Metallurgy experiment

[Pete84]

I was doing some reading regarding the differences in cooling rate between water and oil when used as quenchants. I've gathered from the numerous posts regarding quenchant selection that water is a pretty bad idea unless using a very thick section of metal, otherwise warping and other nasty things are likely to happen. I had pretty well accepted that until I can get a HT furnace, canola oil is my best bet (1084 used primarily). Definitely not trying to beat a dead horse here but....

What threw me for a bit of a loop was in the Heat Treaters Guide...I think, anyway (too much reading)... It said (roughly paraphrasing) that if the temperature of the water was elevated to between 170 and its boiling point (F), the rate of cooling in degrees per second was drastically reduced to the point that it was nearly the same as certain "fast" commercial quenchants. I'm considering HT'ing two equal sized pieces of 1084 to see if there is any credence to this assertion. A couple of questions about that though...

Aside from breaking the pieces post-quench and looking at grains under magnification, how would I determine if it was a beneficial treatment? Look for micro-fractures?

What would be the known drawbacks of a "heated water" (for lack of better term) quench? Is there still a high likelihood of warping and/or breakage?

If this treatment DOES somehow work effectively, would there be a noticeable increase in as-quenched hardness as compared with a canola quench?

Has anyone tried this? What happened, if you did? If I'm being dumb, someone let me know.

 

[sunshadow]

One principal drawback to water is the loss of contact coupling at the steam bubbles. Brine helps with that by providing nucleation sites that keep the bubbles small which evens out the distortion a little

-Page

 

[Pete84]

One principal drawback to water is the loss of contact coupling at the steam bubbles. Brine helps with that by providing nucleation sites that keep the bubbles small which evens out the distortion a little

-Page

Thanks, Page. I appreciate the feedback. I guess that begs a follow-up question or two... not having done a brine or water quench, is there a set ratio of water to salt that is generally advised or does it vary based on the steel being quenched? Didn't find much about that in the HT'ers Guide or somehow skipped over it.

And even assuming the water is adequately heated and the brine solution is appropriate, am I still to understand that this treatment has a lower rate of success than a good old oil quench for 10xx steels?

 

[Atlas Knife Company]

Keep adding salt until an egg floats. I've quenched a number of practice 1084/1075 pieces with hot water(145°) and salt. Decent results, nothing has cracked or warped yet.

 

[LRB]

13 oz. salt per gallon. One common box of salt, 26 oz., makes a two gallon solution.

 

[daizee]

just curious, why go to all the trouble to make water behave like Canola?
(I'm all for experiments and data, I'm just wondering what you want to learn and why)

-Daizee

 

[Pete84]

just curious, why go to all the trouble to make water behave like Canola?
(I'm all for experiments and data, I'm just wondering what you want to learn and why)

-Daizee

It's not so much that I want it to act like canola... it's essentially that with water being one of the fastest quenchants (that I know of), if its properties can be manipulated via heat and/or salinity to speed or slow quenching then it could (in theory) be made to mimic faster or slower oils. Not to mention the "cheap" factor and easy access.

I guess the big question is the risk in doing so and what the effect would be. If I can quench in a heated brine solution and get an extra point or two in HRC or the metal hardens to a deeper level with a minimal increase in risk of warp/cracking, then it might be worth playing with. If the gain is negligible, then it's more to satisfy my own curiosity and increase my understanding of the metallurgical principles in play. (And I'd probably go back to Canola until I can get my hands on a commercial quench oil)

 

[Stacy E. Apelt - Bladesmith]

What you are doing is making water slower. The tradeoff is that water can have incomplete contact....which is what causes warp. Heating water to near the boiling point will bring it near the Mf of many carbon steels, and thus delay the final martensitic conversion. This will decrease the cracking, but not the warp.

The question is well put by daizee....why would you want to make water be less efficient quenchant, when there is a more efficient quenchant. Canola is so cheap that the cost is barely a factor.

 

[Pete84]

What you are doing is making water slower. The tradeoff is that water can have incomplete contact....which is what causes warp. Heating water to near the boiling point will bring it near the Mf of many carbon steels, and thus delay the final martensitic conversion. This will decrease the cracking, but not the warp.

Thank you, Stacy. That actually cleared this whole thing up for me. I didn't understand what about the water quench would cause the warp... the cracking part I understood, but the warp part was eluding me. The back-of-my-mind thought process was that cracking and warp were both caused by the high speed quenching, so I assumed slowing it down would somehow reduce or eliminate those two issues while simultaneously deriving some sort of benefit in the process. I guess I was trying to somehow engineer a work-around for it which, in hindsight, is really putting the cart before the horse since I didn't understand the root cause. :foot:

On the bright side, I have about 5 gallons of canola and 24 feet of steel outside waiting for me to make actual knives rather than tool around more with my water idea any further.

 

[mete]

The most effective brine is a 9% solution.
Microcracks ?? Micro means small so you'll have difficulty seeing them especially if they're totally internal.