A method of submerged arc welding of super duplex stainless steel

Abstract

The application discloses a super duplex stainless steel submerged-arc welding method, which comprises the following steps: step 1, blanking, cutting a base material and processing a test piece with a proper size and a standard required bevel according to a processing drawing; the super duplex stainless steel material of the application adopts Exton 25.10.4.L welding wire to perform backing and subsequent welding of welding beads, so as to reach the requirement of 13mm thickness of argon arc welding beads. Then, SAW Exton 25.10.4.L / 15W welding wire flux is used to perform submerged-arc filling and cover surface welding. When welding is performed, the preheating temperature is increased to at least 80 DEG C by flame heating, the interlayer temperature is controlled to be not lower than 130 DEG C and not higher than 150 DEG C in the welding process, and the heat input is increased to 2.0 KJ / mm, so that the joint has good forming and the integrity of the welding seam is ensured, and the service performance of the super duplex stainless steel is met. By adopting the process method, the welding joint has good root forming and sufficient service performance, and the welding qualification rate of the joint is improved.

Description

Technical Field

[0001] This invention relates to the field of stainless steel welding technology, specifically a submerged arc welding method for super duplex stainless steel. Background Technology

[0002] Duplex stainless steel refers to stainless steel where ferrite and austenite each comprise approximately 50%, exhibiting characteristics of both austenitic and ferritic stainless steels. Compared to austenitic stainless steel, it has a higher ferrite phase content, resulting in higher strength, higher hardness, higher ferromagnetism, higher thermal conductivity, and a lower coefficient of linear expansion. Duplex stainless steel is primarily used in corrosion-resistant applications and has replaced austenitic stainless steel in many environments prone to stress corrosion cracking and pitting corrosion. Compared to ferritic stainless steel, duplex stainless steel exhibits higher toughness, significantly improved resistance to intergranular corrosion, and enhanced weldability. Therefore, during welding, achieving phase equilibrium between ferrite and austenite through comprehensive control of composition and thermal cycling is crucial. When welding thick-walled super duplex stainless steel, submerged arc welding is necessary to improve welding efficiency. The chemical composition of the super duplex stainless steel material used in this invention... Figure 1 As shown. The main added element, chromium, acts as a ferrite-forming element, improving strength, hardness, corrosion resistance, and oxidation resistance; nickel is a strong austenitic element, improving plasticity and toughness; molybdenum is a ferrite-forming element, providing corrosion resistance and oxidation resistance.

[0003] Super duplex stainless steel exhibits excellent weldability; under typical constraint conditions, the weld metal shows very low susceptibility to hot cracking, and when the proportion of duplex structure is appropriate, its cold cracking susceptibility is also low. Duplex stainless steel is based on the Fe-Cr-Ni-N alloy system. The composition of these steels is adjusted so that the microstructure of the base metal consists of 50% ferrite and 50% austenite, hence the name duplex steel. Its microstructure is as follows: Figure 2 As shown.

[0004] At very high temperatures, both the base metal and weld metal of duplex steel are 100% ferrite. As the temperature decreases, austenite gradually precipitates from the ferrite, eventually forming the microstructure of duplex steel. According to... Figure 3 As shown in the isothermal transformation curve of duplex stainless steel, rapid cooling is necessary to avoid the formation of carbides, nitrides, and intergranular phases, and to avoid the "475℃ brittleness" range. However, excessive cooling rates can also leave excessive ferrite near the fusion line. Therefore, post-weld heat treatment should be avoided for duplex steel, as it may cause the precipitation of intergranular (σ) and brittle phases, reducing toughness and corrosion resistance.

[0005] Generally speaking, the more alloy steel element content, the lower the thermal conductivity, and the larger the linear expansion coefficient, and the higher the resistivity. Due to these special physical properties of high alloy steel, large welding deformation and large residual stress will be caused during welding, and the heat input during welding needs to be strictly controlled, and small current multi-layer multi-pass welding is preferred.

