A coal mine hydraulic support submerged arc welding wire with high strength and toughness and a preparation method thereof

Abstract

This invention provides a submerged arc welding wire for coal mine hydraulic supports that combines high strength and toughness in welds, and a method for its preparation. The chemical composition of the submerged arc welding wire, by mass percentage, includes: C: 0.09~0.15, Si: 0.05~0.10, Mn: 1.81~2.30, P≤0.010, S≤0.005, Cr: 0.20~0.45, Ni: 2.30~2.49, Cu: 0~0.09, Mo: 0.51~0.90, Ti≤0.020, Ca≤0.015, V≤0.025, Zr≤0.015, O≤0.004, N≤0.006, with the balance being Fe and other unavoidable impurities. The beneficial effects of the present invention are: (1) By rationally designing the chemical composition, under the process conditions of 20~40 kJ / cm heat input, the yield strength of the weld metal is ≥700 MPa, the tensile strength is between 810~910 MPa, the elongation is ≥22%, and the low-temperature impact toughness at -40℃ is ≥100J; (2) The welding wire preparation process is simple and does not require annealing treatment. When combined with the sintering flux commonly used in engineering, the arc is stable during the welding process, and the weld metal after welding has excellent strength and toughness, which meets the welding requirements of Q690M hydraulic support steel and can promote the large-scale development and application of high-strength hydraulic support steel.

Description

Technical Field

[0001] This invention belongs to the technical field of high-strength welding materials for hydraulic supports in coal mines, specifically relating to a submerged arc welding wire and its preparation method that is compatible with Q690M steel for hydraulic supports in coal mines. The weld metal has a yield strength ≥700 MPa, tensile strength 810~910 MPa, elongation ≥22%, and low-temperature impact toughness ≥100 J at -40℃. Background Technology

[0002] As coal mining progresses towards deeper, higher mining depths and more complex geological conditions, steel-structured hydraulic supports for coal mines face increasingly severe challenges, such as high ground pressure and strong impact tendency. Traditional low-strength steels (such as Q460) are no longer sufficient to meet the requirements for high load-bearing capacity, lightweight construction, and long service life. Compared to Q460, Q690M strength-grade hydraulic support steel offers nearly 50% higher strength. Under the same load-bearing capacity, the structural thickness can be reduced by 20% to 30%, which not only reduces the support's self-weight and facilitates underground transportation and installation but also reduces steel consumption by 10% to 15%, extending service life and offering both economic and environmental benefits.

[0003] In recent years, many organizations have explored the application of Q690M steel in the main load-bearing structural components of hydraulic supports in coal mines, such as the top beams, bases, and shield beams. These main load-bearing components are primarily thick steel plates (≥20 mm), and submerged arc welding is commonly used. To ensure the safety of the entire component, the submerged arc weld not only needs to match the strength of the base material but also should possess excellent low-temperature toughness and weld metallurgical quality. However, due to the high strength of Q690M steel, existing submerged arc welding wires incorporate a large amount of strengthening elements to ensure strength matching. This results in a significant reduction in weld toughness, making it difficult to balance strength and toughness in the weld metal. Furthermore, weld metallurgical quality problems are frequent, and the joint flaw detection pass rate is low. The poor weld metallurgical quality and mechanical properties of existing high-strength Q690M steel submerged arc welding wires severely limit the development and application of high-strength hydraulic support steel. Therefore, there is an urgent need to develop submerged arc welding wires specifically designed for Q690M hydraulic support steel to meet the practical application needs of engineering projects.

[0004] There are almost no research reports in China regarding submerged arc welding wire for hydraulic supports of this strength level. It is generally used to weld with other types of submerged arc welding wire of equal strength to the base material. The applicant has studied publicly available domestic patents on high-strength submerged arc welding wire: Invention patent CN103846571B discloses a high-performance submerged arc welding wire for X100 pipeline steel and its application. It provides a submerged arc welding wire with a yield strength of up to 690MPa and a tensile strength higher than 780MPa. Its chemical composition is controlled by the following requirements in mass percentage (wt.%): C: 0.01~0.05, Mn: 1.4~2.1, Si: 0.1~0.3, Mo: 0.2~0.4, Ti: 0.05~0.1, B: 0.003~0.005, Cr: 0.1~0.4, Cu: 0.2~0.3, Ni: 0.3~0.6, Nb: 0.03~0.08, S<0.005, P<0.005. This welding wire achieves high weld strength primarily through the alloying effects of Mn, Mo, B, and Nb. However, the high B content can lead to an increased hardening tendency, while the increased Nb content will increase the size and number of M / A components. Furthermore, although the welding wire exhibits good toughness at -20℃, its low Ni content may compromise its excellent low-temperature toughness as the temperature drops to -40℃.

