During a hot rolling process, steel is rolled beyond its recrystallization temperature to create a finished rolled steel product. This makes it an easier shape and form for different steel projects such as welding and construction. However, the hot-rolling process requires absolute precision. This article will cover everything you need to know about hot rolling steel to create the best product possible.
Basics of the Hot Rolling Process
Description of the Hot Rolling Process
The process for hot rolling steel is as follows:
- The steel slab or billet is heated to a high temperature in a furnace. This needs to be above its recrystallization temperature.
- The heated steel is passed through a roughing mill, usually a series of large, heavy-duty rolls. This reduces the thickness and width of the steel. It also shapes it into a rough form, like a strip or slab.
- The partly formed steel is passed through an intermediate mill. This shapes the steel’s final dimensions into a specific width or gauge.
- After going through the intermediate mills, the steel goes through a finishing mill. This set of smaller rolls applies a final finish to the steel.
- Once the steel has been rolled into its final shape, it is cooled to room temperature.
Types of Hot Rolling Mills
The different types of hot rolling mills include:
Flat Rolling Mills
Flat rolling mills roll flat products such as sheets and plates. They consist of multiple stands of rolls that are arranged in a series. Each stand performs a specific function, such as roughing, intermediate, or finished rolling.
Shape Rolling Mills
Shape rolling mills are used to produce steel with non-flat sections. This includes rounds, squares, channels, and I-beams. These mills have rolled with specific shapes and grooves to add the cross-sectional shape to the steel.
Bar and Wire Rod Mills
Bar and wire rod mills are used for producing hot roll steel bars and wire rods. These mills have two series of stands for reducing the steel slab or billet size. This allows it to be shaped into bars or wire rods with specific diameters.
Universal Rolling Mills
Universal rolling mills are capable of rolling both shaped and flat products. They have multiple sets of rolls which can be adjusted to roll various types of products. This includes plates, sheets, rails, and sections.
Key Equipment Used in Hot Rolling
The key equipment you need for hot rolling steel includes:
- Reheating furnaces
Reheating furnaces heat the steel slabs or billets to the required rolling temperature. They use different energy sources, such as natural gas and coal.
Rolling mills are the primary equipment used when hot rolling the steel. They come in various types, such as flat rolling mills, shape rolling mills, bar and wire rod mills, and universal rolling mills.
Rolls are the primary tool used in rolling mills to shape steel. Rolls are made of high-quality steel and are built to withstand extreme temperatures and pressures.
Cooling systems are used to control the temperature of the steel during and after the hot rolling process.
Shears and Saws
Shears and saws cut steel products to the desired length after rolling. They can be mechanical or hydraulic and are typically used in plate and hot strip mills.
What Are the Temperature and Speed Concerns to Address During the Hot Rolling Process?
Considerations related to temperature and speed in hot rolling include:
- Rolling temperature: The rolling temperature determines the extent to which the steel’s shape can change. It depends on the type of steel being rolled and your desired end product. If the temperature gets too low, the metal cracks or has an incomplete shape. On the other hand, the steel can lose shape and become soft if the temperature is too low.
- Reduction ratio: This is the reduction in the thickness of the steel as it goes through the rolls. Higher reduction ratios lead to better mechanical properties and higher surface quality. However, it relies on higher rolling forces to work. This increases the risk of surface defects like roll marks and cracks.
- Rolling speed: This is the speed at which steel goes through the rolls of the rolling mills. It affects rolled steel products’ productivity, accuracy, and surface quality. With a higher rolling speed, productivity increases, but so does the risk of surface defects. Alternatively, lower rolling speeds can lead to better surface quality but reduced productivity.
Advantages and Disadvantages of Hot Rolling
Advantages of Hot Rolling
The key advantages of hot rolling include the following:
Improved Mechanical Properties
Hot rolling allows you to shape metal into whatever finished product you want. This improves the mechanical properties of the rolled steel products. The increased level of plastic deformation also reduces internal defects and improves the overall product quality.
Due to its continuous and automated nature, hot rolling results in high productivity. Continuous rolling mills and reheating furnaces also create a continuous flow of material. This removes the need for frequent starts and stops.
Hot rolling is a versatile process that can create products of different shapes and sizes. These include sheets, plates, rods, and bars.
Disadvantages of Hot Rolling
Major downsides of hot rolling include:
Potential for Surface Defects
When you hot roll steel, the high temperatures you create can result in oxidation and scaling on the steel’s surface. This can lead to defects such as pits and cracks.
Higher Energy Consumption
The heating of steel slabs and billets in reheating furnaces demands a lot of energy. Additionally, the high temperatures in the hot rolling process can lead to heat loss in the system. This will add to the energy requirements and increase operating costs.
Varieties of Hot Rolled Steel Products
Common Types of Hot-Rolled Steel Products
There are varieties of products created from hot-rolled steel, including:
- Sheets: These are flat steel products used in projects requiring a wide and thin form of steel. This includes automobile body panels and appliances. Like stainless steel sheets, hot rolled steel sheets are known for their strengths and good mechanical properties.
