# Communities > Bladesmiths, Blacksmiths, Artisans and Professionals > Japanese-Style Sword Makers Cafe >  Lack of Stress Relief and post quench cracking

## Patrick Hastings

Stress relief after Quench. It seems essential with todays popular choices of steels for Japanese style blades. It is my understanding that the Japanese smiths of old had little understanding of Stress relief in ferrous metals. It is hard to imagine a heat-treating formula without the Tempering cycle yet apparently thousands upon thousands of blades were Differentially hardened and Left full on hard. I think it was Daryl Meier that said even Japanese Match lock hammer springs were work hardened to make them springy as opposed to quench and temper. I have heard rumors that some of the greater smiths had been using Stress Relief to keep their blades from being chippy, as we do today. With the mentality of smiths of old any one that figured it out would not be big on sharing the secret. So I dont think it was very wide spread till very late in history.

I find that My 1084 is very sensitive during heat-treat and often a blade that shows no evidence of cracking after quench, will basically start cracking up soon after If I dont temper them. This does not surprise me, its a lot of carbon content. The old Japanese blades I hear in the grapevine had Carbon content ranging from .45 to .70 percent. If I dont stress relieve my steel, it self destructs. 

I am wondering about other makers choices in basic steel or forge welded combinations. Is anybody using a modern steel that is responding in such a way that it could be used full on hard? Not that I would want to, the point is to gather information here not make chippy blades  :Smilie:  I suspect the lower the carbon the more you can get away with this, but Im also wondering how much of that success was due to process not material.

   I hope this is the correct forum for this (yuk yuk)  :Smilie:

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## Joseph Renner

Ive never found 1084 to be very chippy. Give it a light temper, even a flash temper, and it goes tough. If you get a chance take and heat a blade to 460 or so and let it air cool(flash draw it).
After you got an edge on it take it and hack away at some concrete blocks. It will dent more than chip(if any). I credit this too the manganese(for hardness and abrasion resistance) rather than loading up with more carbon. And the good fine grain it is easy to get with thermal cycling, right now Im getting almost invisible grain structures, and I bet you are, too. I normalize at least 6 times for anything over 12" nagasa. No thats not out there, I know of another well known smith who goes 8- 12 for swords.
Definately all in the process and material.
Edit:
I have also tested a blade with a ko-nie hamon, in a similar manner. Denty not chippy.
I think more smiths in japan knew of tempering than we might think.  Japanese sword steel had gone up to .8C, so why werent this blades almost exploding on blunt impact, they must of at least lightly stress releifed. maybe they were doing it in the quench(interuption). who knows.
Joe Renner

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## Patrick Hastings

> _Originally posted by Joseph Renner_ 
> *Ive never found 1084 to be very chippy. Give it a light temper, even a flash temper, and it goes tough. If you get a chance take and heat a blade to 460 or so and let it air cool(flash draw it).
> After you got an edge on it take it and hack away at some concrete blocks. It will dent more than chip(if any). I credit this too the manganese(for hardness and abrasion resistance) rather than loading up with more carbon. And the good fine grain it is easy to get with thermal cycling, right now Im getting almost invisible grain structures, and I bet you are, too. I normalize at least 6 times for anything over 12" nagasa. No thats not out there, I know of another well known smith who goes 8- 12 for swords.
> Definately all in the process and material.
> Edit:
> I have also tested a blade with a ko-nie hamon, in a similar manner. Denty not chippy.
> I think more smiths in japan knew of tempering than we might think.  Japanese sword steel had gone up to .8C, so why werent this blades almost exploding on blunt impact, they must of at least lightly stress releifed. maybe they were doing it in the quench(interuption). who knows.
> Joe Renner*


