KR20150073005A - Austenitic galvanized steel sheet having excellent resistance crack of welding point and method for manufacturing the same - Google Patents
Austenitic galvanized steel sheet having excellent resistance crack of welding point and method for manufacturing the same Download PDFInfo
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- KR20150073005A KR20150073005A KR1020130160786A KR20130160786A KR20150073005A KR 20150073005 A KR20150073005 A KR 20150073005A KR 1020130160786 A KR1020130160786 A KR 1020130160786A KR 20130160786 A KR20130160786 A KR 20130160786A KR 20150073005 A KR20150073005 A KR 20150073005A
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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
- C22C38/001—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
- C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
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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
- C22C38/02—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
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
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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
- C22C38/18—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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- 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
- C22C38/18—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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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
- C23C2/06—Zinc or cadmium or alloys based thereon
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- C—CHEMISTRY; METALLURGY
- 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
Abstract
The present invention relates to an austenitic galvanized steel sheet used for structural members of an automobile body and the like, and more particularly to an austenitic galvanized steel sheet having excellent weld crack resistance and a method for manufacturing the same.
Description
The present invention relates to an austenitic galvanized steel sheet used for structural members of an automobile body and the like, and more particularly to an austenitic galvanized steel sheet having excellent weld crack resistance and a method for manufacturing the same.
2. Description of the Related Art In recent years, the automobile industry has been strongly required to reduce the weight of automobiles in accordance with the regulation of carbon dioxide for reducing global warming. At the same time,
Generally, in order to produce ultra-high strength steel sheets for automobiles, most low-temperature transformed structures are utilized, and a steel sheet having a tensile strength of 1000 MPa or more can be obtained.
However, if the low-temperature transformed structure is used, it is possible to secure an ultra-high strength, but the ductility is relatively decreased and it is difficult to secure an elongation of 20% or more. As a result, there is a problem that it is difficult to apply an ultra-high-strength steel sheet utilizing a low-temperature transformed structure to a component having a complicated shape requiring cold press forming, and there is a limitation in designing a component for a desired application.
Various studies have been continuously carried out in order to recognize such a problem and to produce a steel having good moldability and mechanical properties optimized for an intended use. Of these, austenitic high manganese steel is a steel having excellent strength and formability Which can be suitably applied as an automobile structural member. In addition, a plated steel sheet obtained by plating the above-mentioned austenitic high-manganese steel may be suitably used for securing corrosion resistance of automobile structural members.
When the austenitic-type coated steel sheet is brought into contact with the steel sheet, the temperature of the heat-affected zone of the steel sheet is increased, so that the steel sheet is not only melted in the plating layer, There is a problem that a liquid metal embrittlement (LME) occurs due to the generation of tensile stress due to electrode pressurization, and cracks are generated in the welded portion, and fatigue characteristics and collision characteristics are inferior.
Liquid metal embrittlement (LME) is a phenomenon in which brittleness occurs when a soft material comes into contact with a liquid metal in general and refers to a phenomenon that the liquid metal penetrates rapidly along the grain boundaries of the base material in the presence of tensile stress to cause brittleness.
Accordingly, there is a need to develop an austenitic-plated steel sheet excellent in mechanical properties without causing embrittlement of a liquid metal during welding of the plated steel sheet.
An aspect of the present invention is to provide an austenitic-plated steel sheet which is excellent in strength and ductility as well as resistance to brittle of liquid metal during welding and does not cause weld cracking, and a method for 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) : At least one selected from the group consisting of 0.04% or less (excluding 0), molybdenum (Mo): 0.01 to 1.0%, niobium (Nb): 0.001 to 0.5% and vanadium (V) And an austenitic zinc-plated steel sheet excellent in crack resistance of a welded portion including unavoidable impurities.
[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. The present invention also provides a method of manufacturing an austenitic zinc-plated steel sheet excellent in crack resistance of a welded portion.
According to the present invention, it is possible to provide an austenitic zinc-plated steel sheet which is excellent in resistance to embrittlement of a liquid metal and can suppress the occurrence of cracks in welded portions during welding. Further, the austenitic zinc-plated steel sheet of the present invention can be suitably applied to structural members of automobiles and the like.
