Brass rod test questions.

M

Matlock

Joined
Jun 26, 2002
Messages
125
I'm trying to graduate from RR spike knives to something better. My first attempt is a 5160 (John Deere load shaft) that was hand forged from 1 1/4" round stock. I could not find any of the Texaco type A quenchant that Ed Fowler speaks of in his book Knife Talk, So I hunted around and the next best thing that I could find (and get cheap) was some Exxon Univolt N-61 From the Local Transformer shop. Anyway, I have triple quenched the blade and am in the process of tempering it. I am starting out at 325 deg for two hours and plan to repeat this three times. My question is When do you do the brass rod test? After the first temper, or after all three tempering sessions? If the blade is too brittle, which is what I expect since I am starting out at such a low temprature, do you temper it again 3 times at 25 deg. higher then test again or test after the first temper at the highter temp?
Any thoughts on this would be greatly appriciated.

Matt Matlock
 
Matt...

I would test it after the first temper.

That way you can bump up the temp if it chips out. With 5160 I start at 350F , but it is not a bad idea for the first time going with a little lower temp and testing it. My guess is that you'll want to go up to 350F.

Hope this helps,

Greg
 
I believe you should test after all 3 tempers are done. It takes all 3 to relieve the brittleness left in the steel from the quench. There are several variations and you may have to test your blades with your own methods to feel confident in the outcome.

I have had the best blades with 5160 as follows:
Forge to near shape being careful to not overheat the tip. (leave it fat)
normalize 3 times
anneal 2 times
grind to near shape (tip still fat)
quench 2 times in 130deg. oil
temper soon at 350-375deg. for 2 hours, 3 times (allow the blade to cool to room temp between tempers
Be careful to not over-heat when finish grinding (grind bare-handed and dip often.

Hope this helps
 
I do the brass rod test after the third temper. If it chips bad, go up 25 degrees for three heats then test again. If no chip, the next blade will only get a 10 degree raise in temperature and test on the brass rod. The whole idea is to temper as low as possible. Then test for cut. Bob Brownells is planning on selling Texaco Type A in the near future.
Good Luck and thanks for giving our ideas a try.
 
Metalurgically, this would make little sense. You would be tempering at 350F (slightly higher for other steels) between heats up to around 1550F for hardening. Those heats before hardening would of course completely erase any effect of the tempering heats.

John
 
Basically, how is the 'brass rod test' performed. What am I looking for; chiping?

Thanks; RL
 
RL, you're right, if the edge chips then the blade needs to be retempered at a higher temperature in increments untill it stops chipping. If the edge deforms and doesn't flex back straight then the tempering was done at too high a temperature and the heat treating must be completely redone.
 
Danl: I only temper after the third quench. One important part, when you forge, keep the temp low. 1620 f. is my top forging temperature, when blades fail it is usually due to too high a temp during the forging cycle. Bad steel can also result in failure. You can tell 1625 f by the slag that forms, if it looks like show flakes you are very close to 1625 f. If slag comes off in sheets, you are over 1750 and grain growth can occur. If higher than that you will have blades that may need tempered immediately. I feel this is the source for the necessity for immedite tempering. Another important variable is the cool down rate. Quench the blade to a black heat, then submerge the entire blade in the quenching oil and let it cool to room temperature as slow as it will. The effects of the quench will continue long after the quench. With 5160 you can get away with quenching three times in a day. 52100 will produce a tougher blade if you allow 24 hours between quenches and a night in the home freezer will make for better cutting performance.
 
Ed,

A couple of things.

At what point to you go to the freezer? Between the second and third tempering? Or?

Also, I love that Bowie in the newest Blade. Good stuff. I see that compared to the rather straight Bowies in your book, you have incorporated elements of the "Michael Price grind". A very nice touch.

Finally, I noticed you get multiple hardening lines, for lack of a better word. Do you think this is a product of different depths of hardening on each quench? Or is it that 52100 zone hardens on every quench? (I hope the question is clear.)

John
 
John: I go to the freezer after every quench and after every temper. With 52100 you gain a little with each cycle. 24 hour waits between each cycle. After each quench allow the blade to cool to room temperature and sit for a couple of hours at room temperature, then into the freezer, same with the tempers, put it in the oven set your temp, let it come up, hold for 2 hours then cool down in the oven to room temp, then back to the freezer. When I have a batch of blades waiting for final grinding, I store them in the freezer. 52100 responds well to tincture of time and every little bit helps.

