KR20160077558A - High manganese steel sheet having excellent hot dip aluminium coatability, and method for manufacturing the same - Google Patents

Abstract

According to the present invention, disclosed are an austenite high strength and manganese steel sheet having excellent hot dip aluminum coatability, and a method for manufacturing the same. According to an aspect of the present invention, the austenite high strength and manganese steel sheet having excellent hot dip aluminum coatability comprises: 0.3-0.9 wt% of C; 12-25 wt% of Mn; 0.3-3.0 wt% of Al; 0.6-2.5 wt% of Si; 0.01-0.5 wt% of Ti; 0.05-0.5 wt% of V; an amount equal to or less than 1.0 wt% of Ni (excluding 0 wt%); 0.0005-0.005 wt% of B; and the remainder consisting of Fe and inevitable impurities.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to austenitic high-strength high-manganese hot-dip galvanized steel sheet having excellent plating quality,

The present invention relates to austenitic high-strength high-manganese hot-dip galvanized steel sheet having excellent plating quality and a method for producing the same, and more particularly, to an austenitic high strength steel sheet having excellent plating quality which can be used for impact structural members of automobiles High manganese-fused aluminum-plated steel sheet and a method of manufacturing the same.

In order to reduce environmental problems such as global warming, which has recently been emphasized, there has been a strong demand for lightening of automobiles in accordance with the regulation of carbon dioxide. At the same time, the strength of automotive steel sheets has been continuously increased to improve the collision stability of automobiles.

In order to produce such an ultra-high-strength cold-rolled steel sheet, it is general to utilize a low-temperature transformed structure. However, it is difficult to obtain an elongation of 20% or more at a tensile strength of 1000 MPa or more when a low-temperature transformed structure is used in order to achieve ultra-high strength, and it is difficult to apply to cold- There was a problem that it was difficult to design the free parts that fit.

Thus, various attempts have been made to provide steels that exhibit good moldability and mechanical properties optimized for the intended application, for automotive body construction and similar applications.

For example, Japanese Patent Application Laid-Open Publication No. 2000-223059 discloses a steel sheet comprising 0.5 to 1.5% of C, 0.01 to 0.1% of Si, 10 to 25% of Mn, 0.1% or less of P, , 3.0 to 8.0% of Ni, 0.01 to 0.1% of Mo, 0.01% or less of N, and the balance Fe and unavoidable impurities, a high tensile strength and a tensile strength of 700 to 900 MPa Patent Document 2 discloses a steel sheet having a composition of C: not more than 1.00%, Mn: 7.00 to 30.00%, Al: 1.00 to 10.00%, Si: 2.50 to 8.00%, Al + Si: 3.50 to 12.00% % To 0.01%, Fe, and unavoidable impurities.

However, the above-mentioned inventions have a disadvantage in that not only the impact strength is lowered due to the low yield strength of the steel but also the application of the non-plated material to the automotive steel is limited.

When high manganese steel hot-dip galvanized steel sheet is used as a steel sheet for automobile, parts are processed by press working and then assembled by spot welding or arc welding. At this time, when the high manganese steel hot- The heat affected zone (HAZ) is dissolved by the heat of welding (mouth) and remains as liquid molten zinc. The base structure becomes high temperature compared with other steel species due to high resistance value of high manganese steel. The grain boundary expansion occurs. When the tensile force acts on the heat affected portion in such a state, the molten zinc in the liquid phase penetrates into the crystal grain boundaries of the surface of the welded heat affected portion to generate cracks, thereby causing a liquefied metal embrittlement Quot; LME ").

In order to prevent the occurrence of welding LME of high strength steel galvanized steel sheets, it is known to strengthen the grain boundaries of the base steel sheet or to eliminate the hardness difference between the grain and the grain boundaries. However, the high manganese steel has austenite structure at room temperature, Since this shows the heat input and the thermal expansion coefficient, such a method is not effective in a galvanized steel sheet using a high manganese steel as a plating material.

That is, while the temperature of the welding shoulder portion rapidly rises up to 800 ° C during spot welding, the galvanized layer starts to melt at about 420 ° C and becomes liquid. As the temperature of the welding shoulder portion further increases, the fluidity of the formed liquid rapidly increases And cracking of the welded LME occurs due to penetration into the grain boundaries of the steel sheet.

