Can you forge weld too hot?

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AlaskanHunter

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As I have been working on my brush chopper build, I've been having fits with getting forge welds to stick. I've never had much trouble before, and the only changes that I can pinpoint are the size of my billet (not that big, but bigger than I've ever done before) and a reworking I did of my forge burner to put out more heat. I'm using 15N20. So, is it possible to get a billet too hot (but before sparkler stage) to weld? I've tried dry welds, kerosene welds, and borax fluxed welds. All attempts have been made in a reducing forge atmosphere. All of those methods have had roughly the same results, about a 1/3 chance of sticking. Something I have noticed is that my borax often looks a bit crispy and bubbly just before welding. Am I doing something wrong, or is this just part of the learning curve on welding larger billets?
 
Most smiths forge/forgeweld too hot. It will not prevent welding but will cause excessive grain growth.

Most new guys are impatient and do not give the billet enough soak time at temperature. Less temperature and more soak time = better welds. The bigger the billet the more soak time is needed.

Some steels will crumble if forged too hot.

All steels will loose toughness if forged too hot.

Hoss
 
DevinT said:
Most smiths forge/forgeweld too hot. It will not prevent welding but will cause excessive grain growth.

Most new guys are impatient and do not give the billet enough soak time at temperature. Less temperature and more soak time = better welds. The bigger the billet the more soak time is needed.

Some steels will crumble if forged too hot.

All steels will loose toughness if forged too hot.

Hoss
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If I understand you correctly, you're saying that I may have the outside of the billet hotter than necessary, but the inside still too cool to weld well. My starting billet was 3x8" and about 1" thick. According to my thermocouple I'm running about 2,300- 2,400 F, but that may be a "hot spot" in my forge. I let the billet soak a few minutes after it seems to be about the same color as the forge. Roughly how long should I soak the billet? I've been using Aldo's 1084 and JT's 15N20, this particular billet was all 15N20. Will appropriate normalizing and thermal cycling fix the grain growth, or is the damage permanent once it reaches a certain point?
 
Until recently, mostly 4" hunters, with the occasional 8-10" chef knife thrown in. However the most recent one was a 21" overall length chopper. It has been quite a stretch for my meager skills, perhaps I bit off more than I can chew.
 
I recommend you make shorter more narrow billets. They will heat faster, less area to trap flux, less area to forge weld, and the more you draw it out, the stronger the welds.

I yell at the TV every time a smith on FiF makes a long billet and then is surprised when there are flaws. They would be better off making shorter, taller billets. They always use way too much material.

Hoss
 
I find even a 2.5” thick billet hard to weld by hand, but I have neuropathy. I tried 3” thick, with a little success a few years ago. I’m planning to hand weld my next billets at 2” high, x 1” wide x 4-5” long.
 
You can also fail by striking too hard.
I do pretty good at english, but lacking a better description... Striking too hard squishes the cooler inner layer steel thru the surface layer what may be at proper temperature.
 
2,300°-2,400° seams rather hot. Problem you will get with borax at that temp is it starts to burn (think that’s what happens to it). It will get all hard and crispy and won’t melt. You need to be at the temp where it’s a nice runny liquid and lots of tiny bubbles popping between the layers. If you have fryied the borax then it’s now become a slag inclusion. What do the surfaces look like between then layers that did not weld?
 
JTknives said:
2,300°-2,400° seams rather hot. Problem you will get with borax at that temp is it starts to burn (think that’s what happens to it). It will get all hard and crispy and won’t melt. You need to be at the temp where it’s a nice runny liquid and lots of tiny bubbles popping between the layers. If you have fryied the borax then it’s now become a slag inclusion. What do the surfaces look like between then layers that did not weld?
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It looks crispy black like fried borax in the layers that I've used borax as flux. When I did a dry weld (MIG welded entire perimeter before going into the forge) the unwelded surfaces were surprisingly clean steel - minimal oxidation/scale until open air got to the surface. Sounds like my forge is running too hot, but I'm not leaving it in long enough.
 
