A solder for laser welding and a welding process

Abstract

The application relates to the field of welding, and specifically discloses a welding material for laser tailor welding and a tailor welding process. The welding material comprises a first welding material layer, a second welding material layer and a third welding material layer arranged in sequence, the thicknesses of the first welding material layer, the second welding material layer and the third welding material layer account for percentages d1, d2 and d3 of the total thickness of the welding material, and the percentages are (47-74):(20-35):(6-18) in sequence; each welding material layer takes Fe as a base and adds alloy elements C, Mn, Ni, Si, Ce and B; through the addition of the above elements, the wettability of the welding material to a plated layer is good, and the diffusion of Al in the plated layer to a molten pool is inhibited; the welding material can be directly applied to the welding of a steel plate with a plated layer, and does not affect the welding strength of an integrated automobile structural member; meanwhile, the element contents of the welding material layers are different, so that the welding material can be matched with high-strength hot stamping steel and medium-high-strength hot stamping steel, and can be welded according to different steel materials.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and more specifically, to a welding material for laser welding and a welding process. Background Technology

[0002] In the automotive manufacturing industry, to achieve the goal of reducing vehicle weight, a new manufacturing method has been proposed: laser welding to weld automotive structural components of different thicknesses and materials, followed by hot stamping. However, this method faces numerous practical difficulties, primarily because the steel plates used in automotive structural components typically have an anti-corrosion coating, usually an aluminum-rich coating. During welding, this aluminum-rich coating easily enters the molten pool, where aluminum comes into contact with the solder, forming high-temperature ferrite. The strength of high-temperature ferrite is much lower than that of martensite, resulting in a decrease in the tensile strength of the weld. The tensile strength at the weld affects the forming rate and yield of the integrated automotive structural components during hot stamping. The lower the tensile strength at the weld, the more prone the integrated automotive structural components are to cracking, making it difficult to maintain structural stability.

[0003] To solve the above problems, the relevant technologies adopt the following methods:

[0004] The first method involves removing the coating from the steel plates to be welded before laser welding. While this method helps improve the strength of integrated automotive structural components, the coating thickness varies depending on the material and thickness of the steel plates, significantly increasing costs.

[0005] The second method involves using an oxidizing gas to react with the aluminum in the coating under the action of a protective gas to form aluminum oxide. Although aluminum oxide does not affect the toughness of the weld, actual testing has revealed that the reaction time between the oxidizing gas and aluminum is limited, making it difficult to prevent unreacted aluminum from falling into the molten pool and combining with the solder, which can lead to problems such as cracking in integrated automotive structural components.

[0006] Based on the above, the applicant has provided a solution to the difficulties in the molding process of integrated automotive structural components, which allows the welding material to be directly applied to the welding of coated steel plates without affecting the welding strength of the integrated automotive structural components. Summary of the Invention

[0007] To address the issue of plating affecting welding strength during the welding of integrated automotive structural components, this application provides a laser welding solder and welding process. This process simplifies the welding steps and achieves stronger welding strength, helping integrated automotive structural components maintain excellent stability during subsequent hot stamping processes.

[0008] In a first aspect, this application provides a solder for laser welding, employing the following technical solution:

[0009] A laser welding solder includes a first solder layer, a second solder layer and a third solder layer arranged sequentially, wherein the thicknesses of the first solder layer, the second solder layer and the third solder layer are respectively (47-74):(20-35):(6-18) of the total thickness of the solder.

[0010] The chemical element mass percentage of the first solder layer is as follows: C: 0.01-0.03%, Mn: 1.2-1.8%, Ni: 0.8-1.5%, Si: 0.7-1.2%, Ce: 0.01-0.025%, B: 0.001-0.003%, with the balance made up by Fe.

[0011] The chemical element mass percentage of the second solder layer is as follows: C: 0.03-0.07%, Mn: 1.5-2.0%, Ni: 1.0-1.8%, Si=2.5%-0.056×d2, Ce=0.0008×d2, B: 0.001-0.003%, with the balance made up by Fe;

[0012] The chemical element mass percentage of the third solder layer is as follows: C: 0.06-0.1%, Mn: 1.6-2.2%, Ni: 2.5-5.5%, Si=1.8%+0.05×d3, Ce=0.015%+0.0008×d3, B: 0.001-0.002%, with the balance made up by Fe.

