KR20150073013A - Austenitic galvanized steel sheet having excellent high-temperature formability of welding point and method for manufacturing the same - Google Patents
Austenitic galvanized steel sheet having excellent high-temperature formability of welding point and method for manufacturing the same Download PDFInfo
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- KR20150073013A KR20150073013A KR1020130160796A KR20130160796A KR20150073013A KR 20150073013 A KR20150073013 A KR 20150073013A KR 1020130160796 A KR1020130160796 A KR 1020130160796A KR 20130160796 A KR20130160796 A KR 20130160796A KR 20150073013 A KR20150073013 A KR 20150073013A
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- C—CHEMISTRY; METALLURGY
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
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- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D3/00—Electroplating: Baths therefor
- C25D3/02—Electroplating: Baths therefor from solutions
- C25D3/22—Electroplating: Baths therefor from solutions of zinc
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/001—Austenite
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Abstract
Description
The present invention relates to an austenitic galvanized steel sheet used as a material of a medium for storing hydrogen or LNG, and more particularly to an austenitic galvanized steel sheet excellent in high temperature formability and a method for producing the same.
The prices of kerosene and gasoline, which are obtained by refining oil because of depletion of petroleum resources, are rising rapidly. Recently, researches on utilization of alternative energy other than existing coal energy have been continuously carried out.
Hydrogen is a representative alternative energy resource. It can not only use a large amount of energy released when it reacts with oxygen as a power source for automobiles, but also does not cause pollution.
As a storage medium for storing hydrogen, polymer or ferritic steel material is mainly used. However, hydrogen having a small atomic diameter is easily permeated through these storage media to increase the risk of explosion.
On the other hand, the austenitic high manganese steel has a slow diffusion rate of hydrogen in the steel material and a high solubility of hydrogen, which is suitable as a material for a hydrogen storage vessel.
Further, when the hydrogen storage medium is applied as a fuel means of an automobile, it is appropriate to use an austenitic high-manganese steel as a material thereof in order to guarantee corrosion resistance.
However, when the austenitic-type coated steel sheet is used, the problem of liquid metal embrittlement (LME) due to melting of the plating layer at the forming temperature is required have. This is a major cause of the fracture of the plated steel sheet, and thus it is difficult to design a free part that meets a desired design.
Liquid metal embrittlement (LME) is a phenomenon in which a ductile material is brought into contact with a liquid metal, and in the presence of tensile stress, the liquid metal rapidly penetrates along the grain boundaries of the base material and causes brittleness.
Thus, there is a need to develop an austenitic-plated steel sheet having mechanical properties suitable as a hydrogen storage medium without causing brittleness of a liquid metal at the time of forming a plated steel sheet at a high temperature.
An aspect of the present invention is to provide an austenitic-plated steel sheet which is excellent in resistance to embrittlement of a liquid metal during high-temperature molding and has no cracks or the like, and is excellent in high temperature moldability and a method of manufacturing the same.
An aspect of the present invention is a steel sheet comprising a base steel sheet and a plated layer formed on the base steel sheet, wherein an elongation ratio expressed by the following relational expression 1 is 80%
The base steel sheet comprises 0.4 to 0.8% by weight of carbon, 12 to 20% of manganese (Mn), 1.0 to 3.0% of aluminum (Al), 0.01 to 0.5% of silicon (Si) (P): 0.03% or less (excluding 0), sulfur (S): 0.03% or less (excluding 0), nitrogen (N) : Excellent in high-temperature formability including one or two of 0.04% or less (excluding 0), 0.001 to 0.5% of niobium (Nb) and 0.001 to 0.5% of vanadium (V), the remainder Fe and unavoidable impurities An austenitic zinc-plated steel sheet.
[Relation 1]
Elongation ratio (%) = (high temperature elongation / room temperature elongation) x 100
(Here, the high temperature elongation means elongation at 700 to 900 DEG C, and the room temperature elongation means elongation at 10 to 35 DEG C.)
