Gas shielded welding metal powder type flux-cored wire for 1500MPa-grade hot-formed steel and manufacturing method of gas shielded welding metal powder type flux-cored wire

Abstract

The invention discloses a metal powder type flux-cored wire suitable for 1500MPa-grade hot-formed steel, which is characterized by comprising a carbon steel sheath and a welding wire flux core wrapped in the carbon steel sheath, and the welding wire flux core comprises the following components in percentage by weight: 6-12% of electrolytic manganese, 6-12% of silicon carbide, 6-12% of silicon carbide, 6-12% of silicon carbide, 5-10% of silicon carbide and the balance of iron. 6%-10% of high-carbon ferromanganese; 3%-6% of chromium carbide; 18%-28% of nickel powder; 0.5%-1.5% of silicon carbide; 0.4% to 0.8% of high-purity ferrotitanium; 0.5%-1.5% of rare earth ferrosilicon; 2%-5% of ferrosilicon powder; 6%-10% of molybdenum powder; 0.2% to 0.5% of lithium fluoride; 0.1%-0.3% of titanium-boron alloy and the balance of gas atomization iron powder. The welding wire has the advantages of being good in weldability, high in tensile strength, good in crack resistance and the like. According to the mechanical properties of deposited metal, the tensile strength is larger than or equal to 1040 MPa, the yield strength is larger than or equal to 960 MPa, AKV2 at-40 DEG C is larger than or equal to 27 J, and the ductility is larger than or equal to 13%. The tensile strength of a welded joint obtained by welding 1500MPa hot-formed steel through a lap joint test is greater than or equal to 950MPa, and a fracture position is a heat affected zone of a base metal part.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel welding, in particular to a metal powder type flux-cored wire suitable for 1500MPa grade hot forming steel and a manufacturing method thereof. BACKGROUND

[0002] The 1500MPa grade hot forming steel becomes the core material of key load-bearing components of high-end equipment due to the characteristics of high strength and light weight, and the welding thereof needs to meet the technical requirements of high tensile strength of the welded joint, good low-temperature toughness and low cold crack rate. The existing welding wire and matching welding process have the following problems: 1. Unstable joint quality and serious softening of heat affected zone: the gas shielded welding using the existing welding wire generally has the problems of difficult heat input control and serious softening of heat affected zone, and the strength of the welded joint is unstable; 2. Insufficient process compatibility: some high-strength welding wires need to be preheated to a high temperature to avoid cracks, which conflicts with the demand of high-efficiency assembly line production of automobile manufacturing.

[0003] 3. The traditional metal powder type flux-cored wire is prone to spatter during welding, which affects the surface quality of the hot forming steel, and the weld surface is prone to silicon island, which needs to be polished after welding, affecting the production efficiency. SUMMARY

[0004] The present application relates to the technical field of steel welding, in particular to a metal powder type flux-cored wire suitable for 1500MPa grade hot forming steel and a manufacturing method thereof.

[0005] The welding wire of the present application uses 75%-85% Ar+CO2 protective gas, and the specification is 0.8mm, which is suitable for efficient welding of 1500MPa grade hot forming steel such as automobile body bumper beam and engineering machinery load-bearing component, and the welded joint is reliable and has low crack sensitivity.

[0006] In order to achieve the purpose of the present application, the technical scheme adopted is: A metal powder type flux-cored wire suitable for 1500MPa grade hot forming steel, comprising a carbon steel outer skin and a welding wire core wrapped inside the carbon steel outer skin, wherein, The welding wire core comprises the following components in terms of weight percentage: Electrolytic manganese: 6%-12%; High-carbon manganese iron: 6%-10%; Chromium carbide: 3%-6%; Nickel powder: 18%-28%; Silicon carbide: 0.5%-1.5%; High-purity titanium iron: 0.4%-0.8%; Rare earth silicon iron: 0.5%-1.5%; Silicon iron powder: 2%~5%; Molybdenum powder: 6%~10%; Lithium fluoride: 0.2%~0.5%; Titanium boron alloy: 0.1%~0.3%, The rest is gas atomized iron powder.

[0007] In a preferred embodiment of the present application, the carbon steel strip has the following chemical parameters: C: 0.025%~0.035%, Mn: 0.2%~0.3%, Si: ≤0.03%, P: ≤0.004%, S: ≤0.004%, Al: ≤0.02%, N: ≤0.002%.

