CN113333957A

CN113333957A - laser-MAG (metal active gas) arc hybrid welding method for wide thin plate for ship

Info

Publication number: CN113333957A
Application number: CN202110556617.1A
Authority: CN
Inventors: 靳星; 吴俊平; 徐椿森; 王道远; 张朋彦; 杨玲
Original assignee: Anhui University of Technology AHUT; Nanjing Iron and Steel Co Ltd
Current assignee: Anhui University of Technology AHUT; Nanjing Iron and Steel Co Ltd
Priority date: 2021-05-21
Filing date: 2021-05-21
Publication date: 2021-09-03
Anticipated expiration: 2041-05-21
Also published as: CN113333957B

Abstract

The invention discloses a laser-MAG electric arc hybrid welding method for a marine wide thin plate, which is characterized by comprising the following steps of: preparing a steel plate, preparing a welding material, aligning a copper plate with a semicircular groove to the center of the back of a welding line and tightly attaching the copper plate to the back of the steel plate, introducing pure argon into the groove before welding to protect the back of the welding line, adopting laser-electric arc composite welding without grooving, leaving a gap and forming two sides by single-pass single-side welding. The invention can improve the strength of a heat affected zone, improve the mechanical property of a welding joint, realize high-efficiency welding and ensure better welding joint quality.

Description

laser-MAG (metal active gas) arc hybrid welding method for wide thin plate for ship

Technical Field

The invention belongs to the technical field of special welding, and particularly relates to a laser-electric arc hybrid welding method.

Background

The laser-electric arc hybrid welding combines the advantages of laser welding and electric arc welding, combines two heat sources with completely different energy transmission mechanisms of laser and electric arc together and acts on the same molten pool to form an efficient heat source, so that the penetration depth is increased, the welding speed is increased, the welding efficiency is high, the welding deformation is reduced, the complete penetration of a medium plate can be realized through single welding, and the laser-electric arc hybrid welding is widely applied and popularized in important fields of national economy such as automobiles, machinery, shipbuilding, petrochemical industry, aviation, aerospace, nuclear power and the like.

At present, a large number of wide and thin steel plates with the thickness of 4-6mm and the width of 2400-3000mm are needed to be used in the wide and thin plate welding process of the marine structural member, especially in the upper-layer building of a large passenger liner. In order to ensure the welding quality, the application of laser-electric arc hybrid welding becomes a necessary process technology, and by applying the technology, a groove does not need to be processed on a steel plate, no gap can be left in the assembly of the steel plate, the single-side welding and double-side forming can be realized, the construction difficulty is greatly reduced, and the efficiency is improved. The traditional welding method of the wide thin plate adopts a metal inert gas (MAG) method, needs to be filled with a large amount of welding wires, needs a slow welding speed, has large welding heat input, causes a large width of a welding heat affected zone, has a coarse texture of the heat affected zone, generates an obvious softening phenomenon of the heat affected zone, and has tensile strength reduced by about 1/3 compared with that of a base metal. In the laser-arc hybrid welding method, the energy density is improved due to laser welding, the welding speed is improved compared with that of arc welding, but the phenomenon of softening of a welding heat affected zone is still obvious.

Researchers at home and abroad carry out a great deal of research work on the welding technology of the steel plates, including welding process and weldability, the research focuses on the influence of welding process parameters on the structure and performance, and the research finds that the softening of a heat affected zone is caused by adopting a laser-electric arc composite welding method, and the strength and the hardness are obviously reduced mainly because a coarse martensite structure is formed in a coarse crystal zone of the heat affected zone, so that the post-welding fracture is caused at the part. Welding tests are carried out on a steel plate with the thickness of 1.5mm by adopting a laser by Wangjinfeng, the width of a softening area is found to be 1.2-2.0 mm, the microhardness is reduced by 20 percent compared with that of a base material, the average size of martensite formed in a heat affected area is 70 mu m, and tensile test fracture also occurs in the softening area; the Narasimohan adopts a CO2 laser to perform laser tailor-welding on the steel plate, and finds that the width of a softening zone is 2-4 mm, the microhardness is reduced by 22% compared with that of a base material, the average size of martensite formed in a heat affected zone is 80 mu m, and fracture occurs in the softening zone in a tensile test and a forming test. Therefore, if the size of the softening zone can be reduced and the formation of a very fine martensite structure in the heat affected zone can be controlled, the strength of the welded joint can be effectively improved, and the probability of crack generation and cracking can be reduced.

