JP3156512B2 - Laser welded joint structure between laminated steel sheet and ordinary steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in the structure of a laser welded joint between a laminated steel sheet and a normal steel sheet.

[0002]

2. Description of the Related Art A laminated steel sheet has a polymer resin between the steel sheets, and its workability and workability are completely different from those of a normal steel sheet.
Abnormal shape (gull phenomena) during bending, spot welding becomes difficult, torque decreases at screwed parts, strength of tapping parts is low, sufficient fastening strength cannot be obtained, lamination There are many application problems, such as poor corrosion resistance at the end of the steel sheet.

[0003] As a method of solving these problems, there is a method of improving the laminated steel sheet itself. For example, a method of improving the workability by limiting the elastic modulus and elongation of a polymer resin and increasing the adhesive force with a skin steel plate (Japanese Patent Laid-Open No. 60-8 / 1985)
No. 2349), a method of adding a conductive metal powder to a polymer resin to impart spot weldability (Japanese Patent Laid-Open No. 50-79).
No. 920, JP-B-60-912, JP-A-62
JP-A-87341, JP-A-57-146649, and JP-B-61-29261), by tightening bolts while heating the bolted portions to reduce the thickness of the polymer resin, thereby reducing the torque. For example, there is a method of preventing downing (Japanese Patent Publication No. 63-34324), a method of improving the end face corrosion resistance by using a surface-treated steel sheet with little elution in a corrosive environment (Japanese Patent Publication No. 2-27145), and the like.

[0004] However, while the method of improving the laminated steel sheet itself has some problems in application to some extent, application of the method requires adjustment of the shape of a press die, changes in spot welding conditions, and an increase in work processes. However, the applicability of laminated steel sheets has not been drastically solved.

[0005]

On the other hand, an attempt has been made to replace the problematic portion of the laminated steel sheet with the ordinary steel sheet by joining the laminated steel sheet and the ordinary steel sheet by laser welding. However, this method has a problem that a gas generated by the decomposition of the resin during welding is mixed into the laser-joined portion, so that sufficient joint strength and elongation characteristics that can withstand press molding cannot be obtained. For example, JP-A-59-330
No. 90 discloses that a laminated steel sheet and an ordinary steel sheet are joined by moving a laser beam along a line deviated by 0.1 to 0.5 mm toward the ordinary steel sheet from the joining line of the two steel sheets, and a problematic part of the laminated steel sheet Has been proposed to eliminate the drawbacks in the application of laminated steel sheets by replacing the steel sheets with ordinary steel sheets. However, in this method, the penetration of the laminated steel sheet is insufficient, and sufficient joint strength and elongation characteristics cannot be obtained. There's a problem.

[0006] The present invention provides a laminated steel sheet joint structure which solves the above-mentioned problems in applying the laminated steel sheet, and does not lose the original properties of the laminated steel sheet and is the same as a normal steel sheet. It is an object of the present invention to obtain a welded portion structure of a laminated steel plate and a common steel plate joined by laser welding having a joint characteristic that can be processed under conditions.

[0007]

In the above-described laser welded joint structure between the laminated steel plate and the ordinary steel plate, what is necessary for the joint is that both steel plates have sufficient penetration and that the gas at the joint is And to ensure sufficient joint strength and elongation characteristics that can withstand press molding and the like.

In order to solve the above problems, the present inventors have studied a laminated steel sheet member in which a laminated steel sheet and an ordinary steel sheet are joined by laser welding, and completed the present invention. That is, in the laminated steel sheet member of the present invention, the number of blow holes having a diameter of 0.05 mm or more is 10 / m or less, and the penetration amount a) and b) are in the following ranges at the joint portion. Thickness direction 0.8 × T ≦ d (T is the total thickness of the laminated steel sheet, d is the penetration depth of the joint) b) Thickness direction 0.35 × T ≦ w ≦ 0.75 × T (w Is the penetration width of the joint.) Further, the carbon content in the weld metal of the joint is 0.07% by weight.
It is a laser welded joint structure between a laminated steel sheet and an ordinary steel sheet in which the hardness of the joint is suppressed to 400 Hv or less.

