Variable speed quench that you mix

[JTknives]

I have been doing some experiments with quenching in something i uses every day and that is the coolant we use in out milling machines. you mix it your self with water to the concentration needed. so i did some tests with 1095 as that seams to be the most picky. when quenched in water i got around 65 and when quenched in the coolant i got 62+. as the mix becomes thicker the quenching time goes up. i quenched in different concentrations and could watch the hardness go down with a stronger mix. I also noticed something funny when quenching in the coolant that was diffrent then the water and that was that when quenched in water i would get an instant boil and cooling of the steel. but when quenched in the coolant it would just bubble a little bit for a few seconds then it would boil and cool the steel. it seamed like the coolent guarded the steel from the water at the high temperature then when the steel dropped to a lower lower temp it would cool it faster. it was kinda cool to see. it still over all cooled it fast but when it was at critical temp it seamed to treat it nicer and then drooped its guard and cooled it fast. I would like to continue to test this but where do i go from here?

 

[WalterDavis]

Seems like that would be ideal for quenching steels that are taken thinner (or start out thinner) than normal? Would it maybe help prevent warping and distortion?

 

[silver_pilate]

That is assuming that just because it's not boiling that it is cooling slower. Boiling tends to create an insulating vapor jacket around the steel as the thermal conductivity of vapor is, I believe, significantly less than liquid water. Thus the reason we agitate blades in quench: to prevent a vapor jacket formation and keep liquid, not vapor, in contact with the steel.

Likely, what you're seeing is that the coolant added to water increases water's boiling point so that it can stay liquid and remove heat FASTER than if it was boiling (on the parts being machined). However, the thicker viscosity (among other things) slows the cooling effect relatively, so it is a poor substitute for water in quenching blades, thus the lower RC.

--nathan

 

[john0270]

I have been meaning to do some experimentation with automotive antifreeze, I belive that it would produce similar results. Now what would be relay nice is if you had parks to compare it to, and also some steels that like fast quenches, but like to crack in strait water.

 

[Stacy E. Apelt - Bladesmith]

The increased time in the quench and the delay in the boiling is caused by the increase in the vapor jacket phase. The coolant JT added to the water makes a greater vapor jacket, which insulates the hot blade from the cooler liquid. This slows down the quench start. From JT's data, it appears the the coolant raises the vapor pressure of the quenchant. This may be due to several reasons, but the effect is that the higher the concentration, the slower the quench. The problem may be that merely delaying the start of the quench may not be enough to make the quenchant right for slower quenching steels. Once the vapor jacket collapses, the quenchant will probably act pretty much like water, and be very harsh.

On a side note, this discussion leads somewhat in the direction of the way that polymer quenchants work. The quenchants are water based, and can be mixed to different concentrations. The polymerized media creates a quenchant that has virtually no vapor phase, and this gives a very quick drop below the pearlite nose. At that point the polymer becomes a slow cooling media ( I believe by actually coating the blade with a solid), and allows the steel to slowly cool, then at somewhere around 400F the quenchant reverts to being a thick liquid, and allows the finish of the martensitic conversion. This all greatly lessens the stress of the quench.

I would love to get a five gallon bucket of the concentrate, and try it out, but I have had no success finding it available in less that industrial quantities. I haven't really tried very hard, though. Anyone have a line of a supplier?

Nathan,
From the way JT describes it, he is lowering the boiling point , not raising it.

Salt added to water lowers the vapor pressure (and thus raises the boiling point), however the relationship between the vapor pressure and the boiling point is not linear. There are many factors that control it. Even the depth of the quench tank ( if unagitated) will make for faster cooling at the bottom than the top ( this is more empirical, and not a realistic concern). The concentration of the salt does affect the quench, and more is not better ( with all salts, 10% is the proper amount). There is a sweet spot for other additives, like JT's water soluble cutting/coolant. (BTW, I love that stuff for my band saw coolant. It really controls rust,too.)
Stacy

 

[john0270]

Stacy, are you talking about the stuff that turns water into never ending snot? I think I know where to get some around here if its the same stuff. The stuff I am thinking about is a product you spray onto feilds to keep clumping down for potato harvesting.

 

[Nathan the Machinist]

You want fast at the start, then slower by Ms. It sounds like you're getting the opposite.

There is a sticky at the top about quenching that may be a good read.

 

[Stacy E. Apelt - Bladesmith]

John,
No, I am referring to the Hougton polymer quenchants used in industrial quenching. They are almost as fast as water, but as mild as oil. They are not quite the right thing for blade quenching, though. They are usually used in large section ( big things) quenching, IIRC.

The things I see as possible advantages for our purposes are:
Controllable quench rate (maybe?)
Non-flammable (big plus)
Non-toxic and biodegradable (IIRC)

If you could bring low manganese steels down to below the pearlite nose and then slow the quench rate to avoid cracking the steel it would be great. I have been told of problems with reverse curvature, but that can be dealt with probably. I have been given a lead onto a source, and will let you know what develops.

Stacy