Straightening O1 after temper (while still hot)?

steveo83

steveo83

Joined
Aug 4, 2008
Messages
88
Hi All,
I ran out of time to correct a warp/twist after the quench - it stiffened up as the martensite formed before I was able to completely correct the warp.

So given that I'm bringing the blade back to 450F during the temper I was wondering about the state of the steel during this process and how pliable it is near this temperature...

I found this quote by Stacy - this refers to 1080 steel but is it the same for O1? Is an O1 blade pliable enough at 400F that I can straighten without risk of breaking it?
If this is the case, exactly what state is the steel in when it's sitting at 400 - 450F as opposed to when it cools back to room temp (HRC60-61)?

Quote: "At some point in time the blade will start to stiffen. You will feel the difference easily. Quit all straightening attempts at this point. Once the blade gets to around 400F it starts converting to martensite. The percentage of martensite increases until about 200F when it is above 90% . At room temperature it should be near 100% martensite. Any straightening remaining in need will have to wait until after the temper cycles.I call this secondary straightening, and do it at 400F. You can heat the blade to 400F any time you wish ( as as many times as neded to get the job done) and gently straighten any remaining and newly discovered warpage. This will not affect the blade's temper at all. ( unless you tempered below 400F.)"

Cheers guys,
Steve.
 
At 4xx°, you probably won't be able to bend by hand. I use a scissor-jack press (with a piece of C-channel as a die, and a piece of round stock as a punch), a lot of people use a vice and 3 rods.
 
For straightening hardened blades - 400F minimum.While still hot after temper would be ok.
 
I have found that if (after 1 cycle, of course) you clamp the blade "striaght" to a piece of flatstock that the second cycle "sets" the shape. I use multiple C-clamps and shim if necessary. You don't have to apply additional bend to compensate for any springback because there is none. Whatever shape it goes into the temper oven with is how it comes out.


Rick
 
I've tempered with the kink in it, straightened immediately after pulling it out of the oven, (helps to have a plan and move quickly and carefully) then right back in the oven for another hour or so. Works out pretty much like Rick said. I dont even clamp the blade, just tweak it by hand and put it back in. Clamping might help with thicker stock though, I know for a fact that 5/32 O-1 is fairly resistant to "hand fudging" at 400F, but not impossible! :D -Matt-
 
Do the temper cycles, and when the second one is done, straighten the blade at 400+. If it cools, heat it back up and do some more. The blade is (hopefully) mainly martensite once it reaches 400F after the quench. The tempers just make the brittle martensite into tempered martensite. The process is a slight conversion toward pearlite, but not enough to convert it fully ( unless you get it too hot). When the blade is at 400-450F, the structures are more pliable. Once cooled back to room temp the structures are much more rigid. Using a straightening jig for major bends, or just bending in a vise for minor ones usually solves the problem.
While some folks have printed articles that it helps, I do not agree that pouring water on the blade will help "set" the straightening, nor will it crack the 400-450F blade.Allowing the blade to cool to room temp wile in the jig is the best way to re-set the warp.
 
Thanks everyone for the replies, that clears it right up for me.

I'll definitely try setting the blade in a jig right when it comes out of the temper and allow it to cool while still clamped if straightenig the normal way gives too much grief.

Cheers guys
 
bladsmth said:
Do the temper cycles, and when the second one is done, straighten the blade at 400+. If it cools, heat it back up and do some more. The blade is (hopefully) mainly martensite once it reaches 400F after the quench. The tempers just make the brittle martensite into tempered martensite. The process is a slight conversion toward pearlite, but not enough to convert it fully ( unless you get it too hot). When the blade is at 400-450F, the structures are more pliable. Once cooled back to room temp the structures are much more rigid. Using a straightening jig for major bends, or just bending in a vise for minor ones usually solves the problem.
While some folks have printed articles that it helps, I do not agree that pouring water on the blade will help "set" the straightening, nor will it crack the 400-450F blade.Allowing the blade to cool to room temp wile in the jig is the best way to re-set the warp.
Click to expand...

Oooooooooh..... this is a chance for me to stray off topic... sorry Steveo.:D


Roman Landes once told me that water quenching immediately after each temper cycle can help set up the steel for improved toughness for extreme cold use. Ever heard of this? Would that cut down RA a bit more or am I bass-ackwards in my reasoning, again?


Rick
 
Rick Marchand said:
Oooooooooh..... this is a chance for me to stray off topic... sorry Steveo.:D


Roman Landes once told me that water quenching immediately after each temper cycle can help set up the steel for improved toughness for extreme cold use. Ever heard of this? Would that cut down RA a bit more or am I bass-ackwards in my reasoning, again?


Rick
Click to expand...

