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Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Passivation of SAE 420 steel balls
Q. Sir,
We manufacture SAE 420 steel balls and harden the same to HRC 50 & above.When we try to passivate these balls, after thorough cleaning in 20% nitric acid at 70 °F,about 20% balls get blackened. Examination & comparison of chemistry, hardness & structure of balls that get blackened with those that do not even get tarnished(balls are polished after hardening & before cleaning for subsequent passivation) does not reveal any difference.
Please advise.
Regards,
Sumeer Aggarwal- Delhi, India
2002
A. Why are you using something so close to a type VI solution? That's used for 300 series. Try a type VIII solution, 45 to 55% nitric acid in water, 120 to 130 °F, for about 30 minutes. You should have better results.
You might also consider using a citric acid solution, such as those offered by Stellar Solutions [a finishing.com supporting advertiser].
Lee Gearhart
metallurgist - E. Aurora, New York
2002
SS320 components turn black from heat treatment
Q. hi every one.
I manufacture some products made of SS420. I need to heat treat this material to reach hardness of 45 RC. The problem is, after hardening the surface becomes dark.
I do not know what to do. Besides I can't grind it.
I wonder if anyone could help me.
Thanks.
mechanical engieering - Tehran, Iran
June 26, 2013
A. Your heat treat oven is probably dirty. Most places would use a vacuum furnace with an inert gas quench.
James Watts- Navarre, Florida
July 5, 2013
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