KR20120134390A - Heat resistance cold-rolled steel sheet having excellent formability for working and manufacturing method thereof - Google Patents
Heat resistance cold-rolled steel sheet having excellent formability for working and manufacturing method thereof Download PDFInfo
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- KR20120134390A KR20120134390A KR1020110053259A KR20110053259A KR20120134390A KR 20120134390 A KR20120134390 A KR 20120134390A KR 1020110053259 A KR1020110053259 A KR 1020110053259A KR 20110053259 A KR20110053259 A KR 20110053259A KR 20120134390 A KR20120134390 A KR 20120134390A
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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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
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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
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
- C21D8/0426—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
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
- C21D8/0436—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
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
- C21D8/0473—Final recrystallisation annealing
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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
- C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
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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
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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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
- C21D2211/005—Ferrite
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Heat Treatment Of Sheet Steel (AREA)
Abstract
The present invention relates to a high heat-resistant cold-rolled steel sheet excellent in workability and a method for manufacturing the same, by weight% C: 0.002 to 0.005%, Nb: 0.05 to 0.10%, Mn: 0.07 to 0.55%, Al: 0.01 to 0.10%, P Highly heat-resistant cold-rolled steel sheet having excellent workability including: 0.003 to 0.020%, N: 0.002 to 0.006%, S: 0.015% or less, balance Fe and other unavoidable impurities, and a method of manufacturing the same.
According to the present invention, it can be manufactured at low cost compared to the conventional stainless steel sheet, has various processing characteristics of elongation flangeability, bending property and deep drawing (excellent room temperature workability), and age-resistant by solid element precipitation The increase in yield point does not occur, not only excellent moldability, but also excellent high temperature strength, it is possible to manufacture a high temperature resistant cold rolled steel sheet for processing excellent in shape freezing properties of high-temperature applications.
Description
The present invention relates to a high heat resistant cold rolled steel sheet and a method for manufacturing the same for use in automobiles, home appliances, boilers, and the like, and more particularly, a high heat resistant cold rolled steel sheet and a method for manufacturing the same, which are manufactured by optimizing steel components and process conditions. It is about.
Cast iron is generally used for parts of products such as automobile exhaust systems, household flues, ovens and boilers, but aluminum is melted to secure such high temperature characteristics because it is continuously exposed to high temperatures of several hundred degrees (° C.) and requires high heat resistance. Plated steel sheet, stainless steel sheet, etc. were processed and used.
Here, the high temperature property is one of the characteristics when the processed product is used in a high temperature environment, and includes sag resistance, high temperature strength, and discoloration resistance, and the product property may be degraded due to local temperature rise when using a product such as an automobile exhaust system. High temperature characteristics are required. The sag resistance is a phenomenon in which the steel sheet is repeatedly exposed to high temperature, causing a change in material and sagging. When such a phenomenon occurs, it is difficult to maintain the shape of the molded part. Since the product shape is deformed or destroyed due to deterioration, it is necessary to satisfy the yield strength of 55 MPa or more at a high temperature of about 700 ° C. in order to secure the shape freezing property. Discoloration resistance, which is a surface property for securing, is required.
Conventionally, stainless steel sheet has been mainly used for heat resistance. However, stainless steel sheet is not only expensive to manufacture due to the addition of expensive alloying elements such as Cr and Ni, but also has a grain boundary of Cr and C when heated at high temperature. By combining, grain boundary corrosion occurs in the Cr depleted zone, which is caused by the precipitation of chromium carbide (chromium carbide) at the grain boundary, resulting in poor corrosion resistance.
In addition, in order to secure oxidation resistance at high temperature, an aluminum hot dip galvanized steel sheet may be used, but when the aluminum hot dip galvanized steel sheet is heated to a high temperature of 400 ° C. or higher, an alloy layer at an interface due to the interdiffusion reaction between Fe and Al is grown. There is a problem in that the application can be applied because it loses the gloss of the surface in a short time and the color change is insufficient heat resistance.
