KR102305743B1 - Welded structural member having excellent crack resistance and manufacturing method of the same - Google Patents

Abstract

The present invention relates to a welded structural member having excellent crack resistance and a method for manufacturing the same.

Description

Welded structural member with excellent crack resistance and manufacturing method thereof

The present invention relates to a welded structural member having excellent crack resistance and a method for manufacturing the same.

Zinc-based galvanized steel sheet has excellent corrosion resistance and is used for various purposes such as automobile members, interior and exterior panels of home appliances, and construction members. Among them, Zn-Al-Mg-based plated steel sheet can secure excellent corrosion resistance for a long time, and the demand is increasing as a substitute for conventional zinc-based plated steel sheet and stainless steel.

The reason that the Zn-Al-Mg-based plated steel sheet improves the corrosion resistance of the plated layer compared to the conventional galvanized steel sheet is presumed to be because dense and stable corrosion products are uniformly generated by the action of Mg on the surface of the plated layer. do.

On the other hand, when a welded structural member is manufactured using a Zn-Al-Mg-based plated steel sheet, a gas shielded arc welding method is generally used. However, when arc welding is applied to such a Zn-Al-Mg-based plated steel sheet, there is a problem in that the liquidus temperature of the plating layer is lowered due to the inclusion of Mg, and cracks occur due to the remaining plating layer.

Publication No. 1998-0009498

According to one aspect of the present invention, it is an object of the present invention to provide a welded structural member having excellent crack resistance and a method for manufacturing the same.

The subject of the present invention is not limited to the above. Those of ordinary skill in the art to which the present invention pertains will have no difficulty in understanding the additional problems of the present invention from the contents throughout the present specification.

One aspect of the present invention is

A method for manufacturing a welded structural member obtained by welding a first steel plate and a second steel plate, the method comprising:

welding the first steel plate and the second steel plate using a solid wire by gas shielded arc welding; and

After the welding, comprising the step of water cooling,

It provides a method for manufacturing a welded structural member, wherein at least one of the first steel sheet and the second steel sheet is a plated steel sheet having a Zn-Al-Mg-based plating layer.

In addition, another aspect of the present invention,

a first steel plate;

a second steel plate; and

In a welded structural member having a weld bead to couple the first steel plate and the second steel plate,

At least one of the first steel sheet and the second steel sheet is a plated steel sheet having a Zn-Al-Mg-based plating layer,

The hardness of the plating layer closest to the bead toe portion of the weld bead is 70% or more compared to the hardness of the plating layer before welding, providing a welded structural member.

According to one aspect of the present invention, it is possible to effectively manufacture a welded structural member having excellent crack resistance during arc welding, which is prone to cracking.

In addition, according to an aspect of the present invention, a welded structural member having excellent crack resistance can be manufactured relatively economically without limitation or addition of a steel component.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows typically the cross section of the torch and a base material during gas-shielded arc welding.
2 is a view schematically showing a cross-sectional structure of a fillet welded joint.
3 to 5 are diagrams schematically showing an enlarged cross-sectional structure corresponding to the vicinity of the bead toe portion shown in FIG. 2 .

Conventionally, when a welded structural member is manufactured using a plated steel sheet having a Zn-Al-Mg-based plating layer, a gas shielded arc welding method has been conventionally used. However, when such an arc welding method is used, the liquidus temperature of the plating layer is lowered due to the content of Mg in the plated steel sheet on which the Zn-Al-Mg-based plating layer is formed, and cracks easily occur.

That is, at the time of arc welding of a plated steel sheet, the plated layer is melted on the surface by the arc heat passing through the plated layer. However, the Zn-Al-Mg-based plating layer maintains the molten state for a relatively long time because the liquidus temperature is lower than the melting point of Zn, about 420°C.

Accordingly, in the case of a plated steel sheet having a Zn-Al-Mg-based plated layer, compared to a galvanized steel sheet, the metal of the molten plated metal layer during arc welding stays on the surface of the steel sheet while maintaining the liquid phase. lengthens

Therefore, when the surface of the base steel sheet, which is in a tensile stress state during cooling immediately after arc welding, is exposed to the molten plated metal layer for a long time, the molten plated metal layer invades the grain boundaries of the base steel sheet and causes cracks. When cracks occur due to intrusion of the molten plated metal layer, there is a problem in that the strength, fatigue resistance, corrosion resistance, etc. of the structure are deteriorated.

