JPS6063394A - Galvanized steel sheet with superior weldability - Google Patents

Abstract

PURPOSE:To obtain a galvanized steel sheet with superior weldability by forming an inert film on the surface of the zinc layer of a galvanized steel sheet. CONSTITUTION:An inert film is formed on the surface of the continuous zinc layer of a galvanized steel sheet. An aqueous soln., a colloidal soln. or a slurry dispersion soln. contg. carbonates, phosphates, borates, nitrates, sulfate, chlorides, hydroxides or oxides of one or more among Ti, Al, Ni, Fe, Si, Mn, Co, W, Mo, Ca, B, Be and Zn is applied to the surface of the galvanized steel sheet by about 1-500mg/m<2>, and the sheet is dried after carrying out washing as required to form said inert film. Thus, the weldability of the galvanized steel sheet is improved, and welding stability is ensured.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a galvanized steel sheet with excellent weldability.

(Prior Art) Galvanized steel sheets are generally manufactured industrially by a hot-dip plating method or an electroplating method, but they have the disadvantage that weldability is inferior to that of cold-rolled steel sheets.

11! As is well known, the poor weldability of lead-plated steel sheets is caused by the zinc layer on the surface of the steel sheet, which causes heat generation during welding, and the welding tip (
This may lead to melting and adhesion to the electrode, or partial melting loss of the tip of the tip, or formation of an alloy layer with zinc, which impairs current conduction characteristics, leading to poor welding.

In particular, this tendency becomes more pronounced as the thickness of the galvanized layer increases. On the other hand, compared to the hot-dip plating method, the electroplating method has a problem in that the surface of the plating layer is more active, making welding difficult despite the thin plating.

(Object of the Invention) The present invention has been made to advantageously solve these difficulties, and is characterized by improved weldability by forming an inert film on the surface of the plating layer after galvanizing. It concerns superior galvanized steel sheets. The inert film mentioned here means a film that has the effect of completely suppressing thermal interdiffusion or metal compound formation reactions between the electrode tip and the plating layer during welding, and conversely, a film that does not suppress or promotes these reactions. It is defined as a fully active film if it has the effect of

In other words, galvanized steel sheets are inexpensive and have excellent quality characteristics, so as the need for rust prevention quality increases, they are used in automobiles,
It is widely used in the fields of home appliances and building materials, and is on the rise.

For this reason, quality requirements for weldability have become stricter, and a wide variety of products have been developed for this type of use. For example, a differentially plated steel sheet with different plating thickness on the front and back sides, a single-sided galvanized steel sheet with the other side iron, or an alloyed galvanized steel sheet with the entire plating layer placed on a Fe-Znn alloy layer by heat treatment after plating (both sides). plating or single-sided plating).

However, depending on the location and application, a double-sided galvanized steel plate may be required to ensure performance, and even if it is not acceptable for quality reasons, one side is not alloyed L11! Because lead-plated steel sheets (both sides plated and single-side plated) are required in some cases, deterioration of weldability has become a problem, and galvanized steel sheets with excellent weldability are strongly required in these cases where cooling is required. .

On the other hand, as the areas of use have expanded, not only general cold-rolled steel sheets but also high-strength steel sheets, ultra-deep-drawn steel sheets, bake-hardenable steel sheets, etc. There is a strong demand for galvanized products, but galvanized products that use these steel sheets as plating materials generally have poor weldability, so there is little hope for further improvement in weldability. .

In addition, when galvanizing the above-mentioned special materials, the electroplating method is often used because it is more advantageous in securing plating adhesion and material properties than the hot-dip plating method. . However, in the electroplating method, the surface of the plating layer is active, which is disadvantageous in terms of weldability, and there is a desire to improve weldability. In the electroplating field, in addition to regular galvanizing, Zn-1'c,
Zn-Ni, Zn-Co-M.

Although alloy-plated products such as alloy-plated products are being developed, sufficient performance in terms of weldability has not yet been secured, and further improvements in weldability are desired.

Against this background, the present invention provides a 111L lead-plated steel sheet with excellent weldability, in order to improve the weldability and ensure stability of the galvanized 1Aiil plate and the zinc-based alloy plated steel sheet.

(Structure of the Invention) Next, the present invention will be explained based on the drawings. In Fig. 1, when galvanized steel plates t and 2y are lapped and welded, a welding tip (electrode) 6°7 is attached to the lap part as shown in the figure.
The plated steel plates 1 and 7 are placed in contact and current is applied between the chips 6 and 7.
2 is spot welded. In this case galvanized steel sheet 1
, 2 are galvanized layers 4 plated on the surface of the plated original plate (steel plate) 50 by hot-dip plating or electroplating, respectively;
Furthermore, a surface modification layer 3 is formed on the surface of the plating layer by inactivation treatment using, for example, a chemical. The present invention is a method in which a chemical is applied to the surface of the plating layer to inactivate it after galvanizing by hot-dip plating or electroplating, and by forming a surface modification layer 3, weldability is dramatically improved. This is what we discovered.

