KR20140014500A - 1500mpa-ultra high strength high manganese steel sheet having excellent bendability - Google Patents
1500mpa-ultra high strength high manganese steel sheet having excellent bendability Download PDFInfo
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- KR20140014500A KR20140014500A KR1020120080587A KR20120080587A KR20140014500A KR 20140014500 A KR20140014500 A KR 20140014500A KR 1020120080587 A KR1020120080587 A KR 1020120080587A KR 20120080587 A KR20120080587 A KR 20120080587A KR 20140014500 A KR20140014500 A KR 20140014500A
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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
- 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
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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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
- 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
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0236—Cold rolling
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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
- 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
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0273—Final recrystallisation annealing
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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
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
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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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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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
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
Abstract
The present invention relates to an ultra-high strength high manganese steel sheet having excellent bending workability and a method of manufacturing the same, in weight%, carbon (C): 0.4 to 0.7%, manganese (Mn): 12 to 24%, aluminum (Al) : 1.1 to 3.0%, silicon (Si): 0.3% or less, titanium (Ti): 0.005 to 0.10%, boron (B): 0.0005 to 0.0050%, phosphorus (P): 0.03% or less, sulfur (S): 0.03 1500 MPa grade ultra-high strength with excellent bending workability, characterized in that% or less, nitrogen (N): 0.04% or less, residual iron and other unavoidable impurities, bendability is 6.0 or less, and tensile strength is 1500 MPa or more. Provides high manganese steel sheet.
Description
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel sheet applicable to components such as a bumper, a seal, a seat rail, and members at a collision site. More particularly, the present invention relates to an ultra-high strength high manganese steel sheet having excellent bending workability and a method of manufacturing the same.
Automobile companies have been conducting continuous research on ultra high strength and light weight of automobile materials to prevent environmental pollution, improve fuel efficiency and improve safety. Such materials can be applied to various structural members of similar applications in addition to automobile parts.
Conventionally, in consideration of formability, a low carbon steel series steel having a ferrite matrix is used. However, when low carbon steels are used for steel sheets for automobiles, it is difficult to obtain an elongation of 30% or more at a tensile strength of 800 MPa or more, which makes commercialization difficult. Therefore, high strength steel with a tensile strength of 800MPa or more is difficult to apply to a complicated shape of the component, there is a problem that free component design for the desired use is difficult. In addition, with the current steel sheet manufacturing technology, it is difficult to manufacture a steel having a high tensile strength of 1300 MPa or more and capable of cold press molding or roll forming molding.
In order to solve the above-described problems, Patent Documents 1 and 2 have been proposed. These documents propose an austenitic high manganese steel excellent in ductility and strength.
However, in Patent Document 1, a large amount of manganese component was contained to secure ductility, but work hardening was severely caused in the deformed portion. Therefore, a phenomenon that the steel sheet easily breaks after machining occurred. On the other hand, the high manganese steel proposed in Patent Document 2 has an advantage that ductility is ensured, but there is also a disadvantage in that the addition of a large amount of silicon (Si) is disadvantageous in terms of electric conductivity and molten copper. The steel plates provided in the above Patent Documents 1 and 2 have excellent machinability but have low yield strength and poor impact characteristics.
In recent years, in order to develop the steel material having the high strength and high-quality forming characteristics, the TWIP (Twinning-Welding) method using the fact that the high hardness steel can improve the formability by increasing the work hardening rate due to the twin formation during plastic deformation, Induced Plasticity Steel has been developed. However, TWIP steels also have a limit to increase strength above a certain level, despite having austenite structure.
Thus, the need for high strength steel with good formability and the study of the method of manufacturing the same remain an important task in the related art. In addition, in the case of the ultra-high strength steel of 1500MPa class, although the development is essential due to its excellent tensile strength characteristics, it has been a problem more difficult to implement it in the industry in reality.
