H-beams are the primary load-bearing elements in modern steel construction, and the quality of the finished section begins long before it reaches the fabrication shop. Two fundamentally different production routes dominate the industry: hot rolling, which forms the H-shape from a single piece of steel with no weld seam, and welded fabrication, which assembles the section from three steel plates.
Each route has its own process logic, dimensional capabilities, and quality control requirements. This guide traces both paths from raw material to finished product, covering the critical parameters at each stage.
Part 1: The Hot-Rolling Route
Hot-rolled H-beams are produced as a single, seamless section. The process begins with steelmaking and ends with a straightened, cut-to-length beam that meets dimensional and mechanical specifications.
Step 1: Steelmaking and Refining
The process chain begins upstream of the rolling mill. A representative industrial route for hot-rolled H-beam production follows:
Molten iron → hot metal pretreatment → converter smelting → LF refining → continuous casting of blooms
The steel chemistry is adjusted to the target grade during converter smelting and ladle furnace (LF) refining. Alloying additions are made to achieve the required strength, toughness, and weldability. For demanding grades, cerium-iron rare earth alloys may be added at the argon station to control inclusion shape and improve toughness. Vacuum degassing may be performed as needed to reduce hydrogen and nitrogen content.
Step 2: Continuous Casting of Blooms
The refined steel is continuously cast into blooms—rectangular or near-rectangular semi-finished sections. For H-beam production, a bloom thickness of 200 mm or more is preferred from a productivity standpoint, while a thickness of 350 mm or less is preferred to reduce segregation and ensure uniform heating during hot rolling.
For certain product families, near-net-shape beam blanks may be cast instead of rectangular blooms. Beam blanks approximate the final H-profile, reducing the amount of rolling required to reach the finished shape.
Step 3: Reheating
The bloom is reheated in a walking beam reheating furnace to a temperature suitable for hot rolling. The reheating temperature is typically in the range of 1100 to 1350°C.
The temperature selection is a trade-off:
- Below 1100°C: Deformation resistance increases unacceptably.
- To dissolve carbide- and nitride-forming elements such as Nb: A lower limit of 1150°C or higher is preferred.
- For thin sections: Heating to 1200°C or higher is preferred because cumulative rolling reduction is greater.
- Above 1350°C: Surface scale on the bloom may liquefy and damage the furnace interior, so 1300°C or lower is preferred as an upper limit to suppress structure coarsening.
Step 4: Primary Descaling
After reheating, the oxidized surface layer (mill scale) is removed by high-pressure water descaling. Descaling is critical: if scale is rolled into the surface, it creates surface defects that compromise appearance and corrosion resistance.
Step 5: Roughing (Blooming)
The reheated bloom passes through a blooming mill or breakdown mill, which reduces the cross-section and begins to approximate the H-profile. The roughing stage produces a “rough rolled steel billet having a web and flanges” that is then refined in the finishing train.
Step 6: Universal Rolling (Intermediate and Finishing)
The defining feature of H-beam rolling is the universal mill. A universal mill contains two pairs of rolls:
- Horizontal rolls, which reduce the web thickness.
- Vertical rolls, which reduce the flange thickness and control flange width.
Because both the web and the flanges are reduced simultaneously, the universal mill can produce a true H-profile with parallel flanges in a single pass—something a conventional two-high mill cannot do.
In a typical layout, the mill group performs intermediate rolling by reciprocating rolling, followed by one-pass finishing in a universal finishing mill. A representative industrial line uses 11 stands of universal continuous rolling.
Controlled Rolling and Interpass Cooling
For higher-strength and tougher grades, controlled rolling is employed in the finishing stage. Rolling temperature and reduction are carefully controlled, and water-cooling rolling between passes may be performed for one or more passes to refine the microstructure.
A more specialized technique applies forcible water cooling to the outer surfaces of the flanges during intermediate rolling, prior to final rolling. The cooling is terminated so that the flange outer surfaces return to a temperature above 700°C, and the cooling-and-termination cycle is repeated to refine the microstructure of the flange surface to a predetermined depth. This addresses a specific challenge of H-beams: because the fillet region (where flange and web meet) receives less working than the flange, it is difficult to refine grains there, and surface microstructure control becomes critical for toughness.
Step 7: Hot Sawing and Sampling
After rolling, the beam is hot-sawed to sample and to trim the ends. Samples are taken for mechanical property and chemical composition verification.
