RU2711696C1 - Method of producing cold-rolled steel strip from high-strength manganese steel with trip-properties - Google Patents

Abstract

FIELD: metal rolling.SUBSTANCE: invention relates to cold-rolled steel strip made from high-strength manganese steel with TRIP-properties. Steel contains, wt. %: C: from 0.0005 to 0.9, Mn: from 3.0 to 12, optionally one or more of: Al: up to 10, Si: up to 6, Cr: up to 6, Nb: up to 1.5, V: up to 1.5, Ti up to 1.5, Mo: up to 3, Cu: up to 3, Sn: up to 0.5, W: up to 5, Co: up to 8, Zr up to 0.5, Ta: up to 0.5, Te to 0.5, B: to 0.15, P: max. 0.1, in particular < 0.04, S: max. 0.1, in particular < 0.02, N: max. 0.1, in particular < 0.05, and Ca: up to 0.1, iron and unavoidable impurities are the rest.EFFECT: higher manufacturability of steel strip fabrication due to increased degree of deformation at rolling.26 cl, 1 dwg, 3 tbl

Description

The invention relates to a method for manufacturing a cold rolled steel strip from high strength manganese-containing steel. Steel strip means, in particular, steel stripes as well as steel sheets. Typical tensile strength Rm for these steels is from about 800 MPa to 2000 MPa. Elongation at break A80 has values from about 3% to 40%.

European patent application EP 2 383 353 A2 discloses high-strength steel containing manganese, a steel strip made from this steel, and a method for producing such a steel strip. Steel consists of elements (with a content in weight percent relative to the steel melt): C: up to 0.5; Mn: 4 to 12.0; Si: up to 1.0; Al: up to 3.0; Cr: from 0.1 to 4.0; Cu: up to 4.0; Ni: up to 2.0; N: up to 0.05; P: up to 0.05; S: up to 0.01; the remainder is iron and inevitable impurities. As an option, one or more elements of the group of "V, Nb, Ti" are presented, while the total content of these elements is a maximum of 0.5. It is argued that this steel is different in that it can be produced at lower cost than steel with a high manganese content, and at the same time it has great values in elongation at fracture and, therefore, has a significantly better deformability.

A method of manufacturing a steel strip from high-strength steel containing manganese, as described above, includes the following steps:

- smelting of the above steel melt,

- the production of the initial product for subsequent hot rolling, while the steel melt is poured into a stream from which at least one slab or thin slab is separated as a starting product for hot rolling, or into a cast strip, which is fed into the hot rolling process as a source product

- heat treatment of the starting product to bring the starting product to an initial temperature of hot rolling from 1150 ° C to 1000 ° C;

- hot rolling of the starting product to obtain a hot strip with a maximum thickness of 2.5 mm, while hot rolling stops at a final temperature of hot rolling from 1050 ° C to 800 ° C;

- winding a hot strip with the formation of a coil at a winding temperature ≤ 700 ° C, as an option, annealing the hot strip and then cold rolling it to a maximum thickness of 60% of the thickness of the hot strip.

Depending on the melt point, this steel may contain metastable austenite with the ability to form voltage induced martensite (TRIP effect).

International patent application WO 2005/061152 A1 also describes a method for manufacturing hot strips from deformable lightweight steel, which can be successfully subjected to deep cold drawing, with a Mn content of from 9 to 30 wt.%. In addition to its high tensile strength, the hot strip has TRIP properties. German Patent Document DE 197 27 759 A1, which is publicly available, discloses a heavy-duty austenitic lightweight steel that can be successfully subjected to deep drawing with tensile strength up to 1100 MPa, which also has the properties of TRIP and TWIP. German Patent Document DE 10 2012 111 959 A1, publicly available, discloses a high manganese material with TRIP and TWIP properties that undergoes reinforced hardening and deformation by cold forming at a temperature below ambient temperature, preferably in the range of +25 ° C to - 200 ° C. German Patent Document DE 10 2009 030 324 A1, which is publicly available, discloses steel with a high manganese content, low tendency to hydrogen embrittlement and high tensile strength, at the same time having high elongation at break. Patent application US 2012/0059196 A1 discloses a method for manufacturing a hot strip with a horizontal cast strip. The hot strip consists of the main components of Fe, Mn, Si and Al, has the properties of TRIP and / or TWIP and is suitable for deep drawing. US Pat. No. 6,358,338 B1 also relates to a method for manufacturing a steel strip from steel with a high manganese content. In order to increase tensile strength and tensile ability, the steel strip after cold rolling is subjected to recrystallization annealing. In patent application US 2009/0074605 A1, a steel strip with a high manganese content with excellent crash characteristics and high tensile strength and elongation is obtained, the steel strip being cold rolled after hot rolling and then annealed at a temperature of 600 ° C.

