A welding process for a high-strength low-temperature impact steel according to european standard

Abstract

This invention discloses a welding process for European standard high-strength low-temperature impact steel. First, the carbon equivalent (Ceq) and cold cracking sensitivity coefficient (Pcm) are calculated based on the base metal composition. Based on the synergistic determination of these two factors: if Pcm ≤ 0.26% and 0.45% ≤ Ceq ≤ 0.60%, preheating ≥ 100℃; if Pcm > 0.26%, preheating ≥ 150℃; interpass temperature ≤ 250℃. Second, solid welding wire is supplied with 80% Ar + 20% carbon dioxide gas, and flux-cored welding wire is supplied with ≥ 99.9% carbon dioxide gas. Finally, "dual differentiation" heat input control is implemented according to the type of welding material and the welding position: solid welding wire horizontal welding 0.30–1.15 kJ / mm, vertical welding 1.23–3.68 kJ / mm; flux-cored welding wire horizontal welding 0.47–1.44 kJ / mm, vertical welding 1.28–2.58 kJ / mm. This process significantly reduces the sensitivity of joints to cold cracking through precise temperature control, optimized gas matching, and positional adaptability parameters. It ensures the excellent comprehensive performance of the welded joint at -40℃, with an impact energy KV2≥30 J, tensile strength Rm≥770 MPa, and hardness ≤450 HV10, providing a reliable guarantee for engineering applications.

Description

A welding process for European standard high-strength low-temperature impact steel Technical Field

[0001] This invention relates to the field of high-strength steel welding technology, and more specifically to a welding process for European standard high-strength low-temperature impact steel. Background Technology

[0002] S690QL steel, as a high-strength quenched and tempered steel specified in the European standard EN 10025-6, plays an important role in construction, bridges, ships, and machinery manufacturing due to its excellent mechanical properties and wide applicability. However, its high alloy content also brings severe welding challenges: high sensitivity to cold cracking, stringent requirements for low-temperature toughness (usually requiring an impact energy of ≥30J at -40℃), and difficulty in stabilizing performance during all-position welding.

[0003] In existing technologies, increasing the preheating temperature (usually ≥150℃) is commonly adopted to prevent cold cracking. While this "temperature-for-safety" approach controls cracking to some extent, it easily leads to coarse grains in the heat-affected zone, severely impairing the low-temperature toughness of the joint and creating a bottleneck of "strength meeting standards but insufficient toughness." Therefore, how to reduce the preheating temperature as much as possible while ensuring that cold cracking does not occur has become a key challenge in improving the overall performance of S690QL steel welded joints.

[0004] Furthermore, there is often a lack of systematic optimization in the matching of welding materials and shielding gases. For example, the most suitable welding parameters are not selected according to the type of welding wire (solid / flux-cored), which affects the transition of alloying elements and the stability of weld performance. In addition, few processes can provide a complete and refined set of heat input parameter windows for different plate thicknesses and welding positions, making it difficult to simultaneously meet the comprehensive requirements of high strength, high toughness and low crack sensitivity.

[0005] Therefore, developing a systematic welding process that can reliably prevent cold cracking at lower preheating temperatures while precisely controlling heat input under different operating conditions to ensure excellent low-temperature toughness has become a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0006] This invention provides a welding process for European standard high-strength low-temperature impact steel, which overcomes the defects in the existing S690QL steel welding process, such as the damage to toughness caused by high-temperature preheating and the instability of all-position welding quality due to coarse parameters. It can systematically take into account high strength, high and low temperature toughness, and low crack risk.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a welding process for European standard high-strength low-temperature impact steel, comprising the following steps:

[0008] (1) Calculate the carbon equivalent Ceq and cold cracking sensitivity coefficient Pcm based on the chemical composition of the base material S690QL;

[0009] (2) The minimum preheating temperature is determined based on the cold cracking sensitivity coefficient Pcm and carbon equivalent Ceq of the base material, where:

