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Matt S

Cross Sectioned My first Bloom, What Exactly Am I looking At?

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Sorry in advance that I haven't got any pictures, (old camera, new computer, incompatible without adapter etc...), but i'll do my best to describe what I've got. I took 15lbs of mild steel iron worker punch outs, and using about 35lbs of charcoal melted them into a bloom, then went about consolidating the resulting bloom on the anvil with my 4lb. After about 4 hours of forging I have a rough cylinder 4.5" long, 2.25" in diameter that weighs about 4lbs. I cut all around and most of the way through it with a zip disc on a grinder, and broke it in two, polishing up one half and etching in ferric chloride. There's a lot of activity, and I don't know quite how to interpret it all, this is my first time doing this, and i'm hoping more practiced hands can translate for me. 

Where the grain is broken things are mostly grey, but with some I guess you could say "veins" of bright silver. On the etched piece, from the outside to about 1/2" along the circumference it looks sort of tiger striped, alternating light grey and dark in short bands, beyond that and to the center the dark bands remain, but filling in the space between them is a shade of grey somewhere in between the light and the dark that has a frosty appearance to it, like etched mild steel, but darker. So, I'm assuming the dark areas are carbon rich, the light areas are not, I haven't the slightest idea what to make of the frosty looking middle, or the silver veins in the grain structure.

Edited by Matt S

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Did you use lump charcoal or briquettes?  What kind of furnace?  Blower? Feed rate? Without seeing pictures, you're describing what sounds like a wildly variable carbon content with perhaps some dendritic carbide formation (the veins).  

Yeah, pics would really help. ;)  Can you take a phone pic and email it to yourself and post it that way?  Or even a plain old phone pic? 

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Lump charcoal, Maple Leaf brand, supposed to be a mix of maple, oak and beech. Electric blower, feed rate unknown, it's ancient and heavily worn,  but it's fan is about 8" in diameter, powered by a 1hp 3000rmp motor, and has a 1 1/4" exit pipe. My furnace was stacked firebrick. 4 bricks lain on edge and overlapping to make a square tower. I went 5 rows high, with the air entering  through the second row. The mass of metal was formed level with the air pipe, and did not form below it.

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I would post pictures with my phone, but it's a 5 year old s7 that's survived a double rollover and being dropped in the mud underground. The built in camera didn't have much resolution to start with, add some scratches to the lens and it just won't show much more than a blur in the place of detail.

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I understand, I just upgraded from an 8 year old S3.  Cellphone cameras don't stand much of a chance in a shop environment.

Sounds like the blower may be a bit on the big side (which may account for the whopping loss of steel by weight), but at least you didn't get cast iron, so something worked okay.  Any noticeable slag?  Not much in that mix to form slag, and you don't really need slag for hearth steel making.  I don't have experience actually doing a hearth run, I've only done actual smelting and Aristotle runs.  I have watched hearth melts, but there was a crowd and alcohol was involved...but your puck sounds like the blob that typically emerges from an Aristotle furnace.  

Did you lose any bits during initial consolidation?  If not, then you did something else right.  

However, the puck should form below the tuyere.  Being in the direct blast will both cause decarburization and make the steel go away.  And by feed rate I meant how often did you charge the hearth with fresh steel and charcoal?  The method calls for a hearth full of burning charcoal before the first steel enters the fire, and the steel is added bit by bit as the previous parts melt through the hot zone.  A sand base to the hearth will protect the steel from decarb and oxidation, I have been told.  

Hopefully Emiliano or Mark will jump in here, they have an excellent handle on it.

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Slag, yes, though hard to tell the source of, I suspect the bricks themselves, one got melted pretty good, and another two sort of welded together at the seam. I did lose some during initial consolidation, it really did look more like a bloom than a puck, all sorts of scraggly bits everywhere, my guess is I lost about 2 or 3lbs there, I pulled it out weighing something in the ballpark of 10 lbs. As far as feed rate goes, I filled the stack with charcoal, and when it was burning throughout I began to add the punched pieces. The bricks were still slightly steaming at this point. I'd throw in a small hand full of the pieces, followed by 2 or 3 double hand fulls of charcoal, then top with the next charge of pieces to preheat. I should have been a bit more precise and weighed things out, but each soup can held exactly 5lbs of pieces, and there were about 10-12 charges made with each can. I know for a fact I lost about 2lbs at the end because the lump in the bottom began to cut off my air and didn't melt everything properly. I shifted things around and topped it up with charcoal after my last charge. Also, I did this right in my driveway between the house and garage, it's all sand there...ah the joys of country living.

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Also, as a side note, when i was cutting my way through this thing, I hit spots that made sparks with what looked like 2 or 3 stacked bursts, and some areas with none, but generally the sparks had at least some minor burst to them.

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It's possible you have surface carburization of the punch slugs and maybe not enough time in the fire to really consolidate them the first go-round?  On the subsequent heats to forge it down into your cylinder you'd be losing carbon each heat.  All just guesses.

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