5 hour soak with O1

Let's start from square 1 for all concerned. For the higher alloy steels we get them as speroidized annealed or if we forge them we anneal them. This means that almost all the alloying elements are in the carbides with a matrix of low alloy ferrite. ...We the austenitize with a soak. Soaking dissolves the carbides, then diffuses the carbon and their carbide forming elements throughout the matrix. We then harden forming a carbon and alloy element rich martensite [with some carbides left over]. When we measure hardness we are actually measuring ,for the most part, the hardness of the matrix.If we have not soaked long enough the matrix will not have the carbon that it should have resulting in a softer matrix. ..For a good example of soft matrix plus wear resisting carbides look at Talonite !...Proper hardness testing of carbides requires a micro hardness tester. The more strong carbide formers you have ,W,V,Mo, the higher temperatures and longer soaks needed to dissolve those carbides .....When we temper the martensite we start to precipitate very small carbides which are initially coherent with the matrix .We then have a strong tough wear resistant matrix with further wear resistance from the larger carbides ....Do not confuse this with secondary hardening found in the high V,Mo,W steel [such as S30V] where different carbides of these elements are formed at higher [~ 900F] temperatures.
 
me2 said:
...Kevin, since I failed at your "identify the micrograph" thread earlier, I'm going to try to redeem myself now.
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Don't sweat it, it was not a pass-fail thing, but a great conversation starter. Lets be honest I produced the effects in the micrographs, so I sort of had an edge, who's to say how good I would have done myself on even ground? ;)

me2 said:
...I'm going to guess that, at the lower soak times, the carbides arent disolving, and the elements in the carbides cant contribute to softening resistance as you increase the tempering temperature. Perhaps also, if the micrographs show no difference in carbide size and frequency, then the carbides are disolving, but the elements do not have time to uniformly distribute themselves. I read somewhere, perhaps Verhoeven, that the elements in low alloy steel can take as much as an hour to completely homogenize. I'm not sure what it is about the carbides that look the same.
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Martinsite said:
...I am not casting aspersions on your data. It seems to me that the longer soak times are allowing the formation of tungsten carbide, which is increasing your Rc hardness. What do you think?...
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Me2 and RJ, I appreciate your input. This thread is getting very cool, in that we are really talking about all kinds of aspects now, and I am always open to suggestions and other perspectives to help me figure this stuff out. Aside from mete's input I would also offer the same affects occuring with 1095 testing that I have done, and 1095 would have no carbides other than cementite to offer to the final hardness. R.J. don't sweat my comments about the validity of HRC numbers, they were not toward you at all, I was just getting to it before any readers got around to the same old arguments that I mentioned.

mete thanks for a good clear explanation, if it took you a few paragraphs, imagine how much bandwidth I would have wasted:D
 
mete, an interesting thing you could help to point out here is how not all heating is the same. We get diffusion with heat, but heating below a certain temperature tends to pull carbon out of the matrix and gather it together into the various carbides we are suggesting, the higher the heat below that certain temperature the more the carbon will seperate and ball up. Over that certain temp, due to very different arangements in that matrix the process sort of reverses and the balled up carbides start dissolving and the carbon goes back into solution. (for simplicity's sake I eliminated the $5 words in that last paragraph, those who like, please reinsert terms like Ac1, allotropic shift, bcc-fcc etc...;)).

I bring all of this up since some may get confused as to how one can make heavy carbides while heating at lower temps, and then dissolve them at higher temps. Thus it is possible to have a blade that would skate files real well and cut soft things fine, because of precipitated carbides yet deform rather easily when encountering a hard target, because of a carbon depleted ferritic matrix. It is one case where abrasion resistance and hardness are not interchangeable, and a file and a Rockwell tester will call each other liars.
 
"I bring all of this up since some may get confused as to how one can make heavy carbides while heating at lower temps, and then dissolve them at higher temps. Thus it is possible to have a blade that would skate files real well and cut soft things fine, because of precipitated carbides yet deform rather easily when encountering a hard target, because of a carbon depleted ferritic matrix. It is one case where abrasion resistance and hardness are not interchangeable, and a file and a Rockwell tester will call each other liars."

