Low Temp Forging guidence

SinePari

SinePari

Joined
Oct 24, 2013
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906
Up until recently, my experience in forging has been limited to 1018 and A36 steels. Hot working these higher carbon and alloy steels requires quite a bit more elbow grease than the former medium. I've been doing my homework and reading up on the many options I have available to me when it comes to forging a blade. The only thing that seems to remain consistently crucial to every steel is the heat input and heat treatment; you end up with garbage if you ignore one, the other, and especially both. I understand that some steels are more forgiving than others, one coming to mind is 5160... Stacy's three step process in 5160 grain reduction/ then quench brought me to this question. Granted I was working with a leaf spring, not knowing it's true composition, that little tidbit from raised a great bit of curiosity, and I've been reading up on the proven theory since.

When it comes to forging a blade of known steel, would I benefit from utilizing a controlled temperature furnace as a forge?

The industrial heat treat oven I'm working on getting back into service seems to be a legitimate workhorse when it comes to the rigors of heavy use, and I like having that kind of control over heat input. I would probably work multiple blades at a time, cycling through them in order, enabling them to return to forging temps after each heat. An added benefit hear would not having to worry about overheating the blade, because upon reaching the desired forging temp, they would just soak. Any input will be well received and appreciated.

** The catalyst to this question comes from Ed Fowler's Knife Talk 2; "Uncover the Secrets Hidden Beyond the Blade" (pg. 116)
 
I suppose if you are doing multiple blades at a time it would be nice to make a pid controlled forge. but when forging just one blade it's not absolutely critical.
 
Daniel Rohde said:
I suppose if you are doing multiple blades at a time it would be nice to make a pid controlled forge. but when forging just one blade it's not absolutely critical.
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It's definitely not an issue when gauging heat by color when it comes to plain steel, but from the chapter I'm referencing keeping your heat input within the transition phase and below the carburizing phase. Keeping temp by color seems a bit difficult. I'm sure some smiths are that good, but I'm sure it took them a lifetime of experience. It was an interesting chapter to say the least, as the science makes sense. It also makes sense that the practice was wiped out when it came to the industrialization of the steel forging process...
 
In forging it is the range that matters much more than the heating method. Each steel has a forging range. Go over it and the steel will mush and crumble under the hammer. Go under it and the steel may crack or develop internal damage that will haunt you in HT. There is a real truth in the phrase, "Strike while the iron is hot". If the steel is below the forging range, it will not move well.

For most carbon steels, the forging range is between 1400F and 2100F. I like to stay between 1500 and 1900 for most work. At around 1600F I make my straightening blows.....and quit hitting the steel. Some carbon steels and most stainless steels are "red short" or "hot hard" and don't forge easily. These steels have very specific ranges ( usually higher) and are not for the novice. It is very easy to ruin these steels in forging, which is why they are normally only used for stock removal.

I want to reiterate those temps....when forging steel, quit all hammering at 1400F. Yes, the steel will still be red. If you are hammering the steel when it looses color and turns black, you are forging at 900-1000F, which is very likely to damage the blade. You can do gentle straightening blows to the dull red range, but even the most gentle blows should stop before black.

If you have a PID controlled forge or a commercial HT oven with a bar heating slot ( opening a 2000F oven door repeatedly and removing/inserting blades without special protective gear is a really bad idea) you could set the upper limit to avoid burning up your blades. This is good when working several blades at a time, or when letting them sit for a few minutes while your attention is elsewhere...but to be honest, that isn't the setup any of us will likely have in a home shop.

Do one or two blades at a time. Let them heat to the bright orange yellow range, hammer with well placed blows until it drops to medium red....stop hammering...put back in to heat.

Running your forge at full blast won't help you either. Just run it at the pressure that gets the steel where you want it. I get a chuckle out of folks forging with a forge roaring like a jet engine at take-off. Unless you are making anchors, the forge should be chugging along without a giant plume of flame coming out the ports or a deafeningly loud noise. If you have to raise your voice to talk over the forge...the forge is probably running too hot for forging.
 
