Weird forged results

JTknives

JTknives

Joined
Jun 11, 2006
Messages
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I heat treated all 4 knives last night. I had five to do but when i was cleaning up the dagger blade after normalizing it i noticed that it had a crack on one edge. o well chock it up on the learning score board. but the other 4 heat treated great after they where normalized, no warping or bends at all. for heat treating i soak for 7 min at temp and quench in warm mineral oil.
I got home to put them in the oven for tempering and decided to do a quick file test. but the file just kept biting in on all 4 knives. i tried it along the whole edge and no skating could be found even after filing quite a bit. well i wend to bed very disturbed as i have had nothing but great success from this 5160 in all the dozens of knives i have made from it using the same heat treating method. but these blades where forged so i was very confused. so i decided to sleep on it. in the morning i got up and started thinking was i dreaming that the blades did not harden. so i did a another file test and after removing just a little bit more material bam it was hard. but it was interesting on how much material i had to remove to find the hard center. It almost acted like a laminated blade with a hard core. So i started thinking that i maybe overheated it while forging it so i checked my color chart and i was right in the zone needed around 2000-2200 determined by the posted chart. before i heat treated i ground down the blades a bunch to remove most of the forging texture, some large pits where unavoidable and had to be left. so i hope i did not get that much decarb as that is outrages. the edge looked like i was sharpening it buy the time i got to the hard core. any ideas what could have happened. also the steel seams to finish sand and polish easier then my stock removal blades and is amazingly ridged for how thick it is.



tempcht.gif

Any Ideas, Thanks
 
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What was the ambient light like? That can make a huge difference in how the forge looks. Also you need a reducing atmosphere, feathers of flame dancing out the front of the forge. If your atmosphere is oxidizing then it will decarb much faster. The fewer heat cycles the better also. This will reduce the decarb as well. Judging the temp by eye can be very difficult. A controller and thermocouple will run between $50 and $100. Then you can be more certain of your process.
 
Takes along time to get used to seeing the steel color as a temp. If you do alot of forging then try to heat treat soon after your eyes will lie to you about the color because of you looking at the bright light of the forge, kind of like welding blindness. same as when you are heat treating alot of blades at one time. the last one will most always be a bit hotter than the first.
 
You should invest in a thermal couple and pyrometer. I think you roasted the heck out of them. You cant tell how hot things are by eye unless you have the room nearly dark.
 
I don't remember who did it, but at a conference of blacksmiths a while back they had small groups of skilled smiths look at some pieces of steel that were taken from a controlled oven at known temperatures. They would immediately discern he color and record the temperature on a card. After dozens of tests at different temperatures the results were tallied. The range of guesses varied by over 600F and nearly all were thought to be much less than the actual temperature was......and these were guys who knew steel. Using your eye to gauge temperature is a hard thing to learn without a pyrometer to tell you if you are right.

As far as the blades, this is a common thing in forging, especially in the beginning. Too many heats and too much heat combine to make what is called a "rind". This is a thin skin of decarb that will never harden.All forged blades have it to some degree. It is removed in the shaping and grinding.....usually. Once the blade is sanded down the hard steel is exposed and suddenly the knife works.

I recall one of my knives (before I understood about the rind... heck, before I understood much at all) that I was really annoyed with. I would sharpen it and it wouldn't cut cardboard of paper worth a D**N. I would touch up the edge some more, thinking that I had not sharpened it enough, and still no luck. I was about to junk the knife (I had moved the edge back 1/16" by now) and suddenly the knife cut like there was no tomorrow. I had passed the bad steel and was into the hard stuff. I have since learned that forging in a forge running at full tilt is not a good idea, and that knowing what happens in the steel while you work it is the best way to get the end result you desire.

Sometimes a smith will have a blade that he finishes and after the final polish and etch there is a funny spot or area on the blade that etched very different. It is a place where the decarb is still on the surface. This is often right above the grind line. Going back and re-sanding this area will often remove the problem.

Another common reason it happens ,IMHO, is due to too thin an edge in forging. Thin steel can burn up pretty fast at 2200F, and real fast at 2300F-2400F. Now, you say, I never let my steel get that hot.....and you may well be right.....but lets look at a Little metallurgical physics. The steel is at 2200F the edge is down to a pretty thin section. You are drawing it out a little more. You heat the blade to 2200F ,to make it really plastic, and forge away at the soft hot edge. As your 4 pound hammer strikes the thin section the force is hugely concentrated in one spot. This applies great pressure which suddenly raises the temperature of the steel at the edge bu as much as a couple hundred degrees. This then immediately cools back down in a thousandth of a second. A lot happens in that millisecond. The alloy ingredients get a moment to run around naked yelling "nanny Nanny nanny,you can't catch me." and then they get trapped in all kinds of places where they shouldn't be when the gate gets slammed shut. Now you know all this, and you normalize the steel after forging and before HT. But is it a long enough soak ,and high enough for all this strange behavior to be rectified? In most of the blade, yes (maybe), but in the severely modified edge, no, the damage is permanent or would require a much longer soak to normalize things . Merely thermal cycling the blade will not do it. I also believe that much of the problem with pieces of the edge breaking off and tiny cracks in the edge come from this original problem.

The answer is to forge to a moderately thick and slightly wider edge,normalize and anneal well, grind to a slightly thick edge, normalize one last time,HT, then grind away the rind and expose the good steel. Leaving an extra 1/16-1/8" of edge width to grind off in the final profiling after forging is a good idea anyway. Forging to exact shape is fraught with problems.

Keep pounding (and make a controller for your forge).
Stacy
 
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thats what i thought was happening bad decarb. but now another little peak into the weirdness that is my forged blades. i filed down an area on the tang that was quenched and the file would still bite in and remove material. so i took it to the RC hardness tester and checked it where i was fileing. well what do you know it came in at 58.5 RC so then i tryed to file the little dimple out where i tested the steal and the file bit right in and removed it. is it possible to have a hard material but the grain is so fine that it can still be filed. also one more thing could we look at the rind in another light and maybe call it good if you could control it. i mean if you think about it you end up with a 3 layeres of hardness with just the core hard with the outside still soft. could we not take advantage of this to increase toughness.
 
Dont forget that the file is about 63 rc and the blade is 59 rc. Yes the file will bite normally. You should use a worn file. I presume you ground off all the scale before any tests?
I'm still trying to get Stacy running naked shouting nanny nanny! out of my mind:eek:
 
It severely disturbs me that Bruce is constantly thinking about me naked.
I could understand some of the other chaps here doing that (I will not mention any Portuguese names, Texas gar fishermen, or old moderators), but BRUCE, I am totally shocked.
And to think that I actually considered going to Washington with a good bottle of single malt, going out to the forge, and having a good intercourse with Bruce.( You young folks will probably have to google that word. It is in the dictionary, too, but some of you will probably have to google 'dictionary' to find out what that is, too.).
Stacy
 
What if a person forges and heat treats with a peice of charcoal in the forge, would that help anything? Anyone suggest what model of thermocouple to use? I have a mac tools multimeter with -40 - 2400f range, but I need a sensor that will plug into the meter(prongs 3/4" apart)
 
Stacy thanks but I'm not that kind of guy. I'm flattered though. Bring the single malt and that stainless quench tank. We can try it out.
 
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