KR101115741B1 - Method for manufacturing high manganese hot dip galvanized steel sheet with superior weldability - Google Patents

Abstract

The present invention is to provide a method for easily manufacturing a hot-dip galvanized steel sheet of high manganese steel using high manganese steel as a plating material. To this end, the present invention comprises the steps of annealing heat treatment of high manganese steel;

Pickling high manganese steel subjected to the annealing heat treatment;

Ni-plating the high manganese steel subjected to the pickling;

Heating the Ni-plated high manganese steel; And

It provides a method of manufacturing a high manganese steel hot-dip galvanized steel sheet having excellent plating properties including the step of hot-dip galvanizing the heat-treated high manganese steel.

High Manganese Steel, Manganese Oxide, Ni Plating, Plating

Description

METHODS FOR MANUFACTURING HIGH MANGANESE HOT DIP GALVANIZED STEEL SHEET WITH SUPERIOR WELDABILITY

The present invention relates to a method for manufacturing a hot-dip galvanized steel sheet using high manganese steel having high ductility and high strength characteristics as a plating material, which is used for automobile bodies and structural materials. It relates to a method for producing a steel sheet.

Hot-dip galvanized steel sheet is widely used as a steel sheet for automobiles because of its excellent corrosion resistance, weldability and paintability.

Meanwhile, many types of high strength steels for automobiles have been developed as high strength of automobile bodies and structural materials is required from the viewpoint of fuel efficiency improvement and safety 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 due to the high strength of the steel sheet, many studies have been conducted. As a result, the ductility is significantly improved by incorporating 5 to 35% of manganese into the steel to induce the twinness (TWIN) during plastic deformation of the steel. Austenitic high manganese steels (JP1992-259325, WO 93/013233, WO 99/001585, WO 02/101109, etc.) have been proposed.

In the hot-dip galvanized steel sheet using the high manganese steel as a plating material is annealed in a nitrogen atmosphere containing hydrogen for securing the material and surface activation (reduction).

This atmosphere acts as a reducing atmosphere for Fe, which is a plating material, but as an oxidizing atmosphere for elements that are easily oxidized such as Mn, Si, and Al of high manganese steel. Therefore, when recrystallized annealing high manganese steel to which Mn is added in a large amount in such an atmosphere, the element is selectively oxidized (selectively oxidized) by moisture or oxygen contained in a small amount in the atmosphere, and mainly Mn is formed on the surface of the substrate (plated material). Oxides are produced.

Therefore, when a high manganese steel containing a large amount of Mn is used as the plating material, unplated may be generated by the surface oxide formed during the annealing process, which is a pre-plating process, or the plating layer may be peeled off during processing even if plating is performed.

Until now, as a known technique for preventing the unplating of the hot-manganese hot-dip galvanized steel sheet as described in Korean Patent Laid-Open No. 2007-0067593, by adding elements such as Sb, Sn, As, Te, Mn, Si, etc. There is a method of plating by preventing alloy elements from diffusing to the surface to form oxides.

However, the patent is not possible to prevent the surface oxidation of manganese having a very high oxidizing power by adding a trace amount of elements such as Sb, Sn, AS, Te or less to 0.05% to high manganese steel containing 5 to 35% of manganese, To this end, a large amount of such expensive alloying elements should be added, which is not preferable because it causes an increase in cost.

In addition, Korean Laid-Open Patent Publication No. 2007-0067950 discloses a method in which a thin Si oxide layer is formed on a surface by adding Si to suppress the formation of manganese oxide, thereby plating. However, the patent discloses a stable film having a larger oxidizing power than Mn. There is a problem that it is difficult to improve the wettability with molten zinc because it forms an oxide of the form.

Korean Patent Publication No. 2007-0107138 proposes a method of attaching Al to 50 nm to 1000 nm by pre-annealing vacuum deposition (PVD) to prevent manganese oxide formation and plating. However, since the patent requires a process of vacuum deposition before annealing of the plating process, and Al, which is a plating material to be deposited, is easily oxidized, Al deposited in the annealing process, which is the next process, is wetted by moisture or oxygen in the annealing atmosphere. There is a problem of deteriorating the plating property because it forms a bad aluminum oxide.