Accordingly, the present inventors solve the problem that cracks easily occur when welding as a gas shielded arc welding method, particularly when welding using a solid wire, when manufacturing a welded structural member using a plated steel sheet having a Zn-Al-Mg-based plating layer As a result of intensive study, it was found that cracking caused by penetration of the molten plated metal layer of the Zn-Al-Mg-based plating layer could be suppressed by applying the method of water cooling after welding, and the present invention was completed.

Specifically, one aspect of the present invention is

A method for manufacturing a welded structural member obtained by welding a first steel plate and a second steel plate, the method comprising:

welding the first steel plate and the second steel plate using a solid wire by gas shielded arc welding; and

After the welding, comprising the step of water cooling,

It provides a method for manufacturing a welded structural member, wherein at least one of the first steel sheet and the second steel sheet is a plated steel sheet having a Zn-Al-Mg-based plating layer.

According to an aspect of the present invention, the welded structural member refers to a member obtained by welding at least two steel plates including a first steel plate and a second steel plate, and the present invention relates to at least one of the first steel plate and the second steel plate with Zn - A plated steel sheet having an Al-Mg-based plated layer (hereinafter also referred to as a Zn-Al-Mg-based plated steel sheet) is applied. That is, the plated steel sheet having the Zn-Al-Mg-based plating layer may have a base steel sheet and a Zn-Al-Mg-based plating layer formed on the base steel sheet.

According to one aspect of the present invention, various steel types may be employed as the base steel sheet according to the use, for example, a high-tensile steel sheet may be used, and a thickness of the base steel sheet may be used in the range of 1 to 6 mm.

In addition, the relatively strong bonding with the Zn-Al-Mg-based plated steel sheet in the first and second steel sheets (that is, the remaining steel sheet) is applicable not only to the Zn-Al-Mg-based plated steel sheet, but also to the Zn-Al-Mg-based steel sheet. It can be applied to all steel plates other than the galvanized steel plate. That is, the counter steel sheet may also employ various types of steel according to the use.

According to one aspect of the present invention, in the present invention, the welding refers to a case of joining by arc welding, and in particular, a solid wire may be used as gas shielded arc welding.

The cross section of the torch and the steel plate to be welded during arc welding used in the present invention is schematically shown in FIG. 1 . Specifically, the welding torch is advancing in the direction of the arrow while forming an arc 4 in the welding site 3 on the surface of the welded steel sheet 1 . The shield gas 2 is ejected from the gas nozzle around the electrode and the welding wire located in the center of the welding torch, thereby protecting the arc 4 and the surface of the welding steel sheet 1 exposed to high temperature from the atmosphere. A part of the welding part 3 by the heat input from the arc 4 solidifies rapidly after the welding torch passes to form a bead composed of the weld metal.

2 schematically shows the cross-sectional structure of a welded joint formed in the manufacturing process of a welded structural member, and various types of welded joints by arc welding are used in construction, automobile structures, and the like.

That is, in FIG. 2 , two steel plates 10 and 10 ′ to be welded are overlapped and disposed, and the surface of one of the two steel plates 10 and the cross section of the other steel plate 10 ′ are A weld bead 11 is formed so that both steel plates are joined to each other. At this time, the edge intersection formed by meeting the surfaces of the two steel plates 10 and 10 ′ and the surface of the weld bead 11 is referred to as a bead toe part 12 .

On the other hand, when a welded structural member is usually manufactured using a Zn-Al-Mg-based plated steel sheet, most cracks occur near the bead tow portion 12 described above.

