
EU
Australia
Taiwan,China
Density/m3
GB/T20878
JIS
ASTM
KS
BSEN
AS
CNS
12Cr13
SUS403
403
STS403
403
403
7.75
20Cr13
SUS420J1
420
STS420J1
1.4021
420
420J1
7.75
30Cr13
SUS420J2
STS420J2
1.4028
420J2
420J2
7.75
10Cr17
SUS430
430
STS430
1.4016
430
430
7.70
68Cr17
SUS440A
440A
STS440A
440A
440A
7.70
06Cr19Ni10
SUS304
304
STS304
1.4301
304
304
7.93
022Cr19Ni10
SUS304L
304L
STS304L
1.4306
304L
304L
7.93
06Cr17Ni12Mo2
SUS316
316
STS316
1.4401
316
316
7.98
022Cr17Ni12Mo2
SUS316L
316L
STS316L
1.4404
316L
316L
7.98
06Cr18Ni11Ti
SUS321
321
STS321
1.4541
321
321
7.93
06Cr18Ni11Nb
SUS347
347
STS347
1.455
347
347
7.98

Introduction to corrosion resistance:

During the manufacturing process of stainless steel equipment, performance damage, defects, and some substances that affect the surface, such as: dust, floating iron powder or embedded iron, heat tempering color and other oxide layers, rust spots, grinding burrs, welding arc marks, welding Spatter, flux, welding defects, oil and grease, residual adhesive and paint, chalk and marking pen marks, etc. The vast majority are because they neglected their harmful effects and did not pay attention to them or did not do well. However, they are potentially harmful to the oxidation protective film. Once the protective film is damaged, thinned or changed by other methods, the stainless steel below will begin to corrode. Corrosion is generally not spread over the entire surface, but at or around the defect. This localized corrosion is usually pitting corrosion or crevice corrosion. These two types of corrosion will develop in depth and breadth, while most of the surface is not corroded.

Stainless acid-resistant steel is referred to as stainless steel. It is composed of stainless steel and acid-resistant steel. In short, the steel that can resist atmospheric corrosion is called stainless steel, and the steel that can resist chemical media corrosion is called acid-resistant steel. Generally speaking, steel with chromium content of more than 12% Cr has the characteristics of stainless steel. According to the microstructure after heat treatment, stainless steel can be divided into five categories: ferritic stainless steel, martensitic stainless steel, austenitic stainless steel, Austenitic-ferritic duplex stainless steel and precipitation hardening stainless steel.
The first method for naming stainless steel grades is to use world-wide chemical conformance to indicate chemical composition, and Arabic letters to indicate chemical composition content.

Take China as an example. There are two grades of Chinese stainless steel, the old grade 00Cr19Ni10 and the new grade 022Cr19Ni10.

Why are there two grades? Because most brands in the domestic stainless steel market now use the latest national standards, which have a little change from the old standards, such as carbon content identification and chemical composition content, it is necessary to distinguish clearly when buying stainless steel.

The second method for naming stainless steel grades is to use fixed-digit numbers to represent steel series or numbers.

Take the United States as an example. There are two standards for American stainless steel grades, but the chemical composition and content are the same. It is directly called 304L in the ASTM standard, and S30403 in the UNS standard.

The ASTM standard is represented by three Arabic numerals, the first digit indicates the type of stainless steel, the second and third digits indicate the serial number, and the L behind the 304L grade indicates low-carbon type. The UNS standard is represented by a combination of S+5 Arabic numerals. The first three digits of the 5 Arabic numerals adopt the ASTM standard designation method. The last two digits are used to indicate that the main chemical components are the same but the individual components are slightly different, or contain Distinguish other special chemical elements.

Let me take the Japanese standard as an example. The Japanese stainless steel grade is SUS304L. Japanese stainless steel grades are expressed by SUS+digital grades.

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