What are the differences in processing difficulty between hot-rolled and cold-rolled steel sheets in construction?

The differences in processing difficulty between hot-rolled and cold-rolled steel sheets in construction primarily stem from their inherent properties, such as mechanical performance, surface quality, and dimensional accuracy. These differences directly impact the operational difficulty and effectiveness of processing steps such as cutting, welding, bending, and stamping. The following provides a detailed comparison from the perspective of specific processing techniques:
1. Cutting Processing Difficulty
Hot-rolled steel sheets:
Lower cutting difficulty.
Reason: Hot-rolled steel plates have better toughness and lower hardness (due to reduced internal stress after high-temperature rolling), making them easier to process using both mechanical cutting (sawing, shearing) and thermal cutting (oxy-fuel cutting, plasma cutting).
Characteristics: Thick-gauge hot-rolled steel plates (e.g., 10mm or thicker) are less prone to cracking during thermal cutting. While the cut edges may be rough, they can be used directly without high-precision processing when precision is not required, making them suitable for rough cutting of load-bearing components in construction.
Cold-rolled steel plates:  
Cutting difficulty is slightly higher, especially for thin-gauge plates (≤1mm), where deformation must be carefully managed.
Reason: Cold-rolled steel plates have higher hardness and strength due to cold work hardening, requiring greater pressure during mechanical shearing. Thin plates are prone to warping due to uneven force distribution. During thermal cutting, improper temperature control may cause edge oxidation or deformation (affecting subsequent welding or assembly precision).
Characteristics: Suitable for precision cutting (e.g., laser cutting), requiring control of cutting speed and force to ensure smooth edges. Commonly used for decorative components or thin-walled ductwork processing.
2. Welding Processing Difficulty
Hot-rolled steel plates:
Welding difficulty is low, with strong adaptability.
Reason: Hot-rolled steel plates have low carbon content and alloy element content (mostly low-carbon steel), making it unlikely to form hardened structures during welding, with a small heat-affected zone and low crack tendency; although surface oxide scale (when not acid-washed) may affect welding quality, after rust removal pretreatment, conventional processes such as arc welding and gas welding can be performed stably.
Applications: Welding of steel structure beams and columns in buildings, heavy-duty supports, etc., where high aesthetic requirements for weld appearance are not necessary, can be performed by ordinary welders.
Cold-rolled steel plates:
Higher welding difficulty, requiring control of thermal deformation and weld quality.
Reason: Cold-rolled steel plates undergo cold work hardening, resulting in residual stresses internally. Localized heating during welding can easily cause deformation (especially in thin plates); if not annealed, cracks may form near the weld due to stress release; while the smooth surface (without oxide scale) facilitates stable welding arcs, thin plates are prone to burn-through.
Countermeasures: Use a small current and fast welding process (such as TIG welding), combined with fixtures for fixation. This is suitable for welding precision components like door and window frames and thin-walled ducts, but requires higher welding skills.
3. Bending and Forming Processing Difficulty
Hot-rolled steel plates:
Bending and forming are relatively easy but have lower precision.
Reason: Hot-rolled steel has good toughness and moderate ductility, allowing simple bending at room temperature (e.g., forming a 90° angle). Thicker plates are easier to control when hot-bent (e.g., pipe elbows).  
Limitations: Due to low dimensional accuracy (large thickness tolerances), bending may result in inconsistent springback and uneven edges, making it unsuitable for high-precision forming (e.g., complex irregular cross-sections).
Cold-rolled sheets:  
High bending forming precision, but hardened cold-rolled sheets are prone to cracking, so process parameters must be carefully controlled.  
Reason: Cold-rolled sheets (especially those annealed) have excellent cold formability, uniform thickness, and smooth surfaces. They exhibit minimal springback after bending and can be processed into high-precision irregular components such as C-shaped steel, Z-shaped steel, and lightweight steel studs.
Limitations: Unannealed hard-state cold-rolled sheets (such as cold-rolled hard coils) have high hardness and poor ductility; forced bending may cause cracks at the bend, so they must be annealed to soften before processing; thin sheets must be prevented from wrinkling during bending.
4. Stamping and Punching Processing Difficulty
Hot-rolled sheets:
High stamping difficulty, unsuitable for precision stamping.
Reason: Rough surface, large dimensional tolerances, rapid mold wear during stamping, and limited ductility of the material, which can cause edge tearing; during punching, due to low hardness, burrs may form around the hole edges, requiring additional cleaning.  
Cold-rolled sheets:  
Low stamping and punching difficulty, suitable for precision processing.
Reason: Smooth surface, uniform thickness, good mold adhesion, less likely to jam during stamping, can be processed into complex shapes (such as flanges for ventilation ducts or holes for door and window hardware); after punching, edges are flat with few burrs, requiring minimal post-processing.
5. Surface Treatment Processing Difficulty  
Hot-rolled steel sheets:  
Requires additional pre-treatment before surface treatment, making the process more challenging.
Reason: The surface is covered with iron oxide scale (black skin). If directly painted or galvanized, the coating adhesion is poor and prone to peeling; it is necessary to first remove the oxide scale through processes such as acid washing or sandblasting, increasing construction steps and costs; the surface is rough, requiring more paint to achieve uniform coverage during coating.  
Cold-rolled sheet:  
Surface treatment difficulty is low, with simpler processes.
Reason: The surface is smooth and free of oxide scale, allowing direct application of paint, galvanization, or coating. The coating has strong adhesion, and the smooth surface results in a more aesthetically pleasing appearance after coating (e.g., architectural exterior color-coated sheets).