Stainless steel is a material with tons to offer. Its popularity also means there are seemingly a million different types of stainless steel grades. (Actually, there are a few hundred.)
As a general rule, stainless deserves consideration if your engineering project requires at least one of these three qualities:
- A shiny, beautiful appearance
- Corrosion and oxidation resistance
- Strength at various temperatures
Here’s a stainless steel grades chart so you can get the most out of the metal for your project:
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Stainless Steel Grades Chart
Useful corrosion resistance, particularly in wet abrasion environments. Readily welded and formed.
|Tanks, flues, bins, chutes, rail wagons|
|201||Austenitic||Low nickel, high work hardening.||Cookware, hose clamps|
|301||Austenitic||Combination of strength and ductility to withstand severe forming methods. Corrosion resistance comparable to 302.||Rail cars, automotive components|
|302||Austenitic||Excellent corrosion resistance. High strength and hardness.||Food and drink, sanitary, cryogenic and pressure applications|
|303||Austenitic||Addition of sulfur or selenium gives it best machinability of all austenitic grades, but reduces corrosion resistance compared to 304.||Nuts and bolts, aircraft fittings and gears, bushings|
|Austenitic||Slightly magnetic when cold worked. Excellent corrosion resistance but susceptible to pitting corrosion in warm chloride environments. Excellent toughness|
Accounts for 50% of all stainless steel produced.
|Architecture, kitchens, food processing|
|309S||Austenitic||Resistant to oxidation.||Heating, furnace parts|
|Austenitic||Same mechanical and physical properties as 304 but more resistant to pitting corrosion, especially in warm chloride environments. Virtually non-magnetic.||Marine architectural components, food processing, hot water systems|
|317L||Austenitic||Improved corrosion resistance over 316. 317L is a variation of 317 suitable for heavy-gauge welding.||Pulp and paper machinery, ink and dying processes, acetic acid distillation|
|321||Austenitic||Titanium-stabilized.||Aircraft, heat exchangers (up to intermediate temperatures)|
|400||Ferritic||Corrosion resistance comparable to 409, better surface finish||Caskets, applications requiring better finish than 409|
|409, Aluminized 409||Ferritic||Resists atmospheric and automotive exhaust gas corrosion. Aluminized version adds salt and cosmetic corrosion resistance.||Auto exhaust systems, heat exchangers, furnace liners|
|410, 410H||Martensitic||Resists dry atmospheres, freshwater, mild alkalis and acids, steam, and hot gases. Must harden for best heat and corrosion resistance. 410H has better hardenability.||Bolts, nuts, screws, pump parts and shafts, turbine parts, mine ladder rungs, cutlery, rulers, cold heading|
|420, 420HC||Martensitic||Good resistance in hardened condition to atmosphere. Higher-carbon grade. HC offers better hardenability.||Cutlery, stainless steel hospital equipment, needle valves|
|430, 430F||Ferritic||Good combination of corrosion resistance, formability, mechanical properties. 430F is suitable for high-speed machining, but corrosion resistance is lower.||Automotive trim, refrigerator doors, element supports, cold-headed fasteners|
|431||Martensitic||Excellent resistance to wide variety of corrosive media, approaching that of 304. High tensile, torque strength.||Pump and boat shafts, nuts, bolts, marine hardware|
|434||Ferritic||Molybdenum use improves pitting resistance over 430.||Automotive trim components|
|435 Mod.||Ferritic||Improved formability and weldability.||Automotive trim|
|436||Ferritic||Controlled roping.||Automotive trim|
|439||Ferritic||Titanium-stabilized. 18% chrome alloy with low carbon content. Corrosion resistance to variety of oxidizing environments. Pitting corrosion resistance.||Nuclear, automotive, power generation, chemical processing, consumer appliances|
|440||Martensitic||High-carbon, moderate corrosion resistance, superior strength and hardness.||Knives, ball bearings, gauge blocks, dies|
|444||Ferritic||Resistant to oxidation, corrosion, and stress cracking.||Water heaters, engine components, solar panels|
|904L||Austenitic||‘Super austenitic’ grade with very high corrosion resistance, especially to strong acids and chlorides.||Sulphuric acid service|
|About 50% ferrite and 50% austenitic. High strength and hardness. Resistant to erosion, fatigue, stress corrosion cracking, and pitting and crevice corrosion.||Marine, chemical, and petrochemical industries|
|41003||Ferritic||Excellent weldability, toughness, and fabricating characteristics||Tubing for bus frames, hopper cars, chutes, storage tanks, shipping containers|
|‘Super duplex’ grade with exceptional resistance to hot chlorides and sulfides. High in strength.||Marine, chemical, and petrochemical industries|
Breaking Down the Stainless Steel Categories
Stainless steels are lumped into classes. The most common types of stainless steels include:
The metalworking powers-that-be developed these classes to consolidate chemical and mechanical properties into categories based on the needs of customers’ uses.
1. Austenitic Stainless Steel
Austenitic steels mainly reside in the 200 and 300 series. Austenitics are the most specified stainless steel grades thanks to their excellent formability and corrosion resistance. Grade 304 SS is the most well-known and commonly used austenitic stainless steel.
Austenitic stainless steels contain 15%-30% chromium and 2%-20% nickel for better surface quality, corrosion and wear resistance, and workability. They are nonmagnetic when annealed but — depending on the nickel content and other composition factors — can become slightly magnetic when cold worked.
You may notice “L” or “H” attached to some of the grades. “L” denotes low carbon content, which equals increased corrosion resistance. “H” denotes high carbon content, a sign of increased strength.
2. Ferritic Stainless Steel
This group of 400-series steels contains 10.5%-20% chromium for corrosion protection and resistance to scaling at high temperatures. Heat treating won’t harden them, and they are always magnetic. Carbon content is low. Ferritic stainless is used in cases where resistance to corrosion is key.
Because of its heat resistance coupled with formability, ferritic stainless steel is optimal for welding.
3. Martensitic Stainless Steel
Of the stainless steel types, martensitic is probably the least known.
These steels, also of the 400 series, usually contain 11.5%-18% chromium and have higher levels of carbon than their ferritic counterparts. With its heat resistance, these steels can result in a wide range of useful hardness and strength levels. Martensitic steel is heat treatable but difficult to weld. It’s also magnetic.
Duplex Stainless Steel: The New(er) Category on the Block
There’s a fourth category, too. Newer to the world of stainless steel grades is the duplex category.
Duplex stainless steels represent a combination of austenitic and ferritic stainless steels. Drawing from the best of both metal types, duplex stainless steels boast strength, durability, and improved resistance to chlorides. Using duplex stainless steels — where appropriate — means you won’t have to worry about stress cracking from corrosion or unwanted bending.
Duplex stainless steels are also well-suited for welding and forming.
What Understanding Stainless Steel Types Means to You
Different stainless steel types are made to play different roles in steel tube forming. Make sure your application meshes well with your metal of choice before sending your design to a steel tube manufacturer.
Knowing what stainless steel type is right for your project saves you — and your customers — time, money, and a headache.
Deciding between the two most popular stainless tubing grades, 304 and 316? Check out our guide to their key differences. Need more clarification on what separates 316 and 316L? Keep reading here. Remember, the wrong ingredients can make your project a bad batch from the start.
(Editor’s Note: This article was originally published in November 2017 and was recently updated.)