JP5130486B2 - High corrosion resistance hot-dip galvanized steel - Google Patents

Description

  The present invention relates to a high corrosion resistance surface-treated steel material, and more particularly to a hot corrosion resistant hot-dip Zn alloy-plated steel material.

  Zn (Zinc) -based plated steel is used in a wide range of fields such as automobiles, home appliances, and building materials. However, in order to ensure a long-term rust-preventing effect, it is usually applied with a high adhesion amount of Zn-based plating. .

  The reason for this is that the corrosion rate of Zn plating is slower than that of steel, and Zn, which has a lower corrosion potential than Fe (base iron), exhibits a sacrificial anti-corrosion function where the base iron is exposed. This is because the greater the amount of Zn, that is, the greater the amount of plating attached, the longer the corrosion and rust prevention effects obtained by the consumption of Zn can be maintained for a long time.

  Also, normally, when applying corrosion to steel to ensure corrosion resistance, when flaws reaching the base iron occur in the paint film, the paint swells in accordance with the corrosion of the steel material in and around the collar. Corrosion accompanied by may occur. Even for this corrosion form, the Zn-based plated steel material exhibits excellent corrosion resistance as compared with the bare steel material without plating. In addition, in this specification, the corrosion resistance with respect to the corrosion progress accompanying the swelling of the coating film after a coating is described as a post-coating corrosion resistance. Also for the corrosion resistance after coating, it is advantageous that the plating has a high adhesion amount.

  However, as the plating adhesion amount increases, necessary properties such as workability and weldability of the steel material tend to deteriorate. Therefore, it is desirable to ensure high corrosion resistance with a lower adhesion amount if possible. Therefore, many proposals have heretofore been made to add alloying elements to galvanizing to ensure sufficient corrosion resistance with a low adhesion amount.

  Actually, Zn-Ni alloy plating, Zn-Fe alloy plating, etc. are widely used mainly for automotive steel, and Zn-Al alloy plating is widely used mainly for construction steel. Has been applied. In particular, in order to further improve the corrosion resistance of the Zn—Al-based alloy plating, plated steel materials to which Mg or Si is added are disclosed in Patent Documents 1 and 2, and are put into practical use.

  However, the addition of Al to the plating deteriorates the corrosion resistance after coating depending on the amount of addition. One reason for this is that, when Al is added at a high concentration, the chemical conversion treatment that is responsible for the adhesion between the plating layer and the coating film deteriorates, and the adhesion of the coating film is impaired.

  On the other hand, even if the amount of Al added is a relatively low amount that can ensure sufficient chemical conversion treatment, the solubility of Al in an alkaline environment is higher than that of Zn. When the aqueous solution environment to which the plating is exposed is alkalized by this cathode reaction, the corrosion resistance of the plating is deteriorated, and the problem that the progress of the swelling of the coating film is promoted (called an alkali blister) tends to occur.

  Mg is very effective as an element for improving corrosion resistance other than Al, which can be an additive component of Zn-based plating. However, if Mg is added in a plating bath with less Al, oxide-based dross occurs due to oxidation of Mg, the plating appearance deteriorates, operability deteriorates, and the Mg concentration in the plating bath rapidly increases. There is a problem such as lowering.

  On the other hand, in Patent Document 3, 0.01 to 5% Ca is added to Zn-based plating containing Mg of 0.2 to 15% (hereinafter,% of the component represents mass%) and 0.05 to 1% of Al. A Zn-based plated steel sheet that suppresses oxidation of Mg even when Al is contained at a low concentration of 1% or less and does not cause a bad appearance or worry about oxidation of the bath surface is disclosed.

  In Patent Document 3, a qualitative solution to the problem of adding Mg to a low Al concentration Zn plating bath has been proposed. However, as shown in Patent Documents 1 and 2, the Al content up to about 1% is insufficient to obtain corrosion resistance in a severe corrosive environment.

