Forge damage?

Hey all, I've been working a large Camp Knife made from a leaf spring and used the forge to straighten it out and do a bit of shaping. I was sanding off
the grunge on the belt sander when I noticed there is a crack in the top quarter of the blade that goes about half the thickness of the steel and travels maybe a quarter to a half inch down from the back towards the edge. Now this is a fairly huge piece of steel that was going to serve as a wood chopping, bottle opening, all around heavy use camping blade. What I want to know is if the experienced forging folk out there can tell me if this kind of thing can be repaired? Should I hack the stock short at the crack and start over? Should I just re-adjust the demensions of the blade to grind out the crack? for the record, the steel appears to have some chromium in it so I'm guessing 5160. This is the second time I have run into this problem with what I think is similar material (based on appearence and behavior). Is it possible to heat it up and repair the crack? On the last piece of metal I tried folding the cold metal over in the vise at the crack to see if it would break and it didn't, so I'm guessing this kind of thing is localized. What is the opinion of the experts out there? It's all new to me.
Greyangel
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A fairly common problem with used springs. Stress fractures are common.
You could try forge welding it back together, but might be better off to work around the crack.
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wrote:

used
off
and <<Snip>>
I was wondering if forge weld was an option here but I can't see that it would be very easy without some folding. I think I've already made a different style of knife out of it in my head. You know, something with slimmer lines.
Greyangel
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On Thu, 6 May 2004 06:32:27 -0700, "Greyangel"

there are no mistakes in blade making,, just new blade designs ;o)
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It's not forge damage. It's typical of used springs. If you can get un-used spring cutoffs from a spring fab shop you'd be better off, but used springs are certainly the more common stock, and this is a common problem. I just moved my old truck springs closer to the shop, and chunks fell out of the middle of the stack - they became old springs because they had cracked in service, and some of the cracks went all the way though, so parts fell out. Other cracks may not become obvious until you start to work on them.
IMHO it's best to work around them, rather than to try and fix them. Some people say you should never use springs for this reason, but the price is right (I suppose not using them makes sense if you are a production smith - I'm not).
--
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I went ahead and ground it out. It started life as an oversized Bowie style knife; now its sort of a Fantasy blade. I started with the idea of those "elven fighting knives" that you see on the commercial sites for Lord of the Rings weaponry and kind of let the design work itself out as I went at it on the grinder. Came out pretty cool. Lots of flowing curves. Still too much forge markes on it that need to be planed off on the belt sander but it should make a nice blade and the crack is gone.
At this stage for me I'm just sort of starting with a chunk of metal and seeing where it takes me. Not good enough yet to start and finish with the same idea. I am a bit worried about this crack thing though. As I said, it's not the first time this has happened and it's not the same source for the metal so I assumed I did something to it at the fire. I'm currently attempting to straighten and draw a rather large chuck of metal and I'm not going to be happy if it comes out with a bunch of cracks in it. Different steel though. I don't think there is any real alloy mix there so I'm hoping it'll behave for me. And yes I am making sure I don't work it too cold.
Greyangel
----- Original Message -----
Newsgroups: alt.crafts.blacksmithing Sent: Thursday, May 06, 2004 6:38 AM Subject: Re: Forge damage?

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Greyangel wrote:

