Flux-cored wire for extra-thick maritime work steel high heat input EGW and preparation method of flux-cored wire

Abstract

The invention discloses a flux-cored wire for extra-thick marine steel high heat input EGW and a preparation method of the flux-cored wire, and relates to the technical field of metal welding, the flux-cored wire comprises an outer skin of a double-layer alloy steel strip and powder filled in the outer skin, the filling rate of the powder is 20 + / -5%, and the powder comprises Fe, Mn, Si, Cr, Ni, Mo, V, B, S, Al, MgAl2O4, MgO-TiO2, ReOx and a slag former. According to the preparation method, the metal powder is positively charged, the rare earth nanoparticles are negatively charged through an electrostatic self-assembly technology, the metal powder and the rare earth nanoparticles are mixed with a slag former after being mixed, filtered and freeze-dried, an alloy steel strip is filled with the powder, and then rolling and drawing forming is conducted. In the welding process, the composite inclusions form a core-shell structure, a weld metal structure is regulated and controlled, acicular ferrite nucleation is promoted, and grains are refined, so that the low-temperature toughness and crack arrest performance of a weld are remarkably improved, the rare earth elements are beneficial for changing irregular inclusions into spheres, nucleation sites are increased, interface energy is reduced, and the nucleation rate of acicular ferrite is increased.

Description

Technical Field

[0001] The present invention relates to the technical field of metal welding, and particularly relates to a flux-cored wire for extra-thick offshore steel with high heat input EGW and a preparation method thereof. Background Art

[0002] As a welding method, electro-gas welding (EGW) with high heat input is famous for its high energy density, operation convenience and wide application, and is particularly suitable for the splicing and processing of steel for offshore platforms, shipbuilding and submarine transportation pipelines. With the development of the trend of ship enlargement, the strength of ship plates has been significantly improved, and high-strength steel of EH grade is mostly used, and the thickness of steel plates at key structural parts (such as main decks, stringer plates, hatch coamings, etc.) can reach 120 mm. In addition, the exploration and development of polar oil and gas resources have promoted the extreme environment of the application of offshore steel. These steels need to serve in an ultra-low temperature environment of -60°C, thus posing more stringent requirements for the crack arrest performance of weld metal.

[0003] However, the application of high heat input welding technology results in significant coarsening of austenite grains in weld metal, and then brittle phases such as upper bainite, Widmanstätten structure and side plate ferrite are generated, seriously deteriorating the mechanical properties of the weld, especially the low-temperature toughness and crack arrest performance. To solve this problem, in recent years, countries such as Japan and South Korea with developed shipbuilding industries have widely used oxide metallurgy technology to produce steel for high heat input welding. By introducing dispersed and high-melting-point inclusion particles into the weld, these fine and insoluble particles can effectively pin the austenite grain boundaries and promote the nucleation of beneficial structure - acicular ferrite. This dual action mechanism significantly refines the weld grains and optimizes the weld microstructure, thus greatly improving the low-temperature toughness of the welded joint.

[0004] The existing flux-cored wire for high heat input steel with high strength and high toughness and its preparation method with the patent publication number of CN118417757A pins the grain boundaries of the clad metal by adding Al composite powder loaded with nano-TiN, and the weld microstructure is refined to a certain extent. However, when the heat input is extremely high, the peak temperature of the weld will reach above 1400°C, and at this time, TiN will start to dissolve, and the pinning effect is limited.

[0005] In the prior art, by reasonably matching the strong oxide elements in the flux material and introducing fine and insoluble nano-particles, the efficient nucleation of acicular ferrite in the weld microstructure can be promoted, the grains can be segmented and the microstructure can be refined, and the low-temperature toughness of the welded joint can be improved. However, the strength level and thickness of the ship plates targeted by these technologies in welding applications are relatively low, and the improvement of weld performance is weak, which is not enough to meet the requirements of the crack arrest performance of the weld clad metal of extra-thick offshore steel in a more severe service environment. Summary of the Invention

[0006] The object of the present invention is to provide a flux-cored wire for extra-thick offshore steel with high heat input EGW and a preparation method thereof, so as to solve the problems that the strength level and thickness of the ship plate targeted by the existing welding technology are relatively low, the improvement of the weld performance is weak, and it is not sufficient to meet the requirements of the crack arrest performance of the weld cladding metal of extra-thick offshore steel under more severe service environments.