[0006] Compared with the submerged arc welding process of ordinary duplex stainless steel material, the super duplex stainless steel material is more prone to porosity. Since the super duplex stainless steel material contains a certain amount of N element, during the welding process, if the N diluted into the molten pool is not timely during the overflow process, N2 porosity will be formed, which requires strict control of welding heat input and interpass temperature to prolong the solidification time of the molten pool. SUMMARY

[0007] The purpose of the present application is to provide a super duplex stainless steel submerged arc welding method to solve the problems raised in the background art.

[0008] To achieve the above purpose, the present application provides the following technical scheme:

[0009] A super duplex stainless steel submerged arc welding method, comprising the following steps,

[0010] Step 1, blanking, cutting the base material and processing the test piece with appropriate size and standard required bevel according to the processing drawing;

[0011] Step 2, bevel preparation, alcohol or propanol is used to wipe the inner and outer surfaces of the pipe, and all bevel surfaces and the adjacent 25mm range of the base material need to be free of grease, moisture, oxides, scales, paint, debris and other foreign matter;

[0012] Step 3, back inflation, before the backing welding, argon with a purity of 99.997% must fill the inside of the pipeline, and the oxygen content in the back inflation must be less than 0.05%. Argon with a purity of 99.997% is used for welding, and the back gas supply needs to be maintained until the argon arc welding of the 8mm thick filler metal is completed;

[0013] Step 4, spot welding, a bridge block made of the same material as the base material is used, and the welding spot is on the bevel surface;

[0014] Step 5, preheating, argon arc welding is performed at room temperature, if it is lower than 10℃, an electric oven is used for preheating, the interpass temperature is not more than 100℃, before submerged arc welding, the preheating temperature is increased to at least 80℃ by flame heating, and the interpass temperature is controlled at 130℃-150℃ during welding.

[0015] Step 6, argon arc welding, during the backing welding process, the polarity of the argon arc welding equipment adopts DCEN polarity, high-frequency arc starting, current attenuation and gas delay protection, the delay time is 4s-6s, the thickness of the argon arc welding is controlled, and the thickness of the argon arc welding cannot be less than 13mm;

[0016] Step 7, submerged arc welding, before starting welding, the existing starting and ending points are polished to facilitate smooth transition of the new welding bead; after each layer of welding is completed, the next layer of welding can be carried out only after quality inspection is qualified, the interlayer joints of multi-layer welding are staggered, and the interlayer temperature is strictly controlled to be not more than 150 DEG C; the filling welding is welded to the surface of the weld metal below the joint surface by 0.5mm, and the subsequent surface welding is carried out, and the surface height of the weld should be not more than 3mm;

[0017] Step 8, after the joint is welded for 48 hours, nondestructive testing is carried out, and the testing methods include but are not limited to appearance detection, penetration detection and radiographic detection;

[0018] Finally, the welded joint is subjected to mechanical test, tensile test, bending test, impact test, hardness test, macroscopic metallographic test, microscopic metallographic structure test, ferrite test, pitting test and chemical composition test.

[0019] As a further scheme of the application, the backing and welding of the welding bead in step 6 are carried out by using Exton 25.10.4.L welding wire.

[0020] As a further scheme of the application, the filling and surface welding of the submerged arc in step 7 are carried out by using SAW Exton 25.10.4.L / 15W welding wire flux.

[0021] As a further scheme of the application, when Exton 25.10.4.L is used for welding in step 5, the diameter of the welding wire is 2.4mm, the backing welding current is 88-90A, the backing welding voltage is 9-10V, the welding speed is 48mm / min, and the welding heat input is 1.0-1.1KJ / mm.

[0022] The second layer welding current is 119-121A, the voltage is 10-11V, the welding speed is 78mm / min, and the welding heat input is 0.9-1.1KJ / mm; the subsequent argon arc welding current is 136-206A, the voltage is 10-13V, the welding speed is 114-162mm / min, and the welding heat input is 0.7-1.3KJ / mm.

[0023] As a further scheme of the application, when SAW Exton 25.10.4.L / 15W is used for welding in step 7, the diameter of the welding wire is 2.4mm, the welding current is 300-310A, the welding voltage is 30-32A, the welding speed is 294-318mm / min, and the welding heat input is 1.7-2.0J / mm.

[0024] As a further scheme of the present application: the welding test adopts the base material as UNSS32750 super duplex stainless steel pipe, the pipe wall thickness is machined to 38mm, and the pipe diameter is 273mm.