In addition, in addition to the high temperature characteristics described above, heat-resistant steel sheet is manufactured so that products such as automobile exhaust system, home communication, oven and boiler, etc. are accommodated in a limited space, and formed into a complicated shape by various methods to expand or bend after piping. In addition to the high temperature characteristics, a room temperature processability is also required because a process is required.
In order to solve this problem, Japanese Patent Laid-Open No. Hei 8-319548 intends to manufacture a hot-dip aluminum plated steel sheet having excellent high temperature strength by forming a coating layer on the surface of the steel sheet, but improving the plating conditions rather than improving the characteristics of the steel sheet. Since the present invention is not only difficult to adjust when the plating layer is changed, there is a problem that it is difficult to obtain target heat resistance.
In addition, Japanese Laid-Open Patent Publication No. 9-176816 attempts to improve heat resistance and workability by heat-treating a steel sheet after adjusting aluminum content of Al and solid solution N in steel, but the steel sheet is used at a temperature of 550 ° C. or higher. It is difficult to be applied to a member of, and it is not easy to adjust the amount of the steel component added.
In order to solve the above problems, the present inventors have repeatedly conducted research and experiments and propose the present invention based on the results, and the present invention has high temperature characteristics and room temperature processability, such as automobile exhaust system, home communication, oven and boiler. At the same time, the object of the present invention is to provide a highly heat-resistant cold rolled steel sheet and a method for manufacturing the same, which can be manufactured at low cost by optimizing steel components and process conditions while reducing the amount of expensive alloying elements to be used.
In order to achieve the above object, the present invention provides C: 0.002 to 0.005% by weight, Nb: 0.05 to 0.10%, Mn: 0.07 to 0.55%, Al: 0.01 to 0.10%, P: 0.003 to 0.020%, and N: 0.002. Provides a high heat-resistant cold rolled steel sheet for processing having excellent workability, heat resistance and discoloration resistance including ˜0.006%, S: 0.015% or less, balance Fe and other unavoidable impurities.
At this time, the characteristic of the atomic ratio Nb / C of Nb and C is 2.5-4.5.
In addition, the cold rolled steel sheet is characterized in that the Ti-based carbonitride precipitate is formed.
In addition, the cold rolled steel sheet is characterized in that it is made of an equiaxed ferrite and acicular ferrite structure. Here, the volume fraction of the acicular ferrite structure is also characterized by 5 to 15%.
In addition, the present invention is in the weight percent C: 0.002 ~ 0.005%, Nb: 0.05 ~ 0.10%, Mn: 0.07 ~ 0.55%, Al: 0.01 ~ 0.10%, P: 0.003 ~ 0.020%, N: 0.002 ~ 0.006%, S: 0.015% or less, steel slab containing remainder Fe and other unavoidable impurities is heated and hot rolled, cold rolled after winding, and then cold rolled steel sheet is annealed at a temperature of 800 ° C. or higher, and annealed steel sheet It provides a high heat-resistant cold-rolled steel sheet excellent in workability and heat resistance characterized by cooling at a cooling rate of 30 ℃ / sec or more.
At this time, the steel slab is characterized in that the value of the atomic ratio Nb / C of the Nb and C is 2.5 ~ 4.5.
In addition, the hot rolling is also characterized by finish rolling at 900 ~ 940 ℃.
In addition, the hot rolling is characterized in that it comprises the step of cooling the hot rolled hot rolled plate at a cooling rate of 20 ~ 80 ℃ / sec.
The winding is also characterized by being performed at 560 to 680 ° C.
Furthermore, the annealing treatment is also characterized by being performed at 800 to 900 占 폚.
As described above, according to the present invention, it can be manufactured at a lower cost than the conventional stainless steel sheet, and satisfies various processing characteristics of extension flangeability, bending property, and deep drawing property, and thus has excellent room temperature workability, and solid solution element. It is possible to produce high heat resistant cold rolled steel sheet for processing that can extend the service life of the high temperature applied product by securing the shape freezing property because of its high temperature strength. Can be.