Accordingly, the inventors of the present invention have conducted studies to prevent the occurrence of welding LME during welding and have found that the method of increasing the melting point of the plating layer is very effective. As a result, they have found that when a plating layer is formed on a base steel sheet, The present invention has been accomplished on the basis of the finding that aluminum (Al) is used as the aluminum alloy. That is, if aluminum is used as the plating layer forming material, the aluminum plating layer having a relatively high melting point can effectively reduce the occurrence of welding LME before the plating layer is melted to become a liquid phase or become liquid and penetrate into the grain boundary of the base steel sheet have. However, it is difficult to secure the plating ability of molten aluminum as a large amount of Si, Mn, and Al contained in the steel is formed in the annealing process.

Therefore, there is an urgent need for a technique capable of securing the plating property and the plating adhesion property of the high-strength molten aluminum-plated steel sheet.

International Patent Publication No. WO2011-122237 International Patent Publication No. WO2002-101109

An aspect of the present invention is to provide an austenitic high-strength high-manganese hot-dip coated aluminum-coated steel sheet excellent in the yield strength, plating ability and plating adhesion, and a method for producing the same.

The austenitic high-strength high-manganese hot-dip galvanized steel sheet excellent in plating quality, which is one aspect of the present invention, contains 0.3 to 0.9% of C, 12 to 25% of Mn, 0.3 to 3.0% of Al, 0.3 to 3.0% , Ti: 0.01 to 0.5%, V: 0.05 to 0.5%, Ni: 1.0% or less (excluding 0%), B: 0.0005 to 0.005%, and the balance Fe and unavoidable impurities.

In another aspect of the present invention, there is provided a method for manufacturing a high strength and high manganese hot-dip coated aluminum alloy steel sheet having excellent plating quality, comprising 0.3 to 0.9% of C, 12 to 25% of Mn, 0.3 to 3.0% of Al, Hot rolling comprising 0.6 to 2.5% of Si, 0.01 to 0.5% of Ti, 0.05 to 0.5% of V, 1.0% or less of Ni (excluding 0%), B of 0.0005 to 0.005%, Fe and unavoidable impurities Preparing a steel sheet; Immersing the prepared hot-rolled steel sheet in a pickling bath, washing it after primary pickling, and drying it; Cold rolling the hot rolled steel sheet; Heating the steel sheet at a heating rate of 1.6 to 4.1 占 폚 / s in a reducing atmosphere controlled to a dew point of -30 占 폚 or less; A cracking step of holding the heated steel sheet in a reducing atmosphere at 700 to 850 ° C; Cooling the steel sheet after the cracking step; Immersing the cooled steel sheet in a pickling bath, washing with water after secondary pickling, and drying; Secondary heating at an aluminum plating bath temperature or higher; And forming an aluminum plating layer on the steel sheet.

In addition, the solution of the above-mentioned problems does not list all the features of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS The various features and advantages and effects of the present invention will become more fully understood with reference to the following specific embodiments.

According to the present invention, it is possible to provide an austenitic high-strength high-manganese aluminum-plated steel sheet excellent in yield strength and formability with a yield strength of not less than 700 MPa and a yield strength (YSxEL) of yield strength and elongation of not less than 30,000 MPa%.

The inventors of the present invention have recognized that although a high manganese steel can retain austenite in the microstructure of steel at room temperature due to the addition of a large amount of manganese and carbon in the conventional high manganese steel, Depth study to solve it.

As a result, it is possible to appropriately control the contents of carbon, manganese and aluminum, which perform the function of stabilizing the austenite structure in the steel component system, and to combine the elements forming the fine precipitates, It is possible to provide an austenitic high-manganese-fused aluminum-plated steel sheet excellent in plating quality, and the present invention has been accomplished.

Hereinafter, an austenitic-type high-manganese hot-dip coated steel sheet having excellent plating quality, which is one aspect of the present invention, will be described in detail.

First, the alloy composition of the austenitic high manganese steel excellent in the yield strength of the present invention will be described in detail.

