WO2008072835A1

WO2008072835A1 - Sintered flux for submerged arc welding

Info

Publication number: WO2008072835A1
Application number: PCT/KR2007/005204
Authority: WO
Inventors: Tae Hoon Noh
Original assignee: Kiswel Ltd.
Priority date: 2006-12-13
Filing date: 2007-10-23
Publication date: 2008-06-19
Also published as: KR100774156B1

Abstract

Provided is a sintered flux for submerged arc welding which is applied to austenite stainless steel welding. The flux includes 12.0-20.0wt% SiO2, 18.0-27.0wt% Al2O3, 6.0-12.0wt% ZrO2 6.0-12.0wt% CaO, 7.0-16.0wt% CaF 2, 2.0-5.0wt% MnO, 20.0-29.0wt% MgO, 1.5-4.5wt% Na 203, K 20, Li 20, or a combination thereof, and a remainder including Fe and inevitable impurities, on the basis of the entire weight of the flux. Therefore, it is possible to provide a sintered flux for submerged arc welding which has excellent arc stability and slag detachability during welding, prevents welding defects such as poke marks and pits, and has excellent bead shape.

Description

SINTERED FLUX FOR SUBMERGED ARC WELDING

Technical Field

[1] The present invention relates to a sintered flux for submerged arc welding of austenite stainless steel, and more specifically, to a sintered flux for submerged arc welding which has excellent arc stability and slag detachability during submerged arc welding, prevents welding defects such as poke marks and pits, and has excellent bead shape. Background Art

[2] Currently, stainless steel is widely used in parts of nuclear power plants and in various chemical devices. The larger such parts and devices, the thicker and stronger the stainless steel is required to be. Conventionally, stainless steel has been welded by hand welding and semi-automatic welding. However, when thick stainless steel is welded by hand welding and semi-automatic welding, deposition efficiency decreases and welding defects such as slag inclusion and blowholes easily occur. Recently, stainless steel is being developed which contains large amounts of N, Ti, Mo and the like to increase its strength. However, such elements significantly degrade slag detachability during welding.

[3] Alternatively, thick stainless steel may be welded by narrow gap welding to reduce the number of welding passes. In this case, slag detachability is a very important factor. In fused fluxes currently on the market, when thick, high-tension steel is welded, the welding is performed using low heat input to prevent an effect of dilution of base metal and enhance slag detachability. Further, the surface of the steel is finished by a grinder for each pass. Thus, the conventional technology is quite inefficient. Accordingly, the present invention provides a sintered flux for submerged arc welding which has excellent arc stability and slag detachability during submerged arc welding of austenite stainless steel, prevents welding defects such as poke marks and pits, and has excellent bead shape. Disclosure of Invention

Technical Problem

[4] In order to solve the foregoing and/or other problems, it is an objective of the present invention to provide a sintered flux for submerged arc welding which has excellent arc stability and slag detachability during submerged arc welding of austenite stainless steel, prevents welding defects such as poke marks and pits, and has excellent bead shape. Technical Solution [5] In one aspect, the invention is directed to a sintered flux for submerged arc welding which is applied to austenite stainless steel welding. The flux includes 12.0-20.0wt% SiO 2 , 18.0-27.0wt% Al 2 O 3 , 6.0-12.0wt% ZrO 2, 6.0-12.0wt% CaO, 7.0-16.0wt% CaF 2 ,

2.0-5.0wt% MnO, 20.0-29.0wt% MgO, 1.5-4.5wt% Na O, K O, Li O, or a combination thereof, and a remainder including Fe and inevitable impurities, on the basis of the entire weight of the flux.

[6] In the sintered flux for submerged arc welding, a viscosity rate (VR) defined by the following equation may fall within the range of 8.0-14.0:

[7] 5(CaO + Al₂O₁ + MgO)

VR = (SiO_{2 +}CaF₂)

[8] The flux may be composed of less than 5wt% flux particles with a diameter of more than 1.00mm, 20.0-50.0wt% flux particles with a diameter of 0.5 to less than 1.0mm, 40.0-75.0wt% flux particles with a diameter of 0.20 to less than 0.5mm, and less than 5wt% flux particles with a diameter of less than 0.2mm, with respect to the overall weight thereof.

