1.What is the difference in strength grades between Q355B galvanized steel and Q235B galvanized steel?
Yield strength: The yield strength of Q355B is about 51% higher than that of Q235B, which means that with the same cross-sectional size, Q355B can withstand a larger "load without permanent deformation" (such as load-bearing brackets and robotic arms).
Tensile strength: The upper limit of Q355B's tensile strength is approximately 26% higher than that of Q235B. It can withstand a higher maximum tensile force before breaking, making it suitable for scenarios with high tensile requirements (such as wire rope fixings and bridge rods).
Bending strength: At the same thickness, Q355B is not prone to permanent deformation when bent, and can be used in structures that require bending resistance (such as outdoor billboard frames and vehicle chassis support beams).
2.What is the difference in plasticity between Q355B galvanized steel and Q235B galvanized steel?
Q235B base material: Excellent plasticity, with an elongation after fracture (A) ≥ 26% (for thickness ≤ 16mm).
This translates to greater bending tolerances (e.g., crack-free 180° cold bending) and less cracking during stamping, making it suitable for applications requiring complex cold forming (e.g., bending appliance housings and small structural parts).
Q355B base material: Slightly lower plasticity, with an elongation after fracture (A) ≥ 22% (for thickness ≤ 16mm).
While it can still withstand conventional cold working (e.g., 90° bending), excessive deformation (e.g., 180° dead bending) may cause cracking in the base material or galvanized coating. Controlled deformation is essential during processing, making it more suitable for applications where load-bearing performance is prioritized and light processing is required (e.g., large steel structure supports and load-bearing beams).
3.What is the difference in low temperature toughness between Q355B galvanized steel and Q235B galvanized steel?
Q235B base steel: This is a room-temperature tough steel. Its impact test requirement is "impact absorbed energy ≥ 27J at room temperature (20°C)." There are no requirements for low-temperature environments.
Limitations: In low-temperature environments (e.g., below -10°C), its toughness decreases significantly, making it susceptible to brittle fracture when impacted. It is not suitable for outdoor load-bearing structures in cold northern regions (e.g., outdoor equipment supports in winter, beams in low-temperature workshops).
Q355B base steel: This is a low-alloy, high-strength steel. Its "B" grade stands for "-20°C low-temperature impact qualified," requiring "impact absorbed energy ≥ 34J at -20°C."
Advantages: It maintains excellent impact resistance even in low-temperature environments and is not prone to brittle fracture. It is suitable for outdoor structures in cold regions (e.g., bridge supports in northern China, steel structures for low-temperature cold storage, and municipal guardrails during winter construction).
4.What is the difference in mechanical property stability after welding between the two?
Q235B galvanized steel: The base material contains a low carbon content (≤0.20%) and no special alloying elements. Preheating is not required for welding (for thicknesses ≤20mm). The strength of the welded joint essentially matches that of the base material, making weld cracking less likely. The process threshold is low, making it suitable for small and medium-sized welds (such as household metal frames and small equipment housings).
Q355B galvanized steel: The base material contains alloying elements such as manganese and vanadium (manganese content 0.50%-1.60%). Preheating to 100-150°C is required for thicker steel (≥20mm) or lower ambient temperatures (≤0°C). Otherwise, the joint may crack due to welding stress. However, after welding, the joint's strength (yield and tensile properties) remains close to that of the base material, making it suitable for heavy-load applications requiring "high strength + welding" (such as load-bearing columns in large steel structures and the bases of heavy machinery).
5.What difference do mechanical properties make to applicable scenarios?
Q235B galvanized steel: room temperature, light load, complex cold processing; good plasticity, easy to bend/stamp, no need for preheating for welding, lower cost.
Q355B galvanized steel: low temperature environment, heavy load, impact resistance; high yield / tensile strength, qualified low temperature toughness at -20℃, can withstand greater loads and low temperature impact, suitable for heavy-load structures.