Ultrahigh-strength steel matched 1000MPa-grade Co-containing gas shielded welding wire, ultrahigh-strength steel and welding method

Abstract

The invention provides an ultrahigh-strength steel matched 1000 MPa-grade Co-containing gas shielded welding wire, ultrahigh-strength steel and a welding method. The ultrahigh-strength steel matched 1000 MPa-grade Co-containing gas shielded welding wire comprises the following components in percentage by mass: less than or equal to 0.12% of C, less than or equal to 0.6% of Si, 1.5-3% of Mn, less than or equal to 0.1% of V, less than or equal to 0.08% of Ti, 0.5-1.2% of Mo, 1.5-2.7% of Ni, 1.0-4.0% of Co and less than or equal to 1.1% of Cr, and the atomic ratio of Mo + V to C is 1-1.3. According to the ultrahigh-strength steel matched 1000 MPa-grade Co-containing gas shielded welding wire provided by the invention, the yield strength of deposited metal can be remarkably improved by optimizing the component design of the welding wire and adding a certain content of Co; when gas shielded welding is adopted, weld metal with high yield strength, high tensile strength, high elongation and high impact can be stably obtained, the tensile strength of deposited metal is larger than or equal to 1050 Mpa, the yield strength is larger than or equal to 1000 Mpa, the elongation is larger than or equal to 13%, and the impact energy at the temperature of 50 DEG C below zero is larger than or equal to 47 J.

Description

Technical Field

[0001] The present invention relates to the technical field of steel materials, and in particular to a 1000MPa-grade Co-containing gas shielded welding wire for ultra-high-strength steel, the ultra-high-strength steel, and a welding method. Background Art

[0002] Welding is a crucial process in the construction of large steel structures. To ensure high-quality and efficient production of critical components, ultra-high-strength steel is often used, with semi-automated or automated welding using metal active gas welding (GMAW). This performance and efficiency often surpass those of manual welding rods and submerged arc welding, making GMAW wire one of the most important welding materials for ultra-high-strength steel. Although my country's regulations stipulate yield strength levels of up to 960 MPa or even higher for shipbuilding and offshore engineering steel and naval structural steel, the corresponding equivalent strength-matched welding materials exhibit poor low-temperature toughness, with the impact energy absorbed by the weld deposit typically less than 47 J at -50°C. This level of strength and toughness is primarily used in large deep-sea marine equipment, where critical structures require high resistance to brittle fracture. The difficulty in improving the low-temperature toughness of the weld metal is one of the main reasons why the development and application of welding materials for shipbuilding and offshore steel currently lags behind that of structural steel.

[0003] The strength and toughness of structural steel welds are determined by the alloy composition and microstructure. Since ultra-high-strength steel welds are non-equilibrium solidification structures of multi-component alloys, under certain welding conditions, their microstructure type and characteristics are mainly determined by their alloy composition. Domestic and foreign scholars have conducted extensive research on this topic, but there are also some shortcomings. First, the design of alloy systems for deposited metals of structural steel welding materials is mostly based on the researchers' experience, using trial-and-error analysis of single or multiple element combinations. There is insufficient research on the quantitative relationship between composition, microstructure, and performance, as well as its mechanism, resulting in blindness. Furthermore, there are few reports on research using computer-aided design. Second, existing research on structural steel welding wires mainly focuses on strength levels below 900 MPa, with few reports on the design of ultra-high-strength and toughness welding materials and weld performance at levels of 1000 MPa and above. Currently, the commonly used acicular ferrite microstructure design concept is usually only suitable for welding materials with a yield strength level below 800MPa. Bainite (usually 800~1000MPa) and martensite / bainite duplex (above 900MPa) are the main microstructure types of ultra-high-strength steel welding wire. In particular, since the alloy content of the steel plate matrix is ​​usually high, even if the weld metal deposited by the welding wire is mainly bainite, during actual welding, due to the dilution of the weld metal by the base material, there will usually still be a considerable amount of martensite structure in the weld, resulting in the weld impact toughness being significantly lower than that of the deposited metal. Therefore, how to ensure the ultra-high strength of the weld deposited metal while solving the toughness problem is the key to the present invention.