[0009]

The operation of the present invention will be described with reference to FIG. FIG. 1 is a sectional view schematically showing the basic structure of the present invention. The laminated steel sheet 1 is constituted by sandwiching a polymer resin 3 between the skin steel sheets 2 and 2, and the laminated steel sheet 1 and the ordinary steel sheet 4 are joined by a laser joint 5.

The laminated steel sheet 1 applied to the present invention includes various types of steel sheets, such as a cold-rolled steel sheet, a plated steel sheet, and an alloyed plated steel sheet having a skin thickness of 0.2 to 1.6 mm, for example.
As a polymer resin, for example, about 0.02 to 2 mm polyolefin, polyamide, thermoplastic resin such as nylon,
Alternatively, thermosetting resins such as acrylic resins, polyester resins, epoxy resins, urethane resins, and rubber-modified resins thereof, and the like, which are generally used for laminated steel sheets, may be used. In particular, in order to prevent gas from entering the joint, the thickness of the resin is 0.02 to 0.2 mm.
, And particularly preferably 0.02 to 0.1 mm.

Further, various steel sheets such as a cold-rolled steel sheet, a plated steel sheet, and an alloy-plated steel sheet can be used as the ordinary steel sheet, and the thickness is desirably the same as the total thickness of the laminated steel sheet. Next, according to the laminated steel sheet joint portion structure of the present invention, blow holes having a diameter of 0.05 mm or more are formed at the joint portion.
/ M or less, and the penetration amounts a) and b) are within the following ranges.

A) Plate thickness direction 0.8 × T ≦ d (T is the plate thickness) b) Plate width direction 0.35 × T ≦ w ≦ 0.75 × T The reasons are as follows.

First, the blowhole is a starting point of a crack. Therefore, there is no particular problem when the number of blowholes of 0.05 mm or more is 10 pieces / m or less. The tensile strength of the part is remarkably reduced, and the strength that can withstand the forming process is insufficient. Note that 0.0
Blowholes less than 5mm will not be the origin of cracks
Therefore, there is usually no need to consider it.

If the amount of penetration (in the thickness direction) is less than the above a), poor welding to the lower plate of the laminated steel sheet occurs, and the strength of the joint decreases. Further, if the penetration amount (width direction of the plate) is less than the range of b), sufficient penetration depth cannot be obtained due to insufficient heat input, and poor welding to the lower plate of the laminated steel sheet occurs, and The strength decreases, and the joint breaks during molding. On the other hand, if the penetration amount (width direction of the plate) exceeds the range of the above item a), the heat input is large, so that the gas generated by the decomposition of the resin during welding increases, and blowholes of 0.05 mm or more often occur. As a result, the strength of the joint decreases, and the bead easily burns off.

Next, the amount of carbon in the weld metal at the joint is set to 0.1.
07% by weight or less or the hardness of the joint is 400 Hv
It is more preferably at most 300 Hv. The reason is as follows.

The hardness of the joint greatly affects the workability. If the hardness is large, the elongation characteristics are reduced. In particular, when the hardness of the welded portion exceeds 400 Hv, the elongation is significantly reduced, and breakage occurs near the joint during press forming. When deep drawing is performed, the elongation characteristics are sometimes important, so that the hardness of the welded portion is more preferably 300 Hv or less. Here, since the joint is rapidly cooled from the molten state, it is easy to be baked, so that the hardness of the joint tends to increase. By suppressing this, the hardness of the joint is 400H
In order to reduce the value to v or less, it is possible to take measures such as reducing the shielding gas at the time of welding and gradually cooling the same, or reducing the amount of carbon in the weld metal at the joint to suppress an increase in hardness. Although depending on welding conditions, for example, the hardness of the welded portion can be reduced to 400 Hv or less by setting the carbon content to 0.07% by weight or less.

It should be noted that, unlike the welding of a single plate, a phenomenon peculiar to the welding of a laminated steel plate occurs at the joint portion in the welding of the laminated steel plate. That is, conventionally, it was thought that it was almost negligible. However, carbon generated by the decomposition of the resin in the laminated steel sheet is also mixed in, and the amount of carbon increases to cause a significant increase in hardness, thereby lowering the formability. Therefore, in the case of a laminated steel sheet, the carbon content is 0.07% by weight.
In order to suppress the hardness below, and to reduce the hardness of the welded portion to 400 Hv or less, it is necessary to suppress the amount of the resin penetrating into the weld metal.

