Welding method for improving low-temperature toughness of 550MPa-grade Ti microalloyed high-weather-resistance steel plate welding joint

Abstract

The invention discloses a welding method for improving the low-temperature toughness of a 550MPa-grade Ti microalloyed high-weather-resistance steel plate welding joint, which mainly adopts a laser-MAG composite welding process, and the groove form is a single-sided Y-shaped notch; the chemical components of the adopted welding wire material are close to those of the base material steel plate. The technological parameters of the laser welding are as follows: the included angle between the laser and the welding direction is 83-85 degrees; the defocusing amount is 0 to 0.2 mm; and the laser power is 3800 to 4000 W. The MAG welding process parameters are as follows: protective gas is 85% of Ar and 15% of CO2; the gas flow is 20.0 to 22 mL / min; the welding voltage is 23-24V; the welding current is 240 to 250A; the welding speed is 50-60 cm / min; the advance and retreat frequency of the welding wire is 100-120 Hz, and the diameter of the welding wire is 1.5 The laser-MAG composite welding combined welding method is adopted, the low-temperature impact toughness of a welded joint is improved through research of welding wire material components and combination of reasonable welding process parameters, and the welding method has the advantages of being high in welding efficiency, good in welding quality, excellent in mechanical property and weather resistance of the welded joint and the like.

Description

Technical Field

[0001] The invention relates to the technical field of high-strength weathering steel welding, in particular to a welding method for improving the low-temperature toughness of a 550MPa-grade Ti microalloyed high-weathering steel plate welded joint. Background Art

[0002] Weathering steel, also known as atmospheric corrosion resistant steel, is a low alloy steel between ordinary steel and stainless steel. It is widely used in railways, vehicles, bridges, towers, photovoltaics, high-speed engineering and other steel structures that are exposed to the atmosphere for a long time. At present, the steel plates used for weathering steel for railway containers are mainly 345MPa and 450MPa grade weathering steels with a yield strength of 345MPa and 450MPa. The unit weight is heavy, and the steel consumption and transportation cost are high. As a kind of low alloy high-strength steel, 500MPa grade weathering steel has high strength, good plasticity and toughness, and atmospheric corrosion resistance, and its performance is significantly better than ordinary structural steel.

[0003] High-strength weathering steel has low plasticity and toughness during use, especially the difficulty in balancing easy welding and high corrosion resistance, and matching the corrosion performance of the weld and the base material. Therefore, it is urgent to develop a welding process suitable for high-strength weathering steel. Although the traditional arc welding method has advantages such as multiple welding environments and angles, easy operation, and low cost, the welding quality is relatively general, the heat input is large, and it is easy to have pores and large deformation. Although the stir friction welding process has better welding joint quality, the welding efficiency is low and the process is cumbersome. If welding high-strength materials, the requirements for the stirring head are high. For example, the existing patent CN112899558B discloses a 550MPa grade weathering steel plate with excellent weldability and its manufacturing method, which adopts a low C-low Si-medium Mn low alloy component system and an optimized TMCP process to obtain a small amount of fine ferrite + dispersed bainite structure in the steel plate, and the average grain size of the microstructure is above 15μm. The steel plate has excellent low-temperature toughness, and the welding heat affected zone (HAZ) also has excellent low-temperature toughness during high heat input welding, that is, the impact toughness Akv of the base material and HAZ at -40℃ is ≥100J. Although this method can achieve low-cost and stable mass production, it is limited to the production of medium and thick plates and cannot be used for welding of thin weathering steel plates with smaller thickness.

[0004] Regarding the welding of weathering steel sheets with a thickness not exceeding 16.0 mm, the study found that when using the MAG welding method, there are problems such as softening of the heat affected zone of the weld joint, coarsening of grains and precipitation-strengthened particles, and poor low-temperature impact toughness. Summary of the invention

[0005] Aiming at the technical problems of softening of heat affected zone (HAZ) and deterioration of low temperature impact toughness of welded joints of 550MPa Ti microalloyed high weathering steel plates, the present invention provides a welding method for improving low temperature toughness of welded joints of 550MPa Ti microalloyed high weathering steel plates. A welded joint with excellent comprehensive performance is obtained by an efficient welding method, which solves the problem of poor low temperature toughness of welded joints of 550MPa Ti microalloyed high weathering steel plates and improves welding efficiency.

[0006] The welding method provided by the present invention is applicable to 550MPa grade Ti microalloyed high weathering steel plate, which belongs to high weathering steel for industrial mass production of railway vehicles. The chemical composition of the weathering steel plate is as follows by weight percentage:

[0007] 0.020%≤C≤0.040%, 0.20%≤Si≤0.30%, 0.80%≤Mn≤1.00%, P≤0.012%, S≤0.003%, 0.010%≤Als≤0.045%, 0.055%≤Ti≤0.070%, 0.80%≤Cr≤1.00%, 0.15%≤Ni≤0.25%, 0.30%≤Cu≤0.40%, N≤0.0040%, O≤0.0020%, and the balance is Fe and unavoidable impurities.