[0010] If Pcm ≤ 0.26% and 0.45% ≤ Ceq ≤ 0.60%, the minimum preheating temperature is 100℃; if Pcm > 0.26%, the minimum preheating temperature is 150℃; simultaneously, the maximum interpass temperature during welding should be controlled to ≤ 250℃; (3) Selection of welding materials and shielding gas: When using gas metal arc welding, solid welding wire is selected as the welding material, and flux-cored wire arc welding is used. When solid welding wire is selected, a mixture of carbon dioxide with a volume fraction of 20% and Ar with 80% is used as the shielding gas. When flux-cored wire is selected, carbon dioxide gas with a purity of not less than 99.9% is used as the shielding gas. (4) Welding operation: The welding position includes horizontal welding of PC and vertical welding of PF. The "dual differentiation" heat input control strategy is implemented according to the welding material type and welding position. Among them, when using solid welding wire, the heat input of the horizontal welding position is controlled at 0.30–1.15kJ / mm, and the heat input of the vertical welding position is controlled at 1.23–3.68kJ / mm. When using flux-cored wire, the heat input of the horizontal welding position is controlled at 0.47–1.44kJ / mm, and the heat input of the vertical welding position is controlled at 1.28–2.58kJ / mm.

[0011] Further, in step (1), the carbon equivalent Ceq and the cold cracking sensitivity coefficient Pcm are calculated according to the following formula:

[0012] Ceq=C+Mn / 6+(Cr+V+Mo) / 5+(Cu+Ni) / 15,

[0013] Pcm=C+(Mn+Cu+Cr) / 20+Si / 30+Ni / 60+Mo / 15+V / 10+5B;

[0014] The symbols of each element in the formula represent the mass percentage of that element in the chemical composition of the parent material.

[0015] Furthermore, when the base material thickness is 19.05 mm:

[0016] Solid welding wire is used for welding. For horizontal welding positions, the welding current is 180-230A, the arc voltage is 19.8-24.5V, and the welding speed is 250-600mm / min. For vertical welding positions, the welding current is 140-160A, the arc voltage is 15.8-19.2V, and the welding speed is 50-105mm / min.

[0017] Welding is performed using flux-cored wire. For horizontal welding positions, the welding current is 201-215A, the arc voltage is 24.8-25.0V, and the welding speed is 221-522mm / min. For vertical welding positions, the welding current is 145-170A, the arc voltage is 19.4-22.3V, and the welding speed is 71-86mm / min.

[0018] Furthermore, when the base material thickness is 31.75 mm:

[0019] Solid welding wire is used for welding. The welding current for horizontal welding positions is 180-237A, the arc voltage is 20.5-24.7V, and the welding speed is 231-554mm / min. The welding current for vertical welding positions is 145-160A, the arc voltage is 17.3-19.4V, and the welding speed is 40-75mm / min.

[0020] Welding is performed using flux-cored wire. For horizontal welding positions, the welding current is 189-210A, the arc voltage is 24.2-25.7V, and the welding speed is 231-480mm / min. For vertical welding positions, the welding current is 170-195A, the arc voltage is 21.1-23.7V, and the welding speed is 79-163mm / min.

[0021] Further, the solid welding wire is a metal-core welding wire with a Ni content of 1.40±0.15% and a Mo content of 0.45±0.05%; the flux-cored welding wire is a flux-cored welding wire with a Ni content of 2.25±0.20% and a Mo content of 0.39±0.05%. Preferably, the solid welding wire is CHW-80C welding wire; the flux-cored welding wire is CHT110K3 welding wire.

[0022] Furthermore, the joints welded using this method have a tensile strength Rm≥770 MPa, a Charpy V-notch impact energy KV2≥30 J at -40℃, and a maximum hardness of ≤450 HV10 for the weld and heat-affected zone.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. Low-temperature preheating technology with Pcm and Ceq synergistic judgment: This technology breaks through the traditional mindset that "a high Pcm value must be accompanied by high preheating". By combining Pcm and Ceq for synergistic judgment, and with the premise of coordinating with subsequent system processes, a low-temperature preheating of 100℃ can effectively suppress cold cracking. This significantly reduces the preheating temperature compared to traditional processes (which often require ≥150℃), thus avoiding damage to the toughness of the base material from high heat input from the source and laying the foundation for obtaining high-toughness joints.

