KR20160058289A - Galvanized steel having good spot weldabity and workability, and method for manufacturing the same - Google Patents

Abstract

The present invention relates to an alloying hot dip galvanizing steel plate with excellent machinability and excellent spot welding property, and a manufacturing method for the same. The alloying hot dip galvanizing steel plate comprises: a steel plate; and a Zn-Fe-Mn alloying layer formed on the steel plate. The steel plate comprises: 0.3-1 wt% of C; 8-25 wt% of Mn; 0.1-3 wt% of Si; 0.1-8 wt% of Al; 0.1-2 wt% of Cr; 0.01-0.2 wt% of Ti; 0.0005-0.01 wt% of B; 0.01-0.3 wt% of P; 0.0005-0.01 wt% of S; 0.06-2.0 wt% of Ni; 0.02-0.2 wt% of Sn; and remainder consisting of Fe and inevitable impurities. The Zn-Fe-Mn alloying layer comprises: 2 wt% or greater of Mn; 16-20 wt% of a content sum of Mn and Fe; and the remainder consisting of Zn.

Description

TECHNICAL FIELD [0001] The present invention relates to a galvannealed galvanized steel sheet having excellent workability and spot weldability, and a method of manufacturing the same. BACKGROUND ART < RTI ID = 0.0 >

The present invention relates to a galvanized steel sheet used as an automobile body and a structural member, and a method of manufacturing the same. More particularly, the present invention relates to an alloyed hot-dip galvanized steel sheet excellent in workability and spot weldability and a method of manufacturing the same.

The galvanized steel sheet is excellent in corrosion resistance, weldability and paintability, and is widely used as a steel sheet for automobiles. In addition, from the viewpoint of improving fuel efficiency by reducing the weight of automobiles and increasing the strength of automobile bodies and structural members from the viewpoint of passenger safety, various types of high strength steels for automobiles have been developed.

However, most steels or steels have low ductility as their strength increases, and as a result, a great deal of limitation is required in machining into parts. As a result, a steel material containing 5 to 35 wt% of manganese to induce twin in the plastic deformation of the steel material, resulting in high strength and ductility, An austenitic high manganese steel has been proposed. (Patent Documents 1 to 4)

In addition, there is a growing demand for corrosion resistance in order to use high manganese steel having high strength and high ductility as a steel sheet for automobiles. For example, when a high manganese steel hot-dip galvanized steel sheet is used as an automotive steel sheet, the parts are processed by press working and then assembled by spot welding or arc welding. In this case, The heat affected zone (HAZ) is dissolved by welding (heat) heat and remains as liquid molten zinc, and the base structure becomes high temperature relative to other steel species due to high resistance value of high manganese steel, and high The grain boundary expansion due to the thermal expansion coefficient 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 ").

This weld LME phenomenon is generally observed in hot-dip galvanized steel sheets of high-strength steels, but in particular, in the case of hot-dip galvanized steel sheets of high-strength steels, the steel has a high resistance strength and austenite structure to the surface of the steel plate. It has a high temperature and a high thermal expansion coefficient, which promotes cracking of the subsurface boundary, which makes it easy to penetrate the molten zinc into the grain boundary, thereby being susceptible to the occurrence of weld LME.

In order to prevent the LME of such high strength steel hot dip galvanized steel sheets, there are 1) a pre-pulse welding method in which a pre-pulse is applied and the welding is completed by welding current pulses higher than the preliminary current pulse [% Si] / 17 + [% Mn] /7.5 + [% Ni] / 17 + [% Si] in the high strength hot-dip galvanized steel sheet of 490 MPa or higher, (3) a high-strength hot-dip galvanized steel sheet having a hardness of 580 MPa or higher, wherein the hot-dip galvannealed steel sheet comprises 40% to 95% (Ti) having an average particle size of 3 nm to 200 nm and having an area fraction of 1% to 10% of residual austenite, one or two of ferrite phase, bainite phase, pearlite phase and martensite phase, ), Niobium (Nb), molybdenum (Mo), and zirconium (Zr) based precipitates or complex precipitates are dispersed. (Patent Document 7); 4) a method in which a high-melting-point zinc alloy plating layer is used instead of a pure zinc plating layer having a low melting point in a high manganese steel (Patent Document 8).

