AISI generally only specifies the chemistry of the base metal. The manufacturing process and the state of final heat treat isn't address, hence the mechanical properties are not usually stated. AISI materials are usually the feed stock for various manufacturing operations like machining, forging, stamping, etc. where a final heat treatment is used to provide the desired properties.
ASTM on the other hand specifies the melting method(s), forming operation, final heat treatment, chemistry, and mechanical properties such as ultimate tensile strength, yield strength, elongation, etc.
You can get your dog at the pound, the pet store, or a breeder. You can get your steel at the scrap yard, the warehouse, or directly from the mill. it all depends on the pedigree you are willing to pay for.
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