[0005] Invention patent CN103084752B discloses a high-strength, high-toughness submerged arc welding wire for X100 pipeline steel. Its chemical composition (by mass percentage) is C: 0.01-0.06, Si: 0.30-0.50, Mn: 1.20-1.80, Cr: 0.20-0.50, Ni: 1.50-3.00, P < 0.010, S < 0.005, Ti: 0.01-0.10, Mo: 0.30-0.60, B: 0.001-0.008, Al: 0.01-0.03, Nb: 0-0.06. This welding wire, through optimized alloy element ratios, controls the C+Mn / 10 ratio to be 0.18-0.20% and the Al+Ti+10B ratio to be 0.10-0.115%, effectively ensuring high strength and toughness. However, this welding wire contains a certain amount of Al, which, due to its strong deoxidizing effect during welding, will combine with oxygen, potentially forming numerous irregularly shaped inclusions, or combining with silicate inclusions to form large-sized inclusions, severely reducing the bonding strength with the matrix. Simultaneously, the welding wire contains 0.3~0.5% Si. Considering flux transition, the Si content in the weld is estimated to be between 0.45~0.65%, increasing the size and quantity of M / A components in the microstructure. If Nb is added to the welding wire, the size of the M / A components will further increase. Therefore, the weld after welding with this wire may contain numerous irregular inclusions and hard, brittle M / A components.

[0006] Invention patent CN108247234B discloses a high-strength submerged arc welding wire for steel and its preparation method. The wire's composition (by chemical composition mass percentage) is: C: 0.05–0.09, Mn: 0.6–1.0, Si≤0.10, P<0.01, S≤0.005, Cu: 0.5–1.0, Ni: 0.5–1.0, Cr: 0.3–0.5, Mo: 0.1–0.2, Ti: 0.03–0.05, B: 0.0025–0.005. Through welding wire examples, it can be found that the tensile strength of this welding wire is above 700 MPa, and the impact value at -20℃ is not less than 120 J. However, the high Cu and B content, while ensuring strength, results in high stiffness during welding. The addition of these elements also leads to a high hardening tendency, increasing the risk of welding cracks. Meanwhile, the low Ni and Mo content in the welding wire makes it difficult to guarantee low-temperature toughness at -40℃.

[0007] Furthermore, while the aforementioned patented welding wire incorporates a large number of alloying elements to enhance weld strength and toughness, it fails to adequately consider the manufacturing difficulty of the welding wire. The addition of element B increases the hardening tendency, and its combined addition with elements such as Cu, Cr, and Ni increases the difficulty of wire drawing, thereby raising the manufacturing cost. The high addition of alloying elements makes the metallurgical reaction in the molten pool more complex, easily increasing the viscosity of the molten pool and inhibiting the removal of gases and inclusions. Therefore, the deoxidation of alloying elements and the metallurgical quality of the weld in high-alloy welds also deserve attention. Summary of the Invention

[0008] This invention addresses the problems of existing submerged arc welding of Q690M hydraulic support steel, which struggles to achieve both excellent strength and toughness as well as metallurgical quality, and suffers from high welding wire preparation costs. It provides a submerged arc welding wire for coal mine hydraulic supports that balances high strength and toughness, along with its preparation method. By optimizing the component ratio and preparation method, the wire preparation process is simple, requiring no annealing treatment. Combined with commonly used sintered flux, the arc is stable during welding, and the weld metal exhibits excellent strength and toughness, making it suitable for welding Q690M hydraulic support steel.

[0009] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a submerged arc welding wire for coal mine hydraulic supports that combines high strength and toughness of weld seams, wherein the chemical composition of the submerged arc welding wire, by mass percentage, includes: C: 0.09~0.15, Si: 0.05~0.10, Mn: 1.81~2.30, P≤0.010, S≤0.005, Cr: 0.20~0.45, Ni: 2.30~2.49, Cu: 0~0.09, Mo: 0.51~0.90, Ti≤0.020, Ca≤0.015, V≤0.025, Zr≤0.015, O≤0.004, N≤0.006, with the balance being Fe and other unavoidable impurities, of which the five harmful elements Pb+Sn+As+Sb+Bi≤0.010.