I think I just experienced what you're talking about here. I have a large blade of champalloy that resists the file, slices rope pretty good, but when I chopped wood, the edge crinkled and some broke off. What should I do to fix this blade?

BTW, I'll probably send you the piece of O1 tomorrow. Is your address on your website?

I'm really enjoying this thread. Keep it up guys! I have to go. I've got a lot to do today.
 
A few years ago, a friend of mine and I did an experiment using 52100 flat bars. The bars were 3/4" x .140 x 6" and we used three of them. We put all in a heat treat oven at 1500 degrees. The first one was removed and quenched after 10 minutes or so. The second was removed after 6 hours and quenched and the third was a 24 hour at 1500 degrees before quenching. All three were broke and all three had the same grain structure, according to the eye. It was all very fine grained material in the break. I am very glad to see some one else do something similiar as I was almost called a liar. There were some that refused to believe it but then that is the way things are sometimes. Thanks again for posting your results.
 
This is really a great thread! This may be simplifying things too much, but let me see if I have this right -

For the hypereutectoid steels in this discussion ( O1, 52100) it appears that 1500 is a good soak temp, and probably will not result in any significant grain growth for quite awhile. Is this true for other, slightly simpler steels - ie: is 1500 good for W2? How about 1095 (no real carbide formers)?

Eutectoid simple steels - 1084- would probably need just a short soak, whereas a relatively eutectoid tool steel (L6) would require again a longer soak - also at around 1500?

Finally, lower carbon steels like 5160 usually have a higher autenitizing temp, do they not - ie 1525-1550 or so? If you hit these temps right, presumably you can soak 5160 to get the carbide formers into solution as well.

Basically, as long as you don't exceed the austenitizing temp (like what happens all too easily in the forge, at least to me!) you are not going to experience significant grain growth without a MAJOR long soak, and you may in fact get better solution of the carbide formers, right?

Hopefully I have understood this all right, but with Kevin, RJ and Mete all on this thread I'm sure that any errors will be quickly rectified!

Bill
 
Come to think of it I can see how my last post could be confusing, but then this is a complex and confusing topic. But it needs to also be pointed out that intentional spheroidizing will ball the carbides up enough to take them enirely out of play in the form of course little spheres in the soft ferrite, and this stuff would file and machine quite easily. I often mill speroidized O1/L6 pattern weld, but if you have the stuff in any other condition it will just chew up mills and burn up drill bits. One can see that there is a whole array of conditions that one can have the steel in after thermal treatments, and "good enough" could cover a pretty wide range.

Phillip one needs to look at more possiblities with L6, the carbide laden condition is much more likely when you have enough carbon to do it. Eutectoid steel (around .80%) is right on the borderline and L6 is typically .75% C. If you are going to play with the carbides, well you need to have extra carbon to do it.

billf, by George I think you got it! Except that each steel will have its own preferred autenitizing temp. and 1500F may not be the best for all. one does have to be careful with 1095 because the grains can grow quick once your temp gets too high.
 
raker said:
A few years ago, a friend of mine and I did an experiment using 52100 flat bars. The bars were 3/4" x .140 x 6" and we used three of them. We put all in a heat treat oven at 1500 degrees. The first one was removed and quenched after 10 minutes or so. The second was removed after 6 hours and quenched and the third was a 24 hour at 1500 degrees before quenching. All three were broke and all three had the same grain structure, according to the eye. It was all very fine grained material in the break. I am very glad to see some one else do something similiar as I was almost called a liar. There were some that refused to believe it but then that is the way things are sometimes. Thanks again for posting your results.
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Ray, I am glad that the whole physics/metallurgy thing works in your shop as well. But how did this affect the coefficient of thermal expansion?:D ;)
 
This stuff all sounds so cool! I wish I understood half of it :o . Gonna have to get some books. When are you publishing yours, Kevin?:D
 
Kevin R. Cashen said:
It is one case where abrasion resistance and hardness are not interchangeable, and a file and a Rockwell tester will call each other liars.
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kind of sounds like a pounds per square inch issue. big flat file versus a pin point diamond piercing the steel, the file would have support by the masses:) . any thoughts Kevin? :)
 