[0025] Compared with the prior art, the present application has the beneficial effects that: the super duplex stainless steel material of the present application adopts Exton25.10.4.L welding wire for backing and subsequent welding of the welding bead to achieve the requirement of 13mm thickness of argon arc welding bead; then SAWExton25.10.4.L / 15W welding wire flux is used for submerged arc filling and cover welding. When submerged arc welding, the preheating temperature is increased by at least 80℃ through flame heating, the interlayer temperature is controlled to be not less than 130℃ and not more than 150℃ during welding, and the heat input is increased to 2.0KJ / mm to ensure that the joint has good forming while ensuring the integrity of the weld, and meets the service performance of super duplex stainless steel. Using this process method for welding, the welded joint has good root forming while having sufficient service performance, and the welding qualification rate of the joint is improved. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is the chemical composition table of S32750 in the application.

[0027] Figure 2 It is the microstructure diagram of duplex steel in the application.

[0028] Figure 3 It is the isothermal transformation curve diagram of duplex stainless steel in the application.

[0029] Figure 4 It is the spot welding diagram in the application.

[0030] Figure 5 It is the welding process parameter table in the application.

[0031] Figure 6 It is the impact test result diagram in the application.

[0032] Figure 7 It is the hardness detection diagram in the application.

[0033] Figure 8 It is the point hardness test value diagram in the application.

[0034] Figure 9 It is the 6-point macroscopic metallographic examination diagram in the application.

[0035] Figure 10 It is the 12-point macroscopic metallographic examination structure diagram in the application.

[0036] Figure 11Chemical composition table of weld in the invention.

[0037] Figure 12 Ferrite experimental value table of the welded joint in the invention. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0039] Please refer to Figures 4-12 In the embodiments of the present application, a submerged arc welding method of super duplex stainless steel comprises the following steps.

[0040] Step 1, blanking, cutting the base material and processing the test piece with appropriate size and standard required groove according to the processing drawing; the base material used in the welding test is UNSS32750 super duplex stainless steel pipe, the pipe wall thickness is processed to 38 mm, and the pipe diameter is 273 mm.

[0041] Step 2, groove preparation, alcohol or propanol is used to wipe the inner and outer surfaces of the pipe, and all the groove surfaces and the base material within the range of 25 mm adjacent to the groove surfaces need to be free of grease, moisture, oxide, scale, paint, debris and other foreign matters;

[0042] Step 3, back inflation, before the backing welding, the argon gas with a purity of 99.997% needs to fill the inside of the pipe, and the oxygen content in the back inflation needs to be less than 0.05%. The argon gas with a purity of 99.997% is used for welding, and the back gas needs to be maintained until the 8 mm thick filler metal is completed by argon arc welding;

[0043] Step 4, spot welding, the bridge block with the same material as the base material is used, and the welding spot is on the groove surface, as shown in Figure 4 .

[0044] Step 5, preheating treatment, the argon arc is welded under the condition of room temperature, if lower than 10℃, the electric oven is used for preheating, the interlayer temperature is not more than 100℃, before the submerged arc welding, the preheating temperature is increased by at least 80℃ through flame heating, and the interlayer temperature is controlled at 130℃-150℃ during the welding process.

[0045] Step 6, argon arc welding, during the backing welding process, it is necessary to observe whether there is oxidation, incomplete penetration and excessive protrusion through the root gap. These defects need to be removed and welded again, and this inspection needs to be repeated until the root gap is closed.

[0046] For example, if the undercut and excessive protrusion of the backing pass are not acceptable, the grinding treatment and re-welding should be carried out before the welding of the hot pass. The welding process parameters are shown in Table 1. Figure 5 .

[0047] The polarity of the argon arc welding equipment is DCEN polarity, high-frequency arc starting, current decay and gas delay protection, the delay time is 4s-6s, the argon arc welding thickness is controlled, and the argon arc welding thickness should not be less than 13mm; the backing and welding pass are welded by using Exton 25.10.4.L welding wire.