Accordingly, Figs. 3 to 5 are schematic cross-sectional views of enlarged portions corresponding to the vicinity of the bead tow portion 12 shown in Fig. 2 . Specifically, FIG. 3 schematically shows a cross-sectional state in the vicinity of a high-temperature weld zone immediately after arc heat passes through gas shield arc welding when a welded structural member using a Zn-Al-Mg-based plated steel sheet is manufactured. Before welding, the surface of the steel sheet 10 is covered with a uniform plating layer, but in the vicinity of the bead tow portion 12 due to the passage of the arc, the metal of the plating layer evaporates and disappears. On the other hand, the original Zn-Al-Mg-based plating layer is melted in a portion at a certain distance from the bead tow portion 12 to exist as the Zn-Al-Mg-based hot-dip metal layer 13 . In addition, the original Zn-Al-Mg-based plating layer exists as an unmelted state 14 in a portion farther from the bead tow portion 12 .

4 schematically shows a cross-sectional view of a welded structural member manufactured using a Zn-Al-Mg-based plated steel sheet in the related art. In the case of FIG. 4 , the Zn-Al-Mg-based plating layer is lost in the vicinity of the high-temperature weld area immediately after the arc heat passes through during welding, thereby forming the plating layer evaporation section 15 . Thereafter, the wet diffusion of the Zn-Al-Mg-based hot-dip plated metal layer 13 occurs in the plating layer evaporation section 15, and accordingly, the surface of the steel sheet 10 is Zn-Al up to the bead tow portion 12. -Mg-based hot-dip plated metal layer 13 is covered.

Therefore, in the case of a welded structural member manufactured using a conventional Zn-Al-Mg-based plated steel sheet, as shown in FIG. 4 , up to the bead toe portion 12 is the solidification region of the Zn-Al-Mg-based hot-dip plated metal layer. (16) becomes In this case, as described above, since the liquidus temperature of the Zn-Al-Mg-based molten metal is low, the surface portion of the steel sheet 10 that becomes a solidification region after cooling is a Zn-Al-Mg-based molten metal due to the cooling process after welding. The contact time with the hot-dip plated metal layer is relatively long. Therefore, in the vicinity of the bead toe portion 12 of the steel sheet 10, tensile stress is generated due to cooling after welding, so that the component in the Zn-Al-Mg-based hot-dip plated metal layer enters the grain boundary of the steel sheet 10. easy. For this reason, the component that penetrates into the grain boundary becomes a factor causing cracks in the weld zone.

5 schematically shows a cross-sectional view of a welded structural member manufactured using a Zn-Al-Mg-based plated steel sheet according to the present invention obtained by cooling by a water cooling method in the state of FIG. 3 . In the present invention, a water cooling method is applied immediately after welding. For this reason, the Zn-Al-Mg-based plating layer evaporates and disappears immediately after welding, so that the Zn-Al-Mg-based hot-dip plated metal layer is solidified without reaching the surface of the steel sheet in the plating layer evaporation section 15, so that the stress is concentrated Wetting diffusion by the Zn-Al-Mg-based hot-dip plated metal layer up to the bead toe portion 12 is suppressed. As a result, the plating layer evaporation section 15 is maintained even after cooling. That is, the surface of the steel sheet in the vicinity of the bead toe portion 12 is cooled without contacting the Zn-Al-Mg-based hot-dip metal layer, and accordingly, the Zn-Al-Mg-based surface from the bead toe portion 12 is removed. A plating layer evaporation section 15 of a certain section is secured between the solidification regions 17 of the hot-dip plated metal layer.

Accordingly, in the vicinity of the bead toe portion 12, the intrusion of molten metal components into the steel sheet is prevented, and thus, a welded structural member having excellent crack resistance can be obtained regardless of the steel type of the steel sheet. In addition, in the Zn-Al-Mg-based hot-dip plated metal layer, wetting diffusion can be suppressed by the above-described effect in any welding posture in which the height position of the hot-dip plated metal layer is changed. For example, the same applies to horizontal viewing welding, vertical viewing welding, top viewing welding, etc., including the downward viewing posture.

That is, when manufacturing a welded structural member using a Zn-Al-Mg-based plated steel sheet, the Zn-Al-Mg-based plating layer evaporates and disappears in the vicinity of the weld bead formed during gas shield arc welding. After the arc heat passed, the molten plated metal layer formed by melting the Zn-Al-Mg-based plating layer at a location several mm away from the weld bead immediately spread wetness to the vicinity of the weld bead.

