Black-Annealed Cold Rolled Steel Coil

Black-Annealed Cold-Rolled Steel Coil
lack-annealed cold-rolled steel refers to cold-rolled steel coils that undergo annealing (heat treatment) in a controlled atmosphere without subsequent pickling or surface finishing. This leaves a dark oxide layer (“black” surface) on the steel, distinguishing it from bright-annealed or galvanized products.Key Manufacturing Process**:
1. **Cold Rolling**:
– Steel hot-rolled coils are further processed at room temperature to achieve precise thickness (0.2–3.0 mm) and smoother surfaces.
2. **Annealing**:
– The cold-rolled coils are heated to 650–850°C in a reducing atmosphere (e.g., nitrogen/hydrogen) to relieve internal stresses and improve ductility.
– No pickling or coating is applied post-annealing, retaining the dark oxide layer.

Key Features
– **Surface**:
– Matte black appearance due to residual oxide scale (not as smooth as bright-annealed steel).
– Slightly rougher texture but suitable for painting or further processing.
– **Mechanical Properties**:
– Higher strength and hardness compared to hot-rolled steel.
– Improved formability and uniformity from annealing.
– **Cost**:
– More affordable than pickled or galvanized cold-rolled steel due to fewer post-treatment steps.

#### **Common Materials**:
– Low-carbon steels (e.g., SPCC, DC01).
– High-strength steels (e.g., HSLA grades).

#### **Applications**:
– **General Manufacturing**: Automotive brackets, furniture frames, electrical cabinets.
– **Construction**: Non-critical structural parts, roofing, and cladding (after painting).
– **Industrial Components**: Hydraulic systems, machinery parts requiring moderate corrosion resistance.

#### **Typical Specifications**:
– **Thickness**: 0.2–3.0 mm.
– **Width**: 600–1,500 mm.
– **Surface**: Uncoated, with Fe₃O₄/FeO oxide layer.
– **Standards**: ASTM A1008, JIS G3141, EN 10130.

#### **Advantages**:
– Cost-effective for applications where surface aesthetics are secondary.
– Retains weldability and paint adhesion properties.
– Simplified supply chain due to minimal post-processing.

#### **Disadvantages**:
– Limited corrosion resistance; requires protective coatings for outdoor use.
– Dimensional tolerances slightly less precise than bright-annealed steel.