1.What are the core requirements for common components?
Appearance/forming-oriented: smooth surface (can be painted directly), complex cold forming (such as deep drawing, multiple bending) is preferred, cold rolled, cold rolled sheet has no oxide scale, good soft ductility
Load bearing/cost-oriented: withstand impact/load, good welding performance, control cost (large amount), hot rolling is preferred, hot rolled plate has high toughness, low cost, and excellent weldability
Precision/rust prevention-oriented type: small dimensional error (to avoid installation misalignment), requires galvanizing/coating for rust prevention, cold rolling is preferred, cold-rolled plate has high dimensional accuracy and strong coating adhesion
2.How to choose between cold rolling and hot rolling depending on whether a "visible appearance" is required?
For body panels and exterior trim: Cold-rolled steel is a must.
Reason: Hot-rolled steel has a dark brown scale on its surface, resulting in a high degree of roughness. Even after pickling, it cannot achieve a flawless finish when painted. Cold-rolled steel, on the other hand, has a smooth, scale-free surface, resulting in a uniform gloss after painting, meeting automotive exterior requirements (e.g., doors, hoods, trunk lids).
No (e.g., interior chassis components and frames): Hot-rolled steel is preferred.
Reason: For components hidden within the vehicle body or beneath the chassis (e.g., chassis longitudinal rails and frame crossmembers), appearance is not essential. Surface defects on hot-rolled steel do not affect performance and can save costs.
3.How to choose between cold rolling or hot rolling depending on whether "complex cold forming" is required?
Yes (e.g., deep drawing, multiple bending): Cold-rolled steel is a must.
Reason: Automotive parts requiring complex cold forming (e.g., deep drawing of fuel tanks, multi-angle bending of instrument panel brackets) rely on the soft ductility of cold-rolled steel (fine grains and excellent plasticity after annealing). Hot-rolled steel, on the other hand, has coarse grains and is susceptible to stress concentration cracking during cold forming (e.g., a 90° cold bend of hot-rolled steel may crack, while a 180° bend of cold-rolled steel can be easily achieved).
Typical parts: Fuel tanks (for deep drawing, cold-rolled soft steel SPCE is the preferred choice), door inner panels (for multi-bend reinforcement structures).
No (e.g., for simple cutting and welding): Hot-rolled steel is an option.
Reason: For parts requiring simple "cutting into flat sheets and welding and assembly" (e.g., straight sections of chassis longitudinal beams), hot-rolled steel can meet simple forming requirements and offer lower costs.
4.How to choose between cold rolling and hot rolling depending on whether it needs to "withstand high loads/impacts"?
Yes (e.g., load-bearing structural parts): Hot-rolled plate (or hot-rolled high-strength steel base material) is preferred.
Reason: Hot-rolled plate offers greater toughness (coarser grains after high-temperature rolling, resulting in stronger impact resistance), and can withstand the weight of the vehicle, road bumps, or collisions (e.g., chassis rails need to resist twisting, and truck frames need to withstand heavy loads). Cold-rolled plate, while high in strength, has lower toughness (due to cold work hardening) and is prone to brittle fracture under impact, making it unsuitable for load-bearing core components.
Exception: If the load-bearing component also requires high precision (e.g., the battery pack frame of a new energy vehicle), "cold-rolled high-strength plate" (cold-rolled and quenched to increase strength, achieving a balance between precision and load-bearing performance) is used, but the cost is significantly higher than hot-rolled plate.
No (e.g., interior components, lightweight functional parts): Choose cold-rolled plate.
Reason: Interior components (e.g., seat rails) and lightweight functional parts (e.g., battery trays) do not need to withstand heavy loads and therefore require the dimensional accuracy and formability of cold-rolled plate.
5.How to choose between cold rolling and hot rolling depending on whether "high-precision installation" is required?
Yes (for components with tight assembly clearances): Cold-rolled steel is a must.
Reason: Cold-rolled steel has extremely tight dimensional tolerances (thickness tolerance ±0.01-0.05mm, and the plate shape is smooth and wave-free), ensuring smooth component installation. (For example, the assembly clearance between the instrument panel bracket and the center console must be less than 0.5mm. The precision of cold-rolled steel prevents "sticking" or "squeaking.") Hot-rolled steel, on the other hand, has wider dimensional tolerances (±0.1-0.3mm), making it prone to warping and uneven gaps during installation.
No (for welded frame components): Hot-rolled steel is an option.
Reason: For welded components like chassis crossmembers and frames, even slight dimensional deviations can be adjusted through welding (for example, fine-tuning the position during spot welding). Extreme precision is not required, and the lower cost of hot-rolled steel is a significant advantage.