ASTM A36 is the minimum strength designation - 36 KSI
This is the cheapest structural grade and what most rebar, chanels, angles, etc are made from.

The 70 KSI for AISI 1018 is an average strength rating and most of the added strength does come from being cold worked.

Neither one of these designation has very tight chemical specifications and limited consistancy. If you need that, you would need to specify an ASME grade of steel such as ASME SA515 Grade 70.

Having said all of that, most of the places that sell hot rolled steel bar use a steel that is rated A36/M1020.
JR