N06690 alloy is also known as Inconel 690, Alloy 690, W. Nr. 2.4642.It is a nickel alloy with high chromium content. It has good corrosion resistance, metallurgical stability and mechanical processing performance, and has a wide range of applications in the chemical industry.
Due to the relatively high chromium content of Inconel 690 alloy, it has good oxidation resistance in high-temperature oxidizing gases and oxidizing media. In addition, the alloy has a higher nickel content, which improves the stress corrosion resistance of the alloy in chlorine-containing media and sodium hydroxide solution. This material is widely used in various chemical processes and nuclear power and other fields.
Inconel 690 alloy is prone to hot cracks and pores during welding. Because Alloy 690 solidifies, the liquid film formed by low melting point eutectic or low melting point compound remains in the grain boundary zone, so it is prone to cracking under the action of shrinking force. . And S, P, Pb, Zn, etc. are the main elements that cause the intercrystalline low-melting liquid film. During welding, the contaminants on the groove and welding material are the root causes of thermal cracks and the main cause of porosity. In addition, when argon arc welding is performed on alloys, if the flow rate of argon is inappropriate or the purity is too low, pores will also be generated.
1. Welding method
N06690 has good welding performance. In order to obtain the best corrosion resistance, manual argon tungsten arc welding is required for welding. The diameter of the tungsten electrode is Ø3.0 mm, the nozzle diameter is Ø18 mm, the argon purity is ≥99.99%, and the argon flow rate is 12~14 L/min. Welding wire diameter Ø2.4mm; current adopts DC positive connection, welding current is 120~140 A, welding voltage is 10~14 V, welding speed is 100~160mm/min.
2. Welding wire selection
The welding wire is ERNiCrFe -7, the specification is 2.4.
3. Bevel preparation
Bevel processing should use underwater plasma cutting or high-pressure water cutting. Nickel-based alloy welding pool has large viscosity, poor fluidity, and shallow penetration. Therefore, in order to facilitate penetration and prevent the problem of infusion on the edge of the groove, the groove should be V-shaped and the groove angle needs to be larger, the blunt edge should be thinner, and the root gap should be slightly wider.
4. Cleaning and welding protection before welding
There is an insoluble oxide film on the surface of nickel-based alloy materials, such as nickel oxide, which has a melting point of 2 090 ℃, while the melting point of Inconel 925 material is about 1 350 ℃. If proper methods are not used to remove the surface oxide film before welding, It is easy to make the oxide film become the slag inclusion of the weld and affect the quality of the weld. Therefore, before welding, the groove and both sides must be thoroughly cleaned with a stainless steel wire brush to expose the metallic luster, and strictly scrubbed with acetone to remove oil and other dirt containing S and P.
During the welding process, strengthen the protection of the high-temperature molten pool and the high-temperature weld bead to ensure that the molten pool and the hot end of the welding wire are always under the argon protection of the nozzle to prevent the oxidation of the weld metal. When bottom welding, the backside must be filled with argon protection, and local argon filling protection measures can be adopted. When the pipe is filled with argon, the flow rate should be increased appropriately, and the welding can be carried out after the air in the pipe is exhausted. When welding, the argon gas flow is gradually reduced to avoid the phenomenon that the argon flow is too large and the pressure in the tube is too high, which may cause the back of the weld to appear concave or the root is not penetrated during the forming.
5. Welding sequence
Multi-layer welding is used for welding, and the welding sequence is shown in the figure below. The back cover weld bead should be penetrated and formed uniformly.
● Carry out tack welding before formal welding. The tack welding process is the same as the welding process parameters of formal welding. After tack welding, perform a surface inspection on the solder joints, and no defects such as cracks are allowed, and the surface oxides of the solder joints are removed.
● Surface cracks, pores, and other defects in the welding process should be polished and eliminated before the next weld bead is deposited. The oxide on the surface of each weld bead should be removed with a stainless steel wire brush.
● During the welding process, strictly limit the welding heat input and inter-layer temperature, the heat input is less than 10 kJ/cm, and the inter-layer temperature is controlled below 150 ℃.
● During the welding process, the molten pool and the hot end of the welding wire must always be under the argon protection of the nozzle. The high temperature welding bead is protected by a drag cover. The shielding gas is given 5s in advance, and the gas is stopped after 5s after the arc is extinguished.
● When welding, the welding wire must not swing laterally.
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