Unless your production line already has been using a specific type of heat treating, your design solution will have to analyze which of the three typical heat treating processes best fit your application: flame, induction, or furnace, or some combination of the three, or some additional step. If you are new to heat treating, the number of possible options may seem overwhelming. How can you choose the best one?

Let’s step back and drill down a little here. Heat treating can mean many things, from dropping an entire part into a furnace and quench, from progressive flame hardening that moves over a tiny area heating and quenching in the same cycle. Different heat treating methods produce various depths and hardnesses according to specifications. A more precise term than heat treating, often used interchangeably with “flame hardening,” is “case hardening.” Case hardening describes a method of heat treating that results in a certain depth of hardness on the surface of a part, “encasing” the area. The part is not heated all the way through the way you would see in a furnace for tempering. Case hardening produces a hardness level at a specified depth – ¼” for example, for a hardness of 60 Rockwell using 1045.

So in this blog I’m just going to talk about methods of heat treating that you would use for case hardening. As a maker of flame hardening equipment, this is the method I am most familiar with. And you can use either flame induction or furnaces in a case hardening application. I’ll give some general guidelines for when to use each.

Flame hardening is a localized case hardening process. It’s suitable when you need only a certain area of a part hardened while the rest of the part stays in its original state. Induction is also a common solution for localized case hardening. Induction uses electrical resistance coils to reach desired temperature for case hardening; flame uses fuel gas and oxygen.

Some people think induction produces more consistent results. That may be the case if the heat treater uses just a welding torch and tank of water and calls it flame hardening. But when you invest in a turn-key flame hardening solution that’s designed and built to spec, such as the equipment FTSI builds, you get the types of controls that ensure quality and consistency no matter who operates the machine. Anyone can produce consistent results that meet spec.

As I’ve noted in a number of other places, we generally see clients get the most payoff with induction when they are running large volumes of the same parts. Flame gives the best ROI with smaller volumes and/or a large variety of parts.

Clients often choose furnaces for applications that heat the entire part, but they can also use a furnace to do localized hardening by masking off areas that they don’t want to harden. Carburizing adds carbon to the steel which increases the hardness in the exposed areas. Because furnaces tend to heat the entire part and then quench, you run the risk of introducing more distortion. The less heat you put into a part (localized), the less the part heats up so the less potential for distortion.

We also see combination heat treating where clients use a process of carburization and then flame harden a specific area.
Other heat treating methods you may run across include laser hardening and electron beam hardening. These methods are especially suited for small parts that don’t require a lot of depth.

From an engineering standpoint, you have to figure out the best method for your application. Localized heat treating works much better if you do more machining in the softer areas after the case hardening is done. Frequently we see that some areas of parts need to be more flexible (softer) than others to maintain the needed base structural properties of the whole.

As far as costs go, running parts through furnaces tend to be the least expensive method since many parts can be run through a furnace at the same time. Many heat treaters charge only by the pound for furnace hardening.

But when a part needs localized case hardening, the equipment becomes more expensive and time consuming. The machines need to position parts exactly right and use the flames or coils that heat exactly the specified area for hardening.

I hope that gives you a starting point for a good overview of different heat treating methods and when they’re most likely to be used. There is so much to think about – and many clients we see don’t always have the time or personnel to do all the testing and engineering they would like. A good service provider will help you. As always, if you have any questions about designing your heat treating solution, email me at mark@flametreatingsystems.com or call 919-956-5208.

B13: We want to know your opinion.