热轧钢与冷轧钢：有什么区别？

What is Hot Rolled Steel?

 

Hot rolled steel is steel that has been rolled at high temperatures, specifically over steel’s recrystallization temperature (1,700°F). The high temperature causes the steel to become soft and malleable. This makes the steel easier to shape into different forms, such as beams, sheets, and plates.

Hot rolled steel has a rough and scaly surface, also known as mill scale. The steel also has less precise dimensions, caused by shrinkage during cooling. The edges are often slightly rounded rather than sharp.

 

What is Cold Rolled Steel?

 

Cold rolled steel is steel that has been hot rolled then processed further at or near room temperature in cold reduction mills. The extra processing improves strength, surface quality, and dimensional accuracy. These properties make this steel ideal for applications that require precision and a clean finish.

Cold rolled steel has several key features which differ from hot rolled steel. Cold rolled steel has a smooth and refined surface, precise dimensions, and sharp, well-defined corners. This type of steel is around 20% stronger and harder than hot rolled steel due to the process of strain hardening

 

Key Differences Between Hot and Cold Rolled Steel

 

The key differences between hot rolled steel and cold rolled steel are how they are processed and their resulting properties. Hot rolled steel is processed at over 1,700°F, making it easier to shape but less precise. Cold rolled steel is produced around room temperature, after hot rolling. This produces steel with higher strength, better surface finish and better precision. Other differences lie in these categories: price, distortions, strength, and finish.

Process

 

Hot rolling occurs at 1,700°F, which is above steel’s recrystallization point. At this temperature, steel is malleable and easy to shape. In contrast, cold rolling occurs at or near room temperature, after hot rolling has been done, which improves dimensional accuracy and surface quality.

Price

Hot rolled steel is cheaper because the process involves fewer steps and less labor. Conversely, cold rolled steel is more expensive since it requires additional processing in cold reduction mills which takes more time and requires more labor.

Distortions

 

Hot rolled steel has looser tolerances because cooling causes shrinkage. Cold rolled steel has superior precision, but can develop internal stresses, due to rolling, that may cause warping if not properly treated

Strength

 

The process of strain hardening makes cold rolled steel around 20% stronger and harder than hot rolled steel. Due to the lower strength and higher malleability of hot rolled steel, it is much easier to shape into different forms.

Finish

 

Hot rolled steel has a rough, scaly surface known as mill scale. This means hot rolled steel often needs further processing, such as pickling or grinding, to smoothen out the surface. On the other hand, cold rolled steel already has a smooth, refined surface after rolling.

 

 

 

How to Choose Between Hot Rolled and Cold Rolled Steel?

To decide whether to use hot rolled or cold rolled steel, the nature and requirements of the project need to be considered.

 

Key factors to consider when picking between hot rolled and cold rolled steel:

 

• End use – Identify what the purpose for the steel is. For structural beams, frames, or construction material, hot rolled steel is more suitable. For precision parts and finished products, cold rolled steel is recommended.
• Load-bearing needs – Cold rolled steel should be used if the project requires higher strength and hardness. For general structural uses, hot rolled steel is preferred.
• Appearance – Cold steel has a smooth surface and is more precise, while hot rolled steel has a rough, scaly surface. Therefore hot rolled steel is favoured when appearance is not important.
• Cost – Hot rolled steel is cheaper than cold rolled steel, making it a good choice for large-scale projects. Cold rolled steel is more expensive, and should be used if precision and finish matter more.
• Fabrication requirements – Hot rolled steel is easier to manipulate, e.g. weld, cut, and shape. Cold rolled steel may require further processing to fabricate due to its strength and hardness.
• Safety standards – Certain industries have regulations that dictate which type of steel must be used.

 

 

When to choose hot-rolled steel?

 

Hot rolled steel is the best choice when your project needs affordable, flexible, and easy to shape material. When choosing hot rolled steel, the appearance and precision should not be important. Hot rolled steel is widely used in construction, infrastructure, and heavy manufacturing.

 

 

Common applications include:

 

• Structural components (e.g., I-beams, channels, angles, and columns) in construction.
• Manufacturing of large parts and profiles, including railroad tracks and automotive frames.
• Projects where surface finish and close dimensional tolerances are not essential.
• Welded structures and frames in machinery, equipment, or trailers.
• Base materials for further processing (e.g., forging, welding, or machining).
• Agricultural equipment and heavy machinery components.
• Products that will undergo further fabrication or coating.

When to choose cold-rolled steel?

 

Cold rolled steel is the best option when your project needs high precision, higher strength, and a refined surface finish. This type of steel is recommended for projects that combine aesthetic appeal and durability. Cold rolled steel is widely used in manufacturing, fabrication, and automotive industries.

 

Common applications include:

 

• Precision components: Gears, shafts, engine parts, and bearing housings.
• Consumer products: Home appliances, metal furniture, and file cabinets.
• Automotive parts: Body panels, doors, and structural reinforcements.
• Architectural elements: Metal panels, decorative trim, and exposed structural elements.
• Electrical applications: Motor laminations, electrical cabinets, and enclosures.
• Product fabrication: Items requiring bending, stamping, or high-quality coating/painting.

 

FAQs

Is hot rolled steel cheaper?

 

Yes, hot rolled steel is cheaper than cold rolled steel. This is because hot rolling has fewer steps, so it can be produced faster and in large quantities. Cold rolling is a secondary process that takes place after hot rolling. Therefore, there are more steps, adding manufacturing time and higher energy costs. This results in cold rolled steel typically selling for 20-40% more than hot rolled steel, depending on market conditions. Recent data indicates that hot rolled steel sells for approximately $832 per ton and cold rolled steel sells for between $1,105 and $1,160 per ton.

Does cold rolled steel rust?

 

Yes, cold-rolled steel can rust because it’s mainly made from carbon steel. This makes the steel prone to corrosion when exposed to moisture and air. Protective coating, such as paint, oil, or galvanization, can help prevent rusting.

Can cold rolled steel be used for welding?

 

Yes cold rolled steel can be welded, but there are several factors that need to be considered. Cold rolled steel is stronger and harder than hot rolled steel due to strain hardening. However, this also causes internal stress to develop in the steel. If internal stress is not managed, welding can cause warping, distortion, or cracking.

 

To weld cold rolled steel safely, use low-carbon steel. Also consider preheating or cooling the steel to reduce stress and prevent warping. Additionally, using appropriate welding techniques will help to avoid warping. It is also recommended to follow welding standards for industrial or structural applications.