KR20190020694A - METHOD FOR MANUFACTURING COOLED ROLLED STEEL STRIP WITH TRIP CHARACTERISTICS CONTAINING HIGH-STRENGTH MANGEN-CONTAINING RIG - Google Patents

Abstract

The present invention relates to a method of making a cold rolled steel strip made of a high strength manganese containing strip having TRIP characteristics. Wherein the high strength manganese containing steels contain iron (in weight percent), C: 0.0005 to 0.9, Mn: not less than 3.0 and not more than 12, the remainder being iron containing unavoidable steel- related elements, one or more of the following elements being selectively Al: 10 or less, Si: 6 or less, Cr: 6 or less, Nb: 1.5 or less, V: 1.5 or less, Ti: 1.5 or less, Mo: 3 or less, Cu: 3 or less, Sn: 0.5 or less, W: 5 or less, Co: 8 or less, Zr: 0.5 or less, Ta: 0.5 or less, Te: 0.5 or less, B: 0.15 or less, P: 0.1, especially less than 0.04, S: , N: at most 0.1, particularly at less than 0.05, and Ca: at most 0.1. According to the present invention, in order to improve the corresponding method, the cold rolling to the required final thickness occurs at a temperature of more than 50 캜 and not more than 400 캜 before the first impact.

Description

METHOD FOR MANUFACTURING COOLED ROLLED STEEL STRIP WITH TRIP CHARACTERISTICS CONTAINING HIGH-STRENGTH MANGEN-CONTAINING RIG

The present invention relates to a method of making cold rolled steel strips with TRIP characteristics made of high strength manganese containing steels. Steel strips are understood below to mean steel strips as well as steel strips in particular. Typical tensile strengths of these steels are 800 MPa to 2000 MPa. The elongation at break A80 includes values of about 3% to 40%.

European Patent EP 2 383 353 A2 discloses high strength manganese containing steels wherein the steel strip is produced from such a steel and a method for producing such a steel strip. These steels are composed of the following elements (content is related to steel melt in weight%): 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 content of these elements is at most 0.5. It is known that steel can be produced in a more cost effective manner than steel with high manganese content, and at the same time has a high elongation at break and is characterized by considerably improved deformability in this regard.

A method for producing a steel strip from the above-described high strength manganese-containing steel comprises the following steps of operation:

Melting the above-described molten steel,

- preparing a starting product for subsequent hot rolling, said molten steel being cast from a string into a string separating at least one slab or thin slab as a starting material for hot rolling, or being supplied to the hot rolling process as a starting material Casting into a cast strip, producing a starting product,

- heat treating the product to make the starting product at a hot rolling start temperature of 1150 to 1000 ° C,

Hot rolling a starting product to form a hot strip having a thickness of at most 2.5 mm, the hot rolling step comprising the step of heating the starting product, which is terminated at a hot-rolling end temperature, Hot rolling,

- reeling the hot strip to form a coil at a coiling temperature of less than 700 캜 and optionally annealing the hot strip to cold-roll it to at most 60% of the thickness of the hot strip.

Depending on the alloying location, these steels may contain metastable austenite for stress-induced martensite formation (TRIP effect).

International patent application WO 2005/061152 A1 also describes a method for producing hot strips from successfully cold-deep-drawn deformable low-strength steels having from 9 to 30% Mn by weight. In addition to the high level of tensile strength, the hot strip has TRIP characteristics. German publication DE 197 27 759 A1 also discloses a successfully deep-processed ultra-high strength austenitic low-strength steel having a tensile strength of 1100 MPa or less with TRIP and TWIP characteristics. The German publication DE 10 2012 111 959 A1 is preferably used for cold forming at temperatures in the range of ambient temperatures of + 25 ° C to 200 ° C to improve the harness and deformability, Describe manganese-containing steels. German publication DE 10 2009 030 324 A1 describes high manganese-containing steels with low hydrogen embrittlement tendency and high tensile strength and high elongation at break. The patent application US 2012/0059196 A1 discloses a method for producing a hot strip having a horizontal strip casting installation. The hot strip is composed of major constituents of Fe, Mn, Si and Al and has TRIP and / or TWIP characteristics and is suitable for deep processing. The patent US 6 358 338 B1 also relates to a process for producing steel strips from high manganese containing steels. In order to increase tensile strength and elongation, strip steel is subjected to recrystallization annealing after cold rolling. In patent application US 2009/0074605 A1, high manganese-containing steel strips with excellent impact behavior and high tensile strength and elongation are cold rolled after hot rolling and then annealed at 600 ° C.

German publication DE 10 2012 013 113 A1 also describes TRIP steels with predominantly ferrite-based basic microstructure with residual austenite incorporated. TRIP steels achieve high values of uniform elongation and tensile strength due to cold-hardening.

