a question about the quench curve

[Alan]

Im forging a katana out of 5160 steel.

I want the blade to be fully-hardened and so there was no use of any clay.

I needed the blade to end up with a curve that matches a curve on a sword I already own so I can use its parts and saya.

I forged the blade with the needed curve before the quench.

I was told that the oil quench will not change the curve.

But that is not what happened!!!!

My blade came out of the quench straight.


why?

How did I get a matching curve?    

[Ed Fowler]

Distortion during hardening cycles is not uncommon. Usually due to the forging methods, or hardening, we found that when we added the post forging cycles all distortion ceased.

For those who are not familiar with post forging cycles it is simple:
After forging the blade to the shape you want, heat it to non magnetic and quench it in room temperature Texaco type A quenching fluid for 35 seconds, heat it back up above critical and quench again then to it a third time.

Heat the blade up to critical for a flash normalizing cycle, From non magnetic to magnetic, immediately re heat and repeat, then heat to non magnetic and let it cool slowly to room temperature, then anneal (I use 988 f,) for two hours a couple of times and you should have no problems.

The post forging quenches seem to be the most reliable method of preventing distortion in blades during heat treat.

I have only used Texaco type A oil, other oils may work just as well.

[ChrisAnders]

Oil quenching fully hardened blades tends to pull the point down, like you saw.  Water quenching clay coated blades tends to push the point up.  It's all in what cools first compared to everything else.  There can be a lot going on.  See below.

https://www.reddit.com/r/interestingasfuck/comments/3yeb7o/quenching_a_katana/