In addition, German patent DE 10 2012 013 113 A1, which is in the public domain, describes TRIP steels that have a predominantly ferritic basic microstructure with incorporated residual austenite. Thanks to intensive cold hardening, TRIP steel achieves high values for uniform elongation and tensile strength.

The disadvantage of these manganese-containing steels with the TRIP effect is that in the production of cold rolled steel strip, the degree of deformation achieved is limited due to intensive cold hardening of the material during cold rolling and the associated high load on the rolling mill. To achieve high degrees of cold forming, many cold rolling steps are often required with correspondingly low degrees of deformation, and before the repeated cold rolling step, recrystallization annealing must be carried out in each case to bring the material into a state suitable for cold rolling. This procedure with many stages of cold rolling with intermediate recrystallization annealing is very time-consuming and expensive and involves additional CO ₂ emissions.

Based on the foregoing, the aim of the present invention is to provide a method for manufacturing a cold rolled steel strip from high strength, manganese-containing steel with TRIP properties, in which cold rolling to the desired final thickness can be performed in a more economical and environmentally friendly way. In addition, a production path is provided from steelmaking to cold rolling of the steel strip to the desired final thickness.

This goal is achieved using a method of manufacturing a steel strip having the characteristics of paragraph 1 of the formula. Preferred embodiments of the invention are described in the respective dependent claims.

In accordance with the present invention, a method of manufacturing a cold rolled steel strip from high strength, manganese-containing steel with TRIP properties, with a content (in wt.%):

C: 0.0005 to 0.9

Mn: greater than 3.0 to 12

in this case, the remainder is iron with the inevitable elements associated with steel, when alloyed as an option with one or more of the following elements (with the content in weight percent relative to the steel melt):

Al: up to 10

Si: up to 6

Cr: up to 6

Nb: up to 1.5

V: up to 1.5

Ti: up to 1.5

Mo: up to 3

Cu: up to 3

Sn: up to 0.5

W: up to 5

Co: up to 8

Zr: up to 0.5

Ta: up to 0.5

Te: up to 0.5

B: up to 0.15

P: max. 0.1, in particular <0.04

S: max 0.1, in particular <0.02

N: max 0.1, in particular <0.05

Ca: up to 0.1

characterized in that in order to avoid cold rolling at ambient temperature, rolling to the desired final thickness occurs at a temperature of from 50 ° C to 400 ° C.

In accordance with the present invention, high strength steels are considered to be steel with tensile strength from 800 MPa to 2000 MPa.

The reason for the intense cold hardening of these high-strength manganese-containing steels with the TRIP effect is the fraction of residual austenite contained in the microstructure, in addition to martensite and / or ferrite and / or bainite and / or perlite. This residual austenite can be converted at appropriate ambient temperatures to martensite (the TRIP effect of both ε and α'-martensite), while at ambient temperatures up to about 50 ° C, a significant proportion of the formation of martensite always occurs due to TRIP- effect. This leads to hardening of the material and, in this regard, to an intensive increase in rolling forces during cold rolling, even during the first pass, and is associated with a decrease in the maximum degree of deformation. The cold-rolled strip then has a high level of strength and a low residual deformability. In addition, the effect of mechanical stresses can cause deformation twins (TWIP effect).

In accordance with the present invention, by increasing the deformation temperature before the first pass to a temperature from above 50 ° C to 400 ° C, the mechanism for converting TRIP from austenite to martensite is completely or partially suppressed, and therefore, during rolling, only in one pass of rolling, significantly higher degrees of deformation.

The term “cold rolling” usually refers to cold rolling at ambient temperature. In accordance with the present invention, the term “cold rolling” is also used for cold rolling at elevated temperature. Unlike hot rolling, this elevated temperature in the case of cold rolling, in accordance with the present invention, is clearly lower than the conversion temperature AC1 associated with the transformation of the microstructure. Cold rolling in accordance with the present invention also preferably takes place at a temperature below the homologous temperature when creep processes still do not occur in the steel sheet.

In the only drawing that is attached to this document, the effect of rolling temperature on rolling on the behavior of the material during hardening is illustrated using values characterizing tensile tests. Compared to deformation at an ambient temperature of 20 ° C, at deformation temperatures of 100 ° C or 200 ° C, clearly higher elongation values are achieved with a clearly lower increase in tensile strength.

The preferred condition is that the hot strip or pre-strip is heated to a temperature of from 50 ° C to 400 ° C, preferably from 70 ° C to 250 ° C, or the hot strip or pre-strip is already at a temperature of from 50 ° C to 400 ° C, preferably from 70 ° C to 250 ° C, and then subjected to cold rolling to the desired final thickness at a temperature, before the first pass, from 50 ° C to 400 ° C, preferably from 70 ° C to 250 ° C. By “being at a temperature” is meant that the temperature is the result of a previous step in the process or that this temperature is maintained. The previous process step may mean a reheating step, a continuous or discrete processing step using the heat present in the hot strip or pre-strip, in particular a hot rolling process, or maintaining the temperature in the furnace.