Hereinafter, the cold rolled steel sheet of the present invention will be described in detail.
The inventors of the present invention at 700 ° C satisfying various processing characteristics such as stretch-flangeability, bendability, deep drawing, anti-aging properties, and corrosion resistance at low cost. The present invention was completed by repeating the research and experiment to secure the yield strength of 55MPa or more at the same time. As a result, the present invention contains a very low carbon content in the steel component and controls the amount of Nb and the atomic ratio of Nb and C to form fine Nb-based carbonized precipitates, and by optimizing the annealing and cooling conditions, the volume fraction of acicular ferrite structure It is characterized by manufacturing high-temperature cold-rolled steel sheet for processing, which is suitable for product parts such as automobile exhaust system, home communication, oven and boiler, because it has excellent heat resistance at high temperature, corrosion resistance and aging resistance at room temperature, and workability.
First, the reasons for limiting components of the present invention will be described.
Carbon (C) is an element added for improving the strength of the steel sheet, and in the present invention, carbon is mainly consumed by reaction with Nb to form Nb-based carbide precipitates. As the amount of C added increases, the tensile and yield strength increases, but when excessively added, the workability decreases, so the upper limit is preferably 0.005%. However, if the content is less than 0.002%, sufficient Nb-based precipitates are not formed and the grain size is increased, so that not only a sudden change in the material occurs but also it is difficult to secure high temperature characteristics, so the content of C is limited to 0.002 to 0.005%.
Manganese (Mn) is a solid solution strengthening element that increases the strength of steel and improves hot workability, but is an element that inhibits ductility and workability by MnS formation. Therefore, when Mn is added excessively, ductility falls and it becomes a factor of economic deterioration and center segregation by addition of a large amount of alloying elements, so an upper limit is 0.55%. However, if less than 0.07%, the workability is improved, but it is difficult to secure the target strength, the Mn content is limited to 0.07 ~ 0.55%.
Aluminum (Al) is an element added for deoxidation of molten steel and is preferably contained in an amount of 0.01% or more because it is combined with solid solution elements in steel to improve aging characteristics. However, when excessively added in excess of 0.10%, the amount of inclusions in the steel increases to cause surface defects and workability is lowered, so the Al content is limited to 0.01 to 0.10%.
Phosphorus (P) is an element that improves the strength and corrosion resistance of steel, and it is preferable to contain 0.003% or more in order to secure these properties. However, if the content exceeds 0.020%, it causes central segregation during casting and lowers workability. The content is limited to 0.003 to 0.020%.
Nitrogen (N) exists in solid solution inside the steel and is effective for reinforcing the material. If it contains less than 0.002%, sufficient rigidity cannot be obtained, and the precipitate formation site is reduced. If the content exceeds 0.006%, Since it causes aging and hardening occurs and deteriorates moldability, N content is limited to 0.002% to 0.006%.
Sulfur (S) combines with Mn in the steel to form non-metallic inclusions that act as corrosion initiation points and causes red shortness, so it is desirable to reduce the content as much as possible, so the content of S is limited to 0.015% or less. . However, in order to ensure the said effect reliably, it is preferable to manage at 0.010% or less.
Niobium (Nb) combines with solid solution elements in steel to form Nb-based carbide precipitates to improve aging resistance and workability.Nb-based carbide precipitates increase the strength of steel sheets and suppress grain growth at high temperatures, thereby increasing ferrite. It is preferable to contain 0.05% or more because it provides the effect of refining the particles, but if the content exceeds 0.10%, the material is hardened, which leads to a decrease in the operability of the continuous annealing treatment and deteriorates the surface properties of the steel sheet, thus the content of Nb Is limited to 0.05 to 0.10%.
In order to secure the high temperature and room temperature characteristics targeted by the present invention, it is necessary to consider the effects of precipitate formation and solid solution elements in the steel. For this purpose, it is also important to maintain room temperature aging resistance, processability and high temperature strength at the same time by maintaining the atomic ratio Nb / C of Nb and C in a certain range.