Carbon (C): 0.3 to 0.9 weight%

Carbon is an element contributing to the stabilization of the austenite phase, and as the content thereof increases, there is an advantageous aspect in securing the austenite phase.

Carbon also increases the energy of lamination defects in the steel, thereby increasing the tensile strength and elongation at the same time.

If the content of carbon is less than 0.3%, there arises a problem that decarburization at the time of high-temperature processing of the steel sheet results in formation of an α '(alpha-re-) martensite phase on the surface layer to become vulnerable to delayed fracture, there is a problem.

On the other hand, if the content exceeds 0.9%, the electrical resistivity increases and the weldability may decrease.

Therefore, in the present invention, the carbon content is preferably limited to 0.3 to 0.9%.

Manganese (Mn): 12 to 25 wt%

Manganese is an element that stabilizes the austenite phase with carbon.

If the content of manganese is less than 12%, there is a problem that it is difficult to secure a stable austenite phase due to the formation of α '(alpha re-) martensite phase during deformation.

On the other hand, if the content exceeds 25%, further improvement with respect to an increase in strength, which is a matter of concern of the present invention, does not occur substantially and the manufacturing cost rises.

Therefore, the content of Mn in the present invention is preferably limited to 12 to 25%.

Aluminum (Al): 0.3 to 3.0 wt%

Aluminum is usually added for deoxidation of steel, but the present invention enhances the ductility and delayed fracture characteristics of steel by suppressing the formation of ε (entrance run) -martensite by increasing the stacking fault energy.

If the aluminum content is less than 0.3%, there is a problem that the ductility of the steel is deteriorated due to rapid work hardening phenomenon and the delayed fracture resistance is inferior. On the other hand, when the aluminum content exceeds 3.0% by weight, The main composition is heated, and the oxidation of the steel surface is deepened during the hot rolling, thereby deteriorating the surface quality.

Therefore, in the present invention, the aluminum content is preferably limited to 0.3 to 3.0 wt%.

Silicon (Si): 0.6 to 2.5 wt%

Silicon is an element commonly used as a deoxidizing agent for steel, as in the case of aluminum, but in the present invention, it serves to improve the yield strength and tensile strength of steel by solid solution strengthening. Particularly, in the present invention, it is confirmed that when carbonitride-forming elements titanium and vanadium are added in combination with silicon, the sizes of precipitated carbonitride are miniaturized and finer grains are obtained than when only carbonitride-forming elements are added.

In order to obtain this effect in the present invention, it is preferable that the content of silicon is 0.6% or more. On the other hand, when the content of silicon exceeds 2.5%, a large amount of silicon oxide is formed on the surface during hot rolling, which lowers the acidity and increases the electrical resistivity, resulting in poor weldability. Therefore, the content of silicon in the present invention is preferably limited to 0.6 to 2.5%.

Vanadium (V): 0.05 to 0.5 wt%

Vanadium reacts with carbon or nitrogen to form carbonitride. In the present invention, it plays an important role in increasing the yield strength of steel by forming fine precipitates at low temperatures.

In order to obtain such effects in the present invention, the vanadium content is preferably 0.05 wt% or more. On the other hand, when the content of vanadium exceeds 0.5 wt%, coarse carbonitrides are formed at a high temperature, resulting in deterioration of hot workability and lowering of the yield strength of the steel. Therefore, the content of vanadium in the present invention is preferably limited to 0.05 to 0.5 wt%.

Thinatium (Ti): 0.01 to 0.5 wt%

The content of titanium (Ti) is preferably 0.01 to 0.5%. Titanium reacts with nitrogen in the steel to precipitate nitrides, which improves the formability of hot rolling. In addition, the titanium reacts with carbon in some steel to form precipitation phases, thereby increasing the strength. It is preferable that titanium is contained in an amount of 0.01% or more, but if it exceeds 0.5%, precipitates are formed excessively and deteriorate the fatigue characteristics of the parts. Accordingly, the titanium content is preferably 0.01 to 0.5%.