  Accordingly, there has been a demand for the development of a plating component that improves the bare corrosion resistance of the plating itself with an Al content of 1% or more and exhibits good post-coating corrosion resistance.

Japanese Patent No.3179401 Japanese Patent No. 3179446 JP 2001-81538 A

  An object of the present invention is to provide a highly corrosion-resistant hot-dip Zn-plated steel material having good post-painting corrosion resistance while improving the bare corrosion resistance in a Zn-based hot-dip plated steel material at an Al concentration of 1% or more of the plating component. .

  With reference to the techniques disclosed in Patent Documents 1 to 3, the present inventors have optimized the amount of Al, Mg, and Ca to improve the bare corrosion resistance while improving the corrosion resistance after coating. Worked on the development of Zn-based plated steel.

  Among these components, it was found that Ca, in particular, has the effect of significantly improving the corrosion resistance after coating, depending on the method of addition, but conventionally, Zn-based plating has a stable melting of Ca. However, further research was required to solve this problem.

  In the process, it was found that Ca which does not easily remain in the Zn-based plating remains in the Zn bath after adding and dissolving Mg at a concentration several times higher than that of the other Zn bath. It has been found that in Zn-based plating with sufficient addition of Al, the corrosion resistance after coating is very good even if the Al concentration is 2% or more. In particular, by controlling the concentrations of Al, Mg, and Ca within an optimal balance range, the inventors have found a composition range in which bare corrosion resistance and post-coating corrosion resistance are compatible at a high level.

The present invention has been made based on such findings, and the gist thereof is as follows .

( 1 ) The plating layer contains mass 2%, Al 2-6%, Mg 0.6-4%, Ca 0.06% or more, and the relationship between the components satisfies the following formulas 1 and 2. , and the remainder have a alloy plating layer consisting of Zn and unavoidable impurities, high corrosion resistance hot-dip Zn-based alloy coated steel material, wherein the amount of adhesion alloy plating is 150 g / m ² / single-sided or less.

Mg% ≦ 0.8 × Al% ・ ・ ・ (Formula 1)
0.03 × Mg% ≦ Ca% ≦ 0.1 × Mg% (Formula 2)
Here, Mg%, Ca%, and Al% are mass% contents of Mg, Ca, and Al, respectively.
( 2 ) The high corrosion resistance melt as described in (1 ) above, further comprising one to two kinds selected from Cr, Mn, Co, Ni, and Cu as a component in the alloy plating layer in a total amount of 0.02 to 3 mass%. Zn alloy plated steel.
( 3 ) As a component in the alloy plating layer, 0.02 to 0.5 mass% in total containing one or more selected from Ti, V, Nb, W, Zr, Mo, La, Ce, Hf, and Y The high corrosion resistance hot-dip Zn alloy-plated steel material according to (1) or (2) .
( 4 ) A highly corrosion-resistant coated steel sheet having a coating on the high corrosion-resistant hot-dip Zn alloy-plated steel material according to any one of (1) to ( 3 ).

  The highly corrosion-resistant hot-dip Zn-plated steel material of the present invention achieves high corrosion resistance at both a bare material and a coating material at a high level by effectively using Al, which is a relatively inexpensive additive component. This can be widely applied to automobiles, architecture / housing, etc., while maintaining the same manufacturability as before, improving the life of components, effectively using resources, reducing environmental impact, and maintenance effort -It contributes greatly to industrial development by contributing to cost reduction.

  Hereinafter, the present invention will be described in detail.

  First, the reasons for limiting each component in the plating layer will be described.

  Al is a component added for the purpose of improving bare corrosion resistance, and since its effect is not observed at less than 2%, the lower limit concentration is 2%. On the other hand, if it exceeds 12%, the corrosion resistance after coating deteriorates, and even if the addition amount of Mg or Ca is adjusted, it is difficult to suppress the swelling of the coating film. Therefore, the upper limit concentration of Al is set to 12%. Further, from the viewpoint of spot weldability, if it exceeds 6% (such as remarkable Al diffusion to the electrode tip), the continuous weldability deteriorates, so 6% or less is more desirable.

