SK562011U1 - Method for hot zinc coated flat steel products with improved anticorrosive resistance - Google Patents

Abstract

Method for production of hot zinc-coated plane steel products with improved anti-corrosion resistance in melted zinc alloy consist in that the zinc-magnesium-aluminium bath wherein the plane steel product is hot zinc-coated has temperature 380 - 500 °C and contains from 0.1 to 1.00 % by weight of aluminium, from 0.1 to 1.00 % by weight of magnesium as well as one or more of additional elements in the total amount below 0.2 % by weight, inevitable impurities and the rest is zinc. The annealed plane steel product is before accession to the zinc-magnesium-aluminium bath cooled to the temperature 400 °C - 520 °C.

Description

Process for producing hot-dip galvanized flat steel products with improved corrosion resistance

Technical field

The invention relates to a process for the production of hot-dip galvanized flat steel products with improved corrosion resistance by immersion in a molten zinc alloy, wherein the flat steel product, such as a sheet or strip, passes through a zinc-aluminum-aluminum bath.

BACKGROUND OF THE INVENTION

Steels remain an unbeatable material due to their ability to meet specific user requirements. The development of new types of steel with unique strength-plastic properties proves their irreplaceability even today. Therefore, increasing the corrosion resistance and thus extending the service life of steel materials is still topical. While in Asia and America, zinc-based alloys are used for corrosion protection of steels, i. zinc enriched with other elements, eg. Fe, Al, Mg, Cr, Ni, Co, Mn, European consumers of galvanized sheets prefer traditional pure zinc coatings. The oldest and still most widespread method of coating steel strips is galvanizing steel products by a hot-dip galvanizing process. In the continuous hot-dip galvanizing process, the cold-rolled strip is first annealed continuously at a temperature above 650 ° C. The strip is cooled to about 470-490 ° C prior to entering the zinc melt. The melt in which the web enters usually has a temperature of about 465 ° C and contains, in addition to zinc, a small amount of aluminum. In the production of hot zinc coatings, it is standard to use Al in the zinc bath in an amount of 0.15 to 0.19% Al, a reduced amount of Al in the range of 0.12 to 0.14% in the zinc melt is used in the manufacture of Zn-Fe coatings. After leaving the melt, the excess liquid zinc is wiped off with air knives and returned to the melt, whereby the liquid zinc solidifies on the steel strip as it cools to the melting point of zinc (419 ° C). Understanding the role of Al in the galvanizing process was crucial for the widespread use of the continuous hot-dip galvanizing process. Indeed, Al has been shown to have a higher affinity for steel than for Zn and immediately forms a stable intermetallic Al-Fe (Fe2Als) layer when the steel strip enters the melt. This layer, also known as the inhibitor layer, is extremely thin and its main function is to slow the rate of diffusion between the steel strip and the zinc coating and to achieve thinner and heavier coatings. Although the presence of Al in the melt has a decisive influence on the formability of the coating, it does not affect other properties of the coating, for example to improve its corrosion resistance. Conversely, the presence of Al in the coating can negatively affect the weldability, solderability and even the appearance of white rust. These disadvantages of the zinc coating can be eliminated by adding Mg while increasing the Al content of the zinc melt.

The object of the solution of the known invention described in EP 0594520 under the title "Hot-dip galvanized steel product and its production method" is a process for producing a hot-dip galvanized steel product, wherein the coating is carried out in a zinc melt containing 1 to 3.5% magnesium; 0.5 to 1.5% aluminum and 0.0010 to 0.0060% silicon. This European patent describes the discovery of the effect of the addition of Si in the melt to improve the wettability of the steel sheet by the melt, to eliminate the formation of uncoated spots, to equalize the thickness of the coatings and to improve their quality. Said patent mentions the positive effect of Si addition of Si = 0.0060% to the melt at Mg = 2.55% and Al = 0.93%, the remainder being zinc and impurities. However, as stated in the patent, the rapid consumption of Si in the zinc melt requires regular control of the Si content of the melt with the recommended addition of an Al-Si alloy with 10% Si.

The essence of the technical solution

1. The above drawbacks are largely eliminated by a process for manufacturing hot-dip galvanized flat steel products with improved corrosion resistance by immersion in a molten zinc alloy, wherein the flat steel sheet or strip passes through a zinc melt, according to which the flat steel sheet or strip passes through a zinc-aluminum bath. is a hot dip galvanized steel product having a temperature of 380-500 ° C and contains from 0.1 to 1.00 wt. % aluminum, from 0.1 to 1.00 wt. % magnesium as well as one or more additional elements in a total amount below 0.2 wt. and unavoidable impurities where the remainder is zinc. The annealed flat steel product is cooled to 400 ° C - 520 ° C before entering the zinc-magnesium-aluminum bath.

Wiping excess zinc with air or nitrogen creates a zinc-aluminum-aluminum coating on a flat steel product with a weight of 30 - 150

A g / m unilaterally.

The desired zinc melt composition is achieved using pre-alloyed ingots. The benefit of the invention lies in the substantial improvement of the corrosion resistance of zinc coatings by the addition of Mg and Al to the zinc melt and at the same time in the simplification of the hot-dip galvanizing process without the necessity to control Si in the zinc melt using alloying elements in the melt containing 0.1-1.00%. weight. Al; 0.1-1.00 wt. Mg, total < 0.2 wt. one or more elements such as e.g. Sb, Ni, Cr, Mn, Ti and other impurities. The addition of said elements does not substantially alter the properties of the melt or coating, and are primarily used to prevent slag formation. The addition of Sb improves the wettability of the steel substrate and affects the formation of the zinc flower. The addition of Mg to the zinc melt increases the flowability of the zinc and reduces the melting point of the coating, so that the coatings are produced at a lower temperature of the zinc melt, which allows a reduction in energy consumption in the hot-dip galvanizing process. Said technical solution does not require substantial changes in the production technology compared to the production of traditional zinc coatings. The coatings produced have a better appearance and significantly improved corrosion resistance. Improvement of corrosion resistance to conventional coatings can be used in two ways. The first option is to significantly improve the corrosion resistance when using coarse coatings, which guarantees a longer life of the final products and environmental protection. The second option is to reduce the thickness of the coatings while maintaining the desired corrosion resistance, which allows improved weldability. In addition, the presence of Mg in the coating increases the scratch and abrasion resistance of the coatings.

