Circles in steel after HT

T

TRAVIS R HENNINGER

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Jul 23, 2017
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Can someone tell me what causes these circles in the steel after HT. I am using a homemade forge burning lump charcoal.

The steel is 5160 from Jantz.
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From scale building up on the surface when you heat treated. this is why we remove all the decarb layer after heat treat.
 
It's not a good or bad thing, it's a surface condition. Normalising is most likely what did it. Extended exposure to heat creates lots of scale and some times it forums in little round blister shapes. There is also a layer on the surface called decarb that has had the carbon burned out of it. This is why we normally grind or sand after heat treat. If you don't have a grinder then use a corse grit paper and start sanding till all the scale scaring and decarb is gone then move up in grit and finish the blade. But like I said as long as the heat treat was done right and everything is spot on then it's just a finish issue and not a structural problem.
 
Thanks for the help. The heat treat went well, and the portable hardness tester I am using is showing around 57 Rockwell. Should be ok.

I am hand sanding now.
 
Just remember to get an accurate hardness reading you have to remove the decarb becaus it is much softer the the hardened steel.
 
As a side question, if the OP doesn't mind me jumping in here, how do I know when I am completely through the decarb layer?
 
If it's a simple carbon steel you can just give it a dunk in some ferric chloride. Steel with real low carbon content will etch much lighter color then the hardened steel.
 
I had that happened early on with some O1. It looked like beach sand when i broke it. I am voting for overheating.
 
Just finished it. Plan on abusing it tomorrow to see if it holds up. We will see. I am still figuring it all out. This is knife #4 i am not to worried about the mirror finish yet, until I get the basics down.
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I do. It is not a great picture. The bevel near the tip needs corrected. I will work on that tomorrow. I made a jig to help hold my angles. I am not real good at it yet. But I will keep practicing.
 
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