KR20190042022A - METHOD FOR MANUFACTURING STRENGTH STEEL STRIP WITH IMPROVED CHARACTERISTICS FOR ADDITIONAL TREATMENT - Google Patents

Abstract

The present invention is a method for producing a high strength steel strip with TRIP / TWIP effect, said method being cost effective, wherein the steel strip is characterized by a good combination of improved characteristics, in particular strength and molding properties, Delayed fracture, hydrogen embrittlement, and increased resistance to liquid metal embrittlement. Said method comprising the steps of: - melting molten steel, said molten steel (in weight percent): C: 0.1 or more and less than 0.3; Mn: 4 or more and less than 8; Al: more than 1 and not more than 2.9; P: less than 0.05; S: less than 0.05; N: less than 0.02; (S) (by weight) of one or more of the following elements: Si: 0.05 to 0.7; Cr: 0.1 to 3; Mo: 0.01 to 0.9; Ti: 0.005 to 0.3; B: 0.0005 to 0.01; melting the molten steel, which is optionally added in an electric arc furnace or blast furnace process with selective vacuum treatment of the melt; Casting the molten steel to form a preliminary strip by a horizontal or vertical strip casting process approximating the final dimension or casting a molten steel to form a slab or thin slab by horizontal or vertical slab or thin slab casting process; - heating to a rolling temperature of from 1050 to 1250 占 폚 or in-line rolling with casting heat; Hot rolling a tempered strip or slab or thin slab to form a hot strip having a thickness of 12 to 0.8 mm at a final rolling temperature of 1050 to 800 占 폚; - winding the hot strip at a temperature greater than 200 ° C and less than 800 ° C; Pickling the hot strip; Annealing the hot strip in a continuous or batch annealing facility at an annealing time of 1 minute to 48 hours and a temperature of 540 DEG C to 840 DEG C; Cold-rolling the hot strip at one or more rolling passes to ambient or elevated temperature; - optionally, electrolytically galvanizing or hot-dip galvanizing the steel strip or applying another type of organic or inorganic coating. The present invention also relates to a high strength, cost effective steel strip having improved characteristics during further processing.

Description

METHOD FOR MANUFACTURING STRENGTH STEEL STRIP WITH IMPROVED CHARACTERISTICS FOR ADDITIONAL TREATMENT

The present invention is directed to a method and a corresponding steel strip for producing ultra-high strength steel strips having improved properties for further processing.

Particularly, the present invention relates to a process for the production of hydrogen-induced delayed cracking (delayed fracture), hydrogen embrittlement and increased resistance to liquid metal embrittlement during welding, excellent cold-formability and warm- Manganese-containing TRIP (metastable organic plastic) and / or TWIP (twin-organoplast) steel.

European patent application EP 2 383 353 A2 discloses a manganese-containing steel, a flat steel product formed of this steel and a method of making this flat steel product. The steel has a tensile strength of 900 to 1500 MPa and a fracture elongation (A80) of 4% or more. The maximum elongation at break (A80) is 8%. In addition, the steel consists of the following elements (content is weight percent and relates to steel melt): C: not more than 0.5; Mn: 4 to 12; Si: 1.0 or less; Al: 3.0 or less; Cr: 0.1 to 4.0; Cu: 4.0 or less; Ni: 2.0 or less; N: 0.05 or less; P: not more than 0.05; S: 0.01 or less, and the balance is iron and unavoidable impurities. Optionally, one or more elements are provided from the group of " V, Nb, Ti ", and the sum of the contents of these elements is at most 0.5. When the Mn content is 5 and the Al content is 2, the total amount is 7. The microstructure of this flat steel product consists of 30-100% martensite, tempered martensite or bainite and the remainder is austenite. This steel is characterized in that it can be produced in a more cost effective manner than steel containing a high content of manganese and at the same time has a high breaking elongation value and a considerably improved deformability in this connection. The process for producing a flat steel from the high strength manganese containing steel described above comprises the following steps of operation: melting the molten steel described above, preparing a starting product for subsequent hot rolling, Wherein at least one slab or thin slab is cast into a casting strip which is cast as a starting product for hot rolling or as a starting strip supplied as a starting product to a hot rolling process, Hot-rolling the starting product to form a hot strip having a thickness of up to 2.5 mm, heating the starting product at a reeling temperature of 700 DEG C or less, Reeling the hot strip to form the hot strip. Optionally, the hot strip may be annealed to 250 to 950 占 폚 and subsequently annealed to 450 to 950 占 폚 after cold rolling. In addition, following cold rolling or hot rolling of flat steel products, the product is provided with a metal anti-corrosion coating or an organic coating.