When the hot strip is heated, before cold rolling, to a temperature of from 50 ° C to 400 ° C, preferably from 70 ° C to 250 ° C, the conversion of austenite to martensite by increasing the energy of stacking defects in the first rolling pass is significantly reduced or prevented, therefore, the strip hardens less intensively during cold rolling, and more strain twins form in austenite (TWIP effect). This results in both lower rolling forces and a significantly improved deformation ability of the strip during the rolling process. To compensate for the additional heating of the strip due to deformability during cold forming and to keep the strip temperature in the range optimal for the TWIP effect, between the individual passes of the rolling, optionally, the strip can be cooled, for example, with compressed air or other liquid or gaseous media.

In addition, after rolling, the steel strip contains a significant residual deformability, since deformation twins formed in austenite and residual austenite, which may be present, can completely or partially turn into martensite at ambient temperature through the TRIP effect, this is due to an increase in maximum elongation and, consequently, improved ability to deform to obtain parts from a flat product even without additional annealing associated with the cold process rocking.

In addition, the formation of strain twins leads to improved behavior during subsequent strains with respect to hydrogen-induced delayed cracking and hydrogen embrittlement compared to cold rolling without preheating and the associated annealing process, as an option.

The steel used for the method in accordance with the present invention has a multiphase microstructure consisting of ferrite and / or martensite and / or bainite and / or perlite and residual austenite / austenite. The proportion of residual austenite / austenite may be from 5% to 80%. Residual austenite / austenite can be partially or completely converted to martensite through the TRIP effect when mechanical stress is applied.

The alloy constituting the basis of the invention has the effect of TRIP and / or TWIP upon application of appropriate mechanical stress. Due to intensive hardening (similar to cold hardening) at ambient temperature caused by the TRIP and / or TWIP effect, as well as an increase in the dislocation density, steel reaches very large elongation at break, in particular, uniform elongation and tensile strength. Mostly, this property is achieved due to the presence of residual austenite, only with a manganese content of more than 3 wt.%.

The use of the term “before” in determining the content range, for example, from 0.01 wt.% To 1 wt.%, Means that the limit values of 0.01 and 1 in this example are also taken into account.

The steel in accordance with the present invention is particularly suitable for the production of high-strength steel strip, which may have a metal or non-metallic coating, for example, zinc-based coating. Their application is possible, inter alia, in the automotive industry, shipbuilding, the development of technological equipment, infrastructure, in the aerospace industry and in household appliances. A high proportion of austenite means that steel made in accordance with the present invention is suitable for low temperature stresses.

Preferably, the steel has a tensile strength Rm from> 800 to 2000 MPa, and elongation at break A80 from 3 to 40%, preferably from> 8 to 40%.

Especially homogeneous and homogeneous material properties can be achieved if the steel has the following alloy composition (in wt.%):

C: 0.05 to 0.42

Mn: from> 5 to <10

while the remainder is iron with the inevitable elements associated with steel, when alloyed as an option with one or more of the following elements (in wt.%):

Al: from 0.1 to 5, in particular from> 0.5 to 3

Si: from 0.05 to 3, in particular from> 0.1 to 1.5

Cr: from 0.1 to 4, in particular from> 0.5 to 2.5

Nb: from 0.005 to 0.4, in particular from 0.01 to 0.1

B: from 0.001 to 0.08, in particular from 0.002 to 0.01

Ti: from 0.005 to 0.6, in particular from 0.01 to 0.3

Mo: from 0.005 to 1.5, in particular from 0.01 to 0.6

Sn: <0.2, in particular <0.05

Cu: <0.5, in particular <0.1

W: from 0.01 to 3, in particular from 0.2 to 1.5

Co: from 0.01 to 5, in particular from 0.3 to 2

Zr: from 0.005 to 0.3, in particular from 0.01 to 0.2

Ta: from 0.005 to 0.3, in particular from 0.01 to 0.1

Te: from 0.005 to 0.3, in particular from 0.01 to 0.1

V: from 0.005 to 0.6, in particular from 0.01 to 0.3

Ca: 0.005 to 0.1

Alloying elements are usually added to steel to influence specific properties as needed. The alloying element can thus affect various properties in different steels. Influence and interaction usually depend heavily on the amount, presence of additional alloying elements and the state of the solution in the material. Correlations are volatile and complex. The effect of the alloying elements in the alloy in accordance with the present invention will be described in more detail below. The beneficial effects of alloying elements when used in accordance with the present invention will be described below:

Carbon C: necessary for the formation of carbides, stabilizes austenite and increases strength. A high carbon content impairs weldability, thereby deteriorating the tensile and toughness properties, for this reason the maximum content is set to 0.9 wt.%. The minimum content is set to 0.0005 wt.%. A content of 0.05 to 0.42% by weight is preferred, since in this range the ratio of residual austenite to other phase proportions can be set in a particularly advantageous manner.