   Im not saying that 1084 is chippy at all unless you completly forgo at least some type of stress relief. I am quite satisfied with the performance on my edges and they stand up to cinder blocks quite well in destructive testing. 
I try to avoid "Flash tempering" It was brought to my attention by Kevin C. that lower temps and longer soaks can achieve greater toughness at a given hardness than higher temps with with little to no soak. Im still looking into this but it seems to be panning out. this was already what I was doing with my blades unless I was in a hurry hehe. Relativly low temps and long soaks. I can see it in my engraving tools. I make my own gravers and I use W1 among other steels. The W1 is fast. I need a new graver I just whip it up heat it in the salt bath, queanch and draw a quik color temper or "flash temper" as you call it. These do the job and they are quik. I started making new ones in advance and tempered them like my blades and Ill be damned if they were noticably less chippy and stayed sharp just as long as the Color tempered versions. Tempering is a function of Time and temp. you can increade time and lower temp. until Kevin mentioned it I had never thought about taking advantage of the time factor versus the temp factor, but it seems to have some benificial results so far. 

As too the carbon content on antiques its a crap shoot, but I was thinking more average range not extreme high end examples. I think that smiths that were using steel with .80 carbon content were using stress relief either intensionally or incidentally or their blades would not have survived IMO. even so That only represents a small fraction of the blade making history in Japan. Earlier I think the carbon levels were much lower and tempering was pretty much a msytery.

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## Joseph Renner

I ussually dont flash temper either. But I was curious about what the results on a "traditional"(flash tempering was probably the most common, noone actually knows though) kind of temper would be. With 1084(it seems) a little stress relief goes a long way.  I ussually go with a couple to a few real tempering cycles, to make sure troosite is acheived.
I like W1 for small tools(chisels right now) as its readily available in proper sizes.
Got any pics of your engraving tools, I would like to see them, if you dont mind posting.

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## Dan Pfanenstiel

I've had some trouble with the 1050 I use from Admiral steel. Was applying the clay and hardening at 60 grit finish, without normalizing and losing a lot of blades to cracking in the quench. Even had one blade sitting on the coffee table, an hour after hardening and at 220 grit finish, suddenly crack on me. Ouch. I'm now smoothing the edge down to relieve stress risers and normalizing once or twice. I don't temper unless longer blades, over 12".

Dan

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## Brian VanSpeybroeck

> _Originally posted by Dan Pfanenstiel_ 
> * Ouch. I'm now smoothing the edge down to relieve stress risers and normalizing once or twice. I don't temper unless longer blades, over 12".
> 
> Dan*


I haven't had any problem with cracking in clay coated blades as I have never played very much with this process. I have always martempered or austempered blades and bypassed the traditional water quenched stuff in my education and experimentation. But the "stress riser" thing has me puzzled. Can you explain to me how it works? 

As I understand it, sharp or drastic lines or sudden changes in geometry can become a focal point for stresses when the blade is quenched which in turn leads to cracking. Right?

Thanks,
Brian

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## Patrick Hastings

> _Originally posted by Joseph Renner_ 
> *I ussually dont flash temper either. But I was curious about what the results on a "traditional"(flash tempering was probably the most common, noone actually knows though) kind of temper would be. With 1084(it seems) a little stress relief goes a long way.  I ussually go with a couple to a few real tempering cycles, to make sure troosite is acheived.
> I like W1 for small tools(chisels right now) as its readily available in proper sizes.
> Got any pics of your engraving tools, I would like to see them, if you dont mind posting.*


I dont mind shareing some pics of my tools but, you will have to be patient I cant even keep up with the photos That I'm taking for clients. Im crazy busy, but its  a good busy atleast  :Smilie:

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## Patrick Hastings

> _Originally posted by Dan Pfanenstiel_ 
> *I've had some trouble with the 1050 I use from Admiral steel. Was applying the clay and hardening at 60 grit finish, without normalizing and losing a lot of blades to cracking in the quench. Even had one blade sitting on the coffee table, an hour after hardening and at 220 grit finish, suddenly crack on me. Ouch. I'm now smoothing the edge down to relieve stress risers and normalizing once or twice. I don't temper unless longer blades, over 12".
> 
> Dan*


 Interesting thanks Dan. That is the type of info I was looking for. the length issure makes sense also. The longer a piece is the greater the pull back tension can be and the more likly your weak link stress riser will break. I take my finish up to 100 grit and the very edge I round it off and take it up abit higher in finish aswell.