In other words, in the case of general galvanized steel sheets, when continuous dotting work is performed during welding, the zinc 4 in the plating layer melted by heating
adheres to or reacts with the electrode tip 6.7, forming an alloy layer at the tip of the tip 6.7, impeding electrical conductivity, and at the same time melting and damaging the tip 6.7, significantly shortening the life of the tip 6.7. At the same time, normal nugget formation is impaired and weldability is deteriorated.

As a result of various studies to improve the continuous dot performance during welding, the inventors of the present invention have found that the above-mentioned difficulties can be advantageously solved by forming a surface-modified layer 3 on the surface of the plating layer 4 by chemical treatment. This is what I discovered.

The plating layer 4 referred to here means a plating layer mainly made of zinc (including zinc-based alloy plating) coated by hot-dip plating or electroplating, and of course, in the case of hot-dip plating, the plated It has an alloy layer at the interface of the layers.

Although it is not clear about the mechanism of the improvement in joint yield according to the present invention, the surface modified layer 3r formed by chemical treatment
This is thought to be because the electrical conductivity is I'', which promotes the exothermic reaction during welding and at the same time has the effect of acting as a barrier layer that suppresses direct contact between the metal in the welding layer and the welding tip. In other words, the above-mentioned effect of the surface modified layer 3 has the effect of shifting the nugget formation limit current to the low current side and simultaneously shifting the chip welding current to the high current side, thereby expanding the appropriate welding current range and making the welding work easier. It will improve your sexuality. On the other hand, it has the effect of reducing the wear rate of the tip and at the same time equalizing the wear of the tip, which not only improves the life of the electrode, but also improves continuous dot performance by ensuring stable heat generation during welding. .

Furthermore, according to the findings of the inventors, in order to improve the continuous dot performance, it is assumed that the appropriate current range is large and that the wear of the electrode tip progresses uniformly on the 111 surface. .

In other words, normal galvanized steel sheets are less likely to form nuggets than cold-rolled steel sheets, and the plated steel sheet and the chips are more likely to weld, so the flow range is narrower than normal galvanized steel sheets. When the current density increases, the current density decreases relatively and the heat generation for the steel plate > Therefore, normal welding is impossible, and continuous dotting work must be stopped at this point.

Therefore, it is effective to suppress wear and tear on the tip end as much as possible and at the same time expand the appropriate current range, especially to shift the lower limit of the appropriate current range, that is, the lower limit current for nugget formation, to the lower current side.

On the other hand, the state of wear and tear on the tip of the electrode tip is also important.Partial melting damage or chipping on the tip surface tends to deteriorate weldability. Find out what is important in securing the results.

In addition, as the number of dots increases, the wear of the tip progresses, but if the wear on the tip surface is uniform (((), or if thin mesh-like cracks are formed,
1 piece goes first ☆: i1'' It was confirmed that when the outer peripheral part of the 1 side goes 1 piece first and then 4 pieces (external cut type), the deterioration of weldability is relatively small. /ζ.

In contrast, when the central part of the tip end surface wears out first (fire-prone type), the weldability of bamboo deteriorates significantly.

Based on the above-mentioned knowledge, we investigated various techniques for improving the weldability of galvanized steel sheets and found that it is effective to modify the surface of the plating layer and form an inert film against welding reactions. Ta.

In other words, the essential role of the inert film is, first, to not impair the generation and transmission of welding heat, second, to shift the nugget formation lower limit current to the lowest possible current side, and third, to maintain the upper limit of the appropriate current range. That is, the welding current value is shifted to the high current side.Fourth, the progress of wear at the tip end is made uniform, and the progress of wear of the fire-oriented type is suppressed.

Therefore, the properties necessary for an inert film are: firstly, it should destroy appropriate electrical resistance and promote heat generation to facilitate nugget formation, and secondly, it should have appropriate thermal stability so that it can be used during welding. 'The barrier effect that suppresses direct contact between the electrode tip and the plating layer must be completely cured. Thirdly, during continuous dots, it adheres to the tip of the electrode tip or accumulates as the number of dots increases, which affects the current conduction characteristics. Fourthly, it does not react with the electrode tip, or even if it does react, it promotes erosion of the tip9, and it does not cause internal wear.