  Mg, as well as Al, is an important element for improving the corrosion resistance of Zn plating in the steel sheet of the present invention. If it is less than 0.6%, a clear effect of improving corrosion resistance is recognized compared to when no Mg is added. Since this is difficult, the lower limit concentration is set to 0.6%. As a general rule, the addition of Mg improves both the bare corrosion resistance and the corrosion resistance after coating.However, in the vicinity of the alloy element composition in the present invention, an Mg concentration exceeding 4% had an adverse effect on the corrosion resistance after coating, so the upper limit concentration of Mg. Is 4%. In addition, in the composition of the present invention, the oxidation of Mg is suppressed to some extent by the addition of Ca, but when the Mg concentration exceeds 80% of Al, the oxidation of Mg becomes remarkable even if Ca coexists, In order to impair the stability of the plating bath, such as dross, etc., the upper limit of the amount of Mg added is 80% of the amount of Al added. This relationship is represented by the following formula 1 in the formula.

Mg% ≦ 0.8 × Al% ・ ・ ・ (Formula 1)
Here, Mg% is the mass% addition amount of Mg, and Al% is the mass% addition amount of Al.

  Ca suppresses the oxidation of Mg and improves the stability of the plating bath, thereby improving the surface properties of the plating and also contributing to the improvement of corrosion resistance by suppressing the inclusion of oxides. It is an element that contributes to corrosion resistance by improving the stability of the product in an alkaline environment. Further, it has been newly found out that the element in the concentration range of the present invention has a good contribution particularly to the corrosion resistance after coating.

  There is an appropriate range for the Ca concentration depending on the Mg concentration. When the Mg mass% concentration is Mg%, the lower limit Ca concentration is 0.03% × Mg% in mass%. Below this concentration, the oxidation of Mg by Ca is insufficiently suppressed, and at the same time, the effect on post-coating corrosion resistance is also insufficient. The upper limit concentration of Ca is 0.1 × Mg% in mass%. When this concentration is exceeded, Ca itself begins to be oxidized, and bath surface oxidation is promoted. The inventors think that this is because Ca is difficult to dissolve with Zn alone and shows a certain amount of solid solution only when coexisting with Mg. When the mass% of Ca is expressed as Ca%, the above relationship is expressed by the following formula 2.

0.03 × Mg% ≦ Ca% ≦ 0.1 × Mg% (Formula 2)
For example, FIG. 1 is a graph plotting the Mg concentration and the Ca concentration by selecting a steel type having an Al concentration of 2 to 12% from among the plating components of steel materials used in the examples described later. The area of the solid line is the range of the plating component of the present invention. The ○ plots, which are the components of the present invention, all had good post-painting corrosion resistance, and the ● plots outside the component region of the present invention all had insufficient post-painting corrosion resistance. By these examples, the component range of the present invention was determined.

  Furthermore, in order to improve the corrosion resistance, a total of 0.02 to 3% of one or more selected from Cr, Mn, Co, Ni and Cu can be contained. These elements contribute slightly to the improvement of the bare corrosion resistance, but particularly contribute to improving the corrosion resistance after painting. If the concentration is lower than this lower limit, the effect is not clear.If the upper limit is exceeded, the stability of the bath is impaired, dross generation due to high melting point intermetallic compounds, etc. increases, resulting in deterioration in operability and appearance of plated steel materials. The possibility to do increases.

