Welding wire for 780 MPa grade wheel steel and laser-electric arc hybrid welding process

Abstract

The invention discloses a welding wire for 780 MPa grade wheel steel and a laser-arc hybrid welding process. The welding wire comprises the following chemical components in percentage by weight: 0.06%-0.08% of C, 0.30%-0.80% of Si, 1.80%-2.0% of Mn, 1.5%-2.0% of Ni, 0.20%-0.50% of Cu, 0.20%-0.50% of Mo, 0.04%-0.07% of Nb, 0.06%-0.10% of Ti, 0.03%-0.07% of V, 0.015%-0.10% of RE, less than or equal to 0.010% of S, less than or equal to 0.010% of P and the balance of Fe and inevitable impurities. A welding joint obtained through the welding wire and the process has good mechanical performance, the strength coefficient of the joint is 1.0, the impact absorption energy at the temperature of-20 DEG C is larger than or equal to 120 J, the fatigue limit sigma 0.1b is larger than or equal to 740 MPa, and the structures of a weld zone are mainly acicular ferrite, bainite and a small amount of proeutectoid ferrite.

Description

Technical Field

[0001] The invention relates to a material welding technology, in particular to a welding wire for 780MPa grade wheel steel and a laser-arc composite welding process. Background Art

[0002] As one of the most important parts of commercial vehicles, wheels must not only ensure the safety, handling stability, and comfort of commercial vehicles, but also ensure energy saving and economy. With the dual carbon goals and the demand for lightweight development of automobiles, high-strength and thinning wheels have become one of the important means of reducing vehicle weight, and wheel steel with a tensile strength of 780MPa has gradually been developed and applied.

[0003] In the application process, the main method for wheel steel welding is flash butt welding. Since the use conditions have high requirements on the fatigue performance of automobile wheel steel welded joints, the flash butt welding interface area is prone to coarse Widmanstätten structure, insufficient plasticity, and poor fatigue performance; while the use of laser-arc hybrid welding lacks the necessary supporting welding materials and their application guidance. Therefore, it is urgent to carry out the research and development of 780MPa wheel steel welding wire and its high-efficiency and high-quality welding technology.

[0004] As an efficient and high-quality welding method, laser-arc hybrid welding has the characteristics of fast welding speed, deep penetration, high precision and good adaptability. Laser-arc hybrid welding has the advantages of fast laser welding speed, small heat-affected zone, narrow weld and good weld appearance, and combines the advantages of gas metal arc welding in energy efficiency, gap bridging ability, cooling speed and energy coupling power. The increase in welding speed and the reduction in heat input greatly reduce welding deformation.

[0005] In summary, the use of laser-arc hybrid welding for 780MPa wheel steel can effectively reduce welding deformation, improve the welding quality and efficiency of vehicle thin plate structures, meet the needs of industry applications, and enhance my country's core automotive manufacturing capabilities. However, given the characteristics of laser-arc hybrid welding, there is currently a lack of supporting welding materials for laser-arc hybrid welding of 780MPa wheel steel. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a welding wire for 780MPa grade wheel steel with good welding effect; the present invention also provides a laser-arc composite welding process for 780MPa grade wheel steel.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is that the chemical composition of the welding wire and its weight percentage are: C 0.06%-0.08%, Si 0.30%-0.80%, Mn 1.80%-2.0%, Ni 1.5%-2.0%, Cu 0.20%-0.50%, Mo 0.20%-0.50%, Nb 0.04%-0.07%, Ti 0.06%-0.10%, V 0.03%-0.07%, RE0.015%-0.10%, S≤0.010%, P≤0.010%, and the balance is Fe and unavoidable impurities.

[0008] Furthermore, the welding wire is suitable for 780MPa grade wheel steel with a thickness of 3 to 8 mm.

[0009] The design mechanism of each component of the present invention is: C is the main strengthening element in the weld, and increasing the C content can significantly increase the strength. However, too high a C content will reduce toughness, and too low a C content cannot guarantee weld strength, so the C content is controlled at 0.06% to 0.08%.

