Summary of heat treatment knowledge of carbon steel elbow: Carbon steel elbow needs normalizing and tempering heat treatment, machined ports, wall thickness needs to be burned and machined allowance. Generally, the allowance is 10%-20% of theoretical wall thickness of elbow. The smaller the ratio of elbow wall thickness to section diameter D, the better the fitting performance of elbow with the die, but the more easily the internal arc of elbow loses stability and wrinkles.
According to the characteristics that the volume of metal is constant during plastic deformation, the wall thickness is constant (actual slight thinning) when pushed into shape and the length of elbow arc is equal to the length of tube blank, the formula of exterior diameter of pushed tube blank is deduced. If the exterior diameter of actual selected tube blank is smaller than the Dp value calculated according to the formula, the performance of fitting with the die is good, but the inner arc of elbow is easy to lose stability. Wrinkle. If the external diameter of the tube blank is larger than the Dp value calculated by the formula, the result is just the opposite.
Temperature distribution is an important process parameter, which is directly controlled by the shape of induction coil and the relative position between induction coil and mandrel head. The shape of induction coil is the main factor, while the relative position between induction coil and mandrel head is the secondary factor. As an important technological parameter, the influence of the geometrical shape of carbon steel elbow on the thrust speed is directly controlled by the flow regulation of the hydraulic system. The determination principle of the thrust speed is that the principal compressive stress of the inner wall of the elbow is less than the yield limit of the material at this temperature, and the elbow outer wall elongation is less than the maximum elongation of the material at this temperature.
The determination principle of heating temperature of carbon steel elbow is that the austenitizing temperature of material is above, and the principal compressive stress of inner wall of elbow is less than the yield limit of material at this temperature. The higher the austenitizing temperature of material, the higher the heating temperature; the higher the yield limit of material at high temperature, the higher the heating temperature. The highest temperature of WB36 steel is 8 by medium frequency induction heating. The heating temperatures of A335P22 steel and A335P91 steel are 900-950 and 900-1000 respectively at 50-900 C. The temperature measurement method is a combination of fixed far infrared thermometer and manual far infrared thermometer.
Generally, the higher the carbon content in carbon steel, the greater the hardness and strength, but the lower the plasticity. The mechanical properties mainly depend on the carbon content in the steel, while the steel without a large amount of alloying elements is sometimes referred to as plain carbon steel or carbon steel. Carbon steel, also known as carbon steel, refers to iron-carbon alloys with carbon content less than 2%.
In addition to carbon, carbon steel elbows generally contain a small amount of silicon, manganese, sulphur and phosphorus. According to their uses, carbon steel can be divided into three types: carbon structural steel, carbon tool steel and free cutting structural steel. Carbon structural steel can also be divided into building structural steel and machine-made structural steel.
Carbon steel can be divided into ordinary carbon steel, high quality carbon steel, high quality steel and super quality steel according to the content of phosphorus and sulphur.
According to smelting method, it can be divided into open-hearth steel, converter steel and electric furnace steel; according to deoxidation method, it can be divided into boiling steel, killed steel, semi-killed steel and special killed steel; according to carbon content, carbon steel can be divided into low-carbon steel, medium-carbon steel and high-carbon steel.
Carbon steel elbows (HG20600, GB/T9121, JB/T83) are relatively simple to fabricate and are mainly suitable for pipeline systems with corrosive media. The rigidity of carbon steel elbow is poor, it is suitable for pressure P < 4 MPa, butt welding elbow is rigid, it is suitable for high pressure and temperature.