[0008] The thickness of the weathering steel plate is ≤16.0mm. The mechanical properties are: ReL≥550MPa, Rm≥600MPa, A≥18%, and the impact energy of the full-size specimen of the V-notch at -60℃ is KV 2 ≥60J, 3 / 4 size specimen impact energy KV 2 ≥45J, half-size specimen impact energy KV 2 ≥30J.

[0009] Research has found that when the weathering steel plate is welded by MAG welding, there are problems such as softening of the heat affected zone of the welded joint, coarsening of the grains and precipitation-strengthened particles, and poor low-temperature impact toughness. Therefore, the present invention adopts a laser-MAG composite welding process, and its groove form is a single-sided Y-shaped notch. The low-temperature impact toughness of the welded joint is improved by designing the welding wire composition and reasonable welding process parameters.

[0010] Laser arc welding has high speed, large depth, small deformation, high degree of automation and production efficiency, and can be welded at room temperature or under special conditions. Compared with arc welding process, it can form deeper and narrower welds and heat-affected zones in the molten pool area. The research results of the inventors show that the weld of laser-MAG hybrid welding has a typical "cup-shaped" shape, and the width and area are greatly reduced compared with MAG welds and heat-affected zones, which can avoid grain and precipitation strengthening granular coarsening, thereby improving the strength and toughness of the welded joint.

[0011] Considering that the elements in the welding wire may be burned at high temperature when welding under high power conditions, the chemical composition of the welding wire material in the present invention is designed to meet the requirements of mechanical properties and impact toughness after welding, and also to meet the requirements that the corrosion properties of the welded joint are equivalent to those of the parent material. Therefore, the chemical composition of the welding wire used in the welding method of the present invention is close to that of the parent material. The chemical composition of the welding wire is as follows by weight percentage:

[0012] 0.06%≤C≤0.08%, 0.30%≤Si≤0.40%, 1.50%≤Mn≤1.60%, P≤0.010%, S≤0.003%, 0.075%≤Ti≤0.090%, 1.00%≤Cr≤1.20%, 0.20%≤Ni≤0.30%, 0.30%≤Cu≤0.30%, N≤0.0040%, O≤0.0020%, and the balance is Fe and unavoidable impurities.

[0013] In order to improve welding efficiency and reduce the width and area of ​​the weld and heat-affected zone, the present invention adopts a specific laser-MAG hybrid welding process, and the wire feeding speed is well matched with the droplet transition to realize a "periodic-intermittent" wire feeding process, that is, when the droplet transitions, by controlling the current size and the wire feeding frequency, and then using the lower temperature of the welding wire to realize the "cold-hot" alternation of the welding process, further reducing the width and area of ​​the weld and heat-affected zone, and refining the size of the weld joint grains and precipitated particles. The process parameters of the laser-MAG hybrid welding process are as follows:

[0014] The process parameters of laser welding are: the angle between the laser and the welding direction is 83°~85°; the defocus is 0~0.2mm; and the laser power is 3800~4000W.

[0015] The process parameters of MAG welding are: the shielding gas is Ar and CO 2 The mixed gas is 85% Ar by volume, CO 2 Volume percentage 15%, gas flow rate 20.0~22mL / min, welding voltage 23~24V, welding current 240~250A.

[0016] Wire feeding rate is 7.0~8.0m / min; welding speed is 50~60cm / min; wire advance and retreat frequency is 100~120Hz, and wire diameter is 1.5m / min.

[0017] Compared with the prior art, the present invention is beneficial in that:

[0018] (1) Compared with the existing MAG welding method, the present invention uses the "periodic-intermittent" wire feeding process to improve the welding efficiency while utilizing the large input of "laser-MAG composite welding". The process control and operation are simple. The method welds 550MPa grade Ti microalloyed high weathering steel plates and has the characteristics of high welding efficiency, good welding quality, excellent mechanical properties of welded joints, low temperature impact toughness and weathering resistance.

[0019] (2) The chemical composition of the welding wire material used in the present invention is close to that of the base material, which can avoid the risk of component segregation in micro-regions during welding, leading to deterioration of performance stability, and improve the toughness of the 550MPa grade Ti microalloyed weathering steel welded joint.

