Annealing-free wire rod for 76-mpa-grade high-strength welding wire and preparation method therefor

Abstract

An annealing-free wire rod for a 76-MPa-grade high-strength welding wire. The wire rod comprises the following chemical components in percentage by mass: 0.05-0.10 of C, 0.50-0.80 of Si, 1.60-1.80 of Mn, less than or equal to 0.010 of P, less than or equal to 0.010 of S, 0.15-0.35 of Cr, 0.70-1.10 of Ni, less than or equal to 0.15 of Cu, 0.20-0.40 of Mo, 0.08-0.15 of Ti, 0.002-0.005 of B, less than or equal to 0.02 of V, less than or equal to 0.02 of Nb, less than or equal to 0.02 of Zr, less than or equal to 0.10 of Al, less than or equal to 0.007 of As, and the balance of Fe and inevitable impurities. Further provided is a method for preparing the annealing-free wire rod for a 76-MPa-grade high-strength welding wire. In the wire rod, the content of acicular ferrite is increased, proeutectoid ferrite is reduced, and an effect of refining ferrite grains is achieved, thereby enhancing the strength and toughness of a weld seam. The method achieves continuous drawing of a welding wire without annealing, thereby reducing the costs and energy consumption of the annealing, shortening the processing cycle, and increasing the economic benefits.

Description

A 76kg-grade high-strength welding wire rod that does not require annealing and its preparation method Technical Field

[0001] This invention belongs to the field of special steel production technology, and in particular relates to a 76kg high-strength gas-shielded welding wire rod that does not require annealing and drawing, and its preparation method. Background Technology

[0002] my country's welding materials products are mainly concentrated in the low-to-mid-range welding wire. Among the sub-categories of welding materials, solid welding wire has exceeded welding rods, reaching about 45%, welding rods account for 35.7%, flux-cored welding wire accounts for 9.1%, and submerged arc welding materials account for 9.5%. Among solid welding wire, alloy welding wire accounts for 7%, with high-strength welding wire being the dominant type.

[0003] High-strength welding wire generally uses φ5.5mm wire rod raw material, which is drawn to a minimum of φ1.2mm, with a compression ratio of over 95%. Generally, the wire rod raw material needs to be annealed or intermediate annealed to meet the requirements of wire rod drawing. Annealing costs are high and the production cycle is long.

[0004] In production control, due to the influence of alloys on microstructure transformation, hard phase bainite or Mao island structures can be generated under slow cooling conditions. Without annealing, the easily deformable matrix structure plastically flows around the hard phase structure, generating significant tension. This causes the interface between the matrix and the hard phase structure to break or the brittle hard structure itself to fracture, forming microcracks. As drawing progresses, these microcracks continuously accumulate and grow under tensile stress, eventually resulting in a cup-cone fracture. During the drawing process of 76kg high-strength welding wire rods, the high tensile strength and deformation resistance of the rods place even more stringent requirements on the drawing dies and lubrication conditions. If surface cracks occur during the drawing process of high-strength welding wire rods due to poor local lubrication or angle issues in the dies, the cracks will further propagate, resulting in a chamfered fracture. The initial iron oxide scale on the rod is deeply embedded with an irregular shape. Under high-speed, integrated drawing, accompanied by severe work hardening, this also forms a crack initiation point for a chamfered fracture. During the drawing process of wire rod, improper production technology can also cause breakage. Therefore, the formulation of the drawing process needs to fully consider the reasonable configuration of various process parameters.

[0005] Summary of the Invention

[0006] The purpose of this invention is to solve the problems of high annealing cost, long production cycle and poor performance and quality of existing high-strength welding wires. It provides a 76kg-grade high-strength welding wire rod that does not require annealing, which can realize continuous drawing of welding wire without annealing, save annealing cost and energy consumption, shorten the processing cycle and improve economic efficiency.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A 76kg-grade high-strength welding wire rod that does not require annealing has the following chemical composition by mass percentage: C: 0.05-0.10, Si: 0.50-0.80, Mn: 1.60-1.80, P≤0.010, S≤0.010, Cr: 0.15-0.35, Ni: 0.70-1.10, Cu≤0.15, Mo: 0.20-0.40, Ti: 0.08-0.15, B: 0.002-0.005, V≤0.02, Nb≤0.02, Zr≤0.02, Al≤0.10, As≤0.007, with the balance being Fe and unavoidable impurities.

[0009] Furthermore, the wire rod has a tensile strength ≤950MPa and a reduction of area ≥58%.