However, the conventional method 1) shows an effect in DP (Dual Phase) steel and TRIP (Transformation Induced Plasticity) steel in which the amount of heat input is small during spot welding compared to high manganese steel, but it has austenite structure even at room temperature, And high manganese steel showing high heat input. Conventional method 2) strengthened the austenite grain boundaries of weld heat affected zone by adjusting the content of boron (B) in DP steel or TRIP steel of 490 MPa or more, However, since manganese steel has austenite structure at room temperature and contains a large amount of manganese (Mn), a large amount of boron (B) must be added for strengthening the austenite grain boundary by boron (B) There is a problem. As a result, the addition amount of boron (B) exceeds 0.24, which is the LME sensitivity index, and the excess boron (B) additionally inhibits the plating ability by promoting LME and forming boron oxide (B2O5) not. On the other hand, in the conventional method 3), since the austenite phase formed by the welding is finely divided by the pearlite phase and the martensite phase of the second phase, the austenite phase becomes finer, which complicates the penetration path of the liquid molten zinc, It is possible to prevent the occurrence of welding LME at the time of welding, but it is difficult to improve the welding LME because the secondary phase can not be formed in a high manganese steel which is austenite single phase at all temperatures.

On the other hand, the conventional method 4) discloses a Zn-Ni plating system and a Zn-Fe plating system, which are low-melting point zinc-gold based alloys with a high melting point, and they contain alloy elements such as Ni and Fe, The melting point is increased. However, the amount of alloying elements capable of containing alloying elements in these alloying zinc-based alloys is limited depending on the process and the plating ability. In view of this, the Ni content in the Zn-Ni system is usually around 10 wt%, and the melting point is 490 캜, It is very difficult to prevent the LME crack because the maximum temperature of the welding shoulder portion where the plate LME cracks occurs is much lower than that of 800 DEG C or more. In addition, a suitable Fe content in which the plating layer is not peeled off in the form of powder during processing in the Zn-Fe plating system is 8 to 12%, and the melting point is 600 to 650 ° C to completely prevent the LME crack In order to prevent cracking of LME, the Fe content of the plating layer should be maintained at 12% or more so as to have a melting point of 665 ° C or more. Therefore, it is difficult to prevent powdering from occurring and also to prevent cracking of the LME.

Therefore, in the high manganese steel galvanized steel sheet, the occurrence of the liquid metal brittle crack in the weld heat affected zone during spot welding and the occurrence of the powder ring in which the plating layer is peeled off in the form of powder at the time of working can be prevented. The development of a method is required.

Japanese Patent Laid-Open No. 4-259325 International Publication No. WO93 / 013233 International Publication No. WO99 / 001585 International Publication No. WO02 / 101109 Korea Patent Publication No. 2012-0017955 Japanese Patent Application Laid-Open No. 2006-249521 Japanese Patent Application Laid-Open No. 2006-265671 Korean Application No. 2013-0151804

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a Mn-containing alloyed layer having a high melting point and excellent workability by heating a high manganese steel galvanized steel sheet at a low temperature for a long time, The present invention also provides an alloyed hot-dip galvanized steel sheet excellent in workability and spot weldability that prevents occurrence of powdering while preventing the occurrence of powdering, and a method for producing the same.

The alloyed hot-dip galvanized steel sheet excellent in workability and spot weldability according to one aspect of the present invention is characterized by containing 0.3 to 1% of C, 8 to 25% of Mn, 0.1 to 3% of Si, 0.1 to 8% of Al, The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 0.1 to 2% of Cr, 0.01 to 0.2% of Ti, 0.0005 to 0.01% of B, 0.01 to 0.3% of P, 0.0005 to 0.01% of S, 0.06 to 2.0% A balance steel Fe and other unavoidable impurities; And a Zn-Fe-Mn alloyed layer formed on the base steel sheet, wherein the Zn-Fe-Mn alloyed layer contains Mn in an amount of 2% or more and Mn and Fe in a total amount of 16 to 20 %, And the balance Zn.

