I decided to break it instead

[3fifty7]

I've been at this as a hobby for about 2 years now but with a limited amount of free time I've only been able to forge 15 knives. The majority of them have been 6"-8" hunter/camp knives. I wanted to do something larger this time so I sketched out a 16" chopper.
I started with some 1075 from Aldo. When I forged it to shape, I knew I was on the thin side, then rough ground it preheat treat. I thermal cycled it 3x then heated, quenched and tempered. I picked up a slight warp but was able to get it down next to nothing. After I did a post heat treat grind I really saw how thin it was. I was .09 at the spine with a full flat grind. I added some jimping and a finger choil thinking I would give myself a secondary handhold if I wanted to choke up on the blade. Well I hated the jimping so I ground it out, creating a thin section between it and the choil. I really did not like the blade at this point so I did the minimal finishing and put a garbage handle on it. I could have reprofiled and finished it as a BBQ slicer or something, but I decided to break it instead.
I put a quick toothy edge on it and started to swing. First I chopped 3 slats off of a pallet and chopped twice into the side of the pallet and hit a nail both times. Then I took 6 hard swings into the rim of a 30gal plastic drum. I chopped 6 pieces of 1" sch 40 pvc pipe, I chopped into the bottom of an empty coke can and sliced through a quart Gatorade bottle. The straw that broke the camels back was a 3/16" copper strand I've used as pin stock, it was on a solid table and I chopped it once but the second chop it went TING !

The blade finished at 16"OAL, 10" blade. 1 5/8" height, .09" at the spine. Just under 1" height between the choil and area where I ground the jimping out.

 

[Jsega51]

At least you had fun with it! Seems like it still took a fair beating as well.

 

[BenR.T.]

That grain structure is HUGE! You want to re check your cycling, and hardening temperatures and how you are measuring them.

A blade that thin with the right heat treat will still function just fine, something went wrong it appears.

 

[3fifty7]

I'm measuring with a hope and a prayer at best.
Seriously though a pyrometer of some sort is in my short list (Just after a class I'm trying to schedule in the next month).
I cycled 3 times to nonmagnetic red/orange to my eye, then let it cool to black. For the quench heat I held the blade in until it was orange/yellow (about 30-45 seconds beyond the red/orange I cycled at). Then into warm canola and straight into tempering oven 400f 1 hour, twice.

Possibly too hot when going into the quench?

Thanks for taking the time.

 

[gudspelr]

It’s always good to test what we do. I haven’t used 1075, but I’m sure some of the great smiths on here will help you out with some temps/procedures moving forward. With that said, I’m going to venture a guess that you definitely over heated it. If I’m approaching yellow heat, that’s a long ways over the necessary temp I’m shooting for. It may be worth cutting some “coupons” and use several of them to test whatever some of these guys give advice on. Then you can break them after heat treating and see where they land with the equipment you’ve got. Hope you get things dialed in to where you want them. It can be frustrating at times, but it’s part of the journey and you become that much better because of it.

Jeremy

 

[TK Steingass]

I'm measuring with a hope and a prayer at best.

I agree with Ben - your grain structure is too large - this is due to inadequate grain refinement after forging.....your normalizing temperatures are too high. Do you lower the lighting in your shop to get an accurate representation of the colors?

Another thought - your technique may be a little off - you may be getting the ends of the forging too hot in the forge while waiting for the center (end to end) to color. When the ends come to color - take the blade out of the forge and heat the center of the blade on the forge exit to get the center the same color as the ends.

Shoot me an email if I'm not clear and we can discuss. You may want to go to the knife makers forum to discuss this in depth. Good luck - you'll get it!

 

[3fifty7]

Thanks, when I started I focused on forming, shape and cutting ability. Toughness has not been an issue until I pushed this one. Hopefully I'll get into a class soon and improve my understanding of heat treatment and temp control.

 

[Ben Seward]

Try this method...after forging heat to above critical and let cool to black then do three cycles of holding it at 1100-1200 degrees for 4-5 minutes, letting it cool to black between heats. In total darkness this will be the point that the blade is just starting to show color. It will take alot of in and out of the forge to get it right. For the quench bring the temp up slowly (in a darkened shop) until the thickest part of the blade is non magnetic. Obviously the thinner cross-sections will come up to heat quicker but in and out of the forge works. It helps to be able to put the tip out the other side. You can also put a pipe through the forge to help with hot spots. I temper around 400

 

[3fifty7]

Thanks again, I hope to give it a try next week.

 

[Augus7us]

For normalizing in a forge look up decalescence and recalescence. If you don't have a precise temperature control this can help, at least you know you are hitting the right temps. I was taught this by Mastersmith Timothy Potier, but its been discussed here.

-Clint