Why has my mild steel bent

[Mark RandParticipant @markrand96270]

Note that normalizing and annealing are different processes. With normalizing, the work is allowed to cool more rapidly than in annealing, usually in free air, not by insulating it or furnace cooling it.

Annealed steel has a coarse grain structure and machines like chewing gum. Normalized steel has a finer grain structure and is more pleasent to machine, while still being stress free.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, cold rolling produces stress though-out the the metal that is rolled, not just at the surface of each side, although the stresses are greater on the surfaces of each side. The only true way to overcome the situation is by heat treatment.

It can be seen on the graph above, that normalising is slightly hotter than annealing, and normalising will be a little stronger than annealing, but the temperature has a narrow window, so a controlled temperature environment would be needed.

Regards Nick.

[Bob Unitt 1Participant @bobunitt1]

In the winter I heat any mild steel likely to do that to red-heat in the (log) sitting-room fire and leave it to cool down in the ashes overnight before machining. That seems to get rid of any locked-in stresses. Not done it in the summer, but I'd probably heat it up to red with a propane torch and steal some ashes from the sacks my missus saves for the garden for the cool-down. I've never had it happen with brass though.

[not done it yetParticipant @notdoneityet]

On top, or aside, of this – cold rolled steel is significantly better (mechanically) than hot rolled if strength is important.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by not done it yet on 04/08/2023 14:55:52:

On top, or aside, of this – cold rolled steel is significantly better (mechanically) than hot rolled if strength is important.

.

Something conceptually in common with pre-stressed concrete, I suspect.

MichaelG.

[SillyOldDufferModerator @sillyoldduffer]

Posted by not done it yet on 04/08/2023 14:55:52:

On top, or aside, of this – cold rolled steel is significantly better (mechanically) than hot rolled if strength is important.

Yes, hot rolled is about 20% to 30% weaker than cold rolled. Some example numbers:

Tensile Strength. Hot Rolled 67000psi, Cold Rolled 85000 psi
Yield Strength. Hot Rolled 45000psi, Cold Rolled 70000psi

So,probably better to machine hot-rolled for non-structural parts because the stock won't warp, and to machine cold-rolled whenever strength matters.

I mostly work with cold-rolled steel because starting with clean straight surfaces often saves a lot of time – I rarely have to machine an entire block. Warping is definitely a real problem, but I've only been caught once in 12 years. Took about 5 years before a length warped on me during a cut and it hasn't happened since. Could be the devil looks after his own!

Dave

[Peter Jones 20Participant @peterjones20]

Bonfire night is coming up, can you still have garden bonfires or have the safety Nazi’s stopped that?

Wood burns around 1800F maximum so you can just leave things to cool in the wood ash.

If not, charcoal barbecue although that can get hotter if air dampers ain’t closed.

Personally, I rarely use cold rolled nowadays as hot rolled is so much cheaper and I’m not making highly stressed parts (being retired is great, except for lack of cash)

[Nigel McBurney 1Participant @nigelmcburney1]

take your bms, cut to desired length, heat to red heat for long enough so that it is red right through, iuse large propane torch and firebrick hearth,then leave to cool with the firebricks, this amount of heat treatment should relieve all the stress,then start machining, do not machine and then anneal,I always use this method when making gib head taper keys (en 9) for stationary engines ,full size restoration.  I never use black for machined parts,When I make trolleys for stationary engines I use black flat and angle bar and square or rectangular tube, trolley axles en 8 bright. Recently I bought 6 metre length of 8 x50 black hot rolled fronow import from sources in the  east,no point complaining at my age as I probably will not need any more, so be aware that new black can also cause problems if machined.

[duncan webster 1Participant @duncanwebster1]

But if you keep cold rolled at red heat and let it cool slowly it will adopt the properties of hot rolled (black), so if you are machining all over there is little point starting with bright and going through the red heat routine,

Edit:just spotted Mark’s post above about normalising/annealing, you won’t get that control in your wood burner

[vintage engineerParticipant @vintageengineer]

Mild steel nowadays has a large percentage of recycled steel in it and is utter crap. It can contain any grade of steel in the mix from high grade alloy steel to boron steel. What ever steel is used in modern cars will find it’s way into mild steel.

[vintage engineer]

On vintage engineer Said:

Mild steel nowadays has a large percentage of recycled steel in it and is utter crap. It can contain any grade of steel in the mix from high grade alloy steel to boron steel. What ever steel is used in modern cars will find it’s way into mild steel.

Steel has always been made this way otherwise what would be the point of scrapping old iron and steel?

I have some 1930’s angle iron that has areas that are un-drillable.

This link though old and more concerned with copper and tin causing hot short cracking does explain the use of scrap in the two steel processes.

One wonders what happened to the 1997 projected unusable 155- 300 Mt of scrap steel stockpile for 2015?

[Author]

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