Why is forced patina only showing along edge?

U

Umekubo

Joined
Jan 16, 2016
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23
Happy day everyone! I am forcing a patina on a 1084 knife I made and am wondering why the patina is only showing up along the blade edge. I fully submerged the knife in distilled white vinegar over night. I imagine this would have to do with the heat treat correct? I heat treated in a backyard bbq charcoal forge slow and steady until non magnetic and then a little bit longer, quenched in 150f canola oil for 30 seconds moving up and down and edge to spine, lightly sanded and let cool to room temp, then tempered in kitchen oven at 425 for 2 hours twice. Maybe the edge was heated to a different temp than the rest of the blade during the heat treat? I don't know. I'm new to this. What do you guys think??? Time for some pics.
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Did you edge quench only? It looks like you edge quenched, which differentially hardens the edge compared to the spine.

Either that, or your edge was at critical temp and your spine was not, at the time you quenched.

I think it looks nice either way.
 
Thank you! I quenched the entire blade. Did not edge quench. So then the edge was at critical temp and the spine was not. Now would that create the same benefits that edge quenching would? Like with the spine being softer for a larger heavy use blade. Or is the composition of the metal different when edge quenching opposed to heating the edge more than the spine?
 
how thick is the spine i have a feeling that th 150 oil quench was only fast to the point of getting the bevels hardened (as shown at the plunge cut the extra thickness of the tan provented the plunge to get hard)
 
It is a good thing, differential hardened makes for a tough blade. Looks like you got much the same results as a Japanese style clay coating would have produced for those creating hamon.
 
Ok nice. Thanks a bunch you guys! The spine is .14" thick. And ya, hopefully it isn't too hard.
 
.14" is not very thick. 1084 steel is a deeper (more like medium) hardening steel, so it will harden an entire piece quite easily in thin pieces such as knives. That is as long as the blade is heated evenly.

The way to obtain a hardening line like that is by clay quenching, edge quenching, or by heating only the edge before quench.

At a 425 degree temper I dont think it should be too hard. That is unless you overheated the edge. Did you do any testing?
 
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1084 is not a deep hardening steel. Not the shallowest.
It looks like a nice unexpected result
 
A very nice unexpected result! As long as it wasn't overheated.. During the heat treat I spent most of the time heating the spine and then every now and again I'd flip the knife over to heat the edge. Once the whole blade reached the non magnetic point I put it back in the fire and only focused on heating the edge up a little more moving it back and forth to get the entire length of it. I guess doing that allowed the spine to cool back down. I have not done any testing yet and im not really sure what would be the best way to go about testing it. Maybe sharpen the edge and lightly hit it against something to see if there is any chipping? What would you suggest?
 
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