Once you know you need to harden a piece of steel or cast iron, how do you go about designing the right application for your needs? There’s a lot of ways to go about it: inhouse or outsourced, build something yourself or buy it from a vendor, induction or flame? This next series of blogs will explore those design considerations we hear most often from clients who are looking at cost-benefit analyses of the flame hardening component of their production lines.

All of us are often guilty of being unable to see the forest for the trees. Many clients overlook the most crucial part of a heat treating solution: what is the material being hardened? Picking the material for the piece in question constitutes an engineering problem in itself. Availability of the material, its cost, the form in which it’s delivered, all factor into picking the most suitable material for your application. But the engineer needs first and foremost to understand what the part is going to do. For example, say your heat treat spec wants 55 Rockwell and the engineer chose a 1018 material. You’re not going to get 55 with any kind of heat treating of 1018. The mid-30s is about as good as you’ll get. As I’ve said before, the quantity of carbon determines the level of hardness for a material. (For More: Link to my previous post, “Goldilocks Likes It Just Right And So Do We”)

That means you have to know why you need the area hardened to the level specified. Is it a question of durability or how long and how well it wears? How does the wear occur and what will that material be? For example, crane wheels travel over rails. The wheel and rail both experience wear. Since wheels are easier to replace than the rail, you want the rail to be harder and the wheel softer so that it’s the part wearing out over time. If the rail is at 55 Rockwell the wheel should probably be around 45 Rockwell.

Of all the materials we’ve seen at FTSI over the years, 1045 and 4140 steels produce about the best response to flame hardening. 4140 can get to 44-56 RC at three-sixteenths to a quarter of an inch; 1045 can get to 60-62 RC at an eighth of an inch. To design an effective heat treating solution, knowledge of the material, and why it’s being used, must come first.

After that, you need to analyze the geometry of the part. The heat treating equipment has to be designed around its geometric requirements. Where is the main mass of the part? Are areas of small mass being hardened? The mass determines the speed of both heating and cooling cycles, and how they can be applied.

To use the crane wheel example again, often flanges on the treat area get hardened. You cannot harden the flange all the way through or it can crack in the field (link to previous post). Realizing how thick the flange is tells you how much heat you can use. A thin flange requires a flame head designed to limit the amount of heat applied to that area so you don’t heat it all the way through.

Another example might be a gear tooth in a spin heating application. A very small gear tooth heats up very quickly, and quenches very quickly. A fast quench, if you remember, can also cause cracking. In this case the geometric specifications require a high-polymer quench material to slow down the cooling. Contrast those specs with the ones for a massive, solid 4140 steel part like a crane wheel. Because of the amount of mass, the wheel absorbs so much heat it naturally slows the cooling process. In this case a high polymer quench solution won’t be necessary.

Incidentally, documenting your quench temperature and its concentration, and the temperature of the heat treated area, and flows of fuel and oxygen, all would be required for any facility wanting to be ISO-certified.

Next week, I’ll continue our design discussion with tips for facilities, utilities, and materials handling for heat treating. As always, if you have any questions about designing your heat treating solution, email me at mark@flametreatingsystems.com or call 919-956-5208.

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