How do blacksmiths add carbon to steel
Forged steel. What is steel anyway? 2 ... and what is iron now? 2 How do I recognize steel? 3 ... and where can I find such steel?
1 1 +++ Forging ++++ Tips on handling steel Forged steel This little brochure tells nothing about forging. How to use the hammers is difficult to explain in a book. You have to try it yourself and let yourself be shown. These pages explain how to treat the iron or steel when forging so that it does not crack after forging. That it is well hardened and still does not break. These pages show common mistakes when heating and quenching the steel. Content: What exactly is steel? 2 ... and what is iron now? 2 How do I recognize steel? 3 ... and where can I find such steel? 3 Temperature and heat, some things about heating steel 3 How do I know temperatures? 3 Maximum temperature during forging 4 Safe temperature range 5 Heating 5 Hardening 6 Heating, quenching 6 Slow, fast, partial quenching 7 Tempering 8 Annealing colors 8 Faults in hardening 9 Guy 10
2 2 +++ Forging ++++ Tips for handling steel What actually is steel? Steel is a mixture of iron and carbon. Carbon also occurs frequently in everyday life, for example blacksmith coke and charcoal consist almost entirely of carbon. Hence the black color. The older steels consist only of iron and carbon. More modern steels often have other metals mixed in, such as chromium, nickel, molybdenum, cobalt and others. By the way, a mixture of a metal with other substances is called an alloy. We only work with the older carbon steels (i.e. the iron-carbon mixture) because this is best forged and hardened with simple means. Iron can absorb up to 6% carbon (that is, 60 grams of carbon for 1 kilogram of iron; that's a full hand of charcoal!). The more carbon there is in steel, the harder it is. But it can only be forged up to a maximum of 1.5% carbon. He is too hard about that and, moreover, brittle; he breaks. Steel becomes very hard if you first heat it to embers and then cool it down very quickly (quenched). On the other hand, you shouldn't heat steel well above 1000 degrees, because otherwise it will "burn out". Steel that has been heated up (and cooled down again) is as brittle as glass and completely unusable ... and what is iron? In everyday life, everything that mainly contains iron is now referred to as steel. Probably because steel sounds more expensive and stronger. The term iron hardly appears anymore. Sometimes you can find even older shops with the designation "Eisen", such as "Eisen-Fäustel" or "Eisenwaren und Siedlerbedarf". Pure iron with no or no more than 0.3% carbon cannot be hardened. That's because the carbon isn't just in iron (like the nuts in chocolate). The atoms of carbon combine with those of iron. This connection creates the hardness. If there is very little carbon in the iron, too few of the hard iron-carbon compounds are formed. This "steel" is then almost as soft as pure iron. Almost pure iron has the advantage that it can be heated up to 1300 degrees in the forge. The risk of destroying the workpiece through overheating is low. It also becomes much softer when heated and is therefore very easy to forge. Iron is significantly softer than steel. But as door fittings (hinges), angles for connecting wooden beams or for candlesticks and other items, it is hard enough. It is only unsuitable for tools (i.e. knives, hatchets, chisels, hammers and the like).
3 3 +++ Forging ++++ Tips on handling steel How do I recognize steel? Compared to modern, high-alloy steels, carbon steel has several typical properties: It rusts fairly quickly, polished surfaces turn gray within a few days. If you hold a magnet on steel, it remains magnetic even after removal (goes away again when it is hot). In the case of a grinding test with a (dry) grinding wheel (for example on a drill), it quickly turns blue if you grind an edge. With alloyed stainless steels, it takes much longer ... and where can I find such steel? Smaller pieces can be found at any flea market or junkyard for little or no money. You can use old chisels, files, car springs from carriages (some cars also had such leaf springs). I always look for the rusted, worn out older tools at the flea market. You can't work with it anyway, so I can get a dozen old files or something similar for an average of 4 to 6 euros. When word got around that we needed such files on the PANAMA, some people cleaned up their basement and brought us such old tools as gifts. Temperature and heat, some things about heating steel How do I know temperatures? An indication of the temperature is the black scale that forms on the steel in the fire. The tinder is burned iron. It forms as a thicker layer from 500 degrees and remains almost unchanged up to 900 degrees, only the thickness increases up to 750 degrees. Only from 900 degrees does the layer fall off slightly and form again. So you can see 900 degrees and higher temperatures on it. The temperature can be recognized much more precisely by the color of the glowing steel in the fire. However, no direct sun should fall on the forging, because then the embers appear much darker than they actually are. Too little light is not so good either: the steel then appears brighter than it actually is. Shady daylight is best.
