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tempering color


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I have been reading some and have seen the tempering colors. So if you get to a straw color this means the steel has oxidized and it has reached a certain color.
I am trying to get some carving tools (wood) to as about hard as I can and still be workable, but maybe that's not such a good idea either. Its not that critical that I want to send them away and some of the steel I am not sure, what it is exactly but I think its a high carbon steel.

so I have a oven and can get the temps fairly close, but I don't have any other facility's for testing other than trial and error.

my question is if you soak a piece of steel, after hardening, how accurate are the colors to true harness? Lets say you have a couple of pieces of steel, that you don't really know the makeup of does the color really reflect the true hardness or is it close enough?

If you want to test that, would you break it and see if the grains were very close and fine, and keep experimenting till you get there, or is the grain not a way to tell harness either? a file .

thanks

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The colors also darken over TIME in addition to TEMPERATURE as the oxide coating will increase as the part sits at temperature. This at least holds true for tempering in the "straw" color range, below about 510F. Eventually the coating will thicken enough to have a reddish brown color, but will tend to self seal and not darken anymore at about that color.

Red oxide (Iron(III), Fe2O3) forms at a lower temperature than blue/black oxide (Iron (II) FeO) If only iron(III) is forming you will get pale straw thickening to dark straw. At higher temperatures other chemistry is going on.

Phil

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I would file test after each tempering cycle to get to the desired hardness, assuming the part hardened properly when quenched. You can continue softening the material by tempering, say if you start at 350F for an hour, then check. If unsatisfactory then go 400F for an hour and check with the file. For a woodworking tool that is NOT getting hammered on I would want the whole tool able to have a difficult time filing, but not skating. If the tool was getting hammered on, I would want the but end drawn softer, and would probably wrap the working end with a wet rag and just draw the but end past blue in a fire.

Phil

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What are you making them from? The previous use of the steel may give some indication of what alloy it *may* be.

When using unknown steel you always make up a sample *first* to test out possible heat treatment of it: what should you quench it in? What should your temper it to? (Did your normalize it?)

This helps prevent making up a beautiful set of blades only to find out all the work was wasted because they won't harden right!

Usually you forge something with a similar cross section and then heat to slightly above magnetic and then quench in warm oil. If it cracks it may be an air hardening steel, if it's not hard enough it may be a water/brine hardening steel---if so reheat and quench in brine and see if it hardens properly there. If not, well unknown steel may be *anything*! Discard and try again.

When it hardens correctly then work on tempering: start around 350 degF and bake the hardened piece about an hour---test: if too hard raise the temp 25 deg and try it again---repeat until you get what you like and then repeat at that same temp a couple more times.

Note: oven thermometers are notoriously in accurate so much so that most grocery stores sell auxiliary thermometers---get one and use it!

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With wot Thomas posted above you should be set. Let me add a couple of things: I have done quite a bit of wood carving and have made most of the tools for that. For hard dense woods I temper the blades a little softer than for soft woods, That is to keep the edges from chipping as I work. For soft wood I leave them a little harder so they do not need to be sharpened as often. Longer tools I will use a torch and soften the shank a bit more so it can flex without breaking. Short ones I do not bother. I suggest you make tools and harden and tempar just as noted above. Then use them. If you keep notes of the steel you used and wot you did to it it will help you repeat the good ones and not the bad ones. Making your own give you so many options, and it does not take a long time to get it like you wish.

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thanks, the steel I am using is an auger for a feeding system for chickens,very springy coiled, comes in lengths of about 150'. its about 1/4" by 3/8", I have been making corkscrews out of it and running it up to to about 600 they are blue at that point, and they are fine for that. I have done two batches so far water hardening, and tried 325f, no color, then 350 still no color, I will try again tomorrow and go with oil .
if spark test means much they are very bright white and spread out like fireworks at the end of the spark, no other color like reds or any dullness to it.

I am heating , untwisting , then forging the shape, heating to non magnetic , then quenching, tempering. After the water they are extremely brittle. The ones I just did, they had no color,and I can file, which makes me think I didn't harden them properly. when I first hardened tham I tried a file and it took off an outer layer and then would skate across.or so I thought.
thanks for all the help, It may be that this steel will not work for what I want but I want to keep experimenting with it as I have so much of it.

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It is listed as oil hardening in the original geometry, so if you have not had failures with water hardening you may have been simply lucky, or the manufacturer is using the most gentle profile that gets the desired results (which is fairly likely)
very
http://simple.wikipedia.org/wiki/Carbon_steel

It sounds like the material may work fine for cutting tools or knives. Once you get a handle on a proper heat treat it may be worth trying to make a suitable carving blade and seeing how it works.

Phil

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Try water hardening again. Make sure you get it to a shade above non-magnetic (non-mag is 1414 F, and I want you to shoot for 1500-1550 F for the quench), and get it out of the fire and into the quenchant in a second or so -- no fooling around in between. If that doesn't make it skate a file, then it's probably just too low in carbon to get really hard.

The brittleness you're experiencing indicates some hardening, but it could also be related to large grain size from overheating. Normalize two or three times prior to hardening to reduce the grain.

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Corkscrews should be fine with an oil hardening as they are not supposed to hold an edge.

I would try warm oil for carving tools too and see if that will work and only go to water if you have problems getting hard enough in oil.

Have you read "The Complete Modern Blacksmith" Weygers? He has an entire section of forging and heat treating of wood carving chisels as he was a talented sculptor as well as smith.

Makes a great Christmas gift!

