Welding process and application of low-temperature steel

Abstract

The application discloses a welding process of low-temperature steel, which adopts welding wire with nickel content greater than or equal to 1 wt% to weld the low-temperature steel, and controls the interlayer temperature of the welding process to be less than or equal to 200 DEG C. The welding wire with the nickel content of 1 wt% is adopted to weld, so that the impact toughness of the low-temperature steel weld in a low-temperature environment of-50 DEG C can be met. Meanwhile, the interlayer temperature of the welding process is controlled to be less than or equal to 200 DEG C, so that the impact absorption energy of the heat affected zone is improved, and the low-temperature impact resistance of the low-temperature steel welding is improved. Moreover, the welding current, the welding speed and the welding heat input energy are balanced, so that the low-temperature welding with good low-temperature impact toughness and high production efficiency is realized. The welding quality is improved, and the welding manufacturing cycle is shortened.

Description

Technical Field

[0001] This invention relates to the field of welding, and specifically to a welding process and application of low-temperature steel. Background Technology

[0002] With the accelerating pace of work and increasing work pressure, mining machinery still needs to operate continuously in environments as cold as -50°C. Ore blasting and loading / unloading subject the machinery to significant impact loads. Therefore, the structural components of mining machinery need to have excellent low-temperature impact resistance, especially the weld joints, which are prone to impact fracture in low-temperature environments. Low-temperature steel (alloy steel suitable for applications below -20°C) and low-temperature welding wire are sensitive to welding heat input. Excessive welding heat input significantly reduces the low-temperature impact toughness of the heat-affected zone and weld zone of the weld joint. Insufficient welding heat input results in low welding efficiency, which affects production progress. Therefore, developing a low-temperature steel welding process that provides good low-temperature impact toughness for weld joints while ensuring production efficiency is of great significance for improving welding quality, shortening welding cycles, and ensuring the safe operation of equipment.

[0003] Chinese invention patent application CN112176254A discloses a high-impact toughness cryogenic steel and its welding process, using welding wire with a nickel content of 3.25-3.75 wt%. This method ensures good impact toughness in the weld metal while maintaining its strength and ductility. However, it requires high-nickel content welding wire, resulting in higher costs. Chinese invention patent application CN117506084A discloses a welding method for thick cryogenic container steel. This method reduces the hardening tendency of the joint through preheating and uses a small welding heat input to avoid the formation of coarse microstructures in the weld and heat-affected zone, which would severely reduce its impact toughness. However, preheating is still required before welding, making the process cumbersome. Summary of the Invention

[0004] In order to develop a low-temperature steel welding process with good low-temperature impact toughness of welded joints and to ensure production efficiency, the first aspect of the present invention provides a low-temperature steel welding process, which uses welding wire with a nickel content of ≥1wt% to weld the low-temperature steel, and controls the interpass temperature of the weld to ≤200℃ during the welding process.

[0005] In one embodiment, the carbon equivalent of the welding wire is ≤0.39wt%.

[0006] In one embodiment, the chemical composition of the welding wire includes: C≤0.07wt%, Si 0.5-0.55wt%, Mn≤1.12wt%, S≤0.004wt%, P≤0.01wt%, Cr≤0.03wt%, Ni 1-2.5wt%, Mo≤0.01wt%, Cu≤0.14wt%.

[0007] The chemical composition of the welding wire includes: C≤0.07wt%, Si 0.5-0.55wt%, Mn≤1.12wt%, S≤0.004wt%, P≤0.01wt%, Cr≤0.03wt%, Ni 1-1.5wt%, Mo≤0.01wt%, Cu≤0.14wt%.

[0008] In one embodiment, the chemical composition of the welding wire includes: C 0.07wt%, Si 0.52wt%, Mn 1.12wt%, S 0.004wt%, P 0.01wt%, Cr 0.03wt%, Ni 1wt%, Mo 0.01wt%, Cu 0.14wt%, and Fe supplemented to 100%.

[0009] In one embodiment, the nickel content of the welding wire is 1 wt%.