[0048] When Exton 25.10.4.L is used for welding, the welding wire diameter is 2.4mm, the backing welding current is 88-90A, the backing welding voltage is 9-10V, the welding speed is 48mm / min, and the welding heat input is 1.0-1.1KJ / mm;

[0049] The second layer welding current is 119-121A, the voltage is 10-11V, the welding speed is 78mm / min, and the welding heat input is 0.9-1.1KJ / mm; the subsequent argon arc welding current is 136-206A, the voltage is 10-13V, the welding speed is 114-162mm / min, and the welding heat input is 0.7-1.3KJ / mm.

[0050] Step 7, submerged arc welding, before starting welding, grinding treatment is carried out on the existing starting and ending points to smoothly transition the new welding pass; after each welding pass is completed, the next layer of welding can be carried out only after the quality inspection is qualified, the interlayer joints of multi-layer welding are staggered, and the interlayer temperature is strictly controlled to be not more than 150℃; the filling welding pass is welded to the surface of the weld metal which is 0.5mm lower than the surface of the joint, and then the surface welding is carried out, and the weld surface protrusion should be not more than 3mm; the filling and surface welding of submerged arc welding is carried out by using SAW Exton 25.10.4.L / 15W welding wire and flux.

[0051] When SAW Exton 25.10.4.L / 15W is used for welding, the welding wire diameter is 2.4mm, the welding current is 300-310A, the welding voltage is 30-32A, the welding speed is 294-318mm / min, and the welding heat input is 1.7-2.0J / mm.

[0052] Step 8, after the joint is welded for 48 hours, non-destructive testing is carried out, and the testing methods include but are not limited to: visual inspection, penetration detection and radiographic detection;

[0053] Finally, the welded joint is subjected to mechanical test, bending test, impact test, hardness test, macroscopic metallographic test, microscopic metallographic structure test, ferrite test, pitting test and chemical composition test.

[0054] Experimental results:

[0055] 1. General mechanical property test results: two tensile test tensile strength results were 820 Mpa and 815 Mpa, the tensile fracture position was the base material area, and the tensile test results met the minimum tensile strength requirement of 800 Mpa specified by the base material (UNSS32750).

[0056] 2. Bending test: according to the requirement of ASME BPVC IX, the side bending test can be used for thickness greater than 10 mm, the pressure head diameter of the side bending test is 56 mm, the bending angle is 180°, after four side bending tests, the surface has no welding defect display, which meets the requirement of the standard.

[0057] 3. Impact test: it needs to be carried out in the base material, weld metal and heat affected zone. At a test temperature of -50℃, the receiving value is an average value of 45 J, and a single value is not less than 35 J; according to the requirements of ASME BPVC IX and ASTM A370, the impact test uses a 10*10*55 mm sample, the impact temperature is -46℃ according to the technical requirements, the impact pendulum uses KV8, and the test results are shown in Figure 6 .

[0058] 4. Hardness test: the process evaluation is carried out according to the owner's specification and the standard ASTM A370, and Vickers hardness inspection needs to be carried out in the base material, heat affected zone and weld. At least 3 inspection points are recorded in each area. The hardness detection is shown in Figure 7 , and the test value is shown in Figure 8 .

[0059] 5. Macroscopic metallographic test results are shown in Figure 9 and Figure 10 .

[0060] 6. Chemical composition test: the weld is tested for chemical composition, and the test data is shown in Figure 11 .

[0061] 7. Ferrite and microscopic metallographic test: according to the requirements of the standard or specification, ferrite test needs to be carried out in the base material, heat affected zone and weld according to ASTM E562, and the acceptance value is 30-70%. It is verified that the ferrite value of this welding process is 38-53%, and the specific value is shown in Figure 12 . The microstructure of the weld is ferrite and austenite, and no carbide, nitride and intermetallic phase is found.

[0062] 8. Pitting test: this test is carried out according to ASTM G48 Method A, in a constant temperature solution of 40℃, 60g FeCl3·6H2O+540ml H2O, 4 samples taken from points 3, 6, 9 and 12 on the test piece are placed for 24h, and then the weight loss is detected, which meets the requirement of weight loss rate less than 4g / m2, and the surface of the test piece has no pitting pit under 20X field.