[0007] A flux-cored wire for extra-thick offshore steel with high heat input EGW, comprising an outer skin and a powder. The powder filling rate is 20 ± 5%. The outer skin is a multi-layer alloy steel strip, and the powder is filled therein. The powder comprises the following components by mass percentage: Mn 1.9 - 2.8%, Si 1.1 - 1.6%, Cr 0.1 - 0.8%, Ni 2.3 - 3.6%, Mo 0.2 - 0.7%, V 0.008 - 0.02%, B 0.003 - 0.005%, S 0.001 - 0.55%, ReOx 0.41 - 0.96%, Al 0.22 - 0.34%, MgAl2O4 0.31 - 0.72%, MgO-TiO2 0.32 - 0.51%, slag former 3.5 - 5.4%, and the balance is Fe.

[0008] Preferably, the powder filling rate is the ratio of the powder mass to the sum of the powder and outer skin masses.

[0009] Preferably, the ReOx is rare earth nanoparticles, and cheap (Ce,La)Ox nanoparticles are used, and the atomic ratio of Ce to La is 2:1.

[0010] Preferably, the outer skin is a double-layer structure, the outer layer is an H08Si alloy steel strip, the inner layer is an H10MnCr alloy steel strip, and the single-layer width and thickness of the skin steel strip are 0.2 - 0.4 mm.

[0011] Preferably, the preparation method comprises the following steps:

[0012] Step S1: Weigh metal powders of Mn, V, B, Cr, Ni, Mo, Fe, MgAl2O4 and MgO-TiO2 according to a preset ratio, disperse them in a mixed solution of deionized water and n-propanol in equal proportion, then add 3 - 5 wt% of dodecyl trimethyl ammonium bromide to make the metal particle surfaces carry positive charges, and stir with ultrasonic waves for 30 mins;

[0013] Step S2: Weigh ReOx according to a preset ratio, disperse it in a mixed solution of deionized water and absolute ethanol in equal proportion, then add 1 - 3 wt% of an anionic surfactant to make the rare earth particles carry negative charges, and stir with ultrasonic waves for 30 mins;

[0014] Step S3: Mix the solutions of Step S1 and S2, stir, filter, wash, and freeze-dry to obtain metal powder with rare-earth nanoparticle-reinforced phase on the surface;

[0015] Step S4: Put the composite metal powder obtained in Step S3 and the slag-forming agent into a Y-type powder mixer in proportion and mix for 40 - 50 mins to obtain flux-cored powder;

[0016] Step S5: Process different alloy steel strips into the same size and stack them, use a rolling mill to press them into a U shape, then use a powder feeding device to fill the flux-cored powder made in Step S4 into the U-shaped steel strip, roll and seal it, and then draw it into a wire with a diameter of 1.7 mm after 5 - 7 passes.

[0017] Preferably, the ultrasonic frequency used in Step S1 and S2 is 30 kHZ.

[0018] Preferably, the anionic surfactant in Step S2 is sodium hexametaphosphate.

[0019] Preferably, the ultra-high heat input welding is double-sided double-wire electro-gas vertical welding, the base metal is EH40 or EH47 grade ship plate steel with a thickness of 80 - 100 mm, the base metal groove design is an asymmetric double-sided V-groove, the depth of the front groove is 3 / 5 of the plate thickness, and the groove angle is 8 - 12°; the depth of the back groove is 2 / 5 of the plate thickness, and the groove angle is 5 - 10°.

[0020] Preferably, the welding process parameters are: the welding voltage of the front wire is 36 - 48 V, the welding current is 213 - 341 A, and the welding speed is 44.7 - 65.6 mm / min; the welding voltage of the back wire is 33 - 45 V, the welding current is 192 - 266 A, and the welding speed is 44.7 - 65.6 mm / min. The heat input of the double-wire electro-gas vertical welding is 524 - 814 kJ / cm, and the whole process is carried out in a mixed shielding gas of 80% CO2 and 20% Ar.

