downward warp in heat treat

D

dustfurn

Joined
Oct 2, 2007
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72
I heat treated a straight, 12" long blade i with a very thick spine last night and it developed a pretty pronounced downward bend (the back arched, with the tip dropping).

The steel was w1, and i quenched in mcmaster-car fast quench oil. I re-heated, straightened it (a lot of work, believe me...), normalized twice and tried again...same thing. So then (big mistake), i re-normalized and quenched in 120 degree brine (ping).

How can i avoid this downward bend in the future? any tips?

to recap:

12" w1 blade
heated to 1475 and held for 5 mins
quenched vetically, point down, in fast oil

Thanks,
Dustin
 
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How did you put the blade into the quench? I've had the samething happen once before by going straight in point first. I also had clay on the blade. I never did redo it but have thought of trying it again with clay and quenching spine first. I try to avoid those dreaded pings.....
 
If vertical point down,... was the edge facing north or south? Just curious...
 
Raymond Richard said:
How did you put the blade into the quench? I've had the samething happen once before by going straight in point first. I also had clay on the blade. I never did redo it but have thought of trying it again with clay and quenching spine first. I try to avoid those dreaded pings.....
Click to expand...

oh, so it may be the vertical aspect of it? that's too bad! i just finished my first welded up vertical quench tanks (the welds are oil-tight, too =] ).

Oh well, that gives me something to consider at least....thanks.
 
Point down or edge down shouldn't matter .Agitate ? That can make the difference. Was this steel forged ? How thick is the spine ? Was the 5 min enough to thoroughly heat the spine ?
 
Downward curvature (negative sori/zori) is a result of the edge contracting upon quench,as it changes structure and heads toward the Ms point. The spine is still plastic at this point ,and if clay coated may not have even passed critical yet, so the blade bends easily with the contracting edge.If the spine cools a little too soon ( before the edge reaches Ms), it will become too resistant to bend upward when the martensite expands as it converts (martensite is a larger structure).This can result in a negative sori, or a cracked blade, depending on how fast the blade cools. When everything works right and the chain of events come together in the proper order and timing,the edge lifts back to neutral,or into a positive sori -if the blade geometry is right for it (as in many sword blades). This is done with clay coating and a controlled quench.

If your setup and procedures are giving you a consistent downward curved edge, here are some things to try:
Forge some positive sori into the blade,pre-HT.This may drop to neutral upon quench, and if some remains, it won't be a detraction.
Vary the quench speed on a bare blade -try parks #50, or try AAA.
Clay coat the blade as you would a wakazashi or tanto.
Clay coat the blade,and wipe the clay off the spine surface to make it convert at the same time as the edge.
Make the blade thinner with less meat in the spine.
Make the spine thinner,but leave the blade thicker in the middle, creating a shinogi, or ridge line.
Clay coat the blade and do a standard interrupted water quench.


With fast steels, like W1/2 and 1095,quench should always be fast and smooth. Edge in or point in is personal choice (I use point in). Slide the blade in a slicing motion, or better, have a J-tube re-circulating the oil straight up from the bottom center of the tank. This caries away the vapor jacket and helps speed the oil in removing heat. A recirculating tank is a joy to quench in.
Stacy
 
I used to see the edge shorten in quench pulling the tip down, then went to three - 35 second post forging quenches from critical for 35 seconds each, then normalize, then anneal at about 988f, then harden. Have never seen any warp since. The steel naturally is 52100, the oil Texaco type A at room temp. I have never worked with your steel.

The above works when you forge at the right temp for your steel and do everything right.

Good Luck
 
I always had this happen to some degree when using simple steels. I would suggest you try spine in first. Shallow hardening steels seem prone to do this, while deeper hardening steels, such as 01, will occasionally go the other way, and turn upward slightly. Soaking simple steel a couple of minutes seemed to lessen the degree of droop, in my experience.
 
The cross section of my straight razors is an extreme version of what you're describing: The spine is usually 1/4" or so, and this tapers sharply to .020" at the edge. The blades are 1/2" to 3/4" wide usually.

Anyway, I shape the edge so it's perfectly straight before heat treatment, and often it has a pronounced bow to it after the quench. Measured against a straightedge, the bow is probably 1/16" in the middle of a 3" long edge.

This seems to happen primarily with my 1084. I don't think I've seen it with O1. My W1 blades usually have a different shape that would hide the effect, but I'll bet it happens with W1 as well.

One thing that tends to make the effect more extreme is if I have any sway in the back of the blade. If the blade's back is bowed before the quench, it will be straight afterward and the edge will reflect the original shape of the back.

Steel does weird stuff. :)

Josh
 
The problem is very common and is caused by the expansion of the steel when various parts of the blade transform from austenite to another phase out of sequence. Austenite is a denser atomic stacking for the iron so it takes up the least space, it is also very ductile (remember this part).

Certain blade cross sections are much more susceptible to this and the blade you describe is one of them. Perhaps the most susceptible shape I have encountered is a long, flat ground Scottish dirk- thick spine simple “V” cross section down to an edge with a lesser profile taper (a chefs knife, for instance, doesn’t suffer from the problem). Japanese tanto will suffer from it very badly as well.

