Knowledge
Classification of Stainless Steel
Classification
Generally, Stainless Steel divides into two types, one is the steel resistant to a weakly corrosive medium such as air, steam, and water. Another one is resistant to acid, alkali, salt, and another chemically corrosive medium, called acid-resisting steel. Due to the differences in the chemical composition of the two types, the former is not necessarily resistant to chemical medium corrosion, while the latter has comprehensive corrosion resistance performance, it depends on the alloy component content in the steel.
Usually, according to the metallographic organization, ordinary stainless steel can be divided into three categories: Austenitic Stainless Steel, Ferritic Stainless Steel, and Martensitic Stainless Steel. Based on the three types of metallographic organization, for special needs and purposes, more steel was derived, like Duplex Stainless Steel, PH Stainless Steel, and the High Alloy Steel with less than 50% iron content.
According to the metallographic organization:
1. Austenitic Stainless Steel
Stainless steel whose matrix is dominated by the face-centered cubic crystal structure of Austenitic organization (CY phase), non-magnetic, is strengthened primarily by cold working (Cold working may cause a certain magnetism). The American Iron and Steel Institute specifies the materials by 200 and 300 series numbers, such as 304.
2. Ferritic Stainless Steel
The matrix is dominated by the body-centered cubic crystal structure of the ferrite organization (a phase), magnetic, and generally can not be hardened by heat treatment, but a cold working process can make it slightly strengthened. Such as 430 and 446.
3. Martensitic Stainless Steel
The matrix is dominated by Martensitic organization (body-centered cubic or cubic), magnetic, the mechanical properties can be adjusted by heat treatment. Such as 410, 420, and 440. Martensite stainless steel has an Austenitic structure under high temperatures, which will transform into martensite when cooled to room temperature by a certain cooling rate, it is the hardening process.
4. Austenitic-ferritic (duplex) Stainless Steel
The matrix has both austenite and ferrite two-phase organization, where the content of the lesser phase matrix is generally greater than 15%, magnetic, it can be strengthened by cold working. 329 is a typical duplex stainless steel. Compare with Austenitic stainless steel, duplex steel has higher strength, resistance to intergranular corrosion, and the resistance to chloride stress corrosion and pitting corrosion is significantly improved.
5. Precipitation Hardening Stainless Steel
Stainless steel whose matrix is Austenitic or Martensitic organization and which can be hardened by precipitation hardening treatment. The AISI specifies the material by 600 series numbers, such as 630 (which is 17-4PH).
In general, the corrosion resistance of Austenitic stainless steel is superior. Under a less corrosive environment, ferritic stainless steel can be used. Under a mildly corrosive environment, if the material is required to have high strength or high hardness, Martensitic stainless steel and precipitation hardening stainless steel is a good choice (in addition to other alloy steel).
Character And Application
| Series | ASTM | GB | SUS | Character | Application |
| 200 | 201 | ICr7Mn6Ni5N | SUS201 | It has the characteristics of acid resistance, alkali resistance, high density, no bubbles in polishing, no pinholes, etc. It is a high-quality material for producing various cases, straps, and case backs. | Mainly used for decorative tubes, industrial tubes, and some shallow drawing products |
| 202 | ICr18Mn8Ni5n | SUS202 | With Mn and N instead of part of the nickel, so as to obtain good mechanical properties and corrosion resistance, is a new type of nickel-saving stainless steel, its room temperature strength is higher than 304, in 800 degrees below the better oxidation resistance and medium temperature strength | Mainly used for decorative tubes, industrial tubes, and some shallow drawing products | |
| 205 | OOCr22Ni5Mo3N | SUS2205 | Its Cr, Mo, and N elements are relatively narrow intervals, easy to achieve phase balance (about half of each phase), improving the strength, corrosion resistance, and welding properties of steel, mostly used for high-performance requirements and the need to burst the material, such as oil and gas pipelines. | Used in oil refining, fertilizer, paper, petrochemical, and other seawater and high-temperature nitric acid resistant heat exchangers and cold showers and assembly parts. | |
