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Stainless steel is undoubtedly the best metal to work with in terms of durability and strength. But are all stainless metals equally robust or have the same toughness? The answer is a big NO.
Stainless steel is grouped into 5 main types, which are then divided into several gradings. Now let’s explore them and find out which stainless steel type is best for your requirement.
5 Types Of Stainless Steel
1. Austenitic
Austenitic is the most common type of stainless steel. Chromium and nickel are the major alloying elements in this type of steel. However, some austenitic grades also contain molybdenum and manganese.
Among all other stainless steel types, austenitic has the highest corrosion resistance. Besides, they also have creep resistance properties, which makes them suitable for welding.
Austenitic stainless steels don’t support hardening via heat treatment, but they are hardenable to some extent by cold work. They are non-magnetic in nature. You will find the vast use of these stainless steels in food processing and aerospace applications.
2. Ferritic
Ferritic is magnetic in nature and has less corrosion resistance than austenitic. Though you can’t harden them with heat treatment, they are moderately hardenable with cold treatment.
Its major chemical composition consists of 10.5%- 30% chromium and less than 0.20% carbon. Due to less nickel content, ferritic stainless steel is very affordable. This affordability makes it a suitable material for kitchenware, automotive parts, etc.
3. Martensitic
Martensitic stainless steel contains 0.10% to 1.2% carbon and chromium, ranging from 11.5% to 18%. Unlike austenitic and ferritic, you can harden martensitic stainless steel by heat treatment. This makes it ductile and strong.
However, it has moderate resistance against corrosion. They are widely used in making surgical tools, valves, cutlery, pumps, etc.
4. Duplex (Austenitic-ferritic)
Duplex stainless steel is a combination of austenitic and ferritic steel. Here, both the steel types are mixed in nearly equal proportion, making the duplex a stronger variant. However, the reason behind its higher tensile strength is the use of lower nickel and higher chromium content.
It also has greater anti-corrosive properties compared to regular stainless steel. So, you can use them in an environment that deals with high chlorine concentration.
Moreover, due to lower nickel content, duplex stainless steel is cheaper than most other types. It is used in making pipes, oil rings, and other industrial applications. However, duplex stainless steel is available in the following grades:
a. Standard Duplex Steel
Standard duplex steel is also known as Grade 2205 or EN 1.4462. In this type of duplex steel, austenitic and ferritic are mixed in nearly equal proportions. It has a Pitting Resistance Equivalent Number (PREn) ranging from 28-38.
b. Super Duplex Steel
Super duplex steel has higher mechanical strength than standard duplex steel. Besides, their high PREn range of 38-45 makes them highly resistant to corrosion. Due to such robustness and anti-corrosive properties, super duplex steel is widely used in the chemical, oil, and gas industries.
However, super duplex steel can be of different types, such as:
Duplex 2507 Stainless Steel
Duplex 2507 stainless steel has high thermal conductivity and greater resistance against chloride stress. This duplex steel is made with the following composition:
- Chromium 25%
- Molybdenum 4%
- Nickel 7%
Zeron 100 Stainless Steel
Zeron 100 stainless steel meets a PREn value of 40. It features a 50-50 austenitic-ferritic structure, making Zeron 100 stronger and highly resistant to corrosion.
- Molybdenum 3.6%
- Nickel 7% and
- Chromium 25%
Besides, the addition of copper into Zeron 1000 stainless steel makes it sulphuric acid resistant.
c. Lean Duplex Grades
The corrosion resistance of lean duplex grade is close to regular to regular austenitic. However, comparing mechanical properties and strength, these are better than austenitic. Lean duplex grades are widely used in general applications like construction. Moreover, these are also affordable.
d. Hyper Duplex
Hyper duplex is the strongest variant of duplex stainless steel. Compared to other duplex steel, it has the highest chromium content, about 27%. It comes in three grades
- SAF 2707 HD with PREn 48
- SAF 3107 HD with PREn 50 and
- ESAB Exaton 27.7.5.L with PREn 49
5. Precipitation Hardening
Precipitation hardening stainless steel supports tempering and is hardenable via the aging treatment. This becomes possible due to the addition of alloying elements like copper, niobium, aluminum, molybdenum, etc.
