Some stainless steel welded pipe after the completion of production, after a period of time there is corrosion on the surface, and even cracking, why is that?
Because in the production process of welded pipes, a very important step is ignored, that is, "annealing". In the process of steel smelting and production, we will adjust the element formula to make the steel achieve the characteristics we need, such as Cr, Cr, Ni, N, Nb, Ti, Mn, Mo, Si and other metal elements. The performance we need to improve is the high corrosion resistance of steel, which is what we call stainless steel. The corrosion resistance of stainless steel comes from an element contained in the formula - Cr. When the content of Taipa reaches a peak, the corrosion resistance of steel will be greatly improved. The general Cr content of stainless steel should reach at least 10.5%.
Common corrosion types: intergranular corrosion, stress corrosion
Intergranular corrosion, its the phenomenon of intergranular corrosion in the welding process of welded pipe, due to the high temperature resulting in a chemical reaction between the weld and the internal elements of the material, the carbon element and chromium element in the steel form a chromium compound (Cr23C6), which makes the grain boundary area chromium poor, and ultimately leads to intergranular corrosion.
Stress corrosion comes from the reaction force generated when the steel strip is deformed by external pressure during the welding process in the forming stage, and will remain in the inside of the welded pipe after welding. If not eliminated in time, the hardness of the welded pipe will become particularly high, and it is difficult to carry out the next processing.
In view of these two potential quality problems, how can our equipment achieve a thorough solution?
Features of the Bright Annealing Machine of Hangao Technology Company:
1, fine grain, uniform steel structure and composition.
2, eliminate the internal stress of steel and prevent deformation and cracking.
3, reduce the hardness of steel, improve plasticity, in order to facilitate subsequent processing.
Five detailed features of bright annealing equipment:
1, the furnace body sealing performance is good, poor sealing performance will let the gas loss in the furnace body, can not play a bright role.
2, the water gas in the furnace body will cause the heating water gas to evaporate, and the evaporated water gas will be attached to the surface of the stainless steel pipe and oxidized.
3, the gas pressure in the furnace body, in order to avoid the outside gas penetration into the furnace body, the pressure in the furnace should be greater than the outside pressure.
4, annealing temperature control, whether to achieve the best annealing temperature of steel pipe material.
5, the required gas in the annealing process, stainless steel pipe annealing gas is the first choice of pure hydrogen, because the gas purity is the best, wireless close to 100%, can not be rich in too much oxygen, water gas. Because gas is the primary reason for affecting the quality of stainless steel pipes.
Every time the finishing tube is rolled, it must go through the process of solution treatment. Ta ensure that the performance of the steel pipe meets the technical requirements. and to provide guarantee for the post-process processing or use. Bright solution treatment process of ultra-long seamless steel pipe has always been a difficulty in the industry.
Traditional electric furnace equipment is large,covers a large area, has high energy consumption and large gas consumption, so it is difficult for realize bright solution process. After years of hard work and innovative development, the use of current advanced induction heating technology and DSP power supply. Precision control of heating temperature to ensure that the temperature is controlled within t2C,to solve the technical problem of inaccurate induction heating temperature control. The heated steel pipe is cooled by "heat conduction"in a special closed cooling tunnel, which greatly reduces the gas consumption and is more environmentally friendly.
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