KR930007927B1 - Two-layer plating alloy steel sheet of high corrosion resistance and method for producing the same - Google Patents

Abstract

A surface of the steel plate consists of the first galvanized layer and the second electroplated layer formed on the first galvanized layer. The galvanized layer includes 7-15 wt.% Fe, and has the galvanized amount of 20 g/m2, and then the second electroplated layer includes 5-30 wt.% Zn, 0.1-10 wt.% Mn and balance Fe and has the electroplated amount of 0.5 g/m2. The steel plate is useful for an automoble body and has the improved corrosion resistance and adhesion property of paint.

Description

High corrosion resistant double layer alloy plated steel sheet and its manufacturing method

The present invention relates to a two-layer alloy plated steel sheet used in automobile body shells and the like and a method of manufacturing the same. More specifically, a zinc-iron alloyed molten lead-free galvanizing is the first high-gold layer, iron-zinc-manganese alloy The present invention relates to a high corrosion resistant two-layer alloy plated steel sheet having a second plated layer and a method of manufacturing the same.

Galvanized steel sheet is widely used as automotive material because of its rust prevention property.However, in order to meet the light weight and high anti-rusting pursuit of the vehicle body, which is emerging seriously in terms of environmental pollution and energy saving, that is, high strength in terms of weight reduction There is a need for a plating layer that can improve quality properties such as phosphate treatment, paint adhesion, and corrosion resistance after coating to satisfy the high rust resistance while adopting steel sheet and minimizing coating amount.

As a method for manufacturing a two-layer plated steel sheet having superior plating characteristics as a vehicle material, Japanese Patent Laid-Open Nos. 58-77591, 59-177391, 59-177392, 59-182987, 59-211592 And the methods disclosed in Japanese Patent Application Laid-Open Nos. 58-15554, 60-57518, 63-24080, and the like.

Japanese Patent Laid-Open Nos. 58-77591, 59-177391, 59-177392, and 58-554,554-55480 are mainly Zn-Fe of Zn and Zn-based alloys; Zn-Ni alloy plating layer as a lower layer, and relates to a method for plating the iron-zinc alloy on it, Japanese Patent Laid-Open No. 59-182987 discloses after the iron-zinc alloy plated on the Zn and Zn-based alloy plating layer Japanese Patent Laid-Open Publication No. 59-211592 relates to a method of plating iron-phosphorous alloys by substituting an iron-zinc-based alloy plating layer on Zn and Zn-based alloy plating layers. In the production method, most of them use a sulfate bath, and a chloride bath is used in iron-phosphorus plating of JP-A-59-211592.

When the zinc alloy containing 16 to 30 wt% (weight ratio, used in the following weight ratio) as the second plating layer (surface layer) is disclosed in Japanese Patent Publication No. 63-24080, the phosphate treatment property is low due to the low iron content. This deterioration is not expected to improve the water resistance and paintability. In addition, zinc alloys having an iron content of 60% or more, as shown in Japanese Patent Application Laid-Open Nos. 58-77591, 59-177391, 59-177392, and Japanese Patent Nos. 58-15554 and 60-58518. When the second plating layer (surface layer) is used, there is a problem in that the phosphate treatment property, paintability, and post-painting corrosion resistance change greatly depending on the plating deposition amount and the Fe content of the surface layer. In other words, when the amount of plating adhesion of the surface layer is small and the Fe content is 60 to 70%, the non-uniformity of phosphate coating and phosphophyllite (Phosephophyllite, Zn ₂ Fe (PO ₄ ) ₂ , 4H ₂ O, hereinafter “P-type” The formation of crystals is reduced, resulting in deterioration of phosphate treatment properties, resulting in poor paintability and deterioration in adhesion of coating films.

On the other hand, if the amount of plating adhesion on the surface layer is high and grooves or defects occur in the coating film, due to the high iron content of the surface layer, proper generation is promoted, and corrosion resistance after coating is deteriorated, and the uncoated corrosion resistance of the entire coating layer is lower than that of the single layer plated only on the lower layer. Deterioration occurs.

