Our Guide to Stainless Steel Types for Engineering Applications: Austenitic, Martensitic and Precipitation-Hardening
We want to help you choose the right stainless steel for your application. We know that it can be difficult to remember the differences between the many grades of stainless steel, so we've distilled some of the relative merits and limitations of different grades in this resource written specifically with our customers in mind.
At Automotion Components, we manufacture stainless steel products on our fully automated machines. We can also make bespoke products in a selection of materials to help your ideas come to life!
What is stainless steel?
Stainless steel is distinct from steel - an alloy of iron and carbon - because stainless steel has added chromium (and sometimes also nickel and other elements) that form a protective anti-corrosion layer to slow the formation of rust. Available in many different grades according to differences in the chemical composition and atomic packing of the material, stainless steel is an incredibly versatile metal alloy that has widespread use in engineering applications.
On this page, you can find out more about the unique properties and advantages of different types of stainless steel. Any additional information may be found on our detailed technical information sheet. Click here for a printable, free copy!
General guidance
Advantages of using stainless steel
- Corrosion resistant
- Widely available
- Long service lifespan even with minimal maintenance
- Hygienic
- Polished appearance - also many finishing options available
- Recyclable
Stainless steel has a higher intrinsic value than steel - however, due to its corrosion resistance, when lifecycle cost comparison is carried out, stainless steel is often an economical choice. Stainless steel is cheaper than titanium.
Within the broad umbrella of 'stainless steel', there are price differentials between different types of stainless steel - for instance, AISI 316 stainless steel ("marine grade"; the most corrosion resistant grade) components are more expensive than other austenitic grades because of the higher material and production costs entailed. Another example is precipitation-hardening AISI 630 stainless steel, which is expensive due to the energy costs involved in heat treatment and the fact that it is very hard to machine.
Types of stainless steel
Technical specs
Tables with material properties for six different stainless steel grades (AISI series 303, 304, 316, 416, 440C and 630) can be found on our detailed technical infomation sheet available for free download here.
| Material | Notes |
| Stainless steel: AISI 303 series (Our code: A2) | Austenitic 303 series stainless steel (1.4305) is a machinable stainless steel grade with good corrosion resistance properties. It is supplied in bar form for lathes and milling equipment to produce precision-made components. |
| Stainless steel: AISI 304 series (Our code: A2) | Austenitic 304 series stainless steel (1.4301) is marginally more corrosion resistant than 303 series stainless steel but is supplied in sheet form, rather than bar form. This means that 304 series products must be hot forged. |
| Stainless steel: AISI 316 series (Our code: A4) | Austenitic 316 series stainless steel (1.4401; A4) is an exceptionally corrosion resistant stainless steel grade. It has added molybdenum (2,0 - 2,5%), which helps in the formation and maintenance of the anti-corrosion layer. It can withstand acidic and marine environments. We can also offer passivation and other coatings to protect the anti-corrosion surface. 316 series stainless steel is more expensive than 303/304 series stainless steels. |
| Stainless steel: AISI 416 series (Our code: A6) | Martensitic 416 series stainless steel (1.4005) is a machinable yet strong stainless steel grade. It is a magnetic stainless steel. Customers may choose this grade when they want an intricate product - such as a fastener or bearing - that is stronger than the equivalent product made of austenitic stainless steels. Products made in this material will have lower corrosion resistance than austenitic grades. |
| Stainless steel: AISI 440C series | Martensitic 440C stainless steel is thought to be the hardest of all the stainless steel grades (after heat hardening treatment). It cannot be machined after heat hardening. 440C stainless steel has a relatively low corrosion resistance compared to austenitic stainless steels, although this can be mitigated by the application of protective coatings. |
| Stainless steel: AISI 630 series (Our code: 17-4 PH) | Precipitation hardening 630 series stainless steel (1.4542) has good corrosion resistance and can reach much higher hardnesses and strengths than austenitic stainless steels (although less than martensitic 440C s/s). It has added copper (3,0 - 5,0%) and niobium (0,3%), is not easily machinable, and is therefore relatively expensive. |
What you need to know about austenitic stainless steels:
All stainless steels, and especially the austenitic grades, are renowned for their resistance to corrosion. AISI 303 and 304 series stainless steels are very similar; the main difference is in how they are machined. AISI 303 series s/s is supplied in bar form and is machined into specialist fastenings using lathes and milling equipment. AISI 304 series stainless steel is usually supplied in sheet form and requires hot forging. These grades are both used extensively in construction and automotive applications. Stainless steels can still rust over time, depending on the conditions they are exposed to. Although AISI 303 and 304 stainless steels are appropriate for the majority of applications, if you have an application that may be subject to corrosive conditions, you may wish to consider selecting from our range of AISI 316 stainless steel products or getting in touch to discuss your needs (we can also manufacture components in titanium grades 2 and 5, monel, etc).
AISI 316 stainless steel is a more expensive stainless steel with added molybdenum for corrosion resistance. It is a common choice for applications that may be exposed to corrosive environmental conditions, or to strong chemicals.
In our product numbering and to make things simpler for our customers, we divide our products into the classes “A2”, which encompasses AISI 303 and 304 (am 1.4305 and 1.4301, respectively), and “A4”, which corresponds to AISI 316 (am 1.4401; marine grade). You can find the exact AISI/am specifications in the technical notes for each of our products. Do not hesitate to contact us for written confirmation regarding the dimensions and/or material class of any product you are interested in. Austenitic stainless steels are not inherently magnetic, but can be mildly magnetic after machining and/or processing.
What you need to know about martensitic and precipitation-hardening stainless steels:
If you are looking at products made from martensitic or precipitation-hardening stainless steels, it is likely that the product has been built to withstand heavy loads and/or wear. These grades of stainless steel exhibit superior hardness and strength profiles as compared to austenitic stainless steels - this also makes them quite difficult to machine. These types of stainless steel are magnetic. Due to lower corrosion resistances than austenitic stainless steels, they are best used in clean, dry environments, although a protective coating may be applied to overcome this limitation. Please enquire about finishing options that include protective or decorative coatings.
The exact strengths and hardnesses of these steels depend on how they have been heat treated. You will usually find more information in the product specifications, but if you can't find the measure you are looking for, or if you wish to double check the product's specifications before you order, please contact our sales team, who will be happy to help. We are constantly working to update our pages with more detailed information for our customers.
Applications
Featured products: examples of our engineering products in austenitic and martensitic stainless steel
Captive thumb screw in stock in AISI 303 and 316 series stainless steel. Titanium version also available (more expensive). This is a special thin diameter version, also available with a black finish. See our range of captive screws here.
Stainless steel levelling feet with grippy rubber pads are ideal for laboratories and/or medical settings, among other things. Shown here in 303 series stainless steel; 316 series stainless steel available on request. See our range of anti-vibration levelling feet here.
Slot head shoulder screw in AISI 416 series stainless steel. Hex drive version also in stock (P0131). This product is also manufactured in 303 and 316 series stainless steel (P0130). See our shoulder screw range here.
This linear rail set has to withstand very heavy loads. Therefore it is made from the extremely strong 440C series stainless steel, hardened to HRc 60±2. Nickel plated for extra resistance to corrosion. See more crossed roller rail sets here.
