Tempering talk

[Kevin R. Cashen]

That about sums it up
Thing is until I started listening to guys like this I didn't realize just how refined you could get the whole HT and what great improvements you could make to the blade by using the refined methods. Yes, I could harden a blade with my torch and some ATF and make a decent blade. Now I can get the heat just right with my kiln and pyrometer and know my quench oil is the best and doing its job. I know my dbl temper is doing what it should. I know my newer blades are far superior to my older ones and the best that they can be. Even if both knives will shave, you I know the new one is tougher and will shave longer. We don't want to make good knives. We want to make great knives!

But the real kicker is that for the majority of knives made we are just splitting hairs here. When I see the number of knives that are considered "the best", get a price that matches that claim, yet I know the thing was heated to nonmagnetic so it could be dropped in a bucket of sludge and popped in a toaster oven, I realize that the all knowing consumers, don't know much. I would venture to say that less than 20% of smiths approach the blade conditions that are described in this thread, and a significant number of the other 80% actually try to do the opposite, and yet are held in high esteem by collectors and users. Lets face it all a knife has to do is cut something in order to function, and paper can do the same if you consider how quick it can lay you open, so sadly enough all this fretting about the precise internal conditions of the steel is mostly for your benefit and peace of mind.

The pathetic state of our business these days would dictate that if you have to choose between spending the next 5 years learning how to engrave, embellish and make a pretty knife, or how to obtain maximum results in heat treating, financial success and a mention in a magazine will not come from knowing even the slightest about what the blade is like on the inside. BTW Have you noticed the serious increase in articles telling you who this years "hot" makers will be?:barf: These pieces should insult the intelligence of anybody with enough brain to realize they are nothing more than attempts to icrease the value of certain knives that purveyors would like to sell. And the increase in such propoganda tells you something about the current business cimate if you listen. I will not get much into this though because it wil be included in my Sunday morning diatribe at Ashokan, so if you would like to see Cashen bug-eyed with veins popping and frothing at the mouth, I'll see you there .

 

[Kevin R. Cashen]

Muriatic acid is a 30 % solution of HCl in water. Best to play with it outdoors as the fumes tend to rust everything made of steel. Safety too, eye protection, rubber gloves. Don't heat it that will cause more problems with fumes .You can dilute it [acid into water] but it will take longer .

Muriatic has been about the worst I have found when opening in my shop. Many years ago I had a batch of blades hanging along my finishing wall (back when I had a wall instead of a finishing room), and cracked open a container of muriatic for just a breif time, in short order every blade on my wall was corroding, this stuck with me and to this day any acids with the slightest tendency to fume are kept outside. My vinegar and sulphuric acid mix sets on the cement in front of the shop with a cover.

Unfortunately high temperature salt vapors do pretty much the same thing, as any metal withing 10 feet of my units will attest.

 

[magneto]

So if you would like to see Cashen bug-eyed with veins popping and frothing at the mouth, I'll see you there .

I wish I could be there, but it is a bit to far for me. But if you are ever out this way.....:thumbup::thumbup::thumbup:

Unfortunately high temperature salt vapors do pretty much the same thing, as any metal withing 10 feet of my units will attest.

So how much does the graphite you are using now help with the these fumes?

 

[Chris Meyer]

Lest you all thought that there were no stupid questions, I have two that come to mind.

If I understand correctly; if I am able to properly Austenitize my blade and quench it to form as much Martensite as possible, then temper it two or three times at a temperature specified in my Heat Treaters’ Guide, I will end up with a blade of tempered Martensite and some left over ferrite and carbides. I understand that tempering will have reduced the stresses created by the Martensite transformation, but…

1. Specifically why does this tempering make the steel “softer” and what does it look this look like under the microscope? (I’m hoping that Kevin has an appropriate slide.) What is going on inside and why?
   
   
   (A side by side comparison with Kevin's other picture might help.)
   
   

   

   
   ​
   
   
2. Finally, how can it be that I can either temper my blade for two hours at a time in an oven or temper it a couple times in a matter of seconds with a torch and get the same results? If the results are really the same, how can this be explained? If they are not really the same, is one method clearly better (assuming they are each done properly)?

(As an aside, my current method is the temper three times in an oven to get the edge to the hardness I'm looking for. Then I use a torch to blue the tang and spine to make them easier to work on. I'm too shaky with the torch to do the whole blade with it.)​

Inquiring minds would like to know… Thanks.

 

[steelshaper]

I am with Chris on this. How does time effect temper? 1; time between quench and temper and 2; time at temper ( say 20 min. or 1 hour at 400F) In other words will holding the blade in the salts during temper for a longer time make any change? If it does'nt why not? After quench I clean my blades off and make sure all is well should I hurry right to temper or is it ok to wait?

On another note Is there still room at the Ashokan? From what I understand It is limited, who do I contact to sighn up?

 

[magneto]

What about aging? For O-1 steel I read that you can replace tempering with aging at 230-285 degrees F for 25-100 hours. Is it superior? Is it like auto-tempering (which should be called auto-quenching) in that the slow progression is better than a fast one. It would make sense, like being when you are in a theater and someone yells "FIRE" compared to a slow and steady exit.

