Rolling is a process that uses rollers to change the shape, make it more uniform, and improve the strength of metal. There are two types of rolled steel: hot-rolled and cold-rolled. Each type has unique features that make it suitable for different uses. When picking rolled steel for a project, it’s essential to understand the differences between hot-rolled and cold-rolled steel and how these differences affect their performance.
An Overview Of Hot-Rolled Steel
Hot-rolled steel, a process conducted at high temperatures, typically above 1700°F, exceeding its recrystallisation point, is critical in making it more formable and workable than unprocessed steel.
Process:
- Billet Heating: A large rectangular slab of metal, called a billet, is heated.
- Compression: The heated billet is compressed into a large roll.
- Rolling: The roll passes through a series of rotating rollers to get the desired dimensions.
- Cooling and Packaging: For sheet metal, the rolled steel is coiled and left to cool. For other forms, the steel is cut to size and packaged.
Characteristics of Hot Rolled Steel
Hot-rolled steel often has a scaly finish, which can be removed by pickling, grinding, or sandblasting. It’s considered normalised, meaning it is free from internal stresses since it cools at room temperature.
Its other characteristics include:
- Slightly rounded edges and corners for plate products due to shrinkage and less precise finishing
- Slight distortions
- More malleable, making it easier to shape
- Increased flexibility and toughness
Applications of Hot Rolled Steel
Hot rolled steel shrinks slightly during cooling, so it’s used in applications where exact shape and size are not crucial.
Its common uses include:
- Agricultural equipment
- Automobile parts (e.g., frames and wheel rims)
- Construction materials (e.g., I-beams)
- Railroad equipment (e.g., tracks and railcar components)
An Overview of Cold-Rolled Steel
Cold-rolled steel starts as hot-rolled steel but is further processed by cooling it at room temperature and then annealing or temper-rolling it. This process results in steel with more precise dimensions and various surface finishes. Due to strength hardening, cold-rolled steel is also up to 20% stronger than hot-rolled steel.
Characteristics of Cold Rolled Steel
Cold-rolled steel can often be identified by:
- Better, more finished surfaces with closer tolerances
- Smooth surfaces that feel oily
- Bars that are true, square, and have well-defined edges and corners
- Tubes with better uniformity and straightness
Applications of Cold Rolled Steel
Cold-rolled steel is used where precise tolerances, surface conditions, concentricity, and straightness are essential. It also has a more attractive surface.
Its typical applications include:
- Home appliances
- Metal furniture
- Aerospace structural components
- Automotive parts
Differences Between Hot Rolled Steel and Cold Rolled Steel
The main difference between hot-rolled and cold-rolled steel is the temperature at which they are processed:
- Hot Rolled Steel: Rolled above the material’s recrystallisation temperature, resulting in rough edges and surfaces that may need additional treatment.
- Cold-rolled steel is rolled below the recrystallisation temperature, producing a shiny, smooth surface that can often be used as-is. This process also makes the steel more robust and harder but introduces internal stresses that need to be relieved before further processing.
Some of the other points of differences include:
- Surface Quality: Hot rolled steel has rougher surfaces, while cold rolled steel has smooth, shiny surfaces.
- Material Hardness: Cold-rolled steel is more robust and harder than hot-rolled steel.
- Internal Stress: Cold-rolled steel has more internal stresses, which must be relieved to prevent warping during processing.
Choosing the correct type of steel for your project is essential to avoid unnecessary costs and save time.
Choosing Between Hot Rolled vs. Cold Rolled Steel
Understanding the differences between hot-rolled (HR) and cold-rolled (CR) steel helps you choose the suitable material for your project. Here are some key points to consider:
Application Requirements:
- Choose cold rolled steel for projects needing high precision, tight tolerances, or a smooth surface.
- Hot-rolled steel is suitable for projects where structural integrity is more important than appearance. It is also easier to weld and bend.
Cost Considerations:
- Hot-rolled steel is generally cheaper due to its more straightforward production process and lower finishing needs.
- While cold-rolled steel is more expensive, it offers higher strength and a better surface finish, which might be worth the investment for specific projects.
Desired Material Properties:
- Cold-rolled steel is more robust and more challenging to work on due to the cold working process.
- Hot-rolled steel is more ductile, making it better for forming or shaping applications.
Aesthetic Preferences:
- Cold-rolled steel’s smooth, polished surface is ideal for visible projects.
- Hot-rolled steel’s rougher surface is acceptable for projects that will be coated, painted, or hidden.
Lead Time:
- The availability of specific steel types and grades can affect your choice. Some grades are more readily available in either hot-rolled or cold-rolled form.
Applications/Uses of Ratnabhumi Steeltech Hot-Rolled Steel Products and Why Should You Choose Our Products?
ERW pipes and tubes, known for their exceptional strength, are a reliable choice for many industries. They are used in a variety of applications, from building airports and railway stations to refinery plants and the automobile industry. Their strength and resistance to corrosion and rust make them a dependable choice for buildings in mountainous and coastal areas, and they even replace wood in roofing structures. Their range of sizes makes them suitable for prefabricated structures like sheds and warehouses, further reinforcing their reliability.
They are also used in agricultural & construction projects. In the automobile industry, they are used for truck bodies and heavy vehicle axles. They are famous for building fencing, railings, scaffolding, windows and door frames, ducting, furniture like tables and benches, and even firefighting equipment.
Opting for Ratna Steeltech ERP solutions for bulk purchasing stainless steel ERW pipes ensures you receive high-quality products and exceptional service tailored to various engineering and industrial applications.
For all your ERW pipes or tubes, contact Ratnabhumi Steeltech.