German Patent Publication DE 10 2012 013 113 A1 also describes a so-called TRIP steel which has a ferritic microstructure mainly with incorporated residual austenite which can be converted to martensite during transformation (TRIP effect). The manganese content of the steel strip is 1.00 to 2.25 weight percent. The steel strip is coated and temper rolled in a melting bath. TRIP steels can achieve uniform elongation and tensile strength due to intense cold-hardening. TRIP steels are used especially for structural components such as sheet metal blanks and weld blanks, chassis components and crash-related parts of vehicles.

European Patent EP 1 067 203 B1 discloses a process for producing steel strips. In this case, a thin strip having a thickness of 1.5 mm to 10 mm is cast (by weight%) from molten steel consisting of at least the following elements: C: 0.001 to 1.6; Mn: 6 to 30; Al: 6 or less; P: not more than 0.2; S: 0.5 or less; N: 0.3 or less, and the balance is iron and unavoidable impurities. The thin strip is hot rolled with a reduction degree between 10% and 60%, pickled, cold rolled to a degree of reduction between 10% and 90%, annealed at 800 to 850 ° C for 1 to 2 minutes, do.

Japanese Patent JP 3 317 303 B2 discloses a high strength steel strip having the following composition in weight percent: C: 0.05 to 0.3; Si: less than 0.2; Mn: 0.5 to 4.0; P: 0.1 or less; S: 0.1 or less; Ni: 0 to 5.0; Al: 0.1 to 2.0; And N 0.01 or less. In this case, the following equation is satisfied: Si + Al = 0.5; Mn + 1/3 Ni 1.0. The microstructure contains at least 5% by volume of retained austenite. In a vacuum laboratory furnace, the melt of the above-mentioned steel is melted. By hot forging, a test block having a thickness of 25 mm is produced. It is then heated to 1250 ° C for 1 hour in an electric furnace. Then, hot rolling is performed at 930 to 1150 캜 to achieve a thickness of the steel strip of 5 mm. For the wound simulation, the steel strip is immediately cooled to 500 캜 and annealed at this temperature for 1 hour in an electric furnace.

In view of this, it is an object of the present invention to provide a process for producing an ultra-high strength steel strip consisting of a manganese-containing TRIP and / or TWIP steel having a strength of 1100 to 2200 MPa which is cost effective, The present invention is to provide a method of manufacturing a steel strip having a good combination of characteristics, particularly strength and molding properties, hydrogen induced delayed crack formation, hydrogen embrittlement, and increased resistance to liquid metal embrittlement. Also, ultra high strength, cost effective steel strips with improved characteristics will be provided during further processing.

This object is achieved, in particular, by a method of producing a flat steel product using the above steel having the features of claim 1 and by an ultra-high strength steel strip having the features of claim 10. Advantageous embodiments of the invention are described in the dependent claims.

According to the present invention, there is provided a method for producing an ultra high strength steel strip, comprising the steps of: - melting molten steel, wherein said molten steel comprises (by weight): C: 0.1 or more and less than 0.3; Mn: 4 or more and less than 8; Al: more than 1 and not more than 2.9; P: less than 0.05; S: less than 0.05; N: less than 0.02; (S) (by weight) of one or more of the following elements: Si: 0.05 to 0.7; Cr: 0.1 to 3; Mo: 0.01 to 0.9; Ti: 0.005 to 0.3; B: 0.0005 to 0.01; melting the molten steel, which is selectively added through a process route of an electric arc furnace or blast furnace-steel plant with selective vacuum treatment of the melt; Casting the molten steel to form a preliminary strip by a horizontal or vertical strip casting process approximating the final dimension or casting a molten steel to form a slab or thin slab by horizontal or vertical slab or thin slab casting process; - heating to a rolling temperature of from 1050 to 1250 占 폚 or in-line roll-out with casting heat; Hot rolling a preliminary strip or slab or thin slab to form a hot strip having a thickness of 12 to 0.8 mm at a final rolling temperature of 1050 to 800 占 폚; - winding the hot strip at a temperature greater than 200 ° C and less than 800 ° C; Pickling the hot strip; Annealing the hot strip in a continuous or discontinuous annealing facility at an annealing time of 1 minute to 48 hours and a temperature of 540 DEG C to 840 DEG C; - cold rolling the hot strip at one or more rolling passes at ambient or elevated temperature; - optionally electrolytically galvanizing or hot-dip galvanizing the steel strip, wherein the strength of 1100 to 2200 MPa, hydrogen induced delayed crack formation, hydrogen embrittlement, and liquid metal embrittlement , And a cost-effectively manufactured steel strip with a good combination of strength, elongation and deformation properties and with TRIP and / or TWIP effects during additional mechanical loading.

