A submerged arc welding method for 550MPa high-strength steel with excellent low-temperature crack resistance

Abstract

This invention discloses a submerged arc welding method for 550MPa grade high-strength steel with excellent low-temperature crack resistance, comprising: S1, butt welding two 20-60mm thick 550MPa grade high-strength steel pieces together; S2, selecting submerged arc welding wire and matching flux; S3, symmetrical K-type bevel with an angle of 40-50° and a blunt edge size of 2-4mm, leaving a 2-4mm gap in the bevel assembly; preheating temperature ≥100℃, interpass temperature ≤150℃; no root cleaning required on the reverse side; submerged arc welding current 420-550A, arc voltage 29-35V, welding speed 38-46cm / min, and welding heat input 15-30kJ / cm. The advantages of this invention are that the tensile strength of the welded joint is ≥640MPa, the side bending of the welded joint is d=4a, 180°, without cracks, the impact energy of the weld and heat-affected zone at -60℃ is KV2≥55J, and the crack tip opening displacement CTOD value at -35℃ is δ≥0.21mm.

Description

Technical Field

[0001] This invention belongs to the field of steel material welding technology, and particularly relates to a submerged arc welding method for 550MPa grade high-strength steel with excellent low-temperature crack resistance. Background Technology

[0002] Unlike conventional LNG transport media, liquefied carbon dioxide storage and transportation conditions have extreme characteristics of low temperature and high pressure coupling. To ensure the safety of the transportation process, the steel used for liquid cargo tanks needs to maintain extremely high impact toughness in low temperature environments, while also having excellent resistance to crack propagation, so as to avoid the risk of brittle fracture during service.

[0003] However, in actual shipbuilding, steel welding is an indispensable core process, and the performance of the welded joints directly determines the service safety of the entire cargo tank structure. Existing patent CN113549846A proposes a 550MPa grade marine steel with excellent low-temperature performance and its manufacturing method. This technology focuses only on the composition design and rolling process control of the base material itself, and has not developed a suitable submerged arc welding process system for the special service conditions of liquefied carbon dioxide carriers. In practical applications, it has revealed many significant shortcomings: Firstly, the welding thermal cycle characteristics of 550MPa high-strength steel were not precisely controlled. Under conventional welding parameters, abnormal grain growth is likely to occur in the heat-affected zone, resulting in a significant decrease in the low-temperature impact toughness of the joint. This fails to meet the low-temperature toughness requirements of liquefied carbon dioxide ships below -30℃, and brittle cracks are very likely to develop at the joint during service. Secondly, the selection of matching submerged arc welding materials and the design of flux composition are not clearly defined. The compatibility between existing general marine steel welding materials and this 550MPa high-strength steel is insufficient. The strength and toughness of the weld metal are out of balance, and the control accuracy of diffusible hydrogen content is insufficient. Cold cracks are easily induced during the multi-layer and multi-pass welding process of thick plates, which violates the high crack resistance requirements of liquefied carbon dioxide marine steel. Third, no full-process process specifications for the welding of thick steel plates for liquefied carbon dioxide ships have been formulated, including preheating temperature, interpass temperature, and post-weld heat input control. In actual construction, the process implementation by different construction units varies greatly, which can easily lead to problems such as excessive residual welding stress and uncontrolled joint yield strength ratio. It is difficult to ensure the performance consistency of all welded joints on the ship and cannot meet the stringent inspection standards of classification societies for liquefied carbon dioxide cargo tanks. Summary of the Invention

[0004] The purpose of this invention is to solve the problem that existing 550MPa high-strength steel cannot simultaneously possess low-temperature toughness and high crack resistance. It provides a submerged arc welding method for 550MPa high-strength steel with excellent low-temperature crack resistance, ensuring that the welded joint still has excellent strength-toughness matching and crack propagation resistance in low-temperature environments.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A submerged arc welding method for 550MPa grade high-strength steel with excellent low-temperature crack resistance is proposed. For 20~60mm thick 550MPa grade high-strength steel, by using appropriate welding materials and submerged arc welding process, the method ensures that the tensile strength of the welded joint is ≥640MPa, the side bending of the welded joint is d=4a, 180°, without cracks, the impact energy KV2 of the weld and heat-affected zone at -60℃ is ≥55J, and the crack tip opening displacement CTOD value δ at -35℃ is ≥0.21mm, so that the welded joint achieves good comprehensive performance.