According to another aspect of the present invention, there is provided a method for manufacturing a steel slab, comprising the steps of: reheating a steel slab satisfying the above-described compositional composition to a temperature in the range of 1050 to 1250 占 폚; Finishing the reheated steel slab at 800 to 1000 占 폚 to produce a hot-rolled steel sheet; Winding the hot-rolled steel sheet at 700 ° C or lower; Cold rolling the wound hot rolled steel sheet at a cold rolling reduction rate of 20 to 70% to produce a cold rolled steel sheet; Continuously annealing the cold-rolled steel sheet at 650 to 900 ° C; And a step of plating the cooled cold-rolled steel sheet to obtain a high-temperature formability-improving austenitic zinc-plated steel sheet.
According to the present invention, it is possible to provide an austenitic galvanized steel sheet which is excellent in resistance to embrittlement of a liquid metal and can suppress the occurrence of cracks during high temperature molding. Further, the austenitic zinc-plated steel sheet of the present invention is advantageously applicable as a material of a storage medium such as hydrogen and LNG.
1 is a photograph of a specimen after a tensile test (800 ° C) of Comparative Steel 3 and Inventive Steel 3, wherein (a) is a comparative steel 3, and (b) is Inventive Steel 3.
The present inventors have found that austenite can be obtained by microstructure of steel at room temperature by adding a large amount of manganese and carbon in a conventional high manganese steel. However, when plating is performed to form a galvanized steel sheet at a high temperature, (LME) due to melting, it is difficult to secure an elongation rate, so that the moldability is poor. As a result, it is possible to provide an austenitic galvanized steel sheet excellent in high-temperature formability, capable of securing resistance to embrittlement of a liquid metal when the concentration of deformation is dispersed by finely grinding the crystal grains by controlling the component composition contained in the steel And have completed the present invention.
Particularly, the present invention is characterized in that mechanical properties, particularly high temperature elongation, can be ensured even at a high temperature because of securing resistance against brittleness of a liquid metal at high temperature.
Hereinafter, the present invention will be described in detail.
A galvanized steel sheet excellent in high-temperature moldability according to one aspect of the present invention comprises a base steel sheet and a plated layer formed on the base steel sheet, wherein the base steel sheet contains 0.4 to 0.8% of carbon (C), manganese Mn: 0.01 to 0.5%, Cr: 0.05 to 1.0%, Sn: 0.01 to 0.1%, phosphorus (Mn): 12 to 20% P: not more than 0.03% (excluding 0), sulfur (S): not more than 0.03% (excluding 0), nitrogen (N): not more than 0.04% (excluding 0), the balance Fe and unavoidable impurities, It is preferable to have an austenite single phase structure as the structure.
In addition, the base steel sheet includes one or two selected typical precipitate elements, namely, Nb and V, in order to miniaturize the austenite grain size and promote precipitation strengthening. At this time, the austenite grain size preferably satisfies 4 탆 or less. If the crystal grain size exceeds 4 mu m, the resistance against the embrittlement of the liquid metal by the grain boundary dispersion of the stress can not be sufficiently improved and the high-temperature moldability intended in the present invention can not be secured. More preferably 1 to 4 占 퐉, and even more preferably 2 to 3 占 퐉 is advantageous for improving the resistance.
In fact, according to the present invention, it can be seen that the average grain size of the austenite is about 2 탆 (see Table 2 of the embodiment).
Hereinafter, the reasons for restricting the composition of the alloy component in the present invention will be described in detail. Here, the content of each component means weight% unless otherwise specified.
C: 0.4 to 0.8%
Carbon (C) is an element contributing to the stabilization of the austenite phase, and as the content thereof increases, there is a favorable aspect to secure an austenite phase.
When the content of C is less than 0.4%, α '(alpha re-) martensite phase is formed on the surface layer due to decarburization at the time of high-temperature processing of the steel sheet, which is liable to delayed fracture. On the other hand, There is a problem that coarse carbides are formed at the grain boundaries in high-temperature molding and the moldability is deteriorated. Therefore, the content of C in the present invention is preferably limited to 0.4 to 0.8%.
