KR101220708B1 - High manganese and aluminium galvannealed steel sheet having excellent powdering resistance and method for manufacturing the same - Google Patents

Abstract

The present invention relates to an alloyed hot-dip galvanized steel sheet made of high-manganese high aluminum steel having high strength and high ductility properties as a plating material, and includes a base steel sheet containing 5 to 35% by weight of manganese and up to 6% by weight of aluminum. It includes, The alloyed hot-dip galvanized layer is a Fe-Mn-Zn alloy layer provides a high manganese high aluminum alloyed hot-dip galvanized steel sheet and a method of manufacturing the same.

Description

HIGH MANGANESE AND ALUMINIUM GALVANNEALED STEEL SHEET HAVING EXCELLENT POWDERING RESISTANCE AND METHOD FOR MANUFACTURING THE SAME}

The present invention relates to an alloyed hot-dip galvanized steel sheet, and more particularly, to an alloyed hot-dip galvanized steel sheet made of high-manganese high aluminum steel having high strength and high ductility properties used as a vehicle body or structural material.

Many types of high strength steels for automobiles have been developed as the strength of automobile bodies and structural materials is required from the viewpoint of fuel efficiency improvement and stability due to light weight of automobiles. However, most steel sheets have reduced ductility with increasing strength, which results in many limitations in machining into parts. In order to solve the decrease in ductility according to the high strength of the steel sheet, many researches have been conducted. As a result, the ductility is significantly improved by incorporating 5 to 35% of manganese into the steel so that the steel is organically deformed. Austenitic TWIP steel (Twinning Induced Plasticity) has been proposed.

Since the TWIP steel has a ductility of 60% or more at a high strength of 980 MPa, it is attracting attention as a next-generation automotive steel sheet having high strength and high ductility. However, the TWIP steel has a problem of delayed fracture due to hydrogen embrittlement over time, and in order to prevent this, a high manganese high aluminum type TWIP steel having up to 6% Al added to the high manganese steel has been proposed. .

When manufacturing hot-dip galvanized steel sheet or alloyed hot-dip galvanized steel sheet using high manganese high aluminum TWIP steel as a plating material, it is annealed in a nitrogen atmosphere containing hydrogen for material securing and surface activation. This atmosphere acts as a reducing atmosphere for the base iron, which is a plating material, but as an oxidizing atmosphere for elements that are easily oxidized such as Mn, Si, Al, etc., of TWIP steel of high manganese high aluminum.

Therefore, when recrystallized annealing the high manganese high aluminum TWIP steel to which a large amount of Mn and Al is added in the atmosphere, the alloying element is selectively oxidized (selective oxidation) by the moisture or oxygen contained in a small amount in the atmosphere (plating material ) Surface oxides of Mn, Al and Si are produced mainly on the surface.

When high-manganese high aluminum TWIP steel containing a large amount of Mn and Al is used as the plating material, even when plating is performed or unplated by the surface oxide formed during the annealing process, which is a pre-plating process, Existing oxide films such as Al, Si, and Mn act as barriers to prevent alloying, resulting in unalloying.

As a method to prevent this, there is a technique of performing Ni plating, but as the deposition amount of Ni increases, Al thickening increases proportionally on the Ni plating layer to form a thick Al oxide film, so that unplating occurs. At the time, Al oxide film and Ni plating layer prevent the diffusion of Fe and Mn, so that unalloyation occurs.

On the other hand, if Ni plating is performed thicker than 900 mg / m 2, the Al surface concentration does not occur on the Ni plating layer during annealing, but the alloying delay occurs due to the thick Ni plating layer, and application of high alloying temperature to solve this problem is uneven. When the alloying, and the alloyed hot-dip galvanized steel sheet is processed, powdering occurs in which the alloy layer is peeled into a powder state.

One aspect of the present invention, in the alloyed hot-dip galvanized steel sheet made of high-manganese high aluminum steel plated material, to solve the unplated and unalloyed high-manganese high aluminum alloyed hot-dip galvanized steel sheet having excellent powdering resistance and manufacturing the same It is intended to provide a way to.

