Temperature

• One difference between hot rolling and cold rolling is in the names. Hot rolling is done at higher temperatures and cold rolling at lower ones. Cold rolling is done at room temperature. The "hot" in hot rolling is not simply a little warm, but hot enough to affect the metal's structure. This is roughly 1,500 degrees Fahrenheit. This heat makes the metal become rough, or "scale." It also causes it to recrystallize, which means that the molecules rearrange because of the heat, and when the steel cools, this rearrangement makes the metal different from before heating.
  
  

Strength

• Compared to cold rolled rods, hot rolled rods are softer. The cold rolling process works the metal, which makes it extremely hard. The recrystallization during hot rolling makes the steel slightly softer; it is still steel, though, and very hard compared with other materials.
  
  

Flexibility

• Hot rolled rods are more flexible than cold rolled steel. This is because they are slightly softer. Cold rolled steel can withstand more working from a metal smith, though. Hot rolled steel may be more flexible, but it cannot take as much strain. The process of working the metal can cause hot rolled steel to form cracks if it goes on for too long. This makes hot rolled steel better for projects with less attention needed and cold rolled better for detailed works.
  
  

Color

• There are differences in the appearance of hot and cold rolled steel. Cold rolled metal is a grey color, the color of the metal itself. Hot rolled steel takes on a blue-ish tint because of the heat. The heat causes the steel to recrystallize and introduces more oxygen, which causes a chemical reaction called oxidation. This blue color is the oxidation.
  
  

Texture

• The heat also affects the texture of the steel. The blue oxidation and scaling from the heat makes hot rolled steel rougher compared with cold rolled. Because cold rolled steel does not undergo these processes, it is smoother to the touch and shinier in appearance.
  
  

Treatments

• Cold rolled steel takes treatments such as galvanizing and chemical painting better than hot rolled. This is because the treatments adhere to the metal itself. Hot rolled steel has the layer of oxidization on it, preventing the chemicals from reaching the metal. In order to chemically color, galvanize or otherwise treat the steel, this oxidization must be removed.