As described above, in the prior art, when a high manganese steel containing a large amount of manganese is used as a plating material, even when unplated or plated due to the formation of a thick manganese oxide generated during the annealing process, the base iron of the plating layer and There is a problem that the plating peeling is separated. Therefore, there is an urgent need to develop a technology capable of securing excellent plating properties and excellent plating adhesion of hot-dip galvanized steel sheets.

The present invention is to provide a method for easily manufacturing a hot-dip galvanized steel sheet of high manganese steel using high manganese steel as a plating material.

The present invention comprises the step of annealing heat treatment of high manganese steel;

Pickling high manganese steel subjected to the annealing heat treatment;

Ni-plating the high manganese steel subjected to the pickling;

Heating the Ni-plated high manganese steel; And

It provides a method of manufacturing a high manganese steel hot-dip galvanized steel sheet having excellent plating properties including the step of hot-dip galvanizing the heat-treated high manganese steel.

According to the present invention, it is not only possible to manufacture hot-dip galvanized steel sheet and alloyed hot-dip galvanized steel sheet using 5 to 35% of manganese-containing high manganese steel, which cannot be hot-dipped galvanized by conventional methods, as a plating material. In the manufacture of hot-dip galvanized steel sheet using general high strength steel (eg, IF high strength steel, two-phase composite steel (DP), TRIP steel, etc.) containing alloy elements such as silver Si, Mn, Al, etc. Applicable.

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

The present inventors have analyzed the unplated material in order to determine the cause of unplated when hot-dip galvanizing is performed using high manganese steel containing a large amount of manganese as a plating material, the unplated portion is shown in Figure 1 As shown in Fig. 2, it was found that the thick film-type manganese oxide film formed on the outside was the cause.

On the other hand, as a result of investigating the concentration of the surface oxide according to the reduction conditions of the unplated generating material and the annealing atmosphere of the high manganese steel, as shown in Figure 2, the high manganese steel of the manganese oxide is concentrated on the surface according to the dew point temperature of the annealing atmosphere Although the thickness shows a considerable difference, even if the annealing conditions were changed, it was impossible to secure the plating property by forming a thick manganese oxide in the form of a film.

Accordingly, the present inventors have realized that in the pre-plating pretreatment method, it is possible to secure the plating property by removing the Mn oxide formed during annealing and performing Ni plating.

In the present invention, as shown in Figure 3, the present invention, unlike the conventional hot-dip galvanized steel sheet (GI) manufacturing method, annealing high-manganese steel, pickling, Ni plating, heat treatment and hot dip galvanized hot-dip galvanized steel sheet The present invention provides a method for producing an alloyed hot-dip galvanized steel sheet by manufacturing or performing an alloying treatment after hot-dip galvanizing.

Although not limited to the high manganese steel in the present invention, the high manganese steel is a weight%, C: 0.1 ~ 1.5%, Mn: 5 ~ 35%, Si: 0.01 ~ 3.0%, Al: 0.01 ~ 3.0%, Ni : 0.01 to 1.0%, Ti: 0.01 to 0.2%, B: 0.0005 to 0.006%, the remainder preferably contains Fe and unavoidable impurities.

In the present invention, first, annealing heat treatment of high manganese steel. The annealing heat treatment is preferably performed at a temperature range of 750 to 850 ° C. in a reducing atmosphere having a dew point temperature of 0 to 40 ° C. or higher. In order to form the surface oxides of alloying elements such as Mn, Si, Al and internal oxides directly under the substrate during annealing heat treatment, the dew point temperature of the annealing atmosphere is set to 0 to 40 ° C, and the recrystallization annealing temperature is limited to 750 to 850 ° C. It is preferable.

Since the dew point temperature is 0 ° C or more, it is an oxidizing atmosphere, so not only oxidation of alloying elements such as Mn, Si, and Al, but also oxidation of Fe is formed to form a very thick oxide film. Therefore, removing the oxide film completely under short pickling conditions impossible. In addition, when the dew point temperature is -40 ℃ or less, internal oxides are not formed, and when the surface oxides are removed with an acid solution and reheated for plating, the Mn of the base is further concentrated.