[0021] The advantages of the present invention are as follows: In the flux-cored wire for extra-thick offshore steel with high heat input EGW and its preparation method of the present invention, by introducing MgAl2O4, MgO-TiO2 metal powders and ReOx rare earth nano-powders, during the welding process, the rare earth nano-particles will form composite inclusions with a shell-core structure with metal elements. ReS, Re3S4, Re2O2S, MnS, etc. are distributed on the outer shell of the inclusions, and the Mg-Al-Ti-O system oxides serve as the inner core. The rare earth elements and the Mg-Al-Ti-O system oxides can stabilize austenite, increase the nucleation temperature range of acicular ferrite. Their oxygen sulfides have a very low lattice misfit degree with the ferrite matrix, and can promote the nucleation of acicular ferrite through the mechanism of manganese-depleted zone and low misfit degree, refine the grains, enhance the low-temperature toughness and crack arrest performance of the weld. The rare earth elements help to change the irregular inclusions into spherical shapes, increase the nucleation sites, reduce the interfacial energy, and improve the nucleation rate of acicular ferrite; by adopting the electrostatic self-assembly process, the metal powder particles are positively charged and the rare earth nano-particles are negatively charged. Compared with the ball milling process, this can not only avoid the agglomeration of nano-particles under the action of electrostatic repulsion, but also improve the efficiency and the stability of nano-inclusions in the powder mixing stage; by designing the wire with a double-layer outer skin structure with H08Si alloy on the outer layer and H10MnCrNi alloy on the inner layer, the outer layer alloy has a low melting point, high plasticity, good wear resistance and corrosion resistance, and is easy to draw and form. During the welding process, it can also ensure a stable arc, prevent the flux core from splashing, improve the aesthetics and quality of the weld. The inner layer alloy has a high melting point and high strength, and also contains trace alloys such as Mn, Cr, Ni, etc., which is beneficial to maintaining the strength and low-temperature toughness of the welded joint during the welding of thick plates. By adjusting the melting points and fluidities of the inner and outer layers to cope with different welding heat inputs, the advantages of the inner and outer layer composite structure can be complementary, improving the mechanical properties and weldability of the wire, and meeting the processing requirements of extra-thick ship plate steel with high heat input gas-electric vertical welding. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the weld microstructure in the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] In order to make the technical means, creative features, achieved purposes and effects of the present invention easy to understand, the present invention will be further described below in conjunction with specific embodiments.

[0024] Example 1

[0025] As Figure 1As shown in the figure, a flux-cored wire for extra-thick offshore steel with high heat input EGW, comprising an outer skin and flux powder, with a flux powder filling rate of 21%; the outer skin consists of an outer layer of H08Si alloy and an inner layer of H10MnCrNi alloy, with a total thickness of 0.6 mm; the flux powder comprises the following components by mass percentage: Mn 2.4%, Si 1.3%, Cr 0.5%, Ni 2.9%, Mo 0.45%, V 0.014%, B 0.004%, S 0.28%, (Ce,La)Ox 0.68%, Al 0.28%, MgAl2O4 0.51%, MgO-TiO2 0.42%, slag former 4.4%, and the balance is Fe.

[0026] The preparation method of the flux-cored wire for extra-thick offshore steel with high heat input EGW is as follows:

[0027] Step S1: Weigh metal powders of Mn, V, B, Cr, Ni, Mo, Fe, MgAl2O4 and MgO-TiO2 according to a preset ratio, disperse them in a mixed solution of deionized water and n-propanol in equal proportion, then add 4 wt% of dodecyltrimethylammonium bromide to make the metal particle surface carry a positive charge, and stir with ultrasonic waves at a frequency of 30 kHZ for 30 mins;

[0028] Step S2: Weigh (Ce,La)Ox nanoparticles according to a preset ratio, disperse them in a mixed solution of deionized water and absolute ethanol in equal proportion, then add 2 wt% of anionic surfactant sodium hexametaphosphate to make the rare earth particle surface carry a negative charge, and stir with ultrasonic waves at a frequency of 30 kHZ for 30 mins;

[0029] Step S3: Mix the solutions of Step S1 and Step S2, stir, filter, wash and freeze-dry to obtain metal powders with a rare earth nanoparticle-reinforced phase on the surface;

[0030] Step S4: Put the composite metal powders obtained in Step S3 and the slag former into a Y-type powder mixer and mix for 45 mins to obtain flux-cored powders;

[0031] Step S5: Process double-layer alloy steel strips into a width of 50 mm and a thickness of 0.25 mm and stack them, use a rolling mill to press them into a U shape, then use a powder feeding device to fill the flux-cored wire made in Step S4 into the U-shaped steel strip, roll and seal the mouth, and then draw it into a wire with a diameter of 1.7 mm through 5 - 7 passes.