From the above, according to the present invention, in order to improve the moldability, not only the bead width and the bead depth of the joint portion but also the number of blowholes, but also the hardness and the carbon content of the joint portion are limited. The welding conditions for this purpose include, for example, slow cooling by reducing the amount of shielding gas, and bead width of 0.35 mmT (T
There is a method of making the thickness as small as possible even if the thickness is secured to the thickness.

As described above, the joint portion structure of the present invention can further improve the strength and elongation characteristics of the joint portion, and can withstand more severe molding processing in which cracks occur in the conventional joint portion. .

Next, an application example of the laminated steel sheet joint portion structure of the present invention will be described. FIG. 2 shows an application example of a normal laminated steel sheet to a portion where peeling occurs due to a displacement of a skin steel sheet at the time of press forming, where 1 is a laminated steel sheet and 4 is a normal steel sheet. If peeling occurs, the skin steel sheet may crack in some cases. However, since the joint has sufficient strength and elongation characteristics to withstand press forming, the part to be peeled is replaced with ordinary steel sheet 4. This problem can be solved. As a result, peeling occurs and application to parts that are difficult to apply becomes possible.

3 to 5 show examples of application after forming. Since the laminated steel sheet joint portion structure of the present invention has a joint portion strength that can withstand press forming, it can be formed under the same conditions as ordinary steel sheets. Therefore, by replacing the problematic portion of the conventional laminated steel sheet with the ordinary steel sheet, the same application as the ordinary steel sheet can be achieved.

FIG. 3 shows an example of application to a spot-welded portion where spot welding is difficult because a polymer resin is an electric insulator in a normal laminated steel sheet.
Is a normal steel plate, 5 is a laser weld, and 6 and 6 are electrodes. FIG. 4 shows an example of application to a screwed portion in which torque is reduced at a screwed portion in a normal laminated steel plate, which is problematic. 1 is a laminated steel plate, 4 and 4 are ordinary steel plates, 5 is a laser welded portion, and 7 is a laser welded portion. Is a screwed portion. FIG. 5 shows an example of application to a tapping portion where a normal laminated steel plate does not have sufficient strength to fix a bolt. 1 is a laminated steel plate, 4 and 4 are ordinary steel plates, and 5 is laser welding. Reference numeral 8 denotes a tap processing unit. These problems can be solved by replacing these problems with the ordinary steel plate 4.

When used in a corrosive environment,
In an ordinary laminated steel sheet, corrosion from the interface between the skin steel sheet and the polymer resin, that is, so-called end face corrosion occurs at the end portion, and thus has a disadvantage that the corrosion rate from the end face is higher than that of the ordinary steel sheet. This problem can be solved by replacing the ends with plain steel.

As described above, the joint structure of the laminated steel sheet according to the present invention can further improve not only the strength of the joint but also the elongation characteristic, which has been a problem in the past, and can withstand severe press forming. It is possible to obtain a laser welded binder that achieves both part strength and elongation characteristics. In addition, since the problematic part of the laminated steel sheet may be replaced with ordinary steel sheet, many of the problems when applying the laminated steel sheet can be solved by utilizing the features of the laminated steel sheet, and the application of the laminated steel sheet can be greatly expanded.

[0025]

EXAMPLES Examples of the present invention will be described together with comparative examples. (Example 1) Laser welding of a laminated steel sheet and an ordinary steel sheet was performed at different welding speeds to produce binders having different bead widths. The welding conditions are shown below.

Welding conditions (1) Laminated steel sheet 1) Skin steel sheet; cold-rolled steel sheet, thickness 0.4 mm ^t 2) Polymer resin; thermosetting acrylic resin, resin thickness 50 μm (2) ordinary steel sheet 1) cold-rolled steel sheet 0.8mm ^t (3) Welding conditions 1) Laser type; Carbon dioxide gas 2) Output power; 3 kW, continuous oscillation 3) Shield gas; Ar gas, 5 l / min. 4) Welding speed: 2 to 15 m / FIG. 6 shows the min. bead width and the number of blow holes (having a size of 0.05 mm or more), and FIG. 7 shows the bead width and the penetration depth.
FIG. 8 shows the bead width and the tensile strength of the joint.

