KR20140066593A - Trip steel sheet with excellent galvanizing property and method of manufacturing the steel sheet - Google Patents
Trip steel sheet with excellent galvanizing property and method of manufacturing the steel sheet Download PDFInfo
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- KR20140066593A KR20140066593A KR1020120134016A KR20120134016A KR20140066593A KR 20140066593 A KR20140066593 A KR 20140066593A KR 1020120134016 A KR1020120134016 A KR 1020120134016A KR 20120134016 A KR20120134016 A KR 20120134016A KR 20140066593 A KR20140066593 A KR 20140066593A
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- C—CHEMISTRY; METALLURGY
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- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- 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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- 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
- C21D1/26—Methods of 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/005—Heat treatment of ferrous alloys containing Mn
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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
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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- 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
- C21D8/021—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular fabrication or treatment of ingot or slab
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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
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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
- 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
- C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
- C23G3/00—Apparatus for cleaning or pickling metallic material
- C23G3/02—Apparatus for cleaning or pickling metallic material for cleaning wires, strips, filaments continuously
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
- B21B2001/221—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length by cold-rolling
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Abstract
Description
TECHNICAL FIELD The present invention relates to a TRIP (Transform Induced Plasticity) steel, and more particularly, to a TRIP steel having excellent plating ability by using a heat treatment temperature change during an annealing process and a manufacturing method thereof.
TRIP steels are manufactured through a series of processes including hot rolling, cold rolling and annealing.
In particular, TRIP steels are produced by forming austenite in an annealing process, partially retaining austenite at room temperature through cooling control, and transforming the retained austenite to martensite during plastic deformation.
As described above, since the process of transforming the residual austenite into martensite during the plastic deformation is included in the TRIP steel manufacturing process, the stress concentration is relaxed and the ductility can be improved. Therefore, the produced TRIP steel is advantageous in strength and ductility at the same time.
The TRIP steel generally contains silicon (Si) in an amount of 0.5 wt% or more. Therefore, oxidizing elements such as Si and Mn are selectively oxidized and concentrated on the surface, thereby forming an oxide film on the surface. This oxide film has a problem of deteriorating the plating quality. In order to solve this problem, existing researches use a method of controlling the air-fuel ratio in the direct-fin furnace to form a pre-oxide on the surface and suppress the surface enrichment of Si and Mn by the pre-oxide. However, it is very difficult to precisely control the air-fuel ratio in the furnace. Therefore, if the air-fuel ratio is too high, the pre-oxide film becomes too thick and thereafter the residual oxide that has not been reduced is present in the indirect heating furnace in the reducing atmosphere. Soot is deposited, and so on.
As a background art related to the present invention, Korean Patent Laid-Open Publication No. 10-2009-0066614 (published on June 24, 2009) discloses a high-strength cold-rolled steel sheet, a hot-dip galvanized steel sheet and a manufacturing method thereof excellent in workability .
An object of the present invention is to provide a TRIP steel sheet excellent in plating ability by using heat treatment temperature change during annealing and a method of manufacturing the same.
In order to accomplish the above object, a TRIP steel sheet manufacturing method according to an embodiment of the present invention includes: a hot rolling step of reheating, hot rolling, cooling and winding a steel slab to form hot rolled steel; A cold rolling step of cold rolling the pickled hot rolled steel; An annealing process in which the cold-rolled steel is rapidly heated to 800 to 950 占 폚 for 40 to 80 seconds and then heat-treated at 800 to 950 占 폚; And an austempering step of subjecting the annealed steel to a constant temperature transformation in the bainite transformation temperature range.
In this case, the annealing may be performed at 800 to 950 ° C for 5 to 200 seconds, and then cooled to a bainite transformation temperature at a cooling rate of 10 to 70 ° C / s.