The disadvantage of such manganese-containing steels with TRIP effect is that the degree of deformation that can be achieved during the production of cold rolled steel strips is limited due to the cold hardening of the material during cold rolling and the high load on the roll stands associated with them. In order to achieve a high degree of cold forming, a plurality of cold rolling steps with correspondingly low degrees of deformation are often required, and prior to the new cold rolling step, in each case the recrystallization annealing will loosen the material to enable cold rolling do. This procedure with multiple cold rolling stages with intermediate recrystallization annealing is very time consuming and expensive and involves additional CO ₂ release.

It is an object of the present invention to provide a method of making cold rolled steel strips made of high strength manganese steel with TRIP properties as described above and to cold rolling at the required final thickness in a more economical and ecologically friendly manner . In addition, a manufacturing pathway to the cold-rolled steel strip should be provided with the required final thickness from the melting of the steel.

This object is achieved by a method of manufacturing a steel strip having the features of claim 1. Advantageous embodiments of the invention are described in the respective dependent claims.

The process according to the invention for producing cold-rolled steel strips from high-strength manganese-containing steels with TRIP properties (by weight) comprises:

C: 0.0005 to 0.9

Mn: more than 3.0 but not more than 12

The remainder contains iron, which contains inevitable steel-related elements, and one or more of the following elements are selectively added by alloying (relative to weight percent and to molten steel):

Al: 10 or less

Si: 6 or less

Cr: 6 or less

Nb: 1.5 or less

V: 1.5 or less

Ti: 1.5 or less

Mo: 3 or less

Cu: 3 or less

Sn: not more than 0.5

W: 5 or less

Co: 8 or less

Zr: 0.5 or less

Ta: 0.5 or less

Te: 0.5 or less

B: 0.15 or less

P: maximum 0.1, particularly less than 0.04

S: Up to 0.1, especially less than 0.02

N: at most 0.1, especially less than 0.05

Ca: 0.1 or less

Characterized in that rolling to the required final thickness is carried out at a temperature of from 50 캜 to 400 캜 or more while avoiding cold rolling at ambient temperature.

In the context of the present invention, a high strength steel is understood as a steel having a tensile strength of 800 MPa to 2000 MPa.

The cause of intense cold hardening of these high strength manganese containing steels with TRIP effect is the ratio of retained austenite contained in microstructure to martensite and / or ferrite and / or bainite and / or pearlite. This retained austenite can be converted to martensite at an appropriate ambient temperature (the TRIP effect of both? '-Martensite as well as? -Martensite) and the substantial effect of martensite formation due to the TRIP effect at ambient temperatures below about 50 ° C The ratio always occurs. This leads to an intense increase in the rolling load during cold rolling of the material and, in relation thereto, even during the first pass, and is associated with a reduction in the maximum degree of deformation. Cold rolled strips have high levels of strength and low residual deformation capacity. Also, deformation twin can occur due to the influence of mechanical stress (TWIP effect).

According to the present invention, by raising the strain temperature before the first pass to above 50 DEG C to below 400 DEG C, the TRIP transition mechanism from the austenite to the martensite is totally or partially inhibited and substantially during rolling in one rolling pass High degree of deformation is possible.

The term " cold rolling " relates generally to cold rolling at ambient temperatures. In the context of the present invention, the term " cold rolling " is also used for cold rolling at elevated temperatures. In contrast to hot rolling, in the case of cold rolling according to the invention, this elevated temperature is clearly lower than the AC1 conversion temperature associated with microstructure conversion. The cold rolling according to the present invention preferably occurs under a homologous temperature at which no creeping process still occurs in the steel sheet.

In Fig. 1 which is one attached drawing, the influence of the deformation temperature on the curing behavior of the material during rolling is shown using the characteristic values of the tensile test. An apparently large elongation value is obtained at a strain temperature of 100 DEG C or 200 DEG C compared with a strain at an ambient temperature of 20 DEG C and an apparently low rate of increase of the tensile strength.

The hot strip or pre-strip is heated to a temperature of greater than 50 DEG C to 400 DEG C, preferably 70 DEG C to 250 DEG C, or the hot strip or preliminary strip is heated to a temperature of greater than 50 DEG C to 400 DEG C, And then cold-rolled to the required final thickness at a temperature before the first pass of above 50 占 폚 and below 400 占 폚, preferably between 70 占 폚 and 250 占 폚. By " at temperature "is understood to mean that the temperature is the result of the preceding process step or that the temperature has been maintained. The preceding process step is the heat available in the hot strip or preliminary strip, in particular in the hot rolling process or in the furnace May refer to a continuous or discontinuous treatment step or reheat step using the retention.