[0010] The inventors discovered during experiments that using welding wire with a nickel content of 1 wt% can meet the impact toughness requirements of low-temperature steel welds in environments as cold as -50℃. This is because the 1 wt% nickel content promotes the formation of granular bainite phases from acicular ferrite. Furthermore, controlling the interpass temperature to ≤200℃ prevents excessively high weld pool temperatures and excessive ferrite precipitation during cooling. This application controls the interpass temperature to ≤200℃, preventing overheating during the austenite transformation of the heat-affected zone from a fine base metal structure. The austenite grains are small, and during subsequent cooling, this part of the structure undergoes a phase transformation to lath bainite. The size of the original austenite grains determines the impact absorption energy of the coarse-grained weld region; the larger the original austenite grains, the lower the impact absorption energy in the heat-affected zone. This application controls the interpass temperature, increasing the impact absorption energy of the heat-affected zone and improving impact resistance.

[0011] As one implementation, the welding process is followed by a stress-relief annealing process, with an annealing temperature of 500-550℃ and an annealing time of 2-5 hours.

[0012] As one implementation, the welding process is followed by a stress-relief annealing process, with an annealing temperature of 530°C and an annealing time of 3 hours.

[0013] In one embodiment, the low-temperature steel is Q355E, with the following mass percentages: C 0.13wt%, Si 0.15wt%, Mn 1.3wt%, S 0.003wt%, P 0.01wt%, Cr 0.04wt%, Ni 0.01wt%, Mo <0.01wt%, Cu 0.01wt%, Ti 0.02wt%, Al 0.032wt%, Nb 0.02wt%, impurities 0.36wt%, and Fe supplemented to 100%.

[0014] In one embodiment, the welding includes at least one of manual arc welding or automated arc welding, wherein the welding current of the manual arc welding is 260-300A.

[0015] In one embodiment, the welding voltage for manual arc welding is 27-31V.

[0016] In one implementation, the welding heat input energy of the manual arc welding is 0.6-1.7 kJ / mm.

[0017] In one implementation, the welding heat input energy of the manual arc welding is 0.69-1.6 kJ / mm.

[0018] In one embodiment, the welding speed of the manual arc welding is 300-450 mm / min.

[0019] In one implementation, the automated arc welding process involves 8-10 layers and 11-15 passes.

[0020] In one implementation, the automated arc welding process involves 9-10 layers and 12-14 passes.

[0021] In one implementation, the automated arc welding uses a welding current of 320-360A and a welding voltage of 30-38V.

[0022] In one implementation, the automated arc welding uses a welding current of 320-340A and a welding voltage of 30-32V.

[0023] In one implementation, the automated arc welding has a welding heat input energy of 1.28-1.81 kJ / mm and a welding speed of 360-420 mm / min.

[0024] In one implementation, the automated arc welding process involves 8-10 layers or 10-13 passes.

[0025] In one implementation, the automated arc welding has 8 layers and 10 passes.

[0026] In one embodiment, the diameter of the welding wire used in the manual arc welding is 1.0-1.4 mm; the diameter of the welding wire used in the automated arc welding is 1.4-1.6 mm.

[0027] In one embodiment, the diameter of the welding wire in the manual arc welding is 1.2 mm; the diameter of the welding wire in the automated arc welding is 1.6 mm.

[0028] The second aspect of the present invention provides an application of a welding process for low-temperature steel, which is applied to the plate welding of structural components for mining machinery. The weld has a tensile strength ≥470MPa, a yield strength ≥355MPa, a low-temperature impact absorption energy of -50℃ ≥47J, and a hardness HV10 ≤380.

[0029] In one embodiment, the plate thickness of the structural component is 10-100mm.

[0030] In one embodiment, the plate thickness of the structural component is 20-50mm.

[0031] In one embodiment, the plate thickness of the structural component is 30 mm.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The welding process of the low-temperature steel described in this invention uses welding wire with a nickel content of 1wt% to meet the impact toughness of the low-temperature steel weld in a low-temperature environment of -50℃.

[0034] (2) The welding process of the low-temperature steel described in this invention uses welding wire with a nickel content of 1wt% and controls the interpass temperature to ≤200℃, which improves the impact absorption energy of the heat-affected zone and improves the low-temperature impact resistance of the low-temperature steel welding.

[0035] (3) The welding process of the low-temperature steel described in this invention controls the interlayer temperature of the welding layer to ≤200℃ and balances the welding current, voltage and welding heat input energy, thereby achieving low-temperature welding with good impact toughness and high production efficiency.