According to another aspect of the present invention, there is provided a method of manufacturing a TRIP steel sheet, the method including: a hot rolling step of reheating, hot rolling, cooling and winding a steel slab to form hot rolled steel; A cold rolling step of cold rolling the pickled hot rolled steel; An annealing process in which the cold-rolled steel is rapidly heated to 800 to 950 占 폚 for 40 to 80 seconds and then heat-treated at 800 to 950 占 폚; Subjecting the annealed steel to a constant temperature transformation at a bainite transformation temperature range for 30 to 200 seconds; And a hot dip galvanizing step of hot-dipping the upgraded steel at 460 to 480 ° C.
In the method of manufacturing TRIP steel according to the present invention, the temperature of the steel sheet is rapidly heated to 800 to 950 ° C for the annealing process to increase the reaction rate for forming the preliminary oxide, thereby controlling the thickness of the preliminary oxide to an appropriate amount without changing the existing air- The surface enrichment of silicon and manganese was suppressed and excellent plating properties could be secured.
1 schematically shows a method of manufacturing a TRIP steel sheet according to an embodiment of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention, and how to accomplish them, will become apparent with reference to the embodiments and drawings described in detail below.
However, it is to be understood that the present invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. It is intended that the disclosure of the present invention be limited only by the terms of the appended claims.
Hereinafter, a TRIP steel sheet having excellent plating ability using the heat treatment temperature change according to the present invention and a method of manufacturing the same will be described in detail.
1 schematically shows a method of manufacturing a TRIP steel according to an embodiment of the present invention.
Referring to FIG. 1, the illustrated TRIP steel manufacturing method includes a hot rolling step (S110), a cold rolling step (S120), an annealing step (S130), and an after-tempering step (S140). Referring to FIG. 1, the TRIP steel manufacturing method according to the present invention may further include a hot dip galvanizing step (S150) and further include an alloying heat treatment step (S160).
Hot rolling process
In the hot rolling step (S110), the steel slab is subjected to reheating, hot rolling, cooling, and winding to form hot rolled steel.
Steel slabs are produced through a continuous casting process after obtaining molten steel through a steelmaking process.
Slab reheating is performed to reuse the segregated components during casting. The reheating of the slab is preferably carried out at a temperature of the slab reheat temperature (SRT): 1150 to 1250 ° C. If the slab reheating temperature is lower than 1150 DEG C, there is a problem that the segregated components can not be reused. On the other hand, when the slab reheating temperature exceeds 1250 deg. C, the austenite grain size increases and the crystal grains of the ferrite grains are coarsened, making it difficult to secure the strength.
The slab reheating is preferably carried out for 2 to 3 hours in the above temperature range. When the reheating temperature of the slab is less than 2 hours, the degree of homogenization of the steel slab is insignificant, which may cause deterioration of quality. Conversely, when the slab reheating temperature exceeds 3 hours, it is not economically useful.
The hot rolling is preferably carried out such that the finishing rolling temperature (FDT) is 850 to 950 캜. If the finish rolling temperature is lower than 850 占 폚, excessive electric potential may be introduced into the ferrite during rolling, and coarse grains may be formed on the surface of the steel during cooling or winding. On the other hand, when the finish rolling temperature exceeds 950 DEG C, the size of the ferrite crystal grains increases and the strength can be reduced.
Coiling after cooling is preferably carried out at a coiling temperature (CT) of 550 to 650 ° C. If the coiling temperature exceeds 650 ° C, manganese, silicon, etc. may be segregated. On the other hand, if the coiling temperature is less than 550 占 폚, the ductility is lowered and the workability is difficult to secure.
The hot rolled steel sheet to be used in the TRIP steel sheet production method is not particularly limited, but is preferably 0.1 to 0.20% carbon (C), 0.2 to 1.5% silicon (Si), manganese (Al): 0.3 to 1.0%, Nb: 0.02 to 0.06%, and N (N): 0.02 to 0.06% ): 60 ppm or less, and the remaining iron (Fe) and inevitable impurities can be presented.
Hereinafter, the content of each component contained in the TRIP steel according to the present invention and the reason for addition thereof will be described.
