What is involved with heat treating steel

PineRidge · Feb 15, 2006

I know it's a broad question, so let me give you a few facts.

I'm in the middle of a project and I need some 6' X 7/16" hex steel to be used as a push-rod hardened so that it won't easily flex.

I purchased several lengths of 4140/4142 chrome moly steel in the annealed state. After I'm finished machining and welding it, is it possible for me to do the heat treating or is this something best left to the professionals? Please keep in mind that these are 6' rods, so they are not easily thrown into a bucket of oil for quenching.

I only need to heat treat the steel rod to help eliminate some of the flex, I am not concerned with wear like you might get on a crankshaft.

CurlyDave · Feb 16, 2006

Please keep in mind that these are 6' rods, so they are not easily thrown into a bucket of oil for quenching.

I can't help with how to heat them, but you could easily make up a piece of pipe with a pipe cap to hold oil for quenching. Put the open end of an 8' piece of 3/4" pipe on a sawhorse and the closed end on the ground.

I would be careful about hot oil spurting out of the pipe when putting a red-hot steel rod into it.

I doubt you will get a professional-quality result, but it doesn't sound like you need one.

If you are just looking to reduce flexing, why not use larger diameter steel tubing instead of solid rod for the part? Same weight, much greater stiffness.

Egon · Feb 16, 2006

Make a trough to place the rod in. One could use a stip of galvanised metal etc.

There may be a chance you end with a brittle rod.

Egon

PineRidge · Feb 16, 2006

So you guys are recommending oil quenching over air quenching? I mentioned oil but wasn't sure that was the correct method to use for chrome moly.

MossRoad · Feb 16, 2006

Here's some good reading on heat treating. Hope it helps.

PineRidge · Feb 16, 2006

A lot of good information there, thanks MossRoad.

jmc · Feb 16, 2006

If you are only interested in stiffness, I don't think heat treatment will help.

The material spec on stiffness is "elastic modulus". Look it up for your material and see if it changes for the various hardness states.

Hardening will definitely improve yield strength and ultimate tensile strength. These improvements only allow the part to flex MORE before it yields or breaks. That's not the same thing as being stiffer.

John

Spiffy · Feb 16, 2006

If you have a local shop than can do it I'd opt that route,

If you're trying to combat column buckling, you'll get the best effect if it's treated as evenly as possible. If you get some heat indicator sticks and build yourself a long skinny forge, this may be possible.

Maybe this doesn't need it [just dead load?] but I just don't trust steel unless it's had a little tempering [also needs fairly precise heating]. If you have any impacts, they'll find the pure brittle spots.

So a little planning and equipment gathering could perhaps make the DIY a good option, but if you can find a shop with a 6ft forge or oven that'd be my first choice.

Spiffy · Feb 16, 2006

Just reread, and realized by talking about the negative effects uneven properties could have on column buckling, I may be encouraging a misconception.

Like others mentioned, you really have to look at the elasticity in buckling situations, and you'd probably have the most gains if there is any way to increase the size of your stock.

3RRL · Feb 16, 2006

That link that MossRoad gave has good information in it. I work a lot with 4140, using it for holder block (mold base steel) for plastic injection molds. I buy it in that hardness (around 32Rc/35Rc) and machine pockets, etc for the mold inserts that go into it. That's usually the most common heat treat for that type of steel.

You can further heat treat it by case hardening it where it will become "stiffer". Case and carburize 1/16" deep will give you an outer layer that's super hard (about 60Rc) with interior remaining at about 35Rc. It will increase all aspects of its strength...tensile, elasticity etc. But it will also be more brittle on the casing.

This I would send out to a heat treating shop because the tempering of ANY steel is the most critical and I doubt you can hold temperatures at length of time required to obtain what you desire. Just quenching after heating without tempering will give you a rock hard, super britlle piece of steel.