Manganese Mn: stabilizes austenite and increases strength and toughness, allowing the formation of martensite induced by deformation and / or twinning in alloys, in accordance with the present invention. A content of ≤ 3 wt.% Is not enough to stabilize austenite and this worsens the tensile properties, and at a content of over 12 wt.% Austenite stabilizes too much and this leads to the fact that the strength properties, in particular, the yield strength, are deteriorated. In accordance with the present invention, for manganese steel with an average manganese content, a range of from more than 5 to <10 wt.% Is preferred, since in this range the ratio of the phase proportions to each other and the transformation mechanisms can be influenced in an advantageous way during rolling to the final thickness.

Aluminum Al: increases strength and tensile properties, lowering specific gravity and affects the conversion behavior of the alloy in accordance with the present invention. When the Al content is more than 10 wt.%, The tensile properties deteriorate, and this leads mainly to brittle fracture. For manganese steel, in accordance with the present invention, with an average manganese content, an Al content of 0.1 to 5% by weight is preferred to increase strength, while there is a good degree of extensibility. In particular, a content of> 0.5 to 3% by weight gives a particularly high level of strength and elongation at break.

Silicon Si: inhibits carbon diffusion, lowers specific gravity, and increases strength and tensile and toughness properties. A content of more than 6 wt.% Prevents further processing by cold rolling due to embrittlement of the material. Thus, the maximum content of 6 wt.% Is set. As an option, the content is set from 0.05 to 3 wt.%, Since the content in this range positively affects the deformation properties. A Si content of> 0.1 to 1.5 wt.% Proved to be particularly advantageous for the deformation and conversion properties.

Chromium Cr: increases strength and reduces the rate of corrosion, delays the formation of ferrite and perlite and forms carbides. The maximum content is set to 6 wt.%, Since a higher content leads to a deterioration in tensile properties and a significant increase in costs. For manganese steel having an average manganese content in accordance with the present invention, a Cr content of 0.1 to 4% by weight is preferred in order to reduce the precipitation of large Cr carbides. In particular, a content of> 0.5 to 2.5 wt.% Proved to be beneficial for stabilizing austenite and precipitating fine Cr carbides. In order to achieve advantageous properties when Al and Si are added in addition to Cr, the total Al + Si + Cr content should be more than 1.2% by weight.

Molybdenum Mo: acts as a carbide forming agent, increases strength, and increases resistance to delayed cracking and hydrogen embrittlement. A Mo content of more than 3% by weight impairs tensile properties, and therefore a maximum content of 3% by weight is set. For manganese steel having an average manganese content in accordance with the present invention, a Mo content of from 0.005 to 1.5 wt.% Is preferred in order to avoid precipitation of excessively large Mo carbides. In particular, a content of from 0.01 wt.% To 0.6 wt.% Leads to the deposition of the desired Mo carbides while reducing alloy costs.

Phosphorus P: Phosphorus is a trace element of iron ore, and it dissolves in the iron lattice as a substitute atom. Phosphorus increases hardness and hardenability through mixed crystalline solidification. However, measures are being taken to reduce the phosphorus content as much as possible, since, among other things, there is a strong tendency to segregation due to the low diffusion rate, with a strong decrease in impact strength. The addition of phosphorus to the grain boundaries can cause cracks along the grain boundaries during hot rolling. In addition, phosphorus increases the transition temperature from viscous to brittle behavior by up to 300 ° C. For these reasons, the phosphorus content is limited to a maximum of 0.1 wt.%, While a content of <0.04 wt.% Is preferred for these reasons.

Sulfur S: like phosphorus, bound as a trace element in iron ore. Usually it is undesirable in steel, since it shows a strong tendency to segregation and greatly increases brittleness, while tensile and toughness deteriorate. Therefore, everything possible is done to achieve the lowest, as possible, sulfur content in the melt (for example, by means of deep vacuum treatment). For the above reasons, the sulfur content is limited to a maximum of 0.1 wt.%. In a particularly preferred embodiment, the limit is <0.2 wt.% To reduce the deposition of MnS.

Nitrogen N: Nitrogen is also an element accompanying steel production. When dissolved, it increases the strength and toughness properties in steels with a high manganese content of more than or equal to 4 wt.%. Steel with a lower manganese content <4 wt.%, In the presence of free nitrogen, is prone to a strong aging effect. Nitrogen diffuses even at low temperatures in dislocations and blocks them. Thus, it increases strength coupled with a rapid loss of toughness. You can bind nitrogen in the form of nitrides, for example, by alloying with aluminum, vanadium, niobium or titanium. For the above reasons, the nitrogen content is limited to a maximum of 0.1 wt.%, While a content of <0.05 wt.% Is preferable in order to largely avoid the formation of AlN.