[0006] The specific parameters for the above-mentioned submerged arc welding process include: (1) Bevel type: symmetrical K-type bevel, with an angle of 40~50°, a blunt edge size of 2~4mm, and a 2~4mm gap left for bevel assembly.

[0007] (2) Preheating temperature before welding ≥100℃, interpass temperature ≤150℃; no root cleaning treatment required on the reverse side.

[0008] (3) Submerged arc welding is used. The welding current is 420~550A, the arc voltage is 29~35V, the welding speed is 38~46cm / min, and the welding heat input is 15~30kJ / cm.

[0009] Furthermore, the steel plate to be welded is selected as follows: the yield strength of the base material is ≥550MPa, the tensile strength is 640~820MPa, the elongation is ≥18%, the impact energy at -60℃ is KV2≥100J, and the crack tip opening displacement CTOD value at -35℃ is ≥0.21mm.

[0010] Furthermore, the chemical composition and weight percentage of the steel plate to be welded include: C≤0.15%, Mn: 0.60~1.00%, Si: 0.20~0.50%, S≤0.01%, P≤0.01%, Ni: 0.8~1.8%, Mo: 0.20~0.50%, Nb: 0.20~0.30%, with the balance being Fe and unavoidable impurities.

[0011] Furthermore, the welding material is selected from submerged arc welding wire with a diameter of Φ3.2mm or Φ4.0mm and matching flux, and its deposited metal has a low-temperature impact energy KV2≥60J at -60℃ and a tensile strength≥650MPa.

[0012] Furthermore, the chemical composition and weight percentage of the submerged arc welding wire include: C: 0.03~0.10%, Mn: 1.0~1.5%, Si: 0.1~0.3%, S≤0.010%, P≤0.010%, Ni: 2.20~2.50%, Cu: 0.03~0.06%, Mo: 0.05~0.10%, with the balance being Fe and unavoidable impurities.

[0013] Compared with the prior art, the advantages of the technical solution of the present invention are as follows: (1) This invention effectively suppresses the abnormal grain growth phenomenon in the heat-affected zone of welding, and finally achieves a stable low-temperature impact energy KV2 of -60℃ for the weld and heat-affected zone of ≥55J, which greatly expands the low-temperature service boundary of the material and is suitable for the extreme low-temperature operating conditions of the liquid cargo tank of liquefied carbon dioxide ship, thus avoiding the risk of low-temperature brittle fracture in the joint area from the root. (2) The tensile strength of the welded joint of the present invention can be stably maintained above 640MPa, forming a reasonable high-strength matching relationship with the strength grade of 550MPa of the base material. It will not cause weak areas in the joint due to insufficient weld strength, nor will it cause a decrease in the plasticity and toughness of the joint due to excessive strength. It fully meets the structural bearing design requirements of 20~60mm thick 550MPa grade high-strength steel and is suitable for the load requirements of high-pressure liquid cargo tanks of liquefied carbon dioxide ships. (3) By strictly controlling the impurity content and microstructure uniformity of the weld metal, this invention achieves excellent forming effect of welded joint side bending d=4a and 180° without cracks, effectively avoids the initiation of surface microcracks under cold bending process, and greatly reduces the failure risk of subsequent structure service. (4) The present invention achieves the core index of crack tip opening displacement CTOD value δ≥0.21mm at -35℃ of welded joint, and the crack propagation resistance is improved by more than double. Even under the coupling effect of welding residual stress and low temperature load, it can effectively delay the initiation and propagation of cracks, and meet the high crack resistance requirements of liquid cargo tank structure. (5) The submerged arc welding process of the present invention can achieve stable welding of 550MPa grade high-strength steel plates with a full thickness range of 20~60mm. The joint performance of different batches of steel plates is highly consistent, and no additional construction costs are required. It has a wide range of applications. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the welding bevel of the present invention; Figure 2 Tables showing the tensile and lateral bending properties of the welded joints in Embodiments 1 to 3 of the present invention; Figure 3 Table of impact performance of welded joints in Embodiments 1 to 3 of the present invention; Figure 4The crack tip opening displacement (CTOD) values ​​of the welded joints in Embodiments 1 to 3 of the present invention are given. Detailed Implementation Example 1

