Large diameter seamless steel pipe means outside diameter more than 100MM and the wall thickness is greater 0.2 than the outer diameter of the pipe, Large-diameter seamless steel tube is made from solid tube ingot or the perforation capillary, then through hot rolling and cold rolling or cold dial.
At present China's large diameter seamless steel pipe, the main production process is hot-rolled and heat expansion of large-diameter seamless steel pipe, hot expanded seamless steel pipe specifications for 325mm-1220mm maximum thickest of 120mm, can produce seamless steel pipe thermal expansion Non-national standard dimensions, thermal expansion seamless is what we often say that thermal expansion, density is relatively low but strong contraction rolled steel with oblique method or drawing method to expand a shortage of pipe diameter pipe finishing processes. In a short period of time for the steel thickening to produce non-standard and special types of seamless pipe, and low cost, high production efficiency, the development trend of international rolling fields today.
Large diameter seamless steel pipe by cold drawing, cold-rolled steel products, such as cold forming, heat treatment and without any direct delivery of state called cold-drawn or cold-rolled condition. Compared with hot-rolled (forging) state, high dimensional accuracy cold-drawn steel (rolled) state, good surface quality, low surface roughness, and a high mechanical properties, due to the cold drawn (rolled) steel delivery status oxide surface is not covered, and there is a lot of stress, vulnerable to corrosion or rust, and thus steel cold drew (rolled) state, it's packaging, storage requirements are more stringent, generally need to be kept in the warehouse, and should pay attention to the temperature and humidity control coffers.
Large-diameter seamless steel after hot rolling or forging a special heat treatment and no further direct delivery After cooling, the state is called hot rolling or forging, hot-rolled (wrought) termination temperature is generally 800 ~ 900 ℃, After the general natural cooling in air, so hot rolling (forging) status equivalent to normalizing. The difference is because of hot-rolled (forging) the termination of high and low temperatures, unlike normalizing strict temperature control heating and thus volatility in steel microstructure and mechanical properties than are well done.
Currently, many steel companies controlled rolling, because the finishing temperature control is very strict, and after finishing forced cooling measures taken thus grain refinement of steel, steel delivery have higher mechanical properties. No-Twist controlled cooling of hot-rolled wire rod superior to ordinary hot-rolled wire rod performance is the truth, hot-rolled (forging) state of delivery of steel, the surface is covered with a layer of iron oxide, which has a certain degree of corrosion resistance, storage custody Unlike the strict requirements as cold drawn (rolled) state of delivery of steel, medium-sized steel, thick steel plate can be stored in the open-air yard or through thatch cover. Large diameter seamless steel factory before annealing heat treatment, this condition is called annealing delivery status. Annealing main purpose is to eliminate defects and improve the organization and internal stress left before the procedure and after the procedure to prepare for the organization and performance, alloy structural steel, guaranteed hardenability structural steel, cold heading steel, bearing steel, annealed steel commonly used tool steel, turbine blade steel, heat-resistant stainless steel body cable delivery.
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