The size of the softening zone and the size of the martensite structure formed in the heat affected zone are both related to the heat dissipation rate of the welding process. The heat conduction of the welding seam of the existing laser-electric arc composite welding depends on air transmission, the heat is radiated by utilizing the natural heat radiation way of air, the heat radiation speed is slow, the size of a softening area is large, and the martensite structure formed in a heat affected area is thick. If additional measures can be taken to increase the rate of heat dissipation, the size of the softening zone can be significantly reduced and the martensite grain size can be refined.

Disclosure of Invention

In order to solve the problems of large width of a softening area and thick martensite structure in a heat affected zone of a laser-arc hybrid welding wide thin plate, the invention provides a laser-MAG arc hybrid welding method of a marine wide thin plate, which is characterized by comprising the following steps:

preparing a steel plate: the thickness of the steel plate is 4-6mm, the width of the steel plate is 2400-3000mm, and the steel plate comprises the following elements in percentage by mass: c: 0.08-0.17%, Si: 0.15-0.30%, Mn: 1.1 to 1.7%, Nb: 0.01-0.03%, Ti: 0.01-0.02%, Al: 0.03-0.05% and the balance of Fe; the steel plate is a ferrite and pearlite structure;

preparing a welding material: the diameter of the welding wire is 1.2mm, and the welding wire comprises the following elements in percentage by mass: c: 0.06-0.18%, Si: 0.7-1.2%, Mn: 1.5-1.9%, Cu: 0.2-0.6% of Fe, and the balance of Fe;

aligning a copper plate with a semicircular groove to the center of the back of the welding seam and tightly attaching the copper plate to the back of the steel plate;

pure argon is introduced into the groove to protect the back of the welding seam before welding;

the laser-arc hybrid welding is adopted, no groove is formed, no gap is left, single-pass single-side welding and double-side forming are carried out, and the process parameters are as follows: the welding voltage is 22-33V, the welding current is 260-370A, the welding speed is 1.8-3.0 m/min, the laser power is 3-8 kW, the defocusing amount is 0-2 mm, and the distance between optical fibers is 1-2 mm; the air flow is 20 to 28L/min.

Preferably, the yield strength of the steel plate is 400-460 MPa, the tensile strength is 550-600 MPa, and the elongation is 28-36%.

Preferably, the weld heat affected zone has a structure of a mixed structure of a large amount of fine martensite and a small amount of ferrite.

Preferably, the martensite crystal grains are refined to 30-35% in average size.

Preferably, the thickness of the copper plate is 8mm, and the diameter of the semicircular groove is set according to the thickness of the steel plate.

Preferably, round holes for introducing pure argon are evenly distributed below the semicircular grooves of the copper plate.

The invention adopts the method of laser-electric arc composite welding and clinging to the copper plate on the back of the welding seam, does not form grooves, does not leave gaps, is formed on the single-pass single-side welding and double-side forming, and accelerates the heat dissipation speed through the quick heat-conducting property of the copper plate, thereby avoiding the heat dissipation by air, aiming at reducing the width of a softening zone and refining a martensite structure simultaneously, thereby improving the strength of a heat-affected zone, improving the mechanical property of a welding joint, realizing high-efficiency welding and ensuring better quality of the welding joint.

The wide thin plate for the ship is welded by adopting the laser-MAG electric arc hybrid welding method for the wide thin plate for the ship, the tissue of a welding heat affected zone is a mixed tissue of a large amount of fine martensite and a small amount of ferrite, compared with the tissue of the heat affected zone of the traditional laser-electric arc hybrid welding, the martensite content in the tissue of the heat affected zone is increased, the ferrite content is reduced, the martensite crystal grains are obviously refined, and the tensile strength of a welding joint is obviously improved. The method has the advantages of simple and convenient operation, easy implementation, high welding speed and good welding effect, and provides a new welding method for industrial high-efficiency and high-quality welding.

