How Are Steel Plates Manufactured? The Complete 2025 Process Guide
Bagikan
Table Of Content
Table Of Content
Steel plates are key parts in modern construction, shipbuilding, heavy machinery, and many other industries. Their production follows a precise process with multiple stages.
This process changes raw steel slabs or billets through heating and rolling to get specific sizes and thickness, often ending with controlled cooling and finishing treatments.
Learning how steel plates are made helps us understand why they work well in many tough jobs. This article will first explain how steel is made, then detail the steps of plate manufacturing, finishing work, and quality checks.
Understanding the Foundation: A Primer on How Steel is Manufactured Step by Step
Before making a steel plate, we must first make steel itself. Steel production turns raw materials into a strong, versatile metal. This section explains how steel is made step by step, setting the stage for plate production.
Raw Material Preparation
The main raw materials for steel production are iron ore, coke, and limestone. Iron ore provides the iron.
Coke, made from coal, serves as fuel and helps remove oxygen from the iron ore. Limestone removes impurities.
The quality of these materials matters a lot; high-grade iron ore with few impurities is essential for good steel. A typical mix needs about 1.6 tons of iron ore, 0.5 tons of coke, and 0.25 tons of limestone to make one ton of molten iron.
Iron Making (Blast Furnace)
The blast furnace is where iron ore becomes molten iron, also called hot metal or pig iron.
This happens by the process of reducing iron ore at high temperatures.
Hot air blasts into the furnace, lighting the coke. The carbon in the coke reacts with oxygen in the iron ore, leaving molten iron with high carbon content (about 4-4.5%).
Slag containing impurities floats on the molten iron and gets removed regularly.
Steelmaking (Primary Steelmaking)
The molten iron from the blast furnace (or recycled steel scrap) gets refined into crude steel. This step greatly reduces carbon and removes other impurities.
Two main methods are used: the Basic Oxygen Furnace (BOF) and the Electric Arc Furnace (EAF).
The BOF process uses mostly molten iron (70-80%) with some scrap steel. Pure oxygen blows through the molten metal to remove excess carbon and impurities. This quick process makes a batch of steel in about 40-50 minutes.
The EAF process mainly uses recycled steel scrap, though it can also use direct reduced iron or hot metal. Powerful electric arcs melt the scrap, and oxygen may help refine the steel. Modern steelmaking processes like BOF and EAF work very efficiently.
Worldwide, BOF makes about 70% of steel, with EAF making the other 30%. EAFs can use various raw materials and may save energy, especially when using lots of scrap and powered by clean electricity.
Secondary Steelmaking (Ladle Metallurgy)
After primary steelmaking, the molten steel goes through secondary steelmaking, or ladle metallurgy. This key stage fine-tunes the steel's chemistry and temperature.
The process includes removing excess oxygen, taking out dissolved gases like hydrogen and nitrogen, and adding precise amounts of alloys to get specific grades and properties.
Removing sulfur and controlling inclusions also happens here, greatly affecting the steel's cleanliness and performance.
Casting – Solidifying Molten Steel
The refined molten steel then solidifies into semi-finished shapes. The main method is continuous casting methods.
In continuous casting, molten steel pours from a ladle into a tundish, then into a water-cooled copper mold. As the steel shell hardens, it gets pulled out continuously, cooled by water sprays, and cut to desired lengths.
This efficient process makes consistent quality slabs, blooms, or billets. Slabs, which are rectangular (about 200-300 mm thick, 1000-2500 mm wide), are the main starting material for steel plates.
Ingot casting, an older method where steel goes into individual molds, is less common today but might still be used for very large or special plate production.
The Core Process: From Steel Slab to Finished Plate – How Steel Plates Are Manufactured
With steel slabs made, the journey to create steel plates begins. This section details the main steps that change a thick slab into a precise plate, answering: How are steel plates manufactured?
Starting Material: The Steel Slab (or Billet/Ingot)
Steel slabs are the typical starting material for plate production. These semi-finished products come from the continuous caster or, less often, as ingots.