However, in the present invention, when cooling is completed while retaining the above-described evaporated and lost state, cracking can be effectively prevented by suppressing the penetration of the molten plated metal layer into the vicinity of the weld bead.

Specifically, in the present invention, by applying the optimized water cooling method within a critical time after passing through the welding torch, it was found that the wetting diffusion of the Zn-Al-Mg-based plated steel sheet member was prevented, and the present invention was completed.

That is, the present invention provides a method for manufacturing a welded structural member obtained by welding two steel plates, at least one of which is a Zn-Al-Mg-based plated steel plate, by applying water cooling within a few seconds immediately after welding (that is, after passing through a welding torch). A welded structural member excellent in crack resistance can be effectively provided.

Therefore, according to one aspect of the present invention, even during arc welding, which is prone to cracking, a welded structural member having excellent crack resistance can be effectively provided, and crack resistance is relatively economical without limiting or adding elements of the plating layer. This excellent welded structural member can be provided.

In addition, according to another aspect of the present invention, it is possible to provide a welded structural member having excellent crack resistance efficiently without any restrictions on the type of steel for the base steel sheet of the Zn-Al-Mg-based plated steel sheet, It can also be applied without restrictions on the shape or size of parts.

Specifically, according to one aspect of the present invention, the water cooling may be started within 3 to 10 seconds after passing through the welding torch. By setting the water cooling start time to 3 seconds or more after passing through the welding torch, the welding performance can be secured because it is a critical time that does not affect the progressing torch. In addition, by setting the water cooling start time to 10 seconds or less after passing through the welding torch, crack resistance can be secured by preventing the molten plated metal layer generated after passing through the welding torch from advancing to the vicinity of the welding bead.

In addition, according to an aspect of the present invention, the flow rate of the water cooling ^{may be 15 ~ 60 mm 3} /hr. By the flow rate of the water-cooling by 15㎜ ³ / hr or more, it is possible to sufficiently ensure the cooling effect of the molten coating layer to be produced after passing through the welding torch, the flow rate of the water-cooling supply flow rate to the unnecessary, by more than 60㎜ ³ / hr Pollution of the working environment can be prevented.

In addition, according to one aspect of the present invention, the water cooling may be maintained for 5 to 15 seconds. By setting the water cooling holding time to 5 seconds or more, there is an effect of sufficiently securing the cooling effect of the hot-dip plated layer by water cooling and improving the crack resistance, and by setting the water cooling holding time to 15 seconds or less, unnecessary flow rate supply Pollution of the working environment can be prevented.

That is, according to one aspect of the present invention, it is most preferable to supply a water cooling flow rate of ^{15 to 60 mm 3 /hr to the torch passing portion within 3 to 10 seconds after passing through the welding torch for 5 to 15 seconds.}

On the other hand, another aspect of the present invention,

a first steel plate;

a second steel plate; and

In a welded structural member having a weld bead to couple the first steel plate and the second steel plate,

At least one of the first steel sheet and the second steel sheet is a plated steel sheet having a Zn-Al-Mg-based plating layer,

The hardness of the plating layer closest to the bead toe portion of the weld bead is 70% or more compared to the hardness of the plating layer before welding, providing a welded structural member.

That is, according to the present invention, it is possible to obtain a welded structural member in which the hardness of the plating layer closest to (ie, the closest part) to the bead toe part 12 after welding is 70% or more compared to the hardness of the plating layer before welding.

On the other hand, in the present invention, the hardness of the plating layer closest to the bead toe portion 12 indicates a value obtained by measuring the hardness of the plating layer at the point closest to the bead toe portion 12 .

In addition, in the welded structural member according to an aspect of the present invention, the length from the bead tow portion to the section where the plating layer is evaporated may be 3 to 10 mm, and the length of the plating layer evaporation section 15 is water-cooled immediately after welding. It can be controlled within an appropriate range by adjusting the

Specifically, according to one aspect of the present invention, by making the length of the plating layer evaporation section 15 to 3 mm or more, cracking resistance by preventing the occurrence of cracks due to the hot-dip plated metal layer in the vicinity of the bead tow portion 12 can be ensured, and by setting the length of the plating layer evaporation section 15 to 10 mm or less, the effect of securing corrosion resistance by the formation of the plating layer can be obtained.