Fig. 1 shows a tensile test curve at the high temperature of the comparative steel 3 and the invention steel 2, wherein (a) is the comparative steel 3, and (b) is the steel 2.
Fig. 2 shows microstructural photographs of the comparative steel 3 and the inventive steel 2, wherein (a) is the comparative steel 3, and (b) is the inventive steel 2. Fig.
The present inventors have found that, in a conventional high manganese steel, a large amount of manganese and carbon can be added to secure austenite in the microstructure of steel at room temperature. However, when galvanized steel sheet is produced by plating, The problem of cracking of welded part due to the occurrence of liquid metal embrittlement (LME) due to melting of the plating layer in the heat affected zone was recognized and studied to solve this problem. As a result, it has been confirmed that it is possible to provide an austenitic galvanized steel sheet excellent in resistance to emulsion of a liquid metal when the concentration of deformation is dispersed by finely grinding the crystal grains by controlling the composition of the components contained in the steel. .
Particularly, the present invention is characterized in that mechanical properties, particularly high temperature elongation, can be secured even at a high temperature owing to the securing of resistance to embrittlement of a liquid metal during welding.
Hereinafter, the present invention will be described in detail.
A zinc-coated steel sheet excellent in crack resistance of welded portions according to one aspect of the present invention comprises a base steel sheet and a plating layer formed on the base steel sheet, wherein the base steel sheet contains 0.4 to 0.8% of carbon (C), manganese (Si): 0.01 to 0.5%, Cr: 0.05 to 1%, Sn: 0.01 to 0.1%, phosphorus (Mn) 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), molybdenum (Mo) The remainder Fe and inevitable impurities, and has a single-phase austenite structure as a microstructure.
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 grain size exceeds 4 mu m, resistance to embrittlement of the liquid metal due to grain boundary dispersion of the stress is not sufficiently improved, and the high temperature elongation as 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.
If the content of C is less than 0.4%, there is a problem that α '(alpha re-) martensite phase is formed due to phase transformation at the time of processing and the formability of the steel sheet is deteriorated and becomes vulnerable to delayed fracture. There is a problem that the electrical resistivity is increased and the weldability 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.
When the content of Al is less than 1.0%, there is a problem that the elongation-breaking property is lowered due to the rapid work hardening phenomenon rather than the elongation-breaking property. On the other hand, when the content exceeds 3.0%, the strength is decreased, And there is a problem that the surface quality of the product is deteriorated due to increased oxidation of the steel surface during hot rolling. 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: 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%.
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%.
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.
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.
N: 0.04% or less (excluding 0)
Nitrogen (N) It is an element which accelerates the generation of twin by precipitating fine nitride by acting with Al during solidification process in austenite grain. In general, twinning is formed centering on the nucleus. The nitrides formed at this time act as twin nuclei, which helps to improve the elongation and also to stabilize the austenite.
If the content of N is excessively larger than 0.04%, the nitride may be excessively precipitated and the hot workability and elongation may be lowered. Therefore, in the present invention, the content of N is preferably limited to 0.04% or less.
Mo: 0.01 to 1.0%
Molybdenum (Mo) is an element that affects the austenite thermal stabilization and binds with C to form a fine carbide, thereby increasing the strength. Particularly, Mo plays a very important role in finely maintaining the size of the precipitate when the complex is added with Nb or V described later. In order to obtain such an effect, it is necessary to add Mo at a content of 0.01% or more. However, when the content exceeds 1.0%, the ductility of the steel is lowered and the production cost is increased by an expensive element. Therefore, the Mo content in the present invention is preferably limited to 0.01 to 1.0%.
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 占 폚.
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 manufactured according to the above is excellent in resistance to the embrittlement of the liquid metal intended in the present invention, and has an effect of effectively suppressing cracking of the welded portion during welding.
In particular, the galvanized steel sheet has a high elongation at high temperature as compared with an elongation at room temperature, so that stability at a high temperature 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 temperature, and there is a problem that liquid metal embrittlement occurs due to 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.