[0008] In a preferred embodiment of the present application, the carbon steel strip has the following chemical parameters: C: 0.025%~0.035%, Mn: 0.2%~0.3%, Si: ≤0.03%, P: ≤0.004%, S: ≤0.004%, Al: ≤0.02%, N: ≤0.002%.

[0009] In a preferred embodiment of the present application, the gas atomized iron powder has the following parameters: oxygen content ≤0.1%, bulk density 2.9g / cm 3 , flowability ≤30s / 50g.

[0010] The weld surface obtained by using a certain proportion of the gas atomized iron powder of the present application is clean, and the amount of silicon islands is extremely small, without the need for polishing.

[0011] In a preferred embodiment of the present application, the high-purity titanium iron is titanium iron with a titanium content of 70% or more.

[0012] In a preferred embodiment of the present application, the silicon iron powder is 52# silicon iron powder.

[0013] In a preferred embodiment of the present application, the metal powder type flux-cored wire has a diameter specification of 0.8mm.

[0014] The metal powder type flux-cored wire with a diameter specification of 0.8mm can be better applied to the gas shielded welding of 1500MPa hot forming steel sheet in the automobile industry. The welding with small heat input can be realized by using the wire with this specification.

[0015] In a preferred embodiment of the present application, the particles of each component in the flux core of the wire are 120mesh to 220mesh.

[0016] Because the inventors have found through a large number of experiments that the uniformity and stability of the filling process can be ensured under this particle size, the spatter is small during welding, and the arc stability is good.

[0017] In a preferred embodiment of the present application, the metal powder type flux-cored wire is welded by using 75%~85% Ar+CO2.

[0018] In a preferred embodiment of the present application, the mechanical properties of the deposited metal of the metal powder type flux-cored wire are: tensile strength ≥ 1040 MPa, yield strength ≥ 960 MPa, -40℃ AKV2 ≥ 27 J, elongation ≥ 13%, and the tensile strength of the welded joint of the 1500 MPa hot-formed steel after welding is not less than 950 MPa, and the fracture position is the heat-affected zone of the base material part.

[0019] In a preferred embodiment of the present application, the flux-cored wire accounts for 12% to 13% of the total mass of the metal powder type flux-cored wire, because the inventors have found through a large number of tests that the wire is smoothly drawn without wire breaking phenomenon at this filling ratio.

[0020] The inventors have found through a large number of tests that after the elements of electrolytic manganese (6% to 12%), high-carbon manganese iron (6% to 10%), molybdenum powder (6% to 10%), and chromium carbide (3% to 6%) are proportioned according to the present application, the strength of the weld metal is improved through the synergistic effect of "manganese solid solution strengthening + molybdenum carbide dispersion strengthening + chromium alloying strengthening", and meanwhile, the addition of 18% to 28% nickel powder can reduce the martensite transformation temperature, promote the formation of fine and uniform martensite / bainite mixed structure, and avoid the brittleness caused by coarse martensite.

[0021] A manufacturing method of a metal powder type flux-cored wire suitable for 1500 MPa grade hot-formed steel, comprising the following steps: After the prepared flux-cored wire powder components are baked at 180℃ to 220℃ and kept for 2 to 3 hours, and the flux-cored wire powder components are cooled to not higher than 50℃, the flux-cored wire powder components are mixed and stirred until uniform, with a stirring time of 30 to 60 minutes; The outer skin of the wire steel strip is a carbon steel strip with a specification of 0.8x14mm (chemical composition as shown in Table 2, mechanical properties as shown in Table 3), and the powder is loaded into the carbon steel strip through a forming process at a filling rate of 12% to 13%; The wire is formed by roll die forming, and after the ovality is controlled at the forming offline, the wire is drawn to the metal powder type flux-cored wire through multiple drawing passes.

[0022] The beneficial effects of the present application are as follows: The present application has good welding process by reasonably designing the proportion of various powder in the formula, and the welded joint has high strength and good toughness. The mechanical properties of the deposited metal are: tensile strength ≥ 1040 MPa, yield strength ≥ 960 MPa, -40℃ AKV2 ≥ 27 J, elongation ≥ 13%, and the tensile strength of the welded joint of the 1500 MPa hot-formed steel after welding is greater than or equal to 950 MPa, and the fracture position is the heat-affected zone of the base material part.