By heating the hot strip to above 50 ° C and below 400 ° C, preferably between 70 ° C and 250 ° C, prior to cold rolling, the stacking fault energy in the first rolling pass is increased to substantially reduce the austenite to martensite transition Or avoiding, the strip is hardened less strongly during the cold rolling process and more deformation twinning (TWIP effect) is formed on the austenite. This results in both a low rolling load during the rolling process and a substantially improved deformation capability for the strip. To compensate for additional heating due to the possibility of deformation during cold forming and to maintain an optimum range of strip temperatures for the TWIP effect, cooling of the strip, for example by compressed air or other gas or gaseous media, And can be selectively performed between individual rolling processes.

In addition, after rolling, the steel strips contain significant residual strain capabilities because the austenite residues that may be present and the twisted twins formed in austenite can convert to martensite in whole or in part at ambient temperature due to the TRIP effect. This is associated with an increase in the maximum elongation and hence a deformation capacity to produce a component from a flat product without additional annealing associated with the cold rolling process.

In addition, the formation of deformation twinning leads to improved behavior during subsequent deformation to hydrogen-induced delayed crack formation and hydrogen embrittlement, as compared to cold rolling, optionally without prior heating, with an associated annealing process.

The steel used for the process according to the invention has a multiphase microstructure consisting of ferrite and / or martensite and / or bainite and / or pearlite and residual austenite / austenite. The percentage of retained austenite / austenite may be between 5% and 80%. Residual austenite / austenite can be partially or fully converted to martensite due to the TRIP effect when mechanical stresses are present.

The alloys forming the basis of the present invention have TRIP and / or TWIP effects when subjected to appropriate mechanical stresses. Due to the intense hardening (similar to cold hardening) at ambient temperatures induced by TRIP and / or TWIP effects and increased dislocation density, the steel achieves very high values in terms of elongation at break, particularly uniform elongation and tensile strength do. In an advantageous manner, this property is achieved due to the retained austenite present only in the case of manganese content exceeding 3% by weight.

The use of the word " to " in the definition of the content range means that for example 0.01% to 1% by weight also includes the limit values of 0.01 and 1 in this embodiment.

The steel according to the invention is particularly suitable for producing high strength steel strips which can be provided with metal or non-metallic coatings, for example zinc-based coatings. It can be especially useful in the automotive industry, shipbuilding, plant design, infrastructure, aerospace industry and household appliances. A high proportion of austenite means that the steel produced according to the invention is suitable for low temperature stresses.

Preferably, the steel has a tensile strength (Rm) of greater than 800 MPa but no greater than 2000 MPa and a elongation at break (A80) of 3 to 40%, preferably 8 to 40%.

When the steel has the following alloy composition in weight percent, in particular uniform and homogeneous material properties can be achieved:

C: 0.05 to 0.42

Mn: more than 5 but less than 10

The remainder is iron, which contains inevitable steel-related elements, and one or more of the following elements are selectively added (by weight%) by alloying:

Al: 0.1 to 5, especially 0.5 to 3

Si: 0.05 to 3, especially more than 0.1 and not more than 1.5

Cr: 0.1 to 4, especially 0.5 to 2.5 or less

Nb: 0.005 to 0.4, particularly 0.01 to 0.1

B: 0.001 to 0.08, particularly 0.002 to 0.01

Ti: 0.005 to 0.6, particularly 0.01 to 0.3

Mo: 0.005 to 1.5, particularly 0.01 to 0.6

Sn: less than 0.2, especially less than 0.05

Cu: less than 0.5, particularly less than 0.1

W: 0.01 to 3, especially 0.2 to 1.5

Co: 0.01 to 5, especially 0.3 to 2

Zr: 0.005 to 0.3, especially 0.01 to 0.2

Ta: 0.005 to 0.3, particularly 0.01 to 0.1

Te: 0.005 to 0.3, especially 0.01 to 0.1

V: 0.005 to 0.6, particularly 0.01 to 0.3

Ca: 0.005 to 0.1.

Alloying elements are generally added to the steel to affect certain properties in the desired manner. The alloying elements can thereby affect other properties of the other steel. The effects and interactions are generally highly dependent on the solution state of the material, the presence and amount of other alloying elements. Correlation is diverse and complex. The effect of alloying elements in alloys according to the present invention will be discussed in greater 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 elongation and toughness characteristics, and the maximum content is set at 0.9 wt%. The minimum content is set to 0.0005% by weight. An amount of 0.05 to 0.42% by weight is preferred because the ratio of retained austenite to other phase fractions in this range can be set in a particularly advantageous manner.

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 3 wt.% Is not sufficient to stabilize the austenite, thereby impairing the stretch properties, while exceeding 12 wt.% Stabilizes the austenite too much and consequently reduces the strength properties, especially the yield strength. For the manganese steels according to the invention having an average manganese content, a range of from 5 to less than 10% by weight is preferred because in this range the ratio of phase fraction to each other and the conversion mechanism This is because it can be affected.