Each of the electroplated steel sheets was subjected to a tensile test by observing the microstructure and grain size, processing the specimens into tensile specimens.
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. This can be attributed to the occurrence of liquid metal embrittlement due to the melting of the plating layer at a high temperature.
On the other hand, Inventive Example 1 shows the case where V is added together with Mo, and Inventive Example 2 shows the case where Nb is added together with Mo. It can be seen that the decrease in elongation at 800 deg. This can be attributed to the fact that the liquid metal embrittlement does not occur at a high temperature.
1 shows the tensile test curves of the comparative steel 3 and the inventive steel 2 at a high temperature. In the comparative steel 3 (A), a sharp reduction in elongation was observed as a result of the occurrence of the liquid metal brittleness at 750 ° C or higher, In case of Steel 2, it can be confirmed that the credit ratio does not decrease even if the temperature increases.
2 shows microstructural photographs of the comparative steel 3 and the inventive steel 2, and it can be confirmed that the grain 2 of the invention steel 2 is finer than the comparative steel 3. This is because the fine precipitate phase is formed by the addition of the precipitate-forming element, and the crystal grain refinement effect is sufficiently manifested. Therefore, it can be interpreted that the inventive steel 2 did not cause liquid metal embrittlement at a high temperature because the stress applied to each crystal grain was maintained at a low level during deformation due to grain refinement.
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) : At least one selected from the group consisting of 0.04% or less (excluding 0), molybdenum (Mo): 0.01 to 1.0%, niobium (Nb): 0.001 to 0.5% and vanadium (V) And an austenitic galvanized steel sheet excellent in crack resistance of a welded portion including unavoidable impurities.
[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-type galvanized steel sheet according to claim 1, wherein the base steel sheet has an austenitic single-phase microstructure and is excellent in crack resistance of welded parts having a grain size of 4 탆 or less.
The austenitic-type galvanized steel sheet according to any one of claims 1 to 3, wherein the plating layer is one of a plated layer 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 steel sheet has excellent weld crack resistance.
Wherein the plating treatment is performed by any one of electroplating, hot-dip plating and alloying hot-dip plating.
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| KR1020130160786A KR20150073005A (en) | 2013-12-20 | 2013-12-20 | Austenitic galvanized steel sheet having excellent resistance crack of welding point and method for manufacturing the same |
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| KR1020130160786A KR20150073005A (en) | 2013-12-20 | 2013-12-20 | Austenitic galvanized steel sheet having excellent resistance crack of welding point and method for manufacturing the same |
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| KR20150073005A true KR20150073005A (en) | 2015-06-30 |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2017188654A1 (en) * | 2016-04-28 | 2017-11-02 | 주식회사 포스코 | Ultrahigh-strength and high-ductility steel sheet having excellent yield ratio and manufacturing method therefor |
| KR20200008142A (en) * | 2017-06-20 | 2020-01-23 | 아르셀러미탈 | Zinc coated steel plate with high resistance spot weldability |
| KR20200101647A (en) | 2019-02-20 | 2020-08-28 | 한양대학교 산학협력단 | Supper austenitic stainless steel |
-
2013
- 2013-12-20 KR KR1020130160786A patent/KR20150073005A/en not_active Application Discontinuation
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2017188654A1 (en) * | 2016-04-28 | 2017-11-02 | 주식회사 포스코 | Ultrahigh-strength and high-ductility steel sheet having excellent yield ratio and manufacturing method therefor |
| US10907230B2 (en) | 2016-04-28 | 2021-02-02 | Posco | Ultra high-strength and high-ductility steel sheet having excellent yield ratio and manufacturing method therefor |
| KR20200008142A (en) * | 2017-06-20 | 2020-01-23 | 아르셀러미탈 | Zinc coated steel plate with high resistance spot weldability |
| US11649522B2 (en) | 2017-06-20 | 2023-05-16 | Arcelormittal | Zinc-coated steel sheet with high resistance spot weldability |
| KR20200101647A (en) | 2019-02-20 | 2020-08-28 | 한양대학교 산학협력단 | Supper austenitic stainless steel |
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