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The Newbies Arena Are you new to knife making? Here is all the help you will need.

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  #1  
Old 02-04-2015, 12:04 PM
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Heat Treat Trouble...

Okay guys so I broke a knife that I heat treated with my homemade charcoal forge. After quenching I tested it with a file and it appeared to skate off the surface. Then, I tempered twice at 400 degrees for an hour each time. After I broke the knife, I broke a nicholson file to compare the grain structure. I was shocked to see the difference between the broken pieces.

So my question for you gurus out there is what did I do wrong? Did I overheat? Did I not soak long enough?
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Old 02-04-2015, 12:47 PM
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Ray Rogers Ray Rogers is offline
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Really hard to say. First off, I can't really see much difference in the picture since it is so small. But, just because a file skated off your blade doesn't necessarily mean it is properly hardened. There are crystalline forms that are as hard as properly treated austinite so they would pass the test even though they would leave the blade more brittle than it should be resulting in a relatively fragile finished blade. So, if that happened - and I stress the IF - then that would likely mean you over heated, or possibly under heated, or quenched in the wrong speed oil, or maybe someone could even dream up a few more possibilities.

You mentioned soaking. We don't know what steel you were using or how long you soaked it but soaking too long will surely foul up some steels, usually by letting the steel over heat since any forge be it coal or propane is likely to be idling along at a temp considerably warmer that a simple carbon steel would require.

I've never used a coal forge and I don't know how much coal you have in your forge. I would guess that a small forge with just a few pounds of coal in it could have a hard time holding a high temp, lots of temperature variation depending on how well you tend it. More coal in a larger forge should hold the temp steadier for a longer time but would likely be much hotter than carbon steel would need so careful attention to the soak time would be critical.

Instead of all this guess work maybe the thing to do would be to rough finish a blade, sharpen it, and test it. Do some prying with it to see if it snaps off too easily. Cut and chop with it to see if the edge chips or if it dulls too easily. If it all works out then you're golden. Even so, remember that the next blade would need to be the same steel, heated to the same temp for the same length of time, and quenched in the same medium warmed to the same temp. Vary much from that and the next blade may not be as successful as the test blade ..


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Old 02-04-2015, 01:19 PM
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This steel was 1084. I didn't really let it soak for very long at all. Before tempering I dropped it on a paving stone, tip first, and all it did was chip the concrete paving stone. I also attempted to normalize it one time prior to quenching.


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Old 02-04-2015, 03:51 PM
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Is this a better picture Ray?
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Old 02-04-2015, 04:13 PM
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You'd probably need a macro focus lens to really see the grain. I can see its a light grey color and that's usually good. Maybe - just maybe - it looks like it might be a little lumpy.

At this point you're concerned you may have the steel too hot or maybe too cold so you need to find a way to know where the blade temp is at all times up until the quench. Probably the simplest way to do that is with a magnet. Test often with the magnet as the blade heats up. Be careful not to let the magnet get hot or it will simply stop being a magnet.

Your goal is to know exactly when the steel becomes non-magnetic while the steel is heating up. It won't work correctly if you heat beyond non-mag and then try to catch it on the way down.

Once the blade goes non-mag continue to heat for another 15 to 30 seconds (this varies according to how hot your forge might be so being consistent and testing your results by torture testing your blades as I described earlier is the key to knowing when you have it right). The goal is to go about 100 degrees beyond non-mag and not any further.

Lots of guys who use coal forges try to go by color. That can work if you are very consistent with your process and you have a controlled environment but it only works once you have learned what the appropriate color looks like in your environment. To do that you need to start by testing with that magnet and, frankly, I'd stay with the magnet as color is too subjective...


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Old 02-04-2015, 06:36 PM
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Hard to see much in the pictures. If you blade has noticeably larger grain than the file, I would guess over heat before quench.
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Old 02-04-2015, 11:41 PM
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Looking at your last picture and squinting, the grain does look coarse to my eye. You didn't mention... was this blade forged to shape, or only heat-treated in coal? The blade was over-heated at some point, either when it was being autenized for the quench, or while it was being forged, if it was indeed forged. The soak wouldn't have any effect, unless it was soaked at too high a temperature.