[0032] The double-wire electro-gas vertical welding experiment was carried out with the welding wire prepared by the above steps. The experimental steel was EH47 ship plate steel with a thickness of 80 mm. The groove was an asymmetric double-sided V-groove. The depth of the front groove was 48 mm and the groove angle was 12°; the depth of the back groove was 32 mm and the groove angle was 9°. The relevant welding process parameters were as follows: the welding voltage of the front wire was 45 V, the welding current was 289 A, and the welding speed was 56.4 mm / min; the welding voltage of the back wire was 42 V, the welding current was 253 A, and the welding speed was 56.4 mm / min. The heat input of the double-wire electro-gas vertical welding was 762 kJ / cm, and the whole process was carried out in a mixed protective gas of 80% CO2 and 20% Ar.

[0033] Example 2

[0034] In this example, a flux-cored wire for EGW with high heat input for extra-thick offshore steel was used, which included an outer skin and flux. The flux filling rate was 21%; the outer skin was composed of an outer layer of H08Si alloy and an inner layer of H10MnCrNi alloy, with a total thickness of 0.6 mm; the flux included the following components in mass percentages: Mn 2.3%, Si 1.4%, Cr 0.47%, Ni 2.9%, Mo 0.44%, V 0.015%, B 0.004%, S 0.27%, (Ce,La)Ox 0.71%, Al 0.29%, MgAl2O4 0.52%, MgO-TiO2 0.41%, slag former 4.5%, and the rest was Fe.

[0035] The preparation method of the flux-cored wire for EGW with high heat input for extra-thick offshore steel was the same as that in Experimental Example 1;

[0036] The double-wire electro-gas vertical welding experiment was carried out with the welding wire prepared by the above steps. The experimental steel was EH47 ship plate steel with a thickness of 90 mm. The groove was an asymmetric double-sided V-groove. The depth of the front groove was 54 mm and the groove angle was 12°; the depth of the back groove was 36 mm and the groove angle was 9°. The relevant welding parameters were the same as those in Example 1.

[0037] Example 3

[0038] In this example, a flux-cored wire for EGW with high heat input for extra-thick offshore steel was used, which included an outer skin and flux. The flux filling rate was 21%; the outer skin was composed of an outer layer of H08Si alloy and an inner layer of H10MnCrNi alloy, with a total thickness of 0.6 mm; the flux included the following components in mass percentages: Mn 2.2%, Si 1.4%, Cr 0.54%, Ni 2.7%, Mo 0.46%, V 0.013%, B 0.003%, S 0.29%, (Ce,La)Ox 0.68%, Al 0.28%, MgAl2O4 0.49%, MgO-TiO2 0.43%, slag former 4.3%, and the rest was Fe.

[0039] The preparation method of the flux-cored wire for EGW with extra-thick offshore steel under high heat input is the same as that in Experimental Example 1;

[0040] The double-wire electro-gas vertical welding experiment was carried out with the wire prepared by the above steps. The experimental steel was 100-mm EH47 ship plate steel, and the groove was an asymmetric double-sided V-groove. The depth of the front groove was 60 mm, and the groove angle was 12°; the depth of the back groove was 40 mm, and the groove angle was 9°. The relevant welding parameters were the same as those in Example 1.

[0041] Example 4

[0042] Referring to Example 1, the difference lies in that the experimental steel was EH40 steel plate (80 mm), and the other wire preparation and welding parameters were the same.

[0043] Example 5

[0044] Referring to Example 2, the difference lies in that the experimental steel was EH40 steel plate (90 mm), and the other wire preparation and welding parameters were the same.

[0045] Example 6

[0046] Referring to Example 3, the difference lies in that the experimental steel was EH40 steel plate (100 mm), and the wire preparation process and welding parameters were the same.

