KR20030023635A - Alloyed hot-dip zinc-coated steel sheet with excellent sliding property - Google Patents

Abstract

An alloyed hot dip galvanized steel sheet obtained by forming a hot dip galvanized layer on the surface of a steel sheet and then performing an alloying treatment, wherein the steel sheet or zinc sulfate-sodium chloride electrolyte has a potential of -850 mV or less by being immersed in a zinc sulfate-sodium chloride electrolyte solution. This is a steel sheet in which the amount of electricity flowing when the electric potential is delivered by electrostatic potential electrolysis in the range of -940 mV to -920 mV is 0.5 C / cm 2 or less, and is excellent in workability, in particular, sliding property.

Description

Alloyed Hot-Dip Galvanized Steel Sheet with Excellent Slidability {ALLOYED HOT-DIP ZINC-COATED STEEL SHEET WITH EXCELLENT SLIDING PROPERTY}

Alloyed hot-dip galvanized steel sheets are widely used as anti-rust steel sheets for automobile bodies. When the alloyed hot-dip galvanized steel sheet is processed into an automobile body, press molding is performed, so that not only an antirust property but also excellent sliding property is required.

In the manufacturing process of the alloyed hot dip galvanized steel sheet, a process of forming a hot dip galvanized layer on the surface of the steel sheet by immersing the steel sheet, which is a raw material, in a plating bath, and performing an alloying treatment on the steel sheet having the hot dip galvanized layer to form an alloyed hot dip galvanized layer. It can be roughly divided into the process of

The hot dip galvanized layer formed on the surface of the steel sheet in the plating bath is composed of Zn and Fe intermetallic compounds (ζ, δ1, Γ), and the sliding property of the alloyed hot dip galvanized layer formed by the alloying treatment is the composition of the intermetallic compound. Will fluctuate accordingly. Therefore, various techniques have been proposed to improve the sliding properties of the alloyed hot dip galvanized steel sheet by controlling the composition of the intermetallic compound of the hot dip galvanized layer formed before the alloying treatment.

For example, Japanese Patent Laid-Open No. 9-209106 discloses an alloyed hot dip galvanized steel sheet and an alloyed hot dip galvanized steel sheet. This technique is intended to form an alloyed hot dip galvanized layer having good sliding properties by adjusting components of a steel sheet serving as a raw material. However, if the operating conditions of the plating process are changed, the composition of the hot dip galvanized layer is also changed, and the sliding property of the alloyed hot dip galvanized layer is affected. Therefore, in the technique disclosed in JP-A-9-209106, it is difficult to stably obtain good sliding properties.

In addition, Japanese Laid-Open Patent Publication No. 11-200004 discloses an alloyed hot dip galvanized steel sheet having excellent sliding properties. This technique is to produce alloyed hot-dip galvanized steel sheet having both sliding and plating peeling resistance by depositing crystals containing Ti and Al as main components on the surface of the alloyed hot-dip galvanized layer. However, in order to precipitate crystals containing Ti and Al as main components, Ti must be added to the plating bath. On the other hand, when Ti is added to the plating bath, Ti-Al-based intermetallic compounds (so-called dross) are generated and adhered to the hot dip galvanized layer, which is problematic in view of the surface appearance of the coated steel sheet.

The present invention relates to an alloyed hot-dip galvanized steel sheet excellent in sliding property suitable as an antirust steel sheet for automobile bodies.

BRIEF DESCRIPTION OF THE DRAWINGS It is a longitudinal cross-sectional view of the layout figure which shows typically an example of the electrostatic potential electrolysis apparatus.

2 is a perspective view thereof.

(The best mode for carrying out the invention)

In the alloyed hot-dip galvanized steel sheet of the present invention, the amount of electricity that flows when the potential of the saturated calomel electrode in the zinc sulfate-sodium chloride-based electrolyte is electrolyzed by the potentiostatic method within the range of -940 mV to -920 mV is 0.5 C /. The potential for the saturated calomel electrode when it is 2 cm 2 or less or when immersed in the same electrolyte solution must be -850 mV or less. Depending on the structure and surface shape of the steel sheet serving as the base, both conditions may not always be satisfied at the same time, but when either condition is satisfied, the object can be achieved.

