Reasonable design of welded joints is the key.
Main Measures to Prevent Stress Corrosion Cracking of 3 16 Stainless Steel Pipe; Reasonable design of welded joints, avoiding corrosion media from gathering at the joints, and reducing or eliminating stress concentration at the joints. Reduce or eliminate welding residual stress, and reasonably arrange the welding pass sequence in the process, such as adopting subsection reverse welding. Minimize the constraints on welded joints, and anneal after welding to eliminate stress. When it is difficult to carry out heat treatment, it is necessary to change the surface state of the weldment, carry out shot peening on the sensitized side surface to generate residual compressive stress in this area, or polish, electroplate or spray the sensitized surface to reasonably select the base material and welding material. Superalloy welding materials are usually used, that is, the content of corrosion-resistant alloy elements (Cr, Mo, Ni, etc.). ) The weld metal is higher than the base metal.
Correctly master the welding method
Adopt reasonable welding technology, centralized heat source, small line energy and rapid cooling to reduce carbide precipitation and avoid overheating of joint structure. Ensure that the welded joint is smooth and clean, and welding spatter, arc wear and so on are often the parts where stress corrosion begins. Therefore, the appearance of welded joints is also very important. ? Due to defects such as cracks after hot-rolled tube blanks or high-precision cold-drawn tubes are made into oil cylinders, almost no plastic deformation occurs, and it is generally brittle fracture. Brittle fracture is caused by many reasons.
When designing, materials with suitable cold-brittle transition temperature should be selected according to the working temperature of components. The deformation of cold-drawn large seamless steel pipe is too small, which can not meet the requirements of surface smoothness and dimensional accuracy, and can not meet the strength index of components;
When the deformation is too large, the plasticity and toughness of the 3 16 stainless steel pipe will be reduced too much, and the grains will be stretched too long and too fine, forming a fibrous structure, and the metal will appear obvious anisotropy. The axial direction of cold-drawn seamless steel tube is parallel to the grain elongation direction, and the strength increases; The diameter direction of 3 16 stainless steel is perpendicular to the grain elongation direction, but the strength decreases, while the maximum stress of hydraulic cylinder exists in the radial direction of seamless steel pipe. Excessive deformation is not conducive to giving full play to the performance of cold-drawn pipe. Generally, the fiber structure, dislocation, vacancy and other crystal defects in steel are eliminated by annealing or normalizing. The purpose of annealing is to refine grains, eliminate structural defects, reduce hardness, improve plasticity and facilitate cold working. Precautions should be taken for surface treatment. Stainless steel plates should be stored in special storage racks. Storage racks shall be wooden or carbon steel racks, and the surfaces shall be painted or rubber pads shall be used to isolate them from other metal materials such as carbon steel.
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What are the welding methods of stainless steel?
1, plasma arc welding
Plasma arc welding is the most suitable method for welding stainless steel. Because plasma arc is a dense arc, the arc section is small, the energy is concentrated, the temperature is high, and it can be completely penetrated within a certain thickness range. However, it has not been widely used because of its expensive equipment quotation and short nozzle life.
2. The method and principle of MIG welding.
MIG maintenance welding is the most commonly used method for welding stainless steel. MIG maintenance welding can be divided into MIG maintenance welding, MIG maintenance welding, co2 maintenance welding and flux-cored wire maintenance welding.
Usually, argon, helium or their mixture gas is selected as the maintenance gas of the welding zone. Because there is no coating on the surface of the welding wire, the current can be greatly improved, so the base metal has deep penetration, the welding wire has fast melting speed and high deposition rate, and the output power is greatly improved.
Principle: In MIG maintenance arc welding, the arc between the meltable welding wire and the workpiece to be welded is selected as the heat source to melt the welding wire and the base metal, and the maintenance gas is delivered to the welding area to prevent the arc, the melted welding wire, the molten pool and the nearby base metal from being damaged by the surrounding air. The continuously supplied welding wire metal is continuously melted and transferred to the molten pool, and mixed with the molten base metal to form welding metal, thus connecting the workpieces to each other.
