Over heated?

[spareparts]

A beginner here and to make it worse I live in an upstairs apartment so I can't really get/store/use good equipment.

Anyway I attempted to heat treat my second blade tonight. First one actually turned out ok, I think. I think some of what was wrong is my little homemade forge isn't large enough to handle the length of the blade I was trying to do, the first knife was much smaller and fit in it just fine. The front half of the blade was visually much hotter than the near the handle and I had to leave it in for quite a while before I reached the non-magnetic stage on the blade closer to the handle. By that time the front half of the blade had been beyond that stage for a while.

The steel was 1095 and after quench I noticed many stress cracks in the steel. I also quenched with salt water because a bucket of water is much easier to deal with in my apartment than a bucket of oil. So I went ahead and took a hammer to it to see what was going on inside.

In the first pic I noticed that the grain size was very large and has a sparkle to it when held in the light. In the second pic the grain size is much smaller and more of a dull gray cast to it.

I know I have a long ways to go but thought I'd see if the larger grains were caused by too much heat or the quench media? Had I gone ahead and tempered this blade would it have shattered anyway? I'm assuming that the grain structure in the second photo is closer to what I should be seeing? Any help appreciated.

 

[JasonSCarter]

Yep thats an over heated blade right there! It is possible to fix the grain structure when it over heats like that but it takes lots of time and patience. and most imprtantly Temperature control. Read about normalizing in the stickies. this will be how you refine the grain back down. the second pic's grain size dont look to bad. Just remember there is always room for improvement!

Jason

 

[Stacy E. Apelt - Bladesmith]

Read the sticky, "Working with Three Steels'. It will explain why the steel you chose was the wrong one for your setup. Try a different steel next time.

 

[deker]

I'll agree with what's already been said. Also, the grain growth is a direct result of temperature. The quench medium has nothing to do with grain colony size. If you're going to be using a brine quench, you may want to look into a slightly hypoeutectoid steel like 1050 or 1075. You'll have less to worry about (though brine quenching blades will always be a worrysome process).

Also, I've got a couple of suggestions for working with a small forge:

• From the sound of it, you had the blade in tip first and were waiting for the rest to come up to temp. This is going to cause nothing but what you've already experienced here. My suggestion is to make sure that you have a forge you can pass something all the way through. This way, the tip can be passed out the rear of the forge to keep it cooler until the rest of the blade is up to temp.
• Start heating the tang end first. It has more mass and will take longer to heat. If you get the tang/ricasso areas heated first you will find less trouble in getting the rest of the blade to temp since the heavier parts of the knife won't be acting as a heat sink and stealing the heat from the thinner bits.
• Always keep the piece moving as you heat. This will help avoid hot spots, etc. Just move the whole piece back and forth (or even in and out) f the forge as necessary to keep the heating even.

Good luck and let us know how the next one goes!

-d

 

[Tait]

Heat treating is hard enough to do with a good, digitally controlled kiln.

I was using a torch and thought I had it right - when the hardness tester showed up, I learned I was way off!

It might be a good idea to focus on shaping the knife and send it off for heat treatment when ready - I'd hate to lose a knife because I didn't have the right setup.

 

[Atlas Knife Company]

Excellent pictures of different grain sizes. I'd agree with Deker that you need to keep the blade moving. That's how I was shown how to do it in a forge at Ashokan. They would also pull the blade out repeatedly to let the edge cool down. Since it is thinner it overheats quicker. Letting it soak, motionless, could lead the edge to overheat and the spine to be good.