Hybrid high strength low alloy cold rolled and annealed steel strip and method for producing same

Abstract

The present invention relates to a hybrid high strength low alloy cold rolled and annealed steel strip and a method for making the same.

Description

[Technical field]

[0001] The present invention relates to a hybrid high strength low alloy cold rolled and annealed steel strip and a method for making the same. [Background technology]

[0002] High strength low alloy steels (HSLA steels) are well known in the art. HSLA steels are often used in the automotive industry. HSLA steels are defined e.g. in the specifications of the Verband Der Automobilindustrie (VDA). Reference is made to the VDA 239-100 material specification of August 2016. According to the VDA, cold rolled HSLA steels are designated by a grade number, e.g. CR420LA, where CR stands for cold rolled and the number 420 stands for the longitudinal yield strength Rp 0.2 (abbreviated Rp), and LA stands for low alloy. VDA specifications prescribe the chemical composition of HSLA steels containing Ti and Nb apart from the standard alloying elements C, Mn, Si and Al to provide high strength. However, these ranges in the specifications are still very wide. Another relevant international standard is EN10002-1:2001 for tensile testing of metallic materials.

[0003] Thin HSLA steel strip, plate or blanks are usually coated with an aluminium or zinc coating. When a zinc coating is used, the coating is often applied as a hot dip galvanised or hot dip galvannealed coating.

[0004] Cold rolled HSLA steels at higher strength levels suffer from the disadvantage that their high strength makes it difficult to cold roll the hot rolled steel strip to relatively thin gauges in wide dimensions.

[0005] WO 2016 / 030010 proposes CR460LA, which is based on an HSLA steel containing titanium and vanadium. However, although this grade meets the mechanical property requirements of the relevant standards for CR460LA, the cold-rolled and annealed product suffers from large differences in mechanical properties in different directions (in-plane anisotropy). Moreover, vanadium is a very expensive alloying element which further varies widely. Summary of the Invention [Problem to be solved by the invention]

[0006] It is an object of the present invention to provide an HSLA steel strip which can be cold rolled to relatively thin gauges in wide dimensions to produce HSLA steel plates and blanks having the requisite strength.

[0007] It is a further object of the present invention to provide such an HSLA steel strip, plate or blank which has the required elongation.

[0008] It is a further object of the present invention to provide such an HSLA steel strip, plate or blank which has reduced in-plane anisotropy in the mechanical properties.

[0009] It is another object of the present invention to provide a method for producing such HSLA steel strip. [Means for solving the problem]

[0010] One or more of the above objectives are, in weight percent, C: 0.050~0.090, Nb: 0.030~0.060, Mn: 1.000-1.800, S: maximum 0.015, Si: 0.050 to 0.300, P: maximum 0.015, Al_sol: 0.020~0.080, N: 0.002~0.008, Ca+REM: max. 0.0050, Optionally, B: 0.0001 to 0.0010 Ti: max 0.050 One or more of, and Remainder: Iron and unavoidable impurities A hybrid high strength low alloy (H-HSLA) cold rolled and annealed steel strip consisting of: The steel has a tensile strength Rm of 520 to 680 MPa and a yield strength Rp of 460 to 580 MPa, Rp / Rm is 0.70 to 0.80; The microstructure of the steel comprises a precipitation strengthened ferritic matrix containing polygonal and / or acicular ferrite; A second phase comprising cementite, between 2 and 10 % of martensite optionally accompanied by one or more of pearlite and bainite. This is achieved by the steel strip, [Brief description of the drawings]

[0011] [Figure 1] 1A-B show Klemm etch micrographs of (FIG. 1A) Nb and (FIG. 1B) NbTi, and FIG. 1C-D show Nital etch micrographs of (FIG. 1C) Nb and (FIG. 1D) NbTi. [Diagram 2] FIG. 2A shows the distribution of martensite in the micrograph of the steel of the Klemm etched Nb sample (annealing temperature=820° C.), FIG. 2B shows after processing with ImageJ software, and FIG. 2C shows the size distribution of martensite. [Diagram 3] FIG. 3 shows typical experimental heating and cooling curves. [Figure 4] Table 1 in Figure 4 shows the effect of alloying elements along with the effect of annealing cycle to produce a steel grade with "hybrid" properties. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Conventional duplex stainless steels have a microstructure of martensite dispersed in a clean, and therefore ductile, ferritic matrix, providing an excellent combination of ductility and high tensile strength. The uniquely favorable properties of duplex stainless steels result from the large difference in strength and ductility between the clean ferrite and the martensite.

