Is Blue Beautiful?

Milt

Milt

Joined
Nov 16, 2008
Messages
260
I am working on knife number 3. I hardened the 1095 blade at 1490 degrees, and then tempered 3 times for 1 hour each time at 500 degrees. The blade turned blue. My other 2 knives did not turn blue, but I tempered at 400 degrees. Is blue supposed to happen?

Milt
 
There is Blue....and there is blue. Often a blade will turn strange colors in tempering due to oils and such on the surface.That means nothing, and comes off easily. If the blade was truly turned blue by heat, then that is an indication of being tempered to a spring temper. Blue starts about 550F and gets dark blue at 600F. It will take a bit of light sanding to remove this type of blue.

In a 1095 blade that was properly hardened, a 600F temper is not fatal. It may well be a very tough blade and around Rc 56-57.

Stacy
 
bladsmth said:
There is Blue....and there is blue. Often a blade will turn strange colors in tempering due to oils and such on the surface.That means nothing, and comes off easily. If the blade was truly turned blue by heat, then that is an indication of being tempered to a spring temper. Blue starts about 550F and gets dark blue at 600F. It will take a bit of light sanding to remove this type of blue.

In a 1095 blade that was properly hardened, a 600F temper is not fatal. It may well be a very tough blade and around Rc 56-57.

Stacy
Click to expand...
Something I've always wondered:
If by some failure in heat treat you don't get a blade hard or to it's hardest possible state at quenching, do the colors of tempering then become useless? Like o-1 for example, let's say my soak time wasn't long enough before the quench and I achieved a hardness two points below maximum. Then I temper it to a dark straw color. Would that dark straw be deceiving since I missed optimum by two points? Would that dark straw be two points softer than if I hit the optimum hardness? Or is dark straw always the same hardness no matter what hardness level was reached in the quench?
I hope this makes sense, any info would be greatly appreicated.
Later, Iz
 
Color and hardness are two different things. The temper colors are an indication of how hot the steel got in the temper cycle. If the steel was Rc 62 instead of Rc 64 as quenched, then the temper would be somewhat lower also. Thus a 450F temper might yield Rc 57 instead of Rc58-59 ( numbers are for example, and do nor refer to any actual steel).

Two different steels ( even a piece of mild steel) can have very different hardnesses even though they were tempered to a straw yellow color. The hardness is a function of the steels characteristics and the quench.

Stacy
 
So, the color you get from a given temperature is fairly consistent even with dissimilar steels? (say 1084 vs D2) If I understand that right, it makes colors more useful, not less.

Mind you, I was a printer for a long dang time, don't get me started on how different eyes see the same color under different light...
 
in the ens the hardness tester id the king

color of temper is like color of steel pre quench reading it leave a bunch in the air
also i have tempered steels at 1000f and they still are rc 62
some even gain harness at that temp
so color alone will not get you anything more then just a guess
 
James_Terrio said:
So, the color you get from a given temperature is fairly consistent even with dissimilar steels? (say 1084 vs D2) If I understand that right, it makes colors more useful, not less.

Mind you, I was a printer for a long dang time, don't get me started on how different eyes see the same color under different light...
Click to expand...

NO, I get different colors from different blades using the same oven and temp. I think it is the type of steel, how clean it is, exposure to chemicals, length of time, the atmoshere in the oven etc etc. Like Butch said a good thermometer beats color any time.
 
This is why it is so important to test EVERY blade that leaves your shop, put a cheap 2X4 handle on it and test it hard before you start you final finish, you will get lots of rewards in the long run. It's no fun to have one that will not hold an edge when its all finished. Good luck with you testing.
 
bladsmth said:
Color and hardness are two different things. The temper colors are an indication of how hot the steel got in the temper cycle. If the steel was Rc 62 instead of Rc 64 as quenched, then the temper would be somewhat lower also. Thus a 450F temper might yield Rc 57 instead of Rc58-59 ( numbers are for example, and do nor refer to any actual steel).

Two different steels ( even a piece of mild steel) can have very different hardnesses even though they were tempered to a straw yellow color. The hardness is a function of the steels characteristics and the quench.

Stacy
Click to expand...

Thanks, Stacy.
That's something I've been wondering for a while now.
Milt,
Sorry for hijacking your thread for a bit.
Later,
Iz
 
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