When the atomic ratio Nb / C of Nb and C is 2.5 to 4.5, Nb-based carbide precipitates form solid solution elements in the steel to secure room temperature aging resistance and processability, and by appropriately controlling the annealing and cooling conditions. By forming fine Nb-based precipitates to suppress grain growth at high temperatures, it is possible to secure excellent high temperature characteristics by controlling the ferrite microstructure. However, when the value of Nb / C is less than 2.5, there is a problem that the room temperature aging resistance and workability deteriorate due to excessive solid solution elements in the steel, and the precipitation amount of the Ti-based precipitates is insignificant and excellent high temperature strength cannot be secured. In addition, when the value exceeds 4.5, the material hardens, the temperature of the recrystallization is rapidly increased, the surface properties deteriorate and the workability of the post-process is lowered. Therefore, the value of Nb / C is 2.5 to 4.5. It is limited to.
The cold rolled steel sheet of the present invention comprises the above components and consists of the balance Fe and other unavoidable impurities. And alloy elements may be further added to improve the properties of the present cold-rolled steel, if necessary, it is not interpreted to be excluded from the scope of the present invention by the addition of alloy elements not identified in the embodiment of the present invention.
On the other hand, the cold-rolled steel sheet of the present invention is characterized by consisting of an equiaxed ferrite (polygonal ferrite) and acicular ferrite tissue, the needle-like ferrite tissue is a kind of bainite that is nucleated and grown in the mouth of austenite before transformation As it is nucleated and grown from fine non-metallic inclusions dispersed in steel, ferrite laths are relatively excellent in ductility and toughness due to the disordered structure in which ferrite laths form a high angle boundary with each other. . Therefore, the present invention by controlling the conditions of the annealing and cooling process appropriately secures the volume fraction of the needle-like ferrite structure 5-15% to form a high-potential-density type microstructure to suppress abnormal growth of grains at high temperature to increase the high temperature strength By securing it, heat resistance can be improved. If the volume fraction of the acicular ferrite structure is less than 5%, it is difficult to secure the high temperature strength, so that target heat resistance is difficult to be obtained. If the volume fraction of the acicular ferrite structure is more than 15%, the workability is deteriorated by hardening of the material. There is a problem, and the volume fraction of the needle ferrite is limited to 5 to 15%.
Hereinafter, the manufacturing method of the high heat resistant cold rolled steel sheet excellent in workability of this invention is demonstrated in detail.
After reheating the steel slab having the composition described above, it is hot rolled, cold rolled after winding, and cooled at a cooling rate of 30 ° C./sec or higher for an annealing steel sheet at a temperature of 800 ° C. or higher to produce a high heat resistant cold rolled steel sheet having excellent workability. Can be.
After reheating the steel slab formed like the above-described component system at a normal temperature, the finish rolling temperature during hot rolling is 900 to 940 ° C. If the finish rolling temperature is less than 900 ° C, the hot rolling is completed in a relatively low temperature region. When the final formed grains are mixed and workability and rolling property are lowered, and when the finish rolling temperature exceeds 940 ° C, uniform hot rolling is not performed throughout the thickness, resulting in insufficient grain refinement, which is caused by grain coarsening. Since impact toughness falls, finish rolling temperature is restrict | limited to 900-940 degreeC.
After the hot finish rolling, the hot rolled steel sheet is cooled at a run-out table at a cooling rate of 20 to 80 ° C./sec. If the cooling rate is less than 20 ° C./sec, the grain growth is promoted. This is because coarse crystal grains are formed, which is a factor of deterioration of strength and workability, and when the cooling rate exceeds 80 ° C / sec, it acts as a cause of variation of materials due to non-uniform width cooling.
After cooling in the runout table, the hot rolled steel sheet is wound at a temperature of 560 ~ 680 ℃. When the coiling temperature is less than 560 ℃, the material of the hot rolled material is somewhat hardened, so that the load in the cold rolling process, which is the next process, becomes large, making it difficult to secure rolling property, and the nonuniformity of the width direction increases, resulting in a difference in the production behavior of low-temperature precipitates. Due to this material variation is caused workability is lowered, there is a problem that the high temperature characteristics are deteriorated. In addition, when the coiling temperature exceeds 680 ℃, there is a problem that the structure of the final product is produced coarse, deterioration of workability and corrosion resistance, the coiling temperature is limited to 560 ~ 680 ℃.