[0004] The general consensus is that within the Ni content ranges of 0, 2, 4, and 6%, the weld metal microstructure shifts from predominantly granular bainite to predominantly lath bainite and / or lath martensite, with weld metal microhardness increasing while the average width of columnar grains decreases. Proeutectoid grain size increases with Ni content above 4%. Above 6%, weld toughness typically decreases due to the formation of massive martensite or bainite, a decrease in the proportion of retained austenite, a reduction in high-angle grain boundaries, and severe segregation of superimposed components.

[0005] Due to limited research on high-strength and toughness welding wires with a yield strength of 1000 MPa, this review summarizes research papers on welding wires with a yield strength of 900 MPa and above. For bainitic welds, the primary alloying elements are still typically C, Mn, Ni, Mo, and Cr. The matrix is ​​primarily composed of bainite and granular bainite, with possible presence of small amounts of martensite and acicular ferrite. Bainite and martensite primarily serve as strengthening phases, while granular bainite and acicular ferrite primarily serve as toughening phases. Zhang Tianli et al. achieved a good strength-toughness balance by reducing the C content (0.02–0.04%), but the yield strength was only 800–900 MPa. Furthermore, in some cases, bainite laminae in the weld may coalesce to form aggregated bainite, resulting in reduced impact toughness. Keehan et al. suggest that the amount of aggregated bainite in the weld should be controlled by reducing the Ni and Mn contents.

[0006] In martensite / bainite welds, martensite provides an upper strength limit and a certain level of toughness, while upper and lower bainite contribute to achieving a high-strength, high-toughness combination. This technical approach typically involves manipulating the compositional combination of Mn and Ni to enhance strength while minimizing toughness degradation. When dendrites form upper bainite plus coarse aggregated bainite, with martensite precipitating between dendrites, toughness is significantly compromised. Deoxidation is particularly important for martensite / bainite welds, primarily using C to deoxidize and promote carbide precipitation. Its addition level is typically between 0.07% and 0.1%. Higher additions can cause lath martensite to transform into twinned martensite, reducing toughness. Si primarily deoxidizes and promotes the formation of acicular ferrite, resulting in a strong solid-solution strengthening effect but also a significant impact on toughness. Mn, Ni, Cr, Mo, and Cu primarily contribute to solid-solution strengthening and delay the austenite-ferrite transformation, with relatively low toughness degradation.

