Grade Overview
Q235 equal angle follows GB/T 700, while Q345 equal angle was originally defined in GB/T 1591. In the 2018 revision of GB/T 1591 the lower alloy grade was renamed Q355, and Q345 remains widely quoted in trade for stock that meets the earlier specification. Both grades are hot rolled L sections with equal legs and are used as chords, bracing and connection members in buildings. The yield strength difference of about 110 MPa allows a lighter angle for the same load when the higher grade is used, so grade selection has a direct effect on steel weight and cost.
Mechanical Properties Compared
For thickness up to 16 mm, Q235 has a minimum yield strength of 235 MPa and a tensile strength of 370 to 500 MPa. Q345 and Q355 have a minimum yield strength of 345 MPa and 355 MPa respectively with a tensile strength of 470 to 630 MPa. Elongation is 26 percent for Q235 and 22 percent for the higher grade.
| Grade | Minimum Yield MPa | Tensile Range MPa | Typical Carbon Percent |
| Q235B | 235 | 370 to 500 | 0.20 maximum |
| Q345B | 345 | 470 to 630 | 0.20 maximum |
| Q355B | 355 | 470 to 630 | 0.20 maximum |
The higher strength grades achieve their properties through microalloying with niobium, vanadium or titanium plus controlled rolling, and they require a qualified welding procedure when the thickness exceeds the range covered by the prequalified details.
Dimensions and Detailing
Equal angles for buildings range from 40 by 40 mm to 200 by 200 mm, with thickness from 4 mm to 20 mm. Leg thickness determines the shear capacity of the connected leg, while the leg width determines the number of bolts that can be fitted. Bolted connections should maintain the minimum edge and pitch distances required by the design code, and where the angle is used as a tension member, the net section through the bolt holes is often the governing check. Welded connections should be detailed so that the weld is placed away from the free toe of the leg to reduce stress concentration.
Corrosion Protection and Fabrication
Both grades are weldable with ordinary carbon steel consumables, although the higher strength grade benefits from a controlled heat input to protect the toughness of the heat affected zone. Cutting, punching and drilling practice is the same for either grade. For exposed building structures, hot dip galvanizing gives the longest maintenance free life, while painting and powder coating are used where appearance matters. In composite floors, the angle is sometimes used as an edge form and should be protected on the faces that remain exposed.
Typical Applications
Roof trusses and portal frame bracing.
Composite floor edge angles and shear connectors.
Curtain wall and facade support brackets.
Stair and platform framing.
Tower and mast legs where higher strength is required.
Frequently Asked Questions
Q: Is Q345 the same as Q355?
They describe the same nominal strength family, and the current GB/T 1591 designation is Q355, while Q345 refers to the earlier edition of the standard.
Q: Which grade should be used for building bracing?
Q235 is usually sufficient for light bracing, while Q345 or Q355 is chosen where the brace force is high and a lighter member reduces fabrication and transport cost.
Q: Can the two grades be welded together?
Yes. A qualified procedure is required, and the consumable should match the lower or higher strength grade according to the design assumption.
Q: What thickness range is available for equal angles?
Equal angles are produced from about 4 mm to 20 mm leg thickness, depending on leg size, and heavier sections are available as built up members.
Q: How should the angle be protected outdoors?
Hot dip galvanizing to a coating mass suited to the corrosivity category is the usual choice, with paint systems used for appearance or for touch up on site.