Ray, I am glad that the whole physics/metallurgy thing works in your shop as well. But how did this affect the coefficient of thermal expansion?
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In a flat pattern of damascus, the thermal expansion can cause a curve in your blade if you use succeeding layers of steel with ascending levels of coefficient of linear expansion. This will also produce a very bold pattern if you can't come up with enough different steels (if the nickel content is present in the alternation layers) :)

That is the best I can do for now. :)
 
raker said:
In a flat pattern of damascus, the thermal expansion can cause a curve in your blade if you use succeeding layers of steel with ascending levels of coefficient of linear expansion. This will also produce a very bold pattern if you can't come up with enough different steels (if the nickel content is present in the alternation layers) :)

That is the best I can do for now. :)
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I was just having fun with you Ray, if you remember that year at the Scagel. Ray, had some great questions at one of my lectures at the Scagel event, and then in the middle of it all he asked me how one of my point was effected by the mean coefficient of thermal expansion. He let me go on for some time trying to tie two together, until letting me off the hook by saying he was just messing with me by throwing a term at me from the spec sheet and watching me wrestle with it for the enjoyment of the crowd. It was kind of funny. I like your aswer better thatn mine;) .
 
Kevin R. Cashen said:
Come to think of it I can see how my last post could be confusing, but then this is a complex and confusing topic. But it needs to also be pointed out that intentional spheroidizing will ball the carbides up enough to take them enirely out of play in the form of course little spheres in the soft ferrite, and this stuff would file and machine quite easily. I often mill speroidized O1/L6 pattern weld, but if you have the stuff in any other condition it will just chew up mills and burn up drill bits. One can see that there is a whole array of conditions that one can have the steel in after thermal treatments, and "good enough" could cover a pretty wide range.

Phillip one needs to look at more possiblities with L6, the carbide laden condition is much more likely when you have enough carbon to do it. Eutectoid steel (around .80%) is right on the borderline and L6 is typically .75% C. If you are going to play with the carbides, well you need to have extra carbon to do it.
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Let's see if I have this straight. For a hypoeutectoid steel which also has carbide formers in it (like L6), if it gets soaked too long or quenched to many times, enough of the carbon will get used up in carbides that there won't be enough left for martensite formation. Right?

I wasn't playing around with carbides on purpose. Here's what happened with this knife. I quenched it the first time (with maybe a ten minute soak), wasn't real happy with it, then shortly thereafter realized my oven was off. I tried to compensate for the temp being off, and soaked and quenched it again. Then I got the thermocoupler working and soaked and quenched again. After the second quench, it did very well cutting rope, and even chopping wood. After the third quench, the edge deformed when I tried to chop with it.

You told me in another thread you only soak L6 for five minutes. Is this why?

If I re-sphereoidized this blade and gave it a 5 minute soak, would that work?
Or is it too late for this piece?

So soaking is not bad in the sense of grain growth, but it is if you don't have enough carbon for both the carbides and martensite.

I think I understand now. Eureka? :D
 
Dan Gray said:
kind of sounds like a pounds per square inch issue. big flat file versus a pin point diamond piercing the steel, the file would have support by the masses:) . any thoughts Kevin? :)
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The same applies with rockwell testing and microhardness testing. Rockwell sort of gives an average value around the area of penetration, while the microhardness tests can pinpoint hardness of a very precise area. A while back, I showed some of my images of 1095 loaded with pearlite. That steel had grains of martensite totally surrounded by moats of fine pearlite, it tore my new file up trying to cut it at all, but the rockwell needle pushed things around and found an average hardness that was very dissapointing. The stuff may slice paper like crazy, but harder materials would push it around in a similar way.
 
Kevin.

Would you be able to give an opinion on what length of time a 'soak' should be for O1 and 52100?......I was going on the steel manufacturers specs which suggested half an our per inch thickness, and taking into account blade profiles and thickness, I was calculating it to be around 4 or 5 mins .....Would you suggest a longer soak as your O1 experiment seems to suggest?.

I soak at 1550F for 52100 which is the upper limit of the manufacturers specs....For a longer soak, would it be advisable to lower the temperatue slightly (ie 50F)... or maintain the temperature at 1550F?

Thanks.
 
