View Full Version : Quench During Forging


cactusforge
07-14-2004, 10:32 AM
This will be a good place to ask a question that I have wondered about. I have read that some blade smiths advocate quenching a blade during the forging process, who thy are I don't remember, CRS I guess. I have tried this and not seen any results other than getting rid of scale. Now that we have expert/experienced smiths and metallurgist watching this forum can we get some opinions. Gib

Quenchcrack
07-14-2004, 01:06 PM
By quenching, I assume you mean a dunk in the slack tub to get it down to a safe handling temperature? If you are using a high carbon steel, this sounds risky if the blade has not been ground smooth. Hammer marks, scale, decarb, sharp corners, etc can all create stress risers that can result in a crack. If you have to cool it down, maybe oil quenching or waiting until the blade is at a black heat would be safer. If you are asking can a blade be quenched when it is near net shape and does it do any good, the answer is yes. While quenching is always risky, a blade that has been austenitized and quenched 2-3 times will have better toughness, hardness and abrasion resistance. If it doesn't crack or warp. :evil

cactusforge
07-14-2004, 02:27 PM
Quenchcrack, I had always used oil/ATF for a quench fluid. When heat treating I do use a triple quench and a triple draw on 5160. On 10XX steel I have not found it to be of much value. Thanks for your answer. Gib

Quenchcrack
07-14-2004, 09:25 PM
I visited your website, Gib. Really nice work! I also prefer the more rustic style but I did not know it was a Neo-Tribal thing. I started making Celtic skeleton knives from single turns of a 3" RR coil a couple of years ago after not making a knife for over 15 years. My problem is that I no longer have my belt grinder and never did own any polishing equipment. I just got too lazy to rub them up by hand!

cactusforge
07-14-2004, 10:48 PM
Quench, Thanks for visiting cactusforge. If you spend some time at the outpost you will find some amasing things, you don't need a lot of equipment. Tai Goo builds his knives with out a lot of tooling, does his finishing with a file. You can forge right down to the cutting edge thickness, forging the bevel with no grinding required. Gib

Kevin R. Cashen
07-15-2004, 11:15 PM
... If you are asking can a blade be quenched when it is near net shape and does it do any good, the answer is yes. While quenching is always risky, a blade that has been austenitized and quenched 2-3 times will have better toughness, hardness and abrasion resistance. If it doesn't crack or warp. :evil

Quenchcrack, you would make a whole group of bladesmiths jump for joy if you could provide a description of a mechanism or cause and effect, that is not just grain refinement or more complete carbide dissolution. Have you encountered other phenomena resulting from multiple quenches? Are you recommending that the quench cycling be done at the time of final heat treatment or can it be done as a preparatory treatment following say forging?

What sort of performance gains are you describing? Some smiths have communicated 5 times the level of performance from a blade quenched 3 times at the time of the final heat treatment (quench hardening, of course tempering would follow).

Quenchcrack
07-16-2004, 12:41 PM
It is a well known phenomenon that mechanical properties of a piece quenched more than once go up with the same cycle times and temperatures. By properties I mean toughness, strength, hardness and ductility. As you observed, this is probably a function of more complete dissolution of the carbides and grain refinement. Tempered martensite will transform to austenite faster than ferrite/pearlite created by normalizing. The fine carbides in tempered martensite dissolve quicker and can diffuse over greater distances leading to a more homogeneous microstructure. It is not without dangers, however because every time the iron goes though a transformation to martensite, there is a volumetric expansion. That means that guards may not fit right, holes may get smaller, etc. This is one of those practices that sounds like rumors or urban legends but it really does work. I would probably not endorse quenching during forging since you would likely reheat the blade and un-do everything the first quench did. I think it works best when done at the time of heat treating. Just remember to re-heat very slowly after quenching or you may get cracking due to thermal shock. The re-heat for subsequent quenches probably tempers the blade, meaning you don't need to quench, temper, reheat. I am thinking here of oil or water quenched blades, I am not ready to pontificate with any certainty regarding air-hardening tool steels. Tool steels are usually very high alloy, high carbon and the structure is tempered martensite with massive alloy carbides. Those alloy carbides provide much of the abrasion resistance and I don't know how they might behave with multiple hardening cycles. Anyone have any experience with this?

Kevin R. Cashen
07-16-2004, 11:34 PM
Quenchcrack, I would like to thank you for the most concise and logical description of this that I have yet encountered on the internet. The grain refinement and carbide dispersion are the aspects that have been discussed in the past, as well as the increased dangers of distortion. Other than the more familiar work done by Stickels, are there other sources you can recommend on the effects of quenching from varying prior microstructures on carbide refinement?

Are there any quantifiable numbers on the amount of increased abrasion resistance, or impact strength of such treated steel, in comparison to a single quench with longer soak times?

