Weird water quench harmonic explosion

[JTknives]

I'm not much for water or brine quenching as most of the steels I use are the deep hardening type. But I have been playing with some steel I have that is a medium carbon steel (guessing). I can quench in heated AAA and comes out hard but has a weird skin on it when I brake it. It's like the skin is not hard but the center is, I can file a good amount on the edge and then it hits the hard core and skates. I did a water and brine test in a shallow dish on a small chunk. Hardened like glass and no skin so I thought hum let's make a test blade. I have made other test blades and oil quenched them and thy came out nice and straight (long fillet knives). So I thought it would be time to try this steel in a brine quench. I grabbed my water tank which is a 2.25-2.5 diamater tube that's waste high with a round disk welded onto the bottom. I use it for quenching tongs and cooling blades when grinding. It's easy to hall around the shop holds a good amount of water and it's stainless. So I thought it would be perfect for a blade. I dump out the water and put in some salt and fill it back up. Set next to the forge and heat up the blade. Once heated in one smooth stroke I pull and quench. I was greeted with what I can onley describe as a harmonic explosion. The tube rang and very quick zip. The water surface bounced like there was a speaker under it. I pulled out the blade and it was slightly warped but rock hard. So I heated and straightened it and thought I will do just a quick quench. Will go in and out as fast as I can. So heated back up and one smooth stroke I pulled and tryied to quickly plunge and retract the blades in less then a sec. Well I plunged it and the same thing (harmonic explosion) pulled it fast once I hit full quench depth. Blade comes out slightly steaming, was only in the water like a half sec. All color gone and not very hot. What is happening? I'm guessing the tube is vibrating and disrupting the quench. But that's just a guess. Next time I'm out I will try and record it.

 

[mete]

The quenchant boils and the bubbles form and collapse. I'm sure that's where the sound comes from. The collapse of the bubble can have have enough force to dent the metal as has been found with aluminum.

 

[JTknives]

That's what I was thinking. Something is speeding up the quench to crazy speeds. I'm wondering if it's the vibration of the boiling reverberating off the small tube. This then bounces back to the blade collapsing the vapor jacket. I'm thinking this process basically is a run away reaction increasing in speed with every cycle. I have quenched in water befor, big round stock bars of 17-4 in 55gal drums of water and nothing like this happened.

 

[Stacy E. Apelt - Bladesmith]

First thing I would do is make a wider quench tank. The diameter is not enough to allow convection and the vapor jacket to properly expand and collapse. 4" is tight, 6" wide is good. Cut the top off an old 240cf compressed gas tank and it is perfect.