What is the difference between SS316/SS304 and SS316L/SS304L?

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.

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40 comments

    Hi
    Can you give me an idea about the corresponding heat number for :
    1- 3/4” 10 unc x 53/4” 316 bolt and nut
    2- 1” 8 un x 53/4” 316 bolt and nut
    Seriously needed for analysis on fasteners to order for our gas project. Your reply will be appreciated.

    Thanks

    @Amavi- We would be happy to help, but we are not sure exactly what you are asking. We have summaries of the chemical and mechanical requirements for these grades on our website if that might help.

    @Srikanth- Bolts made to 304 or 316 do not have any marking requirements. Individual manufacturers may choose to mark their bolts, but it is not required. Bolts made to the ASTM bolting standards, ASTM F593 or A193 have specific requirements, and those can be found on our website.

    @Bhagwan- typically 316 stainless is more corrosion resistant, however for specific applications like this, a metallurgist should be consulted.

    @Wojciech- Magnetic properties can vary a bit depending on what manufacturing processes have been performed on the steel. Some processes can increase or decrease magnetism as the grain structure gets altered. A metallurgist may be able to more clearly explain the specifics.

    Can we use 304 bolts, nuts & Washers, near to sea area ? Also How long 304 bolts can withstand against Corrosion ?

    @Antony- SS304 is commonly used in many close-to-sea applications, but you’d need to consult with an engineer to see if that is the best material for your specific application and to determine what the expected service life would be.

    Hi,

    Can you provide the comparison for SS410 & SS316 in terms of strength and corrosion resistance?
    I am looking for material which is high strength and good corrosion resistance. Thanks.

    @Young- Typically speaking, ss410 is stronger than ss316, and ss316 is more corrosion resistant than ss410. However, there are manufacturing processes and heat treatment options that can drastically increase or decrease both strength and corrosion resistance. We would need to know many more specifics in order to answer your question.

    Hi,
    Could you please let me know what is hardness of SS316 and SS304 which i need to know for selecting the material for our application in paper factory.

    Thanks,
    Manu

    @Manu- The only hardness required by A193 is a maximum of 223 HBN, there is no mimimum. Otherwise both 304 and 316 have identical tensile and yield values, 75ksi minimum tensile, 30ksi minimum yield.

    Hi,

    Can you give me the similar comparison or differences between SS 321 and SS 304 also SS 321 and SS 316.

    Thanks in advance for your reply.

    Regards,

    Virupaksh

    @Virupaksh- Mechanically, 321/304/316 are identical, unless subsequent processing has been done. Chemically, 321 has titanium added to it, and has similar other elements to 316. 304 has slightly less Nickel than both 316 and 321. A complete comparison can be done by looking at the ASTM A276 standard.

    Hi,

    Could you direct me to the appropriate ASTM specification for a 3/4 inch countersunk stainless steel bolt?

    Regards,
    Jyotirmoy

    @Jyortirmoy – Most of the off the shelf countersunk stainless bolts will not be manufactured to an ASTM standard, simply to 304/316 chemistry. If you require an ASTM standard, F593 is the general purpose ASTM standard, but they would need to made special in order to be certified to F593, as the industry has been slow to adopt the F593 standard.

    Hi everyone,

    I am looking for a stainless steel that is easily turned, optically “looks” the same as SS316L, but more reasonably priced than SS316L. Any suggestions?

    For the lower price I am willing to trade off some Corrosion resistance properties. Price and corrosion resistance of SS304 is well suited for my purpose, however SS304 has a yellowish color which does not suit the application.

    Thanks in advannce for your inputs!!

    dear sir
    in orifice meters .which material is recommended to manufacture the orifice plate ss304 or ss316.
    the product is dry gas.
    operating pressure:21-70 bar.
    flow rate:15mmscfd

    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.

    @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.

    @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.

    @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.

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