Mn: 12 to 20%
Manganese (Mn) is an element stabilizing the austenite phase together with carbon. When the content is less than 12%, it is difficult to secure a stable austenite phase due to formation of α '(alpha re-) martensite phase during deformation, , Oxide defects are caused on the surface of the steel sheet, and the production cost is increased. Therefore, in the present invention, the content of Mn is preferably limited to 12 to 20%.
Al: 1.0 to 3.0%
Aluminum (Al) is usually added for deoxidation of steel, but in the present invention it enhances the ductility and resistance to delayed fracture of steel by inhibiting the formation of ε (Epsilon) -martensite phase by increasing the stacking fault energy.
If the content of Al is less than 1.0%, there is a problem that the elongation rate is lowered due to the rapid work hardening phenomenon and the delayed fracture characteristic is inferior. On the other hand, when the content exceeds 3.0%, nitride is formed Which causes deterioration of the moldability and damping of the main composition and oxidation of the steel surface during hot rolling causes a problem of deteriorating the surface quality of the product. Therefore, in the present invention, the content of Al is preferably limited to 1.0 to 3.0%.
Si: 0.01 to 0.5%
Silicon (Si) is usually used as a deoxidizing agent for steel, like aluminum, and does not significantly affect the stacking defect energy. Such Si is contained in an amount of about 0.01% in the steelmaking process, and there is a problem that an excessive cost is incurred when the Si is to be removed. If the content of Si exceeds 0.5%, a large amount of silicon oxide is formed on the surface during hot rolling, which deteriorates acidity and lowers the surface quality of the coated steel sheet. Therefore, the content of Si in the present invention is preferably limited to 0.01 to 0.5%.
Cr (Cr): 0.05 to 1.0%
Chromium (Cr) is an element effective for improving the plating characteristics and increasing the strength of steel. In order to obtain such an effect, it is preferable to add Cr at a content of 0.05% or more. However, when the content exceeds 1.0%, chromium carbide is formed to deteriorate the delayed fracture characteristics, and the production cost is increased, which is not preferable. Therefore, the content of Cr in the present invention is preferably limited to 0.05 to 1.0%.
Tin (Sn): 0.01 to 0.1%
Tin (Sn) is an element which, together with Cr, improves the plating property and improves the strength of steel. In order to obtain such an effect, it is preferable to add at least 0.01%, but if the content is too much and exceeds 0.1%, the manufacturing cost sharply increases, which is not preferable. Therefore, the content of Sn in the present invention is preferably limited to 0.01 to 0.1%.
Phosphorus (P): 0.03% or less (excluding 0)
Phosphorus (P) is an element which is inevitably contained in the production of steel, and it is preferable to control it as low as possible because it reduces the workability of steel by segregation and deteriorates quality such as cracking of performance, and theoretically limits the content of P to 0% However, it is inevitably added to the manufacturing process inevitably. Therefore, it is important to manage the upper limit, and in the present invention, it is preferable to be limited to 0.03% or less.
Sulfur (S): 0.03% or less (excluding 0)
Sulfur (S) is an element which is inevitably contained in the production of steel and forms a coarse manganese sulfide (MnS), which can cause defects such as flange cracks and reduce the hole expandability of the steel sheet, . In theory, it is possible to limit the content of S to 0%, but it is inevitably added inevitably to the manufacturing process. Therefore, it is important to manage the upper limit, and in the present invention, it is preferable to be limited to 0.03% or less.
Nitrogen (N): 0.04% or less (excluding 0)
It reacts with Al during the solidification process in the nitrogen (N) austenite crystal grains to precipitate fine nitrides to promote the generation of twin, thereby improving the strength and ductility of the steel sheet during molding. However, when the content exceeds 0.04%, excessive nitrides are precipitated and the hot workability and elongation can be lowered. Therefore, in the present invention, the content of N is preferably limited to 0.04% or less.
As described above, the present invention can improve the effect of precipitation strengthening by a fine carbide by including one or two kinds of V and Nb.