Before processing, slabs get checked for surface defects. Any cracks or imperfections are removed, often by scarfing (using a torch to melt away defects) or grinding, to ensure a quality final plate.
Reheating the Steel
The prepared slabs must be heated evenly to a temperature that makes them easy to shape. This temperature is typically above the point where the steel can reform its grain structure, allowing for easier shaping and better properties.
Slabs go into reheating furnaces, such as walking beam furnaces or pusher-type furnaces. These furnaces slowly heat the steel to about 1100°C to 1250°C (2012°F to 2282°F) for common carbon steels. Even heating is crucial to avoid problems during rolling.
Hot Rolling – The Primary Shaping Process
Hot rolling is the heart of steel plate manufacturing. The hot slab passes repeatedly between sets of large, powerful rolls.
Each pass makes the slab thinner and longer, and somewhat wider. The huge forces reshape the steel, and the high heat makes this shaping possible.
Different types of rolling mills are used. Reversing mills pass the slab back and forth through one set of rolls, changing the gap between rolls each time. Steckel mills have heated coil boxes on both sides of a reversing mill, allowing thinner plates to be made. Tandem mills have several rolling stands in a line, where the plate gets thinner as it moves through each stand.
An important distinction exists between Plate Mill Plates (PMP) and Continuous Mill Plates (CMP), also known as Hot Strip Mill Plates.
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Feature
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Plate Mill Plates (PMP)
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Continuous Mill Plates (CMP) / Hot Strip Mill Plates
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Starting Material
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Ingots or thick slabs
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Thinner slabs
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Rolling Process
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Rolled one plate at a time, often in reversing mills
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Rolled continuously in a hot strip mill, then cut
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Typical Thickness
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Thicker (e.g., >40mm, up to several hundred mm)
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Thinner to medium (e.g., common up to 25mm, can be thicker from some mills)
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Typical Width/Length
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Can be very wide and long, custom sizes available
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More standardized widths from coil, length cut to order
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Production Volume
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Lower volume, more specialized
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Higher volume, more economical for standard sizes
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Surface Finish
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Can vary, may require more surface conditioning
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Generally good, uniform surface from continuous process
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Applications
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Heavy structural, shipbuilding, boilers, pressure vessels, large machinery components
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General construction, lighter structural, some machinery, automotive parts (from cut coil)
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Flexibility
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Higher for custom chemistries and dimensions
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Less flexible for very small, specialized orders
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Internal Quality
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Can be excellent with proper ingot/slab casting & rolling
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Generally good, consistent due to continuous process
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PMPs are often made for very thick plates, special alloys, or custom sizes not easily made in a continuous mill. CMPs are usually more cost-effective for standard sizes and thinner gauges.
During hot rolling, the steel's rough grain structure becomes finer and more even, which improves its properties, especially toughness. Careful control of rolling temperatures, reductions per pass, and total reduction is vital for achieving the desired thickness, width, flatness, and properties.
Controlled Cooling / Direct Quenching (Optional but Important for Properties)
Right after hot rolling, many modern steel plates undergo controlled cooling or direct quenching. This isn't just letting the plate cool in air; it involves specific cooling methods to get better properties.
Processes like Thermo-Mechanical Controlled Processing (TMCP) combine specific rolling schedules with carefully controlled cooling rates. Accelerated cooling systems use water jets to cool the plate much faster than air would.
Direct quenching rapidly cools the plate from the rolling temperature to a much lower temperature. These processes can create fine-grained structures, giving higher strength, better toughness, and improved weldability, often reducing the need for expensive alloys or later heat treatments.
Cutting and Sizing
Once the plate has been rolled and (if needed) cooled in a controlled way, it is cut to its final or near-final size.
Different cutting methods are used depending on the plate thickness, edge quality needed, and production volume. Shearing works well for thinner plates.
For thicker plates, heat-based cutting methods like flame cutting, plasma arc cutting, or laser cutting are used. Each method has benefits in terms of speed, precision, and how much the cut edge is affected by heat.