[0015] To make the present invention clearer, the following description, in conjunction with the accompanying drawings, further illustrates a submerged arc welding method for 550MPa grade high-strength steel with excellent low-temperature crack resistance. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the present invention.

[0016] This embodiment provides a submerged arc welding method for 550MPa grade high-strength steel with excellent low-temperature crack resistance, including the following steps: (a) Welded steel plates: The base material is 550MPa grade high-strength steel with excellent low-temperature crack resistance, having a yield strength ≥550MPa, tensile strength 640~820MPa, elongation ≥18%, impact energy KV2≥100J at -60℃, and crack tip opening displacement CTOD value δ≥0.21mm at -35℃. The welded test plate assembly is 20mm+20mm, and the test plate size is 800mm long × 200mm wide × 20mm thick.

[0017] (ii) Welding materials: The welding material used is Φ3.2mm submerged arc welding wire and matching flux. The low-temperature impact energy (KV2) of the deposited metal at -60℃ is ≥60J, and the tensile strength is ≥650MPa. The chemical composition and weight percentage of the submerged arc welding wire used are as follows: C: 0.03~0.10%, Mn: 1.0~1.5%, Si: 0.1~0.3%, S≤0.010%, P≤0.010%, Ni: 2.20~2.50%, Cu: 0.03~0.06%, Mo: 0.05~0.10%, with the balance being Fe and unavoidable impurities.

[0018] (III) Welding parameters: See Figure 1 The bevel type is K-type bevel, the bevel angle is 46°, the blunt edge is 2mm, and the bevel assembly gap is 4mm.

[0019] Preheat to 100℃ before welding, and maintain an interpass temperature of 100~150℃. No root cleaning is required before welding the reverse side. Selecting the following welding process can ensure that the root pass on the front side is not burned through and that the back side weld is fully penetrated.

[0020] Submerged arc welding was used, with a welding current of 420A, an arc voltage of 29V, a welding speed of 46cm / min, and a welding heat input of 15kJ / cm. Example 2

[0021] This embodiment provides another submerged arc welding method for 550MPa grade high-strength steel with excellent low-temperature crack resistance, including the following steps: (a) Welded steel plates: The base material is 550MPa grade high-strength steel with excellent low-temperature crack resistance, having a yield strength ≥550MPa, tensile strength 640~820MPa, elongation ≥18%, impact energy KV2≥100J at -60℃, and crack tip opening displacement CTOD value δ≥0.21mm at -35℃. The welded test plate assembly is 40mm+40mm, and the test plate size is 800mm long × 200mm wide × 40mm thick.

[0022] (ii) Welding materials: The welding material used is Φ3.2mm submerged arc welding wire and matching flux. The low-temperature impact energy (KV2) of the deposited metal at -60℃ is ≥60J, and the tensile strength is ≥650MPa. The chemical composition and weight percentage of the submerged arc welding wire used are as follows: C: 0.03~0.10%, Mn: 1.0~1.5%, Si: 0.1~0.3%, S≤0.010%, P≤0.010%, Ni: 2.20~2.50%, Cu: 0.03~0.06%, Mo: 0.05~0.10%, with the balance being Fe and unavoidable impurities.