Advantageous Effects

[9] According to the invention, the chemical composition, the VR, and the flux-particle distribution of the sintered flux for submerged arc welding are controlled. Therefore, it is possible to provide a sintered flux for submerged arc welding which has excellent arc stability and slag detachability during welding, prevents welding defects such as poke marks and pits, and has excellent bead shape. Best Mode for Carrying Out the Invention

[10] The present inventor has discovered that controlling the composition of a sintered flux for submerged arc welding as described below yields superior arc stability, poke mark resistance, slag detachability, pit resistance, and bead shape.

[11] Hereinafter, components of a sintered flux for submerged arc welding according to the invention, which is applied to austenite stainless steel welding, and reasons for limiting the amounts of the components will be described.

[12] SiQ. : 12.0-20.0wt%

[13] SiO is an acidic component and serves to adjust the viscosity and melting point of molten slag, thereby enhancing bead shape and slag detachability.

[14] When the amount of SiO in the entire flux is less than 12.0wt%, viscosity is so insufficient that bead width becomes non-uniform. Further, a spreading property is reduced so that convex beads are formed, that is, welding beads are not uniform. Furthermore, slag detachability is reduced and welding defects easily occur. When the amount of SiO exceeds 20.0wt%, the basicity of molten slag is reduced so that oxygen within deposited metal increases. Then, toughness is degraded and viscosity becomes so excessive that non-uniform beads are formed and slag detachability is degraded.

[15] As for a SiO- supply source, quartz (SiO ), quartz sand (SiO ), wollastonite (CaSiO ) and the like can be added in the form of an oxide or oxide complex.

[16] AL Q_ : 18.0-27.0wt%

[17] Al O is a neutral component and serves to enhance slag fluidity so as to stabilize slag shape. Further, since Al O has a strong affinity for oxygen, it enhances welding performance without increasing the amount of oxygen in the welded metal. In addition, Al O adjusts the viscosity and melting point of molten slag such that bead shape is enhanced. When welding is performed, Al O enhances arc concentration and stability, thereby improving welding performance.

[18] When the amount of Al O in the entire flux is less than 18.0wt%, the viscosity and melting point are reduced so that bead widths and grains become non-uniform. Further, welding defects such as undercut and the like may occur. When the amount of Al O exceeds 27.0wt%, the melting point of molten slag increases, and fluidity is reduced so that arc stability is degraded. Further, the viscosity of molten slag increases, and a bead spreading property is so insufficient that convex beads are formed, that is, bead shape is degraded. In addition, welding defects such as slag inclusion and the like occur.

[19] As for an Al 2 O 3 supply source, bauxite Al 2 O 3 -H 2 O, aluminum oxide (Al 2 O 3 ) and the like can be used.

[20] ZrO. : 6.0-12.0wt%

[21] ZrO is an effective component for improving slag detachability. When the amount of ZrO in the entire flux is less than 6.0wt%, its effect is insignificant. When the amount of ZrO exceeds 12.0wt%, a generated amount of slag increases so that welding defects such as slag inclusion and the like occur. Further, slag is hardened and solidified so rapidly that bead shape and slag detachability are degraded.

[22] As for a ZrO supply source, zirconia (ZrO ), zircon sand (ZrSiO ) and the like can be used.

[23] CaO: 6.0-12.0wt%

[24] CaO is a basic component and serves to adjust basicity and viscosity and to reduce the amount of oxygen in welded metal, thereby enhancing the toughness of a welded metal portion. However, CaO increases the melting point of molten slag such that slag inclusion is caused. Therefore, it is necessary to limit the amount of CaO.