[0013] Furthermore, the thickness percentages d1, d2, and d3 between the first solder layer, the second solder layer, and the third solder layer are (60-65):(25-30):(10-15), respectively.

[0014] Furthermore, the chemical element mass percentage of the first solder layer is as follows: C: 0.02%, Mn: 1.5%, Ni: 1.0%, Si: 0.9%, Ce: 0.015%, B: 0.002%, with the balance made up by Fe.

[0015] Furthermore, the chemical element mass percentage of the second solder layer is as follows: C: 0.05%, Mn: 1.8%, Ni: 1.4%, Si = 2.5 - 0.056 × d2, Ce = 0.0008 × d2, B: 0.002%, with the balance made up by Fe.

[0016] Furthermore, the chemical element mass percentage of the third solder layer is as follows: C: 0.08%, Mn: 2.0%, Ni: 4.0%, Si = 1.8 + 0.05 × d3, Ce = 0.015 + 0.0008 × d3, B: 0.002%, with the balance made up by Fe.

[0017] Secondly, this application provides a welding process for laser welding solder, which adopts the following technical solution:

[0018] A welding process for laser welding solder includes the following steps:

[0019] The aforementioned welding material is placed on the weld seam of the steel plate base material to be spliced; the ratio of the weld seam width W between the steel plate base materials to be spliced ​​to the overall width L of the welding material is controlled to be 1.2≤W / L≤1.5, and the ratio of the weld seam depth H between the steel plate base materials to be spliced ​​to the overall thickness D of the welding material is 0.75≤H / D≤0.9.

[0020] Laser welding is performed on the steel plate base materials to be spliced ​​to form the initial weld;

[0021] The initial weld is quenched and cooled to form a welded joint.

[0022] Furthermore, in the laser welding step, the ratio of welding speed S1 to solder feed speed S2 is controlled to be 1.15 ≤ S1 / S2 ≤ 1.2.

[0023] Furthermore, in the laser welding step, the shielding gas is controlled to be carbon dioxide.

[0024] Furthermore, in the quenching and cooling step, the initial weld is held at 850℃-930℃ for 1-5 minutes, followed by cooling, with the cooling rate controlled at ≥25℃ / s.

[0025] Furthermore, in the quenching and cooling step, the initial weld is held at 900°C for 3 minutes, followed by cooling, with the cooling rate controlled at ≥25°C / s.

[0026] Based on the above solution, this application has at least the following advantages:

[0027] First, this application uses a three-layer solder structure. By changing the composition of each layer of solder, the solder can be used to weld hot-formed steel of different materials.

[0028] The first solder layer is mainly composed of C, Mn, Si, Ni, Ce, and B. Ce, in combination with Si, reduces the surface tension of the liquid solder. The first solder layer is in contact with the aluminum-rich coating on the surface, making it easy to wet the coating. It forms high-melting-point compounds with Al, reducing the possibility of Al diffusion into the molten pool. Ni can form and stabilize austenite. In combination with Mn, it expands the austenite region, improves the plasticity and toughness of the weld, and increases the corrosion resistance of the weld. The three elements Mn, Ce, and Si work together to deoxidize, which helps Al form protective aluminum oxide on the weld surface, improving the corrosion resistance of the weld. Ce's strong affinity for oxy and sulfide inhibits the formation of MnS and promotes the formation of equiaxed crystals, thereby refining the grain size and effectively reducing the generation of weld cracks. Ce and B work together to have a synergistic effect in refining the grain size of the weld and heat-affected zone, reducing the weld's susceptibility to hot cracking.

[0029] The second and third solder layers have the same composition as the first solder layer, but different elemental contents. The C, Mn, and Ni elements are gradually increased in the second and third solder layers, making the solder compatible with both high-strength and medium-to-high-strength hot-stamped steels, allowing for welding of different steels. Simultaneously, the content of elements such as Si and Ce is adjusted according to the thickness of the second and third solder layers. As the thickness ratio of the solder layers changes, the melt flow rate of the solder changes in a stepwise manner during welding, reducing the possibility of uneven melt pool flow leading to poor weld formation. The different wettability of the first and third solder layers allows the solder to select the more compatible side for welding based on the carbon equivalent of the hot-formed steel, reducing problems such as weld protrusions and undercut, and contributing to improved weld mechanical properties.