If the alloyed hot-dip galvanized steel sheet having an electric charge amount of 0.5 C / cm 2 or less at the time of electrostatic potential electrolysis, good characteristics can be obtained in various tests for evaluating sliding properties. As the end point of the electrostatic potential electrolysis, the electrolytic current density decreases with the progress of the electrostatic potential electrolysis, and a time point of reaching 5 mA / cm 2 is selected. As a test for evaluating sliding property, a cylindrical cup drawing test with a flat bottom can be exemplified. The electropotential electrolysis is performed in the range of -940 mV to -920 mV for the saturated calomel electrode with an alloyed hot dip galvanized steel sheet as an anode in a zinc sulfate-sodium chloride based electrolyte. The reason for setting the potential at -940 mV to -920 mV is to selectively deliver a portion of the alloyed hot dip galvanized layer having a large influence on the sliding property. Electrolysis is performed in the zinc sulfate-sodium chloride-based electrolyte solution because the electrolyte solution has a small chemical dissolution action of the alloyed hot dip galvanized layer and is hardly affected by an oxide film or the like formed on the surface of the plating layer. In addition, when the electrolyte is changed, the potential to selectively electrolyze the portion of the alloyed hot dip galvanized layer with a large influence on the sliding property changes, so the change must be confirmed by a preliminary test.

The lower the potential when the alloyed hot-dip galvanized steel sheet is immersed in the zinc sulfate-sodium chloride based electrolyte, the smaller the amount of electricity flowing during electrostatic potential electrolysis. An example of the electropotential electrolytic apparatus 1 is shown in FIG. 1, FIG. An alloyed hot-dip galvanized steel sheet (sample) 2 is used as an anode, and the counter electrode (cathode) 3 is used as a platinum ring or a platinum plate, for example, and each is connected to the apparatus 7 for setting potential by the platinum wire 5. . It is preferable to set the potential to a potentiometer, and reference electrodes RE4 such as saturated calomel electrodes and silver-silver chloride electrodes are used as potential references.

The electrolytic solution 6 uses an aqueous zinc sulfate-sodium chloride solution which has a small chemical dissolution action of the alloyed hot dip galvanized layer and which is hardly affected by an oxide film or the like formed on the surface. The zinc sulfate concentration is preferably 1 to 50 mass% and the sodium chloride concentration is 1 to 30 mass%. The alloyed hot-dip galvanized steel sheet of the present invention is not defined by the manufacturing method, but the alloying conditions are controlled by, for example, the method as disclosed in JP-A-7-41925 or JP-A-10-130802. It can manufacture by precisely adjusting plating and alloying conditions. In particular, by controlling Al content in a plating layer high, it controls on alloying conditions which are higher temperature than usual.

Moreover, in order to produce the alloying hot-dip galvanized layer which has the characteristics of the alloyed hot-dip galvanized steel sheet of this invention, the plating adhesion amount 40-60 g / m <2> of a single side of a plating layer, 9-13 mass% of Fe content in a galvanized layer, 0.20-Al content It is preferable to set it as 0.30 mass%, Pb content 0.002 to 0.2 mass%, Mn content 0.001 to 0.1 mass%, Si content 0.0001 to 0.01 mass%, P content 0.0001 to 0.01 mass%. Mn, Si, and P do not necessarily need to be contained simultaneously.

Although the steel type is not limited, For example, ultra low carbon steel (for example, C 0.0020-Si 0.01-Mn 0.10-P 0.01-Al 0.030-Ti 0.025-Nb 0.010 mass%) etc. is preferable. In particular, when one or both of the B content of 0.0002 to 0.015 mass% and the Sb content of 0.002 to 0.015 mass% are satisfied, a steel sheet having a plating layer having particularly excellent sliding properties can be obtained.

(Initiation of invention)

An object of the present invention is to provide an alloyed hot-dip galvanized steel sheet which can solve the problems described above and stably obtain excellent sliding properties.

The inventors have investigated in detail the alloyed hot dip galvanized layer having good sliding properties.

The present inventors investigated the electrolytic behavior at that time by using various alloyed hot-dip galvanized steel sheets as anodes, using zinc sulfate-sodium chloride aqueous solution as an electrolyte, and electrolytically alloying hot-dip galvanized layer by electropotential electrolysis. As a result of investigating the relationship between the electric quantity required for electrostatic potential electrolysis and the sliding property, when the potential when immersed in the electrolytic solution is below a certain value or when the total electric quantity until the completion of the electrostatic potential electrolysis is a certain amount or less, the sliding property is good. I found out.

