A36 mild carbon steel alloy. Common structural steel in U.S.A. Minimum yield of 36,000 PSI (250 MPa) and ultimate tensile strength of 58,000 to 80,000 PSI (400-550 MPa). Please enter your postal code to check availability. 1-1/2" x 3 Mild Steel Round Tubing. A36 mild carbon steel alloy with 16 gauge walls. Common structural steel in U.S.A. Minimum yield of 36,000 PSI (250 MPa) and ultimate tensile strength of 58,000 to 80,000 PSI (400-550 MPa).