[0010] Si is dissolved in ferrite structure and has solid solution strengthening effect, which is a strengthening alloy element. The increase of Si content promotes the formation of MA components in the weld, which reduces the weldability and low temperature impact toughness of the material. Therefore, the Si content is controlled within 0.30% to 0.80% as much as possible.

[0011] Mn is the main alloying element in steel. Appropriate Mn can promote and refine acicular ferrite to improve strength; in addition, Mn can also promote weld deoxidation. However, excessive Mn content will cause Mn segregation and produce large blocky MA components, resulting in coarse grains and reduced toughness. Therefore, the Mn content is controlled at 1.80% to 2.00%.

[0012] Ni is an important alloying element in welds. Adding appropriate Ni on the basis of low C can not only improve strength but also have less damage to toughness. Ni can also reduce the resistance to dislocation movement in the lattice and reduce the interaction energy between dislocations and interstitial elements, thereby promoting stress relaxation, reducing the brittle transition temperature, and significantly improving the low-temperature toughness of the material. At the same time, considering the control cost and low-temperature toughness requirements, the Ni content is generally controlled at 1.5% to 2.0%.

[0013] Appropriate Cu element can improve the corrosion resistance of steel and the conductivity of welding wire, but a large Cu content will increase the tendency to crack, so the Cu content must be strictly controlled, and the Cu content should be controlled at 0.20% to 0.50%.

[0014] Mo can reduce the phase transition temperature, inhibit the formation of proeutectoid ferrite, promote the transformation of acicular ferrite, increase the proportion of acicular ferrite, and improve the precipitation strengthening effect of carbonitrides. Therefore, Mo can improve strength, refine grains, reduce the ductile-brittle transition temperature, and improve the precipitation strengthening effect of Nb carbonitrides. This welding wire sets Mo between 0.20% and 0.50%.

[0015] The Nb element in steel can refine austenite grains, increase the strength of steel, and improve welding performance. It can have a strong inhibitory effect on recrystallization, resist the grain coarsening of Mn and the negative welding effect brought by Si. Considering the high Mn content of the present invention, the Nb content is controlled at 0.04% to 0.07%.

[0016] V can refine the grains, improve strength and toughness, and can form carbides with C to further improve the strength of the weld, so the V reduction is controlled at 0.03% to 0.07%.

[0017] Ti can form fine dispersed composite oxides during welding, which can provide nucleation sites for acicular ferrite, thereby promoting the formation of acicular ferrite. In addition, these oxides can also appear at the austenite grain boundaries, thereby effectively inhibiting the coarsening of grains, improving the weldability of the material, and improving the low-temperature impact toughness. Therefore, the Ti content can be controlled at 0.06% to 0.10%.

[0018] S easily forms compounds such as FeS and MnS in the weld and segregates at the grain boundaries. Since the sulfide eutectic temperature is low and distributed in a network, it will reduce the impact toughness of the material. During the welding process, S easily promotes the formation of hot cracks and reduces weldability, so the S content in the weld must be strictly controlled to 0.010% or less.

[0019] Phosphide can be generated in steel and can be completely dissolved in ferrite, which has a significant impact on the weld and easily causes cold brittleness. Due to the low melting point of phosphide, segregation will form at the grain boundary during rapid cooling, resulting in hot cracks. Although the increase in P content can improve the strength and hardness of the weld, it will also cause a sharp drop in the plasticity and toughness of the material. Therefore, the P content is controlled at 0.010% or less.

[0020] RE can improve the size and shape of inclusions in the weld metal, achieving the purpose of purifying the weld metal. Appropriate rare earth elements can also improve the low-temperature toughness and process performance of the weld. The rare earth element content of the welding wire of the present invention is set at 0.015% to 0.10%.

[0021] In order to solve the above technical problems, the process of the present invention adopts the above welding wire, and the welding process parameters adopted are: laser power 4.5~6.0kW, wire spacing 3~5mm, welding speed 1.0~2.0m / min, wire feeding speed 5~10m / min, welding voltage 20~28V, welding current 160~280A.

[0022] Furthermore, the welding process uses a protective gas with the following volume ratio: Ar+2%~5%O2 or Ar+5%~20%CO2 mixed gas.