[0036] (4) The welding process of the low-temperature steel described in this invention does not require preheating before welding, the welding process is simple, and the welding quality is high and the welding manufacturing cycle is short.

[0037] (5) The welding process of the low-temperature steel described in this invention uses welding wire with a nickel content of 1wt%, which has low welding wire cost and controls the interlayer temperature of welding to ≤200℃, making temperature control easy and manufacturing energy consumption low. Attached Figure Description

[0038] Figure 1 This is a microstructure diagram of the weld structure in Example 1;

[0039] Figure 2 This is a microstructure diagram of the weld structure in Example 2;

[0040] Figure 3 This is a microstructure diagram of the weld structure in Example 3;

[0041] Figure 4This is a microstructure diagram of the weld structure in Example 4;

[0042] Figure 5 This is a microstructure diagram of the weld structure in Example 5;

[0043] Figure 1-5 In China: 1. Acicular ferrite; 2. Proprecipitated ferrite; 3. Granular bainite; 4. Pearlite.

[0044] Figure 6 This is a microstructure diagram of the coarse-grained region of the heat-affected zone in Example 1;

[0045] Figure 7 This is a microstructure diagram of the coarse-grained region of the heat-affected zone in Example 2;

[0046] Figure 8 This is a microstructure diagram of the coarse-grained region of the heat-affected zone in Example 3;

[0047] Figure 9 This is a microstructure diagram of the coarse-grained region of the heat-affected zone in Example 4;

[0048] Figure 10 This is a microstructure diagram of the coarse-grained region of the heat-affected zone in Example 5. Detailed Implementation

[0049] Example 1

[0050] A welding process for low-temperature steel is described, in which welding wire with a nickel content ≥1wt% is used to weld the low-temperature steel. The welding parameters and post-weld treatment are shown in Table 1 below.

[0051] Table 1

[0052]

[0053]

[0054] The post-weld stress-relief annealing process has an annealing temperature of 530℃ and an annealing time of 3 hours.

[0055] The low-temperature steel is Q355E, with the following mass percentages: C 0.13wt%, Si 0.15wt%, Mn 1.3wt%, S 0.003wt%, P 0.01wt%, Cr 0.04wt%, Ni 0.01wt%, Mo <0.01wt%, Cu 0.01wt%, Ti 0.02wt%, Al 0.032wt%, Nb 0.02wt%, and impurities 0.36wt%.

[0056] The mechanical properties of low-temperature steel Q355E are as follows: tensile strength is 525MPa, yield strength is 404MPa, low-temperature impact absorption energy at -50℃ is 168J, and elongation is 32%.

[0057] The chemical composition of the welding wire includes: C 0.07wt%, Si 0.52wt%, Mn 1.12wt%, S 0.004wt%, P 0.01wt%, Cr 0.03wt%, Ni 1wt%, Mo 0.01wt%, and Cu 0.14wt%.

[0058] The carbon equivalent of the welding wire is 0.341 wt%.

[0059] Performance testing

[0060] 1. Tensile strength: The tensile strength was tested according to the national standard test method GB / T 228.1 Metallic materials - Tensile testing - Part 1: Test method at room temperature.

[0061] 2. Weld impact absorption energy KV2: The impact resistance of the weld was tested according to the national standard test method GB / T 229 Metallic Materials Charpy Pendulum Impact Test Method.

[0062] 3. Impact absorption energy KV2 of the heat-affected zone: The impact resistance of the heat-affected zone of the weld was tested according to the national standard test method GB / T 229 Metallic Materials Charpy Pendulum Impact Test Method.

[0063] 4. Weld hardness: The weld hardness shall be tested in accordance with the national standard test method GB / T 231.1 Metallic materials Brinell hardness test - Part 1 Test method.

[0064] The performance test results are shown in Table 2.

[0065] Table 2

[0066]

[0067]

[0068] The test results show that: the heat input of Examples 1 and 4 was too large and the interpass temperature was not controlled, resulting in the weld pool temperature being too high. During the cooling process, more proferrite precipitates in the weld. The heat input of Example 4 was too high, and the proferrite precipitates grew more severely, resulting in a significant decrease in the impact performance of the weld zone.

