Hot Rolled Vs Cold Rolled Steel: The Ultimate Guide
This guide compares all vital details about hot rolled steel and cold rolled steel. So, before deciding whether to choose hot rolled vs cold rolled steel, read this guide – it will help you choose perfect material.
Features Of Hot Rolled Steel
Slightly Rounded Corners: Hot rolled steel has slightly rounded corners and edges in plate products which is caused by low precision and shrinkage.
Highly Malleable: Highly malleable and can be fabricated into different shapes because heating teel to higher temperatures improves malleability.
A few Distortions: During hot rolling, the scaly finish happens because of the rolling procedure, however, it can be corrected through pickling or grinding.
Increased Toughness and Ductility: Hot rolled steel is normally very ductile and tough because during hot rolling, all the internal stresses are removed.
Normalized Steel: When steel is hot rolled, it also undergoes normalization.
Features Of Cold Rolled Steel
Tighter Tolerances: Cold rolled steel offers tighter dimensional tolerances due to the fact that the process does not interfere with its microstructure. Applications like aerospace industry that require precision, prefer to use this method.
Smoother Surfaces: Cold rolling produces steel parts with smooth surfaces and edges since there are no remnants deposited on the surface. Square and well-defined edges bars made through cold rolling of steel have square and defined corners and edges.
Uniform and Straight: Parts produced through cold rolling steel have enhanced concentric straightness and uniformity compared to those made through hot rolling.
Advantages Of Hot Rolled Steel
Slightly Cheaper: Hot rolled steel is slightly cheaper compared to cold rolled steel because the formation processes are easier. Also, working with hot rolled steel saves on energy consumption.
High Flexibility: At high temperatures hot rolled steel can be highly flexible and can be formed into any shape as required.
Wide Usage: Hot rolled steel has tons of uses because it is mostly in the form of sheets. They are suitable for most projects that don’t require tighter tolerances.
Fast Formation: Since hot rolled steel is highly malleable and easy to form, manufacturers take shorter time working with them.
Advantages Of Cold Rolled Steel
Durable: When steel is rolled at room temperature, it gets to be more durable because this results into work hardening.
Tight Dimensions: Even though cold rolled steels come in various sizes, they are thinner than when hot rolled hence the tighter tolerances.
Smooth Texture: Cold rolling procedures flatten and compress steel billets making grains to elongate at the microscopic level smoothing and packing them tightly.
Increased Accuracy: Steel sheets don’t expand during cold rolling hence retaining the dimensions leading to the formation of accurate parts.
Cost-Effective: Cold rolled steel does not need further metal processes because it is hard and shiny.
Disadvantages Of Hot Rolled Steel
Less Durable: Hot rolling makes steel weaker compared to cold rolling because of the heat application which interferes with the normal structure.
Roughness: Roughness can be felt though touch or seen under a microscope and hot rolled steel has a very rough surface.
High Equipment Cost: Since hot rolling requires heat to raise the temperatures to the required level, manufacturers are forced to invest highly on equipment.
Low Accuracy: Hot rolled steels are not capable of adhering to tight tolerances because the steel has to undergo various changes.
Works With Larger Parts: Hot rolling can only work with large section steels.
Disadvantages Of Cold Rolled Steel
Less Flexible: Cold rolling does not raise the temperature of the steel hence it remains hard making it difficult to comfortably manipulate.
High Cost: High cost is incurred during the equipment set up stage and also during operations, a lot of energy is consumed.
Low Speed: Cold rolling is a slower process compared to the hot rolling due to the fact that the steel is very hard and not easy to form.
Limited Complexity: With cold rolling, manufacturers cannot manipulate steel as easily as it is with hot rolling.
Limited Reductions: Steel parts cannot be reduced through cold rolling.
Differentiating Hot Rolled Steel From Cold Rolled Steel
Below is a table showing the differences between hot rolled steel and cold rolled steel considering their mechanical properties.
|Properties||Cold rolled steel||Hot rolled steel|
|Elongation in 2’’||28||36|
|Yield strength||70000 psi||45000 psi|
|Reduction of size||55||58|
|Tensile strength||85000 psi||67000 psi|
Other factors that can be used to differentiate between hot rolled steel and cold rolled steel are discussed below.
Surface Quality And Appearance
Hot rolled steel usually has rough surfaces and edges due to the fact that remnants are left on the surface. These remnants happen because of rapid cooling from extremely high temperatures. Cold rolled steel on the other hand, portrays smoother edges and surfaces because the temperatures are never raised.
