A while back I was watching the lodge foundry video and liked how they use scrap steel in the cast iron mix for the frying pans. On a similar note I get questions about melting steel because hobby casters find that scrap steel is easier to get than scrap cast iron. I always reply with the answer that crucible furnaces are great steel oxidizers but not melters. Two to three hundred years ago steel was melted in crucibles but they were sealed from the furnace atmosphere with lids. So I thought why not make a video about using steel in a cast iron melt. I don’t have a crucible lid so a 50mm layer of coke would protect the steel from the furnace atmosphere. The method I use does not melt steel it relies on free graphite in molten cast iron to be absorbed by the steel. So I wait for about ten minutes after the last piece of cast iron has been added, then about six steel slugs weighing 19 grams each were thrown into the crucible. A steel rod is used to push the steel slugs underneath the coke layer. Some slugs would stay in that coke layer and because the temperature is well above cast iron melting point the steel would absorb carbon from the coke and the melting point would be lowered, from there it will dribble into the molten cast iron below. The 10% steel mix is a conservative figure, the carbon content in the resulting mix will be lowered slightly therefore raising the melting point. This is a good thing because the tensile strength will increase! If a 50/50 mix of cast iron and steel is used the carbon content will be almost halved allowing for the small carbon content in steel. If you try to cast this mix it will need to be very hot to fill a mold because of the higher melting point. Another problem that will surface is as the carbon content is lowered a lot, steel will take so much more time to dissolve in the melt. When this happens the coke layer on top becomes very important. A cast iron with a low carbon content will absorb carbon from anywhere it can get it, so that is why a thick layer of coke in needed, it will also absorb graphite from crucible walls. A cast iron that is close to the eutectic point of 4.3% will absorb very little graphite from the crucible walls. This method works really well because small pieces of steel are used. The one down side to this method is that steel has to be cut, cast iron can be broken with a hammer. I first tried cutting large pieces of steel with an angle grinder but soon realised that there must be a better way. I did the rounds of the workshops close to me and found the place that made the steel slugs. I am very impressed on how it raised the tensile strength and it was still easy to machine. After many years of breaking wedge tests it is easy to tell if a cast iron was going to be very strong. ESC you should try this method when casting your crankshafts.
That's interesting Ironsides. I did a quick search for coke, but no joy, and the petoleum coke is high sulfer. Your chips still look like cast iron, are they larger and slightly more ductile like steel turnings?
D cell batteries have a carbon rod through the centre and I have used them but it hard to get a lot of them. Welding supply companies sell gouging rods made from carbon and from memory they were not too expensive. Charcoal burns very quickly at that temperature. The chips still look like cast iron I have machined from other melts.
Interesting video. In the early days, I always assumed that the melting point of steel (2750 F) was much higher than the melting point of cast iron (2100-2200 F), and I also assumed (incorrectly) that steel would not melt even at the pour temperature of gray iron (pour temparature of gray iron varies). But when I did get one of my iron melts very hot, and stirred it with a 1/2" steel rod, the end of the rod dissolved within about 30 seconds. I was very surprised, and about all I could say at the time was "DANG !!!!", as I held the rod up looking at the missing end. The Navy Foundry Manual mentions that the iron rod method is one way to determine the temperature of your iron melt. Chapter 17, page 245 of the Navy Foundry Manual mentions that if the end of a rod (soft iron rod they call it, but the same thing happened with me with a mild steel 1/2" rod) melts off, then the melt is at 2800 F or hotter. And it mentions that a bubbling action can be observed in molten iron at approximately 2800 F. The Southwest Steel Casting site mentions that steel is poured around 3000 F, and this would seem to correlate with what ironsides said about steel needing a higher pouring temperature than gray iron. It would be interesting to see some testing on the iron/steel blend, and see how it compares with tensile strength, hardness, brittleness, malleability, etc. The machinability of the iron-steel mix appears to be very good from the video.
Ironsides: have you ever tried silicon carbide as a replacement for ferrosilicon when recycling steel?.
