The specifications of seamless steel pipes are usually expressed by the outer diameter * wall thickness (unit: mm). According to the production method, seamless steel tubes can be divided into two categories: hot-rolled seamless steel tubes and cold-rolled (dial) seamless steel tubes. Hot-rolled seamless steel pipes are divided into general steel pipes, low and medium pressure boiler steel pipes, high pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, petroleum cracking pipes, geological steel pipes and other steel pipes. Cold-rolled (dial) seamless steel pipe in addition to general steel pipe, low and medium pressure boiler steel pipe, high pressure boiler steel pipe, alloy steel pipe, stainless steel pipe, petroleum cracking pipe, other steel pipes, including precision steel pipe, carbon thin-walled steel pipe, alloy thin Wall steel pipe, stainless steel thin-walled steel pipe, special-shaped steel pipe, etc. The outer diameter of hot-rolled seamless pipe is generally larger than 32mm, the wall thickness is 2.5-75mm, the outer diameter of cold-rolled seamless steel pipe can be 6mm, the wall thickness can be 0.25mm, the outer diameter of thin-walled pipe can be 5mm, the wall thickness is less than 0.25mm, cold Rolling is more accurate than hot rolling. In pipeline engineering, hot-rolled pipes are often used when the pipe diameter exceeds 57 mm, and cold-drawn (rolled) pipes are often used when the pipe diameter is less than 57 mm.
Generally, the seamless steel pipe is made of high-quality carbon steel such as 10#, 20#, 30#, 35#, 45# or low-alloy structural steel such as 16Mn or 5MnV or hot-rolled steel of 40Cr, 30CrMnSi, 45Mn2, 40MnB or the like. Cold rolled. Seamless pipes made of low carbon steel such as 10# and 20# are mainly used for fluid conveying pipes. Seamless tubes made of medium carbon steel such as 45# and 40Cr are commonly used to make mechanical parts, such as parts for automobiles and tractors. Generally, seamless steel pipes are required to ensure strength and carry out flattening tests. The hot rolled steel pipe is delivered in a hot rolled state or a heat treated state; the cold rolling is delivered in a heat treated state.
Hot rolling, as the name suggests, has a high temperature of the rolled piece, so the deformation resistance is small and a large amount of deformation can be achieved. Taking the rolling of the steel sheet as an example, the thickness of the continuous casting blank is generally about 230 mm, and after rough rolling and finish rolling, the final thickness is 1 to 20 mm. At the same time, due to the small width-to-thickness ratio of the steel plate, the dimensional accuracy requirement is relatively low, and the shape problem is not easy to occur, and the convexity is mainly controlled. For the requirements of the organization, it is generally achieved by controlled rolling and controlled cooling, that is, controlling the rolling temperature, finish rolling temperature and crimping temperature of the finishing rolling to control the microstructure and mechanical properties of the strip.
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