[0010] Furthermore, the chemical composition of the submerged arc welding wire satisfies 0.01≤Sp≤0.11, where Sp is the formula for controlling the liquid-solid phase precipitated particles: Sp=(9V+3Ti) / (1.5Si+Mn+2Ti+5Zr+7Ca).

[0011] Furthermore, the chemical composition of the submerged arc welding wire satisfies 810≤Rm≤910, where Rm is the formula for controlling the intensity: Rm=9.8×(36+61.32[C]+4.8[Si]+6.9[Mn]+5.5[Cr]+5.1[Ni]+11.03[Cu]+19.6[Mo]+41.6[Ti+Ca+V+Zr]).

[0012] Furthermore, the chemical composition of the submerged arc welding wire contains two or three of the trace elements Ti, Ca, V, and Zr.

[0013] Furthermore, the submerged arc welding wire is paired with a basicity of 2.0 ≤ B. Ⅱ For sintered flux with W≤2.2, under process conditions of 20~40 kJ / cm heat input, the weld metal yield strength is ≥700 MPa, tensile strength is between 810~910 MPa, elongation is ≥22%, and low-temperature impact toughness at -40℃ is ≥100 J.

[0014] Furthermore, in the weld metal, 1mm 2 The proportion of inclusions larger than 1 micrometer in the region shall not exceed 10%, and the proportion of acicular ferrite in the columnar crystal region of the weld shall not be less than 75%.

[0015] This invention also provides a method for preparing submerged arc welding wire for coal mine hydraulic supports that combines high strength and toughness of the weld, comprising the following steps: (1) Preparation of wire rod for welding wire: Welding wire steel is smelted according to the chemical composition and proportion of submerged arc welding wire, and a casting billet with the required composition is prepared; then it is forged at 1000~1100 ℃, held at 1100~1200 ℃ for 2 h, descaled at 1020~1050 ℃, fine rolled at 860~920 ℃, and reduced in diameter at 780~800 ℃ to prepare wire rod for submerged arc welding wire with a diameter φ of 6.5mm; (2) Preparation of welding wire by wire rod drawing: φ6.5 mm wire rod is reduced in diameter on the welding wire production line to obtain φ4.0 mm submerged arc welding wire, without annealing treatment in the intermediate process; (3) Copper plating of welding wire: Copper is uniformly plated on the surface of submerged arc welding wire using a chemical method to obtain finished submerged arc welding wire.

[0016] Furthermore, the φ6.5 mm wire rod is reduced in diameter three times to obtain a φ4.0 mm submerged arc welding wire. The diameters after the three reductions are φ5.5 mm, φ4.8 mm and φ4.0 mm, respectively.

[0017] Furthermore, the thickness of the copper plating is 0.15 to 0.18 micrometers.

[0018] The beneficial effects of the present invention are: (1) By rationally designing the chemical composition, under the process conditions of 20~40 kJ / cm heat input, the yield strength of the weld metal is ≥700 MPa, the tensile strength is between 810~910 MPa, the elongation is ≥22%, and the low-temperature impact toughness at -40℃ is ≥100J; (2) The welding wire preparation process is simple and does not require annealing treatment. When combined with the sintering flux commonly used in engineering, the arc is stable during the welding process, and the weld metal after welding has excellent strength and toughness, which meets the welding requirements of Q690M hydraulic support steel and can promote the large-scale development and application of high-strength hydraulic support steel.

[0019] The present invention will now be described in detail with reference to the accompanying drawings. Attached Figure Description

[0020] Figure 1 This is a comparison diagram of the weld formation and radiographic testing results of the submerged arc welding wire embodiment and the comparative example in this invention. Figure 1 In the diagram, a1 is an observation diagram of the weld formation of the submerged arc welding wire in Example 1, a2 is a radiographic inspection result diagram of the submerged arc welding wire in Example 1, b1 is an observation diagram of the weld formation of the submerged arc welding wire in Comparative Example 1, and b2 is a radiographic inspection result diagram of the submerged arc welding wire in Comparative Example 1.

