800 MPa-grade high-strength steel large heat input welding flux-cored wire and preparation method and application thereof

Abstract

The invention belongs to the technical field of welding, and relates to an 800 MPa-grade high-strength steel large heat input welding flux-cored wire and a preparation method and application thereof.The flux-cored wire comprises a coating layer and a core material, and the core material comprises, by weight, 15%-23% of low-carbon ferromanganese powder, 7%-8% of aluminum powder, 12%-18% of nickel powder, 6%-8% of calcium fluoride, 4%-6% of quartz, 5%-6% of rutile and the balance iron powder. 7-10% of ferromolybdenum, less than or equal to 3% of ferroboron, less than or equal to 2% of ferrotitanium, 0.5-1% of ferrochromium and the balance of reduced iron powder; and the coating layer is made of low-carbon steel. Under the high heat input welding condition of 200-400 kJ / cm electro-gas welding, the tensile strength of weld metal is larger than or equal to 800 MPa, and the impact energy at the temperature of 20 DEG C below zero is larger than 70 J.

Description

Technical Field

[0001] The present invention relates to the technical field of welding, and specifically provides an 800 MPa grade high-strength steel submerged arc welding flux-cored wire for high heat input, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, in the field of manufacturing large-scale equipment such as shipbuilding, offshore platforms, and oil pipelines, with the enlargement of engineering components, in order to reduce the consumption of steel, 800 MPa grade high-strength steel is often used as the processing material, and high strength has become the development trend in this field. Welding is usually used as the connection method in these manufacturing fields. In order to improve the welding efficiency of high-strength steel, high heat input welding methods such as electro-gas welding, submerged arc welding, and electroslag welding have gradually been applied in the welding of medium and thick plates. However, when ordinary high-strength steel is welded with high heat input, the peak temperature of the welding HAZ increases and the cooling rate slows down, resulting in serious coarsening of austenite grains, further coarsening of intra-austenite lath bainite structure, and an increase in the distribution of MA components, leading to an increase in stress concentration points and ultimately seriously deteriorating the toughness of the welding HAZ.

[0003] To solve this problem, domestic and foreign research institutions have successively carried out research and development work on 800 MPa grade high heat input welding steel, and proposed an upgraded version of the "oxide metallurgy" technology. By adding a large amount of non-metallic inclusions to 800 MPa grade high-strength steel, the nucleation and growth of lath bainite structure are promoted and cross-arranged, restricting the growth of each other's laths, thereby refining the grain structure of the welding HAZ, and defining such a structure as a multi-orientation bainite structure. This type of structure can extend the crack propagation path, thereby greatly improving the impact toughness of the welding HAZ. However, at present, the weld metal microstructure formed by domestic high-strength steel welding materials under high heat input welding conditions is coarse and the impact toughness is low, which cannot meet the requirements of high heat input welding of high-strength steel. Summary of the Invention

[0004] To solve the problems existing in the prior art, the main object of the present invention is to provide an 800 MPa grade high-strength steel submerged arc welding flux-cored wire for high heat input, a preparation method thereof, and an application thereof. The flux-cored wire of the present invention can have a weld metal with a high strength of 800 MPa grade and good low-temperature impact toughness under the high heat input and high-efficiency welding conditions of 200 - 400 kJ / cm.

[0005] According to one aspect of the present invention, the present invention provides the following technical solutions:

[0006] An 800MPa grade high-strength steel submerged arc welding flux-cored wire for high heat input welding, comprising a coating layer and a core material. The core material, by weight percentage, consists of: 15-23% of low-carbon ferromanganese powder, 7-8% of aluminum powder, 12-18% of nickel powder, 6-8% of calcium fluoride, 4-6% of quartz, 5-6% of rutile, 7-10% of ferromolybdenum, ≤3% of ferroboron, ≤2% of ferrotitanium, 0.5-1% of ferrochrome, and the balance being reduced iron powder; the material of the coating layer is low-carbon steel.