[25] When the amount of CaO is less than 6.0wt%, its effect is insignificant. When the amount of CaO exceeds 12.0wt%, the melting point and viscosity of molten slag increase so that bead shape and slag detachability are degraded and welding defects such as poke marks occur. [26] As for a CaO supply source, wollastonite (CaSiO ), dolomite (MgCO -CaCO ), anorthite (CaO-Al O -SiO ) and the like can be used.

2 3 2

[27] Call : 7.0-16.0wt%

[28] CaF is a basic component and serves to reduce the melting point and viscosity of molten slag such that slag fluidity is enhanced and bead shape is improved. Further, when welding is performed, CaF reacts with oxygen to generate fluorine gas such that partial vapor pressure is reduced. Thus, it helps to reduce oxygen and hydrogen and enhance the toughness of welded metal.

[29] When the amount of CaF is less than 7.0wt%, its effect is so insignificant that bead shape and toughness of welded metal are not excellent. When the amount of CaF exceeds 16.0wt%, arc becomes so unstable that bead shape and slag detachability are degraded. Further, the generated gas has a bad smell, and welding defects such as poke marks, undercut and the like occur.

[30] As for a CaF supply source, fluorspar (CaF ) or the like can be used.

[31] MnO: 2.0-5.0wt%

[32] MnO is an effective component for improving bead shape. In particular, during highspeed welding, MnO serves to improve bead shape and prevent welding defects such as undercut and the like. When the amount of MnO is less than 2.0wt%, its effect is insignificant. When the amount of MnO exceeds 5.0wt%, CO reaction in a molten weld pool becomes so severe that bead shape and slag detachability are considerably degraded.

[33] As for a MnO supply source, ferro-manganese, manganese oxide (MnO) and the like can be used.

[34] MgQ: 20.0-29.0wt%

[35] MgO is a basic component and serves to increase the basicity of molten slag and reduce the amount of oxygen within welded metal, which enhances the toughness of welded metal. Further, when welding is performed, MgO stabilizes arc and improves slag detachability and bead shape. However, since MgO increases the melting point of molten slag such that slag inclusion may be caused, there is a limit to the amount of MgO that can be added.

[36] When the amount of MgO is less than 20.0wt%, its effect is insignificant, and slag adheres to the surface of welding beads such that the slag detachability is degraded. When the amount of MgO exceeds 29.0wt%, arc becomes unstable, and convex beads are formed, thereby degrading bead shape. Further, the melting point of slag excessively increases so that slag detachability is degraded, and welding defects such as poke marks and the like occur.

[37] As for an MgO supply source, magnesite (MgCO ), magnesia clinker (MgO), dolomite (MgCO -CaCO ) and the like can be used. [38] Na. O. K O. Li O. or a Combination Thereof: 1.5-4.5wt% 'C

2

[39] Na O, K O, and Li O are important components for securing arc stability. In particular, during high-speed welding, Na O, K O, and Li O serve to maintain arc stability. When the total concentration of Na O, K O, and Li O is less than 1.5wt%, their effect of enhancing arc stability is insignificant. When Na O, K O, Li O, or a combination thereof exceeds 4.5wt%, convex beads are formed, thereby degrading welding performance. Further, arc is considerably unstable and hygroscopic resistance increases dramatically.

[40] Na O, K O, and Li O are added from water glass, cryolite (Na AlF ), potassium

2 2 2 3 6 titanate (K TiO ), Li-Si and the like, which are generally used for manufacturing a sintered flux for submerged arc welding.

