Summary for 18-8 stainless passivation Discussion
Passivation methods for 18-8 stainless steel depend on the exact alloy, because "18-8" is only a generic name for a family of austenitic stainless steels. Jennifer Louie asked whether ASTM A967 provides a standardized passivation method for 2 mm by 8 mm dowels, and Toby Padfield replied that the first step is to identify the specific grade. He noted that Type 304 is one common 18-8 grade and is listed in ASTM A967 by UNS designation as S30400 in Figure X1.1. Once the exact grade is known, he said to use the appropriate nitric or citric acid composition. A second reply added that 18-8 generally refers to 300-series stainless steels with about 18% chromium and 8% nickel, with 304 most common but 302 and 303 also fitting the description.
Q. Want to passivate 18-8 stainless steel dowels which are 2mm diameter by 8mm long. The ASTM A967 does not list
18-8 stainless on treatment table. Is there a standardized passivation method for this material?
Jennifer Louie
medical device manufacturer – San Diego, California, USA
2004
A. 18-8 is a generic description for a range of austenitic stainless steels. Type 304 is one such grade, which is identified by its UNS designation in Figure X1.1 of ASTM A967 as S30400. You should find out the specific grade of 18-8 stainless in question, and then use the appropriate Nitric or citric acid composition.
Toby Padfield
Automotive module supplier – Michigan
2004
A. 18-8 stainless steel is a generic term for austenitic stainless steels that comprise 18% chromium and 8% nickel. They are part of what is called the “300 series” stainlesses. The most common grade is
304, but other specialised steels that fit this description are 302 and 303. There are subgroups of these for very specialised steels with special properties.
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
A. 18-8 stainless steels can be passivated with any of the processes in ASTM A967. However, if it is 303 you special treatment to remove sulfur.
Lee Kremer
Stellar Solutions, Inc.
McHenry, Illinois
2004
2007
Q. Lee,
You’ve mentioned that in order to remove sulfur from 303 SS a special treatment is required. Can you share what the “special treatment” consist of?
Thanks for your help,
Javier Reyes
QC Manager
Javier Reyes
– Anaheim, California, US
A. Javier:
It is necessary to treat the parts with hot alkaline (NaOH or KOH) solution prior to passivation. This removes most of the sulfides from the surface so that they do not bleed our or turn yellow when exposed to moisture. Customers use a variety of times and temperatures, but we recommend AT LEAST 15 minutes at 60-70 deg.C.
Regards,
Lee
Lee Kremer
Stellar Solutions, Inc.
McHenry, Illinois
2007