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Carbon steel plates used in construction are classified by their chemical composition and mechanical properties, with grade designations varying by national standard. The Chinese GB/T standard covers Q235B (yield strength ≥235 MPa) and Q345B (yield strength ≥345 MPa), while ASTM A36 (yield strength ≥250 MPa / 36 ksi) is the most common international designation. For shipbuilding and offshore applications, classification society grades such as AH36, DH36, and EH36 apply, with the letter indicating impact test temperature (A: 0°C, D: -20°C, E: -40°C).
Each grade differs in carbon content, manganese levels, and micro-alloying elements that influence weldability, toughness, and strength. Q235B has a carbon equivalent typically below 0.40%, making it readily weldable without preheating for plates under 30 mm thickness. Q345B achieves higher strength through controlled manganese content (up to 1.60%) and micro-alloying with niobium or vanadium, but may require preheating for thicker sections during welding.
Jinan Zunkai Materials stocks all these grades in a range of thicknesses and can advise on grade substitution when specific designations are not available in the required dimensions.
For general structural steelwork, building frames, platforms, and secondary members where design stress is moderate, Q235B or A36 plates offer the most economical solution. These grades provide adequate strength for most commercial and industrial buildings when paired with proper connection design.
Q345B (equivalent to S355JR under EN 10025) is specified for primary structural members, bridge components, crane girders, and high-rise building columns where higher strength allows reduced section thickness and lower overall steel weight. The 40-50% higher yield strength compared to Q235B means designers can reduce plate thickness while maintaining load capacity.
For marine construction, ship hulls, and offshore platforms, AH36 and DH36 plates are mandatory under classification society rules. These grades combine the strength of Q345B-level material with guaranteed low-temperature impact toughness. DH36 maintains minimum 34J impact energy at -20°C, making it suitable for structures operating in cold waters.
Pressure vessel plates and boiler plate grades (such as Q245R and Q345R under GB 713) are used for tanks, reactors, and heat exchangers where elevated temperature strength and creep resistance are required. These grades include additional quality controls on sulfur and phosphorus content.
Plate thickness selection is governed by structural calculations, but procurement teams should also consider standard mill production ranges. Common thickness increments are 6, 8, 10, 12, 15, 20, 25, 30, 40, 50, 60, 80, 100, and 120 mm. Non-standard thicknesses may require mill rolling and longer lead times.
Width options at Zunkai Materials include 1,500 mm, 2,000 mm, and 2,500 mm as standard, with 3,000 mm and wider available on mill order. Surface condition matters: hot-rolled plates retain mill scale suitable for subsequent painting or galvanizing; shot-blasted and primed plates are ready for immediate fabrication and welding.
All construction-grade plates should be supplied with EN 10204 3.1 mill test certificates showing heat analysis and mechanical test results. For critical applications, EN 10204 3.2 certificates with third-party inspection witness are available. Impact testing requirements (temperature and minimum absorbed energy) must be clearly specified in the purchase order.
Zunkai Materials maintains traceability from mill heat number to delivered plate, ensuring full material pedigree for quality audits and project documentation.
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