Hardening mild steel...

PuffTheMagicDragon said:
What you were doing was a simple form of casehardening, nothing more. It is/was useful where one wished a surface to be somewhat wear-resistant. Casenit was simply an ancient method in 'modern' clothing, making it a less disagreeable process than it used to be. It replaced the age-old method of placing the mild steel object inside an iron tube that was filled with such things as crushed bones, hooves and other similar carbon rich material. The tube was then sealed and then placed in a forge until the whole thing was glowing orange-red and then left to 'soak' at that temperature for several hours. Inside there was no oxygen and so the MS object could 'absorb' some of the carbon into its surface. Quenching would fix this carbon in the metal surface.
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Exactly.There seems to be some confusion between hardness and toughness .
 
Heating steel then rapidly cooling it will give it a smaller crystalline structure which will be harder but more brittle. Slow cooling it will make it softer and easier to work. Basic metallurgy. You can turn a cheap screwdriver into a useable chisel that way. It's also why a smith heats up metal bar in a forge repeatedly while working it.
 
Perhaps the first question to ask Nigel is, is the washer really mild steel? He may (understandably) have simply assumed it was.
TBH I don't know how one would establish if a bit of steel really is mild steel.
 
jokerboat said:
Heating steel then rapidly cooling it will give it a smaller crystalline structure which will be harder but more brittle. Slow cooling it will make it softer and easier to work. Basic metallurgy. You can turn a cheap screwdriver into a useable chisel that way. It's also why a smith heats up metal bar in a forge repeatedly while working it.
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Eh??
 
Rigger Mortice said:
Perhaps the first question to ask Nigel is, is the washer really mild steel? He may (understandably) have simply assumed it was.
TBH I don't know how one would establish if a bit of steel really is mild steel.
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Easy. Heat it to cherry red then quench it. Then run a file across it. If you get a dull sound and the file marks it, it's mild steel and didn't harden. If the file scrapes across it leaving it unmarked and it virtually rings, then you've successfully hardened it.
 
Hypocacculus said:
Easy. Heat it to cherry red then quench it. Then run a file across it. If you get a dull sound and the file marks it, it's mild steel and didn't harden. If the file scrapes across it leaving it unmarked and it virtually rings, then you've successfully hardened it.
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Basic school boy stuff again, put it against a grindstone, if the sparks split in to smaller sparks it indicates more carbon and is hi carbon steel.
Stu
 
"Mild steel" is really a misnomer because it is not really a proper 'steel'.

You can get an idea of whether a ferrous object is make out of high-carbon or low-carbon steel if you hold it against a (spinning) grinding wheel. You will see a difference in the colour of the sparks...due to the amount of carbon present. Try it with ordinary nails and then with masonry nails.
 
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30boat said:
It'll do nothing for mild steel.
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Sorry to disagree but many years ago as ome of a group of apprentice agricultural engineers we were given the task of making a cold chisel. Cutting and grinding was the easy bit. Then we had to harden the edge. Heat to cherry red and quench in anything with a high carbon content. Oil, sugar, sawdust or proper stuff like Casenit etc.

Well to cut a long story short I got reprimanded on my attempt as the test was to cut a steel rod and my chisel wouldn't it was not case hardened enough. Being a stroppy youngster, I repeatedly heated and quenched it over several days whenever the boss was not about. Being sure my chisel would now be hard enough I re presented it for testing. As I walked across the workshop I dropped the thing, it hit the concrete floor and shattered like glass.

So you can certainly harden as well as case harden mild steel, it just takes a while!
 
Sophie19 said:
Sorry to disagree but many years ago as ome of a group of apprentice agricultural engineers we were given the task of making a cold chisel. Cutting and grinding was the easy bit. Then we had to harden the edge. Heat to cherry red and quench in anything with a high carbon content. Oil, sugar, sawdust or proper stuff like Casenit etc.

Well to cut a long story short I got reprimanded on my attempt as the test was to cut a steel rod and my chisel wouldn't it was not case hardened enough. Being a stroppy youngster, I repeatedly heated and quenched it over several days whenever the boss was not about. Being sure my chisel would now be hard enough I re presented it for testing. As I walked across the workshop I dropped the thing, it hit the concrete floor and shattered like glass.

So you can certainly harden as well as case harden mild steel, it just takes a while!
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With all due respect while I believe the events occured just as you state, you are unlikely to have been using mild steel; you will have been given carbon steel in an annealed, or soft state when it is indistinguishable from mild steel. Uneven heating and overheating is the most likely source of the cracking and it's not unusual to crack steel like this. Quenching in oil is not the same as case hardening.
 
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Fantastic thread.
Here is another question on treating steel.

Many years ago when building a pipe fence complete with standard galvanised (I think) plumbing fittings. I ran out of of the 3 pipes at 90 degree fitting, used on corners, the oly one I had available was covered in old grease inside and out.

I decide to heat it to a cherry red to burn out the crud, then dropped it some old engine oil to cool it.

But here's the ting, many years later 15+, it's the only joint that has no sign of corrosion?

Anyone know what caused this?

Good luck and fair winds.
 
oldsaltoz said:
I decide to heat it to a cherry red to burn out the crud, then dropped it some old engine oil to cool it.

But here's the ting, many years later 15+, it's the only joint that has no sign of corrosion?
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I discovered the same thing. Also by accident!
It has to be old engine oil and I've always assumed that it was the carbon by products of combustion that gave the finish. Quite a smart matt black effect.
 
nigelmercier said:
Sizes are approximate ...

I need to pull a 30mm OD bearing off an 8mm shaft. There is only 2mm clearance behind the bearing, so no room to get my puller jaws in. I've made a 2mm mild steel, 50mm diameter M10 washer with a 10mm slot to the edge, forming a C shape, the hole is 10mm to clear a circlip behind the bearing.

I can slot the C-washer behind the bearing, and put the puller jaws on the circumference. However, I'm pretty sure that as soon as I apply any pressure, the steel is going to bend.

As a metalwork numpty, what do I do to the steel to stop it bending?
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Easy - 2 off 2mm X 50mm hardened steel wedges 30mm wide with an 8mm slot - slide one in behind the bearing from each side then drive them together - bearing will pop off
 
cliff said:
Easy - 2 off 2mm X 50mm hardened steel wedges 30mm wide with an 8mm slot - slide one in behind the bearing from each side then drive them together - bearing will pop off
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No can do, the surface behind the bearing is the commutator: too fragile.

I'm going to give it a try, but I will cut down the C-washer diameter in 3 places so the jaws of the puller are as close as possible to the commutator, this should reduce the bending moment.
 
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Does the shaft have a thread on the end? If you are replacing the bearing, find a bit of tube with 30mm OD, tack weld it onto the bearing, washer over the end, few confangled nuts and washers and you can wind off the bearing. Its how we got inner bearings off Lambretta cranks.

Or, find a bit of steel plate, bore a 30mm hole in it, cut it into halves, clamp these around the bearing to get hold of it, then either tap tap tap the shaft or confound some threaded bar and nuts/wahsers to wind it off.
 
Mild steel EN1A/230M07 C 0.15% max
Bendable steel EN2A/040A10 C 0.08-0.13
GQ steel 080A15 C 0.13-0.18
Mild steel En3B/070M20 C 0.25 max
Medium tensile EN6/080M30 C 0.35 max
Key steel EN6A/080M30 C 0.35 max
Medium carbon EN8/080M40 C 0.35-0.44
Case harden EN32B/080M15 C 0.12-0.18
Silver steel Stubs BS1407 C 1.1-1.2
All percentages
 
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