I have a small batch of fillet knives that I want to make using 440C for the first time. Bought 1/16" 440c, drew up sketches, layout the design and profiled the knives into blanks. I plan to grind the blades after the heat treat. Since this is a stainless steel I bought aluminum quench plates and stainless heat treat foil for the heat treat. I purchased an Evenheat 27" LB kiln a little over a year ago. Up to now I only used it for heat treating carbon steel knives. Since 440C is a stainless steel, I created a new heat treat schedule where I pre-heat the blades at 1400F and hold for 10 minutes followed by ramping to 1900F and holding for 30 minutes.
I wrapped the blades with the stainless steel foil and formed packages to limit any air and minimize scale build up. I placed the packages into the kiln and began the program. The program ran through the 1400F step correctly and got to 1900F without issues. While at 1900F the hold was cut short lasting only 5 minutes and the program aborted. Not knowing what happened, I quickly wrote a new program to hold the 440C at 1900F for 60 minutes allowing 30 minutes for the original hold and 30 minutes for the quench process. The temperature recordings were all over the place and erratic. Generally the kiln temperature rises pretty steady. I ended up aborting all my attempts to get it back to temp. I left the steel in the forge and decided not to quench since I did not know what the actual temperature was at and it did not soak long enough.
The following day I called EvenHeat Support. Evenheat determined that the TAP controller I had was malfunctioning and is sending me a new unit. I should receive it mid-week. Evenheat Support was very helpful and I can't say how much I appreciated all their help.
So now I need your wisdom on the blades I left in the over. Since I did not quench them, will I have any issues with repeating the original program? Is the steel in a bad state now that I left it in the kiln and allowed it to return to room temperature? What about the stainless steel foil packages I made. Should I remove the foil pouches and repackage the blades with fresh foil or can I just stick the original pouches back in the kiln and restart the program? Any help here would be appreciated. I would like to salvage these blades and would hate to throw these in the trash. Please give me your opinions.
Scott
I wish I knew more about stainless - especially in that scenario.
But, I always keep in mind something I was told over 20 years ago - "Always stack the deck in your favor". With that foil having spent at least some time at that high temp, personally I would re-wrap them with new foil. And maybe toss in a little piece of brown wrapping paper to eat up any oxygen in the pack. I hope you are using the high temp foil. I would. One goes a couple huundred degrees higher than the lower temp foil.
Karl B. Andersen
Journeyman Smith
Thanks Karl. I am using the high temp foil so I hope I can salvage them.
Scott
I've heat-treated a single batch of 440C blades and I have been pleased with the results. Wrapped in 321 SS foil, quenched in a hand press with aluminum plates, and finished the quench(to my home shop capabilities) in a dry ice/acetone bath. The aluminum press was intended to limit warping and it worked for me. Do you think your filet blades will have warped from the interrupted HT process? Time, tool wrap, and additional processing on faulty materials are all costly. An inspection might settle several questions. Maybe inspect one or two and reassess? Thanks for sharing your experience. I'd like to hear what you do.
Jesse I have at least one of the longer fillet knives that is visually bowed within the pouch. This one may turn out to be a good experiment to see what happens on reheat treating 440C. The other pouches appear relatively straight. At the moment I have not unwrapped them, hoping someone had a similar experience and could shed further knowledge on what to do. I am still waiting for the new Tap controller to arrive so there is no rush at the moment.
Scott, I have only used 440 a few times and I have never experienced what you have. I am using info on HT from Latrobe. Here is a link to the data sheet: https://drive.google.com/file/d/1X40GhM3zlE02bhVg1F-Hd4RljgSiVdIi/view?usp=sharing
I'm no metallurgist, but maybe if you tried annealing the blades before the next attempt that might remove any stresses caused by the weirdness in heating. Maybe I'm clueless.
Joshua States
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Thanks Joshua for the info from Latrobe. I will check the hardness and see if I will need to anneal it first. What a pain this whole experience has been. Good news I did receive the new Tap controller replacement tonight. Plan to install it in the morning.
Well I did a schedule run this time without the knives in it to see if the new Tap controller would make it through the schedule without fail. It did. I repacked the knives into new Stainless steel foil. Two of them were very warped from the interrupted cycle. I ran the schedule with no problem and quenched with aluminum plates. All 5 knives came out straight as an arrow. I did a cryo treatment with dry ice and denatured alcohol for 30 minutes and then allowed them to return to room temperature. The tempered in over at 375 F for 2 hours. Cooled to room temp again and re-tempered at 375 F for another 2 hours. No warping at all. Rockwell is around 60 so its where it should be. Now to see if I can grind 1/16" blades with any precision.
Thanks for the support. I think I can safely say that I salvaged the blades.
