Q235 is a widely used Chinese standard mild carbon structural steel specified in GB/T 700, the Chinese standard for carbon structural steels. The designation Q refers to yield strength and 235 to the minimum yield strength in MPa. It is known for excellent weldability, formability, and cost-effectiveness, and it is suitable for general structural applications including buildings, bridges, machinery, vehicles, and storage containers.
What Q235 Steel Is
Q235 is a plain carbon structural steel, not a high-strength low-alloy steel. Its strength comes mainly from carbon and manganese, with no significant alloying additions. The steel is available in four metallurgical grades, Q235A, Q235B, Q235C, and Q235D, which differ in the guaranteed chemical limits and the level of toughness. Grade B is the most common for general structural use, while Grades C and D provide better low-temperature toughness. Q235 has widely recognized equivalents in other national systems, including ASTM A36 in the United States, EN S235JR, S235J0, and S235J2 in Europe, JIS SS400 in Japan, IS 2062 E250 in India, and DIN St37-2 in Germany. The grades are broadly comparable, but substitution should be confirmed by the design engineer because the guaranteed values and test conditions differ.
Grades and Chemical Composition
The maximum chemical limits for the four grades are as follows. Carbon is 0.22 percent for Q235A, 0.20 percent for Q235B, and 0.17 percent for Q235C and Q235D. Silicon is 0.35 percent and manganese 1.40 percent for all grades. Phosphorus is 0.045, 0.045, 0.040, and 0.035 percent for Grades A, B, C, and D respectively, and sulfur is 0.050, 0.045, 0.040, and 0.035 percent respectively. Lower carbon, phosphorus, and sulfur improve toughness, weldability, and ductility.
Mechanical and Physical Properties
Q235 has a minimum yield strength of 235 MPa for thickness up to 16 mm and a tensile strength of 370 to 500 MPa, with Brinell hardness typically in the range of 100 to 130 HB. The steel shows good ductility and toughness, and it can absorb energy under impact or dynamic loads without fracturing. Typical physical values include a thermal conductivity of 49 to 53 W per meter per kelvin, a coefficient of thermal expansion of about 11.3 to 11.6 times 10 to the minus 6 per kelvin, and a Poisson ratio of 0.24 to 0.28.
Product Forms and Processing
Q235 is produced in a wide variety of forms, including wire, coil, sheet, rod, flat bar, round bar, channel, tube, rebar, I-beam, and C-channel. It is supplied in hot-rolled, cold-rolled, or cold-drawn conditions, with surface options such as non-oiled, anti-rust oil, or galvanized finishes. The material supports arc, resistance, and gas welding, and it can be cut, bent, punched, and drilled with standard equipment.
Typical Applications
Structural beams, columns, and frameworks for buildings and bridges
Roof structures, purlins, and scaffolding
Machinery frames, gearbox housings, and mechanical parts such as rods, screws, and brackets
Vehicles, containers, boilers, and transmission towers
Agricultural machinery, railway tracks, and metal furniture frames
Frequently Asked Questions
What does Q235 mean? Q stands for yield strength and 235 for the minimum yield strength of 235 MPa in the GB/T 700 designation.
Is Q235 a high-strength low-alloy steel? No, Q235 is a plain carbon structural steel; its strength comes from carbon and manganese without significant alloying.
What is the difference between Q235A, Q235B, Q235C, and Q235D? The grades differ in chemical limits and toughness, with D having the lowest carbon, phosphorus, and sulfur and the best low-temperature performance.
What is the tensile strength of Q235? The tensile strength is 370 to 500 MPa and the minimum yield strength is 235 MPa for thickness up to 16 mm.
Is Q235 weldable? Yes, Q235 has excellent weldability and supports arc, resistance, and gas welding.
What is the American equivalent of Q235? ASTM A36 is commonly considered the closest American equivalent, subject to design confirmation.