CN109642263B - Method for producing a high-strength steel strip with improved properties during further processing, and such a steel strip - Google Patents
Method for producing a high-strength steel strip with improved properties during further processing, and such a steel strip Download PDFInfo
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- CN109642263B CN109642263B CN201780051643.0A CN201780051643A CN109642263B CN 109642263 B CN109642263 B CN 109642263B CN 201780051643 A CN201780051643 A CN 201780051643A CN 109642263 B CN109642263 B CN 109642263B
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C1/00—Refining of pig-iron; Cast iron
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0236—Cold rolling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- Heat Treatment Of Sheet Steel (AREA)
Abstract
The invention relates to a method for manufacturing a high-strength steel strip with TRIP/TWIP effect, comprising the following steps: melting the steel melt; casting the steel melt into a prefabricated strip or slab; heating to a rolling temperature of 1050 ℃ to 1250 ℃ or rolling in-line from casting heat; hot rolling the pre-strip or slab to a hot rolled strip having a thickness of 12mm to 0.8mm at a final rolling temperature of 1050 ℃ to 800 ℃; coiling the hot rolled strip at a temperature above 200 ℃ to 800 ℃; pickling the hot rolled strip; annealing the hot rolled strip in a continuous or discontinuous annealing plant for a time period of from 1 minute to 48 hours at a temperature of from 540 ℃ to 840 ℃; cold rolling the hot rolled strip in one or more rolling passes at an elevated temperature of 60 ℃ to 450 ℃. The invention also relates to a high strength and cost-effective steel strip with improved properties for further processing.
Description
Technical Field
The invention relates to a method for producing an ultra-high-strength steel strip with improved properties during further processing, and to a corresponding steel strip.
In particular, the invention relates to the manufacture of steel strip made of manganese containing TRIP (transformation induced plasticity) and/or TWIP (twinning induced plasticity) steel having excellent cold and warm formability, increased resistance to hydrogen induced delayed crack formation (delayed fracture), hydrogen embrittlement and liquid metal embrittlement during welding.
Background
European patent application EP 2383353 a2 discloses a manganese-containing steel, a flat steel product made of this steel and a method for producing this flat steel product. The steel has a tensile strength of 900-1500MPa and an elongation at break A80 of at least 4%. The maximum elongation at break a80 is described as 8%. Furthermore, the steel consists of the following elements (contents in weight percent and related to the steel melt): c: to 0.5; mn: 4 to 12.0; si: up to 1.0; al: up to 3.0; cr: 0.1 to 4.0; copper: 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 balance being iron and unavoidable impurities. Optionally, one or more elements from the group "V, Nb, Ti" are provided, wherein the sum of the contents of these elements is at most equal to 0.5. For a Mn content of 5 and an Al content of 2, the total amount is 7. The structure of the flat steel product consists of 30 to 100% of martensite, tempered martensite or bainite, the remainder being austenite. The steel is characterized in that it can be produced in a more cost-effective manner than a steel containing a high manganese content, while having a high elongation at break and, associated therewith, a significantly improved deformability. The method for manufacturing the flat steel product by the high-strength manganese-containing steel comprises the following working steps: -melting the aforesaid steel melt, -manufacturing a starting product for subsequent hot rolling in such a way that the steel melt is cast into a steel strip (at least one slab or sheet bar is separated from the steel strip as a hot rolled starting product) or cast into a cast steel strip as a starting product to be supplied to a hot rolling process, -heat treating the starting product to bring the starting product to a hot rolling starting temperature of 1150-1000 ℃, -hot rolling the starting product to form a hot rolled strip having a thickness of at most 2.5mm, wherein the hot rolling is terminated at a hot rolling end temperature of 1050-800 ℃, -coiling the hot rolled strip at a coiling temperature ≦ 700 ℃ to form a coil. Alternatively, the hot rolled strip may be annealed at 250 ℃ to 950 ℃, followed by cold rolling, and then annealed at 450 ℃ to 950 ℃. Furthermore, after cold or hot rolling of the flat steel product, the product is provided with a metal corrosion protection coating or an organic coating.
Furthermore, german laid-open patent application DE 102012013113 a1 has described so-called TRIP steels having a predominantly ferritic basic microstructure with retained austenite which can be transformed into martensite during deformation (TRIP effect). The manganese content of the steel strip is between 1.00 and 2.25 wt.%. The steel strip is coated and smoothed in a molten bath. Due to its strong cold hardening, TRIP steels reach high values of uniform elongation and tensile strength. TRIP steel is used in particular for structural parts, chassis parts and crash-related parts of vehicles, as sheet metal blanks and as welded blanks.