The method for producing a galvannealed steel sheet excellent in workability and spot weldability according to another aspect of the present invention is characterized in that it comprises 0.3 to 1% of C, 8 to 25% of Mn, 0.1 to 3% of Si, 0.1 to 3% of Si, 0.1 to 8% of Cr, 0.1 to 2% of Cr, 0.01 to 0.2% of Ti, 0.0005 to 0.01% of B, 0.01 to 0.3% of P, 0.0005 to 0.01% of S, 0.06 to 2.0% of Ni, Sn : 0.02 to 0.2%, the balance Fe and other unavoidable impurities; Forming a galvanized layer on the base steel sheet to produce a hot-dip galvanized steel sheet; And heating the hot-dip galvanized steel sheet at 400 to 450 ° C. for 6 to 24 hours to form a Zn-Fe-Mn alloyed layer.

According to the present invention, a hot-dip galvanized steel sheet having a high manganese steel as a base steel sheet is heated at a low temperature for a long time to form a zinc-plated layer into a Zn-Fe-Mn system without further processing such as addition of alloying elements or pre- It is possible to provide an alloyed hot-dip galvanized steel sheet excellent in workability and spot weldability in which generation of powdered rings in which the plating layer is peeled off in the form of powder at the time of processing is suppressed, .

FIG. 1 is a graph showing the temperature distribution of hot-dip galvanized steel sheets during spot welding.
2 is a Zn-Mn binary phase diagram showing the temperature region of the shoulder portion during spot welding.

Hereinafter, preferred embodiments of the present invention will be described. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. Embodiments of the present invention are also provided to more fully describe the present invention to those skilled in the art.

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.

The inventors of the present invention have studied the change of the plating layer during welding in order to develop a technique for preventing the occurrence of welding LME at the time of welding. As a result, it was found that the liquid phase formed by dissolving the plating layer of the welding shoulder portion at the time of welding infiltrated into the grain boundary of the base steel sheet, resulting in welding LME cracking. As shown in Fig. 2, it refers to the tap portion of the dome-shaped welding electrode. Since the cooling water does not flow to the inside of the shoulder portion, the LME is mainly generated because the temperature is higher than the other portions.

More specifically, the temperature of the welding shoulder portion during welding, particularly spot welding, rapidly increases from 641 to 846 ° C, as seen in FIG. 1, whereas the zinc plating layer starts to melt at about 420 ° C to become a liquid phase, As the temperature further increases, the galvanized layer is melted and the fluidity of the formed liquid rapidly increases. As a result, the welded LME cracks occur due to penetration into the grain boundaries of the base steel sheet.

In order to prevent welding LME occurrence of high manganese steel hot dip galvanized steel sheets, the melting point of the plating layer should be at least 641 ° C, which is the minimum temperature of the weld shoulder portion of Fig.

2, the melting point of the plating layer is required to be 665 DEG C or higher, which is higher than the minimum temperature of the shoulder portion. At this time, the plating layer is formed of Zn-Fe (Capital Gamma) of? Alloyed layer and liquid zinc (L), and the Fe content of the plated layer is required to be 12% or more.

That is, in the case of the Zn-Fe alloy layer, when the Fe content of the plating layer is 12% or more, the melting point of the plating layer increases to 665 DEG C, The temperature of the shoulder portion is not dissolved up to 665 DEG C and diffusion of Fe occurs from the intermediate steel sheet kept in the solid phase so that the plating layer is further alloyed and the melting point of the plating layer is greatly increased. It is possible to prevent the point welding LME caused by the welding.

However, welding LME cracks in high-Mn hot-dip galvanized steel sheets can prevent welding LME cracks in high-Mn hot-dip galvanized steel sheets by containing more than 12% of Fe in the Zn-Fe alloy layer. When the Fe content is more than 12%, a brittle Γ phase is formed, so that a powder ring in which the plating layer is peeled off in the form of a powder during the part processing is generated and the corrosion resistance is deteriorated.

