One of the benefits of working with stainless steel is its resistance to corrosion. Unfortunately, some people experience issues with stainless steel fasteners and wonder why their fasteners are breaking or getting nicks like cheap screws from the dollar store. Why isn’t this robust metal holding up?
It’s actually the fact that stainless steel is built to avoid corrosion that makes it more susceptible to thread galling. The varied grades of alloy create an oxidized surface to protect it from corrosion, but when pieces of stainless steel are compressed tightly together – especially if they’re the same grade – it is nearly impossible for the atoms to differentiate themselves from one piece of stainless steel to another, so they fuse and create some of these problems:
- A bulge forms on one of the two surfaces due to the transfer of atoms. As the friction between the fasteners increases, this bulge grows and damages underlying metal.
- Threads (either male or female) can tear away from their host piece of stainless steel, completely breaking the fastener or the tool responsible for turning it.
- Molecular level-problems, which are not visible at all to the naked eye, can cause a bolt’s threads to seize or to twist off completely. Your supplier claims there’s nothing wrong with the product he’s selling you, but you continue to have these annoying instances where molecular-level problems quickly expand into something that can damage an entire machine.
Does any of this sound familiar?
Fortunately, there are ways to avoid stainless steel thread galling on your fasteners:
- When you install the fasteners, slow down the RPM speed.
- Coat individual pieces of stainless steel – especially their threads – with a lubricant and keep them well-lubricated as time and use wear on.
- Use different alloy grades for the different pieces of each fastener. Because the materials will have a different hardness, they’ll be less likely to fuse with one another.
Below is a list of common causes of galling and prevention steps.