Quench Help? Bubbling Surface

D

danhowl

Joined
Aug 22, 2017
Messages
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Anyone recognize this? Started happening a couple weeks ago. Thought maybe my oil (canola) was contaminated, so I replaced and still have it. Have tried to keep my heat treat/quench process consistent--heating oil with steel chip while the blades are soaking.

QuenchQ.jpg

These show the bubbling. Both have been tempered after. Bubbling is quite light and disappear with light sanding/grinding.
 
Steal was over heated. It will blister when it gets over heated. This is common in the tip ogblades because it’s much thinner. This is why you flip the blade around and heat the tang first then Flip back around and heat the blade
 
JTknives said:
Steal was over heated. It will blister when it gets over heated. This is common in the tip ogblades because it’s much thinner. This is why you flip the blade around and heat the tang first then Flip back around and heat the blade
Click to expand...
 
Yep. The one on right snapped an inch back from tip when I was hitting tang for pin hole.
 
On top of this post: When you do overheat the steel like above would the steel not file test good at first? Thick mill scale layer?
 
Maineiac1 said:
On top of this post: When you do overheat the steel like above would the steel not file test good at first? Thick mill scale layer?
Click to expand...

Mill scale layer?
Mill scale is the hard black scale layer that is on the bar when it comes from the mill.

The problem with the blistering is that it shows it was over heated. Now if you over heat the steel and quench there is a few problems that show up. There is a good chance the grain size of the steel is now MUCH larger then if it was at the corect lower temp. This larger grain size makes the steel much more brittle. Next problem you have is the likelihood of it cracking in the quench also just increased dramatically. This is not to mention the carbon in the steel that got turned into gas and floated away leaving a deep decarb layer. None of the above things are good that’s why we STRESS proper and accurate heat control.
 
JTknives said:
Mill scale layer?
Mill scale is the hard black scale layer that is on the bar when it comes from the mill.

The problem with the blistering is that it shows it was over heated. Now if you over heat the steel and quench there is a few problems that show up. There is a good chance the grain size of the steel is now MUCH larger then if it was at the corect lower temp. This larger grain size makes the steel much more brittle. Next problem you have is the likelihood of it cracking in the quench also just increased dramatically. This is not to mention the carbon in the steel that got turned into gas and floated away leaving a deep decarb layer. None of the above things are good that’s why we STRESS proper and accurate heat control.
Click to expand...
A few days ago I HT one blade from 52100 . Grind /both side bevel / on blade was disaster because I try to grind free hand so i use this to make some test .....heated with big torch between two soft fire brick .No that I over heat tip /about inch and half from tip / of blade but it get bright yellow color . To get that temp was easy and fast , it was thin blade . I break after HT that blade and found inside very , very fine grain ? There was no time for grain to grow up I suppose because of really short time of heating , maybe all last about four minutes ? I wonder how long time should take grain to start grow up ?
 
Grain growth is a factor of time and temperature. Temperature is far more powerful that time. 30 minutes at 1500F is not going to grow much grain at all. 1 minute at 1800F will significantly grow grain. Bright yellow color is much too hot for HT. You should be at a bright red for HT. Color may look different in varying light and to different people. That is why using a magnet to find where it becomes non-magnetic is important. The temperature that the blade stops sticking to the blade is about 50-75°F below the desired HT temp. Heat just a shade brighter than whatever it looks like and you are there.
 
JTknives said:
Mill scale layer?
Mill scale is the hard black scale layer that is on the bar when it comes from the mill.

The problem with the blistering is that it shows it was over heated. Now if you over heat the steel and quench there is a few problems that show up. There is a good chance the grain size of the steel is now MUCH larger then if it was at the corect lower temp. This larger grain size makes the steel much more brittle. Next problem you have is the likelihood of it cracking in the quench also just increased dramatically. This is not to mention the carbon in the steel that got turned into gas and floated away leaving a deep decarb layer. None of the above things are good that’s why we STRESS proper and accurate heat control.
Click to expand...

Mill scale, yes I knew that but farted in my brain. Is it the decarb layer I hear people say that after heat treat sometimes they get a soft outer layer that must be sanded off to get to good steel underneath? leads me back to my file test
 
I had the same feature at the beginning. And the good advices above will help you out.
The thing i still don't know it is what those "blisters" actually are. Many hypothesis had been proposed, from carbide clusters to carbon depleted regions, and even a quenchant's etching at play, but i still don't have a metallurgist's answer.
 
I've had the same thing happen to me. Check out the thread at:
https://www.bladeforums.com/threads/need-low-cost-heat-treating-method.760489/#post-8532984

Quote: "your surface blisters are either just overheating the surface, or possibly getting surface infusion of carbon (kind of like case hardening) which lowers the melting temperature at the surface where the charcoal then touches the blade and spot overheats it."

I think this is what my problem was and what you may be experiencing. Check out the thread listed above.

- lonepine
 
On my second knife, and far too ambitious. The first heat treated beautifully, but it was a stubby little folder, this time I had a go at a hand filed sguan duh, and was using a very large torch bought to retemper stone tools.

because the blade was so thin and I must have overheated so much, (get it non-magnetic and then a bit more the man said..) I ended up with a surface like alligator skin.
After much filing and sanding the second attempt isn’t good, it refuses to harden, all the flavour having been burnt out...
Thank you all for this thread!
 
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