A36 and A307 – The Differences
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.