[0007] Summarizing the existing patents, "A high-efficiency non-post-heating welding method for 1100MPa ultra-high-strength steel thick plates (CN202410625524)" invented a high-efficiency non-post-heating welding method for 1100MPa ultra-high-strength steel thick plates. The welding wire used therein is mentioned, and the chemical composition range is: C ≤ 0.15%, Si ≤ 0.8%, 1.5% ≤ Mn + Cr + Mo ≤ 3.0%, Ni ≤ 9%, carbon equivalent ≤ 0.9%; the yield strength of the welding wire is ≥ 1000MP a, tensile strength ≥1100MPa, elongation ≥14%, -50℃ impact absorption energy ≥47J, however, the welding wire is TIG welding wire and MIG welding cannot be used; "A welding process for low-alloy ultra-high strength steel with a yield strength of 1400MPa (CN202311406244)" and "A welding process for low-alloy ultra-high strength steel with a yield strength of 1300MPa (CN202311407113)" also mentioned MIG welding wire C: 0.05~0.12wt%, Si: 0.3~0.55wt%, Mn: 1.2~1.6wt%, Cr: 0.1~0.8wt%, Ni: 1.8~2.9wt%, Mo: 0.5~1.2wt%, Ti: 0~0.3wt%, V: 0~0.1wt%, P: 0~0.02wt%,S:0~0.02wt%,but this patent does not give the toughness level of the weld metal deposited by the welding wire. According to the professional knowledge in this field, the yield strength of the welding wire under normal conditions is only about 900~950MPa. Since the yield strength of the base material reaches 1300~1400MPa, the low-matching joint formed by the low-strength weld + high-strength base material can reach the level of the base material in tensile strength under appropriate joint design and mechanical conditions. This patent combines post-weld water spray cooling and welding tempering welds to increase the tensile strength of the 4mm thick steel plate joint from 1250MPa to 1700MPa, and the KV2 at -40℃ reaches 27J. Therefore, it mainly attempts to solve the problem of strength and toughness of the weld joint from a process perspective. When the steel plate thickness is high, the effect of this method will be significantly reduced. "A welding method for ultra-high-strength Q1300E steel plates (CN202111420426)" is suitable for 8-15mm steel plates and uses commercial welding wires with tensile strength grades of 1200MPa (filler) and 1000MPa (primer). The 1000MPa high-strength steel wire is T Union GM-120 with a wire diameter of 1.2mm. The deposited metal has a tensile strength of ≥980MPa, an elongation of ≥15%, and an impact energy of ≥47J at -40°C. The main chemical composition and weight percentages are: C=0.10, Si=0.80, Mn=1.80, Cr=0.35, Mo=0.60, Ni=2.25, with the remainder being Fe and unavoidable impurities. The 1200MPa high-strength steel wire is BÖHLERalform® 1100 L-MC with a wire diameter of 1.2mm, the deposited metal tensile strength ≥1180MPa, elongation ≥12%, -40℃ impact energy ≥47J; the main chemical composition and weight percentage are: C=0.09, Si=0.40, Mn=1.40, Cr=0.70, Mo=0.50, Ni=2.70, the balance is Fe and unavoidable impurities. The shielding gas is a mixture of argon and carbon dioxide, with a gas flow rate of 18~22L / min, of which the volume percentage of argon is 75%~82%, and the volume percentage of carbon dioxide is 18%~25%. The yield strength level is not mentioned. According to common sense, the yield strength is usually 0.9~0.95 times the tensile strength; "A solid copper-free welding wire for gas shielded welding of 1500MPa grade ultra-high strength steel (CN201510806207)" invented a solid copper-free welding wire for gas shielded welding of 1500MPa grade ultra-high strength steel, which has a tensile strength of >1500MPa, a yield strength of >1350MPa, an elongation after fracture of >12%, and an impact strength of >60J at -20℃; the shielding gas is 98%Ar+2%O, and the chemical composition weight percentage of the welding wire is: C≤0.04%; Mn 2.0-2.3%; Si0.05-0.20%; P≤0.006%; S≤0.003%; Ni3.0-3.5%; Cr0.60-0.80%; Mo0.80-1.00% (Ni+Cr+Mo≥4.5%); Ti0.05-0.08%; the rest are Fe and unavoidable impurities. There is no copper plating on the surface, but according to the welding current and welding speed provided, the welding method used is TIG gas shielded welding; "A 1000MPa grade high-strength gas shielded solid welding wire for engineering machinery (CN201611023016)" The chemical composition of the welding wire is C0.087~0.089, Si+Mn1.91~1.94, Ni 2.31~2.42, Mo0.84~0.86, Cr0.54~0.56, Al0.02~0.03, Ti0.043~0.065, P 0.006-0.009, S0.002-0.004, the balance being Fe and unavoidable impurities; the shielding gas is Ar + 20% CO2; the mechanical properties of the deposited metal in the welded state can achieve tensile strength Rm ≥ 1100 MPa, yield strength R ≥ 950 MPa, elongation after fracture A ≥ 15%, reduction of area Z ≥ 50%, and KV ≥ 40 J at -40°C. It is mainly composed of a mixed structure of fine lath martensite and bainite, and is primarily used in engineering machinery. Since the steel used in engineering machinery is generally small in size and rarely used at low temperatures, and is usually not subject to large dynamic loads, its impact toughness requirements are not high; "A boron-containing rare earth fine-grain reinforced high-strength steel welding wire molten steel and high-strength steel welding wire and production method thereof (CN115502608A)" invented a deposited metal Rp0.2≥1000MPa, Rm≥1060MPa, A≥13% gas shielded welding wire, its -40℃ KV2≥58J, the composition control range is 0.06%~0.12% C, 0.40%~1.00% Si, 1.20%~2.40% Mn, not more than 0.020% P, not more than 0.015% S, not more than 0.01% Cu, 1.00%~4.00% Ni, 0.20%~1.0% Cr, 0.60%~1.0 0% Mo, 0.02%-0.10% B, 0.004%-0.01% rare earth elements, no more than 0.0080% N, no more than 0.0060% O, no more than 0.0003% H, and the balance being Fe and unforeseen impurities. The weight contents of the B and rare earth elements are controlled by the added amounts, but this invention primarily utilizes the grain-refining strengthening effects of B and rare earth elements to improve performance. The upper limit of the C content is relatively high, ultimately resulting in low elongation. It is generally used in engineering machinery. Summary of the Invention