[0025] 2. Adopt a "dual differentiation" heat input control strategy: The first differentiation is based on the metallurgical characteristics of welding materials: solid welding wire (rich in argon) has a concentrated arc and uses a lower heat input to refine grains and optimize toughness; flux-cored welding wire (carbon dioxide gas) requires a higher heat input to ensure metallurgical reaction and molten pool stability.

[0026] The second difference is based on the mechanical behavior of the molten pool: horizontal welding (PC) requires low heat input to prevent the molten pool from flowing downwards; vertical upward welding (PF) requires high heat input to maintain the stability of the molten pool and achieve upward deposition.

[0027] This strategy couples the type of welding material with the welding position to form a precise process matching matrix, ensuring the performance homogeneity and high reliability of all-position welded joints, which is a key guarantee for the successful achievement of low-temperature preheating.

[0028] 3. A synergistic process system of "low-temperature preheating - optimized gas - precise heat input" was constructed: low-temperature preheating reduces the risk of embrittlement in the heat-affected zone; targeted gas matching optimizes the arc characteristics and metallurgical process; and "dual differentiated" heat input precisely compensates for and controls the cooling process. These three elements work together to systematically resolve the contradiction of simultaneously achieving high strength, high toughness, and low crack sensitivity.

[0029] 4. Excellent overall performance: Through the above-mentioned synergistic control, a good match between high strength, high and low temperature toughness and low hardness of the welded joint has been successfully achieved, breaking through the bottleneck of difficulty in achieving both strength and toughness in traditional processes. Attached Figure Description

[0030] Figure 1 is a schematic diagram of the bevel design of the butt joint with a plate thickness of 19.05mm (Group 1) in an embodiment of the present invention;

[0031] Figures 2 and 3 are schematic diagrams of the multi-layer, multi-pass welding sequence of two welding materials (plate thickness 19.05 mm) in Embodiments 1 and 3 of the present invention;

[0032] Figure 4 is a schematic diagram of the bevel design of the butt joint with a plate thickness of 31.75mm (Group 2) in an embodiment of the present invention;

[0033] Figures 5 and 6 are schematic diagrams of the multi-layer, multi-pass welding sequence of the 31.75mm thick test plate in Embodiment 2 of the present invention, which is welded with solid welding wire.

[0034] Figures 7 and 8 are schematic diagrams of the multi-layer, multi-pass welding sequence of a 31.75mm thick test plate using flux-cored welding wire in Embodiment 4 of the present invention.

[0035] Figure 9 shows macroscopic metallographic photographs of the welded joints in various embodiments of the present invention. Detailed Implementation

[0036] The following provides a detailed description of the specific implementation method of the European standard high-strength low-temperature impact steel welding process of the present invention.

[0037] 1. Test materials

[0038] The experiment of this invention used two sets of base materials of different thicknesses and two different types of welding materials, the specific information of which is as follows:

[0039] 1.1 Base Material

[0040] The base material used was S690QL steel plate conforming to EN 10025-6:2019 standard, and its specific chemical composition and basic mechanical properties are shown in Table 1. A 19.05mm thick steel plate was designated as Group 1, and a 31.75mm thick S steel plate as Group 2. Based on the data in the table, their carbon equivalent (CEq) and cold crack sensitivity coefficient (Pcm) were calculated respectively. The Pcm values ​​of the S690QL base material used in the experiment (0.25% for Group 1 and 0.26% for Group 2) were both higher than the threshold (e.g., 0.20%) commonly set in traditional processes requiring preheating at 150℃. However, this invention did not simply employ high-temperature preheating. Instead, based on the synergistic judgment principle of Pcm ≤ 0.26% and Ceq within the range of 0.45%-0.60%, the weldability was comprehensively evaluated, and the minimum preheating temperature was scientifically set to 100℃. This initiative aims to explore whether, under lower preheating conditions, the dual goals of suppressing cracks and maintaining toughness can be achieved through subsequent strict gas matching and heat input control.

[0041] Table 1: Composition and properties of the S690QL base material used in the experiment

[0042]

[0043] 1.2 Welding materials

[0044] Based on the principle of equal strength matching of welded joints, and taking into account indicators such as nickel content, elongation, ultra-low temperature impact absorption energy and diffusible hydrogen content of welding wire, welding materials were selected, and one solid welding wire and one flux-cored welding wire were selected respectively. Their key characteristics are shown in Table 2.