V: 0.001 to 0.5%
Vanadium (V) is an element which forms carbonitride by bonding with carbon and nitrogen. In particular, vanadium (V) is an important element for making crystal grains finer because it forms a fine precipitate phase at a low temperature. If the content of V is less than 0.001%, the above effect can not be sufficiently obtained. On the other hand, if the content exceeds 0.5%, coarse precipitates are formed at high temperature to deteriorate hot workability and reduce grain refinement effect. Therefore, the content of V in the present invention is preferably limited to 0.001 to 0.5%.
Nb: 0.001 to 0.5%
Niobium (Nb) is an element which forms a carbonitride like V and is also an element favorable for grain refinement. If the content of Nb is less than 0.001%, the above effect can not be sufficiently obtained. On the other hand, if the content exceeds 0.5%, coarse precipitates are formed at high temperature to cause casting cracks. Therefore, the content of Nb in the present invention is preferably limited to 0.001 to 0.5%.
The remainder of the present invention is iron (Fe). However, in the ordinary steel manufacturing process, impurities which are not intended from the raw material or the surrounding environment may be inevitably incorporated, so that it can not be excluded. These impurities are not specifically mentioned in this specification, as they are known to any person skilled in the art of steel making.
Hereinafter, a method for producing the galvanized steel sheet provided by the present invention will be described in detail as a preferable example.
The galvanized steel sheet of the present invention can be produced by a reheating-hot rolling-winding-cold rolling-continuous annealing-plating process of a steel slab satisfying the composition of the composition proposed in the present invention, Will be described in detail.
Steel slab reheating
In the present invention, it is preferable to carry out a step of reheating the steel slab and homogenizing the steel slab before performing the hot rolling. More specifically, it is preferable to reheat the steel slab to a temperature in the range of 1050 to 1250 ° C.
If the reheating temperature exceeds 1250 DEG C, crystal grain size increases and surface oxidation tends to occur to decrease the strength or to dislocate the surface, which is not preferable. In addition, since the liquid phase film is formed on the columnar phase boundary of the performance slab, there is a fear that cracks may occur during the subsequent hot rolling. On the other hand, when the reheating temperature is less than 1050 DEG C, it is difficult to secure the finishing rolling temperature at the time of hot rolling, and the rolling load due to the temperature decrease increases, so that it is difficult to sufficiently roll to a predetermined thickness. Therefore, in the present invention, the reheating step is preferably performed at a temperature in the range of 1050 to 1250 ° C.
Hot rolling
The reheated steel slab is preferably hot-rolled to produce a hot-rolled steel sheet. At this time, the finish rolling is preferably performed at 800 to 1000 占 폚.
If the rolling temperature is less than 800 DEG C during the finish rolling, there is a problem that the rolling load becomes high and the rolling mill becomes difficult and adversely affects the quality of the inside of the steel sheet. On the other hand, if the finish rolling degree is higher than 1000 캜, excessively high temperature may cause surface oxidation during rolling. Therefore, in the present invention, the finish rolling temperature during hot rolling is preferably limited to 800 to 1000 占 폚, more preferably 950 to 1000 占 폚.
Coiling
The hot-rolled steel sheet produced in the above-described manner is wound, and the coiling temperature is preferably 700 ° C or lower.
If the coiling temperature is too high at the time of coiling, a thick oxide film and internal oxidation are generated on the surface of the hot-rolled steel sheet, which makes it difficult to control the oxide layer during the pickling process. Therefore, the winding step is preferably carried out at 700 DEG C or lower.
Since the steel material of the present invention maintains the austenite single phase even at room temperature, the material of the hot-rolled steel sheet does not change according to the coiling temperature. However, if the coiling temperature is less than 300 캜, separate cooling by cooling water injection is required to reduce the temperature of the steel sheet, which causes a problem of causing an unnecessary increase in the process ratio. Therefore, it is more preferable to carry out the winding in the temperature range of 300 to 700 ° C.