Carbon (C) is added to ensure strength of the steel. Carbon also serves to stabilize the austenite phase according to the amount that is concentrated in the austenite phase.
The carbon is preferably added in an amount of 0.12 to 0.20 wt% of the total weight of the steel. When the addition amount of carbon is less than 0.12 wt%, the second phase fraction in the TRIP steel according to the present invention is lowered and it is difficult to secure sufficient strength. If the content of carbon exceeds 0.20 wt%, the strength is increased but the weldability may be greatly reduced.
Silicon (Si) acts as a deoxidizer in the steel. Silicon also stabilizes the ferrite and contributes to strength. Silicon also serves to increase the ferrite fraction by promoting austenite-ferrite transformation.
The silicon is preferably added in an amount of 0.2 to 1.5% by weight based on the total weight of the steel. If the addition amount of silicon is less than 0.2% by weight, the silicon addition effect can not be obtained properly. On the contrary, when the addition amount of silicon exceeds 1.5% by weight, an oxide such as Mn 2 SiO 4 is formed on the surface in the annealing step despite the rapid heating of the steel sheet, thereby deteriorating the plating property.
Manganese (Mn) contributes to the improvement of the strength of the steel through solid solution strengthening and penetration. In addition, manganese stabilizes austenite to facilitate the formation of retained austenite and martensite.
The manganese is preferably added in an amount of 2.0 to 3.0% by weight based on the total weight of the steel. When the content of manganese is less than 2.0% by weight, the effect of addition thereof is insufficient and it is difficult to secure the strength. On the other hand, when the addition amount of manganese exceeds 3.0 wt%, a manganese band structure is formed and the segregation increases sharply, which deteriorates the workability and weldability of the steel.
Phosphorus (P) contributes to improving the strength of steel by solid solution strengthening, but if it is contained excessively, it causes hot brittleness and deteriorates weldability.
Accordingly, in the present invention, the content of phosphorus is limited to 0.02% by weight or less of the total weight of the steel in consideration of the above points.
Sulfur (S) inhibits the toughness and weldability of steel and increases MnS nonmetallic inclusions in steel.
Therefore, in the present invention, the content of sulfur is limited to 0.001% by weight or less of the total weight of the steel in consideration of the above-mentioned points.
Aluminum (Al) acts as deoxidizer with silicon to remove oxygen in steel to prevent cracking during slab manufacturing. In particular, aluminum forms an FeAl 2 O 4 oxide on the surface favorable for plating wettability. In addition, aluminum bonds with nitrogen (N) in the steel to form AlN to make the structure finer.
In the present invention, in order to compensate for the decrease in the amount of silicon (Si) that reduces the plating ability by forming an oxide such as Mn 2 SiO 4 on the surface in the over-addition, the addition amount of aluminum (Al) By weight or more. However, if aluminum is added in an amount exceeding 1.0 wt% of the total weight of the steel, the heating and holding temperature in the annealing step after the cold rolling step becomes higher than the normal working temperature, which may hinder productivity. Therefore, in the present invention, the amount of aluminum added is limited to 0.3 to 1.0 wt% of the total weight of the steel.
Niobium (Nb) forms a niobium-based carbonitride precipitate. The niobium-based carbonitride precipitates interfere with grain boundary growth during hot rolling and anomalous reverse annealing, and is refined when grain refinement is performed, thereby improving strength and ductility. In addition, niobium improves steel strength through solid solution strengthening in iron (Fe).
The niobium is preferably added in an amount of 0.02 to 0.06% by weight based on the total weight of the steel. If the addition amount of niobium is less than 0.02% by weight, the effect of addition thereof is insufficient and it is difficult to expect improvement in strength and the like. On the contrary, when the addition amount of niobium exceeds 0.06% by weight, processability and moldability are deteriorated.
Nitrogen (N) contributes to the formation of niobium carbonitride, but when contained in large amounts, the molten zinc has a problem in that it is supersaturated in the cooling process or the cooling process of the alloying process to lower the uniform elongation.
