Stainless Steel Grades
There are 150 plus stainless steel grades that have been discovered and expanded to use in various applications, each grade exhibits unique chemical composition and mechanical properties, and knowing the characteristics of these grades is necessary, this helps to select the correct grade for your use.
There are many grades of stainless steel and equivalents, they are defined by different standards, for example, ASTM and EN/DIN.
Five Types Of Stainless Steel
There are five types of stainless steel depending on their metallurgical microstructure, each group has particular alloying elements and composition that will affect stainless steel properties and uses.
- Austenitic stainless steels
- Martensitic stainless steels
- Ferritic stainless steels
- Duplex (ferritic-austenitic) stainless steels
- Precipitation-hardening (PH) stainless steels
Austenitic Stainless Steel
Austenitic stainless steel has austenite as the primary microstructure, Austenitic Stainless Steel grades consist of high Chromium and Nickel content, generally, it contains at least 16% chromium and 6% nickel.
Austenitic Stainless Steel grades have excellent corrosion and heat resistance with good mechanical properties (good formability and weldability) over a wide range of temperatures.
The austenitic grades are non-magnetic in the solution annealed condition, They cannot be hardened through heat treatment but can be hardened through cold-working, cold working increases their strength and may then be magnetic with a cold forming process. The most common austenitic alloys are iron-chromium-nickel steels and are the most widely used stainless steel grades.
Typical grades are given as follows:
- 304, standard 18/8 grade, the most commonly used stainless steel grade
- 316, contains 16% to 18% chromium and 11% to 14% nickel. It also has molybdenum added to the nickel and chrome of the 304.
- 316L is low carbon of 316 grade, the addition of molybdenum alloy improves corrosion resistance, particularly in chloride environments
- 321, Titanium addition of at least five times the carbon content, lowers the risk of weld decay
- 904L, high Chromium content increases general corrosion, pitting and stress corrosion cracking resistance
Typical applications for austenitic stainless steels are in the food industry, catering and kitchen equipment, process industries, building, architecture and transport.
Ferritic stainless steels
Ferritic stainless steel grades usually have chromium as an alloying element., the chromium content is 15%~30%, with a body-centered cubic crystal structure. This kind of steel generally has no nickel or a very small addition of nickel, sometimes containing a small amount of Mo, Nb, Ti, and other elements.
This kind of steel has average corrosion resistance and poor fabrication characteristics, it is magnetic.
These grades contain Chromium alloy with the absence of Nickel and moderate corrosion resistance, they cannot be hardened by heat treatment, cost saving grades, but not as good for welding.
409
Applied for no corrosion or mild corrosive environment, such as container, bus, car, display frame, etc.
430
widely used, most of the performance with 304 similar, general indoor use, has good corrosion resistance. Typical 430 is often used as a substitute for 304 of the materials used in kitchen facilities, dishwashers, pots, etc.
430Ti,439,441
Good weldability and formability, in most cases is better than 304 for sink, heat exchange tube, automobile exhaust systems, and the welding position of washing machines, the grade can even replace 304 for performance requirements higher occasions.
434,436,444
Adding molybdenum to increase the corrosion resistance, used for hot water tank, solar water heater, automobile exhaust system, electric kettle, microwave oven parts, etc.. 444 of the corrosion resistance and the equivalent of 316.
445,446,447
More chromium and molybdenum increased corrosion resistance and oxidation resistance, corrosion resistance and oxidation resistance is better than 316, the typical use of coastal and other corrosion-resistant environments, JIS447 corrosion resistance is equal with metal titanium.
Ferritic stainless steel is less expensive than other types due to the lower nickel content, its cost is lower and more stable, therefore they can be as a supplement to 304 stainless steel (304 steel is still the most widely used, the most common), Ferritic stainless steel has been proved that in many of the original think can only be used Austenitic stainless steel (300 series) application fields, ferrite stainless steel is an extremely excellent alternative material.
- 409, decreased chromium content, Automotive exhaust grade
- 430, A basic Ferritic grade, used for mildly corrosive environments, like nitric acid, sulfur gases, and many organic and food acids
- 436, columbium added for corrosion and heat resistance
- 446, higher chromium content improves corrosion and scaling resistance at high temperatures
Typical applications are washing machines, countertops, refrigerators, dishwashers, cooker hoods, tableware and restaurant equipment, architectural use (mainly indoor), transport industry e.g. exhaust systems in automotive and structural hollow sections in heavy transport.
Martensitic stainless steels
Martensitic Stainless Steels consist of high carbon and lower chromium content. Like ferritic grades, it is magnetic. It does display poor weldability compared to other grades but it has higher hardenability and can be heat treated to improve properties.
