HEAT TREATING QUESTION

[DANA HOLMAN]

WELL I GOT MY FIRST BLADE IN THE FIRE TO HEAT TREAT, EVERY THING WENT FINE, MY QUESTION IS DOES MOST OF THE CLEANUP ON THE BLADE START WITH THE BELT SANDER OR BY HAND, THE REASON I ASK THIS IS I WENT TO CLEAN UP THE BLADE BY HAND AND COULD NOT GET ALL OF IT TO COME OFF, AND SOME SPOTS OF THE BLADE LOOKED LIKE THE METAL WAS BLISTARD, IS THIS NORMAL? I THINK THE BLADE GOT TO HOT OR FROM THE CHARCOAL TOUCHING THE BLADE.
THANKS FOR ANY INFO.

[ALW]

Not to get off of your subject, but I've had blisters show on the few blades when quenched them.  I was using warmed motor oil.  What causes this.  I couldn't get them out with hand sanding so I just left them.

Aaron

[DANA HOLMAN]

ALW
I USED VEG OIL THAT WAS WARMED TO ABOUT 160 DEGREES, WHAT DID YOU USE FOR HEATING TREATING YOUR BLADE?

[ALW]

I used warmed motor oil.  I heated up a couple of railroad spikes and dropped them in to warm it up.  Not sure exactly what the temp was though.  But it was warm to the touch.  One was an old file and one was an old mower blade.

Aaron

[mwmwmb]

I recently made my first knife and had these and i took some work with 80grit on the sander and then i worked up in grit by hand. I used a propane torch for heating and heated veg oil to 180.

[Jeremy]

What you're seeing on the blade is called scale and is normal.  There are several ways to help prevent excessive scale formation while hardening a blade.  You can buy a powder (can't remember the name right now) that is put on the hot steel (at about 600 degrees or so).  It melts and coats the steel, preventing the oxidation.  It works very well, but produces fumes that aren't good to breath.
The best option for controlling scale is to control the atmosphere in you forge chamber.  For a propane forge that means optimizing the flame coming out of your burner.  For a charcoal forge that means proper fire maintenance and a good chamber formed in the mound of fuel with the right about of air being forced through the whole thing.
'Nuff of that.

Did you check to make sure your blade was fully hardened after the quench?  Did a file scate across it?  What temperature did you temper the fully hardened blade at?

If you have lots of scaling on your hardened and tempered blade, you're best bet it to go right back to the belt grinder.  I normally grind my knives about 85-90% complete before hardening, leaving the edge about the thickness of a dime and finishing it to 220-400 grit.  Immediately out of the quench - after checking to make sure it hardened properly - I hit it (at least part of it) with 120-180 grit it see some shiny steel.  Then I draw the temper back in the oven.  Then I go back and do my final grind, progressing through up the grits before hand rubbing the whole blade.

[Jeremy]

I did my first couple of knives the same way, but didn't have a grinder.  Doing it by hand just takes longer.

[DANA HOLMAN]

THANKS JEREMY
I HEAT TREATED THE BLADE TO BRITE ORANGE AND CHECKED IT WITH MY MAGNET, LEFT IT IN THE FIRE 2-3 MIN. LONGER THEN QUENCH IT(DID NOT KNOW IT WOULD GO BACK TO MAGNET AFTER I DEMAGNITIZE IT) CHECK IT WITH MY FILE, (LEFT I LITTLE SCRATCH)
I THEN PUT IT IN THE OVEN, I DID NOT CLEAN THE SCALE OFF BEFORE I PUT IT IN THE OVEN, SHOULD I HAVE DONE THIS? I DID GET ALL THE SCRATCHS OUT BUT THOUGHT I COULD DO BY HAND.
P.S. I DID FIND KILN BRICK THIS MORNING 10 MILES FROM ME. GONA GET ME SOME TODAY.
THANKS

[ALW]

Jeremy, thanks for the info.  I pretty much did the same thing that Dana did.  Check with a magnet, soak for a couple more minutes, etc....  After I finished the quenching and heat treating I cleaned it up with the belt sander.  It quickly removed the scale (except in a few pitted areas).  But it didn't remove the little "blisters".  They almost look like spots were the metal bubbled up.  But I'm a complete novice at this.  I'll try and manage my fire better the next time and see if that helps.  

If I can get a knife right now that will gut, skin, and cut up a deer without needing sharpened I'm happy even if it's not as shiny as a new penny!  LOL....  Thanks again to all on here for the great info.

Aaron

[Phoenix 1967]

Those Bubbles or blisters is where Carbon from the interior migrates to the surface. Things always go from highest concentration to lowest. When you get these blisters on the surface, it means there was more carbon in the steel than in the atmosphere around it. This is known as an oxidizing fire. (you have more air than fuel in the fire) This causes the carbon migration and scale to form. The "Bubbles" have a higher carbon content than the surrounding steel,Thus are VERY hard to sand out. If you are using carcoal, it means that you need more coals below the steel... with Gas, you need more fuel pressure to compensate for the excess oxygen.

[DANA HOLMAN]

THANKS GUYS
I REALLY DON'T MEAN TO ASK SO MANY QUESTIONS BUT YOU GOT TO LEARN SOMEWHERE, MAYBE ONE DAY I'LL UNDERSTAND THE HOLE THING ABOUT STEEL, BUT FOR NOW I'LL JUST LEAN ON YOU GUYS, IF YOU DON'T MIND. I'LL TRY TO POST THE THREE KNIVES I'M WORKING ON NEXT WEEK,
THANKS AGAIN

[Phoenix 1967]

Allways glad to help

[Steve Nuckels]

Interesting!  Does the degrade or compromise the steel?


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IN GOD WE TRUST

[Phoenix 1967]

To a minimal extent, depending on how many times, and how long it goes on. You find carbon migration to be a major problem when forge welding, as manny heats,folds, heats, etc, can remove a significant amount of carbon from the steel. Proper atmosphere in a fire is very important when drawing a blade from a large bar, because of the number of heats required. ('course i'm talking hand hammering here, it's much less an issue with a power hammer or press)

[Todd Robbins]

An overnight soak in vinegar really helps to remove scale.  That scale is rough on belts, but comes right off after the vinegar treatment.

Todd