One aspect of the present invention, by controlling the content of the austenite stabilizing element and aluminum components, and the conditions of each step of the manufacturing method, to ensure ultra-high strength of 1500MPa class without special additional components, at the same time excellent bending workability This technique is secured to provide a technique for obtaining an ultra-high strength steel sheet that can be used not only for the structural member of the vehicle body but also for a complicated inner plate material.
One aspect of the present invention, in weight%, carbon (C): 0.4-0.7%, manganese (Mn): 12-24%, aluminum (Al): 1.1-3.0%, silicon (Si): 0.3% or less, Titanium (Ti): 0.005 to 0.10%, Boron (B): 0.0005 to 0.0050%, Phosphorus (P): 0.03% or less, Sulfur (S): 0.03% or less, Nitrogen (N): 0.04% or less, balance iron and Provided is 1500MPa class ultra-high strength high manganese steel sheet having excellent bending workability, comprising other unavoidable impurities, having bendability of 6.0 or less and tensile strength of 1500 MPa or more.
Another aspect of the invention, the step of homogenizing by heating the ingot or playing slab having the above-described composition range to 1050 ~ 1300 ℃, the step of hot rolling finishing the homogenized ingot or playing slab at 850 ~ 1000 ℃ Hot rolling of the hot rolled steel sheet at 400 to 700 ° C., Cold rolling of the wound steel sheet, Continuous annealing of the cold rolled steel sheet at 400 to 900 ° C., 30 to 30 Provided is a method for producing a 1500MPa class ultra high strength high manganese steel sheet having excellent bending workability, including re-rolling at a rolling rate of 50%.
According to an aspect of the present invention, while securing an ultra high strength having a tensile strength of 1500MPa class, it is possible to secure an ultra-high strength high manganese steel having excellent physical properties having bendability and good elongation of 6.0 or more. Due to its high strength, the 1500MPa or more grade steel is an ultra high strength that is not easy to be implemented in an industry other than that of variously manufactured 1100MPa grade steel, and in one aspect of the present invention, without adding a special component, high aluminum content Through the control and the manufacturing steps disclosed below it becomes possible to implement the ultra-high strength steel of the strength. The steel sheet manufactured from the ultra-high strength manganese steel is applicable to various purposes, such as the collision member and various structural members of the vehicle.
1 is a steel in accordance with the manufacturing method of the steel sheet according to another aspect of the present invention when the steel ingot satisfying the component system (Sample 5 of Table 1) of one aspect of the present invention, before the re-rolling step (Fig. 1 (a Fig. 1) and later (Fig. 1 (b)) is a result of color etching the grain boundary of the microstructure of the steel sheet and observed the change with an optical microscope.
Figure 2 is a comparative example (FIG. 2 (a), the specimen 2 of Table 1) and the invention example (FIG. 2 (b), Table 1 prepared according to the manufacturing method of ultra-high strength high manganese steel sheet which is an aspect of the present invention) Photographs of the specimens after 90 ° bending test with specimens 9).
The present inventors have intensively studied to solve the problem that high strength can be secured by adding a large amount of manganese in the conventional high manganese steel, but it is difficult to ensure ductility and molding was not easy. As a result, even without the addition of additional components, by controlling the composition of the steel composition and re-rolling the manufactured steel at a high rolling rate, it was possible to manufacture a super high strength steel sheet of 1500MPa grade excellent in bending workability.
Accordingly, the present invention controls the contents of carbon, manganese, and aluminum, which perform the stabilization function of the austenite structure in the steel component system, thereby securing a complete austenite phase at room temperature, and generating deformation twins during plastic deformation. The present invention relates to an ultra-high strength steel sheet of 1500MPa grade, which is secured with excellent bending workability by optimizing and securing ultra high strength through re-rolling of steel manufactured under high rolling rate.
Hereinafter, the present invention will be described in more detail.
First, with respect to ultra high strength steel which is an aspect of the present invention, the reason for limiting the components will be described in detail. At this time, the content of the component element means all weight%.