Folks have mentioned pre-existing cracks in old springs. I've seen a few but not many. There is another possibility: I was told by an instructor that you should never just re-heat after forging and quench for hardening. Get rid of any serious hammer marks with light hammering (hot). Reheat and let cool in air, i.e. "normalize". Then heat to "cherry" and quench, clean and temper.
Ted
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Hey GA, if the cracks were not there before you started then yeah it probably is something you did. Cracks often indicate forging too cold. If the cracks first appear like hairlines, usually running lengthwise, this is probably the case. Oil hardening steel (O-1) seems especially unforgiving of this sin. However if the surface of the steel is all gross and pitted and fissures or ruptures appear then this is caused by overheating and forging too hot. What kind of heat source you are using? Are you hand forging or power forging? Not that this matters much as you can always find ways to screw up when forging tools. There are two things you need to develop if you want to forge usable edged tools or weapons. The first is the ability to judge temperature by eye. At the very least, you must learn to recognize the high and low forging range. For spring steels and and similar plain carbon tool steels the upper limit is going to be around bright orange. Try and avoid frequent yellow heats. Hammering below dull red with all but very light blows is to be avoided. The second thing you need to develop is hammer control. Early on be most concerned with attaining smooth flat surfaces. Keep the anvil free of loose scale. Try wetting the anvil during the final light forging heats. This helps pop off heavy scale and will leave the surfaces quite glossy. This will make subsequent cold work a lot easier and quicker. For me, if a crack appears at any stage of making a blade, it goes directly to the scrap pile. I don't even think twice. Good luck Angel, develop good habits and it will pay off.
Glen G.
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Cool, Good information. I have pretty much gotten over the temptation to keep hammering after the glow begins to fade. Bright orange is about the best my forge setup will manage and as soon as it gets to dull red the work goes back in the fire. The cracks I've seen are small lines that start at the edge and aim crosswise to the length of the piece (knive stock). The last one didn't even penetrate the thickness of the stock. I am sure that the damage was not there before the forging. I'm trying not to hit it too hard if I can help it now (hand hammering). The other problem with putting a lot of muscle into the hammer strokes is that you get a less even surface out of it. Been trying to straighten out a big heavy (about 1 inch square) piece of railroad steel (not rail). I've had to lay into it pretty hard to get any movement out of that stuff. Quite a shock transitioning from that to a smaller (1/4 inch or so) piece of metal. Way different approach to the forge work. I should get the big one drawn out soon so I expect it to get easier to work with as I progress.
Greyangel

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Hey GA, from what you describe it is very possible that you are forging at to low a heat. I don't know how your finances are or how handy you are., but I would recommend putting together a decent forge. it doesn't have to be very big. A good atmospheric burner can be built for ten bucks! There are some companies that sell small amounts of fiber insulation and $50 or so should cover a knife makers forge. You will recover the cost in fuel savings in a very short time. Also, there is a blacksmiths tool called a "slick", some call it a "flatter". This is used as a finishing tool. It is basically a 3" square face with a shank. It is held on a handle and is designed to be struck with a sledge or heavy hand hammer. It can be awkward to use by yourself but it can be done and the results are dramatic. All but the deepest boo boos will be slicked down.
G.
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Hmmm. If the metal is at color I don't see how this can be. It does seem to make a difference in overall work when the forge is fully soaked but still the metal is what is at issue here. As for me being handy... I'm new at this so mistakes are made. I'm learning though.
I kind of like my forge setup right now. I have a not quite assembled Riel burner in my garage That I plan on finishing and I do plan to do a forge chamber with Kaowool and.. whatever the name of the refractory sealant is. The two big drawbacks to my current setup is that the torch is probably not very conservative. Lots of air blowing around but I am out in the back yard without a shed for cover. The other is that I've never seen it at anything hotter than bright orange heat to slightly higher. Thinking about it though, I've never really opened up the torch valve beyond what I felt was needed so I don't really know what it will do. I try to idle it as much as possible to conserve fuel. On the plus side, I can set up and tear down in minutes. I don't know how big it will need to be untill I'm using it so it's inherently adaptable to blade size which is what I want it for anyway. Actually I like this feature so well I was thinking of just facing some bricks with refractory to make them more efficient for the interior spaces. I've also thought about making casted segments for the chamber that can be run end to end for the length needed for the blade that is being worked. This way I can just cap off the chamber or add sections on the fly. So, yeah I could have a more efficient set up but this works for me for now and untill I know what it is that I really want out of it

Sounds like cheating. Where can I find one? I like the idea. I'll be looking for a suitable piece of steel to make into one. After my experiences with working thick stuff I don't think I'm gonna try to forge anything that big. Hmmm, give me an idea. I've got a piece of railroad rail that I use as an anvil and I had a friend under cut the top rail so I've got a 6 inch length of the footing and webbing without the top. Still really heavy stuff. I've been working on sharpening the top so that it'll be a self standing hot cutoff. I'll bet a piece of that stuff would make a killer "flatter" since a lenth about 3 inches with the footter profiled a bit smaller (or not?) and the top flattend would make a killer stamping type tool. Ahh the wonders of railroad steel! Sorry, I'm rambling. Good Ideas! than's why I'm here.
Greyangel

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GA, do yourself a favor, read that again, only slower this time. ;)