Cold rolling
It is preferable that the rolled steel sheet is pickled to remove the oxide layer and then subjected to cold rolling in order to match the shape and thickness of the steel sheet to produce a cold rolled steel sheet. At this time, it is preferable that the cold rolling is performed at a cold reduction ratio of 20 to 70%.
If the cold rolling reduction rate in the cold rolling is less than 20%, it is difficult to secure a desired thickness and difficult to shape the steel sheet. On the other hand, when the cold rolling reduction rate exceeds 70%, the cold rolling load becomes large, .
Continuous annealing
The cold-rolled steel sheet is preferably subjected to continuous annealing in a continuous annealing line. In this case, the continuous annealing is preferably performed in a temperature range of 650 to 900 ° C.
If the annealing temperature in the continuous annealing is less than 650 캜, it is difficult to ensure sufficient workability and there is a problem that sufficient transformation is not caused to maintain the austenite phase at a low temperature. Further, the steel of the present invention is an austenitic steel which does not require a phase transformation, and can be sufficiently annealed under ordinary annealing conditions since it can secure sufficient workability when it is heated to a recrystallization temperature or more. Preferably 650 to 900 < 0 > C.
Plated
It is preferable that the continuously annealed cold rolled steel sheet is plated to produce a plated steel sheet intended in the present invention. At this time, it is preferable that the plating treatment is carried out by one of the electroplating method, the hot-dip plating method and the alloying hot-dip plating method, and the plating layer formed therefrom is preferably zinc-based.
The electroplating method can be performed by electroplating under conventional methods and conditions conventionally used. When the hot-dip coating method is used, it can be dipped in a zinc plating bath to produce a hot-dip coated steel sheet. In the case of the alloying hot- The alloyed hot-dip coated steel sheet can be produced by performing ordinary alloying hot dip treatment.
In general, when an electroplating process or an alloying hot dip coating process is performed on a typical transformed structure steel, an appropriate heat treatment condition is often required. However, since the steel of the present invention is composed of austenite single phase structure and does not undergo transformation, Since there is no significant difference in mechanical properties even if there is no condition, the steel sheet can be produced by plating under normal conditions.
The zinc-plated steel sheet of the present invention produced according to the above is excellent in resistance to the embrittlement of the liquid metal intended in the present invention, and has the effect of effectively suppressing cracking during high-temperature molding.
In particular, the galvanized steel sheet has a high elongation at high temperature as compared with an elongation at room temperature, so that stability against high temperature molding can be secured.
More specifically, the galvanized steel sheet of the present invention preferably has an elongation ratio expressed by the following relational expression 1 of 80% or more. If the elongation ratio is less than 80%, stable mechanical properties can not be secured at high temperatures, resulting in problems of moldability as well as embrittlement of the liquid metal by the melting of the plating layer.
[Relation 1]
Elongation ratio (%) = (high temperature elongation / room temperature elongation) x 100
(Here, the high temperature elongation means elongation at 700 to 900 DEG C, and the room temperature elongation means elongation at 10 to 35 DEG C.)
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 )
A steel ingot having the composition shown in the following Table 1 was homogenized for 1 hour in a heating furnace at 1200 占 폚 and then rolled at a finish rolling temperature of 900 占 폚 to prepare a hot-rolled steel sheet. Thereafter, the hot-rolled steel sheet was rolled at a coiling temperature of 450 ° C, and then cold rolled at a cold-reduction rate of 50% after pickling to produce a cold-rolled steel sheet. Then, continuous annealing heat treatment was performed by setting the annealing temperature to 780 캜 and the over-heating temperature to 400 캜. Thereafter, the cold-rolled steel sheet subjected to the continuous annealing was electroplated with a zinc adhesion amount of 55 mg / m 2 to prepare an electroplated steel sheet.
The grain size of each electroplated steel sheet was measured, and tensile test was performed by processing the tensile specimen.