In the case of the iron-phosphorus system disclosed in Japanese Patent Laid-Open Publication No. 59-182987, the increase of brittleness of the plating layer by phosphorus and the Fe and phosphorus (P) ions in the plating bath are not only deposited in the initial process of the upper plating but also zinc and There is a problem in that the upper plating layer is peeled off due to adhesion deterioration of trace amounts of Fe and P precipitates due to electroless substitution reaction.

Zinc and zinc-based alloy plating (Zn-Fe, Zn-Ni, Zn-Co, etc.) layer can protect the cold-rolled steel sheet, which is a metal, by its excellent sacrificial anticorrosion, but in the harsh corrosive environment of automobiles When the coating film on the outer surface or the inside of the car body receives a loss of acid, a large amount of zinc is contained. Therefore, water penetrated under the coating film reacts with zinc to form a corrosion product such as powdered zinc hydroxide, and at the same time, hydroxide ions are generated to change into an alkaline atmosphere. It dissolves the phosphate coating and further promotes the penetration of moisture into this corrosion product. This is considered to be a big factor in deteriorating the water-resistant adhesiveness of a coating film, water-resistant adhesiveness of a coating film, and corrosion resistance after coating.

Therefore, in the two-layer plated steel sheet, there is a need to improve the coating quality performance in order to improve the corrosion resistance of the zinc and zinc-based alloy plated layer and to be used in harsh corrosive environments such as steel sheets used for automobile body panels. One of the coating quality performances of the steel plate for vehicle body panels is paint adhesion. As a method of evaluating secondary adhesion of paint, there is a water resistance test. In general, water-resistant adhesion test is carried out with chemical conversion treatment (phosphate treatment), electrodeposition coating, intermediate coating, and top coating on materials that correspond to the outer surface of automobiles. This is a test to evaluate the adhesion of the coating film to the degree of peeling off the tape when the pattern scale is inserted and the vinyl tape is peeled off. In general, phosphopyrite or phosphite (Hpeite: Zn ₃ (PO ₄ )) may be present in the phosphate coating film. ₂₎ 4H ₂ O. Hereinafter, the presence of many P-type crystals in the crystal improves water-tightness, and the better the phosphate treatment, the better the Cation-type electrodeposition coating after the phosphate treatment. Therefore, in terms of performance of automobile body, the surface appearance after middle and top coating is good and the corrosion resistance after painting is improved by improving adhesion between plating layer and coating film. It is known as.

According to the findings of the present inventors, a cold rolled steel sheet generally known to be excellent in phosphate treatment has a proper amount of Fe, C, Mn, Cr oxides, etc. distributed on the surface, thereby forming local electrons during phosphate treatment. It was evaluated to promote the reaction. On the other hand, in pure railway gold by electroplating, the initial reaction is slow and the phosphate grains coarsen due to the formation of stable oxide film on the surface.

Therefore, the present inventors have repeatedly conducted experiments and studies in view of the above problems and findings, and the iron-zinc-manganese alloy plating layer containing a small amount of manganese in the iron-zinc alloy plating having a high iron content has a single plating state. Insufficient ability of corrosion-resistant cold rolled steel sheet than zinc and zinc-based alloy plated steel sheet, but after plating the metal coating layer containing a large amount of zinc in the lower layer, and electroplating the iron-zinc-manganese alloy on the upper layer, It was confirmed that the phosphate treatment property and water tightness resistance can be improved, and based on this, the two-layered steel sheet and the zinc-iron alloy electroplating layer as the first plating layer and the iron-zinc-manganese alloy electroplating layer as the second plating layer The manufacturing method was applied for a patent in Korean stimulation patent application No. 90-22636.

However, in order to further improve the rust resistance of an automobile body under air pollution and corrosive environments that are deteriorating day by day, there is a demand for better quality rustproof steel sheets.

