What an Angle Section Is
An angle is a structural steel profile with two legs meeting at a right angle, produced as equal-leg and unequal-leg sections. Angles are rolled from carbon structural steel grades and are used for bracing, frames, brackets, trusses and light structural members. Because an angle resists loads mainly along its legs, its mechanical properties determine the permissible stresses, the buckling checks and the connection design, so the grade and its guaranteed values are the first thing to specify.
Yield Strength
Yield strength is the stress at which the steel starts to deform permanently, and it is the primary design value in most structural codes. Common angle grades and their minimum yield values for the base thickness range are:
Q235B per GB/T 700: 235 MPa.
S235JR and S275JR per EN 10025-2: 235 and 275 MPa.
SS400 per JIS G3101: 245 MPa for thickness up to 16 mm.
Q355B per GB/T 1591 and S355JR per EN 10025-2: 355 MPa.
A36 per ASTM A6: 250 MPa, and A572 Grade 50: 345 MPa.
The yield value sets the design strength in the code formula, so a higher grade directly reduces the required section size.
Tensile Strength and Elongation
Tensile strength is the maximum stress the angle can carry, and elongation measures ductility, which controls forming and gives warning before fracture. For structural carbon angles, typical minimum tensile values are 370 to 500 MPa for Q235, 360 to 510 MPa for S235JR, 400 to 510 MPa for SS400, and 470 to 630 MPa for S355JR and Q355B. Elongation requirements are typically 20 to 26 percent minimum depending on grade and thickness. Ductility matters because angles are often bent, punched and welded during fabrication, and brittle material fails without warning.
Impact Toughness
Impact toughness describes the ability of the steel to absorb energy at a given temperature without fracturing, and it is critical for outdoor structures in cold climates. The quality suffix of the grade sets the impact requirement: for example S235JR and S355JR require 27 J at 20 degrees Celsius, S355J2 requires 27 J at minus 20 degrees Celsius, and Chinese grade Q355D requires 34 J at minus 20 degrees Celsius. A36 and Q235B angles do not guarantee impact values unless supplementary requirements are added, so cold-climate projects should specify a grade with a low-temperature impact test.
Modulus of Elasticity and Section Properties
All carbon steel grades share a modulus of elasticity of about 200 GPa, which is used in deflection, buckling and vibration calculations. The geometric properties of the angle, including the leg dimensions, thickness, area, moment of inertia and radius of gyration, convert the material strength into member capacity. These section properties are tabulated in the product standard, such as GB/T 706, EN 10056 or ASTM A6, and the measured leg and thickness dimensions must fall inside the tolerance band so the design tables remain valid.
Verifying Properties on Delivery
On delivery, confirm the grade and standard on the Mill Test Report and check the chemical composition and mechanical test results against the specification limits. Measure the leg width, thickness and length and compare them with the tolerance standard. For load-bearing angles, require the yield, tensile and elongation values from the actual heat, and for low-temperature service confirm that the impact test results meet the grade requirement at the specified temperature.
Frequently Asked Questions
Q: What is the most important mechanical property of an angle?
Yield strength is the primary design value, because structural codes base the permissible stress on it, while tensile strength and elongation confirm ductility and reserve capacity.
Q: What yield strength does a Q235 angle have?
A Q235 angle has a minimum yield of 235 MPa for the base thickness range, with tensile strength between 370 and 500 MPa.
Q: Which angle grade is used for cold climates?
Grades with guaranteed low-temperature impact values such as S355J2 or Q355D are preferred, because they are tested at minus 20 degrees Celsius or lower.
Q: Do all carbon steel angles have the same stiffness?
Yes, the modulus of elasticity is about 200 GPa for all carbon steel grades, so stiffness depends on the section geometry, not on the grade.
Q: How are angle properties verified on delivery?
By checking the Mill Test Report chemistry and mechanical values against the standard, and by measuring the leg, thickness and length dimensions against the tolerance table.