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Normalizing cold rolled bright mild steel

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Peter Simpson 117/01/2020 13:53:37
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Looking to make a couple of radius rods for my BR Standard Class 2 over the next couple of days. As I intend to machine theses out of 1" x 3/4" BMS will there be any benefit in heating the blanks up to cherry red and letting them cool slowly prior to milling them to final profile. Will the normalizing stop - reduce the bending effect of machining normal cold rolled steel ?

SillyOldDuffer17/01/2020 14:57:51
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Pedant alert - Peter probably means Stress Relief rather than Normalisation because the latter is done at a higher temperature and alters the crystalline structure of the steel.

Stress relieving is done at a lower temperature, 650C rather that 850C, ie just glowing dull red, not bright. It might be worth doing.

Recommended procedure is to hold the steel at dull red heat for 1 hour per 25mm of thickness and then allow it to cool slowly in air.

For a long time I had no trouble machining Bright Mild Steel to the point I thought the bending stories might be old wives tales. And then one fine day a job went completely bananas, proving it's all true! However I've cut lots of BMS without trouble, possibly luck, maybe my usual cutting direction is benign, or perhaps steel is made these days in a way that reduces the problem. If the Radius rod is easy to make, I'd just go for it. If a lot of work is likely to go down the drain due to bending, then I'd heat relieve first, or - more likely - dodge the problem by using Black instead!

Provided the steel isn't overheated, there's no harm in warming it up and letting it cool. And it might do some good. But note 1hr/25mm is demanded for guaranteed results, anything less may be a waste of heat.

Dave

Phil P17/01/2020 16:16:25
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I keep meaning to chuck a few bits of bright mild steel in the living room fire, and then retrieve them the following morning when it has all cooled down and see how it machines.

Apparently that works but I need to see it for myself.

Phil

Baz17/01/2020 17:04:00
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Phil P, that method works very well, I have been doing it for years, make sure that your pieces are oversize all round to allow for scale on the surfaces.

not done it yet17/01/2020 17:07:26
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Presumably, one might just as well start with hot rolled or a known higher carbon steel if one is going to heat cycle it?

Peter Simpson 117/01/2020 17:40:54
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The problem is the likes of Kennions etc do not stock black steel stock. Everybody stocks BMS.

Nigel McBurney 117/01/2020 17:51:05
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I remember reading in ME in the 1970s in an article by a master loco builder that a good way to avoid the stress relieving problem and be able to use a free machining material was to make items like the motion of locos from bright round bar or if stainless motion was required then use stainless round. Round bar has far less iif any built in stress and round is available in far more specification many being free machining. I can never understand why anyone even considers black hot rolled steel ,,thats for fabricators and blacksmiths.

Andrew Johnston17/01/2020 19:24:34
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Posted by Nigel McBurney 1 on 17/01/2020 17:51:05:
I can never understand why anyone even considers black hot rolled steel ,,thats for fabricators and blacksmiths.

Cost, availability, less prone to rust and machining time.

It's boring enough hogging connecting or eccentric rods out of rectangular sections, let alone round. Bright round is stressed, but if material is removed symmetricallty, ie, turned, no distortion results. Milling it is a different story.

Andrew

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