The typical thickness range of the preliminary strip is 1 mm to 35 mm and for slabs and thin slabs is 35 mm to 450 mm. The slab or thin slab is hot rolled to form a hot strip having a thickness of 12 mm to 0.8 mm or a preliminary strip cast to approximate a final dimension is hot rolled to form a hot strip having a thickness of 8 mm to 0.8 mm desirable. The cold strip according to the present invention has a thickness of 3 mm or less, preferably 0.1 to 14 mm.

In the context of the process according to the invention, the preliminary strip produced by a two-roller casting process and approximating the final dimensions and having a thickness of 3 mm or less, preferably 1 mm to 3 mm, is already understood as a hot strip. Thus, the preliminary strips made of hot strips do not have a 100% cast structure due to the introduced deformation of the two rollers traveling in opposite directions. Thus, hot rolling does not require separate heating and hot rolling since it already occurs in-line during a two-roller casting process.

Cold rolling of the hot strip may occur at ambient or advantageously elevated temperatures prior to the first rolling pass in one or more rolling passes.

Cold rolling at elevated temperatures is advantageous to reduce rolling forces and to assist in the formation of deformation twinning (TWIP effect). The advantageous temperature of the material rolled before the first rolling pass is 60 to 450 占 폚.

When cold rolling is performed in a plurality of rolling passes, it is advantageous to intermediate heat or cool the steel strip between the rolling passes to a temperature of 60 to 450 DEG C, since the TWIP effect works in a particularly advantageous manner in this area. Depending on the rolling speed and the degree of deformation, additional cooling can be performed which is caused by moderate heating, for example by the degree of very low deformation and rolling speed, and by heating the material with rapid rolling and high degree of deformation.

After cold stripping of the hot strip at ambient temperature, the steel strip is advantageously annealed in a continuous annealing facility, preferably at a temperature of 720 DEG C to 840 DEG C, preferably for an annealing time of 1 to 15 minutes, in order to restore sufficient shaping characteristics. Optionally, the annealing can be performed by a discontinuous annealing facility at a temperature of 550 ° C to 820 ° C and an annealing time of 30 minutes to 48 hours. If necessary for obtaining specific material properties, this irrigation process may be carried out by rolling the steel strip at an elevated temperature.

After the annealing treatment, the steel strip is advantageously cooled to a temperature of from 250 캜 to room temperature and, if necessary, reheated to 300 - 450 캜 to adjust the mechanical properties required in the aging process, if necessary, And then cooled to room temperature. The aging treatment can be advantageously carried out in a continuous annealing plant.

If necessary, the steel strip can be temper rolled after cold rolling, so that the surface structure necessary for the final application is adjusted. The temper rolling can be carried out, for example, by the Pretex® method.

In one advantageous development, steel strips produced in this manner obtain additional coatings on an organic or inorganic basis instead of or after electrogalvanizing or hot dip galvanizing. For example, it may be an organic coating, a synthetic coating or a lacquer or other inorganic coating such as, for example, an iron oxide layer.

Steel strips produced in accordance with the present invention can be used as metal sheets, metal sheet portions or blanks, or can be further processed to form longitudinal or spiral seam-welded pipes.

In addition, steel sheets or steel strips are suitable in a manner particularly advantageous for further processing to form parts by cold forming or warm forming, for example, the automotive industry, infrastructure construction and engineering.