[0013] Conventional HSLA steels have a carbon content of 0.05-0.25% to maintain formability and weldability. Other alloying elements include manganese and small amounts of copper, nickel, niobium, nitrogen, vanadium, chromium, molybdenum, titanium, calcium, rare earth elements or zirconium. Copper, titanium, vanadium and niobium are added for strengthening purposes, with the aim of modifying the microstructure of carbon steels (which is usually a fine-grained ferrite-pearlite aggregate) and producing a very fine dispersion of alloy carbides in a nearly pure ferrite matrix to produce precipitation-hardened ferrite.

[0014] The inventors have discovered that, with careful balancing, it is possible to combine the advantages of conventional duplex and conventional HSLA in a hybrid HSLA. This H-HSLA combines the formability of duplex stainless steels, resulting from a hard martensite phase in a ductile clean ferrite matrix, with the strength of a precipitation hardened ferrite-pearlite aggregate. The uniquely favorable properties of duplex stainless steels arise from the large difference in strength and ductility between clean ferrite and martensite, yet strengthening the ferrite by grain refinement and precipitation strengthening is counterintuitive.

[0015] If the annealing temperature and time are intentionally limited to inhibit the growth of strengthening precipitates, the ferritic matrix may contain unrecrystallized ferrite. The presence of unrecrystallized ferrite may contribute to the overall strength, but this may come at the expense of some degree of anisotropy. In order to limit the degree of anisotropy, the recrystallized fraction is preferably at least 85%, preferably at least 87%. Thus, by controlling the recrystallized fraction, the degree of anisotropy and the mechanical property values ​​can be adjusted accordingly.

[0016] The presence of some unrecrystallized ferrite in the ferritic matrix is ​​very important, since it allows the realization of the required higher strength levels. However, it should not be too high, taking into account the required low anisotropy. The recrystallized fraction of the ferritic matrix microstructure is preferably at least 85%, preferably at least 90%, more preferably at least 95%, and even more preferably at least 98%. Preferably, the average grain size of the ferritic matrix is ​​at least 4 μm. Preferably, the average grain size of the ferritic matrix is ​​at most 9 μm. Preferably, the average grain size of the ferritic matrix is ​​4-8 μm. This average grain size is measured at 1 / 10 of the thickness t, just below the surface of the steel strip.

[0017] The steel strip comprises the claimed properties in the uncoated, coated or temper rolled state. The steel strip may be temper rolled in an optional temper rolling (also known as skin pass rolling) step. The steel strip may also be coated with a metal coating in an optional coating step. The steel strip also comprises the aforementioned mechanical properties after the optional temper rolling and / or the optional metal coating. This is not necessarily the case after subsequent forming operations such as stamping, bending, deep drawing, or after warm or hot press forming.

[0018] The optional metallic coating functions primarily as protection against corrosion of the steel strip.

[0019] The hybrid HSLA according to the invention requires the addition of niobium (Nb) and optionally titanium (Ti) as alloying elements. The presence of Nb is necessary for grain refinement and precipitation strengthening. The optional Ti also contributes to precipitation strengthening, but also helps in the formation of martensite, which allows the reduction of other elements such as manganese (Mn) and Nb.

[0020] The steel according to the invention also contains a higher concentration of silicon (Si) compared to the common HSLA grades. Si acts as a solid solution strengthening element, making it possible to achieve the target strength. However, since Si is a ferrite promoting element and is known to cause problems on the surface of hot rolled steel strip due to sticky oxides, its concentration must be limited in order to maintain the ability to form martensite in the microstructure of the steel and to maintain a good surface quality. This surface quality concerns not only the surface of hot rolled steel strip, but also that of cold rolled steel strip and even that of galvanized steel strip. The presence of carbon (C) is necessary for solid solution strengthening, the formation of carbides and the formation of second phases such as bainite and especially martensite. At values ​​above 0.090% by weight, the risk of too much volume of hard second phases increases, while below 0.050% by weight, the risk of too little volume of hard second phases increases. To reduce the risk of too high a volume fraction of hard second phases, the steel preferably contains max. 0.085 wt.% C, more preferably max. 0.080 wt.% C. Also, a slightly lower carbon content reduces the amount of pearlite and / or cementite.