[0023] The present application adopts small-diameter welding wire, can realize one gas shielded welding of 1500MPa hot forming steel with small heat input, the softening influence of heat affected zone is small, and the heat affected zone can form martensite and bainite strong and tough structure through accurate control of heat input, so as to ensure that the tensile strength of the welded joint is stable and greater than or equal to 950MPa, the fracture position is located in the heat affected zone (non-welding zone), and the joint is reliable. When welding, 75%-85% Ar+CO2 gas protection is used, the weld forming is beautiful, there is no slag on the weld surface, the silicon island is less, the inclusions in the weld are few, and there is no need to clean the slag, so that continuous automatic and semi-automatic high-efficiency welding can be realized, and the welding efficiency during production is improved.

[0024] The raw materials used in the metal powder type flux-cored wire suitable for 1500MPa grade hot forming steel provided by the present application are all high-grade raw materials, wherein the oxygen content of the gas atomized iron powder is less than or equal to 0.1%, the loose bulk density is 2.9g / cm 3 , the flowability is less than or equal to 30s / 50g, and the S and P impurity contents are extremely low. Under the specification and flux ratio of the present application, a good 1500MPa grade hot forming steel welded joint can be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The present application is illustrated by the schematic diagrams of embodiments 1-3.

[0026] Figure 2 The present application is illustrated by the schematic diagrams of embodiments 1-3. DETAILED DESCRIPTION

[0027] The present application will be further described below in combination with specific embodiments.

[0028] The welding wire is composed of a carbon steel strip and a flux core, the specification of the carbon steel strip is 0.8mm*14mm, and the chemical elements of the carbon steel strip need to meet at least: C: 0.025%-0.035%, Mn: 0.2%-0.3%, Si: ≤0.03%, P: ≤0.004%, S: ≤0.004%, Al: ≤0.02%, N: ≤0.002%, and the filling rate of the flux core is 12%-13%.

[0029] The working principle of the present application is that: The manganese elements in the electrolytic manganese and high-carbon ferromanganese can react with the oxygen in the weld metal during welding, and play a deoxidizing role.

[0030] Manganese elements are provided for the weld metal to realize alloying. The manganese elements can improve the strength and hardness of the steel, refine the grains, and improve the tensile strength and yield strength of the steel. In the present application, the reasonable content of electrolytic manganese (6%-12%) and high-carbon ferromanganese (6%-10%) is beneficial to improve the toughness and crack resistance of the weld metal.

[0031] Chromium carbide: mainly plays a role of infiltration alloy, the reasonable content of chromium carbide (3%~6%) in the application can improve the strength and hardness of the weld, and has red hardness and high temperature oxidation resistance.

[0032] Nickel powder: appropriate nickel powder can improve plastic toughness, but too high Ni content will increase the hot cracking sensitivity. In the application, the reasonable content of nickel powder (18%~28%) can improve the toughness by improving the microstructure of the weld metal: under the high temperature environment of welding, the nickel powder is uniformly melted into the weld metal, on the one hand, it can reduce the "martensite transformation temperature" of the weld, promote the formation of fine and uniform martensite / bainite mixed structure (instead of coarse martensite), and reduce the brittleness of grain boundary; on the other hand, nickel element can inhibit the segregation of harmful inclusions (such as FeS, P compound) in the grain boundary of the weld, avoiding the risk of "intergranular fracture" caused by inclusions.

[0033] Silicon carbide: through the dual role of auxiliary deoxidization and process stability optimization, it becomes a key auxiliary component to ensure the performance of the weld and the weldability, and the reasonable content of silicon carbide (0.5%~1.5%) in the application meets the functional requirements and avoids excessive addition leading to high carbon content (causing cold cracking) or excessive silicon content (reducing toughness).

[0034] High-purity ferrotitanium: the high-purity ferrotitanium (0.4%~0.8%) in the application contains 70% titanium, and the binding force between Ti and oxygen is very large. The reasonable content of high-purity ferrotitanium in the application has stronger deoxidizing ability than ordinary ferrosilicon alone, 2FeO+Ti→TiO2+2Fe. On the other hand, Ti can combine with N to reduce the gas in the weld metal.

