JPH05222571A - Galvanized steel sheet excellent in arc weldability - Google Patents

Abstract

PURPOSE:To reduce the generation of blowholes at the time of welding by providing the surface of a galvanized steel sheet with projecting embossing of specified height. CONSTITUTION:The surface of a galvanized steel sheet is provided with projecting embossing of >=1mum height. As the method for the embossing, e. g. a transferring method by a rolling roll is suitably used. As for the embossing, its effect is not different in either case of being before galvanizing and after galvanizing. In this way, the reliability in the joined part can remarkably be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a galvanized steel sheet having excellent arc weldability.

[0002]

2. Description of the Related Art The bonding strength of a bead portion formed by arc welding is greatly reduced by a blowhole formed in the bead. In the case of non-plated materials such as cold-rolled steel sheets and hot-rolled steel sheets, broholes are rarely formed. However, in the case of a galvanized steel sheet, it is difficult to suppress the formation of brohol. The cause of the occurrence of bloholes in the galvanized steel sheet is that the zinc component in the plating layer present at the joint interface dissolves into the steel plate and wire components during the bead formation process and remains vaporized. As a method to solve this problem, by applying a special paint to the surfaces that will be the bonding interface, certain components contained in the paint oxidize zinc, which has a low evaporation temperature, before it evaporates. A method for suppressing the generation of brohol has been reported. In addition, the wire component is low Si,
It has been reported that a method of improving the bead quality by lowering the surface tension of the molten pool at the time of welding by facilitating the discharge of brohol by lowering the Mn. However, even with such a method, it is difficult to completely avoid the blowhole at the time of arc welding, and there are great expectations for the development of the industrially most effective means.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in order to advantageously solve such a requirement, and provides a galvanized steel sheet capable of greatly improving the blowholes in the beads during arc welding.

[0004]

A feature of the present invention relates to a galvanized steel sheet excellent in arc weldability in which a convex emboss having a height of 1 μm or more is provided on the surface of the galvanized steel sheet. That is, the characteristic of galvanized steel plate joining by arc welding is that the low melting point and low boiling point zinc present at the joining interface is taken into the molten pool and remains as bubbles even after the outer wall of the molten pool solidifies, and the entire bead solidifies. In the process of forming brohol. Therefore, in the non-plated steel sheet in which the low boiling point component is not contained in the joint portion, the generation of this kind of blowhole is eliminated. From this point of view, considering the measures against the blowhole during arc welding of the galvanized steel sheet, it can be said that it is difficult to avoid the blowhole completely unless the intrusion of zinc into the molten pool is excluded. Therefore, when the behavior of the galvanized steel sheet during arc welding was analyzed in detail, when a molten pool was formed at the joint interface, the zinc around it was already melted and vaporized, and most of the zinc remained Although excluded, it was revealed that the zinc emission in the overlapping portion was relatively slower than that in the free surface portion. It was also clarified that the discharge of zinc in the overlapping portion was improved by increasing the gap in the overlapping portion.

On the basis of such knowledge, the optimization of the surface morphology of the steel sheet whose surface is generated by the rolling method was examined.
As a condition for promoting the elution of zinc and the discharge of zinc vapor and suppressing the generation of brohol, it has been found that it is effective to provide a convex emboss with a height of 1 μm or more. The embossing shape may be any shape such as a cylinder, a triangular pyramid, a rectangular parallelepiped, a cube, and a half cylinder. Further, regarding the distance between the embosses and the width dimension of the groove between the embosses, the presence of the groove between the embosses makes it possible to easily discharge the zinc vapor generated in the overlapping portion and avoid the occurrence of the blowhole. As a method of embossing the surface of the galvanized steel sheet, for example, a transfer method using a rolling roll is optimal. Further, the effect of embossing is not different before or after galvanizing.

[0006] However, there are various galvanized steel sheets produced by various manufacturing methods such as hot dipping, electroplating, vapor deposition, and thermal spraying. The plating composition includes pure Zn, Zn, Fe, and Zn. And Ni, Zn and Al, Zn
And Mn such as Mn, containing one or more alloy elements and impurity elements for improving various functions such as corrosion resistance. Further, ceramic fine particles such as SiO ₂ , Al ₂ O ₃ and TiO ₂ Some have oxides or organic polymers dispersed in the plating layer, some have a single composition in the thickness direction of the plating layer, and some have a composition that changes continuously or in a layered manner. Some upper layers contain Fe or Ni as a main component and various alloy elements such as Zn and P.

