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Is all grade 304 stainless steel the same? What is "A-304"? 1

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audiobahn1000

audiobahn1000

Coastal
Aug 24, 2009
4
US
I am researching the corrosion resistance between different brands of 304 SS bolts. I am trying to determine if all grade 304 SS bolts are made the same or if some are more resistant to corrosion in a costal marine environment then others. Please note that my question only refers to 304 SS and not 316 SS.

So far I have found that every manufacturer I am studying states their bolts are made of "grade 304 stainless steel". However there is a wide price difference between seemingly identical bolts. The most expensive manufacturer stated their bolts are "A-304" stainless steel.

So what does the "A" refer to in A304 and is A304 different then standard 304? Lastly, is all grade 304 stainless steel created equal or is there such thing as "cheap" 304 SS and "quality" 304 SS?
 
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304 is pretty cheap stuff anyway, but from some sources its even cheaper and quality can be a problem. We've had some bad experiences working with products of China, Russia, and some other questionable areas. If your going to buy products from there you're at risk and should increase documentation and testing requirements accordingly.

ASTM A304 is a specification document for multiple grades of carbon steel. It doesn't include SS. ASTM A240 is a specification for multiple grades of SS plate, strip, and sheet for instance and includes 304 or UNS S30400. 304 fasteners are under ASTM A193 and are identified as "B8".

Cold working is a variable to be aware of.
 
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For corrosion resistance, you need to be concerned with more than just chemical composition (which can vary among suppliers). Heat treatment (to prevent sensitization) and surface finishing (pickling, passivation, etc.) are important to provide the best corrosion resistance.

You should ask for fasteners to meet consensus standards, like ASTM A 193 Standard Specification for Alloy-Steel and Stainless Steel Bolting Materials for High-Temperature Service or ASTM F 593 Specification for Stainless Steel Bolts, Hex Cap Screws, and Studs or ISO 3506-1 Mechanical properties of corrosion-resistant stainless steel fasteners — Part 1: Bolts, screws and studs. Then, you will know that the parts meet specific requirements for chemical composition, mechanical properties, etc.
 
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I contacted the manufacturer and they said by "A-304" they mean AISI304. Is AISI304 simply grade 304?
 
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audiobahn1000;
If the supplier meant this as 304 stainless steel, so be it. However, material procurement should be to a particular standard or material specification with a UNS designation so that you have traceability of the material, and heat treatment requirements to avoid confusion.

I would suggest you follow the advice above and procure fasteners to an ASTM specification.

In general, 304 stainless steel can vary somewhat in terms of high or low end ranges of Cr and No contents, and condition of material supplied. The main driver for maximum corrosion resistance is the requirement for solution treatment in the ASTM specification.
 
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304 SS bolting can be furnished in the solution treated condition (maximum corrosion resistance with picklng & passivating)) or cold worked/cold finished conditions (poorer corrosion resistance and much more susceptible to stress corrosion cracking).

 
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