[0008] In view of this, the present invention aims to provide a 1000MPa-grade Co-containing gas shielded welding wire for ultra-high-strength steel, ultra-high-strength steel, and a welding method. This aims to address the problem that existing 1000MPa-grade welding wires cannot achieve high yield strength, high tensile strength, high elongation, and high impact energy.

[0009] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0010] A 1000MPa grade Co-containing gas shielded welding wire for ultra-high-strength steel includes the following components in percentage by mass: C≤0.12%, Si≤0.6%, Mn=1.5-3%, V≤0.1%, Ti≤0.08%, Mo=0.5-1.2%, Ni=1.5-2.7%, Co=1.0-4.0%, Cr≤1.1%, and the atomic ratio of Mo+V to C is 1-1.3.

[0011] Furthermore, the mechanical properties of the deposited metal obtained by the welding wire after welding meet at least one of the following characteristics:

[0012] (1) Tensile strength ≥1050Mpa;

[0013] (2) Yield strength ≥1000Mpa;

[0014] (3) Elongation ≥ 13%;

[0015] (4) Impact energy at -50℃ ≥47J.

[0016] Furthermore, the diameter of the welding wire is 1.2 mm.

[0017] An ultra-high-strength steel is welded using the above-mentioned gas shielded welding wire, wherein the mass percentage of the ultra-high-strength steel includes C≤0.12%, Si≤0.6%, Mn=1.5~3%, V≤0.1%, Ti≤0.08%, Mo=0.5~1.2%, Ni=1.5~2.7%, Co=1.0~4.0%, Cr≤1.1%, and the atomic ratio of Mo+V to C is 1~1.3.

[0018] A method for welding ultra-high strength steel, used for welding the ultra-high strength steel described above, comprises the following steps:

[0019] (1) Beveling the ultra-high strength steel;

[0020] (2) Preheating before welding;

[0021] (3) Start welding;

[0022] (4) Heat treatment after welding.

[0023] Furthermore, in step (1), the high-strength steel is provided with a V-shaped groove, and the groove angle is 5 to 15 degrees.

[0024] Furthermore, in step (2), the preheating temperature is 100-150°C.

[0025] Furthermore, in step (3), the welding parameters are as follows: the shielding gas is a mixture of 95% Ar + 5% CO2 or 97.5% Ar + 2.5% CO2, the gas flow rate is 15-25 ml / min, the current is 210-240 A, the voltage is 24-28 V, and the welding speed is 25-35 cm / min.

[0026] Furthermore, in step (4), the heat treatment temperature is 200-250° C., and the treatment time is 1.5-2.5 h.

[0027] Furthermore, the thickness of the ultra-high strength steel is 20-40 mm.

[0028] Compared with the prior art, the ultra-high-strength steel supporting 1000MPa grade Co-containing gas shielded welding wire, ultra-high-strength steel, and welding method described in the present invention have the following advantages:

[0029] 1) The ultra-high-strength steel provided by the present invention is matched with a 1000MPa grade Co-containing gas shielded welding wire. By optimizing the design of the welding wire composition and adding a certain amount of Co, the yield strength of the deposited metal can be significantly improved.

[0030] 2) When the gas shielded welding wire and high-strength steel in the present invention are welded, a stable high yield strength, high tensile strength, high elongation, and high impact weld metal can be obtained by gas shielded welding. The tensile strength of the deposited metal is ≥1050Mpa, the yield strength is ≥1000Mpa, the elongation is ≥13%, and the impact energy at -50°C is ≥47J. DETAILED DESCRIPTION

[0031] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below.

