Many of our customers send us heat-treated hardened steel parts. And we love working with those parts! But if there are any process control issues with the heat treatment that create a carbon-rich surface, this can cause significant problems with the part’s surface preparation and less than desirable results with zinc plating.

We aren’t experts in heat treating, so we don’t know all the things that can go wrong with the process to cause the carbon-rich surface. We do know that one possible reason can be related to the atmosphere in the oven, such as when a crack in the oven inadvertently allows oxygen to enter. We’ve also seen carbon build-up when heat treaters have sent us parts that were improperly oil-quenched.

The photo above shows three different heat-treated parts.

The part on the left is ideal; there are no spots that will pose any problems. However, the other two parts have speckles (middle) and dark spots (right) that are the result of carbon-rich surface. Left alone, these parts will not only remain dull looking, they could become blistered and vulnerable to corrosion. Of course, we can remove these speckles and spots for you, but it would require a secondary process (putting them in our galvanizing barrels where our glass beads can work their magic), but this causes both a time delay and increased costs.

To minimize the odds of these problems cropping up, we would simply suggest that you ask your heat-treaters to ensure that they’re taking the proper steps to prevent carbon from building up on your parts.