[0030] Second, the thickness of each solder layer in this application is optimized so that the thickness of each solder layer is within a moderate range, which helps to match the flow rate of each solder layer in the molten pool step by step, and the thermal stress between each solder layer is gradually dispersed, reducing the possibility of stress concentration points, thereby improving the fracture elongation of the weld joint and improving the overall toughness of the weld; the mechanical properties of the weld are further improved.

[0031] Third, adjust various parameters of the welding process, adjust the ratio between weld size and solder size, and adjust the melting point of each solder layer. Due to the increased amount of alloying elements added in the third solder layer, the melting point of the third solder layer is the lowest. The third solder layer preferentially contacts and fills the bottom of the weld, while the first solder layer contacts and wets the aluminum-rich coating on the surface. At the same time, control the welding rate and solder feed rate to reduce the possibility of defects such as accumulation and undercut in the weld joint, thereby improving the welding strength. Detailed Implementation

[0032] Example

[0033] Example 1

[0034] A laser welding solder has the following structure: a first solder layer, a second solder layer and a third solder layer are stacked sequentially, wherein the percentages of the thickness of the first solder layer, the thickness of the second solder layer and the thickness of the third solder layer to the total thickness of the solder, d1, d2 and d3, are 47:35:18, respectively.

[0035] Each solder layer is prepared according to the following proportions:

[0036] The chemical element mass percentage of the first solder layer is: C: 0.01%, Mn: 1.2%, Ni: 0.8%, Si: 0.7%, Ce: 0.01%, B: 0.001%, with the balance made up by Fe;

[0037] The chemical element mass percentage of the second solder layer is as follows: C: 0.03%, Mn: 1.5%, Ni: 1.0%, Si = 2.5 - 0.056 × 35 = 0.54%, Ce = 0.0008 × 35 = 0.024%, B: 0.001%, with the balance made up by Fe;

[0038] The chemical element mass percentage of the third solder layer is as follows: C: 0.06%, Mn: 1.6%, Ni: 2.5%, Si = 1.8 + 0.05 × 18 = 2.7%, Ce = 0.015 + 0.0008 × 18 = 0.0294%, B: 0.001%, with the balance made up by Fe.

[0039] Example 2

[0040] A laser welding solder has the following structure: a first solder layer, a second solder layer and a third solder layer are stacked sequentially, wherein the percentages of the thickness of the first solder layer, the thickness of the second solder layer and the thickness of the third solder layer to the total thickness of the solder, d1, d2 and d3, are 47:35:18, respectively.

[0041] Each solder layer is prepared according to the following proportions:

[0042] The chemical element mass percentage of the first solder layer is: C: 0.02%, Mn: 1.5%, Ni: 1.0%, Si: 0.9%, Ce: 0.015%, B: 0.002%, with the balance made up by Fe;

[0043] The chemical element mass percentage of the second solder layer is as follows: C: 0.05%, Mn: 1.8%, Ni: 1.4%, Si = 2.5% - 0.056 × 35% = 0.54%, Ce = 0.0008% × 35% = 0.028%, B: 0.002%, with the balance made up by Fe;

[0044] The chemical element mass percentage of the third solder layer is as follows: C: 0.08%, Mn: 2.0%, Ni: 4.0%, Si = 1.8% + 0.05 × 18% = 2.7%, Ce = 0.015% + 0.0008 × 18% = 0.0294%, B: 0.002%, with the balance made up by Fe.

[0045] Example 3

[0046] A laser welding solder has the following structure: a first solder layer, a second solder layer and a third solder layer are stacked sequentially, wherein the percentages of the thickness of the first solder layer, the thickness of the second solder layer and the thickness of the third solder layer to the total thickness of the solder, d1, d2 and d3, are 47:35:18, respectively.