FIG. 6 shows that the number of blow holes increases as the bead width increases. FIG. 7 shows that the penetration depth increases as the bead width increases. Next, from FIG. 8, the bead width is 0.3 to 0.6.
It can be seen that a high tensile strength can be obtained in the range of about mm. In this range, even in the tensile test, no break at the joint was observed, and the joint had good properties. Further, this range corresponds to a range where the blow holes are 10 holes / m or less and the penetration depth is 0.64 mm or more. The reason why the tensile strength decreases as the bead width increases is that the number of blow holes increases. On the other hand, the reason why the tensile strength decreases as the bead width decreases is that the penetration depth decreases.

From the above, in order to obtain a sufficient tensile strength, it is necessary that the number of blow holes is 10 / m or less and the penetration depth is 0.64 mm (0.8 mmT) or more. I understand.

FIG. 9 shows a range in which an appropriate tensile strength can be obtained when the thickness of the skin steel sheet is changed (0.2 to 1.6 mm). From the figure, the appropriate tensile strength is 0.3
It can be seen that it is obtained in the range of 5 mmT to 0.75 mmT.

Example 2 Similarly, a laminated steel sheet and a normal steel sheet were joined by laser welding, and the hardness of the joint was examined. The welding conditions are shown below.

Welding conditions (1) Laminated steel sheet 1) Skin steel sheet; cold-rolled steel sheet, sheet thickness 0.5 mm ^t 2) Polymer resin; ethylene-acrylate copolymer (polyolefin), resin thickness 50 μm (2) ordinary Steel plate 1) Cold rolled steel plate, thickness 1.0mm ^t (3) Welding conditions 1) Laser type; carbon dioxide gas 2) Output; 3kW, continuous oscillation 3) Shield gas; Ar gas, 20 l / min. 4) Welding Speed: 2 to 6 m / min. For each of these binders, the hardness and carbon content of the joint were measured, and ^50H × ^100W × so that the joint was located on the side wall as shown in FIG. Press molding was performed on a 100 ^L mm square cylinder. The results are summarized in Table 1.

[0032]

[Table 1]

The hardness of the test materials 1 and 2 (Comparative Example) was high because of the large amount of carbon, which was due to quenching. The reason for the large amount of carbon was that the bead width was wide and the carbon amount in the resin was low. This is probably because a lot of them melted. In Test Material 3 (Example), both the hardness and the carbon content were within the range of the present invention, and the moldability was good.

From the above, the carbon content of the welded portion was set to 0.0
By controlling the hardness of the welded portion to 7% by weight or less and the hardness of the welded portion to 400Hv or less, a laser welded binder excellent in workability can be obtained. (Example 3) Based on the above results, laser welding was performed under various welding conditions and evaluated. Table 2 summarizes the evaluation results of the laser-bonded portion in Examples and Comparative Examples.
(Example) and Table 3 (Comparative Example).

The laser welding conditions are shown below. Welding conditions (1) Laminated steel sheet 1) Skin steel sheet; cold-rolled steel sheet, sheet thickness 0.5 mm ^t 2) High polymer resin: ethylene-acrylate copolymer (polyolefin), resin thickness 50 μm thermosetting acrylic resin , Thickness 50μm (2) ordinary steel sheet 1) cold-rolled steel sheet, thickness 1.0mm ^t (3) welding conditions 1) type of laser; carbon dioxide gas 2) output; 2-5kW, continuous oscillation 3) shielding gas; Ar gas , 0 to 20 l / min. 4) Welding speed: 2 to 15 m / min. Evaluation of joint part Press formability (test conditions are in accordance with Example 2) ○: No crack near joint part ×: Near joint part As is clear from Table 2, Examples 1 to 6 within the scope of the present invention were performed.
In the press molding test, cracks did not occur at the joints, and the joint properties were good.

