There are four kinds of stainless steel seamless steel pipe production methods: hot rolling, hot extrusion, cold rolling and cold drawing. Their production characteristics from plastic deformation resistance, and spread, several aspects of this application and the sensitive degree of thermal conductivity and oxidation resistance of observation. The following are described in detail.
Martensitic stainless steel is very easy to perforate at high temperature when it is a single austenite structure, but the perforation of the martensitic stainless steel is obviously reduced if it contains two phase tissues. The heating temperature of stainless steel pipe is usually 1130-1160 degrees, and the temperature of the furnace tail is below 900 degrees. The final rolling temperature is greater than the critical point transformation temperature. The low carbon content is higher than 850 degrees, and the high carbon can not be greater than 925 degrees. Martensitic stainless steel increases with the increase of carbon content, and the strength and hardness of stainless steel will also increase significantly, but the plasticity will weaken. Therefore, it is best to use the mandrel to pull out when cold drawing, because it is easy to burst after empty drawing.
The high temperature plasticity of austenitic stainless steel is related to the residual alpha phase. Usually the plasticity decreases with the increase of the alpha phase. In addition to alpha phase, there are other residual phases in austenitic stainless steel, such as various kinds of carbides and intermetallic compounds. The plasticity of the superfluous relative stainless steel will have an effect, and the extent of its influence depends on the quantity and state. The plastic properties of the stainless steel material will be greatly deteriorated by the reticular formation at the grain boundary during heating. The ductility of austenitic stainless steel is low at high temperature, and the deformation resistance of the stainless steel will become larger. The reasonable deformation parameters and temperature parameters should be paid special attention to in the use of oblique piercing.
Because ferritic stainless steel is a single phase structure and no phase transformation occurs. Therefore, the grain growth is serious when the heating time is long and the temperature is high, which will significantly weaken the plasticity of stainless steel. The maximum heating temperature of the stainless steel pipe billet is 1000-1060. In this range of temperature, stainless steel will have excellent plasticity. The heating temperature before the cold – drawn hammer is 700-850 degrees C, and the carburization should be avoided and the water quenched after the hammer. Because ferrite chrome stainless steel will have room temperature brittleness, cold processing performance is relatively weak, cold drawing is easy to crack and pull off, so it is best to draw at a certain temperature, and the speed of pulling and pulling is not too large. When the cold rolled ferritic stainless steel pipe is rolled, the deformation degree of the stainless steel pipe is not higher than 40%-48%. According to the grain refinement degree, the degree of deformation can be raised to 55%-65% in the following channel. In order to prevent cracks in the stainless steel pipe when rolling, the temperature rise of the stainless steel pipe is favorable when rolling, so in most cases, when the stainless steel pipe is rolled, there is no need to use the emulsion cooling tool and metal.
Austenitic and martensitic stainless steels have large deformation resistance, work hardening tendency is also large, and the recrystallization speed is slower at high temperature, so the cold rolling stainless steel needs special attention to equipment and motor capability. Both ferritic or semi ferritic low carbon stainless steel and ordinary carbon steel have similar deformation resistance.
Stainless steel spread greatly, the spread degree of martensitic stainless steel is 1.3 times of carbon steel; austenitic stainless steel is 1.35-1.5 times that of ferritic stainless steel is 1.55-1.6 times. Therefore, it is necessary to pay attention to control the transverse deformation and take a relatively small ellipticity. Cold and hot rolling pipe groove ovality is higher, and to take the small pass deformation, so as to avoid the above defects, in the absence of tension reducing when the stainless steel pipe wall thickness is larger, and the reduction of the groove ovality mill to get bigger.
The sensitivity of the corresponding force
The ferritic stainless steel has the normal temperature brittleness, the cold working sensitivity is high, the stress sensitivity is low during hot rolling, and the water quenching can be carried out after rolling. The sensitivity of martensitic stainless steel to crack is higher, and the cooling should not be too fast after hot rolling. Austenitic stainless steel has low sensitivity to crack and can be quenched after hot rolling.
The low temperature thermal conductivity of stainless steel is poor, but the coefficient of linear expansion is greater than that of carbon steel. In order to ensure the quality of heating, low temperature (<800 C) is selected for slow heating.
Because the stainless steel has certain antioxidant properties, the iron oxide skin formed by heating is low. However, there are chromium and nickel oxide in iron oxide skin, which is very dense, and it is difficult to acid pickling during cold processing. Often use HF+HNO3 to do acid washing or alkali acid compound acid washing.
Source: China Stainless Steel Pipes Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)