The steel strips with improved characteristics during further processing have a microstructure consisting of 10 to 80% of austenite by volume, 10 to 90% of martensite, the remainder of ferrite having a ratio of less than 20% And has a TRIP / TWIP effect. In this case, a proportion of at least 20% of the martensite is present in the annealed martensite and optionally a proportion of more than 10% of the austenite is present in the form of an annealing or modified twin.

Due to the annealing treatment according to the invention, the steel strip has particularly fine particles with an average particle size of the phase component:

- austenite: less than 500 nm

- martensite, ferrite, bainite: less than 650 nm.

Due to the final annealing of cold strips produced at ambient or elevated temperatures, the austenite is in a metastable state and optionally has a twisted twin so that when a mechanical force is applied (e. G., Molded) And is partially converted to martensite.

The austenite ratio of steel according to the present invention can be partially or completely converted to martensite when mechanical stress is applied (TRIP effect).

The alloys according to the invention have twinning during plastic deformation (TWIP effect) when a corresponding mechanical load is applied. Due to the cold hardening induced by the TRIP and / or TWIP effect, the steel obtains high values in terms of breaking elongation, particularly uniform elongation and tensile strength.

The steel according to the invention can be formed in a particularly advantageous manner by warm forming at 60 to 450 DEG C because the stability of the austenite at these temperatures at least partially inhibits the conversion of austenite to marcensite (TRIP effect), 50-100% of the starting austenite is retained and partially converted to the modified twinning (TWIP effect). Deformation twinning can be converted to martensite by consuming more energy at room temperature (TRIP effect, eg increased energy absorption capacity at impact). The residual elongation that remains until the part breaks up considerably during hot forming compared to cold forming. In addition, the prevention of the TRIP effect during warm-forming leads to a significant improvement in undesirable hydrogen-induced effects (delayed crack formation, hydrogen embrittlement). Also, warm forming serves to increase the 0.2% elastic limit of the advantageously molded material, and the sheet thickness can advantageously be reduced.

The process according to the invention can be used to produce very cost-effective steel strips with only the carbon, manganese and aluminum elements in addition to the required alloy concept in addition to iron. The required annealing process can be advantageously performed by continuous annealing which is considerably more economical than batch type annealing.

The steel strip prepared according to the process according to the invention advantageously has an elastic limit (Rp0.2) of 300 to 1550 MPa, a tensile strength (Rm) of 1100 to 2200 MPa and a breaking elongation A80 ), And high strength tends to be associated with lower rupture elongation and vice versa.

- Rm of more than 1100 MPa and less than 1200 MPa: 25000 MPa% or more and 45000 MPa% or less Rm x A80

- Rm of not less than 1200 MPa and not more than 1400 MPa: 20000 MPa% or more and 42000 MPa% or less Rm x A80

- Rm of not less than 1400 MPa but not more than 1800 MPa: Rm of not less than 10000 MPa% and not more than 40000 MPa%

- Rm greater than 1800 MPa: 7200 MPa% or more and 20000 MPa% or less Rm x A80

Specimen body A80 is used for breaking elongation test according to DIN 50 125.

The elongation and toughness properties are advantageously improved by the onset of the TRIP and / or TWIP effect of the alloy according to the invention.

Steel strips prepared in accordance with the present invention provide excellent combinations of strength, stretch and strain properties. Moreover, the manufacture of this manganese steel according to the present invention having a medium-to-high molecular weight content based on the alloying elements C, Mn, Al (medium to medium intergranular) is very cost effective.

As the Al content increases, the steel has a small amount of Al and has a relatively low density compared to other manganese steels having a medium-to-high molecular weight content. The manganese steel according to the invention is also characterized by increased resistance to delayed cracking (delayed fracture), hydrogen embrittlement and liquid metal embrittlement during welding.

The use of the term " to " such as, for example, from 0.01 to 1% by weight in the definition of the content range means that the limit values - e.g., 0.01 and 1 - are also included.