Carbon (C): 0.4 to 0.7%
Carbon (C) is an element contributing to the stabilization of the austenite phase. Therefore, there is a favorable aspect to the formation of the austenite phase as the addition amount increases. However, in the present invention, it is preferable to limit the carbon content to 0.4 to 0.7%. When the content of carbon is less than 0.4%, cracks are generated in processing and ductility is lowered because α '(alpha re-) martensite phase is formed at the time of transformation of the phase. In addition, when the carbon content exceeds 0.7%, the electrical resistance inside the steel increases, and when the 3-layer welding is applied during the production process, the weldability may deteriorate.
manganese( Mn ): 12 to 24%
Manganese (Mn) is an essential element for stabilizing the austenite phase with carbon. In the present invention, the content of manganese is preferably limited to 12 to 24%. When the content of manganese is less than 12%, an α '(alpha-re-) martensite phase damaging the formability is generated, the strength is increased but the ductility is rapidly decreased and the work hardening rate is also decreased. In addition, when the content of manganese exceeds 24%, generation of twinning is inhibited and strength is increased, but ductility is decreased. In addition, as the content of manganese increases, cracking occurs well during hot rolling, and manufacturing cost is increased, which is disadvantageous from the economical point of view.
aluminum( Al ): 1.1 to 3.0%
Aluminum (Al) is usually added for the purpose of deoxidizing steel, but in the present invention, it is added in order to improve ductility and improve delayed fracture resistance. That is, although aluminum is an element for stabilizing the ferrite phase, there is also an aspect in which the stacking fault energy (Stacking Fault Enegy) is increased at the slip surface of the steel to suppress the formation of the ε-martensite phase to improve ductility and resistance to delayed fracture. In addition, aluminum suppresses the formation of? -Martensite phase even when the content of manganese is low, thereby contributing to improving the workability while minimizing the content of manganese. The present invention is particularly significant by improving the bending workability while ensuring the strength of the ultra-high strength steel by appropriately adjusting the content of the aluminum component, controlling the twin fraction.
In the present invention, the content of aluminum is preferably limited to 1.1 to 3.0%. When the amount of aluminum added is less than 1.0%, the ε-martensite phase is generated to increase the strength, but there is a disadvantage in that the ductility decreases rapidly. On the other hand, when the content exceeds 3.0%, the occurrence of twinning is suppressed, ductility is reduced, casting is deteriorated during continuous casting, and oxidation of the surface of the steel sheet during hot rolling occurs to a great extent, thereby lowering the surface quality of the product.
silicon( Si ): Not more than 0.3%
Silicon (Si) is an element which functions to strengthen the solid solution, and is a component that increases the yield strength of the steel sheet by reducing crystal grain size by the employment effect. In general, when silicon is excessively added, a silicon oxide layer is formed on the surface to lower the melting strength. However, when an appropriate amount of silicon is added to the high manganese steel, a thin silicon oxide layer is formed on the surface, and the oxidation of manganese is inhibited. Therefore, according to one aspect of the present invention, it is possible to prevent formation of a thick manganese oxide layer formed after rolling in a cold-rolled steel sheet as an addition of a silicon component, to prevent corrosion proceeding in a cold- And it is possible to maintain excellent surface quality as the base steel sheet of the electroplating material.
On the other hand, if the addition amount of silicon is excessively increased, a large amount of silicon oxide is formed on the surface of the steel sheet during hot rolling, which deteriorates acidity and lowers the surface quality of the hot-rolled steel sheet. In addition, when hot-annealing at the time of high-temperature annealing in the continuous annealing step and the continuous hot-dip coating step, the surface of the steel sheet is melted and plated, the wettability of molten zinc is reduced on the surface of the steel sheet. Therefore, in order to avoid the above-mentioned problems, the silicon content is preferably 0.3% or less.
Phosphorus (P) and sulfur (S): 0.03% or less
Normally, phosphorus (P) and sulfur (S) are elements that are inevitably contained in the production of steel. In the present invention, the content thereof is preferably limited to 0.03% or less. Phosphorus components cause segregation and reduce the workability of the steel. The sulfur component forms coarse manganese sulfide (MnS), which causes defects such as flange cracks and reduces the hole expandability of the steel sheet. Therefore, it is preferable to suppress the content thereof to the above-mentioned 0.03% or less.