Rick, I'm not Stacy, but Roman told me the same thing ref. toughness in extreme cold conditions.
He also told me that a water "quench" right after coming out of the temper would help to prevent "precipitations". When I asked him what type of "precipitations" he was talking about, he stated that it depended on the type of steel.
I don't think that doing the water quench out of the tempering oven will do anything at all about the RA.
- Mitch
 
What Roman was referring to is true.
However,I was talking about a straightening technique. Some makers, including Bill Moran,have said that bending the 400F blade is a straightening jig and then pouring cold water on the blade will "set" the new shape. Others who have written magazine articles have stated that water quenching from temper will crack or damage the blade. In all respect for these fine folks, the un-bending of a blade will be from the force applied to the blade, not "shocking" it straight. In the same light, there is no change of structure in water quenching a 400F blade that will damage it. As Roman Landes has pointed out, a rapid drop to room temp is beneficial, and the old practice of slowly cooling to room temp between tempers is not as good as taking it to the sink and running water over the blade. I temper, rinse to cool, and put right back in the oven.

In regards to Roman's comments, the degree of complexity of the steel is the main factor in his observations. Too often readers of metallurgical papers feel that a particular process is universal. The reality is that what works for CPM154 is not necessarily what works for 1080.
 
I have read the same thing-that quenching from tempering can result in higher toughness; though not in reference to knife steels specifically. but this is from an old source, in reference to high chromium and nickle steels tempered in excess of 900 F-so not exactly knife making applicable Stacy is right, as usual about the difference between various steels
 
bladsmth said:
... Too often readers of metallurgical papers feel that a particular process is universal. The reality is that what works for CPM154 is not necessarily what works for 1080.
Click to expand...



This is all too true. As a person who has read a few metallurgy texts in his time let me say that one needs to approach them with a careful method for harvesting the information, papers on individual studies are even more prone to misinterpretation. Never consider one source as the final word on any topic, and always verify with follow up study. I always try to triangulate, i.e. find the same information from at least two other independent sources before running with it, which is not always easy since many people in a field tend to influence or borrow from each other. The reason for this triangulation is not only that the source may need verifying, but, as Stacy pointed out, to be certain you are interpreting the information in the correct context. Verhoeven’s book is a wonderful resource for bladesmiths wanting to add metallurgy to their collection of tools, but I have seen it misinterpreted more than almost any other work.

The topic at hand is one that is so complex that using it in a generalized context, as Stacy points out, can lead in unexpected directions.

The quench from the tempering heat, and yes I do it too, has many possible effects with less definitive understanding of the end results, but industry uses it in different circumstances. I keeping with the current discussion will forego the effects for retained austenite, but instead elaborate a bit on the “precipitates” mentioned. The most established situation regarding this is in the phenomenon of Temper Embrittlement (TE), which is not the tempering problem we see between 450F and 550F for the simple steels we work with, but is a real problem in richer alloys tempered to above 700F and then slow cooled. The slow cooling allows embrittling impurities to collect in grain boundaries, thus fast cooling reduces the opportunities for the problem. The tempering ranges for TE, however, are not common in steels bladesmiths would prefer to use.

TME or Tempered Martensite Embrittlement is the problem we face between 450F and 550F in simple steels and is due to the decomposition of retained austenite (RA) or other sources of free cementite which will then form between the packets of martensite and cause the brittle condition. It is not as dependant on cooling rate as TE but since it is connected with RA extended time in the temperature range that affects RA will come into play. The key would be to avoid RA as much as possible to begin with, and then watch how long or how deep you go into the problem range and quenching immediately couldn’t hurt.

How this pertains to the initial thread topic is this- O1 is VERY resistant to softening in the temper and one may find themselves having to venture into this problem range in order to get the plasticity required to straighten the blade. If it is just O1 by its self the best way to handle it would be to temper it out without bothering with the warp. Then afterwards, clamp the tip in a padded vice and hold a wet rag, or better yet wet cera-wool on the edge while heating the spine with a torch. When the spine turns blue in the area to be straightened- just push it straight. The temperatures will actually be beyond the range for TME and the straightening can be done with care and precision.
 
I do a variation of that with 01. I heat the spine blue, bend a little beyond straight, then pour water on it. Sometimes I have to repeat, but in the end I get it straight. Any harm in this?
 
No.
In this case the water is a quick cooling medium. Its purpose is to cool the blade down before the heat migrates too far into the edge..... which it does well.
 
Kevin, Stacy, thanks. I have been waiting to straighten my first composite sword out of fear. I did the torch/cerra wool trick, and it is finally straight. I appreciate you guys who know taking the time to lay things out in this format for those of us who are working to learn.

kevin c.
 
Thanks Stacy. I have posted about that proceedure in the past, at least a couple of times, and was told that was a bad way to straighten. Mete', and Kevin, I am pretty sure, said I should not do that, but never said why. I have done it that way for many years, after seeing Bill Moran do it on a video. It works, and it works well. Sometimes I have even over done it, and had to repeat to re-straighten from the other direction. I put the blade in my vise, usually the tang and ricasso area, heat the spine in the area I think where the problem is, over bend a tad or so, then pour water on it while holding in place. The water cooling locks it. I watch the colors very closely, and never allow them to get very close to the edge. I have never experienced an adverse result.
 
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