  Furthermore, it is also effective from the viewpoint of improving corrosion resistance to contain a total of 0.02 to 0.5% of one or more selected from Ti, Nb, W, Zr, Mo, La, Ce, Hf, and Y. . These elements also contribute slightly to the improvement of bare corrosion resistance. In particular, they have the effect of suppressing the blackening of the phenomenon that the plating surface becomes black due to the growth of the oxide film in the atmosphere due to changes over time after manufacturing. high. If the concentration is less than this lower limit, the effect is not clear.If the upper limit is exceeded, dross generation of refractory intermetallic compounds and oxides increases, bath stability is impaired, operability deterioration and appearance of plated steel The possibility of occurrence of defects increases.

  Note that Fe is contained in the plating by about 0.02 to 3% depending on the reaction between the steel material of the base material and the plating bath, depending on the operating conditions such as bath composition, bath temperature, ingress base material temperature, immersion time, and plating adhesion amount. However, this is considered an inevitable impurity and is not particularly defined in the present invention.

The coating amount of the plated steel material according to the present invention is 150 g / m ² or less per side from the viewpoint of ensuring spot weldability, but is preferably 50 g / m ² / single side or less. The smaller the adhesion amount, the better the spot weldability, but a minimum adhesion amount of 10 g / m ² is necessary to ensure corrosion resistance. Desirably, the range of 15 g / m ² or more and 50 g / m ² or less provides a good balance between corrosion resistance and spot weldability. However, if the weldability after plating is sacrificed to some extent, the amount of plating can be allowed up to 180 g / m ² / single side.

  When the plating of the present invention is applied to a steel sheet, it is usually used with the same amount of plating applied on both sides, but the amount of plating on the front and back is changed, or the corrosion resistance of one side is reliably ensured by painting or the like. If it is such a use, the steel plate which made plating adhere only to one side is also useful, and all are the scope of the present invention.

  The material of the steel material as the base material of the steel material of the present invention is not particularly limited, and Al killed steel, extremely low carbon steel, high carbon steel, various high strength steels, Ni, Cr-containing steel, and the like can be used. There is no particular limitation on the pretreatment processing of the steel material such as steel making method, steel strength, hot rolling method, pickling method, cold rolling method and the like.

  Regarding the plating manufacturing method, the present technology can be applied to any hot-dip plating method regardless of the manufacturing method such as Sendzimir type, flux type, or pre-plating type.

  The highly corrosion-resistant hot-dip zinc-based plated steel material of the present invention has excellent bare corrosion resistance, so it can be used without any problems even without painting.In particular, it is coated from the features of the present invention that can improve the corrosion resistance after painting. Further, a coated surface-treated steel material having a coating film on the plating surface can be said to be a preferable application form. Although the kind of coating film to be used is not specifically limited, For example, a polyester resin, an amino resin, an epoxy resin, an acrylic resin, a urethane resin, a fluorine resin, etc. are mentioned as an example. A thermosetting resin coating film can also be suitably used, and examples thereof include epoxy polyester paints, polyester paints, melamine polyester paints, and urethane polyester paints.

  Surface-treated steel materials as shown in Table 1 were produced using a cold-rolled steel plate with a thickness of 0.8 mm, an equilateral angle steel with a thickness of 10 mm and a side length of 10 cm, and a hot-rolled steel plate with a thickness of 10 mm as a base material.

  As the plating bath, a high-purity metal was mixed and dissolved to prepare the desired component, but after melting pure Zn, a part of Al was dissolved in the order of Mg, and Ca was added last as an Al-Ca alloy. did.

  The cold-rolled steel sheet was cut into 10 cm × 10 cm, and then plated with a batch type hot dipping test apparatus manufactured by Reska. The steel plate subjected to reduction annealing was attached by being immersed in a plating bath. The basis weight was adjusted by air wiping.

  The equilateral angle steel was cut into a 10 cm square in the longitudinal direction and the hot rolled steel plate was cut into a 10 cm × 10 cm square, and was subjected to the immersion plating by the flux method using a crucible furnace. The amount of adhesion was adjusted by the immersion time and the drawing speed.

  Said plating test piece was used for each evaluation test described below.