This is because it is difficult to secure the material below the annealing temperature of 750 ° C. Above 850 ° C, it is not preferable because the pickling condition needs to be strengthened due to the softening of the material due to the high temperature and the surface concentration of the alloying element and the formation of a thick oxide film.

The atmosphere gas at the time of annealing is not particularly limited, but is preferably 15% hydrogen and the remainder is nitrogen.

After the annealing heat treatment is performed, a pickling step of removing the surface oxide film formed in the annealing process with an acid solution is performed. In the pickling process, the pickling time is determined according to the operation speed. If the pickling temperature is also high, it is preferable to carry out at room temperature because it is not preferable due to corrosion of equipment and generation of toxic gas.

Therefore, the adjustable factor among the pickling conditions is limited to 5 to 15% in the present invention as the acid concentration of the acid solution. If the acid concentration is less than 5%, it is not possible to completely remove the surface oxide film, and more than 15% is not preferable because superacid occurs.

Ni-plating which performed the said pickling is performed. At this time, it is preferable to perform plating adhesion amount so that it may become 10-90 mg / m <2>. Ni plating by plating pretreatment is because Ni is excellent in electroplating efficiency and wettability with molten zinc. When the amount of Ni plating is less than 10 mg / m 2, it is impossible to prevent the surface concentration of Mn during the next heat treatment.

When the Ni plating deposition amount exceeds 90 mg / m 2, the surface concentration of Mn and the like is completely prevented, and the surface concentration prevention effect of Mn and the like is the same, but the alloying reaction is delayed by acting as a barrier that prevents the alloying reaction during the alloying process. And there is a problem of generating various alloying defects. In addition, the use of a large amount of plating solution due to the increase in the amount of plating deposition, resulting in an increase in cost is not economically preferable.

The Ni plating is performed, followed by heat treatment. The heat treatment is preferably heated to a temperature range of 480 ~ 800 ℃ in an atmosphere where the dew point temperature is 0 ~ -70 ℃. When the dew point temperature of the heat treatment atmosphere exceeds 0 ° C., the selective oxidation film is formed by the surface concentration and oxidation of Mn, Si, and Al of the alloying elements, so that unplating occurs, and the dew point temperature of the heat treatment atmosphere is low. A lower value is preferable because it can prevent the surface concentration of the alloying element, but it is not preferable because a large amount of auxiliary equipment is required to remove the moisture or oxygen of the gas in order to maintain the dew point of the heating atmosphere below -70 ° C.

The lower the heat treatment temperature is advantageous because the lower the surface temperature of the alloying element can be prevented, but usually the plating bath temperature is 440 ~ 460 ℃, when the heat treatment temperature is lower than the plating bath temperature, Because the steel sheet is taken away, it is required to be higher than 480 ° C slightly above the plating bath temperature. On the other hand, if the heat treatment temperature exceeds 800 ℃ unplated by the re-concentration and surface oxidation of Mn in the substrate, even if plating is not preferable because the plating peeling occurs during processing.

After the heat treatment, hot dip galvanizing or alloying hot dip galvanizing is performed.

In the manufacture of hot-dip galvanized steel sheet, the Al concentration of the plating bath is appropriately 0.21 to 0.25% by weight. This is because the Al in the plating bath reacts preferentially with the steel sheet when the annealed steel sheet is deposited in the plating bath to reduce the oxide film on the surface of the steel sheet and form a Fe-Al-Zn- (Ni) film, which is a ductile interfacial layer. , It is advantageous to manage Al concentration of plating bath high because it plays a role of inhibiting growth of vulnerable Zn-Fe intermetallic compound, but floating dross of Fe-Al occurs when Al concentration of plating bath exceeds 0.25% by weight. It is preferable to limit the upper limit to 0.25% by weight since it is easy to perform the flow pattern in which the plating layer flows down.

On the other hand, when manufacturing the alloyed hot-dip galvanized steel sheet is limited to the plating bath Al concentration of 0.1 ~ 0.13% by weight. If the Al concentration of the plating bath is less than 0.1% by weight, alloying occurs preferentially in the portion where Ni is not attached due to the formation of a non-uniform interface inhibitory layer, and locally overalloys the powder. When the Al concentration of the plating bath exceeds 0.13% by weight, a thick interfacial inhibitor layer is formed. Therefore, the alloying reaction is delayed, thereby increasing the alloying temperature and weakening the powder gamma phase (Γ), which is weak in powdering resistance. It is not preferable because it forms.

