Understanding stainless-steel grades
When it comes to stainless steel, there is a lot to consider. In this article we cover:
What is stainless steel?
What are grades of stainless steel?
Stainless steel grades and stainless steel grade chart
Comparing stainless steel grades
What is stainless steel?
First, let's look at what a stainless steel is. They’re iron-based alloys, containing at least 10.5% chromium. The chromium protects the iron and prevents rusting, a property known as passivation.
What are grades of stainless steel?
"Stainless” isn’t an entirely accurate description. It’s more stain resistant than stainless. The different grades of stainless steel will eventually break down. Stainless-steel tarnish, depending on the grade, can take years to develop, so stainless steel is still a great material if corrosion resistance is what you’re looking for. These are the factors which affect the stainless steel grade.
Is stainless steel just a coating?
No. The alloys are melted into the steel itself. Stainless steels are comprised of different combinations of various metals. The next question might be, “What’s the best grade of stainless steel?” Stainless-steel grades and stainless steel applications go hand in hand. Choosing the right one comes down to determining which alloy will work best for your application.
What are stainless steel families?
|
Family |
Weldability |
Ductility |
High-temp resistance |
|
Austenitic stainless steel |
High |
High |
High |
|
Ferritic stainless steel |
Low |
Medium |
High |
|
Martensitic stainless steel |
Low |
Low |
Low |
|
Duplex stainless steel |
High |
Medium |
Low |
|
Precipitation hardening stainless steel |
Low |
Medium |
Low |
Stainless-steel grade falls within these families, which reflect metallurgical structure of stainless steels.
|
Family |
Summary |
Characteristics |
Use |
|
Austenitic stainless steels |
-Contains a minimum of 16% chromium and 6% nickel -Most widely used stainless steels in the world |
-Excellent corrosion resistance -Excellent performance at both high and low temperatures -Non magnetic when annealed -Superb hygienic qualities with outstanding cleanability |
-Common to food and healthcare applications -Popular for manufacturing outdoor enclosures |
|
Ferritic stainless steels |
-Amount of chromium ranges between 10.5% to 18% -Low nickel content (up to 1%) makes it especially cost effective - Lower thermal expansion coefficient and higher thermal conductivity than austenitic stainless steel |
-Good corrosion resistance -Magnetic -Resists stress corrosion cracking |
-Excellent for applications involving heat transfer, such as cooking utensils -Also popular in the automotive industry for exhausts and fuel lines |
|
Martensitic stainless steels |
-Chromium content ranges between 10.5% and 18%, with 0.15% carbon and 0.1% manganese - Carbon content enables tempering and hardening |
-Corrosion resistance in mild environments -Magnetic -Inability to be cold formed |
-Knife blades -Surgical instruments -Razor blades |
|
Duplex stainless steels |
-High chromium and low nickel content -Combines the best of the austenitic and ferritic families -Annealed structure is 50% austenitic and 50% ferritic -Low nickel content means low cost |
-Excellent pitting-and-crevices corrosion resistance -High resistance to stress corrosion cracking -High yield strength -Poor formability and machinability -Magnetic |
-Heat exchangers Also used in: -Off-shore oil and gas installations -Chemical and petrochemical plants |
|
Precipitation hardening stainless steel |
-Contains 17% chromium and 4% nickel -Strength can be developed by adding titanium, aluminium and other alloys |
-Good to excellent corrosion resistance -Can develop high strength with simple heat treatments -Welding can reduce corrosion resistance by over-aging and sensitisation -Magnetic |
-Nuclear waste casks -Turbine blades Also used in: -Aerospace industry -Pulp-and-paper industry equipment |
Stainless steel grades and stainless steel grade chart
What does 304 mean in stainless steel? It’s the grade. Within the families are grades, each with specific properties. The grades are not about stainless-steel quality – each is formulated for a purpose – and not all grades are right for every application. The best stainless steel for manufacturing kitchen appliances won’t be the best for ball bearings.
A word about standards: The American Iron and Steel Institute (AISI) and the Society of Automotive Engineers (SAE) each devised steel specifications for years, which were often interchangeable. Due to the similarities, they were combined into one, overlapping AISI/SAE system. The AISI designation is no longer officially used, but the name is still used informally. EN are the standard for European stainless-steel grades, though AISI/SAE is extremely popular.