| 304 | 1Cr18Ni9 (O6Cr18Ni100 | SUS304 | As a widely used steel, it has good corrosion resistance, heat resistance, low-temperature strength, and mechanical properties. Good hot workability such as stamping and bending, no heat treatment hardening phenomenon (non-magnetic, use temperature -196℃-800℃) | The food industry, household goods (1, 2 types of tableware, kitchen cabinets, indoor plumbing, water heaters, boilers, bathtubs) | |
| 300 | 304j1 | SUS304j1 | Cu should be added to its formability, especially the wire drawing and aging crack resistance is good, and can be complex shape product forming. Its corrosion resistance is the same as 304 steel | Insulated bottles, kitchen sinks, pots, kettle-insulated lunch boxes, door handles, and textile processing machines. | |
| 304L | OOCr19Ni10 | SUS304L | As a low C 304 steel, its corrosion resistance is similar to 304 steel in general conditions, but after welding or stress relief, its resistance to grain boundary corrosion is excellent. In the absence of heat treatment, it can also maintain good corrosion resistance, generally used in the 400 below (non-magnetic, use temperature -196 ℃ - 800 ℃) | It is used in chemical, coal, and petroleum industries with high requirements for resistance to grain boundary corrosion, field open-air machinery, building materials, heat-resistant parts, and parts with heat treatment difficulties. | |
| 321 | ICr18NI9TI | SUS321 | Add Ti element to 304 steel to prevent grain boundary corrosion suitable for use at 430℃-900℃ temperature | Agriculture, ship parts, atomic energy industry, aircraft, exhaust pipe, boiler ladle auto parts windshield wiper, muffler, molded products | |
| 300 | 316 | oCr17nI12Mo2 | SUS316 | Mo should be added, so its corrosion resistance, atmospheric corrosion resistance and high-temperature strength are particularly good, and they can be used under harsh conditions. Excellent process hardening property (non-magnetic) | Marine equipment, chemical, dyestuff, paper, oxalic acid, fertilizer, etc. production equipment, the photographic, food industry, coastal facilities, ropes, CD rods, screws bolts, nuts |
| 316L | ooCr17Ni14Mo2 | SUS316L | As a low C series of 316 steel grade, it has the same characteristics as 316 steel, except that its resistance to grain boundary corrosion is superior. | 316 steel applications with special requirements for resistance to grain boundary corrosion | |
| 309S | oCr23Ni13Mo2 | SUS309s | 23Cr-13Ni high alloy steel stainless steel, excellent corrosion resistance, and strength, suitable for the working temperature of 1000 ℃ parts | Exhaust machines, heat treatment furnaces, heat exchangers, etc. | |
| 310S | oCr25Ni20Si2 | SUS310s | Excellent oxidation resistance, corrosion resistance, and high-temperature resistance. Because of the higher percentage of chromium and nickel, 310S has much better creep strength and can continue to operate at high temperatures, providing good resistance to high temperatures | Boilers, exhaust machines, heat treatment furnaces, heat exchangers, etc. | |
| 400 | 409L | 00Cr12Ti | SUS409L | The cheapest type. It has a better high temperature corrosion resistance and high-temperature strength due to the addition of the Ti element. It is ferritic stainless steel (chromium steel) | Automobile exhaust, heat exchangers, containers, etc. that are to be welded without heat treatment |
| 410 | 1Cr13 | SUS410 | It is representative steel of martensitic steel, which is strong but not suitable for use in harsh corrosive environments. Good machinability, heat treatment surface hardening (magnetic) | Knife blades, mechanical parts, oil refining equipment, bolts, slave, pump rods, type 1tableware(knives, forks) | |
| 410S | 0Cr13 | SUS410 | |||
| 420J1 | 2Cr13 | SUS420J1 | High hardness after quenching, good corrosion resistance (magnetic) | Tableware (knives), turbine blades | |
| 420J2 | 3Cr13 | SUS420J2 | After quenching, it has a higher hardness than 420J1 steel (magnetic) | Knife blades, pipe nozzles, valves, plate rulers, cutlery (scissors, knives) | |
| 430 | 1Cr17 | SUS430 | As a representative steel grade of ferritic steel, it has a low thermal expansion, excellent formability, and oxidation resistance | Heat-resistant appliances, burners, home appliances, type 2 tableware, kitchen sinks, exterior decorative materials, bolts, nuts, CD rods, screens | |
| 444 | Water tank special board |
