Gas shielded welding method for high-strength and high-toughness DP540 dual-phase steel

Abstract

The invention discloses a high-strength and high-toughness DP540 dual-phase steel gas shielded welding method which comprises the following steps: adopting an equal-strength matching principle, and selecting an MERI TS-6 solid welding wire as a welding material; argon-rich gas containing 80% of Ar and 20% of CO2 is adopted as protective gas, and the gas pressure flow is 18-24 L / min; x-shaped groove double-face butt welding is carried out, the angle of an X-shaped groove is 35 degrees, the blunt variable is 2 mm, and the dry extension length of a welding wire is 15-20 mm; the welding current is controlled between 180 A and 250 A, the welding voltage is controlled between 20 V and 23 V, the welding speed is controlled between 30 cm / min and 50 cm / min, and the welding heat input is controlled between 5 kJ / cm and 10 kJ / cm; and the temperature between welding passes is controlled to be less than or equal to 150 DEG C. According to the obtained joint, the tensile strength is larger than or equal to 600 MPa, the yield strength is larger than or equal to 440 MPa, the percentage elongation after fracture is larger than or equal to 27%, the weld impact is larger than or equal to 90 J, and the heat affected zone impact is larger than or equal to 100 J.

Description

Technical Field

[0001] The present invention relates to the technical field of steel material welding, and in particular to a gas shielded welding method for high-strength and toughness DP540 duplex steel. Background Art

[0002] DP540 duplex steel is widely used in automotive, rail transit, and engineering machinery due to its high strength (tensile strength ≥ 540 MPa), good ductility (elongation ≥ 20%), and lightweight advantages. However, problems such as softening of the heat-affected zone (HAZ), crack sensitivity, and mismatched weld properties during welding have restricted its large-scale application in critical structural components. The microstructure of DP540 duplex steel consists of a ferrite matrix and a dispersed martensite phase. This dual-phase structure gives it an excellent balance of strength and toughness, but it also leads to the following technical difficulties during welding: Softening of the heat-affected zone (HAZ): The welding thermal cycle causes the martensite in the HAZ to temper or partially austenitize, resulting in a decrease in hardness in this area (for example, the hardness of the coarse-grained zone may decrease by 15%-20%), which becomes the source of tensile fracture. For example, the tensile strength of the coarse-grained zone of a flash butt weld may drop to 517 MPa due to coarse grains and martensite decomposition, which is lower than the 540 MPa standard of the base material. Crack sensitivity: Hydrogen intrusion during welding (e.g., from damp electrodes or impure shielding gases) can easily trigger hydrogen-induced delayed cracking, particularly in the hardened HAZ (e.g., near the fusion line). Hydrogen diffusion and stress concentration, combined, significantly increase the risk of crack propagation. Weld performance mismatch: Traditional welding materials (e.g., ER50-6 welding wire) differ significantly from the DP540 base material in composition and phase transformation behavior, which can easily lead to excessive strength (hardness ≥ 250 HV) and insufficient plasticity in the weld zone, resulting in a weak connection structure of "hard and brittle weld-softened HAZ." Summary of the Invention

[0003] The present invention aims to provide a high-strength and toughness DP540 duplex steel gas shielded welding method. Based on the commonly used steel composition system, performance indicators and welding methods, the invention can meet most DP540 duplex steel welding production requirements; the obtained joint has a tensile strength of ≥600MPa, a yield strength of ≥440MPa, an elongation after fracture of ≥27%, a weld impact of ≥90J, and a heat-affected zone impact of ≥100J.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] The present invention provides a high-strength and toughness DP540 dual-phase steel gas shielded welding method, comprising:

[0006] The DP540 duplex steel gas shielded welding adopts the principle of equal strength matching, and the welding material is MERITS-6 solid welding wire with a tensile strength of ≥580MPa, a yield strength of ≥460MPa, and an elongation of ≥26%;

[0007] The shielding gas for gas shielded welding is 80% Ar + 20% CO2 rich argon gas, and the gas pressure and flow rate are controlled between 18 and 24 L / min. The double-sided butt welding is performed with an X-groove angle of 35°, a bluntness of 2mm, and a wire extension length of 15-20mm.

[0008] No preheating treatment is required before welding DP540 duplex steel;

[0009] For gas shielded welding of DP540 duplex steel, the welding current is controlled between 180-250A, the welding voltage is controlled between 20-23V, the welding speed is controlled between 30-50cm / min, and the welding heat input is controlled between 5-10kJ / cm;

[0010] The temperature between welding passes is controlled at ≤150℃.

[0011] Furthermore, the DP540 dual-phase steel contains C, Si, Mn, Cr, Ni, Mo, Nb, and V as main alloying elements, wherein the weight percentage of the chemical composition is: C: 0.07%, Si: 0.35%, Mn: 1.65%, Cr: 0.36%, Al: 0.03%, P: 0.013%, S: 0.001%, and the rest is Fe and impurities.

[0012] Furthermore, the welding current is 180A, the arc voltage is 20V, and the welding speed is 31cm·min -1 .

[0013] Furthermore, the welding current is 200A, the arc voltage is 22V, and the welding speed is 36cm·min -1 .

[0014] Furthermore, the welding current is 250A, the arc voltage is 23V, and the welding speed is 40cm·min -1 .

[0015] Furthermore, the dual-phase steel welding heat input E is 5.3-9.6 kJ / cm.