I forgot to "jump" you about something. ;)
You mentioned your flame had yellow tips, right? :(
If so... your setup sucks. ;)
Yellow flame is showing you it's too cool and/or doesn't have enough air (oxygen) to burn the -carbon- the way you want it to be burning it.
The "easier to burn" hydrogen is burning and leaving behind the carbon.
Just like coal/coke, charcoal or oil-fired, "it's the carbon". :)
<was it Hamm's or Olympia that's slogan was "It's the Water"?>
If your flame doesn't have yellow tips... well then... ooops. ;)

And not forced air from a blower or special ventury setup for top heat/temperature which is a product of the -mixture- and its -speed-.
If you want to read up on it, when you get close, you'll find what you're looking for under- "explosive mixtures". I looked into several sources but by far the best one was my old 50's Encyclopedia Britanica. Went through it like you knew nothing, at the speed like you knew it all. Just the way I like it. ;)
More modern Encyclopedia's sucked. :/

That's just a guess tho, right? :)
Alvin in AZ
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From...what..you...were... saying... (huh? oh sorry) So let me get this straight. If the inside of the forge gets to glowing bright orange and the metal gets to bright orange that should put me in the right range, right? Jumping ahead of the message a bit, the orange flames that I mentioned happens only when the wind blows up the ...uh mouth of the forge where I have the torch. You saw the picture I posted right? At normal operation there is no orange flame. When the wind is not messing with the mix then it's hard to say that there is a color to the flame at all. I understand that there are rich and lean mixtures that happen in the forge but no doubt I don't understand what I am seeing as well as I should. If I kick up the flow on the needle valve for the torch I can get a richer and by venturi hotter mix going. The normal that I run at is because I've found that it will keep a nice conservative but (I think) adaquate heat going in the forge chamber. As the chamber starts to get heat soaked so does the propane tank start to chill and the pressure begins to back off a bit. It has seemed to me that this was a fortuitous natural adjustment to less required fuel since by this time the brick is starting to radiate pretty good and all I want is to keep it at temperature.

I would say that I have a very transparent blue cone from a couple of inches out from the torch out to about 12 to 16 inches. The cone kind of expands outward as it get farther from the torch. I figure I have an optimum area of about 10 inches or so before the main heat starts to slack off At the back of the forge where I have it partially open (to prevent heat from blasting back at the torch) there are definately orange flame escaping but that is probably the mixing with fresh air as it escapes the chamber. I have tried blowing air in behind the torch and this gives me a bunch of orange flame (same as a gust of wind). Kind of backwards from what I would expect but I'm guessing this is because the extra draft is not mixing well with the gas when so far removed from the source? I know, sounds like I don't know what I'm talking about. That's 'cause I don't really. It's all part of the grand experiment. I'm learning all kinds of things about forging and knifemaking and it all takes time to put it together.

Call it a behavioral study. It's a lot of experimentation right now and I've been falling into rhythms that seem to work. As for optimum forging heat I sort of have to go by the color of the metal but how it gets there could probably be tuned up. Everything I have read suggests that I really don't want to forge it into the white heats I can and will experiment with kicking the forge gas up see how that goes. As a friend of mine mentioned, I really need to visit a working setup at the local college to get a visual on what folks who know what they are doing are doing. I will finish the Riel Burner soon as well and check the difference in operation.
Back to earlier conversations on Railroad steel: Found another gem laying beside the tracks here in town. It's a wedged shaped thing that weighs at least a couple of pounds. A bit like a splitting wedge but with a longer tapir. Probably 12 to 14 inches long with a half round hollow along one side and a much thinner ridge of steel sticking out from the opposite side with a bunch of 1/4 inch or so holes drilled through it. It has a cross section of about 2 inches and about 3 or four inches wide at the big end. Kind of too big to consider trying to shape it much but then again it would make a great wood splitter or a hammer head or it could be pounded out to an ax head... oh my! ;). I spark tested it and it appears to be the same material as those little formed lumps of steel I found earlier. Really dark orange spark; really short and curly cue shaped. Weird stuff. I'll have to experiment to see if it can be hardend but if so then its got serious potential.
"GA"
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Greyangel wrote:

Orange reddish flame indicates too lean, bright yellow indicates too rich. Think about what you're actually seeing. The color of an open flame tells you how energetic the reaction is. The more energetic the reaction, the more energy is liberated into the surrounding environment, that's why blue stars are hotter than yellow or red ones. (We covered the chemistry of combustion extensively back in airplane mechanic's school, of course there's a two-page formula that goes with this lecture...) You can't make horsepower by pumping air, you've gotta burn fuel. Quit worrying about the mileage and get the temp up. If you're having real expansion cooling problems, set the tank in a bucket of room temp water to keep the propane warm.

