Duplex stainless steel is a kind of excellent corrosion resistance of high strength and ease of manufacturing and many other excellent performance of steel. Austenitic stainless steel, it has many similarities, but there are important differences. In the welding of duplex stainless steel, it is the difference between austenitic stainless steel, austenitic stainless steel weld solidification process is easy to produce hot cracking tendency. The duplex stainless steel has very good resistance to thermal cracking, hot cracking during welding with little regard. The main problem of duplex

stainless steel electrode heat affected zone is not the weld metal and heat affected zone of the problem is corrosion resistance, toughness, reduce or weld cracking. Welding focus is to consider the temperature at 450 ~ 850 ℃ to stay within the shortest time.
A material
Welding procedure qualification materials.
1.1 The test board material with ASME SA-240 S31803 duplex stainless steel plate.
1.2 â‘  welding filler metals: the choice of welding consumables should be considered with the base metal chemical composition and mechanical properties of phase-equipped welding materials. The welding of welding material deposited metal strength, ductility and toughness can not be welded steel below the minimum value. Should also be possible to weld defects, welding process, welding specifications, welding equipment and groove type and other factors into account. According to duplex stainless steel SA-240 (S31803) characteristics of duplex stainless steel wires used for model ER2209 filler metal, such deposited metal wire with austenitic - ferritic phase organization, its characteristics have higher tensile strength and good resistance to stress corrosion or corrosion resistance point. â‘¡ gas: argon gas, and its purity is 99.95%.
2 Welding electrodes

Miller's by the United States (Syncrowave250) TIG welding machine. Welded stainless steel used (GTAW) welding DCSP (DCEN), the negative electrode, the workpiece is positive. ï¿  2.4mm2% thorium electrode using tungsten (AWS 5.12 specification EWTh-2 category) by the electrode (tungsten rod) was ground into 25 ~ 30 ° angle to control the arc.
3 fabrication
3.1, plasma and laser cutting austenitic stainless steel and duplex stainless steel using the same processing methods, plasma cutting equipment with conventional processing.
3.2 The processing of duplex stainless steel groove joints must be designed to help complete penetration, and to avoid solidification of the weld metal did not exist in the base metal fusion. Groove machining instead of the best plasma cutting and grinding wheels.
3.3 clean-up before welding the workpiece before welding on both sides of 100mm within the groove with acetone or alcohol to clean up.
4 Welding Technology
The development of welding materials and welding consumables should be based on the mother weldability to select the appropriate welding procedure specification. For the duplex stainless steel, the use of (GTAW) welding, filler metal normally used for the higher content of alloying elements of nickel metal fill. Positioning welding, the back of the gas should be used, the length of each place is not less than 15mm, the positive DC power supply polarity (DCEN), the first layer of single-pass welding, two to seven multi-pass welding, interpass temperature limited to 150 ℃ below the range, so that follow-weld heat affected zone have enough time to cool.
4.1 The duplex stainless steel layer can withstand the temperature relatively high heat input, weld metal solidification crack after the organization better than duplex stainless steel weld metal. The main purpose of the control layer is to prevent the temperature of 450 ~ 850 ℃ stay too long may cause intergranular corrosion and heat-affected zone. Therefore, the temperature between layers can be limited to below 150 ℃ quilt cover and improve the intergranular corrosion of the heat affected zone corrosion resistance and toughness.
4.2 The gas most commonly used inert gas, and promising the purity of 99.95% or higher, the implementation of protection of dry argon bath. Arc welding should be a few seconds before the start of gas, arc and then maintain a few seconds, enough to keep the best time to weld and heat affected zone of duplex stainless steel cooling to the oxidation temperature range below. The effective work of the electrode within the gas diffusion network using the back seam (sieve pore gas) gas flow rate of 12 ~ 18L/min pure argon protection.
5 welding operations
According to process requirements, with (GTAW) welding, is on the back of 99.99% Ar gas are used for protection, weld positioning welding, in the butt at the side of the arc, to start pulling in the arc welding parts, welding gun horizontal swing, to be metal melting continuous filler wire during welding. Location weld length should be not less than a 15mm, the first root in the welding filler filler metal when welding start and end ground to a smooth transition to repair the tilt angle. Right to left using welding torch, welding torch angle and workpiece angle of 60 ~ 800, the angle between wire and workpiece to carry 150 to 250.
Tungsten rod welding the first set of generally out of gas about 5 ~ 7mm more focused arc, root penetration and easy fusion.
Welding the second to seven multi-pass welding should be to minimize the weld groove within the residence time of red-hot temperature, interpass temperature control within the 80 ~ 150 ℃, until the groove filled.
6 post-weld heat treatment
Duplex stainless steel does not require heat treatment. Otherwise it would be inter-phase or duplex stainless steel brittle phase precipitates, lower toughness and corrosion resistance.
7 Inspection
â‘  visual inspection after welding seam: several times with the naked eye or a magnifying glass joint surface, the weld surface, there is no lack of penetration, incomplete fusion, surface porosity, weld defects such as tumors. â‘¡ NDT: X-ray inspection and testing standards by JB/T4730-2005 ASME-â…¨ volume QW-191 testing standard film standard. â‘¢ mechanical properties: According to the ASME-â…¨ welding procedure qualification requirements, respectively, to obtain side bending, back bending and tensile specimens of the two, after the samples were tensile, bending, hardness, mechanical properties of gold equivalent.
8 Conclusion
Test results showed that the duplex stainless steel with hand-tungsten inert gas welding (GTAW) welding, ASME SA-240 (S31803) duplex stainless steel welding procedure done. The results showed that out of the seam welding method of performance evaluation can be assured, the welding procedure qualification report (PQR) and welding instructions (WPS) is qualified. In the actual production is feasible.