[0045] Table 2: Welding materials used in the experiment

[0046]

[0047] 2. Welding process and procedures

[0048] The core process steps of this invention include: determining the preheating temperature based on the Pcm and Ceq values ​​of the base material, selecting the matching of welding materials and shielding gas, and "dual differentiation" heat input control. Taking test plates with thicknesses of 19.05 mm (Group 1) and 31.75 mm (Group 2) as examples, four sets of comparative tests were conducted, and the specific process schemes are shown in Table 3. According to the preheating judgment principle of this invention, the Pcm and Ceq of Group 1 and Group 2 both meet the conditions of "Pcm ≤ 0.26% and 0.45% ≤ Ceq ≤ 0.60%", therefore, the minimum preheating temperature for all tests is determined to be 100℃, and the maximum interpass temperature is strictly controlled to be ≤250℃.

[0049] Group 1 (19.05mm) bevel design is shown in Figure 1, and welding sequence examples are shown in Figures 2 and 3. Detailed process parameters for Example 1 (solid welding wire) are shown in Table 4, and parameters for Example 3 (flux-cored welding wire) are shown in Table 6. Group 2 (31.75mm) bevel design is shown in Figure 4, and welding sequence examples are shown in Figures 5-8. Detailed process parameters for Example 2 (solid welding wire) are shown in Table 5, and parameters for Example 4 (flux-cored welding wire) are shown in Table 7. In all examples, the heat input for horizontal and vertical welding is strictly controlled within the window specified in step (4) of claim 1 of this invention for the corresponding welding material type.

[0050] Table 3: Summary of Welding Process Schemes and Key Parameters

[0051]

[0052] Table 4: Welding process parameters for two examples in Example 1

[0053]

[0054] Table 5: Welding process parameters for two examples in Example 2

[0055]

[0056] Table 6: Welding process parameters for two examples in Example 3

[0057]

[0058] Table 7: Welding process parameters for two examples in Example 4

[0059]

[0060] 3. Test Results and Performance Analysis

[0061] 3.1 Non-destructive Testing: After welding, all welded joints underwent visual and non-destructive testing (including magnetic particle testing (MT) and ultrasonic testing (UT)). All results were satisfactory, with no surface or internal cracks found. The test results demonstrate that under a low-temperature preheating condition of only 100℃, combined with a shielding gas of 80%Ar + 20% carbon dioxide (solid welding wire) or pure carbon dioxide (flux-cored welding wire), and a targeted "dual-differentiated" heat input, no cold cracks were found in any of the welded joints during non-destructive testing. This fully verifies the feasibility and reliability of the low-temperature preheating scheme proposed in this invention, breaking the traditional mindset that "high Pcm requires high preheating."

[0062] 3.2 Mechanical property test results: The mechanical property test results of the joints are shown in Table 8. All welded joints in all embodiments meet the requirements of tensile strength Rm≥770MPa and impact energy KV2≥30J at -40℃.

[0063] Table 8: Test Results of Mechanical Properties of Welded Joints

[0064]

[0065] 3.3 Microstructure and Hardness Analysis: Macroscopic metallographic examination of all joints (EN ISO 17639) revealed no defects or welding flaws (see attached Figure 9 for a schematic macroscopic photograph). Hardness testing (ISO 9015-1 HV10) showed that the hardness values ​​of the weld, heat-affected zone, and base metal of all joints were below the requirement of 450 HV10.

[0066] The above embodiments fully verify the effectiveness of the welding process method of the present invention. By using Pcm and Ceq to collaboratively determine the preheating temperature, optimize gas matching, and implement "dual differential" heat input control, the system systematically solves the core technical problems of cold crack sensitivity, difficulty in ensuring low-temperature toughness, and poor adaptability to all-position welding in S690QL high-strength steel welding. This process has clear parameters, is highly operable, and has significant industrial application value.