On the other hand, according to one aspect of the present invention, the Zn-Al-Mg-based plating layer is, in mass%, Al: 1-20.9%, Mg: 0.04-10%, Ti: 0.1% or less (including 0%), B: 0.05% or less (including 0%), Si: 2% or less (including 0%), Fe: 2.5% or less (including 0%), the balance may be composed of Zn and other unavoidable impurities. In addition, in the present invention, by making the composition of the plating layer as described above, the object of the present invention of securing crack resistance during welding can be more effectively achieved.

In addition, according to one aspect of the present invention, the plating adhesion amount per side of the Zn-Al-Mg-based plating layer may be ^{50 ~ 250 g / m 2 .} The corrosion resistance of the plated steel sheet can be secured by setting the plating adhesion amount per side of the plating layer to 50 g/m ^{2 or more, and by setting it to 250 g/m 2} or less, blowholes are prevented from occurring during welding, thereby securing the strength of the welded part. have.

That is, by controlling the plating adhesion amount per single side of the plating layer to be more than an appropriate amount, the corrosion resistance effect of the plating layer can be sufficiently secured, and the effect of the anticorrosion method due to the sacrificial action of the plating layer can be sufficiently obtained.

Therefore, as in the present invention, when a plating layer evaporation section is generated in the vicinity of the weld bead generated after passing through the welding torch, it is preferable to control the ^{plating adhesion amount per one side of the plating layer to 50 to 250 g/m 2 , and 50 to 200 g/m 2} It is more preferable to control by m ^{2 .}

On the other hand, the composition of the plating layer described above reflects the composition for hot-dip plating, and the method of hot-dip plating is not particularly limited, but it is preferable from an economical point of view to use a generally known in-line annealing type hot-dip plating facility.

Hereinafter, the component system of the plating layer will be described preferentially.

Al: 1-20.9%

Al improves the corrosion resistance of the plated steel sheet and suppresses the generation of Mg oxide-based dross in the plating bath. In order to obtain such an effect, it is necessary to secure an Al content of 1% or more. By setting it as 1% or more, it is possible to ensure corrosion resistance and the effect of preventing dross, and by setting it to 20.9% or less, overgrowth of the soft Fe-Al alloy layer on the underside of the plating layer is prevented, and plating adhesion can be secured.

Mg: 0.04~10%

Mg produces a uniform corrosion product on the surface of the plated layer, thereby remarkably increasing the corrosion resistance of the plated steel sheet. On the other hand, by setting the Mg content to 0.04% or more, the effect of improving corrosion resistance can be secured, and by setting it to 10% or less, Mg oxide-based dross generation can be suppressed to secure the quality of the plating layer. In addition, the Mg content is more preferably 1% to 5%.

Ti: 0~0.1%

When Ti is contained in the hot-dip plating bath, there is an advantage in that the range of alloys of other components during hot-dip plating is increased, and thus the degree of freedom of manufacturing conditions is expanded. On the other hand, by containing Ti in an amount of 0.1% or less, the effect of increasing the alloy range of other components can be exhibited. In addition, it is more effective to set the Ti content to 0.0005 to 0.005%, and by setting the Ti content to 0.005% or more, there is an effect of increasing the range of other component alloys. On the other hand, by setting the Ti content to 0.005% or less, it is possible to suppress poor appearance of the plating layer surface due to the formation of precipitates.

B: 0~0.05%

The addition of B in the hot-dip plating bath also increases the alloy range of other components during hot-dip plating, thereby increasing the degree of freedom of manufacturing conditions. On the other hand, by containing B at 0.1% or less, the effect of increasing the alloy range of other components can be exhibited. In addition, it is more effective to set the B content to 0.0001 to 0.005%, and by setting the B content to 0.0001% or more, there is an effect of increasing the range of other component alloys. It is possible to suppress the appearance defect of the surface of the plating layer due to this.