The bowie was quenched to the exact same level in the oil each time. What you see I call hardening zones that I feel reflect or are influenced by the martensitic structure inside the blade as well as the structure of the steel on the surface itself. There are a lot of variables involved and a lot of what I just stated is theory (why not what you see). I believe the outside geometry influences the martensitic structure inside when hardening, providing the opportunity to get real involved. I believe that it is possible to grind one geometry, harden, then grind to a differing geometry and take advantage of this phenomon as a functional attribute. That Bowie is an example. Hopefully we will have some definate answers in the next 6 months.

Thank you for the kind words about the Bowie in my ad. It is the product of a lot of time and thought. Her sister passed all the tests I feel would indicate a truly high performance blade. The modified Michael Price Grind is a real opportunity to push your abilities to the limit, keeps it interesting. I am very pleased that you noticed! Thanks
 
I never really got an answer as to how the brass rod test is to be performed. I have asked this on more than just this post before. I get answers about what to look for - like chipping and such.

Maybe I should ask it this way: What is it that the poor unsuspecting brass rod is subjected to? Is it whittled? Is it chopped? Is it wacked at? HOW DO YOU PERFORM THE BRASS ROD TEST?

Thanks; Roger
 
Hi Roger,

hopefully I can answer your question. Clamp the brass rod horizontally into your vise then take your sharpened blade and place the edge in a 15°-20° on the rod. Start at the choil area and with enough pressure to make the edge slightly flex, pull the edge over the rod. If the edge flexes back you tempered right. You could also check just certain areas of the edge by applying pressure to check if the edge chips.
Hope it helped, Cyrus
 
Another try at the explanation. It is just like a slicing action accross the brass rod, except instead of cutting into the rod, you draw the edge across the rod by pulling the spine of the blade to you thus simply stroping the edge on the rod. Flex the edge from riccaso to tip. Keep enough pressure on the edge to make it flex up. The edge should return, a small portion may remain raised as a 'wire edge'. Interestingly, the depth of the wire edge is an indicator of the nature of the steel. A very short wire edge that comes off as fine particles indicates you have pushed the steel to its limit. This statement applies to 5160 and 52100, I do not know about other steels. I would guess they are similiar.

Presently we test each blade through 8 flexes, right and then left, they will do more, but that is plenty enough test.

Should a blade chip, hone the flexed area off from the blade, before you temper again, other wise you may be flexing the edge again on the next flex test, thus contaminating your test with previous tests. Before you finish the blade, remember to sharpen away the flexed area, or you will be selling a blade that has already done more work that will probably be required through the rest of its servicable life.

If you can find a copy of my video, there is a demonstration in it.

Good luck
 
Thanks for all the great info!

Ed, I love your book, and can't wait for Knife Talk II.

Matt
 
I too, want to say, thanks Ed for all the info. I also loved
your first Knife Talk. I didn't know there was a Knife Talk II.
I can't wait!
Ed I wish I could understand more of your discussion of grinding
one geometry, heat treating then grinding another to take
advantage of the new geometry. Does this mean that the martensitic
boundry becomes less acute as the blade is thinned. Are you referring
to the possibility that it is more advantageous to have a boundry that is not straight across the thickness of the blade but notched when viewed cross sectionally. I don't know if I am making myself clear. It would seem that the blade would be stronger if this boundry
was not more square across the cross section of the blade.
 
Thanks a bunch. It is clear now. I'll get a couple brass rods on my next supply order.

Roger
 
Don: When you break a differentially hardened blade, you will see an upsidedown cone (pointing toward the spine) of fine grain. The nature of this cone is dictated by the nature of the steel itself, chemistry, grain structure and the stuff the bladesmith has done to it and the geometry of the blade. You can grind thick and thin along the blade and the cone that forms will vary ever so slightly, it does not take much to mean a lot. The significant aspect of what happens is the grain matrix. Solid 14 grain is probably going to be brittel. 14 AND FINER makes a big difference. The transition bands reflect the cone and the matrix. I am a long way from understanding the science of what, but I do know that purely from a performance view, it can work very well and the variables are limitless. It is just a fun place to explore.

Don and Matt, thanks for the kind thoughts about Knife Talk.
 
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