Nickel (Ni): 1.0 wt% or less (excluding 0%)

When the steel contains a large amount of Si, Mn and Al, heat treatment is performed in a reducing atmosphere of 700 to 850 ° C in order to secure materials, so that Si, Mn, Al alone or a composite oxide having high oxygen affinity is formed on the steel sheet surface layer, If it is plated by immersion in a plating bath, a large amount of unplated is generated and the plating property is poor. When a small amount of nickel (Ni) is added to the steel in order to improve the plating ability, the surface enrichment of Mn, Al, and Si in the steel is effectively suppressed to suppress the formation of surface oxides in the annealing process, . However, when the content exceeds 1.0 wt%, it is difficult to secure economical efficiency in terms of cost competitiveness. Therefore, it is preferable to limit the nickel content to 1.0 wt% or less in the present invention.

Boron (B): 0.0005 to 0.005 wt%

The boron (B) is preferably 0.0005 to 0.005%. When boron is added in a small amount, the grain boundary of the cast steel is strengthened to improve the hot rolling property. If the boron content is less than 0.0005%, the above effects can not be expected. If the boron content is more than 0.005%, further improvement in performance can not be expected and the cost is increased. Therefore, the content thereof is preferably 0.0005 to 0.005%.

The remainder Fe and unavoidable impurities. On the other hand, addition of an effective component other than the above-mentioned composition is not excluded.

At this time, the steel sheet contains 0.5% or less of Cr (not including 0%), 0.5% or less of Mo (not including 0%), 0.05% or less of Nb (not including 0% , Sb: not more than 0.1% (not including 0%), and Sn: not more than 0.1% (not including 0%).

Hereinafter, a method for producing austenitic high-strength high-manganese hot-dip coated steel sheet as another embodiment of the present invention will be described in detail as a preferred example for producing the above-described austenitic high-strength high-manganese hot-dip galvanized steel sheet.

The steel sheet satisfying the above composition is heated. According to one aspect of the present invention, it is important to control the dew point during the heating. This is because it is necessary to suppress the concentration of Si, Mn, and Al oxides on the surface of the steel sheet as much as possible by controlling the dew point. If the dew point exceeds -30 ° C, Mn in the steel reacts with oxygen to form a thick Mn oxide on the surface layer of the steel sheet, so that the wettability of the aluminum is weakened. Therefore, it is preferable to control the dew point in the heating and crack sections to -30 캜 or less so that the concentration of Si, Mn, and Al oxides on the surface of the steel sheet can be suppressed as much as possible.

In addition, one aspect of the present invention is to control the heating rate of the heating zone. Since the heating rate is directly related to the line speed, that is, productivity, the heating rate is faster within a range that does not adversely affect the quality of the steel sheet good.

However, when the line speed is increased to increase the heating rate, there is a possibility that the welding portion breaks with the leading coil and the occurrence of meandering of the steel plate to one side is increased, so that the heating rate can not be increased indefinitely.

Also, if the heating rate of the heating zone is decreased, Si, Mn, and Al are thickened on the surface of the steel sheet to form a thick oxide layer, thereby causing unplated after the aluminum plating, and detaching the plating layer.

Therefore, the heating rate in the heating zone affects the thickness of the annealed oxide layer, which is an important parameter for determining the plating ability and the plating detachment in the subsequent aluminum plating process.

Specifically, according to one aspect of the present invention, the heating rate during heating is preferably controlled to 1.6 to 4.1 ° C / s. If the heating rate is less than 1.6 ° C / s, the productivity of the steel sheet deteriorates. In addition, Si, Mn, and Al concentrations increase on the surface of the steel sheet during the heating process, Plating may occur after plating and the plating layer may be peeled off. Further, when the heating rate exceeds 4.1 DEG C / s, there is a possibility that the welding portion breaks with the preceding coil and the occurrence of meandering of the steel sheet to one side is increased, and the heating rate can not be increased indefinitely.

Thereafter, the heated base steel sheet may be cracked at 700 to 850 ° C. When the temperature is lower than 700 ° C, the temperature is lower than the A ₁ transformation point (726 ° C), and an austenitic single phase structure can not be obtained.

On the other hand, if the temperature is higher than 850 DEG C, not only the fuel and energy consumption used for raising the annealing furnace temperature are increased but also secondary steel recrystallization results in a steel sheet having excellent tensile strength or elongation, Al oxide is formed thickly, and after the aluminum plating, the annealing oxide existing at the interface between the plating layer and the steel sheet may cause unplated generation and peeling of the plating.