Aluminum Al: improves strength and elongation properties, decreases relative density, and affects the conversion behavior of alloys according to the present invention. An Al content of more than 10% by weight results in lowered elongation properties and mainly results in brittle fracture behavior. In the manganese steel according to the present invention having an average manganese content, an Al content of 0.1 to 5 wt% is preferable in order to increase the strength with a good elongation. In particular, the content by weight of not less than 0.5 and not more than 3, in particular, enables high levels of strength and elongation at break.

Silicon Si: interferes with the diffusion of carbon, reduces relative density, and increases strength and elongation and toughness properties. The content of more than 6% by weight prevents further processing by cold rolling by brittleness of the material. Therefore, a maximum content of 6% by weight is set. Optionally, an amount of 0.05 to 3% by weight is set, because the content of this range has a positive effect on the deformation properties. A Si content of greater than 0.1 and less than or equal to 1.5 weight percent has been shown to be particularly advantageous for strain and conversion characteristics.

Cr Cr: improves strength and reduces corrosion rates, delays formation of ferrite and pearlite, and forms carbides. The higher the content, the lower the stretching properties and the higher the cost, so the maximum content is set at 6 wt%. In the manganese steel according to the present invention having an average manganese content, a Cr content of 0.1 to 4% by weight is preferred in order to reduce precipitation of coarse Cr carbide. In particular, the content of weight percentages of greater than 0.5 and less than 2.5 has proved to be advantageous for stabilizing austenite and precipitating fine Cr carbide. In order to obtain the advantageous properties of Al and Si addition in addition to Cr, the total content of Al + Si + Cr should be more than 1.2% by weight.

Molybdenum Mo: acts as a carbide former, increasing strength and increasing resistance to delayed crack formation and hydrogen embrittlement. The Mo content exceeding 3% by weight lowers the stretching property, so that a maximum content of 3% by weight is set. In the manganese steel according to the present invention having an average manganese content, an Mo content of 0.0005 to 1.5% by weight is preferable in order to avoid precipitation of an excessively large Mo carbide. In particular, the content of 0.01% to 0.06% by weight leads to precipitation of the desired Mo carbides and reduces the alloy cost.

Phosphorus is a trace element of iron ore and dissolved as a substituting atom in iron atoms. 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 maximum of 0.1 wt.%, With a content of wt.% Less than 0.04 being advantageously required for the reasons stated above.

Sulfur S: Like phosphorus, it is bound by trace elements of iron ore. It is not generally required in steel, because it exhibits a strong tendency to segregation and has a large embrittlement effect in which softening 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 vacuum treatment). For the reasons stated above, the sulfur content is limited to a maximum of 0.1% by weight. In a particularly preferred manner, it is limited to less than 0.2 weight percent to reduce the precipitation of MnS.

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 containing free nitrogen tend to have a strengthening 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 means of aluminum, vanadium, niobium or titanium alloys. For the reasons stated above, the nitrogen content is limited to a maximum of 0.1% by weight, and a content of less than 0.05% by weight is preferably required to substantially avoid the formation of AIN.

Microalloy elements are generally only added in very small amounts (less than 0.1% by weight per element). Unlike alloying elements, they act primarily by the formation of precipitates, but can also affect the properties of the dissolved state. Despite the addition of small amounts, the microalloy elements greatly affect the manufacturing conditions, processing characteristics and final properties.

Typical fine alloying elements are vanadium, niobium and titanium. These elements can be dissolved in the iron lattice to form carbides, nitrides and carbonitrides with carbon and cyanide.

Vanadium V and niobium Nb: these form carbides in particular and act in a grain refinement manner, thereby simultaneously improving strength, toughness and elongation properties. A content of more than 1.5% by weight does not provide any further advantage. Alternatively, for vanadium and niobium, a minimum content of 0.005 wt.% Or more and a maximum content of 0.6 (V) or 0.4 (Nb) wt.% Are preferably provided so that the alloying element advantageously provides grain refinement. Further, in order to achieve an optimal grain refinement while improving the economic feasibility, the content of V may be continuously limited to 0.01 to 0.3 wt%, and the content of Nb may be continuously limited to 0.01 to 0.1 wt% .

Tantalum Ta: Tantalum acts as a carbide forming agent in a grain refining manner in a manner similar to niobium, thereby simultaneously improving strength toughness and stretching properties. A content exceeding 0.5% by weight does not further improve the properties. Therefore, a maximum content of 0.5% by weight is selectively set. A minimum content of 0.005% by weight and a maximum content of 0.3% by weight, which can advantageously be produced by grain refinement, are preferred. In order to improve the economic feasibility and optimize the grain refinement, the content of 0.01 wt% to 0.1 wt% is desirably desired.

