A2 different colors post plate quench?

S

SamaraVolk

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Apr 17, 2014
Messages
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I recently received my Evenheat oven and attempted to heat treat my first non carbon steel knife. I cut out an A2 blank, put it in SS foil, ramped the oven to 1425f (held for 20 minutes), ramped to 1775f (held for 30 minutes) then immediately plate quenched the blade. When I removed it from the foil, half of the knife is a normal steel color and the other half is like a rainbow blue. Sort of like the Aurora Borealis. It looks quite interesting but was wondering what it means. I did put some paper inside the foil. Thanks
 
Just some contaminates on the blade,will not hurt anything.Sometimes a small pin hole will also cause this allowing oxygen in.
 
I've always wondered how plate quench work , since bevels have no contact with plate ?
 
The plates mostly keep the blade straight and speed up cooling by contact with the handle and flats on the blade. The pearlite nose in stainless is so long they will harden in open air.
 
Thanks guys. This is going to be the second knife I grind post heat treatment. I did my first 1084 grind post heat treat for the first time and I'm happy with the results. That being said, I never used A2 before. One more thing came up that has me a little puzzled. The A2 came out soft (using hardness testing files, that's all I have). The hardness seems to be between 45 and 50!! My procedure was: 1) SS envelope with small piece of paper 2) ramp to 1425 and hold for 15 minutes 3) ramp to 1750 and hold for 30 minutes 4) aluminum plate quench 5)2 temper cycles for 2 hours at 450. I did not slow ramp to 1425. Could this be my problem. Also, I did not clean the blade prior to testing with the files. Thanks
 
I've heat treated a lot of A2 and it's always been pretty reliable at 1750 and air quench. I think your first step is to verify that your furnace is hitting 1750. I would wrap a small coupon of A2 and let it soak at 1750 for 30 minutes, then pull it out and cut the foil packet to get it out. Let it sit in open air. When cool check that with your file before tempering.

Second I would verify your 450 temper was actually 450.

What material are your plates and how thick are they?
 
Thanks for the reply. I used 2 3/4" plates sitting on top of each other. So 1.5" of aluminum plate on top and bottom. My oven is new but I know that means the thermocouple may not be accurate.
 
You didn't clamp them together in a vise? Just set the plates on top of the knife? To get good thermal conductivity you should clamp them.
 
No I did not. I only did what I have seen online. Some guys put weights on the plates. Some guys just let them cool in still air, and some use compressed air. Any expertise is appreciated.Thanks
 
Cooling in still air or with plates that are compressed to get full surface contact will cool faster than with just the weight of the plates alone. I believe you may have actually insulated the knife during the quench causing it to auto temper.
 
I was not aware that cooling in still air is better than with plates and some pressure. Thanks for this insight.
 
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I do A-2 all the time , just finish the knife , your file test may just have been done in some soft carbon not yet removed . You cannot get all the air out of the foil .
Like Stan said the plates help to keep things flat and straight and cool faster but as A-2 is an air cool steel they are not needed . Weights just help to keep them flat

A lot of folks use woodworking quick vise clamps which I think Kuraki may have been referring to , they are great .

I soak mine at 1775 for 40 minutes
 
How deep have you filed? There shouldn't be much decarb if you were foil wrapped air tight.
 
When I get home tonight, I'll clean the knife and retest. I did not go deep at all. I just skim the file over the knife to see if it "bites"
 
your heat treat #s should put you in the Rc range of 60 , if you do not have that after cleaning all up your oven is off .
 
Well don't I feel like the village idiot. As some folks have mentioned, there was a layer of carb on the knife. I cleaned the knife and ran the Tsubosan files over the blade. 50 and 55 could not bite into the steel. 60 feels like it is trying hard to bite. 65 definitely bites in the steel. So I am guess the knife is around 60 or so. I will finish the knife as is. Thanks to everyone who responded. Charles
 
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