[jimmyseymour]

Originally Posted by Mike Blue

A few comments:



Ahem. Stress relieving occurs in two types. The first is to relieve internal stresses generated by heavy machining of clamped pieces. The second is tempering which relieves the internal stresses in steel caused by martensite formation against areas of non-martensite. I could use your Japanese sword example because that is a perfect illustration. So, the fact is, not personal opinion, stress relief is desirable when one of the above conditions exists in the material.

Thanks for proving my point. The opion was about normalization and spheroidization. Sorry will try to go slower next time.

Martensite formation occurs at the speed of sound (770 miles per hour at 68F at sea level, about 13548 inches per second). Even in a great big bowie knife (1/4-5/16ths of an inch thick at the spine), I don't think that any wiggling about a human being could do will cause a warp to occur in the short amount of time available between the initial quench and the formation of martensite, unless some very specific conditions are controlled. About the only way to significantly alter quenching both sides of a blade to cause one side to cool faster than the other, would be to lay only one side of the blade on the surface of the quench bath.

And how did those brainiacs come up with that number? How can you possibly time that? Are they taking photographs of the change and time it that way? I would hate to be the guy with the stop watch trying to get that one right.

From what you describe, the vapor jackets are very transient and the bubbles would break down and be replaced by the liquid quenchant as fast as they form. That amount of time is not as fast as the formation of martensite. The more likely conditions that could be affected by martensite formation are the changes occuring in the grain structure as a result of the transition from austenite to martensite or pearlite. Those could easily be affected within the amount of time available and could contribute to warping. Another likely condition is that the steel is still in the metastable phase and has not completed conversion to martensite and is "more plastic" than hard yet. In that state banging off the inside of the tank or possibly even the resistance to motion afforded by a thick cold oil could bend the blade against the resistance of motion provided by your hand. It wouldn't be the motion itself, or the vapor jacket, but specific conditions in the steel though. I admit, it's a lot easier to think that it's the vapor jacket.

Actually it's called a vapor barrier because it causes a barrier. That is why boiler tubes will destroy themeselves from improper cooling if a barrier builds up between the tube wall and the cooling water. The barrier is self sustaining and the only thing the operators can do is correct there actions that caused it. To much heat, to much flow, not enough flow, wrong chemistry, etc...

You were okay up to the point of whacking it with a wooden mallet. The copper block treatment is to relieve the sori, the formal curve that makes it a Japanese sword. That technique is not used to straighten a warped blade. I've seen 1/2 steel plate straightened with a rosebud torch and a little hammer. Good smiths have good techniques, but not all of them work in all conditions.

So how does a wooden mallet make it wrong? Oh because you didn't say it.