  The adhesion amount of each plating was measured by the mass loss when the plating layer was acid-dissolved, and the alloy components in the plating were quantified by ICP (inductively coupled plasma emission) spectroscopic analysis of the solution in which the plating layer was acid-dissolved.

Bare corrosion resistance conforms to the salt spray test (SST) described in JIS-Z-2371 for unpainted test materials. Evaluated by weight loss. Corrosion weight loss of less than 2 g / m ² is “◎”, 2-5 g / m ² is “◯”, and 5 g / m ² or more is “×”.

  After coating, the corrosion resistance test was carried out by degreasing the test material with a commercially available alkaline degreasing solution (pH = 10.5, 40 ° C, 1 minute immersion), followed by chemical conversion treatment for automobiles (Surfdyne 2500MZL made by Nippon Paint), followed by cation for automobiles. After electrodeposition coating (Nippon Paint V20, 20μm, baking at 170 ° C for 20 minutes), left for a day and night, the test surface is covered with a coating and plating, and reaches the steel substrate. It was provided with a knife and subjected to a combined cycle corrosion test in accordance with SAE J2234. Corrosion resistance after coating is evaluated by the coating blister width after 2000 hours, the maximum blister width is less than 3mm “◎”, 3mm to less than 5mm “○”, 5mm to less than 8mm “△”, 8mm or more “×” "

  In the blackening resistance test, each test material was changed in L value (lightness) with a color difference meter for the color change before and after being placed in a constant temperature and humidity test machine set at a temperature of 50 ° C and a relative humidity of 95% for 48 hours. (ΔL) was measured. When ΔL <3, blackening was not visually recognized as “◎”, and when ΔL was 3 or more, blackening began to be visually recognized slightly, so “◯”. When ΔL is 5 or more, it is not suitable as a product, and “x” is given. In the range of this example, no ΔL was 5 or more.

Weldability evaluation was carried out only on test materials having a cold-rolled steel sheet as a base material, and the same level of test materials were subjected to a spot welding test under the welding conditions shown below, and the number of consecutive hit points was investigated. A Cu—Cr electrode having a tip diameter of 4.5 mmφ, a tip angle of 120 degrees, and an outer diameter of 13 mmφ was used. Ten cycles of energization were performed with a 50 Hz power source. Pressurization was performed with a pressure of 1.7 kN for 30 cycles before energization, 10 cycles after energization, and no up-down slope. In addition, the welding current value in the continuous spot property investigation is the current value I ₁ (kA) and the welding current value I ₂ (kA) at which the nugget diameter indicated by 4√t when the plate thickness is t (mm). Using the average value, the maximum number of hit points with a 4√t nugget diameter maintained was determined. Those with 4000 or more consecutive hit points are marked as “Excellent”, especially as spot weldability is excellent, and “○” is the one with less than 4000 points but with 3000 or more consecutive hit points. , “△” means that the number of consecutive hit points is less than 3000 points but 2000 points or more. Those that did not reach 2000 were rated as “x”.

  The evaluation of dross property is made by visually observing the state of dross during plating production, "X" when there is a lot of dross and plating is difficult, the amount of dross is small and plating production is easy, and the surface quality of the attached plating is also good. The thing was made into "(circle)".

  The evaluation results of each test are shown in Table 1. In addition, steel types with an Al concentration of 2 to 12% were selected, and post-coating corrosion resistance data are shown in Fig. 1 in relation to Mg concentration and Ca concentration during plating. ○ is a component of the present invention example, and ● is a component of the comparative example. The area of the solid line is the range of the plating component of the present invention. All of the ○ plots, which are the components of the present invention, have good post-painting corrosion resistance, and all the ● plots outside the component region of the present invention have insufficient post-painting corrosion resistance.

  As shown in Table 1, the hot-dip Zn-based alloy-plated steel material of the present invention balances bare corrosion resistance and post-coating corrosion resistance at a high level, and in the case of dross generation, and in the case of a steel plate, further in terms of spot weldability , Hold enough performance.