This type of steel is of high strength and has corrosive resistance similar to austenitic steel. Therefore, precipitation-hardening steel is suitable for applications that require high durability, resistance, and stretch. For instance, this stainless steel is used in the military, aerospace, and automotive industries.
Comparison Chart Between Different Stainless Steel Types
| Type Of Stainless Steel | Austenitic | Ferritic | Martensitic | Duplex | Precipitation Hardening |
|---|---|---|---|---|---|
| Magnetic Response | Generally No | Yes | Yes | Yes | Yes |
| Work Hardening Rate | Very High | Medium | Medium | Medium | Medium |
| Corrosion Resistance | High | Medium | Medium | Very High | Medium |
| Hardenable | By Cold Work | No | Quench & Temper | No | Age Harden |
| Ductility | Very High | Medium | Low | Medium | Medium |
| High-Temperature Resistance | Very High | High | Low | Low | Low |
| Low-Temperature Resistance | Very High | Low | Low | Medium | Low |
| Weldability | Very High | Low | Low | High | High |
Elements Used To Make Different Type Of Stainless Steel
Chromium
Chromium is the most used alloying element in stainless steel. This builds a protective layer around the steel, making it anti-corrosive. Besides, higher chromium content ensures better resistance against high temperatures. It further hardens the steel and improves wear resistance and magnetic induction.
Carbon
The inclusion of carbon makes the steel strong and durable. However, high content reduces its weldability and anti-corrosive properties. To get better resistance against corrosion, look for stainless steel with low carbon and high chromium content.
Nickel
Nickel is an expensive metal, so it is used in small amounts to cut costs. However, nickel works great for boosting the formability and weldability of steel. At high temperatures, high nickel-content stainless steels are much stronger than other variants. The most popular stainless steel grades, 304 and 316, contain high nickel content. This makes them highly durable but expensive, too.
Other Alloying Element
Besides the above-mentioned major metals, stainless steel also contains other elements. These are as follows:
- Manganese: Mn
- Copper: Cu
- Silicon: Si
- Sulfur: S
- Tantalum: Ta
- Boron: B
- Niobium: Nb
- Phosphorus: P
- Nitrogen: N
- Molybdenum: Mb
- Titanium: Ti
- Selenium: Se
- Tungsten: W
- Iron: Fe
These metals and their proportion differs for different grades of steel.
Grades of Stainless Steel
| Grades Of Stainless Steel | Composition % |
|---|---|
| 201 | Carbon: 0.15, Manganese: 5.5–7.5, Silicon: 1, Chromium: 16–18, Nickel: 3.5–5.5, Phosphorus: 0.045, Sulfur: 0.015, Nitrogen: 0.25 |
| 202 | Carbon: 0.15, Manganese: 7.5–10, Silicon: 1, Chromium: 17–19, Nickel: 4–6, Phosphorus: 0.045, Sulfur: 0.015, Nitrogen: 0.25 |
| 205 | Chromium: 16.5–18, Manganese: 14–15.5, Nickel: 1–1.75, Nitrogen: 0.4 |
| 2507 | Chromium: 25, Nickel: 7, Molybdenum: 4, Nitrogen: 0.28, Tungsten: 0.7, Copper: 0.7 |
| 301 | Carbon: 0.05–0.15, Manganese: 2, Silicon: 2, Chromium: 16–19, Nickel: 6–9.5, Phosphorus: 0.045, Sulfur: 0.015, Nickel: 0.11, Molybdenum: 0.8 |
