kb0fhp

I got that, too. That's....surprising. Viscosity is supposed to be the big thing with oil, and my P-50 sure feels a whole lot less viscous than, say, canola. Huh.

 

Paging Doctor MacKenzie.

You Rang?

BTW, I know George Totten very well (as well as his co-authors) - all very good. I will see them either in Shanghai this May or in Brazil in July.

You are correct - the P-50 that you are using has a very light viscosity - about 50 SUS. Most of the canola products are around 500 SUS or so. Canola works well - it has a high flash, a high boiling point (which contributes to a high transition from nucleate boiling to convection. This also contributes to a fast quench with good distortion properties. However, from a commercial aspect, they are expensive, and hydrophillic - they pick up water and tend to emulsify. That makes them difficult to clean. It can leave a residue like burned on residue on the bottom of a pan.

That said, it has a very nice cooling curve and is capable of high temperatures - but breaks down fairly fast....

I may be mistaken, but my understanding is that using a carbon cover (which I think just floats on top of the molten salt) has a couple of beneficial effects. First, I'm think it reduces out gassing by the salt, so one gets less salt vapor drifting around the shop. (Always a good thing, no?) Also, I beleive it helps some with salt bath chemestry so that rectification is needed less frequently. Lastly, I think the carbon has some insulating properties so that less enegery is required to maintain the bath at temperature. None of this is huge, of course, and quite possibly, it's just not worth the trouble. If you look at the photos on Tim Zowada's website, you can see that he uses a carbon cover at least some of the time, so I figured it might be worth trying.

Use of a carbon cover is common. Contact me at smackenzie@houghtonintl.com and I will see what I can do for you.

Scott

Thank you all for your answers. Mar-Tempering is the name I was looking for. I could use a standard Q&T. I've not made up my mind yet. I thought I'd get a tougher tool with the Mar-quench. I might be totally under a misconception ! They are small chisels for working soft steel and copper alloys. Thanks again.

 

Tony G

Martempering or Mar-Quenching is primarily done for controlling distortion while achieving the desired hardness. Martempering can be done on either the 5160 or W1.

Bump

Agree with bump, found graphic offensive though. Don

interesting piece, particularly how dramatic the effect of the clay wash is on the rate of cooling in the first seconds. would there be a similar effect in an oil quench? sorry for my ignorance, but i'm not sure if a stable vapour stage is a factor in the (relatively) slow cooling rate of oil quenching?

Actually it does. You get a stable vapor phase with oil. Using surface roughness you can speed it up (or you can slow it down if the roughness is too much and the bubbles "stick"). I would imagine clay would do a similar thing.

All my computer hardware is, at present, Mac OSX based. I do have a couple of PC laptops, but they are both old ones that need some work.

 

I was not aware that it could be done that way though, thank you, Scott ! I will look into it further.

I think they have some simple boards that would work thru a firewire or USB port....

I have always had a problem with a silver (Ag) cylinder to calibrate the heat extraction rate. It is a very interesting bit of work though, to be sure.

 

I would like to embed fine wire thermocouples into a blade every couple inches or so of length and at different depths in from the spine and do a real time graphing of quenching a real sword. But my personal research budget will not support that at this time (largely due to hardware costs for the i/o board to get the t/c into the computer, and the graphing software). I would gladly donate the time and the blade and clay to do it, but have not been able to get that sorted, yet. Maybe someday.

You can get a cheap I/O board from Omega and use about a 50Hz acquisition rate then graph it in Excel....it works well

http://www.shibuiswords.com/tatsuoinoue.htm

I have met Dr. Inoue and have seen him give this presentation. Very fascinating.....

Different types of Martensite

Decarb is the loss of carbon from the surface from an oxidizing atmosphere. You end up with a fully ferritic structure if the carbon is completely depleted. Carburizing is the exact opposite.

Hi Harper,

As I understand things:

I would not call martensite a grain per se..its a body centered tetragolan crystal.

Lathe forms in lower carbon steels ..below about 0.6% carbon and plate forms mostly above 1%...the levels between can form a mixture...BUT this depends upon austenizing temp and chemistry as some elements can form carbides which can bind the carbon until very high temps are reached at which point that bond breaks and they will let go of the carbon...and unless you put the carbon into solid solution it can not form martensite in the first place.

Lathe is more needle like in appearance than plate.

Keep in mind that a single grain is composed of many cubic structures and therefore the body centered tetragonal martensite is not a single structure taking up the entirety of the grain.

It is also less dense and can act as a grain refiner on its own with multiple quenches.

 

There are a few new books out

G.B. Olson editor "Martensite" ASM 1992 is one

also there are a few technical articles out there.

 

Don Fogg had a video of martensite forming (got from Batson?) in a lab...interesting as you see nothing and then it is simply there...it forms very fast and to me it looked like it grew from one point. Maybe someone could put that on YOUTUBE?

 

I also recommend Vander Vort's metallographic work as he has some colored microscopy which shows interesting things.

 

I know Greg Olson. I am working with Questek on a couple of projects - like the special corrosion resistant steel for landing gear applications and one for wind turbine grades.....

 

I have more questions then you do....

 

Oddly enough Prof Geg Olson from Northwestern was in my shop a few weeks ago with four students and we were forging some of that special Questek Stainless that he designed.......if I had known I could have asked him your questions.

 

Too much to learn...

Ric

don't quench in water - unless you're shooting for a fancy hamon and positive sori, there is no reason for it, and you're just asking for trouble, particularly with double edged pieces.