Drawings

FIG. 1 is a metallographic picture of a welded steel plate heat-affected zone microstructure of example 1;

FIG. 2 is a metallographic picture of a welded steel plate heat-affected zone microstructure of comparative example 1;

fig. 3 is a schematic view of a copper plate with semicircular grooves.

Detailed Description

Example 1

A marine wide thin plate laser-MAG electric arc hybrid welding method is characterized by comprising the following steps:

preparing a steel plate: the wide thin plate for the welded shipbuilding ship is 4mm in thickness, 2400mm in width and 8000mm in length, and the steel plate comprises the following elements in percentage by mass: c-0.12%, Si-0.25%, Mn-1.67%, Nb-0.028%, Ti-0.017%, Al-0.042%, and the balance of Fe; the yield strength of the steel plate is 430MPa, the tensile strength of the steel plate is 568MPa, and the elongation is 32%; the steel plate is a ferrite and pearlite structure;

preparing a welding material: the diameter of the MAG welding wire is 1.2mm, and the mass percentage of each element of the welding wire is as follows: c-0.10%, Si-1.0%, Mn-1.57%, Cu-0.26%, and the balance of Fe;

a semicircular groove copper plate with the thickness of 8mm, the length of 8000mm, the width of 50mm and the diameter of 3mm is aligned with the center of the back of the welding seam and is tightly attached to the back of the steel plate.

the laser-electric arc composite welding is adopted, and the technological parameters are as follows: the welding voltage is 22-24V, the welding current is 260-270A, the welding speed is 2.8m/min, the laser power is 3.3kW, the defocusing amount is 0mm, and the distance between filaments is 1 mm; the air flow rate is 20L/min.

After welding, a plate-shaped tensile sample is cut out and subjected to a room temperature tensile test, and the tensile strength of a welded joint is 565MPa, the average grain size of martensite in a heat affected zone is 28 microns, the grain refinement degree reaches 31%, and the metallographic structure is a mixed structure of a large amount of fine martensite and a small amount of ferrite as shown in figure 1.

At present, the existing welding platform for laser-arc hybrid welding is made of integrated steel, and the back of a welding seam is in contact with a thick steel plate, so that the heat dissipation speed of the back of the welding seam of the laser-arc hybrid welding is low, and martensite grains are thick.

The copper plate with the semicircular groove is adopted to be attached to the back face of the welding line of the steel plate, the copper plate serves as a liner of the back face of the welding line, and the groove face is attached to the steel plate, so that welding forming and heat dissipation are guaranteed. The schematic diagram of the structure of the copper plate is shown in fig. 3, and preferably, the semicircular groove is located on the central axis of the copper plate, and the length of the copper plate is equal to that of the welding seam.

A copper pipe with the diameter of 2mm is welded under the semicircular groove of the copper plate, the outer wall of the lower portion of the copper pipe is flush with the bottom of the copper plate, and then a circular hole with the diameter of 2mm is drilled at the interval of 20mm below the semicircular groove, so that the circular hole is communicated with the copper pipe. Before welding, argon is introduced into the copper pipe, so that the argon enters the groove through the small hole and fills the groove. In the welding process, make the welding seam back molten bath receive the guard action of flowing argon gas always, simultaneously because the argon gas in the recess has certain pressure, also have certain "lift" effect to the molten bath at the welding seam back, make when the welding arc of welding seam front fluctuates slightly, the influence that the molten bath at the welding seam back can receive reduces, be favorable to the welding seam back to take shape simultaneously, this kind of copper backing plate can also play the effect of welding seam back force-forming when the welding arc of front has great fluctuation, make the weld seam back the weld width be unlikely to too wide. Therefore, the copper backing plate can enable the weld joint formed by one-side welding and two-side welding of laser-arc composite welding to have better stability, the welding deformation is small, the grain refinement is obvious, and the performance of the welding joint is more uniform.