[0021] Figure 2 These are typical inclusion observation diagrams of the submerged arc welding wire weld seams in the embodiments and comparative examples of the present invention. Figure 2 In the diagram, a is an image of inclusions in the submerged arc weld of Example 2, and b is an image of inclusions in the submerged arc weld of Comparative Example 2.

[0022] Figure 3 This is a comparison diagram of the microstructure of the columnar crystalline region and the heat-affected zone of the weld bead in the embodiment and the comparative example of the submerged arc welding wire of the present invention. Figure 3In the diagram, a1 is a microstructure diagram of the columnar crystalline region of the submerged arc welding wire weld in Example 4, a2 is a microstructure diagram of the heat-affected zone of the weld bead of the submerged arc welding wire weld in Example 4, b1 is a microstructure diagram of the columnar crystalline region of the submerged arc welding wire weld in Comparative Example 3, and b2 is a microstructure diagram of the heat-affected zone of the weld bead of the submerged arc welding wire weld in Comparative Example 3. Detailed Implementation

[0023] This invention provides a submerged arc welding wire for coal mine hydraulic supports that combines high strength and toughness in welds. The chemical composition of the submerged arc welding wire, by mass percentage, includes: C: 0.09~0.15, Si: 0.05~0.10, Mn: 1.81~2.30, P≤0.010, S≤0.005, Cr: 0.20~0.45, Ni: 2.30~2.49, Cu: 0~0.09, Mo: 0.51~0.90, Ti≤0.020, Ca≤0.015, V≤0.025, Zr≤0.015, O≤0.004, N≤0.006, with the balance being Fe and other unavoidable impurities.

[0024] The design basis for each chemical component in this invention is as follows.

[0025] C: C can increase strength, but excessive amounts will reduce weldability and toughness. The present invention has a low C content, which can reduce cracking during wire rod rolling and wire drawing, improve drawing stability, and, in combination with other alloying elements, increase the strength of the weld metal. The C content in the present invention is 0.09~0.15%, preferably 0.10~0.12%.

[0026] Si: Silicon is one of the main deoxidizers in the welding process, but when its content is high, it is easy to generate large-sized silicate inclusions and M / A components. Considering the transfer of Si into the weld through the flux, the Si content in this welding wire is relatively low. In addition, its low content can reduce the risk of wire breakage during the wire drawing process and reduce the hardness of the wire rod and the welding wire. In this invention, the Si content is 0.05~0.10%, preferably 0.06~0.09%, and more preferably 0.07~0.08%.

[0027] Mn: Manganese can significantly improve the strength and hardness of weld metal, promote deoxidation and desulfurization, and improve hot working performance. Increasing the Mn content can reduce hot brittleness during rolling, but it may cause segregation and work hardening during drawing. In excessive amounts, the wire drawing may require appropriate annealing treatment, increasing the cost of wire drawing. In this invention, the Mn content is 1.81~2.30%, preferably 1.86~2.25%, and more preferably 1.95~2.12%.

[0028] P and S are generally considered harmful in welds, so their content is minimized. This invention controls P ≤ 0.010% and S ≤ 0.005%, which can reduce hot brittleness and cold brittleness, improve the workability of rolling and drawing, and improve the toughness and metallurgical quality of welds.

[0029] Cr: Chromium can improve the strength of the weld and the stiffness of the welding wire, but its increase will increase the oxidation tendency, requiring more precise temperature control during rolling. Moreover, excessive Cr content will also increase the M / A component, increasing hardness. In this invention, the Cr content is 0.20~0.45%, preferably 0.28~0.43%, and more preferably 0.35~0.40%.

[0030] Ni: Nickel is crucial for ensuring stable low-temperature toughness in welding wire and can reduce brittleness. However, high nickel content significantly increases the viscosity of the molten pool, deteriorating the metallurgical quality of the weld and potentially increasing the risk of segregation during drawing. In this invention, the Ni content is 2.30~2.49%, preferably 2.31~2.48%, and more preferably 2.36~2.45%.

[0031] Cu: The addition of copper to the welding wire can improve the workability, and the fine Cu-rich precipitation can also play a precipitation strengthening role. However, when the copper content is high, it may cause hot brittleness of the weld. Considering the copper plating of the welding wire and the role of other elements, Cu is added in trace amounts in this invention, with a content of 0~0.09%, preferably 0.03~0.08%, and more preferably 0.05~0.06%.

