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Etching steel before painting and endurance

Hello,

After TIG welding a 4130 and 4340 alloy race car A-Arm, I spray it with dilute phosphoric acid to etch off the phosphate coating from the mill and to clean off any oxides just minutes before I spray paint with enamel.

My concern is that the etching somehow would reduce fatigue strength of the metal or the weld. Back in school we used to etch metalurical samples to look at grain boundaries under the microscope, so I figured this can enhance micro structural defects.

The practical side of this question is really if it is ok to etch steel prior to painting.

Thanks,

Erik Shahoian
- San Jose, California, USA

Beats me. My guess, though, is that it's probably OK to do this.

Don Ferris
- San Diego, California

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