[41] In the present invention, not only is the composition of flux controlled, but a relational expression for expressing a viscosity rate is set. When the viscosity rate is properly controlled within the following numerical range, welding performance is improved:

[42] Viscosity Rate (VR): 8.0-14.0

[43] The VR introduced in the invention is derived from the consideration that the components affecting slag melting point and viscosity during submerged arc welding considerably affect arc stability, bead shape, and welding defects. The present inventor has recognized that, among the components of the flux, CaO, Al O , and MgO increase the melting point of slag and the viscosity of mixed slag, but SiO and CaF reduce the melting point of slag and the viscosity of mixed slag. The present inventor has defined the VR as follows:

^[44] 5(CaO ₊ AIp_{1 +} MgO)

YK =

(SiO_{2 +}CaF₂)

[45] That is, when the viscosity of slag is excessively high, the fluidity of slag is reduced during welding such that arc becomes unstable and bead spreading properties become insufficient. Accordingly, bead shape is degraded. Further, slag inclusion is frequently caused so that welding defects occur. On the contrary, when the viscosity of slag is excessively low, bead width becomes non-uniform so that bead shape is degraded. Further, slag detachability is reduced and welding defects occur.

[46] If the VR defined by the above-described expression is less than 8.0, the viscosity of slag becomes excessively low so that bead widths and grains become non-uniform. Further, skew beads are easily formed and welding defects such as pits and undercut easily occur. On the contrary, when the VR exceeds 14.0, the viscosity of slag becomes excessively high so that bead shape is degraded. Further, slag detachability and arc stability are also degraded because of the reduction in slag fluidity.

[47] The contents of the sintered flux for submerged arc welding according to the invention can be measured using Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES), X-ray Fluorescence Spectrometry (XRF), and the like.

[48] Reasons for limiting particle diameters of the sintered flux for submerged arc welding will be described in detail below.

[49] If the sintered flux in which the respective flux components having the above- described compositional ratios are mixed does not have proper flux-particle distribution, arc stability and bead shape are degraded, and welding defects such as pits, poke marks and the like easily occur. Therefore, the flux according to the invention is composed of less than 5wt% flux particles with a diameter of more than 1.00mm, 20.0-50.0wt% flux particles with a diameter of 0.50 to less than 1.00mm, 40.0-75.0wt% flux particles with a diameter of 0.20 to less than 0.50mm, and less than 5wt% flux particles with a diameter of less than 0.20mm, with respect to the overall weight thereof.

[50] When the weight ratio of the flux particles with a diameter of more than 1.00mm exceeds 5.0wt%, flux particles with a large diameter increase, so that the space between the flux particles increases. Then, arc protection and arc stability are reduced, bead shape is degraded, and poke marks are easily generated.

[51] When the weight ratio of the flux particles with a diameter of 0.5 to less than

1.00mm is less than 20.0wt%, it is highly likely that poke marks are generated. When the weight ratio of the flux particles exceeds 50.0wt%, convex beads are formed, thereby degrading bead shape.

[52] When the weight ratio of the flux particles with a diameter of 0.20 to less than

0.5mm is less than 40.0wt%, the overall flux particles become coarse so that arc protection, arc stability, and bead shape are degraded. When the weight ratio of the flux particles exceeds 75wt%, gas is not smoothly discharged, so that welding defects such as poke marks, pits and the like occur.

[53] When the weight ratio of the flux particles with a diameter of less than 0.20mm exceeds 5.0wt%, the flux particles with a small diameter increase, so that welding defects such as poke marks, pits and the like occur.

[54] The diameters of the flux particles of the sintered flux for submerged arc welding can be measured on the basis of the Standard Test Method for Sieve Analysis of Metal Powders (ASTM B214). Mode for the Invention

[55] Examples

[56] Hereinafter, the effects of Examples of the sintered flux for submerged arc welding according to the invention will be described in detail and compared with Comparative Examples that deviate from the ranges of the invention.

[57] Table 1 [Table 1] [Table ]

[58] [59] Table 2 [Table 2] [Table ]

[60] [61] Table 3 [Table 3] [Table ]

[62] Tables 1 and 2 show the type and the chemical components of welding base metal and welding wire for performing welding using the sintered flux for submerged arc welding of austenite stainless steel according to an exemplary embodiment of the present invention. Table 3 shows welding conditions. Further, Tables 4 and 5 show results in which submerged arc welding of austenite stainless steel is performed using the sintered flux for submerged arc welding according to the exemplary embodiment of the present invention.

