Plate quenching problem

R

Rob!

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Feb 9, 2000
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Just had a disturbing problem with heat treat - and worse, I screwed up a customer's blades - or the first ones we put through. The blades are fillet knives - 16 inches long with a pronounced distal taper - starting from 1/16 inch 440C.

They are double wrapped and tightly sealed. When I opened the door and grabbed them with the pliers they curled up like a potato chip. I plate quenched them but they still show unacceptable wavy edges. Way too much to even try straightening.

I'm returning his remaining blades and replacing the steel, but I'd sure like to learn from this (and not by using the rest of his blades). I feel just sick about this. :(

I've never seen another blade curl like that coming out of the oven. Has anyone else had experience with this phenomena? They came out nice and clean - cryo to just over 60 and tempered back to 58 as requested.

Thanks

Rob!
 
i try to grind hard anythign thiner then 3/32
it saves me alot of worry grindign half or less bevel on the blade then heat treat
on 1/16 no grind at all before but thats jut me
 
16 inches long made from 1/16" stock and distal tapered also? I cant see how you can even touch them without bending something. Too thin I would say. I have made that size and sent them to Paul Bos but he doesnt handle them when they are hot. He hangs his blades in a big oven. I also do all the grinding after heat treating.

I wonder if you could sandwich them inside thicker steel just to support them while handling and plate quenching?
 
Somebody was just telling me the other day how they heat treat razor blades in the factory. He said they make long, tall (but not deep) stacks of alternating steel and copper strips, clamped tight and just quench them as a unit....

Mike
 
Rob, clarify something . Are you saying that you heat treated someone else's blades ? If so how do you know what was done by him ?
 
mete said:
Rob, clarify something . Are you saying that you heat treated someone else's blades ? If so how do you know what was done by him ?
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Yes, they were someone elses blades - and I don't know what was done to them before I got them. But I have no reason to suspect anything less than good craftsmanship. They are already at a relatively high level of finish - and I have done 1/16 blades at this level of finish before with very good results (though never quite so long). I believe this is a 'tried and true' pattern that he has used for some time. He sent me 40 blades.

I was careful with them. They are double wrapped in high temp foil - suspended front and back in fire brick holders to keep them away from the coils - each one spine down and point forward and removed that way. The pliers hold from the back of the handle end and they are transferred, touching the plate spine first and gently laid on side before the second plate is added. By that time, it didn't matter. The plates were trying to staighten a twisted mess. They weren't even out the door of the oven before the deformation started.

Rob!
 
You shouldn't have to double wrap them if you're careful about sealing them .Did you stress relieve before you HTed ? What were the times and temperatures for the whole process ?
 
Preheat to 1425 - hold 5 - (recommended for thick sections of complex parts) Complex?? eh! maybe.

Continue heat to 1875 - hold 15 min - remove (deformity happens right here) and plate quench still in envelope. 2 minutes later blades are hand cool. Removed from foil and check a couple - RHC 59.

Cryo overnight hanging in Liquid nitro.

Remove in morning - let warm to room temp and RHC again - just a touch over 60.

Double temper at 350 (2 hrs each) aiming for 57-58 - all came out within a hair of 58.

Rob!

FWIW, these are stock removal blades.
 
i cant believe that it take that it takes that long for the blades to be hand cool
how much perssure are you usign on the plates
i cool full size chefs knives (3/32thick) to hand holdign in less then 20 sec
i ll have to time it now to make sure but i know that there done way before 1 min
 
You are right - they are hand cool in less than a minute. They usually sit there for 2 minutes while I'm fiddling with other things.

Rob!
 
Preheats are basically for large parts to minimize time at higher temperatures.I would have tried a stress relieve maybe 1250 F for an hour or two. The only thing I can think of is some wierd stresses introduced at the mill or stresses introduced by grinding.....1875 F for 15 min - that seems very short time especially when double wrapped ,25-30 min would be better.
 
I'm with mete on the stress relieving prior to heat treat, that is something I had to learn "the hard way" too :o . It has made a BIG difference in how my thinner blades come out.
 
Thanks guys. I'll try stress relief. I am going to make some blades in the same pattern and will experiment on my own. Of course, I can't duplicate the grinding.

The Crucible spec sheet for 440C doesn't show soak times at all. Admiral says 5 minutes and do not overheat - time or temperature.

House of tools used to go 20 minutes at temp for 440C. I picked 15 as a compromise considering the very thin sections. The hardness response was almost exactly as expected.

Mete, How long would you soak 440C at temperature?

Rob!
 
Rob, out of curiosity, what is the temp of your shop and is there any draft that could go in the oven when you open the door? Thanks.

Good luck, hope you solve what has to be a &^%$#&^%$-type problem.

One other thought: when you say double wrapped, do you two mean complete envelopes? I wonder if they could be sort of stressing each other as they cool in the first temp drop as the door opens and acting like a lever of sorts on a blade that is just at that length and thinness it can flex it??? Sorta fringe, i know, but I'm trying to grasp straws for you.
 
I think that those knives are way too thin. I used to make filleting knives from 3/32 nds thick and often had warpage problems on heat treat. As a result I only work with thicker steels and don't even bother with making filleting knives anymore unless it is a real dire request from a friend or a collector I know well. When I do use 3/32 thick stock I make smaller blades under 5 inches without any problems.
 
Hello Rob:

A Fillet knife is one of the most hardest knives to heat treat and and to grind. You need to use thicker steel before you heat treat. When you are finished heat treating the knife. I would suggest that you surface grind the blade down, but leaving reasonable amount to finish out your knife. In doing so, you will avoid warping and it will not end up like glass that will break. Just another reason why I prefer a hard edge and a soft back on my blades. I hope this was of help to you, and pray that God bless your knife making skills.
Barkes
When I leave this world I would like to be known by the one who make his knives from start to finish.

http://my.hsonline.net/wizard
1.812.526.6390
 
I have been making kitchen knives out of 1/16" A2 for about 5 years now and the only ones I ever had warp were oil quenched. Since I started plate quench them about three years ago, there haven't been any that warped. With the 1/16 kitchen knives though I don't do any distal taper and just grind a deep acute bevel to zero for the edge, which leaves most of the thickness in most of the blade width. I have made some fillet knives like this and it has worked well up to about 13" OAL.
 
fitzo said:
Rob, out of curiosity, what is the temp of your shop and is there any draft that could go in the oven when you open the door? Thanks.
quote]

I thought of that Mike. The shop was cold, but in the summer the difference between the oven and shop would be 1800 - and right now, it's maybe 1840. I can't see the temp difference being a big warping issue. The shop is enclosed no drafts were present. I also thought about the double envelope but the outer envelope is large enough to allow for lots of expansion / contraction, and the two envelopes don't stick to each other.

I think from all this, I'm going to start doing a stress relief cycle for all thin section blades. It was particlarly frustrating because I've done lots of other equally thin blades without ever having one warp. I even put in one blade that had a distinct 'bow' and it came out of HT straight.

I agree with many of you that these blades are too thin for my current practices. That doesn't mean the maker has to change his blades. It means I have to addapt my practices. Thanks for all the help.

Rob!
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