KR20020047576A - Manufactuing methods of galvannealed sheet steels with good anti-powdering - Google Patents

Abstract

PURPOSE: A method for manufacturing galvannealed sheet steels with good anti-powdering is provided, in which by the addition of cerium in plating solution, the growth of gamma-phase, an intermetallic compound of zinc and iron, is restricted. CONSTITUTION: The method is characterized in that 0.005-0.02wt% of cerium is added in conventional plating solution of which aluminium concentration is 0.12-0.14wt% so that the growth of gamma-phase, an intermetallic compound of zinc and iron, is restricted thus securing excellent powdering resistance. The plating solution is coated on one surface of a steel sheet in an amount of 60g/m¬2 to 100g/m¬2.

Description

Post-Plated Alloying Hot-Dip Galvanized Steel Sheet with Excellent Powdering Properties {Manufactuing methods of galvannealed sheet steels with good anti-powdering}

The present invention relates to a method for producing an alloyed hot-dip galvanized steel sheet, in particular, by adding cerium (Ce) in the plating bath to suppress the growth of the capital gamma phase, which is an intermetallic compound of zinc-iron, alloyed hot-dip galvanized steel sheet having excellent powdering properties It relates to a manufacturing method of.

In general, alloyed hot-dip galvanized steel sheet is heated through a hot dip zinc bath during a continuous hot dip plating process, and the galvanized steel sheet is heated in an alloy heat treatment facility installed directly above the hot-dip zinc bath before the zinc-coated layer on the surface is completely solidified. It is prepared by rapid cooling in an air cooling stand.

In this alloying reaction, the zinc and the base iron of the plating layer in the alloying furnace to produce an alloy layer by diffusion reaction and the reaction is stopped as it cools to room temperature. At this time, the zinc-iron alloy phase and its characteristics have a capital gamma phase (Γ) and a capital gamma source (Γ1) phase at the interface with the base iron, and these phases have an iron content of 24 to 31 at, respectively. % And 18.5 ~ 23.5at% and its lattice structure consists of body centered cubic system and face centered cubic system.

Double capital gamma phase is the weakest phase and is the main cause of powdering of alloy layer during processing. In addition, the delta (δ) phase is present on the upper portion of the capital gamma phase, and the iron component is 8.5-13 at% and has a hexagonal lattice structure, so that the processability is excellent and the coefficient of friction is lower than that of the capital gamma layer.

The zeta (ζ) phase present in the uppermost layer has iron content of 6.7 ~ 7.2at% and consists of monoclinic lattice structure, which has the best workability among the alloy phases, but has a high coefficient of friction, causing flaking of the alloy layer during processing. Done.

These phases are formed by the alloying reaction between zinc and the base iron in the plating layer by thermal diffusion. The alloying heat treatment temperature, alloying heat treatment time, cooling rate after the alloying heat treatment, and the components in the hot dip galvanizing bath are used in the alloy layer. The distribution will be different.

In general, when manufacturing a hot-dip galvanized steel sheet is performed in a hot-dip galvanizing bath containing about 0.12 ~ 0.14wt% of aluminum. When aluminum is more than 0.14wt%, the concentration of aluminum in the plating bath is controlled to be less than 0.14wt% because the thickness of the iron-aluminum-zinc ternary compound formed at the interface between the base iron and the plating layer is thickened to delay the alloying reaction. desirable.

In addition, in the case of plating amount, about 60g / m ² per side is used. If the amount is more than 60g / m ² , the corrosion resistance is increased by the increase of plating amount, but the completion time of alloying reaction that is completely alloyed to the surface layer during alloying reaction increases the plating layer. The thickness of the ternary alloy layer of iron-aluminum-zinc generated at the base iron interface increases, causing a problem of deterioration of the powder resistance during processing.

Conventionally, in order to solve this problem, a method of manufacturing a semi-alloyed hot dip galvanized steel sheet by increasing the aluminum content in the plating bath or lowering the alloying temperature below 500 ^° C. has been used. However, when the aluminum in the plating bath is increased, the alloying temperature must be increased, and thus, the powdering property is deteriorated due to the growth of the capital gamma phase, which is an alloy phase of zinc-iron in the plating layer.

In order to solve the above problems, the present invention adds cerium (Ce) to the hot dip galvanizing bath to suppress the growth of the capital gamma phase, which is an alloy phase of zinc-iron, which is produced during the alloying process, thereby providing excellent post-plating alloyed hot dip zinc alloy. An object thereof is to provide a method for producing a coated steel sheet.