Stainless-steel grade chart
Below includes the composition of stainless-steel grades.
|
Designations |
Chemical Composition AISI-Type/SAE & EN Standards (Major elements only) % content is a maximum unless a range is indicated |
|||||||||||
|
AISI-type/ SAE |
EN |
C, ≤ |
Mn, ≤ |
P, ≤ |
S, ≤ |
Si, ≤ |
Cr |
Ni |
Mo |
N, ≤ |
Other Elements ≤, UOS |
|
|
Austenitic stainless steel |
302 |
1.4324 |
0.15 |
2.00 |
0.045 |
0.03 |
0.75 |
17.0-19.0 |
8.0-10.0 |
– |
0.10 |
– |
|
303 |
1.4305 |
0.15 |
2.00 |
0.2 |
≥0.15 |
1.00 |
17.0-19.0 |
8.0-10.0 |
– |
– |
– |
|
|
304 |
1.4301 |
0.08 |
2.00 |
0.045 |
0.03 |
1.00 |
18.0-20.0 |
8.0-11.0 |
– |
– |
– |
|
|
304L |
1.4307 |
0.03 |
2.00 |
0.045 |
0.03 |
1.00 |
18.0-20.0 |
8.0-11.0 |
– |
– |
– |
|
|
308 |
1.4303 |
0.08 |
2.00 |
0.045 |
0.03 |
1.00 |
19.0-21.0 |
10.0-12.0 |
– |
– |
– |
|
|
310 |
1.4845 |
0.25 |
2.00 |
0.045 |
0.03 |
1.5 |
24.0-26.0 |
19.0-22.0 |
– |
– |
– |
|
|
316 |
1.4401 |
0.08 |
2.00 |
0.045 |
0.030 |
1.00 |
16.0-18.0 |
10.0-14.0 |
2.00-3.00 |
– |
– |
|
|
316L |
1.4404 |
0.03 |
2.00 |
0.045 |
0.030 |
1.00 |
16.0-18.0 |
10.0-14.0 |
2.00-3.00 |
– |
– |
|
|
317 |
1.4449 |
0.08 |
2.00 |
0.045 |
0.03 |
1.00 |
18.0-20.0 |
11.0-15.0 |
3.0-4.0 |
0.1 |
– |
|
|
321 |
1.4541 |
0.08 |
2.00 |
0.045 |
0.03 |
1.00 |
17.0-19.0 |
9.0-12.0 |
– |
0.10 |
≥ Ti 5×(C+N), ≤ 0.70 |
|
|
347 |
1.4550 |
0.08 |
2.00 |
0.045 |
0.03 |
1.00 |
17.0-19.0 |
9.0-12.0 |
– |
– |
≥ Cb 10 × C, ≤ 1.00 |
|
|
904L |
1.4539 |
0.02 |
2.00 |
0.045 |
0.035 |
1.00 |
19.0-23.0 |
23.0-28.0 |
4.00-5.00 |
0.1 |
Cu 1.00-2.00 |
|
|
Martensitic stainless steels |
409 |
1.4512 |
0.030 |
1.00 |
0.040 |
0.015 |
1.00 |
10.50-12.50 |
– |
6 x (C+N) to 0.65 |
– |
|
|
430 |
1.4016 |
0.12 |
1.00 |
0.04 |
0.03 |
1.00 |
16.0-18.0 |
– |
– |
– |
– |
|
|
430F |
1.4105 |
0.12 |
1.25 |
0.06 |
≥0.15 |
1.00 |
16.0-18.0 |
– |
– |
– |
– |
|
|
444 |
1.4521 |
0.025 |
1.00 |
0.04 |
0.03 |
1.00 |
17.5-19.5 |
1.00 |
1.75-2.50 |
0.035 |
Ti+Cb 0.20+4 × (C+N)-0.80 |
|
|
Martensitic stainless steels |
410 |
1.4006 |
0.08-0.15 |
1.00 |
0.04 |
0.03 |
1.00 |
11.5-13.5 |
– |
– |
– |
– |
|
416 |
1.4005 |
0.15 |
1.25 |
0.06 |
≥0.15 |
1.00 |
12.0-14.0 |
– |
– |
– |
– |
|
|
420 |
1.4021 |
0.15, ≥ |
1.00 |
0.04 |
0.03 |
1.00 |
12.0-14.0 |
– |
– |
– |
– |
|
|
431 |
1.4057 |
0.2 |
1.00 |
0.04 |
0.03 |
1.00 |
15.0-17.0 |
1.25-2.50 |
– |
– |
– |
|
|
440A |
1.4109 |
0.60-0.75 |
1.00 |
0.04 |
0.03 |
1.00 |
16.0-18.0 |
– |
≤0.75 |
– |
– |
|
|
440B |
1.4112 |
0.75-0.95 |
1.00 |
0.04 |
0.03 |
1.00 |
16.0-18.0 |
– |
≤0.75 |
– |
– |
|
|
440C |
1.4125 |
0.95-1.20 |
1.00 |
0.04 |
0.03 |
1.00 |
16.0-18.0 |
– |
≤0.75 |
– |
– |
|
|
Duplex stainless steels |
2205 |
1.4462 |
0.03 |
2.00 |
0.03 |
0.02 |
1.00 |
22.0-23.0 |
4.5-6.5 |
3.0-3.5 |
0.14-0.20 |
– |
|
2304 |
1.4362 |
0.03 |
2.5 |
0.04 |
0.03 |
1.00 |
21.5-24.5 |
3.0-5.5 |
0.05-0.60 |
0.05-0.60 |
– |
|
|
PH |
15-5 PH / 631 |
1.4568 |
0.07 |
1 |
0.04 |
0.03 |
1 |
14.0-15.5 |
3.5-5.5 |
– |
– |
2.5-4.5 Cu; 0.15-0.45 Nb |
|
17-4 PH / 630 |
1.4542 |
0.07 |
1 |
0.04 |
0.03 |
1 |
15.5-17.5 |
3.0-5.0 |
– |
– |
3.0-5.0 Cu; 0.15-0.45 Nb |
|
Data is indicative only and not to be relied upon in place of full specification. Properties and values vary with temper, product and product dimensions. Consult with product manufacturer. No liability will be accepted.
