Welding method of a yield strength 1400mpa grade ultra-high strength steel plate

Abstract

The present application relates to a kind of yield strength 1400MPa grade ultra-high strength steel plate welding method.Welding steel plate thickness 4~20mm, chemical composition, production process and mechanical properties meet the requirements specified in Chinese patent CN107338393B.Preparation steps include: (1) V-shaped groove processing;(2) pretreatment, steel plate preheating 100~120℃;(3) using 90KG grade low-strength welding wire, low heat input single-sided welding double-sided forming method for MAG welding.The interpass temperature is controlled at 90~110℃(4) postwelding slow cooling.The present application has excellent comprehensive mechanical properties of welded joint.Welded joint strength >1150MPa;Welding seam-40℃ low temperature impact toughness Akv≥35J;Heat-affected zone-40℃ low temperature impact toughness Akv≥27J;Can meet the use requirements of engineering machinery with ultra-high strength steel.

Description

Technical Field

[0001] This invention belongs to the field of gas shielded welding technology, specifically relating to a welding method for tempered ultra-high strength steel plates with a yield strength of 1400MPa. Background Technology

[0002] As construction machinery and equipment become larger and lighter, the strength levels of tempered ultra-high-strength steel plates used in construction machinery are also continuously increasing. Currently, 960MPa yield strength ultra-high-strength steel plates are gradually being domestically produced; 1100MPa yield strength steel plates are gradually replacing imports. 1300MPa yield strength steel plates are still in the research and development stage domestically and have not yet achieved mass engineering applications. Research and reports on steel plates with yield strengths above 1400MPa are limited. With the increase in steel plate strength, the alloy content and carbon equivalent of tempered steel plates are constantly increasing, leading to a significant increase in welding difficulty. Welded joints experience high stress and decreased impact toughness, making them prone to hot and cold cracking, severely limiting the widespread application of ultra-high-strength steel plates. The development of matching welding processes for tempered ultra-high-strength steel plates has become an urgent problem for steel manufacturers to solve.

[0003] Chinese patent CN109226941B discloses a GMAW welding method for thin Q1100E low-alloy ultra-high-strength steel plates. The steel plate thickness is 8–12 mm. To address the problem of welding cracking, the invention employs preheating at a high temperature (180–200℃) before welding, followed by hydrogen removal treatment at a temperature above 100℃ for at least 4 hours after welding. The welded joint strength of the steel plate is <1100 MPa.

[0004] Chinese patent CN105522262B discloses a welding method for low-alloy ultra-high-strength steel with a yield strength of 1100 MPa. The invention uses high-strength welding wire of grade 1000 MPa or higher for CO2 gas shielded welding, achieving a weld joint strength of 1100 MPa. However, this invention requires a high preheating temperature of 150–170°C before welding; post-weld hydrogen removal treatment is also necessary, with a holding temperature of 200–250°C for at least one hour. This method is costly and has low welding efficiency.

[0005] Chinese patent CN105598596B discloses a method for non-preheating combined welding of high-strength steel with a tensile strength of 1200MPa, but the tensile strength of the welded joint of this invention is only 780MPa.

[0006] Chinese patent CN114131159A discloses a welding method for ultra-high strength Q1300E steel plates. The steel plate thickness is 8-15mm. A V-groove is made for plates 8-12mm thick, and an X-groove for plates 12-15mm thick, with both grooving angles at 60°. The preheating temperature of the steel plate is 170-190℃. To improve the strength of the welded joint, this invention uses two types of welding wire. A 1000MPa high-strength welding wire is used for the root pass, followed by a 1200MPa high-strength welding wire for the fill pass. The thick plate welding process employs alternating forward and reverse welding, making the process complex and difficult to promote in practical production applications.

[0007] In summary, to solve the problem of welding cracking in ultra-high strength steel plates, existing welding processes mostly adopt high-temperature preheating (preheating temperature above 150℃) and hydrogen removal treatment (holding at 100℃ or 200℃ or above) before welding. This method is inefficient, and the highest strength level is only 1300MPa. There is no research on welding processes for ultra-high strength steel plates with yield strength above 1400MPa. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a welding method for quenched and tempered ultra-high strength steel plates with a yield strength of 1400MPa, which solves the problems of difficult welding, complex welding process and poor performance of welded joints.

[0009] The technical solution adopted by this invention to solve the above problems is: a welding method for ultra-high strength steel plates with a yield strength of 1400MPa, wherein the welding method includes slit processing, pretreatment, welding, and post-weld heat preservation treatment, wherein:

[0010] (1) Splitting process

[0011] The welded steel plate is cut with a V-shaped notch, the notch angle is 50°, and the blunt edge is 2mm.