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 1.5% by weight lowers the stretching property, so that a maximum Ti content of 1.5% by weight is set. Optionally, a minimum content of 0.005 and a maximum content of a maximum content of 0.6% by weight, in which Ti precipitates advantageously, are set. Preferably, a minimum content of 0.01 wt.% And a maximum content of 0.3 wt.% Are provided, ensuring optimum sedimentation behavior at low alloy cost.

Tin Sn: Tin increases strength, but accumulates under the scale layer and at grain boundaries at high temperatures, similar to copper. A maximum content of 0.5 wt.% Or less is selectively provided because of the infiltration into the grain boundaries resulting in the formation of a low melting point phase and associated cracking of the microstructure and brittle solder. For the reasons stated above, a content of less than 0.2% by weight is preferably set. A content of less than 0.05% by weight is particularly advantageously advantageous in order to avoid low melting point phases and cracking in the microstructure.

Copper Cu: Reduces corrosion rate and increases strength. The content of more than 3% by weight lowers the productivity by forming a low melting point phase during casting and hot rolling, so that a maximum content of 3% by weight is set. Optionally, a maximum content of less than 0.5% by weight can be set so that the occurrence of cracks during casting and hot rolling can advantageously be prevented. A Cu content of less than 0.1 wt.% Proved to be particularly advantageous in avoiding low melting point phases and avoiding cracking.

Tungsten W: acts as a carbide generator to increase strength and heat resistance. When the W content exceeds 5 wt%, the softening property is lowered, so that the maximum content is set to 5 wt%. Optionally, a maximum content of 3% by weight and a minimum content of 0.01% by weight are preferably set so that precipitation of the carbide occurs preferably. In particular, a minimum content of 0.2 wt.% And a maximum content of 1.5 wt.% Are preferred, which ensures that the optimum settling behavior is possible at low cost.

Cobalt Co: Increases steel strength, stabilizes austenite and improves heat resistance. The content of more than 8% by weight lowers the stretching property, so that the maximum content is set to 8% by weight. Optionally, a maximum content of 5 wt% or less and a minimum content of 0.01 wt% are set to advantageously improve strength and heat resistance. Preferably, a minimum content of 0.3% by weight and a maximum content of 2% by weight are provided, which in turn affects the austenite stability with strength properties.

Zirconium Zr: acts as a carbide generator and improves strength. The Zr content exceeding 0.5% by weight lowers the stretching property, so that the maximum content is set to 0.5% by weight. Optionally, a maximum content of 0.3 wt.% And a minimum content of 0.005 wt.% Are set, in which carbide is advantageously precipitated in this range. Preferably, a minimum content of 0.01 wt.% And a maximum content of 0.2 wt.% Are provided to advantageously enable optimal carbide precipitation at low alloy cost.

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 0.15% by weight greatly reduces the properties of the stretch and toughness, so that the maximum content is set to 0.15% by weight. Optionally, a minimum content of 0.001% by weight and a maximum content of 0.08% by weight are used, wherein the strength increasing effect of boron is advantageously used. A minimum content of 0.002% by weight and a maximum content of 0.01% by weight, which are guaranteed to enable optimal use for strength increase while improving the conversion behavior, are preferred.

Tellurium Te: improves corrosion resistance and mechanical properties and machinability. In addition, Te increases the strength of the MnS, resulting in a smaller extent in the rolling direction during hot rolling and cold rolling. The content of more than 0.5% by weight lowers the properties of stretching and toughness, so that the maximum content is set to 0.5% by weight. Optionally, a minimum content of 0.005 wt% and a maximum content of 0.3 wt% are set to increase the robustness of the existing MnS and improve the mechanical properties. In addition, a minimum content of 0.01 wt% and a maximum content of 0.1 wt% are preferred, which ensure that optimization of the mechanical characteristics is possible while reducing costs.

Calcium Ca: Used to modify non-metallic oxide inclusions that may act as stress concentration points and cause undesired fracture of the alloy due to microstructure inclusions that weaken the metal complex. In addition, Ca improves the homogeneity of the alloy according to the present invention. A minimum content of 0.0005% by weight may be required to achieve a corresponding effect. A content of greater than 0.1% by weight does not provide any further advantage in the modification of the inclusions, which impairs productivity and should be avoided due to the high vapor pressure of Ca in the molten steel. Thus, a maximum content of 0.1% by weight is provided.