[0047] Each solder layer is prepared according to the following proportions:

[0048] The chemical element mass percentage of the first solder layer is: C: 0.03%, Mn: 1.8%, Ni: 1.5%, Si: 1.2%, Ce: 0.025%, B: 0.003%, with the balance made up by Fe;

[0049] The chemical element mass percentage of the second solder layer is as follows: C: 0.07%, Mn: 2.0%, Ni: 1.8%, Si = 2.5% - 0.056 × 35% = 0.54%, Ce = 0.0008 × 35% = 0.028%, B: 0.003%, with the balance made up by Fe;

[0050] The chemical element mass percentage of the third solder layer is as follows: C: 0.1%, Mn: 2.2%, Ni: 5.5%, Si = 1.8% + 0.05 × 18% = 2.7%, Ce = 0.015% + 0.0008 × 18% = 0.0294%, B: 0.002%, with the balance made up by Fe.

[0051] Examples 4-6

[0052] A laser welding solder differs from Example 2 in that the thickness ratio of each solder layer is different, as detailed below:

[0053] In Example 4, the percentages of the thickness of the first solder layer, the thickness of the second solder layer, and the thickness of the third solder layer to the total solder thickness, d1, d2, and d3, are 74:20:6, respectively.

[0054] Each solder layer is prepared according to the following proportions:

[0055] The chemical element mass percentage of the first solder layer is: C: 0.02%, Mn: 1.5%, Ni: 1.0%, Si: 0.9%, Ce: 0.015%, B: 0.002%, with the balance made up by Fe;

[0056] The chemical element mass percentage of the second solder layer is as follows: C: 0.05%, Mn: 1.8%, Ni: 1.4%, Si = 2.5% - 0.056 × 20% = 1.38%, Ce = 0.0008% × 20% = 0.016%, B: 0.002%, with the balance made up by Fe;

[0057] The chemical element mass percentage of the third solder layer is as follows: C: 0.08%, Mn: 2.0%, Ni: 4.0%, Si = 1.8% + 0.05 × 6% = 2.1%, Ce = 0.015% + 0.0008 × 6% = 0.0198%, B: 0.002%, with the balance made up by Fe.

[0058] In Example 5, the percentages of the thickness of the first solder layer, the thickness of the second solder layer, and the thickness of the third solder layer to the total solder thickness, d1, d2, and d3, are 60:25:15, respectively.

[0059] Each solder layer is prepared according to the following proportions:

[0060] The chemical element mass percentage of the first solder layer is: C: 0.02%, Mn: 1.5%, Ni: 1.0%, Si: 0.9%, Ce: 0.015%, B: 0.002%, with the balance made up by Fe;

[0061] The chemical element mass percentage of the second solder layer is as follows: C: 0.05%, Mn: 1.8%, Ni: 1.4%, Si = 2.5% - 0.056 × 25% = 1.1%, Ce = 0.0008% × 25% = 0.02%, B: 0.002%, with the balance made up by Fe;

[0062] The chemical element mass percentage of the third solder layer is as follows: C: 0.08%, Mn: 2.0%, Ni: 4.0%, Si = 1.8% + 0.05 × 10% = 2.3%, Ce = 0.015% + 0.0008 × 10% = 0.023%, B: 0.002%, with the balance made up by Fe.

[0063] In Example 6, the percentages of the thickness of the first solder layer, the thickness of the second solder layer, and the thickness of the third solder layer to the total solder thickness, d1, d2, and d3, are 60:30:10, respectively.

[0064] Each solder layer is prepared according to the following proportions:

[0065] The chemical element mass percentage of the first solder layer is: C: 0.02%, Mn: 1.5%, Ni: 1.0%, Si: 0.9%, Ce: 0.015%, B: 0.002%, with the balance made up by Fe;

[0066] The chemical element mass percentage of the second solder layer is as follows: C: 0.05%, Mn: 1.8%, Ni: 1.4%, Si = 2.5% - 0.056 × 30% = 1.1%, Ce = 0.0008% × 25% = 0.02%, B: 0.002%, with the balance made up by Fe;

[0067] The chemical element mass percentage of the third solder layer is as follows: C: 0.08%, Mn: 2.0%, Ni: 4.0%, Si = 1.8% + 0.05 × 15% = 2.55%, Ce = 0.015% + 0.0008 × 15% = 0.027%, B: 0.002%, with the balance made up by Fe.