The present invention includes a base steel sheet containing 5 to 35% by weight of manganese and up to 6% by weight of aluminum and an alloyed hot dip galvanized layer, wherein the alloyed hot dip galvanized layer is a Fe-Mn-Zn alloy layer having excellent powdering resistance. Provided is a high aluminum alloyed hot dip galvanized steel sheet.

In addition, the present invention comprises the step of Ni-Fe-based plating or Fe-plated steel sheet containing 5 to 35% by weight of manganese, up to 6% by weight of aluminum;

Annealing the plated steel sheet;

Hot-dip galvanizing the annealed steel sheet; And

It provides a method of manufacturing a high manganese high aluminum alloyed hot-dip galvanized steel sheet having excellent powdering resistance, including the step of producing an alloying hot dip galvanizing by alloying after the hot dip galvanizing.

According to the present invention, an alloyed hot-dip galvanized steel sheet can be produced by using a high-manganese high aluminum steel (particularly TWIP steel) containing 5 to 35% of manganese and up to 6% aluminum, which could not be alloyed by hot dip galvanizing. In addition, alloyed hot-dip galvanized steel sheet using general high strength steel (IF high strength steel, two-phase composite steel (DP), TRIP steel, etc.) containing a large amount of alloying elements such as Si, Mn, Al, etc. as a plating material There is an advantage to manufacture.

In addition, since Fe required for alloying can be supplied from the plating, there is an advantage that alloying is possible at low temperatures.

Conventional plating process for the production of alloyed hot-dip galvanized steel sheet containing high manganese high aluminum steel (particularly TWIP steel) containing 5 to 35% by weight of manganese and up to 6% by weight of aluminum as the base steel plate (plating material) Or Ni plating, an inhibition layer is formed at the plating layer / ferrous iron interface due to the decrease in the wettability caused by the film-type aluminum oxide (Al-O) film formed on the surface of the iron in the annealing process before plating. Not confirmed.

In particular, when using a high manganese high aluminum steel containing 5 ~ 35% by weight of manganese and up to 6% by weight as a plating material, as the amount of Ni plating adhesion increased, unplating and plating peeling occurred. When Ni-plated high-manganese high aluminum steel is annealed before plating, the Ni-plated layer diffuses into the base to form an alloy phase such as Ni-Fe-Mn directly under the base. This is because Al diffuses and thickens across the Ni plating layer to the surface of the Ni plating layer. The reason is that the Al spreaded on the surface of the Ni plating layer is because the solid solution Al concentration is high, and the diffusion rate of Al in Ni is high.

As the Ni plating adhesion increases in steel, especially TWIP steel, which is actually a high manganese high aluminum steel, the surface concentration of Mn and Si decreases proportionally, but Al increases proportionally. This is because the Ni plating layer can prevent the diffusion of Mn and Si, but rather prevents the diffusion of Al.

Therefore, in the high manganese steel with high concentration of manganese, it is possible to prevent the surface diffusion of Mn by Ni plating, thereby preventing the deterioration of plating property due to the formation of Mn oxide, but high manganese containing up to 6% by weight of Al concentration in the steel In high aluminum steel, when the Ni plating adhesion increases, the base Al increases in proportion to the surface thickening and oxidation to form a thick Al oxide film, so that unplating occurs and the alloying treatment becomes meaningless.

Therefore, the present inventors studied a method for preventing Al thickening and Al oxide (Al-O) film formation formed during annealing of high manganese high aluminum steel, an appropriate amount of Ni-Fe plating or Fe instead of Ni plating By plating, it was possible to prevent the unplating by preventing the surface concentration of Al and the formation of Al oxide film. Also, since the Fe needed in the alloying treatment (Zn-Fe) of the zinc plating layer (Zn layer) was supplied from the plating layer, low alloying was achieved. Alloying is possible at temperatures, and due to diffusion of Mn through the Ni-Fe plated Fe film, the alloy layer has a high ductility Fe-Mn-Zn composite alloy layer unlike the conventional Fe-Zn alloy layer. Recognizing the advantage that powder separation (powdering) of the layer does not occur, the present invention has been achieved.

Hereinafter, the present invention will be described in detail.

