Distinguishing Hot Rolled Steel Vs Cold Rolled Steel
A common question we encounter at Creatingway is which one is better; hot rolled steel or cold-rolled steel. One of the most important tasks of an engineer is choosing the appropriate material. This is normally dependent on the final product application. The selection process is tricky since there is a wide array of metal in existence. These two metals, in particular, have their own merits and uses. There are types of steel that produce excellent home appliances. Others find use in the automobile, construction, and marine industry.
However, there is one more distinction to make. Materials with similar chemical composition may have different features. This guide will cover the differences between hot rolled and cold rolled steel.
The Differences Between Hot Rolled and Cold Rolled Steel
The Hot Rolled Steel
Hot-working is a more common practice than cold working. This is since it takes up less energy and force to accomplish. Manufacturers use it in compressive forming techniques. Examples include extrusion, rolling, and forging.
What is the Hot Rolling Method?
Hot rolling occurs above a material’s recrystallization temperature. In the case of steel, the temperature is above 1,000 degrees. The initial material is normally steel slabs or billets. We first heat the material above the aforementioned temperature. The next step involves feeding it to the rolling machinery. Continuous rolling will result in the intended final shape. This is usually a metal sheet that is 3mm and upwards in thickness.
What’re The Characteristics?
It is usually easy to shape metal at high temperatures with minimal delays. It is thus possible to manufacture large quantities with it than cold rolling. This ensures that the market price for hot rolled steel is lower. Cooling of the steel takes place at room temperature. We call this process normalizing. During this process, the material’s microstructure changes. This helps in increasing its toughness and ductility. Ductility is a key feature when subjecting a workpiece to forming processes. It allows manufacturers to any material depending on the design.
However, it does not possess the best quality. It undergoes slight shrinkage during cooling. This results in the steel metal having some internal stress. Additionally, stress contributes to irregularities during measurement. Moreover, it may cause distortion. The material’s tolerances may range between 2 to 5 %. Additionally, the steel’s surface may have a scaly finish. This is due to an oxide layer that forms at elevated temperatures. In the case of steel bars, the corners may be round.
Uses of Hot Rolled Steel
Hot rolled steel is an excellent choice when tight tolerances are not necessary. This is the case in many fields. Their price advantage matters more than its precision. A few common uses are namely in:
- Automobile frames
- Pipes and tubes
- Railroad tracks
- Doors and shelving
- Railroad car parts
The Cold Rolled Steel
Cold working is a metal forming technique that holds several advantages over hot working. Processes that fall under cold working include cold rolling and cold drawing. Cold drawing is ideal for manufacturing sheet metal. Cold drawing is ideal for manufacturing round or rectangular bars.
What Is the Cold Rolling Method?
Cold rolling takes place at temperatures below a material’s recrystallization point. The process commences like hot rolling. The material takes up the desired shape with minimal resistance. We then leave the metal to cool at room temperature. Afterward, we feed the half-finished product to cold reduction mills. Here, it undergoes rolling until it attains a thickness between 0.5-3 mm mild steel.
For the case of stainless steel, it achieves a thickness between 0.5-5mm. We normally cool the material using an oil. Moreover, the oil acts as a lubricant as the rolling process takes place. The rolling speed increases as the metal sheet gets thinner between the rolls. Deformation and wear are, therefore, possible if the oil was not present. You can easily identify cold roll steel by its glossy and smooth surface.
The working occurs below the materials recrystallization temperature. This ensures strain hardening takes place. The rolls cause plastic deformation. Consequently, cold-rolled steel ends up having a higher yield strength than hot rolled steel. For instance, a hot rolled steel product may possess a yield strength of 235 MPa. A cold rolled steel of the same chemical composition possesses a 365 MPa yield strength.
The main merits of cold working are:
- Clean surface
- Accurate finished dimensions
- Better strength properties
Uses of Cold-rolled Steel
The mentioned merits make cold-rolled steel applicable in many scenarios. Finished products require minimal surface finishing as they are already smooth. A few of its uses are namely:
- Structural parts
- Metal furniture
- Water heaters
- Home appliances
- Frying pans
- Fan blades
- Computer cabinets
- Metal containers.
When selecting the appropriate material for your product, we advise our clients to first understand the differences between these manufacturing methods. It is pointless to spend money on something you do not need. For any quotes or further inquiries, kindly contact us at Creatingway for help.
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