Large-diameter seamless steel pipes are cold-formed steel materials that are directly delivered without any heat treatment, which is called cold-drawn or cold-rolled state. Compared with the hot-rolled (forged) state, the steel in the cold-drawn (rolled) state has high dimensional accuracy, good surface quality, low surface roughness, and higher mechanical properties. Since the surface of the steel delivered in the cold-drawn (rolled) state is not covered with oxide scale and has large internal stress, it is very easy to be corroded or rusted. Therefore, the packaging, storage, and transportation of steel in the cold-drawn (rolled) state have stricter requirements. Generally, they need to be kept in the warehouse, and attention should be paid to the temperature and humidity control in the warehouse.
Large-diameter seamless steel pipe steel is no longer subjected to special heat treatment after hot rolling or forging. It is directly delivered after cooling, which is called a hot-rolled or hot-forged state. The termination temperature of hot rolling (forging) is generally 800-900℃, and then it is generally cooled naturally in the air, so the hot-rolled (forged) state is equivalent to normalizing treatment.
The difference is that the hot rolling (forging) termination temperature is high or low, unlike the normalizing heating temperature which is strictly controlled, so the fluctuation of steel structure and performance is greater than normalizing. Many steel companies use controlled rolling. Because the final rolling temperature is strictly controlled and forced cooling measures are taken after final rolling, the grain of steel is refined and the delivered steel has higher comprehensive mechanical properties. This is why the performance of non-torsion-controlled hot-rolled wire rods is superior to that of ordinary hot-rolled wire rods. The steel delivered in the hot-rolled (forged) state has a certain corrosion resistance because the surface is covered with a layer of iron oxide. The storage and transportation requirements are not as strict as those of the steel delivered in the cold-drawn (rolled) state. Large and medium-sized steel and medium and thick steel plates can be stored in open-air cargo yards or covered.
Large-diameter seamless steel pipe steel is annealed and heat treated before leaving the factory. This delivery state is called an annealed state. The purpose of annealing is mainly to eliminate and improve the organizational defects and internal stresses left over from the previous process, and to prepare the organization and performance for the subsequent process. Alloy structural steel, structural steel to ensure hardenability, cold heading steel, bearing steel, tool steel, steel for turbine blades, and stainless heat-resistant steel for ropes are often delivered in an annealed state.
Post time: Jun-04-2025