What are the differences between A36 and A307?

ASTM A36 is a steel (raw material) specification, while ASTM A307 is a fastener specification. In other words, once you take A36 round bar and cut it, thread it, bend it, forge a head on it, or otherwise process it and turn it into a fastener, it becomes an A307 bolt.

Often times, ASTM A307 bolts (and all thread rod) are manufactured from A36 steel, but not always. A36 material should always be weldable and if A307 rods are manufactured from A36 steel, they will be weldable as well. However, A307 bolt can be made from other steels which, in rare instances, may not be weldable. Specify the supplemental requirement “S1” which is the A307 specification that outlines the requirements for weldability. If a steel other than A36 is used to manufacture the A307 rods, the chemistry should be checked to assure weldability.

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8 comments

    Dane,

    If you order an A307 Grade A bolt to the S1 supplemental requirement is it considered a P-1 material for Sec. IX weld procedure requirements? Or is it an unclassified material that requires a separate qualified weld procedure specification?

    Thanks.

    @Jon- Apologies, but we are not familiar enough with that welding requirement to properly answer your question.

    Can we weld the ASTM 307A bolt (machined bolt) to a 36 plate? Is welding can be performed on high strength bolts? And a307A belongs to high strength bolts.

    @Marven- Most A307A bolts are made from low carbon steel and should be weldable to your A36 plate. However to be certain, you should obtain a copy of the bolt MTR and review the chemistry to make sure it is consistent with weldable steel. A307A is not considered to be a high strength bolt.

    @Jafeth- ASTM A307 is a finished fastener standard that calls out dimensions, chemistry, mechanical requirements, and all other aspects of the fastener. ASTM A36 is a raw steel standard that covers only the raw material as it comes from the steel mill. There are many differences between the two, many of which are laid out in this FAQ. A307 grade B is specifically for flange connections and can cover headed bolts or studs.

    Dear Dane

    Our clients request UBOLT according to ASTM A307 Grade B.
    In this case it can be manufactured with bars on A-36?.
    I await your prompt response.

    Thank you.

    @Yanniz- It is possible, yes, however A307B does have some requirements that A36 does not, so you would need to make sure your A36 has the necessary testing to meet A307B.

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