The alloyed hot-dip galvanized steel sheet of the present invention comprises a base steel sheet containing 5 to 35% by weight manganese, up to 6% by weight of aluminum and an alloyed hot-dip galvanized layer, the alloyed hot-dip galvanized layer comprises a Fe-Mn-Zn alloy layer. .

The content of Mn in the alloy layer is preferably 1% by weight or more, and the sum of Fe and Mn is preferably 12% by weight or less. Mn of the alloy layer is an element that improves the ductility of the alloy layer, when the Mn content in the alloy layer is less than 1% by weight, the alloy is not an alloyed hot-dip galvanized steel sheet, and the sum of Fe and Mn in the alloy layer is 12% by weight. If it exceeds, there is a concern that powdering may occur in which the plating layer is dropped in powder form when processed by over alloying.

The base steel sheet is not particularly limited as long as it is a steel containing high manganese high aluminum. Examples of the preferred composition range of the base steel sheet include, by weight, C: 0.1 to 1.5%, Mn: 5 to 35%, and Si: 0.1 to 3%, Al: 0.01 to 6%, Ni: 0.01 to 1%, Ti: 0.01 to 0.2%, B: 0005 to 0.006%, and the rest preferably contains Fe and other unavoidable impurities.

Hereinafter, the manufacturing method of the alloying hot-dip galvanized steel sheet of the present invention will be described in detail.

First, Ni-Fe-based plating or Fe-based plating is performed on the surface of a high manganese high aluminum base steel sheet containing 5 to 35 wt% manganese and up to 6 wt% aluminum.

The Ni-Fe-based plating is performed to prevent Al concentration and Al oxide (Al-O) film formation formed during annealing of high manganese high aluminum steel, which is a plating material. It can not prevent the surface concentration of Al and the oxide film formation that occurs during Ni plating, but it is based on Ni-based plating because it can prevent the surface concentration of Mn, Si, another alloying element, and the surface of Al It is possible to prevent diffusion and alloying at low alloying temperature because Fe is required from the outside to form interfacial inhibition layer at the plating layer / ferrous iron interface and alloying during hot dip plating, and diffusion of Mn through Fe-coated Ni-Fe plating For this reason, Fe-based plating was performed together.

When the Ni-Fe-based plated high manganese high aluminum base steel sheet is annealed, not only the surface concentration of Al but also the concentration of alloying elements such as Mn and Si is reduced, and the moisture and oxygen in the atmosphere are caused by the Ni-Fe plating layer. Because of the blocking, surface oxidation of alloying elements such as Mn, Al, and Si is prevented to form a multi-alloy phase of Mn-Ni-Fe-Al-Si. When the high manganese high aluminum base steel plate having such a multi-phase alloy phase is deposited in the plating bath, the multi-phase alloy phase preferentially reacts with Al, which is an active element of the plating bath, and thus Mn-Ni-Fe-Al is formed at the interface between the plating layer and the base iron. An interfacial alloy phase of -Si-Zn is formed. When such an interfacial alloy layer is formed, the wettability with the molten zinc is improved, so that unplating is not generated.

When the hot-dip galvanized steel sheet thus prepared is alloyed, Fe can be alloyed at a low alloying temperature because Fe is supplied from the Ni-Fe-based and Fe-based plating layers, and Mn through the Ni-Fe-plated Fe film. Due to the diffusion of the alloy layer has a high ductility Fe-Mn-Zn composite alloy layer, unlike the conventional Fe-Zn alloy layer has the advantage that powder peeling (powdering) of the alloy layer does not occur during processing.

In order to exhibit the same effect in Ni-Fe plating, it is preferable that the Ni fraction of a plating layer is 30 weight% or less. This means that if the Ni fraction in the plating layer exceeds 30% by weight, unplating occurs due to the surface diffusion of Al and the formation of an oxide film, and to prevent this, unplating occurs when the coating deposition amount is increased, and uneven alloying occurs when the alloying temperature is increased. Since powdering occurs, the content of Ni is preferably 30% by weight or less.

