Marquenching and drawing back the hardness in the spine questions

[Black cat]

Ive been reading all afternoon about heat treating 1084 for this large chopper.
I quench in canola as its all ive been able to track down so far.
I have an HT oven.
My results till now have been somewhat hit or miss.
One blade was tough as f***! Another seemed soft.
All come out of the quench warped.

With this large blade im thinking of an edge of 61rc and a slightly softer spine if possible.
I HT at 1500 hold for 10 and into the quenchant vertically using a slicing motion.
When cooled to a temperature where I can hold the blade I put it into the oven at 400 for one hour to temper, then cool. Repeat temper at 400 2 more times.

I just read about marquenching and it sounds like it would suit my style more. Quench to 450-430 then remove to air cool.
Thats where im a bit lost ? How in the world do I know when its droped in temperature to the 450-430 range ? Heat gun... Guess... Touch it or is it generally that temperature and lower ? Do I take it out of the quench when it is just about cool enough to touch ?

The other technique I saw mentioned torching the spine after the HT and quench to further soften the spine. Is this... Idk. What is this lol.
I understand the principle but how do I do this and will it be of any benefit to me ?
Is it just a few quick passes with the torch till the steel blues ? Is it after the HT scale is removed ? Is it before or after the 400 degree temper ?

Thanks

 

[Bruce Bump]

Your warped blades could be a couple things. there is no need to move the blade around in the oil. that right there may add the chances of warping. The other thing is you probably have stress in the steel before you put it in the oven. You should do a stress relief cycle. I use 980f for 30 mins before ramping up to 1500f.
You oil is fine although I like tough quench from Brownells or better yet Parks 50. Point down quench is good unless you want a soft back. Don't use a torch to soften the back it doesn't give consistent results. Instead do a horizontal quench of just the edge and slowly lower the rest of the blade into the quench. It will flame up so be careful. Another method is to heat just the edge with a torch and quench point down. this will harden just the edge and leave a soft back with a spring temper in the middle somewhere. Makes for a tough blade.
You don't need so many tempering cycles. One hour at 395 should give you a 61 at the edge.
I don't know if you are forging your blades but you should normalize them if you are. Heck you should normalize them anyway as you don't know what they went through at the mill. There may be large grain and stress even from bar stock.
Hope this helps.

 

[TacticallySharp]

Bruce has covered it pretty well. I'm just adding a couple of images:


Using a torch to edge harden.


Harden blade edge in wet sand drawing back the spine.

Edit: for some strange reason photo are upside down.

Always normalize to help relieve stress before quenching. Since I started doing it I haven't had any warped blades.

 

[LRB]

I can see no reason to use a torch to harden a blade when one has an oven with accurate heat control. There is no way to get an accurate even temp with a torch, and no way to accurately provide a decent soak. A fully hardened and tempered blade, then soft backed, makes a stronger blade than an edge quench. Very easily done with pan of water and a propane torch if soft backing is desired. There is also no reason to go as high as 1500° for the hardening quench. 1475° with a 5 minute soak is plenty enough, with no risk of any grain growth. Normalizing and heat cycling to reduce grain size would be wise for 1084, but an hour or two at 1200° for stress relief afterwards would not hurt either.

 

[Black cat]

Thanks for the help! Its coming along pretty good so far. I think from all this ive devised a game plan and should be ready for heat treat tomorrow if all goes well.

 

[wdtorque]

Update?

 

[Black cat]

Well after many days and hours of grinding and sanding and shaping its ready for heat treat.
had a hell of a time getting it flat... I lay it on a flat surface and make adjustments but for the life of me I cant figure out why it doesnt seem quite right. The steel arrived warped and twisted so that made it awkward. I sanded to 150 grit.
I wrapped all but the last inch of the handle in steel foil and normalized at 1600 F as per Cashens notes and air cool.
next I will de stress the steel then HT 1475 for 10 min and quench. The only quench tub I could find only allows oil up to the start of the handle. Will that be enough ? Or idk can I flip it over to quench the handle ?
Other than that it seems good so far. Eyeballing the blade it seems straight inevery way. How do you guys check that your blades are perfectly straight. By sight or is there a better way ? Other than that... Terrible day for injuries.
sliced my finger on the steel foil and bled like a stuck pig. Then five minutes later got boiling plastic all over my other finger. Half my index finger is blistered pretty bad all across the joint. Feels like its on fire.
But thats learning