Therefore, the inventors of the present invention have a surface state similar to that of a cold rolled steel sheet and have a high iron content in the plating layer composition, so that the phosphate treatment is excellent, and the metal is not easily powdered in the alloying elements of the upper plating system. The present invention focuses on the fact that the metal ion in the plating bath can improve plating adhesion by adding ions which are less likely to precipitate due to electroless reaction with zinc, that is, metal ions which are less than zinc. In the present invention, the present invention is to plate the iron-zinc-manganese alloy galvannealed galvannealed (galvannealed, referred to as "GA") in two layers, plating adhesion, phosphate treatment, water resistance To provide a two-layer alloy plated steel sheet and its manufacturing method that can be used for automotive exteriors with excellent adhesion and corrosion resistance after painting. There is a purpose.

Hereinafter, the present invention will be described in detail.

The present invention is a two-layer plated steel sheet having a first plated layer and a second plated layer on the surface of the steel sheet, wherein the first plated layer has an iron (Fe) content of 7% by weight (hereinafter referred to as "%") zinc-iron alloying As a hot-dip galvanized layer, the plating amount thereof is 20 g / m 2 or more per steel sheet name; The second plating layer is an iron-zinc-manganese alloy electroplating layer composed of 5 to 30% of zinc, 0.1 to 10% of manganese, and residual iron (Fe), and has a high corrosion resistance two-alloy plated steel sheet having a plating adhesion of 0.5 g / m 2 or more. It is about.

The present invention also provides a zinc-iron alloyed molten zinc plated layer as a first plated layer on a steel plate surface, and a second plated layer formed on the first plated layer to produce a two-layer alloy plated steel sheet. The total concentration of ferrous ions, zinc ions, and manganese ions is 0.5 mol / To a solubility limit, zinc and manganese ions in the total metal ion concentration in a molar ratio of 1 to 40 mol%, and a total concentration of chloride ions of at least 5.0 mol / Phosphorus chloride bath has a pH of 1.0 to 4.0, a current density of 20 to 250 A / dm 2 and a relative flow rate of 20 to 20 m / min. The present invention relates to a method for producing a high corrosion-resistant double-alloy plated steel sheet, characterized in that the second plating layer is formed by electroplating under an electrolytic condition (mpm).

EMBODIMENT OF THE INVENTION Hereinafter, the reason for numerical limitation of this invention is demonstrated.

In the 1st plating layer of this invention, when plating amount is less than 20 g / m <2>, since sufficient corrosion resistance is difficult to ensure, it is preferable to limit it to 20 g / m <2> or more.

In addition, the reason for limiting the iron content in the zinc-iron alloyed molten zinc of the first plating layer in the range of 7 to 15% is that the inventors confirmed that the iron content in the zinc-iron alloyed zinc plating is less than 7%. This is because it is not easy to alloy iron and zinc in the plating layer, and it is not easy to improve the corrosion resistance, so that spangle pattern appearing on the surface of the hot dip galvanized plate is easily generated. Due to excessive alloying, the thickness of the `` phase (Fe ₃ Zn ₁₀ ) '' formed between the plating layer and the base metal (cold rolled steel, Fe) increases due to excessive alloying. It's a problem.

However, in terms of uncoated corrosion resistance, surface rust resistance and plating adhesion, the content of iron in the first plating layer is most preferably 9-12%.

The second plating layer is an iron-zinc-manganese alloy electroplating layer on the first plating layer, and the plating deposition amount is limited to 0.5 g / m 2 or more, and at the plating deposition amount of less than 0.5 g / m 2, it is impossible to completely cover the first plating layer. This is because the characteristics of the first plating layer are so strong that the effect to be obtained in the present invention cannot be satisfied. In other words, the plating deposition amount of less than 0.5g / ㎡ does not completely cover the first plating layer, so that the phosphate coating is non-uniform during phosphate treatment, and the film is composed of many "H-type" grains, resulting in poor phosphate treatability and post-processing. Water adhesion is also degraded due to surface appearance difference during electrodeposition coating and poor adhesion of electrodeposition coating film.

Although the upper limit of the plating amount of the second plating layer is not specifically determined, it is possible to compensate for the defects of the first plating layer and to prevent the quality characteristics such as plating adhesion, phosphate treatment property, electrodeposition coating property, and corrosion resistance after coating from being damaged. It is desirable to limit the amount of plating deposition equivalent to that of the first plating layer in consideration of the production cost in view of the purpose and economical point of view.

