The following information will provide you with a comprehensive understanding of the different types of stainless steel, making it easier for you to choose the appropriate type for your needs.
Currently, the most used stainless steels are 304 and 316.
In terms of cost, 304 stainless steel is significantly cheaper than 316 stainless steel.
You can select the appropriate type of stainless steel based on your specific needs.
Stainless Steel Grades
The following table summarizes the different stainless steel series and their specific types, along with their main characteristics and typical applications.
| Series | Stainless steel type | Features and applications |
|---|---|---|
| 200 | In general | Contains chromium, nickel, manganese; austenitic stainless steel. |
| 300 | In general | Contains chromium, nickel; austenitic stainless steel. |
| 301 | Specific | Good malleability, fast hardening, good weldability, superior abrasion resistance and fatigue resistance up to 304. |
| 302 | Specific | Same corrosion resistance as 304, greater resistance due to high carbon content. |
| 303 | Specific | Easier machining than 304, small amounts of sulfur and phosphorus added. |
| 304 | Specific | General model, 18/8 stainless steel, class GB 0Cr18Ni9. |
| 309 | Specific | Better temperature resistance than 304. |
| 316 | Specific | Used in the food industry and surgical equipment, anti-corrosion, better anti-chloride corrosion resistance, “Marine steel”, used in nuclear fuel recovery. |
| 321 | Specific | Reduced risk of corrosion in welded joints due to titanium, similar to 304. |
| 400 | In general | Ferritic and martensitic stainless steel. |
| 408 | Specific | Good heat resistance, poor corrosion resistance, 11% Cr, 8% Ni. |
| 409 | Specific | Cheap, used as car exhaust, ferritic (chrome steel). |
| 410 | Specific | Martensitic (high strength chromium steel), good wear resistance, low corrosion resistance. |
| 416 | Specific | Improved processing properties due to the addition of sulfur. |
| 420 | Specific | “Blade class” martensitic steel, used in surgical instruments, very shiny. |
| 430 | Specific | Ferritic, decorative use, good forming property, low temperature resistance and corrosion resistance. |
| 440 | Specific | Used for razor blades, models: 440A, 440B, 440C, 440F (easily processed). |
| 500 | In general | Heat resistant chrome alloy steel. |
| 600 | In general | Martensite precipitation hardening stainless steel. |
| 630 | Specific | Common precipitation-hardened type, 17-4; 17% Cr, 4% Ni. |
Stainless Steel Classification
The main chemical composition of stainless steel can be divided into several categories, including chromium stainless steel, chromium-nickel stainless steel, chromium-manganese-nitrogen stainless steel, chromium-nickel-molybdenum stainless steel, ultra-low carbon stainless steel, high molybdenum content stainless steel and high purity stainless steel.
Classification based on the properties and application of steel includes nitric acid stainless steel (nitric grade), corrosion-resistant stainless steel, stressed stainless steel, high-strength stainless steel, among others.
In terms of functional characteristics, stainless steel can be divided into low-temperature stainless steel, non-magnetic stainless steel, easy-cutting stainless steel and ultraplastic stainless steel.
It is also classified based on its metallographic structure, which includes ferrite stainless steel (F), martensite stainless steel (M), austenitic stainless steel, austenitic-ferritic duplex stainless steel (AF), austenite-martensite duplex stainless steel (AM), and precipitation hardened stainless steel (PH).
Mechanical Properties of Stainless Steel
Comparison of the mechanical properties of stainless steel
| Classification | Composition (%) | Temperability | Corrosion resistance | Machinability | Weldability | Magnetism | ||
|---|---|---|---|---|---|---|---|---|
| W | Cr | No | ||||||
| ferrite | <0.35 | 16 | 27 | / | Good | Good | Good | he has |
| martensite | <1.20 | 11 | 15 | Self-hardening | he has | he has | bad | he has |
| austenite | <0.25 | >16 | 7 | / | Good | Good | Good | / |
The above classification only considers the matrix structure.
In addition to the three basic types of stainless steel, it also includes composite stainless steel such as martensite-ferrite and austenite-ferrite, as well as precipitation-hardened stainless steel such as martensite-carbide stainless steel.
Detailed Introduction to Stainless Steel
The table below provides a concise overview of each steel type, highlighting their main characteristics, examples and typical applications.
