Structural and HSLA Steel

Structural steels are carbon-manganese plate, bar and sections sold to a guaranteed minimum yield strength rather than a chemistry — A36 and S235JR at about 235–250 MPa, A572 Gr 50, S355J2 and Q355B at 345–355 MPa. High-strength low-alloy (HSLA) grades add small amounts of niobium, vanadium or titanium and a fine-grained rolling practice to reach 420–700 MPa (S690QL: 690 MPa yield, quenched and tempered) while staying weldable without preheat in moderate thickness. They are used as delivered: cut, bent and welded, never hardened.

A36 (or S235JR / Q235B on EN and GB drawings) for frames, brackets and general weldments where stiffness rather than strength sets the section. A572 Gr 50, S355J2 and Q355B are the default when the drawing gives a strength: about 40 % more yield than A36 with the same welding practice, and S355J2 adds a guaranteed −20 °C impact value for cold service. A992 is the rolled wide-flange beam grade in North America; A588 and S355J2W are the weathering grades that form a tight rust patina on unpainted bridges and outdoor structure. A514 and S690QL are quenched and tempered to about 690 MPa yield for cranes, booms and lifting gear, and S700MC is the thermomechanically rolled sheet for truck chassis that still bends at a tight radius. Above that, S960QL is for telescopic boom sections where weight decides.

S1100QL has the highest yield strength in the series at 1,150 MPa; Q960Q follows at 1,010 MPa. Values are for each grade's default condition.

Q235D (machinability very good, 70/100), then S275J2 (68/100).

No. These grades are strengthened by cold work and softened by annealing, not by heat treatment; the conditions are listed on each grade page.

A572 Gr 50 gives 345 MPa minimum yield against 250 MPa for A36, welds and cuts with the same procedures, and costs only a little more, so it is the better buy when the design is strength-limited. A36 remains the choice when stiffness sets the section (a beam under a deflection limit gains nothing from higher yield) or when existing stock and weld procedures are written around it.

Close enough to substitute in most structures: all three guarantee about 345–355 MPa yield and 470–630 MPa tensile. The letters differ in what is tested — J2 requires 27 J Charpy at −20 °C, JR at +20 °C, and Q355B at +20 °C, while A572 has no impact requirement unless a supplementary test is ordered. For cold service or dynamic loading specify the J2 (or Q355D, −20 °C) variant explicitly.