Precision Machining 316 Stainless Steel

Stainless steel is one of the best and most commonly used materials for precision machined parts.

There’s a seemingly endless variety of stainless steel alloys, which makes it harder to choose the best one for your specific machined parts.

Spex uses many different stainless steel alloys to manufacture tons of precision parts. 316 stainless steel is also called marine-grade stainless steel, because it’s highly resistant to water and chemical corrosion. This alloy is harder and more expensive to machine compared to 303 and 304. But, when you need the extra durability, 316 is a good option for machined parts and components.

We’ll provide you with an overview of the 316 and 316L stainless steel, and help you decide if it’s the right choice for your part.

What is 316 stainless steel?

316 stainless steel is and austenitic alloy best known for its excellent corrosion resistance. This alloy is slightly more expensive, but it has all of the benefits of stainless steel: good strength and high resistance to corrosion.

In general, stainless steel is a hard metal, making it more difficult and expensive to machine precision parts. The 316 alloy is an even harder stainless steel, so it might not be your first choice. Special cutting tools and extra care is needed during the machining process.

This alloy is used for parts that require a greater level of corrosion resistance.

To classify different alloys, there are families of stainless steel, and specific grades within the family. 316, and other 300 grade stainless steels, are in the austenitic family. This is the most widely used family across the world. The austenitic stainless steels are made with austenite base, which is a combination of carbon and a nonmagnetic form of iron.

There’s also different varieties of 316, including 316L and 316H. When you’re identifying carbon steel grades, an L usually means there’s lead added to the alloy. However, in the case of 316L stainless steel, the L stands for Low Carbon. And the H in 316H stands for High Carbon.

There is no lead added to 316 stainless steel.

Regular 316SS contains a maximum of 0.08% carbon. 316L contains a max of 0.03%, and 316H contains a max of 0.10% carbon. That difference may seem insignificant, but it’s not. The 316L alloy has even better corrosion resistance than regular 316 alloy, and the higher-carbon 316H alloy is stronger in high temperature work environments.

The higher or lower carbon content only changes the amount of iron in the alloy. So none of the other elements in the 316 alloys are different.

Composition of 316 Stainless Steel

Element	Percentage
Iron (Fe)	62 - 69%
Chromium (Cr)	16 - 18%
Nickel (Ni)	10 - 14%
Molybdenum (Mo)	2 - 3%
Manganese (Mn)	2%
Silicon (Si)	0.75%
Nitrogen (N)	0.10%
Carbon (C)	0.08% (316L - 0.03, 316H - 0.10)
Phosphorous (P)	0.045%
Sulfur (S)	0.03%

Common applications

316 stainless steel is very common–especially for marine parts, and parts that will be exposed to harsh chemicals. 316 stainless steel is commonly used for:

Chemical processing equipment
Laboratory equipment
Marine parts and fittings
Pharmaceutical equipment
Valve and pump parts
Engine parts
Heat exchangers
Appliances and cookware

Because of the added molybdenum, this alloy is ideal for outdoor, marine, and chemical environments.

The chemical resistant properties of 316 make it usable for harsher environments compared to 303 or 304 alloys. Even though 316 is more expensive and difficult to machine, the lifetime of the part makes it less expensive in the long run, depending on the working environment.

Machinability

316 stainless steel doesn’t have the best machinability compared to free machining alloys like 303 stainless steel. The added nickel and molybdenum make the metal harder, which means sharper cutting tools and slower speeds are necessary during machining.

316 has a machining cost factor of 5.6 when compared to standard steel. The machining cost factor is about double compared to 303 stainless steel. 316 is about the same as machining titanium. It can be machined using a CNC mill, CNC turning, or with a Swiss screw machine. This alloy can also be welded or hot formed.

Corrosion resistance

One of the reasons why 316 stainless steel is used is because of the added molybdenum. This element improves the alloy’s resistance to acid environments, alkalis, and chloride pitting.

When 303 is in a moist environment, it forms rust and is subject to rapid-pitting corrosion. That’s why using 316 is preferred for marine applications, and oil rig parts where salt water is present.

Heat resistance

Most stainless steel alloys have good heat resistance. 316 doesn’t have a noticeable higher heat resistance. It actually has a slightly lower melting point than 304SS. But, the 316H alloy that contains a bit more carbon is better for high working temperatures.

You can visit our material page to compare the different options for your next CNC machining project. If you have any other questions about choosing the right materials, reach out to our team.