Accordingly, the inventors of the present invention have conducted research on a method for suppressing all of the occurrence of powder ring during welding and LME of welding, and as a result, it has been found that the high manganese steel is continuously heated after hot dip galvanizing, Instead of continuous galvannealed galvanized steel sheet manufacturing process which takes place within a short time, high-manganese steel is processed into hot-rolled galvanized steel sheet or parts and then heated at low temperature for a long time to alloy, It has been found that formation of the Fe-Mn based alloying layer can suppress both generation of powder LME and powdering during processing, and the present invention has been completed.

The alloyed hot-dip galvanized steel sheet excellent in workability and spot weldability according to one aspect of the present invention comprises 0.3 to 1% of C, 8 to 25% of Mn, 0.1 to 3% of Si, 0.1 to 8% of Al, 0.1 to 2% of Cr, 0.01 to 0.2% of Ti, 0.0005 to 0.01% of B, 0.01 to 0.3% of P, 0.0005 to 0.01% of S, 0.06 to 2.0% of Ni, 0.02 to 0.2% of Sn, , The balance Fe and other unavoidable impurities; And a Zn-Fe-Mn alloyed layer formed on the base steel sheet, wherein the Zn-Fe-Mn alloyed layer contains Mn in an amount of 2% or more and Mn and Fe in a total amount of 16 to 20 %, And the balance Zn.

As described above, the Zn-Fe-Mn alloyed layer containing Mn in an amount of 2% or more, the sum of contents of Mn and Fe in the range of 16 to 20%, and the remainder Zn has a sufficiently high melting point, have.

Further, since the Zn-Fe-Mn alloyed layer is dispersed in the Zn-Fe-Mn alloyed layer in comparison with the Zn-Fe alloyed layer in which Mn is not contained or contained in a very small amount and a brittle Γ phase is dominant, So that the powdering phenomenon in which the plating layer is peeled off in the form of powder at the time of processing does not occur.

Preferably, the content of Mn in the Zn-Fe-Mn alloyed layer is 2 to 6% by weight and the content of Fe is 10 to 18% by weight, but the present invention is not limited thereto.

Hereinafter, a method for producing an alloyed hot-dip galvanized steel sheet excellent in workability and spot weldability, which is another aspect of the present invention, will be described.

The method for producing a galvannealed steel sheet excellent in workability and spot weldability according to another aspect of the present invention is characterized in that it comprises 0.3 to 1% of C, 8 to 25% of Mn, 0.1 to 3% of Si, 0.1 to 3% of Si, 0.1 to 8% of Cr, 0.1 to 2% of Cr, 0.01 to 0.2% of Ti, 0.0005 to 0.01% of B, 0.01 to 0.3% of P, 0.0005 to 0.01% of S, 0.06 to 2.0% of Ni, Sn : 0.02 to 0.2%, the balance Fe and other unavoidable impurities; Forming a galvanized layer on the base steel sheet to produce a hot-dip galvanized steel sheet; And heating the hot-dip galvanized steel sheet at 400 to 450 ° C. for 6 to 24 hours to form a Zn-Fe-Mn alloyed layer.

According to an aspect of the present invention, the step of forming the galvannealed steel sheet may include the step of forming the galvannealed steel sheet before the step of forming the alloying layer.

Steps to prepare the base steel

The base steel sheet used in the present invention is preferably high manganese steel containing 8-25 wt% of Mn in high strength steel, but is not limited thereto.

More specifically, for example, the base steel sheet may contain 0.3 to 1% of C, 8 to 25% of Mn, 0.1 to 3% of Si, 0.1 to 8% of Al, 0.1 to 2% of Cr, 0.01 to 0.2% of Ti, 0.0005 to 0.01% of B, 0.01 to 0.3% of P, 0.0005 to 0.01% of S, 0.06 to 2.0% of Ni and 0.02 to 0.2% of Sn and the balance Fe and other unavoidable impurities Lt; / RTI >

Step of producing a hot-dip galvanized steel sheet

The base steel sheet is immersed in a zinc plating bath by a conventional method for producing a hot-dip galvanized steel sheet to prepare a hot-dip galvanized steel sheet.

More specifically, for example, a galvanized steel sheet having a plating bath temperature of 460 to 500 ° C is immersed for 3 to 5 seconds to prepare a hot-dip galvanized steel sheet by adjusting with an air knife such that the coating amount of one surface is 45 to 90 g / can do.