[0012] (2) Pretreatment

[0013] Use a grinding wheel to clean the bevel and surrounding areas, removing iron oxide scale, rust and oil stains. Control the gap of the welded joint assembly to 1-2 mm. Preheat the steel plate to 100-120℃.

[0014] (3) Welding

[0015] The welding shielding gas is a mixture of argon and carbon dioxide; argon volume percentage is 80% and carbon dioxide volume percentage is 20%; the gas flow rate is 22-26 L / min, and MAG welding is performed using a single-sided welding and double-sided forming method;

[0016] (4) Post-weld heat preservation treatment: After welding, the steel plate is kept warm and slowly cooled to room temperature.

[0017] Preferably, the MAG welding specifically involves a single root pass with a heat input of 4–8 KJ / cm; followed by multi-layer, multi-pass welding with a heat input of 8–12 KJ / cm, with the interpass temperature controlled at 90–110°C, and weld cleaning to remove oxide scale after each pass.

[0018] Preferably, the welded steel plate has a thickness of 4-20 mm, a yield strength > 1400 MPa, a tensile strength > 1600 MPa, an elongation ≥ 8%, and an Akv ≥ 30 J at -40℃.

[0019] Preferably, the chemical composition of the welded steel plate by weight percentage is C: 0.24%, Si: 0.25%, Mn: 0.90%, Cr: 0.60%, Ni: 1.45%, Mo: 0.50%, Nb: 0.02%, V: 0.03%, Ti: 0.001%, Al: 0.05%, B: 0.0015%, with the remainder being Fe and unavoidable impurity elements.

[0020] Preferably, the welding process uses 90 kg-class gas-shielded welding wire with low strength matching to the base material. The welding wire diameter is 1.2 mm, with a yield strength of 920 MPa, tensile strength of 980 MPa, elongation of 16%, and low-temperature impact energy of 53 J at -40℃.

[0021] Preferably, the chemical composition of the welding wire by weight percentage is: C: 0.07-0.10%, Si: 0.60-0.90%, Mn: 1.60-1.80%, Cr: 0.35-0.50%, Ni: 2.00-2.20%, Mo: 0.45-0.60%, with the remainder being Fe and unavoidable impurity elements.

[0022] Preferably, the weld microstructure is a multiphase microstructure consisting mainly of acicular ferrite and bainite with a small amount of martensite.

[0023] Preferably, the welded joint strength is >1150 MPa; the weld's low-temperature impact toughness Akv at -40℃ is ≥35 J; and the heat-affected zone's low-temperature impact toughness Akv at -40℃ is ≥27 J; which can meet the requirements for the use of ultra-high strength steel in engineering machinery.

[0024] Compared with the prior art, the advantages of the present invention are as follows:

[0025] The welding base material of the present invention has higher strength, with a yield strength greater than 1400MPa and a tensile strength greater than 1600MPa.

[0026] This invention employs low-strength matching and uses 90Kg-grade low-strength welding materials, which can effectively enhance the low-temperature toughness of welded joints of 1400MPa-grade ultra-high-strength steel, while also reducing costs.

[0027] The welding of this invention uses a lower preheating temperature (100-120°C) and interpass control temperature (90-110°C), and no post-weld heating hydrogen removal treatment is required, resulting in low energy consumption and high production efficiency.

[0028] This invention employs a single-pass, multi-layer, multi-pass welding method, resulting in lower welding heat input and reducing the heat-affected zone. The weld microstructure is a multiphase structure dominated by acicular ferrite and bainite with a small amount of martensite, see [link to details]. Figure 2 The presence of acicular ferrite significantly increases the low-temperature toughness of the welded joint, while bainite and martensite significantly increase the strength of the welded joint, ensuring that the welded joint strength can reach over 1150 MPa even when using 90 kg grade low-strength welding materials. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the welding bevel and assembly of the present invention.

[0030] Figure 2 This is the metallographic structure of the weld in an embodiment of the present invention. Detailed Implementation

[0031] The invention will be further explained below with reference to examples.

[0032] This embodiment relates to a welding method for quenched and tempered ultra-high strength steel plates with a yield strength of 1400MPa, including the following steps:

[0033] (1) The butt-welded steel plate is made of 20mm Q1400E quenched and tempered ultra-high strength steel plate. The yield strength of the steel plate is 1438MPa; the tensile strength is 1668MPa; the elongation is 12%; the low temperature impact energy at -40℃ is 41J; the chemical composition by weight percentage is C: 0.24%, Si: 0.25%, Mn: 0.90%, Cr: 0.60%, Ni: 1.45%, Mo: 0.50%, Nb: 0.02%, V: 0.03%, Ti: 0.001%, Al: 0.05%, B: 0.0015%, and the remainder is Fe and unavoidable impurity elements.