 

[T Blade]

...... it wil be included in my Sunday morning diatribe at Ashokan, so if you would like to see Cashen bug-eyed with veins popping and frothing at the mouth, I'll see you there .

Kevin,
I'll have my camera for this one :thumbup:

 

[mete]

Temperature is much more an influence than time for tempering.I'd like to see a complete study on the O-1 'aging', more than just hardness....Tempering reduces stresses and changes dimensions of the tetragonal crystal. The higher the temperature the shorter the crystal becomes .This is not seen in an optical microscope but some of the changes can be seen with an electron microscope.You should see a change in the number of dislocations .Crystal dimension changes are measured through x-ray crystallography. ..A quick torch temper is not in any way a proper temper. It takes time to do that , 1 hour at least !

 

[Phillip Patton]

The pathetic state of our business these days would dictate that if you have to choose between spending the next 5 years learning how to engrave, embellish and make a pretty knife, or how to obtain maximum results in heat treating, financial success and a mention in a magazine will not come from knowing even the slightest about what the blade is like on the inside. BTW Have you noticed the serious increase in articles telling you who this years "hot" makers will be?:barf:

Actually, Kevin, I think that's the whole point. It's advertising, not education, and I didn't realize anyone was claiming otherwise.
What I object to in the magazines is not the advertising, but the blatant misinformation and hype. One of the recent issues of a certain magazine had one of the worst articles I've ever read.

These pieces should insult the intelligence of anybody with enough brain to realize they are nothing more than attempts to icrease the value of certain knives that purveyors would like to sell. And the increase in such propoganda tells you something about the current business cimate if you listen. I will not get much into this though because it wil be included in my Sunday morning diatribe at Ashokan, so if you would like to see Cashen bug-eyed with veins popping and frothing at the mouth, I'll see you there .

Hey, watch it pal! I was mentioned in one of those articles. I know what you mean though. I was excited to see my name in print, but I cringed to think I might be associated with the publication and some of the BS that's in it. Oh well.

 

[Kevin R. Cashen]

...So how much does the graphite you are using now help with the these fumes?

I sprinkle a silicon carbide powder in the top of the salts, this is primarily to keep the neutrality and the carbon in my blades, but if enough is applied it does indeed porvide a nice barrier on the surface that greatly reduces the vapors.

 

[Kevin R. Cashen]

1. Specifically why does this tempering make the steel “softer” and what does it look this look like under the microscope? (I’m hoping that Kevin has an appropriate slide.) What is going on inside and why?
   
   
   (A side by side comparison with Kevin's other picture might help.)
   
   

   

   
   ​

1. 
   
   I must apologize for that, I had intended to do the exact side by side that you request when I posted that image, but time factors became a problem with the sample preparation, and I am now in a crunch before I have to travel to two lectures in the next 2 weeks, so it may have to wait. I had been told I would be doing another metallographic lecture at the ABS Mid America expo in Ohio, but I have seen no mention of it in my list of demo's. I would like to say that I would have just such a slide perpared for then, but definitely I will get it for Ashokan.
   
   mete covered the crystallographic changes quite well, but the overall changes under the microscopic will be a darkening of the entire structure due to the increase in tempering carbides and a sublte "softening of the edges" of all those jagged needles.
   
   
   

   [*]Finally, how can it be that I can either temper my blade for two hours at a time in an oven or temper it a couple times in a matter of seconds with a torch and get the same results? If the results are really the same, how can this be explained? If they are not really the same, is one method clearly better (assuming they are each done properly)?

(As an aside, my current method is the temper three times in an oven to get the edge to the hardness I'm looking for. Then I use a torch to blue the tang and spine to make them easier to work on. I'm too shaky with the torch to do the whole blade with it.)​

Inquiring minds would like to know… Thanks.

As mete pointed out, a few minutes with a torch is no comparison to a proper temper. The reason you are able to see the effects to quickly with a torch is that you are throwing much more heat than you realize into the blade. It is a misleading (but perhaps fortunate) coincidence that the oxide colors are also accelerate by this excess heat so that you can at least have some sort of indicator.

Heat will always trump time, but time will yield more controllable and solid results. There has been some indication that a blade taken to a given HRC by extended time instead of higher temperatures could have a greater toughness at that same hardness. Selectively torching areas after they are hardened is a good way to handle things and was the way I did it for some time, until I switched to techniques that allow me to virtually finish the blade entirely before the heat treatment. So I wouldn't worry about gettign godd at torching things, as it is not a proper way to do things in comparison to what you may already be doing.

 

[Any Cal.]

So then, since this is primarily for the maker, here is a question.

In a general sense, (not dependant on grinds/blade shape), what types of steels are simply better than others, without significant compromises being made to gain in other areas?

This is assuming that each was heat treated properly, so as to provide the full benefit of the steel. Are any of the super steels actually better in all areas? Do any actually support a wide variety of grinds and shapes?

The reason I ask is, if a blade is being HT properly, are the newer steels good all around performers, in a variety of uses, or are they simply changing the compromises?