European patent EP 1067203B 1 discloses a method of manufacturing steel strip. In this case, a thin strip with a thickness of 1.5mm to 10mm is cast (in weight percent) C from a steel melt consisting of at least the following elements: 0.001 to 1.6; mn: 6 to 30; al: to 6; p: to 0.2; s: to 0.5; n: to 0.3, the balance being iron and unavoidable impurities. The thin strip is hot rolled at a reduction degree of between 10% and 60%, pickled, cold rolled at a reduction degree of between 10% and 90%, and recrystallization annealed at 800 ℃ to 850 ℃ for 1 to 2 minutes.
Japanese patent JP 3317303B 2 discloses a high strength steel strip having the following composition in weight percent: c: 0.05-0.3; si: <0.2, Mn: 0.5-4.0; p: less than or equal to 0.1; s: less than or equal to 0.1; ni: 0 to 5.0; al: 0.1-2.0 and N is less than or equal to 0.01. In this case, the following equation is satisfied: si + Al ═ 0.5; mn +1/3Ni is more than or equal to 1.0. The microstructure contains more than or equal to 5 volume percent of residual austenite. The melt of the aforementioned steel is melted in a vacuum laboratory furnace. By hot forging, a test piece having a thickness of 25mm was produced. It was then heated to 1250 ℃ in an electric furnace for 1 hour. Subsequently, hot rolling was performed at 930 ℃ to 1150 ℃ to obtain a steel strip thickness of 5 mm. For the coiling simulation, the strip was immediately cooled to 500 ℃ and annealed in an electric furnace at this temperature for 1 hour.
Disclosure of Invention
Starting from this, it is an object of the present invention to provide a method for producing an ultra high strength steel strip consisting of a TRIP and/or TWIP steel containing manganese, having a strength between 1100 and 2200MPa, which is cost-effective and wherein the steel strip has improved properties during further processing, in particular a good combination of strength and formability, increased resistance to hydrogen induced delayed crack formation, to hydrogen embrittlement and to liquid metal embrittlement. Furthermore, an ultra-high strength and cost-effective steel strip is provided, which has improved properties during further processing.
This object is achieved by a method and an ultra high strength steel strip for manufacturing a flat steel product, in particular using the above-mentioned steel, having the following characteristics.
According to the present invention, a method for manufacturing an ultra high strength steel strip is proposed, comprising the steps of: -melting a steel melt containing (in weight%): c: 0.1 to < 0.3; mn: 4 to < 8; al: >1 to 2.9; p: < 0.05; s: < 0.05; n: < 0.02; the balance being iron, including unavoidable steel-related elements, wherein one or more of the following elements (in% by weight) are optionally added by alloying via the process route of a blast-furnace-steelworks or electric arc furnace process (each of which optionally vacuum-treating the melt): 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; -casting a steel melt into a pre-strip by means of a horizontal or vertical final dimension strip casting process, or into a slab or thin slab by means of a horizontal or vertical slab or thin slab casting process, -heating to a rolling temperature of 1050 to 1250 ℃ or rolling in-line from the casting heat, -hot rolling the pre-strip or slab or thin slab into a hot rolled strip of thickness 12 to 0.8mm at a final rolling temperature of 1050 to 800 ℃, -coiling the hot rolled strip at a temperature of above 200 to 800 ℃, -pickling the hot rolled strip, -annealing the hot rolled strip in a continuous or discontinuous annealing plant for an annealing time of 1 minute to 48 hours at a temperature of 540 to 840 ℃, -cold rolling the hot rolled strip in one or more rolling passes at room temperature or at an elevated temperature, -optionally galvanising or hot galvanizing the strip, a cost-effectively manufactured steel strip is provided having a strength of 1100 to 2200MPa, a good combination of strength, elongation and formability properties, and an increased resistance to delayed crack formation, hydrogen embrittlement and liquid metal embrittlement, which also has a TRIP and/or TWIP effect under mechanical stress.