The reason for limiting the zinc content to 5 to 30% in the iron-zinc-manganese alloy electroplating layer of the second plating layer is that when the zinc content is less than 5%, the plating layer strongly exhibits the characteristics of iron (Fe). If the adhesion amount is increased, not only the homeostatic effect of corrosion resistance is weak, but also the plating adhesion is deteriorated by the increase of the internal stress of the plating layer, and if it exceeds 30%, it is difficult to secure the phosphate treatment and water resistance of the cold rolled steel sheet. to be.

In addition, the limit of manganese content in the iron-zinc-manganese alloy electroplating layer, which is the second plating layer, is in the range of 0.1 to 10%, which is based on the improvement of plating adhesion, phosphate treatment resistance, and water resistance, and the content of manganese in the vicinity of zinc content of 30%. If the content is less than 0.1%, it is not expected to improve the phosphate treatment property, but when the manganese is added at 0.1% or more, the phosphate treatment property and water-adhesion resistance are improved, but when the content of more than 10% manganese is contained, the second plating layer This is because problems such as deterioration of processing due to poor adhesion and discoloration of surface appearance due to oxygen present in the plating layer are likely to occur.

In general, zinc-iron alloyed hot dip galvanizing (GA) is a zinc hot dip galvanized layer (GI material) of the zinc plating layer (GI material) is transformed into a Zn-Fe alloy layer by the heat treatment-diffusion reaction, continuous hot dip galvanizing line (hereinafter referred to as In the “CGL”), a steel sheet or strip passed through a galvanizing bath is alloyed. In order to manufacture a GA steel sheet for processing, it is preferable to use Ti addition polar carbon steel or Ti-Nb complex addition ultra low carbon steel. In the case of hot-dip galvanizing, the plating reactivity and the alloying treatment characteristics are severely changed according to the steel components, and therefore, strict control of various conditions is required to produce a stable quality GA material. Especially, powdering in which the plating layer falls off in the form of powder during processing Phenomenon is a weakness of GA material, mainly due to alloying of plating layer. Factors affecting the alloying reactivity of the GA material include the steel component of the material, the continuous annealing condition, the strip bath temperature, the plating bath temperature, the plating deposition amount, the alloying treatment rate and time, the cooling rate after the alloying treatment, and the like. In particular, the Al concentration in the plating bath should be adjusted in consideration of the line speed and the GA (爐) length of the CGL as factors that affect the speed, alloy layer structure and surface morphology of the alloying board.

In addition, in the case of Ti-added steel, Fe-Al-based or Fe-Al-Zn-inhibiting layers, which suppress Zn-Fe interdiffusion during hot dip galvanization, are vulnerable, and thus Zn-Fe intermetallic compounds ( An intemetallic compound forms at the Fe / plated interface. Such intermetallic compounds may cause cracks in the plating layer in the hot dip plating process, and deteriorate the quality of the GA material during the alloying process, which is a post process. Therefore, it is advisable that the rigid portion be added as little Ti as possible, and a very low carbon steel material having a composite addition of Nb having the same effect as Ti addition is preferable.

On the other hand, in the method for producing an alloy plated steel sheet according to the present invention, the alloying hot-dip galvanizing of zinc-iron alloy as the first plating layer can be carried out by a conventional method, for example, Ti-Nb composite addition ultra-low carbon steel Material, continuous annealing temperature 755 ℃, strip bathing temperature 430 ℃, plating bath temperature 460 ℃, Al content in plating bath was maintained at 0.13%, and after 8-12 seconds deposition at alloying temperature 480 ~ 500 ℃ The method performed on the plating conditions of 30 degree-C / sec is mentioned.

The zinc-iron-based GA material produced by GA method is more excellent in corrosion resistance than the iron-zinc alloy plate material produced by electroplating method, and when coated, even if the painted surface is destroyed or scratches occur, It shows the effect of suppressing the corrosion of, for example, in the manufacture of plating after plating plating amount of 40g / ㎡ or more, the hot-dip plating method can reduce the manufacturing cost compared to the electroplating method.