At this time, the electroplated steel sheet was processed in accordance with JIS No. 5 standard, and then tensile test at room temperature was evaluated using a universal tensile tester. Further, the electroplated steel sheet was processed into a tensile specimen standard of Gly 3500, 3500 was used to evaluate the tensile test at 800 占 폚. The results of tensile tests conducted at room temperature and 800 ° C are shown in Table 2 below.
(In Table 2, 'elongation ratio (%)' is a value calculated by ((elongation at 800 ° C / elongation at room temperature) x 100)
As shown in Tables 1 and 2, in the case of Comparative Examples 1 to 3 which do not satisfy the composition of the composition proposed in the present invention, it is confirmed that the elongation at the time of deformation at 800 占 폚 sharply decreases. It can be seen that this is caused by the occurrence of liquid metal embrittlement due to melting of the plating layer at a high temperature, and therefore, high-temperature moldability can not be secured.
On the other hand, Inventive Examples 1 and 2 show a case where a small amount of Nb is added, and Inventive Example 3 shows a case where V is added together with Nb, all of which show that the elongation at the time of transformation at 800 ° C does not decrease, . This can be seen from the fact that the embrittlement of the liquid metal does not occur at a high temperature, and therefore, the high-temperature moldability can be secured.
FIG. 1 shows a photograph of a specimen after the high temperature (800.degree. C.) tensile test of Comparative Steel 3 (a) and Invention Steel 3 (b).
As shown in Fig. 1, in Comparative Steel 3, brittle fracture occurred after 800 占 폚 tensile test, while in Inventive Steel 3, soft fracture occurred. This is because, in the case of Comparative Steel 3, liquid metal embrittlement occurs due to the melting of the plating layer in the high-temperature forming, and in Inventive Steel 3, fracture occurs only after sufficient plastic deformation without the influence of liquid metal embrittlement.
As a result, the austenitic zinc-plated steel sheet according to the present invention is excellent in resistance to embrittlement of a liquid metal, and thus can maintain moldability even at a high temperature.
Claims (5)
The base steel sheet comprises 0.4 to 0.8% by weight of carbon, 12 to 20% of manganese (Mn), 1.0 to 3.0% of aluminum (Al), 0.01 to 0.5% of silicon (Si) (P): 0.03% or less (excluding 0), sulfur (S): 0.03% or less (excluding 0), nitrogen (N) : Excellent in high-temperature formability including one or two of 0.04% or less (excluding 0), 0.001 to 0.5% of niobium (Nb) and 0.001 to 0.5% of vanadium (V), the remainder Fe and unavoidable impurities Austenitic galvanized steel sheet.
[Relation 1]
Elongation ratio (%) = (high temperature elongation / room temperature elongation) x 100
(Here, the high temperature elongation means elongation at 700 to 900 DEG C, and the room temperature elongation means elongation at 10 to 35 DEG C.)
The austenitic galvanized steel sheet according to claim 1 or 2, wherein the microstructure is austenite single phase structure and the grain size is 4 탆 or less.
The austenitic-type galvanized steel sheet is excellent in high-temperature moldability, which is a plating layer of any one of an electroplating layer, a hot-dip galvanized layer and an alloyed hot-dip galvanized layer.
Finishing the reheated steel slab at 800 to 1000 占 폚 to produce a hot-rolled steel sheet;
Winding the hot-rolled steel sheet at 700 ° C or lower;
Cold rolling the wound hot rolled steel sheet at a cold rolling reduction rate of 20 to 70% to produce a cold rolled steel sheet;
Continuously annealing the cold-rolled steel sheet at 650 to 900 ° C; And
A step of plating the cooled cold rolled steel sheet
Wherein the high-temperature formability is excellent.
Wherein the plating treatment is performed by any one of an electroplating method, a hot dip galvanizing method, and a galvannealing hot dip galvanizing method, wherein the galvanized steel sheet is excellent in high temperature formability.
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| KR1020130160796A KR20150073013A (en) | 2013-12-20 | 2013-12-20 | Austenitic galvanized steel sheet having excellent high-temperature formability of welding point and method for manufacturing the same |
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