Straightening O1 Sword after Heat Treatment

[duurza]

So I heat treated my O1 sword and while removing it horizontally from the propane forge, stupid and clumsy me bumped the blade against the top of the forge and set a slight warp mad. I quenched it into boiling water as I had simulated and after around 8 seconds, pulled it out and let it air cool. Based on my simulation data, I knew I had around 60 seconds to fix it before martensite would begin to form but I was too nervous about doing more damage to it that I just figured I would try to fix later.

I've already tempered it on the stove and got a pale yellowish red for steel.

Anyone have any suggestions as to undoing as much of that warp as possible? The warp caused a minor sabre-ing of the blade towards the point but other than that, everything else is about the same as before the heat treat. I looked down the edge and everything is straight except for the warped part.

Notes:

1) The sabre-ing I don't mind. Initially when I filed this, it was too difficult to get a distal taper. I am planning on grinding material away on the curved side to get rid of the sabre-ing and get that taper.
2) Looking down the edge, I could technically just do more stock removal to remove that warp but it will take a long time.

Regarding the quench with boiling water:

It seemed ok to me. One huge issue was that the quench tank was too small. The vapor jacket formed just as desired to provide the desired cooling rate BUT I think the jacket was too thick for the tank and ended up forcing water out of the tank. If I ever do this again, I will make sure to get a quench tank large enough to relieve the steam.

 

[Stacy E. Apelt - Bladesmith]

Boiling water is a very, very poor quenchant.
Too small volume of quenchant is also bad.
The water bath should have 7-9% salt and at about 120-130F. You should have at least 4" of quenchant around the blade in all directions when the sword is in the tank. On most swords, that is 10 gallons or more. Tempering over a flame is only partly tempered.The structures have only slightly converted. Temper should be done in an oven for two hours each cycle for a sword to have sufficient toughness to survive. If the blade is too long for your kitchen oven, let one end stick out the top corner of the door and bake for an hour, then turn around and bake the other end for an hour. Cool off and repeat. I would be very leary of using a sword with a sub-par temper.

Normally, you straighten the blade with straightening tools/sticks, wooden mallets, and gloved hands. You can bend, pound, twist, etc. all you want for about a minute in most cases. When doing the quench, I have a 2X4 with a slot cut in it clamped in the post vise. I set the blade in the slot and bend/twist as needed right out of the quench tank. You can get it perfect in 10-15 seconds that way.

Straightening after tempering should be done at 450F after at least a 30 minute soak. Even then, it is sphincter clenching at times. If it cools, stick back in the oven for another 15 minutes and try again. A heat gun will spot-heat a small area. Use a laser pyrometer (a cheap HF one will work for this) to check the blade temperature and shoot for about 450F.




Make a set of sword straightening sticks. They are two slabs of 2X4" oak/hickory/locust about 24" long ( you can use plain pine 2X4s, too). Shape one end of each into 1.5" wide handles that allow a good grip. About 3" back from the other ends, cut a slot 1/4" wide and 2" deep in the side of the slat. Rest the sticks on a tabletop or anvil, and set the sword in the two slots with the bend between them. The handles are pulled apart or pushed together to apply a bending force. For straightening a gentle curve, place the sticks far apart.For straightening a kink, place close on each side of the kink. For a twist, lift one and lower the other. If the blade is clamped in a vise, use one or both slats to torque the blade to remove the twist.

 

[J W Bensinger]

I am amazed that O1 survived that quench. I suspect it was the violence of the quench that warped it, not the bump-swords warp pretty regularly even in the correct quenchant. Stacy's right on here.

 

[JTknives]

WARNING swords take a lot of flex to straighten and then all the sudden thy snap. It happened to me and ever sence then I don't even bother trying to straighten after the quench. I straighten by clamping the blade/sword to a large bar of straight steel. Clamp it so the blade is straight and then put it in the oven and temper for 2hrs. After tempering remove the clamps and presto straight. This is most effective on the first temper and all tempers after that are less effective and most of the time require shining past straight to compensate for the spring back.

 

[duurza]

Boiling water is a very, very poor quenchant.
Too small volume of quenchant is also bad.
The water bath should have 7-9% salt and at about 120-130F. You should have at least 4" of quenchant around the blade in all directions when the sword is in the tank. On most swords, that is 10 gallons or more. Tempering over a flame is only partly tempered.The structures have only slightly converted. Temper should be done in an oven for two hours each cycle for a sword to have sufficient toughness to survive. If the blade is too long for your kitchen oven, let one end stick out the top corner of the door and bake for an hour, then turn around and bake the other end for an hour. Cool off and repeat. I would be very leary of using a sword with a sub-par temper.