In the case of electroplating an iron-zinc-manganese alloy, which is a second plating layer formed on the first plating layer, the total metal ion concentration of ferrous ions, zinc ions and manganese ions is 0.5 mol / It is maintained in the solubility limit range, and the total metal ion concentration is 0.5 mol / If it is below, the cathode precipitation efficiency will be lowered, and the productivity will be lowered. On the other hand, if the solubility limit is exceeded, there is a problem in that solid precipitate is formed. In the plating bath of the second plating layer, ferrous ions, zinc ions, and manganese ions may be introduced in the form of chlorides, sulfates, and the like. The zinc and manganese contents of the second coating layer may be zinc in the total metal ion concentration in the plating bath. And manganese ion concentration ratio can be appropriately selected. That is, the zinc and manganese ion concentrations in the total metal ion concentration in the plating bath in order to stably deposit the iron-zinc-manganese alloy coating film having a desired zinc alloy composition of 5-30% and manganese content 0.1-10% in the plating layer. Should be kept in the range of 1 to 40 mol% in molar ratio.

Total chloride ion concentration in the plating bath of the second plating layer was 5.0 mol / , Preferably 6.0 mol / To solubility limits, with a total chloride ion concentration of 5.0 mol / In the case of less than, the electrical conductivity of the plating bath is low, the alloy composition of the plating layer is non-uniform, and the precipitation of manganese hardly occurs.

In the plating bath of the present invention, inorganic plating bath conductivity aids such as potassium chloride, ammonium chloride, sodium chloride and calcium chloride may be added alone or in a mixture as a method of adding chloride ions. However, the addition of organic compounds such as sodium acetate (CH ₃ COONa), citric acid (CHO), tartaric acid, etc. should be limited in kind and amount of addition to the range that does not affect the internal stress of the plating layer, that is, deterioration of processability.

Relative flow rate used in the present invention is a relative moving speed of the steel through the plating bath, it should be maintained at a position of 20 to 200mpm. If the relative flow rate is less than 20mpm, the alloy composition of the iron-zinc-manganese alloy plating layer by the low current density plating is unstable, and the surface contamination is a problem due to the low speed.

The reason for limiting the current density to 20 to 250 A / dm 2 is because the achievement of manganese is difficult at a current density of 20 A / dm 2 or less, and when the current density is 250 A / dm 2 or more, it exceeds the limit current density range. This is because a kind of tanning (Burning) occurs in which the plating surface is black and coarse grains are generated, thereby degrading the plating adhesion of the second plating layer.

If the plating liquid pH is less than 1.0, the plating liquid is strongly acidic, so it is unsuitable in terms of dissolving and electroless substitution reaction of the lower layer of the first plating layer and reduction of the negative electrode deposition efficiency. ^Since hydroxide precipitates of Fe (OH) ₃ are formed by the production of ferric ions (Fe ^{3 ±} ) by oxidation of ²⁺ ), problems such as corrosion of equipment and surface contamination are generated, so a pH range of 1.0 to 4.0 is preferable. In addition, even in the relationship between the pH of the plating liquid and the ferric ion concentration, when the ferric ion concentration and pH in the plating liquid are high, defects such as precipitation alloy composition of the plating layer, surface streaks, and stains are generated, so the plating solution pH is within the above range. .

There is no particular limitation on the plating liquid temperature, but it is effective as long as it is in the range of 30 to 70 ° C. which is a temperature used for ordinary electroplating.

Hereinafter, the present invention will be described in detail through examples.