[0047] Comparative Example 1

[0048] Referring to Example 1, the difference lies in that (Ce,La)Ox was not contained in the flux-cored powder of the wire, and the rest of the process was the same.

[0049] Comparative Example 2

[0050] Referring to Example 1, the difference lies in that the traditional ball milling process was used instead of the electrostatic self-assembly process for powder mixing, and the rest of the process was the same. The specific process of the ball milling process was as follows: The powders of Mn, V, B, Cr, Ni, Mo, Fe, MgAl2O4, MgO-TiO2, and (Ce,La)Ox were put into a ball mill in proportion, and it rotated forward and backward for 30 minutes, and then heated and dried. The obtained composite powder and the slag forming agent were put into a Y-type powder mixer and mixed for 30 minutes to obtain the flux-cored powder.

[0051] Comparative Example 3

[0052] Referring to Example 1, the difference lies in that the wire sheath was a single-layer structure of H10MnCrNi alloy with a thickness of 0.5 mm, and the rest of the process was the same.

[0053] The microstructure observation and mechanical property tests were carried out on the welds obtained in Examples 1 to 6 and Comparative Examples 1 to 3, and the experimental results were recorded in the following table:

[0054]

[0055] Table 1 Microstructure Morphology Characteristics of Weld Metals in Examples and Comparative Examples

[0056]

[0057] Table 2 Mechanical Property Test Results of Weld Metals in Experimental Examples and Comparative Examples

[0058] Combined with the tabular data, in the present invention, by introducing MgAl2O4, MgO-TiO2 metal powders and ReOx rare earth nano-powders, during the welding process, the rare earth nano-particles will form composite inclusions with a shell-core structure with metal elements, which can stabilize austenite, increase the nucleation temperature range of acicular ferrite, and there is an extremely low lattice misfit degree between its oxysulfide and the ferrite matrix, which can promote the nucleation of acicular ferrite through the mechanism of manganese-depleted zone and low misfit degree, refine the grains, enhance the low-temperature toughness and crack arrest performance of the weld. The rare earth elements help to change the irregular inclusions into spherical shapes, increase the nucleation sites, reduce the interfacial energy, and improve the nucleation rate of acicular ferrite; by adopting the electrostatic self-assembly process, the metal powder particles are positively charged and the rare earth nano-particles are negatively charged. Compared with the ball milling process, this can not only avoid the agglomeration of nano-particles under the action of electrostatic repulsion, but also improve the efficiency and the stability of nano-inclusions in the powder mixing stage; by designing the welding wire with a double-layer outer skin structure with H08Si alloy on the outer layer and H10MnCrNi alloy on the inner layer, the outer layer alloy has a low melting point, high plasticity, good wear resistance and corrosion resistance, and is easy to be drawn into shape. During the welding process, it can also ensure a stable arc, prevent the cored wire from splashing, improve the appearance and quality of the weld. The inner layer alloy has a high melting point and high strength, and also contains trace alloys such as Mn, Cr, and Ni, which is beneficial to maintaining the strength and low-temperature toughness of the welded joint during the welding of thick plates. By adjusting the melting points and fluidities of the inner and outer layers to cope with different welding heat inputs, the advantages of the inner and outer layer composite structures can be complementary, improving the mechanical properties and weldability of the welding wire, and meeting the processing requirements of gas-electric vertical welding with large heat input for extra-thick ship plate steel.

[0059] As is known by common technical knowledge, the present invention can be implemented by other embodiments that do not depart from its spirit or essential features. Therefore, the above-disclosed embodiments are illustrative in all aspects and not exclusive. All changes within the scope of the present invention or within the scope equivalent to the present invention are encompassed by the present invention.

Claims

1. A flux-cored welding wire for extra-thick marine steel with high heat input EGW, characterized by: The invention comprises an outer skin and powder, wherein the powder filling rate is 20±5%, the outer skin is a multi-layer alloy steel strip, and the powder is filled therein, wherein the powder comprises the following components in percentage by mass: 1.9-2.8% of Mn, 1.1-1.6% of Si, 0.1-0.8% of Cr, 2.3-3.6% of Ni, 0.2-0.7% of Mo, 0.008-0.02% of V, 0.003-0.005% of B, 0.001-0.55% of S, 0.41-0.96% of ReOx, 0.22-0.34% of Al, 0.31-0.72% of MgAl2O4, 0.32-0.51% of MgO-TiO2, 3.5-5.4% of slag-forming agent, and the rest of Fe.

