The Different Grades of Stainless Steel

Depending on the requirements of your job, you have to choose the right tools. Yet, it's just as important to choose the right grade of stainless steel for your parts in order to ensure strength at varying temperatures, corrosion and oxidation resistance, and even the finished appearance you want.

That's why we're going to take a deep dive into the different grades of stainless steel, clarify which grades are best depending on their purpose, and discuss how stainless steel is classified.

Here is your complete guide to stainless steel:

Why use stainless steel?

Stainless steel is chosen for a multitude of applications due to its corrosion resistance. Since corrosion is a significant factor in the failure of parts, stainless steel adds reliability and durability.

What is stainless steel?

Stainless steel is a generic term referring to an overall category of steel. In truth, stainless steel is any iron-carbon alloy that contains a minimum of 10.5 percent chromium and a maximum of 1.2 percent carbon. The chromium in the alloy is what gives it the corrosion resistance and durability for which stainless steel is best known.

Stainless steel grades and performances

In the following chart, you'll find a breakdown of the different grades of stainless steel, as well as their most common uses.

Stainless Steel Grades

Grade	Category	Characteristics	Uses
200 series (201)	Austenitic	Contains chrome, nickel and manganese and features high work hardening but less corrosion resistance.	Clamps, door hardware, hoses
301	Austenitic	Withstands severe forming methods due to strength and ductility. Good weldability and can be hardened through machining.	Automotive components
302	Austenitic	High hardness due to carbon levels plus strength and corrosion resistance.	Food and drink applications
303	Austenitic	Easily machined with the addition of sulfur and phosphorus. Less corrosion resistance than 304 grade.	Fittings, bushings and gears for aircraft, , nuts and bolts
304	Austenitic	Most common grade of 18/8 steel, providing improved toughness and corrosion resistance under non-marine conditions.	Grills, kitchen appliances, internal parts, outdoor kitchen cabinetry
309	Austenitic	Offers improved temperature resistance compared to 304 grade	Parts used in heating
316	Austenitic	Anti-chlorine corrosion resistance due to addition of molybdenum.	Food industry, surgical equipment, marine steel for swimming pool and seawater applications
321	Austenitic	Lower risk of corrosion of weld joint due to increased stability provided by titanium.	Aircrafts
409	Ferritic	Resistant to corrosion due to automobile exhaust.	Most common for auto exhaust pipes
410	Martensitic	Resists wear but provides poor corrosion resistance.	Bolts, nuts, screws
420	Martensitic	"Blade-grade" stainless steel.	Surgical instruments
430	Ferritic	Easily formed but offers poor temperature and corrosion resistance	Decorative items and car accessories
440	Martensitic	High strength and hardness	Razor blades, knives, ball bearings

In addition to grades of stainless steel, you'll also find

500 Series – Heat resisting chromium alloys

600 Series - Martensitics precipitation hardening alloys

Ferritic/Austenitic Combinations – Including UR52N and 2205 often used in the chemical, petrochemical and marine industries.

Stainless steel structure

As you may have noticed, the grades of stainless steel are divided into three categories: Austenitic, Ferritic and Martensitic. This classification depends on their structure and composition. The three types will have differing levels of the elements carbon, chromium and nickel. Each element confers its own traits on the steel.

Carbon can work to boost the stainless steel's mechanical properties. However, if the levels of the element are too high, it can also decrease corrosion resistance. Chromium on the other hand is highly corrosion resistant. Therefore, stainless steel with higher levels of chromium can be relied upon when corrosion is an issue. The nickel found in stainless steel works as a stabilizer which preserves its austenitic structure and normal temperatures.

Let's take a quick look at the three different categories of stainless steel.

Austenitic stainless

The only non-magnetic stainless, austenitic stainless steel makes up the majority of stainless production. It also offers a high level of corrosion resistance with levels of nickel that allow it to maintain an austenitic structure.

Ferritic stainless

Although corrosion resistant thanks to its chromium levels, ferritic stainless is less durable than austenitic grade stainless steel because it lacks nickel.

Martensitic stainless

With high carbon levels, martensitic stainless is strong, yet less corrosion resistant due to low concentrations of chromium.

Composition of stainless steel and choosing the right grade for your needs

Changes in the composition of stainless steel can also affect its traits. For example, added molybdenum or nitrogen improves corrosion resistance, while manganese acts as a stabilizer.

Because of these changes in structure and composition, different types of stainless steel play very different roles. Choosing the right type of stainless steel can save you or your clients both time and money down the road.