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topic 17615

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 70deg 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.


Sumeer Aggarwal
- Delhi, India


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.

lee gearhart
Lee Gearhart

SS320 components turn black from heat treatment

June 26, 2013

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.

Mehdi Rahimi
mechanical engieering - Tehran, Iran

July 5, 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

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