- Coils: Hot rolled steel coils are continuous strips of steel that are wound into stainless steel coils and used to manufacture pipes.
- Plates: Hot rolled steel plates are used for projects that require thicker and larger steel sheets. This includes construction equipment and heavy machinery.
- Bars: Hot rolled steel bars are straight and long steel products used in machinery manufacture and construction.
Uses and Applications of Hot-Rolled Steel
Hot-rolled steel has multiple applications across various industries including:
Hot-rolled steel has multiple uses in the automotive industry, including:
- Automotive body panels: Hot-rolled steel sheets are commonly used to produce body panels such as doors, hoods, and fenders. This is due to its toughness and impact resistance which provide crash protection and durability.
- Chassis and structural components: Hot-rolled steel plates are used to produce automotive chassis and structural components. These include frame rails and suspension components.
Hot-rolled steel is used in the construction industry in the following ways:
- Steel framing: Hot-rolled steel is used for steel framing systems in residential and commercial constructions. This includes the construction of stainless steel channels, steel studs, and tracks that create the framework of ceilings, walls, and roofs.
- Sheet piling: Hot rolled sheets are used to create sheet piling for construction projects that need bulkheads and retaining walls. The sheet piles are driven into the ground to create a barrier that provides structural support and prevents soil erosion.
- Energy industry: Hot-rolled steel is used to manufacture pipes, pressure vessels, and tanks. These are used in power plants and renewable energy facilities.
- Storage and material handling: Hot-rolled steel produces racks, shelves, and containers. It is also used for manufacturing components such as frames and beams.
Quality Control in Hot Rolling
Quality control measures are vital to the hot rolling process to ensure the final product meets the required standards. These measures include:
- Process monitoring: Hot rolling mills have various sensors which ensure the process goes smoothly. These include pressure sensors, temperature sensors, speed sensors, and load cells. They provide data on pressure, temperature, speed, and load and guarantee the process is within the desired range.
- Inspection of incoming materials: Incoming raw materials like raw steel billets must be inspected before they are fed into the machine. This involves dimensional inspection, visual inspection, and testing of mechanical properties.
- Process inspection: During the hot rolling process, regular inspections will be carried out to assess the quality of the rolled products. This would involve visual inspection and dimensional inspection. It would also include non-destructive testing techniques like ultrasonic testing and magnetic particle testing.
Hot Rolling Defects and Remedies
Common Defects in Hot-Rolled Steel
The common defects affecting hot-rolled steel include:
- Surface defects: These happen on the surface of the rolled steel and include pits, scars, and scratches. They can also affect the appearance and corrosion resistance of the final product.
- Inclusions: Inclusions are non-metallic particles trapped in the hot rolled steel during the rolling process. They can be oxides or sulfides and reduce the rolled metal’s toughness.
- Lamination: Lamination is the separation of layers in the steel due to improper bonding during the rolling process. This can reduce the integrity and strength of the steel and lead to failure under load.
Possible Remedies to Defects in Hot Rolled Steel
There are multiple remedies for defects in hot-rolled steel, including:
- Adjusting roll parameters: You can optimize roll parameters such as temperature, rolling pressure, rolling speed, and pass reduction.
- Enhancing Material Preparation: Proper preparation of incoming materials, such as removing scale and inspecting for surface defects. This ensures the materials meet your specifications for the project.
- Regular maintenance and calibration: You must regularly maintain hot rolling equipment such as rollers, guides, and cooling systems. This will guarantee optimal performance and reduce the risk of defects.
Hot Rolling Technologies
Advanced Hot Rolling Technologies
There are different advanced rolling technologies that are used to boost productivity. These include:
- Steckel mill: This hot rolling mill can roll thick and thin steel plates during the same process. It creates room for a wider range of steel grades and reduces energy consumption.
- Continuous casting and rolling: This is a combined process where the steel is constantly cast into slabs and billets. Next, the steel is directly fed into the rolling mill for hot rolling. This removes the need for separate casting and reheating processes.
- Accelerated cooling: This process is where hot steel is quickly cooled after rolling to control its properties and microstructure. It can be done through water quenching, spraying, or air cooling.
Benefits of Advanced Hot Rolling Techniques
Advanced hot-rolling technologies offer multiple benefits, including:
- Increased productivity: Advanced hot rolling allows faster rolling speeds, improved material use, and shorter cycle times.
- Improved product quality: Advanced hot rolling technologies give you full control over the steel’s properties, microstructure, and surface finish. This leads to fewer surface defects and improved surface finishes.
- Energy savings: Advanced hot rolling technologies like microalloying and controlled rolling reduce the need for extra heating treatment steps. Additionally, technologies like accelerated cooling can reduce the time and energy for cooling hot rolled steel. This improves process efficiency and reduces energy consumption.
Hot-rolled steel can be used in different areas ranging from the automotive industry to the manufacturing industry. However, it has the potential for increased surface defects and energy consumption. Always inspect materials and use the best hot-rolled steel possible to avoid this. You can also use advanced hot-rolling technologies to improve your process and create the best products.
To get started with hot rolled steel, contact Tuolian Metal for the best products you can buy.