[0007] According to another aspect of the present invention, the present invention provides the following technical solution:

[0008] A preparation method of an 800MPa grade high-strength steel submerged arc welding flux-cored wire for high heat input welding, comprising the following steps:

[0009] S1. Weigh various dried powder raw materials according to the composition of the core material, and fully stir and mix them evenly to obtain the core material powder of the required submerged arc welding flux-cored wire.

[0010] S2. Roll the low-carbon steel strip into a U-shaped groove, pour the core material powder obtained in step S1 into the U-shaped groove, and use a submerged arc welding flux-cored wire forming unit to prepare an 800MPa grade high-strength steel submerged arc welding flux-cored wire for high heat input welding.

[0011] According to another aspect of the present invention, the present invention provides the following technical solution:

[0012] An application of an 800MPa grade high-strength steel submerged arc welding flux-cored wire for high heat input welding in the welding of 800MPa grade high-strength steel.

[0013] The beneficial effects of the present invention are as follows:

[0014] The present invention provides an 800MPa grade high-strength steel submerged arc welding flux-cored wire for high heat input welding, its preparation method and application. The submerged arc welding flux-cored wire comprises a coating layer and a core material. The core material, by weight percentage, consists of: 15-23% of low-carbon ferromanganese powder, 7-8% of aluminum powder, 12-18% of nickel powder, 6-8% of calcium fluoride, 4-6% of quartz, 5-6% of rutile, 7-10% of ferromolybdenum, ≤3% of ferroboron, ≤2% of ferrotitanium, 0.5-1% of ferrochrome, and the balance being reduced iron powder; the material of the coating layer is low-carbon steel. Under the condition of high heat input welding of gas-electric vertical welding with 200-400 kJ / cm, the tensile strength of the weld metal is ≥800 MPa, and the impact energy at -20°C is greater than 70 J. Description of the Drawings

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or in the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0016] Figure 1 It is the microstructure diagram of the weld metal in Embodiment 1 of the present invention.

[0017] The realization of the object of the present invention, its functional characteristics and advantages will be further described in conjunction with the embodiments with reference to the accompanying drawings. Specific embodiments

[0018] The following will clearly and completely describe the technical solutions in the embodiments. Obviously, the described embodiments are only some of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0019] The present invention draws on the preparation principle of high heat input high-strength steel and develops a flux-cored wire that can be matched with 800 MPa grade high-strength steel by using an upgraded version of the "oxide metallurgy" technology. By reasonably proportioning the components of the flux-cored wire for high heat input of 800 MPa grade high-strength steel, under the condition of high heat input welding, a large number of high melting point (Ti, Si, Ca, Al, Mn)O, MnS non-metallic composite inclusions can be generated in the liquid high-temperature weld above 1700 °C. During the cooling process of the weld metal, some of the inclusions can serve as the nuclei for austenite grain nucleation, increasing the austenite nucleation sites. And the inclusions distributed at the austenite grain boundaries will pin the austenite grain boundaries, preventing the growth of austenite grains and refining the austenite grains. During the austenite phase transformation process, the inclusions in the austenite grains of the traditional 500 MPa grade weld metal can induce the formation of slender intragranular acicular ferrite tissue. However, the flux-cored wire for high heat input of 800 MPa grade high-strength steel of the present invention can provide more alloying elements that can be dissolved in the intragranular acicular ferrite grains, making the original cross-distributed acicular ferrite transform into multi-orientation bainite tissue. The inclusions in the austenite grains can serve as nuclei to promote the nucleation and growth of lath bainite tissue in different directions, forming an organization of cross arrangement with each other and restricting the growth between each lath, thereby refining the grain structure of the weld metal, extending the path of crack propagation, forming a high-strength and high-toughness multi-orientation bainite tissue, and realizing the high heat input welding of high-strength steel.