Typical thicknesses of the prefabricated strip range from 1mm to 35mm, and for slabs and thin slabs, from 35mm to 450 mm. Preferably, provision is made for the slab or thin slab to be hot-rolled to a hot-rolled strip with a thickness of 12mm to 0.8mm, or for the prefabricated strip cast to approximately the final size to be hot-rolled to a hot-rolled strip with a thickness of 8mm to 0.8 mm. The thickness of the cold-rolled steel strip according to the invention is at most 3mm, preferably 0.1 to 1.4 mm.
In the context of the above-described method according to the invention, a prefabricated strip produced using a twin-roll final dimension casting process and having a thickness of less than or equal to 3mm (preferably 1mm to 3mm) has been understood as hot-rolled strip. The prefabricated strip produced as hot-rolled strip does not have a 100% cast structure due to the deformations introduced by the two rolls running in opposite directions. Therefore, hot rolling has been performed on-line in the twin roll casting process, so that separate heating and hot rolling can be optionally eliminated.
The cold rolling of the hot strip can be carried out in one or more rolling passes at room temperature or advantageously at elevated temperature before the first rolling pass.
It is advantageous to carry out the cold rolling at elevated temperature in order to reduce the rolling force and to contribute to the formation of deformation twins (TWIP effect). The advantageous temperature of the rolled material before the first rolling pass is 60 ℃ to 450 ℃.
If the cold rolling is carried out in a plurality of rolling passes, it is advantageous to heat or cool the steel strip to a temperature of 60 ℃ to 450 ℃ between the rolling passes, since the TWIP effect is produced in a particularly advantageous manner in this region. Depending on the rolling speed and the degree of deformation, intermediate heating can be carried out, for example at very low degrees of deformation and rolling speeds, and additional cooling can also be carried out, the material being heated as a result of rapid rolling and high degrees of deformation.
After cold rolling the hot-rolled strip at room temperature, the steel strip should advantageously be annealed in a continuous annealing plant, in particular in a continuous annealing plant, advantageously for an annealing time of 1 to 15 minutes at a temperature of 720 ℃ to 840 ℃ in order to restore sufficient formability. Alternatively, the annealing may be performed by means of a discontinuous annealing apparatus at a temperature of 550 ℃ to 820 ℃ and an annealing time of 30 minutes to 48 hours. This annealing process can also be used in the case of rolling steel strip at elevated temperature if it is desired to obtain specific material properties.
After the annealing treatment, the strip is advantageously cooled to a temperature of 250 ℃ to room temperature and then, if necessary, heated again to a temperature of 300 ℃ to 450 ℃ during the ageing treatment and held at this temperature for up to 5 minutes and then cooled to room temperature in order to adjust the desired mechanical properties. The ageing treatment can advantageously be carried out in a continuous annealing installation.
If desired, the strip may be flattened after cold rolling to adjust the surface texture required for the final application. Can be, for example, passed through
The method is used for leveling.
In an advantageous development, the steel strip produced in this way is provided with an additional coating based on organic or inorganic substances after or instead of electrolytic or hot galvanizing. They may be, for example, organic coatings, synthetic material coatings or lacquers or other inorganic coatings, for example iron oxide layers.
The steel strip produced according to the invention can be used either as a metal sheet, a metal sheet section or a slab, or can be further processed to form a longitudinal or spiral seam welded pipe.
Furthermore, the steel sheet or strip is suitable in a particularly advantageous manner for further processing by means of cold forming or semi-hot forming to form components, as in the automotive industry, in the infrastructure construction and in the engineering sector.
The steel strip with improved properties during further processing has a TRIP/TWIP effect with a microstructure consisting (in% by volume) of 10 to 80% austenite, 10 to 90% martensite, the remainder being ferrite and bainite with a total proportion of less than 20%. In this case, at least a 20% share of the martensite is present as annealed martensite, and optionally > 10% share of the austenite is present in the form of annealed or deformed twins.
Due to the annealing treatment according to the invention, the steel strip has particularly fine grains, the average grain size of its phase components:
-austenite: less than 500 nm
Martensite, ferrite, bainite: less than 650 nm.
Due to the final annealing of the cold-rolled strip produced at room temperature or at elevated temperature, austenite is present in a metastable state and optionally has deformation twins, so that it is partially transformed into martensite upon the action of mechanical forces (e.g. forming) by the TRIP effect.
When mechanical stresses are applied, the austenitic part of the steel according to the invention may be partially or completely transformed into martensite (TRIP effect).