[0032] Mo: Molybdenum can significantly strengthen the grains while improving strength and toughness. However, increasing its content may increase the deformation resistance during rolling, making drawing difficult. Excessive content can also lead to an increase in the size and number of M / A components. In this invention, the Mo content is 0.51~0.90%, preferably 0.59~0.87%, and more preferably 0.65~0.74%.

[0033] Ti: Titanium in welds is a strong deoxidizer, protecting against the oxidation of Si and Mn. The micron-sized Ti oxide inclusions formed by its oxidation reaction promote the nucleation of acicular ferrite, refining the weld metal, while nano-sized oxides pin the original austenitic grain boundaries. However, high Ti content increases the size of inclusions and reduces the bonding ability between the matrix and inclusions in the weld. In this invention, the Ti content is ≤0.020%, preferably 0.008~0.017%, and more preferably 0.010~0.012%.

[0034] Ca: Adding trace amounts of Ca to the welding wire can reduce the impact of residual rust on the steel surface on the weld quality. It can also combine with Ti for deoxidation, reducing the oxygen content of the weld. However, increasing its content can intensify the metallurgical reaction in the weld, reducing its metallurgical quality; therefore, it must be added in trace amounts. In this invention, the Ca content is ≤0.015%, preferably 0.008~0.014%, and more preferably 0.010~0.013%.

[0035] V: During the solidification process of weld metal, vanadium can combine with C and N to form nanoscale fine particles, playing a role in second-phase strengthening. It can also pin grain boundaries and refine austenite grains. However, an increase in its content may also increase the risk of weld cracking, especially in high-strength welds, so its content must be strictly controlled. In this invention, the V content is ≤0.025%, preferably 0.017~0.023%, and more preferably 0.019~0.020%.

[0036] Zr: In welds, Zr can also interact with Ti and other materials to achieve deoxidation and denitrification. Furthermore, its submicron / micron-sized oxide inclusions possess high heterogeneous nucleation capabilities, and nanoscale inclusions can pin grain boundaries. However, high Zr content may lead to the formation of large-sized inclusions. In this invention, the Zr content is ≤0.015%, preferably 0.009~0.013%, and more preferably 0.011~0.013%.

[0037] High-strength weld metal is more sensitive to porosity and inclusions. To ensure the metallurgical quality and density of the weld, the content of O and N must be strictly controlled. The content of O should be ≤0.004%, and the content of N should be ≤0.006%.

[0038] The five harmful elements mainly affect grain boundary embrittlement and hot cracking. In high-strength welds, the content of these five elements should be strictly limited. The content of the five harmful elements Pb+Sn+As+Sb+Bi ≤ 0.010%.

[0039] Furthermore, although Ti, Ca, V, Zr and trace elements such as O, N, and C in steel can generate particles that pin the original grain boundaries and promote heterogeneous nucleation of ferrite, when there are too many types, various inclusions or precipitates will recombine in the liquid or solid phase, forming large-sized inclusions or precipitates, reducing their bonding ability with the matrix and increasing the risk of cracking. Therefore, two or three of Ti, Ca, V, and Zr are added to the welding wire of the present invention.

[0040] In addition to the above-mentioned requirement to reasonably control the chemical composition range of each element, the following innovative technical requirements must also be set to accurately regulate the relative addition amounts of certain key elements. To ensure that the welding wire achieves both good metallurgical quality and high strength and toughness, the composition must also meet the chemical composition matching requirements in the relationship formulas Sp and Rm.

[0041] Sp is the formula for controlling the liquid-solid phase precipitates: Sp = (9V + 3Ti) / (1.5Si + Mn + 2Ti + 5Zr + 7Ca) where 0.01 ≤ Sp ≤ 0.11. High-strength welds require sufficiently refined microstructures, but due to their high strength, they are highly sensitive to inclusions and precipitates. Increasing the size of inclusions and precipitates reduces their bonding ability with the matrix. By controlling the proportions of V, Ti, Si, Mn, Ti, Zr, and Ca to match Sp between 0.01 and 0.11, inclusion modification can be achieved, while simultaneously refining the liquid-solid phase precipitates. The modified inclusions become effective heterogeneous nucleation sites, providing a high proportion of acicular ferrite. The refined precipitates not only exert a second-phase strengthening effect but also pin the original austenitic grain boundaries, restricting the competitive growth of acicular ferrite in small areas, thus achieving a weld microstructure dominated by refined acicular ferrite.

