1.What role does the annealing process play in eliminating cold work hardening?
Background: After cold rolling, the strip steel undergoes severe plastic deformation, resulting in grain breakage and increased dislocation density, resulting in high hardness and poor ductility (cold hard state).
Annealing effect: Through recrystallization annealing (usually heated to above the recrystallization temperature, such as 700~850℃), the broken grains are re-nucleated and grown.
Eliminate internal stress, reduce hardness, and restore ductility and deep drawing performance.
Significance: Meet subsequent processing requirements (such as bending and stamping) and avoid cracking.
2.What effect does the annealing process have on the surface coating?
Background: If rolling oil, iron powder or oxides remain on the surface of cold-rolled strip, direct galvanizing will result in poor coating adhesion.
Annealing: Annealing in a reducing atmosphere reduces the surface oxides to pure iron.
High temperature decomposition and volatilization of residual grease to obtain a clean and active surface.
Significance: Ensure direct metallurgical reaction between zinc liquid and steel matrix to form a strong Fe-Zn alloy layer.
3.What effect does annealing process have on mechanical properties?
Process control: Continuous annealing: by controlling the heating rate, holding temperature/time, and cooling rate, the grain size and phase composition can be precisely adjusted.
Hood annealing: suitable for mass production to obtain a more uniform structure (but the cycle is longer).
Target performance: Deep drawing steel: coarse equiaxed ferrite grains (increase r value, n value).
Structural steel: moderately fine grain strengthening to ensure strength.
4.What effect does annealing have on the hot-dip galvanizing process?
Process connection: After annealing, the strip directly enters the zinc pot (about 460℃), and the temperature needs to be kept matching. The continuous annealing line (CAL) and the galvanizing line (CGL) are connected in series to achieve "annealing-galvanizing" integration. Advantages: avoid secondary heating, save energy and reduce surface oxidation.
5.What effect does annealing process have on deep drawing performance?
Through the annealing process, the development of favorable texture is promoted, the plastic strain ratio of the plate is improved, and the high-end needs such as automotive plates are met.