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I Forge Iron

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How does one know how long to soak a piece of steel at a given temperature to heat the core to temp and allow the metal to move?  I was working a stout piece of 1045 (John Deere hydraulic cylinder piston rod I found at scrap yard) that was about 2 inch diameter, and found it far harder than forging 1/2" spring steel.  As I sat and pondered how limited the metal movement was I have come to think that I only heated the outside of the cylinder to forging temp, but the core might have been below forge temp.  Or am I on the wrong track?

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No you are on exactly the right track.  Industrially there are certainly formulas for how long it takes to fully heat a steel billet pertaining to the material size, relative heat of the forge and material radiative qualities and relative thermal mass of the forge enclosure ..., but most of us just let it soak till it starts to move more easily I suspect.  As JHCC also notes, you will likely need a big hammer (and a striker if you can find one), or a power hammer and/or hydraulic press to push around medium carbon steel at 2" diameter.  When I'm trying to reduce down that size of stock I typically use a 4.5# hammer and soak the stock until it is a good high yellow color.  First heating will take quite a while, but afterwards if you keep it hot things will go quicker.

2" 1045 is great stock for hammers or things like axe drifts, what are you making?

Also note that this heavy stock takes a real long time to cool down to handling temperatures.  Be careful, or you can get a nasty burn (don't need to ask how I know that).

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11 minutes ago, Latticino said:

most of us just let it soak till it starts to move more easily I suspect

Very true, but remember that if your forge is running very hot, the outside may burn before the inside comes up to temperature (kind of like a roast in the oven).

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Latticino, I've known a couple of people who have melted their stock in their gas forges...(one of them being me----I had increased the pressure on my burner to deal with not having replaced the liner in a timely manner; then when I did replace the liner it was running *very* *hot* indeed and a moment of inattention....)

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21 hours ago, Irondragon Forge & Clay said:

With coal to soak a large piece, I heat till it looks right color wise then stop the air flow and let it sit, then apply air and repeat several times, being careful not to overheat.

I was just dealing with this on Saturday. I was having a xxxx of a time tapering and drawing out some larger round bar because I was so afraid of burning the end while the larger sections were still heating up. I don't know why it never occurred to me to just turn off the blower.

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3 hours ago, ThomasPowers said:

Latticino, I've known a couple of people who have melted their stock in their gas forges...(one of them being me----I had increased the pressure on my burner to deal with not having replaced the liner in a timely manner; then when I did replace the liner it was running *very* *hot* indeed and a moment of inattention....)

Thomas,

That would be one screaming hot gas forge.  I never let mine get that hot, even if it was capable (and it may not be with the current residential natural gas/forced air burner assembly).  I'd be worried at that temperature about cooking the lining.  Mine runs in the yellow/white range and I can keep tool steel in it all day if I don't mind wasting gas, decarb and scaling away the stock.

Coal fires can certainly heat thick stock, and have done for many centuries.  It is just a little harder and needs attention to proper fire control, location in the hot coal pile, rotation to avoid hot spots...  As others have said, a deep fire is your friend, and stay out of the oxidizing zone.  Like I said: "finesse".

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7 hours ago, Desmond Redmon said:

I was working a stout piece of 1045 (John Deere hydraulic cylinder piston rod I found at scrap yard) that was about 2 inch diameter, and found it far harder than forging 1/2" spring steel.

1/2 inch square is 1/2 x 1/2 in area. So 2 x 2 inches is the same as assembling 16 pieces of 1/2 square and joining them together. Based on volume alone, you can then guess that it would take 16 times the heat to get the 2 x 2 up to the same temperature.  This involves a soaking heat so you do not flash fry the outside of the stock.

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23 hours ago, Latticino said:

Also note that this heavy stock takes a real long time to cool down to handling temperatures.

Check, sitting on a 4x4x1/2 to cool it burned the polyurethane off the top of the workbench when I let it cool while I ate...

23 hours ago, Latticino said:

2" 1045 is great stock for hammers or things like axe drifts, what are you making?

I am making a 3# or so hammer for driving nails into 80 year old oak chicken house framing (somehow a standard claw hammer just doesn't have the oomph.)  I cheated and drilled a 1/2" hole to start drifting the hole out to an engineering hammer drift I made up from 1x1 O1 I had on hand (I didn't have any S7 laying about).

 

21 hours ago, Irondragon Forge & Clay said:

With coal to soak a large piece, I heat till it looks right color wise then stop the air flow and let it sit, then apply air and repeat several times, being careful not to overheat.

And Anvil's comment: Both of those sound like fine advice I will give them a try Thursday when my striker goes to preschool :-)

16 hours ago, Glenn said:

1/2 inch square is 1/2 x 1/2 in area. So 2 x 2 inches is the same as assembling 16 pieces of 1/2 square and joining them together. Based on volume alone, you can then guess that it would take 16 times the heat to get the 2 x 2 up to the same temperature.  This involves a soaking heat so you do not flash fry the outside of the stock.

I'm kind of embarrassed to say that I missed the volume aspect since I was thinking of the issue as being effectively 1/2 of the actual cross section (guess that is what comes from programing machines in radius rather than diameter).

Thank each of you for the insights and advice!  As so often happens however I am left with many more questions now that I 

16 hours ago, Glenn said:

On a side note. Don't hydraulic shafts have a chrome coating that could be dangerous to burn off?

Last and certainly not least, Cr VI can be produced in any oxygen rich environment at greater than 400C as far as I have been able to find.  While in theory I suppose I could take the risk and try to heat the Cr plate off in the oxygen depleted zone in this case I turned the Cr plate off by .03" to expose the 1045 core on an old metal lathe a friend has (two of the ten shafts were case hardened and just got sent back to the scrap yard).  Worked pretty well to cut the blanks at 4" and just run a surface cut right under the plating since the plating notched the HSS cutting point. My next shirt from Glenn will be the In Rust We Trust!

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Somewhere i seem to think i heard 15 miniuts per inch of part thickness was a good rule of thumb  i would want to heat at a lower temp untill the part has a uniform temp just below it's curie point then ramp up to forging temp to avoid scaling the surface too much. 

 

Just my 2 centavos

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