3, process arc
Manual arc welding is a kind of welding method with manual arc covered electrode. In the process of manual arc welding, the covered electrode and the workpiece are locally heated to a molten state by using the arc between the covered electrode and the workpiece. The droplets at the end of the covered electrode are mixed with the molten base metal to form a molten pool, which moves forward with the arc, and the liquid metal in the molten pool gradually cools and crystallizes to form a weld. Manual arc welding of stainless steel is the most widely used, which can be used to weld all kinds of stainless steel. It is characterized by small heat affected zone, easy quality assurance, simple equipment and sensitive operation, and can adapt to the technical requirements of various welding directions and different plate thicknesses. Now stainless steel covered electrode can basically meet the welding requirements of various stainless steels, and the choice of covered electrode is almost unrestricted. The disadvantage is low production capacity; Poor working conditions; The requirements for welders are very high, and in many cases welders must have corresponding qualifications; Some materials for welding deposited metal can not meet the application requirements, such as ultra-high purity stainless steel; The thin plate with the workpiece thickness usually below 65438 0 mm is not suitable for manual arc welding.
4. Submerged arc active welding is to cover a layer of granular fusible flux on the welding arc.
A welding method without exposing arc light. At present, it is mainly used for welding austenitic stainless steel plates, which is characterized by large welding current, large penetration depth and small workpiece groove. High welding speed and high production capacity; The weld metal condenses slowly, and there is more time for metallurgical reaction between liquid metal and molten flux, which reduces the possibility of porosity in the weld. The weld is beautifully formed. Good working environment, simple operation and relatively simple requirements for welders. Disadvantages are large welding heat input, wide heat affected zone and rough weld arrangement; Special consideration should be given to the cooperation between welding wire and flux when selecting materials; Welding orientation can only be flat welding orientation; We can't directly investigate the relative orientation of arc and groove, so we must have active tracking equipment.
5, tungsten inert gas shielded welding
Tig welding can be divided into three types: manual welding, semi-active welding and active welding. Tig welding is widely used in stainless steel. Used to all-round welding, generally no splash, beautiful weld formation. I am especially used to welding thin parts. Gig is often used as backing when welding grooves of many thick parts, which avoids the defects of cracks and difficult slag removal in manual arc welding. Inert gas can effectively block air, is insoluble in metal, is not conducive to metal reaction, and can ensure the chemical composition requirements of stainless steel. The disadvantages are deep melting, low deposition speed, low production power and high production cost.
6, laser welding-stainless steel laser welding machine
Laser welding can realize spot welding, butt welding, lap welding and sealing welding of thin-walled materials and precision parts.
High laser power, high weld depth-width ratio, small heat affected zone, small deformation and fast welding speed.
The weld seam is of high quality, smooth and beautiful, free of air holes, and the toughness of the material after welding is at least equal to that of the base metal.
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The four-dimensional ball screw worktable adopts imported servo control system, and can be equipped with rotating worktable, which can realize automatic welding such as spot welding, direct welding and ring welding.
Wide application range, high precision and high speed.
The current waveform can be adjusted at will, and different waveforms can be set according to different welding materials to match the welding parameters and requirements, so as to achieve the best welding effect.
Used for laser welding of carbon steel, common alloy steel, stainless steel and different steels, stainless steel-low carbon steel, 4 16? Stainless steel -3 10 stainless steel, 347 stainless steel-Hastelloy nickel alloy, nickel electrode-cold forged steel, bimetal with different nickel content, metals such as titanium, nickel, tin, copper, aluminum, chromium, niobium, gold, silver and their alloys? Welding between the same materials such as gold, steel and kovar alloy. Copper nickel, nickel titanium, copper titanium, titanium molybdenum, brass copper, low carbon steel copper and so on? Welding between dissimilar metals. Mobile phone batteries, jewelry, electronic components, sensors, watches, precision machinery, communications, handicrafts and other industries.
Generally speaking, in addition to the above, welders should not forget that there is another very important factor, that is, the choice of covered electrode, because the choice of covered electrode directly affects the welding effect. At present, covered electrode brands with more sales and good reputation in the market are Atlantic and Jinqiao. The price of the former is slightly higher than that of the latter. Users can choose their own brands according to their own characteristics. It should be noted, however, that covered electrode coated materials contain a lot of iron powder, so there are requirements for storage environment and storage time. Therefore, when using covered electrode money, we should carefully check whether there is moisture and rust in the covered electrode. If there is a coated covered electrode, it is likely that the coated covered electrode has been seriously deteriorated and the medicinal properties have fallen off, so this batch of coated covered electrode must be scrapped.
Close? Welding between the same materials such as gold, steel and kovar alloy. Copper nickel, nickel titanium, copper titanium, titanium molybdenum, brass copper, low carbon steel copper and so on? Welding between dissimilar metals. Mobile phone batteries, jewelry, electronic components, sensors, watches, precision machinery, communications, handicrafts and other industries.
The above is the stainless steel 3 16l welding introduced by Bian Xiao. I hope I can help you!
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