Cold Rolled Mild Steel

COLD ROLLED STEEL

Cold-rolled sheets are thin steel sheets that have been processed at room temperature after being hot-rolled. Due to their superior strength, smooth surface, and precise dimensions, they are widely used in industries such as automotive, construction, appliances, and furniture.  

Cold rolling is the main process used to roll steel at room temperature. First, the cleaned steel coil is unwound and fed into the cold rolling mill. In this mill, the steel passes through a series of rollers at room temperature between 60 degrees Celsius  and 180 degrees Celsius, which gradually reduces the thickness of the steel to the desired level. Cold rolling makes the steel stronger and harder, and it also improves the surface finish and accuracy of dimensions. Another benefit of cold rolling is that it can increase the strength of steel by up to 20 percent through strain hardening (metal is bent, stretched, or compressed beyond its elastic limit, the movement of dislocations within its crystal structure is restricted). Depending on the final thickness needed, the steel may go through several rolling stands or passes, with each one gradually reducing the thickness. The smooth surface finish of cold-rolled steel facilitates easy painting and coating, which is crucial for automotive interiors. 

The cold rolling process work-hardens (the process deforming steel to make it harder and stronger) the steel, making it brittle. To restore ductility, the cold-rolled steel undergoes an annealing process. During annealing, the cold-rolled steel is heated to a specific temperature below its recrystallisation point in a controlled atmosphere to prevent oxidation. The steel is maintained at this temperature for a set period to allow recrystallisation, which softens the steel and restores its ductility. After soaking, the steel is slowly cooled to room temperature. The cooling rate can be controlled to achieve specific mechanical properties.

Tempering is an optional step that may follow annealing, depending on the desired properties of the steel. The annealed steel may undergo a light rolling pass known as temper rolling or skin passing. This process improves flatness, surface texture, and uniformity and minimises the risk of stretcher strains, also known as Lüders lines, during subsequent forming operations. After the cold rolling and annealing processes, the steel is prepared for final processing.

Categorisation based on different IS standards:

IS 513 (Part 1):2016 CR2 

IS 513 (Part 2):2016 is a standard for cold reduced carbon steel sheet and strip with high tensile and multi-phase steel. It specifies the chemical composition, mechanical properties, and tolerances for CR1 and CR2 grade steel.    

Cold Rolled Steel Applications

Automotive Industry:

Cold-rolled Grain Oriented steel is commonly used for manufacturing car body panels, including doors, bonnets, roofs, and fenders. Cold-rolled steel's high strength and excellent formability make it ideal for forming the complex shapes required for these components. Additionally, it is used to make interior components such as seat frames, instrument panels, and other structural elements. The smooth surface finish of cold-rolled steel allows for easy painting and coating, which is essential for automotive interiors.

Construction Industry:

In the construction industry, cold-rolled steel is often used for roofing sheets and wall cladding due to its durability, strength, and ability to withstand harsh weather conditions. It is also used to construct lightweight structural components like studs, tracks, and joists for non-load-bearing walls and partitions. Furthermore, CR steel is used for framing in pre-engineered buildings and modular construction, providing a strong, lightweight, and versatile solution. 

Appliance Manufacturing:

Cold-rolled steel is widely used in the manufacturing of home appliances like refrigerators, washing machines, ovens, and microwaves. Its high strength-to-weight ratio and smooth finish make it ideal for these products' outer casings and structural components. It is also used for enclosures and frames for various electronic devices, offering protection and a sleek appearance.   

Furniture Industry:

Cold-rolled steel is also extensively used for making office furniture, including filing cabinets, desks, and shelving units, where strength, durability, and ease of fabrication are important. It is also used to manufacture home furniture, such as metal beds, chairs, and tables, where a strong and durable material is required. 

Electrical Industry:

Cold-rolled steel is used in the electrical industry to make electrical panels, switchgear, and enclosures due to its excellent electrical conductivity, durability, and ability to easily form into precise shapes and sizes. It also produces transformer cores, which require high permeability and low core loss to improve efficiency.  

Packaging Industry:

In the packaging industry, cold-rolled steel is used to manufacture steel drums and containers for storing and transporting various liquids and solids. The material's strength and resistance to impact make it suitable for handling both hazardous and non-hazardous materials.

Aerospace Industry:

The aerospace industry uses cold-rolled steel to manufacture various structural components that require high strength, precision, and lightweight properties. It is used in brackets, panels, and other non-critical structural parts. Cold-rolled steel is also used in aircraft interiors, including seating frames and other components that require high strength-to-weight ratios. 

Consumer Goods:

Cold-rolled steel is used in manufacturing bicycles and sporting equipment due to its high strength and formability, making it ideal for producing durable and lightweight frames and components. It is also commonly used for making hand tools like wrenches, pliers, and screwdrivers because of its toughness and ability to withstand wear and tear. 

 Agricultural Equipment:

Cold-rolled steel is used to manufacture various parts of agricultural machinery, such as ploughs, cultivators, and harvesting equipment. Its high strength and resistance to bending and wear make it suitable for demanding agricultural applications.   

Industrial Equipment:

Cold-rolled steel makes various parts and components for industrial machinery, including gears, shafts, and bearings. Its precision and durability are critical for the reliable performance of industrial equipment. 

Medical Equipment:

Cold-rolled steel is used in the medical equipment industry to produce hospital equipment like beds, trolleys, and medical storage units. The material’s hygiene, durability, and ease of cleaning makes it ideal for these applications.  

FAQs 

Q:What is cold-rolled sheet metal? 

A: Cold-rolled sheet metal is a form of steel that has undergone a cold-rolling process, where it is cold worked and shaped at room temperature. This process enhances its strength, malleability, dimensional accuracy, and surface finish.

Q: What are the advantages of using cold-rolled sheet metal?

A: Cold-rolled sheet metal offers several advantages, including improved surface finish, tight dimensional tolerances, and better formability compared to hot-rolled sheet metal. Cold-rolled sheets can become as thin as 0.35 mm thickness. 

Q: What are the common applications of cold-rolled sheet metal? 

A: Cold-rolled sheet metal is widely used in industries such as automotive, construction, appliances, furniture, and manufacturing. It is commonly used for making components such as body panels, chassis parts, roofing, cladding, electrical appliances, and precision-formed parts. It is also a base material for Galvanised Plain Sheet, Galvalume Steel Sheet and Pre-Painted Galvalume Steel.  

Q: How does cold-rolled sheet metal differ from hot-rolled sheet metal?

A: Cold-rolled sheet metal is processed at room temperature, which enhances its mechanical properties and surface finish, making it smoother and more precise in terms of dimensions. On the other hand, hot-rolled sheet metal is formed at high temperatures, resulting in a rougher surface and the potential presence of scale due to oxidation during the cooling process.

Comparison: 

Q: What is the thickness range available for cold-rolled sheet metal? 

A: Cold-rolled sheet metal typically ranges from 0.1 millimetres to 3 millimetres in thickness. The specific thickness depends on the application and industry standards, such as in the automotive, appliance, or construction sectors.   

Q: Is cold-rolled sheet metal corrosion-resistant? 

A: Cold-rolled sheet metal itself is not inherently corrosion-resistant, but it can be made resistant by applying rust-preventative oil or coatings, such as galvanisation or painting, at the exit end of the temper mill. For example, galvanised cold-rolled steel is commonly used in automotive body panels, where corrosion resistance is crucial.