Step of molding the hot-dip galvanized steel sheet

Generally, in the method of producing a galvannealed steel sheet, a step of continuously forming an alloying layer is performed after hot dip galvanizing, but in the present invention, the step of forming an alloying layer may be performed discontinuously, A step of molding a hot-dip galvanized steel sheet may be selectively added before the step.

Zn - Fe - Mn system Alloying layer  Forming step

After hot-manganese steel is hot-dip galvanized or hot-manganese steel is hot-dip galvanized, it is molded into parts and then heated at 400 to 450 ° C for 6 to 24 hours to form a Zn-Fe-Mn alloyed layer.

According to a general method for producing a galvannealed steel sheet, after the hot-dip galvanizing process, the coating layer is continuously heated at a temperature of 500 ° C or higher for a short time within 20 seconds, so that the amount of Fe is quantitatively large, Since the diffusion amount of Mn is only a small amount, the plating layer forms a Zn-Fe alloyed layer. In order to prevent spot weld LME cracks from occurring in such a Zn-Fe alloyed layer, it is required to form an alloyed layer containing at least 12% of Fe. In this case, the Zn-Fe alloyed phase in which a brittle Γ- There is a problem that powdering occurs in which the plating layer is peeled off in the form of powder during processing.

In contrast, in the present invention, by heating for 6 to 24 hours at 400 to 450 ° C, which is a low temperature before and after the melting point of zinc, the diffusion amount of Fe is reduced unlike the case where the heating is performed at a temperature higher than 500 ° C., . Therefore, the Mn content of the plated layer is increased, and the plated layer is formed of a Zn-Fe-Mn based alloying layer. The Zn-Fe-Mn based alloying layer has improved ductility of the plating layer compared to the Zn-Fe based alloying layer in which the Mn is not contained or is contained in a very small amount and the brittle Γ phase is dominant, so that the plating layer is peeled off in powder form .

When the heating temperature is lower than 400 ° C, the plating layer is difficult to be alloyed. When the heating temperature is higher than 450 ° C, the plating layer is reused by heating at a temperature higher than the melting point of zinc to inhibit surface appearance after alloying. It is undesirable because the content becomes excessive and powdering occurs during processing. Therefore, the heating temperature is preferably 400 to 450 DEG C

When the heating time is less than 6 hours, the plating layer is not sufficiently alloyed, and when heating is performed for 24 hours or more, alloying is excessively advanced, so that the heating time is preferably 6 to 24 hours.

Since the alloyed hot-dip galvanized steel sheet of the present invention contains a large amount of Mn in the alloying layer by heating at a low temperature for a long time, powdering does not occur during processing even when the Fe content of the alloyed layer is 12% or more. That is, in the present invention, the total alloying degree (Fe + Mn,%) of alloy elements including not only the Fe content of the plating layer but also the Mn content is maintained at 16% or more, It was possible to prevent both.

Therefore, in the present invention, a hot-dip galvanized steel sheet having a high manganese steel as a plating material is heated at a low temperature of 400 to 450 DEG C for 6 to 24 hours so that the zinc plating layer has a Mn content of 2% or more and a total alloying degree of Fe and Mn (Fe + Mn,%) of 16 to 20% so that the entire plating layer becomes a Zn-Fe-Mn alloyed layer.

Preferably, the content of Mn in the Zn-Fe-Mn alloyed layer is 2 to 6% by weight and the content of Fe is 10 to 18% by weight, but the present invention is not limited thereto.

In the present invention, the welding method capable of improving the weldability may be spot welding, but the present invention is not limited thereto. Even in welding such as arc welding, laser welding, etc. widely known in the related art, Welded LME cracks are generated in the heat affected zone, so that the application of the present invention can also obtain the effect of preventing welding LME cracks.

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 )

The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 0.55% of C, 15% of Mn, 0.6% of Si, 2% of Al, 0.1% of Cr, 0.1% of Ti, 0.001% of B, 0.017% : 0.3%, Sn: 0.03%, and the balance Fe and other unavoidable impurities. The slab was homogenized at a slab reheating temperature of 1150 DEG C, and descaled to a finish rolling temperature of 1080 DEG C and hot-rolled at a finish hot temperature of 900 DEG C to produce a hot-rolled steel sheet having a thickness of 2.4 mm.

