The main production process of large-diameter seamless pipe is hot-rolled large-diameter seamless steel pipe and heat-expanded diameter seamless steel pipe. The largest seamless pipe sizes are 325mm-1220mm and the thickest is 200mm.
Large-diameter seamless steel pipes are cold-drawn, cold-rolled and other cold-formed steel, and the state of direct delivery without any heat treatment 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 steel delivered in the cold-drawn (rolled) state is not covered by oxide scales, and there is a large internal stress, it is easily corroded or rusted. Therefore, steel products in the cold drawn (rolled) state have stricter requirements for packaging, storage and transportation, and generally need to be kept in the warehouse, and attention should be paid to the temperature and humidity control in the warehouse.
After hot rolling or forging, large diameter seamless steel pipes are no longer subjected to special heat treatment, and are delivered directly after cooling, which is called hot rolling or hot forging state. The termination temperature of hot rolling (forging) is generally 800~900°C. After that, it is generally cooled naturally in the air, so the hot rolling (forging) state is equivalent to normalizing treatment.
The difference is that the termination temperature of hot rolling varies from high to low, unlike the strict control of normalizing heating temperature, so the fluctuation of steel structure and performance is larger than that of normalizing. Many iron and steel enterprises adopt controlled rolling. Due to the strict control of the final rolling temperature and the forced cooling measures after the final rolling, the grains of the steel are refined, and the delivered steel has high comprehensive mechanical properties. This is the reason why cold and hot rolled wire rods are superior in performance to ordinary hot rolled wire rods. Steel delivered in hot rolled state. Because the surface is covered with a layer of iron oxide scale, it has certain corrosion resistance. The requirements for storage, transportation and storage are not as strict as those delivered in the cold-drawn (rolled) state. Large and medium-sized steel and medium-thick steel plates can be stored in the open yard or after being covered with thatch.
Large-diameter seamless steel pipes are annealed and heat-treated before leaving the factory. This delivery state is called the annealed state. The purpose of annealing is mainly to eliminate and improve the organizational defects and internal stress left over from the previous process, and to make preparations for the structure and performance of the subsequent process. Alloy structural steel, structural steel with guaranteed hardenability, cold heading steel, bearing steel, tool steel, steel for steam turbine blades, and cable-shaped stainless heat-resistant steel are usually delivered in the annealed state.
Large-diameter seamless steel pipes are cold-drawn, cold-rolled and other cold-formed steel, and the state of direct delivery without any heat treatment 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 steel delivered in the cold-drawn (rolled) state is not covered by oxide scales, and there is a large internal stress, it is easily corroded or rusted. Therefore, steel products in the cold drawn (rolled) state have stricter requirements for packaging, storage and transportation, and generally need to be kept in the warehouse, and attention should be paid to the temperature and humidity control in the warehouse.
After hot rolling or forging, large diameter seamless steel pipes are no longer subjected to special heat treatment, and are delivered directly after cooling, which is called hot rolling or hot forging state. The termination temperature of hot rolling (forging) is generally 800~900°C. After that, it is generally cooled naturally in the air, so the hot rolling (forging) state is equivalent to normalizing treatment.
The difference is that the termination temperature of hot rolling varies from high to low, unlike the strict control of normalizing heating temperature, so the fluctuation of steel structure and performance is larger than that of normalizing. Many iron and steel enterprises adopt controlled rolling. Due to the strict control of the final rolling temperature and the forced cooling measures after the final rolling, the grains of the steel are refined, and the delivered steel has high comprehensive mechanical properties. This is the reason why cold and hot rolled wire rods are superior in performance to ordinary hot rolled wire rods. Steel delivered in hot rolled state. Because the surface is covered with a layer of iron oxide scale, it has certain corrosion resistance. The requirements for storage, transportation and storage are not as strict as those delivered in the cold-drawn (rolled) state. Large and medium-sized steel and medium-thick steel plates can be stored in the open yard or after being covered with thatch.
Large-diameter seamless steel pipes are annealed and heat-treated before leaving the factory. This delivery state is called the annealed state. The purpose of annealing is mainly to eliminate and improve the organizational defects and internal stress left over from the previous process, and to make preparations for the structure and performance of the subsequent process. Alloy structural steel, structural steel with guaranteed hardenability, cold heading steel, bearing steel, tool steel, steel for steam turbine blades, and cable-shaped stainless heat-resistant steel are usually delivered in the annealed state.