Martensitic stainless steel will have lower corrosion resistance when compared with austenitic and ferritic grades with the same chromium and alloy content, Martensitic stainless steel is very hard and strong.
- 410, the standard martensitic grade for slight corrosion applications
- 416, good machinability
- 420, Higher hardness martensitic grade, contains increased carbon to improve mechanical properties.
- 431, the best corrosion resistance properties of all the martensitic grades. It has excellent tensile and torque strength and good toughness
Martensitic grades are often used in applications where high strength and wear resistance is demanded, such as for shafts, knives and for wear and press plates
Duplex (ferritic-austenitic) stainless steels
Duplex grades are a combination of austenitic and ferritic material, having very high strength, and better toughness and ductility than the ferritic grades.
Duplex stainless steel(DSS), refers to the Ferritic stainless steels and Austenitic stainless steels each accounting for about 50%, generally relatively less content also needs at least 30% stainless steel. In the case of low C content, Cr content is 18%~28%, and Ni content is 3%~10%. Some steels also contain Mo, Cu, Nb, Ti, N, and other alloy elements.
Duplex is a mixture of austenitic and ferritic stainless steel. Thus, it has the properties of both, It has high chromium and low nickel concentration. With high tensile strength and good weldability. Duplex stainless steel has excellent corrosion resistance but is also a kind of low-nickel stainless steel.
- 2205, the most widely used duplex grade, has high resistance to pitting and stress corrosion
- 2507, super duplex grade, the high chromium, molybdenum, and nitrogen levels provide excellent resistance to pitting, crevice, and general corrosion.
Typical applications for duplex stainless steels are process industries, pulp & paper, oil & gas applications, desalination, chemical tankers (cargo tanks), pressure vessels and structural applications in harsh climates. Super duplex stainless steels are found in marine installations, oil & gas, flexible pipes, umbilicals and desalination plants.
Stainless steel grades depending on three-digit designation can be also grouped into
- 200 Series
- 300 Series
- 400 Series
- 500 Series
- 600 Series
Stainless Steel Grades And Equivalents
There are several stainless steel grade systems in the world, each standard has a unique No. or name, in many cases, these grades can be equivalent, due to their the same or similar chemical composition and properties.
- ASTM, American Society for Testing and Materials
- EN, European Standard
- DIN, German Standard
- JIS, Japanese Industrial Standards
- GB, Chinese Standard
- BS, British Standards
| EN Designation | Alternative Designations | |||||
|---|---|---|---|---|---|---|
| Steel name | Steel number | AISI | UNS | GB | BS | Generic/Brand |
| Ferritic stainless steels | ||||||
| X2CrNi12 | 1.4003 | S40977 | 3CR12 | |||
| X2CrTi12 | 1.4512 | 409 | S40900 | 409S19 | ||
| X6CrAl13 | 1.4002 | 405 | S40500 | 405S17 | ||
| X6Cr17 | 1.4016 | 430 | S43000 | 430S17 | ||
| X3CrTi17 | 1.4510 | 439 | S43035 | |||
| X2CrMoTi18-2 | 1.4521 | 444 | S44400 | |||
| X6CrMoNb17-1 | 1.4526 | 436 | S43600 | |||
| X2CrTiNb18 | 1.4509 | 441 | S43932 | 18CrCb | ||
| Austenitic stainless steels | ||||||
| X2CrNiN18-7 | 1.4318 | 301LN | S30153 | |||
| X2CrNi18-9 | 1.4307 | 304L | S30403 | 022Cr19Ni10 | 304S11 | |
| X2CrNi19-11 | 1.4306 | 304L | S30403 | |||
| X2CrNiN18-10 | 1.4311 | 304LN | S30453 | 304S51 | ||
| X5CrNi18-10 | 1.4301 | 304 | S30400 | 06Cr19Ni10 | 304S15 | |
| X6CrNiTi18-10 | 1.4541 | 321 | S32100 | 06Cr18Ni11Ti | 321S31 | |
| X6CrNiNb18-10 | 1.4550 | 347 | S34700 | 06Cr18Ni11Nb | 347S31 | |
| X2CrNiMo17-12-2 | 1.4404 | 316L | S31603 | 022Cr17Ni12Mo2 | 316S11 | |
| X5CrNiMo17-12-2 | 1.4401 | 316 | S31600 | 06Cr17Ni12Mo2 | 316S31 | |
| X6CrNiMoTi17-12-2 | 1.4571 | 316Ti | S31635 | 06Cr17Ni12Mo2Ti | 320S31 | |
| X2CrNiMo17-12-3 | 1.4432 | 316L | S31603 | 316S13 | ||
| X2CrNiMoN17-3-3 | 1.4429 | 316LN | S31653 | |||
| X3CrNiMo17-13-3 | 1.4436 | 316 | S31600 | 316S33 | ||