The alloy according to the invention also has twinning (TWIP effect) during plastic deformation when subjected to corresponding mechanical stresses. Due to the strong cold hardening caused by the TRIP and/or TWIP effect, the steel reaches high values in elongation at break, in particular in uniform elongation and tensile strength.
The steel according to the invention can then be shaped in a particularly advantageous manner by semihot forming at 60 ℃ to 450 ℃, since the austenite stability at these temperatures at least partially inhibits the austenite transformation to martensite (TRIP effect), with 50 to 100% of the starting austenite being retained and optionally partially transformed into deformation twins (TWIP effect). The deformation twins can be transformed into martensite at room temperature, wherein further energy is dissipated (TRIP effect, e.g. increased energy absorption in the event of a collision). During semi-hot forming, the residual elongation remaining until part failure increases significantly compared to cold forming. Furthermore, the prevention of the TRIP effect during the semi-hot forming brings about a considerable improvement with respect to the undesirable effects caused by hydrogen (delayed crack formation, hydrogen embrittlement). Moreover, the semi-thermoforming advantageously results in an increase of the 0.2% yield point of the formed material, so that for example the sheet thickness can advantageously be reduced.
The method according to the invention can be used to produce very cost-effective steel strips with an alloy concept, in which only the elements carbon, manganese and aluminium are required in addition to iron. The required annealing treatment can advantageously be carried out by continuous annealing, which is much more economical than batch annealing.
The steel strip produced according to the method of the invention advantageously has a yield point rp0.2 of 300 to 1550MPa, a tensile strength Rm of 1100 to 2200MPa and an elongation at break a80 of more than 4 to 41%, with high strengths tending to be associated with lower elongations at break and vice versa:
-Rm over 1100 to 1200 Mpa: rm × A80 ≥ 25000 until 45000 MPa%
-Rm over 1200 to 1400 Mpa: rm × A80 is more than or equal to 20000 and up to 42000 MPa%
-Rm over 1400 to 1800 Mpa: rm × A80 is more than or equal to 10000 and up to 40000 MPa%
-Rm over 1800 Mpa: rm × A80 is not less than 7200 and up to 20000 MPa%
The sample A80 was used for the elongation at break test in accordance with DIN 50125.
By the occurrence of the TRIP and/or TWIP effect of the alloy according to the invention, the elongation properties and toughness are advantageously improved.
Steel strip produced according to the invention provides a good combination of strength, elongation and deformability. Furthermore, the manganese steel according to the invention with a medium manganese content (medium manganese steel) based on the alloying elements C, Mn, Al is very economical to produce.
Due to the increased Al content, the steel has a lower relative density than other alloyed manganese steels containing a small amount of Al and having a medium manganese content. The manganese steel according to the invention is also characterized by an increased resistance to delayed crack formation (delayed fracture) and to hydrogen embrittlement and liquid metal embrittlement during welding.
The use of the term "to", for example, 0.01 to 1% by weight, in the definition of the content range is meant to also include the limit values — 0.01 and 1 in this case.
Alloying elements are often added to the steel in order to influence specific properties in a targeted manner. The alloying elements can thus influence different properties of different steels. The interactions and interactions are generally highly dependent on the presence, amount, and state of solution in the material of other alloying elements. The correlation is variable and complex. The role of the alloying elements in the alloy according to the invention will be discussed in more detail below. The positive effect of the alloying elements used according to the invention will be described below:
c, carbon C: it is required to form carbides, stabilize austenite and increase strength. Higher C contents impair weldability and lead to impairment of elongation and toughness, so that the maximum content is determined to be less than 0.3% by weight. In order to obtain sufficient material strength, a minimum addition of 0.1 wt.% is required.
Manganese Mn: stabilizing austenite, increasing strength and toughness, and enabling deformation-induced martensite formation and/or twinning in the alloy according to the invention. A content of less than 4 wt% is insufficient to stabilize austenite, thereby impairing elongation characteristics, while austenite contents of 8 wt% and more are too high in stability, and thus strength properties (particularly 0.2% yield point) are lowered. For manganese steels according to the invention with a medium manganese content, a range of 4 to <8 wt.% is preferred.
Aluminum Al: an Al content of more than 1 wt.% improves the strength and elongation properties, reduces the relative density and affects the transformation properties of the alloy according to the invention. An Al content exceeding 2.9 wt% impairs elongation characteristics. The higher Al content also significantly impairs the casting characteristics in the continuous casting process. This results in increased costs in casting. An Al content of more than 1 wt.% delays the precipitation of carbides in the alloy according to the invention. Thus, a maximum content of 2.9 wt.% and a minimum content of more than 1 wt.% is determined.