Therefore, it is preferable to control the cracking temperature to 700 to 850 캜. However, in order to further improve the effect of the present invention, it is more preferable to control the crack temperature to 726 to 820 캜.

At this time, it is preferable that the reducing atmosphere gas is a mixed gas composed of 3 to 20% of hydrogen and the balance of nitrogen. If the hydrogen content in the reducing gas is less than 3%, reduction of the iron oxide film inevitably formed on the surface of the steel sheet does not occur sufficiently, resulting in peeling of the plating layer due to the residual oxide layer. If the hydrogen content exceeds 20% It is preferable to control the hydrogen content to 3 to 20% because the cost and explosion risk increase.

Thereafter, the base steel sheet can be cooled. The method of cooling is not particularly limited, and any method may be used.

Next, the base steel sheet may be immersed in a pickling bath in primary and secondary stages to remove the oxide formed in the hot rolling scale or the annealing process of the base steel sheet. The pickling method for removing the hot-rolled scale or the annealed surface oxide is not particularly limited. If the temperature of the pickling bath is lower than 70 ° C, the hot-rolled scale or the annealed surface oxide can not be effectively removed, and the plating ability and the adhesiveness due to the residual oxide ≪ / RTI > If the temperature of the pickling bath is higher than 90 ° C, the surface steel oxide may be over-picked along with the removal of the surface oxide, resulting in poor plating and adhesion due to the residual oxide.

Thereafter, the step of reheating the base steel sheet to a temperature not lower than the aluminum plating bath temperature in a reducing atmosphere of a mixed gas composed of 3 to 20% of hydrogen and the balance of nitrogen can be carried out before the base steel sheet is washed and dried and then drawn into the molten aluminum plating bath have. When the reheating heat treatment temperature is lower than the melting point of aluminum of 660 캜, the reactivity between the steel sheet Fe and the molten aluminum is low, and the Fe-Al alloy phase is not sufficiently formed on the plating layer and the base surface, which may lead to poor plating adhesion.

Next, the cooled ground steel sheet may be immersed in a plating bath to form a plated layer. The method of forming the plating layer is not particularly limited. However, if the temperature of the plating bath is less than 660 DEG C, the viscosity of the plating bath is increased and the degree of mobility of the roll that winds the steel sheet is decreased Thereby causing a slip between the steel strip and the roll, thereby causing defects in the steel strip.

When the temperature of the plating bath exceeds 700 캜, dissolution of the steel sheet is accelerated to accelerate the generation of Fe-Al compound-type dross, thereby causing unplated formation. Therefore, in order to minimize the occurrence of defects in the steel sheet, it is preferable to control the temperature of the plating bath to 660 to 700 占 폚.

Meanwhile, after the plating step, the molten aluminum plated steel sheet may be further subjected to an alloying heat treatment. By controlling the alloying heat treatment temperature to 720 DEG C or higher, a sufficient Fe content can be ensured in the aluminum plating layer, and by controlling the temperature to 840 DEG C or lower, it is possible to prevent the powdering phenomenon in which the plating layer falls off during processing in excess of Fe content in the plating layer have.

Hereinafter, the present invention will be described more specifically by way of examples. It should be noted, however, that the following examples are intended to illustrate the invention in more detail and not to limit the scope of the invention. The scope of the present invention is determined by the matters set forth in the claims and the matters reasonably inferred therefrom.

(Example 1)

The steel ingot having the composition shown in the following Table 1 was homogenized in a heating furnace at 1180 ° C for 1 hour and then rolled at a finish rolling temperature of 900 ° C to prepare a hot-rolled steel sheet. Thereafter, the hot-rolled steel sheet was rolled at a coiling temperature of 300 ° C, followed by primary pickling, washing with water, and drying, followed by cold rolling at a cold-reduction rate of 55% to produce a cold-rolled steel sheet. Then, the primary annealing was performed by setting the annealing temperature to 790 캜. A nitrogen gas containing 5% hydrogen was blown and heat treated at a dew point of -33 DEG C and a heating rate of 2.9 DEG C / s.