| X2CrNiMo18-14-3 | 1.4435 | 316L | S31603 | 316S13 | ||
| X2CrNiMoN17-13-5 | 1.4439 | 317LMN | S31726 | |||
| X1NiCrMoCu25-20-5 | 1.4539 | N08904 | 015Cr21Ni26Mo5Cu2 | 904S13 | 904L | |
| X1CrNiMoCuN20-18-7 | 1.4547 | S31254 | 015Cr20Ni18Mo6CuN | 254SMO | ||
| X6CrNiMoNb17-12-2 | 1.4580 | S31640 | ||||
| X2CrNiMo18-15-4 | 1.4438 | 317L | S31703 | 022Cr19Ni13Mo3 | 317S12 | |
| X1CrNiMoCuN24-22-8 | 1.4652 | S32654 | 654SMO | |||
| X1NiCrMo31-27-4 | 1.4563 | N08028 | Sanicro 28 | |||
| X1CrNiMoCuN25-25-5 | 1.4537 | N08932 | ||||
| X1CrNiMoCuNW24-22-6 | 1.4659 | S31266 | ||||
| X1NiCrMoCuN25-20-7 | 1.4529 | N08925 | 1925hMo | |||
| Austenitic stainless steels – heat resisting Grades | ||||||
| X15CrNiSi20-12 | 1.4828 | |||||
| X9CrNiSiNCe21-11-2 | 1.4835 | S30815 | 253 MA | |||
| X12CrNi23-13 | 1.4833 | 309 | S30900 | 309S24 | ||
| X8CrNi25-21 | 1.4845 | 310S | S31000 | 06Cr25Ni20 | 310S24 | |
| X6CrNiSiNCe19-10 | 1.4818 | S30415 | 153 MA | |||
| X6NiCrSiNCe35-25 | 1.4854 | S35315 | 353MA | |||
| X10NiCrSi35-19 | 1.4886 | N08330 | 330 | |||
| Austenitic-ferritic stainless steels | ||||||
| X2CrMnNiN21-5-1 | 1.4162 | S32101 | 2101 LDX | |||
| X2CrNiN23-4 | 1.4362 | S32304 | 2304 | |||
| X2CrNiMoN12-5-3 | 1.4462 | S31803/S32205 | 022Cr23Ni5Mo3N | 2205 | ||
| X2CrNiMoN25-7-4 | 1.4410 | 2507 | ||||
| X2CrNiMoCuEWN25-7-4 | 1.4501 | S32760 | Zeron 100 | |||
“L” and “H” Stainless Steel Standard Grades
The common austenitic grades of stainless steel, 304 and 316, are also available with controlled low or high carbon contents, known as “L” and “H” variants, with particular applications.
Low carbon or “L” grades are used to prevent or delay sensitization of stainless steel at elevated temperatures and the resulting lower corrosion resistance. The problematic temperature zone is 450-850 °C, encountered during welding or specific application environments. “L” grades are often available in thicker selection sizes, greater than about 5mm in flat products.
High carbon or “H” grades are used for higher strength.
“L” Grades Of Stainless Steels
The low carbon “L” grades are used where high-temperature exposure will occur, including welding of medium or heavy sections. The low carbon is one way of delaying or preventing grain boundary carbide precipitation (often referred to as sensitisation) which can result in intergranular corrosion in corrosive service environments. there is an incubation time before the precipitation of carbides at temperatures in the range of about 450-850°C. The time for precipitation to occur is highly dependent upon the amount of carbon present in the steel, so low carbon content increases resistance to this problem. Because of their application area, the “L” grades are most readily available in plate and pipe, but often also in round bar. In the absence of heavy section welding, or high-temperature exposure, the corrosion resistance of the standard and “L” grades are usually identical.
“H” Grades Of Stainless Steels
“H” grades are higher carbon versions of standard grades and have increased strength, particularly at elevated temperatures (generally above 500 °C). Long-term creep strength is also higher. “H” grades are primarily available in plate and pipe. Applicable grades are most commonly 304H and 316H, but high carbon versions of 309, 310, 321, 347 and 348 are specified in ASTM A240/A240M. These grades are susceptible to sensitization if held in the temperature range of 450-850 °C. Once sensitized, impaired aqueous corrosion resistance and some reduction in ambient temperature ductility and toughness will result (usually irrelevant in high-temperature applications).
What Is The Differences Between “L” Grades And “H” Grades
Composition limits for 304 and 304L are identical except for carbon content (304L does permit up to 12.0%Ni, compared to 10.5% max for 304 -but given the cost of nickel it is usual for both grades to have close to the minimum of 8.5%, so there is no practical difference). Neither grade has a minimum carbon content specified. A carbon content of 0.02% for example complies with both 304 and 304L specifications.
