If you’re in construction, automotive, or manufacturing, hot rolled steel is likely a core material in your projects. It’s affordable, versatile, and easy to work with—making it one of the most widely used steels globally. This guide breaks down everything you need to know, from how it’s made to where it’s used, helping you choose and source hot rolled steel confidently.
1. Hot Rolled Steel: Manufacturing Process
Hot rolled steel starts as raw iron and goes through a precise, high-temperature process to form its final shape. Here’s the step-by-step hot rolling process flow:
- Raw Material Preparation: Iron ore is melted in a blast furnace to make molten steel, which is cast into billets (round/square for bars) or slabs (flat for sheets/plates) via continuous casting.
- Reheating: Billets/slabs are heated in a reheating furnace to 1,100–1,300°C (2,012–2,372°F)—this softens the steel for rolling.
- Roughing Mill: The heated metal is fed into a roughing mill (large rollers) to reduce its thickness by 50–70%. Operators control rolling force and reduction ratio (thickness before/after rolling) to hit initial specs.
- Finishing Mill: Next, the metal moves to a finishing mill (smaller, more precise rollers). Here, rolling speed (up to 10 m/s for coils) and roll profile (roller shape) are adjusted to create the final product—like hot rolled coils, plates, or bars.
- Descaling: During rolling, a rusty layer called mill scale forms. High-pressure water jets remove this scale in a process called scale removal (or descaling) to improve surface quality.
- Coiling/Cutting: For sheets/coils, the hot steel is wound into hot rolled coils (called hot band production). For plates/bars, it’s cut to length with shears.
- Cooling: The steel cools naturally (no quenching) to room temperature—this gives it its soft, ductile properties.
Key Fact: The entire process relies on tight temperature control—too hot, and the steel sags; too cool, and it’s hard to roll. A major mill in China reports that optimizing temperature reduced defects by 18%.
2. Hot Rolled Steel: Properties and Applications
Hot rolled steel’s unique properties make it ideal for specific jobs. Let’s break down its strengths, limitations, and top uses.
Core Properties
| Property | Typical Values (Mild Steel) | Why It Matters |
|---|---|---|
| Tensile Strength | 370–500 MPa | Strong enough for structural loads (e.g., beams) |
| Yield Strength | 250–350 MPa | Bends without breaking (good for forming) |
| Elongation | 20–30% | Ductile—can be stretched into shapes |
| Surface Finish | Rough (mill scale residue) | Needs grinding/painting for visible parts |
| Dimensional Accuracy | ±0.1mm (lower than cold rolled) | Acceptable for non-precision parts |
| Weldability | Excellent | Easy to weld without preheating |
Limitations to Note
- Corrosion Resistance: Poor—uncoated hot rolled steel rusts quickly outdoors (needs painting/galvanizing).
- Hardness: Low (110–130 BHN)—not ideal for wear-prone parts (use AR400 instead).
Top Applications
Hot rolled steel’s affordability and strength make it a staple in these industries:
- Construction: Used for structural steel (beams, columns), pipeline (water/gas lines), and building frames. A skyscraper in Dubai used 12,000 tons of hot rolled plates for its core structure.
- Automotive: Makes automotive components like chassis rails and engine brackets (its ductility allows bending into complex shapes).
- Machinery: Used for industrial machinery frames, gears, and shafts—easy to machine and weld.
- Appliances: Forms the inner frames of washing machines and ovens (hidden parts where surface finish doesn’t matter).
- Shipbuilding: Creates hull plates and decking—its toughness withstands ocean waves.
Common Product Forms
- Hot rolled plates: Thick (6–200mm) for heavy structures (e.g., bridge girders).
- Hot rolled sheets: Thin (1–6mm) for appliances and automotive parts.
- Hot rolled bars: Round/square (10–100mm) for fasteners and machine parts.
- Hot rolled coils: Continuous rolls for mass production (e.g., sheet metal for HVAC ducts).
