A question regarding quench...

[SinePari]

I've recently forged my first 5160 blade. I followed the normalization schedule post forging as follows; heat to nonmagnetic> quench, heat to nonmagnetic> air cool to touch, heat to nonmagnetic- air cool to touch...

Grind; with a flap wheel mind you...

Heat to non-magnetic> quench I had a mix of mineral oil and canola oil @125F.

X2 Temper @ 375F for 2 hours, then cool to touch...

Question;

In my reading/research on 5160, there was some stipulation that stated once it turned black from the oil quench it was safe to quench in water... I understand the severe flaws associated with water quench being a no-go with 5160, as in will most likely "tink"... Obviously that is from the thermal shock of going from critical to -1000F in less than a second... This little stipulation of water-quenching @ black has me thinking all kinds of crazy... Be it that water is more dense than oil, could you "layer" you quench medium? Say a good 4 inches of oil floating atop a few gallons of water?

I hope I'm not speaking crazy as I understand the brine and water quench as being the most stressful quench mediums, but also yielding the hardest result pre temper...?

Nothing spectacular, just freestyle'd it... My first blade; so those taking part aren't bored by a wall of text...

 

[mete]

No layers please ! Just dunk it in water then into oil , works fine. Remember you will be agitating in the quench. Time in water will take a bit of experimenting.

 

[Stacy E. Apelt - Bladesmith]

First, you have it backward. It is fast cooling rate in water to below 1000F, and then slower in oil or air from 900F down. It is called an interrupted quench. This only helps fast quench steels. 5160 isn't a fast quenching steel. Water quench followed by oil is done by some folks to get the max hardness without breakage in steels like 1095 and W2, but I doubt it gains anything that a fast oil wouldn't give. Best solution is the proper oil type.

People have tried to do the oil/water layering thing in the quench tank beore....it doesn't work. You just ruin the oil quickly.....and the quench is backward, as noted above.



Second, your normalization schedule isn't right.
There are two basic methods of preparing the steel usually found on the internet:
Triple normalizing - heat and cool in air several times, usually at 1650F,1450F,1250F - accomplishes the stress removal very well, but does nothing to refine the grain. This is a common practice, and does no harm to any steel. On stock removal blades, it is enough to prepare the steel for final hardening. In a forged blade, there may be more severe grain and internal condition issues that are better dealt with by Thermal Cycling.

Triple austenitization accomplishes grain refinement to various degrees, depending on the temps and hold times. It does nothing to reduce stress, and may even add some. There are those who use this method, largely based on one makers procedures, but I can find no metallurgical reason for it making the blade harder or superiorly finer grained.
Those who want to use this method should refer to other people for advice on temperatures and procedures, as I don't do it or recommend it.

Here is more detail on my opinion:
I call the process that can gain the finest grain and hardest blade - Thermal Cycling.
It starts with grain refinement, proceeds with normalization and stress relief, and ends with hardening and tempering.
Start with a high end austenitization at around 1650F, a soak ( if needed and your equipment allows), and air cooling to black from 1650F (in some cases, a quench is used instead of air cooling, but is normally not needed)
Next, a cycle at low end austenitization, about 1450F, to re-refine the grain as small as possible...followed by a quench. Cool in the quenchant to room temp.
Then, a sub-critical soak at 1250-1350F and air cooling to below 900F to remove all stress and prepare the blade for the final hardening quench. You can water cool once the steel cools to black.
The final step is the actual austenitization and quench to harden the blade...followed by a double temper.


My normal procedure is:
1) Heat to well above non-magnetic (1550-1650F) and let cool to room temp (I water quench to speed the cooling once the steel is black/900F, or you can let it air cool )
2) Heat to just slightly ABOVE non-magnetic (1425-1450F) and quench. Cool to room temperature in the quenchant.
3) Heat to just BELOW non-magnetic (1250-1350F), hold here for a few minutes, and cool to room temp. (the blade may be water cooled after it turns black, or allowed to air cool)
4) Heat to the target temperature ( normally between 1450F and 1525F) and hold for sufficient time to allow the alloying to go into solution ( varies by steel type), then quench in the proper quenchant for the steel type. Allow to cool in the quenchant, or air cool after 5-10 seconds of quench. This step is the actual hardening step.
5) Temper twice for 1 hour each, with a water cooling between tempers. ( 400-425F is my normal temper)

 

[SinePari]

Thanks guys. I have some things I'd like to address in the blades profile so I'll take it for another round and utilize the method above...

 

[CWendling]

I do prettymuch the same as Stacy, except I do the normalization/cycling after forging. Then initial grind, and then harden