Stainless steel type 316 and type 304 are raw material grades for stainless steel. Stainless steel fasteners are sometimes referred to and ordered as their raw material grades (such as SS 316 and SS304) and sometimes referred to and ordered as their ASTM specification. The common ASTM specifications that cover stainless steel bolts are A193, A320 and F593. Type 316 stainless has a unique chemical composition which includes 16% chromium, 10% nickel and 2% molybdenum. Type 304 stainless has 18% chromium, 8% nickel and no molybdenum (this is where the “18-8” designation comes from). Stainless steel 316 is more resistant to chlorides than stainless steel 304, making it the preferred material for marine construction.
Sometimes, a type “SS316L” or type “SS304L” bolt will be specified in a particular application. The “L” at the end of these designations refers to the low carbon content of the steel. Stainless steel certified to 316L or 304L will have a maximum of 0.03% carbon, versus the 0.08% maximum that regular 316 and 304 can have. Low-carbon stainless steel bolts are used to avoid corrosion problems that are caused by welding, as the lower carbon content reduces the “sensitization effect” (the precipitation of chromium carbides at grain boundaries) caused by the high temperatures involved in welding. Since carbon is the principal hardening element in steel, low-carbon bolts have reduced hardness but are easier to weld.
The difference in carbon content does not affect the overall corrosion resistance of the steel, and low-carbon stainless steel bolts can be ordered to each of the A193, A320 and F593 specifications. When you order a low-carbon stainless steel bolt, just let us know about this requirement and our expert estimators will be sure to provide you with the correct material.
I have a large boat kept in salt water. Which SS do you recomend?
Also, I have airplanes onw hich I plan on changing all screws to SS. Which SS do you suggest. They mainly ar on inspection plates and are not structrial.
The boat needs are not structrial as well.
Do you sell small quaities?
Thank you very much for your assistance.
John Thill, President
Garrett Development
@John Thill – we cannot make any recommendations, but of the two most common stainlesses (304 and 316), 316 is the more corrosion resistant. We can sell small quantities, however small screws are not really something we get into. Please feel free to contact us with your specific needs and if we can help, we will.
How would u Identify the materials ss316 and b8m??
@Sharbin – B8M (ASTM A193) bolts should be marked per the specification (mark is “B8M”) on the head of the bolt or at one end of the stud. SS316 is sometimes marked “316”, but not always, it will depend of the manufacturer. If the bolt is not marked, you would need to consult a test lab and they could perform some testing to determine the grade of fastener.
Hello,
What is require percentage of molybdenum in SS304 Material????? as per standard
@Dhananjay – There is no requirement for Molybdenum in 304 stainless. There are typically trace amounts, but it is not required. By contrast, stainless 316 requires 2.00-3.00% Molybdenum.
I need SS BOLT SS316 grade torque valu chart
@Harun – I am sorry, but we do not have any values for stainless steel fasteners. As with most torque values, they will be application specific and we are not able to make any recommendations.
Could you please tell me the differences in HEAT and STRENGTH TOLERANCES between Grade 8, 304SS, and 316L Bolts and NUTS?
Thank you
@Jim – The minimum strength requirements for bolts made to the above grades are identical, 30ksi minimum yield, 75ksi minimum tensile. For nuts, it will depend on the manufacturer. Nuts made per 304/304L or 316/316L may or may not be proofloaded since 304/316 is a material call out, not a nut specific one. For nuts made to A194 gr.8 or gr.8M, they should both be proofloaded to 80ksi for heavy hex, and 75ksi for finished hex.