[0010] Furthermore, the metallographic structure of the wire rod is mainly composed of granular bainite.

[0011] Furthermore, the local iron oxide scale embedding depth of the wire rod is ≤15um.

[0012] Furthermore, the welding wire produced by drawing the wire rod has a tensile strength of ≥760MPa, a yield strength of ≥660MPa, an elongation of ≥15%, and an AKV impact value of ≥100J at -20℃.

[0013] The functions and mechanisms of each component in this invention are as follows:

[0014] C: C is one of the strongest alloying elements in terms of strengthening effect. As the C content increases, higher tensile strength and hardness can be obtained, but plasticity and toughness will decrease significantly, worsening weldability. To obtain good impact toughness, the C content should be controlled between 0.05% and 0.10%.

[0015] Si: As one of the main alloying elements in welds, Si has a strong deoxidizing effect. Within a certain range, it can significantly improve the strength and toughness of steel. At the same time, it transitions into the weld to reduce the oxidation of Cr and Ni, improve the fluidity of the molten pool, and reduce weld inclusions. However, Si also forms a Si-rich oxide layer on the surface of the wire rod, causing the iron oxide scale to become sticky. To ensure the metallurgical reaction in the weld, the Si content is controlled at 0.50–0.80%.

[0016] Mn: Mn is also a major deoxidizer, which reduces the oxygen content of weld metal and increases the strength and crack resistance of weld metal. Mn also has a desulfurization effect. However, as the Mn content increases, it will cause hard phase in the microstructure due to segregation. Therefore, Mn should be controlled at 1.60-1.80%.

[0017] Cr: The addition of Cr can improve the strength of the weld, but when its content is high, it will drastically reduce the low-temperature toughness and molten pool fluidity of the weld, which is not conducive to the removal of gas and inclusions in the weld and affects the metallurgical quality of the weld. The addition of Cr will cause the cooling CCT curve of hot-rolled wire rod to shift, slow down the phase transformation rate, and be unfavorable to microstructure control. Therefore, Cr should be controlled at 0.15-0.35%.

[0018] Mo: Appropriate addition of Mo can expand the bainite region, increase the content of acicular ferrite in the weld, and improve the strength and toughness of the weld. Therefore, the Mo content should be controlled at 0.20-0.40%.

[0019] S and P: S forms a low-melting-point eutectic with Fe, leading to hot brittleness, reducing the plasticity and impact toughness of the weld, and worsening atmospheric corrosion resistance. P has a strong segregation effect; excessive P content easily causes hot cracking. Phosphates themselves are hard and brittle, easily causing cold brittleness in steel, reducing the plasticity and toughness of the steel. Therefore, P and S should be controlled at ≤0.010%.

[0020] Ni: Ni can refine ferrite grains and improve the low-temperature impact toughness of steel. At the same time, the addition of Ni can also refine the rust layer crystals, improving the steel's resistance to atmospheric corrosion. Therefore, the Ni content should be controlled at 0.70–1.10%.

[0021] Ti: In oxide metallurgy, harmful inclusions in steel are treated to make them more beneficial, reducing their size and dispersing them evenly. This has a beneficial effect on the microstructure and grain changes during processing (such as welding). Welding wire steel usually adds Ti to achieve the effect of oxide metallurgy. In this welding wire, Ti is controlled at 0.08-0.15%.

[0022] The welding wire of this invention incorporates Si, Mn, Cr, Ni, Mo, and microalloying elements in specific proportions. To control the segregation of these five harmful elements at grain boundaries during the welding thermal cycle, which could lead to increased brittleness in the heat-affected zone, the content of As is controlled to be ≤0.007%. Through precise control of the composition range, the mechanism of action of impurity elements, the microstructure and properties of the deposited metal, and the strengthening mechanism of the deposited metal, the performance of the weld metal is optimally optimized.

[0023] To further achieve the objectives of this invention, a method for preparing 76kg-grade high-strength welding wire rod without annealing is also provided, comprising a converter, an LF furnace, continuous casting, and rolling of the wire rod, specifically:

[0024] (1) The charging sequence during the converter tapping process is deoxidizer → alloy → modified refining slag → lime. The bottom blowing of the converter adopts full-process argon blowing. During the converter tapping process, silicon-manganese alloy, lime 5.5kg / t, and modified refining slag 3.5kg / t are added.

[0025] (2) Add lime to the LF furnace in small amounts according to the slag condition and sulfur content. The target basicity is controlled below 3.0. After the white slag is formed, alloying of Ti and B is carried out. The static stirring time is ≥10min.