In addition, a minimum content (in wt%) of more than 6.5 and less than 10 should be maintained for the sum of Mn and Al so that the desired conversion characteristics can be ensured. The content of Mn + Al of 10 wt% or more deteriorates castability, thereby reducing the yield and thus increasing the cost. In the case where the Mn + Al content is 6.5 wt% or less, sufficient austenite stability cannot be secured to obtain desired transformation characteristics.
Silicon Si: the optional addition of Si in an amount greater than 0.05 wt.% may hinder carbon diffusion, reduce relative density and improve strength and elongation characteristics and toughness. Further, improvement of cold rolling property can be seen by alloying addition of Si. Contents of more than 0.7 wt.% lead to embrittlement of the material and have a negative effect on the hot and cold rollability and coatability (e.g. by galvanization). Thus, the maximum content was determined to be 0.7 wt% and the minimum content was determined to be 0.05 wt%.
Chromium Cr: the optional addition of Cr increases the strength and reduces the corrosion rate, retards the formation of ferrite and pearlite and forms carbides. The maximum content is determined to be 3% by weight, since higher contents result in impaired elongation properties. The minimum Cr content for efficacy was determined to be 0.1 wt.%.
Molybdenum Mo: mo is optionally added as a carbide former, increasing strength and increasing resistance to delayed crack formation and hydrogen embrittlement. The Mo content exceeding 0.9 wt% impairs the elongation characteristics, so that the maximum content of 0.9 wt% and the minimum content of 0.01 wt% required for sufficient efficacy are determined.
Phosphorus P: are trace elements from iron ore and are dissolved in the iron lattice as substitutional atoms. Phosphorus increases hardness and improves hardenability through solid solution strengthening. However, attempts are generally made to reduce the phosphorus content as far as possible, since it exhibits a strong tendency to liquation, in particular due to its low diffusion rate, and greatly reduces the toughness level. The adhesion of phosphorus to grain boundaries may cause cracks along the grain boundaries during hot rolling. In addition, phosphorus increases the transition temperature from ductile to brittle by up to 300 ℃. For the reasons described above, the phosphorus content is limited to a value of less than 0.05 wt.%.
S, sulfur: like phosphorus, it is bound as a trace element in iron ore. In steel it is generally undesirable because it exhibits a tendency to extensive liquation and has a great embrittlement effect, thereby impairing elongation properties and toughness. It is therefore attempted to achieve as low a sulphur content in the melt as possible (for example by deep desulphurisation). For the reasons described above, the sulfur content is limited to a value of less than 0.05 wt%.
N: as well as elements relevant in steel manufacture. In the dissolved state, it improves the strength and toughness of steels with higher manganese contents containing 4 wt.% or more Mn. Lower Mn alloy steels with free nitrogen below 4 wt.% tend to have strong aging effects. Nitrogen diffuses into and blocks dislocations even at low temperatures. Thus, it produces an increase in strength associated with a rapid loss of toughness. It is possible to incorporate nitrogen in the form of nitrides, for example by alloying with aluminum or titanium, where in particular aluminum nitride has a negative effect on the formability of the alloy according to the invention. For the reasons described above, the nitrogen content is limited to less than 0.02 wt%.
Titanium Ti: acts as a carbide former in a grain refining manner, thereby improving strength, toughness and elongation characteristics simultaneously and reducing intergranular corrosion. The Ti content exceeding 0.3 wt% impairs elongation characteristics, and thus the maximum Ti content is determined to be 0.3 wt%. Alternatively, the minimum content is determined to be 0.005 to bind nitrogen and advantageously precipitate Ti.
B, boron B: delays austenite transformation, improves hot formability of the steel and increases strength at ambient temperature. Even if the alloy content is low, the effect can be achieved. The content of more than 0.01 wt% greatly impairs elongation characteristics and toughness, so that the maximum content is determined to be 0.01 wt%. Alternatively, the minimum content of 0.0005 wt% is determined to advantageously utilize the effect of increasing the strength of boron.