[0032] The present invention predicts the yield strength through material calculation and optimizes the welding wire composition. The specific steps of yield strength prediction based on material composition and phase composition characteristics are as follows:

[0033] The first step is to calculate the total strength increment σ of bainite / martensite structure based on the annealed pure iron strength of 55MPa, taking into account solid solution strengthening, dislocation strengthening, grain refinement strengthening and precipitation strengthening. B , the volume fraction of the corresponding tissue is f B :

[0034] σ B =k×[(△ 2 σ dis +△ 2 σ refine ) 0.5 +△σ sol +△σ y ] (1)

[0035] Where k is the correction factor, which is related to the welding process, etc., and can usually be taken as 1.1~1.4 to correct the impact of welding non-equilibrium state on strength analysis.

[0036] △σ base =(△ 2 σ dis +△ 2 σ refine ) 0.5 +△σ sol It mainly characterizes the strengthening increment of the bainite / martensite matrix itself, and does not include the precipitation strengthening increment of the second phase in the martensite / bainite matrix.

[0037] Dislocation strengthening △σ dis There is usually the following relationship between the dislocation density ρ and the dislocation density ρ:

[0038] △σ dis =2αGbρ 0.5 +75.46 (basic strength, unit MPa) (2)

[0039] G is the shear modulus, which is 69 GPa calculated using α-Fe; b is the Burgers vector. <111> / 2 dislocation mode, is 0.249nm; α is the proportional coefficient, which is 0.5 for α-Fe based materials. Based on the estimated value of the weld dislocation density, △σ can be finally calculated dis ≈364MPa.

[0040] Grain refinement strengthening strength increment △σ refine The Hall-Petch relationship is used for calculation, where the Hall-Petch coefficient k is 17.4 (using the average diameter of the original austenite grains) or 30 (using the average diameter of the martensite blocks). According to the level of the original austenite grain size, △σ refine ≈172MPa.

[0041] △σ sol For the solid solution strengthening increment, the following formula can be used: △σ sol =4570×w(C) 0.5 +84×w(Si)+31×w(Mn)+151×w(Ni)+30×w(Cr)+11×w(Mo)+73×w(V)+38×w(Cu)+80×w(Ti)+45×w(Co)+32×w(Al). This formula combines the characteristics of the existing ferrite solid solution strengthening and martensite solid solution strengthening formulas, reasonably considers the combined effect of Ni on the promotion of martensitic phase transformation and the solid solution softening of the matrix, and also takes into account the increase in dislocation shear stress and the intensification of lattice brittleness caused by Co and Al, as well as the precipitation strengthening effect of Cu and Ti on part of the matrix.

[0042] △σ y The calculation is based on the incremental formula for dislocation cutting (soft phase below 10nm) or dislocation bypassing (hard phase or soft phase above 10nm). For this patent, most of the second phase is carbide-type hard phase, and the thermal cycle conditions are basically similar. Therefore, it can be assumed that the second phase size has a similar distribution. For this type of second phase, its strengthening increment can be simplified to a function of the second phase volume percentage f1: △σ y1 =138×(f1 / 0.47) 0.5 Considering that the size of cementite, M23C6 and M7C3 is micron-sized, the above carbides are not included in f. For soft phases such as Ni3Ti, Cu-containing phases, and fine Laves phases, the strengthening increment calculation formula can also be simplified, and the relationship between △σ and the soft phase volume percentage f2 is y 2 =95×(f2 / 1.1) 0.5 Total strengthening amount △σ y =△σ y1 +△σ y2 .

[0043] Considering that the ultra-high strength steel weld metal may have a volume fraction fγ , yield strength σ γ The retained austenite, the final total yield strength of the material σ s =f B σ B +f γ σ γ , where σ γ =(36.2×C+2.05×Si+0.38×Mn+1.48×Mo+1.89×V+4.1×Nb+0.46×W+2.68×Ti+0.725×G×(13.5 / 1000)0.6+50.4×N+6.46)×9.8, where G is the diameter of retained austenite (μm).