Moreover, when performing Ni-Fe plating, it is preferable that plating adhesion amount is 50-700 mg / m <2>. If the plating adhesion amount is less than 50 mg / m 2, the surface diffusion of Al and Al oxide film formation cannot be prevented as described above. Therefore, unplating occurs during hot dip plating. If the plating adhesion amount exceeds 700 mg / m 2, a thick plating film is formed. Unalloying occurs because of the limited diffusion of Mn. Therefore, it is preferable to set it as 50-700 mg / m <2>.

In addition, at the time of single Fe plating, in order to exhibit the effect of the Ni-Fe plating system described above, it is preferable that at least 300 mg / m 2 or more of Fe plating deposition is required. This is because Fe-based plating is advantageous to prevent the surface diffusion of Al compared to Ni-Fe-based plating, but because it is disadvantageous to prevent the surface diffusion of Si and Mn, a thicker Fe plating layer is required to prevent this. Therefore, it is preferable that the Fe plating adhesion amount of this invention is 300 mg / m <2> or more.

An annealing treatment is carried out on the base steel sheet subjected to the plating. The annealing treatment is not particularly limited and is based on the usual annealing method. As a preferable example, annealing atmosphere dew point temperature is 0-60 degreeC and annealing temperature is performed on the conditions of 750-900 degreeC.

The annealed steel sheet is hot dip galvanized. The plating bath Al concentration of the hot dip galvanizing is preferably 0.08 to 0.13% by weight. If the Al concentration of the plating bath is less than 0.08%, alloying occurs preferentially at the portion where the Ni-Fe film is not formed due to non-uniform interface formation, and locally overalloysed, and the Al concentration of the plating bath exceeds 0.13%. In this case, an interface inhibitor layer is formed not only at the portion where the Ni-Fe film is not formed but also at the portion where the Ni-Fe film is formed, thus delaying the alloy reaction to increase the alloying temperature and causing powdering.

After the hot dip galvanizing, an alloying treatment is performed. The alloying temperature is preferably performed at 500 to 540 ° C. lower than that of the Ni-based plating material due to the supply of Fe in the initial Ni-Fe coating and the continuous supply of Fe in the base iron. If the alloying temperature is lower than 500 ° C, the Ni film and the interfacial inhibition layer prevent the alloying of the entire plating layer by interfering with the zinc plating layer and Fe and Mn, and the Ni film and the interfacial inhibition layer when the alloying temperature exceeds 540 ° C. It is not preferable because the surface defects such as powdering occurs during processing due to over alloying by excessive diffusion and of mutual diffusion.

As such, Ni-Fe- or Fe-based high-manganese high aluminum alloyed hot dip galvanized steel sheet is supplied with Fe required for alloying from the plating layer, so that alloying is possible at a low alloying temperature and Mn through a Ni-Fe-plated Fe film. Due to its easy diffusion, the alloy layer has a ductile Fe-Mn-Zn composite alloy layer unlike the conventional Fe-Zn alloy layer, so that powder peeling (powdering) of the alloy layer does not occur during processing. .

Hereinafter, embodiments of the present invention will be described in detail. The following examples are intended to illustrate one preferred embodiment of the present invention, the present invention is not limited by the following examples.

(Example 1)

In Example 1, high-manganese high aluminum steel is used as the base steel sheet (plating material), and Ni-Fe-based and 100% Fe-based plating with 50% Ni-50% Fe and 30% Ni-70% Fe, respectively, is performed. The plating quality and powder resistance of each alloyed hot dip galvanized steel sheet were evaluated, and the results are shown in Table 1.

The base steel sheet (plating material) was used as a cold rolled steel sheet of high manganese high aluminum steel having a thickness of 1.2mm, Ni-Fe-based plating and Fe plating was plated by the coating weight of Table 1, Ni-plated cold-rolled steel sheet hydrogen After 15%, the rest is nitrogen, and the dew point temperature is -40 ℃, it is maintained in annealing conditions at annealing temperature of 800 ℃ for 40 seconds, then recrystallized annealing, and deposited in zinc plating bath with Al concentration of 0.07 ~ 0.14% Then, the plating was carried out by adjusting the air knife so that the amount of plating on one side was 60 g / m 2. After performing the hot dip galvanizing, alloying treatment was performed continuously. At this time, alloying treatment temperature was performed at 480-560 degreeC for 35 second.