A hot-dip galvanized flat steel product with improved corrosion resistance according to the invention describes a method of continuously manufacturing a hot-dip galvanized flat steel product with improved corrosion resistance, wherein the cold-rolled flat steel product is continuously annealed in a hot-dip galvanizing line to recrystallize the structure and achieve the desired values properties. After annealing, the flat steel product is cooled to a temperature of 400 - 520 ° C and is then fed into the galvanizing bath below the surface of the zinc-magnesium-aluminum melt. The final thickness of the zinc coating is achieved by wiping excess zinc with air or nitrogen from the surface of the strip by a pneumatic slot nozzle above the melt level. During the zinc plating, the melt temperature of the zinc alloy is controlled in the range of 380-500 ° C.

Example of technical solution

In hot-dip galvanized flat steel products with improved corrosion resistance on a continuous hot-dip galvanizing line in a zinc-aluminum alloy, the cold-rolled flat steel product is continuously annealed on a hot-dip galvanizing line in order to recrystallize the structure and achieve the desired properties. After annealing, the flat steel product is cooled to a temperature of 400-520 ° C and subsequently enters the molten zinc-magnesium aluminum alloy. The zinc-magnesium-aluminum bath comprises aluminum and magnesium with a content of from 0.1 to 1.00% by weight. % aluminum and from 0.1 to 1.00 wt. % magnesium as well as one or more additional elements in a total amount below 0.2 wt. such as Sb, Ni, Cr, Mn, Ti and the necessary impurities, the remainder being zinc. The final thickness of the zinc coating is achieved by scraping off excess zinc with air or nitrogen from the surface of the strip by means of a pneumatic slit nozzle above the surface of the zinc-magnesium-aluminum melt. During hot-dip galvanizing, the temperature of the zinc-magnesium-aluminum melt is controlled in the range of 380-500 ° C. The zinc-magnesium-aluminum coating formed on the flat steel product weighs 30-150 g / m ^{2 on} one side.

To test the corrosion resistance of manufactured flat steel products with improved corrosion resistance, a neutral salt fog corrosion test was chosen. The main criterion of the corrosion resistance of a zinc-magnesium-aluminum coating is its first corroding into the base material (steel sheet). On the surface, the first formation of so-called. red rust. The reference coating was a traditional hot-dip galvanized sheet.

For comparison, examples of zinc-magnesium-aluminum melt (ZnMgAl) and traditional melt (Zn) composition, weight of coatings and approximate times to coat corroding are shown in the table for comparison.

melt coating corrosion Al [%] Mg [%] Type weight [g / m] indicative time to overcoating [hours] 0.20 0 Zn (Galvanized) 50 25 0.20 0 70 40 0.20 0 100 50 0.20 0 150 80 0.50 0.10 Zn-Mg-Al 80 75 0.40 0.60 50 150

0.75 0.65 50 200 0.95 0.65 70 250 0.75 0.65 120 350

The advantage of said hot-dip galvanized flat steel product with improved corrosion resistance according to the invention on a continuous hot-dip galvanizing line is their improved corrosion resistance achieved by enriching the zinc coating with magnesium and aluminum. In these zinc-magnesium-aluminum coatings, the corrosion resistance to traditional zinc coatings has been improved several times. The coatings produced have an improved appearance and, moreover, the presence of Mg in the coating increases the scratch and abrasion resistance of the coatings. A further advantage of the hot-dip galvanized flat steel product with improved corrosion resistance according to the invention lies in the simplification of the hot-dip galvanizing process without the need to control the amount of Si in the zinc melt. This solution does not require substantial changes in the production technology compared to the production of traditional zinc coatings. The addition of Mg to the zinc melt increases the flowability of the zinc and decreases the melting point of the coating, the coatings being produced at a lower melt temperature, thereby allowing a reduction in the energy consumption of the hot-dip galvanizing process.

Wiping off excess zinc with air or nitrogen creates a zinc-aluminum-aluminum coating on a flat steel product having, for example, a weight of 30

A

- 150 g / m on one side.

Industrial usability

The use of this hot-dip galvanized flat steel product with improved corrosion resistance is possible in a variety of industries such as construction, automotive, consumer, electrical, white goods, and others.

The applicability of these materials is further enhanced by the application of organic and inorganic coatings.

Claims (1)

PROTECTION REQUIREMENTS A method for producing hot-dip galvanized flat steel products with improved hot-dip corrosion resistance in a molten zinc alloy, wherein the flat steel sheet or strip passes through a zinc melt characterized in that the zinc-aluminum-aluminum bath in which the hot flat steel product is hot-galvanized 380-500 ° C and contains from 0.1 to 1.00 wt. % aluminum, from 0.1 to 1.00 wt. % magnesium as well as one or more additional elements in a total amount below 0.2 wt. and unavoidable impurities wherein the remainder is zinc, wherein the annealed flat steel product is cooled to 400 ° C - 520 ° C prior to entering the zinc-magnesium-aluminum bath.