[0016] Furthermore, the obtained joint meets the following requirements: tensile strength ≥ 600MPa, yield strength ≥ 440MPa, elongation after fracture ≥ 27%, weld impact ≥ 90J, heat-affected zone impact ≥ 100J, the weld microstructure is bainite + ferrite, and the heat-affected zone structure is ferrite and pearlite.

[0017] Compared with the prior art, the present invention has the following beneficial technical effects:

[0018] Based on the above-mentioned gas shielded welding method for DP540 duplex steel, the resulting joint has a tensile strength of ≥600 MPa, a yield strength of ≥440 MPa, an elongation of ≥27%, a weld impact strength of ≥90 J, and a heat-affected zone impact strength of ≥100 J. The weld microstructure is composed of bainite and ferrite, while the heat-affected zone structure is composed of ferrite and pearlite. The joint of the present invention has superior strength and toughness, achieving excellent performance matching that of the parent material. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will be further described below with reference to the accompanying drawings.

[0020] Figure 1 The weld microstructure of the present invention;

[0021] Figure 2 This is the heat affected zone microstructure of the present invention. DETAILED DESCRIPTION

[0022] During implementation, a comparative analysis was conducted on different gas shielded welding methods for DP540 duplex steel. The gas shielded welding process parameters for different embodiments are shown in Table 1, and the corresponding joint mechanical properties for different embodiments are shown in Table 2.

[0023] Table 1 Gas shielded welding process parameters for different embodiments

[0024]

[0025] The DP540 duplex steel in each embodiment is made of the same material, with C, Si, Mn, Cr, Ni, Mo, Nb, and V as the main alloying elements. The chemical composition by weight is as follows: C: 0.07%, Si: 0.35%, Mn: 1.65%, Cr: 0.36%, Al: 0.03%, P: 0.013%, S: 0.001%, and the remainder is Fe and impurities.

[0026] Table 2 Mechanical properties of joints corresponding to different embodiments

[0027]

[0028] As shown in Tables 2 and 3, when the welding heat input E of DP540 duplex steel is within the range of 5.3-9.6 kJ / cm, the tensile fracture location is consistent with the base material, and all mechanical properties meet welding requirements. When the welding heat input exceeds 16 kJ / cm, excessive weld metal deposits result in unnecessary wire waste, and the heat-affected zone (HAZ) increases, making it more susceptible to fracture. When the welding heat input is less than 5 kJ / cm, multiple passes are required, increasing the risk of interpass weld defects, causing inclusions in the weld, and reducing production efficiency. The DP540 duplex steel gas shielded welded joints welded in Examples 1 to 3 of the present invention exhibit superior strength and toughness, matching the properties of the base material and meeting the requirements of engineering applications.

[0029] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A gas shielded welding method for high-strength and toughness DP540 duplex steel, characterized by: include: The DP540 duplex steel gas shielded welding adopts the principle of equal strength matching, and the welding material is MERITS-6 solid welding wire with a tensile strength of ≥580MPa, a yield strength of ≥460MPa, and an elongation of ≥26%; The shielding gas for gas shielded welding is 80% Ar + 20% CO2 rich argon gas, and the gas pressure and flow rate are controlled between 18 and 24 L / min. The double-sided butt welding is performed with an X-groove angle of 35°, a bluntness of 2mm, and a wire extension length of 15-20mm. No preheating treatment is required before welding DP540 duplex steel; For gas shielded welding of DP540 duplex steel, the welding current is controlled between 180-250A, the welding voltage is controlled between 20-23V, the welding speed is controlled between 30-50cm / min, and the welding heat input is controlled between 5-10kJ / cm; The temperature between welding passes is controlled at ≤150℃.

2. The high-strength and toughness DP540 dual-phase steel gas shielded welding method according to claim 1, characterized in that: The DP540 dual-phase steel contains C, Si, Mn, Cr, Ni, Mo, Nb, and V as main alloying elements, wherein the weight percentage of the chemical composition is: C: 0.07%, Si: 0.35%, Mn: 1.65%, Cr: 0.36%, Al: 0.03%, P: 0.013%, S: 0.001%, and the rest is Fe.

3. The high-strength and toughness DP540 dual-phase steel gas shielded welding method according to claim 1, characterized in that: Welding current 180A, arc voltage 20V, welding speed 31cm·min -1 .

4. The high-strength and toughness DP540 dual-phase steel gas shielded welding method according to claim 1, characterized in that: Welding current 200A, arc voltage 22V, welding speed 36cm·min -1 .

5. The high-strength and toughness DP540 dual-phase steel gas shielded welding method according to claim 1, characterized in that: Welding current 250A, arc voltage 23V, welding speed 40cm·min -1 .

6. The high-strength and toughness DP540 dual-phase steel gas shielded welding method according to claim 1, characterized in that: The dual-phase steel welding heat input E is 5.3-9.6 kJ / cm.

7. The high-strength and toughness DP540 dual-phase steel gas shielded welding method according to claim 1, characterized in that: The obtained joint meets the following requirements: tensile strength ≥ 600MPa, yield strength ≥ 440MPa, elongation after fracture ≥ 27%, weld impact ≥ 90J, heat-affected zone impact ≥ 100J, weld microstructure is bainite + ferrite, and heat-affected zone structure is ferrite and pearlite.

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