Hi,
I am seeking advice on macroetching coupons of forged 15-5 PH to improve the visibility of grain flow.
For the initial attempts (pictured), the process was not tightly controlled. The specimens were milled and lapped to get a smooth surface. I used a room-temperature bath of Fry's Reagent, which did not produce any visible results.
Following ASTM E381 guidance, I used a 50% HCl solution in a large beaker heated on a hot plate (targeting 70-80C) for several hours, with a single stir bar positioned to the side. However, the solution may not have reached or maintained the desired temperature due to its volume. I also attempted gradual additions of 3% hydrogen peroxide, although not at room temperature as described in E381. Some grain flow is visible but not to the desired contrast.
In subsequent (unpictured) trials, I used smaller samples (without forge scale on the edges), prepared in the same manner (milled and lapped). These were etched in a lower-volume 50% HCl solution at an estimated 80 deg-C, with a higher amount of gradually added hydrogen peroxide. Immediately prior to etching, the surfaces were lightly rubbed with Scotch-Brite, and surface residue (scum) was removed midway through the process. Despite these adjustments, there was no significant improvement in revealing grain flow.
As a next step, I plan to use the slightly more-detailed procedures in ASTM E340 and/or repeat with fresh, clean solution. I would prefer to avoid HF, but I am open to alternative etchants or process adjustments. Thanks for any information that the ASM community can provide.
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Tiffany Liu
Dow
Orange TX
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