From Fire to Finish, A Comprehensive Guide to Hot, Cold, and ESP Steel Coil Manufacturing

From iron to finished steel products, complex processes are required, yielding different categories. Hot-rolled steel coils and cold-rolled steel coils are the most common types, with hot-rolled coils serving as the raw material for cold-rolled coils and as a standalone product for sale and use.

These two categories have significant differences in process characteristics, advantages/disadvantages, and applications. Additionally, the new ESP process product can also confuse users. This article attempts to analyze and compare these three types of products.

Hot-Rolled Steel Coils

Process Characteristics

Hot-rolled steel coils are made by rolling steel ingots at high temperatures. During this process, the steel is heated to above the recrystallization temperature, typically between 1000°C and 1250°C, giving it good plasticity and low deformation resistance. After hot rolling, the steel surface will have a layer of scale, which is usually removed before use (pickling or shot blasting).

Advantages

Good Mechanical Properties: Hot-rolled steel coils, after high-temperature rolling, have good comprehensive mechanical properties such as strength, plasticity, and toughness.

High Production Efficiency: The hot-rolling process has fewer steps and a large reduction in thickness, resulting in high rolling efficiency.

Lower Cost: Due to the shorter production process of hot rolling, energy consumption is reduced, so the production cost for the same specifications is relatively lower than cold rolling.

Disadvantages

Low-Dimensional Accuracy: The dimensional accuracy and surface finish of hot-rolled steel coils are not as good as those of cold-rolled steel coils.

Residual Stress: Rapid cooling during the hot-rolling process can produce residual stress, which may affect its subsequent processing performance.

Poor Surface Quality: Due to the presence of scale on the steel plate during rolling, it is easy to cause scale indentation, and even after pickling and leveling, residual marks cannot be eliminated.

Applications

Hot-rolled steel coils are widely used in construction, bridges, ships, machinery manufacturing, and other fields. Patterns plates, beam steel, crane arm steel, and others are mostly made using hot-rolling processes.

Cold-Rolled Steel Coils

Process Characteristics

Cold-rolled steel coils are further rolled from hot-rolled steel coils at room temperature.

During the room temperature cold rolling process, dimensions can be precisely controlled, followed by specific heat treatment to obtain the desired properties.

Advantages

High Dimensional Accuracy: Cold-rolled steel coils have high dimensional accuracy in thickness, width, and other dimensions.

Excellent Mechanical Properties: Through cold rolling and subsequent heat treatment, higher strength and hardness can be achieved, as well as good plasticity.

Good Surface Quality: Cold-rolled steel coils have no scale, high surface finish, and are suitable for direct use in manufacturing various parts.

Disadvantages

High Production Cost: Cold rolling has many processes and complex procedures, with high energy consumption, so the production cost is higher than hot-rolled steel coils.

Low Production Efficiency: The process of cold rolling is complex, with cumbersome material circulation, resulting in lower production efficiency than hot rolling.

Applications

Cold-rolled steel coils are mainly used for manufacturing parts with high requirements for dimensional accuracy and surface quality, such as automobiles, home appliances, electronic products, etc.

ESP (Endless Strip Production)

ESP production lines are considered the third technological revolution in the steel industry after oxygen converter steelmaking and continuous casting, representing the highest level of hot-rolled strip technology in the world today.

#1 Many people used to think that ESP was a cold-rolled product, but in fact, ESP is a thin specification hot-rolled pickled product.

ESP uses a new process of endless strip rolling, achieving continuous production from molten steel to hot-rolled coils on the coiler, capable of producing ultra-thin hot-rolled steel coils such as 0.8mm.

Process Characteristics

Endless Rolling: The most significant feature of ESP technology is the continuous production from molten steel to hot-rolled coils without interruption.

Compact Process: The continuous casting and rolling processes are directly connected, eliminating intermediate links such as slab yards and heating furnaces.

High-Speed Production: The continuous casting machine is designed with a high pulling speed, up to 7.0m/min, greatly increasing production efficiency.

High Precision Control: Advanced control technology is used to precisely control the thickness, width, and flatness of the product.

Advantages

Energy Saving and Emission Reduction: Since intermediate heating links are omitted, ESP production lines greatly reduce the consumption of energy and water.

High Yield: The yield from molten steel to hot-rolled coils can reach 97%-98%, far higher than traditional processes.

Reduced Investment Cost: Compact equipment layout reduces equipment and plant investment.

Improved Product Quality: Able to produce ultra-thin specifications of hot-rolled steel coils, with typical thin specifications of 0.8mm (or even thinner), and excellent product performance.

Disadvantages

High Initial Investment: Although the cost can be reduced in the long term, ESP technology is not yet widespread, and the initial investment is relatively high.

Technical Threshold: Fully automated and continuous production lines, any link cannot have problems, otherwise, the whole line will stop, so the skills of operators and maintenance personnel are required to be higher.

Low Flexibility: Due to the high degree of automation and continuousness of the production line, it is not as flexible as traditional production lines in changing product types.

Applications

Hot instead of cold, in scenarios where surface and performance requirements are not high, but the thickness of the specification is thin, it can fully replace cold-rolled products.

Common Questions and Answers

Question 1: What is the core advantage of ESP?

Low production cost + low carbon emissions, because the process is compact, so the production cost of ESP is greatly reduced, and because the process is compact, the energy waste in the middle links is very little, and waste is low, so carbon emissions are low.

From this perspective, the outbreak of ESP technology is not now, but when Europe and the United States vigorously promote carbon tariffs, the hot-dip galvanized steel coils based on ESP substrate will have a greater export advantage.

Question 2: What is the difference between hot-rolled, cold-rolled, and ESP of the same specification?

Taking 2.0mm thick C material as an example:

Production cost: ESP < Hot rolling < Cold rolling

Surface quality: Cold rolling > ESP > Hot rolling

Production precision: Cold rolling > ESP > Hot rolling

Question 3: What is the difference in surface quality among the three products?

Comparing surface quality, the roughness of hot-rolled coils after pickling and leveling is relatively high, and the surface undulations are slightly larger after washing off the scale, sometimes with scale peak patterns.

Cold rolling is cleaned of scale and then rolled at room temperature. After pickling, the deformation amount is large, and the original surface undulations are flattened, mainly endowed with roughness by the cold rolling rolls, and the surface is more smooth and uniform.

ESP is essentially a hot-rolled pickled thin plate, and before leaving the factory, it is usually pickled and leveled, and the surface quality is closer to cold-rolled products.

Question 4: Will ESP greatly compress the living space of hot-rolled and cold-rolled?

It will not greatly compress, but it will have an advantage in economic specifications and grades.

This question depends on the proportion of a variety of steel and commercial general materials. Traditional cold and hot rolling still have advantages in making a variety of steel (complex steel grades with multiple specifications), especially for users to fine-tune performance space.

ESP has an ultimate cost advantage in making a single specification of ordinary grades in volume, especially as a coating base plate.

To put it bluntly, ESP technology makes the originally low-priced general materials cheaper, and the advantage is reflected in the economy, but to say that it is better than cold rolling in quality is an overstatement.

Question 5: How to find a qualified and trustworthy supplier?

As an authorized dealer of Baosteel, Baohui Steel Limited has been serving this industry for over two decades. We are very familiar with and knowledgeable about new technologies such as hot-rolled steel, cold rolled steel, and ESP steel. For any needs and technical inquiries about steel, please feel free to contact us. We have professional steel experts ready to provide one-on-one answers and services.

‍