4 4 +++ Forging ++++ Tips for working with steel Those from the glow colors: Temperature 520 to 580 Black 580 to 650 Brown red 650 to 750 Dark red 750 to 780 Dark cherry red 780 to 800 Cherry red 800 to 830 Light cherry red 830 to 880 Light red 880 Up to 1050 yellow red 1050 to 1150 dark yellow 1150 to 1250 light yellow Maximum temperature when forging If iron can be heated up to 1300 degrees, but steel only slightly above 1000 degrees, the assumption is that this is related to the carbon in iron. It's really like that. Therefore, a more precise representation of the temperatures follows here. However, most of the time we don't know how much carbon is in iron. 0 to 0.3% carbon maximum 1300 degrees (glows white in the forge) 0.3 to 0.6% carbon maximum 1200 degrees (glow light yellow) 0.7 to 1.0% carbon maximum 1100 degrees (glow yellow) 1 , 0 to 1.5% carbon maximum 1050 degrees (glows light yellow-red)
5 5 +++ Forging ++++ Tips for handling steel Safe temperature range With steel you are on the safe side if it does not glow completely yellow, but still contains a hint of red. It's just warm enough at 723 degrees. Since it glows in a cherry red. So if it is taken out of the forge in a light red-yellow color, you can hammer on it until it only glows a darker cherry red. Then off to the forge again! With iron it is very straightforward: it can be heated to almost incandescent and even worked on when it is no longer glowing. But then you need a lot more strength. However, even with iron, thin spots should not be forged in an incandescent or too cold manner. Then cracks could appear. The heating is actually quite simple: go to the forge and you're done. Unfortunately, a bit can go very wrong here. The coke should burn for a few minutes after lighting so that all impurities (especially sulfur) are burned off. Sulfur in particular makes steel brittle when it reacts with iron in the heat (for chemists: iron sulphide is formed, more precisely iron sulfide. Also exists as a natural mineral: fool's gold or pyrite). The steel can be "decarburized" at the following points. It loses carbon and thus hardness. First of all, this takes place in the edge layers of the steel. With a knife, the thin cutting edge would be too soft. Never heat the forging quickly from the cold. Always lay at the edge of the fire first and then deeper into the fire after a few minutes. Finish forgings as quickly as possible. The longer they have to stay in the fire (or the more often they have to come back in), the worse. Finish the forging "on a ride". Do not take a break in the meantime and then heat it up again from the cold state. The steel can also be overheated. Excessively high temperatures in the embers lead to coarse-grained, brittle steel. If air is added, the steel quickly decarburizes and becomes too soft or it burns.
6 6 +++ Forging ++++ Tips on handling steel Steel can also burn. At over 1200 degrees, oxygen from the air penetrates deep into the steel and partially burns it internally. It is then completely unusable and breaks easily both cold and warm. It needs a lot of air to burn. So you should always be careful that both the air from above and from the blower below do not come directly to the forging. Hardening If you forged something out of steel, you can harden it. To do this, you heat it up as you would with forging and then quench it in water. When hardening, heating is particularly careful because the forging is already finished. There may be a few hours of work involved. So here are a few pointers. Heating The maximum temperature during heating also depends on the carbon in the iron. Fortunately, it is nowhere near as extreme as when heated. For files with a fairly high proportion of charcoal, the piece should just be heated to dark red / cherry red (approx. 780 degrees). In typical forged steel (wagon springs of carriage wagons), the carbon content is lower. Here you can heat up to a lighter cherry red color (830 degrees). Quenching If the steel is now heated, it is quenched. The easiest way to do this is with water. It is there everywhere, and above all you have no problem with "garbage disposal". You can just tip it away or use it to water flowers. And it doesn't cost anything. Especially with thick pieces (even if heated unevenly), cracks can occur because the steel cools down at different rates. The forging should be agitated a bit in the water so that it cools more evenly.