EXAMPLE

A second plating layer was formed on the test piece plated with zinc-iron alloy molten zinc with the first plating layer under the plating solution composition and plating conditions as shown in Table 1 below. As described above, the specimens on which the second plating layer was formed were measured and evaluated for plating adhesion, phosphate treatment resistance, water adhesion, and corrosion resistance after coating, and the results were compared with the results for the specimens plated by the conventional method and the comparative method. Shown in

The plating adhesion in Table 1 was evaluated by the degree of plating layer peeling by vinyl tape after 180 ° bend the sample formed with the second plating layer as described above, the phosphate treatment property by X-ray diffraction after phosphate treatment by immersion type phosphate treatment method P-type film ratio, appearance of phosphate film, and the shape, density and size of the film grains by scanning electron microscopy (SEM) were comprehensively evaluated. In addition, the water-resistance resistance of the sample was immersed in immersion-type phosphate treatment, 20 占 퐉 of cationic gel electrodeposition coating, 30 占 퐉 coating, 30 占 퐉 coating, and 30 占 coating coat, so that the total film thickness was about 80 占 퐉. After taking out, the cross-cut was made of 2mm intervals (Cross-cut) was evaluated to the extent to peel off the tape when peeling off by attaching a vinyl tape.

After coating, corrosion resistance test was carried out in the same way as water tightness test by phosphate treatment, electrodeposition coating, middle coating, and top coating, and the "X" cross cut to the base metal (cold rolled steel) was added to constant temperature (49 ℃), humidity ( Cyclic Corrosion Test (CCT) and Brine in 100 cycles (50 days) with 12 cycles of 1 hour (Cycle), such as drying, at a relative humidity of 90 to 100%) and 49 ° C or less than 50%. Salt Spray Test (JIS Z 2371) The corrosion width and the depth of corrosion after 1000 hours were evaluated.

Each evaluation result was expressed as follows.

⊙: Very good ◎: Very good ○: Excellent

△: Normal X: Slightly defective XX: Poor

TABLE 1

Comparative material 1-3 shown in Table 1 is the case that the manganese content, zinc content in the upper plating layer which is the second plating layer is out of the scope of the present invention, Comparative material 4 is the plating deposition amount of the second layer plating layer of the present invention 1 is a cold rolled steel sheet which is not subjected to plating treatment, conventional material 2 is a single layer electroplating steel sheet of pure zinc, and conventional material 3 is a zinc-iron alloy electroplating steel sheet having 15% iron content. , Conventional material 4 is a zinc-nickel alloy electroplated steel sheet having a nickel content of 12%, and conventional material 5 is an alloyed hot dip galvanized steel sheet (GA material) having an iron content of 12%.

As shown in Table 1, Inventive material 1-4 in accordance with the present invention can be seen that the superior in plating adhesion, phosphate treatment, water tightness, corrosion resistance after coating than Comparative Materials 1-4 and conventional materials 1-5. have.

Claims (2)

In a two-layer plated steel sheet having a first plated layer and a second plated layer on the surface of the steel sheet, the first plated layer is a zinc-iron alloyed hot-dip galvanized layer having an iron content in the range of 7 to 15% by weight, and its plating adhesion amount is 20 g / s on one side of the steel sheet. More than ㎡; The second plating layer is an iron-zinc-manganese alloy electroplating layer composed of 5 to 30% by weight of zinc, 0.1 to 10% by weight of manganese and residual iron (Fe), and the plating amount thereof is 0.5 g / m 2 or more. High corrosion resistant two layer alloy plated steel sheet. In the method for producing a bi-alloy galvanized steel sheet in which a zinc-iron alloyed hot-dip galvanized layer is formed on the surface of a steel sheet as a first plating layer, and a second plating layer is formed on the first plating layer, zinc and manganese ions in an acid-hydrochloric acid electric railway bath The total concentration of ferrous ions, zinc ions and manganese ions was added with hydrochloride containing To solubility limit, zinc and manganese ions in the total metal ion concentration in a molar ratio of 1 to 40 mol%, chloride ion concentration of at least 5.0 mol / The composition of the plating bath is adjusted to be; The pH of the plating bath was 1.0 to 4.0, the current density was 20 to 250 A / dm 2, and the relative flow rate was 20 to 20 m / min. A method for producing a high corrosion resistant double alloy plated steel sheet, characterized in that the second plating layer is formed by electroplating under phosphorus electrolytic conditions.