 

i'm not sure about the low-temp salts, they should be pretty quick getting past the pearlite nose, but whether they're fast enough, i don't know - i don't know enough about them. Hopefully someone will chime in who does. You could maybe make a small test blade and see if it hardens in the salts? my guess is it will, but it's just a guess...

 

if not, i'd go with an oil quench - with high carbon shallow hardening steels like 1095, 1086M, W2, W1 etc, i think the most important thing is a long soak time, which should be no problem with your set up.

 

my heat treating setup is very low tech, so i generally try to soak just over non mag for a minute or two, and then bump up the temp around 50f - 75f just before the quench, which is the only way i can get a hamon in oil on these steels. without clay, after three normalisations, if i bring it to just above non mag, and quench straight away in warm oil, it'll harden about 1/3rd of the blade; if you're not using clay, then depending on your normalizing you'll probably still get a differential hardness in oil, and if you polish and etch for it you'll see some kind of transition line, but for viking pieces this seems to have been common.

 

as for the size of the quench tube, 4 -6" diameter should do you fine, and a few inches longer than your blade - i use two or three malt whisky tubes taped together sitting in a jug and filled with old veggie oil, when i have to jerry-rig something for longer blades, and it holds up fine for my purposes, although it's obviously not ideal - the greater the diameter the more efficient the heat transfer, and peanut or canola oil should be faster than veg.

So the oil doesn't heat up too much and keep you safe - figure a gallon of oil pper pound of part. Anything more than that and you will be fine. I would look at having agitation running up the length of the tube - will do wonders to keep the vapor phase down and get a nice even quench.

Douglas,

 

It will not blend with the oil and will filter out. Filtering doesn't need done after every quench unless it is a very easy thing to do. I've built the quench tanks with a 3/4" drain and plug so I don't have to pour the oil out of the top into the filter. Vertical quench tanks holding 1-5 gallons are easy enough to pour out of. Horizontal tanks in that range are a pain... there's going to be a mess of some size to deal with.

 

Mike

The clay used will not hurt the oil if it flakes off. Simple filtering will go a long way to make the oil last longer. Most of the clay will settle to the bottom - not big deal. Commercial heat treaters abuse their oil a lot more than any one of you will. For your oil, it should last a lifetime - you really have to abuse it to make it go bad.

Scott,

 

Where would moving a blade in the quench and using an impeller in the quench fall on the severity factor chart?

 

Mike

Standard metallurgist answer - it depends. It depends on how rapidly you move the part or agitate the oil. Beyond the SA answer, I would relaistically expect most oils to fall in the .2 - .35 range. You can estimate the relative hardness from the correlations of H factor to equivalent round from the old Grossman charts (from Practical Guide for Metallurgists, by Timken - a wonderful text):

I've been looking at this thread for a while and I have a question. By that chart it looks like a shallow hardening steel (W2 or 1095) Quenched in soft warm water might not harden, am I looking at this correctly?

 

Matt

Yep - I would probably say that - especially in the absence of agitation.

I appreciate the kind words regarding Houghton. If you PM me - or email me at work (smackenzie@houghtonintl.com) I can help you find the right oil for you. There are many type - depending on the application.

Scott

I'd love to hear Scott's take on this. Brine is faster, all else equal. I have read that it's also less harsh, and I don't think the two claims are necessarily inconsistent. The explanation I've read is that the vapor jacket phase of the quench tends to cause really uneven cooling, creating internal stresses. The salts in the brine disrupt the vapor jacket phase and eliminate those stresses. Or something like that.

 

Scott?

Brine is faster - the relative ranking can be done using Grossman H-Values:

http://www.quenchtek.com/pdf_files/technic...y%20Factors.pdf

It can be made faster with surfactants, etc.

i have read the salt helps prevent a vapor barrier from forming

Yes - salt acts as a nucleation site for bubble formation and makes the vapor phase less stable. Try a bit of surfactant in it (aka super quench) to make it faster.

Scott,

 

Have you ever seen similar data on water quenches with ultrasonic aggitation... or any other medium with ultrasonic aggitation?

 

Mike

Ultrasonic quenching in water has been used - it was first cited by the Russians a long time ago in some post WWII literature. I had to strain to translate it. It has also been tried for aluminum with good results. Trouble is that you use a lot of energy to get the ultrasonic energy into the part. It is easier just to use an impeller.

great info and chart thanks !!

 

 

where did the chart come from ??

 

D. Scott MacKenzie, PhD

Heat Treating (Aluminum and Steel)

Quenching (Water, Polymer, Oil, Salt and Mar-Tempering)

 

 

is this a book ??? i didnt see it on amazon ??

I am trying to remember - I think it is in one of my books on quenching of aluminum - or heat treating of steel. It may be in both - I am shameless to use in multiple sources.

I wonder if the vapor phase would be increased quenching into a carbonated water?

Yes - vapor phase would be elongated in carbonated water....

liquid nitrogen is minus 196C but probably not much heat capacity

Liquid nitrogen is a very slow quench because it goes right to vapor. creates a very long and stable vapor phase. The same would be said for alcohol - it would have a long vapor phase. Not a good idea.

Look at http://www.ferrochrome.co.za/for_sale.htm

They sell Ferrochrome - it would melt easier that way. There are other suppliers too - you might be able to get a freebie if you ask nice.

Cutting them up is the only way to see what's in there, Scott.

I know - but it is too bad because it was a nice piece of work. I am surprised he didn't just forge some cable and look at it.

The hardness of the water can have a huge impact on the cooling rate. The softer the water, the more stable the vapor phase (and the slower the overall quench. See the attached picture comparing distilled water and hard water at various temperatures.