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Tim Mitchell

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Tim Mitchell last won the day on December 10 2017

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About Tim Mitchell

  • Birthday 08/06/1975

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    http://www.buffaloriverforge.com

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    New South Wales, Australia
  • Interests
    blacksmithing, knifemaking, wootz manufacture, carpentry, astronomy.

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  1. AA stands for Atomic Absorbtion and it is a kind Optical Emissions Spectrometry.... Just the old time word for it
  2. Will, you need to test for Carbon which XRF cannot detect. Any carbon determination using XRF is a subtractive amount and is worthless. Basically they use the elemental profile to guess at what your steel is and that can pinpoint your carbon, but yours isn't a standard steel and so they have nothing to compare it with and any carbon figure is a sum of all the errors in the detection of the other elements... worthless. You need to get Spectral AA analysis for all elements or you need to get Leco analysis for carbon, sulphur and then use XRF for Phosphrous, Silicon, vanadium, manganese etc. XRF is still not very accurate so the Spectral analysis is much better. We are talking about very small amounts here. You only need 0.05% Phosphorous for the ingot to develop cold shortness and not much sulfur to get hot shortness. Grey cast iron increases the silicon level in the ingot which can cause formation of graphite in the ingot so white is definitely best...
  3. One other thing, the old method of using long roasting periods for ingots may have been to help remove any remaining sulfur in the steel. They would roast the ingots in Hyderabad for a long time, pull them out, hit one with a hammer and if it broke they would put them back in and roast them again. This was either because their carbon content was too high.... or it was because they were needing to get any remaining sulfur down to a level where their ingots were no longer hot short and could be forged. So if you do have sulfur in the ingot a good long roast will help to get some of it out of your existing ingots.... just a thought.
  4. Will, happy to help. The green glass is fine, it actually has some copper in it to create the colour and so that does help the melt a bit. Al used to use the green glass and it never caused him problems and that is what I use and have never had issues. Concerning heats... High heat is above Acm.... if you know what that is. Low heat is at least 100°C below Acm. So for 1.6% C ingot high heat is 1050 - 1100°C and low heat would be around 800°C. The issue is that if you have lower carbon (1%C) then your Acm point is 820°C and so forging at a mid orange heat is too high... However I think your issue is too much carbon not too little. The problem is that if you are trying to forge above Acm with an unknown ingot carbon percentage, then you will cause problems for yourself. You will have more failures than success. Some ingots in the 1.5% carbon range can only be forged at 800°C or lower or you will crack them... this is because of higher impurities that make them hot short. Giving it a good roast in the gas forge for 1 hour should decarb the outside of the ingot enough for you to do a gentle forging.. But if you forged the ingot at a mid orange heat and had it crumble then you have very few possible explanations. 1) Your carbon content is too high.... waay too high. 2) your sulphur level is too high... 3) you didn't roast it properly.. coupled with sulphur in the ingot 4) you forged too fast and hard. There are a few other less likely possibilities but I think what you are dealing with is one of these, or a combination of these. Calcium is not an alloying ingredient it is a fluxing ingredient, it helps to reduce porosity in the ingot, it removes some phosphrous. Most of the old ingots had some Manganese to help remove Sulfur and it helps with the overall quality of the steel. I wouldn't do the long roast until you know that you are getting consistent and good quality ingots or it will be a waste of time and fuel. It won't make much difference to cracking the ingot or not if sulphur has been your issue. A good 6 hour roast would be helpful though (in iron oxide) and then a decarb in the forge for around an hour. It only takes a small amount of Phosphorous to make your steel cold short especially at higher carbon levels. I would add some calcium to your melt... a large spoonful of crushed shell, in order to reduce that from being a problem. It is easy to have a highish phosphorous bloomery iron. Unless you know your blooms are low in phosphrous (from your charcoal source) I would be adding something to reduce that and to help kill the gasses in the ingot as a matter of course. Cheers, Tim.
  5. Thanks Joshua, I will have to play around with this a bit. I loved the blade in that thread... very nice pattern and the coffee etch really is startling in it's contrast. I also like the comments about normalising and graphite spray to remove the lines... Were the lines due to decarburisation of the outside of the bars while welding? That is what it looks like to me.. Gary thanks for the info on your method too... I like the idea of going straight from the ferric into the coffee without cleaning the blade... it makes sense.
  6. Joshua, do you mix the mixture of Instant coffee with boiling water or do you use cold? This is the first time that I have heard about using a coffee etch. It seems some people use it on Wootz as well with success.