[0034] (2) A 90 kg-grade gas shielded welding wire with low strength matching to the base material is used. The wire diameter is 1.2 mm, the yield strength is 920 MPa, the tensile strength is 980 MPa, the elongation is 16%, the low-temperature impact energy at -40℃ is 53 J, and its chemical composition by weight percentage is: C: 0.08%, Si: 0.75%, Mn: 1.75%, Cr: 0.45%, Ni: 2.10%, Mo: 0.55%, and the remainder is Fe and unavoidable impurity elements.

[0035] (3) The welded steel plate is cut with a V-shaped notch, the notch angle is 50°, and the blunt edge is 2mm. See Figure 1 .

[0036] (4) Use a grinding wheel to clean the bevel and the surrounding sides, remove iron oxide scale, rust and oil stains, control the gap of the welded joint assembly to 2mm, and preheat the steel plate to 100℃.

[0037] (3) The welding shielding gas is a mixture of argon and carbon dioxide; argon volume percentage is 80%, carbon dioxide volume percentage is 20%; gas flow rate is 25 L / min. MAG welding is performed using a single-sided welding and double-sided forming method. A root pass is performed with a welding heat input of 6 KJ / cm; then a multi-layer, multi-pass welding is performed with a heat input of 10 KJ / cm, and the interpass temperature is controlled at 100℃. After each pass, the weld bead is cleaned to remove oxide scale.

[0038] (4) After the steel plate is welded, it is covered with insulation cotton to cool it slowly to room temperature.

[0039] The welded joint of Q1400E ultra-high strength steel plate, welded using the example welding process, showed good fusion, with no macroscopic cracks on the surface or at the root, and passed ultrasonic testing. The mechanical properties of the welded joint are shown in Table 1.

[0040] Table 1 Tensile, impact, and bending properties of this embodiment

[0041]

[0042] Although preferred embodiments of the present invention have been described in detail above, it should be clearly understood that various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A welding method for ultra-high strength steel plates with a yield strength of 1400 MPa, characterized in that: The welding method includes sectioning, pretreatment, welding, and post-weld heat preservation, wherein: (1) Splitting process The welded steel plate is cut with a V-shaped notch, the notch angle is 50°, and the blunt edge is 2mm. The welded steel plate has a thickness of 4-20 mm, a yield strength > 1400 MPa, a tensile strength > 1600 MPa, an elongation ≥ 8%, and an Akv ≥ 30 J at -40℃. The chemical composition of the welded steel plate by weight percentage is C: 0.24%, Si: 0.25%, Mn: 0.90%, Cr: 0.60%, Ni: 1.45%, Mo: 0.50%, Nb: 0.02%, V: 0.03%, Ti: 0.001%, Al: 0.05%, B: 0.0015%, with the remainder being Fe and unavoidable impurity elements; (2) Pretreatment Use a grinding wheel to clean the bevel and surrounding areas, removing iron oxide scale, rust and oil stains. Control the gap of the welded joint assembly to be 1-2mm. Preheat the steel plate to 100-120℃. (3) Welding The welding shielding gas is a mixture of argon and carbon dioxide; argon accounts for 80% by volume, and carbon dioxide accounts for 20% by volume; the gas flow rate is 22–26 L / min, and MAG welding is performed using a single-sided welding and double-sided forming method; specifically, the MAG welding involves a root pass with a heat input of 4–8 KJ / cm, followed by 8–12 KJ / cm... Multi-layer, multi-pass welding is performed with a heat input of KJ / cm. The interpass temperature is controlled at 90-110℃. After each pass, the weld bead is cleaned to remove oxide scale. The welding process uses 90 kg-class gas-shielded welding wire with low strength matching to the base material. The welding wire diameter is 1.2 mm, with a yield strength of 920 MPa, tensile strength of 980 MPa, elongation of 16%, and low-temperature impact energy of 53 J at -40℃. The chemical composition of the welding wire by weight percentage is: C: 0.07-0.10%, Si: 0.60-0.90%, Mn: 1.60-1.80%, Cr: 0.35-0.50%, Ni: 2.00-2.20%, Mo: 0.45-0.60%, with the remainder being Fe and unavoidable impurity elements. (4) Post-weld heat preservation treatment: After welding, the steel plate is kept warm and slowly cooled to room temperature.

2. The welding method for an ultra-high strength steel plate with a yield strength of 1400 MPa according to claim 1, characterized in that... The weld microstructure is a multiphase structure consisting mainly of acicular ferrite and bainite with a small amount of martensite.

3. The welding method for an ultra-high strength steel plate with a yield strength of 1400 MPa according to claim 1, characterized in that... The welded joint strength is >1150 MPa; the weld's impact toughness at -40℃ is Akv ≥35 J; the heat-affected zone's impact toughness at -40℃ is Akv ≥27 J; it can meet the requirements for ultra-high strength steel used in engineering machinery.

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