Steel is rolled using two types of processes – cold rolling and hot rolling. Well, when steel is rolled at more than the temperature of re-crystallisation, it is called hot rolled steel. When steel is rolled at a lower temperature, it is called cold rolled steel. For example, grade Q235A/B,SS400 are hot rolled steel but SPCC, ST12, DC01 are cold rolled steel.
Cold rolling is a metal working process in which metal is deformed by passing it through rollers at a temperature below its recrystallization temperature. Cold rolling increases the yield strength and hardness of a metal by introducing defects into the metal's crystal structure. These defects prevent further slip and can reduce the grain size of the metal, resulting in Hall-Petch hardening.
The metallurgical process of Hot rolling, used mainly to produce sheet metal or simple cross sections from billets describes the method of when industrial metal is passed or deformed between a set of work rolls and the temperature of the metal is generally above its recrystallization temperature, as opposed to cold rolling, which takes place below this temperature. Hot rolling permits large deformations of the metal to be achieved with a low number of rolling cycles.
Because the metal is worked before crystal structures have formed, this process does not itself affect its microstructural properties. Hot rolling is primarily concerned with manipulating material shape and geometry rather than mechanical properties. This is achieved by heating a component or material to its upper critical temperature and then applying controlled load which forms the material to a desired specification or size.
Theoretically, the only difference between hot rolled and cold rolled steels is that hot rolled steel is rolled to its final dimensions while hot enough to scale (over 1700 degrees F) while cold rolled steel is rolled to its final dimensions well below scaling temperatures
The finished tolerances on hot rolled steels are looser than on cold rolled. Not only the plus or minus tolerance from nominal size, but the "square-ness" of the product. And, from our personal experience that there’s a lot of trapezoidal A36 out there. So, if you need a specific size and you are going to go to a “surplus” place, bring your ruler, square and micrometer to make sure you get what you need.
You’d get fewer slag or carbon inclusions with cold rolled steels.
One other difference that may be of interest to the blacksmith is that if you buy "1018”cold rolled steel", you can be pretty sure that it has close to a 0.18% carbon content and few other impurities. But the spec for A36 can let the carbon content go as high as 0.29% and it can contain many more impurities. More carbon makes it harder to forge.
You generally have to pay about twice as much money for cold rolled steel as for hot rolled steel, for reasons which are probably obvious from the above.
Bebon international is specialized in manufacturing and selling every kind of hot rolled steel and cold rolled steel . We are the professional hot rolled steel supplier and exporter. If you need the hot rolled steel price and cold rolled steel price, please don’t hesitate to contact with us.
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Tags: hot rolled steel , cold rolled steel