The production route according to the invention to a final steel strip with a required final thickness from steel melt to high strength manganese containing steel of less than 10 mm, preferably less than 4 mm, comprises the following steps:

Melting the molten steel, wherein the molten steel comprises (by weight):

C: 0.0005 to 0.9

Mn: not less than 3.0 and not more than 12,

The remainder is iron, which contains inevitable steel-related elements, and one or more of the following elements are selectively added (by weight%) by alloying:

Al: 10 or less

Si: 6 or less

Cr: 6 or less

Nb: 1.5 or less

V: 1.5 or less

Ti: 1.5 or less

Mo: 3 or less

Cu: 3 or less

Sn: not more than 0.5

W: 5 or less

Co: 8 or less

Zr: 0.5 or less

Ta: 0.5 or less

Te: 0.5 or less

B: 0.15 or less

P: maximum 0.1, particularly less than 0.04

S: Up to 0.1, especially less than 0.02

N: at most 0.1, especially less than 0.05

Ca: 0.1 or less

Casting a molten steel to form a preliminary strip by a horizontal or vertical strip casting process approaching the final dimension or forming a slab or slab by a horizontal or vertical slab or thin slab casting process; Casting a molten steel to form a molten steel,

Hot rolling the slab or thin slab to reheat the slab or thin slab to 1050 ° C to 1250 ° C and then forming a hot strip, or reheating the preliminary strip prepared to approximately final dimensions to 1000 ° C or 1200 ° C Hot working the preliminary strip to form a hot strip, or hot working the preliminary strip without reheating from the casting heat so as to form a hot strip with any intermediate heating between the individual rolling passes of the hot rolling, ,

Winding the hot strip at a coiling temperature between 820 ° C and ambient temperature,

Optionally annealing the hot strip with the following parameters:

Annealing temperature: 580 to 820 占 폚, annealing time: 1 minute to 48 hours,

Rolling the hot strip to a required final thickness of less than 10 mm on the rolled strip at a temperature prior to the first pass of above 50 ° C and below 400 ° C while avoiding cold rolling at ambient temperature,

Optionally annealing the steel strip with the following parameters:

Annealing temperature: 580 to 820 占 폚, annealing time: 1 minute to 48 hours,

- optionally pickling and / or temper rolling the steel strip,

Optionally coating the steel strip with a corrosion resistant coating.

With regard to the additional advantages, please refer to the above mention.

The typical thickness range of the preliminary strip is from 1 mm to 35 mm and for slabs and thin slabs from 35 mm to 450 mm. Rolled or hot rolled to form a hot strip having a thickness between 8 mm and 1 mm, the preliminary strip being hot rolled or cast to approximately final dimensions to form a hot strip having a thickness of 20 mm to 1.5 mm . The cold-rolled steel strip produced according to the present invention has a thickness of, for example, greater than 0.15 mm and less than 10 mm.

The reheating temperature in the range of 720 캜 to 1200 캜 is provided to hot-roll the preliminary strip from the casting heat to form a hot strip with selective intermediate heating between the individual rolling passes of the hot rolling process. If less rolling passes are required, the reheating temperature may be selected at the lower end of the range.

The hot strip may optionally be heat treated at a temperature ranging from 580 DEG C to 820 DEG C for 1 minute to 48 hours, wherein the high temperature is associated with a shorter treatment time and vice versa. Annealing may occur in both a batch-type annealing process (longer annealing time) and, for example, in a continuous annealing process (shorter annealing time). The selective annealing serves to increase the residual austenite fraction of the hot strip prior to the cold rolling process and / or to reduce the strength, thereby advantageously improving the deformation properties for subsequent processing.

After the hot rolling process, cold rolling is performed with the hot strip at elevated temperature according to the present invention to set a thickness of 0.15 mm to 10 mm for the steel strip required for final use. Then, if it is necessary to be combined with the coating process and finally the temper rolling process, the additional annealing process can optionally be carried out by setting the surface structure necessary for the final use.

Preferably, the steel strip is galvanized, metallically, inorganicly or organically coated by hot-dipping or electrolysis.

The steel strip produced by the process according to the invention has a tensile strength (Rm) of not less than 800 MPa but not more than 2000 MPa and an elongation (A80) of 3 to 40%, preferably 8 to 40%. In this case, the high level of strength is related to the low elongation at break, and vice versa.

The cold-rolled steel strip produced in accordance with the present invention may be produced, for example, by cold forming at ambient temperature to form parts, or by warm-forming at a temperature of less than 60 and less than AC3, It can be machined into sheet metal parts, coils or panels, and the intermediate annealing can be omitted depending on the application due to the considerable residual strain capability.

In further processing steps, the cold-rolled steel strip produced in accordance with the present invention may be machined to form a pipe having a longitudinal or helical weld seam, which in this case is also produced by a substantial residual deformation capability of the steel strip Depending on the application, intermediate annealing can be omitted. The pipe may thus comprise an outer and / or inner metal, organic or inorganic coating.

Pipes manufactured in this manner can be further deformed to form the part, for example, drawn or expanded or deformed using the internal high pressure, and further processed.

Therefore, it is mainly used in automobile or utility vehicle industry, engineering, white goods, construction, and is used at temperatures below 0 ℃ and used as ballistic steel. Ballistic steel is used to protect vehicles and buildings from shells and explosions and to have high levels of hardness and toughness.