[63] Here, the respective raw material fluxes are converted into water glass which is dried and sintered to form a sintered flux for submerged arc welding having the chemical composition shown in Tables 4 and 5. The present invention is not limited to the above-described manufacturing method.

[64] In Tables 4 and 5, remainders of respective flux components represent trace amounts of BaO, FeO, TiO , Fe, and other impurities contained in the respective raw material fluxes.

[65] [66] Table 4 [Table 4]

[67] [68] Table 5

[Table 5]

[69] [70] Table 6 shows results of evaluating welding performance on the respective sintered fluxes for submerged arc welding after welding is performed by the above-described welding method. The evaluation results are represented by Excellent (O), Normal (Δ), and Poor (x).

[71] [72] Table 6

[Table 6] [Table ]

[73] [74] When the flux having the composition of Tables 4 and 5 was used to perform welding by using the base metal represented in Table 1 and the welding wire of Table 2, a variation in welding current (a value obtained by subtracting the minimum welding current from the maximum welding current) was used to evaluate arc stability. The detailed arc stability evaluation criteria were shown in Table 7.

[75] [76] Table 7 [Table 7] [Table ]

[77] When welding was performed under the same conditions as the evaluation of arc stability, poke mark resistance was evaluated as follows. When no poke mark was generated on a bead surface, it was represented by 'Favorable (O) '. When the number of generated poke marks ranged from 1 to 4, it was represented by 'Normal(Δ) '. When the number of generated poke marks was equal to or more than 5, it was represented by 'Poor (x)'. Further, slag detachability was evaluated as follows. When slag covering a welding zone was removed by physical means such as a hammer or brush and did not remain on a bead surface but was clearly detached, it was represented by 'Favorable (O) '. If the slag was not detached but remained on a bead surface, it was represented by 'Poor (x)'. In the evaluation of pit resistance, when no pit is generated in a weld zone, it is represented by 'Favorable (O) '. When a pit was generated, it was represented by 'Poor (x)'. In the evaluation of bead shape, when a skew bead or under was not generated and a bead width and a bead grain were uniform, it was represented by 'Favorable (O)'. When a skew bead or undercut was generated or bead widths and bead grains were not uniform, it was represented by 'Poor (x)'.

[78] As shown in Table 6, all of Examples 1 to 8 of the invention exhibited favorable results.

[79] In Comparative Example 9, the amount of CaF was less than the numerical range of the invention, and the amount of SiO exceeded the numerical range of the invention. Therefore, bead shape and slag detachability were not excellent.

[80] In Comparative Example 10, the amount of CaO was less than the numerical range of the invention, and the amounts of Al O and MgO exceeded the numerical ranges of the invention. Therefore, welding defects such as poke marks were generated, bead shape was not excellent, and arc stability was insufficient.

[81] In Comparative Example 11, the amount of ZrO was less than the numerical range of the invention, and the amount of CaF exceeded the numerical range of the invention. Therefore, arc stability and slag detachability were not excellent so that bead shape was degraded, and welding defects such as poke marks and pits occurred.

[82] In Comparative Example 12, the amounts of SiO and MnO were less than the numerical ranges of the invention, Na O , K O, Li O, a combination thereof, and the VR exceeded the numerical ranges of the invention. Therefore, arc stability was degraded, bead shape was not excellent, and welding defects occurred.

[83] In Comparative Example 13, the amount of MgO was less than the numerical range of the invention, and the amounts of ZrO and CaO exceeded the numerical ranges of the invention. Therefore, slag detachability and bead shape were not excellent, and poke marks were generated.

[84] In Comparative Example 14, the amounts of Al O and Na O , K O, Li O or a

2 3 2 3 2 2 combination thereof were less than the numerical ranges of the invention, and the amount of MnO exceeded the numerical range of the invention. Therefore, slag detachability and bead shape were not excellent, poke marks were generated, and arc stability was insufficient.