Nitrogen (N): not more than 0.04%
Nitrogen (N) reacts with aluminum during the solidification process in the austenite grains to precipitate fine nitrides, promoting the generation of twin, and improving the strength and ductility in the process of forming the steel sheet. However, in the present invention, the upper limit is preferably limited to 0.04%. When the content exceeds 0.04%, the nitride is excessively precipitated to lower the hot workability and elongation.
titanium( Ti ): 0.005 to 0.10%
Titanium (Ti) is a strong carbide element that forms a carbide by binding with carbon. The carbide formed at this time is an element effective for refining crystal grains because it inhibits crystal grain growth. When titanium is added in combination with boron (B), a high-temperature compound is formed in the columnar phase boundary to prevent grain boundary cracking. In the present invention, the content of titanium is preferably limited to 0.005 to 0.10%. When the content is less than 0.005%, it is difficult to obtain the above-mentioned effect. When the content exceeds 0.10%, excessive titanium segregates in the crystal grain boundaries to cause ingangles, or the precipitate phase is excessively coarsened, .
Boron (B): 0.0005 to 0.0050%
The boron (B) is added together with the above-mentioned titanium to form a high-temperature compound at the grain boundaries to prevent grain boundary cracking. In the present invention, the content of boron is preferably limited to 0.0005 to 0.0050%. When the boron content is less than 0.0005%, the above-mentioned effect is difficult to obtain. When the boron content is more than 0.0050%, the boron compound is formed and the plating ability can be lowered.
The steel that satisfies the above-described component system exhibits excellent bending workability and good elongation while maintaining ultra high strength of 1500 MPa or more, and has excellent advantages in terms of formability. The 1500MPa or more grade steel is an extremely high strength that is difficult to implement in the industry due to its high strength, in one aspect of the present invention without the addition of a special component, the control of the high aluminum content and through the manufacturing steps disclosed below High strength steels can be implemented.
In particular, according to an aspect of the present invention, while having a high tensile strength of at least 1500MPa or more, and at the same time bendability is 6.0 or less, a steel having excellent mechanical properties can be provided.
Next, another aspect of the present invention, a method for producing a 1500MPa class ultra-high strength high manganese steel sheet from the steel ingot or slab having the above-described composition content, and the reason for controlling the desired numerical value in each step of the production method This will be described in detail.
According to an aspect of the present invention, the ingot or cast slab composed of the component system and composition range as described above is heated or homogenized by a continuous casting process, and then manufactured into a hot rolled steel sheet through hot rolling and hot rolling, or The hot rolled steel sheet may be cold rolled and annealed to produce a cold rolled steel sheet, or the cold rolled steel sheet may be manufactured to a galvanized steel sheet by electro galvanizing or hot dip galvanizing. In the following, the ingot or playing slab is referred to simply as slab.
Heating step ( Homogenization Treatment): 1050 to 1300 DEG C
According to one aspect of the present invention, a high manganese steel slab having the above composition can be heated and homogenized. In this case, the heating temperature is preferably 1050 to 1300 占 폚. The reason why the lower limit of the heating temperature is 1050 占 폚 is that if the heating temperature becomes too low, it becomes difficult to secure the temperature during finish rolling, and the rolling load increases due to the decrease in temperature, and rolling to a predetermined thickness can not be performed sufficiently. On the other hand, the reason why the upper limit of the heating temperature is 1300 ° C is that the higher the heating temperature, the higher the crystal grain size of the performance slab, the more the surface oxidation is generated, , Cracking may occur during hot rolling because a liquid film is formed in the columnar phase boundary of the slab.
Hot Rolling Step: Finish hot rolled at 850 ~ 1000 ℃
The slab which has been homogenized by the heating can be hot-rolled into a steel sheet. At this time, the temperature of the finish hot rolling is preferably controlled to 850 to 1000 占 폚. The reason why the lower limit of the finish hot rolling temperature is 850 占 폚 is that if the finish rolling temperature is excessively lowered, the rolling load becomes high and the finish of the rolling mill becomes complicated and the quality of the steel sheet is adversely affected. The reason why the upper limit temperature is 1000 deg. C is that if the rolling finishing temperature is excessively increased, surface oxidation occurs during rolling.
