Hot Rolled H Beam Q235 and SS400: Product Overview
Hot rolled H beams are produced by rolling reheated blooms through universal mills that form the web and flanges simultaneously, so the section exits the mill with a parallel flange face, a defined flange-to-web radius and a consistent weight per metre. This differs from welded H sections, where the flange-to-web joint is a fusion weld. The hot rolled version has a continuous grain flow that runs through the fillet radius, giving predictable behaviour under static and repeated loading, and its parallel flanges simplify bolted connection design and end-plate detailing. Q235 and SS400 are the two grades most often supplied for general construction, industrial workshops and warehouse frames, and because their mechanical properties are close they are frequently treated as alternatives in the same project.
Q235 and SS400 Compared
Q235 is specified in GB/T 700-2006 and SS400 in JIS G 3101. The designation systems are not identical: Q235 denotes a minimum yield strength of 235 MPa for thickness up to 16 mm, while SS400 refers to a minimum tensile strength of 400 MPa, with a minimum yield strength of 245 MPa for the same thickness range. In service the two behave very similarly.
| Property | Q235 (GB/T 700-2006) | SS400 (JIS G 3101) |
|---|---|---|
| Minimum yield strength, t ≤ 16 mm | 235 MPa | 245 MPa |
| Tensile strength | 375–500 MPa | 400–510 MPa |
| Maximum carbon | 0.22% (grade A) | 0.25% |
| Maximum phosphorus | 0.045% | 0.050% |
| Maximum sulphur | 0.050% (grade A) | 0.050% |
| Impact testing | Grade B tested at +20 °C, grade D at −20 °C | Not mandatory for the base grade |
Both grades are low-carbon structural steels with low carbon equivalent, so they weld with ordinary consumables and need no special storage beyond normal cleanliness. When a design demands verified low-temperature toughness, a Q235 grade with a defined impact test, or a normalised or micro-alloyed grade supplied to ASTM A572/A572M or GB/T 1591, should be selected instead of relying on the base specification.
Section Sizes, Mass and Tolerances
Hot rolled H sections are standardised in the GB/T 11263 HW, HM and HN series and in the corresponding JIS G 3192 range. Flange widths commonly run from 100 mm to 400 mm, section heights from 100 mm to 900 mm, flange thickness from 6 mm to 32 mm and web thickness from 4.5 mm to 20 mm. Frequently specified sizes and their nominal masses are listed below.
| Designation (H × B × t1 × t2) | Mass (kg/m) | Typical role |
|---|---|---|
| 100 × 100 × 6 × 8 | 17.2 | Purlins, secondary framing, mezzanine beams |
| 150 × 150 × 7 × 10 | 31.5 | Light roof beams, small spans |
| 200 × 200 × 8 × 12 | 50.5 | Multi-storey frames, floor beams |
| 300 × 300 × 10 × 15 | 94.5 | Main frames, moderate crane girders |
| 400 × 400 × 13 × 21 | 172 | Heavy columns, long-span transfer beams |
The mass per metre of any H section is obtained from the section area multiplied by the density of steel, taken as 7.85 g/cm³: web area plus twice the flange area, expressed in the same units, then converted to kilograms. Rolled tolerances in GB/T 11263 and JIS G 3192 govern section height and flange width deviation, flange squareness, web off-centre, longitudinal bow, and the permissible variation in mass, and they are tighter than the tolerances applied to welded sections of the same nominal size.
Fabrication and Welding
Q235 and SS400 H beams cut, drill, cope and weld with standard shop equipment. Their low carbon content keeps the risk of hydrogen-induced cracking low, and shielded metal arc, gas metal arc and flux-cored arc welding all produce sound joints, generally without preheating for material under 20 mm thick. Above that thickness, or when welding at low ambient temperature, preheating in the range 50–100 °C is prudent, and consumables should be stored and handled to avoid moisture pickup. Beam-to-column connections usually combine shop welding of stiffeners and end plates with site bolting, and hole positions drilled with tungsten-carbide tooling hold their tolerance well. Thermal cutting leaves a heat-affected edge that should be dressed back before a full-penetration weld is deposited, and weld access holes must be cut to the radius given in the connection detail to avoid a notch at the flange web junction.
Surface Condition and Corrosion Protection
As-rolled H beams leave the mill with a dark mill scale surface and a light oxide layer. Mill scale offers no lasting protection, and because it is cathodic to the underlying steel it can accelerate localised attack if left under a paint film, so blast cleaning to a recognised surface preparation grade is normally specified before coating. Hot-dip galvanizing to ISO 1461 or ASTM A123/A123M provides a zinc coating of typically 70–85 µm on thick sections and is well suited to exposed, humid or coastal sites. Shop-applied epoxy, polyurethane or alkyd systems are used for indoor and sheltered structures, with a zinc-rich primer recommended where the steel will remain exposed. Beams can also be supplied shot blasted, primed, or cut to project lengths with a saw or plasma process, with the cut ends of galvanised material sealed by a zinc-rich repair coating.
Frequently Asked Questions
Q: What is the difference between Q235 and SS400 H beams?
Q235 is a GB/T 700-2006 grade with a 235 MPa minimum yield strength, while SS400 is a JIS G 3101 grade defined by a 400 MPa minimum tensile strength and a 245 MPa minimum yield strength. Their chemistry and weldability are close, so in many general structural applications they are treated as interchangeable, although a project specification may require one standard to be followed.
Q: Which standards cover hot rolled H sections?
Section dimensions and tolerances are given in GB/T 11263 for the HW, HM and HN series and in JIS G 3192 for Japanese sizes, while the material grades are covered by GB/T 700 and JIS G 3101. General tolerance requirements for rolled shapes may also be referenced through ASTM A6/A6M when a project uses American practice.
Q: How is the weight per metre of an H beam calculated?
Multiply the cross-section area by the density of steel, 7.85 g/cm³. For a nominal parallel-flange section the area equals web height times web thickness plus twice the flange width times flange thickness. A 200 × 200 × 8 × 12 mm beam works out at about 50.5 kg/m and a 300 × 300 × 10 × 15 mm beam at about 94.5 kg/m.
Q: Can Q235 and SS400 H beams be welded on site?
Yes. Both are low-carbon steels that accept shielded metal arc, gas metal arc and flux-cored arc welding with standard consumables. Preheating is generally unnecessary below 20 mm thickness in mild weather, but thicker sections, low ambient temperatures and heavily restrained joints call for preheat in the 50–100 °C range and for dry, correctly stored electrodes.
Q: How are hot rolled H beams protected against corrosion?
Because Q235 and SS400 contain no chromium or other passivating element, protection comes from a coating. Hot-dip galvanizing to ISO 1461 or ASTM A123/A123M is typical for outdoor structures, while blast cleaning followed by a zinc-rich primer and an epoxy or polyurethane topcoat is used for sheltered and painted applications. Coastal and chemical plant environments normally require a duplex system.
Q: What dimensional tolerances apply to hot rolled H beams?
Rolled sections are checked for section height and flange width deviation, flange thickness, flange squareness, web off-centre and longitudinal bow, with the permissible limits set out in GB/T 11263 or JIS G 3192. Mass variation against the nominal value is also controlled, and inspection reports record the measured values for each heat.
Q: Where are Q235 and SS400 H beams most commonly used?
Typical applications include industrial workshop frames carrying overhead cranes, warehouse main frames with long column spacings, multi-storey building frames and mezzanines, equipment support structures, and temporary works such as trestles and platforms. The parallel flanges make them convenient for bolted steelwork as well as welded frames.