500-550 degreeC of the alloying process temperature at the time of manufacturing the said alloying hot-dip galvanized steel sheet is preferable.

Hereinafter, embodiments of the present invention will be described in detail. However, the following examples do not limit the present invention.

(Example)

As shown in Table 1, C: 0.6% by weight, Mn: 18% by weight, Si: 0.2% by weight, Al: 1.5% by weight, Nb: 0.03% by weight, V: 0.1% by weight, S: 0.008% by weight. Recrystallize the high manganese steel containing%, balance Fe and other impurities for 15 seconds at an annealing temperature of 480 ° C to 800 ° C in a reducing atmosphere with 15% hydrogen, nitrogen as the remainder and 0 ° C to -60 ° C dew point. The annealing treatment was performed, and then cooled to room temperature at a cooling rate of 15 ° C./sec to prepare an annealing material.

The surface oxides of the alloying elements such as Si and Mn formed during the annealing process were deposited in 5-20% hydrochloric acid solution to remove the oxides formed during the annealing process, followed by Ni plating of 10-100 mg / m 2, followed by continuous dew point temperature. Is heated at a heating temperature of 0 to 70 ° C. and 460 to 850 ° C. and plated on one side by depositing in a zinc plating bath having a concentration of 0.23 wt% and a zinc plating bath having a concentration of 0.09 to 0.15 wt%, respectively. Air kneading was carried out to adjust the adhesion amount to 60 g / m 2, or hot dip galvanization followed by alloying treatment. The alloying temperature at the time of alloying process was performed at 500-550 degreeC.

Evaluation of the plating quality of the hot-dip galvanized steel sheet thus prepared was evaluated the degree of unplated generation and the degree of plating adhesion superiority based on the following criteria.

The degree of unplating was obtained by image processing of the surface appearance after hot dip galvanizing, and the area of the unplated portion was obtained and graded according to the following criteria.

-Grade 1: No plating defect

-Grade 2: Unplated average diameter is less than 1mm

-Grade 3: 1 ~ 2mm distribution of unplated average diameter

-Grade 4: Average unplated diameter of 2-3mm

-Grade 5: Unplated average diameter of 3mm or more

In addition, the plating adhesion of the hot-dip galvanized steel sheet was evaluated by peeling degree of the plated layer during the taping test after bending the 0T-bend test based on the following criteria.

-Grade 1: No peeling

-Level 2: Peel less than 5%

-Grade 3: Less than 5 ~ 10%

-Grade 4: Less than 10 ~ 30%

-Grade 5: Over 30% peel

In addition, the powdering properties of the alloyed hot-dip galvanized steel sheet was evaluated by the following criteria for the width (width) of the alloy layer coating on the tape attached to the inner portion of the bend after 60 ° bending test.

-Grade 1: No peeling

-Grade 2: Peel width less than 2mm

-Grade 3: Peel Width 2 ~ 5mm

-Grade 4: Peel Width 5 ~ 10mm

-Grade 5: Peeling width over 10mm

Table 1 shows the results of evaluating the unplated grade, the plating adhesion index and the powdering properties of the alloyed hot dip galvanized steel sheet according to the annealing treatment, pickling, Ni plating, and heat treatment conditions.