Typically, microalloying elements are added only in very small amounts (<0.1 wt.% Per element). Unlike alloying elements, they usually work due to the formation of precipitation, but can also affect the properties in a dissolved state. Despite the small amounts added, the microalloying elements strongly influence the production conditions, workability and final properties.

Typically, microalloying elements are vanadium, niobium and titanium. These elements can dissolve in the iron lattice with the formation of carbides, nitrides and carbonitrides with carbon and nitrogen.

Vanadium V and niobium Nb: contribute to the grinding of grains, in particular through the formation of carbides, while improving the properties of strength, toughness and extensibility. The content of more than 1.5 wt.% Does not provide additional benefits. As an option, for vanadium and niobium, a minimum content of more than or equal to 0.005% by weight is preferably set. and a maximum content of 0.6 (V) or 0.4 (Nb) wt.%, at which the alloying elements preferably provide grinding of the grains. In addition, in order to increase economic feasibility, while ensuring optimal grain refinement, the V content can still be limited from 0.01 wt.% To 0.3 wt.% And the Nb content from 0.01 to 0.1 weight. %

Tantalum Ta: tantalum acts similarly to niobium, as a carbide-forming agent they contribute to the grinding of grains, while the properties of strength, toughness and extensibility are improved. A content of more than 0.5 wt.% Does not provide further improvement in properties. Thus, as an option, a maximum content of 0.5% by weight is set. Preferred is a minimum content of 0.005% by weight and a maximum content of 0.3% by weight, at which grain refinement can be advantageously achieved. In order to increase economic feasibility and optimize grain grinding, a content of 0.01 wt.% To 0.1 wt.% Is particularly preferred.

Titanium Ti: promotes grain refinement as a carbide forming agent, while at the same time, strength, toughness and tensile properties are improved, and intergranular corrosion is reduced. A titanium content of more than 1.5 wt.% Worsens the tensile properties, and therefore, a maximum Ti content of 1.5 wt.% Is set. As an option, a minimum content of 0.005 wt.% And a maximum content of 0.6 wt.% Are set, with Ti mostly precipitated. Preferably, the minimum content of 0.01 wt.% And the maximum content of 0.3 wt.%, Which ensures optimal behavior during deposition at low cost for the alloy.

Tin Sn: Tin increases strength, but, like copper, accumulates under a layer of scale and at grain boundaries at higher temperatures. This leads, due to penetration into the grain boundaries, to the formation of low-melting phases and, therefore, cracks in the microstructure, and to the brittleness of the solder, and therefore, the maximum content ≤ 0.5 wt.% Is specified as an option. For the above reasons, a content of <0.2 wt.% Is preferred. To avoid fusible phases and cracks in the microstructure, a content of <0.05 wt.% Is particularly preferred.

Copper Cu: lowers corrosion rate and increases strength. When the content is more than 3 wt.%, The processing capabilities are deteriorated due to the formation of low-melting phases during casting and hot rolling, and therefore a maximum content of 3 wt.% Is set. As an option, a maximum content of <0.5 wt.% Is specified at which cracking during casting and hot rolling can be prevented in an advantageous manner. In order to avoid fusible phases and cracks in the microstructure, a Cu content of <0.1 wt.% Was particularly preferred.

Tungsten W: tungsten acts as a carbide-forming agent, it contributes to increased strength and heat resistance. A tungsten content of more than 5% by weight impairs tensile properties, and therefore a maximum content of 5% by weight is set. As an option, a maximum content of 3% by weight and a minimum content of 0.01% by weight are specified at which carbide precipitation occurs in a preferred manner. In particular, it is preferable that the minimum content of 0.2 wt.% And the maximum content of 1.5 wt.%, Which makes possible optimal behavior during deposition at low cost for the alloy.

Cobalt Co: cobalt increases the strength of steel, stabilizes austenite and increases heat resistance. When the content is more than 8 wt.%, The tensile properties deteriorate, and therefore the maximum content of 8 wt.% Is set. As an option, a maximum content of ≤ 5 wt.% And a minimum content of 0.01 wt.% Are set, which advantageously increases strength and heat resistance. Preferably, the minimum content of 0.3 wt.% And the maximum content of 2 wt.%, Which favorably affects the stability of austenite along with strength properties.

Zirconium Zr: Zirconium acts as a carbide forming agent and increases strength. A zirconium content of more than 0.5% by weight impairs tensile properties, and therefore a maximum content of 0.5% by weight is set. As an option, a maximum content of 0.3% by weight and a minimum content of 0.005% by weight are specified, since carbides predominantly precipitate in this range. Preferably, the minimum content of 0.01 wt.% And the maximum content of 0.2 wt.%, Which favorably provides optimal deposition of carbides at low cost for the alloy.