[0021] Conventional hot-rolled HSLA steels rely on the grain-refining properties of microalloying additions due to the retardation of recrystallization during hot rolling, and to a lesser extent, on precipitation hardening. Cold-rolled HSLA steels rely on precipitation hardening and, to a much lesser extent, on grain refinement. It has therefore proven difficult to obtain high-strength cold-rolled HSLA steels with sufficient formability. In WO 2016 / 030010, CR460LA is proposed, which is based on HSLA steel containing titanium and vanadium. However, although this grade meets the mechanical property requirements of the relevant standards for CR460LA, the cold-rolled and annealed product suffers from large differences in mechanical properties in different directions (in-plane anisotropy).

[0022] The presence of the elements C, Si, Nb and optionally Ti and second phases in the right proportions allows the production of a steel grade with hybrid properties of high yield stress, high elongation and low anisotropy. The steel according to the invention is therefore a hybrid between HSLA steel and a dual-phase steel. This hybrid property is therefore due to the joint effect of precipitation strengthening (HSLA aspect) and the presence of second phases, mainly martensite (dual-phase aspect). The volume fraction of martensite is therefore very important. If the volume fraction is too low (<2%), the material behavior approaches the usual standard HSLA grades. If the volume fraction is too high (>10%), the material behavior approaches the dual-phase (DP) grades with too low yield stress. For hybrid HSLA, 0.70≦Rp / Rm≦0.80. If this ratio is less than 0.70, the steel behaves like a DP steel and has too low yield stress. When this ratio exceeds 0.80, the steel behaves similarly to standard HSLA, the grades having low total elongation and high in-plane anisotropy. The presence of 2-10% martensite can very significantly eliminate the in-plane anisotropy of the mechanical properties.

[0023] The optional addition of Ti promotes the formation of martensite, which allows Mn to be reduced, while Nb is used for grain refinement. The presence of Ti also aids in recrystallization during annealing of cold rolled material at low temperatures (<850°C). At similar annealing temperatures, HSLA without Ti will have less recrystallization and a lower percentage of martensite. It will therefore have higher anisotropy and lower elongation values. Without Ti, a higher annealing temperature is required and the strength will be lower due to the coarsening of Nb(C,N) precipitates. The steel optionally contains at least 0.001% by weight titanium, preferably at least 0.005% by weight titanium, and / or up to 0.035% by weight, preferably up to 0.020% by weight titanium.

[0024] To make the steel according to the invention more suitable for hot stamping and direct hardening applications, small amounts of boron (B) may optionally be added to the steel. The steel preferably comprises at least 0.0002% by weight (=2 ppm) and / or at most 0.0010% by weight (=10 ppm), preferably at most 0.0008% by weight, more preferably at most 0.0006% by weight. Too much boron leads to the formation of too much martensite and bainite, which increases the strength too much and reduces the formability of the steel so that it no longer meets the requirements of CR460LA.

[0025] These steels contain sulfur (S) and phosphorus (P) as more or less unavoidable impurities, the amounts of which should be limited to the lowest possible values ​​technically and economically. The steels preferably contain a maximum of 0.010% by weight of S, or preferably a maximum of 0.005% by weight of P.

[0026] Manganese is an austenite-forming element and if its content is too high, the risk of martensite formation increases, especially when the silicon content is low, as is the case in the steel according to the invention. A Mn content that is too low leads to strength values ​​that are too low. The steel according to the invention preferably comprises at least 1.200% by weight Mn, more preferably at least 1.350% by weight Mn and / or preferably at most 1.600% by weight Mn, more preferably at most 1.550% by weight Mn.

[0027] To improve edge elongation or bending in some applications, high strength low alloy steel grades may optionally be specified with sulphide inclusion control. Special steelmaking practices are used to control the shape and content of primarily manganese sulphide inclusions. Manufacturers may initially limit sulphide inclusions through ultra-low sulphur steelmaking practices. To control inclusion shape, manufacturers may also utilize calcium (Ca) and / or rare earth elements (REM, e.g. Ce) additions to the molten steel. Small, spherical particles are preferred. Thus, the optional Ca+REM refers to the combined amount of calcium and rare earth elements, such as Ce, in the steel for sulphide inclusion control. If present, the preferred minimum amount of either of these elements is 0.0005 wt.%.