If all else fails, try reducing the volume of the box. Pack the heat in as small a space as you can get away with.
Charly
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The more I read what you're setup's like, the more sure I am you aren't getting hot enough for forging.
At night, bright orange -to me- is about 1600F. YMMV
The insides of my insulated fire brick heat treating furnace gets a full yellow color in no time and I'm using 1/4 the flame you are.
Funny how this must sound to you. :)
Efficientcy is key here, propane is a marginal fuel.
You are pouring propane in there so fast your bottle is chilling down. How can it not be hot enough?
I was doing and thinking the same as you right up until my change to insulated fire bricks. (insulation)
Now, the propane lasts forever and the whole thing is very subdued and pleasant instead of sounding like a jet-engine -and- I'm getting more heat. BTW, I'm just heat treating, not forging, and the extra heat was helpful.
Whatever type of insulation you decide to use, you'll like it. At least that's what I see from here. <squinting hard>
Alvin in AZ
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Ok, having listened (really) to all the arguments I fired up the brick pile and looked really hard at how it behaved. I tried closing the end of it off and a lot of kickback came out at the burner. Kind of scary and the stupid weed burner still has some zinc coating left on it that I immediatly noticed was putting a nasty irritating vapor into the immediate area. I pulled the end cap off and vacated the vicinity for a minute. Examining the interior of the forge at normal operation I decided that the only part of the chamber that is getting any good heat is where the blue portion of the flame is dominant. The brick is soaking off the heat fairly rapidly elswhere. There are indeed little yellow salamanders dancing around in the chamber most of the time though not so much once it all starts to warm up. I took a knife that I made out of some of that railroad scrap and tried to harden it. in order to get a reasonably even heat to it it pretty much has to be in the torch blast zone. This was a polished piece of metal and through a couple of normalizations it put on a lite film of scale. I then heat it to bright orange and stuck it edge wise into some mineral oil. Big thin flakes of scale drifted off into the oil. After it was cooled to the point where I could handle it, I took some sanding paper (500 grit) and buffed off most of the carbon/scale. The scale was only a light film really. I checked it for hardness with a file and was dissappointed to find that I scratched it pretty easily. Ok back to the forge. This time I set the pan of oil on the hot bricks on top of the forge and let it heat up to maybe a little over 100 degrees. Not hot enough to burn me when I stuck my finger in it but really warm. Having moved the oil off to the side but a bit closer than before, I then fired up the torch again and heated the knife up to a good solid bright orange and stuck it in the oil edgewise but fully submerged and swished it around for a bit giving it plenty of time to cool. When I check it with the file this time it did resist a lot better but still seemed to have softer spots. I didn't really want to scratch the hell out of it if I could help it. I got the impression that the hardness is not very evenly distributed. Just to be on the safe side I put it in toaster oven at 325 for an hour. Figure I'll put a sharp edge on it and beat up a two by four to see how it holds up. If it doesn't hold an edge well up and down the blade then I'm thinking of trying a water quench. Just for the record, the blade is about an eighth inch thick or a little more at the thickest part.
So what did I conclude from all this? Yeah, the forge setup runs dirty and doesn't hold heat worth a damn. The torch needs to be replaced with a better design and I'll be buying some Kaowool soon. Guess its time to put together that Riel burner that I've got half built in the garage. Still got questions about the blowback though. Seems like without an escape hole the fire wants to come back on the torch. Then I guess any gas forge has two openings. One for the torch and one for sticking the metal in and out.

I know it's a long way so I try to paint a good picture ;)
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YeeeHaaaaw! :) Some of us might have been "shown". :( But... I'll bet most of us fiNgured it out by ourselves, just that way. :)

If you weren't kept up all night coughing then you didn't get a bad dose of it. :)

Oooops. :/

That part sounds good.

