Generally, steels that are resistant to corrosion by weak corrosive media such as atmosphere, steam, and water are stainless steel, and steels that are resistant to chemically aggressive media such as acid, alkali, and salt are acid-resistant steels. Stainless steel and acid-resistant steel are generally referred to as stainless acid-resistant steel, referred to as stainless steel. Chromium is the main alloying element, and nickel, molybdenum, titanium, niobium, molybdenum, etc. are often added. Stainless steel pipes are mainly made of austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, duplex stainless steel and precipitation hardened stainless steel. Stainless steel pipes are widely used in petroleum, chemical, paper, fertilizer, automotive, aircraft, power station, decoration and other fields. The production method of the stainless steel thick-walled pipe may be hot rolling, hot extrusion, cold rolling and cold drawing. In recent years, due to the advancement of continuous casting and rolling technology and the application of various new welding technologies and non-destructive testing technologies, the quality of Q235 hot plates has been continuously improved, and stainless steel seamless tubes can be partially replaced in various fields of use. About 20% lower. Currently, stainless steel pipes in industrial applications account for 50% of welded pipes and seamless pipes. Production characteristics of stainless steel seamless pipe (1) Plasticity. Martensite stainless steel has no difficulty in perforating a single austenitic structure at high temperatures, but the perforation performance is reduced when a duplex structure is present. The billet heating temperature is generally 1130～1160°C (center temperature), the temperature at the end of the furnace should be less than 900°C, the finishing temperature should be higher than the critical point transition temperature, the low carbon is not lower than 850°C, and the high carbon is not more than 925. °C. As the carbon content increases, the strength and hardness of the steel increase, and the plasticity decreases. When cold drawing, the core rod should be pulled out as much as possible, and it is easy to burst after being pulled out. The high temperature plasticity of austenitic stainless steel is related to the residual α phase. Generally, the plasticity decreases as the α phase increases. In addition to the alpha phase, there are other residual phases in the austenitic stainless steel, such as various forms of carbides, intermetallic compounds, and the like. The plasticity of these extra-relative stainless steel thick-walled tubes has an effect, and the degree of influence depends on their quantity and state. When heated, the excess phase is distributed in the form of a network on the grain boundary, which will significantly deteriorate the plasticity of the metal. American standard seamless pipe has low plasticity at high temperature and large deformation resistance (see metal deformation resistance). When using cross-rolling perforation (see two-roll cross-rolling perforation), special attention should be paid to selecting reasonable deformation parameters and temperature parameters. After austenitic stainless steel is solution treated (usually after quenching after rolling), it exhibits a single-phase austenite structure, which is characterized by high σb, but low σs, large elongation and toughness, and good cold deformation performance. Therefore, a large amount of ball deformation can be taken. However, the work hardening is large during cold deformation, so the processing performance is poor. Ferritic stainless steel is a single-phase structure with no critical transition point (phase change). Therefore, when the billet is heated for a long time and the temperature is high, the grain grows seriously, resulting in a significant decrease in the plasticity of the steel. The maximum temperature of the tube billet heating is 1000-1060 °C. The steel has good plasticity (perforation properties) in this temperature range. The heating temperature before the cold-drawn hammer is 700-850 ° C. It is necessary to prevent carburization during heating and water quenching after the hammer. Since ferritic chromium stainless steel has room temperature brittleness, poor cold workability, and easy cracking and unplugging during cold drawing, it is best to draw it under certain temperature conditions (see pipe temperature drawing), and the drawing speed should not be too large. When the ferritic stainless steel pipe is cold-rolled, the deformation degree of the pipe material during rolling is not more than 40% to 48%. In the subsequent passes (after surface preparation and heat treatment), the degree of deformation can be increased to 55% to 65% depending on the degree of grain refinement. In order to avoid cracking of the steel pipe during rolling, the temperature rise of the pipe during rolling is advantageous, and therefore, in many cases, the steel pipe is not used to cool the tool and the metal. (2) Deformation resistance. Both austenitic and martensitic stainless steels have high deformation resistance, high work hardening tendency, and slow recrystallization speed at high temperatures. Therefore, special attention should be paid to equipment and motor capability when cold rolling such steel. Ferritic or semi-ferritic low carbon stainless steels have the same deformation resistance as general carbon steel. (3) Wide exhibition. Stainless steel has a wide spread (transverse deformation), martensitic stainless steel is 1.3 times wider than carbon steel, austenitic stainless steel is 1.35 to 1.5 times, and ferritic stainless steel is 1.55 to 1.6 times. Therefore, it is necessary to pay attention to controlling the lateral deformation during the cross-rolling and perforation, and a small ellipticity should be taken. The elliptical shape of the cold and hot rolled pipe should be larger, and the amount of deformation of the pass should be taken to avoid the ear, etc., and the wall thickness of the stainless steel pipe is thickened without tension reduction (see the pipe without tension reduction). Larger, while the hole diameter of the reducer should be larger. (4) Sensitivity to stress. Ferritic stainless steel has brittleness at room temperature, cold processing has high sensitivity to stress, and sensitivity to stress during hot rolling is small, and water quenching after rolling. Stainless steel thick-walled tubes are more sensitive to cracks, and can not be cooled too quickly after hot rolling. Generally, stack cooling is adopted. Austenitic stainless steel has low sensitivity to cracks and can be water quenched after hot rolling. (5) Thermal conductivity. The Q235 hot plate has poor thermal conductivity at low temperature, and the coefficient of linear expansion is larger than that of carbon steel. To ensure the heating quality, low temperature (800 ° C) slow heating should be adopted.