number
Annealing Condition Pickling condition Ni plating Heating condition Plating bath condition Alloying Drawing surface quality Remarks
Temperature
(℃) time
(second) Dew point temperature
(℃) density
(%) time
(second) Adhesion
(Mg / ㎡) Dew point temperature
(℃) Temperature
(℃) time
(second) Al concentration
(%) Temperature
(℃) Temperature
(℃) Unplated Grade Plating Adhesive Index Powdering Index One 800 40 -40 0.23 460 5 5 Conventional example 2 480 60 -40 0.23 460 5 5 Conventional example 3 800 40 -40 10 5 90 0.23 460 3 4 Comparative example 4 800 40 0 10 5 90 -40 800 40 0.23 460 One One Inventive Example 800 40 -20 10 5 90 -40 800 40 0.23 460 One One Inventive Example 800 40 -40 10 5 90 -40 800 40 0.23 460 One One Inventive Example 800 40 -60 10 5 90 -40 800 40 0.23 460 3 4 Comparative example 800 40 10 10 5 90 -40 800 40 0.23 460 3 4 Comparative example 5 800 40 -40 10 5 9 -40 800 40 0.23 460 4 5 Comparative example 800 40 -40 10 5 100 -40 800 40 0.23 460 One One Comparative example 800 40 -40 10 5 90 -40 800 40 0.23 460 One One Inventive Example 800 40 -40 10 5 50 -40 800 40 0.23 460 One One Inventive Example 800 40 -40 10 5 15 -40 800 40 0.23 460 One One Inventive Example 6 800 40 -40 - - 90 -40 800 40 0.23 460 3 3 Comparative example 800 40 -40 5 5 90 -40 800 40 0.23 460 One One Inventive Example 800 40 -40 10 5 90 -40 800 40 0.23 460 One One Inventive Example 800 40 -40 20 5 90 -40 800 40 0.23 460 2 3 Comparative example 7 800 40 -40 10 5 90 0 800 40 0.23 460 One One Inventive Example 800 40 -40 10 5 90 -20 800 40 0.23 460 One One Inventive Example 800 40 -40 10 5 90 -40 800 40 0.23 460 One One Inventive Example 800 40 -40 10 5 90 -70 800 40 0.23 460 One One Inventive Example 800 40 -40 10 5 90 10 800 40 0.23 460 3 4 Comparative example 8 800 40 -40 10 5 90 -40 460 40 0.23 460 One One Inventive Example 800 40 -40 10 5 90 -40 550 40 0.23 460 One One Inventive Example 800 40 -40 10 5 90 -40 650 40 0.23 460 One One Inventive Example 800 40 -40 10 5 90 -40 750 40 0.23 460 One One Inventive Example 800 40 -40 10 5 90 -40 850 40 0.23 460 2 3 Comparative example 9 800 40 -40 10 5 90 -40 800 40 0.10 460 520 One One One Inventive Example 800 40 -40 10 5 90 -40 800 40 0.13 460 520 One One One Inventive Example 800 40 -40 10 5 90 -40 800 40 0.12 460 520 One One One Inventive Example 800 40 -40 10 5 90 -40 800 40 0.15 460 520 One One 5 Comparative example 800 40 -40 10 5 90 -40 800 40 0.09 460 520 3 4 5 Comparative example 10 800 40 -40 10 5 90 -40 800 40 0.12 460 480 One One 4 Comparative example 800 40 -40 10 5 90 -40 800 40 0.12 460 570 One One 5 Comparative example

As shown in the results of Table 1, in the annealing treatment, pickling, Ni plating, heat treatment proposed in the present invention, the annealing temperature is 750 ℃ ~ 850 ℃, annealing conditions of the dew point temperature is more than -40 ℃ Annealing at 5 ~ 15%, pickling in 5 ~ 15% aqueous hydrochloric acid solution to remove surface oxide, and then Ni plating at 10 ~ 90mg / ㎡, and then dew point temperature 0 ~ -70 ℃, heating temperature 480 ~ Inventive examples heated at 800 ° C. under the heat treatment conditions are capable of preventing the surface concentration of the alloying element Mn during the heat treatment even at a small Ni plating amount due to the internal oxide under the substrate formed during the annealing process. It was possible to manufacture a high manganese hot dip galvanized steel sheet having no plating and excellent plating property without plating peeling during processing.

In addition, after the heat treatment under the above operating conditions in the process of the present invention, the plating bath Al concentration is plated at 0.1 ~ 0.13% of the range of the present invention and then alloyed at the alloying temperature 500 ~ 550 ℃ alloying of the present invention The hot-dip galvanized steel sheet was able to manufacture an alloyed hot-dip galvanized steel sheet having excellent alloying processability without the formation of unalloyed and powdered powder by forming a thin and uniform interface inhibitory layer.

On the contrary, in the comparative example in which only Ni plating was applied to the cold rolled steel sheet as in the conventional example in which only the annealing treatment and the heating treatment were performed, as in the steel sheets 1 and 2, and the steel sheet 3, the unplated was formed by the formation of a thick manganese oxide film. Even if plating was performed, the plating layer was peeled off during processing by the manganese oxide at the interface, which was not preferable.