Alloying elements are usually added to the steel to affect specific properties in the desired manner. Alloying elements can affect other properties of other steels. The effects and interactions are generally highly dependent on the amount, the presence of additional alloying elements and the solution state of the material. Correlation is diverse and complex. The effect of alloying elements in alloys according to the present invention will be discussed in more detail below. The positive effects of alloying elements used in accordance with the present invention will be described below:

Carbon C: necessary to form carbides, stabilize austenite and increase strength. The higher the C content, the lower the welding characteristics and the lower the tensile and toughness characteristics, so that the maximum content is set to less than 0.3 wt%. A minimum addition amount of 0.1 wt% is required to achieve sufficient strength for the material.

Manganese Mn: Stabilizes austenite, increases strength and toughness, and enables transformation-induced martensite formation and / or twinning in the alloy according to the present invention. A content of less than 4 wt.% Is not sufficient to stabilize the austenite, thereby impairing the elongation properties, while at least 8 wt.% Stabilizes the austenite too much and consequently reduces the strength properties, in particular the 0.2% elastic limit. In the manganese steel according to the present invention having a medium-to-high molecular weight content, a range of 4 to 8 wt% is preferable.

Al Al: An Al content of greater than 1 wt% improves strength and elongation properties, reduces relative density and affects the conversion behavior of the alloy according to the present invention. An Al content exceeding 2.9% by weight lowers the stretching properties. The higher Al content also significantly reduces the casting behavior in the continuous casting process. This increases the cost of casting. An Al content exceeding 1% by weight delays precipitation of carbides in the alloy according to the invention. Therefore, a maximum content of 2.9 wt% and a minimum content of more than 1 wt% are set.

Also, for the sum of the minimum contents of Mn and Al, a minimum content of more than 6.5 to 10% by weight should be maintained to ensure the desired conversion behavior. When the content of Mn + Al is 10% by weight or more, the main composition is lowered, and accordingly, the output is decreased, thereby increasing the cost. When the content of Mn + Al is 6.5 wt% or less, sufficient austenite stability can not be assured against the preferable conversion behavior.

Silicon Si: The selective addition of Si in excess of 0.05% by weight interferes with the diffusion of carbon, reduces the relative density, and increases the strength and elongation and toughness properties. The improvement of the cold rolling property can be found by adding Si by alloying. The content of more than 0.7% by weight results in the embrittlement of the material, for example by zinc plating, and negatively affects the hot and cold rolling properties and coating properties. Therefore, a maximum content of 0.7 wt% and a minimum content of 0.05 wt% are set.

The selective addition of chromium Cr: Cr improves strength, reduces corrosion rates, delays formation of ferrite and pearlite, and forms carbides. The maximum content is set to 3% by weight because a high content causes a deterioration of the stretching property. The minimum Cr content for efficacy is set at 0.1% by weight.

The selective addition of molybdenum Mo: Mo acts as a carbide former, increasing strength and increasing resistance to delayed crack formation and hydrogen embrittlement. Mo content of more than 0.9% by weight lowers the stretching property, so that a maximum content of 0.9% by weight and a minimum content of 0.01% by weight are required for sufficient efficacy.

Phosphorus is a trace element of iron ore and is dissolved as a substituting atom in the iron lattice. Phosphorus increases hardness and improves hardenability through solid solution curing. However, attempts are generally made to reduce the phosphorus content as much as possible, since it generally exhibits a strong tendency to segregation due to the low diffusion rate and greatly reduces the level of toughness. Attachment of phosphorus to grain boundaries can cause cracks along grain boundaries during hot rolling. In addition, phosphorus increases the transition temperature from toughness to brittle behavior up to 300 ° C. For the reasons stated above, the phosphorus content is limited to a value of less than 0.05% by weight.

Sulfur S: Like phosphorus, it is bound by trace elements of iron ore. It is generally not required in steel, because it exhibits a strong tendency to segregation and has a large embrittlement effect in which the stretching and tensile properties are degraded. Thus, attempts are made to achieve the amount of sulfur in the melt as low as possible (e.g., by deep desulfurization). For the reasons stated above, the sulfur content is limited to a value of less than 0.05% by weight.

Nitrogen N: Equivalent to steelmaking. And improves the strength and toughness of a steel having a high manganese content of 4 wt% or more in the melted state. Low Mn alloy steels containing less than 4 wt% Mn with free nitrogen tend to have a strong aging effect. Nitrogen diffuses evenly at low temperatures and is equally blocked. Thus, the strength increases with a sharp decrease in toughness. For example, it is possible to bond nitrogen in the form of a nitride by the addition of aluminum or titanium by alloying, and particularly aluminum nitride has a negative effect on the strain characteristics of the alloy according to the present invention. For the reasons stated above, the nitrogen content is limited to less than 0.02% by weight.

