Large diameter carbon steel pipe
Posted by zora li on March 14th, 2023
Large-diameter carbon steel pipe refers to a large-diameter seamless steel pipe with an outer diameter greater than 100MM and a wall thickness greater than 0.2 of the outer diameter of the pipe. It is made of a solid ingot or a perforated capillary tube by hot rolling or cold rolling. Roll or cold call.
At present, the main production process of large-diameter seamless steel pipes in my country is hot rolling and thermal expansion of caliber seamless steel pipes. The seamless pipe is what we often say that the thermal expansion, the density is relatively low but the steel with strong shrinkage is used to expand the diameter of the pipe by the oblique method or the drawing method. It is the development trend of the international rolling field to produce non-standard and special type seamless pipes for steel thickening in a short period of time, with low cost and high production efficiency.
Large-diameter seamless steel pipes are cold-formed, cold-rolled, and heat-treated without any direct delivery status called cold-drawn or cold-rolled steel. Compared with the hot-rolled (forged) state, the cold-drawn (rolled) state steel has high dimensional accuracy, good surface quality, low surface roughness, and high mechanical properties. Due to the oxidation surface of the cold-drawn (rolled) steel delivery state It is not covered, has a lot of stress, and is easy to corrode or rust. Therefore, the packaging and storage requirements for steel in cold drawn (rolled) state are relatively strict, and generally need to be put into storage, and attention should be paid to temperature and humidity control warehouses.
The state of large-diameter seamless steel after hot rolling or forging, which has undergone special heat treatment and is no longer directly delivered after cooling is called hot rolling or forging. The termination temperature of hot rolling (forging) is generally 800-900 °C, and it is usually air-cooled after natural cooling. , so the hot rolling (forging) state is equivalent to normalizing. The difference is that because the hot rolling (forging) end temperature is high and the low temperature is different, the heating temperature is not strictly controlled like normalizing, so it does a good job in the structure fluctuation and mechanical properties of the steel. At present, many steel mills control rolling, because the final rolling temperature control is very strict, and forced cooling measures are taken after final rolling, so that the steel grains are refined, and the delivered steel has high mechanical properties. This is the reason why the performance of hot-rolled wire rods with untwisted controlled cooling is better than that of ordinary hot-rolled wire rods. The steel materials delivered in the hot-rolled (forged) state are covered with a layer of iron oxide on the surface, which has a certain degree of corrosion resistance. The strict requirements for delivery in the cold-drawn (rolled) state are different. Medium-sized steel and thick steel plates can be stored in the open air or with a thatch cover. Before the annealing heat treatment of large-diameter seamless steel mills, this state is called the annealing delivery state. The main purpose of annealing is to eliminate defects and improve the residual structure and internal stress before the process, and prepare for the structure and performance after the process. Alloy structural steel, structural steel with guaranteed hardenability, cold heading steel, bearing steel, and annealed steel are commonly used tool steels , steam turbine blade steel, heat-resistant stainless steel body cable delivery.