In order to achieve the above object, the present invention is produced during the alloying reaction by adding 0.005 ~ 0.02wt% cerium to a hot dip galvanizing bath containing 0.12 ~ 0.14wt% of aluminum, which is a plating bath condition of a conventional alloyed hot dip galvanized steel sheet generating the alloy onto isolated and, coating weight provides a method for preparing a coated galvannealed steel sheet characterized in that after such a ^{60g / m 2 ~ 100g / m} 2 per plate attached on one side.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention is zinc-aluminum- produced during the alloying reaction by adding 0.005 to 0.02wt% of cerium to a hot dip galvanizing bath containing 0.12 to 0.14wt% of aluminum, which is a plating bath condition when manufacturing a conventional alloyed hot dip galvanized steel sheet. by thereby generating the ternary alloy of iron phase formed in a layer onto the isolated suppressed from being deteriorated by gender powdering and attaching a coating weight in each steel plate on one side ^{60g / m 2 ~ 100g / m} 2 range sikimeuroseo corrosion resistance existing alloying It is characterized by a method of producing a post-plated alloyed hot-dip galvanized steel sheet which is much more excellent than the hot-dip galvanized steel sheet.

The reason for limiting the cerium added to the hot dip galvanizing bath to 0.005 ~ 0.02wt% is that when the content is less than 0.005wt%, the effect of adding cerium is insignificant. When the zinc-iron alloy phase grows and powdering property deteriorates, and when it is 0.02 wt% or more, an alloy phase of cerium and zinc is excessively formed, dross is produced, and this dross floats in a plating bath, and plating is performed. This is because it affects the fluidity of the bath and also adversely affects the surface quality by being attached to the steel sheet.

Further, the reason for limiting the coating weight to ^{60g / m 2 ~ 100g / m} 2 is to ensure that all the requirements of the American automotive steel hole corrosion 10 years and over corrosion five years, the alloy when the 100g / m ² or more This is because flaking may occur during processing due to a long time and an increase in plating amount, and when it is 60 g / m ² or less, it is difficult to satisfy 10 years of hole corrosion and 5 years of front corrosion.

Hereinafter, the present invention will be described in more detail with reference to the following examples.

In the equipment for continuously manufacturing hot-dip galvanized steel sheet, ultra-low carbon steel with a plate thickness of 0.8 mm is heat-treated in a reduction furnace of 80mpm speed, immersed in a plating bath containing cerium for 3 seconds at a plating bath temperature of 460 ^o C, and then wiped with gas. Table 1 shows the results of evaluating powdering properties by adjusting the one-side plating amount to 60 to 100 g / m ² and alloying in an alloying furnace.

Symbols used in Table 1 are as follows.

PI (powdering index) excellent 1 PI 5 bad

P.I. 2 or less: Excellent P.I. 3 or higher: bad

Alloying degree: Iron content in the coating layer (wt%)

As shown in Table 1, in Comparative Example Specimens (1,2) without adding cerium, the powdering index was poor as 4 or more even when the plating deposition amount was 60 g / m ² or more, and Comparative Example Specimen (3 to 6) In this case, even though cerium is added, its content is less than 0.005 wt%, so that the powdering index is 4, and the powdering property is not significantly improved compared to Comparative Samples (1, 2). If the added amount is more than 0.02wt%, the powdering property is improved to some extent, but dross is generated in the plating bath to damage the surface appearance.

However, in the specimens of the present invention (A ~ H), the amount of cerium added is 0.005 ~ 0.02wt% and the plating amount is 60 ~ 100 g / m ² to satisfy all of the scope of the present invention powdering index 2 or less powdering property The alloyed hot-dip galvanized steel sheet with excellent surface quality was also produced because it was excellent and did not generate dross.

As described above, according to the present invention, by adding cerium to the hot dip galvanizing bath and performing post plating, the zinc-aluminum-iron ternary alloy phase generated during the alloying reaction can be suppressed from being formed in a layered form to form an isolated phase. Accordingly, an alloyed hot dip galvanized steel sheet having excellent powdering performance and surface quality could be manufactured.

Claims (1)

0.005 to 0.02 wt% of cerium is added to a hot dip galvanizing bath containing 0.12 to 0.14 wt% of aluminum, which is a plating bath condition of a conventional alloyed hot dip galvanized steel sheet, to form an alloy phase produced during the alloying reaction as an isolated phase, and the amount of plating A method for producing a post-plated alloy galvanized hot-dip galvanized steel sheet, characterized in that 60g / m ² ~ 100g / m ² is attached per one side of the steel sheet.