  7. A few years late.... but it wasn't anything that you did in polishing of the blade. The area along the entire blade edge where the pattern has dissolved is where the quenching of the blade has formed martinsite on the edge. This is common and expected to have the watered patterns at the edge be masked by the crystal structure of the blade. Martinsite is harder than the Pearlite body of the sword, but the price you pay for the hardness is that the pattern shows less well or not at all. Sword blades also are quenched to differing degrees due to their curve and that will affect the degree of martinsite that is formed in that place and the resulting hardness of the edge in that location. This effect can be seen in a blade that is quenched very quickly, such as a water quench... not recommended at all..., making the whole blade martinsite and it can almost entirely obscure the pattern. Hope that helps.
  8. To answer your question specifically about thermocycling, the purpose of thermocycling is to soften the outside of the ingot in order to stop the ingot crumbling under the hammer as you forge if it has a little sulphur in it, so the thermocycling is done in a gas forge with a slightly oxidizing flame. This is normally done (by Al and myself) at around 1050 to 1100 degrees C for a 1.5% -1.6% C ingot. It does help to make the ingot easier to forge through the repeated annealing cycles, which applies to both a gas and coal. But if you do this in a coal forge you won't get the same effect of decarburizing the outside of the ingot, unless you turn the ingot frequently and make sure that it gets plenty of air during the process. The traditional roasting of the ingot was for a slightly different reason though. It was primarily to start to break down the dendritic structure allowing the ingot to be forged easily and maximizing the spacing of the cluster sheets in the final forged ingot. The roasting allows the impurities in the Inter-Dendritic Regions (IDR) to migrate slowly and even out in the ingot. If you do this too long you erase the pattern and have to remelt to get it back. But it dissolves the smaller or secondary dendrites first leaving the larger ones just slightly reduced. This means that the boldness of the final pattern will be increased. You want to have large dendrites and slow solidification times but that causes porosity in the middle of the ingot if you solidify it too slowly and the excessively large dendrites will prevent you from forging the ingot. Long roasting of the ingot helps to correct for the dendrites being too large as it helps to dissolve them partly, it doesn't help with porosity though. Most of the old ingots had porosity that is why they forged them so the underside of the ingot became the surface and edge of the blade and any porosity was contained within the blade itself. The old ingots were often 5 or 6 inches in diameter and more like a discus instead of the modern ingot style. This made the ingots more likely to get porosity in the middle of the top as well.. But generally speaking you want to avoid it and not solidify the ingot too slow or it will cause you problems even if you do a long roast. Long answer with a bit of extra information.... Cheers, Tim.
  9. On reading this in the morning with fresh eyes I wanted to add something. IF you forged from above Acm and continued to forge the ingot as it cooled to be cool to the touch you will also cause problems. You should not forge the ingot to below the A1 temp (727°C) and if you did that using an ingot which was high in bloomery iron then you were approaching the area of causing problems from "Cold Shortness" as bloomery iron often has Phosphorous in it which makes the iron brittle if forged too low. I wouldn't expect problems from forging an ingot from around 900°C unless you did forge it too cold at first with phosphorous in it, but it would be a problem if you have too much sulphur and forged at that temperature. Bloom steel can make great crucible steel IF it is clean and comes from good ore AND if you don't have too much Phosphorous in the wood you are using for charcoal. My advice is that trying to make crucible steel from bloom iron with unknown carbon content and then adding crushed charcoal into it (which donates carbon to the ingot) is like playing Russian roulette. You are flirting with disaster. Making good crucible steel in the old days was a highly skilled art and it took them much time and effort to work out what would work and how to make their raw materials produce good steel.... if it could. Also it was an art-form to forge out the ingots well without wrecking them. SO... start your time of making crucible steel with known ingredients with known carbon content and impurities and then you will have a much better chance of success.
  10. One further note... The first ingot has clear porosity issues as seen from the center and it doesn't look as well fused as the second one, that will also contribute to the crumbling of the ingot. The second one seems to be much better fused and may forge better if you give it a good roasting. The bloomery iron will also have silica in a large amount which you can help to remove using some calcium added to your ingot melt. Both calcium and magnesium added to a melt help to remove silica as flux if my memory serves me correctly.