Boron B: slows down austenite conversion, improves the hot forming ability of steels, and increases strength at ambient temperature. It achieves its effect even with a very low content in the alloy. A content of more than 0.15 wt.% Greatly degrades the tensile and toughness properties, therefore, a maximum content of 0.15 wt.% Is set. As an option, a minimum content of 0.001 wt.% And a maximum content of 0.08 wt.% Are specified, in which the property of boron to increase strength is advantageously used. Preferably, the minimum content of 0.002 wt.% And the maximum content of 0.01 wt.%, Which ensures optimal use to increase strength, while improving conversion behavior.

Tellurium Te: improves corrosion resistance, mechanical properties and workability. In addition, Te increases the hardness of MnS, which results in less extension in the direction of rolling during hot rolling and cold rolling. A content of more than 0.5 wt.% Worsens the tensile and toughness properties, therefore, a maximum content of 0.5 wt.% Is set. As an option, a minimum content of 0.005 wt.% And a maximum content of 0.3 wt.% Are set, which favorably improves the mechanical properties and increases the hardness of the present MnS. In addition, it is preferable that the minimum content of 0.01 wt.% And the maximum content of 0.1 wt.%, Which ensures the optimization of mechanical properties, while at the same time reducing the cost of the alloy.

Calcium Ca: Calcium is used to modify non-metallic oxide inclusions, which otherwise can cause unwanted destruction of the alloy due to inclusions in the microstructure, which will become stress concentration points, weakening the metal composite. In addition, calcium improves the uniformity of the alloy in accordance with the present invention. To achieve the corresponding effect, a minimum content of 0.0005 wt.% Is required. With a content of more than 0.1 wt.% Calcium, there are no additional advantages in the modification of inclusions, with a deterioration in processing capabilities, and this should be avoided due to the high vapor pressure of calcium in steel melts. Therefore, a maximum content of 0.1% by weight is set.

The production path, in accordance with the present invention, from steelmaking to finished steel strip with a desired final thickness of less than 10 mm, preferably less than 4 mm, from high-strength steel containing manganese, includes the following steps:

- smelting steel melt containing (in wt.%):

C: 0.0005 to 0.9

Mn: 3.0 to 12

while the remainder is iron with the inevitable elements associated with steel, when alloyed as an option with one or more of the following elements (in wt.%):

Al: up to 10

Si: up to 6

Cr: up to 6

Nb: up to 1.5

V: up to 1.5

Ti: up to 1.5

Mo: up to 3

Cu: up to 3

Sn: up to 0.5

W: up to 5

Co: up to 8

Zr: up to 0.5

Ta: up to 0.5

Te: up to 0.5

B: up to 0.15

P: max. 0.1, in particular <0.04

S: max 0.1, in particular <0.02

N: max 0.1, in particular <0.05

Ca: up to 0.1

- casting steel melt to obtain a pre-strip by means of a horizontal or vertical strip casting process approaching the final dimensions, or casting steel melt to produce a slab or thin slab by means of a horizontal or vertical casting process of a slab or thin slab,

- re-heating the slab or thin slab to a temperature of 1050 ° C to 1250 ° C and then hot rolling the slab or thin slab to obtain a hot strip, or re-heating the pre-strip, made closer to the final dimensions, to a temperature of 1000 ° C up to 1200 ° C and then hot rolling the pre-strip to obtain a hot strip, or hot rolling the pre-strip without re-heating from the heat of casting to obtain a hot strip with intermediate heating, as an option, between the individual passes of the rolling during hot rolling,

- winding a hot strip at a winding temperature between 820 ° C and ambient temperature,

- as an option, annealing a hot strip with the following parameters:

annealing temperature: 580 - 820 ° С, annealing duration: from 1 minute to 48 hours,

- with the exception of cold rolling at ambient temperature, rolling a hot strip with the required final thickness of less than 10 mm to a rolled steel strip at a temperature, before the first pass, from above 50 ° C to 400 ° C.

- as an option, annealing a steel strip with the following parameters:

annealing temperature: 580 - 820 ° С, annealing duration: from 1 minute to 48 hours,

- as an option, acid cleaning and / or training of a steel strip,

- as an option, application of a corrosion-resistant coating to a steel strip.

For additional benefits, reference is made to the above statements.

The usual thickness ranges for the pre-strip are from 1 mm to 35 mm, and for slabs and thin slabs, from 35 mm to 450 mm. The preferred condition is that the slab or thin slab is hot rolled to obtain a hot strip having a thickness of 20 mm to 1.5 mm, or a pre-strip cast close to the final dimensions is hot rolled to obtain a hot strip having a thickness from 8 mm to 1 mm. A cold rolled steel sheet made in accordance with the present invention has a thickness of, for example, from> 0.15 mm to 10 mm.

Reheat temperatures ranging from 720ºC to 1200ºC are provided for hot rolling the pre-strip from cast heat to produce a hot strip with intermediate heating, as an option, between the individual passes of the rolling process during hot rolling. If only a few passes are required, the reheat temperature can be selected from the bottom of this range.

