Hot rolling is a method of producing metal sheets and coils. This technique requires the following steps:
- Heating metal billets. Thick metal billets must achieve 1,000° F and higher to become easily malleable.
- Rolling the billets and forming metal sheets. Heated billets are placed between two rolls and squeezed to reduce their thickness.
- Leaving metal sheets to cool down.
It’s easy to produce thin metal sheets and coils this way. However, hot rolling has some drawbacks. Check the three undesirable hot-rolled steel properties.
1. Decreased Durability
Under high temperatures, metal crystals rearrange, resulting in stress-free grains. This process is called recrystallization. Recrystallization makes metal weaker but increases its ductility and toughness. So it explains why glowing-hot metal is so soft and malleable.
Since steel becomes softer after hot rolling, it requires further heat treatment or cold rolling to gain the necessary strength. It happens due to a couple more factors besides recrystallization.
Steel contains non-metallic inclusions (such as oxides) that form on its surface under high temperatures. During hot rolling, these inclusions blend with the metal surface and give it a layered structure.
This process is called delamination, and it slightly affects the final quality of metal sheets. They become softer and weaker as delamination causes microcracks in the metal structure.
Residual stress is the stress that remains in an object after the external force is applied. It can occur due to high temperatures and plastic deformation, such as stretching or flattening. It can also take place once metal cools down unevenly.
Due to the nature of hot rolling, the resulting metal products retain some residual stress. While it is self-balanced, it makes the metal less durable and more prone to deformation and fatigue.
2. Unstable Dimensions
Hot metal tends to expand and shrink to its original size when it cools down. Since the thermal extension is inevitable during hot rolling, it’s challenging to control the dimensions of the resulting steel sheets when they cool down. Cooling slightly wraps and distorts a hot-rolled steel sheet.
3. Rough Finish
You can’t make locker cabinets with hot-rolled steel as it is. Since hot metal cools down unevenly and residual stress builds up, tiny scars and stains can occur on the metal surface.
As a result, a rough, scarred finish needs extra polishing procedures before you can paint it. Here they are:
When and Why You Need Hot-Rolled Steel
Although hot-rolled steel is less durable and aesthetically-pleasing than its sleek, polished cold-rolled counterpart, many industries buy millions of tons of it yearly.
Hot-rolled steel prices are 20% lower than those of cold-rolled steel, so many businesses buy it for projects where precision and aesthetics are not a big deal. Different hot-rolled steel grades find application in the following industries:
- Architecture – framing, i-beams, and metal sheets.
- Automotive – truck frames.
- Agriculture – parts of harvesters and tractors.
- Art – steel sculptures.
- Railroad – railroad tracks and trains.
- Many more industries require cheap, tough metal.
So if you prefer toughness to aesthetics and precision, Metinvestholding and other international steel suppliers will provide you with high-class hot-rolled steel products at affordable prices.
Hot-rolled steel isn’t as hard and polished as cold-rolled steel, but it is suitable for industries where price matters more than glossy metal finish. The main drawbacks of hot rolled steel products are their decreased durability, slightly distorted shapes, and rough texture. But if you need tough steel sheets, pipes, or i-beams at affordable prices, hesitate no more and buy hot-rolled steel.