[0035] Rare earth ferrosilicon: in the metal powder type flux-cored wire of the application, the rare earth ferrosilicon mainly plays a synergistic role of "rare earth elements" and "silicon elements", and the reasonable content of rare earth ferrosilicon (0.5%~1.5%) in the application mainly plays a role of refining grains, auxiliary deoxidization and improving the toughness of the weld.

[0036] 52# ferrosilicon: high-efficiency deoxidization, reducing the impurity content of the weld, and ensuring the basis of high-strength steel welding strength.

[0037] Deoxidization is realized through the strong chemical activity of silicon (Si): under the high temperature environment of welding, the silicon in 52# ferrosilicon will react with the free oxygen in the weld metal, and the generated SiO2 can be discharged from the weld with the slag, thereby significantly reducing the oxygen content of the weld metal and reducing the damage of oxidized inclusions to the strength of the weld.

[0038] Meanwhile, the deoxidizing effect of the reasonable content of 52# ferrosilicon (0.5%~1.5%) in the application and other deoxidizing components (such as high-purity ferrotitanium and silicon carbide) in the flux core form a synergistic complementation.

[0039] The silicon element can also reduce the surface tension of the molten pool metal, making the molten pool more easily spread, avoiding defects such as "unfused" and "poor weld formation" caused by poor flowability of the molten pool, especially when the inventors of the present application found through a large number of experiments that when a 0.8mm small-diameter welding wire of the present application is used for small heat input welding, it can ensure that the molten pool uniformly covers the area to be welded, and improves the weld formation quality.

[0040] Molybdenum powder: mainly plays the role of alloying and strengthening the weld, the reasonable content of molybdenum powder (6%-10%) is mainly added as an alloying agent to improve the strength of the weld zone, and through the regulation of the microstructure of the weld and the heat-affected zone by molybdenum element, the grain coarsening and softening area of the heat-affected zone under the action of high temperature welding is reduced, and the uniformity of the overall strength of the welded joint is ensured. The stable carbide formed by molybdenum can reduce the existence of free carbon in the weld, reduce the risk of forming low-melting-point eutectic by carbon and S / P elements, thereby reducing the generation of hot cracks; at the same time, the effect of molybdenum element on refining the grain size of the weld can reduce the probability of grain boundary segregation and reduce the cold crack sensitivity.

[0041] Lithium fluoride: during the welding process, a reasonable amount of lithium can promote the stable combustion of the arc, and the addition of fluoride is beneficial to reducing the diffusible hydrogen content in the weld and improving the weld fluidity.

[0042] Titanium boron alloy: the boron element brought by a reasonable amount of titanium boron alloy (0.1%-0.3%) can adjust the alloy composition of the weld, avoid insufficient strengthening due to too low boron content, or cause brittleness due to too high boron content. Titanium boron alloy "can increase the hardenability and form a strong and stable compound with carbon". During the cooling process of welding, boron element can reduce the pearlite transformation temperature of steel, promote the formation of martensite / bainite and other strong and tough microstructures in the weld and heat-affected zone, and reduce the softening range of the heat-affected zone.

[0043] Gas-atomized iron powder: the gas-atomized iron powder has an extremely low oxygen content of ≤0.1%, a loose bulk density of 2.9g / cm 3 , and a fluidity of ≤30s / 50g, which can increase the melting speed of the welding wire and improve the deposition efficiency. The particle shape of the gas-atomized iron powder is uniform, the surface is smooth, and the fluidity is good. It helps to ensure that the arc is stable during the welding process, the spatter is small, and the weld formation is beautiful. It can also be used as a carrier of alloying elements, such as nickel, chromium, molybdenum, etc., to adjust the chemical composition of the weld metal, thereby meeting the requirements of 1500MPa hot forming steel welding on the mechanical properties of the weld, such as improving the strength, toughness, and fatigue resistance of the weld. Embodiment 1-3: A gas shielded welding metal powder type flux-cored wire for 1500MPa grade hot forming steel and a manufacturing method thereof.