[0044] The second step involves developing a prediction model for yield strength, tensile strength, elongation, and Charpy impact energy based on the established welding material database. Incorporating a multi-objective optimization algorithm, the team optimized the alloy composition, using yield strength and elongation as constraints and maximizing Charpy impact energy and minimizing yield strength ratio as target parameters. The team then proposed a design solution and output the performance predictions based on the data-driven prediction model.

[0045] For the proposed design, software such as Thermo-Calc was used to calculate the content of each phase, as well as the composition of the matrix and retained austenite. Strength was then calculated using the method described in the first step. When calculating the content and composition of each phase, it is recommended to calculate the state corresponding to 200-600°C, as this is closer to the actual situation. Strength errors caused by the microstructure can be corrected using the k value in Equation (1).

[0046] If the calculated strength result is close to the strength prediction value corresponding to the design solution provided by the prediction model (within an error of no more than 50 MPa), the design result can be considered reliable. If the error exceeds 50 MPa, adjustments are made based on the given design solution. Software such as Thermo-Calc is used to calculate the content of each phase, as well as the composition of the matrix and retained austenite. Strength calculations are then performed using the method described in the first step. This process of repeated adjustments and calculations is repeated to determine possible weld alloy designs to ensure yield strength.

[0047] The third step is to judge the strength and toughness based on the alloy design scheme given in the second part, as well as the corresponding content of each phase, the composition of the matrix and retained austenite: Generally, 10-20% retained austenite can be considered to be beneficial to toughness and reduce the yield ratio; the higher the total volume fraction of carbide-type second phases, the higher the yield ratio; the lower the second phase precipitation temperature, the higher the toughness; in particular, for Mo and V-containing second phases, when the total volume fraction and the precipitation temperature of each second phase are close, the higher the proportion of orthorhombic Mo6C and MoC, hexagonal Mo2C and (Mo,V)C, face-centered cubic VC and TiC, etc., the lower the degree of deterioration of toughness.

[0048] The above three steps optimize the alloy composition of the weld for a given alloy system. Based on this, the target composition of the welding wire can be adjusted appropriately based on the degree of alloy burnout during the smelting and welding processes, resulting in a final welding wire formulation.

[0049] Specifically, the present invention proposes a 1000MPa grade Co-containing gas shielded welding wire for ultra-high strength steel. Specifically, in the selection of gas shielded welding wire components, the specific explanation is as follows:

[0050] (1) The selection of W (C) components should increase the upper limit of yield strength as much as possible without causing a significant increase in cold crack sensitivity and brittleness, thereby ensuring comprehensive performance.

[0051] (2) The W (Si) content is controlled to an upper limit of 0.6% to achieve a good deoxidation effect and a certain solid solution strengthening effect.

[0052] (3) Considering the problem of reduced toughness caused by high yield strength, it is proposed to improve it by increasing the content of retained austenite. Although the effect of increasing w(Ni) is obvious, Rp 0.2 To achieve a stable strength of 1000 MPa, it's necessary to balance the trade-off between increasing Ni and increasing retained austenite while maintaining strength. Increasing w(Cr) and w(Mn) also contributes to increased retained austenite and solid solution strengthening. Initially, w(Cr) is proposed to be 0.9-1.4%, w(Ni) to be 1.5-2.2%, and w(Mn) to be 1.5-3%. This allows for a higher retained austenite content at a lower Ni content, thus avoiding the formation of massive martensite or bainite and reducing the adverse effects of severe compositional segregation on toughness.

[0053] (4) Based on w(C), combined with calculation and experiment, Ti, V and Mo are added to form carbides in the weld and micro-alloying is performed. It is preferred that w(Ti) ≤ 0.08%, w(Mo) = 0.5~1.2%, w(V) ≤ 0.10% and the atomic ratio of (Mo+V) to C is 1~1.3. Further reducing w(Cr) to below 1.1% can make the carbides basically all TiC, VC and hexagonal semi-coherent carbides (Mo, V)C and Mo2C, Cr 23 The volume fraction of C6 does not exceed 0.1%, thereby further increasing the precipitation strengthening increment from 110 MPa to more than 260 MPa.

