The 5160 "How I do it" Thread

[GHEzell]

Originally Posted by Burke

Alan l and ghezell,

How are you guys seeing recalescence in your heat source?

I take it out of the heat for a second and look at it, check it with a magnet, then back in the heat. When the magnet starts to weaken, then it's time to watch carefully. With my forge, I can see what's happening inside pretty well at hardening temps, though I doubt it's good for the eyes to stare too long. I watch the 'bright' move up the blade from the edge back, taking pains to keep the tip from getting hotter than everything else while it does it's thing. Once I saw it a few times it became easy to spot.

Yeah, real scientific...

[Dan Graves]

Ed, From your website "Once the final quench/cool cycle is complete, grind off the scale with a 120 or 220 grit, and get ready to temper." It has been my understanding that you are to get the blade in the tempering oven right after it cools enough to pick up bare handed. Is there a reason you do this? Great thread.

[Burke]

Dan,

to paraphase Ed from an earlier post, blade size cross sections do not necessarily follow the rules of metalurgy right to the letter. I have hardly ever went from a quench right into a temper. My normal practice is to wait twenty four hours between hardning and tempering. I do this for everything that I make even with a water quench. I haven't had one blade break during this wait time. I have had blades crack/break when quenching in water but if they survive the quench they are good.

Also to clear up some terminology:

recalescence

SYLLABICATION: re?ca?les?cence
PRONUNCIATION: rk-lsns
NOUN: A sudden glowing in a COOLING metal caused by liberation of the latent heat of transformation.

decalescence

SYLLABICATION: de?ca?les?cence
PRONUNCIATION: dk-lsns
NOUN: A sudden slowing in the rate of temperature increase in a metal being heated, caused by endothermic structural changes and resulting in a darkening of the metal.

So if some of you guys are quenching after you see RECALESCENCE then you are not getting MARTINSITE.

[Alan L]

Thanks for clarification of terminology, Bill! Decalescence is the term I'm looking for. I use the method Dr. Batson taught me, in a coal forge. That is, after the fire is almost burned down I build a "cave" in the coals, roofed with a steel plate and surrounded by more coals. When I think the temperature in there is about 1525 or so, I put the blade in and keep it moving with as little air added as possible until I start seeing the shadows swirling in the steel, or decalescence. When the last of the shadows are gone from the part I want hardened, be that the whole blade or just the edge portion, I quench in 130 degree vet-grade mineral oil. This can take up to 15-20 minutes for the blade to come up to temperature, and results in little to no scale.

Dr. Batson said that this works for any simple or low-alloy steel, but you need to know if there should be soak time involved. The slow rate of heating for me results in the edge soaking for about 5 minutes while the back is coming up to heat. From what I've read, this is enough to dissolve the few carbides you get in 5160. I know it's not long enough a soak for something like W-2.

Hope that helps explain what I'm trying to say!

[Karl B. Andersen]

I'm glad you came in on this Bill.
I was threatening a post on the same facet of heat treating, and you managed to get it in just a few sentances.
The key words in the above description are "COOLING" and "...a metal being heated".
One is on the way up, the other on the way down!
One is a knife, the other is a letter opener.

[cdent]

Is it just me, or is it tougher to see decalescence in 5160 rather than some of the higher carbon common forging steels?

Karl, I also appreciate your comment earlier about scale size. I've been trying to keep it at sort of ground pepper size and make adjustments if it comes out of the fire and forms sheets. It's become my indicator that I'm reducing temps, but I wasn't sure.

Have a great weekend, Craig

[GHEzell]

Originally Posted by Burke

Also to clear up some terminology:

recalescence

SYLLABICATION: re?ca?les?cence
PRONUNCIATION: rk-lsns
NOUN: A sudden glowing in a COOLING metal caused by liberation of the latent heat of transformation.

decalescence

SYLLABICATION: de?ca?les?cence
PRONUNCIATION: dk-lsns
NOUN: A sudden slowing in the rate of temperature increase in a metal being heated, caused by endothermic structural changes and resulting in a darkening of the metal.

So if some of you guys are quenching after you see RECALESCENCE then you are not getting MARTINSITE.

Thanks for the correction... decalescence was indeed what I should have said.

[Burke]

Originally Posted by cdent

Is it just me, or is it tougher to see decalescence in 5160 rather than some of the higher carbon common forging steels?

I don't have any trouble seeing decalescence when hardening but I have noticed that when thermal cycling 5160 the first cycle it is really hard to see the recalescence during cooling but it gets easier with subsequent cycles.

[cwp]

Originally Posted by Ed Caffrey

Don't get me wrong, I have nothing against the metallurgy of what we do. I strongly believe in it, and I apply it every time I forge a blade. What I do have issue with is all the "experts" who believe that the only "correct" answer is one that can be scientifically proven, and who generally have no practical experience in the field of question.

