AISI 1040 square pipe

general characteristics of AISI 1040
AISI 1040 is a medium carbon, medium tensile steel supplied as forged or normalized. This steel shows good strength, toughness and wear resistance.
AISI 1040 is a medium-carbon engineering steel that is suitable for flame or induction hardening. It is a versatile forging material with mechanical properties that are appropriate for a full range of applications. The steel can be readily welded and machined providing correct procedures are followed.
 AISI 1040 chemical composition

equivalent grades of 1040

AISI 1040 square tube heat treatment  
 This steel responds well to hardening by heat treatment at 1550 to 1650 F followed by water quench and then tempering to strength level desired. 
weldability
This grade is readily welded with the correct procedure. Welding in the through hardened or flame or induction hardened conditions is not recommended.