The Secret Sauce of Heat Treating

Mark and Flame Ring

Why would anybody write a blog about heat treating? I mean, itís just a means to an end. What you really want is a production line thatís producing parts according to hardness specifications so that in the field, the part stands up to repeated abuse and doesnít fail before its time. For many folks, heat treating in general, and flame hardening in particular, is one of those backroom processes where itís just better not to know. Like making sausage. Or even worse, when you DO try to find out how to make the sausage, the sausage shop wonít tell you whatís in it.

Thatís why Iím writing this blog. Thereís a lot of missing and mis-information out there about heat treating in general and flame hardening in particular. Plus, more longtime heat treating technicians are retiring and taking their experience with them. So the time has come for a blog to get some of that hard (no pun) Ėearned knowledge out to everyone who needs to heat treat a part.

Letís start with the drawing and hardness specification for your part. You get handed that and the responsibility for figuring out how to meet the specs for the hardness depth and pattern. Where do you start? The most reasonable place is starting where you are. You look at what processes you already have that could meet the spec. Maybe your company already uses inhouse heat treatment processes, either carburizing or induction or flame. Itís natural not to want to reinvent the wheel even, or especially, if you have to harden it. But you quickly find out that parts is NOT parts, and one process makes more sense for one type situation than another.

For example, letís say your hardness spec for a gear uses 1018 steel and youíre already running a carburizing furnace and think you could just add this new part to the existing production line of the oven. Sounds good. But the oven will have to be recalibrated to handle this part at the proper temperature, which will take time to do, and hardening the entire gear in the oven runs the risk of greater distortion in the pattern, so you would need to mask the areas that you donít want hardened. So what you might save in material costs with cheaper steel you just lost in increased time and material handling, and at the risk of distortion when the masking isnít done properly.

Your ROI calculation might actually improve if you started with a higher carbon steel, such as 1045, and bought a flame or induction solution to create exactly the hardness pattern and depth of your specified areas. If you have extremely high volume and only one part to set up, induction probably produces the better ROI. But if you have lower volumes and/or you need the flexibility to set up hardening for several different parts, you should look at flame.

Iíve been in the heat treating and flame hardening business for over twenty years, and before that I was working with my dad who started this company over forty years ago. Weíve helped dozens of customers wrestle with these questions and more, and in this blog I want to start sharing some answers about the ďsecret sauceĒ of flame hardening, and not just answers but also some key questions that folks need to know they should ask when they are analyzing heat treating options for their production lines. I guess what Iím hoping to do with this blog is create a place for conversations between novice and longtime heat treater, idle browser and serious production-driven decision maker alike. Letís capture and share as much knowledge about heat treating as possible so it can be passed on to and improved by a new generation of engineers.

So in my future posts, Iíll be sharing answers about solving heat treating issues like cracking or distortion and questions you should ask early in the design process. If you want to ask me to cover a specific heat treating topic or anything related to flame hardening as well, email me at or call 919-956-5208. Happy heat treating!

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