Aldo's Blue #2 Heat Treat Problem

S

StuNY

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Feb 16, 2014
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Scratching my head on this one, should know better than to just grind a knife in a new steel without testing some coupons first! Oh well, made a 240mm Gyuto and put in the oven at 1500 degrees for 10 minutes. Veg oil quenched. All looked great until hardness test- about 40 HRC : (

So went back to drawing board, made a few coupons. Tried 1500/10min water quench, 1550/7min water, and 1550/15min oil quench. Everything pretty consistently around 40 HRC.

Anybody offer any advice here? I have heard that Parks 50 is best quench but didn't have any handy. Think that would make the difference? Sure seems like something is waaaaay out of whack!

Thanks,
Stuart
 
Did you measured the hardness after removing the decarburated layer? if not, that would explain the low RC values as the temperatures you mentioned look OK, I would not risk at 1550F (845C) in water, but 1500F sounds good in preheated oil.


Pablo
 
PEU said:
Did you measured the hardness after removing the decarburated layer? if not, that would explain the low RC values as the temperatures you mentioned look OK, I would not risk at 1550F (845C) in water, but 1500F sounds good in preheated oil.


Pablo
Click to expand...

Yes, I ground the surface before measuring. Then for laughs took a file to them and it cut pretty well. something definitely wrong. 1550 into water quench was pretty exciting. Thanks for the suggestion though!
 
These low alloy steels need a very fast quench, there can be many reasons for it to not fully harden, a few comes to mind: slow quench oil, cold oil, slow transition from oven/forge to quench bath, not enough time at forge/oven, using stainless foil to protect the blade...


Pablo
 
IIRC, you made an electric HT oven. Great job on it by the way. Have you had success HT'ing other materials yet?
 
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I agree with lu1967, you have the wrong steel. there is no way that blue steel would not harden at 1500 and water unless you waited five seconds to get it into the water.
 
Having great success w cpm 154, O1 and 52100 w the oven so I don't think it is that. Aldo wrote "blue#2" on it and it matches the dimensions listed on his site. Oil and water both warmed up before quench. 10min at 1500 about the right time? Saw something in data sheet about bringing steel up to temp slowly. Will try ramping it later today- at full on the oven hits 1500 in 7-10 minutes- maybe too fast?
 
I agree, ramping would be the next thing I would try. Not going above 1500 and a 10 min soak should work. If not, call Aldo.
 
I don't know blue. On the other hand, I had a batch of 1084 from Aldo that wouldn't harden without a set of thermal cycles from 1650/1575/1500. Could be so spheriodized that all the carbon isn't getting into solution without the higher heats. Try it and see.
 
It was the ramp time! Ran another sample and ramped to 1500 for 20 minutes instead of full on. Cold water quenched. Getting 65 HRC out of the quench!!! That was what I was hoping for. Thanks for all the suggestions!
Oh, I put a lot of time grinding the original blade that I got the heat treat wrong on. Can I just heat treat it again or do I need to anneal first? I thought I read that it is not a good idea to heat treat multiple times?
Thanks,
Stuart
 
Most likely it will be fine with a new HT. It wouldn't hurt to give it a normalization cycling first, then HT at the new format.

I also would pre-heat your oven to 900F and insert the steel, ramping slower to the target.
 
Great news! Was hoping I didn't waste the effort. I don't see a normalizing temp in the datsheet- is it similar process to 52100?
 
For blue steel, the specs for 52100 will work fine.....especially if it is super-sheriodized.


The deal with Hitachi blue #2 is the tungsten. That plus the .40% chromium need enough time to get properly distributed. This is also why it needs to be a tad hotter than a simpler steel, like Hitachi white #1
 
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I have hardened two chef's knives out of Aldo's Blue 2 in Parks 50. One received a normalizing/thermal cycling and hardened at 1490F (soak for 15 minutes). One was simply hardened at 1525F (soak for 15 minutes). AFTER the decarb layer was ground off, both of the blades just made a joke out of a file skate test (I have no way to RC value a blade)...guessing 65 or 66 out of quench. 400F tempers result in edges that are still a bit chippy. Water (brine) would harden this steel like crazy, and is what Hitachi uses to quench their steel for testing and numbers. Are you SURE you have ground through the entire decarb layer? -StuTX (suspect the veg oil quench...but 40 is super low for that even)
 
Thanks Stacy, preheat at 800 then ramp to 1500 over 10 minutes and soak for 10 minutes worked great. Did the normalizing routine I used for aldo's 52100 first to the original knife. knife was at 66 hrc out of the quench. Saved!- for a minute or two. Then it turned into a lesson learned. Had a slight bow in it, so I put it in my handy tempering oven jig that straightens out bows- except I forgot to run the first temper cycle first. You guessed it, I got to inspect the very fine grain! Snapped right in half when I tightened the screws to take the bow out. Just sat there in disbelief- but at least I won't make that mistake again. The grain under a loupe looked like a very fine light grey powder FWIW
 
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