Quench plates...thermal conductivity of copper400, alum@175?

A

ate1675

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Aug 19, 2013
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I am looking into quenching 15n20 alone and Im seeing oil to Quench plates of aluminum. Ilooked up what else "sucks "heat because I have some different stones,slate ,soapstone, marble in slabs and wondered if these could be used as plates and came across a thermal conductivity wiki and it gave numbers for all sorts of things.As I looked I saw all the things in everyones annealing ,hardening and tempering recipes,and was wondering if anyone knows why we throw stuff in oil and brine when coppers numbers are higher.Can it be faster and smoother?I was trying to find thick alum.& dont have any here so I was going to stack up some thinner stuff until I saw copper is more thermal conductive and has higher heat transfer coefficients. I then thought PENNIES! As it turns out nowadays they're 95%zinc(which has a w/mk# of 116 ,the rating used in the wiki, the higher the better, and only 5% cu. But, pennies from 1962-1981, which shouldnt be too hard to find, are the reverse,95%cu & 5%zinc,with some tin.I think I found my Quench plates!I think they will also form better around the contours of a blade than plates, I also will try a big ball of wire ripped out of a few electric motors for even better conformity.I would put a link ,but I dont know how.Very interesting info to me,google egineeringtoolbox.com/thermal-conductivity-d 429.html any thoughts?-mikey j
 
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I'm not sure you understand all those numbers you were looking at, and I am sure you don't understand the quenching phase of heat treatment. It mainly has to to with conversion speed from different structures, and the speed needed to super-cool austenite.

Different metals have different needs as to rate of cooling and other things that determine what type of quenchant and what speed they need. The commercial quenchants are designed to be fast where fast is needed and slower where slower is needed. Some things, like canola oil, work pretty well as a quenchant for many groups of steel. In the air hardening group, air is the normal quenchant. Quench plates are used in this group to somewhat speed the quench , but mostly to avoid warp.

Quench plates , even copper, would be too slow for many steels.

Suffice to say that the quenchants needed have been well worked out by people who understand those numbers and many other technical things.

And then there is marquenching, and aus-quenching, and bainite...........


A good analogy would be hammers. If all you needed to do was hit a nail hard enough to pound it in, all hammers would be a #10 sledge.
But some nails need smaller hammers, and some jobs need different head shapes, some metals need a very soft hammer face, and some metals need to be really walloped....thus we have dozens of different hammer types. Each one is right for its mating task, and wrong for most others.
 
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Ignoring all other absurdities, thermal conductivity through wire bundles, compared to homogeneous material sucks. I work as an aerospace engineer on electric motor and generator design, and I can assure you that your wire bundle idea, while very creative, will not give you a hard blade, unless the steel used would have hardened in air anyway. There is simple too much air in your bundle, however hard you mush it. Also, you aren't considering conductivity across boundaries, meaning wire to wire or penny to penny.

Learn the basics by standing on the shoulders of giants...all the knife makers before you, and the engineers and metallurgist that work this stuff out for a living. When you have the basics and can make a half decent knife, that is the time to start experimenting.
 
I need to quench 1, 15n20 blade 6"long 1'wide and.95 "thick.I can harden 1075,84,and 5160 successfully,and make half descent knives.I guess my question would really be ,if I can get this blade into and out of the oil and want to plate Quench it from @900 -800deg.f.& I dont have thick aluminum onhand could I fold it up in the middle of a bundle of copper wires like a book , even on all sides , and in depth, and squeeze it in a vise to air harden ? I read about alot of guys plates and most were alum ,some steel and a few copper,which led me to the thermal wiki,some had fans on them or kept them in the freezer til needed.As I understand it and can attest to some harder areas on my 15n20, where it was cut at the store I got it from with a cutoff wheel,it does actually air harden somewhat,so for" plates" to squeeze this from 800 deg.down as Ive read people do with monosteel 15n20 blades do I need something in plate form or could this work ? Would copper plates work better than aluminum?Should I not think and type at the same time?I dont need an answer for the last thing.
 
I do not have CCT for 15n20, but IF it is air hardening, than you DO NOT need to increase cooling speed. Plates are for warp protection.
And I would NOT use wires. Even if squeezed, they would still contain lots of air pocket. In fact, their cooling speed could be worse than for just moving air...
 