After the wound steel sheet is subjected to pickling treatment and cold rolling to a target thickness, the steel sheet undergoes a continuous annealing process at a temperature of 800 ° C. or higher for recrystallization and microstructure control. The annealing temperature of 800 ° C. or more corresponds to a temperature for sufficiently securing the transformation driving force of the needle-like ferrite structure. If the annealing temperature is less than 800 ° C., there is a problem in that the volume fraction of the acicular ferrite structure present in the microstructure of the target steel sheet cannot be obtained, thereby making it difficult to secure excellent high temperature characteristics. However, since the surface defects of the steel sheet may increase during high temperature annealing, the annealing temperature is preferably managed at 900 ° C. or less.
The annealed steel sheet can secure a volume fraction of the target acicular ferrite structure through a cooling process, for which the cooling rate is maintained at 30 ℃ / sec or more. This is because when the cooling rate is less than 30 ° C./sec, it is difficult to obtain a volume fraction of the target acicular ferrite structure due to slow cooling.
Hereinafter, the present invention will be described in more detail with reference to Examples.
Invented steels 1 and 2 and Comparative steels 1 to 5 prepared by melting the composition as shown in Table 1 below under the process conditions as shown in Table 2 to produce cold rolled steel invention materials 1 to 5 and Comparative materials 1 to 10 After that, the volume fraction of the acicular ferrite structure and the characteristics at room temperature and high temperature were evaluated for each of the prepared cold rolled steel sheets.
Yield elongation phenomenon of the characteristics shown in Table 3 was indicated as occurring when the elongation was generated by measuring the yield point elongation through the tensile test, and not occurring when the elongation did not occur. After the steel sheet was processed, it was divided according to the degree of surface bending, and the bending index representing this was divided into five stages, and 1 to 2 stages with relatively small bending were satisfactory. Was determined to be defective.
In addition, the sag resistance test was determined to be defective when the sagging of the steel sheet after measuring the sagging of the steel sheet after heating the material of 250mm in length, 30mm in width for 100 hours at 700 ℃ using a heat treatment equipment, The high temperature yield strength test determined that the yield strength was less than 55 MPa at 700 ° C., and the quality was good if the yield strength was more than 55 MPa.
In addition, the workability test was judged to be defective when a work crack occurred during normal temperature processing.
At this time, in Table 1, the value of the atomic ratio Nb / C of Nb and C refers to the ratio of the value obtained by dividing the weight percentage of each element component by its atomic weight, respectively.
As shown in Table 3, Inventive Materials 1 to 5 in which the steel components and the process conditions satisfy the scope of the present invention did not occur in the yield point elongation and good bending resistance was excellent in aging resistance, Nb-based carbide precipitates The yield strength at high temperature and the sag resistance after heat treatment (sag resistance) were good due to the formation of and the optimization of the volume fraction of the needle-like ferrite structure.
On the other hand, although the steel components of Table 1 and the like are the invention steels satisfying the scope of the present invention, Comparative Materials 1 to 5, in which some of the process conditions of Table 2 are out of the scope of the present invention, are mostly low in volume fraction of acicular ferrite structure. It did not have high temperature characteristics, and workability and aging resistance were also poor in many cases.
In addition, although the process conditions of Table 2 satisfy the scope of the present invention, Comparative Materials 6 to 10 in which the steel components C, Nb, or the atomic ratio of Nb and C of Table 1, etc., are outside the scope of the present invention, the volume of the acicular ferrite structure The fractions were low and often had poor room temperature and high temperature characteristics. Among them, Comparative material 7 had no yield point stretching phenomenon and good bending resistance, so that aging resistance and workability were good, but sag resistance and high temperature yield strength corresponding to high temperature characteristics were poor. Because it is out of range. In addition, Comparative Materials 8 to 10 had a high amount of solid carbon in steel, which was poor in workability and aging resistance, and had a low Nb / C value, resulting in a small amount of Nb-based precipitates, and a low volume fraction of acicular ferrite structure. It was poor and it was difficult to satisfy | attain a normal temperature workability and a high temperature characteristic simultaneously.