Detailed Description
Tests were carried out to investigate the mechanical properties of steel strips made according to the invention and consisting of the exemplary alloy 1. Apart from iron and melting-induced impurities, alloy 1 contains essentially the following elements, the contents of which are expressed in wt.%:
| alloy (I) | C | Mn | Al | Si |
| Alloy 1 | 0.2 | 7.0 | 1.1 | 0.5 |
For comparison purposes, a steel strip made of alloy 1 above was cold rolled (i.e. at room temperature and therefore below 50 ℃) and rolled according to the invention at 250 ℃. The rolling forces measured were as follows:
cumulative rolling force is understood to be the sum of the rolling forces of the individual passes in order to obtain a comparable measure for the force consumption. The rolling force was normalized to a bandwidth of 1000 mm. The degree of deformation e is defined as the quotient of the thickness change Δ d of the steel strip under consideration and the initial thickness d0 of the steel strip under consideration. The reduction in rolling force is a calculated reduction in rolling force at 250 ℃ compared to the rolling force at the time of cold rolling.
Elongation at break a80 was also determined:
the elongation characteristic value represents the elongation in the rolling direction. It is clear that there is a considerable increase in yield point, while the elongation at break remains unchanged.
Claims (20)
1. A method for manufacturing an ultra high strength steel strip having the TRIP/TWIP effect, comprising the steps of:
-melting a steel melt containing, in weight%: c: 0.1 to < 0.3; mn: 4 to < 8; al: >1 to 2.9; p: < 0.05; s: < 0.05; n: < 0.02; the balance of iron, including inevitable steel-related elements;
-casting the steel melt into a prefabricated strip by means of a horizontal or vertical final dimension strip casting process, or into a slab by means of a horizontal or vertical slab casting process,
heating to a rolling temperature of 1050 ℃ to 1250 ℃ or rolling in-line from the casting heat,
-hot rolling the prefabricated strip or slab at a final rolling temperature of 1050 ℃ to 800 ℃ into a hot rolled strip having a thickness of 12mm to 0.8mm,
-coiling the hot rolled strip at a temperature higher than 200 ℃ to 800 ℃,
-pickling the hot-rolled strip,
-annealing the hot-rolled strip in a continuous or discontinuous annealing plant for a time ranging from 1 minute to 48 hours at a temperature ranging from 540 ℃ to 840 ℃,
-cold rolling the hot rolled strip in one or more rolling passes at an elevated temperature of 60 ℃ to 450 ℃.
2. The method of claim 1, wherein the step of melting the steel melt comprises: in a blast furnace-steelworks process route or in an electric arc furnace process, one or more of the following elements are added by alloying in% by weight: 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.
3. The method according to claim 2, wherein the melt is treated under vacuum in the blast furnace-steelworks process route or in an electric arc furnace process.
4. The method of claim 1, further comprising: the steel strip is electrolytically galvanized or hot-galvanized or another organic or inorganic coating is applied.
5. The method of claim 1, wherein the strip is selectively reheated or cooled to a temperature of 60 ℃ to 450 ℃ between rolling passes during the cold rolling process in the plurality of rolling passes.
6. The method according to any one of claims 1 to 5, characterized in that after cold rolling at elevated temperature the steel strip is annealed in a continuous annealing plant at a temperature of 720 ℃ to 840 ℃ for an annealing time of 1 minute to 15 minutes or by means of a discontinuous annealing plant, wherein the annealing time is 30 minutes to 48 hours and the temperature is 550 ℃ to 820 ℃.
7. A method according to claim 6, characterized in that after the annealing treatment the strip is cooled to a temperature below 250 ℃ to room temperature, subsequently reheated to a temperature of 300 ℃ to 450 ℃ and held at this temperature for up to 5 minutes and then cooled to room temperature.
8. Method according to any one of claims 1 to 5, characterized in that the strip is flattened after cold rolling.
9. The method according to claim 4, characterized in that the steel strip is given an additional coating based on organic or inorganic material after electrolytic galvanising or hot galvanising.
10. A method according to any one of claims 1-5, characterized in that the steel strip is further processed into a component by means of cold forming or semi-hot forming.
11. The method of claim 10, wherein the semi-thermoforming is performed at a temperature of 60 ℃ to 450 ℃.
12. An ultra-high strength steel strip with TRIP/TWIP effect manufactured by the method of any one of claims 1 to 11, having an alloy composition comprising, in weight%: c: 0.1 to < 0.3; mn: 4 to < 8; al: >1 to 2.9; p: < 0.05; s: < 0.05; n: < 0.02; the balance of iron, including unavoidable steel-related elements, and having a structure which consists of, by volume%, 10-80% of austenite and 10-90% of martensite, and the balance of ferrite and bainite in a total amount of less than 20%; wherein the average grain size of the phase components of the ultra-high strength steel strip is as follows:
-austenite: less than 500 nm
Martensite, ferrite, bainite: less than 650 nm.