[0042] Rm is the formula for controlling strength: Rm = 9.8 × (36 + 61.32[C] + 4.8[Si] + 6.9[Mn] + 5.5[Cr] + 5.1[Ni] + 11.03[Cu] + 19.6[Mo] + 41.6[Ti + Ca + V + Zr]) and 810 ≤ Rm ≤ 910. Since hydraulic supports in coal mines may be subjected to dynamic loads during application, good fatigue resistance is required. Ensuring equal or even super-strong strength matching between the weld metal and the base metal is key to achieving good fatigue performance of the joint. However, excessively high weld strength increases the susceptibility to fatigue crack initiation and raises the risk of cracking at the weld toe. By considering the transition of alloying elements in the flux and the loss of alloying elements during welding, specifying that the element ratio Rm in the welding wire to control strength should be within the range of 810~910 can effectively reduce the risk of fatigue fracture of the weld metal and improve the fatigue performance of the joint.

[0043] To achieve control over the entire process of welding wire composition design, preparation, and welding, this invention also provides a method for preparing the above-mentioned submerged arc welding wire.

[0044] The preparation method of submerged arc welding wire includes the following steps: (1) Preparation of wire rod for welding wire: Welding wire steel is smelted according to the chemical composition and proportion of submerged arc welding wire, and a casting billet with the required composition is prepared. Then, it is forged at 1000~1100 ℃, kept at 1100~1200 ℃ for 2 h, dephosphorized at 1020~1050 ℃, fine rolled at 860~920 ℃, and reduced in diameter at 780~800 ℃ to prepare wire rod for submerged arc welding wire with a diameter of φ6.5 mm. (2) Wire rod drawing to prepare welding wire: The φ6.5 mm wire rod is reduced in diameter three times on the welding wire production line from φ6.5 mm to φ5.5 mm to φ4.8 mm to φ4.0 mm to prepare submerged arc welding wire. There is no annealing treatment in the middle process, which can not only effectively ensure the high strength of the welding wire, but also effectively reduce the cost of the welding wire drawing process. (3) Copper plating of welding wire: Copper is uniformly plated on the surface of submerged arc welding wire using a chemical method to obtain the finished submerged arc welding wire. The thickness of the copper plating in step (3) is 0.15 to 0.18 micrometers.

[0045] During welding, the submerged arc welding wire should be paired with a basicity of 2.0 ≤ B. ⅡW With a sintering flux concentration ≤2.2 and a heat input of 20~40 kJ / cm, weld metal with high strength, toughness, and excellent metallurgical quality can be obtained. The weld metal exhibits a yield strength ≥700 MPa, tensile strength between 810~910 MPa, elongation ≥22%, and low-temperature impact toughness ≥100 J at -40℃. Within 1 mm of the weld... 2 The proportion of inclusions larger than 1 micrometer in the region is no more than 10%, and the proportion of acicular ferrite in the columnar crystal region of the weld is no less than 75%. This not only improves the bonding ability between particles and the matrix and reduces the tendency to crack, but also provides high-density, large-angle grain boundaries in the columnar crystal region, which can effectively hinder crack propagation. In addition, the high proportion of acicular ferrite can mutually inhibit growth during secondary heating, avoiding the formation of large-sized polygonal ferrite in the heat-affected zone of the weld, thus reducing the problems of weld embrittlement and softening.

[0046] The submerged arc welding wire of the present invention will be further explained and described below with reference to specific embodiments.

[0047] Seven heats of welding wire steel according to the embodiments of the present invention and three heats of welding wire steel according to the comparative examples were prepared in a 100 kg vacuum induction furnace. The elemental composition of the welding wire steel according to the embodiments of the present invention meets the requirements of the present invention. The welding wire steels of the embodiments and the comparative examples were melted and cast sequentially according to a certain elemental composition ratio to obtain as-cast alloy billets. The composition of the welding wire steels of the embodiments and the comparative examples was analyzed according to GB / T 4336 "Spark Source Atomic Emission Spectroscopy Analysis Method (Conventional Method) for Carbon Steel and Medium and Low Alloy Steels". The specific chemical composition is shown in Table 1.