[0020] The 800MPa grade high-strength steel hot-wire flux-cored wire of the present invention has a tensile strength of the weld metal ≥ 800MPa and an impact energy at -20°C greater than 70J under the condition of hot-wire gas shielded arc welding with a heat input of 200 - 400kJ / cm.

[0021] The number of inclusions in the weld metal prepared by using the 800MPa grade high-strength steel hot-wire flux-cored wire of the present invention ≥ 8000 pieces / mm 2 , preferably, the number of inclusions can be, for example, 8000 pieces / mm 2 , 8050 pieces / mm 2 , 8100 pieces / mm 2 , 8150 pieces / mm 2 , 8200 pieces / mm 2 , 8250 pieces / mm 2 , 8300 pieces / mm 2 , 8350 pieces / mm 2 , 8400 pieces / mm 2 , 8450 pieces / mm 2 , 8500 pieces / mm 2 or any range between any two of them; there is no massive proeutectoid ferrite at the austenite grain boundaries of the weld metal, and the interior of the austenite grains is a multi-orientation bainite structure with lath intersections, the average grain size is 8 - 12μm, and the proportion of the fine multi-orientation bainite structure is greater than 95%.

[0022] The present invention is applicable to large equipment manufacturing industries such as shipbuilding, offshore platforms, pressure vessels, and bridges. Through high strengthening, the usage amount of the original materials can be reduced, the lightweight of large equipment can be achieved, and the welding manufacturing efficiency can be greatly improved, and the mechanical properties of the weld metal can be effectively guaranteed.

[0023] According to one aspect of the present invention, the present invention provides the following technical solution:

[0024] An 800MPa grade high-strength steel hot-wire welding flux-cored wire, comprising a coating layer and a core material. The core material, by weight percentage, consists of: 15 - 23% of low-carbon ferromanganese powder, 7 - 8% of aluminum powder, 12 - 18% of nickel powder, 6 - 8% of calcium fluoride, 4 - 6% of quartz, 5 - 6% of rutile, 7 - 10% of ferromolybdenum, ≤ 3% of ferroboron, ≤ 2% of ferrotitanium, 0.5 - 1% of ferrochrome, and the balance is reduced iron powder; the material of the coating layer is low-carbon steel.

[0025] Preferably, the content of ferroboron is not 0, and the content of ferrotitanium is not 0.

[0026] Preferably, the low-carbon ferromanganese is FeMn88C0.2, FeMn84C0.4 or FeMn84C0.7; the purity of the aluminum powder, nickel powder, and reduced iron powder is ≥98%; the molybdenum content in the ferromolybdenum is 55-75 wt%; the boron content in the ferroboron is 5-25 wt%; the titanium content in the ferrotitanium is 25-45 wt%; the chromium content in the ferrochrome is 40-65 wt%.

[0027] Preferably, the silica content of the quartz is ≥97 wt%, and the titanium dioxide content of the rutile is ≥95 wt%.

[0028] According to another aspect of the present invention, the present invention provides the following technical solutions:

[0029] A method for preparing a flux-cored wire for welding high-strength steel with a heat input of 800 MPa, comprising the following steps:

[0030] S1. Weigh various dried powder raw materials according to the core material composition, and stir them evenly to obtain the core powder of the required flux-cored wire;

[0031] S2. Roll the low-carbon steel strip into a U-shaped groove, pour the core powder obtained in step S1 into the U-shaped groove, and use a flux-cored wire forming machine set to prepare a flux-cored wire for welding high-strength steel with a heat input of 800 MPa.

[0032] Preferably, degreasing, rust removal, and drying are also carried out before rolling the low-carbon steel strip into a U-shaped groove.

[0033] Preferably, the thickness of the low-carbon steel strip is 0.8 mm and the width is 12 mm.

[0034] Preferably, the particle size range of the core powder is 60-80 mesh.

[0035] Preferably, a wire blank tube with a diameter of 4.3 mm filled with core powder is obtained after forming, and after 13 passes of wire drawing forming, a finished wire with a diameter of 1.2 mm is finally obtained.

