DIY "hot blued" steel parts
I was skeptical at first, but this turned out really cool! ⬇️
I needed a protective coating for parts on a machine that I'm building. No matter how much I polished and cleaned the steel, it was leaving black residue on the finished product. Hot blueing seems to have completely taken care of that issue. It also looks pretty dang cool.
By heating the part up to the 400-600°F range and quenching in oil, you get a protective oxide layer that prevents "bad" oxidation or rust. At higher temperatures, the oxide layer gets thicker and refracts light differently, resulting in different colors. The final color of the part is dependent on the maximum temperature reached. Since there ends up being more of a temperature gradient when you use an open flame like I did, each part ends up looking pretty unique.
Here are a few things that I learned:
-Boiled linseed oil doesn't smell great, but it also didn't splatter or smoke when I quenched the parts, which was a major bonus in my book. It's also relatively inexpensive. Vegetable oil, motor oil, and WD-40 are other popular choices.
-This takes a while, and with bigger parts I used a propane torch in addition to the camp stove to heat quicker and more evenly. If I'm going to be doing much more of this, I'll need an oven so that I can do a batch and walk away for a while.
-This is probably not a good option for parts exposed to corrosive chemicals or the outdoors, but it's great for indoor use.