In the results of Table 1 below, the degree of unplating was graded by obtaining the area of the unplated portion by image treatment of the surface appearance after hot dip galvanizing.

-1 grade: no plating defect

-2 grade: uncoated average diameter less than 1mm

-3 grade: uncoated average diameter 1 ~ 2mm distribution

-4 grade: Uncoated average diameter is 2 ~ 3mm distribution

-5 grade: Unplated average diameter is over 3mm

In the process of evaluating the powder resistance of alloyed hot-dip galvanized steel sheet, 1) V-machining the specimen at 60 degrees. 2) Flatten the V-processed specimen again. 3) A transparent cellophane tape is attached to the inner V-processing part. 4) Separate the transparent cellophane tape from the specimen and attach white paper. 5) The peeling width of the alloy layer was measured by image processing.

The degree of powdering of the alloyed hot-dip galvanized steel sheet was graded based on the peeling width of the alloy layer thus measured. (Material thickness: 0.9-1.2mm)

-1 grade: Peel width less than 3.5mm

-2 grade: Peel width 3.51 ~ 5.5mm

-3 grade: Peel width 5.51 ~ 6.5mm

-4 grade: Peel width 6.51 ~ 8mm

-5 grade: Peel width more than 8.01mm

number Plating weight
(Mg / ㎡) Annealing condition Plating bath condition Unplated Alloying conditions Alloying properties Remarks 50Ni-50Fe 30Ni-70fe 100Fe Temperature
(℃) time
(s) dew point
(℃) Al
(wt%) Temperature
(℃) Temperature
(℃) time
(s) Alloying degree Fe (%) Alloying degree Mn (%) Powdering index 1-1 - - - 800 40 -40 0.11 460 5 - - - - - Comparative example 1-2 90 - - 800 40 -40 0.11 460 2 520 35 5 1.2 Unalloyed Comparative example 1-3 300 - - 800 40 -40 0.11 460 One 520 35 4 0.5 Unalloyed Comparative example 1-4 500 - - 800 40 -40 0.11 460 One 520 35 2 0.2 Unalloyed Comparative example 1-5 - 20 - 800 40 -40 0.11 460 3 - - - - - Comparative example 1-6 - 50 - 800 40 -40 0.11 460 2 520 35 5 4 One Inventive Example 1-7 - 300 - 800 40 -40 0.11 460 One 520 35 7 2.5 One Inventive Example 1-8 - 500 - 800 40 -40 0.11 460 One 520 35 7 1.5 One Inventive Example 1-9 - 700 - 800 40 -40 0.11 460 2 520 35 7 One One Inventive Example 1-10 - 800 - 800 40 -40 0.11 460 2 520 35 7 0.2 Unalloyed Comparative example 1-11 - - 250 800 40 -40 0.11 460 3 - - - - - Comparative example 1-12 - - 300 800 40 -40 0.11 460 2 520 35 7 5 2 Inventive Example 1-13 - - 500 800 40 -40 0.11 460 One 520 35 7 3 One Inventive Example 1-14 - - 800 800 40 -40 0.11 460 2 520 35 8 1.4 One Inventive Example

50-700 mg / m2 (1-6 to 1-9) specimens with 30Ni-70Fe-based plating and 300 mg / m2 or more (1-12 to 1-14 specimens) In all, it was confirmed that alloying degree of Mn was excellent, ductility improved, and powdering resistance was excellent.

However, if the plating content (1-2 to 1-4 specimens) to which the excessively high content of Ni is added and the plating deposition amount is out of the range, unalloying occurs or powdering occurs during processing with overalloying, which is undesirable. Could.

