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Nitrided sheet metal parts warp after pickling

October 18, 2016

Q. Hi,
We are liquid Nitriding and zinc finishing company.

I carry out Liquid Nitriding of a sheet metal part (1.5 mm mild steel) and subsequently I'm using 10% H2SO4 for the scale removal. After which I do Caustic for the component for 30 minutes and then again do pickling with 5% HCl before putting in Acid Zinc Plating bath. I'm facing a serious issue of twisting of the part despite the liquid Nitriding.
I want to know which out of HCl or H2SO4 is better to use in pickling process (after liquid nitriding process) to avoid hydrogen embrittlement of Mild Steel (sheet metal components)?

What concentration of preferred pickling acid (to avoid hydrogen embrittlement) out of HCl or H2SO4 should be used which doesn't affect the metal 1.5 mm sheet metal of Mild steel?

aman uppal
Nitriding and plating company - chandigarh, UT, India

October 2016

? Hi Aman. I assigned a title to your posting which I hope is correct. The part is "twisting"? Do you mean it lacks strength and will twist under a load, or do you mean it becomes warped as a result of the processing? Why do you think hydrogen embrittlement causes this warping and that using a different acid will reduce it?


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Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

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