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I sent a number of emails out and got a call from one rep, he thinks it might be 1070 because it is the one they sell the most of and most popular. they sell 1050, 1070, and 1095 in a blue tempered state. I will see if I get some more feedback.

I have weygers book but can't remember where it is! will be finding it soon, I am reading "hardening, tempering , and heat treatment" by tubal cain, trying to get the basic ideas stuck in my head, but still have a way to go. I hope to have some more time off here and do some more experimenting. thanks again for all the help.

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We always say that using an unknown steel is a crap shoot. I will often use plain carbon, high carbon, drill rod for your kind of tools. It has about 0.95% to 1% carbon content. It comes scale free and annealed in three foot lengths from McMaster-Carr, MSC, or Travers Tool. After forging, it should be normalized. Although it is spoken of as water hardening steel, most specs will say when quenching thin sections, quench in oil. "Thin" is hardly ever defined, however. The oil is a slightly slower quench than water and is less harsh, so when used, there is less chance of warping or cracking. After hardening an inch or so of the business end, we sometimes "chase color." This means that when you apply heat behind the hardend portion, the colors run in bands toward the cutting end. The colors show on bare metal, so the tool is abraded. When the proper color (temperature) reaches the end, you can quench to "hold the temper." For end-to-end tools like chisels, chasing color always puts a 'softer' temper behind the final cutting edge temper. The old timers called this a 'cushion,' kind of a shock absorber for the tool, especially nice, if it is a tool of direct percussion or indirect percussion. The tempering chart I use as a guide for carbon steel is in the British book, "Metals for Engineering Craftsmen" London, 1964. There is a list of tools and their corresponding temper colors. For wood carving, I would attempt the tempering range of copper color (509F) to purple (527F). Axes and adzes go to a slightly softer temper, full blue (554F), because they are tools of direct percussion. The entire temper color 'rainbow' runs from 428F to 626F. The temper colors are not always used on high alloy steels, because many of those steels have elevated temperatures when compared to plain carbon steel.

There was a special case in the video, "The Gunsmith of Williamsburg," where Mr. Gusler was carving the stock butt of hard maple on the end grain. He tempered his chisel to a straw (446F), a relatively hard temper. The chisel was a paring tool, not mallet struck.

Commercially sold high carbon steels normally run from 0.70% to 1.3% carbon content and if a high quality, may be sold as W1, an American Iron and Steel Instutute / Society of Automotive Engineers [AISI/SAE] number.

In the U.S., we live in the TEMPERate zone of the world, not too hot, not too cold. When you temper a tool, you make it not too hard nor too soft for the job at hand. In terms of human emotion, when you temper your feelings, you don't harden them; you soften them.

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If I read this correctly you have some 'steel' tools you want to Heat Treat then Temper? or just Heat Treat and use? Could be I just am not understanding because I just woke up....



tempering IS a heat treat, IE using temperature variance to make a granular change in the steel. Get more sleep :)
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  • 2 weeks later...

You will learn some, so in that respect it makes sense. Running the colors allows the spine or back end (knife, tool) to become softer, which can be beneficial, and oven tempering helps make sure the entire tool or blade is drawn to at least a certain temper. If you consult a temper color chart, dark straw/purple is just over 500F.

http://www.bluebladesteel.com/temper_colors_chart.html

The temperature you draw temper to is less important than the performance of the metal. At 425 is the blade sharpenable and does it hold and edge suitably?

Have you been sanding or grinding the metal to see the colors? You can only see color on clean bright metal, as the colors are oxide film, and scale is a thick layer of the same oxides.

Phil

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thanks for the reply, by the way , since the colors are made with oxidation, will I get stronger colors with heat outside ( flame or piece of hot steel) of a tempering oven, then in it?

Yes I have been sanding the steel to see the color, when I do it with flame or on a hot piece of steel I can see them very clearly. But in the oven it seem more difficult, I may have been getting light straw at 425 or so, but not sure about it , like I can kind of see it but not like when I use flame, also flame has the advantage of see all the colors from blue on up as a reference. I will keep working at it.

As far as far as edge I am looking at keeping a cutting blade sharp longer, so I am thinking that yellow straw would give me a hard edge that would be harder to sharpen but would hole the edge longer, perhaps that is too simple of an obversation, and should rely on more hands on testing?


I am trying to get the temper down for this particular steel so I can make a batch of them, Its much faster to do it with flame and cheaper, but I would like to get some consistancy with the oven and also be able to do 20 at a time or so.

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When you "run the colors" you are watching the oxide form at a rate determined by the alloy and the temperature (in air, can't forget the oxidizer). Because a lot of alloys respond the same the color is pretty accurate for the temperature reached, even though the charts are made for simple iron/carbon steels.

When you oven temper you should be using a thermometer to verify your temperature. An inexpensive dial oven temperature can be had at the grocery for under $10.

The two processes are different. I think your problem is you see them as the same, because they should produce similar results.

When oven tempering, the temper colors will not "run" but will evenly form to the heat the steel reached (if you cleaned it bright) but the oxide layer will slowly thicken as it soaks at that temperature, at least for below 500F, so your temper color may (or may not) appear darker than if you ran the color to the same temperature.

For 425F you are going to pale straw. This may still look clear after an hour. When running the colors, taking to a slightly higher temperature (dark straw, purple) compensates for the short period of time running the colors takes. The chemistry occurring during tempering is also time dependent, not just temperature dependent, which is why oven tempering is recommended for 2 hour minimum total time.

Phil

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