Step 8: Controlled Cooling
The beam is transferred to a walking beam cooling bed, where it cools under controlled conditions. Cooling rate affects the final microstructure and residual stress distribution. Uneven cooling between the thicker web-flange junction and the thinner flange tips can introduce residual stresses and distortion if not managed.
Step 9: Straightening
After cooling, the beam passes through a straightening machine to correct any bending, camber, or twist developed during rolling and cooling. Straightness is critical for fit-up during fabrication and erection.
Step 10: Inspection and Cutting
The straightened beam undergoes inspection of appearance and surface quality, followed by final sawing to commercial lengths. Inspection covers dimensions (web height, flange width, web and flange thickness), straightness, surface defects, and—for critical applications—ultrasonic testing for internal defects.
Hot-Rolling Process Summary
| Stage | Key Parameter | Purpose |
|---|---|---|
| Steelmaking | Chemistry per grade | Achieve mechanical properties |
| Casting | Bloom thickness 200–350 mm | Balance productivity and segregation |
| Reheating | 1100–1350°C | Enable deformation; dissolve alloying elements |
| Descaling | High-pressure water | Remove surface scale |
| Roughing | Breakdown mill | Reduce section, form rough profile |
| Universal rolling | Horizontal + vertical rolls | Form parallel flanges and web simultaneously |
| Controlled cooling | Walking beam cooling bed | Control microstructure and residual stress |
| Straightening | Roller or press straightener | Correct bending and twist |
| Inspection | Dimensional, visual, UT | Verify specification compliance |
Part 2: The Welded (Built-Up) Route
Welded H-beams—often called BH beams (built-up H beams)—are fabricated by welding three steel plates together to form an H-shaped cross-section. This route is used when the required section is larger than what can be produced by rolling, when a custom geometry is needed, or when production economics favor plate fabrication.
The Two Main Fabrication Methods
Two principal fabrication sequences are used for BH beams:
1. Pre-assembly method: Three steel plates are assembled and welded into an H-shape, and then scalloping or other processing is performed. In this sequence, the beam is welded first, then detailed.
2. Groove-first method: Scallop cutting and other processing are performed first, and then the three steel plates are welded together into an H-beam. This sequence prepares the plate edges for welding before assembly, which can improve access and weld quality at the beam ends.
Welding Processes
The four main fillet welds connecting the web to the two flanges can be made by submerged arc welding (SAW) , gas shielded welding, high-frequency welding, or manual metal arc welding. Submerged arc welding is the dominant industrial process and may use single-wire, twin-wire, or triple-wire configurations.
For single-wire SAW, welding is typically performed in the flat (downhand) position to ensure good weld formation and penetration.
A Recent Innovation: smarTABH®
A significant development in BH beam fabrication is JFE Steel’s smarTABH® method, developed with Utsunomiya University, Nihon Sekkei, and Yonemori Corporation. The method eliminates the need for conventional scallop back welding and processing of beam end joints. Instead, welding is performed up to solid tabs placed near the scallop area, which creates a larger flexible area at the beam flange. This realizes greater plasticity than conventional methods, mitigating concentrated stress and strain during seismic events.
The method applies to beam sections with flange thicknesses up to 40 mm and does not restrict beam height or width, making it suitable for a wide range of applications. It can also be used for BH beams with widened flange ends. The load-bearing capacity and plastic-deformation performance of joints made with this method have been verified through structural testing and finite element analysis.
Deformation Control in Welded H-Beam Fabrication
Welding introduces non-uniform heating and cooling, which generates residual stress and distortion. Practical measures for controlling deformation in welded H-beam fabrication include:
- Reserving shrinkage allowance to compensate for weld contraction.
- Applying reverse deformation (pre-setting) before welding so that the beam distorts into the desired shape.
- Developing a rational welding procedure specifying pass sequence, heat input, and interpass temperature.
- Pre-cambering to offset predicted deflection.
Correction methods for the three main distortion modes—flexural deformation, camber deformation, and angular deformation—are applied after welding to bring the beam within tolerance.