In the present invention, the content of nitrogen is limited to 60 ppm or less of the total weight of the steel sheet.
Cold rolling process
In the cold rolling step (S120), the hot-rolled steel is pickled and cold-rolled. The rolling reduction during cold rolling can be about 50% or more.
Annealing process
In the annealing step (S130) of the present invention, the cold-rolled steel is rapidly heated to 800 to 950 占 폚 for 40 to 80 seconds and then heat-treated at 800 to 950 占 폚.
Normally, in the production of TRIP steel sheet, the steel sheet is heated to about 650 to 700 ° C for the annealing process. In this case, there is a problem that recrystallization does not occur, silicon and magnesium are concentrated on the surface at the beginning of the annealing process, and an oxide which adversely affects the plating ability is formed.
However, in the present invention, the steel sheet is rapidly heated to 800 to 950 DEG C within 40 to 80 seconds. As a result, despite the recrystallization, surface enrichment of silicon and manganese could be suppressed and the plating ability could be improved because pre-oxides were formed before the silicon and manganese moved to the surface, Barrier).
In the present invention, the annealed step (S130) is performed by heating and holding the cold-rolled steel at 800 to 950 ° C for 5 to 200 seconds, and then cooling to a bainite transformation temperature at a cooling rate of 10 to 70 ° C / s. When the annealing temperature is less than 800 ° C, the physical properties, particularly, the tensile strength are lowered. If the annealing temperature exceeds 950 ° C, the productivity may be a problem. When the heating holding time is less than 5 seconds, the austenite phase is not sufficiently formed during the heating and holding, and it is difficult to control the fraction of the ferrite and the second phase. If the heating holding time exceeds 200 seconds, productivity is lowered.
In the annealing step, the ferrite transformation and pearlite transformation can be avoided at an average cooling rate of 10 to 70 DEG C / s from the annealing temperature, and quenched to the bainite transformation temperature. When the cooling rate at this time is less than 10 ° C / second, pearlite is formed at the time of cooling, and the residual austenite (γ) finally obtained is small. On the other hand, when the cooling rate exceeds 70 ° C / s, it is difficult to apply to a cooling method using roll quenching or gas jet.
The cooling rate is controlled to the bainite transformation temperature. In the present invention, the bainite transformation temperature range may be approximately 500 to 400 占 폚. When the control is terminated prematurely at a higher temperature than the bainite transformation temperature zone and thereafter cooled at a significantly slower rate, for example, the retained austenite (γ) is not easily generated and excellent elongation can not be ensured. On the other hand, when cooling is carried out at the cooling rate to the lower temperature region than the bainite transformation temperature region, the amount of the residual austenite (?) Transformed into the ruthenium is increased, so that it is difficult to ensure excellent elongation.
Austempering process
After the annealing step, the annealing step (S140) is preferably carried out for 30 to 200 seconds at the bainite transformation temperature to thermally transform the annealed steel. By maintaining the temperature at the above-mentioned temperature range for 30 seconds or more, the concentration of C in the retained austenite (γ) can be efficiently progressed in a short time to obtain a stable large amount of retained austenite (γ) It is possible to reliably manifest the TRIP effect by the < / RTI > On the other hand, if the temperature holding time exceeds 200 seconds, the TRIP effect due to the residual austenite (?) Can not be sufficiently exhibited.
Hot dip galvanizing process
In the hot-dip galvanizing process (S150), hot-tempered steel is hot-dip galvanized.
Hot dip galvanizing can be carried out in such a manner that the annealed steel is continuously dipped in a plating bath in which the temperature of 460 to 480 캜 is maintained.
The plating temperature is preferably 460 to 480 캜. When the plating temperature is lower than 460 DEG C, it is difficult to sufficiently coat the surface of the steel. Conversely, when the plating temperature exceeds 480 DEG C, the plating adhesion may be lowered.