[0036] Preferably, the filling rate of the core powder is 14.8-15.2%.

[0037] According to another aspect of the present invention, the present invention provides the following technical solutions:

[0038] An application of a flux-cored wire for welding high-strength steel with a heat input of 800 MPa in the welding of 800 MPa high-strength steel.

[0039] Preferably, single-pass vertical electro-gas welding is used.

[0040] Preferably, the welded base material is 800 MPa high-strength steel with a thickness of 20-40 mm, and 20 vol% CO is used during the welding process 2+80 vol% Ar mixed gas is used as the shielding gas.

[0041] The technical solution of the present invention will be further described below in conjunction with specific embodiments.

[0042] The components of the core materials used in the following examples and comparative examples are as follows: low-carbon ferromanganese is FeMn88C0.2; the purity of aluminum powder is 99.5%; the purity of nickel powder is 99.5%; the purity of reduced iron powder is 99%; the molybdenum content in ferromolybdenum is 60 wt%; the boron content in ferroboron is 15 wt%; the titanium content in ferrotitanium is 40 wt%; the chromium content in ferrochrome is 50 wt%; the silicon dioxide content of the quartz is 97.3 wt%, and the titanium dioxide content of the rutile is 95.5 wt%.

[0043] Example 1

[0044] A preparation method of an 800 MPa grade high-strength steel hot heat input welding flux-cored wire includes the following steps:

[0045] S1. By weight percentage, the components of the core material are: 17% of low-carbon ferromanganese powder, 7% of aluminum powder, 15% of nickel powder, 6% of calcium fluoride, 4% of quartz, 5% of rutile, 8% of ferromolybdenum, 1.5% of ferroboron, 1% of ferrotitanium, 0.5% of ferrochrome, and the balance is reduced iron powder; weigh and take various dried powder raw materials according to the core material composition, and stir evenly to obtain the required flux-cored wire core material powder;

[0046] S2. Shear a low-carbon steel strip with a thickness of 0.8 mm and a width of 12 mm, remove oil and rust by ultrasonic wave, dry it and roll it into a U-shaped groove, pour the core material powder into the U-shaped groove, with a filling rate of 15%, and use a flux-cored wire forming machine set to prepare an 800 MPa grade high-strength steel hot heat input welding flux-cored wire with a diameter of 1.2 mm.

[0047] Welding is carried out using the above-mentioned 800 MPa grade high-strength steel hot heat input welding flux-cored wire with a diameter of 1.2 mm. The welding method is single-pass vertical electrogas welding. The welding base material is 30 mm of 800 MPa grade high-strength steel. During the welding process, 20 vol% CO 2 +80 vol% Ar mixed gas is used as the shielding gas. The prepared 800 MPa grade high-strength steel hot heat input flux-cored wire is welded under the electrogas welding condition of 305 kJ / cm. The tensile strength of the weld metal is 813 MPa, and the impact energy at -20 °C is 72 J. The microstructure of the weld metal is as Figure 1 shown, and the number of inclusions ≥ 8000 pieces / mm 2 , all of which are multi-orientation bainite structures with lath cross-arrangement.

[0048] Example 2

[0049] A preparation method for a flux-cored wire for welding high-strength steel of 800 MPa grade with high heat input, comprising the following steps:

[0050] S1. By weight percentage, the composition of the core material is: 21% of low-carbon ferromanganese powder, 7.5% of aluminum powder, 12% of nickel powder, 7% of calcium fluoride, 5% of quartz, 5% of rutile, 8% of ferromolybdenum, 1% of ferroboron, 1% of ferrotitanium, 0.8% of ferrochrome, and the balance is reduced iron powder; Weigh various dried powder raw materials according to the composition of the core material, and stir evenly to obtain the core material powder of the required flux-cored wire.