The invention adopts the copper backing plate as an accurate control method. The diameter of the semicircular groove in this embodiment is 3mm, which is the size used when the thickness of the welded wide thin plate is 4 mm. When wide sheets of 5mm and 6mm thickness are welded, the semicircular groove diameters may be increased to 4mm and 5mm, respectively.

Comparative example 1

The same steel plate and welding wire as those in example 1 and the same welding process were used, no copper backing plate was applied to the back surface during welding, the tensile strength of the welded joint was 535MPa, the average grain size of martensite in the heat affected zone was 43 μm, and the microstructure thereof is shown in fig. 2, and the degree of refinement of martensite grains was far less than that in example 1.

Example 2

preparing a steel plate: the wide thin plate for the welded shipbuilding ship is 5mm in thickness, 2800mm in width and 8500mm in length, and the steel plate comprises the following elements in percentage by mass: c-0.09%, Si-0.29%, Mn-1.15%, Nb-0.022%, Ti-0.015%, Al-0.039%, and the balance of Fe; the yield strength of the steel plate is 440MPa, the tensile strength of the steel plate is 588MPa, and the elongation is 35 percent; the steel plate is a ferrite and pearlite structure;

preparing a welding material: the diameter of the MAG welding wire is 1.2mm, and the mass percentage of each element of the welding wire is as follows: c-0.12%, Si-0.78%, Mn-1.75%, Cu-0.22%, and the balance of Fe;

aligning a semicircular groove copper plate with the thickness of 8mm, the length of 8500mm, the width of 50mm and the diameter of 4mm to the center of the back of the welding seam and tightly attaching the copper plate to the back of the steel plate;

the laser-electric arc composite welding is adopted, and the technological parameters are as follows: the welding voltage is 26-28V, the welding current is 290-300A, the welding speed is 2.2m/min, the laser power is 4.6kW, the defocusing amount is 0mm, and the distance between filaments is 1 mm; the air flow rate was 23L/min.

After welding, a plate-shaped tensile sample is cut out to be subjected to a room temperature tensile test, and the tensile strength of a welded joint is 579MPa, the average grain size of martensite in a heat affected zone is 34 mu m, the grain refinement degree reaches 32%, and the metallographic structure is a mixed structure of a large amount of fine martensite and a small amount of ferrite.

Comparative example 2

The same steel plate and welding wire as described in example 2 and the same welding process were used, and no copper backing plate was applied to the back surface during welding, and the tensile strength of the welded joint was 550MPa, the average grain size of martensite in the heat affected zone was 49 μm, and the degree of refinement of the martensite grains was much less than that in example 2.

Example 3

preparing a steel plate: the wide thin plate for the welded shipbuilding has the thickness of 6mm, the width of 3000mm and the length of 7000mm, and the steel plate comprises the following elements in percentage by mass: c-0.16%, Si-0.17%, Mn-1.55%, Nb-0.016%, Ti-0.011%, Al-0.032%, and the balance of Fe; the yield strength of the steel plate is 455MPa, the tensile strength of the steel plate is 598MPa, and the elongation is 33%; the steel plate is a ferrite and pearlite structure;

preparing a welding material: the diameter of the MAG welding wire is 1.2mm, and the mass percentage of each element of the welding wire is as follows: c-0.08%, Si-1.2%, Mn-1.65%, Cu-0.29%, and the balance of Fe;

aligning a semicircular groove copper plate with the thickness of 8mm, the length of 7000mm, the width of 50mm and the diameter of 5mm to the center of the back of the welding seam and tightly attaching the copper plate to the back of the steel plate;

the laser-electric arc composite welding is adopted, and the technological parameters are as follows: the welding voltage is 30-33V, the welding current is 350-370A, the welding speed is 1.8m/min, the laser power is 6kW, the defocusing amount is 0mm, and the distance between filaments is 1 mm; the air flow rate was 27L/min.

After welding, a plate-shaped tensile sample is cut out to be subjected to a room temperature tensile test, and the tensile strength of a welded joint is 592MPa, the average grain size of martensite in a heat affected zone is 43 mu m, the grain refinement degree reaches 34%, and the metallographic structure is a mixed structure of a large amount of fine martensite and a small amount of ferrite.

