Am I blackening steel correctly?

Then you are using it for the right purpose, it is not intended for structural work, this applies to both BMS and black steel. Here is a quote of a typical chemical analysis for 070M20 (EN3A), the bright version is EN3B.

**LINK**

It should conform at least roughly to that analysis, I don't see a mention of boron in there, I know it's hard to test this, but if it isn't conforming to these numbers, it isn't mild steel by definition. And i'd imagine it certainly wouldn't be what the common stockists will be offering. If you go to a scrap yard or recycling plant for steel, you can expect the lottery that comes with it.

Michael W

Edited By Michael-w on 02/01/2017 18:41:38

I would suggest that the problem that vintage engineer refers to is one of cheapo recycling. Poor homogenisation of the constituents while in the melting pot? Certainly there would be variations between batches but that should, with quality control, be minimised.

The problems could be avoided, but at a price as usual.

I have some old 1935 C section steel used for telecoms racking some parts cut / drill well and some spots are hard.

So mixed scrap in steel is nothing new.

I remember old 60's/70's jap cars rusting rather badly.

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:D

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Thank you for your polite response.

There is a hot process that takes place at about 140deg C, you can buy the stuff from heat treatment supply companies. It has caustic soda in it, and other salts. I consider it safe to use if you take the appropriate precautions.

They will also give you the instructions for it's proper use. It does not work on stainless steels or steels with a high chrome content. But us great for MS or heat treated A2 tool steel and P20 that I know of, does not effect a steels temper as the 140C is below the steels tempering range.

Neil

60's 70's ? There were hardly any around then. There were a few about in the 80's but serious numbers came later. That's when they had steel supply limitations. Also near the start of oil technology getting well ahead of car engines and as far as the manufacturers were concerned lasting far to long.

There was a lot of crap mild steel around during wwII. My father told me that they had a name for it in toolrooms - park railings. As they were collecting them and resmelting them. There can still be crap pieces of steel about but sorry I don't think that has anything to do with recycling the stuff.

John

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John

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I'm surprised no-one has mentioned the FIAT story [myth?] discussed here: **LINK**

http://message.snopes.com/showthread.php?t=30479

See post #13 if you can't be bothered reading the whole page.

MichaelG.

Off topic to the OP but on topic as far as recycled steel goes...

The most free cutting mild steel I've ever used came from some 're-purposed' plastic coated rods from a 1990s vintage clothes airer (and I still have about half a dozen 3ft lengths)!