SinePari said:
It's definitely not an issue when gauging heat by color when it comes to plain steel, but from the chapter I'm referencing keeping your heat input within the transition phase and below the carburizing phase. Keeping temp by color seems a bit difficult. I'm sure some smiths are that good, but I'm sure it took them a lifetime of experience. It was an interesting chapter to say the least, as the science makes sense. It also makes sense that the practice was wiped out when it came to the industrialization of the steel forging process...
Click to expand...
I haven't fond it to be very hard but it does take practice you may want to ask directly Ed at his forum and I know he'd be very happy to answer any of your questions http://www.knifetalkonline.com/smf/
 
bladsmth said:
In forging it is the range that matters much more than the heating method. Each steel has a forging range. Go over it and the steel will mush and crumble under the hammer. Go under it and the steel may crack or develop internal damage that will haunt you in HT. There is a real truth in the phrase, "Strike while the iron is hot". If the steel is below the forging range, it will not move well.

For most carbon steels, the forging range is between 1400F and 2100F. I like to stay between 1500 and 1900 for most work. At around 1600F I make my straightening blows.....and quit hitting the steel. Some carbon steels and most stainless steels are "red short" or "hot hard" and don't forge easily. These steels have very specific ranges ( usually higher) and are not for the novice. It is very easy to ruin these steels in forging, which is why they are normally only used for stock removal.

I want to reiterate those temps....when forging steel, quit all hammering at 1400F. Yes, the steel will still be red. If you are hammering the steel when it looses color and turns black, you are forging at 900-1000F, which is very likely to damage the blade. You can do gentle straightening blows to the dull red range, but even the most gentle blows should stop before black.

If you have a PID controlled forge or a commercial HT oven with a bar heating slot ( opening a 2000F oven door repeatedly and removing/inserting blades without special protective gear is a really bad idea) you could set the upper limit to avoid burning up your blades. This is good when working several blades at a time, or when letting them sit for a few minutes while your attention is elsewhere...but to be honest, that isn't the setup any of us will likely have in a home shop.

Do one or two blades at a time. Let them heat to the bright orange yellow range, hammer with well placed blows until it drops to medium red....stop hammering...put back in to heat.

Running your forge at full blast won't help you either. Just run it at the pressure that gets the steel where you want it. I get a chuckle out of folks forging with a forge roaring like a jet engine at take-off. Unless you are making anchors, the forge should be chugging along without a giant plume of flame coming out the ports or a deafeningly loud noise. If you have to raise your voice to talk over the forge...the forge is probably running too hot for forging.
Click to expand...

Gratze!

I only forge in the "red" during my finishing heats, and I always move to a really light hammer. This really helps out when I move to hand sanding. That's strange coming from me considering my past two knives, but ornate forging is completely different than forging a blade... Or is it? <- The jarring reality... I think that's wherein lies my struggle for wanting forged texture in blades, because the final product distinctively differs from stock removal blades. In the learning process, slowly but surely, I'm understanding why that texturing is an undesirable trait.

I would only want to use the furnace route for those advanced steels, and by "advanced steel" I mean anything that's not forge practice. It might not be the norm, but if it aids in keeping an more precise heat input, then I'm all for it. Do professionals run this kind of set up when it comes to those "heat sensitive steels?

I say this partly on the basis of control, and partly on how unbelievably costly propane is. It's not so much that I run it too high, just that I have three burners... I keep it just past the point of those annoying chugger farts, and turn it up, only if forge welding... ***For all those looking to invest in a forge, be warned that a three-burner forge for a beginner blade smith is a bit overkill. It works well for bigger items such as those used in sculpture, which is still it's main purpose for me; but blades? not so much.


Until then, I have some leaf springs to burn through... practice,practice,practice.
 
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