[0063] It will be apparent to those skilled in the art that the application is not limited to the details of the above-exemplified embodiments and that the present application can be implemented in other particular forms without departing from the spirit or essential characteristics thereof. Although the present specification describes the embodiments in detail, each embodiment does not include only one technical solution, and the present specification is described in this way only for the sake of clarity, and those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that those skilled in the art can understand.

Claims

1. A method of submerged arc welding of a super-duplex stainless steel, characterized in that: The method comprises the following steps: Step 1, blanking, cutting the base material and processing the test piece with appropriate size and standard required bevel according to the processing drawing; Step 2, bevel preparation, alcohol or propanol is used to wipe the inner and outer surface of the pipe, all bevel surfaces and the base material within 25mm range adjacent to the bevel surfaces need to be free of grease, moisture, oxide, scale, paint, debris and other foreign matters; Step 3, back inflation, before the backing welding, the purity of 99.997% argon gas needs to fill the inside of the pipeline, the oxygen content in the back inflation needs to be less than 0.05%, the backing welding is carried out by using the argon gas with the purity of 99.997%, and the back gas needs to be kept until the 8mm thick filler metal is completed by the argon arc welding; Step 4, spot welding, the bridge block with the same material as the base material is used, and the welding spot is on the bevel surface; Step 5, preheating treatment, the argon arc welding is carried out under the condition of room temperature, if the temperature is lower than 10℃, the electric oven is used for preheating, the interlayer temperature is not more than 100℃, before the submerged arc welding, the preheating temperature is increased by at least 80℃ through the flame heating, and the interlayer temperature is controlled to be 130℃-150℃ during the welding process; Step 6, argon arc welding, during the backing welding process, the polarity of the argon arc welding equipment is DCEN polarity, high-frequency arc striking, current attenuation and gas delay protection, the delay time is 4s-6s, the thickness of the argon arc welding is controlled, and the thickness of the argon arc welding is not less than 13mm; Step 7, submerged arc welding, before starting the welding, the existing starting and ending points are polished to facilitate the smooth transition of the new welding bead, after the welding of each welding bead is completed, the next layer of welding can be carried out only after the quality inspection is qualified, the interlayer joints of the multi-layer welding are staggered, and the interlayer temperature is strictly controlled to be not more than 150℃; the filler welding is welded to the welding seam metal surface which is lower than the joint surface by 0.5mm, and the subsequent cover welding is carried out, and the welding seam surface excess height should be not more than 3mm; Step 8, the nondestructive testing is carried out on the welded joint 48 hours after the welding, and the nondestructive testing modes include but are not limited to appearance detection, penetration detection and radiographic detection; Finally, the mechanical test, tensile test, bending test, impact test, hardness test, macroscopic metallographic test, microscopic metallographic structure test, ferrite test, pitting test and chemical composition test are carried out on the welded joint; The backing and welding of the step 6 are carried out by using the Exton 25.10.4.L welding wire; When the step 6 is carried out by using the Exton 25.10.4.L, the diameter of the welding wire is 2.4mm, the backing welding current is 88-90A, the backing welding voltage is 9-10V, the welding speed is 48mm / min, and the welding heat input is 1.0-1.1KJ / mm; The second layer welding current is 119-121A, the voltage is 10-11V, the welding speed is 78mm / min, and the welding heat input is 0.9-1.1KJ / mm; the subsequent argon arc welding current is 136-206A, the voltage is 10-13V, the welding speed is 114-162mm / min, and the welding heat input is 0.7-1.3KJ / mm; The welding test of the step 1 adopts the base material of the UNS S32750 super duplex stainless steel pipe, the pipe wall thickness is processed to 38mm, and the pipe diameter is 273mm.

2. A super-duplex stainless steel submerged arc welding method according to claim 1, characterized in that, The submerged arc filling and welding in step 7 is performed using SAW Exton 25.10.4.L / 15W welding wire flux.

3. A method of submerged arc welding of a super-duplex stainless steel according to claim 2, characterized in that When welding in step 7 using SAW Exton 25.10.4.L / 15W, the welding wire diameter is 2.4 mm, the welding current is 300-310 A, the welding voltage is 30-32 A, the welding speed is 294-318 mm / min, and the welding heat input is 1.7-2.0 J / mm.

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