Ed, being an engineer, and spending way to much time in at a University, I think the problem with the guy is not that it can't be proven scientifically, but that he hasn't seen it and is to lazy to want to think about it himself. These are the worst type of people to run into in the Academic world.

I personally believe that everything you are seeing could be shown through the scientific method. It would cost money, but we are at a point in this world where we can look at each and every atom along a slice, remove a layer, and look at the next layer, etc.

Doing this would probably be of benefit to those who study metallurgy, they could probably even get a theory to predict it.

Anyway, I think this attitude is all laziness, and nothing at all about scientific inquiry, after all, the basis of scientific inquiry is theory, experiment, new theory when the last was proven wrong. All the really good scientist embrace things when they challenge the established dogma.

[Karl B. Andersen]

Originally Posted by Burke

I don't have any trouble seeing decalescence when hardening but I have noticed that when thermal cycling 5160 the first cycle it is really hard to see the recalescence during cooling but it gets easier with subsequent cycles.

Bill, I see the same thing in almost every 5160 blade I make. Sometimes, on the first cycle, it happens so fast I can't even see it! Then easier to follow in the second and third.
That fact alone tells me that with 5160/52100, SOMETHING occurs within that steel that gets progressively more acute with successive cycles. Maybe this is a manifestation of what benefits these steels with the triple quench when using O/A.?

[Burke]

That could be Karl, I was kinda tinking that it had to do something with the grain getting smaller with each successive cycle.

[Ed Caffrey]

To answer the question posted earlier about tempering immediately after hardening.....

If I'm conducting a multiple quench, I will wait, allowing the blade to cool down to room temp IN THE/WITH THE QUENCH OIL. If I am doing a single quench, as soon as the blade is cool enough to handle, it goes into the tempering oven.

The reason(s) I do this is because I have never had any problems (stress cracks) occur when multiple quenching and allowing the blade to cool down to room temp in the oil. I really can't put a specific time frame on it, but suffice to say that I do allow it to come to room temp. After the final quench in a multiple quenching cycle, I get the blade(s) into the temper oven as soon as the oil is near room temp. I do this because on several occasions, for one reason or the other, I left blades sit on the bench overnight (both multiple and single quenched) only to find the edges full of tiny cracks when I was about to put them in the tempering oven. I've had this occur with both 5160 and 52100, as well as single and multiple quenched situations.

So, as the thread title reads, "How I do it" is:

5160: Single quench goes into the tempering oven as soon as its cool enough to handle. Multiple quenched blades go into the tempering oven once the final quenching cycle it complete, and the blade(s) have cool IN THE OIL to near, or at room temp. If I'm conducting a multiple quench on 5160, I try to time it so that I do the first hardening before I close the shop down in the evening. Then the second hardening takes place the next morning, followed by the third quench taking place around noon, or when the blade/oil have cooled back down to room temp.

[chiger]

Originally Posted by Karl B. Andersen

That fact alone tells me that with 5160/52100, SOMETHING occurs within that steel that gets progressively more acute with successive cycles. Maybe this is a manifestation of what benefits these steels with the triple quench when using O/A.?

Hey Karl,

I'm not metallurgist or expert on thermal dynamics, but I think I have an ideal that might account for what you are seeing. Steel is just like people, water and everything else in the world. It will tend to do the easiest thing first. You know, path of least resistance.

As we all know, heat migrates to cold. The migration occurs at the easiest, closest, most conductive places first and so occurs quickly. That's the path of least resistance. On subsequent cycles and as the steel becomes homologous, the lines of migration take longer because it's covering longer distances through stretched out lines of low resistance. So you can see them better. Just a thought.

Oh, and on tempering water quench steels quickly. If you don't and it doesn't crack...you've just been lucky. 25 years and nothing. Then, just the right blade shape or thickness or something and snap. I have pictures! And it happen in less than an hour. As soon as it's quenched I RUN to the oven.

chiger,

[Carey Quinn]

"If I'm conducting a multiple quench, I will wait, allowing the blade to cool down to room temp IN THE/WITH THE QUENCH OIL. If I am doing a single quench, as soon as the blade is cool enough to handle, it goes into the tempering oven."

That's really interesting Ed. Would you mind telling us what determines whether you are using a single or multiple quench.

Thanks,
Carey

[Ed Caffrey]

Generally if a blade is being edge quenched, then it gets multiples. In some cases I would fully quench (such as survival/combat type knives). The difference for me is that for a single quenched 5160 blade, I allow it to soak (using the salt pot) at 1425F for about 3-4 mins prior to the quench. For an edge quench it gets three quenches, with no soak time at 1550F, where in I try to only get that part of the blade that I want to harden, up to temp. With these procedures I get the same hardness/matrix structure in each blade, and can use the tempering to regulate the hardness vs toughness aspect.

I did a lot of playing around, and spent a bit of $$ for the spectrographing to get that figured out.