| 302 | Carbon: 0.15, Manganese: 2, Silicon: 1, Chromium: 17–19, Nickel: 8–10, Phosphorus: 0.045, Sulfur: 0.03 |
| 302B | Chromium: 17–19, Nickel: 8–10, Carbon: 0.15, Manganese: 2, Silicon: 2–3, Phosphorus: 0.045, Sulfur: 0.03 |
| 303 | Chromium: 18, Nickel: 9, Sulfur: 0.15–0.35, Copper: 1 |
| 303Se | Carbon: 0.15, Manganese: 2, Silicon: 1, Chromium: 17–19, Nickel: 8–10, Selenium: 0.15, Sulfur: 0.06, Phosphorus: 0.2 |
| 304 | Chromium: 17.5–19.5, Nickel: 8–10.5, Carbon: 0.07, Manganese: 2, Silicon: 1, Phosphorus: 0.045, Sulfur: 0.015 |
| 304H | Carbon: 0.04–0.08, Manganese: 2, Chromium: 17.5–19.5, Nickel: 8–11, Silicon: 1, Phosphorus: 0.035, Sulfur: 0.015, Nitrogen: 0.1 |
| 304L | Carbon: 0.03, Manganese: 2, Chromium: 17.5–20, Nickel: 8–12, Silicon: 1, Phosphorus: 0.035, Sulfur: 0.015, Nitrogen: 0.11 |
| 304N | Carbon: 0.06, Manganese: 2, Silicon: 1, Chromium: 18–20, Nickel: 8–11, Phosphorus: 0.045, Sulfur: 0.015, Nitrogen: 0.12–0.22 |
| S30430 | Carbon: 0.04, Manganese: 2, Iron: 63.9–72, Chromium: 17–19, Nickel: 8.5–10.5, Copper: 3–4 |
| 305 | Carbon: 0.06, Manganese: 2, Silicon: 1, Chromium: 17–19, Nickel: 11–13, Phosphorus: 0.045, Sulfur: 0.015, Nitrogen: 0.11 |
| 308 | Carbon: 0.08, Manganese: 2, Silicon: 1, Chromium: 19–21, Nickel: 10–12, Phosphorus: 0.045, Sulfur: 0.015, Nitrogen: 0.11 |
| 309 | Carbon: 0.2, Manganese: 2, Silicon: 1.5–2.5, Chromium: 19–21, Nickel: 11–13, Phosphorus: 0.045, Sulfur: 0.015, Nitrogen: 0.11 |
| 310 | Carbon: 0.25, Manganese: 0.2, Silicon: 1.5, Chromium: 24–26, Nickel: 19–22, Phosphorus: 0.045, Sulfur: 0.03 |
| 314 | Carbon: 0.2, Manganese: 2, Silicon: 1.5–2.5, Chromium: 24–26, Nickel: 19–22, Phosphorus: 0.045, Sulfur: 0.015, Nitrogen: 0.11 |
| 316 | Carbon: 0.07, Manganese: 2, Silicon: 1, Molybdenum: 2–2.5, Chromium: 16.5–18.5, Nickel: 10–13, Phosphorus: 0.045, Sulfur: 0.015, Nitrogen: 0.11 |
| 316F | Carbon: 0.08, Manganese: 2, Silicon: 1, Molybdenum: 1.75–2.5, Chromium: 16–18, Nickel: 10–14, Phosphorus: 0.2, Sulfur: 0.1 |
| 316H | Carbon: 0.04–0.08, Boron: 0.0015–0.005, Manganese: 2, Silicon: 1, Molybdenum: 2–2.5, Chromium: 16.5–18.5, Nickel: 10–13, Phosphorus: 0.035, Sulfur: 0.015, Nitrogen: 0.11 |
| 316L | Carbon: 0.03, Manganese: 2, Silicon: 1, Molybdenum: 2–3, Chromium: 16.5–19, Nickel: 10–15, Phosphorus: 0.045, Sulfur: 0.015, Nitrogen: 0.11 |
| 316Ti | Carbon: 0.08, Titanium: 0.7, Manganese: 2, Silicon: 1, Molybdenum: 2–2.5, Chromium: 16.5–18.5, Nickel: 10.5–13.5, Phosphorus: 0.045, Sulfur: 0.015 |
| 317 | Carbon: 0.08, Manganese: 2, Silicon: 1, Molybdenum: 3–4, Chromium: 18–20, Nickel: 11–15, Phosphorus: 0.045, Sulfur: 0.03, Nitrogen: 0.11 |
| 317L | Carbon: 0.03, Manganese: 2, Silicon: 1, Molybdenum: 3–4, Chromium: 17.5–19.5, Nickel: 13–17, Phosphorus: 0.045, Sulfur: 0.03, Nitrogen: 0.11 |
| 317LM | Carbon: 0.03, Manganese: 2, Silicon: 1, Molybdenum: 4–5, Chromium: 16.5–18.5, Nickel: 12.5–14.5, Phosphorus: 0.045, Sulfur: 0.015, Nitrogen: 0.12–0.22 |
| 321 | Carbon: 0.08, Manganese: 2, Titanium: 0.7, Silicon: 1, Chromium: 17–19, Nickel: 9–12, Phosphorus: 0.045, Sulfur: 0.015 |
| 347 | Carbon: 0.08, Manganese: 2, Nb: 1, Silicon: 1, Chromium: 17–19, Nickel: 9–12, Phosphorus: 0.045, Sulfur: 0.015 |