[0067] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A welding process for European standard high-strength low-temperature impact steel, characterized in that, The steps include: (1) Calculate the carbon equivalent Ceq and cold crack sensitivity coefficient Pcm based on the chemical composition of the base material S690QL; (2) The minimum preheating temperature is determined based on the cold cracking sensitivity coefficient Pcm and carbon equivalent Ceq of the base material, wherein: if Pcm ≤ 0.26% and 0.45% ≤ Ceq ≤ 0.60%, the minimum preheating temperature is 100℃; if Pcm > 0.26%, the minimum preheating temperature is 150℃; at the same time, the maximum interpass temperature during the welding process is controlled to be ≤ 250℃; (3) Selection of welding materials and shielding gas: When using gas metal arc welding, solid welding wire is selected as the welding material, and flux-cored wire arc welding is used. When solid welding wire is selected, a mixture of 20% carbon dioxide and 80% Ar is used as the shielding gas. When flux-cored wire is selected, carbon dioxide gas with a purity of not less than 99.9% is used as the shielding gas. Welding operation: Welding positions include horizontal welding of PC and vertical welding of PF. According to the type of welding material and welding position, a "dual differentiation" heat input control strategy is implemented. Among them, when using solid welding wire, the heat input of the horizontal welding position is controlled at 0.30-1.15kJ / mm, and the heat input of the vertical welding position is controlled at 1.23-3.68kJ / mm. When using flux-cored wire, the heat input of the horizontal welding position is controlled at 0.47-1.44kJ / mm, and the heat input of the vertical welding position is controlled at 1.28-2.58kJ / mm.

2. The welding process for European standard high-strength low-temperature impact steel according to claim 1, characterized in that, In step (1), the carbon equivalent Ceq and the cold crack sensitivity coefficient Pcm are calculated according to the following formulas: Ceq=C+Mn / 6+(Cr+V+Mo) / 5+(Cu+Ni) / 15, Pcm=C+(Mn+Cu+Cr) / 20+Si / 30+Ni / 60+Mo / 15+V / 10+5B; where each element symbol represents the mass percentage content of the element in the chemical composition of the base material.

3. The welding process for European standard high-strength low-temperature impact steel according to claim 1, characterized in that, When the base plate thickness is 19.05mm: For solid welding wire, the welding current for horizontal welding positions is 180-230A, the arc voltage is 19.8-24.5V, and the welding speed is 250-600mm / min; for vertical welding positions, the welding current is 140-160A, the arc voltage is 15.8-19.2V, and the welding speed is 50-105mm / min. For flux-cored welding wire, the welding current for horizontal welding positions is 201-215A, the arc voltage is 24.8-25.0V, and the welding speed is 221-522mm / min; for vertical welding positions, the welding current is 145-170A, the arc voltage is 19.4-22.3V, and the welding speed is 71-86mm / min.

4. The welding process for European standard high-strength low-temperature impact steel according to claim 1, characterized in that, When the base plate thickness is 31.75mm: For solid welding wire, the welding current for horizontal welding positions is 180-237A, the arc voltage is 20.5-24.7V, and the welding speed is 231-554mm / min; for vertical welding positions, the welding current is 145-160A, the arc voltage is 17.3-19.4V, and the welding speed is 40-75mm / min. For flux-cored welding wire, the welding current for horizontal welding positions is 189-210A, the arc voltage is 24.2-25.7V, and the welding speed is 231-480mm / min; for vertical welding positions, the welding current is 170-195A, the arc voltage is 21.1-23.7V, and the welding speed is 79-163mm / min.

5. The welding process for European standard high-strength low-temperature impact steel according to claim 1, characterized in that: The solid welding wire is a metal-core welding wire with a Ni content of 1.40±0.15% and a Mo content of 0.45±0.05%; the flux-cored welding wire is a flux-cored welding wire with a Ni content of 2.25±0.20% and a Mo content of 0.39±0.05%.

6. The welding process for European standard high-strength low-temperature impact steel according to claim 1, characterized in that: The solid welding wire is CHW-80C welding wire; the flux-cored welding wire is CHT110K3 welding wire.

7. The welding process for European standard high-strength low-temperature impact steel according to claim 1, characterized in that: The joints welded using this method have a tensile strength Rm≥770 MPa, a Charpy V-notch impact energy KV2≥30 J at -40℃, and a maximum hardness of ≤450 HV10 for the weld and heat-affected zone.

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