Protecting CDA 260 Brass from Dezincification while annealing
Protecting CDA 260 Brass from Dezincification while annealing
(OP)
We currently anneal quite a bit of our raw CDA 260 brass and find that as we approach annealing temperatures of 900-1000 deg. F, our product dezincifies to such a great extent that no amount of mechanical or chemical finishing can make the part look correct again. Does anyone have any tips as to how to anneal 70%Cu/30%Zn brass? Thanks.





RE: Protecting CDA 260 Brass from Dezincification while annealing
RE: Protecting CDA 260 Brass from Dezincification while annealing
Probably, too much time at too high a temperature with too much oxygen present. Also, verify that the initial composition is correct ($ Cu = 1.44 x $ Zn, so cheating incentive), higher Zn might segregate as more oxidizable beta-phase.
Are the annealing parameters based on existing cold work? Cold-worked C26000 recovers about 75% of its elongation potential at 800 oF (1 hour).
Combusted natural gas, air-to-gas adjusted to give 0.5 to 1% hydrogen after drying, is the most widely used protective atmosphere for the anneal of copper and copper alloys. Direct firing (w/o drying), even with slight excess of gas, may cause discoloration and staining of the metal by water vapor during cooling.
-- Metal Handbook Volume 4 Heat Treating, pages 719-728.
RE: Protecting CDA 260 Brass from Dezincification while annealing
RE: Protecting CDA 260 Brass from Dezincification while annealing
Obviously, this annealing process results in an oxide film on the brass, which can be removed with a warm solution of blended acid salts (sulfate/flouride) or a cold dilute solution of hydrogen peroxide/ammonium biflouride. The parts can then burnished to a bright finish.
RE: Protecting CDA 260 Brass from Dezincification while annealing
For more info on the acidic descaling solutions mentioned above, plus tumble cleaning, electrocleaning, electropolishing & bright dip solutions, see ASTM B281, 'Standard Practice for Preparation of Copper and Copper-Base Alloys for Electroplating and Conversion Coatings.'
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