[0069] In Examples 1 and 4, the coarse-grained region of the heat-affected zone (HAZ) of the base metal experienced severe overheating during the austenite transformation from a fine base metal structure due to high heat input and uncontrolled interlayer temperature. This resulted in the coarsest austenite grains in this region. During subsequent cooling, this area underwent a phase transformation into lath bainite. The size of the original austenite grains determines the impact energy absorbed by the coarse-grained weld microstructure; the larger the original austenite grains, the lower the heat-affected zone impact energy absorbed.

[0070] Comparing Examples 2 and 3, post-weld stress-relief annealing did not significantly alter the microstructure and had little impact on the strength, hardness, and impact toughness of the weld.

[0071] Comparing Example 5 and Example 2 (manual arc welding), Example 5 used 1.6mm welding wire (automated arc welding, which is more efficient), while Example 1 used 1.2mm welding wire. Although the current in Example 5 was 60A higher than that in Example 2, resulting in a significant improvement in welding efficiency, Example 5 also controlled the interpass temperature and welding heat input. Therefore, the final weld zone and heat-affected zone coarse grain structure were better, and the impact toughness was also higher.

[0072] Figure 1 The middle part consists of coarse proprecipitated ferrite, a large amount of granular bainite, and a small amount of acicular ferrite. Figure 2 The middle part consists of a small amount of proprecipitated ferrite, a large amount of granular bainite, and a small amount of acicular ferrite. Figure 3 The middle part consists of a small amount of proprecipitated ferrite, a large amount of granular bainite, and a small amount of acicular ferrite. Figure 4 The middle part consists of a large amount of coarse proprecipitated ferrite + coarse acicular ferrite + pearlite; Figure 5 The middle part consists of a small amount of proprecipitated ferrite, a large amount of granular bainite, and a small amount of acicular ferrite.

[0073] Figure 6 It includes lath bainite, and the original austenite grains are coarse. Figure 7 The middle part consists of a large amount of lath bainite and a small amount of granular bainite, and the original austenite grains are fine. Figure 8 The middle part is lath-shaped bainite, and the original austenite grains are coarse; Figure 9 The middle part is lath-shaped bainite, and the original austenite grains are fine; Figure 10 The middle part is lath-shaped bainite, and the original austenite grains are fine.

Claims

1. A welding process for low-temperature steel, characterized in that, Welding is performed with welding wire containing ≥1wt% nickel to low-temperature steel, and the interpass temperature is controlled to ≤200℃ during the welding process; The carbon equivalent of the welding wire is ≤0.39wt%; the chemical composition of the welding wire includes: C≤0.07wt%, Si 0.5-0.55wt%, Mn≤1.12wt%, S≤0.004wt%, P≤0.01wt%, Cr≤0.03wt%, Ni 1-2.5wt%, Mo≤0.01wt%, Cu≤0.14wt%.

2. The welding process for low-temperature steel according to claim 1, characterized in that, The welding process is followed by a stress-relief annealing process, with an annealing temperature of 500-550℃ and an annealing time of 2-5 hours.

3. The welding process for low-temperature steel according to claim 1, characterized in that, The welding includes at least one of manual arc welding or automated arc welding, wherein the welding current of the manual arc welding is 260-300A.

4. The welding process for low-temperature steel according to claim 3, characterized in that, The manual arc welding voltage is 27-31V, and the welding speed is 300-450mm / min.

5. The welding process for low-temperature steel according to claim 3, characterized in that, The welding heat input energy for the manual electric arc welding is 0.6-1.7 kJ / mm.

6. The welding process for low-temperature steel according to claim 3, characterized in that, The automated arc welding has a welding current of 320-360A, a welding voltage of 30-38V, a welding heat input energy of 1.28-1.81kJ / mm, and a welding speed of 360-420mm / min.

7. The welding process for low-temperature steel according to claim 3, characterized in that, The diameter of the welding wire used in the manual arc welding is 1.0-1.4 mm; the diameter of the welding wire used in the automated arc welding is 1.4-1.6 mm.

8. An application of a welding process for low-temperature steel according to any one of claims 1-7, characterized in that, When used in plate welding of structural components for mining machinery, the weld tensile strength is ≥470MPa, the weld yield strength is ≥355MPa, the weld low-temperature impact absorption energy at -50℃ is ≥47J, and the weld hardness HV10≤380.

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