  11. Will Urban, Firstly... well done for jumping in and having a crack at making some crucible steel. Unfortunately when you start to make alloys with inspecific amounts of elements in them you can have some failures before you have success. If you have patience and get the right advice you can have a good chance of making a good product in the end. Now for some dissecting of your process and ingredients and possible problems.... 1) you have used brown glass which contains Iron Sulphate compounds to give the glass the colour of brown, this sulphur will go into your melt and it will make your ingot hot short. Meaning it will do exactly what you show, it will disintegrate when you forge it. Use green glass for your flux not brown glass. 2) you don't know your carbon content in your ingot so you have no precise idea where Acm is. Acm (the A cementite line on an Iron-Carbon Phase Diagram) changes depending on your carbon content. So if you have no experience with forging ingots before (you need a lot of experience to forge blind as far as carbon content goes) then you will be forging either too low to get a cluster sheet formation or you will be forging too high and will lose your pattern entirely. This isn't really an issue unless you have significant impurities in your ingot that make your ingot hot short, so forging high will cause you problems. You are shooting in the dark, so the long and short of it is forge at low temperatures unless you know your ingots can handle it. 3) having sulphur in your ingot which definitely came from your glass but may have also have come from your bloomery iron, will mean that you may not be able to forge your ingots at anything more than a low temperature. The ingots which were forged with the method that you are trying to use were very pure from sulphur and so they were able to be forged higher. The ingots that had higher levels of sulphur were forged at lower temperatures and they formed more dendritic patterns. The way that they removed sulphur from ingots in the old days was to roast the ore very well before the bloom process, to add manganese to the crucible and calcium to help remove some of the sulphur from the ingot as slag. 4) you have a very pronounced dendritic pattern on the top of your ingots which tells me that you probably used a slow solidification on those ingots. You may have solidified them too slow, if you did they will cause you lots of problems to forge and they can fracture as you try to forge them. The way to try and make them forgeable is to roast them for a long time. Al used to do a 16 to 30 hour roast at 1100°C (for 1.6%C) in a can filled with iron oxide (it stops you from losing too much carbon due to oxygen contacting the ingot). The long roasting helps to homogenise the structure in the ingot, dissolving the smaller dendrites and weakening the larger ones. This helps to make the ingot more forgeable and to make the pattern more visible widening the spaces between the final cluster sheets. When you are cooling your ingots just turn the furnace off and let it cool down naturally, there are few furnaces which will keep the molten liquid in that state long enough to cause problems. If you try to ramp the fuel down you will often cause yourself problems. One caution about roasting an ingot.... You have to make sure that you are roasting the ingot above the Agr (A graphite) line on the phase diagram, which unfortunately is not shown on many diagrams. It is about 50 deg c above Acm. If you do a long roasting below this temperature you WILL cause your ingot to become filled with graphite and porosity which will ruin your ingot. You may have all or only some of these problems, I listed them so you can better identify what may have gone wrong with these ingots. If you give me some more information I will try to fine tune my advice for you. I think that you have sulphur in your ingots, I also think that you have too much carbon in your ingots and that you may have solidified them too slowly. It is hard to tell without some kind of analysis or physical inspection of the ingots but that is my hunch. Hopefully you do better next time... keep trying and you will have success. Cheers, Tim.
  12. Right you are Jerrod! Thanks for clarifying. I agree that smelts are very complex with more variables and unpredictability than a crucible steel melt.
  13. I think that Jerrod was meaning "Melt", not "Smelt" which implies a direct ore reduction. Making crucible steel in a crucible in a furnace is usually referred to as a "Melt" whereas making Iron in a Bloom Furnace is called a "Smelt". There was a kind of wootz that was made in an open bloom furnace by remelting cast iron prills from the bloom process into an ingot in a quartz grit lined furnace floor. This was done in Salem and possibly elsewhere in India by a specific caste. When the iron had cooked off enough carbon it would solidify in the bottom of the furnace and then be removed and cooled. It is unknown if this produced a significant pattern or not. These ingots fit the description of ingots that were seen by Abbott and also the ingots that were sent to Faraday and Mushet. Abbott's account seems to indicate that they are the same ingots made from the same process as described in Salem and they did produce a pattern. It was not uncommon to have quartz grit in the underside and a more ductile region on the top as described by Mushet.
  14. Thanks for the clarification Jeroen, I do remember something about them industrially using coke over the molten copper in the old days to avoid picking up Oxygen and Hydrogen. Perhaps it wasn't picking up carbon in the copper readily I was remembering, but just the effects of carbon when introduced in the melt of an Iron Carbon Copper alloy. The original research that was done on Iron copper alloys back in the late 1800s by several different researchers showed that the higher the carbon content of an iron copper alloy ingot, the more brittle it is and the less able to be forged. The copper acts as a hardener for the Iron and the carbon compounds the hardening and embrittlement effect as it is also a hardening element. I haven't gone over my copper iron alloy notes for some time, I will have to dig them out
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