[0068] Comparative Examples 1-3

[0069] A laser welding solder differs from Example 1 in that: Comparative Examples 1-3 are all single-layer solders, as detailed below:

[0070] In Comparative Example 1, the chemical element mass percentage of the solder was: C: 0.01%, Mn: 1.2%, Ni: 0.8%, Si: 0.7%, Ce: 0.01%, B: 0.001%, with the balance made up by Fe.

[0071] In Comparative Example 2, the chemical element mass percentage of the solder is as follows: C: 0.03%, Mn: 1.5%, Ni: 1.0%, Si = 2.5% - 0.056 × 35% = 0.54%, Ce = 0.0008 × 35% = 0.024%, B: 0.001%, with the balance made up by Fe.

[0072] In Comparative Example 3, the chemical element mass percentage of the solder is as follows: C: 0.06%, Mn: 1.6%, Ni: 2.5%, Si = 1.8% + 0.05 × 18% = 2.7%, Ce = 0.015% + 0.0008 × 18% = 0.0294%, B: 0.001%, with the balance made up by Fe.

[0073] Comparative Example 4

[0074] A laser welding solder differs from Example 1 in that the thickness ratio of each solder layer is different, as detailed below:

[0075] The percentages of the thickness of the first solder layer, the thickness of the second solder layer, and the thickness of the third solder layer to the total solder thickness, d1, d2, and d3, are 40:30:30, respectively.

[0076] Each solder layer is prepared according to the following proportions:

[0077] The chemical element mass percentage of the first solder layer is: C: 0.01%, Mn: 1.2%, Ni: 0.8%, Si: 0.7%, Ce: 0.01%, B: 0.001%, with the balance made up by Fe;

[0078] The chemical element mass percentage of the second solder layer is as follows: C: 0.03%, Mn: 1.5%, Ni: 1.0%, Si = 2.5% - 0.056 × 30% = 0.82%, Ce = 0.0008 × 30% = 0.024%, B: 0.001%, with the balance made up by Fe;

[0079] The chemical element mass percentage of the third solder layer is as follows: C: 0.06%, Mn: 1.6%, Ni: 2.5%, Si = 1.8 + 0.05 × 30% = 3.3%, Ce = 0.015% + 0.0008 × 30% = 0.039%, B: 0.001%, with the balance made up by Fe.

[0080] Application examples and comparisons

[0081] A welding process for laser welding solder is carried out according to the following steps:

[0082] The solder is placed on the weld seam of the steel plate base material to be spliced; one type of steel plate base material to be spliced ​​is 22MnB5 with a coating thickness of 30μm; the other type of steel plate base material to be spliced ​​is HS1000 with a coating thickness of 30μm.

[0083] The ratio of the weld width W between the base steel plates to be spliced ​​to the overall width L of the weld is controlled to be W / L=1.2, and the ratio of the weld depth H between the base steel plates to be spliced ​​to the overall thickness D of the weld is H / D=0.9.

[0084] Laser welding was performed on the steel plate base material to be spliced, and the ratio of welding speed S1 to solder feed speed S2 was controlled to be S1 / S2=1.15. Carbon dioxide was used as the shielding gas to form the initial weld.

[0085] The initial weld was quenched and cooled at 850℃ for 5 minutes, followed by cooling at a rate of 25℃ / s. After cooling, a welded joint was formed.

[0086] Application Examples 1-6 and Comparative Examples 1-4 all employ the above-described welding process, differing only in the source of the solder, as detailed below:

[0087] The solder used in Application Example 1 was prepared according to Example 1;

[0088] The solder used in Application Example 2 was prepared according to Example 2;

[0089] The solder used in Application Example 3 was prepared according to Example 3;

[0090] The solder used in Application Example 4 was prepared according to Example 4;

[0091] The solder used in Application Example 5 was prepared according to Example 5;

[0092] The solder used in Application Example 6 was prepared according to Example 6;

[0093] The solder used in Comparative Example 1 was made from Comparative Example 1;

[0094] The solder used in Comparative Example 2 was made from Comparative Example 2;

[0095] The solder used in Comparative Example 3 was made from Comparative Example 3;

[0096] The solder used in Comparative Example 4 was made from Comparative Example 4.