For example, hot-dip galvanized steel sheet, iron-zinc alloyed hot-dip galvanized steel sheet, aluminum mainly containing zinc, hot-dip galvanized steel sheet such as iron, alloy in which only the lower layer is alloyed in the cross-sectional direction of the plating layer Hot-dip galvanized steel sheet (generally referred to as half alloy), single-sided iron-zinc alloyed hot-dip galvanized layer, galvanized steel sheet consisting of other-side hot-dip galvanized layer, zinc on these plated layers by electroplating, vapor deposition plating, etc., Steel plate plated with a metal containing iron or nickel as a main component, or electrogalvanized steel plate, zinc, nickel, chromium or other alloy electroplated steel plate, or a single alloy layer or a multi-layer alloy electroplated steel plate and these plated layers There are a plated steel sheet coated with an organic film, a vapor-deposited steel sheet of zinc and a zinc-containing metal, and the like. Other, SiO
There is a dispersion-plated steel sheet in which ceramic particles such as ₂ , Al ₂ O _{3 and the} like, TiO ₂ oxide particles and an organic polymer are dispersed in zinc or zinc alloy plating. The present inventors can suppress the generation of blowholes during arc welding by imparting embossing with a height of 1 μm or more (the upper limit is suitably 500 μm) to the surface regardless of the type of galvanized steel sheet. Found.

[0008]

EXAMPLES Examples of the present invention are shown in the table together with comparative examples.

[0009]

[Table 1]

[0010]

[Table 2]

Note 1): Types of galvanized steel sheet are AS: hot-dip galvanized steel sheet (7 to 13% of iron content, residual zinc after hot-dip galvanizing, hot-dip galvanized), Gi: hot-dip galvanized steel sheet, EG : Electrogalvanized steel sheet, EL (Excellite): Lower layer iron 15%, residual zinc (weight per unit area 20 g / m ² ),
Electroplated steel sheet with upper layer iron 85%, residual zinc (weight per unit area 3 g / m ² ), ZL (Zinclite): nickel 12%, electroplated steel sheet with residual zinc (weight per unit area 20 g / m ² ), AS-
E: 85% iron on top of AS, residual zinc (weight per unit area 3 g /
m ²⁾ a material obtained by electroplating, ZL-E: 85% iron in the upper layer of ZL, the remaining zinc (basis weight 3 g / m ²⁾ obtained by electroplating, any steel sheet thickness is ordinary steel 2.30mm ..

Note 2): A method for evaluating the generation of brohol. Main arc welding conditions: Two pieces of fillet welding are used, and a welding current is used so that the penetration of the lower plate side of the stack is 35% of the plate thickness. The welding speed is 1000 mm / min, the wire is 1.2 mm in diameter, and Nittetsu Welding Industry YM24S is used. The shielding gas was Ar 80% + CO ₂ 20%, and the flow rate was 25 l /
It was set to min. The welding position was horizontal, the torch angle was 60 ° from horizontal, and the torch advance angle was 0 °. Evaluation of blowholes: All the weld beads were subjected to an X-ray transmission test to detect all blowholes, and the number of blowholes per 100 mm weld length was evaluated.

Note 3) Embossing form Embossing of various shapes as shown in FIG. 1 is applied. The groove width between the embosses was 10 μm minimum and 10 mm maximum.

[0014]

By doing so, it becomes possible to greatly reduce the occurrence of broholes during arc welding of galvanized steel sheets, and to greatly improve the reliability of the joint. In addition, the galvanized steel sheet can be easily applied to automobiles, home appliances, etc., and has a great industrial effect.

[Brief description of drawings]

FIG. 1 is a diagram showing various embossed shapes according to the present invention.

Claims (1)

[Claims] 1. A galvanized steel sheet excellent in arc weldability, which is obtained by providing a convex embossment having a height of 1 μm or more on the surface of a galvanized steel sheet.