Hot rolled coiling Step: 400 ~ 700 ℃
Thereafter, the hot-rolled steel sheet can be hot-rolled. The coiling temperature is preferably 400 to 700 占 폚 or less. The reason why the lower limit temperature at the hot rolling is 400 占 폚 is that the cooling water must be injected after hot rolling in order to lower the temperature. To lower the temperature to below 400 占 폚, too much cooling water is required, This is because there is a problem that the property is deteriorated. The reason why the upper limit temperature is 700 ° C is that when the hot rolled coiling temperature is too high, a thick oxide film and internal oxidation occur on the surface of the hot rolled steel sheet, so that the oxide layer can not be easily removed during the pickling process.
Cold rolling step
After the above hot rolling step, cold rolling can be carried out under ordinary conditions to control the shape and thickness of the steel sheet. At this time, the cold rolling rate is preferably adjusted to meet the thickness required by the customer, and is preferably carried out for the purpose of controlling the strength and elongation.
Continuous annealing Step: 400 to 900 ° C
Thereafter, the cold-rolled steel sheet can be continuously annealed. At this time, the continuous annealing temperature is preferably 400 to 900 DEG C, which is for obtaining excellent plating properties and high strength. More specifically, when the annealing temperature is too low at the time of continuous annealing, it is difficult to secure sufficient workability and the austenite transformation sufficient to maintain the austenite phase at a low temperature is not sufficiently carried out. However, if the annealing temperature is too high, the strength may be lowered to 1000 MPa or less through over-recrystallization or grain growth, and in particular, it is difficult to obtain excellent plating property due to increased amount of oxide on the surface during hot-
Plating step: hot dip galvanizing, electroplating, or Alloying The hot-
When a coated steel sheet is required, the cold-rolled steel sheet produced by the above-described manufacturing conditions is immersed in a plating bath to produce a hot-dip coated steel sheet, or electroplated to produce an electroplated steel sheet or an alloyed hot- can do.
In order to produce the electroplated steel sheet, it is possible to perform electroplating under ordinary methods and conditions. Further, the cold-rolled steel sheet subjected to the continuous annealing can be subjected to a conventional alloying hot-dip coating treatment to produce an alloyed hot-dip coated steel sheet.
Usually, the heat treatment conditions in the electroplating or alloyed hot dip galvanizing process affect most of the generalized textured steel, so that appropriate heat treatment conditions are often required. However, the high manganese steel according to the present invention has austenite single- There is no significant difference in mechanical properties even if there is no special heat treatment condition. Therefore, the steel sheet can be produced by plating under normal conditions.
Re-rolling step : Rolling rate 30-50%
Then, according to the manufacturing method forming one aspect of the present invention, while rerolling while controlling the rolling rate to the steel sheet subjected to the above process. That is, the above-described manufacturing method of the present invention is intended to overcome the disadvantage that it is difficult to realize high strength in terms of the strength of the TWIP steel while exploiting the advantages of forming the high-strength of the TWIP steel.
The steel sheet manufactured as described above, for example, a cold rolled steel sheet, a hot-dip galvanized steel sheet, an alloyed hot-dip galvanized steel sheet, or an electroplated steel sheet manufactured by the above-described conditions may increase strength through work hardening by re-rolling. The re-rolling process is preferably performed by one of a skin pass mill, a double reduction process, a hot rolling process, and a continuous rolling process.
In addition, the re-rolling at this time is preferably carried out under a rolling rate of 30 to 50% for the purpose of securing an ultra high strength steel of 1500 MPa class. This, when the rolling rate is less than 30%, there is a problem that does not implement the ultra high strength, which is the core purpose of the present invention, if it exceeds 50%, the bending workability is greatly deteriorated and excellent intention in one aspect of the present invention This is because the bending workability is not secured.