[0097] Application Example 7

[0098] A welding process for laser welding solder is carried out according to the following steps:

[0099] The solder prepared in Example 5 was placed on the weld of the steel plate base material to be spliced; one of the steel plate base materials to be spliced ​​was 22MnB5 with a coating thickness of 30μm; the other steel plate base material to be spliced ​​was HS1000 with a coating thickness of 30μm.

[0100] The ratio of the weld width W between the base steel plates to be spliced ​​to the overall width L of the weld is controlled to be W / L=1.3, and the ratio of the weld depth H between the base steel plates to be spliced ​​to the overall thickness D of the weld is H / D=0.85.

[0101] Laser welding was performed on the steel plate base material to be spliced, and the ratio of welding speed S1 to solder feed speed S2 was controlled to be S1 / S2=1.18. Carbon dioxide was used as the shielding gas to form the initial weld.

[0102] The initial weld was quenched and cooled at 900℃ for 3 minutes, followed by cooling at a rate of 25℃ / s. After cooling, a welded joint was formed.

[0103] Application Example 8

[0104] A welding process for laser welding solder is carried out according to the following steps:

[0105] The solder prepared in Example 5 was placed on the weld of the steel plate base material to be spliced; one of the steel plate base materials to be spliced ​​was 22MnB5 with a coating thickness of 30μm; the other steel plate base material to be spliced ​​was HS1000 with a coating thickness of 30μm.

[0106] The ratio of the weld width W between the base steel plates to be spliced ​​to the overall width L of the weld is controlled to be W / L=1.3, and the ratio of the weld depth H between the base steel plates to be spliced ​​to the overall thickness D of the weld is H / D=0.85.

[0107] Laser welding was performed on the steel plate base material to be spliced, and the ratio of welding speed S1 to solder feed speed S2 was controlled to be S1 / S2=1.18. Carbon dioxide was used as the shielding gas to form the initial weld.

[0108] The initial weld was quenched and cooled at 900℃ for 3 minutes, followed by cooling at a rate of 25℃ / s. After cooling, a welded joint was formed.

[0109] Application Example 9-10

[0110] The welding process for laser welding solder differs from that in Application Example 7 in that the base material of the steel plates to be welded is of a different type, as detailed below:

[0111] In Application Example 9, one type of steel plate base material to be spliced ​​is 22MnB5 with a coating thickness of 30μm; the other type of steel plate base material to be spliced ​​is HS500 with a coating thickness of 30μm.

[0112] In Application Example 10, one type of steel plate base material to be spliced ​​is HS1000 with a coating thickness of 30μm; the other type of steel plate base material to be spliced ​​is HS500 with a coating thickness of 30μm.

[0113] Performance testing

[0114] Mechanical properties: Tensile tests were conducted on the welded joints according to the testing standard GB / T 2651-2023. The test results are shown in Table 1 below.

[0115] Stability: The welded joint was heated to 450℃ and hot-stamped. The fracture location of the welded joint after stamping was observed and the fracture elongation was measured.

[0116] Table 1. Performance test data of Application Examples 1-10 and Comparative Application Examples 1-4

[0117]

[0118] in conclusion

[0119] The test data shows that:

[0120] First, Application Example 1 is compared with Application Comparative Examples 1-3. The same size of solder and the same welding process are used. However, the average tensile strength and yield strength of the weld structure made by Application Comparative Examples 1-3 are reduced. This shows that when the solder of the single structure is used to weld different types of steel, the degree of wetting of the solder on the steel is different, resulting in uneven flow of the molten pool. The mechanical properties of the weld are deteriorated, which leads to the fracture of the weld joint during hot stamping.

