newbie heat treat problems

rustyrazor

rustyrazor

Joined
Oct 13, 2011
Messages
1,774
first time firing up the ole evenheat since getting it wired up. I tried five 12c27 blades, and 2 came out well but 3 came out soft enough to cut with a file relatively easy. all were plate quenched at the same time with the only difference being the time it takes to pull blades out and lay them on the aluminum blocks and the time it took to cut them out of the foil and chuck em into the dry ice slurry. three questions I guess, why did some turn out and others not? was it likely the ones I did first that cooled wrong that ended up soft? can I simply normalize them and start fresh or is the steel ruined somehow? and should I have taken two or three at a time rather than all 5 at once to keep the times more strict?

formula I used (from sandvik):
1. soak @ 1975 (I went for 15 minutes)
2. plate quench as fast as possible and let cool for 5 minutes.
3. place in dry ice/acetone slurry
4. temper at 300F for 30 mins, twice

since I totally blew my 440c blade as well, I can assume this won't be my last questions so thanks in advance

Royce
 
First, you need to determine that the blades are really soft. Grind them down a bit and re-test. A proper Rockwell hardness test after the clean-up would be very helpful.

Second, there is no need to rush the plate quench. Just take it from the oven and place it in the plates.

Third, you need to check that your oven temps are what you think they are.
 
yep. all 3 were 12c27. I can file the 3 of them pretty easily... file doesn't glide at all. I will clean them up and check them and get them to a RC tester to see what they came out at, and you're right a good thermometer to check heat temps could take that out of the equation. I also read that you have to get them to the plates in less than 10 seconds from 1975F in order to get the proper quench (5-8 seconds is what I read) that is why i'm thinking the two that got hard were the last two... hence they were less time from furnace to plates. i'm thinking i'm going to do them individually next time from furnace to plates to get a better grip on my time variation. a
 
Just a wild guess... Considering a scenario - 5 blades closely placed on the rack. So, the 2 outside blades are OK, while the inside 3 could be they didn't get enough heat.
 
From the way you describe your process are you saying you removed all five blades from the oven at the same time?
 
Could you describe your quench process in more detail? Its a bit fuzzy. Also, until you get things dialed in I wouldn't heat treat more than 2 blades at a time. I plate quench on some stainless, but do each knife separately and I don't do more knives than I can quench effectively.. Plates heat up, soak times get lengthened etc the more you need to get done in a short window, the faster you may try to work. Hurrying isn't fast, smooth is fast.
 
woodwrkr221 said:
From the way you describe your process are you saying you removed all five blades from the oven at the same time?
Click to expand...

I just caught that, too. If you plate quenched five blades at one time, I can see all sorts of problems.

The normal procedure is to do one blade, take it out of the plates after a few minutes, and then do the next. Make sure the oven has rebounded to 1975 before removing the next blade. If needed, cool the plates between quenches ( if they rise to become hot to your hands).
 
yeah, stacy and woodwrkr, I totally did all 5 at once.. thought it would be enough time and enough of a sink... wrong obviously. also never thought of the 2 outside ones cooling faster and the inside ones being insulated and cooling slower. good catch bluntcut, those could be my good ones, I am not sure. I am going to try em again in a week when I get more dry ice. next time, I will definitely be quenching only one at a time and see if that changes things. I will document each detail totally to the minute and if they come out well, I will post the RC and we can at least have a decent idea of what went wrong with less variables... I made a mess out of this one trying to save time/money... like you said Ricky slow is smooth, smooth is fast. you'd think I would have learned that by now.

thanks

Royce
 
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