Titanium Ti: acts as a grain refinement method as a carbide forming agent, at the same time improving strength, toughness and elongation properties and reducing inter-crystalline corrosion. The Ti content exceeding 0.3 wt% lowers the stretching property, so that a maximum Ti content of 0.3 wt% is set. Optionally, Ti is advantageously precipitated and a minimum content of 0.005 is set to bind the nitrogen.

Boron B: Delays austenite conversion, improves the hot forming properties of steel and increases strength at ambient temperature. This achieves its effect even with a very low alloy content. The content exceeding 0.01% by weight greatly reduces the properties of the stretch and toughness, so that the maximum content is set to 0.01% by weight. Alternatively, a minimum content of 0.0005% by weight is set, in which the strength increasing effect of boron is advantageously used.

Tests were conducted to investigate the mechanical properties of steel strips made according to the present invention and composed of the exemplary alloy 1. Alloy 1 contains an extract of the following elements in the stated amounts by weight, in addition to iron and melt-induced impurities:

For comparison, the steel strips produced from Alloy 1 were cold rolled, i. E., Rolled at room temperature below < RTI ID = 0.0 > 50 C < / RTI > The measured rolling force is given by:

The cumulative rolling force is understood to sum the rolling forces of the individual passes to obtain a comparable measure of power consumption. The rolling force was normalized to a band width of 1000 mm. Deformation degree (e) is defined as the quotient of the thickness change (Δd) of the steel strip under investigation and the initial thickness (d0) of the steel strip under investigation. The reduction in rolling force is a calculated reduction in the rolling force at 250 DEG C compared to the rolling force during cold rolling.

The elongation at break (A80) was also determined:

The elongation property value indicates elongation in the rolling direction. It is clear that there is a significant increase in the elastic limit while the break elongation is the same.

Claims (18)

