1.What is the definition of hot rolled delivery status?
The base material (Q345B steel plate) is pickled and hot-dip galvanized directly after hot rolling, without undergoing cold rolling or annealing. Its delivery status is marked as "hot rolled + hot-dip galvanized" (electrogalvanizing rarely uses hot-rolled base material). The hot-rolled base material has a microstructure of "ferrite + pearlite" with relatively coarse grains (20-40μm). However, controlled laminar cooling after hot rolling ensures that its mechanical properties meet the Q345B standard.
2.What are the characteristics of hot-rolled delivery status?
Thickness Range: Mostly medium-thick gauges ranging from 3.0-12.0mm (hot-rolling is difficult to produce thinner substrates).
Mechanical Properties: Yield strength 345-355MPa, tensile strength 470-620MPa. Toughness slightly lower than cold-rolled (impact energy 34-38J), but stable strength suitable for load-bearing.
Surface Quality: Minor traces of oxidation may be present (removable by pickling). After galvanizing, the surface has a typical hot-dip galvanized matte finish with no noticeable gloss.
3.What is the definition of cold rolled delivery status?
The base material (Q345B steel plate) is first hot-rolled to a medium-thick gauge (3-5mm), then cold-rolled to the target thin gauge (0.2-3.0mm). Finally, it undergoes pickling and galvanizing (hot-dip or electroplating). The delivery status is marked as "cold rolled + hot-dip galvanized / electroplated galvanized." The cold rolling process produces "cold work hardening" (grain refinement to 10-20μm). Some products undergo additional recrystallization annealing (to eliminate internal stress and improve toughness). Therefore, the cold-rolled state can be further divided into "cold-rolled hardened (CR-H)" and "cold-rolled annealed (CR-A)."
4.What are the characteristics of cold rolled delivery status?
Thickness Range: 0.2-3.0mm thin gauge with extremely tight thickness tolerance (±0.05mm), flat plate shape (camber ≤3mm/m);
Mechanical Properties:
Cold-rolled hardened: Yield strength 370-380MPa (cold work hardening increases strength), elongation 20%-22%, suitable for simple forming without subsequent bending;
Cold-rolled annealed: Yield strength 345-360MPa, elongation 22%-25%, and improved toughness (impact energy 38-45J), suitable for complex processes such as cold bending and stamping;
Surface Quality: The cold-rolled substrate has a smooth surface, and after galvanizing (especially electrogalvanizing), it can achieve a bright silver color with high surface precision and no obvious defects.
5.What is the annealing delivery status definition and process logic?
To address the high internal stress and poor formability of cold-rolled hardened substrates, a recrystallization annealing process (heating to 600-700°C, holding for a period, and then slow cooling) is added after cold rolling and before galvanizing to eliminate cold work hardening and improve microstructure uniformity. The delivery state is marked as "cold-rolled annealing + galvanizing." This state is essentially an optimized version of the cold-rolled state. The key difference lies in reducing internal stress and improving formability through annealing, rather than changing the substrate type.