[0051] S2. Cut a low-carbon steel strip with a thickness of 0.8 mm and a width of 12 mm, remove oil and rust by ultrasonic wave, dry it and roll it into a U-shaped groove, pour the core material powder into the U-shaped groove, with a filling rate of 15.1%, and use a flux-cored wire forming machine set to prepare a flux-cored wire for welding high-strength steel of 800 MPa grade with high heat input and a diameter of 1.2 mm.

[0052] Welding is carried out using the above-mentioned flux-cored wire for welding high-strength steel of 800 MPa grade with high heat input and a diameter of 1.2 mm. The welding method is single-pass vertical electrogas welding. The welded base material is high-strength steel of 800 MPa grade with a thickness of 25 mm. During the welding process, a 20 vol% CO 2 +80 vol% Ar mixed gas is used as the shielding gas. The prepared flux-cored wire for welding high-strength steel of 800 MPa grade with high heat input is welded under the electrogas welding conditions of 325 kJ / cm. The tensile strength of the weld metal is 820 MPa, the impact energy at -20 °C is 75 J, and the number of inclusions ≥ 8000 pieces / mm 2 All are multi-orientation bainite structures with lath cross-arrangement.

[0053] Example 3

[0054] A preparation method for a flux-cored wire for welding high-strength steel of 800 MPa grade with high heat input, comprising the following steps:

[0055] S1. By weight percentage, the composition of the core material is: 18% of low-carbon ferromanganese powder, 7.5% of aluminum powder, 14% of nickel powder, 7% of calcium fluoride, 5.5% of quartz, 5% of rutile, 10% of ferromolybdenum, 0.5% of ferroboron, 1% of ferrotitanium, 1% of ferrochrome, and the balance is reduced iron powder; Weigh various dried powder raw materials according to the composition of the core material, and stir evenly to obtain the core material powder of the required flux-cored wire.

[0056] S2. Cut a low-carbon steel strip with a thickness of 0.8 mm and a width of 12 mm, remove oil and rust by ultrasonic wave, dry it and roll it into a U-shaped groove, pour the core material powder into the U-shaped groove, with a filling rate of 14.8%, and use a flux-cored wire forming machine set to prepare a flux-cored wire for welding high-strength steel of 800 MPa grade with high heat input and a diameter of 1.2 mm.

[0057] Welding is carried out using the above-mentioned 800 MPa grade high-strength steel hot-wire welding flux cored wire with a diameter of 1.2 mm. The welding method is single-pass vertical electro-gas welding. The base metal for welding is 800 MPa grade high-strength steel with a thickness of 40 mm. During the welding process, 20 vol% CO 2 + 80 vol% Ar mixed gas is used as the shielding gas. The prepared 800 MPa grade high-strength steel hot-wire welding flux cored wire is welded under the electro-gas welding conditions of 350 kJ / cm. The tensile strength of the weld metal is 815 MPa, the impact energy at -20 °C is 73 J, and the number of inclusions is ≥ 8000 per mm 2 , and all are multi-orientation bainite structures with lath cross-arrangement.

[0058] Comparative Example 1

[0059] The difference from Example 1 is that the core material does not include rutile.

[0060] Welding is carried out using the 800 MPa grade high-strength steel hot-wire welding flux cored wire with a diameter of 1.2 mm prepared in this comparative example. The welding method is single-pass vertical electro-gas welding. The base metal for welding is 800 MPa grade high-strength steel with a thickness of 30 mm. During the welding process, 20 vol% CO 2 + 80 vol% Ar mixed gas is used as the shielding gas. The prepared 800 MPa grade high-strength steel hot-wire welding flux cored wire is welded under the electro-gas welding conditions of 305 kJ / cm. The tensile strength of the weld metal is 810 MPa, but the impact energy at -20 °C is only 33 J, and the number of inclusions is ≥ 8000 per mm 2 , but the inclusions cannot induce the nucleation of lath bainite. Most are lath bainite structures with parallel distribution, which cannot play a role in hindering crack propagation and cannot improve the impact energy of the weld metal.