The hot strip can optionally be heat-treated in the temperature range between 580 ° C and 820 ° C from 1 minute to 48 hours, with higher temperatures correlating with shorter processing times and vice versa. Annealing can occur both in the process of annealing of a discrete type (longer annealing time) and, for example, in the process of continuous annealing (shorter annealing time). Additional annealing serves to reduce strength and / or to increase the fraction of residual austenite of the hot strip before the cold rolling process, whereby the deformation properties are advantageously improved for the subsequent process.

After the hot rolling process, the hot strip is cold rolled at a temperature elevated in accordance with the present invention to specify a thickness of ≥ 0.15 mm to 10 mm for the steel strip as required for end use. After that, as an option, an additional annealing process can be carried out, and if necessary connected with the coating process, and, finally, a training process is carried out, by means of which the surface structure necessary for the end use is set.

Preferably, the steel strip is hot dip galvanized or electrolytically galvanized or coated with a metal, inorganic or organic coating.

The steel strip manufactured by the method in accordance with the present invention has a tensile strength Rm from> 800 to 2000 MPa and an elongation at break A80 from 3 to 40%, preferably from> 8 to 40%. In this case, high levels of strength are generally associated with lower elongation at break and vice versa.

The cold-rolled steel strip made in accordance with the present invention can then be processed, for example, as a sheet metal section, coil or panel by cold forming at ambient temperature or by warm molding at temperatures from 60 ° C to a temperature below AC3, preferably < 450 ° C, with the receipt of the part, and in this case, due to the significant residual ability to deform, you can do without intermediate annealing depending on use.

In subsequent processing steps, a cold-rolled steel strip made in accordance with the present invention can be processed to produce pipes with longitudinal or spiral welds, and in this case, due to the significant residual deformation ability of the steel strip, it is possible to do without intermediate annealing in depending on use. Thus, the pipe may have an outer and / or inner metal, organic or inorganic coating.

A pipe made in this way can then be further subjected to deformation, for example, elongated or expanded, or subjected to deformation using internal high pressure and further processed to obtain a part.

Fields of application, therefore, are primarily the automotive industry and mechanical engineering, large household electrical appliances, construction, as well as use at temperatures below 0 ° C and as ballistic steel. Ballistic steels are used to protect vehicles and buildings from shelling and explosions, and have a high level of hardness and toughness.

Tests were conducted to study the mechanical properties of steel strips made in accordance with the present invention, using, for example, alloys 1 to 4. Alloys 1 to 4 contain the following elements in the indicated amounts in wt.%:

For comparison purposes, steel strips made from the above alloys 1 to 4 were cold rolled, that is, at ambient temperature and therefore below 50 ° C, and also rolled, in accordance with the present invention, at a temperature of 250 ° C. The measured rolling forces are shown below:

The cumulative rolling force is understood as the addition of the rolling forces of the individual passes in order to obtain a comparable measure of the expenditure of force. The rolling force has been standardized to a strip width of 1000 mm. The degree of deformation e is defined as the ratio between the change in the thickness Δd of the investigated steel strip and the initial thickness d0 of the studied steel strip. The decrease in rolling force is the calculated decrease in rolling force at a temperature of 250 ° C compared with the rolling force in cold rolling.

Elongation at failure A50 was also evaluated:

Values characterizing elongation refer to elongation in the rolling direction.

Claims (78)