[0026] (3) The superheat of the 150*150mm billet is 24℃, the casting speed is 2.1m / min, the water content adopts the weak cooling mode, and the continuous casting adopts protective casting and argon pouring operation.

[0027] (4) The wire rod is rolled in a walking beam furnace with a preheating section temperature of 600℃, heating section I temperature of 900℃, heating section II temperature of 1010℃, soaking section temperature of 1100℃, initial rolling temperature of 1030℃, final rolling temperature of 860℃, and wire drawing temperature of 860℃. After delayed cooling in the Stellmore line, a wire rod with a specification of φ5.5mm is obtained.

[0028] Furthermore, in step (1), the converter tapping conditions are: the tapping C content is 0.05%, the tapping P content is 0.006%, and the tapping temperature is 1635℃.

[0029] Furthermore, in step (4), the tensile strength of the wire rod is ≤950MPa, the reduction of area is ≥58%, the metallographic structure of the wire rod is mainly granular bainite, the wire rod is rolled from a large R-angle billet, and the local iron oxide scale embedding depth of the wire rod is controlled to be ≤15um.

[0030] Compared with the prior art, the advantages of the technical solution of the present invention are as follows:

[0031] (1) The high-strength welding wire rod of the present invention achieves anneal-free drawing on an integrated continuous drawing production line, saving annealing costs and energy consumption while shortening the processing cycle. The wire rod made of this steel material has a tensile strength ≤950MPa and a section reduction rate ≥58%.

[0032] (2) The high-strength welding wire rod of the present invention has optimized the composition design, which is conducive to increasing the content of acicular ferrite, reducing proeutectoid ferrite, and refining the ferrite grains, thereby improving the strength and toughness of the weld.

[0033] (3) The high-strength welding wire of the present invention has a reasonable composition ratio. After processing, the welding wire has good fluidity of the molten pool during welding, and the weld has excellent metallurgical quality. Its deposited metal has a tensile strength ≥760MPa, yield strength ≥660MPa, elongation ≥15%, and AKV impact value ≥100J at -20℃.

[0034] (4) The production process of high-strength welding wire rod of the present invention is solidified, and it is easy to realize its smelting, rolling and other processes. With reasonable composition design, billet heating system and rolling system, it can be promoted on a large scale in the industry. Attached Figure Description

[0035] Figure 1 is a metallographic diagram of the 76kg-grade high-strength welding wire rod of the present invention that does not require annealing. Detailed Implementation

[0036] Example 1

[0037] To make the present invention clearer, the following description, in conjunction with the accompanying drawings, further illustrates a non-annealing 76kg high-strength welding wire rod and its preparation method. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0038] This embodiment provides a 76kg-grade high-strength welding wire rod that does not require annealing. Its chemical composition, by mass percentage, includes: C: 0.05–0.10, Si: 0.50–0.80, Mn: 1.60–1.80, P≤0.010, S≤0.010, Cr: 0.15–0.35, Ni: 0.70–1.10, Cu≤0.15, Mo: 0.20–0.40, Ti: 0.08–0.15, B: 0.002–0.005, V≤0.02, Nb≤0.02, Zr≤0.02, Al≤0.10, As≤0.007, with the balance being Fe and unavoidable impurities.

[0039] During preparation, the smelting method involves a converter + LF furnace + continuous casting of 150*150mm billets + rolling of wire rods. The specific operations are as follows:

[0040] (1) Converter tapping conditions: C content in tapped steel is 0.05%, P content in tapped steel is 0.006%, and tapping temperature is 1635℃. The charging sequence during tapping is: deoxidizer → alloy → modified refining slag → lime. Argon blowing is used throughout the bottom blowing process of the converter. During the tapping process, silicon-manganese alloy, lime 5.5kg / t, and modified refining slag 3.5kg / t are added.

[0041] (2) In the LF furnace, lime is added in small amounts according to the slag condition and sulfur content. The target basicity is controlled below 3.0. After white slag, Ti and B are alloyed. The static stirring time is ≥10min. The superheat of the 150*150mm billet is 24℃, the casting speed is 2.1m / min, the specific water volume adopts the weak cooling mode, the continuous casting adopts protective casting, and the argon pouring operation is started.