Even worse than the cooling rate and inequality of using wire bundles to plate quench, they would exert uneven pressure on the super-cooled austenitic blade, very likely causing warp or ripples in the blade.

ate1675 - I understand what you are trying to say, but what you don't understand is that you are asking the wrong question.
15N20 is an oil quench steel. The TTT has the pearlite nose at over 10 seconds. This means that you have as long as ten seconds to drop the temperature to the 800-900°F point. Below that point, even cooling is what is wanted.....not speed. On a thin profile or longer blade, quench plates may be used to retard warp, but either leaving the blade the oil bath, or pulling the blade and cooling in air is the normal method for most 15N20 blades.

You may have been confused by reading a discussion between people where someone says that the cooling curve for 15N20 is so slow that you could almost do it like an air hardening steel. Yes, it does not need a fast quench...no, it is not an air hardening steel. Air hardening 15N20 will greatly reduce the hardness.

Here are the standard procedures for 15N20:
Stress relief - Heat to 1200°F and hold for 30-60 minutes. Cool in air.
Hardening - Heat slowly and evenly to 1500-1550°F and hold for 10-30 minutes. Quench in medium speed oil. Once the blade lowers to 400°F, cool in air to ambient. Immediately temper twice at 400-450°F.
 
If you were to have solid copper plates they would be superior to aluminum plates. Also much more expensive and a lot heavier. The heavier would be good. But, I do air hardening steels all the time with aluminum. Only thing I do a bit different is I set my plates up with internal water channels and pump cold water through them. Not for more speed though. I did that so I could do multiple blades one after the other with a single set of plates.

15N20 isn't a air hardening steel. I don't have its chart either, but I know it is close to steels like 1085, 1095 and the like. That is one of the reasons everyone likes those combos for Damascus. Because they HT similar. So you have to quench it pretty fast to get good results. It may be possible with a real good set of plates, and real thin pieces. Also, your 900-800f is right at the tail end of the part of the quench that actually does the job. Taking it out of the oil there and messing with it would be counter productive. Even a setup that allowed you to immediately slam it in between copper plated would slow your quench, not speed it. Almost any oil will be faster than any plate, let alone the time spend in the transfer. Now after about 700f putting it in between some plates would help assure straightness as the process that forms martensite is already locked in at that temp and necessary cooling speed is way way slower.

Another reason we use plates is because air hardening steels need higher temps to harden. (1850-2100) These would destroy the steel if not protected from the atmosphere. Although is it possible to protect the steel with an inert atmosphere most enclose in a stainless foil packet to exclude the oxegen. But when cooling the foil and the small air pockets inside it insulates the steel a little, taking it off at 1850 is difficult and slow which is why fast hardening steels can not use foil to prevent decarb.

Sticking it in a bunch of wires and clamping it in a vice at any temp above about 400 on its way down from austensitic would most likely cause it to become misshaped. You need to keep everything even until the process is complete.

One thing you are missing is that steel cooling behaves different than heating. 15n20 at 900 on the way up to 1500 is stiff. At 8-900 on the way down it is easily deformed. I can bend a piece of bar rather easily at 7-600f on the way down. This is the area people like to check their blades and work them straight if they warp.

It is good to think outside the box. But first you need to find everything in the box.
 
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i have thought about putting a 1/4 icnh copper face on my AL plates but copper woudl hav eot gte much cheaper. my 6x18x1 AL plates heat up a good bit but i think it woudl be cheaper for me just to buy a 2nd set of plates rather then mil cooling flutes and pump water into them

like has been said its all about getting the steel under 1K f after that its not a big deal
 
I see,thanks.Im not aware of the changes in the steel along its entire path,all these explainations were very helpful.
 
Lets say that you decide you want to work a steel that all the folk on here agree would benefit from being squeezed in plates, and you wanted aluminum plates, where have you tried to find them?

I have yet to plate quench anything, but I have collected enough aluminum to have three or four sets of plates, and it was all free. All of it was being thrown away by engineering companies. Some was scrap because the machining had messed up, some was the end of a run and excess to requirements. Some was tooling plates which were no longer needed. And if I needed more, I would keep checking in my local scrap yard. Last time I was there they had a dump truck load of 4"x4"x7" aluminum blocks from some engineering works and would have sold me some by weight. It is luck of the draw what they have, but I would expect that other scrap dealers have similar stuff turn up regularly.

Good luck.
 
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