Preventing post quench warping on a longer blade

[JoshAraujo]

I recently made a few knives, and of them a Kukri I made warped after quenching. As you can imagine, its always a pain to straighten out a warped blade.

Now, I'm planning to make a longer blade - A sword. A wakizashi to be precise

Any tips on preventing the longer blade from warping after a quench? I'll be attempting a differential treatment for a hamon

 

[samuraistuart]

Josh, there are a few ways to deal with warping. Before harden/quench, do a stress relief. 1200f for a couple hours is plenty. Another method.... You can always straighten during Ms-Mf. To boil that down simply, the steel is still austenite as it cools down to around 400f. That period of 900 down to 400, the blade will be easily bendable with a gloved hand. So quench the blade, making sure to leave the blade in the oil long enough to beat the pearlite nose (around 10 seconds is plenty good). Pull the blade out after that 10 second count, and straighten with gloved hands. Back into oil until ambient.

Post heat treat straightening......do the 3 point clamping method during tempering. A search in the Shop Talk section will give you results on how to do that. Temp must be 400f or above to be effective. Works very well. Make sure that whatever you use as the pivot point/fulcrum is softer than your steel (to avoid unwarranted scratches). Brass rod works very well.

 

[kevin -the professor]

Yes, to what stuart said. Get the best heat resistant gloves you can find, and pull the blade out of the quenchant (if it is water, after about 8 sec, or oil about 10). Straighten fast. The hardest part is seeing through all of the smoke/steam. If you can get the blade straight in that 20 sec or so window, everything will be golden. If not, don't worry. Especially with a dif hardened blade, you will be able to get it straight later.