[0061] Comparative Example 2

[0062] The difference from Example 1 is that the core material does not include ferrochrome.

[0063] Welding is carried out using the 800 MPa grade high-strength steel hot-wire welding flux cored wire with a diameter of 1.2 mm prepared in this comparative example. The welding method is single-pass vertical electro-gas welding. The base metal for welding is 800 MPa grade high-strength steel with a thickness of 30 mm. During the welding process, 20 vol% CO 2 + 80 vol% Ar mixed gas is used as the shielding gas. The prepared 800 MPa grade high-strength steel hot-wire welding flux cored wire is welded under the electro-gas welding conditions of 305 kJ / cm. The tensile strength of the weld metal is 756 MPa, but the impact energy at -20 °C is 43 J, and the number of inclusions is ≥ 8000 per mm 2, in this comparative example, the addition of ferrochrome was not carried out, which reduced the solution strengthening effect of the matrix structure, resulting in insufficient strength of the weld metal and also a lower low-temperature impact energy.

[0064] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structural transformation made using the content of the specification of the present invention under the inventive concept of the present invention, or direct / indirect application in other related technical fields, is included in the patent protection scope of the present invention.

Claims

1. A 800MPa grade high strength steel high heat input welding flux cored wire, characterized in that: It comprises a coating layer and a core material, wherein the core material comprises, by weight percentage, 15-23% low-carbon ferromanganese powder, 7-8% aluminum powder, 12-18% nickel powder, 6-8% calcium fluoride, 4-6% quartz, 5-6% rutile, 7-10% ferromolybdenum, ≤3% ferroboron, ≤2% ferrotitanium, 0.5-1% ferrochrome, and the remainder is reduced iron powder; the coating layer is made of low-carbon steel.

2. A method for preparing the 800MPa grade high strength steel high heat input welding flux cored wire according to claim 1, characterized in that: The steps include: S1. Weigh various powder raw materials after drying according to the core material composition, stir them thoroughly and evenly to obtain the required flux-cored welding wire core material powder; S2, rolling the low carbon steel strip into a U-shaped groove, pouring the core material powder described in step S1 into the U-shaped groove, and using a flux-cored welding wire forming unit to prepare 800MPa grade high-strength steel high heat input welding flux-cored welding wire.

3. The method for preparing the 800MPa grade high strength steel high heat input welding flux cored wire according to claim 2, characterized in that: The thickness of the low carbon steel strip is 0.8 mm and the width is 12 mm.

4. The method for preparing 800MPa grade high strength steel high heat input welding flux cored wire according to claim 2, characterized in that: The particle size of the core powder ranges from 60 to 80 mesh.

5. The method for preparing the 800MPa grade high strength steel high heat input welding flux cored wire according to claim 2, characterized in that: After forming, a welding wire blank tube with a diameter of 4.3 mm and filled with core material powder is obtained. After 13 drawing passes, a finished welding wire with a diameter of 1.2 mm is finally obtained.

6. The method for preparing 800MPa grade high strength steel high heat input welding flux cored wire according to claim 2, characterized in that: The filling rate of the core powder is 14.8-15.2%.

7. Use of the 800MPa grade high strength steel high heat input welding flux-cored welding wire according to claim 1 in welding 800MPa grade high strength steel.

8. The use according to claim 7, characterized in that: Single-pass vertical gas-electric welding is adopted; the welding base material is 800MPa grade high-strength steel with a thickness of 20-40mm, and a 20vol% CO2+80vol% Ar mixed gas is used as the protective gas during the welding process.

9. The use according to claim 7, characterized in that: The tensile strength of the weld metal is ≥800MPa, and the impact energy at -20℃ is greater than 70J.

10. The use according to claim 7, characterized in that: There is no massive proeutectoid ferrite at the austenite grain boundaries of the weld metal. The interior of the austenite grains is a multi-directional bainite structure with cross-distributed laths. The average grain size is 8-12μm, and the proportion of multi-directional bainite structure is greater than 95%.

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