[0054] (5) Based on (4), the maximum yield strength can only reach about 950 MPa, which is still far from the target yield strength (≥1030 MPa). At this time, consider adding Co. Co can be infinitely dissolved in the ferrite matrix and will not precipitate a second phase. Under the guidance of this idea, according to the "second step" repeatedly adjust the alloy design scheme, and finally achieve the following results:

[0055] Effect 1: Co can maintain a higher dislocation density in the weld and increase the unstable stacking fault energy of α-Fe, so that for every 1 / 16 molar concentration of Co, the dislocation slip shear stress is increased by about 20% compared with pure iron. Combined with the solid solution strengthening effect, the yield strength of the ferrite matrix can be increased by 38 MPa for every 1% increase in w(Co).

[0056] Effect 2: Co promotes the partial decomposition of retained austenite and slightly increases the content of TiC, VC, and hexagonal semi-coherent carbides (Mo,V)C and Mo2C. The relationship between w(Co) and the reduction in the volume fraction of retained austenite is approximately 0.8×w(Co)+0.2. The strengthening effect brought about by the increase in the volume fraction of carbides is not considered here. Since the yield strength of retained austenite is about 125MPa, and the yield strength of the ferrite matrix can reach about 1000MPa or more, the yield strength increase brought about by the decomposition of retained austenite can reach (0.8×w(Co)+0.2)×875MPa. In summary, adding 1~4% Co can increase the yield strength by 71~440MPa based on (3).

[0057] (6) After adding Co, the dislocation slip resistance increases. In order to alleviate the hardness and brittleness of the matrix, the Ni content can be appropriately increased according to w(Co). Ni can reduce the dislocation slip shear stress by about 20% compared with pure iron, and increase its upper limit by 20%, w(Ni) = 1.5~2.7% to offset the adverse effects of Co.

[0058] (7) In summary, the final mass percentage of the components of the welding wire of the present invention is: C≤0.12%, Si≤0.6%, Mn=1.5~3%, V≤0.1%, Ti≤0.08%, Mo=0.5~1.2%, Ni=1.5~2.7%, Co=1.0~4.0%, Cr≤1.1%, the atomic ratio of Mo+V and C is 1~1.3, and the balance is Fe and other inevitable impurity elements. In particular, Co=1.0~4.0%, Rp 0.2 It can reach above 1000MPa, A≥13%, and KV2≥47J at -50℃.

[0059] After the alloy design is completed, conventional induction melting / arc melting + electric furnace refining / electroslag remelting are used to ensure the uniformity of the alloy ingot composition and the S and P content. Conventional rolling and wire drawing processes are then used to produce wire rod, with a diameter reduction of φ1.2mm or other commonly used specifications. During the subsequent ultra-high-strength steel welding process, preheating is first performed at a temperature of 100-150°C. During welding, the shielding gas is a mixture of 95% Ar + 5% CO2 or 97.5% Ar + 2.5% CO2 at a flow rate of 15-25ml / min. After the ultra-high-strength steel welding process is completed, post-treatment is required, with a post-heat treatment temperature of 250°C and a treatment time of 2h.

[0060] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0061] Example 1

[0062] For 30mm thick 1000MPa high-strength steel, the welding wire diameter is 1.2mm, and the chemical composition of the welding wire is shown in Table 1. The chemical composition of the high-strength steel is the same as that of the welding wire. Gas shielded welding according to the present invention was used for welding, and the specific welding process was as follows: a. V-grooving the high-strength steel with a groove angle of 10° and a root of 18mm; b. Preheating the high-strength steel to 100°C; c. Welding parameters were: a 95% Ar + 5% CO2 mixture as shielding gas, a gas flow rate of 15-25ml / min, a current of 210-240A, a voltage of 24-28V, and a welding speed of 25-35cm / min. After the welding process was completed, the post-heat treatment temperature was 250°C and the treatment time was 2h. The composition of the deposited metal after welding is shown in Table 2.

[0063] Table 1 Chemical composition of welding wire (wt%), the balance is iron and inevitable impurities.

