Phosphate coating for stainless steel 1

[JHWC]

Hi All,

I would like to know the reason why phosphate coating is not suitable for stainless steel?

Saw one of the posts stated that Cr contents above 5% is not suitable. In wiki, it stated high nickel contents.

May I know why and how it affects the SS?

Thanks for the guidances in advance.

Jeffrey

 

[yudhichen]

I think the reason lies on galvanic chart. Some of the idea for picking coating element was using
less noble (anodic) element vs base material according to galvanic chart.

 

[TVP]

The passive layer on the surface of the stainless steel does not allow for the formation of a stable zinc phosphate crystal. Why do you want a phosphate coating on a stainless steel part? If it is for adhering a lubricant for subsequent cold forming, other systems are used such as oxalate coatings or directly-applied MoS₂.

 

[JHWC]

Hi TVP,

I was going through some of the engineering standards for the current company I work in. I observed that the phosphate coating cannot be done in SS but can be done LAS. I was wondering why is it so. One of my colleagues was telling me that the previous company he worked in, tried to do phosphate coating on SS but the coating can be scrapped off easily.

I understand now that it is due to the passive layer of the stainless steel. Thanks for providing me the details. Appreciated.

Cheers,
Jeffrey