Un-Blackening Steel

[RichardNParticipant @richardn]

When silver brazing (CupAlloys 455 with EF flux powder) I tried soldering lumps of steel (2" dia, about 5/8" long, attaching 1/2" diameter bars) the other day, cleaned with wet/dry with oil, then acetone, then fluxed and soldered, and all good. Except everything not fluxed has a solid hot blacked finish. Maybe I dropped the pieces into water while too warm?

How do I remove the black finish- my acid pickle says for copper alloys, and the flux residue just flakes off, and wet/dry takes far more elbow grease than I have to spare. I thought the acid pickle was to help remove the flux which came off far more easily than expected.

Muriatic (brick cleaner)?

Citric acid?

Don't quench while hot after soldering and appreciate a solid even blackened finish?

[RichardNParticipant @richardn]

Cleaning up after silver brazing

[JasonBModerator @jasonb]

Brick patio cleaner (Hydrochloric)  will shift it as well a smill scale on black (hot rolled) steel

Don't put it in when red hot, ideally let it cool until you can touch it, quench in water first if in a hurry.

After soldering

10mins in the brick cleaner and just a gentle scrub with an old toothbrush.

Edited By JasonB on 26/06/2016 20:42:41

[RichardNParticipant @richardn]

Will that be a decent overnight soak, or likely a few minutes? I've no idea how deep and how quick the blackening will be removed!

Will I get much impact on dimensions?

Thanks for the quick response

Edit: just seen the pictures and time- perfect info, many thanks!

Edited By RichardN on 26/06/2016 20:46:15

[JasonBModerator @jasonb]

The mill scale I find needs about half an hour.

Soldering will depend on how long you were heating and the exact steel used. Just watch the first bits you do to get a feel for it and give a rub with the brush to see how it is going. Overnight and you might see a slight loss of material so don't forget its in the pot.

It also removes the more stubborn Tenacity5 or HT5 flux which normal pickle does not shift very well.

Rinse it off well and get some oil on the surface as it will rust quickly afterwards. Also best not done or stored inside the workshop as the fumes will rust other metal.

Another example

[RichardNParticipant @richardn]

Thanks- you must have a well organised photo library to find the images so quickly!

Looks like I need to hunt down some different brick cleaner- I thought it was Muriatic (HCl) but it seems my bottle in the garage COSHH states NaOH… Would be unwise to start mixing the two on a driveway…

I think my sievert burner (240g/hour) was struggling to get up to temperature outside in the wind, so took a while to get the heat up- and the steel was a mix of black bar and a box of boot sale offcuts- will have to play with it more for practice!

[Roger HeadParticipant @rogerhead16992]

Jason, could you give us a bit of an idea on the scale of those photos i.e. dia/thickness of the large disc. Is the vertical shaft butted onto the disc, or is it in a hole? What power burner (gph or kW equiv) would you have used?

Thanks, Roger

[Thor 🇳🇴Participant @thor]

Hi Richard,

If the bottle in your garage says NaOH you could soak the acid pickled parts in a dilute solution of NaOH (to neutralize the acid) before rinsing in water. And of course be careful when handling acid and alkaline solutions. I use a solution of sodium bicarbonate to neutralize steel parts after pickling in acid.

Thor

[JasonBModerator @jasonb]

Roger, first photo the two round ends are 5/8" dia and about an inch long, bars are 1/4 x 3/4 and 1.625 long. They are the bearing caps for this engine

Disk is 3.125" dia and from 12mm thick hot rolled (black) plate, yes there is a small recess in the plate to take the end of the flange. This is it on a 6" rotary table

I only have a cheapish bullfinch torch and would say the burner I use is 5 to 6 kW, 4.5kg propane bottle

[Roger HeadParticipant @rogerhead16992]

Thanks Jason.

Roger

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