13. The ultra high strength steel strip of claim 12 wherein one or more of the following elements are added by alloying in weight%: 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.
14. The ultra-high strength steel strip of claim 12 wherein the sum of the Mn and Al contents in weight percent satisfies the following requirements: 6.5< Mn + Al < 10.
15. The ultra-high strength steel strip of claim 12 wherein at least a 20% fraction of martensite is present as annealed martensite.
16. The ultra-high strength steel strip of any one of claims 12 to 15, wherein > 10% of the austenite fraction is present in the form of annealed or deformed twins.
17. The ultra-high strength steel strip of any one of claims 12 to 15 wherein the steel has a tensile strength Rm of 1100 to 2200MPa, a 0.2% yield point rp0.2 of 300 to 1550MPa and an elongation at break a80 of greater than 4 to 41%.
18. The ultra-high strength steel strip of any one of claims 12 to 15, characterized by the following dependence of the tensile strength Rm in MPa on the elongation at break a80 in%:
-Rm over 1100 to 1200 MPa: rm × A80 is more than or equal to 25000 to 45000 MPa%
-Rm over 1200 to 1400 MPa: rm × A80 is more than or equal to 20000 to 42000 MPa%
-Rm over 1400 to 1800 MPa: rm multiplied by A80 is more than or equal to 10000 to 40000 MPa%
-Rm over 1800 MPa: rm multiplied by A80 is more than or equal to 7200 to 20000 MPa.
19. The ultra-high strength steel strip of any one of claims 12 to 15, wherein the galvanized steel strip has an additional inorganic or organic coating on the galvanized layer in the event that the steel strip is electrolytically galvanized or galvannealed.
20. The ultra-high strength steel strip of claim 19 wherein the inorganic coating is a metallic coating.
Applications Claiming Priority (5)
| Application Number | Priority Date | Filing Date | Title |
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| DE102016115618.3A DE102016115618A1 (en) | 2016-08-23 | 2016-08-23 | Process for producing a high-strength steel strip with improved properties during further processing and such a steel strip |
| DE102016115618.3 | 2016-08-23 | ||
| DE102016121002 | 2016-11-03 | ||
| DE102016121002.1 | 2016-11-03 | ||
| PCT/EP2017/070913 WO2018036918A1 (en) | 2016-08-23 | 2017-08-18 | Method for producing a high-strength steel strip with improved properties for further processing, and a steel strip of this type |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN109642263A CN109642263A (en) | 2019-04-16 |
| CN109642263B true CN109642263B (en) | 2021-02-26 |
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| CN201780051643.0A Active CN109642263B (en) | 2016-08-23 | 2017-08-18 | Method for producing a high-strength steel strip with improved properties during further processing, and such a steel strip |
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| US (2) | US20190185951A1 (en) |
| EP (1) | EP3504349B1 (en) |
| KR (1) | KR102401569B1 (en) |
| CN (1) | CN109642263B (en) |
| RU (1) | RU2714975C1 (en) |
| WO (1) | WO2018036918A1 (en) |
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| WO2019209933A1 (en) | 2018-04-24 | 2019-10-31 | Nucor Corporation | Aluminum-free steel alloys and methods for making the same |
| CN108998741B (en) * | 2018-05-29 | 2020-02-14 | 西南交通大学 | Ultrahigh-strength toughness medium manganese transformation induced plasticity steel and preparation method thereof |
| WO2021089851A1 (en) * | 2019-11-08 | 2021-05-14 | Ssab Technology Ab | Medium manganese steel product and method of manufacturing the same |
| CN111621624B (en) * | 2020-05-11 | 2021-10-22 | 北京交通大学 | Process method for improving hydrogen-induced delayed fracture resistance of medium manganese steel |
| CN111850410B (en) * | 2020-07-30 | 2022-02-15 | 吉林建龙钢铁有限责任公司 | Cold-hard coiled plate for packing belt and preparation method thereof |