Si: 0~2%

When Si is contained in the hot-dip plating bath, excessive growth of the Fe-Al alloy layer formed at the interface between the plating master plate and the plating layer is suppressed, and it is advantageous in improving the workability of the hot-dip Zn-Al-Mg-based plated steel sheet. Therefore, by setting the Si content to 2% or less, the above-described effect of improving the workability of the plated steel sheet can be exhibited. On the other hand, it is more effective to set the Si content to 0.005 to 2%, and by setting the Si content to 0.005% or more, the effect of suppressing excessive growth of the Fe-Al alloy layer is exhibited, and by setting the Si content to 2% or less It is possible to suppress an increase in the amount of DOS in the hot-dip plating bath.

Fe: 0~2.5%

In the hot-dip plating bath, Fe is easy to mix with the characteristic of immersing the steel sheet. Accordingly, Fe may be included in the plating layer in an amount of 2.5% or less, and by setting the Fe content to 2.5% or less, the corrosion resistance and quality of the plated steel sheet can be secured. On the other hand, more preferably, the Fe content may be 0.0001 to 2.5%, and by setting the Fe content to 0.0001% or more, it is economical because additional cleaning costs do not occur.

(Example)

A cold-rolled steel strip having a plate thickness of 1.5 mm and a plate width of 1000 mm having the composition shown in Table 1 was passed through a hot-dip plating line showing the composition shown in Table 3 to prepare a hot-dip Zn-Al-Mg-based plated steel sheet having various plating layer compositions.

Next, gas shielded arc welding was performed under the welding conditions shown in Table 2 below, and the influence of the shielding gas composition on the molten metal embrittlement cracking resistance was investigated. The plating layer composition, plating adhesion amount, water cooling conditions, and hardness values are shown in Tables 3 and 4.

division Chemical composition (wt%) characteristic C Si Mn Al Ni Cr Mo 400MPa class high tensile steel grater 0.17 0.01 0.5 0.03 0.015 0.03 0.003

Hot-dip Zn-Al-Mg alloy plated steel sheet plating layer composition Plating layer composition of Table 3 steel plate for plating Low carbon steel in Table 1 size Plate thickness 1.5 mm, plate width 200 mm, plate length 200 mm Plating amount Coating amount in Table 4 welding wire KC-25M welding gas 80% Ar + 20% CO ₂ Welding gas flow 15 L/min welding current 150A welding voltage 20V welding speed 0.5 m/min bead length 314mm

Table 4 below shows the results of crack occurrence and hardness value change rate for the above-described experiments. When the conditions prescribed in the present invention are satisfied, it can be seen that the length of the plating layer evaporation section 15 is secured and liquefied metal embrittlement cracking is prevented.

[Method for testing molten metal embrittlement cracking resistance]

As shown in FIG. 6, gas shield arc welding was performed under the welding conditions shown in Table 2 in the center of a 200 mm × 200 mm test piece (molten Zn-Al-Mg-based plated steel sheet member) to perform welding between the test pieces. Specifically, after passing the welding starting point S in a clockwise direction from the welding starting point S, the beads were also overlapped and welding was progressed, and welding was performed to the welding end point E after the overlapping part of the welding bead was generated. During welding, the test piece 22 was made into the state restrained on the flat plate. This test was conducted under a condition in which molten metal embrittlement cracks could easily occur by giving constraint conditions.

After welding, radioactive non-destructive testing was performed to determine the presence or absence of "melted metal embrittlement cracking", and the results are shown in Table 4 based on the following criteria.

◎: No cracks

○: Surface cracks There are only traces of cracks of 5 μm or less, and hardly occurs.

×: surface cracks exceeding 5㎛ and propagated cracks occurred

[Method of measuring length and hardness value change rate of evaporation section of plating layer]

A cross section perpendicular to the bead direction including the weld bead and its adjacent steel plate was subjected to mirror polishing and etching in a nitric acid concentration of 0.2% by volume nital solution, followed by observation with a scanning electron microscope. The length of the plating layer evaporation section 15 shown in FIG. 5 was measured by observing the vicinity of the bead toe part 12, and the plating layer hardness near the bead toe part 12 after welding and the plating layer hardness before welding were measured, and the rate of change is shown in Table 4 below.