Through this, it is possible to provide ultra-high strength steels having excellent bendability of 6.0 or more, while securing ultra-high strength of 1500MPa level, which is difficult to be implemented in the industry at present.
1 is one of the specimens according to the component system of the steel sheet, which is an aspect of the present invention (Sample 5 in Table 1) before the re-rolling step according to the manufacturing method of the ultra-high strength steel sheet is another aspect of the present invention (Fig. 1 (a) ) And after (FIG. 1 (b)), the grain boundary of the microstructure of the steel sheet was color etched, and the change was observed with an optical microscope. Compared with before the re-rolling step, it can be seen that after the size of the grain size decreases, twin density is increased to increase the tensile strength and yield strength of the steel. Through this, even in the case of the other inventions, it can be determined that the tensile strength and the yield strength after re-rolling have excellent collision characteristics.
Thus, the steel sheet manufactured according to the manufacturing method of the ultra-high strength high manganese steel sheet according to an aspect of the present invention is an ultra-high strength steel sheet with a tensile strength of 1500MPa or more, and at the same time can be secured excellent workability of 6.0 or less bending workability.
Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are only illustrative of the present invention in more detail and do not limit the scope of the present invention.
( Example )
In the following examples, for the ingot having the component system shown in Table 1 below, each process of the manufacturing method of ultra-high strength high manganese steel sheet according to an aspect of the present invention was performed.
Specifically, for each specimen having the composition shown in Table 1, after maintaining a high temperature for 1 hour in a 1200 ℃ heating furnace, hot rolling was performed. At this time, the hot rolling finish temperature was set to 900 ℃, the winding was carried out at 650 ℃ after hot rolling. Thereafter, pickling was performed using the hot-rolled steel sheet, and cold rolling was performed at a cold rolling rate of 50%. Thereafter, the cold rolled specimen was subjected to continuous annealing simulation heat treatment at an annealing temperature of 800 ° C. and an overaging temperature of 400 ° C. Thereafter, the heat treatment material was re-rolled at different rolling rates.
Table 2 below shows the mechanical properties of the inventive examples and the comparative examples before and after the re-rolling step (rolling rate of 30 to 50%) when performing each step according to the manufacturing method for each specimen of the steel ingot having the composition of Table 1 The test results are shown.
For each of the specimens, the tensile test was performed using a universal tensile tester after processing the tensile test specimen in JIS No. 5 standard, the results are shown in Table 2 below.
In addition, for each specimen, by measuring the elongation (Total-EL) and 90 degree bendability (minimum R / t) before and after re-rolling in accordance with the conventional method in the art to measure the 1500MPa class super While maintaining the high strength, it was evaluated whether the mechanical properties excellent in the workability was implemented, and divided the invention example and the comparative example are shown in Table 2 below.
The specific analysis of each Psalm is as follows.
As shown in Table 1 below, the specimens 3 to 9 correspond to the invention examples corresponding to the composition disclosed in one aspect of the present invention. Specimens 1 and 2 correspond to comparative examples in which the content of aluminum (Al) is small and does not correspond to the composition of the present invention.
Specimen 3 to 9 satisfies the composition of the composition disclosed in the present invention, when re-rolled by a rolling rate of 30-50%, the amount of twinning and dislocation formation during tensile test deformation is appropriate, tensile strength of 1500MPa or more, bending workability 6.0 or less Could be secured. Comparing Test Examples 7-1 and 7-2, Test Examples 8-2 and 8-3, and Test Examples 9-2 to 9-5, when a rolling rate of 30 to 50% was applied, the tensile strength was 1500 MPa or more. It can be seen that ultra high strength is realized. In particular, through Test Example 9-5, it can be seen that when the rolling rate exceeds 50%, the bending workability of the steel is significantly deteriorated.
On the contrary, the specimens 1 and 2 corresponding to the comparative examples were inferior due to the low aluminum content, even though the re-rolling step was performed, the bending workability and delayed fracture resistance did not enter the level controlled by the present invention.