On the other hand, as shown in Table 3, in Comparative Example 1, the number of blow holes and the amount of penetration in the plate width direction were out of the range of the present invention, and cracks occurred at the joints in the press molding test. Comparative Examples 2 and 5 have a carbon content of 0.0
It exceeded 7% by weight and the hardness exceeded 400 Hv, and cracks occurred at the joints in the press molding test. In Comparative Example 3, the number of blowholes, the amount of penetration in the plate width direction, the amount of carbon in the joint, and the hardness of the joint were all outside the range of the present invention, and cracks occurred in the joint in the press molding test. In Comparative Example 4, the penetration amounts in the plate thickness direction and the plate width direction were out of the range of the present invention, and cracks occurred at the joints in the press forming test. The underlined part of the data of the comparative example indicates that it is outside the scope of the present invention. The number of blowholes was determined from the X-ray transmission image of the welded portion in the weld line direction (pieces / m) in accordance with JIS-Z3104.

[0037]

[Table 2]

[0038]

[Table 3]

[0039]

As described above, according to the present invention, a laser welded joint between a laminated steel sheet having a vibration damping property and light weight and a normal steel sheet has a sufficient joint strength and elongation characteristics. Defects in application can be covered with ordinary steel plates, and the same forming and construction as ordinary steel plates can be performed while maintaining vibration damping properties and light weight. Thereby, the use of the laminated steel sheet is greatly expanded, and an industrially useful effect is brought.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a basic structure of the present invention.

FIG. 2 is a perspective view showing an example in which the present invention is applied to a press-formed part.

FIG. 3 is a sectional view showing an example in which the present invention is applied to a spot welded part.

FIG. 4 is a diagram showing an example in which the present invention is applied to a screwing portion.

FIG. 5 is a diagram showing an example in which the present invention is applied to a tapping portion.

FIG. 6 is a view showing a relationship between a bead width and the number of blow holes when laser welding a laminated steel sheet and an ordinary steel sheet.

FIG. 7 is a view showing a relationship between a bead width and a penetration depth when laser welding a laminated steel sheet and a normal steel sheet.

FIG. 8 is a view showing a relationship between a bead width and a tensile strength in a welded joint obtained by laser welding a laminated steel sheet and a normal steel sheet.

FIG. 9 is a view showing the relationship between the total thickness of the laminated steel sheet and the bead width when the thickness of the skin steel sheet is changed.

FIG. 10 is a perspective view showing a rectangular tube press-formed part formed in Example 2.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Laminated steel plate, 2 ... Skin steel plate, 3 ... Polymer resin, 4 ... Normal steel plate, 5 ... Laser joint part, 6 ... Electrode, 7 ... Screw part, 8 ... Tap processing part

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yasunori Matsuda 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (56) References JP-A-1-210172 (JP, A) JP-A-5 -245670 (JP, A) JP-A-5-318154 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B23K 26/00-26/32

Claims (2)

(57) [Claims] In a laser welded joint structure between a laminated steel sheet having a polymer resin sandwiched between steel sheets and an ordinary steel sheet, the joint has a blow hole having a diameter of 0.05 mm or more having a diameter of 10 mm or more.
Press workability, characterized in that the amount of carbon in the weld metal at the joint is suppressed to 0.07% by weight or less . laser welded connection structure and excellent <br/> laminated steel and ordinary steel plate. A) Thickness direction 0.8 × T ≦ d (T is the total thickness of the laminated steel sheet, d is the penetration depth of the joint) b) Thickness direction 0.35 × T ≦ w ≦ 0.75 × T (W is the penetration width of the joint) 2. A laser welded joint structure between a laminated steel sheet and a normal steel sheet having a polymer resin sandwiched between steel sheets, wherein the joint has a blow hole having a diameter of 0.05 mm or more.
Pieces / m or less, and-penetration amount below i) is in the range of b), characterized in that the hardness of the bonded portion was less 400Hv
Laser welded joint structure between laminated steel sheet and ordinary steel sheet with excellent press workability . A) Thickness direction 0.8 × T ≦ d (T is the total thickness of the laminated steel sheet, d is the penetration depth of the joint) b) Thickness direction 0.35 × T ≦ w ≦ 0.75 × T (W is the penetration width of the joint)