Dull Polish in 440c and 420B NIMO
Question: We are ball making people.
Question:
We are ball making people. We find dull polish problem during passivation of 440c and 420b nimo steel. J.S.
Answer:
Not having much to go on with your question, there could be a couple possibilities. First is that the balls would need to be clean (oil and grease free) before passivation. This would involve some sort of process that would wash the parts with a solvent or an aqueous based solution with a detergent.
Second could be the removal of heat tint and/or scale from the parts. If this is present on the part, it will not be removed by most passivating solutions. Most cleaning solutions intended to remove oxidation, scale or heat tint from parts will include hydrofluoric acid along with nitric acid to provide an actual etch to the base stainless.
The next possibility is the passivation solution. The same passivating solutions used for austenitic stainless steel (300 series) are not necessarily recommended for ferritic (400 series stainless steel). The ferritic stainless steels, especially those with higher carbon content such as those mentioned will typically start out with 20% by volume nitric acid and 5% by weight of sodium dichromate. You will need to use caution with this mixture due to its corrosivity, oxidizing potential and the toxicity of the chromate. Make sure that the process complies with workplace and environmental regulations.
Related Content
-
Explore Cleaning Chemistry, Metal Finishing Applications and Wastewater Treatment Solutions
Hubbard-Hall Celebrating 175 years of excellence, Hubbard-Hall presents chemistry and equipment.
-
NASF/AESF Foundation Research Project #122: Electrochemical Approaches to Treatment of PFAS in Plating Wastewater - 6th Quarterly Report
The NASF-AESF Foundation Research Board has selected a project on addressing the problem of PFAS and related chemicals in plating wastewater streams, studying PFAS destruction via electrooxidation and electrocoagulation. This sixth quarter report covers the continued assessment of eight perfluoroalkyl acids PFAAs most commonly found in wastewaters, by electro-oxidation with a Magnéli phase Ti4O7 anode across a range of anodic potentials in solutions, exploring the reaction mechanisms. To summarize, the PFAAs start to exhibit degradation behavior when the anodic potential reaches a level where water oxidation occurs, suggesting that the hydroxyl free radicals generated via water oxidation play a role in PFAA degradation.
-
NASF/AESF Foundation Research Project #120: Electrochemical Destruction of Perfluorooctanesulfonate in Electroplating Wastewaters – January – December 2023
This NASF-AESF Foundation research project report covers quarterly reporting for the year 2023 at the University of Illinois at Chicago. The objective of this work is to utilize a cost-effective reactive electrochemical membrane (REM) for the removal of PFAS from synthetic electroplating wastewater. Discussed here are the oxidation of PFOA with three different catalysts, development of a method for detecting PFAS, as well as work on 6:2-fluorotelomersulfonic acid (6:2 FTS) and electrodeposited bismuth/tin oxide catalysts.