Normally, you straighten the blade with straightening tools/sticks, wooden mallets, and gloved hands. You can bend, pound, twist, etc. all you want for about a minute in most cases. When doing the quench, I have a 2X4 with a slot cut in it clamped in the post vise. I set the blade in the slot and bend/twist as needed right out of the quench tank. You can get it perfect in 10-15 seconds that way.

Straightening after tempering should be done at 450F after at least a 30 minute soak. Even then, it is sphincter clenching at times. If it cools, stick back in the oven for another 15 minutes and try again. A heat gun will spot-heat a small area. Use a laser pyrometer (a cheap HF one will work for this) to check the blade temperature and shoot for about 450F.




Make a set of sword straightening sticks. They are two slabs of 2X4" oak/hickory/locust about 24" long ( you can use plain pine 2X4s, too). Shape one end of each into 1.5" wide handles that allow a good grip. About 3" back from the other ends, cut a slot 1/4" wide and 2" deep in the side of the slat. Rest the sticks on a tabletop or anvil, and set the sword in the two slots with the bend between them. The handles are pulled apart or pushed together to apply a bending force. For straightening a gentle curve, place the sticks far apart.For straightening a kink, place close on each side of the kink. For a twist, lift one and lower the other. If the blade is clamped in a vise, use one or both slats to torque the blade to remove the twist.

All of the straightening has to be done while the steel is hot right? Basically immediately after pulling out of the oven at the end of at temper cycle?

 

[duurza]

I am amazed that O1 survived that quench. I suspect it was the violence of the quench that warped it, not the bump-swords warp pretty regularly even in the correct quenchant. Stacy's right on here.

The reason why I used water (BOILING WATER) was that the heat transfer coefficient of the vapor jacket (though pretty low for plain carbon steels) was perfectly within the range for O1. This is all theoretical of course.

And no, it wasn't the violence of the quench that warped it. I did not have enough clearance in front of me nor behind me while taking the blade out of the forge so I accidentally bumped a portion against the top of the forge which set the warp.

According to my simulation data, after pulling out of the quench, it should have been at around 400 C at which I would have had around 100 seconds to reliably manipulate it before it air cooled below 220 C (pretty basic heat transfer calculations so I would trust the data). Since I was clumsy enough to bump the blade, I decided it might be better if I tried fixing it later rather than doing any more damage.

 

[Stacy E. Apelt - Bladesmith]

All of the straightening has to be done while the steel is hot right? Basically immediately after pulling out of the oven at the end of at temper cycle?

Yes ... or in the tempering oven as JT suggested.



A centuries old method of removing warp or bend from long blades was done this way:

Temper and clean up the blade to bright steel.
Place in a clamp/vise and expose the warp/bend. The sword straightening sticks mentioned earlier work well here, too.
While an assistant is pulling/bending the blade past straight, apply heat to the outside of the bend. It can be a small torch, or a bar or red hot iron. try to keep in the upper half of the blade between the spine and middle, avoiding putting too much heat in the edge. Watch for color changes on the surface, removing the heat just before the blue starts. Check and repeat if needed, adjusting the amount of over bend as needed.
This is very close to the way Peter's HT removes warp from blade with a small torch.

 

[duurza]

Yes ... or in the tempering oven as JT suggested.



A centuries old method of removing warp or bend from long blades was done this way:

Temper and clean up the blade to bright steel.
Place in a clamp/vise and expose the warp/bend. The sword straightening sticks mentioned earlier work well here, too.
While an assistant is pulling/bending the blade past straight, apply heat to the outside of the bend. It can be a small torch, or a bar or red hot iron. try to keep in the upper half of the blade between the spine and middle, avoiding putting too much heat in the edge. Watch for color changes on the surface, removing the heat just before the blue starts. Check and repeat if needed, adjusting the amount of over bend as needed.
This is very close to the way Peter's HT removes warp from blade with a small torch.

Alright thanks!

I'll probably straighten the warp with a vice and stick it in the oven for tempering. Less work needs to be done. As for the sabre-ing, I will probably just remove enough material on the opposite side to even it out. Gives me that distal taper anyway.