Then, the steel sheet was maintained (cracked) at a temperature of 680 ° C for 60 seconds to be reheated in a reducing atmosphere after secondary pickling, washing with water and drying, cooling and then the steel sheet was immersed in the plating bath for 5 seconds Air wiping was performed to maintain the coating adhesion amount on the surface at 70 g / m 2.

The yield strength (Mpa), the elongation (%), the product of the yield strength and the elongation were evaluated for the steel sheet after the plating process, and the results are shown in Table 2 below.

Psalm NO. C
(weight%) Mn
(weight%) Al
(weight%) Si
(weight%) Ti
(weight%) V
(weight%) Ni
(weight%) B
(weight%) Inventory 1 0.69 17.6 1.38 1.0 0.069 0.22 0.3 0.0023 Inventory 2 0.51 16.7 0.88 2.0 0.064 0.2 0.25 0.0019 Inventory 3 0.53 16.9 0.44 2.1 0.068 0.21 0.28 0.0021 Honorable 4 0.74 15.6 1.69 2.1 0.072 0.29 0.15 0.0026 Inventory 5 0.70 18.8 1.77 2.0 0.078 0.3 0.22 0.0018 Inventory 6 0.32 19.4 0.96 2.0 0.070 0.23 0.26 0.0022 Comparative Example 1 0.5 17.6 1.43 2 0.0 0.0 0.32 0.002 Comparative Example 2 0.49 15.8 2.02 0.0 0.073 0.2 0.18 0.0022 Comparative Example 3 0.51 17.3 1.36 0.6 0.077 0.0 0.28 0.0019 Comparative Example 4 0.5 16.5 1.35 0.0 0.068 0.0 0.12 0.0023 Comparative Example 5 0.47 17.6 1.54 One 0.0 0.23 0.24 0.0018 Comparative Example 6 0.31 20 0.99 1.8 0.075 0.21 0.26 0.0015

Psalm NO. Yield strength (Mpa) Product of yield strength and elongation (Mpa%) Elongation (%) Inventory 1 743 42,351 57.0 Inventory 2 815 32,111 39.4 Inventory 3 768 32,947 42.9 Honorable 4 906 34,790 38.4 Inventory 5 901 33,157 36.8 Inventory 6 788 30,023 38.1 Comparative Example 1 545 23,762 43.6 Comparative Example 2 622 29,234 47 Comparative Example 3 561 32,538 58 Comparative Example 4 524 29,396 56.1 Comparative Example 5 636 33,326 52.4 Comparative Example 6 782 27,761 35.5

It can be confirmed that Examples 1 to 6 satisfying all the compositions of the present invention have a yield strength of 700 MPa or more and a yield strength x elongation of 30,000 MPa% or more.

On the other hand, in Comparative Example 1, the yield strength of 700 MPa or more could not be obtained as a steel to which vanadium and titanium were not added.

In Comparative Example 2, when 0.2% vanadium was added, the yield strength was slightly improved as compared with Comparative Example 1, but the yield strength of 700 MPa or more could not be obtained because no silicon was added.

Comparative Example 3 was a steel to which 0.6% of silicon was added. However, the yield strength was slightly improved as compared with Comparative Example 1, but vanadium was not added, and a yield strength of 700 MPa or more could not be secured.

In Comparative Example 4, the elongation was excellent without adding silicon and vanadium, but the yield strength of 700 MPa or more could not be secured.

In Comparative Example 5, it was not possible to secure a yield strength of 700 MPa or more in a steel grade to which titanium was not added.

In Comparative Example 6, when 0.31% of carbon was added, the yield strength was excellent, but the yield strength x elongation of 30,000 MPa% or more could not be secured in order to maintain the elongation.

(Example 2)

The steel ingot having the composition shown in the following Table 1 was homogenized in a heating furnace at 1180 ° C for 1 hour and then rolled at a finish rolling temperature of 900 ° C to prepare a hot-rolled steel sheet. Thereafter, the hot-rolled steel sheet was rolled at a coiling temperature of 300 ° C, followed by cold rolling at a cold-reduction rate of 55% after the first pickling to produce a cold-rolled steel sheet. Then, the annealing temperature was set to 790 ° C, and nitrogen gas containing 5% hydrogen was blown thereon, and the first crack heat treatment was performed in a reducing atmosphere. After the second pickling, the reheating heat treatment temperature was 680 占 폚 in the above reducing atmosphere. Were heated according to the dew point and the heating rate shown in Table 3 below.