[0023] The beneficial effects of the above technical solution are as follows: the present invention provides a 780MPa wheel steel laser-arc hybrid welding supporting welding material and welding process, the obtained welded joint has good mechanical properties, the joint strength coefficient is 1.0, the -20℃ impact absorption energy is ≥120J, and the fatigue limit σ 0.1b ≥740Mpa, the microstructure of the weld zone is mainly acicular ferrite, bainite and a small amount of proeutectoid ferrite. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0025] Figure 1 This is a microstructure diagram of the laser-arc hybrid welding weld zone obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0026] Example 1: The welding wire for 780MPa grade wheel steel and the laser-arc hybrid welding process are described as follows.

[0027] For 6 mm thick 7800 MPa grade wheel steel, the following welding wire is used for laser-arc hybrid welding. The chemical composition weight percentage of the welding wire is: C 0.065%, Si 0.80%, Mn 1.95%, Ni 2.0%, Cu 0.28%, Mo 0.35%, Nb0.07%, Ti 0.06%, V 0.047%, RE 0.075%, S 0.010%, P 0.008%, and the balance is Fe and unavoidable impurities.

[0028] The welding parameters are: laser power 5.5kW, filament spacing 4mm, welding speed 1.4m / min, wire feeding speed 6m / min, welding voltage 22V, current 200A, and the shielding gas is a mixed gas with a volume ratio of 98%Ar+2%O2.

[0029] The microstructure of the laser-arc hybrid welding weld zone is mainly composed of acicular ferrite, bainite and a small amount of proeutectoid ferrite, such as Figure 1As shown. The welded joint has good mechanical properties, the tensile specimen breaks at the base material, the welded joint strength coefficient is 1.0, the -20℃ impact absorption energy is 125J, and the fatigue limit σ 0.1b It is 820MPa.

[0030] Example 2: The welding wire for 780MPa grade wheel steel and the laser-arc hybrid welding process are described as follows.

[0031] For 8 mm thick 780 MPa grade wheel steel, the following welding wire is used for laser-arc hybrid welding. The chemical composition weight percentage of the welding wire is: C 0.08%, Si 0.60%, Mn 1.80%, Ni 1.85%, Cu 0.20%, Mo 0.50%, Nb0.067%, Ti 0.10%, V 0.06%, RE 0.015%, S 0.007%, P 0.005%, and the balance is Fe and unavoidable impurities.

[0032] The welding parameters are: laser power 6.0kW, filament spacing 5mm, welding speed 1.2m / min, wire feeding speed 7.5m / min, welding voltage 23.3V, welding current 212A, and the shielding gas is a mixed gas with a volume ratio of 95%Ar+5%O2.

[0033] The obtained laser-arc hybrid welding weld zone microstructure is mainly composed of acicular ferrite, bainite and a small amount of proeutectoid ferrite. The obtained weld joint has good mechanical properties. The tensile specimen breaks at the base material. The weld joint strength coefficient is 1.0, the -20℃ impact absorption energy is 125J, and the fatigue limit σ 0.1b It is 815MPa.

[0034] Example 3: The welding wire for 780MPa grade wheel steel and the laser-arc hybrid welding process are described as follows.

[0035] Except that the protective gas used is a mixed gas of 97% Ar+3% O2 ​​by volume, the rest is the same as Example 1.

[0036] The microstructure of the laser-arc hybrid weld zone is mainly acicular ferrite, bainite and a small amount of proeutectoid ferrite. The welded joint has good mechanical properties. The tensile specimen breaks at the base material. The strength coefficient of the welded joint is 1.0, the impact absorption energy at -20℃ is 141J, and the fatigue limit σ 0.1b It is 843MPa.

[0037] Example 4: The welding wire for 780MPa grade wheel steel and the laser-arc hybrid welding process are described as follows.

[0038] For 4 mm thick 780 MPa grade wheel steel, the following welding wire is used for laser-arc hybrid welding. The chemical composition weight percentage of the welding wire is: C 0.06%, Si 0.30%, Mn 1.9%, Ni 1.5%, Cu 0.40%, Mo 0.45%, Nb0.04%, Ti 0.085%, V 0.03%, RE 0.10%, S 0.010%, P 0.010%, and the balance is Fe and unavoidable impurities.