On the other hand, in Comparative Example deviated from the dew point temperature condition in the annealing treatment of the present invention in steel No. 4, the alloying element Mn forms a thick manganese oxide film due to the surface thickening and oxidation from the base material, so that unplating occurs and plating adhesion is not preferable. Did.

In the comparative example outside the Ni adhesion amount range of the present invention in steel No. 5, the comparative example outside the dew point temperature of the present invention in heat treatment at steel number 7, and the comparative example outside the heating temperature range of the present invention in heat treatment at steel No. 8, Ni plating was It is not enough to prevent the surface concentration of alloying elements such as Mn, so that the Mn re-concentrates on the surface and forms a thick film of manganese due to oxidation, which causes unplating, and when processed by manganese oxide formed at the interface even when plating The plating layer was peeled off, which was not preferable.

On the other hand, when the pickling was not performed in the comparative example outside the pickling conditions of the present invention in steel No. 6, Mn oxide was not removed, and thus the unplating and plating adhesion were inferior. Although plating to plating adhesion is excellent, it is not preferable to form a carbide film during alloying treatment.

In addition, in the comparative examples in which the Al concentration or the alloying temperature of the plating bath is out of the scope of the present invention during plating and subsequent alloying in the inventive processes in steel Nos. 9 and 10, unalloyed with high alloying temperature and nonuniform interfacial inhibition layer formation. Or an alloying defect such as powdering occurs.

1 is a photograph observing the cross section of the conventional unplated material of high manganese steel.

Figure 2 is a graph showing the thickness change of the surface oxide (manganese oxide) according to the dew point temperature change at the annealing temperature 800 ℃.

Figure 3 is a flow chart showing the manufacturing process of the conventional hot-dip galvanized steel sheet (GI) and the present invention hot-dip galvanized steel sheet (GI).

Claims (9)

Annealing the high manganese steel to a heating temperature of 750 to 850 ° C. in a reducing atmosphere having a dew point temperature of 0 to 40 ° C .; Pickling high manganese steel subjected to the annealing heat treatment; Ni-plating the high manganese steel subjected to the pickling; Heating the Ni-plated high manganese steel; And Hot-dip galvanizing the heat-treated high manganese steel Method of producing a high manganese steel hot-dip galvanized steel sheet comprising a plating property. The method according to claim 1, The high manganese steel is by weight, C: 0.1-1.5%, Mn: 5-35%, Si: 0.01-3.0%, Al: 0.01-3.0%, Ni: 0.01-1.0%, Ti: 0.01-0.2%, B: 0.0005 to 0.006%, the remainder is a method of producing a high manganese steel hot-dip galvanized steel sheet having excellent plating properties containing Fe and unavoidable impurities. delete The method according to claim 1, The pickling is a method for producing a hot-manganese hot-dip galvanized steel sheet having excellent plating properties by using an acid solution having an acid concentration of 5 to 15%. The method according to claim 1, The Ni plating is a method of producing a high manganese steel hot-dip galvanized steel sheet excellent in plating properties to be carried out so that the adhesion amount of 10 ~ 90mg / ㎡. The method according to claim 1, The heat treatment is a method of producing a high manganese steel hot-dip galvanized steel sheet having excellent plating properties performed at a temperature of 480 ~ 800 ℃. The method according to claim 1, The hot-dip galvanizing is a method of producing a high manganese steel hot-dip galvanized steel sheet having excellent Al plating content of 0.21 to 0.25% by weight, and the rest is immersed in a plating bath made of Zn and unavoidable impurities. The method according to claim 1, A method for producing a high manganese steel hot dip galvanized steel sheet having excellent plating property after performing the hot dip galvanizing and performing alloying treatment. The method according to claim 8, The hot-dip galvanizing is 0.1 to 0.13% by weight of Al, the rest is carried out by immersing a high manganese steel in a plating bath made of Zn and unavoidable impurities, the alloying treatment is excellent plating properties performed at a temperature of 500 ~ 550 ℃ Method for producing hot-manganese hot-dip galvanized steel sheet.

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