A method of making ultra-high strength steel strips having a TRIP / TWIP effect,
The method comprising:
- melting the molten steel, wherein the molten steel has (by weight): C: 0.1 or more and less than 0.3; Mn: 4 or more and less than 8; Al: more than 1 and not more than 2.9; P: less than 0.05; S: less than 0.05; N: less than 0.02; (S) (by weight) of one or more of the following elements: Si: 0.05 to 0.7; Cr: 0.1 to 3; Mo: 0.01 to 0.9; Ti: 0.005 to 0.3; B: 0.0005 to 0.01; melting the molten steel, which is optionally added in an electric arc furnace or blast furnace process with selective vacuum treatment of the melt;
Casting the molten steel to form a preliminary strip by a horizontal or vertical strip casting process approximating the final dimension or casting a molten steel to form a slab or thin slab by horizontal or vertical slab or thin slab casting process;
- heating to a rolling temperature of from 1050 to 1250 占 폚 or in-line roll-out with casting heat;
Hot rolling the preliminary strip or slab or thin slab to form a hot strip having a thickness of 12 to 0.8 mm at a final rolling temperature of 1050 to 800 占 폚;
Reeling the hot strip at a temperature of more than 200 ° C and not more than 800 ° C;
Pickling the hot strip;
Annealing the hot strip in a continuous or discontinuous annealing facility at an annealing time of 1 minute to 48 hours and a temperature of 540 DEG C to 840 DEG C;
- cold rolling the hot strip at one or more rolling passes at ambient or elevated temperature; And
- optionally electrolytically galvanizing or hot-dip galvanizing the steel strip or applying another organic or inorganic coating;
A method of manufacturing an ultra high strength steel strip. The method according to claim 1,
Wherein the cold rolling step is performed at a temperature of 60 to < RTI ID = 0.0 > 450 C,
A method of manufacturing an ultra high strength steel strip. 3. The method of claim 2,
During cold rolling in a plurality of rolling passes, the steel strip is selectively heated or cooled to between 60 and < RTI ID = 0.0 > 450 C < / RTI &
A method of manufacturing an ultra high strength steel strip. 4. The method according to any one of claims 1 to 3,
After the step of cold rolling at the above room temperature or elevated temperature, the steel strip is annealed in a continuous annealing facility at an annealing time of 1 to 15 minutes and a temperature of 720 캜 to 840 캜, or at a temperature of 550 캜 to 820 캜 for 30 minutes ≪ / RTI > annealed at < RTI ID = 0.0 >
A method of manufacturing an ultra high strength steel strip. 5. The method of claim 4,
After the annealing process, the steel strip is cooled to a temperature of at least room temperature below 250 占 폚, subsequently reheated to 300-450 占 폚, maintained at this temperature for 5 minutes or less,
A method of manufacturing an ultra high strength steel strip. 6. The method according to any one of claims 1 to 5,
The steel strip may be temper-rolled after the cold rolling step,
A method of manufacturing an ultra high strength steel strip. 7. The method according to any one of claims 1 to 6,
The steel strip is obtained after electroplating or dipping zinc plating to obtain an additional coating on an organic or inorganic basis,
A method of manufacturing an ultra high strength steel strip. 8. The method according to any one of claims 1 to 7,
The steel strip is further processed to form the part by cold forming or warm forming,
A method of manufacturing an ultra high strength steel strip. 9. The method of claim 8,
Wherein the warm-forming takes place at a temperature of 60 to < RTI ID = 0.0 > 450 C,
A method of manufacturing an ultra high strength steel strip. As ultra-high strength steel strip with TRIP / TWIP effect,
Wherein the steel strip comprises, by weight: C: 0.1 to less than 0.3; Mn: 4 or more and less than 8; Al: more than 1 and not more than 2.9; P: less than 0.05; S: less than 0.05; N: less than 0.02; The remainder being iron, including inevitable steel-related elements;
An alloy (in weight%) of one or more of the following elements: Si: 0.05 to 0.7; Cr: 0.1 to 3; Mo: 0.01 to 0.9; Ti: 0.005 to 0.3; B: 0.0005 to 0.01; is optionally added,
The microstructure is composed of 10 to 80% of austenite (by volume), 10 to 90% of martensite, the balance of ferrite and bainite together having a ratio of less than 20%
Ultra high strength steel strip. 11. The method of claim 10,
The sum of the contents of Mn and Al satisfies the equation 6.5 < Mn + Al < 10 (by weight)
Ultra high strength steel strip. 11. The method of claim 10,
A proportion of at least 20% of the martensite is present as an annealed martensite,
Ultra high strength steel strip. 13. The method according to any one of claims 10 to 12,
A proportion of more than 10% of the austenite is present in the form of an annealing or modified twin,
Ultra high strength steel strip. 14. The method according to any one of claims 10 to 13,
The steel strip comprises:
Austenite: less than 500 nm;
- martensite, ferrite, bainite: having an average particle size of phase component of less than 650 nm;
Ultra high strength steel strip. 15. The method according to any one of claims 10 to 14,
The steel strip has a tensile strength (Rm) of 1100 to 2200 MPa, a 0.2% elastic limit (Rp0.2) of 300 to 1550 MPa, and a breaking elongation (A80) of more than 4%
Ultra high strength steel strip. 16. The method according to any one of claims 10 to 15,
The tensile strength Rm (MPa) and the elongation at break A80 (%) were:
- Rm of not less than 1100 MPa but not more than 1200 MPa: Rm x A80 of not less than 25000 MPa% and not more than 45000 MPa%;
- Rm of not less than 1200 MPa but not more than 1400 MPa: Rm x A80 not less than 20000 MPa% and not more than 42000 MPa%;
- Rm of not less than 1400 MPa but not more than 1800 MPa: Rm × A80 of not less than 10000 MPa% and not more than 40000 MPa%; And
- Rm in excess of 1800 MPa: 7200 MPa% to 20000 MPa% Rm x A80;
Ultra high strength steel strip. 17. The method according to any one of claims 10 to 16,
The galvanized steel strip may have additional metal, inorganic or organic coatings on the galvanized coating,
Ultra high strength steel strip. 18. The method according to any one of claims 10 to 17,
The steel strip is produced by a process according to any one of claims 1 to 9,
Ultra high strength steel strip.