(Example 2)

In Example 2, the plating properties when the conditions of Al in the plating bath and the conditions of the alloying process were changed were observed and the results are shown in Table 2. The change in the concentration of Al in the plating bath and the change in temperature of the alloying conditions are as shown in Table 2, and the alloying properties thereof were evaluated in the same manner as in Example 1 above.

number 30Ni-70Fe plating weight
(Mg / ㎡) Annealing condition Plating bath condition Alloying conditions Alloying properties Remarks Temperature
(℃) time
(s) dew point
(℃) Al
(wt%) Temperature
(℃) Temperature
(℃) time
(s) Alloying degree Fe (%) Alloying degree Mn (%) Powdering index 2-1 300 800 40 -40 0.07 460 520 35 10.2 5.7 4 Comparative example 2-2 300 800 40 -40 0.08 460 520 35 8.3 4 2 Inventive Example 2-3 300 800 40 -40 0.11 460 520 35 7 2.5 One Inventive Example 2-4 300 800 40 -40 0.13 460 520 35 6 1.5 One Inventive Example 2-5 300 800 40 -40 0.14 460 520 35 3.5 0.5 Unalloyed Comparative example 2-6 300 800 40 -40 0.11 460 480 35 4.5 0.7 Unalloyed Comparative example 2-7 300 800 40 -40 0.11 460 500 35 6 1.7 One Inventive Example 2-8 300 800 40 -40 0.11 460 520 35 7 2.5 One Inventive Example 2-9 300 800 40 -40 0.11 460 540 35 8.2 3.5 One Inventive Example 2-10 300 800 40 -40 0.11 460 560 35 9.5 4.2 3 Comparative example

As shown in Table 2, when the Al content of the plating bath satisfies 0.08 ~ 0.13% by weight (2-2 to 2-4 specimens), and the alloying temperature satisfies 500 ~ 540 ℃ (2-7 2-9 specimens), it was confirmed that the alloy layer contains a certain amount of ductility excellent in ductility, it is possible to manufacture a hot-dip galvanized steel sheet of high manganese high aluminum steel with excellent powdering resistance.

On the other hand, when out of the plating bath conditions or alloying conditions, unalloyed, or due to excessive alloying, rather than powdering during processing was confirmed that it was not preferable.

Claims (10)

Manganese steel sheet containing 5 to 35% by weight, up to 6% by weight of aluminum and an alloyed hot-dip galvanized layer, the alloyed hot-dip galvanized layer is a Fe-Mn-Zn alloy layer, the Mn content of the alloy layer is 1 weight A high manganese high aluminum alloyed hot-dip galvanized steel sheet having a powder resistance of more than% and excellent in powdering resistance of a sum of Mn and Fe of 12% by weight or less.
delete delete The method according to claim 1,
The base steel sheet by weight% C: 0.1 ~ 1.5%, Mn: 5 ~ 35%, Si: 0.1 ~ 3%, Al: 0.01 ~ 6%, Ni: 0.01 ~ 1%, Ti: 0.01 ~ 0.2%, B : 0005 ~ 0.006%, high manganese high aluminum alloyed hot dip galvanized steel sheet with excellent powdering resistance including Fe and other unavoidable impurities.
Ni-Fe-based plating or Fe-plating the steel sheet containing 5 to 35% by weight of manganese, up to 6% by weight of aluminum;
Annealing the plated steel sheet;
Hot-dip galvanizing the annealed steel sheet; And
Preparing an alloyed hot dip galvanized by alloying after the hot dip galvanizing.
Method for producing a high manganese high aluminum alloyed hot-dip galvanized steel sheet having excellent powdering resistance.
The method according to claim 5,
The Ni-Fe-based plating is a method of manufacturing a high manganese high aluminum alloyed hot-dip galvanized steel sheet having excellent powdering resistance, including that the Ni content is 30% by weight or less.
The method of claim 6,
The Ni-Fe-based plating is a method for producing a high manganese high aluminum alloyed hot-dip galvanized steel sheet excellent in powdering resistance, the plating adhesion is carried out in the range of 50 ~ 700mg / ㎡.
The method according to claim 5,
The Fe-based plating is a method of producing a high manganese high aluminum alloyed hot-dip galvanized steel sheet excellent in powdering resistance to be carried out in the plating coating amount of 300 mg / ㎡ or more.
The method according to claim 5,
The Al concentration of the plating bath during the hot dip galvanizing is a method of manufacturing a high manganese high aluminum alloyed hot dip galvanized steel sheet excellent in powdering resistance of 0.1 to 0.25% by weight.
The method according to claim 5,
The alloying method of producing a high manganese high aluminum alloyed hot-dip galvanized steel sheet excellent in powdering resistance performed in the temperature range of 500 ~ 540 ℃.