As a result, it is possible to optimize the compositional conditions of the steel and the conditions of the manufacturing process (especially annealing and cooling conditions) to form fine Nb-based carbide precipitates, and to control the volume fraction of the needle-like ferrite structure to satisfy both workability and heat resistance simultaneously at low cost. The heat resistant cold rolled steel sheet could be manufactured.
The above embodiment is only one example, and the present invention is not limited thereto. Any thing that has substantially the same structure and the same effect as the technical idea described in the claim of the present invention is included in the technical scope of this invention.
Claims (11)
A high heat resistant cold rolled steel sheet having excellent workability, wherein the atomic ratio Nb / C of Nb and C is 2.5 to 4.5.
The cold rolled steel sheet is a high heat resistant cold rolled steel sheet, characterized in that the Nb-based carbide precipitates are formed.
The cold rolled steel sheet is a high heat-resistant cold-rolled steel sheet, characterized in that consisting of an equiaxed ferrite and acicular ferrite structure.
A high heat resistant cold rolled steel sheet, characterized in that the volume fraction of the acicular ferrite structure is 5 ~ 15%.
The steel slab is a method for producing a high heat resistant cold rolled steel sheet having excellent workability, characterized in that the value of Nb / C ratio of Nb / C is 2.5 ~ 4.5.
The hot rolling is a method for producing a high heat resistant cold rolled steel sheet having excellent workability, characterized in that the finish rolling at 900 ~ 940 ℃.
The hot rolling is a method for producing a high heat resistance cold rolled steel sheet, characterized in that the step of cooling the hot rolled hot rolled sheet at a cooling rate of 20 ~ 80 ℃ / sec.
Said winding is performed at 560-680 degreeC, The manufacturing method of the high heat resistant cold-rolled steel sheet excellent in workability.
The annealing treatment is carried out at 800 ~ 900 ℃ high manufacturing method of high heat resistant cold rolled steel sheet, characterized in that.
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Cited By (1)
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| KR20190078406A (en) * | 2017-12-26 | 2019-07-04 | 주식회사 포스코 | Cold rolled steel sheet having excellent high temperature mechanical properties as well as room temperature workability and method of manufacturing the same |
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| KR20190078406A (en) * | 2017-12-26 | 2019-07-04 | 주식회사 포스코 | Cold rolled steel sheet having excellent high temperature mechanical properties as well as room temperature workability and method of manufacturing the same |
| WO2019132384A1 (en) * | 2017-12-26 | 2019-07-04 | 주식회사 포스코 | Cold-rolled steel sheet having excellent high-temperature properties and room-temperature workability, and method for manufacturing same |
| CN111527228A (en) * | 2017-12-26 | 2020-08-11 | Posco公司 | Cold-rolled steel sheet having excellent high-temperature characteristics and room-temperature workability, and method for producing same |
| EP3733906A4 (en) * | 2017-12-26 | 2020-11-04 | Posco | Cold-rolled steel sheet having excellent high-temperature properties and room-temperature workability, and method for manufacturing same |
| JP2021509435A (en) * | 2017-12-26 | 2021-03-25 | ポスコＰｏｓｃｏ | Cold-rolled steel sheet with excellent high-temperature characteristics and room-temperature workability and its manufacturing method |
| CN111527228B (en) * | 2017-12-26 | 2021-12-21 | Posco公司 | Cold-rolled steel sheet having excellent high-temperature characteristics and room-temperature workability, and method for producing same |
| US11578379B2 (en) | 2017-12-26 | 2023-02-14 | Posco | Cold-rolled steel sheet having excellent high-temperature properties and room-temperature workability |
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