Hot rolled steel is processed at temperatures high above its recrystallization temperature, approximately 17000F. At this point the steel can be manipulated into various shapes as required. On the other hand, cold rolled steel is only processed when the steel is ready to make new grains.
This is because bending and rolling destroys grains reducing its strength hence the need for annealing. Annealing process takes place at temperatures between 1333 to 14000F (slightly above recrystallization point).
Hard And Strength Of Steel
Hot rolling of steel requires raising the temperatures so high above the recrystallization temperature and cooling it rapidly to room temperature. At this rate, the stress points are not able to regain their grains making the end product less strong and less hard.
Cold rolling of steel results into a stronger and harder steel which is also very malleable because of the uniform microstructure.
Steel hardness and strength depend on the number of internal stresses a steel metal has. Looking at a cold rolled steel, all the internal stresses are present hence making the metal harder and stronger. While hot rolled steel which is less hard and less strong has been rid of all the internal stresses.
Cold rolled steel presents slight distortions on the surfaces and the edges when formed or bent. This is because cooling leads to deposits of remnants on the surface. In contrast, cold rolled steel presents well defined, squared edges and corners with excellent straightness and uniformity.
Generally, cold rolled steel is slightly more expensive than hot rolled steel. The difference in the cost is due to the different production operations for each.
Steel Cold Rolling Process (Step-by-step Process)
Steel material is passed through a set of processes in a pickling line including hydraulic acid baths and scale breaker machines. Such processes are meant to eliminate any oxide film or surface scales that may cause surface flaws during the process.
Cold Rolling Stage
After pickling, the steel material is moved to tandem mills where cold rolling takes place to the required thickness. An automated shape adjustment procedure is put in place through the use of equipment put in place.
Electrolytic Cleaning Stage
An electrolyte cleaning system is put in place after the cold rolling stage and just before the annealing process. The cold rolled steel is moved to this place where various contaminants and lubricant oil are removed from the part.
After the electrolytic cleaning of the part, it is taken to the annealing stage where strength and toughness are acquired. Annealing can be done through two different methods including continuous annealing and batch annealing.
Skin Pass Stage
Following annealing, the cold rolled steel may still have some extra skin that may need to be removed. Therefore, at the skin pass stage, surface defects like stretch marks are removed leaving the surface smooth and lustrous.
Steel Hot Rolling Process (Step-by-step)
At the reheating stage, steel material is taken a conditioning step consisting of a furnace and scale breakers. The scale breakers are responsible for removing thick scales on the surface of the steel metal. Thick scales are removed to prevent them from forming on the surfaces of hot slabs.
Roughing process takes place after the reheating stage where steel is rolled into materials with the required dimensions. A roughing mill is used to give the steel a proper shape, width and thickness automatically.
At the exit and entry sections of the mill used for roughing, the strip of the material is rolled. Rolling takes place in the direction of the width using an edger in an automatic width control system.
Finishing Rolling Stage
Finishing rolling stage is necessary for adjusting the width and the thickness of the hot rolled steel part. Finishing rolling gives the steel a specified dimension with a smooth surface and a shape as was predetermined.
Run-out And Coiling
After the finishing mill, the steel strips are taken to a run-out table for coiling to take place. At the run-out table, the hot rolled steel is sprayed with a medium, usually water, to aid in the cooling process.
- Mechanical components
- Rods, bars, sheets and strips
- Metals furniture
- Home appliances.
- Agricultural equipment
- Metal buildings
- Automotive frames and wheel rims
- Structural components
- Railroad equipment
People Also Ask:
Comparing cold rolled steel and hot rolled steel in terms of strength and durability, cold rolled steel is better. In terms of dimensional tolerances, cold rolled steel is still better compared to hot rolled steel. However, in terms of malleability and formability, hot rolled steel is a better choice.
Cold rolled steel has various uses in different industries for instance in the aerospace industry it can be used for making aerospace components. Other uses of cold rolled steel include making rods, strips, bars, sheets, furniture, home appliances and mechanical components.
Hot rolled steel does not have surface finish but due to the high temperatures during the process, it acquires an oxide coating. The coating may prevent rusting for a short time; however, rusting may take place later during the application.
Hot rolled steel is cheaper compared to cold rolled steel because it does not need to undergo other energy consuming processes. The main reason why cold rolled steel in more expensive is because of extra processes like annealing meant to remove internal stresses.
Polishing is done to improve the surface finish to the required appearance. Grinding process ensures that the original size tolerance range is acquired.
Turning is used for removing the imperfections on the surface. And finally cold drawing improves the tensile and yield strengths.