[0039] The welding parameters are: laser power 4.5kW, filament spacing 3mm, welding speed 1.4m / min, wire feeding speed 5m / min, welding voltage 20.4V, welding current 160A, and the shielding gas is a mixed gas with a volume ratio of 95%Ar+5%CO2.

[0040] The microstructure of the laser-arc hybrid weld zone is mainly acicular ferrite, bainite and a small amount of proeutectoid ferrite. The welded joint has good mechanical properties. The tensile specimen breaks at the base material. The strength coefficient of the welded joint is 1.0, the impact absorption energy at -20℃ is 122J, and the fatigue limit σ 0.1b It is 805MPa.

[0041] Example 5: The welding wire for 780MPa grade wheel steel and the laser-arc hybrid welding process are described as follows.

[0042] For 6 mm thick 780 MPa grade wheel steel, the following welding wire is used for laser-arc hybrid welding. The chemical composition weight percentage of the welding wire is: C 0.068%, Si 0.68%, Mn 2.0%, Ni 1.8%, Cu 0.50%, Mo 0.20%, Nb0.057%, Ti 0.086%, V 0.07%, RE 0.045%, S 0.007%, P 0.006%, and the balance is Fe and unavoidable impurities.

[0043] The welding parameters are: laser power 5.5kW, filament spacing 5mm, welding speed 1.0m / min, wire feeding speed 5m / min, welding voltage 20V, welding current 160A, and the shielding gas is a mixed gas of 80%Ar+20%CO2 by volume.

[0044] The obtained laser-arc hybrid welding weld zone microstructure is mainly composed of acicular ferrite, bainite and a small amount of proeutectoid ferrite. The obtained weld joint has good mechanical properties. The tensile specimen breaks at the base material. The weld joint strength coefficient is 1.0, the -20℃ impact absorption energy is 120J, and the fatigue limit σ 0.1b It is 778MPa.

[0045] Example 6: The welding wire for 780MPa grade wheel steel and the laser-arc hybrid welding process are described as follows.

[0046] Except for the following process parameters, the rest are the same as in Example 5: welding speed 2.0 m / min, wire feeding speed 10 m / min, welding voltage 28 V, welding current 280 A, and the shielding gas used is a mixed gas of 88% Ar + 12% CO2 by volume.

[0047] The microstructure of the laser-arc hybrid welding weld zone is mainly acicular ferrite, bainite and a small amount of proeutectoid ferrite. The obtained weld joint has good mechanical properties. The tensile specimen breaks at the base material. The weld joint strength coefficient is 1.0, the impact absorption energy at -20℃ is 137J, and the fatigue limit σ 0.1b It is 740MPa.

Claims

1. A 780MPa grade wheel steel welding wire, characterized in that: The chemical composition of the welding wire and its weight percentage are: C 0.06% ~ 0.08%, Si 0.30% ~ 0.80%, Mn 1.80% ~ 2.0%, Ni 1.5% ~ 2.0%, Cu 0.20% ~ 0.50%, Mo 0.20% ~ 0.50%, Nb 0.04% ~ 0.07%, Ti 0.06% ~ 0.10%, V 0.03% ~ 0.07%, RE 0.015% ~ 0.10%, S ≤ 0.010%, P ≤ 0.010%, the balance is Fe and unavoidable impurities.

2. The 780MPa grade wheel steel welding wire according to claim 1, characterized in that: The welding wire is suitable for 780MPa grade wheel steel with a thickness of 3 to 8 mm.

3. A laser-arc hybrid welding process for 780MPa grade wheel steel, using the welding wire according to claim 1, characterized in that: The welding process parameters are: laser power 4.5~6.0kW, wire spacing 3~5mm, welding speed 1.0~2.0m / min, wire feeding speed 5~10m / min, welding voltage 20~28V, welding current 160~280A.

4. The laser-arc hybrid welding process for 780 MPa grade wheel steel according to claim 3, characterized in that: The welding process adopts the protective gas with the following volume ratio: Ar+2%~5%O2 or Ar+5%~20%CO2 mixed gas.

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