| 348 | Carbon: 0.08, Manganese: 2, Nb: 0.8, Tantalum: 0.1, Silicon: 1, Chromium: 17–19, Nickel: 9–13, Phosphorus: 0.045, Sulfur: 0.03 |
| 330 | Carbon: 0.08, Manganese: 2, Silicon: 0.75–1.5, Chromium: 17–20, Nickel: 34–37, Phosphorus: 0.03, Sulfur: 0.03 |
| 384 | Carbon: 0.08, Manganese: 2, Silicon: 0.75–1.5, Chromium: 17–20, Nickel: 34–37, Phosphorus: 0.03, Sulfur: 0.03 |
| 409 | Carbon: 0.03, Titanium: 0.65, Manganese: 1, Silicon: 1, Chromium: 10.5–12.5, Phosphorus: 0.04, Sulfur: 0.015 |
| 410 | Carbon: 0.08–0.15, Manganese: 1.5, Silicon: 1, Chromium: 11–13.5, Nickel: 0.75, Phosphorus: 0.04, Sulfur: 0.015 |
| 420 | Carbon: 0.15–0.42, Manganese: 1–1.5, Silicon: 1, Chromium: 12–14, Phosphorus: 0.04, Sulfur: 0.015 |
| 430 | Carbon: 0.08, Manganese: 1, Silicon: 1, Chromium: 16–18, Phosphorus: 0.04, Sulfur: 0.015 |
| 434 | Carbon: 0.08, Molybdenum: 0.9–1.4, Manganese: 1, Silicon: 1, Chromium: 16–18, Phosphorus: 0.04, Sulfur: 0.015 |
| 440C | Carbon: 0.95–1.2, Molybdenum: 0.4–0.8, Manganese: 1, Silicon: 1, Chromium: 16–18, Phosphorus: 0.04, Sulfur: 0.03 |
| 904L | Carbon: 0.02, Copper:1.2–2, Molybdenum: 4–5, Manganese: 2, Nickel: 24–26, Silicon: 0.7, Chromium: 19–21, Phosphorus: 0.03, Sulfur: 0.01, Nitrogen: 0.15 |
How To Select The Ideal Stainless Steel Type?
Consider Application
The composition of different types of stainless steel affects its properties. This is why you must connoisseur the application before choosing the right steel type. For instance, in industrial applications that require high strength, choose precipitation-hardened stainless steel.
Again, for general use, like kitchenware and cutleries, austenitic and martensitic stainless steel are good to go.
| Stainless Steel Type | Ideal Application |
|---|---|
| Austenitic | Pipes, exhaust systems, domestic items like- saucepans, cutlery, etc. |
| Ferritic | Sinks, dishwashers, food/pharmaceutical processing equipment, etc. |
| Martensitic | Aerospace and automotive components, knives, scissors, cutlery, etc. |
| Duplex | Pressure vessels, heat exchangers, bleaching equipment, etc. |
| Precipitation-hardened | Nuclear, aerospace, gas, and oil industry |
Surrounding Environment
The durability of the stainless steel is affected by its surrounding environment. For instance, in an environment dealing with frequent water contact, choose a stainless steel type with high chromium content. With high anti-corrosion properties, 304-grade stainless steel is good for general use.
Again, in marine applications, buy stainless steel that contains chlorine-resistant elements like- molybdenum. This makes grade 316 stainless steel excellent for marine use. It has a high chlorine resistance property and is suitable for an environment with salty seawater.
Grade Requirement
Just knowing the type of stainless steel will not work; grades also matter. For instance, austenitic steel of grade 304 is the most used steel variant, but these are not fit for marine applications. To operate in the marine, you need austenitic steel with grade 316. This is why considering grade requirements is essential.