If the newer steels REQUIRE special considerations, along w/ special HT, does that mean that for most, w/out those considerations, they would actually be less desirable in a physical way, even though more marketable?

 

[Kevin R. Cashen]

I am with Chris on this. How does time effect temper? 1; time between quench and temper and 2; time at temper ( say 20 min. or 1 hour at 400F) In other words will holding the blade in the salts during temper for a longer time make any change? If it does'nt why not? After quench I clean my blades off and make sure all is well should I hurry right to temper or is it ok to wait?

On another note Is there still room at the Ashokan? From what I understand It is limited, who do I contact to sighn up?

I hope I covered some of your questions as well in my previous post. For more information on Ashokan you can go to: Ashokan Bladesmithing Seminar

 

[Kevin R. Cashen]

What about aging? For O-1 steel I read that you can replace tempering with aging at 230-285 degrees F for 25-100 hours. Is it superior? Is it like auto-tempering (which should be called auto-quenching) in that the slow progression is better than a fast one. It would make sense, like being when you are in a theater and someone yells "FIRE" compared to a slow and steady exit.

I agree that it should be preferrable to call "martempering" marquenching as it is not meant to be a tempering operation but an isothermal quench. But auto-tempering is a side effect of marquenching that is indeed a form of tempering, although incomplete and NOT a replacement for any sort of proper tempering, which must follow.

 

[Kevin R. Cashen]

Actually, Kevin, I think that's the whole point. It's advertising, not education, and I didn't realize anyone was claiming otherwise.
What I object to in the magazines is not the advertising, but the blatant misinformation and hype...

I see it as presented as some sort of a buyers guide, when indeed all it is is shameless advertising and attempted manipulation the market for personal and political reasons. The misinformation and hype is inspired by the underlying advertising value. Advertising is good, it is how the mags stay in business, but I just prefer that honest approach of keeping it in the advertising sections and attempting the use of real information or entertainment in the articles.

 

[Phillip Patton]

I see it as presented as some sort of a buyers guide, when indeed all it is is shameless advertising and attempted manipulation the market for personal and political reasons. The misinformation and hype is inspired by the underlying advertising value. Advertising is good, it is how the mags stay in business, but I just prefer that honest approach of keeping it in the advertising sections and attempting the use of real information or entertainment in the articles.

They have the entertaining part down.

 

[Phillip Patton]

I agree that it should be preferrable to call "martempering" marquenching as it is not meant to be a tempering operation but an isothermal quench. But auto-tempering is a side effect of marquenching that is indeed a form of tempering, although incomplete and NOT a replacement for any sort of proper tempering, which must follow.

Kevin, I have a question (which I will try to phrase coherently) :

Let's say you have two samples of steel, both from the same piece. One piece is quenched in oil, and not taken out until it's room temperature. After it's cool, it's 65 RC. Then you temper it at 475 degrees, after which it's 60 RC.
The second sample, you marquench, and the knife auto-tempers some.
Then you let the blade get to the Ms point, after which it's only 63 RC, because of the auto tempering.
Here's the question: Would you have to take the second sample to 475 to get 60 RC, or will it not have to go that hot?

 

[Stacy E. Apelt - Bladesmith]

Phillip,
I'll take a stab at that, and Kevin will correct me if I'm wrong.

The second sample would yield approximately the same Rc60 after a 475F temper. The lower Rc63 is just a partial temper, and the resultant final Rc is a product of the total time and maximum temperature. There could be a slightly lower final Rc (58.8-58.9) due to the fact that the total time (auto-temper + temper time) in tempering is longer than the first sample.
Stacy

 

[Kevin R. Cashen]

Stacy covered it as far as they will both sort of catch up to each other in subsequent tempers and require the same heat. However I noticed something different since I am able to do shorter tempering cycles with the salt, there seems to be a stage for alpha martensite (as quenched untempered) where the drop in hardness is quicker if the initial hardness is higher than necesarry (water quenched, above 65HRC etc...). THis means nothing to the finished knife but it is an interesting trend that I spotted in my numbers. If your total quenched one was 66HRC and your marquenched piece was 62HRC, 30 minutes in the temper would see the 62HRC not drop as fast to 60-61 while the 66HRC would very quickly catch up with its counterpart. This could very well be tied to a drop in dislocations while the BCT is reverting to BCC. But by the time both are 60HRC the differences would no longer be very noticeable.

One other difference is consistency of HRC readings. By the second temper the marquenched piece will be reading in a much tighter range than the traditional quenched piece which will cath up after the third temper. Once again these are just interesting observations and not any suggestions on my part that it has any noticeable effect on the final blade. I am not shouting eureka and claiming to have found the secret that will make my knives better than everybody elses, I have just noted anomolous trend in the numbers and find it interesting.

 

[Deweyknives]

What is the differance between several tempering cycles or one long one? I assume reaching ambient temp is benaficial in between, but why? What does it do for the steel? If you do two or three cycles at 400 degrees and the blade is 60RC after the first temper[just picking numbers here], what is another cycle at 400 degrees doing to improve the steel without changing the hardness?