Attempts have been made to investigate the mechanical properties of steel strips made according to the present invention, for example, using alloys 1 to 4. Alloys 1 to 4 contain the following amounts of the following elements in weight percent:

alloy C Mn Al Si Cr Mo One 0.2 7.0 2.0 0.5 1.0 - 2 0.2 7.0 0.9 0.5 - - 3 0.27 7.4 2.2 0.5 1.2 - 4 0.21 7.2 2.5 0.5 1.2 0.16

For comparison purposes, the steel strips made from the alloys 1 to 4 mentioned above were cold rolled, i. E. Cold rolled at an ambient temperature of less than 50 캜, and also rolled according to the invention at 250 캜. The measured rolling load is given by:

alloy Cumulative rolling load [kN] - Cold rolling Cumulative rolling load [kN] - 250 ℃ Degree of deformation (e = d / d0) [%] Decrease of rolling load [%] One 103000 59000 44 ca. 43 2 144000 55000 44 ca. 62 3 161000 63000 44 ca. 60 4 107000 56000 44 ca. 43

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

The elongation at break (A50) was also evaluated:

alloy Elongation at break A50 [%] Cold rolling Elongation at break A50 [%] Rolling at 250 占 폚 One 2.0 15.5 2 2.5 20.5 3 3.5 19.0 4 3.0 18.5

The elongation property value represents the elongation in the rolling direction.

Claims (25)