3. Hot Rolled Steel: Market and Trade
The global hot rolled steel market is massive—driven by construction and automotive demand. Here’s a snapshot of its key trends and dynamics:
Market Size & Growth
- Global Market: Valued at $320 billion in 2023, with a 4.5% annual growth rate (expected to reach $400 billion by 2028).
- Top Producers: China (50% of global output), India, Japan, and the U.S. A Chinese mill like Baosteel produces 30 million tons of hot rolled steel yearly.
- Top Consumers: China (construction boom), the U.S. (automotive and infrastructure), and Europe (industrial machinery).
Trade Dynamics
- Key Exporters: China (exports to Southeast Asia), Japan (exports to the U.S. and Europe), and South Korea.
- Key Importers: Vietnam (construction), Mexico (automotive parts for the U.S.), and Germany (machinery).
- Price Fluctuations: Prices depend on iron ore costs (a major input) and demand. In 2023, prices rose 12% when iron ore prices spiked due to mine closures.
Market Drivers & Challenges
- Drivers: Global infrastructure spending (e.g., U.S. Bipartisan Infrastructure Law) and electric vehicle (EV) production (needs steel for batteries and frames).
- Challenges: Trade tariffs (e.g., U.S. 25% tariff on steel imports) and environmental regulations (mills must reduce carbon emissions).
4. Hot Rolled Steel: Quality and Standards
To ensure you’re getting high-quality hot rolled steel, look for compliance with global standards and strict quality control.
Key Standards
| Standard Organization | Common Specs | Use Case |
|---|---|---|
| ASTM (U.S.) | ASTM A36 (structural steel), ASTM A1011 (sheets) | Construction, automotive |
| AISI (U.S.) | AISI 1018 (mild steel bars) | Machinery parts, fasteners |
| JIS (Japan) | JIS G3101 SS400 (structural steel) | Shipbuilding, bridges |
| DIN (Europe) | DIN EN 10025 S235JR (mild steel) | Industrial frames, pipelines |
| ISO (Global) | ISO 630 (structural steel plates) | Cross-border projects |
Quality Control Measures
Mills use these steps to ensure quality:
- Chemical Composition Testing: Checks for elements like carbon (0.15–0.25% for mild steel) and manganese (1.0–1.6%) to ensure strength.
- Mechanical Testing: Performs tensile tests (to measure strength) and impact tests (to check toughness at low temperatures).
- Microstructure Analysis: Examines grain size (fine grains = stronger steel) and inclusion content (fewer inclusions = less brittleness).
- Dimensional Inspection: Uses calipers and laser scanners to verify thickness, width, and straightness (meets dimensional tolerances).
- Surface Inspection: Checks for defects like cracks, pits, or excess mill scale (removed via descaling).
Pro Tip: Always ask for a Mill Test Report (MTR) when buying hot rolled steel—it proves compliance with standards and includes test results.
Yigu Technology’s Perspective
At Yigu Technology, we prioritize hot rolled steel that meets ASTM and ISO standards to ensure client projects are reliable. For construction clients, we supply ASTM A36 hot rolled plates—optimized for welding and structural loads. For automotive parts makers, we offer hot rolled coils with tight thickness control (±0.05mm) to reduce waste. We also help clients navigate market fluctuations by locking in prices for 3–6 months, protecting them from iron ore-driven cost spikes. Our quality checks include chemical and mechanical testing, so clients trust they’re getting steel that performs.
FAQ
- Is hot rolled steel better than cold rolled steel for structural projects?
Yes—hot rolled steel has higher ductility and weldability, making it ideal for beams, columns, and pipelines. Cold rolled steel is harder but more expensive, so it’s better for precision parts (e.g., electronics casings). - How do I prevent hot rolled steel from rusting?
Add a protective coating: paint it (for indoor parts), galvanize it (zinc coating for outdoor use), or apply a rust-inhibiting oil (for machinery parts in storage). Uncoated hot rolled steel should be used indoors or in dry environments. - Can hot rolled steel be machined?
Yes—it’s easy to drill, cut, and mill due to its low hardness. However, its rough surface may require sanding after machining for precision parts. For high-wear parts, machine hot rolled steel first, then heat-treat it to increase hardness.
