A chance to grow, I think

[Gerald Boggs]

A chance to grow, I think, if I don't wear out my arm :-)  Just received an order to forge 100 railroad spike knifes.  I've got months to do them, so I'll forge them in small batches.  It's got me thinking it might be time to get press.

 

Edited May 20 by Gerald Boggs

[Joël Mercier]

Are you going to use some sort of superquench to get a sorta real edge? 

[Gerald Boggs]

No, the client understands the limitations of RR spike blades.  Although, now that you've asked, maybe I'll give superquench a try.  I vaguely remember the recipe, anyone have it to share?

[Joël Mercier]

Anyways, that is indeed a good opportunity to develop muscle memory. Just don't overwork yourself and get hurt huh? 

[Matt Walker]

 

superquench.pdf When I made this years ago Shaklee wasn't  handy. I used a surfactant from a local farm supply, intended as a wetting agent for use with herbicides. Never heard such a scream as this stuff causes.

Edited May 20 by Matt Walker

[Gerald Boggs]

 

Thanks

 

[Carlos Lara]

Interesting thanks Matt. I'm curious what the difference is between the superquench made without the surfactant (just dish soap and salt) vs. superquench (what does the fancy surfactant do?). Also, I wonder if the Japanese put any salt or other ingredients into the water they use to quench their swords?

[Gary LT]

@Gerald Boggs, Hey Gerald, here’s what I’ve used a long time ago. Might have to try one again. I also did edge quench alone using this stuff.

GARY LT

ngredients

• 5 gallons water
• 5 lbs salt
• 28oz bottle of Dawn blue dish washing detergent 
• 8oz bottle of JetDry or other rinse aid.

Do NOT reduce the total quantity, you need the heat capacity from using a large bucket.

Store in a sealed container to avoid evaporation. When the mixture turns yellow/green, it is used up and you need to make a new batch.

Instructions

1. Mix thoroughly, but gently so you don’t form bubbles.
2. Heat metal to critical temperature
3. Submerge immediately and keep in constant motion. If the metal doesn’t “scream” it wasn’t hot enough.
4. Rinse immediately to avoid flash rusting. Then oil if appropriate.
5. Do not temper. Any tempering at all will remove the hardness.

[Gerald Boggs]

Thanks, between you and Matt, I now know what a surfectant is and that it's easy to find.

[Alan Longmire]

17 hours ago, Carlos Lara said:

Interesting thanks Matt. I'm curious what the difference is between the superquench made without the surfactant (just dish soap and salt) vs. superquench (what does the fancy surfactant do?). 

 

The surfactant speeds it up even more than dish soap alone.  All liquid quenches go through three phases of heat removal: Vapor, nucleate boiling (this just means bubbles forming where water can touch, or nucleate, nothing to do with particle physics!), and convection.  In plain water, you get the vapor phase when the hot steel enters the quench first, which is the slowest way of removing heat since it's literally a jacket of superheated steam that prevents the water from cooling the steel as fast as possible.  When the steel cools enough for liquid water to actually tough it, nucleate boiling starts.  This is rough on steel, because of all the little bubbles starting up all over the surface and removing heat unevenly, and this is where it's most likely to crack.  Once the steel is at and below the boiling point, convection, or direct heat transfer from steel to liquid water, takes over and cools the steel quickly to the temperature of the water bath.

 

Adding salt reduces the time spent in the nucleate boiling phase of the quench, which both speeds the quench and lowers overall stresses on the steel.

 

Adding the dish soap and surfactant eliminates the nucleate boiling completely, as the doctored water is now so fluid is jumps from vapor directly to convection, with the now-superheated water forming bubbles AFTER it leaves the surface of the steel.  This is such a violently fast cooldown it pretty much work-hardens the steel, which is why it is only used on low carbon steels like RR spikes.  If you quench, say, 1095 in superquench, it explodes.  Steels with enough carbon to harden in plain water can't take it.

 

17 hours ago, Carlos Lara said:

Also, I wonder if the Japanese put any salt or other ingredients into the water they use to quench their swords?

 

Not ordinarily, although they do heat the water first to reduce the shock.  Obligatory mention that the tamahagane steel they use is VERY shallow hardening and needs a fast quench to harden at all.  It will form a hamon (temper line) through quenching alone because of how shallow-hardening it is.  The traditional claying of the spine is done to do two things: 

 

1. it helps control the edge of the hamon, and it does this by

 

2. interrupting the nucleate boiling phase at the edge of the hamon, (giving that first crisp edge), and slowing down the quench speed just enough prevent surface hardening under the clay once it's past about 1/16" thick, which allows a wider transition zone from the martensitic edge to the ferritic or pearlitic spine, leaving that frosty band of mixed pearlite/martensite/bainite/ferrite that shows up when properly polished.  

[Matt Walker]

Wow, Alan, Outstanding explanation! 

[Gerald Boggs]

Alas, the job fell through.  Part of me is a little glad, don't mind forging a few RR spike knifes, but a 100 was a bit much.  On the other hand, I would have gotten pretty good at them.