Alloying heat treatment process
In the present invention, the alloying heat treatment step (S160) may be performed for stable growth of the hot-dip galvanized layer.
In the present invention, the steel after completion of the hot dip galvanizing is reheated to a temperature of 490 to 540 占 폚 and then subjected to an alloying heat treatment, followed by cooling to 200 to 300 占 폚 at a temperature of 20 to 50 占 폚 / s to perform an alloying heat treatment step (S150).
When the alloying heat treatment temperature is lower than 490 ° C, stable growth of the hot-dip galvanized layer is difficult. On the other hand, if the alloying heat treatment temperature exceeds 540 占 폚, the plating adhesion may be lowered.
Further, the cooling performed after the alloying heat treatment can be carried out for securing the martensite fraction. When the cooling rate is less than 20 DEG C / s or the cooling termination temperature exceeds 300 DEG C, the martensite fraction securing effect is insignificant. Conversely, if the cooling rate exceeds 50 DEG C / s or the cooling end temperature is less than 200 DEG C, it is difficult to control the martensite fraction due to excessive quenching.
The TRIP steel according to the present invention has a composite structure including ferrite, retained austenite, and other phases through the above-described processes such as a hot rolling process, a cold rolling process, an annealing process including rapid heating, . The other phase may be at least one of bainite and martensite.
Further, as a result of the hot dip galvanizing of the TRIP steel according to the present invention, the plated area was less than 0.1% and the plating property was also excellent.
Example
Hereinafter, the configuration and operation of the present invention will be described in more detail with reference to preferred embodiments of the present invention. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense.
The contents not described here are sufficiently technically inferior to those skilled in the art, and a description thereof will be omitted.
1. Manufacture of TRIP steel plate
The steel sheet comprises 0.15% of C, 0.5% of Si, 2.5% of P, 0.01% of P, 0.001% of S, 0.4% of Al, 0.05% of Nb and 50 ppm of N and the balance Fe and unavoidable impurities The steel slabs were reheated at 1200 캜 for 2 hours, finishing hot-rolled at 900 캜, cooled to 600 캜 and wound. Thereafter, cold rolling was carried out at a reduction ratio of 50% after the pickling treatment. Thereafter, the steel sheet was heated to the temperature described in 1 for 60 seconds, and heat treatment was performed for 100 seconds. After cooling to 450 DEG C at an average cooling rate of 30 DEG C / s, austempering was performed for 150 seconds. Thereafter, hot-dip galvanizing was performed at 465 ° C, and then alloying heat treatment was performed at 520 ° C.
[Table 1]
2. Surface Property Evaluation
The surface physical properties were evaluated by measuring the uncoated areas.
Referring to Table 1, in the case of the steel sheet according to Comparative Example 1 in which rapid heating was not performed, the uncoated area showed 0.8%, but in the case of the steel sheets according to Examples 1 and 2 in which the rapid heating was performed, Which is less than 0.1%.
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. I will understand.
Accordingly, the true scope of protection of the present invention should be defined by the following claims.
S110: Hot rolling
S120: Cold rolling process
S130: annealing step
S140: Austempering process
S150: Hot-dip galvanizing process
S160: Alloying heat treatment process
Claims (10)
A cold rolling step of cold rolling the pickled hot rolled steel;
An annealing process in which the cold-rolled steel is rapidly heated to 800 to 950 占 폚 for 40 to 80 seconds and then heat-treated at 800 to 950 占 폚; And
And subjecting the annealed steel to a constant temperature transformation at a bainite transformation temperature region.
The annealing step
Heating at 800 to 950 캜 for 5 to 200 seconds, and cooling to a bainite transformation temperature at a cooling rate of 10 to 70 캜 / s.
In the hot rolling process,
The reheating is carried out at a temperature of 1150 to 1250 占 폚,
The hot rolling is carried out at a finish rolling temperature of 850 to 950 캜,
Wherein the winding is carried out at 550 to 650 占 폚.