division Zn-Al-Mg-based plating layer composition (%, balance: Zn) Zn Al Mg Si Ti B Fe Invention Example 1 95.45 4.5 0.05 Invention Example 2 89.93 6.4 3.1 0.5 0.05 0.02 Invention example 3 68.17 20.9 9.8 0.5 0.02 0.01 0.6 Invention Example 4 94.66 4.5 0.04 0.3 0.5 Invention Example 5 88.3 6.7 3.1 1.5 0.4 Invention example 6 89.65 6.5 3.3 0.5 0.04 0.01 Invention Example 7 85.8 11.2 2.8 0.2 Invention Example 8 74.1 14.8 7.6 1.5 2 Invention Example 9 69.3 18.1 8.3 2 2.3 Invention example 10 71.2 19.1 8.9 0.5 0.3 Invention Example 11 94.22 4.8 0.06 0.8 0.1 0.02 Invention Example 12 80.55 14.3 5.1 0.05 Invention Example 13 76.9 13.8 9.3 Invention Example 14 97.9 0.5 1.6 Invention Example 15 90.8 6.2 2.9 0.1 Invention Example 16 69.7 20.5 9.5 0.3 Invention Example 17 93.9 4.5 1.1 0.5 Invention Example 18 86.5 8.3 2.5 2.7 Invention Example 19 68.98 21 9.9 0.11 0.01 Invention Example 20 90.07 6.3 3 0.5 0.12 0.01 Invention Example 21 76.4 15.3 6.8 1.5 Invention example 22 93.6 5.5 0.9 Invention Example 23 67.7 21.5 8.1 2.7 Invention Example 24 70.15 18 9.2 1.3 0.15 1.2 Comparative Example 1 89.93 6.4 3.1 0.5 0.05 0.02 Comparative Example 2 75.4 17.5 7.1 Comparative Example 3 87.13 12.5 0.04 0.3 0.03 Comparative Example 4 90.2 6.7 1.2 1.5 0.4 Comparative Example 5 89.65 6.5 3.3 0.5 0.04 0.01 Comparative Example 6 89.95 6.3 2.5 1.2 0.04 0.01 Comparative Example 7 93.9 4.4 1.2 0.5

division before welding
plating layer
Hardness
(Hv) Plated
adhesion amount
(g/m ² ) test requirements crack
Occurrence hardness value
rate of change
(Before welding
plating layer
prepare%) after welding
Water cooling start
Time
(candle) flux
(mm ³ /hr) water cooling
duration
(candle) Invention Example 1 114.2 50 3 35 5 ◎ 87% Invention Example 2 148.4 135 9 31 10 ◎ 71% Invention example 3 218.6 60 8 28 5 ◎ 73% Invention Example 4 124.7 89 6 35 15 ◎ 81% Invention Example 5 166.1 110 3 55 13 ◎ 88% Invention example 6 149.9 85 5 45 8 ◎ 83% Invention Example 7 142.9 55 7 32 10 ◎ 78% Invention Example 8 228.7 65 10 21 9 ◎ 73% Invention Example 9 246.6 125 8 15 5 ◎ 70% Invention example 10 205.9 67 6 60 8 ◎ 71% Invention Example 11 126.6 148 10 12 3 ◎ 81% Invention Example 12 161.7 175 5 48 11 ◎ 76% Invention Example 13 196.6 161 6 31 7 ◎ 73% Invention Example 14 125.8 34 8 13 15 ○ 65% Invention Example 15 140.5 92 15 35 11 ○ 54% Invention Example 16 204.9 180 5 33 One ○ 61% Invention Example 17 129.8 45 8 11 4 ○ 63% Invention Example 18 172.2 80 13 35 8 ○ 62% Invention Example 19 206.1 40 3 5 11 ○ 69% Invention Example 20 148.3 25 4 31 3 ○ 68% Invention Example 21 195.7 290 12 38 7 ○ 61% Invention example 22 121.9 240 12 50 10 ○ 57% Invention Example 23 225.1 155 8 35 One ○ 65% Invention Example 24 232.4 180 4 32 3 ○ 59% Comparative Example 1 148.4 135 - - - × 53% Comparative Example 2 179.4 280 - - - × 55% Comparative Example 3 121.7 120 - - - × 50% Comparative Example 4 150.0 230 - - - × 53% Comparative Example 5 149.9 85 - - - × 52% Comparative Example 6 152.3 200 - - - × 51% Comparative Example 7 130.8 183 - - - × 55%

As shown in Table 4, in the case of Inventive Examples 1 to 13 in which water cooling was applied while satisfying the composition of the plating layer prescribed in the present invention, cracks were not observed in the weld, and the rate of change of the hardness value before and after welding was also 70% more could be obtained.

