straighten after ht?

[willy m]

hi all. i read here somewhere that if i quench a blade and pull it out after it has cooled enough to harden and it has a small bend that i may be able to straighten it carefully if i get it before it cools too much. have i correctly understood this? i can quench a blade that is up to heat, pull it out after a few seconds while its still hot and straighten any bends carefully that may have happened while quenching? and i should be able to do this with my heavily gloved hands? and then after straightening and cooling the rest of the way my quenched blade is ready to draw temper. is this correct? because i did this on monday and it went pretty well. afterwards i did a file check and it seemed to be ok. (1065) is this process ok or does it sacrifice something i havent thought about? thanks,willy

 

[mete]

You have to quench down to around 600 F then you have a limited time to bend it before the martensite transformation .In any case you should never try to bend a blade below 400 F.

 

[kungfumo]

Ya I learned that the hard way yesterday, when I got done with a nice short Japanese short sword, it had a nice curve to it when I pulled it out, so I thought I would try bending it back before it cooled too much, but it had cooled too much and I broke it in 2 :grumpy::grumpy::grumpy:

 

[Kevin R. Cashen]

The method you describe is martempering (or more accurately marquenching but industry prefers martempering for some reason). I have used this method on one form or another on virtually very blade I have made for the last 12 to 14 years. While mete is correct that if you get crazy with a blade that is in the transition from austenite to martensite it can punish you, however slight adjustments can be easily made down to around 60% martensite. It is easy to gauge the time to stop due to the resistance you will feel as things set up. Some steel will allow you to correct them for quite a bit longer than others. Something like 1084 will let you know it is time to leave it alone long before L6 will. I have been able to move bend and restraighten L6 for up to 8 minutes after removing from 400F salts. I once tried to tie 5160 rods into knots quickly before they set up but found that, while I could make them look like pretzels, by the time I went to tighten the loop down enough austenite was kicking over into martensite that the steel would pull apart before I could cinch it.

You will notice that a blade quenched this way will Rockwell out about 1 or 2 points lower, but don’t be alarmed that is due to some autotempering that has already occurred, by the time you finish tempering properly you will come out the same as a traditional quenched piece, but with some added impact toughness due to the low stress conditions of martensite formation.

Not only will you be able to straighten the blade if it does warp, but this method will also eliminate a lot of warping as well due to the more gradual and even transition through the hardening zone. I do believe however that it is best to come as close to Ms without going under as possible before the interrupt. I would shoot for around 450F. if possible, interrupting too high could invite other structures to form and could also run the risk of putting the edge under Ms and then having too much heat bleed back into it when the cooling effects of the quenchant is removed.

 

[Sam Salvati]

Marquenching FTW hehe! Kevin do you know of any suppliers of specific marquenching oil (in small quantities) or do you just use your low temp salts only?