The hot-rolled steel sheet was wound at a coiling temperature of 450 ° C. Further, in order to remove the scale of the hot rolled steel sheet after hot rolling, the hot rolled steel sheet was immersed in an aqueous hydrochloric acid solution to be pickled. The concentration of the hydrochloric acid aqueous solution was 13%, the pickling temperature was 80 ° C, and pickling was carried out for 50 seconds. After the pickling process, it was cold-rolled at a reduction ratio of 50% to obtain a cold-rolled steel sheet having a thickness of 1.2 mm.

The cold-rolled steel sheet was subjected to a heat treatment at an annealing temperature of 750 占 폚 for 40 seconds under a reducing atmosphere of 5 vol% of hydrogen and the balance of nitrogen at a dew point temperature of -40 占 폚, and the plated material was cooled to 480 占 폚.

Subsequently, the steel sheet was immersed in a galvanizing bath having a plating bath Al concentration of 0.13% and a plating bath temperature of 460 DEG C for 3 to 5 seconds to adjust the coating amount of one surface to 45 g / m < 2 & .

The hot-dip galvanized steel sheet was subjected to alloying treatment by heating in an inert atmosphere at a heating temperature of 300 to 520 DEG C shown in Table 1 below for a heating time of 20 seconds to 48 hours to produce an alloyed hot-dip galvanized steel sheet.

The degree of alloying and resistance to powdering were measured on the steel sheet thus prepared, and the results are shown in Table 1 below.

In this case, the degree of alloying is obtained by dissolving the plated layer with a dilute acid solution, quantitatively analyzing the content of Fe and Mn by ICP, and the powdering property is evaluated by measuring the content of the alloying layer coating on the tape attached to the inner- The width (width) is evaluated based on the following criteria.

-1 Class: No peeling

-2 grade: When the peeling width is 2 mm or less

-3 grade: When the peeling width is 2 to 5 mm

-4 grade: When the peeling width is 5 ~ 10mm

Class-5: When the peeling width is 10 mm or more

Two-ply welding was carried out in which two identical materials were overlapped and welded by using the galvannealed galvanized steel sheets prepared in Examples 1 to 6 and Comparative Examples 1 to 5 in the following [Table 1]. As the welding method, pre - pulse welding was performed, and the current was a direct current. The electrode component was a Cu-Cr alloy, and the dome diameter was 6 mm. The pre-pulse was performed for 11 cycles at a welding current of 5.5 kA, and after one cycle of cooling, about 12 cycles for 2 pulses. At this time, the pressing force was 3.6 KN.

The degree of alloying and the spot weld crack length after the spot welding were measured, and the results are shown in Table 1 below.

In this case, the weld LME crack depth at the spot weld is measured by the length of the crack propagated from the surface of the shoulder portion, which is the spot welded heat affected portion, to the inside of the substrate by observing a cross section of the nugget portion with an optical microscope.

The degree of alloying after the spot welding was analyzed quantitatively of Fe and Mn contents by EDS (Energy Dispersive Spectrometer) point analysis on the center portion of the cross section of the nugget portion.

The spot welding LME evaluation standard of the galvannealed steel sheet of the present invention was evaluated by whether welding LME crack occurred or not.

division Alloying condition Alloying degree My powdering castle After spot welding
Alloying degree
(Fe + Mn) (%) Spot welding
Crack depth
(탆) Alloying
Temperature
(° C) Alloying
time
(city) Fe (%) Mn (%) Fe + Mn
(%) Good 1 <-> 5 Poor Example 1 400 6 10.57 5.52 16.09 2 20.41 0 Example 2 400 12 12.46 4.71 17.17 2 21.2 0 Example 3 400 24 12.67 3.53 16.20 2 20.53 0 Example 4 450 6 12.55 2.91 15.46 3 22.47 0 Example 5 450 12 14.92 2.41 17.33 3 21.61 0 Example 6 450 24 17.5 2.16 19.66 3 27.52 0 Comparative Example 1 520 20 seconds 12 0.05 12.05 5 19 0 Comparative Example 2 300 48 2.27 0 2.27 One 4.4 150 Comparative Example 3 350 24 2.36 0 2.36 One 7.3 120 Comparative Example 4 500 6 22.27 2.34 24.61 5 32.68 0 Comparative Example 5 500 3 20.41 2.67 23.08 5 31.2 0