2. The flux-cored welding wire for extra-thick marine steel with high heat input EGW according to claim 1, characterized in that: The medicine powder filling rate is the ratio of the medicine powder mass to the sum of the medicine powder and the outer skin mass.

3. The flux-cored welding wire for extra-thick marine steel with high heat input EGW according to claim 1, characterized in that: The ReOx is a rare earth nanoparticle, which is a cheap (Ce, La)Ox nanoparticle, and the atomic ratio of Ce to La is 2:

1.

4. The flux-cored welding wire for extra-thick marine steel with high heat input EGW according to claim 1, characterized in that: The outer skin is a double-layer structure, the outer layer is a H08Si alloy steel strip, the inner layer is a H10MnCr alloy steel strip, and the single-layer width and thickness of the outer skin steel strip are 0.2-0.4 mm.

5. The flux-cored welding wire for extra-thick marine steel with high heat input EGW and the preparation method thereof according to claim 1, characterized in that: The preparation method comprises the following steps: Step S1: weighing Mn, V, B, Cr, Ni, Mo, Fe, MgAl2O4 and MgO-TiO2 metal powders according to a preset ratio, dispersing them in a mixed solution of deionized water and n-propanol in equal proportions, then adding 3-5wt% dodecyltrimethylammonium bromide to make the surface of the metal particles positively charged, and stirring with ultrasound for 30mins; Step S2: ReOx is weighed according to a preset ratio and dispersed in a mixed solution of deionized water and anhydrous ethanol in equal proportions, and then 1-3 wt% of anionic surfactant is added to make the surface of the rare earth particles negatively charged, and ultrasonic stirring is performed for 30 minutes; Step S3: mixing the solutions of step S1 and step S2, stirring, filtering, washing and freeze-drying to obtain a metal powder having a rare earth nanoparticle reinforcement phase on the surface; Step S4: putting the composite metal powder obtained in step S3 and the slag-forming agent into a Y-type powder mixer in proportion and mixing them for 40 to 50 minutes to obtain a core powder; Step S5: Process different alloy steel strips into the same size and stack them, press them into a U-shape using a roller, and then use a powder feeding device to fill the flux core made in step S4 into the U-shaped steel strip. After rolling and sealing, it is drawn into a welding wire with a diameter of 1.7 mm through 5 to 7 passes.

6. The flux-cored welding wire for extra-thick marine steel with high heat input EGW and the preparation method thereof according to claim 5, characterized in that: The ultrasonic frequency used in steps S1 and S2 is 30 kHz.

7. The flux-cored welding wire for extra-thick marine steel with high heat input EGW and the preparation method thereof according to claim 5, characterized in that: The anionic surfactant in step S2 is sodium hexametaphosphate.

8. The flux-cored welding wire for extra-thick marine steel with high heat input EGW and the preparation method thereof according to claim 5, characterized in that: The ultra-large heat input welding is double-sided double-wire gas-electric vertical welding. The base material is EH40 or EH47 grade ship plate steel with a thickness of 80 to 100 mm. The base material groove is designed as an asymmetric double-sided V-shaped groove. The front groove depth is 3 / 5 of the plate thickness and the groove angle is 8 to 12°; the back groove depth is 2 / 5 of the plate thickness and the groove angle is 5 to 10°.

9. The flux-cored welding wire for extra-thick marine steel with high heat input EGW and the preparation method thereof according to claim 8, characterized in that: The welding process parameters are as follows: the welding voltage of the front welding wire is 36-48V, the welding current is 213-341A, and the welding speed is 44.7-65.6mm / min; the welding voltage of the back welding wire is 33-45V, the welding current is 192-266A, and the welding speed is 44.7-65.6mm / min. The heat input of the double-wire gas-electric vertical welding is 524-814kJ / cm, and the whole process is carried out in a mixed protective gas of 80% CO2 and 20% Ar.

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