Defeating the vapor jacket

G

grizzled gizzard

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Aug 31, 2010
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Does anyone else use a very thin clay mud bath on a blade to defeat the vapor jacket when quench hardening? Basically, a guy stirs up a bucket of water with a lot of clay in it to give the blade a thin coat of clay. The light clay coating is dried, then the blade is heated and quenched. The clay somehow defeats the vapor jacket completely. All you hear when the red hot blade is quenched in warm water is just a very muted "pfist", with no boiling of the water at all.

I hate to bring names up, but this is a very successful Master smith.

Anyone? Anything?
 
A clay wash is a good way to avoid the shock in quench. It can also retards scale and decarb. It, however can slow down the quench slightly,too. The steel should be suitable for the quench speed delivered.
Careful attention to avoiding overheating, and the proper quench media are other ways to get the best results in hardening. Most violent quenching sounds are caused by too hot steel being plunged into too cold oil. This also results in a lot of warped and cracked blades. If you heat the blade by eye, it is almost a sure bet you will over-heat it. The clay covers the blade, and makes you use some better way to determine the temperature.

I apply a clay wash to most larger blades. Thin satanite is what I use. I do agree that it delivers a more even quench. I don't know about merely a ,"Pfffft", but it does sound different.

The vapor jacket is a physical property of the quench media. It forms when the heat is transfered from the blade to the media and vaporizes the media in a thin layer around the blade. The noise is the jacket collapsing and then reforming as the heat is transfered, insulated by the vapor, cools, collapsed, and re-vaporize. This will happen the same way with a specific media in most all situations.That is why you should match the media to the steel and temperatures used. The temperature of the blade inserted, and its ability to transfer heat are the outside influences on the jacket formation and collapse rate.

Warning:
Just because you read something in a magazine, or on a forum, it doesn't make it good advise. Doesn't matter if it is a good magazine or a good forum ( like Bladeforums). Also, just because a master smith said it or does it does not mean the word is Gospel.
I have had terrible damascus made by master smiths, read metallurgical bunk posted and printed by master smiths, and heard stories of an almost supernatural nature about some of their abilities to make steel do things it can't do.

Trying the process or material out and seeing how it works for you is the way to tell fact from fiction. Do side by side comparisons of many blades to decide, not one blade.
 
a clay wash woudl be better called a slip but yes i slip coat my water quench blades and then add a bit of clay to the spine
im not a water quench pro tho
 
bladsmth said:
A clay wash is a good way to avoid the shock in quench. It can also retards scale and decarb. It, however can slow down the quench slightly,too.
Click to expand...

I agree with Stacy's outlook on this, but I would like to add some commentary on the above bit. Research has been done (I forgot the organization that did the work, the news came to me second hand from Jesus Hernandez. He may be able to shed a bit more light) showing that a slip coat of clay actually increases quench speed. I believe the reasoning given is that the surface irregularity of the clay creates A LOT of additional nucleation points to kick off the vapor phase, then the added surface area created by the rough texture of the clay then provides a greater surface area for cooling when the vapor jacket collapses and you head towards convection.

I know that Jess can explain it more fully, but that's my recollection from my conversations with him on this topic.

-d
 
Yes, I have read that info.
I started to leave out the slower quench comment, but there are a lot of variables in a clay coated blade.
If done right as far as thickness and such, and under perfect circumstances ( a lab) - it will slightly increase the drop rate past the pearlite nose during the vapor phase.
However, many folks who use a clay wash/coat do not carefully heat and soak the blade at an exact temperature, and the results may not be the same as a lab. If the blade is overheated,and the wash is a bit thick, the wash can act as a minute insulator for a short time, allowing the blade to retain the heat a few milliseconds longer.

In either case, the clay will not eliminate/defeat the vapor phase. The micro-nucleation of the clay grains will cause the vapor jacket to form in many more and smaller bubbles, and thus the transfer of heat to the medium will be more even.
 
Yes, I believe that the goal in what I was taught about this is a more uniform and quicker heat transfer. I was also learning it in relation to a particular water quenched steel, and I was assuming that it would be better for quenches were there were higher blade temps quenching in relatively colder quenchents.

I would be using a high temp oven to assure the optimal pre-quench temperature of the steel, and a quenchent heated to it's optimal temperature as well. I am trying to avoid having to use agitation of the quenchent, so that I can use a slicing back and forth motion of the blade in an elongated tank.
 
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