440C heat treating

K

KenH

Well-Known Member
Hello all - I had Sandvik's 12C27 on my mind this morning, put in oven for 5 minute/blade at 1975ºF. After plate quenching I tested the blades and only had 52 RC. Hmmm, A good bit low I'm thinking - I was expecting more along the lines of 60+ Rc. I put blades in freezer for a -5ºF freeze (Sandvik says -5ºF is good for about 1 point, and -95ºF for 2 to 2.5 points) then remembered it was NOT 12C27, but 440C blades.

While Sandvik does NOT recommend re-heat treating any of the Sandvik steels, what about 440C - can it be annealed then re-heat treated? OR - does it even need to be annealed prior to re-heat treating?

Comments, suggestions, or guidance please,

Ken H> (Hey, getting old 'n forgetful is better than the alternative)
 
OK, more research shows it should be OK to re-heat treat 440C by annealing first. This is "assumed" by the info for forging 440C - it says to "cool to room temperature, then anneal after forging". From this, I'm "assuming" it's ok to re-heat treat by annealing, then re-heat treat.

Ken H>
 
I talked peter at peters HT . He tells me you can bring 440C to full hardness in oil. I have ht some blade 2-3 times and did not have any problems. However not with 440C ? Each time you HT it must be normalised / annealed between each ht. I have ht 440c its not anything like or near as difficult as some of the new stainless steels , in my opinion the better stainless steels should be sent to HT shop like Peters. quote; From this, I'm "assuming" it's ok to re-heat treat by annealing, then re-heat treat.................. that should work fine.
there are some makers who use only stainless , would hope one of those may comment .
Bubba
 
Thanks for the confirmation Bubba - I just wasn't sure when I posted my question, and didn't find the info on first search. After posting I did find the page I quoted the info from.

This is a GREAT place to get good info and to double check my own understanding. This EvenHeat oven sure is a LOT less hassle than the old gas forge using a muffler pipe with TC inserted to muffler pipe for heat treating. AND - having a Rockwell tester allows me to have some idea of hardness - WITH the understanding that "hardness" is not the only concern - there is also "toughness" to consider.

Sure is a lot of fun learning all this stuff.

Ken H>
 
I'm going to stick my neck out and suggest you don't need to anneal. Just rewrap -reheat to about 1875 - soak for about 30 minutes - plate quench for 60/61 or air quench for 59/60. Cryo, dry ice or better will get you to 62 or so. It's still 440C. Temper back to 59 or so. Just to be sure, you did foil wrap right? Also, 440C needs the longer soak at temp to get the chromium into solution.

Also, it's going to take longer to get a blade up to temp in your kiln than it did in your forge. 5 minutes may not even have the steel up to temp yet.
 
Well sir, I suspect you are correct that just re-heat treating without annealing "should' be ok, but I don't know. How would a person know if this worked or not? I'm sure the metal would get harder. Would a good test be re-heat treat, quench, check Rc hardness, then if it did get hard.... say 60/61 Rc, then break a piece to check grain size? If grain looked like a grey finish with no visible grain (like a file broken)- would this indicate a successful blade?

Yes, I do wrap in stainless foil - boy, foil is NICE!!! A blade comes out looking good, almost still polished - even when heat treated in the forge.

On the 5 minutes, remember I was thinking "Sandvik 12C27" and they recommend 5 minutes for a .100" thick blade, 6 minutes for a .118" blade. Talking with a Sandvik engineer he indicated no real soak time was required, only to get to temperature for a couple of minutes.

Ken H>
 
This is the way I would handle this one too. You will need to use the electric oven and go to about 15 min soak. A forge isnt controled enough in my opinion for stainless steels. Just run it through a stress relieving soak and than ramp up to the proper temp.
Knifemaker.ca said:
I'm going to stick my neck out and suggest you don't need to anneal. Just rewrap -reheat to about 1875 - soak for about 30 minutes - plate quench for 60/61 or air quench for 59/60. Cryo, dry ice or better will get you to 62 or so. It's still 440C. Temper back to 59 or so. Just to be sure, you did foil wrap right? Also, 440C needs the longer soak at temp to get the chromium into solution.

Also, it's going to take longer to get a blade up to temp in your kiln than it did in your forge. 5 minutes may not even have the steel up to temp yet.
Click to expand...
 
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Thank you for your input Bruce - I was thinking this would be good, but didn't know. I'm a bit dis-appointed in the temperature control of the electric oven. There is 50F to 60F difference in the bottom and top temperatures in the oven at 800F range, so if the SetPro is set for 800, the bottom where the blade is located, the blade might only be seeing 750F. Not sure how much difference there is at 1950F range.

Bruce, you're right - the gas forge is a real bugger to hold 1950F for 5 minutes, much less for 15 minute for 440C. For 5 minutes I've been able to hold 1950F ±15F pretty good, but that's only for 5 minutes.

Thanks again for all the help,

Ken H>
 
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