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Heat Treating and Metallurgy Discussion of heat treatment and metallurgy in knife making.

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  #1  
Old 04-06-2011, 05:31 PM
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Odd pattern "etched" into steel after HT. What is this?

Hey guys,
I've noticed that sometimes after I heat treat a blade and grind the scale off the steel has this "irregularity" or whatever you might call it almost "etched" into the steel. It does grind out, but I'm curious as to what exactly I'm looking at, and if I'm doing something wrong to be seeing this.



Sorry for the crappy cell phone pic, but hopefully you can tell what it is and maybe someone can recognize what's happening here.


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Old 04-06-2011, 11:04 PM
Ed Tipton Ed Tipton is offline
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I am not sure, but I have noticed similar "etchings" when I have overheated the steel...and specifically when my flame was "oxidizing". I use a propane forge, and whenever I get the steel too hot with an oxidizing flame, I sometimes get this which I have attributed to maybe having burned the carbon from the steel. You mentioned that you get this after HT, but I'm wondering if perhaps it is not already there before you do your HT, and possibly hidden from view by scale.
One thing I have been doing is that after forging, I go to the grinder and "fine tune" my blade profile and remove any "irregularities" and stress risers that resulted from the forging. Then, after "cleaning up" the blank, I return it to my forge where I take it up past non-magnetic temp...then quench...then temper. Since using this sequence, I have not had this type of problem. I am not sure that I've correctly analyzed the cause, but I do know that my problem went away after I started using the above sequence. Hope this helps.
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Old 04-07-2011, 11:36 AM
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Decarb


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Old 04-07-2011, 07:06 PM
son_of_bluegras son_of_bluegras is offline
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It's hard to tell from that picture. It could be decarb as was mentioned. Or some sort of carbon or alloy banding/separation.

What steel? Heat treat procedures? Does it happen regardless of alloy? Any other details?

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Old 04-07-2011, 08:49 PM
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The steel pictured is CRA 1095, which up to this point is essentially the only steel I make knives from.
That particular knife was quenched in 130*F Veg. Oil, but I have noticed a similar effect at times when quenching with Parks 50 (which I use exclusively for 1095 now).

As for HT recipe/procedure, I bring the rough ground blade up to 1475*F in my homemade HT oven, let it sit for 5 or 10 minutes, and then quench in Parks 50 at room temperature. (At this point, it's about 50*F which according to Park's MSDS is acceptable).

I'll then clean the blade off and temper at 400*F, after which I grind the scale off and occasionally notice this effect to an extent on some blades.


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Old 04-08-2011, 07:27 AM
Ed Tipton Ed Tipton is offline
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Again, I doubt that what is happening is ocurring during the tempering phase. I have never seen anything even close to that happening as a result of tempering. You never mentioned what type of forge you are using, but when I first started I was using a coal forge. With coal, it's very easy to egt the steel too hot...and it's not easy to tell if you have an oxidizing or carbonizing heat. When I switched over to propane, I set my regulator low enough that even if I leave the blade in the heat for an extended time, there is no danger of it overheating. Since I do not do any pattern welding or any forge welding, this works for me, since all I am trying to do is reach a good forging temp.
I believe your problem is that you are burning the carbon (decarb) out of the steel with too much oxidizing heat. Try working you steel at a lower temp...and if possible avoid the oxidizing flame. Using a properly regulated propane forge will help you in achieving this.
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Old 04-08-2011, 08:31 AM
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I probably should have specified, but I do strictly stock removal using Cold Rolled Annealed flat stock. No forge is involved.

I simply profile and bevel the flat stock and put it in the HT oven, which never gets above 1475F.


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Old 04-08-2011, 01:13 PM
WBE WBE is offline
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Get yourself some ATP anti scale. It is water based and paints on. Brownell's has it, as well as some other machine shop suppliers.
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Old 03-03-2012, 11:21 PM
DJS_Skinner DJS_Skinner is offline
 
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I Have Gotten That a Few Time On Some Blades ,And Was Told It Was From Over Heating the Metal.
It Looks Like The Metal Has Blisters On It. I Have Yet to Find That it Has Hurt the Steel After Wards and If you Like it Incorperate it into the Blade if you Like Or Sand It Off When you Finish the Blade.
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Old 03-04-2012, 08:22 AM
tuskbuster tuskbuster is offline
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i noticed the same on a few blades when i was useing a wood coals .and attributed it to that as i dont see it in my propane now .as was said i left the look in the blade and it gave it a nice aged look
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