As a result of various studies on a wide range of agents for forming an inert film that breaks down, we have found that an inert film that advantageously achieves the object of the present invention by treatment with a limited number of chemicals, such as those described below, has the following properties: found that it is possible to form We have invented a galvanized steel sheet with excellent weldability by modifying the surface of the plating layer through chemical treatment. The conditions for forming this film will be described further below. The above example of welding galvanized steel sheets is for double-sided plated steel sheets, but it can of course be applied to differential thickness galvanized steel sheets where the plating layer thickness is different on one side and the other side. lead plating,
Even in galvanized steel sheets with zinc-iron alloy plating on the other side, galvanized steel sheets on one side with iron on the other side &f
Even in the case of IFL plates, the weldability can be reliably improved by forming a surface-modified layer on the surface of the plating layer of each galvanized GLTNI plate by, for example, chemical treatment.

In case of double-sided plating, electrode tip.

It is also effective to apply chemical treatment only to the side of the plated surface that comes into direct contact with the metal. In this case, since only one side is treated, there is an advantage that the treatment cost can be reduced.

As mentioned above, the method for forming a surface modified layer on the surface of a galvanized layer is to apply galvanization or zinc-based alloy plating to a steel sheet by electroplating or hot-dip plating, and then
By applying an aqueous solution containing one or more metal salts, washing with water if necessary, and drying, a surface modified layer that is advantageous for weldability can be easily formed.

As a result of examining a wide range of inorganic salts as agents to be applied, we found Ti, Al, Ni, Fe, Si, M.
n, Co.

Inorganic salts consisting of the elements W, Mo, Ca, B, Be, and Zn are effective, and carbonates, phosphoric acids, boric acids, nitric acids, and sulfuric acids consisting of one or more elements from the above-mentioned elements are effective. chlorides, hydroxides, oxides (
We have found that metal salts (hereinafter collectively referred to as metal salts) are effective.

When applied to the surface of the plating layer as an aqueous solution, colloidal solution, or slurry-like dispersion solution containing one or more metal salts related to the above-mentioned elements, the above-mentioned effect as an inert film is exhibited.

The effect of improving weldability is observed when the coating amount is in the range of 1 to 500 m97 m. If it is 500 Mg/+12 or more, the effect of improving weldability is small compared to the coating amount, resulting in large economic losses, and in addition, deterioration in workability, paintability, etc. is observed, which is not preferable. On the other hand, although an improvement effect is observed when the content is less than 1 mg/IIC, there is a disadvantage that the degree of improvement and welding stability are inferior.

Furthermore, among these metal salts, Ni, Mn, and B have the risk of increasing the hardness of the nuggets too much and causing them to become brittle when mixed into the nuggets.

1st rank is not very impressive, also Co, W, Mo
Salts such as salts are expensive. In addition, Ti, Aj?, etc. are elements that are less likely to mix into the steel when heated to high temperatures by electric current, and less likely to react with electrodes. , Si, Ca
etc. are more preferable from the viewpoint of thermal stability.

On the other hand, nitric acids, sulfuric acids, and chlorides can form corroded surfaces on the cut edges of steel sheets, and boric acids can cause nugget embrittlement when B produced through thermal decomposition gets mixed into the steel. Therefore, carbonates, phosphoric acids, hydroxides, and oxides are more preferable.In particular, for automobile steel sheets, phosphate treatment is often performed as a base treatment for painting. We have found that phosphoric acids are the most desirable in terms of their compatibility with the above. In particular, the phosphoric oxides of T1, Ad, and Ca, which are mentioned in the examples below, are excellent because they have little reaction with electrodes. Alternatively, 1.e-based metal salts are also effective, and have advantages such as being relatively inexpensive and not deteriorating the surface quality properties necessary for automotive applications.

The method for applying the chemical to the surface of the plating layer may be any conventionally known method, such as a dipping method, a spray method, a roll drawing method, and the like. Examples of methods for adjusting the amount of coating include a gas wiping method, a roll squeezing method, and a spraying method. The concentration of the treatment bath may be any suitable concentration that can ensure the above coating amount, and the method of forming the film may be any of the reaction type, adsorption type, and coating type, which should be selected as appropriate depending on the use of the plated steel sheet. Bye. Therefore, the pH and temperature of the bath may be determined depending on the method of forming the film selected above. In addition, it is effective to add various additives and surfactants to improve the viscosity of the treatment bath, the stability of the bath, or the homogeneity of the modified layer film.

The method for forming a modified layer on the surface of a plated layer by chemical treatment has been described in detail above, but after coating, it may be simply dried by shaking or, if necessary, washed with water and dried. When washing with water, brushing or high-pressure spray cleaning is used in combination to effectively remove the coating liquid and dust on the surface of the plating layer in order to ensure rust prevention, plating appearance, and coating performance. It is valid. The drying temperature is not particularly limited as long as it can completely remove moisture by evaporation, but it is especially important to dry +! iA degree 100
It is also effective to burn the coating by heat treatment in the range of ~450°C.