Kevin R. Cashen said:
The same applies with rockwell testing and microhardness testing. Rockwell sort of gives an average value around the area of penetration, while the microhardness tests can pinpoint hardness of a very precise area. A while back, I showed some of my images of 1095 loaded with pearlite. That steel had grains of martensite totally surrounded by moats of fine pearlite, it tore my new file up trying to cut it at all, but the rockwell needle pushed things around and found an average hardness that was very dissapointing. The stuff may slice paper like crazy, but harder materials would push it around in a similar way.
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thank you Kevin. :thumbup:
 
Kevin Davey: You need to be careful about extrapolating the Mfgr's recommendations to knife blade thicknesses. Though I have not HT'd thousands of blades made from simple, carbon steels, I'm going to go out on a limb and say that, using an accurate, calibrated furnace and some sort of protective media like SS foil, I would not hesitate to soak a carbon steel knife for 10-20 minutes. 10 minutes for an 1/8" thick blade, perhaps, and 20 minutes for a 1/4" thick blade
This does not apply to HT using a forge, or in an unprotected atmosphere, either.

I have become convinced after HT'ing many, many blades that with proper temperature control and a choice of Austenitizing temperatures at or slightly below the mid-range specified for a given steel, that under-soaking will result in more degradation to knife performance than over-soaking.
 
Phillip Patton said:
Let's see if I have this straight. For a hypoeutectoid steel which also has carbide formers in it (like L6), if it gets soaked too long or quenched to many times, enough of the carbon will get used up in carbides that there won't be enough left for martensite formation. Right?
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Not soaked too long, but cycled improperly this would be my concern. in simplified terms, heating below critical will gather carbon together, heating above critical will disolve it into solid solution- austenite. One atomic arrangement wants to reject the extra carbon, but if you heat enough to go to the other atomic arangment it is very accommodating to that carbon.

...You told me in another thread you only soak L6 for five minutes. Is this why?

If I re-sphereoidized this blade and gave it a 5 minute soak, would that work?
Or is it too late for this piece?...
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I was giving my minimum recomendations on the time, take it to the proper temperature, and soak it good and long to get everything in solution, and then quench to trap it there. There is a lot to be said as to where you put the carbides when they form. Many, very fine and evenly distributed carbides will give very good abrasion resistance. A few very large round ones will just get ripped out and offer little. If they collect in the grain boundaries they cause embrittlement, and slow cooling once things are into solution may allow this to happen, this is one of the reasons I like spheroidal type annealing over lamellar (heating beyond critical and insulating in wood ash, vermiculite etc...), even though they require longer soaks.

Soaking at proper temps will cause the stuff to go into solution. Carbon trapped in martensite will begin to move again when we temper at higher temperatures. initially the tempering carbides will be too small to make out with an optical microsope but as you get hotter the carbon will pool up more making the carbides larger. Carbide formers will have an affinity for the carbon so that is where it will gather. This is how heating below critical can seperate the carbon out. This bunched up carbon will need some time to redissolve when you reach critical, if you do not allow for this time you will have plenty of undissolved carbides left over after the quench, so you can see how multiple cycles can effect things. How fine or coarse they are will be a function of the rate of heating.

Some folks may think they have discovered some new wild phenomenon with this stuff, but none of it is new, folks Like Edgar Bain had this stuff figured out and explained back in the 1930's and 1940's.

Heat your L6 to 1500-1520F and soak for perhaps 10 minutes and you should find things back to where you want them.

P.S. I know it is just a matter of time before somebody starts splitting hairs with the less than precise terms I am using here. Sometimes you just want to discuss this stuff with folks who aren't total nerds, and you have to resort to plain English, but it can become very frustrating when one crowd picks at you for the techno-babble, while the other is waiting to pounce as soon as you misspell "arret refroidissement". It is one of the reasons knowledgable folks refrain from sticking their necks out for these talks, I can only hope that folks will cut me some slack here.
 
Side note: This thread has proven to me that while I have have quality results through testing and use, my setup leaves so much to be desired. As a science dork at heart, I have taken this thread very seriously. Can anyone get a forced air forge to regulate at the exact temp suitable to soak for 20 minutes? I know I cant.....and that says something.....with tax refunds coming back, that oven is looking awful tempting.....

Great thread guys, a real eye opener!
 
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