[0028] The cold rolled and annealed steel strip is optionally provided with a metallic coating, which is preferably applied by hot-dip coating, although cold application techniques such as PVD, CVD or electro-deposition can also be employed.

[0029] In one embodiment of the present invention, the metallic coating may be a hot-dip galvanized (GI) coating formed in a continuous process by passing a steel sheet through a molten bath having a zinc content of at least 99% (all coating percentages are by weight % unless otherwise specified). The metallic coating is a zinc alloy coating. The metallic coating may be an electrogalvanized (EG) coating having a zinc content of at least 99.9% formed electrolytically in a continuous coating process on a suitably prepared steel surface.

[0030] The metallic coating may be a zinc-iron alloy coating produced by immersing the prepared steel strip in a molten bath containing at least 99% zinc content and subsequent annealing resulting in diffusion of iron into the zinc layer. The resulting zinc-iron coating usually has an iron content of up to 13% by mass and is called a galvanic (GA) coating. The metallic coating may be an aluminum-silicon (AlSi) coating formed by passing the prepared steel strip through a molten aluminum bath with a silicon content of 8-11%.

[0031] The metallic coating may be a zinc-magnesium (MZ) coating, formed by passing the prepared steel strip through a bath of molten zinc alloyed with magnesium and aluminum. 2 Al 5 The coating (including the barrier layer) comprises 0.3-4.0% Mg and 0.3-6.0% Al, optionally up to 0.2% of one or more additional elements, unavoidable impurities, and the balance zinc. More preferably, the content of alloying elements in the coating comprises 1.0-2.0% magnesium and 1.0-3.0% aluminum, optionally up to 0.2% of one or more additional elements, unavoidable impurities, and the balance zinc. In an even more preferred embodiment, the zinc alloy coating comprises up to 1.6% Mg and 1.6-2.5% Al, optionally up to 0.2% of one or more additional elements, unavoidable impurities, and the balance zinc.

[0032] According to a second aspect, the present invention relates to a method for producing a hybrid dual-phase steel strip according to the invention as described herein above and as claimed in any one of claims 1 to 11, comprising the following steps: - continuously casting a steel slab or a steel strip and hot rolling the slab or the steel strip into a hot rolled steel strip, The hot rolled steel strip has, in weight percent, C: 0.050~0.090, Nb: 0.030~0.060, Mn: 1.000-1.800, S: maximum 0.015, Si: 0.050 to 0.300, P: maximum 0.015, Al_sol: 0.020~0.080, N: 0.002~0.008, Ca: max. 0.0050, Optionally, B: 0.0002~0.0006 Ti: 0.001 to 0.050 One or more of, and Remainder: Iron and unavoidable impurities The composition is The hot-rolled steel strip has a thickness of 2.0 to 4.5 mm, wherein finish rolling is performed while the steel strip has an austenitic microstructure; cooling the hot rolled steel strip after finish rolling, preferably at a cooling rate of at least 30° C. / s; coiling the cooled steel strip at a coiling temperature CT of 500-660°C and cooling the coiled steel strip to ambient temperature; the coiled steel strip is uncoiled, pickled, and cold-rolled at a reduction ratio of 40 to 80%; Continuous annealing of the cold rolled steel strip, i. heating the steel strip; ii. intercritically annealing the steel strip; iii. cooling the intercritically annealed steel strip to an intermediate temperature; iv. optionally, holding the strip at the intermediate temperature for a time t_oa between 5 and 100 seconds; v. Optionally, hot dip coating the steel strip; vi. further cooling the steel strip to a post-annealing coiling temperature at a cooling rate sufficient to induce martensite formation in the annealed steel strip, i.e., a cooling rate greater than the critical cooling rate; vii. Winding the steel strip Steps performed by: wherein said steel strip is optionally provided with a metal coating by a) hot dip coating in step v or b) by a cold application technique after step vii; Optionally, temper rolling the coated steel strip at a reduction of 0.05-3.00%; wherein the optionally coated and optionally temper rolled steel strip has a tensile strength Rm of 520-680 MPa and a yield strength Rp of 460-580 MPa, with Rp / Rm being 0.70-0.80; - coiling the coated steel strip or cutting the coated steel strip into plates or blanks; Optionally, thereafter, forming the coated steel strip, sheet or blank by cold forming operations such as stamping, bending, deep drawing, etc., or by warm or hot press forming. The present invention is also embodied in the method, which includes:

[0033] The importance of the steel composition has already been explained. The various processing steps all contribute to achieving a delicate hybrid balance between the properties of standard HSLA and those of standard DP. For example, high cooling rates are necessary to form sufficient (but not too much) amounts of second phases such as bainite and especially martensite.