As can be seen from Table 1, Examples 1 to 6 show that the whole hot-dip galvanized galvanized steel sheet is subjected to a heat treatment at an alloying temperature of 400 to 450 ° C for 6 to 24 hours to form an Fe-Zn-Mn alloyed layer as a whole , And the degree of alloying (Fe + Mn,%) was 16 to 20%. In addition, the content of Mn was 2% or more, so that the powdering resistance was excellent, and the alloying of the shoulder portion of the special plate was further advanced, and welding LME crack did not occur.

As in Comparative Examples 2 and 3, when the alloying temperature was less than 400 ° C, the plating layer was hardly alloyed even after a long period of time, and when the degree of alloying was 3% or less, the plating layer was dissolved and liquidified, .

In the case of alloying treatment at an alloying temperature of 500 ° C or higher as in Comparative Examples 4 and 5, the plating layer is re-dissolved by heating at a temperature equal to or higher than the melting point of zinc to inhibit surface appearance after alloying, It is understood that when the content is 20% or more, powdering occurs during processing.

Also, as in Comparative Example 1, when the high-manganese steel is produced by a conventional method of producing a galvannealed steel sheet by alloying at 520 ° C for 20 seconds in the process of hot-dip galvanizing and then solidifying the plating layer, the Fe content of the plated layer is 12.05 %, LME cracking did not occur, but powdering occurred during processing due to formation of brittle plating layer structure.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the scope of the present invention is not limited to the disclosed exemplary embodiments, but various modifications and changes may be made without departing from the scope of the invention. To those of ordinary skill in the art.

Claims (6)

0.1 to 3% of Al, 0.1 to 2% of Cr, 0.01 to 0.2% of Cr, 0.01 to 0.2% of Ti, 0.0005 to 5% of B, 0.01 to 0.3% of P, 0.0005 to 0.01% of S, 0.06 to 2.0% of Ni, 0.02 to 0.2% of Sn, balance Fe and other unavoidable impurities. And
A Zn-Fe-Mn-based alloying layer formed on the base steel sheet,
The Zn-Fe-Mn based alloying layer contains, by weight%, Mn: not less than 2%, sum of Mn and Fe: 16 to 20%, and the balance Zn, .
The galvannealed steel sheet according to claim 1, wherein the content of Mn in the Zn-Fe-Mn alloyed layer is 2 to 6% by weight and the content of Fe is 10 to 18% by weight.
0.1 to 3% of Al, 0.1 to 2% of Cr, 0.01 to 0.2% of Cr, 0.01 to 0.2% of Ti, 0.0005 to 5% of B, 0.01 to 0.3% of P, 0.0005 to 0.01% of S, 0.06 to 2.0% of Ni, 0.02 to 0.2% of Sn, balance Fe and other unavoidable impurities.
Forming a galvanized layer on the base steel sheet to produce a hot-dip galvanized steel sheet; And
And heating the hot-dip galvanized steel sheet at 400 to 450 ° C for 6 to 24 hours to form a Zn-Fe-Mn-based alloyed layer.
The method for producing an alloyed hot-dip galvanized steel sheet according to claim 3, comprising the step of forming a hot-dip galvanized steel sheet before the step of forming an alloying layer.
4. The method according to claim 3, wherein the Zn-Fe-Mn alloyed layer contains, by weight%, at least 2% of Mn, at least one of Mn and Fe in an amount of 16 to 20% A method for producing a galvannealed steel sheet with excellent alloying.
6. The method of manufacturing a galvannealed steel sheet according to claim 5, wherein the content of Mn in the Zn-Fe-Mn alloyed layer is 2 to 6 wt% and the content of Fe is 10 to 18 wt% Way.

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