Speed is very important. Certain steels when coupled with certain quench mediums... there is no such thing as "fast enough".

You've got to learn to see the arrest point. :)
One way to help you find the arrest point is to use a magnet? :/ Austenite is non-magnetic.
I don't like the magnet method for heat treating knife blades. You could try it out at first as a learning tool tho?
My favorite way to see it is to get an old file and get it really hot (too hot) and pull it from the fire at night and watch it cool.
The file will grow duller and duller then all of a sudden the outside edges will "flash" brighter for a second then the center will do the same a few seconds later. It doesn't all go down through the arrest point and release its "extra heat energy" all at once unless you control it's cooling rate somehow. But the demonstration is best in the air so you get a double shot at seeing it.
After seeing that you can more easily recognize it as you heat it up, which is not as obvious.
The outside edges of the file will prob'ly go through the arrest point un-noticed but then the edges will begin to brighten back up again and when the center actually cools some, that's when it's easy to see and you won't mistake its look. It is soaking up the extra heat energy that it will release later when it drops back down through the arrest point.
It'll have a cooled down looking "shadow" in the center or in the case of a knife blade the thicker sections will have a "shadowy look" to them. Heat the piece just until the color evens out and quench it... it'll get full hard if you get it in the quench tank quick enough and it's the right quenchant. ;)
The steel itself shows you when it's ready for quenching.
Cool huh? :)
Quench some of that railroad junk in brine at least for learning. If it warpes on you no sweat just get the process seen and learned then try switching to oil for a more gentle quench for your thin stuff.

Oil should be able to harden the thin edge, if there is one, but prob'ly won't do a good job on that thickness of plain medium to high carbon steel.
I've heard it said "that it might be called a water-quench but they always really mean brine". <shrug>

I'm sure you're going to like it. :)

I don't know if it can be seen in my picture or not but the brick at the rear isn't sealing off the end of the oven, there's a gap for exhaust. I vary how that last brick sets depending on which way the air outside is moving from. Also I've found if I want high heat for the entire length it's best to turn up the fire a little and open the "exhaust port" wider.
There. :) I believe I've typed out here on a.c.b everything I (think I) know about my heat treating furnace. :) I'm sure there is a lot more to know that I may never figure out. :)
Except for one more little detail. I heat up the "handle" of the knife through a little "side slot" between the bricks very close to the burner. I stick the thick handle part of the (thinly hollow ground) knife blade in there and get it to glowing good, pull it out and grab it with my pliers, for the rest of the heat treating process.
See? The dangged ol' thick part needs a head start or it won't get to quenching temperature when the thin part does. Pretty obvious after it's spelled out like that huh? :/ I want the handle to be hard at least half way up for the slab handled kitchen knives I make.
"it's easy when you know how" -my best friend

Good job at that, no kidding. :)
Alvin in AZ
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...snip...
Why? I'll argue than an ideal situation for a knife is the edge hard, and the bulk of the knife not hard. Or, if it be hardened evenly, the edge kept cooler while the rest is tempered quite a bit higher than the edge - more or less the same result either way, subject to more argument. Harder edge, springier body. Can't say I've done all that much with making this work perfectly in practice, but it seems like the place to be aiming for.
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wrote:

Depends on the purpose of the blade. My own opinion is that differential hardening is great for big ugly general destruction blades (my preferred type) but if you want a cutter then by God make it hard as you can without shattering it. Especially for Kitchen knives!
GA (See you guys got me doing it now!)
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If he were getting a hard case that would be cool I guess. :) Didn't sound like it was working out so good, so far tho.
That all might change after he gets the arrest-point figured out? :)

Because my knives are thin bladed "old hickory" kitchen style knives. There has to be "some" heat treating up inside the handle otherwise the knife will bend where the metal meets the wood and stay bent. :/

I agree, if you are speaking for yourself, and aren't saying it has to be "ideal" for me too. ;)
I'm weird, I make them different from most everyone else, for sure different hardnesses and toughness than the factories "have to" with their lifetime guarantees and all.

No arguement coming from here. :)

I'm weird, we got that straight at least? ;) What I'm all about is getting the hardest and best edge holding I can get and not the least bit interested in making more tough, thick, clunky knives... the "world is full of 'em" and don't feel like I need to make more of those. YMMV :)
Alvin in AZ
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