Hot-Rolled vs. Welded H-Beams: Process Comparison
| Feature | Hot-Rolled H-Beam | Welded (BH) H-Beam |
|---|---|---|
| Seam | None | Four fillet welds (web-to-flange) |
| Section size | Limited to mill roll sizes | Unlimited—any plate combination |
| Dimensional accuracy | Mill tolerances | Can match or exceed rolled tolerances |
| Residual stress | From rolling and cooling | From welding (higher, localized) |
| Production volume | High (continuous mill) | Low to medium (job-specific) |
| Cost | Lower for standard sizes | Higher per tonne; economical for custom/large sections |
| Primary application | Standard structural sections | Large-span, heavy, or custom geometry |
Part 3: Quality Control Across Both Routes
In-Process Control
| Checkpoint | Hot-Rolled Route | Welded Route |
|---|---|---|
| Chemistry | Ladle analysis before casting | Plate certification (mill test certificates) |
| Heating temperature | Furnace thermocouples; 1100–1350°C | Preheat and interpass temperature monitoring |
| Rolling/forming | Roll gap, pass schedule, interpass cooling | Fit-up alignment, root gap, bevel angle |
| Welding | Not applicable | Weld parameter monitoring; visual inspection per pass |
| Cooling | Cooling bed uniformity | Controlled cooling after welding to limit distortion |
| Straightening | Straightness measurement after straightener | Post-weld straightening or correction |
Finished Product Verification
Both routes require verification of:
- Dimensions: Web height, flange width, web and flange thickness, length, squareness.
- Straightness and twist: Typically within specified tolerances (e.g., ≤0.1% of length for straightness).
- Surface quality: Freedom from cracks, laps, seams, and excessive scale.
- Mechanical properties: Tensile, yield, elongation, and impact toughness—verified by sampling in the hot-rolled route and by plate certification plus weld testing in the welded route.
- Weld integrity (welded route): Visual inspection, and where specified, ultrasonic or radiographic testing of the four main fillet welds.
Frequently Asked Questions
Q1: What is the fundamental difference between hot-rolled and welded H-beams?
Hot-rolled H-beams are formed as a single piece of steel by passing a heated bloom through universal mills, producing a seamless section with no weld. Welded H-beams are fabricated by welding three steel plates (two flanges and one web) into an H-shape, allowing unlimited section sizes but introducing weld seams and welding residual stress.
Q2: Why is a universal mill essential for hot-rolled H-beams?
A universal mill has both horizontal rolls (which reduce the web) and vertical rolls (which reduce the flanges) operating simultaneously. This allows the true H-profile with parallel flanges to be formed efficiently. A conventional two-high mill cannot reduce the web and flanges in the same pass.
Q3: What reheating temperature is used for hot-rolled H-beams?
The bloom is typically reheated to 1100–1350°C. Below 1100°C, deformation resistance is too high; above 1350°C, surface scale may liquefy and damage the furnace. For grades containing Nb, 1150°C or higher is preferred to dissolve carbonitrides.
Q4: What is controlled rolling and why is it used?
Controlled rolling is a method in which rolling temperature and reduction are carefully controlled, often with interpass water cooling, to refine the austenite grain structure. This improves strength and toughness without requiring additional alloying. It is particularly important for H-beams because the fillet region receives less working than the flanges.
Q5: What are the two main welded H-beam fabrication methods?
The pre-assembly method assembles and welds three plates into an H-shape first, then performs scalloping and detailing. The groove-first method performs scallop cutting and edge preparation first, then welds the three plates together.
Q6: What is the smarTABH® method?
smarTABH® is JFE Steel’s welding method for built-up H-beams that eliminates conventional scallop back welding. Welding is performed to solid tabs near the scallop area, creating a larger flexible area in the beam flange that improves plastic deformation capacity under seismic loading.
Q7: How is distortion controlled in welded H-beam fabrication?
Key measures include reserving shrinkage allowance, applying reverse deformation before welding, developing a rational welding procedure (pass sequence and heat input), and pre-cambering. Post-weld correction addresses flexural, camber, and angular deformation.
Conclusion
H-beam production follows one of two distinct process routes, each with its own logic and capabilities.
The hot-rolled route begins with steelmaking and continuous casting, proceeds through reheating and descaling, and uses universal rolling to form the H-profile with parallel flanges in a single-piece section. Controlled rolling, interpass cooling, and controlled cooling on the walking beam bed refine the microstructure, while straightening and inspection ensure dimensional accuracy. This route delivers standard sections at high volume with no weld seam.
The welded (BH) route fabricates the section from three steel plates, using submerged arc welding as the dominant joining process. It offers unlimited section size and custom geometry at the cost of weld seams and welding-induced residual stress. Modern innovations such as smarTABH® are improving both fabrication efficiency and seismic performance.
