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A guide to machining stainless steel

Stainless steel is one of the metals APT regularly machines. But what is it used it for, what makes it a good choice of material and how do we machine it? In this article, we’ll explain what stainless steel is and why it could be the right choice for your products.

Connector Valve - Stainless Steel | Hydraulics

What is stainless steel?

Stainless steel is an alloy of Iron with a minimum of 10.5% Chromium and variable amounts of Carbon, Silicon and Manganese.

The Chromium gives stainless steel its anti-corrosion properties, by creating a layer of oxide on its surface. The higher the Chromium content, the better its resistance to corrosion.

There are five types of stainless steel:

1. Austenitic

These are the most common kind and have Nickel, Manganese and Nitrogen added, so they can be welded and formed more easily. The Nickel also helps to increase their resistance to stress corrosion cracking.

The steels are work hardened, which makes them strong and tough, but also pliable. They may be slightly magnetic, depending on their composition and how they’re worked.

2. Ferritic

Ferritic stainless steels contain a higher concentration of Chromium and a little Carbon.

The high Chromium levels make them more resistant to stress corrosion cracking, but less pliable and able to be formed. The steels also lose their toughness when welded.

Adding Molybdenum means they can be used in more harsh conditions, such as sea water. These steels can’t be hardened with heat treatment and are magnetic.

3. Duplex

These steels are around a 50/50 mix of the austenitic and ferritic types, which makes them stronger and more resistant to stress corrosion cracking. They are also magnetic.

4. Martensitic

Like ferritic steels, these are high in Chromium, but have higher levels of Carbon, which means they can be hardened and tempered. The steels are magnetic and offer high strength and moderate corrosion resistance, but are not generally recommended for welding or forming.

5. PH

PH stands for Precipitation Hardening. It refers to the heat treatment technique that’s used to give these steels their high strength. The strength is intensified with the addition of elements such as Aluminium, Copper and Nobium.

PH steels can be machined into more complex shapes without risk of distortion. Their corrosion resistance properties are similar to those of standard austenitic steels.

What is stainless steel used for?

Stainless steel has a wide range of applications, from domestic kitchen accessories to international transport.

APT machines all grades of stainless steel for a range of engineering sectors.

The three we most commonly use are:

4305 (303) a cheaper stainless steel, mainly used for general applications such as bolts, fasteners, springs and wire.
4301 (304) a heat-treatable stainless steel, used where strength and toughness is a main requirement.
4401 (316) a high-class austenitic grade, used in food and hygiene applications, such as food processing, brewing, water treatment and pharmaceutical equipment.

Why do customers choose stainless steel?

Fire and heat resistance

Stainless steel is resistant to elevated temperatures and pressures.

Corrosion resistance

It offers exceptional corrosion resistance, which means it can be used in a variety of environments. Highly alloyed steels can even resist corrosion when exposed to acid and alkaline solutions.

Premium aesthetic

It’s available in a variety of surface finishes. It has the look of a premium product and maintains its appearance.


It offers exceptional strength, even at a reduced thickness. Often used in Aerospace applications.


It’s easy to clean and maintain, so it meets the sterile hygiene requirements of the food processing, water treatment and pharmaceutical industries.

How is stainless steel machined?

APT has several processes for machining stainless steel. They include:

Mill Turning, for machining different shapes.
Threading, to create a variety of screw threads.
Boring, to make cylinders, pipes and assemblies.
Broaching, for machining holes, teeth and keyways.
Burnishing, to improve the surface of the metal.

Do you need stainless steel components?

APT specialises in stainless steel components for a range of applications, including those where high strength, sterility and anti-corrosion are of particular importance.

To find out more, or get a quote for subcontract manufacturing, please call the team on 0116 287 0051 or send a message using the enquiry form on our contact page.