Further, since the hot dip plating bath of the present invention component has a lower viscosity than the hot dip plating bath of the component outside the present inventive component range, a plated steel sheet having a low adhesion amount of 20 g / m ² or less could be easily produced. For example, No. 18 steel according to the present invention and No. 50 comparative steel were produced with the same parameters for controlling the amount of deposition, such as the drawing speed, wiping conditions, and plating bath temperature. However, the adhesion amount, whereas No.50 of the comparative example was 60 g / m ^2, was the No.18 In 20 g / m ² of the present invention embodiment.

With a low viscosity plating bath, it is easy to reduce the adhesion amount even under the same adhesion amount control conditions, and at the same time, the dispersion of the adhesion amount is reduced, which is also advantageous in reducing the adhesion amount. However, for example, as in the example of No. 20, in order to achieve an extremely low adhesion amount such as 8 g / m ² , in addition to the problem that the drawing speed needs to be extremely slow, the corrosion resistance also There is a problem that the deterioration becomes significant. That is, when the average adhesion amount is low, the plating corrosion loss is larger than the plating adhesion amount in the portion where the adhesion amount is small, and thus the plating layer disappears. Coating weight is very low adhesion amount to cut the 10 g / m ² of test material even average corrosion weight loss after the corrosion test 5 g / m ² or less, in cross-section observation after the corrosion test, it remained almost the plating layer The part which is not observed is recognized in half of the whole, and the deterioration of the corrosion resistance is remarkable. If the adhesion amount is 10 g / m ² or more, the portion where the plating layer does not remain is 10% or less of the whole, and if it is 15 g / m ² or more, the portion where the plating layer does not remain is not observed. .

  Those having an Al concentration of 6% or less and those containing one or more selected from Cr, Mn, Fe, Co, Ni and Cu are particularly excellent in corrosion resistance after coating. Those containing one or more selected from Ti, Nb, W, Zr, Mo, La, Ce, Hf, and Y have improved blackening resistance.

  The comparative steel material that is not in the component range of the plated steel material of the present invention, even if the corrosion resistance is excellent, the corrosion resistance after coating is not sufficient, depending on the component, the dross generation can not be suppressed, and the dross generation cannot be suppressed remains Dross also deteriorated the bare corrosion resistance.

The figure which showed the relationship between Mg density | concentration and Ca density | concentration with the component of an Example about the corrosion resistance after coating.

Claims (4)

In the plating layer, in mass%, Al is 2 to 6%, Mg is 0.6 to 4%, Ca is 0.06% or more, and the relationship of each component is a range satisfying the following formula 1 and formula 2, balance have a alloy plating layer consisting of Zn and unavoidable impurities, high corrosion resistance hot-dip Zn-based alloy coated steel material, wherein the amount of adhesion alloy plating is 150 g / m ² / single-sided or less.
Mg% ≦ 0.8 × Al% ・ ・ ・ (Formula 1)
0.03 × Mg% ≦ Ca% ≦ 0.1 × Mg% (Formula 2)
Here, Mg%, Ca%, and Al% are mass% contents of Mg, Ca, and Al, respectively. Further, as a component in the alloy plating layer, one or two selected from Cr, Mn, Co, Ni, Cu
The high corrosion resistance hot-dip Zn-based alloy-plated steel material according to claim 1, containing 0.02 to 3 mass% in total of seeds or more. The component in the alloy plating layer further contains one or more selected from Ti, V, Nb, W, Zr, Mo, La, Ce, Hf, Y in a total amount of 0.02 to 0.5 mass%. The high corrosion resistance hot-dip Zn alloy-plated steel material according to 1 or 2 . High corrosion resistance coating plated steel material characterized by having a coating on the plating of highly corrosion-resistant hot-dip Zn-based alloy coated steel material according to any one of claims 1-3.

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