Annealing was carried out for 60 seconds at the temperatures shown in Table 3 below in order to primarily crack in a reducing atmosphere. Thereafter, the steel sheet was immersed in a plating bath for 5 seconds, and air wiping was performed to maintain the coating adhesion amount on the surface to 70 g / m 2.

In order to evaluate the plating performance of the steel sheet after the plating process, the area coverage of the aluminum plated layer with respect to the total area of the plated surface was measured and shown in Table 3 below. For the cross-section observation, the specimen was cut into 15 × 15 mm 2, the cross section was polished, and the plating layer was observed with a scanning electron microscope (SEM). In order to measure the plating adhesion of the steel sheet, a specimen having a size of 30x80 mm 2 was bent at an angle of 180 °, and a bending test was performed. 0T bending was performed according to the material properties of the steel sheet in such a range that the material did not break. When a transparent vinyl tape is attached to the bending portion, the plate is peeled off when the plate is peeled off, and the plate is peeled off when the plate is not peeled.

division dew point
(° C) Heating rate
(° C / s) Crack temperature
(° C) Aluminum plated layer
Coverage area ratio (%) Plated
Adhesiveness Inventory 1 -42 1.8 756 98 Non-exfoliation Inventory 2 -64 3.6 831 97 Non-exfoliation Inventory 3 -36 4.1 793 95.5 Non-exfoliation Honorable 4 -44 2.9 773 95 Non-exfoliation Inventory 5 -53 3.3 822 98 Non-exfoliation Inventory 6 -35 3.1 844 98.5 Non-exfoliation Comparative Example 1 -16 3.0 872 62 Exfoliation Comparative Example 2 -32 1.4 710 77 Exfoliation Comparative Example 3 -44 2.9 873 80 Exfoliation Comparative Example 4 -36 1.0 815 73 Exfoliation Comparative Example 5 -43 3.5 688 94 Non-exfoliation Comparative Example 6 5 2.3 803 80 Exfoliation

As shown in Table 3, Examples 1 to 6 satisfied the conditions controlled by the present invention in both the heating zone heating rate, the dew point and the cracking step temperature, and the coated area percentages of the aluminum plating layer were all 95% It is very excellent, and there is no peeled portion, and it can be confirmed that the plating adhesion is excellent.

In Comparative Example 1, the dew point in the heating zone exceeded the condition of the present invention, and due to the high dew point, a thick band-like Mn oxide was formed on the surface of the steel sheet, and the plating detachment phenomenon occurred. In addition, when the annealing temperature of the crack section exceeds the condition of the present invention, the material of the steel, that is, the tensile strength or elongation, is less than the desired level by the secondary recrystallization and the time taken to reach the annealing temperature is relatively long, The diffusion of Si, Mn or Al in the steel increases to the surface of the steel sheet to form Si, Mn or Al oxides in the form of stripes at the interface between the steel sheet and the base steel sheet, resulting in the increase in the plating disadvantage and the plating detachment.

In Comparative Example 2, since the heating rate in the heating zone was less than the condition of the present invention, and the time required for reaching the target annealing temperature was long, the diffusion of Si, Mn or Al in the steel increased to the surface of the steel sheet, Si, Mn or Al oxides are formed in a strip shape. As a result, the alloying inhibition layer was unevenly formed on the surface of the steel sheet after the aluminum plating process, so that the coating area ratio of the aluminum plating layer was only 77%, resulting in a poor plating property and a plating peeling.

On the other hand, since the annealing temperature does not meet the conditions of the present invention, the amount of Si, Mn or Al concentrated on the surface of the steel sheet in the annealing process is reduced due to the annealing process at a low annealing temperature, but the austenite single phase structure is not formed, Or elongation did not meet the desired level.

