Summary for 303 stainless steel corrosion resistance Discussion
303 stainless steel corrosion resistance is the key issue in this thread: Colin McClennan asked whether 303 SS etching in 38% H2SO4 under vacuum could explain why 304 did not show the same problem. Ted Mooney replied that it could, noting that 303 is the free-machining version of 304 and contains controlled manganese sulfides that help chips break but can hurt corrosion performance; he said he and others have seen passivation problems with 303 that they do not see with 304, and he would believe 303 is inferior in that service. Later, Terry Jamison commented more generally that engineers often specify 303, 304, 321, or 347 without understanding machining implications. A separate question about magnetism in 304 and the meaning of 303HS was answered by Ted Mooney, who explained that cold work can make austenitic stainless steels more magnetic and said he did not see evidence that 303HS has an accepted meaning.
Q. I notice etching in a 303 Stainless steel item when submersed in 38% H2SO4 under vacuum. It seems to me that 304 did not exhibit the same problem. Is this correct?
Colin McClennan
electronics mfgr – Providence, Rhode Island, USA
2004
A. Could be, Colin. 303 is the free machining version of 304 — meaning it has controlled amounts of ‘dirt’, manganese sulfides, which cause the machining chips to break easily. We, and others, have noticed passivation problems with 303 that we don’t see with 304. I have no experience with your particular corrosive, but could easily believe 303 is inferior to 304.
Lee Gearhart
metallurgist – E. Aurora, New York
2004
A. I agree with Lee that 303 will usually be less corrosion resistant than 304. You may find that soaking the 303 first in hot NaOH solution or similar will help you immensely by removing the sulfides from the surface before passivation.
Lee Kremer
Stellar Solutions, Inc.
McHenry, Illinois
2004
Q. None the less, is 303 considered a CRES?
Thanks
TJ
Terry Jamison
– Glendora, California, USA
March 22, 2012
A. Hi, TJ. I personally don’t know of any document that puts a fine point on the required parameters of CRES.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
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March 22, 2012
March 23, 2012
I ask that question because, over the past 45 years I’ve been involved in machining, there has always been the occasional snide remark we make when quoting a job that gives the option of 304, 321, 347, 303. Those callouts are usually stuck on a print by an engineer who has never machined any of those materials.
Cheers.
TJ
Terry Jamison [returning]
Mfg – Glendora, California, USA
Q. Why is 304 so magnetic? And what is the difference between 303 and 303HS
Rogelio Rangel
– harlingen Texas USA
October 24, 2012
A. Hi Rogelio. Here is an extract from www.azom.com/article.aspx?ArticleID=1140
All austenitic grades have very low magnetic permeabilities and hence show almost no response to a magnet when in the annealed condition; the situation is, however, far less clear when these steels have been cold worked by wire drawing, rolling or even centerless grinding, shot blasting or heavy polishing. After substantial cold working Grade 304 may exhibit quite strong response to a magnet, whereas Grades 310 and 316 will in most instances still be almost totally non-responsive.
The change in magnetic response is due to atomic lattice straining and formation of martensite. In general, the higher the nickel to chromium ratio the more stable is the austenitic structure and the less magnetic response that will be induced by cold work.
I don’t see much evidence that “303HS” has any accepted meaning. Although HS could stand for high speed, I don’t see agreement on that.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
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October 24, 2012
A. In response to the question about the various grades of materials, many engineers will list materials that all exhibit the strength, corrosion resistance and compatibility characteristics they need regardless of machinability.
In some cases, a vendor might not have the original material on the shelf but a similar material they do have will suffice. Then the engineering might be revised to include the less common, though available, materials.
303 would be conventionally accepted as a CRES simply due to the fact that it exhibits similar corrosion resistant properties to other corrosion resistant steels.
While 303 is easier to machine than 304, 304 is usually easy enough to not justify the ~20% increase in material cost.
Brian Herr
Marlen International – Riverside, Kansas, USA
March 17, 2016