[0121] Second, Application Example 1 and Application Comparative Example 4 form a single comparison. Although the solder used in Application Comparative Example 4 has a three-layer structure, the content of elements such as Si and Ce in the second and third solder layers is too high, which leads to the formation of coarse rare earth inclusions in the weld joint, which in turn leads to a decrease in the toughness of the weld joint.

[0122] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0123] Furthermore, the above-described embodiments merely illustrate several implementation methods of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A solder for laser welding, characterized in that: It includes a first solder layer, a second solder layer and a third solder layer arranged in sequence, and the percentages of the thickness of the first solder layer, the thickness of the second solder layer and the thickness of the third solder layer to the total thickness of the solder, d1, d2 and d3, are (47-74%):(20-35%):(6-18%), respectively. The chemical element mass percentage of the first solder layer is as follows: C: 0.01-0.03%, Mn: 1.2-1.8%, Ni: 0.8-1.5%, Si: 0.7-1.2%, Ce: 0.01-0.025%, B: 0.001-0.003%, with the balance made up by Fe. The chemical element mass percentage of the second solder layer is as follows: C: 0.03-0.07%, Mn: 1.5-2.0%, Ni: 1.0-1.8%, Si=2.5%-0.056×d2, Ce=0.0008×d2, B: 0.001-0.003%, with the balance made up by Fe; The chemical element mass percentage of the third solder layer is as follows: C: 0.06-0.1%, Mn: 1.6-2.2%, Ni: 2.5-5.5%, Si=1.8%+0.05×d3, Ce=0.015%+0.0008×d3, B: 0.001-0.002%, with the balance made up by Fe.

2. The laser welding solder as described in claim 1, characterized in that: The thickness percentages d1, d2, and d3 between the first solder layer, the second solder layer, and the third solder layer are 60%:(25-30%):(10-15%), respectively.

3. The laser welding solder as described in claim 1, characterized in that: The chemical element mass percentage of the first solder layer is: C: 0.02%, Mn: 1.5%, Ni: 1.0%, Si: 0.9%, Ce: 0.015%, B: 0.002%, with the balance made up by Fe.

4. The laser welding solder as described in claim 3, characterized in that: The chemical element mass percentage of the second solder layer is as follows: C: 0.05%, Mn: 1.8%, Ni: 1.4%, Si = 2.5% - 0.056 × d2, Ce = 0.0008 × d2, B: 0.002%, with the balance made up by Fe.

5. The laser welding solder as described in claim 4, characterized in that: The chemical element mass percentage of the third solder layer is as follows: C: 0.08%, Mn: 2.0%, Ni: 4.0%, Si = 1.8% + 0.05 × d3, Ce = 0.015% + 0.0008 × d3, B: 0.002%, with the balance made up by Fe.

6. A welding process for laser welding solder, characterized in that: Includes the following steps: The laser welding filler metal of any one of claims 1-5 is placed on the weld seam of the steel plate base material to be spliced; the ratio of the weld seam width W between the steel plate base materials to be spliced ​​to the overall width L of the filler metal is controlled to be 1.2≤W / L≤1.5, and the ratio of the weld seam depth H between the steel plate base materials to be spliced ​​to the overall thickness D of the filler metal is 0.75≤H / D≤0.9; Laser welding is performed on the steel plate base materials to be spliced ​​to form the initial weld; The initial weld is quenched and cooled to form a welded joint.

7. The welding process for a laser welding solder as described in claim 6, characterized in that: In the laser welding process for spliced ​​steel plate base materials, the ratio of welding speed S1 to solder feeding speed S2 is controlled to be 1.15≤S1 / S2≤1.

2.

8. The welding process for a laser welding solder as described in claim 6, characterized in that: In the laser welding process for spliced ​​steel plate base materials, the shielding gas is controlled to be carbon dioxide.

9. The welding process for a laser welding solder as described in claim 6, characterized in that: In the initial weld quenching and cooling step, the initial weld is held at 850℃-930℃ for 1-5 minutes, and then cooled, with the cooling rate controlled at ≥25℃ / s.

10. The welding process for a laser welding solder as described in claim 9, characterized in that: In the initial weld quenching and cooling step, the initial weld is held at 900℃ for 3 minutes, and then cooled, with the cooling rate controlled at ≥25℃ / s.

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