[0044] The method in Embodiment 1-3 is: The raw materials in the application are screened in advance for particle size, and the added electrolytic manganese, high-carbon manganese iron, chromium carbide, nickel powder, silicon carbide, high-purity ferrotitanium (containing 70% titanium), rare earth ferrosilicon, 52# ferrosilicon powder, molybdenum powder, lithium fluoride, titanium boride alloy are all controlled to be 120-220 mesh powder particles, and the balance is gas-atomized iron powder (same particle size requirement of 120-220 mesh), and the proportions in Table 1 are configured.

[0045] Table 1: Proportions of flux cored wires in Examples 1-3 The prepared flux powder components of the above examples are baked at 180-220°C and kept for 2-3h, and after the flux powder components of the flux cored wire are cooled to not higher than 50°C, the flux powder components of the flux cored wire are mixed and stirred for 30-60min until uniform.

[0046] The outer sheath of the welding wire steel strip is a carbon steel strip with a specification of 0.8x14mm (chemical composition as shown in Table 2, mechanical properties as shown in Table 3), and the powder is filled into the carbon steel strip at a filling rate of 12%-13% through a forming process, and five 20-30cm welding wires are cut at the end of the forming process for filling rate detection (three repeated tests).

[0047] The mixed and uniform powder is filled into the carbon steel strip through a forming process, and is formed by roller die rolling, and the ovality is controlled to be 0.2mm at the end of the forming process, and the powder cored wire with a specification of 0.8mm suitable for 1500MPa hot formed steel is obtained by fine drawing multiple passes.

[0048] Table 2: Content of chemical components of low-sulfur and low-phosphorus carbon steel strip

[0049] Table 3: Main mechanical properties of low-sulfur and low-phosphorus carbon steel strip

[0050] 2. The 1500MPa hot formed steel gas shielded welding metal powder cored wire obtained in the above Examples 1-3 is subjected to deposition test, and 75%-85% Ar+CO2 gas shielded welding is adopted, the welding current is 180-200A, the welding voltage is 21-23V, the welding speed is 200-280mm / min, the gas flow is 15-20L / min, and the dry extension length is 15-20mm. The test results of the chemical composition (mass fraction %) of the deposited metal are shown in Table 4, and the mechanical properties of the weld metal are shown in Table 5. The detection standards of each mechanical property in Table 5 are from GB / T2652 Welding seam and deposited metal tensile test method.

[0051] Table 4: Component content table of chemical composition of deposited metal in Examples 1-3

[0052] Table 5 Mechanical properties of deposited metal in Examples 1-3

[0053] The 1500MPa hot forming steel gas shielded welding metal powder type flux-cored wire prepared by the Examples 1-3 of the present application was used to carry out welding test on 2mm thick 1500MPa hot forming steel by welding robot: the protective gas was selected to be 75%-85% Ar+CO2, the welding current was controlled to be 100-140A, the welding voltage was adjusted to be 20-24V, and the wire feeding speed was set to be 4-5m / min; after welding, lap joints were prepared and tensile test was carried out, and the fracture of the welding joints is shown in Table 6.

[0054] The 1500MPa hot forming steel welding wire ER110S-G of the prior art was used as a comparative example (wire diameter specification 1.2mm), the same welding base material (2mm thick 1500MPa hot forming steel) and protective gas (75%-85% Ar+CO2) were used, and the welding process parameters were set as follows: welding current 190-210A, welding voltage 20-24V, and wire feeding speed 5-6m / min; lap joints were also prepared and tensile test was carried out, and the test results are shown in Table 6.

[0055] Table 6 Fracture of lap joints of Examples 1-3 and the prior art

[0056] 3. As can be seen from Table 5 (mechanical properties of deposited metal) and Table 6 (fracture of lap joints), the 1500MPa hot forming steel gas shielded welding metal powder type flux-cored wire prepared by the Examples 1-3 of the present application has outstanding weld tensile strength - the tensile strength of the deposited metal is 1066-1092MPa, and the tensile strength of the lap joint is 959-1002MPa, and the data of the three groups of examples has small fluctuation, and the performance stability is excellent.

[0057] At the same time, the lap joint formed by the wire has good forming effect, the weld surface is clean, the silicon island content is small and there is no crack, and the fracture position after tensile test is in the heat affected zone (see Figure 1 ); compared with the fracture position of the comparative example ER110S-G wire after tensile test (see Figure 2 ), the tensile strength of the joint of the wire of the present application is significantly higher, which fully proves that the welding joint quality is stable and reliable, and can meet the welding performance requirements of 1500MPa hot forming steel.