[0048] Table 1 Chemical composition (wt.%, balance Fe) of welding wire steel in Examples 1-7 and Comparative Examples 1-3 .

[0049] The welding wire steel used in the examples and comparative examples underwent wire rod rolling, wire drawing, and copper plating. Table 2 summarizes the key process parameters for different welding wire steels during preparation. The results show that, using the welding wire preparation process provided by this invention, the welding wire preparation in the examples exhibits high stability, no wire breakage, and stable copper plating on the welding wire surface, thus improving the wire breakage problem during drawing of the welding wire in the comparative example.

[0050] Table 2. Main process parameters for the preparation of submerged arc welding wire in Examples 1-7 and Comparative Examples 1-3 .

[0051] Welding tests were conducted on typical butt joints of the prepared example and comparative welding wires. The specific welding process parameters are shown in Table 3. The welding test plate was made of Q690M coal mine hydraulic support steel with a thickness of 24 mm, yield strength of 736 MPa, tensile strength of 895 MPa, elongation of 22.5%, and average impact value at -40 ℃ of 234 J.

[0052] Table 3. Submerged arc welding process parameters for Examples 1-7 and Comparative Examples 1-3 .

[0053] During the welding process, the surface quality of the welding wires in the examples and comparative examples was observed. The surface quality of the welds in Example 1 and Comparative Example 1 is shown in the figure below. Figure 1 (a1) and Figure 1 (b1). The weld bead produced using the welding wire of this embodiment is straight and smooth, while the weld bead produced using the welding wire of the comparative example has obvious deep grooves, a curved weld bead, and a rough surface, indicating poor fluidity of the molten pool, incomplete spreading, and obvious slag inclusions. After welding, the welds of the embodiment and the comparative example were subjected to radiographic testing, and the results are shown in the figures below. Figure 1 (a2) and Figure 1 (b2). Radiographic testing results showed that the weld seam welded with the comparative welding wire had cracks along the weld seam direction and large-sized pores, while the weld seam of the embodiment had no obvious defects. In addition, macroscopic cross-sections of the joints in the defect-free areas of the embodiments and comparative examples were taken, and the weld composition was detected. The results are shown in Table 4.

[0054] Table 4 Chemical composition (wt.%, balance Fe) of the weld metal after welding with submerged arc welding wires of Examples 1-7 and Comparative Examples 1-3 .

[0055] After the composition analysis was completed, the macroscopic cross-section of the joint was polished with 100x~1500x sandpaper. The inclusions were observed and photographed under a metallographic microscope. The inclusion morphology of Example 2 and Comparative Example 2 is shown in [reference needed]. Figure 2 (a) and Figure 2 (b) In the examples, the inclusions are more dispersed and refined, while in the comparative examples, the inclusions are larger and more irregular, resulting in weaker adhesion to the matrix. A statistical analysis of inclusions in the 1 mm² region of the examples and comparative examples was conducted, and the results are shown in Table 5. In the examples, the inclusion size larger than 1 μm in the 1 mm² region was no more than 7.5%, indicating smaller inclusions that effectively reduced stress concentration near the inclusions and improved adhesion to the matrix. In the comparative examples, the inclusion size larger than 1 μm in the 1 mm² region exceeded 17%.

[0056] Table 5. Size distribution of inclusions in submerged arc welds of Examples 1-7 and Comparative Examples 1-3 .

[0057] The macroscopic cross-sections of Examples 1-7 and Comparative Examples 1-3 were etched with 4% nitric acid alcohol. The microstructure of the columnar grain region and the heat-affected zone of the submerged arc weld was observed under a metallographic microscope. The experimental results are shown in [Figure number missing]. Figure 3 The results show that in the columnar crystal region of the weld, the weld of this embodiment has no large-sized blocky ferrite precipitated along the grain boundaries, and the microstructure is relatively uniform, mainly composed of acicular ferrite and granular bainite. In contrast, the columnar crystal region of the weld in the comparative example has large-sized blocky ferrite, and the acicular ferrite and granular bainite in the microstructure are coarse. The heat-affected zone of the weld bead refers to the area of ​​the heat-affected zone of the previous weld bead when the next weld bead fills the weld bead. It has undergone a reheating and cooling process. Compared with the embodiment, the heat-affected zone of the weld bead in the comparative example is mainly composed of equiaxed blocky ferrite, while the embodiment still has a large amount of acicular ferrite, and the blocky ferrite formed is also relatively fine.