1. A method of manufacturing a cold rolled steel strip from high strength, containing manganese steel with TRIP properties, including: - smelting steel melt containing, wt.%: C: 0.0005 to 0.9; Mn: 3.0 to 12; if necessary, one or more elements from the group consisting of: Al: up to 10; Si: up to 6; Cr: up to 6; Nb: up to 1.5; V: up to 1.5; Ti: up to 1.5; Mo: up to 3; Cu: up to 3; Sn: up to 0.5; W: up to 5; Co: up to 8; Zr: up to 0.5; Ta: up to 0.5; Te: up to 0.5; B: up to 0.15; P: max. 0.1, in particular less than 0.04; S: max 0.1, in particular less than 0.02; N: max 0.1, in particular less than 0.05; Ca: up to 0.1; iron and inevitable impurities - the rest; - horizontal or vertical casting of a steel melt to obtain a pre-strip close to the final dimensions, or to obtain a slab or thin slab, - obtaining a hot-rolled strip by re-heating the slab or thin slab to a temperature of 1050 to 1250 ° C and hot rolling, or re-heating the pre-strip to a temperature of 1000 to 1200 ° C and hot rolling, or hot rolling the pre-strip without re-heating , if necessary, with intermediate heating, between individual rolling passes during hot rolling, - winding hot rolled strip at a temperature below 820 ° C, - if necessary, annealing the hot rolled strip with the following parameters: annealing temperature: 580–820 ° С, annealing duration: from 1 minute to 48 hours, - cold rolling of the annealed hot rolled strip to the desired final thickness at a temperature of from 50 to 400 ° C, - if necessary, annealing a cold-rolled steel strip with the following parameters: annealing temperature: 580–820 ° С, annealing duration: from 1 minute to 48 hours, - if necessary, acid cleaning and / or training of cold-rolled steel strip, - if necessary, applying to the cold-rolled steel strip a metal, organic or inorganic anti-corrosion coating. 2. The method according to p. 1, characterized in that the cold rolling to the desired final thickness is carried out by a hot-rolled strip having a temperature of from 70 to 250 ° C. 3. The method according to p. 1 or 2, characterized in that the hot-rolled strip or pre-strip is heated to a temperature of from 50 to 400 ° C, preferably from 70 to 250 ° C, or a hot-rolled strip or pre-strip at a temperature of above 50 to 400 ° C, preferably from 70 to 250 ° C, are cold rolled to the desired final thickness. 4. The method according to any one of paragraphs. 1-3, characterized in that the cooling of the hot rolled strip to a temperature of from 50 to 400 ° C, in particular to a temperature of from 70 to 250 ° C, is carried out between the passes during cold rolling. 5. The method according to any one of paragraphs. 1-4, characterized in that the steel contains, wt.%: C: 0.05 to 0.42. 6. The method according to any one of paragraphs. 1-5, characterized in that the steel contains, wt.%: Mn: from more than 5 to less than 10. 7. The method according to any one of paragraphs. 1-6, characterized in that the steel contains, wt.%: Al: from 0.1 to 5, in particular from more than 0.5 to 3. 8. The method according to any one of paragraphs. 1-7, characterized in that the steel contains, wt.%: Si: from 0.05 to 3, in particular from more than 0.1 to 1.5. 9. The method according to any one of paragraphs. 1-8, characterized in that the steel contains, wt.%: Cr: from 0.1 to 4, in particular from more than 0.5 to 2.5. 10. The method according to one of paragraphs. 7–9, characterized in that the total content of Al, Si and Cr is more than 1.2 wt.%. 11. The method according to any one of paragraphs. 1-10, characterized in that the steel contains, wt.%: Nb: from 0.005 to 0.4, in particular from 0.01 to 0.1. 12. The method according to any one of paragraphs. 1-11, characterized in that the steel contains, wt.%: V: from 0.005 to 0.6, in particular from 0.01 to 0.3. 13. The method according to any one of paragraphs. 1-12, characterized in that the steel contains, wt.%: Ti: from 0.005 to 0.6, in particular from 0.01 to 0.3. 14. The method according to any one of paragraphs. 1-13, characterized in that the steel contains, wt.%: Mo: from 0.005 to 1.5, in particular from 0.01 to 0.6. 15. The method according to any one of paragraphs. 1-14, characterized in that the steel contains, wt.%: Sn: less than 0.2, in particular less than 0.05. 16. The method according to any one of paragraphs. 1-15, characterized in that the steel contains, wt.%: Cu: less than 0.5, in particular less than 0.1. 17. The method according to any one of paragraphs. 1-16, characterized in that the steel contains, wt.%: W: from 0.01 to 3, in particular from 0.2 to 1.5. 18. The method according to any one of paragraphs. 1-17, characterized in that the steel contains, wt.%: Co: from 0.01 to 5, in particular from 0.3 to 2. 19. The method according to any one of paragraphs. 1-18, characterized in that the steel contains, wt.%: Zr: from 0.005 to 0.3, in particular from 0.01 to 0.2. 20. The method according to any one of paragraphs. 1-19, characterized in that the steel contains, wt.%: Ta: from 0.005 to 0.3, in particular from 0.01 to 0.1. 21. The method according to any one of paragraphs. 1-20, characterized in that the steel contains, wt.%: Te: from 0.005 to 0.3, in particular from 0.01 to 0.1. 22. The method according to any one of paragraphs. 1-21, characterized in that the steel contains, wt.%: B: from 0.001 to 0.08, in particular from 0.002 to 0.01. 23. The method according to any one of paragraphs. 1-22, characterized in that the steel contains, wt.%: Ca: 0.005 to 0.1. 24. The use of cold rolled steel strip of high strength, containing manganese steel with TRIP properties, manufactured by the method according to any one of paragraphs. 1–23, as a material for the production of parts by hot molding, cold forming or warm molding, for the production of pipes with longitudinal or spiral welds, for the production of parts for the automotive industry, mechanical engineering, large household electrical appliances, in construction. 25. The use of cold-rolled steel strip of high strength, containing manganese steel with TRIP properties, manufactured by the method according to any one of paragraphs. 1 - 23, as a material for the production of parts used in the low temperature range from 0 to -273 ° C. 26. The use of cold rolled steel strip of high strength, containing manganese steel with TRIP properties, manufactured by the method according to any one of paragraphs. 1–23, as ballistic steel.

Images