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## Patrick Hastings

> _Originally posted by Brian VanSpeybroeck_ 
> *
> 
> I haven't had any problem with cracking in clay coated blades as I have never played very much with this process. I have always martempered or austempered blades and bypassed the traditional water quenched stuff in my education and experimentation. But the "stress riser" thing has me puzzled. Can you explain to me how it works? 
> 
> As I understand it, sharp or drastic lines or sudden changes in geometry can become a focal point for stresses when the blade is quenched which in turn leads to cracking. Right?
> 
> Thanks,
> Brian*


    Yea you have the basic idea right. 
 One good example of this is large steel sea going vessels. 
Large steel vessels are not all that rigid they flex this way and that constantly the stress will concentrate on the door jam corners if they are square like in your house. It was found out early on that every door that had a square jam would crack from the inside corners out and those cracks would just continue to spread from there. The rounded jams distribute the stress and prevent cracking. thats why ship doors are oval ish or atleast have radioused corners.

 Every grind line you have on the blades surface will concentrate stress especially if it was done with a new crisp belt and the grooves are distinc versus rounded. The thing is you will have that stray grind line that is abit deeper than the rest and it will get more than the normal share of stress and is the weak link.   

Tecnically all this fuss about crisp lines on a polish is counter productive. everywhere you have a super crisp ridge cuases acute stress to concentrate in that area. The one stress riser you can't get rid of is the Cutting edge, but theoretically the strongest blade would be the one with all the edges rolled as opposed to being crisp.  It would atleast have a longer fatigue life. 
  Its like glass. Glass can take a pretty good load and has some flex too it, but you put one little imperfection in the polished surface and suddely it wont carry half as much strees with out failure. Thats how you cut glass. You scor the surface (create a stress riser) then apply stress and the glass breaks on the Scor quite predictably.

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## M. Williams

Back to the comments about 1084. If any of you have used a lot of it, do you find that multiple normalizations; i.e grain size reduction processes; is an aid in reducing edge cracks not caused by stress risers? I am getting good curvature and hamon but I get cracks developing within seconds of quenching. Going strictly by colors and magnetism on the heat. With tap water at about 120 degrees. My cracking run generally to the top of the hamon then  laterally towards the tip. Perhaps more temp control is in order. mike

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## Joseph Renner

> _Originally posted by Patrick Hastings_ 
> *
> 
> I dont mind shareing some pics of my tools but, you will have to be patient I cant even keep up with the photos That I'm taking for clients. Im crazy busy, but its  a good busy atleast *


Paitience, I tried that once, I will try it again  :Stick Out Tongue:

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## Joseph Renner

> _Originally posted by M. Williams_ 
> *Back to the comments about 1084. If any of you have used a lot of it, do you find that multiple normalizations; i.e grain size reduction processes; is an aid in reducing edge cracks not caused by stress risers? I am getting good curvature and hamon but I get cracks developing within seconds of quenching. Going strictly by colors and magnetism on the heat. With tap water at about 120 degrees. My cracking run generally to the top of the hamon then  laterally towards the tip. Perhaps more temp control is in order. mike*


Lots of normalizations help reduce grain size, releive stress and cause consistent grain, all good for the upcoming quench.
Cracks within seconds is definately a sign of something wrong(to me). When I get cracks they tend to be at the mid-end of the quench.
Using magnet and color your quenching at 1500F or so, kinda risky(Im austenizing at 1400-1450,with soak), with 1084. And it might not hurt to pull up the quenchants temp either. 
1084 curves a lot, enough to tear the edge apart if not using mune-yaki(basicly hardening the spine), a lot of the time. 
The cracks tend to only run in the martensite, as it more brittle.

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## Dan Pfanenstiel

The normalizing, in addition to minimizing the stress risers, helped with cracking some but it also helps control the warpage that I was having trouble with. Doesn't eliminate it though.

Can't see any reason not to normalize. 

Dan

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