[0042] (3) Rolled wire rod: Walking beam furnace, preheating section temperature 600℃, heating section I temperature 900℃, heating section II temperature 1010℃, soaking section temperature 1100℃, initial rolling temperature 1030℃, final rolling temperature 860℃, wire drawing temperature 860℃, after delayed cooling on the Stellmore line, φ5.5mm wire rod is obtained. The tensile strength of the wire rod is ≤950MPa, and the reduction of area is ≥58%. The specific mechanical properties are shown in the table below:

[0043] In this embodiment, the metallographic structure of the wire rod is mainly granular bainite, as shown in Figure 1. It is rolled from a large radius billet, and the local iron oxide scale embedding depth of the wire rod is controlled to be ≤15um. The welding wire drawn from the wire rod has a tensile strength of ≥760MPa, a yield strength of ≥660MPa, an elongation of ≥15%, and an AKV impact value of ≥100J at -20℃.

[0044] This invention enables anneal-free drawing of 76kg-grade high-strength welding wire rods, saving annealing costs and energy while shortening the processing cycle. Furthermore, the weld metal properties of the produced welding wire steel meet technical requirements. The wire rods made from this steel material have a tensile strength ≤950MPa, a reduction of area ≥58%, a microstructure dominated by granular bainite, and a localized iron oxide scale embedding depth ≤15µm. The welding wires drawn from these wire rods exhibit a weld metal tensile strength ≥760MPa, a yield strength ≥660MPa, an elongation ≥15%, and an AKV impact value ≥100J at -20℃.

[0045] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A 76kg-grade high-strength welding wire rod that does not require annealing, characterized in that: Its chemical composition, by mass percentage, includes C: 0.05–0.10, Si: 0.50–0.80, Mn: 1.60–1.80, P≤0.010, S≤0.010, Cr: 0.15–0.35, Ni: 0.70–1.10, Cu≤0.15, Mo: 0.20–0.40, Ti: 0.08–0.15, B: 0.002–0.005, V≤0.02, Nb≤0.02, Zr≤0.02, Al≤0.10, As≤0.007, with the balance being Fe and unavoidable impurities.

2. The 76kg-grade high-strength welding wire rod without annealing according to claim 1, characterized in that: The wire rod has a tensile strength ≤950MPa and a reduction of area ≥58%.

3. The 76kg-grade high-strength welding wire rod without annealing according to claim 1 or 2, characterized in that: The metallographic structure of the wire rod is mainly granular bainite.

4. The 76kg-grade high-strength welding wire rod without annealing according to claim 1 or 2, characterized in that: The local iron oxide scale embedding depth of the wire rod is ≤15um.

5. The 76kg-grade high-strength welding wire rod without annealing according to claim 1 or 2, characterized in that: The welding wire produced by drawing the wire rod has a tensile strength of ≥760MPa, a yield strength of ≥660MPa, an elongation of ≥15%, and an AKV impact value of ≥100J at -20℃.

6. A method for preparing 76kg-grade high-strength welding wire rod without annealing as described in claim 1, comprising a converter, an LF furnace, continuous casting, and rolling wire rod, characterized in that: (1) The charging sequence during the converter tapping process is deoxidizer → alloy → modified refining slag → lime. The bottom blowing of the converter adopts full-process argon blowing. During the converter tapping process, silicon-manganese alloy, lime 5.5kg / t, and modified refining slag 3.5kg / t are added. (2) Add lime to the LF furnace in small amounts according to the slag condition and sulfur content. The target basicity is controlled below 3.

0. After the white slag is formed, alloying of Ti and B is carried out. The static stirring time is ≥10min. (3) The superheat of the 150*150mm billet is 24℃, the casting speed is 2.1m / min, the water content adopts the weak cooling mode, and the continuous casting adopts protective casting and argon pouring operation. (4) The wire rod is rolled in a walking beam furnace with a preheating section temperature of 600℃, heating section I temperature of 900℃, heating section II temperature of 1010℃, soaking section temperature of 1100℃, initial rolling temperature of 1030℃, final rolling temperature of 860℃, and wire drawing temperature of 860℃. After delayed cooling in the Stellmore line, a wire rod with a specification of φ5.5mm is obtained.

7. The method for preparing the 76kg-grade high-strength welding wire rod without annealing according to claim 6, characterized in that: In step (1), the converter tapping conditions are: the tapping C content is 0.05%, the tapping P content is 0.006%, and the tapping temperature is 1635℃.

8. The method for preparing the 76kg-grade high-strength welding wire rod without annealing according to claim 6, characterized in that: In step (4), the tensile strength of the wire rod is ≤950MPa, the reduction of area is ≥58%, the metallographic structure of the wire rod is mainly granular bainite, and it is rolled from a large R-angle billet to control the local iron oxide scale embedding depth of the wire rod to ≤15um.

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