Rc test on 52100

kevin dewey i tried to email you back but it wont go thru. do you have another email address i can email you at?
 
I somehow missed the replies in this thread, so I will play catch up.

Steel supplier is Sullivan Steel in New Jersey... they specialize in 52100 bearing quality steel which I believe is manufactured by Ovako Steel in Norway.

My heat treat process is nothing new. I do the usual things to refine the grain after forging, (either multiple normalising , or sometimes multiple quenching x 2..before the final quench harden).
Use a digital oven/kiln and all my thermal and hardening heats are set at 1550F.
I have been experimenting with soaking at 1550F to see what happens, no noticable visible grain growth, the Rc hardness has increased from my shorter soaks..

The figures quoted were square sample pieces (full quenches)....I am quenching blades tip first and getting the same results (on the ricasso and tang) ...it seems to me that this gives a slightly faster quench than a full austenite edge quench where the heat is retained in the spine.......so a full quench in my shop relates to a slightly harder 'as quenched' blade.

My tempering temperatures have had to increase to 500F + to bring the hardness down to the 59/60 range...and the blades are almost blued by the time the tempering has finished!

Yeild strength.....I have found that my full hardened blades that have been tempered (to Rc 60) will flex to around the 45 degree mark and return to true without any additional temper designed into the spine... pass 45 and they will snap.


I use Chevron 70 quench oil at 140F ambient...a medium to fast quench ( slightly faster than Texaco type A).

Steel specs as supplied from the manufacturer ..(I buy in bulk....been using this same stock for the last 3 years).

C .98
Cr 1.39
Si .21
Mn .27
P .011
S .009
N .17
Mo .05
Cu .182
V .004
AI .030
Ti ppm 7
O ppm 4.2

Bill..You can of course send me any samples for testing, but if they are pretty , then you may not get them back...:)

Ray...May see you at Batsons, but definately Blade.

PimpinSquee...I will send you another email

Kevin.
 
I will be looking for you , Kevin.
Take care and keep up the good work. You might make a competition blade for Batson's to see how it does. I want to but will probably not.
 
Kevin,

Thanks for all the info.

I was talking to Randall Graham about W1 and he was recommending tempering at around 475-500F to get down around 58RC.

I really believe that many who are now using digital controls and dedicated HT oils/salts are going to have to up tempering temps from what many have used in the past simply because they are doing a very good job of grain refinement and hardening.

"Use a digital oven/kiln and all my thermal and hardening heats are set at 1550F. I have been experimenting with soaking at 1550F to see what happens, no noticable visible grain growth, the Rc hardness has increased from my shorter soaks."

Could you please clarify this? What do you mean by "shorter soaks"?

Thanks,

John
 
John Frankl said:
Kevin,



Could you please clarify this? What do you mean by "shorter soaks"?

Thanks,

John
Click to expand...

Hi John.

I used to use the triple quench technique, and doing it this way I used to just wait till critical temperature was reached, soak for a minute or so then quench.

I then extended the soak times to 5 minutes but still using the triple quench harden.

Then I played with 10 min soaks with a single quench...though I may have used a double quench somewhere after forging to refine the grain...or I may have just done the more usual triple normalise.

Currently I now soak at temperature for a full 15 minutes after grain refinement and do just one hardening quench. It seems to me that the longer the soak, the more hardness (when compared to shorter soaks).....In theory I think I am achieving more martensite transformaton, which is why I have had to considerably increase the tempering temperatures.

I had concerns about the grain growing on soaks, but using a loupe, there seems to be no significant difference.

My intention s to keep manipulating the soak times till I find what I think the optimum is ....and then I am interested to see if cryogenics will make any improvements.

Eventualy I hope to fit a handle and finish a knife I am happy with ....lol
 
Kevin, you are doing it pretty much the way I would. I like to zero in on things by making up a series of samples and labeling them in minutes soaked and then put them all in to austenitize at once. As each chosen time interval goes by I quench the next sample. When all done I Rockwell the samples and then break them to examine grain before preparing the ends for metallographic examination.

HRC will increase with soak time until you reach a plateau where HRC will level off. This is due to the amount of carbide that is left undissolved in shorter soaks and getting more of that trapped carbon into solution with longer times. Eventually you will reach a limit on dissolving the carbides, due to alloying, and the HRC should level off at a maximum. I like to find this point because it allows me to not burn more energy and fuel than is necessary, I have no concern for grain growth however, since the leftover fine carbides will not allow this to happen.

The soak time will depend very heavily upon prior condition due to the normalizing or annealing you used. I get a pretty good handle on what is happening with the metallographic examination. The Rockwell tests will tell me the hardness is increasing to maximum, the fracture examination tells me there are no detrimental effects to grain and toughness/strength, but the metallograph tells why it is happening. You can see the carbides getting smaller and fewer as time goes on. Grain boundary cementite disappears and only fine chromium carbides are left when proper soak is used.
 
Both Kevins are now making sense. I was thrown by the word "shorter" when in fact it seems you are talking about longer, to a point.

Thanks again,

John
 
If you are experiencing higher HRC values than you expect, it may be due to austenizing at a higher temperature than prescriped. If you have a scrap piece, heat treat it and breat off a corner (wear protective clothing) and see what the grain structure looks like. If it is a little coarse you might think about reducing your austenizing temperature. If not, Merry Christmas!

Jim A.
 
DAMNENG said:
If you are experiencing higher HRC values than you expect, it may be due to austenizing at a higher temperature than prescriped. If you have a scrap piece, heat treat it and breat off a corner (wear protective clothing) and see what the grain structure looks like. If it is a little coarse you might think about reducing your austenizing temperature. If not, Merry Christmas!

Jim A.
Click to expand...

What grain? :D
 
I haven't done the soak time at 1550 for a long period of time but have done a 24 hour soak at 1500 and there was no grain growth at all. The grain size of 3 pcs that were in the oven from 1, 6 and 24 hours were all the same size after quenching. The outside of the pcs were different due to time exposed to the high temperature.
Kevin had soaked and checked the grain size at 1550. I soak mine for 20 minutes at 1550 before quenching. This is about 115 degrees above critical, give or take a bit. I temper around 460 to 475 and get a Rc of about 57. The batch of my steel has is different from Kevins. This is what I have to do to mine.
 
Thanks Ray.
Thats interesting about those long soak times, ......bet you had some high electric bills that quarter:)


The steel supplier suggested a hardening temperature of between 1525 and 1550 for this steel mix.....In reality, I could probably drop my temperature a touch, but would not want to exceed it...I am probably right on the line.
 
I do notice that you have a bit more carbon in your batch than I do. You also have some vanadium and more moly. I also have a touch of nickel in mine. That is one more reason to buy the biggest batch you can when your buying or at least know that it will all be the same batch. I am still working on a batch of 8 ton that I acquired about 10 or 11 years ago. I have also gotten some smaller round bars and they have different mill specs than the bigger round bar.
The electric bill was a school project and actually, holding the temperature doesn't use that much juice, I think. :)
 
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