| Type of SS | Main features | Examples | Uses |
|---|---|---|---|
| Ferritic Steel | – Stainless steel with low carbon and chromium content. – Chromium content > 14%. – Contains elements such as Mo, Ti, Nb, Si, Al, W, V. – Predominantly ferrite-forming elements. – Corrosion resistant and oxidation resistant. – Poor mechanical properties and processability. |
Cr17, Cr17Mo2Ti, Cr25, Cr25Mo3Ti, Cr28 | Anti-acid structures, antioxidant steel. |
| Ferrite-Martensitic Steel | – In Y+A or δ phase at high temperatures. – Transforms into the YM phase in cold conditions. – Consists of ferrite and martensite. – The amount of ferrite varies. – Chromium content typically between 12-18%. – Possibility of partial hardening. |
0Cr13, 1Cr13, 2Cr13, Cr17Ni2, Cr17W4, Cr11MoV, etc. | Various applications depend on the specific grade. |
| Martensitic Steel | – In phase Y at quenching temperatures. – Transforms into martensite when cooled. – Similar properties to ferritic-martensitic steel, but with superior mechanical performance. – No free ferrite in the structure. |
2Cr13, 2Cr13Ni2, 3Cr13, 13Cr14NiWVBA, etc. | Various applications similar to ferritic-martensitic steel. |
| Martensite-Carbide Steel | – Fe-C alloy with high carbon content. – Contains 12% or more chromium. – Heated to normal quenching temperature. – Hardened martensite and carbide structure. – Corrosion resistance equivalent to stainless steel with 12-14% chromium. |
4Cr13, 9Cr18, 9Cr18MoV, 9Cr17MoVCo | Cutting tools, bearings, springs, medical instruments. |
| Austenitic Steel | – High concentration of stabilizing elements. – Wide Y phase zone at high temperatures. – Austenitic structure at normal temperatures. – Can be strengthened by cold deformation. – Susceptible to intercrystalline and stress corrosion. |
18-8, 18-12, 25-20, 20-25Mo, Cr18Mn10Ni5, etc. | Various industrial applications benefit from strain hardening. |
| Austenitic-Ferritic Steel | – Limited stable austenite elements. – State of the austenitic-ferritic phase. – The composition and amount of ferrite vary. – Higher yield strength compared to pure austenitic steel. – Less susceptible to stress corrosion and hot cracking during welding. – Low pressure processing performance and high susceptibility to pitting corrosion. |
Various chromium-manganese stainless steels | Industries that require high yield strength and corrosion resistance. |
| Austenite-Martensitic Steel | – Ms point lower than ambient temperature. – Forms austenite after treatment with solid solution. – Transforms into martensite during cooling or heating processes. – High strength but lower corrosion resistance than standard austenitic steel. – Developed in the 1950s, known as precipitation-hardened half-austenitic stainless steel. |
17Cr-7Ni-A1, 15Cr-9Ni-A1, 17Cr-5Ni-Mo, etc. | Aviation, rocket and missile industries; It is not widely used in machine manufacturing. Ultra-high strength steel. |
1. Ferritic steel
Low-carbon chromium stainless steel with a chromium content greater than 14%, chromium stainless steel with a chromium content equal to or greater than 27% and with additional elements such as molybdenum, titanium, niobium, silicon, aluminum, tungsten and vanadium .
In the chemical composition, the elements that form ferrite occupy a dominant position, and the matrix structure is mainly iron-based.
This type of steel is known as ferritic, has a tempered form (solid solution), and small amounts of carbides and intermetallic compounds can be observed in the annealing and aging structures.
Examples of such steels include Cr17, Cr17Mo2Ti, Cr25, Cr25Mo3Ti and Cr28.
Ferritic stainless steel is relatively resistant to corrosion and oxidation due to its high chromium content, but it has poor mechanical properties and processability.
It is mainly used in anti-acid structures and as anti-oxidant steel.
2. Ferrite-martensitic steel
This type of steel is in the Y+A (or δ) phase at high temperatures, and transforms into the YM phase when it approaches cold.
It retains ferrite and exists as martensite and ferrite at normal temperatures.
The amount of ferrite in the structure can vary from a few percent to several tens of percent, depending on the composition and heating temperature.
Examples of this type of steel include 0Cr13, 1Cr13, 2Cr13 with chromium near the upper limit and carbon near the lower limit, Cr17Ni2 steel, Cr17W4 steel, as well as many modified hot strength steels with 12% chromium based on 1Cr13 (which are also known as heat-resistant stainless steels), such as Cr11MoV, Cr12WMoV, Cr12W4MoV, 18Cr12WMoVNb, etc.
Ferritic-martensitic steel can exhibit partial hardening and obtain mechanical properties, but these are greatly influenced by the ferrite content and distribution.
The chromium content in this type of steel is typically between 12-14% and 15-18%.
The former has the ability to resist weak atmospheric and corrosive media, and has good damping and a small coefficient of linear expansion.
The latter type has corrosion resistance comparable to ferritic acid steel with the same chromium content, but still retains some of the disadvantages of high chromium ferritic steel.
3. Martensitic steel
Under normal quenching temperatures, martensitic steel is in phase Y, but this phase only remains stable at high temperatures. The M phase is commonly stable around 300°C and transforms into martensite upon cooling.
This type of steel includes 2Cr13, 2Cr13Ni2, 3Cr13 and some hot-strengthened steels with 12% modified chromium, such as 13Cr14NiWVBA and Cr11Ni2MoWVB steels.
The mechanical properties, corrosion resistance, process performance and physical properties of martensitic stainless steel are similar to those of ferrite-martensitic stainless steel with 2-14% chromium.