[85] In Comparative Examples 15 and 16, the VRs were less than the numerical range of the invention. The viscosity of slag was reduced so that the bead shape was not uniform. Further, welding defects such as pits and poke marks occurred.

[86] In Comparative Examples 17 and 18, the VRs exceeded the numerical range of the invention. Therefore, the viscosity of slag was increased so that bead shape was degraded. Further, fluidity of slag was reduced so that slag detachability and arc stability were degraded.

[87] Table 8 shows results in which eight fluxes are manufactured by discriminating the flux-particle distribution of the fluxes with respect to Example 1 of the invention described above. Table 9 shows results in which welding performance is evaluated for the sintered fluxes for submerged arc welding, which have the particle distributions shown in Table 8. The evaluation was performed under the welding conditions described in Tables 1 to 3, and the evaluation results were represented by Excellent (O), Normal (Δ), and Poor (x).

[88]

[89] Table 8

[Table 8] [Table ]

[90] [91] Table 9 [Table 9] [Table ]

[92] [93] As shown in Tables 8 and 9, when a flux manufactured according to Examples of the invention was composed of 5.0wt% flux particles with a diameter of more than or equal to 1.00mm, 20.0-50.0wt% flux particles with a diameter of 0.50 to less than 1.00mm, 40.0-75.0wt% flux particles with a diameter of 0.20 to less than 0.50mm, and 5.0wt% flux particles with a diameter of less than 0.20mm with respect to the overall weight of the flux, arc stability, poke mark resistance, slag detachability, pit resistance, and bead shape of the flux were excellent.

[94] In Comparative Example 23 of Table 8, the weight ratio of flux particles with a diameter of 0.50 to less than 1.00mm was lower than the range of the invention, and the weight ratio of flux particles with a diameter of 0.20 to less than 0.50mm was higher than the range of the invention. Therefore, welding defects occurred and poke mark resistance and pit resistance were not excellent.

[95] In Comparative Example 24 of Table 8, the weight ratio of flux particles with a diameter of more than 1.00mm was higher than the range of the invention. Therefore, the arc stability and bead shape were degraded, and poke mark resistance and pit resistance were insufficient.

[96] In Comparative Example 25 of Table 8, the weight ratio of flux particles with a diameter of 0.20 to less than 0.50mm was lower than the range of the invention, and the weight ratio of flux particles with a diameter of less than 0.20mm was higher than the range of the invention. Therefore, welding defects occurred. Further, bead shape was not excellent and arc stability was insufficient.

[97] In Comparative Example 26 of Table 8, the weight ratio of flux particles with a diameter of 0.50 to less than 1.00mm was higher than the range of the invention. Therefore, bead shape was not excellent and poke mark resistance was insufficient.

Claims

[1] A sintered flux for submerged arc welding which is applied to austenite stainless steel welding, wherein the flux comprises 12.0-20.0wt% SiO , 18.0-27.0wt% Al 2 O 3 ,

6.0-12.0wt% ZrO₂ 6.0-12.0wt% CaO, 7.0-16.0wt% CaF₂, 2.0-5.0wt% MnO, 20.0-29.0wt% MgO, 1.5-4.5 wt% Na 203 , K 20, Li 20, or a combination thereof, and a remainder including Fe and inevitable impurities, on the basis of the entire weight of the flux. [2] The sintered flux for submerged arc welding according to claim 1, wherein a viscosity rate (VR) of the flux, defined by the following equation falls within the range of 8.0-14.0:

5(CaO + Al₂O₁ + MgO)

VR =

(SiO_{2 +}CaF₂)

[3] The sintered flux for submerged arc welding according to claim 1, wherein the flux is composed of less than 5wt% flux particles with a diameter of more than 1.00mm, 20.0-50.0wt% flux particles with a diameter of 0.5 to less than 1.0mm, 40.0-75.0wt% flux particles with a diameter of 0.20 to less than 0.5mm, and less than 5wt% flux particles with a diameter of less than 0.2mm, with respect to the overall weight thereof.