| CN112226679B (en) * | 2020-09-14 | 2022-06-21 | 包头钢铁（集团）有限责任公司 | Cold-rolled 980 MPa-grade martensitic steel and production method thereof |
| CN114606430B (en) * | 2022-03-01 | 2023-05-12 | 兴机电器有限公司 | Low-carbon Fe-Mn-Al-Si TWIP steel and preparation method thereof |
| CN115261739A (en) * | 2022-08-03 | 2022-11-01 | 海宁瑞奥金属科技有限公司 | Stirring head material |
| CN116005078B (en) * | 2023-01-14 | 2024-09-24 | 重庆大学 | Manufacturing method of lamellar heterogeneous structure high-strength steel |
| CN116219300A (en) * | 2023-02-15 | 2023-06-06 | 武汉科技大学 | Boron microalloyed high-strength plastic cold-rolled medium manganese steel and preparation method thereof |
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| DE3935965C1 (en) * | 1989-10-26 | 1991-05-08 | Mannesmann Ag, 4000 Duesseldorf, De | |
| JP3317303B2 (en) | 1991-09-17 | 2002-08-26 | 住友金属工業株式会社 | High tensile strength thin steel sheet with excellent local ductility and its manufacturing method |
| FR2796083B1 (en) | 1999-07-07 | 2001-08-31 | Usinor | PROCESS FOR MANUFACTURING IRON-CARBON-MANGANESE ALLOY STRIPS, AND STRIPS THUS PRODUCED |
| KR101027250B1 (en) * | 2008-05-20 | 2011-04-06 | 주식회사 포스코 | High strength steel sheet and hot dip galvanized steel sheet having high ductility and excellent delayed fracture resistance and method for manufacturing the same |
| JP5287770B2 (en) * | 2010-03-09 | 2013-09-11 | Ｊｆｅスチール株式会社 | High strength steel plate and manufacturing method thereof |
| EP2383353B1 (en) * | 2010-04-30 | 2019-11-06 | ThyssenKrupp Steel Europe AG | High tensile steel containing Mn, steel surface product made from such steel and method for producing same |
| PL2700728T3 (en) * | 2011-04-21 | 2018-03-30 | Nippon Steel & Sumitomo Metal Corporation | High-strength cold-rolled steel sheet with highly uniform stretchabilty and excellent hole expansibility, and process for producing same |
| DE102012013113A1 (en) | 2012-06-22 | 2013-12-24 | Salzgitter Flachstahl Gmbh | High strength multiphase steel and method of making a strip of this steel having a minimum tensile strength of 580 MPa |
| CN102758133B (en) * | 2012-07-26 | 2013-12-25 | 宝山钢铁股份有限公司 | 1000MPa-level automobile steel with high product of strength and elongation and manufacturing method thereof |
| CN102912219A (en) * | 2012-10-23 | 2013-02-06 | 鞍钢股份有限公司 | TRIP steel plate with high product of strength and elongation and preparation method thereof |
| RU2631219C2 (en) * | 2013-05-06 | 2017-09-19 | Зальцгиттер Флахшталь Гмбх | Method of manufacturing items from light structural steel and items from light structural steel |
| WO2015011510A1 (en) * | 2013-07-25 | 2015-01-29 | Arcelormittal Investigación Y Desarrollo Sl | Spot welded joint using high strength and high forming and its production method |
| DE102015112889A1 (en) * | 2015-08-05 | 2017-02-09 | Salzgitter Flachstahl Gmbh | High-strength manganese-containing steel, use of the steel for flexibly rolled flat steel products and production methods together with flat steel product for this purpose |
| US11414720B2 (en) * | 2016-01-29 | 2022-08-16 | Jfe Steel Corporation | High-strength steel sheet for warm working and method for manufacturing the same |
| CN106244918B (en) * | 2016-07-27 | 2018-04-27 | 宝山钢铁股份有限公司 | A kind of 1500MPa grades of high strength and ductility automobile steel and its manufacture method |
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- 2017-08-18 US US16/323,222 patent/US20190185951A1/en not_active Abandoned
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| EP3504349A1 (en) | 2019-07-03 |
| CN109642263A (en) | 2019-04-16 |
| WO2018036918A1 (en) | 2018-03-01 |
| US20210147953A1 (en) | 2021-05-20 |
| KR20190042022A (en) | 2019-04-23 |
| US20190185951A1 (en) | 2019-06-20 |
| RU2714975C1 (en) | 2020-02-21 |
| EP3504349B1 (en) | 2024-04-03 |
| KR102401569B1 (en) | 2022-05-23 |
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