304H has the same composition specification as 304 except for the carbon range of 0.04-0.1 0% (note the minimum limit for carbon) and that the 304H does not have the 0.10% nitrogen maximum limit which applies to both standard and “L” grades. Also, all austenitic “H” grades must have a grain size of ASTM No. 7 or coarser.
The relationship between 316, 316L and 316H is the same as that between the 304 series of stainless steels. Only the carbon contents differentiate 316, 316L and 316H grades (and the nitrogen and grain size limits mentioned above). Carbon contents are listed in Table 1 (from ASTM A240/A240M). Specifications for some other products, particularly tube and pipe, have a carbon limit of 0.035% or 0.040% maximum for 304L and 316L, but are otherwise the same.
TABLE 1:
| Grade | UNS Number | Specified Carbon Content (%) |
|---|---|---|
| 304 | S30400 | 0.08 max |
| 304L | S30403 | 0.030 max |
| 304H | S30409 | 0.04 – 0.10 |
| 316 | S31600 | 0.08 max |
| 316L | S31603 | 0.030 max |
| 316H | S31609 | 0.04 – 0.10 |
Mechanical property specification differences are illustrated in Table 2 (from ASTM A240/A240M). In practice, steel mills generally ensure that the “L” grade heats meet the strength requirements of standard grades, ie all 304L will have yield/tensile properties above 205/515 MPa, so will meet both standard and “L” grade requirements.
TABLE 2:
| Grade | UNS Strength (MPa) min | Tensile Strength (MPa) min | Yield (%) min | Elongation Hardness (HB) max | Brinell Hardness (HRB) max | Rockwell |
|---|---|---|---|---|---|---|
| 304 | S30400 | 515 | 205 | 40 | 201 | 92 |
| 304L | S30403 | 485 | 170 | 40 | 201 | 92 |
| 304H | S30409 | 515 | 205 | 40 | 201 | 92 |
| 316 | S31600 | 515 | 205 | 40 | 217 | 95 |
| 316L | S31603 | 485 | 170 | 40 | 217 | 95 |
| 316H | S31609 | 515 | 205 | 40 | 217 | 95 |
Dimensional and other requirements are the same for standard, “L” and “H” grades.
Pressure vessel codes (e.g. AS 121 O) and pressure piping codes (e.g. AS4041) give allowable working pressures for each of the grades at nominated elevated temperatures. These codes allow higher pressure ratings for standard grades than for “L” grades. The codes do not permit the use of “L” grades above 525″C (AS4041) or 425″C (AS1210). Both codes include a clause stating that for use above 550″C the standard grades must contain at least 0.04% carbon. 304 or 316 materials with 0.02% carbon are therefore not permitted for these elevated temperatures, whether called “L” or not. At temperatures from ambient up to this high-temperature cut-off “L” grade heats with the standard grade pressure ratings would be permitted, so long as the material was in full compliance with the standard grade composition and mechanical property specifications. As discussed above, it is normal practice for this condition to be met.
The pressure vessel codes give the same allowable pressure rating for “H” grades as for standard grades -this is logical as the “H” grades are simply the standard grades with their carbon contents controlled to the top half of the range, or slightly above.
Alternative Grade Usage
Because of availability issues, it is sometimes desirable to use a product labeled as a standard grade when an “L” or “H” grade has been specified, or vice versa. Substitution can be made under the following conditions:
- “L” grades can be used as standard grades so long as the mechanical properties (tensile and yield) conform to the standard grade requirements and high-temperature strength is not a requirement. “L” grades usually comply with standard grade requirements, but Mills’ test certificates need to be checked on a case-by-case basis. It is common for steel mills to supply “L” heat when standard grades have been ordered. The practice is legitimate and should not present problems to fabricators or end users.
- Standard grades can be used as “L” grades as long as their carbon content meets the “L” grade maximum limits.
- It is increasingly common for “dual certified” products to be stocked – particularly in plate, pipe and bar. These materials fully comply with both 304 and 304L or 316/316L. Dual certified product is deliberately intended to fulfill requirements for both standard and “L” grades, but cannot be used in applications for “H” grades. If an application requires an “H” grade, this must be specified at the time of order. Standard grades can often be used in place of “H” grades so long as their carbon contents meet the “H” limits (generally 0.04-0.1 0%). Grain size requirements may have to be satisfied by extra testing. The product and its test certificate may describe it as a standard 304 or 316 unless it was originally manufactured as an “H” grade. Details of the test certificate will confirm grade compliance.
- “H” grades can be used as standard grades so long as their carbon contents are 0.08% maximum, and nitrogen 0.10% maximum. This is likely, but would need to be checked.