As there is no free ferrite in the structure, its mechanical performance is superior to that of the aforementioned steel, but its thermal sensitivity to heat treatment is lower.
4. Martensite-carbide steel
The Fe-C alloy contains 0.83% carbon.
On stainless steel, the S points are shifted to the left due to the chromium. Steel with 12% chromium and 0.4% or more carbon, as well as steel with 18% chromium and 0.3% or more carbon, belong to hypereutectoid steel.
This type of steel is heated to the normal quenching temperature, and the secondary carbide cannot be completely dissolved in the austenite, so the hardened structure is composed of martensite and carbide.
There are not many types of stainless steel that fall into this category, but some stainless steels with higher carbon content, such as 4Cr13, 9Cr18, 9Cr18MoV, and 9Cr17MoVCo steel.
If quenched under low temperature, 3Cr13 steel with carbon near the upper limit can also have such a structure.
Due to their high carbon content, although the above three types of steel contain more chromium, their corrosion resistance is only equivalent to that of stainless steel with 12-14% chromium.
This type of steel is mainly used in parts that require high hardness and good wear resistance, such as cutting tools, bearings, springs and medical instruments.
5. Austenitic steel
This type of steel has a high concentration of stabilizing elements and a wide Y-phase zone at high temperatures.
After cooling, the Ms point drops below room temperature, resulting in an austenitic structure at normal temperatures.
This category includes chromium-nickel stainless steel, such as 18-8, 18-12, 25-20, and 20-25Mo, as well as low-nickel stainless steel that uses manganese instead of some nickel and nitrogen, including Cr18Mn10Ni5, Cr13Ni4Mn9 , Cr17Ni4Mn9N and Cr14Ni3Mn14Ti steel.
Austenitic stainless steel has many benefits, including the ability to be strengthened by cold deformation methods through strain hardening, despite poor heat treatment properties.
However, it is also susceptible to intercrystalline corrosion and stress corrosion cracking, which can be mitigated through the use of alloying additives and process measures.
6. Austenitic-ferritic steel
Due to the limited amount of stable austenite elements, steel does not have a pure austenitic structure at room temperature or at high temperatures, resulting in an austenitic-ferritic phase state. The composition and amount of ferrite can vary greatly depending on the heating temperature.
Many types of stainless steel fall into this category, including low carbon 18-8 nickel-chromium steel, 18-8 nickel-chromium steel with titanium, niobium and molybdenum, with ferrite being particularly visible in the structure of the cast steel.
Other examples include chromium-manganese stainless steel with more than 14-15% chromium and less than 0.2% carbon (such as Cr17Mn11) and most chromium-manganese-nitrogen stainless steel that has been studied and applied in industry.
Compared to pure austenitic stainless steel, this type of steel has several advantages, including greater yield strength, greater resistance to intergranular corrosion, reduced sensitivity to stress corrosion cracking, less tendency to hot cracking during welding and good casting fluidity.
However, it also has several disadvantages, such as poor pressure processing performance, high susceptibility to pitting corrosion, and tendency to exhibit C-phase brittleness and weak magnetism under strong magnetic field conditions.
These advantages and disadvantages are directly related to the presence of ferrite in the structure.
7. Austenite-martensitic steel
The Ms point of this steel is lower than room temperature, facilitating the forming and welding of austenite after solid solution treatment.
Martensitic transformation can generally be achieved through two processes.
- After solid solution treatment, heating to 700-800°C causes the austenitic body to transform into a metastable state due to the precipitation of carbonized chromium. The Ms point then rises above room temperature, resulting in the transformation of austenite to martensite during the cooling process.
- Direct cooling between points Ms and Mf after solid solution treatment also results in the transformation of austenite into martensite.
The second method provides better corrosion resistance, but the solid solution treatment and cryogenic interval should not be too long, otherwise the cold strengthening effect will be reduced due to the aging stability of austenite.
After treatment, an aging process is carried out at 400-500 degrees to enhance the intermetallic compound.
Examples of steel grades that fall into this category include 17Cr-7Ni-A1, 15Cr-9Ni-A1, 17Cr-5Ni-Mo, and 15Cr-8Ni-Mo-A1.
Austenite-martensitic steel, also known as austenitic-maraging stainless steel, is a new type of stainless steel developed and applied since the 1950s.
It is also referred to as precipitation-hardened half-austenitic stainless steel due to the presence of ferrite in addition to austenite and martensite in its structure.
These steels are characterized by their high strength (C can reach 100-150) and good thermal strengthening performance, but their corrosion resistance is lower than that of standard austenitic stainless steel due to the low chromium content and the precipitation of chromium carbide during heat treatment.
High strength is achieved by sacrificing some corrosion resistance and other properties such as non-magnetism.
Austenite-martensitic steel is mainly used in the aviation and rocket missile industries, but is not widely used in machine manufacturing and is sometimes classified as a type of ultra-high-strength steel.
