The difference between hot rolled strip and cold rolled strip is mainly reflected in the processing technology, performance characteristics and application fields, the following is a detailed comparison:
1. Processing temperature and technology
Hot rolled strip steel
• Temperature:
Rolling above the metal recrystallization temperature (usually 1100-1300℃).
• Process:
1. The billet is heated to red hot state;
2. Multi-pass roughing and finishing rolling;
3. Natural cooling or controlled cooling to form an oxide layer (iron sheet).
• Features:
Good metal plasticity at high temperature, low rolling force, high efficiency, but obvious surface oxidation.
Cold rolled strip steel
• Temperature: Rolling at room temperature (below recrystallization temperature).
• Process:
1. Hot-rolled coil as raw material, pickling to remove the oxide layer;
2. Cold rolling deformation (work hardening);
3. Annealing treatment (restore ductility and eliminate stress);
4. Finishing (such as leveling, cutting).
• Features:
requires multiple processes, strict size control, high surface quality.
2. Surface quality and dimensional accuracy
Hot rolled strip steel
• There is an oxide layer on the surface, which is rough and may have micro-cracks, pitting and other defects.
• Thickness is usually ≥1.2mm with large tolerance (±0.1-0.5mm).
Cold rolled strip steel
• Smooth surface, no oxidation, can be galvanized or painted.
• Thinner thickness (0.1-3mm), small tolerance (±0.01-0.05mm), suitable for precision machining.
3. Mechanical properties
Hot rolled strip steel
• Low strength and hardness (such as Q235 hot rolling yield strength of about 235MPa).
• Good toughness, high ductility, suitable for stamping.
• Residual stress, easy to deform.
Cold rolled strip steel
• Work hardening to improve strength (such as the yield strength after cold rolling can reach more than 300MPa).
• High hardness but poor toughness, need annealing to restore plasticity.
• Good dimensional stability, low residual stress.
4. Application field
Hot rolled strip steel
• Building structures (H-beams, Bridges), pipelines, vehicle frames, containers, etc.
• Suitable for scenes with low surface requirements and moderate strength.
Cold rolled strip steel
• Automotive panels, home appliance housings (such as refrigerators, washing machines), precision instruments, tin plates (cans), etc.
• For applications where smooth surfaces, high precision or subsequent coating treatments are required.
5. Cost and production cycle
Hot rolled strip steel
• Low energy consumption (single roll molding), low cost.
• Short production cycle, suitable for large quantities.
Cold rolled strip steel
• Complex process (pickling, cold rolling, annealing, etc.), high cost.
• Long production cycle, high added value.
6. Other differences
• Microstructure: the hot rolled grain is coarse, the cold rolled grain is broken and refined, and the uniform recrystallization structure is formed after annealing.
• Environmental protection: hot rolling produces more carbon emissions at high temperature, cold rolling pickling needs to treat wastewater.
• Material selection: Cold rolling raw materials need high quality hot rolled coil, low impurity content.
Summary: How to choose
• Hot rolling: low cost, thick specifications, structural parts.
• Selective cold rolling: high precision, thin wall, high appearance requirements or deep drawing molding.
Understanding the difference between the two helps to rationally select materials according to strength, cost and appearance requirements, and optimize product design and production costs.