The below chart will help you to identify grades under different types of stainless steel:
| Type Of Stainless Steel | Grades |
|---|---|
| Austenitic | 384, 348, 347, 330, 321, 317, 316, 314, 310, 309, 308, 305, 304, 303, 302, 301, 205, 202, 201 |
| Ferritic | 430, 434, 409, 439, 444 |
| Martensitic | 440, 416, 420, 422, 431, 414, 410, 403 |
| Duplex | LDX2101, 2507, 2304, 2205, And 4 classes: standard duplex, super duplex, lean duplex and hyper duplex |
| Precipitation-hardened | 17-4, 13-8, 15-5 |
Formability or Weldability
For good formability, ferritic and austenitic stainless steels work better than martensitic steels. For best results, go with grades 304 or 430. Besides offering food formability, you can also use these steels for welding with other metals.
Melting Point
Stainless steels can resist high temperatures. However, their melting point depends on the alloy element. So, for applications that deal with high temperatures, you must choose stainless steel grades with higher melting points.
The chart below shows the melting points of the most common stainless steel grades:
| Grade Of Stainless Steel | Melting Point in Celsius | Melting Point in Fahrenheit |
|---|---|---|
| Grade 304 | 1400°-1450°C | 2552°-2642°F |
| Grade 316 | 1375°-1400°C | 2507°-2552°F |
| Grade 430 | 1425°-1510°C | 2597°-2750°F |
| Grade 434 | 1426°-1510°C | 2600°-2750°F |
| Grade 410 | 1480°-1530°C | 2696°-2786°F |
| Grade 420 | 1450°-1510°C | 2642°-2750°F |
Corrosion Resistance
Austenitic stainless steel wins the race when it comes to corrosion resistance. It has the highest rust resistance property among all other types.
So, in applications that need greater anti-corrosion properties, choose grade 316 austenitic stainless steel. However, cheaper ferritic and martensitic stainless steel also offers good resistance against corrosion.
Strength, Ductility, and Toughness
Without considering the weight-bearing capacity of your application, choosing the right stainless steel variant is not possible. However, grade 440C stainless steel has the highest strength and hardness. So, you can use this for a robust application.
However, for the best combination of strength, ductility, and toughness, buy stainless steel with high nickel and chromium content.
Magnetic Response
Chromium addition in steel alloy makes it more magnetic. In contrast, stainless steels with nickels have less magnetic properties.
Austenitic stainless steel with 300 series is non-magnetic. In contrast, ferritic and martensitic steel with grade 400 series are magnetic. So, you can use this for applications like the construction of kitchen appliances, automotive trim, etc, that require magnetic features.
Availability & Cost
304-grade steel is widely available and the most used stainless steel. Nevertheless, the price of the stainless steel depends on its quality. This is what makes the austenitic/300 series the most expensive stainless steel variant for its greater strength and high corrosion resistance.
So, if you want to save your money on maintenance and durability, austenitic is a good option. However, for an affordable solution, you can go with ferritic and martensitic.
Conclusion
To pick the ideal stainless steel type, consider its application, corrosion resistance, and strength requirement. This will help you select the ideal grade.
However, for designing and machining any type of stainless steel, Richconn is your ultimate solution. We are experts in providing professional CNC machining services. Check out our service page and contact us with your manufacturing needs!
FAQs
Why is 316 stainless steel more expensive than 304?
316 stainless steel is more expensive than 304 due to the presence of high nickel content. Besides, it has higher resistance against chlorine and better weldability. Though 304 is a cheaper alternative, it can’t match 316’s quality.
Which type of stainless steel is best?
Austenitic stainless steel is best due to its high anti-corrosive properties, greater strength, toughness, and ductility. However, you must consider the application of the steel to find the best type.
How long can stainless steel last?
On average, stainless steel can last for 50 years. However, with proper maintenance, they can last as long as 100 years or even more.
What is the hardest stainless steel?
Martensitic stainless steel of grade 440C is the hardest stainless steel. It has a high carbon content that makes it stronger and suitable for applications like shafts.
What is the biggest advantage of stainless steel?
Stainless steel is highly durable and 100% recyclable. Besides, they are anti-corrosive and have greater strength to meet any application needs.
Which is better, 304 or 420 stainless steel?
304 and 420 stainless steel has very different properties. 304 has a higher anti-corrosive property than 420. Whereas 420 is harder than 304. Therefore, you must consider application requirements to decide which is best for your needs.