This invention is completed after further research based on this knowledge.

The present invention is characterized in that the potential of the saturated calomel electrode when immersed in an electrolyte of zinc sulfate-sodium chloride is -850 mV or less. Alloyed hot dip galvanized with excellent workability, in particular sliding, characterized in that the amount of electricity flowing when electrolyzed by electropotential electrolysis in the range of -940 mV to -920 mV in the electrolytic solution of 0.5 C / cm 2 or less Steel plate.

Moreover, when the said electric quantity is 0.3 C / cm <2> or less, it has more favorable sliding property.

The test material of the ultra low carbon steel having the composition shown in Table 1 was made into a slab by continuous casting after melting in a converter. The slab was heated at 1150 to 1250 ° C., the final finishing temperature of the hot rolling process was set at 920 ° C., and wound up at 550 ° C. to produce a 3.2 mm thick hot rolled sheet coil, and then the black skin was removed by pickling. Cold rolling was performed to form a cold rolled steel sheet having a thickness of 0.8 mm.

C (mass%) Si (mass%) Mn (mass%) P (mass%) Al (mass%) Ti (mass%) Nb (mass%) Sb (mass%) B (mass%) 0.0020 0.01 0.10 0.01 0.030 0.025 0.010 0.007 0.0005

This cold rolled steel sheet was produced in a continuous hot dip galvanizing line at an annealing temperature of 790 to 830 캜. The plate | board penetration temperature to a plating bath was 460-470 degreeC, the bath temperature of the plating bath was 460-470 degreeC, and the alloying temperature was 490-530 degreeC. The plating adhesion amount of one side was 40-50 g / m <2>, and it manufactured so that the plating adhesion amount of both surfaces may be the same.

The alloyed hot-dip galvanized steel sheet was punched into a circle having a diameter of 15 mm, and then electropotentially electrolyzed at a potential of -930 mV for the saturated caramel electrode. 20 mass% zinc sulfate-10 mass% sodium chloride aqueous solution was used for electrolyte solution. The amount of electricity flowing from the start of electrolysis was measured by electrolysis until the current density became 5 mA / cm 2. The time required for electrolysis was about 10-20 minutes. The end point determination of the electrostatic potential electrolysis was made at the time point when the electrolytic current density decreased and reached 5 mA / cm <2>. However, because the current value is small in the vicinity of the end point, even if a slightly lower value is selected for the end point determination, there is no influence on the measurement of electric quantity and accurate evaluation is possible.

Moreover, the immersion potential of the sample with respect to the saturated calomel electrode in the said electrolyte solution was made into the sample using the steel plate punched in the said circular shape.

For evaluation of sliding property for comparison, after applying a conventional antirust oil of 1.5 g / m 2, a flat cup drawing test having a diameter of 33 mm was performed, and the limit drawing ratio was determined. The limit drawing ratio is indicative of good sliding property as the rating number is smaller. The results are shown in Table 2, with a marginal drawing ratio of 2.0% or more, 1, 1.9 to 2.0%, 2, 1.8 to 1.9%, 3, 1.7 to 1.8%, 4, 1.7% or less.

In all the coated steel sheets having an electric quantity of 0.5 C / cm 2 or less, the sliding property exhibited good sliding property of "Evaluation 3" or less, whereas in the comparative example exceeding 0.5 C / cm 2, the sliding property was poor in "Evaluation 5". In particular, all of the plated steel sheets having an electric quantity of 0.3 C / cm 2 or less exhibit particularly excellent sliding properties with "evaluation 1".

Moreover, all the steel plates with an immersion potential of -850 mV or less show a favorable sliding property with a sliding property below "Evaluation 3".

In the present invention, it is possible to provide an alloyed hot dip galvanized steel sheet which can stably obtain excellent sliding properties.

Claims (2)

Processability, in particular sliding, characterized in that the amount of electricity flowing when the potential of the saturated calomel electrode in electrolytic solution of zinc sulfate-sodium chloride is electrolytically generated by the electrostatic potential electrolysis within the range of -940 mV to -920 mV Alloyed hot dip galvanized steel sheet with excellent properties. An alloyed hot dip galvanized steel sheet having excellent workability, in particular sliding property, having a potential of -850 mV or less at a saturated calomel electrode when immersed in a zinc sulfate-sodium chloride-based electrolyte solution.