Q:What is the effect of cold rolling on mild steel?
A:Grain deformation: Cold rolling causes ferrite grains to elongate along the rolling direction, forming fibrous structures and producing work hardening (significantly increased strength and hardness, decreased plasticity and toughness).
Texture formation: {110}<001> texture (cubic texture) may be produced, affecting deep drawing performance.
Q:What is the effect of cold rolling on high carbon steel?
A:1. Changes in structure and properties
Cementite distribution: The cementite lamellae in the pearlite structure are flattened and arranged alternately with ferrite into fibers, and the hardness is significantly improved (HV increases from 200-250 in hot rolled state to 350-450).
Work hardening sensitivity: The higher the carbon content, the greater the work hardening index, and the brittleness increases after cold rolling. 2. Processing applicability
Advantages: After cold rolling, it can be directly used for springs (such as steel strip springs) and tool blanks, taking advantage of the high hardness characteristics.
Precision cold rolling (such as cold rolled strip steel) can control the thickness tolerance of ±0.01mm to meet the needs of precision parts.
Limitations: The pass reduction rate needs to be strictly controlled (single pass ≤15%) to avoid edge cracking;
Spheroidizing annealing (temperature 750-780℃) is required after cold rolling to improve cutting performance, otherwise the tool is easy to wear.
Q:What effect does cold rolling have on low alloy steel?
A:1. Changes in structure and properties
Effects of alloy elements: Mn, Si and other solid solution strengthening elements intensify work hardening, and the strength increase after cold rolling is higher than that of low carbon steel (yield strength can reach 500-600MPa).
Possible phase change: Steels containing Cr, Mo and other elements may produce a small amount of martensite after cold rolling, increasing brittleness.
2. Processing applicability
Advantages: High strength properties are suitable for structural parts (such as cold-rolled steel sections and automobile beam steel). Grains can be refined through controlled rolling and controlled cooling processes (with rapid cooling after rolling), taking into account both strength and toughness.
Limitations: Stress relief annealing (temperature 500-600℃) is required after cold rolling to eliminate internal stress and prevent aging cracking; Weldability decreases with increasing alloy content, and preheating treatment is required.
Q:What effect does cold rolling have on stainless steel?
A:1. Changes in structure and properties
Cold rolling causes strain-induced martensitic transformation of austenite, which significantly improves strength and hardness, but slightly reduces corrosion resistance.
After cold rolling, the grains of ferritic stainless steel are refined, the degree of work hardening is lower than that of austenitic steel, and the plasticity is well maintained (elongation ≥ 20%), which is suitable for deep drawing parts (such as kitchen sinks).
2. Processing applicability
After cold rolling, the surface roughness Ra≤0.8μm can be directly used as a decorative plate (such as mirror stainless steel). The corrosion resistance and plasticity of austenitic stainless steel can be restored by solution treatment (quenching at 1050-1100℃).
Q:What effect does cold rolling have on silicon steel?
A:1. Changes in structure and properties
Grain orientation control: Cold rolling + annealing can form a Gossian texture ({110}<001>), significantly improve magnetic permeability and reduce iron loss.
Decarburization treatment: After cold rolling, high temperature annealing (900-1100℃) is required to decarburize to a carbon content of ≤0.003% to prevent carbides from hindering the movement of magnetic domains.
2. Processing applicability
Cold-rolled thin-gauge (0.1-0.35mm) silicon steel is the core material for high-efficiency motors and transformers.
Restrictions:
During rolling, the roughness of the roller surface must be strictly controlled to avoid damage to the insulating coating; the finished product needs to be coated to prevent short circuits between sheets.