How are you judging austenizing temperature?


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Old 02-05-2015, 07:11 AM
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Pics are not detailed enough for me, but the first does appear a bit grainer than the file. Need a macro shot.
Really difficult to judge colors in a coal forge unless you have really developed those skills.
As Ray mentioned the magnet will get you very close. Lock in a mental picture of the color at the point where the steel becomes non-magnetic on the rising temp. The brighter color just beyond this point is your true critical temp and the color you are looking for. Vary hard to regulate in coal without a pipe tunnel oven inserted in the bed of your coals (black iron pipe buried in coals). You do not want the color to go any brighter this includes the tip and other thin parts.....not so simple. In my experience, most get their steel too hot, 1084 at critical is a darker almost black red, not bright red to orange. It takes lots of practice to learn how to read and control your heat/colors as well as a consistent ambient working light source. Why most smiths work under cover and heavy shade (plus it's cooler).
Gas forges are a bit easier to work with in this aspect and can, with tinkering and proper torch/needle valves/regulators, make this reasonably easy.

I'd say practice with the magnet and reduce as many variables as possible.


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Old 02-05-2015, 10:15 AM
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Hey guys,

Thanks for the help everyone,

So this knife was not forged, just heat treated in the forge. I'm judging austenizing temperature by color. We have a programmable furnace at work that I've heat treated in before and I based my color off of the color of the knife in and coming out of the furnace. The color I saw in there was a bright orange at 815 C(approximately 1500 F it's just controlled in C). Maybe that's my mistake and the color in the forge is different due to different lighting.

Ray,

My problem with the magnet is that if I pull the knife out of the furnace to test it, it cools pretty quickly. I guess I might start heat treating before grinding bevels though to prevent that cooling so I can use a magnet effectively.

Yeah Crex, I've wanted to do a pipe tunnel for a while, I just can't find a source of non-galvanized steel near me.


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Old 02-05-2015, 11:53 AM
Doug Lester Doug Lester is offline
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Your blade should not be cooling off too quickly to test with a magnet. It's just pull the blade out and run it across the magnet and right back in. You are right about color changing due to ambient lighting, it's not good to go by and can easily lead to over or under heating.

Doug


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Old 02-05-2015, 06:44 PM
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Plumber's supply - cast or ductile iron 4"
Gas company supplier - black iron 4"
Most hardware stores can find you some 4" in either
Talk to them about "drops" - cut offs chunks, usually free

Yepper, surrounding ambient light makes all the difference in color perception.

1450 to 1475 on 1084, 1500's a bit high.


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  #12  
Old 02-07-2015, 10:50 PM
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Well today I messed up the hidden tang handle of a knife heat treated at the same time as the knife I broke and posted about. So I sharpened it up and did some testing. I cut 50 ft of 550 paracord into 600 pieces with a one inch section of the blade and it was still shaving sharp. Then I used a hammer to baton that section of the knife into some wood. Shaving sharp again. I continued batoning until it wouldn't shave and I didn't observe any chipping on the blade. I also dropped it from a few feet tip first onto concrete and I did observe some damage to the sharpened edge on the tip. Finally, I'd seen a knifemaker cut pennies using a knife and his hammer before. So I tried it and..... success! I cut several up, usually in three whacks of the hammer. When I checked the edge it wasn't shaving sharp, but it wasn't damaged either. I guess next thing I'll do is break it and observe the grain.

So to everyone out there how does this testing sound to you? Was it a success?

Also, if the other blade that I originally posted about was heat treated once before and then I heat treated it again, could this have caused problems with the grain?


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Old 02-08-2015, 08:42 AM
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Sounds pretty successful to me. I wouldn't hit the blade with a hammer though, that can crack or deform a good blade. Using an actual baton - a heavy wooded stick or mallet - is safer ....


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1084, art, blade, carbon, charcoal forge, cold, degrees, edge, file, forge, forged, heat, heat treat, homemade, hot, iron, knife, quenched, simple, small, steel, stone, supply, surface


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