What is 18/8 stainless steel?
Sometimes you’ll see 304 grade stainless steel referred to as 18/8. This refers to 304’s average composition of 18% chromium and 8% nickel. What is 18/10 stainless steel? Again, 18% chromium but this time, 10% nickel. This also meets the 304 stainless-steel standard.
But what about stainless-steel grades 18/10 vs. 18/8 when both fall within the 304 range?The additional nickel in 18/10 provides a bit more corrosion resistance and tolerance to heat.
Comparing stainless steel grades
Let’s look at some more comparisons, which will help you see how other alloys affect the grade.
304 vs. 316 stainless steel
These are the two most widely used stainless steels, with 304 grade stainless steel being the more popular. A large part of that has to do with economics. Stainless steel 304 is considered a medical stainless steel. Find out more in our guide, What is surgical steel?
The cost of stainless steel typically depends on the alloys involved, and a large proportion of those costs comes down to the chromium content. Now consider that 316 grade stainless steel contains a minimum 2.0% molybdenum. As good as 304 is at standing up to oxidation, 316 is more corrosion resistant, and better able to withstand harsh environments.
Molybdenum is also an expensive element, which makes 316 the more expensive grade. Whether you choose 304 or 316 stainless steel comes down to your application and budget.
Learn more about these two grades in our guide, 304 vs 316 stainless steel.
304 vs 316 stainless steel strength
That minimum 2.0% molybdenum in grade 316 also gives it more strength than 304. Molybdenum strengthens and hardens steel, though its primary function is to stand up to corrosion from chlorides, such as salt.
304 vs. 321 stainless steel
These are also very similar. Stainless steel 304 has good oxidation resistance up to 1598˚F (870˚C) in intermittent service. In continuous service, it’s 1697˚F (925˚C). Fabrication methods, such as forging, require hot working. This occurs after uniform heating to 2100˚F - 2300˚F (1149 - 1260˚C).
Stainless steel 321 is essentially 304 stabilized by titanium additives. This reduces or prevents carbide precipitation during welding. It's also why stainless steel 321 is the preferred grade for applications when the range of temperatures doesn't exceed 1652˚F (900˚C). This combines high strength, scaling resistance and phase stability with corresponding aqueous corrosion resistance.
304 vs. 430 stainless steel
What is the difference between 304 and 430 stainless steels? They look very similar, except when it comes to the price tag. Stainless steel 430 costs less than 304 due to the composition. Whereas 304 stainless steel contains nickel, 430 stainless steel contains none. This not only makes 304 stainless steel more corrosion resistant, but also more expensive. If you're mulling over 304 stainless steel vs 430 stainless steel, then weigh the life span of your application against your budget to arrive at your decision.
Learn more about these two grades in our guide, 304 vs 430 stainless steel.
Stainless steel 420 vs. 304
Grade 420 stainless steel has an extremely high tensile strength when hardened and stress relieved. Normally, 420 has a tensile strength of around 586 MPa. While this is high, it doesn't exceed that of 304, which is 621 MPa. However, when hardened and stress relieved, 420's tensile strength reaches 1,586 MPa – that's more than double 304 when annealed. Consequently, 420 is a better choice for heavy-duty applications. In fact, the 400 range includes the hardest grades.
Can you harden 304 stainless steel? These are austenitic steels, so none of these grades can be hardened by heat treatment. 304 stainless steel (or austenitic steels) hardness can be improved with work hardening, however. Also, a solution treatment or annealing can be done by rapid cooling after heating to 1850˚F - 2048˚F (1010°C - 1120°C).
Which is better, 304 or 410 stainless steel?
These grades share 84% of their average alloy compositions. Grade 410 has 0% nickel, so it costs less than 304. It’s also popular for high-stressed parts and components, as they offer a combination of strength and corrosion resistance. Grade 304 is softer but has more corrosion resistance. Grade 410 is better, for instance, for making fasteners. Grade 304 is better, for example, for manufacturing a wider variety of products, from white goods to electrical cabinets.
To learn more about stainless steel for your enclosure design, you’ll also need to know about the components you’ll need. Check out our Quick Guide: Industrial Components for Outdoor Cabinets.
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