Try hot cutting your ends in a bit by pounding the backside of an axe. It will force a weld on those locations, you can then weld only an edge of the steel and pop it open like a folder and pour flux inside, close it gently by pressing down and reheat to temp, from there work from the welded seam out to squish out any scale and flux, reheat and let it air cool then heat again.

Bring it to a close welding temp for your steel and draw it then fold it. Low carbon needs a higher temp the higher carbon steels can weld at a lower temp. It depends on what content you have, the nickle in 15n20 bonds at a relatively lower heat.

In general 3 folds erases any defects from 3 folds previous.
 
A few other things i can add is it helps to thermo cycle your billet do an initial heat remove flux your sides heavy and scrub it in, and then heat, after a weld do a heat flux and reheat. It may seem wasted heats but it will prevent inclusions and thermo cycle your billet allowing the welds to take.

The second peice.of advice i have is check the surface of your hammer, if you have a flat hammer its awesome for beveling and forging angles but you lose the focused impact and it will cause slip planes.
 
DevinT said:
I recommend you make shorter more narrow billets. They will heat faster, less area to trap flux, less area to forge weld, and the more you draw it out, the stronger the welds.

I yell at the TV every time a smith on FiF makes a long billet and then is surprised when there are flaws. They would be better off making shorter, taller billets. They always use way too much material.

Hoss
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So I’m new to all this! Funny you should mention FiF... My boys (and I) are fascinated with the program and it’s become our Friday family night viewing! Now it’s my job to learn the science and understand what they’re talking about so I can explain in layman terms for prima aged kids. My question to you is any suggestions where/what I could read? as I mentioned I’m a complete novice. I don’t need things to be oversimplified but explained completely. Thanks
 
CazJBoyes said:
My question to you is any suggestions where/what I could read?
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I'd start with the sticky threads at the top of the forum.

Sticky Threads - All The Good Info You Want In One Place

The stickies have all been condensed into this new super-sticky. This will free up the top of the forum, but make all the good info just a click or two away. Each will have its own segment, and all the info is still there. Any additional info that you folks think should be added to the...
www.bladeforums.com www.bladeforums.com
 
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Welcome Caz,
As a new member you will see al threads the same. Look at the dates on them before posting a new comment or question. This thread is five years old. The OP hasn't posted in three years. It is best to start a new thread f you have a question than to resurrect an old thread by Necoposting. You can link the old thread if it has info you are asking about.
Also, fill out your profile with your location and some info about yourself. It helps us give better answers and maybe an offer from a nearby smith for a shop visit, materials, or tools.

Dr. Larrin Thomas ,the son of Devin T (Thomas) in this thread, is a noted authority on blade steel and his book Knife Engineering is invaluable for knifemakers. It is about steel and the science of working with it and hardening.
There are dozens of books on the basics of knifemaking around. Some are more current than others. If you want more suggestions on them best to start a new thread.

FIF is fun to watch, but in no way about how to properly make knives. You can pick up a bit from it if you already forge, but it is not a teaching show. Finding a local smith or blacksmith guild is a good way to learn how to forge.

Also, starting with stock removal from a bar of good knife steel is the wisest way to learn. My simple tutorial "How to Instructions for making a knife" is a good read for a new person - https://www.bladeforums.com/threads/how-to-instructions-for-making-a-knife.694673/

You need very little equipment to learn knifemaking . Files and sandpaper, some hand tools, a good hacksaw, and a few simple shop tools most folks either have around or have a friend who has them.
 
Joseph Gardner said:
The second peice.of advice i have is check the surface of your hammer, if you have a flat hammer its awesome for beveling and forging angles but you lose the focused impact and it will cause slip planes.
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Hey Joseph, I struggled a lot with a recent forge weld and as I recall I was using a flat faced hammer, and one of the problems was the steel layers skating across each other after the tack welds I used had failed. I was surprised because I had successfully forge welded that way before.

Are you saying it's better to use a rounded face?
 
Joe last visited the site in Nov 2018. He more than likely won't be answering your question.
Just me, but i use a mildly rounded face and run a bead on each corner and middle of billet.
 
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