[0064]

[0065] Performance Testing

[0066] 1. The yield strength was predicted by the composition of the deposited metal after welding the high-strength steels of Examples 1 to 6. The results are shown in Table 2.

[0067] Table 2 Chemical composition of the weld (wt%), the balance being iron and unavoidable impurities.

[0068]

[0069] 2. The actual yield strength, tensile strength, elongation, and impact energy of the welds of the high-strength steels of Examples 1 to 6 after welding with welding wire were tested. The test results are shown in Table 3.

[0070] Table 3 Weld mechanical properties test results

[0071]

[0072] Note: R p0.2 / MP a is the yield strength, R m / MP a is the tensile strength, A / % is the elongation, and KV2 / J is the impact energy at -50℃.

[0073] By comparing Table 2 and Table 3, it can be seen that the w(Co) of Example 1 is relatively low, and the measured Rp0.2 is relatively low; the w(Co) of Example 5 is relatively high, and the measured A and -50℃ KV2 / J are relatively low.

[0074] The yield strength prediction values ​​in Examples 1 to 6 in Table 2 and the actual yield strength test results in Examples 1 to 6 in Table 3 are basically similar, indicating that the yield strength prediction by the weld in the present invention has a certain degree of credibility.

[0075] It can be seen from Examples 1 to 6 in Table 3 that when the Co content of the present invention is 1% to 4%, the tensile strength is ≥1050 MPa, the yield strength is ≥1000 MPa, the elongation is ≥13%, and the -50°C impact energy is ≥47 J. This shows that the deposited metal of the welding wire of the present invention after welding has high yield strength, high tensile strength, high elongation, and high impact resistance.

[0076] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined by the claims.

Claims

1. A 1000MPa grade Co-containing gas shielded welding wire for ultra-high strength steel, characterized in that: The invention comprises the following components in percentage by mass: C≤0.12%, Si≤0.6%, Mn=1.5~3%, V≤0.1%, Ti≤0.08%, Mo=0.5~1.2%, Ni=1.5~2.7%, Co=1.0~4.0%, Cr≤1.1%, and the atomic ratio of Mo+V and C is 1~1.

3.

2. The gas shielded welding wire according to claim 1, characterized in that: The mechanical properties of the deposited metal obtained by the welding wire after welding meet at least one of the following characteristics: (1) Tensile strength ≥1050Mpa; (2) Yield strength ≥1000Mpa; (3) Elongation ≥ 13%; (4) Impact energy at -50℃ ≥47J.

3. The gas shielded welding wire according to claim 1, characterized in that: The diameter of the welding wire is 1.2 mm.

4. An ultra-high strength steel welded with the gas shielded welding wire according to any one of claims 1 to 3, characterized in that: The components of the ultra-high strength steel include C≤0.12%, Si≤0.6%, Mn=1.5~3%, V≤0.1%, Ti≤0.08%, Mo=0.5~1.2%, Ni=1.5~2.7%, Co=1.0~4.0%, Cr≤1.1%, and the atomic ratio of Mo+V and C is 1~1.

3.

5. A method for welding ultra-high strength steel, for welding the ultra-high strength steel according to claim 4, characterized in that: The steps include: (1) Beveling the ultra-high strength steel; (2) Preheating before welding; (3) Start welding; (4) Heat treatment after welding.

6. The welding method according to claim 5, characterized in that In step (1), the high-strength steel is provided with a V-shaped groove, the groove angle is 5-15°, and the root is 16-20 mm.

7. The welding method according to claim 5, characterized in that In step (2), the preheating temperature is 100-150°C.

8. The welding method according to claim 5, characterized in that In step (3), the welding parameters are as follows: the shielding gas is a mixture of 95% Ar + 5% CO2 or 97.5% Ar + 2.5% CO2, the gas flow rate is 15~25ml / min, the current is 210~240A, the voltage is 24~28V, and the welding speed is 25~35cm / min.

9. The welding method according to claim 5, characterized in that: In step (4), the heat treatment temperature is 200-250°C, and the treatment time is 1.5-2.5h.

10. The welding method according to claim 5, characterized in that: The thickness of the ultra-high strength steel is 20-40 mm.

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