No I have not, I have 25kg sack of silicon carbide from a foundry auction that I should try. I have heard that it is not as good as ferrosilicon.
I'd been doing some reading on the subject, this one I posted earlier over in another topic: http://www.afe.polsl.pl/index.php/e...properties-of-synthetic-nodular-cast-iron.pdf The researchers who wrote the article tested the properties of melts up to 100% scrap steel when making nodular iron with silicon carbide instead of ferrosilicon. They ended up with iron of superior mechanical properties when using silicon carbide instead of ferrosilicon : "The mechanical properties in the meltages with SiC additive (i.e. meltages 1 to 5) are generally better than in the meltages with FeSi additive (i.e. meltages 6 to 10), especially in the meltages with higher amount of steel scrap in the charge."
Mark, I did read that article. You need to reread it as you have misunderstood what the chart actually said on page 94. Melts 1-5 uses silicon carbide as well as ferrosilicon. As they were making ductile iron, silicon carbide will not turn flake graphite in a nodular shape. They used ferrosilicon alloyed with magnesium to create the nodules in cast iron. In the far right hand corner of the chart is another separate addition of ferrosilicon. This addition is to make sure that the ductile iron is machineable, magnesium is a very powerful carbide stabilizer. Since the turn of the century I have attended many iron foundry auctions and the first thing I do at those auctions is to see where they store all of the ferro alloys. This is to enlighten me on how they make cast iron. Not one of those iron foundries had silicon carbide. When the G.M.H iron foundry closed down in Melbourne seven years ago I spent a lot of time in the storeroom where they kept their ferro alloys. There were some really weird metals and non metals they added to cast iron, tin was one of them but there was no silicon carbide. You would think that with a multinational company like G.M.H. having a team of metallurgists and labs to analyze their iron they don’t use silicon carbide. At that time they were the biggest iron foundry in Australia. Oddly enough I got that sack of silicon carbide from a brass foundry! I have heard that silicon carbide is slow to dissolve in cast iron that’s why I have never used it and this is why iron foundries use ferrosilicon because it dissolves very quickly into cast iron. Now that I have read that article I will try it in a future melt, maybe I will need to add less ferrosilicon. One of my very early videos on youtube was about using 100% steel in my waste oil furnace. It worked and the casting was machineable but it took 2.5 hrs from a cold start to pouring the mold. Most iron melts with that furnace take between 50-60 minutes. It proved a point that it could be done but extra wear and tear on my crucible and furnace plus standing next to a hot furnace makes it not viable. Have a look at my video.
I did see the added FeSiMg7 and thought it had some other function as they had recorded it separately. According to Wikipedia, silicon carbide gets burnt in steel mill furnaces to raise the temperature of the melt and to deoxidise it. Iron foundry use of SiC is a relatively recent use according to the articles I've read. If a non ferrous foundry had some metallugical grade SiC it might have been used to make silicon bronze. My main interest in silicon carbide is that it shows up in various articles where it replaced ferrosilicon use completely in the melt but they are mostly using induction furnaces. It melts at 2700 degrees C so it takes 20 minutes to dissolve and stabilise in molten iron (in an induction furnace with magnetic stirring of the melt). Scrap iron is hard to come by here in Far North Queensland, I have heard the nearest foundry: Northern Iron and Brass melts scrap steel in their big induction furnaces and adjust the composition as they go to get the desired iron properties. It'd be great to melt iron with steel and still get a decent result with a home furnace and to be able to use commonly available silicon carbide would be a bonus.
I suspect that silicon carbide would be very hard to come by and the most likely place would be a foundry supply company. I don't think that it would be available in Nth QLD.
The abrasive grade is actually higher purity than the metallurgical grade so I thought I'd substitute abrasive grade. When they make it in an electrical furnace from silica sand or clay and coke the purest stuff is closest to the arc, there is green silicon carbide which is purer and stronger and harder than blue/black SiC which forms further out from the green and lastly there is metallurgical grade which forms last and contains other forms of carbides like Si2C2.