The steel slab
0.1 to 0.20% of C, 0.2 to 1.5% of Si, 2.0 to 3.0% of Mn, 0.02% or less of P, 0.001% or less of S, 0.3 to 1.0% of Al, 0.02 to 0.06% of Nb, , N: 60 ppm or less, and the balance of Fe and unavoidable impurities.
A cold rolling step of cold rolling the pickled hot rolled steel;
An annealing process in which the cold-rolled steel is rapidly heated to 800 to 950 占 폚 for 40 to 80 seconds and then heat-treated at 800 to 950 占 폚;
Subjecting the annealed steel to a constant temperature transformation at a bainite transformation temperature range for 30 to 200 seconds; And
And a hot dip galvanizing step of hot-dip galvanizing the above-tempered steel at 460 to 480 ° C.
Further comprising the step of annealing the steel after the hot dip galvanized steel is reheated to a temperature of 490 to 540 캜 to perform an alloying heat treatment and cooling the steel at 200 to 300 캜 at a temperature of 20 to 50 캜 / Steel manufacturing method.
The annealing step
Heating at 800 to 950 캜 for 5 to 200 seconds, and cooling to a bainite transformation temperature at a cooling rate of 10 to 70 캜 / s.
In the hot rolling process,
The reheating is carried out at a temperature of 1150 to 1250 占 폚,
The hot rolling is carried out at a finish rolling temperature of 850 to 950 캜,
Wherein the winding is carried out at 550 to 650 占 폚.
The steel slab
0.1 to 0.20% of C, 0.2 to 1.5% of Si, 2.0 to 3.0% of Mn, 0.02% or less of P, 0.001% or less of S, 0.3 to 1.0% of Al, 0.02 to 0.06% of Nb, , N: 60 ppm or less, and the balance of Fe and unavoidable impurities.
Wherein the microstructure comprises ferrite and retained austenite.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| KR1020120134016A KR20140066593A (en) | 2012-11-23 | 2012-11-23 | Trip steel sheet with excellent galvanizing property and method of manufacturing the steel sheet |
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| Application Number | Priority Date | Filing Date | Title |
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| KR1020120134016A KR20140066593A (en) | 2012-11-23 | 2012-11-23 | Trip steel sheet with excellent galvanizing property and method of manufacturing the steel sheet |
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| KR20140066593A true KR20140066593A (en) | 2014-06-02 |
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| KR1020120134016A KR20140066593A (en) | 2012-11-23 | 2012-11-23 | Trip steel sheet with excellent galvanizing property and method of manufacturing the steel sheet |
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| Country | Link |
|---|---|
| KR (1) | KR20140066593A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109504900A (en) * | 2018-12-05 | 2019-03-22 | 鞍钢股份有限公司 | Ultrahigh-strength cold-rolled phase-change induced plasticity steel and preparation method thereof |
| CN115181889A (en) * | 2021-04-02 | 2022-10-14 | 宝山钢铁股份有限公司 | 1180 MPa-grade low-carbon low-alloy hot-dip galvanized dual-phase steel and rapid heat treatment hot-dip galvanizing manufacturing method |
-
2012
- 2012-11-23 KR KR1020120134016A patent/KR20140066593A/en not_active Application Discontinuation
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109504900A (en) * | 2018-12-05 | 2019-03-22 | 鞍钢股份有限公司 | Ultrahigh-strength cold-rolled phase-change induced plasticity steel and preparation method thereof |
| CN115181889A (en) * | 2021-04-02 | 2022-10-14 | 宝山钢铁股份有限公司 | 1180 MPa-grade low-carbon low-alloy hot-dip galvanized dual-phase steel and rapid heat treatment hot-dip galvanizing manufacturing method |
| CN115181889B (en) * | 2021-04-02 | 2023-08-11 | 宝山钢铁股份有限公司 | 1180 MPa-level low-carbon low-alloy hot dip galvanized dual-phase steel and rapid heat treatment hot dip galvanizing manufacturing method |
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