[0058] In addition, the radiographic test was performed on the fusion test plates of the above-mentioned Examples 1 to 3, and the result was Grade I, without the generation of defects such as pores and cracks, and the reference standard was GB / T 3323 Radiographic Examination of Welded Joints of Metal Fusion Welding.

Claims

1. A metal powder-cored welding wire suitable for 1500MPa grade hot-formed steel, characterized in that, It consists of two parts: a carbon steel outer sheath and a welding wire core wrapped inside the carbon steel outer sheath. The flux core of the welding wire comprises the following components, calculated by weight percentage: Electrolytic manganese: 6%–12%; High-carbon ferromanganese: 6%–10%; Chromium carbide: 3%–6%; Nickel powder: 18%–28%; Silicon carbide: 0.5%–1.5%; High-purity ferrotitanium: 0.4%–0.8%; Rare earth ferrosilicon: 0.5%–1.5%; Ferrosilicon powder: 2%–5%; Molybdenum powder: 6%–10%; Lithium fluoride: 0.2%–0.5%; Titanium-boron alloy: 0.1%~0.3%, The remainder is gas-atomized iron powder.

2. The metal powder-cored welding wire suitable for 1500MPa grade hot-formed steel as described in claim 1, characterized in that, The chemical parameters of the carbon steel strip are: C: 0.025%~0.035%, Mn: 0.2%~0.3%, Si: ≤0.03%, P: ≤0.004%, S: ≤0.004%, Al: ≤0.02%, N: ≤0.002%.

3. The metal powder-cored welding wire suitable for 1500MPa grade hot-formed steel as described in claim 1, characterized in that, The carbon steel strip has a specification of 0.8mm × 14mm.

4. The metal powder-cored welding wire suitable for 1500MPa grade hot-formed steel as described in claim 1, characterized in that, The oxygen content of the atomized iron powder is ≤0.1%, and the loose packing density is 2.9 g / cm³. 3 Flowability ≤30s / 50g.

5. The metal powder-cored welding wire suitable for 1500MPa grade hot-formed steel as described in claim 1, characterized in that, The high-purity ferrotitanium is ferrotitanium with a titanium content of 70% or more.

6. The metal powder-cored welding wire suitable for 1500MPa grade hot-formed steel as described in claim 1, characterized in that, The ferrosilicon powder is 52# ferrosilicon powder.

7. The metal powder-cored welding wire suitable for 1500MPa grade hot-formed steel as described in claim 1, characterized in that, The diameter of the metal powder-cored welding wire is 0.8 mm.

8. The metal powder-cored welding wire suitable for 1500MPa grade hot-formed steel as described in claim 1, characterized in that, Each component in the welding wire core is made of 120-220 mesh powder particles.

9. A metal powder-cored welding wire suitable for 1500MPa grade hot-formed steel as described in claim 1, characterized in that, The metal powder-cored welding wire is used for welding with 75%–85% Ar + CO2. The mechanical properties of the deposited metal of the metal powder-cored welding wire are: tensile strength ≥1040MPa, yield strength ≥960MPa, AKV2 ≥27J at -40℃, elongation ≥13%, and the tensile strength of the welded joint of 1500MPa hot-formed steel is not less than 950MPa, with the fracture location being the heat-affected zone of the base metal. The flux core of the welding wire accounts for 12% to 13% of the total mass of the metal powder flux core welding wire.

10. A method for manufacturing a metal powder-cored welding wire suitable for 1500MPa grade hot-formed steel according to any one of claims 1-9, characterized in that, Includes the following steps: Baking the prepared flux core components at 180℃~220℃ and holding for 2~3 hours; after the flux core components have cooled to no higher than 50℃, mixing and stirring them for 30~60 minutes until homogeneous. The outer sheath of the welding wire steel strip is made of carbon steel strip with a specification of 0.8×14mm (chemical composition as shown in Table 2, mechanical properties as shown in Table 3). The powder is loaded into the carbon steel strip at a filling rate of 12% to 13% through the forming process. The metal powder-cored welding wire is formed by rolling with a roller die, and after the ellipticity is controlled during the forming process, it is drawn through multiple fine drawing passes to obtain the metal powder-cored welding wire.

Images