Comparative example 3

Using the same steel plate and welding wire as described in example 3 and the same welding process, without applying a copper backing plate on the back surface during welding, the tensile strength of the welded joint was 567MPa, the martensite average grain size in the heat affected zone was 64 μm, and the martensite grain refinement degree was much lower than that in example 3.

Claims

1. A marine wide thin plate laser-MAG electric arc hybrid welding method is characterized by comprising the following steps:

2. The laser-MAG arc hybrid welding method for the marine wide thin plate as claimed in claim 1, wherein the steel plate has a yield strength of 400 to 460MPa, a tensile strength of 550 to 600MPa, and an elongation of 28 to 36%.

3. The laser-MAG arc hybrid welding method for marine wide thin plates as claimed in claim 1, wherein the texture of the welding heat affected zone is a mixed texture of a large amount of fine martensite + a small amount of ferrite.

4. The laser-MAG arc hybrid welding method for ship wide plates as claimed in claim 3, wherein the martensite grains are refined to 30-35% in average size.

5. The laser-MAG arc hybrid welding method for marine wide thin plates as claimed in claim 1, wherein the copper plate has a thickness of 8mm and the semicircular groove diameter is set according to the thickness of the steel plate.

6. The laser-MAG arc hybrid welding method for ship wide thin plates as claimed in claim 1, wherein circular holes for introducing pure argon gas are evenly distributed under the semicircular grooves of the copper plate.

7. The marine wide-sheet laser-MAG arc hybrid welding method of claim 1, wherein:

the thickness of the steel plate is 4mm, the width of the steel plate is 2400mm, the length of the steel plate is 8000mm, and the steel plate comprises the following elements in percentage by mass: c-0.12%, Si-0.25%, Mn-1.67%, Nb-0.028%, Ti-0.017%, Al-0.042%, and the balance of Fe;

the welding wire comprises the following elements in percentage by mass: c-0.10%, Si-1.0%, Mn-1.57%, Cu-0.26%, and the balance of Fe;

the laser-arc hybrid welding has the following technological parameters: the welding voltage is 22-24V, the welding current is 260-270A, the welding speed is 2.8m/min, the laser power is 3.3kW, the defocusing amount is 0mm, and the distance between filaments is 1 mm; the air flow rate is 20L/min.

8. The marine wide-sheet laser-MAG arc hybrid welding method of claim 1, wherein:

the thickness of the steel plate is 5mm, the width is 2800mm, the length is 8500mm, and the steel plate comprises the following elements in percentage by mass: c-0.09%, Si-0.29%, Mn-1.15%, Nb-0.022%, Ti-0.015%, Al-0.039%, and the balance of Fe;

the welding wire comprises the following elements in percentage by mass: c-0.12%, Si-0.78%, Mn-1.75%, Cu-0.22%, and the balance of Fe;

the laser-arc hybrid welding has the following technological parameters: the welding voltage is 26-28V, the welding current is 290-300A, the welding speed is 2.2m/min, the laser power is 4.6kW, the defocusing amount is 0mm, and the distance between filaments is 1 mm; the air flow rate was 23L/min.

9. The marine wide-sheet laser-MAG arc hybrid welding method of claim 1, wherein:

the thickness of the steel plate is 6mm, the width is 3000mm, the length is 7000mm, and the steel plate comprises the following elements in percentage by mass: c-0.16%, Si-0.17%, Mn-1.55%, Nb-0.016%, Ti-0.011%, Al-0.032%, and the balance of Fe;

the welding wire comprises the following elements in percentage by mass: c-0.08%, Si-1.2%, Mn-1.65%, Cu-0.29%, and the balance of Fe;

the laser-arc hybrid welding has the following technological parameters: the welding voltage is 30-33V, the welding current is 350-370A, the welding speed is 1.8m/min, the laser power is 6kW, the defocusing amount is 0mm, and the distance between filaments is 1 mm; the air flow rate was 27L/min.