CLAIMS What is claimed is: 1. A method of making a cold rolled steel strip from a high strength manganese containing steel having TRIP properties,
The high-strength manganese-containing steel (in weight%):
C: 0.0005 to 0.9
Mn: not less than 3.0 and not more than 12,
The remainder being iron containing inevitable steel-related elements, one or more of the following elements being selectively added (by weight%) by alloying:
Al: 10 or less
Si: 6 or less
Cr: 6 or less
Nb: 1.5 or less
V: 1.5 or less
Ti: 1.5 or less
Mo: 3 or less
Cu: 3 or less
Sn: not more than 0.5
W: 5 or less
Co: 8 or less
Zr: 0.5 or less
Ta: 0.5 or less
Te: 0.5 or less
B: 0.15 or less
P: maximum 0.1, particularly less than 0.04
S: Up to 0.1, especially less than 0.02
N: at most 0.1, especially less than 0.05
Ca: 0.1 or less,
Cold rolling to the required final thickness is carried out at a temperature before the first pass of > 50 DEG C to 400 DEG C,
A method of making a cold rolled steel strip from a high strength manganese containing steel. The method according to claim 1,
The cold rolling to the required final thickness is carried out at a temperature prior to the first pass of cold rolling from < RTI ID = 0.0 > 70 C < / RTI &
A method of making a cold rolled steel strip from a high strength manganese containing steel. 3. The method according to claim 1 or 2,
The hot strip or the preliminary strip is heated to a temperature of greater than 50 DEG C to 400 DEG C, preferably 70 DEG C to 250 DEG C, or the hot strip or preliminary strip is heated to a temperature of greater than 50 DEG C to 400 DEG C, preferably 70 DEG C to 250 DEG C And then cold-rolled to the required final thickness at a temperature before the first pass of above 50 ° C and below 400 ° C, preferably between 70 ° C and 250 ° C,
A method of making a cold rolled steel strip from a high strength manganese containing steel. 4. The method according to any one of claims 1 to 3,
The cooling of the strip to a temperature of 50 DEG C to 400 DEG C, especially 70 DEG C to 250 DEG C,
A method of making a cold rolled steel strip from a high strength manganese containing steel. 5. The method according to any one of claims 1 to 4,
Wherein the steel contains 0.05 to 0.42% by weight of C,
A method of making a cold rolled steel strip from a high strength manganese containing steel. 6. The method according to any one of claims 1 to 5,
Wherein the steel contains more than 5 wt% and less than 10 wt%
A method of making a cold rolled steel strip from a high strength manganese containing steel. 7. The method according to any one of claims 1 to 6,
The steel contains 0.1 to 5% by weight, in particular more than 0.5 to 3% by weight of Al,
A method of making a cold rolled steel strip from a high strength manganese containing steel. 8. The method according to any one of claims 1 to 7,
Wherein the steel contains 0.05 to 3% by weight, especially 0.1 to 1.5% by weight, of Si,
A method of making a cold rolled steel strip from a high strength manganese containing steel. 9. The method according to any one of claims 1 to 8,
Wherein the steel contains 0.1 to 4% by weight, especially 0.5 to 2.5% by weight, of Cr,
A method of making a cold rolled steel strip from a high strength manganese containing steel. 10. The method according to any one of claims 7 to 9,
Wherein the steel has a total content of Al, Si and Cr of more than 1.2% by weight,
A method of making a cold rolled steel strip from a high strength manganese containing steel. 11. The method according to any one of claims 1 to 10,
The steel contains 0.005 to 0.4% by weight, especially 0.01 to 0.1% by weight of Nb,
A method of making a cold rolled steel strip from a high strength manganese containing steel. 12. The method according to any one of claims 1 to 11,
The steel contains 0.005 to 0.6% by weight, especially 0.01 to 0.3% by weight of V,
A method of making a cold rolled steel strip from a high strength manganese containing steel. 13. The method according to any one of claims 1 to 12,
The steel contains 0.005 to 0.6% by weight, especially 0.01 to 0.3% by weight of Ti.
A method of making a cold rolled steel strip from a high strength manganese containing steel. 14. The method according to any one of claims 1 to 13,
The steel contains 0.005 to 1.5% by weight, especially 0.01 to 0.6% by weight of Mo,
A method of making a cold rolled steel strip from a high strength manganese containing steel. 15. The method according to any one of claims 1 to 14,
The steel contains less than 0.2% by weight, especially less than 0.05% by weight of Sn,
A method of making a cold rolled steel strip from a high strength manganese containing steel. 16. The method according to any one of claims 1 to 15,
The steel contains less than 0.5% by weight, especially less than 0.1% by weight of Cu.
A method of making a cold rolled steel strip from a high strength manganese containing steel. 17. The method according to any one of claims 1 to 16,
The steel contains 0.01 to 3% by weight, especially 0.2 to 1.5% by weight, of W,
A method of making a cold rolled steel strip from a high strength manganese containing steel. 18. The method according to any one of claims 1 to 17,
The steel contains 0.01 to 5% by weight, especially 0.3 to 2% by weight of Co,
A method of making a cold rolled steel strip from a high strength manganese containing steel. 19. The method according to any one of claims 1 to 18,
The steel contains 0.005 to 0.3% by weight, especially 0.01 to 0.2% by weight of Zr,
A method of making a cold rolled steel strip from a high strength manganese containing steel. 20. The method according to any one of claims 1 to 19,
The steel contains 0.005 to 0.3% by weight, in particular 0.01 to 0.1% by weight of Ta,
A method of making a cold rolled steel strip from a high strength manganese containing steel. 21. The method according to any one of claims 1 to 20,
The steel contains 0.005 to 0.3% by weight, especially 0.01 to 0.1% by weight of Te,
A method of making a cold rolled steel strip from a high strength manganese containing steel. 22. The method according to any one of claims 1 to 21,
Said steel comprising 0.001 to 0.08% by weight, especially 0.002 to 0.01% by weight of B,
A method of making a cold rolled steel strip from a high strength manganese containing steel. 23. The method according to any one of claims 1 to 22,
Wherein the steel contains Ca in an amount of 0.005 to 0.1 wt%
A method of making a cold rolled steel strip from a high strength manganese containing steel. 24. The method according to any one of claims 1 to 23,
The cold-rolled steel strip having a required final thickness of less than 10 mm, preferably less than 4 mm is produced,
The manufacture of the cold rolled steel strip comprises:
- melting the molten steel according to any one of claims 1 to 23;
Casting a molten steel to form a preliminary strip by a horizontal or vertical strip casting process approaching the final dimension or forming a slab or slab by a horizontal or vertical slab or thin slab casting process; Casting molten steel;
Hot rolling the slab or slab to reheat the slab or thin slab to 1050 to 1250 占 then forming the hot strip or reheating the preliminary strip prepared to approximately final dimensions to 1000 占 폚 to 1200 占 폚 Hot working the preliminary strip to form a hot strip, or hot working the preliminary strip without reheating from the casting heat so as to form a hot strip with any intermediate heating between the individual rolling passes of the hot rolling, ;
Winding the hot strip at a coiling temperature between 820 ° C and ambient temperature;
Optionally annealing the hot strip with the following parameters:
Annealing temperature: 580 to 820 캜, annealing time: 1 minute to 48 hours;
- cold rolling the hot strip or the preliminary strip after the steps according to claims 1 to 3;
Optionally annealing the steel strip with the following parameters:
Annealing temperature: 580 to 820 캜, annealing time: 1 minute to 48 hours;
Optionally acid-cleaning and / or skin-pass rolling the steel strip; And
- optionally coating the steel strip with a metal, organic or inorganic corrosion-resistant coating;
A method of making a cold rolled steel strip from a high strength manganese containing steel. Manufacture of components for use in automotive and utility vehicle industry and engineering, white goods, construction or at low temperatures in the range below 0 ° C to -273 ° C or for use as ballistic steel, or as longitudinal or helical weld seams Use of a steel strip produced according to any one of claims 1 to 24 for producing a pipe with a seam or for producing a part by hot forming, cold forming or warm-forming.

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