Microstructure and mechanical properties of 27simn steel tube

27simn steel ingot is made of perforated or solid tube through the capillary, and then call is made hot-rolled, cold-rolled or cold. The specifications of the seamless steel pipe are expressed by the outer diameter * wall thickness in millimeters. Seamless steel tubes are divided into two types: hot rolled 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 is divided into 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, and also includes carbon thin-walled steel pipe and alloy thin-walled steel pipe. Stainless steel thin-walled steel pipe and special-shaped steel pipe. 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. 
　　Generally, the seamless steel pipe is formed by hot-rolled or cold-rolled low-alloy structural steels such as 10, 20, 30, 35, 45, etc., such as 16Mn and 5MnV, or 40Cr, 30CrMnSi, 45Mn2, 40MnB, and the like. Seamless pipes made of low carbon steel such as 10 and 20 are mainly used for fluid conveying pipes. 45, 40Cr and other medium carbon steel seamless pipes are used to make mechanical parts, such as the force parts of automobiles and tractors. Generally, seamless steel pipes are required to ensure strength and flattening test. 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 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.