Do you know the six delivery status of steel-Part 1
1. Hot rolled state
The steel is no longer subjected to special heat treatment after hot rolling or forging, and is delivered directly after cooling. It is called hot rolling or hot forging. The end temperature of hot rolling (forging) is generally 800 to 900 ℃, and then generally in the air Natural cooling, so the state of hot rolling (forging) is equivalent to normalizing treatment. The difference is that because the termination temperature of hot rolling (forging) is high or low, unlike normalizing, the heating temperature is strictly controlled, so the fluctuation of steel structure and performance is greater than that of normalizing. At present, many steel companies use controlled rolling, because the temperature control of the final rolling is very strict, and forced cooling measures are taken after the final rolling, so the grain of the steel is refined, and the delivered steel has higher comprehensive mechanical properties. It is the reason that the cold-rolled wire rod without torsion control is superior to the ordinary hot-rolled wire rod. The steel delivered in the hot-rolled (forged) state has a certain corrosion resistance due to the surface covered with a layer of iron oxide, so it is stored and stored The requirements are not as strict as the steel delivered in cold drawn (rolled) state. Large and medium-sized steel and medium-thick steel plates can be stored in the open-air yard or after being covered.
2. Cold drawn (rolled) state
The cold-formed, cold-rolled and other cold-formed steel products are directly delivered without any heat treatment, which is called cold-drawn or cold-rolled state. Compared with the hot rolled (forged) state, the cold drawn (rolled) state steel has high dimensional accuracy, good surface quality, low surface roughness, and has higher mechanical properties. Due to the cold drawn (rolled) state, the steel is delivered The surface is not covered with oxide scale, and there is a lot of internal stress, which is very susceptible to corrosion or rust. Therefore, the cold drawn (rolled) steel has strict requirements for packaging, storage and transportation, and generally needs to be kept in the warehouse. And should pay attention to the temperature and humidity control in the warehouse.
3. Normalizing state
The steel is heat-treated by normalizing before leaving the factory. This delivery state is called normalizing. Since the normalizing heating temperature (Ac3+30-50°C for hypoeutectoid steel and Accm+30-50°C for hypereutectoid steel) is more strictly controlled than the hot rolling termination temperature, the structure and properties of the steel are uniform. Compared with the annealed steel, due to the faster normalizing cooling rate, the amount of pearlite in the steel structure increases, and the grains of the pearlite layer and steel are refined, so it has higher comprehensive mechanical properties and is beneficial to improvement The Wei structure of low-carbon steel and the cementite network of hypereutectoid steel can prepare the structure for further heat treatment of the finished product. Carbon-bonded steel and combined steel are often delivered in normalized condition. Certain low-alloy high-strength steels such as 14MnMoVBRE and 14CrMnMoVB steel also require normalized delivery in order to obtain a bainite structure.