Thread: Insufficient heat for hardening?

Hi folks,

I am half-way through my first razor attempt (4 at once), but I think I have discovered some troubles with my heat treat efforts.

I built a small forge out of fire brick and castable refractory cement, and got myself a Bernzomatic 8000 torch head, which pokes in through the side near the rear. I have a thread going in the Workshop called 'Another Newbie'.

My issue is that I think I have insufficient heat. The forge chamber is just under 2" wide and just over 2" high, and I have tried to use a piece of mild steel flat stock as a tray to hold the razor edge-up in the forge. I heated one razor with propane and just barely reached a red glow, but I think it didn't soak far enough toward the heel or the spine. After quenching in warm vegetable oil, a file seemed to skate over part of the blade but grabbed near the heel. Same on razor #2 when I used mapp gas. It was probably about 15*C outside (50*F) so I may have been fighting uphill.

I'm wondering if I should try to reduce the size of the chamber, get rid of the metal tray, or anything else. Since I was running the forge on the bbq grill, I may try leaving one side on to heat the general area in case the fire bricks aren't insulating enough. Anyway, any ideas are welcome.

The standard way to determine when you are at critical temperature, is when the steel becomes non-magnetic. A cheap pickup magnet works fine. Leave the blade at critical temp for a couple of minutes, and then quench. You can use this test to see if you are getting high enough temp in your forge. You should be able to get up to temp with map gas. Good luck, and keep us informed.

Based on your description, part of the edge was at the correct temperature. The key is to have a uniform temperature over the intended portion to harden. Skip's recommendation for a magnet test will also help you develop the necessary judgement of color since you arent' dependent on a thermocouple or other measurement. Color is just fine as long as it's above what your steel requires to harden. I might suggest holding the razor with tongs and moving it within the hot spot inside your forge to help the heel and toe attain the same even heat that the belly of the blade did. So as your eye judges the toe is too hot, remove it from the heat and allow it to cool down. The heel will continue to pickup heat as the toe cools (conduction), then back in the fire and allow the whole blade to heat evenly.

Getting all this right on a small sample (you've only made a few blades) is a coincidence. Once you've done a hundred you'll have learned a lot.

Could it possibly be something with how you quenched the blade?

Or perhaps the torch is not powerful enough to bring the entire chamber up to a high termperature?

Originally Posted by dcraven

Could it possibly be something with how you quenched the blade?

There could be a number of factors that make it possible for the quench to be the problem. Steel hardens in the quench at the speed of sound (see John Verhoeven's book on heat treatment). First it depends on the steel being used. That hasn't been mentioned yet. But if the operator was too slow in getting from the heat to the quench tank, the heel could have cooled just enough to miss the hardening curve. And Bruno's point could be a correct influence too, the heel may simply have not gotten hot enough while the speed from heat to quench was enough.

It depends. Variables are always the things that make a puzzle more interesting.

Crap. Tried the next two with mapp gas. They're from O1 bar stock.

I heated them until I could see a dull glow that wouldn't get brighter. I could get a brighter glow by placing the blade right in the torch path, but that only warped one of them.

Both are being scratched by my file at the cutting edge for sure.

My quench was warm vegetable oil, but it never flared up. Not sure if I was too slow, but it seems hard to be faster. Here are a few pics.

I am also learning about the importance of wide shoulders... So that the hone doesn't catch and change the angle at the heel.

I didn't expect the grind to done on these before heat treat but I went a bit too far on the grinder. As such, I took both blades to the King 1200 to see how the lines look and they are pretty wobbly!

Scratches from the file. Could my file be too new or too hard? Cheapo.

The file is cutting.