Welding method for super duplex stainless steel using flux-cored wire pulse arc transfer

Abstract

The application discloses a welding method of a flux-cored wire pulse arc transition for super duplex stainless steel, and adopts a GMAW (gas metal arc welding) welding device, the device adopts a variable slope and variable inductance control, and has a constant voltage power supply with the ability of generating a pulse arc current; the pulse arc transition method is adopted, specifically, two power supplies are used to provide two-pole output power, and a pulse is provided through conversion of the power supply; the process specifically comprises the following steps: processing a groove and a blunt edge alignment gap of the stainless steel to be consistent; welding a weld seam by using welding material in a protective gas; an arc starting point of welding is the welding joint itself, and the arc starting point outside the welding zone can be removed by fine polishing; and positioning welding is performed by using a mechanical positioning mode. The use of the welding method makes the weld metal and the base metal adjust to a higher direction of austenite to improve toughness, and compensates for the toughness loss caused by the increase of the oxygen content of the weld metal due to the use of the welding flux.

Description

TECHNICAL FIELD

[0001] The application relates to a welding method of a flux-cored wire pulse arc transition for super duplex stainless steel, and belongs to the technical field of welding processes. BACKGROUND

[0002] Super duplex stainless steel is austenite + ferrite in a metallographic structure, and the two-phase structure is about 50% or so, so that the super duplex stainless steel has double performance of austenitic stainless steel and ferritic stainless steel, has good mechanical properties and corrosion resistance, has excellent resistance to point corrosion, stress corrosion and crevice corrosion, can be used in severe, high-temperature and strong-corrosion environments, and is widely applied. In a traditional welding process, the use of welding flux increases the oxygen content of weld metal, thereby causing the loss of toughness of a product. Therefore, a welding process needs to be designed to adjust the weld metal and base material to a higher austenite direction to improve toughness and further improve corrosion resistance. SUMMARY

[0003] In view of the problems in the prior art, the application provides a welding method of a flux-cored wire pulse arc transition for super duplex stainless steel, so as to solve the above technical problems.

[0004] In order to achieve the above purpose, the technical scheme adopted by the application is as follows: a welding method of a flux-cored wire pulse arc transition for super duplex stainless steel, characterized by,

[0005] The equipment adopts GMAW (gas metal arc welding) welding equipment, the equipment adopts variable slope and variable inductance control, has a constant voltage power supply capable of generating a pulse arc current, adopts a pulse arc transition method, and specifically adopts two power supplies to provide two-pole output power and provide pulses through power conversion;

[0006] The process specifically includes the following steps: processing a groove and a blunt edge at a welding position of the stainless steel, aligning the gap; welding the weld joint by using welding material in the protective gas; the arc starting point of welding is the welding joint itself, and the arc starting point outside the welding area can be removed by fine polishing; and the welding is positioned by a mechanical positioning mode.

[0007] Further, the protective gas includes argon, helium, nitrogen, oxygen and carbon dioxide, wherein the content of argon accounts for 80% of the volume content of the protective gas, and the contents of helium, nitrogen, oxygen and carbon dioxide account for 20% of the volume content of the protective gas.

[0008] Further, the gas flow rate range of the protective gas used for welding the weld joint by using welding material is 12-16 L / min.

[0009] Further, the welding material is selected as flux-cored wire, the flux is automatically supplied by the welding torch, the flux provides part of the alloying elements of the weld metal and the slag, and the current and voltage are 150-200A, 22-28V and 60-110A, 20-24V in flat welding and vertical welding.

[0010] Further, the interpass temperature of each pass is cooled to below 150 DEG C, so that the heat affected zone of the subsequent welding pass has sufficient cooling time.

[0011] Further, the flux is a flux material with high nickel content for filling the metal.

[0012] Further, the diameter of the welding wire is 1-1.6 mm, the welding wire is kept clean and dry, and is placed in a container with a cover, the flat welding position has the best welding effect, and the welding torch is kept as close to vertical as possible to minimize the amount of air inhaled in the shielding gas.