Figure 2 is a comparative example (FIG. 2 (a), specimen 1 of Table 1) and the invention example (FIG. 2 (b), Table 1 of the ultra-high strength high manganese steel sheet prepared in accordance with an aspect of the present invention) It is the photograph of the test piece after the 90 degree bending workability test of the test piece 9). In the case of the invention example to which the Al component is added, it can be visually confirmed that the bending property of the ultra high strength steel is excellent by controlling the twin fraction. In the case of the comparative example, even if the bending angle is smaller than the invention example, it can be confirmed that the crack occurs after the bending test.
Claims (4)
1500MPa grade ultra-high strength high manganese steel sheet having excellent bending workability, having bendability of 6.0 or less and tensile strength of 1500MPa or more.
The steel sheet is a cold rolled steel sheet, hot-dip galvanized steel sheet, alloyed hot-dip galvanized steel sheet, characterized in that 1500MPa class super high strength high manganese steel sheet having excellent bending workability.
Hot-rolling the homogenized ingot or the performance slab to a finish hot rolling temperature of 850 to 1000 占 폚;
Rolling the hot-rolled steel sheet at 400 to 700 ° C;
Cold rolling the rolled steel sheet;
Continuously annealing the cold-rolled steel sheet at 400 to 900 占 폚; And
The method of manufacturing a 1500MPa class ultra-high strength high manganese steel sheet having excellent bending workability, including the step of re-rolling the continuous annealing steel sheet at a rolling rate of 30 to 50%.
The re-rolling step is a method of manufacturing a 1500MPa-class ultra-high strength high manganese steel sheet having excellent bending workability, including one of a rough pass (Skin Pass Mill), double rolling (Double Reduction), hot rolling and continuous rolling.
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
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| KR102045717B1 (en) | 2018-07-12 | 2019-11-18 | 주식회사 포스코 | High manganese steel having reduced rate of surface cracking and method of manufacturing the same |
| KR20200132165A (en) | 2019-05-15 | 2020-11-25 | 주식회사 포스코 | High manganese slab having reduced rate of surface cracking and method of manufacturing the same and high manganese steel sheet using the same |
| 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 |
| US10968506B2 (en) | 2015-12-24 | 2021-04-06 | Posco | High-manganese hot-dip aluminum-coated steel sheet having excellent coating adhesion |
| KR20210157716A (en) | 2020-06-22 | 2021-12-29 | 한상관 | By storing a large amount of river water to create an artificial fish farm and at the same time to reduce the generation of fine dust, it improves the polluted air in the atmosphere, and at the same time, preferentially discharges clean water molecules with a heavy specific gravity so that the polluted river water is converted into clean river water. A nature-friendly water purification eco-friendly method that naturally purifies the water quality of reservoirs, lakes, dams, lagoons, rivers, and rivers while producing a large amount of electricity using a nature-friendly eco-friendly water storage system configured to purify |
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US10968506B2 (en) | 2015-12-24 | 2021-04-06 | Posco | High-manganese hot-dip aluminum-coated steel sheet having excellent coating adhesion |
| 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 |
| KR102045717B1 (en) | 2018-07-12 | 2019-11-18 | 주식회사 포스코 | High manganese steel having reduced rate of surface cracking and method of manufacturing the same |
| KR20200132165A (en) | 2019-05-15 | 2020-11-25 | 주식회사 포스코 | High manganese slab having reduced rate of surface cracking and method of manufacturing the same and high manganese steel sheet using the same |
| KR20210157716A (en) | 2020-06-22 | 2021-12-29 | 한상관 | By storing a large amount of river water to create an artificial fish farm and at the same time to reduce the generation of fine dust, it improves the polluted air in the atmosphere, and at the same time, preferentially discharges clean water molecules with a heavy specific gravity so that the polluted river water is converted into clean river water. A nature-friendly water purification eco-friendly method that naturally purifies the water quality of reservoirs, lakes, dams, lagoons, rivers, and rivers while producing a large amount of electricity using a nature-friendly eco-friendly water storage system configured to purify |
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