Further, in Comparative Example 3, the annealing temperature of the crack section exceeded the condition of the present invention, and the steel material, that is, the tensile strength or elongation, was less than the desired level by secondary recrystallization and the time taken to reach the annealing temperature was relatively long As the annealing temperature increases, the diffusion of Si, Mn or Al in the steel increases to the surface of the steel sheet, and Si, Mn or Al oxide is formed in the form of stripes at the interface between the steel sheet and the steel sheet. As a result, even after the heat treatment in the reducing atmosphere, the plating layer is detached by the Si, Mn, or Al oxide remaining on the interface between the plating layer and the steel sheet after the aluminum plating.

In the comparative example 4, the heating rate in the heating section does not meet the conditions of the present invention, resulting in a decrease in the productivity of the steel sheet in the actual operation line, and at the same time, the heating rate is low and the time taken to reach the target annealing temperature becomes long. As a result, the Si, Mn, and Al oxide layers formed on the surface of the steel sheet become thick, so that Si, Mn, and Al oxides remain in the form of strips at the interface between the plated layer and the steel sheet after aluminum plating even if the heat treatment is performed in a reducing atmosphere. Respectively.

In Comparative Example 5, since the annealing temperature in the crack region did not meet the conditions of the present invention and the annealing temperature was low, the surface enrichment of Si, Mn, and Al was not so severe as less annealed oxide was formed on the surface of the steel sheet. Had a coverage area ratio of 94% and good plating adhesion, but did not form austenite single phase structure and the yield strength or elongation of the steel did not satisfy the desired level.

Finally, in Comparative Example 6, since the dew point in the crack region exceeded the condition of the present invention, a thick Mn oxide in the form of a band was inevitably formed on the surface of the steel sheet, resulting in poor wettability of aluminum during aluminum plating. The coating area ratio of the aluminum plating layer was limited to 80% by the Mn oxide, thereby lowering the plating property.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims. It will be possible.

Claims (5)

The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 0.3 to 0.9% of C, 12 to 25% of Mn, 0.3 to 3.0% of Al, 0.6 to 2.5% of Si, 0.01 to 0.5% of Ti, 0.05 to 0.5% (Excluding 0%), B: 0.0005 to 0.005%, the balance Fe, and unavoidable impurities.
The method according to claim 1,
Mo: not more than 0.5% (not including 0%), Nb: not more than 0.05% (not including 0%), Sb: not more than 0.1% By weight or less, and 0% or less (not including 0%) and Sn: 0.1% or less (not including 0%) are further included. Further, the austenitic High Strength High Manganese Aluminum Plated Steel Sheet.
The method according to claim 1,
Austenitic high strength, high strength, high manganese aluminum coated steel sheet having a yield strength of not less than 700 MPa, and having a plating quality of not less than 30,000 MPa% of yield strength and elongation.
The method according to claim 1,
The austenitic high-strength high-manganese hot-dip coated aluminum-coated steel sheet excellent in plating quality, wherein the oxide formed on the plating layer and the base interface of the steel sheet is one or more of Si-based oxide, Mn-based oxide and Al-based oxide.
The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 0.3 to 0.9% of C, 12 to 25% of Mn, 0.3 to 3.0% of Al, 0.6 to 2.5% of Si, 0.01 to 0.5% of Ti, 0.05 to 0.5% (Excluding 0%), B: 0.0005 to 0.005%, the balance Fe, and unavoidable impurities;
Immersing the prepared hot-rolled steel sheet in a pickling bath, washing it after primary pickling, and drying it;
Cold-rolling the dried hot-rolled steel sheet;
Heating the steel sheet at a heating rate of 1.6 to 4.1 占 폚 / s in a reducing atmosphere controlled to a dew point of -30 占 폚 or less;
A cracking step of holding the heated steel sheet in a reducing atmosphere at 700 to 850 ° C;
Cooling the steel sheet after the cracking step;
Immersing the cooled steel sheet in a pickling bath, washing with water after secondary pickling, and drying;
Secondarily heating the dried steel sheet to an aluminum plating bath temperature or more; And
Forming an aluminum plating layer on the steel sheet; And a high-quality austenitic high-strength high-manganese-molten aluminum-plated steel sheet.