[0013] Further, in order to meet the requirements of various material thicknesses and joint design, the flexibility of heat input is large, and the heat input can be calculated according to the following formula; the heat input is in the range of 0.5-2.5 KJ / mm.

[0014] Heat input (KJ / mm) = (V*A) / (S*1000)

[0015] Wherein: V= voltage, A= current, S= moving speed.

[0016] The beneficial effects of the present application are:

[0017] 1. The present application adopts automatic GMAW professional equipment, uses variable slope and variable inductance control, and has a constant voltage power supply with the ability to generate pulse arc current. This method requires two power supplies to provide two-stage output power, and the pulse is provided by power conversion. In the spraying transition stage, the metal transition amount is large, and in the granular droplet transition stage, the metal transition amount is small, and this combination has the advantages of high metal deposition rate and limited heat input;

[0018] 2. The present application is suitable for economically depositing a large amount of weld metal, and can be used for automatic welding of simple-shaped structures. The GTAW method is used for supplement to obtain the best control in complex operation;

[0019] 3. The present application adopts flux-cored wire combined with GMAW method, the flux is automatically supplied by the welding torch, the flux provides part of the alloying elements of the weld metal and the slag, the weld is protected from air oxidation and pollution, and the heat affected zone is protected by the shielding gas provided by the welding torch. The nickel content in the flux-cored wire is high so that the austenite content in the weld metal is higher than the near-equilibrium base material structure, thereby realizing stable welding and improving the toughness of the weld.

[0020] The use of the present welding method causes the weld metal and base metal to adjust in the direction of higher austenite to improve toughness, and compensate for the toughness loss caused by the increase of oxygen content in the weld metal due to the use of flux. Embodiments

[0021] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below through embodiments. However, it should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the scope of the present application.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs, and the terms used herein should be interpreted only as the terms are commonly used by those skilled in the art to which this application belongs unless otherwise defined. The terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application.

[0023] The present application uses automatic GMAW professional equipment, uses variable slope and variable inductance control, and has the ability to generate pulse arc current. The advantages of the constant voltage power supply are: this method requires two power supplies to provide two levels of output power, and the pulse is provided by power conversion. In the spray transfer stage, the metal transfer amount is large, and in the granular droplet transfer stage, the metal transfer amount is small. This combination has the advantages of high metal deposition rate and limited heat input.

[0024] When welding duplex steel with GMAW method, the most commonly used filler metal is a "matching" filler metal with slightly higher nickel. Super duplex stainless steel filler metal has been successfully used to weld 2205 base metal. The welding wire diameter is Φ1-Φ1.6mm, keep clean and dry, placed in a covered container, flat position welding effect is best, the welding torch should be kept as close to vertical as possible, so that the amount of air inhaled in the protective gas is minimized.

[0025] In order to meet the requirements of various material thicknesses and joint designs, the flexibility of heat input selection is large, which can be calculated according to the following formula, and the heat input is generally in the range of 0.5-2.5KJ / mm.

[0026] Heat input (KJ / mm) = (V*A) / (S*1000)

[0027] Where: V = voltage; A = current; S = moving speed.

[0028] GMAW is also known as inert gas shielded metal arc welding (MIG), which is particularly suitable for welding large amounts of weld metal economically and can be used for automatic welding of simple shaped structures. GTAW method is used to supplement and obtain optimal control in complex operations.

[0029] Equipment: GMAW requires specialized equipment, constant voltage power supply with variable slope and variable inductance control, and the ability to produce pulsed arc current. GMAW should be direct current reverse polarity (DCRP).

[0030] Pulsed arc transfer: This method requires two power supplies to provide two-stage output power, and the pulse is provided by the power supply conversion. The metal transfer amount is large in the spray transfer stage, and the metal transfer amount is small in the granular droplet transfer stage. This combination has the advantages of high metal deposition rate and limited heat input.

[0031] Protection: The argon content of the protective gas of the GMAW method is 80%, and the rest is 20% of helium, nitrogen, oxygen and carbon dioxide. The addition of these gases can improve the weldability of the welded member and the performance of the finished product, and the gas flow rate can be in the range of 12-16 L / min according to the transfer mode, transfer speed and welding wire diameter (Φ1-Φ1.6mm). The welding process should avoid the welding wire from being too long to protect it in the gas protection state. A good gas delivery system is critical, and effective measures should be taken to prevent the protective gas from being sucked into the air.