7 7 +++ Forging ++++ Tips for handling steel Slow quenching If you add soap to the water or heat it up, the quenching happens less quickly. It can also be used to harden high-carbon steels and thick forgings more safely. (Much milder quenching agents: oil, glycerine, tallow) Quick quenching If, on the other hand, you add table salt or use cold water, the steel cools down significantly faster. This is suitable for low-carbon steels, but also for thinner workpieces where the risk of cracking is low (other powerful quenching agents: water with acid). Partial quenching In general, you only need to harden the areas that actually have to be hard in use, especially the cutting edge on a knife. On the one hand, hardened areas are so hard that you can hardly drill a hole, file or saw on it. Hardened steels are also more brittle; they break more easily. With the knife, it would be very good if only the cutting edge was hardened. Then the knife won't break easily, and you can still drill holes in the shaft with a good drill to attach a handle. Here a broach for leather work after forging and hardening, made from an old file. The darker scale of the tip can be clearly seen, which has hardened to about the center of the picture. Of course, the awl still has to be ground and polished (shown on the screen about twice the original size). For partial quenching, just immerse the point in the water that is to be hardened. It is also possible to cover areas with clay that should not be hardened. The clay is carefully dried over a forge fire. The forging is then heated and quenched.
8 8 +++ Forging ++++ Tips for handling steel Tempering The quenched steel has what is known as "full hardness". It is extremely hard, but almost as brittle as glass. There are only a few uses for such a hardness (for example the fire steel for striking fire with a flint). A knife completely hardened in this way will break if you drop it on a stone. If you warm it up again, the steel becomes more elastic again, but it also loses its hardness. Even so, the steel is still hard enough for all uses. The tempering temperatures range between 200 and 310 degrees. The higher the temperature, the softer the steel is. You have to estimate the temperatures yourself. Steel tarnishes in clearly visible colors when it gets hot (when sawing, grinding or flexing iron, this type of blue discoloration often occurs). Annealing colors, temperatures and applications Here, too, a color table. Only this time, the steel does not glow, it is colored on the surface. In "real" the colors have a beautiful metallic shimmer, which is difficult to depict on paper. 210 white yellow 220 light yellow 230 yellow 240 dark yellow extremely hard steel very hard steel (chisel for hard materials) 250 yellow brown 260 brown red 270 purple red 280 violet 290 dark blue 300 cornflower blue 310 light blue hard steel (hacksaws) hard steel (screwdrivers, punch) elastic steel (springs , Knives) soft steel (hatchets, axes, scythes)
9 9 +++ Forging ++++ Tips for handling steel Because the forging has the tinder on it after quenching, it looks black and is rough. In order to recognize the tempering colors, you need bare metal. So you take a file (or sandpaper) and grind down the tinder at one point until you can see enough bare metal. Then you heat the piece over the (!), Under no circumstances in the forge fire and watch carefully when it turns yellow. Then hold it a little higher so that the colors emerge slowly and you can take it out at the desired color. Now it is finally cooled in the water. In the case of larger forgings that have only been hardened in one place, the residual heat in the non-quenched steel is sufficient for tempering. You only need to file (or sand) a bit of metal until it is bare and wait until the desired color appears without heating it up again. Then cool in the water. Be careful when filing! The steel can still have 300 to 400 degrees in some places with partially quenched pieces! Hardening errors Unfortunately, hardening (heating + quenching + tempering) can destroy the entire workpiece. Should this ever happen, you can look it up in the following old table from a textbook from 1985. Perhaps the error is found:
10 10 +++ Forging ++++ Tips on handling steel The following forged piece should be a chopping knife for chopping herbs. It is forged from an old file. When I was quenched, I noticed that the blacksmith's tongs made a strange crunching noise on the hand. As if the steel is alive. The result were these many small cracks, which are unfortunately, unfortunately, easy to see here. In the table you can see that either too high heating or too fast (hard) quenching can be the cause. Well, when it comes to heating, I always take care with steel. But it was a cold March day, the water was close to zero. So next time I should use warm water, preferably with soap. The picture is approximately original size. Credits If you've actually managed to read this booklet, you can only hope that the tips helped. If you have hints, suggestions, ideas, incomprehensible or too long text passages to criticize, then write to the address in the footer!
11 11 +++ Forging ++++ Tips on handling steel Note from the NAGEL editorial team: This brochure was written by Stefan Bistrosch, who works at the Panama adventure playground in Dresden. He kindly made them available to us for our website. We would like to thank you very much for this. We wish the readers a lot of fun and pleasant learning. For some time now, forging has started in a number of institutions that are organized in the ABA professional association; this mainly on adventure playgrounds. We would be delighted if this brochure could enrich our work.
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