[0023] (III) Welding parameters: The bevel type is K-type bevel, the bevel angle is 45°, the blunt edge is 3mm, and the bevel assembly gap is 3mm.

[0024] Preheat to 100℃ before welding, and maintain an interpass temperature of 100~150℃. No root cleaning is required before welding the reverse side. Selecting the following welding process can ensure that the root pass on the front side is not burned through and that the back side weld is fully penetrated.

[0025] Submerged arc welding was used, with a welding current of 500A, an arc voltage of 32V, a welding speed of 41cm / min, and a welding heat input of 23kJ / cm. Example 3

[0026] This embodiment provides another submerged arc welding method for 550MPa grade high-strength steel with excellent low-temperature crack resistance, including the following steps: (a) Welded steel plates: The base material is 550MPa grade high-strength steel with excellent low-temperature crack resistance, having a yield strength ≥550MPa, tensile strength 640~820MPa, elongation ≥18%, impact energy KV2≥100J at -60℃, and crack tip opening displacement CTOD value δ≥0.21mm at -35℃. The welded test plate assembly is 60mm+60mm, and the test plate size is 800mm long × 200mm wide × 60mm thick.

[0027] (ii) Welding materials: The welding material selected is Φ4.0mm submerged arc welding wire and matching flux. The low-temperature impact energy KV2 of the deposited metal at -60℃ is ≥60J, and the tensile strength is ≥650MPa. The chemical composition and weight percentage of the submerged arc welding wire used are as follows: C: 0.03~0.10%, Mn: 1.0~1.5%, Si: 0.1~0.3%, S≤0.010%, P≤0.010%, Ni: 2.20~2.50%, Cu: 0.03~0.06%, Mo: 0.05~0.10%, with the balance being Fe and unavoidable impurities.

[0028] (III) Welding parameters: The bevel type is K-type bevel, the bevel angle is 45°, the blunt edge is 4mm, and the bevel assembly gap is 2mm.

[0029] Preheat to 100℃ before welding, and maintain an interpass temperature of 100~150℃. No root cleaning is required before welding the reverse side. Selecting the following welding process can ensure that the root pass on the front side is not burned through and that the back side weld is fully penetrated.

[0030] Submerged arc welding was used, with a welding current of 550A, an arc voltage of 35V, a welding speed of 38cm / min, and a welding heat input of 30kJ / cm.

[0031] After the welding methods described in Examples 1-3 above, the mechanical properties of the welded joint were tested. The tensile and bending, impact, and crack tip opening displacement (CTOD) values ​​of the welded joint are as follows: Figures 2 to 4 As shown.

[0032] Since welding process parameters affect the thermal cycling process of welded joints and lead to element loss, they influence the performance of the weld metal and heat-affected zone. This invention investigates the effects of different welding processes on the comprehensive mechanical properties and welding quality of welded joints. The tensile properties, bending properties, and the impact energy (KV2) of the weld and heat-affected zone at -60℃ and the crack tip opening displacement (CTOD) value at -35℃ were measured. The results show that when welding using the parameters described in this invention, the welded joint exhibits excellent comprehensive mechanical properties: tensile strength ≥ 640 MPa, side bending (d = 4a), 180° without cracks, impact energy (KV2) of the weld and heat-affected zone at -60℃ ≥ 55 J, and crack tip opening displacement (CTOD) value at -35℃ ≥ 0.21 mm.

[0033] 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 submerged arc welding method for 550MPa grade high-strength steel with excellent low-temperature crack resistance, characterized in that: S1, connect two pieces of 20~60mm thick 550MPa high-strength steel; S2, Select appropriate submerged arc welding wire and matching flux; S3, using the above-mentioned submerged arc welding wire to perform submerged arc welding on high-strength steel, specifically: S31, the bevel type adopts a symmetrical K-type bevel with an angle of 40~50°, a blunt edge size of 2~4mm, and a 2~4mm gap is left for bevel assembly; S32, preheating temperature ≥100℃, interpass temperature ≤150℃; no root cleaning required on the reverse side; S33 uses submerged arc welding with a welding current of 420~550A, an arc voltage of 29~35V, a welding speed of 38~46cm / min, and a welding heat input of 15~30kJ / cm.