This is an oil based phenomenon as water cools things fast enough to avoid it, thus guys who switch from water to oil in making katana will find that their sori suddenly turns upside down on them. And understanding this problem is best aided by studying Japanese yaki-iri techniques. The worst method I found to use in the quenching of dirks is point down. It induced the worst curvature due to both parts being given the same cooling rate and one totally beating the other to the punch.

There are several factors involved here. If side of the blade makes pearlite at 1000F it will expand and pull the other side, if that other side is still ductile it may accommodate this, if it is not it will act as an anchor and pull the blade into a curve. The same is true for the martensitic conversion, but much more prone to the anchoring effect. You also have normal thermal contraction vs. expansion going on.

The first thing I would do is get away from vertical quenching of single edged blades, unless you are set up for marquenching. I found spine down horizontal quenching with proper agitation most effective in treating the problem in my shop. Also interrupting the quench near Ms allows a more even transformation with less tugging.

Another aspect that cannot be overlooked is the balance of blade area that transforms versus that which hasn’t yet, so that the shallower hardening the steel quenched in oil the great the chances of pearlite winning the struggle, meaning the spine besting the edge in the struggle for power.
 
Kevin, immensely informative, as usual. I have been quenching my razors point down, so I'll give the edge up thing a shot.

What's a good ballpark for interrupting the quench using fast oils like Parks #50? Is it safe to take the blade out once it's no longer glowing?

Josh

Kevin R. Cashen said:
The problem is very common and is caused by the expansion of the steel when various parts of the blade transform from austenite to another phase out of sequence. Austenite is a denser atomic stacking for the iron so it takes up the least space, it is also very ductile (remember this part).

Certain blade cross sections are much more susceptible to this and the blade you describe is one of them. Perhaps the most susceptible shape I have encountered is a long, flat ground Scottish dirk- thick spine simple “V” cross section down to an edge with a lesser profile taper (a chefs knife, for instance, doesn’t suffer from the problem). Japanese tanto will suffer from it very badly as well.

This is an oil based phenomenon as water cools things fast enough to avoid it, thus guys who switch from water to oil in making katana will find that their sori suddenly turns upside down on them. And understanding this problem is best aided by studying Japanese yaki-iri techniques. The worst method I found to use in the quenching of dirks is point down. It induced the worst curvature due to both parts being given the same cooling rate and one totally beating the other to the punch.

There are several factors involved here. If side of the blade makes pearlite at 1000F it will expand and pull the other side, if that other side is still ductile it may accommodate this, if it is not it will act as an anchor and pull the blade into a curve. The same is true for the martensitic conversion, but much more prone to the anchoring effect. You also have normal thermal contraction vs. expansion going on.

The first thing I would do is get away from vertical quenching of single edged blades, unless you are set up for marquenching. I found spine down horizontal quenching with proper agitation most effective in treating the problem in my shop. Also interrupting the quench near Ms allows a more even transformation with less tugging.

Another aspect that cannot be overlooked is the balance of blade area that transforms versus that which hasn’t yet, so that the shallower hardening the steel quenched in oil the great the chances of pearlite winning the struggle, meaning the spine besting the edge in the struggle for power.
Click to expand...
 
No! That would be too soon. I have found that around a six or seven count gets you in the neighborhood. What you need to do is work out Ms for the steel you are using. If you pull out of the #50 at just the right time there should be a light oil coating covering the blade with just a few fain wisps of vapor, heavy smoking is too hot and comfortable to touch would be too cool to be considered an marquench.
 
I agree with Kevin, heavy smoking is too hot and comfortable to touch with bare hands is too cool. Once it more or less stops smoking and you can handle it with gloves reasonably well, it's just about right... with most steels I've used anyway.
 
Great--that's very helpful. If Kevin and Tai agree, the info must be good. :D

I'm using 1084 and W1, mainly. I think Ms is right around 400 to 425 F for the 1084, and I'd guess that it's close to that with W1. I'll have to see if I can dig out a TTT chart for my W1...

Josh
 
Ed Fowler said:
I used to see the edge shorten in quench pulling the tip down, then went to three - 35 second post forging quenches from critical for 35 seconds each, then normalize, then anneal at about 988f, then harden. Have never seen any warp since. The steel naturally is 52100, the oil Texaco type A at room temp. I have never worked with your steel.

The above works when you forge at the right temp for your steel and do everything right.

Good Luck
Click to expand...

Heya Ed! Good to see you still hanging around!
Thanks for the input.

… keeping busy,… still making some knives?

Hope all is well. :)
 
Thanks Tai: Feeling better than I have in 5 years, Docs figuring stuff out - I hope!
Good times on the Willow Bow and continue to learn every day.
Take Care Friend
 
Ed Fowler said:
Thanks Tai: Feeling better than I have in 5 years, Docs figuring stuff out - I hope!
Good times on the Willow Bow and continue to learn every day.
Take Care Friend
Click to expand...


Glad to hear that Ed!

I've been having a few aches and pains, but holding up O.K., I still spend some time in the shop, almost everyday. :)
 
Get to know your quenchant....Watch, listen, feel as it goes through
the phases. When it stops boiling, it's entered the induction phase.
You can pull the blade and check the temp with an infared thermometer
(sears).. From this you can determine at what temp your quenchant
enters induction phase, and how close that is to Ms for your steel,
and when to pull the blade for an interupted quench.
 
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