[0032] Flux-cored wire (FCW): Flux-cored wire is used with GMAW method, which automatically supplies filler flux through the welding torch. The flux provides some of the alloying elements of the weld metal and slag, protects the weld from air oxidation and contamination, and provides protective gas through the welding torch to protect the heat-affected zone. The high nickel content in the flux-cored wire makes the austenite content in the weld metal higher than the near-equilibrium base metal structure. When using flux-cored wire, the same source of welding wire used in the welding procedure qualification should be used to avoid production instability. For 1.2mm, the current and voltage for flat and vertical welding are 150-200A, 22-28V and 60-110A, 20-24V.

[0033] Process requirements: (1) The alignment gap of the bevel and the blunt edge of the base metal machined groove should be consistent; (2) Avoid using copper backing plate, as copper may cause rapid cooling in some cases; (3) The welding arc starting point should be on the welding joint itself, and the arc starting point outside the welding zone will cause the local welding point to cool too fast, resulting in local high ferrite content and loss of corrosion resistance. If there is an arc starting point outside the welding zone, fine grinding can be used to remove it; (4) Full gas protection should be used for tack welding. Tacking should be mechanically positioned, not using tack welds; (5) The interpass temperature should be cooled to below 150°C, so that the heat-affected zone of the subsequent welding pass has sufficient cooling time.

[0034] The use of the welding method makes the weld metal and the base metal adjust to the higher direction of austenite to improve the toughness, and compensates the toughness loss caused by the increase of the oxygen content of the weld metal due to the use of the flux. The welded product of the duplex stainless steel, especially the super duplex stainless steel, is particularly suitable for the places with poor climate environment, such as the coastal, seabed, chemical industry and other places with strong corrosion, and is also particularly suitable for important and key national projects, such as nuclear power plants, civil air defense projects and the like, and has great significance.

[0035] The above merely describes the preferred embodiments of the present application, and is not used to limit the present application, and any modification, equivalent replacement or improvement within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A welding method for super duplex stainless steel using flux-cored welding wire with pulsed arc transfer, characterized in that, The equipment employs GMAW (Gas Shielded Metal Arc Welding) welding equipment, which utilizes variable slope and variable inductance control and a constant voltage power supply capable of generating pulsed arc current. It employs a pulsed arc transfer method, specifically using two power supplies to provide output power to two poles, which is then converted by the power supply to provide pulses. The process specifically includes the following steps: When machining bevels and aligning blunt edges at welded joints in stainless steel, the clearance should be consistent. Welding is performed using welding materials in a shielding gas atmosphere; the arc initiation point is located on the weld joint itself, and the arc initiation point outside the welding area is removed by fine grinding; mechanical positioning is used for tack welding. The protective gas includes argon, helium, nitrogen, oxygen, and carbon dioxide, wherein argon accounts for 80% of the volume of the protective gas, and helium, nitrogen, oxygen, and carbon dioxide account for 20% of the volume of the protective gas. The gas flow rate range for welding seams using welding materials in a shielding gas atmosphere is 12-16 L / min. The welding material selected is flux-cored welding wire, and the flux is automatically supplied by the welding torch. The flux provides some of the alloying elements and slag of the weld metal. The current and voltage for flat and vertical welding are 150-200A and 22-28V and 60-110A and 20-24V, respectively. The temperature between each pass is cooled to below 150°C, allowing sufficient cooling time for the heat-affected zone of subsequent weld passes; The flux is a flux material with nickel as the filler metal; The welding wire diameter is Φ1-Φ1.6mm. Keep it clean and dry, and place it in a covered container. The welding effect is best when the welding position is flat. Keep the welding torch as close to vertical as possible to minimize the amount of air drawn into the shielding gas. To meet the requirements of various material thicknesses and joint designs, the heat input is in the range of 0.5-2.5KJ / mm.