Quenchcrack
07-17-2004, 07:38 AM
Kevin, thanks, coming from you, I am flattered.

My comments are probably a systhesis of many sources and personal experience but for theory, I think George Krauss is the best on heat treating. His book "Steel and its Heat Treatment" is a very thorough discussion of what is happening on the microstructural level. Used copies of his books are in the $100+ range, though.

One of the first lessons to be learned about heat treating is that carbon content controls the hardness of the martensite. However, carbon that is not in solution does NOT contribute to the hardness of martensite. Carbon tied up as carbides effectively reduces the carbon content of the steel. So how do you get that carbon back into solution? Soaking at temperature is one way but is difficult in a forge and tends to scale the piece. Heating hotter helps, too. That is why I promote heating hotter than non-magnetic. Normalizing is a good way to dissolve big carbides and re-precipitate them a fine carbides. It also refines the grain size. Above all else, DO NOT ANNEAL prior to hardening. Annealing is intended to soften the steel by forming BIG CARBIDES, which is exactly what you do not want prior to hardening.

I do not have any hard numbers regarding the percentage improvement in the properties by multiple quenching, I only know that it is true. In 30 years of heat treating, I have had to re-heat treat a lot of steel and I quickly learned that the second, or, occasionally, third run gave better properties. I would guestimate that the average properties went up 15%-25%.

Mark Williams
07-17-2004, 08:11 AM
Hi There,

So what would be a good procedure to decrease grain size prior to quenching, especially after annealing to do stock removal? Normalizing?

Thanks

Kevin R. Cashen
07-17-2004, 10:31 AM
Quenchcrack, I am flatterd that somebody with your experience would take time to put up with my questions. I keep my eyes open for George Krauss's work whenever I can, his "Principles of Heat Treatment of Steel" is one of the most treasured books on my shelves. It is one of the few texts that I have found, that dedicates the deserved amount of pages to lathe and plate martensite as well as upper and lower bainite morphologies, I have recommended it many times.

You are correct, once again, in pointing out that because I work with the salt baths, I have the luxury of worrying about exact soak times at temperature. Bladesmithing by its tradition is a forge and a quench bucket, so the short times repeated is an easier route while avoiding scale.

As for annealing, I work mostly with O1 and L6, some degree of softening is necesarry for me, if I want to do any sort of machining and keep my abrasive budget from going higher than it already is.

I really must repeat how refreshing it is to have somebody who can give such straight forward and clear answers on this topic. When the question and answers are clear and free from hype, all of the controversy just sort of fades away. Your estimates of 15-25% are much more reasonable and lends more credibility than some of the claims out there. Unfortunately C.A. Stickels report focused on the size and dispersion of the carbides so while it offers plenty of metallographic examples, there is an absence of numbers dealing with physical testing of the resulting properties :(

raker
07-17-2004, 10:46 AM
This has been a very informative discussion about heat treating, about as good as any I have every read. I learned some more and am glad that this information is shared. It will hopefully help a lot of newbies in their quest for the ultimate blade.
Thanks again, Kevin and Quenchcrack.
Ray
I keep getting better Kevin and I will be able to keep up with you again in the cutting contests. :)

cactusforge
07-17-2004, 10:46 AM
Quench, Will the multiple quench method work with all steel, I had the impression that it worked best with 5160, 52100 and that it was not much help using 10XX steels. Gib

Quenchcrack
07-17-2004, 12:28 PM
A good process to refine the grain size and disburse the carbides is to normalize 2-3 times, using a lower temperature each time. The exact temperature will depend on the steel and the carbon content but if you heat to, say, 1650F, then 1600F, then, 1550F and quench, you should get some improvement.

I think it is probably true that the higher alloy, higher carbon steels do respond better to multiple quenching. Tool steels with high chromium and vanadium are especially difficult to austenitize because the alloy carbides are stable up to about 1850F. !0XX steels really form only cementite, or iron carbide which dissolves at lower temperatures. However, I would not hesitate to recomend multiple normalizing or quenching even on plain carbon steel.

The move toward finer and finer grain size has lead us to iron alloys with no grains at all: amorphous metals, or metallic glass, has some amazing properties. I expect to see a custom blade made from this material one of these days but it will have to be made by stock removal. If you heat it up, you lose the amorphous structure.

Oh and Kevin, my copy of Krauss's book is autgraphed by the author........ :D

fitzo
07-17-2004, 01:05 PM
Are you familiar with Liquid Metal, Bob? It's a new high-tech amorphous alloy technology. RW CLark and a couple of others have produced blades from the stuff. It was written up in one of the knife mags a few months back. There are also threads here (CKD) and at Blade Forums that discuss it, should you elect to do a search.