[0058] Sampling was conducted on qualified weld metal samples from the examples and comparative examples to test the mechanical properties of the weld metal. Tensile property sampling and testing of the weld metal were performed according to GB / T 228.1 standard, while impact sampling and testing were performed according to GB / T 2650 standard. Three impact samples were taken from each sample to reduce error. The statistical results of the mechanical property tests are shown in Table 6. The results indicate that the weld metal from the welding wire in this example achieves both good strength and toughness. However, the weld metal from the comparative example exhibits insufficient strength or toughness.

[0059] Table 6. Mechanical property test results of weld metals after submerged arc welding wire in Examples 1-7 and Comparative Examples 1-3 .

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A submerged arc welding wire for coal mine hydraulic supports that combines high strength and toughness in the weld, characterized in that, The chemical composition of the submerged arc welding wire, by mass percentage, includes: C: 0.09~0.15, Si: 0.05~0.10, Mn: 1.81~2.30, P≤0.010, S≤0.005, Cr: 0.20~0.45, Ni: 2.30~2.49, Cu: 0~0.09, Mo: 0.51~0.90, Ti≤0.020, Ca: 0.008~0.014, V≤0.025, Zr≤0.015, O≤0.004, N≤0.006, balance being Fe and other unavoidable impurities. Among them, the five harmful elements Pb+Sn+As+Sb+Bi≤0.010; The chemical composition of the submerged arc welding wire satisfies 0.01 ≤ Sp ≤ 0.11, where, Sp=(9V+3Ti) / (1.5Si+Mn+2Ti+5Zr+7Ca); The chemical composition of the submerged arc welding wire satisfies 810 ≤ Rm ≤ 910, wherein, Rm=9.8×(36+61.32[C]+4.8[Si]+6.9[Mn]+5.5[Cr]+5.1[Ni]+11.03[Cu]+19.6[Mo]+41.6[Ti+Ca+V+Zr]); The submerged arc welding wire is used with a basicity of 2.0 ≤ B. ⅡW With sintered flux ≤2.2, under process conditions of 20~40 kJ / cm heat input, the weld metal yield strength is ≥700 MPa, tensile strength is between 810~910 MPa, elongation is ≥22%, and low-temperature impact toughness at -40℃ is ≥100 J.

2. The submerged arc welding wire according to claim 1, characterized in that, The chemical composition of the submerged arc welding wire contains two or three of the trace elements Ti, Ca, V, and Zr.

3. The submerged arc welding wire according to claim 1, characterized in that, 1mm in weld metal 2 The proportion of inclusions larger than 1 micrometer in the region shall not exceed 10%, and the proportion of acicular ferrite in the columnar crystal region of the weld shall not be less than 75%.

4. A method for preparing submerged arc welding wire for coal mine hydraulic supports that combines high strength and toughness of the weld, based on the submerged arc welding wire according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Preparation of wire rod for welding wire: Welding wire steel is smelted according to the chemical composition and proportion of submerged arc welding wire, and a casting billet with the required composition is prepared; then it is forged at 1000~1100 ℃, held at 1100~1200 ℃ for 2 h, descaled at 1020~1050 ℃, fine rolled at 860~920 ℃, and reduced in diameter at 780~800 ℃ to prepare wire rod for submerged arc welding wire with a diameter φ of 6.5 mm; (2) Preparation of welding wire by wire rod drawing: φ6.5 mm wire rod is reduced in diameter on the welding wire production line to obtain φ4.0 mm submerged arc welding wire, without annealing treatment in the intermediate process; (3) Copper plating of welding wire: Copper is uniformly plated on the surface of submerged arc welding wire using a chemical method to obtain finished submerged arc welding wire.

5. The preparation method according to claim 4, characterized in that, A φ6.5 mm wire rod is reduced in diameter three times to obtain a φ4.0 mm submerged arc welding wire. The diameters after the three reductions are φ5.5 mm, φ4.8 mm and φ4.0 mm, respectively.

6. The preparation method according to claim 4, characterized in that, The thickness of the copper plating is 0.15 to 0.18 micrometers.

Images