On the other hand, although the composition of the plating layer prescribed in the present invention was not satisfied, in the case of Inventive Examples 14 to 24 in which water cooling was applied, there were only traces of cracks in the welded portion and almost no cracks.

On the other hand, in Comparative Examples 1 to 7 in which the composition of the plating layer specified in the present invention was satisfied but air cooling was applied without water cooling, cracks occurred in the weld area, and the rate of change of the hardness value before and after welding was also less than 70%.

In addition, in the case of Comparative Examples 1 to 7, the length of the plating layer evaporation section 15 in the test piece was less than 3 mm, and the crack caused by the deepest hot-dip metal layer was from the bead tow part 12 in most samples. The distance occurred in a site|part within 3 mm.

On the other hand, in Examples 1-24 of the present invention, molten metal embrittlement cracks were not observed, and the length of the plating layer evaporation section 15 was also 3 mm or more.

1: Welded steel plate
2: shield gas
3: Weld area
4: arc
5: welding wire
6: electrode
7: welding torch
10, 10': 2 steel sheets welded
11: Weld Bead
12: bead tow
13: Zn-Al-Mg-based hot-dip plated metal layer
14: unmelted Zn-Al-Mg-based plating layer
15: plating layer evaporation section
16: Solidification region of Zn-Al-Mg-based hot-dip metal layer
17: Solidification region of Zn-Al-Mg-based hot-dip metal layer
18: conventional plating metal layer
20: steel pipe
21: plating metal layer
22: test piece
23: weld bead
24: bead overlap
S: welding start point
E: Weld end point

Claims (9)

A method for manufacturing a welded structural member obtained by welding a first steel plate and a second steel plate, the method comprising:
welding the first steel plate and the second steel plate using a solid wire by gas shielded arc welding; and
After the welding, comprising the step of water cooling,
At least one of the first steel sheet and the second steel sheet is a plated steel sheet having a Zn-Al-Mg-based plating layer,
The water cooling is started within 3 to 10 seconds after passing through the welding torch, and the water cooling is maintained for 3 to 15 seconds.
delete The method of claim 1,
The flow rate of the water cooling is 15 ~ 60mm ³ /hr will, the manufacturing method of the welded structural member.
The method of claim 1,
The water cooling is maintained for 5 to 15 seconds, a method of manufacturing a welded structural member.
The method of claim 1,
The Zn-Al-Mg-based plating layer is, in mass%, Al: 1-20.9%, Mg: 0.04-10%, Ti: 0.1% or less, B: 0.05% or less, Si: 2% or less, Fe: 2.5% Hereinafter, the remainder is composed of Zn and other unavoidable impurities, a method of manufacturing a welded structural member.
a first steel plate;
a second steel plate; and
In a welded structural member having a weld bead to couple the first steel plate and the second steel plate,
At least one of the first steel sheet and the second steel sheet is a plated steel sheet having a Zn-Al-Mg-based plating layer,
The hardness of the plating layer closest to the bead toe of the weld bead is 70% or more of the hardness of the plating layer before welding, a welded structural member.
7. The method of claim 6,
The plating adhesion amount per side of the plating layer is 50 ~ 250g / m ² Will, a welded structural member.
7. The method of claim 6,
The length from the bead tow portion to the section where the plating layer is evaporated is 3 to 10 mm, a welded structural member.
7. The method of claim 6,
The Zn-Al-Mg-based plating layer is, in mass%, Al: 1-20.9%, Mg: 0.04-10%, Ti: 0.1% or less, B: 0.05% or less, Si: 2% or less, Fe: 2.5% Hereinafter, a welded structural member consisting of the remainder Zn and other unavoidable impurities.

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