Heat treat "speed" ???

A

Angus McGunnigl

Joined
May 22, 2002
Messages
1,485
I am using the one brick forge and was wondering what "slow and steady" would mean when heating the blade to non-magnetic prior to the quench.

I have a knife ready, made from a old file(Nicholson).

I have "practiced" heating some scrap steels(mower blades) and it seems that the area near the firehole heats up first. This does make complete sense to me. However, will that area become TOO hot and be damaged in some way??

I know that what I'm trying to do is very basic and low-tech, but I actually think if I can complete this knife, it'll look nice. Maybe it will even cut !

Am I fretting too much ??

Any thoughts appreciated.

Merry Christmas.
 
I heat treat now with my forge at full temp, which is 2200F but I use a combination of constantly agitating the blade through the hot spot trying to keep either the edge or spine positioned to 'cut' the flame so that the heating is even on both sides of the blade; in conjunction to that I pull the blade out while it is 'pre-heating' so that the thinner areas that are heating up quickly don't get too hot and spread some of their heat to the thicker areas, this slow's down the severity of the forges high heat rate.

That's just what I do.

Also do a google search for decalescence, when decalescence is complete, that is when you quench.


If you just sit the blade in one spot and you get a hot spot, bad things could happen, it could crack at worst or only harden where it is hot enough and have soft spots
 
Since you asked I will try and explain the problems here.

A one brick forge is a simple device to heat up steel. It is not controlled or even in its heating. If the blade is constantly stroked in and out of the forge, you will get the most even heating of the blade. A OBF works OK for forging, but has problems with HT.

The hot spot in a OBF is very hot compared to the rest of the chamber. Allowing the forge to run for 5-10 minutes before putting in the blade will help a bit, but the blade will be much hotter in the spot where the flame comes in if it sits still.

A good file is made from a high carbon steel. Normal analysis is similar to 1095 or W2. These steels need a more controlled temperature and soak time than a OBF can easily deliver.

Overheating the edge and spot overheating of the blade is a serious problem with any blade, and especially problematic with high carbon steels.

These problems are not unsurmountable with your OBF, but will most likely lead to a lesser quality blade than using a full size forge or a HT oven. That doesn't mean it will be junk, just not 100% as good as it could be.

Ways to overcome the problems;[/B]

Leave a thick edge on the blade, to allow for removal of a thicker decarb and scale layer on the knife after quench.

Use fast oil, warmed to 120-130F to quench in. Other quenchants may not do the hardening sufficiently.

After running the forge for 10 minutes to heat up the chamber, stroke the blade in and out through the hot spot, trying to evenly heat up the blade from tip to tang. The part of the tang past the ricasso does not need to be hardened, so don't worry about getting it as hot as the rest of the blade. It is the cutting part of te balde you want to concentrate your attention on. Use an extension pick up magnet (HF for $1) to check the blade regularly. As it heats up to a red color, the blade will become non-magnetic. At this point the blade is about 1350F. You want to heat it about 100-150 degrees hotter, so observe the color at non-magnetic and continue stroking as the color gets about a shade or two brighter. Try to maintain this color for several minutes if possible. HT is best done in subdued light, to see the colors better. Bright siunlight will make it nearly impossible to tell the colors.

Quench in one straight plunge,tip first. Move the blade up and down for a count of ten. Pull the blade out and check for warpage ( The oil on the blade may catch fire , don't panic, just wipe it off with a rag to snuff the flames.) Immediately straighten the warps or twists using a hammer and the anvil, a vise, or gloved hands. Do it quickly, as you only have about 10-15 seconds before the austenite starts converting into hard and brittle martensite. If the blade gets stiff while straightening....QUIT or it will snap. Put the blade back in the warm oil and let cool down for two minutes.
As always when heat treating or forging knives, have sufficient fire extinguishing equipment and supplies nearby and have a cover for the quench tank.

Wipe the oil off the blade, gently wash it with dish soap, and immediately put in the kitchen oven which you have pre-heated to 350F. Temper for two hours. After this first temper, you can check the edges, clean it up more, etc., and if all is OK, do a second temper at 350-400F.

Give it a try and see how well it goes.

The first chance you get, build a larger forge with at least an 8X3" cylindrical chamber.

Let us know how it worked out,
Stacy
 
Thanks for the responses. I'm enjoying the learning process.

I'm upping my membership soon and will hopefully have a picture to show.

Thanks again.
 
Take this with a grain of salt. In gunsmithing they say don't let the flame touch the steel when heat treating. Put the steel on a piece of 1/4 plate and heat the bottom of the plate and the parts heat evenly. Many times the parts are small and thin. They are heating with a torch, not a forge. I have a little experience HTing knives and what I do is put a piece of 1/4 x 2.5 inch sq tube 2 ft long in a vice insert the knife / file whatever and heat the botton of the tube with a rose bud. They heat very evenly and I have had good success. My 2c
 
You can try to direct your flame above the blade to get the heat to even out a little bit. You will still have a temp problem but maybe a little less. Also can you put a piece of metel just inside the hole to direct the flame away from the blade? Still keeping the flame inside the brick, this may help.

One last point so guy using a forge put a pipe in the forge and heat the pipe to get more uniform heat distribution, not sure you have the room for that but consider.
 
Stacy mentioned two things that I found really important when using a 1-brick or 2-brick forge for heat treating... subdued light and stoking. As near dark as you can get will allow you to notice color change and color difference easier. The stroking is like painting heat onto the steel. Where there is more steel (thickness), it needs more paint. Working towards perfectly even color end to end and top to bottom is what you are after.

I typically start holding the blade and put heat into the ricasso, flipping sides, turning the blade side ways, trying to keep the blade in the center of the hole so the heat wraps around, moving the blade in and out of the forge almost constantly, moving slower for thick areas and faster for thin.

When color starts showing on the tang behind the ricasso, I switch to holding the tip of the tang and put more heat into the ricasso, but still moving the entire blade in and out of the hot spot and the forge (to monitor color eveness). Usually I'll start seeing more heat in the ricasso than in the blade, soon. As I see difference in color, I work to catch the cooler areas up to the hotter ones. Once the blade comes out of black, a person can't leave the thinner areas in the hot spot very long or they will get too hot, too fast.

When I first started using a 2-brick for heat treating, I ran the regulator almost full open and couldn't keep up with the heat gain (eveness). So I tried too little heat and that doesn't work either. In the end, it's a matter of attention to detail and it really doesn't take a long time or a huge effort to get very evenly heated blades. It does help to be using eutectoid or hypoeutectoid steel but if a person is hard headed enough, W1/W2 and O1 can be heat treated as well as they can be done in easier to work with forges.

Mike
 
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