The plating layer forming the inert film of the present invention is mainly made of zinc coated by hot-dip plating, electroplating, etc., but for the purpose of improving corrosion resistance, paint adhesion, chemical conversion treatment, etc. Ni.

Sn, Cr, Ti, Mg, Al, Pb, S
Also in a zinc-based alloy plated steel sheet containing one or more of i, Fc, Co, Mo, Cu, etc., to form the same content, dispersed, or an intermetallic compound of these,
Of course, it can be effectively applied.

Furthermore, the present invention can be similarly effectively applied to two-layer plated zinc-based alloy plated steel sheets, multi-layer plated zinc-based alloy plated steel sheets, and the like.

Further, the plated original plate is a steel plate, but is not particularly specified. Furthermore, C: 0.01% or less ultra-low carbon steel sheets and these steel sheets contain C, Si, 'I'i, and Nb.

Weldability can be effectively improved even in plated steel sheets containing one or more of P, Cr, Mn, Cu, N, Alt, etc. 1. (Effect of the invention) It is recognized that weldability deteriorates, and when the plating layer thickness is increased to further improve corrosion resistance, deterioration of weldability becomes a problem, but the present invention can also be applied in such cases. For example, it has the advantage of effectively improving weldability and reliably maintaining good welding characteristics.

By applying the present invention, it is possible to extend the replacement period for tips, and there is also the effect of reliably improving weldability, such as increasing the number of continuous welding points and improving welding quality. In addition, by inactivating the surface layer of the plating layer with the modified layer, there is an effect that mold deformation during press working is further improved, and the adhesion of foreign substances to the surface 471 is reduced.

(Example) Examples of the present invention are listed in Table 1 along with comparative examples.

Note 1 The alloying treatment on the other side (versus both sides) shown in the plating mode refers to the process in which the amount of plating adhering is controlled by gas wiping washing immediately after the plated steel strip is pulled up from the plating bath in the hot-dip galvanizing line, and then the alloying process is performed. The other side only (or both sides) was heated at t530°C for 10 seconds, and the entire plating layer on the other side (or both sides) was changed to iron-111.
1 lead alloy layer (approximately 10% Fe).

On the other hand, alloy plating is performed using a sulfuric acid-based plating bath in an electroplating line at a current density of 13° Aldn2.
This is an electrodeposited zinc alloy plating layer.

Note 2. Ad-quilt and Ti-8U shown as plating original plate
LC indicates a Wj plate having the chemical components in steel shown in Table 2.

Table 2 Note 3゜The method of applying the treatment liquid is immersion in the specified treatment bath (5se
After step c), the coating amount was adjusted using a gas wiping method, and then dried using a hot air dryer.

In Example 9, the treatment liquid was spray applied for 5 seconds, then sprayed and washed with water, and then dried.

Note 4 Weldability was evaluated by the number of dots in a continuous workability test. The welding conditions are as follows.

■) Pressure force 2sOKgf 2) Initial pressurization time 2211z 3) Current application time 8l-IZ 4) Holding time 5117゜5) Welding current 1 n
1 ``1-lower limit forming nugget diameter 36φ'' Ichihara (KA
)) 6) Plate thickness Q, 31m 7) Tip tip is 1.1 diameter 57 trowel (circle ≦; 11-inch type) When welding, plate two plates with one side of the plated steel plate on the top and the other side on the bottom. (2) The 11'iI plates were stacked together and subjected to a continuous dot test.

The end point of the number of continuous hits was determined with a nugget diameter of 3.5 mm as the lower limit.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of the present invention. 1.2... Galvanized steel sheet 3... Chemically treated surface modification layer (inert film) 4.
... Galvanized layer 5 ... Plated original plate 6 ... Welding electrode (chip) Procedural amendment October 77, 1981 Kazuo Wakasugi, Commissioner of the Patent Office■, Indication of case Patent application No. 7 of 1988 '? 0r72 No. 2, Name of the invention Galvanized steel sheet with excellent weldability 3, Relationship with the amended case Patent applicant address 2-6-3 Otemachi, Chiyoda-ku, Tokyo Name Name
(665) Nippon Steel Corporation Representative Takeshi 1) Yutaka 4, Agent Address: 105 (503) 4.877
Address: 8th floor, Daiichi Mori Building, 1-12-1 Nishi-Shinbashi, Minato-ku, Tokyo (1) On page 18, line 1o of the specification, "13°A no dn2J" is corrected to "130A/d1n2." (2) Amend Table 1 of the 17th Tei as shown in the attached sheet.

Claims (1)

[Claims] A galvanized steel sheet with excellent weldability that has an inert film formed on the surface of a zinc-based continuous coating layer.