[0020] (3) The strength of the weathering steel welded joint obtained by the present invention is above 680MPa, the full-size impact toughness of the weld at -60°C is above 80J, the 3 / 4-size impact toughness is above 60J, and the half-size impact toughness is above 40J; the full-size impact toughness of the heat-affected zone at -60°C is above 60J, the 3 / 4-size impact toughness is above 45J, and the half-size impact toughness is above 30J.

[0021] (4) The welding method provided by the present invention is also suitable for welding railway vehicle underframes, power towers, bridge steel structures, etc. that serve in low-temperature environments, providing an efficient welding method for the connection and construction of high-strength weathering steels.

[0022] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the laser-MAG composite welding method adopted in the present invention. DETAILED DESCRIPTION

[0024] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0025] Based on the welding method for improving the low temperature toughness of the welded joint of 550MPa grade Ti microalloyed high weathering steel plate of the present invention, three embodiments are provided. The chemical composition of the steel plate (parent material) and welding wire of embodiments 1-3 is shown in Table 1, and the remainder is Fe and unavoidable impurities.

[0026] Table 1 Chemical compositions of steel plates (parent materials) and welding wires of Examples 1-3

[0027]

[0028]

[0029] For the base materials and welding wires of Examples 1-3, two sets of specific welding process parameters are respectively used for welding. For example, for the base materials and welding wires of Example 1, two sets of welding process parameters of Examples 1-1 and 1-2 are used. The welding process parameters are detailed in Table 2.

[0030] Table 2. Welding process parameters

[0031]

[0032] According to the welding process parameters in Table 2, the performance indicators of the welded joint are shown in Table 3.

[0033] Table 3. Performance test results of welded joints

[0034]

[0035]

[0036] The above description is only a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A welding method for improving the low temperature toughness of a 550MPa grade Ti microalloyed high weathering steel plate welded joint, characterized in that: The laser-MAG composite welding process is adopted, and the groove form is a single-sided Y-shaped notch; the chemical composition of the welding wire material used is close to that of the parent steel plate. The chemical composition of the welding wire is as follows by weight percentage: 0.06%≤C≤0.08%, 0.30%≤Si≤0.40%, 1.50%≤Mn≤1.60%, P≤0.010%, S≤0.003%, 0.075%≤Ti≤0.090%, 1.00%≤Cr≤1.20%, 0.20%≤Ni≤0.30%, 0.30%≤Cu≤0.30%, N≤0.0040%, O≤0.0020%, and the balance is Fe.

2. The welding method for improving the low temperature toughness of a 550MPa grade Ti microalloyed high weathering steel plate welded joint according to claim 1, characterized in that: The process parameters of laser welding are: the angle between the laser and the welding direction is 83°~85°; the defocus is 0~0.2mm; and the laser power is 3800~4000W.

3. The welding method for improving the low temperature toughness of a 550MPa grade Ti microalloyed high weathering steel plate welded joint according to claim 2, characterized in that: The process parameters of MAG welding are: the shielding gas is a mixture of Ar and CO2, with Ar volume percentage of 85% and CO2 volume percentage of 15%; the gas flow rate is 20.0~22mL / min; the welding voltage is 23~24V; and the welding current is 240~250A.

4. The welding method for improving the low temperature toughness of a 550MPa grade Ti microalloyed high weathering steel plate weld joint according to claim 3, characterized in that: The wire feeding rate is 7.0-8.0 m / min, the welding speed is 50-60 cm / min, the wire advance and retreat frequency is 100-120 Hz, and the wire diameter is 1.5 m / min.

5. The welding method for improving the low temperature toughness of a 550MPa grade Ti microalloyed high weathering steel plate weld joint according to any one of claims 1 to 4, characterized in that: The chemical composition of the weathering steel plate is as follows by weight percentage: 0.020%≤C≤0.040%, 0.20%≤Si≤0.30%, 0.80%≤Mn≤1.00%, P≤0.012%, S≤0.003%, 0.010%≤Als≤0.045%, 0.055%≤Ti≤0.070%, 0.80%≤Cr≤1.00%, 0.15%≤Ni≤0.25%, 0.30%≤Cu≤0.40%, N≤0.0040%, O≤0.0020%, and the balance is Fe.

6. The welding method for improving the low temperature toughness of a 550MPa grade Ti microalloyed high weathering steel plate weld joint according to claim 5, characterized in that: The thickness of the weathering steel plate is ≤16.0 mm.

7. The welding method for improving the low temperature toughness of a 550MPa grade Ti microalloyed high weathering steel plate weld joint according to claim 6, characterized in that: The mechanical properties of the weathering steel plate are: ReL≥550MPa, Rm≥600MPa, A≥18%, the impact energy of the full-size specimen of the V-notch at -60°C KV2≥60J, the impact energy of the 3 / 4-size specimen KV2≥45J, and the impact energy of the half-size specimen KV2≥30J.

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