2. The submerged arc welding method for 550MPa grade high-strength steel with excellent low-temperature crack resistance according to claim 1, characterized in that: In step S1, the yield strength of the base material is ≥550MPa, the tensile strength is 640~820MPa, the elongation is ≥18%, the impact energy at -60℃ is KV2≥100J, and the crack tip opening displacement CTOD value at -35℃ is ≥0.21mm.

3. The submerged arc welding method for 550MPa grade high-strength steel with excellent low-temperature crack resistance according to claim 1 or 2, characterized in that: In step S1, the chemical composition and weight percentage of the steel plate to be welded include: C≤0.15%, Mn: 0.60~1.00%, Si: 0.20~0.50%, S≤0.01%, P≤0.01%, Ni: 0.8~1.8%, Mo: 0.20~0.50%, Nb: 0.20~0.30%, with the balance being Fe and unavoidable impurities.

4. The submerged arc welding method for 550MPa grade high-strength steel with excellent low-temperature crack resistance according to claim 1 or 2, characterized in that: In step S2, the welding material is selected as submerged arc welding wire with a diameter of Φ3.2mm or Φ4.0mm and matching flux, and the low-temperature impact energy KV2 of the deposited metal at -60℃ is ≥60J, and the tensile strength is ≥650MPa.

5. The submerged arc welding method for 550MPa grade high-strength steel with excellent low-temperature crack resistance according to claim 4, characterized in that: In step S2, the chemical composition and weight percentage of the submerged arc welding wire include: C: 0.03~0.10%, Mn: 1.0~1.5%, Si: 0.1~0.3%, S≤0.010%, P≤0.010%, Ni: 2.20~2.50%, Cu: 0.03~0.06%, Mo: 0.05~0.10%, with the balance being Fe and unavoidable impurities.

6. The submerged arc welding method for 550MPa grade high-strength steel with excellent low-temperature crack resistance according to claim 1 or 2, characterized in that: In step S3, the tensile strength of the welded joint is ≥640MPa, the side bending of the welded joint is d=4a, 180°, there are no cracks, the impact energy of the weld and heat-affected zone at -60℃ is KV2≥55J, and the crack tip opening displacement CTOD value at -35℃ is δ≥0.21mm.

7. The submerged arc welding method for 550MPa grade high-strength steel with excellent low-temperature crack resistance according to claim 1 or 2, characterized in that: In step S3, the bevel type is a K-type bevel with a bevel angle of 46°, a blunt edge of 2mm, and a bevel assembly gap of 4mm; the preheating temperature is 100℃, the interpass temperature is 100~150℃; the submerged arc welding current is 420A, the arc voltage is 29V, the welding speed is 46cm / min, and the welding heat input is 15kJ / cm.

8. The submerged arc welding method for 550MPa grade high-strength steel with excellent low-temperature crack resistance according to claim 1 or 2, characterized in that: In step S3, the bevel type is a K-type bevel, the bevel angle is 45°, the blunt edge is 3mm, and the bevel assembly gap is 3mm; the preheating temperature is 100℃, the interpass temperature is 100~150℃; the submerged arc welding current is 500A, the arc voltage is 32V, the welding speed is 41cm / min, and the welding heat input is 23kJ / cm.

9. The submerged arc welding method for 550MPa grade high-strength steel with excellent low-temperature crack resistance according to claim 1 or 2, characterized in that: In step S3, the bevel type is a K-type bevel with a bevel angle of 45°, a blunt edge of 4mm, and a bevel assembly gap of 2mm; the preheating temperature is 100℃, the interpass temperature is 100~150℃; the submerged arc welding current is 550A, the arc voltage is 35V, the welding speed is 38cm / min, and the welding heat input is 30kJ / cm.

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