Leveling
Hot rolling and cooling can sometimes cause waves or buckles in the plate. To make sure the plate is flat enough, it passes through a leveler.
Roller levelers have a series of offset rolls that bend the plate back and forth as it moves through, relieving internal stress and making a flat, even product. This step is crucial for plates used where precise fitting is needed.
Finishing Touches and Quality Assurance
After the main shaping processes, steel plates often get more treatments to meet customer needs and always undergo strict quality checks. These final steps ensure the plates will work well for their intended use.
Heat Treatment (Post-Rolling, if not done during controlled cooling)
Depending on the steel grade and desired properties, plates may get additional heat treatments after rolling and cutting.
Annealing involves heating the steel to a specific temperature and then cooling it slowly, mainly to soften the steel, improve machinability, and reduce internal stress.
Normalizing means heating the steel above its upper critical temperature, then air cooling it. This refines the grain structure and improves evenness of properties, especially toughness.
Quenching and Tempering (Q&T) is a two-step process. Quenching heats the steel to a high temperature and then rapidly cools it (in water or oil) to make it very hard. This is followed by tempering, which reheats the plate to a lower temperature and holds it there to reduce brittleness, relieve stress, and get the right balance of hardness, strength, and toughness. Q&T plates are known for high strength and excellent toughness, good for demanding uses.
Surface Treatments (Optional)
Some uses require specific surface conditions.
Shot blasting or abrasive blasting removes mill scale (an oxide layer formed during hot rolling) and cleans the plate surface. This creates a better surface for painting or coating.
Pickling involves dipping the plate in an acid bath to remove scale and rust.
Plates may also be primed or painted to prevent rust or for appearance, depending on how they'll be used.
Quality Control and Testing – Ensuring Excellence
Quality control is a key part of steel plate manufacturing, done at various stages to ensure the final product meets all requirements.
Dimensional checks verify thickness, width, length, and flatness against the ordered tolerances.
Mechanical testing is crucial. Tensile tests measure yield strength, tensile strength, and elongation. Impact tests check the plate's toughness and resistance to breaking, especially in cold temperatures. Hardness tests check the surface hardness.
Non-destructive testing (NDT) methods find internal or surface defects without damaging the plate. Ultrasonic testing (UT) detects internal flaws like laminations or inclusions. Magnetic particle testing (MT) and liquid penetrant testing (PT) find surface-breaking defects.
Chemical analysis verifies that the steel composition meets the specified grade requirements.
Complete documentation, including Mill Test Certificates (MTCs), provides traceability and confirms that the plate meets relevant industry standards from ASTM, EN, API, or other organizations. These certificates show the chemical composition, mechanical properties, heat treatment, and testing results for each plate or batch.
Applications and Importance of Steel Plates
The careful manufacturing process creates steel plates that are essential across many industries. Their versatility, strength, and durability make them basic materials for modern society.
In construction, steel plates help make structural sections for buildings, bridges, and stadiums. Shipbuilding needs various grades of steel plates for hulls and superstructures that can withstand harsh ocean conditions.
Pressure vessels, boilers, and storage tanks used in oil and gas, chemical, and power industries are built from special steel plates designed for high-pressure and high-temperature service. Heavy machinery and equipment, from earthmovers to industrial presses, use thick, high-strength plates for their frames and key parts.
The car industry uses steel plates (often cut from coil) for vehicle frames and safety components. In the energy sector, plates make wind turbine towers, offshore platforms, and pipelines. The precision and quality control in manufacturing ensure these plates work reliably and safely in their demanding roles.
Conclusion
The process of how steel plates are manufactured shows advanced engineering and metallurgical science. It starts with careful steel production, followed by a series of controlled shaping and heating processes.
From reheating massive slabs to precisely rolling them to thickness, often using advanced cooling strategies and finishing treatments, each step matters. The extensive quality checks ensure that the final steel plates have the specific properties needed for their intended uses.
As a result, steel plates serve as the strong foundation for countless structures and machines, highlighting their vital role in global infrastructure and industrial development. The complexity and precision involved ensure these common materials continue to support progress and innovation.