[0034] The coiling temperature is also an important parameter since it determines the starting condition of the hot-rolled strip for the subsequent processing steps. The coiling temperature is preferably a maximum of 650° C.

[0035] The cold rolling reduction is preferably at most 75%, more preferably at most 70%. A lower cold rolling reduction limits the rolling forces during cold rolling, thereby reducing the risk of shape defects in the steel strip.

[0036] The continuous annealing after the first cold rolling step is an intercritical annealing treatment that involves heating and holding at a temperature between Ac1 and Ac3 temperatures to obtain partial austenitization of the cold rolled steel strip. The microstructure after continuous annealing comprises a precipitation strengthened ferrite matrix with polygonal and / or acicular ferrite; cementite, 2-10% martensite, and optionally a second phase with one or more of pearlite and bainite; the recrystallization fraction of the ferrite matrix is ​​at least 85%. The cooling rate after annealing must therefore be higher than the so-called critical cooling rate to induce the austenite to martensite transformation in the resulting continuously annealed and cold rolled steel strip. This critical cooling rate can be defined as the slowest cooling rate at which unstable austenite can be transformed into stable martensite and can be easily determined by routine experimentation. If the post-annealing coiling temperature is lower than the Mf temperature, the martensite is stable.

[0037] In one embodiment, the temper rolling reduction is up to 2.50%, preferably up to 1.30%, more preferably up to 0.80%. The temper rolling reduction is preferably at least 0.10%, more preferably at least 0.20%. The temper rolling reduction is important to obtain the desired final properties, strip shape and surface texture.

[0038] The optional temper rolling reduction can be important to obtain the right balance between the final properties and the surface quality (aspects such as flatness, waviness, and camber). The balance is not always the same. In some cases, the importance of the flatness of the strip may take precedence over the mechanical properties (provided that the requirements imposed by the relevant standards are met), and in other cases, the mechanical properties may take precedence. Chemistry and processing can be manipulated to balance the various requirements somewhat, but always within the requirements of the relevant standards. Some temper rolling requires a temper rolling reduction (TRR) of up to 3.00%. However, a higher TRR impairs the formability potential of the steel, so the TRR should be as low as possible to balance the surface and shape requirements of the strip with the strength and formability requirements. The temper rolling reduction is preferably up to 2.50%, more preferably up to 1.30%, and even more preferably up to 1.00%. The reduction in the skin pass rolling is preferably at least 0.10%, more preferably at least 0.20%, even more preferably at least 0.50, and even more preferably at least 0.65%.

[0039] The method of producing the cold rolled and annealed hybrid dual phase steel strip optionally includes the application of a metallic coating, preferably by hot-dip coating, although cold application techniques such as PVD, CVD or electro-deposition can also be employed.

[0040] According to another aspect, the invention is also embodied in the use of the steel produced according to the invention in automotive applications. The automotive applications of the steel according to the invention may consist of, but are not limited to, applications in the body structure, inner and outer panels, doors and trunk closures, chassis or suspension, or in wheels, fuel tanks, steering and braking systems. The automotive applications may be in passenger cars or in other vehicles such as trailers, trucks, trains, civil engineering vehicles, etc. EXAMPLES

[0041] Examples and Figures The invention will now be described with the aid of the following non-limiting examples and figures.

[0042] Cold rolled and annealed products The results shown in Table 1 in Figure 4 and the annealing cycles considered show the effect of the alloying elements as well as the effect of the annealing cycle to produce steel grades with "hybrid" properties. Too high Nb, Ti or C contents give steel grades with Rp / Rm>0.8 and containing a high percentage of non-recrystallized regions. A decrease in Si concentration makes it difficult to reach the VDA strength specifications. A comparison between Nb and NbTi alloys shows that the samples containing Ti have higher strength and are less sensitive to changes in annealing temperature due to the formation of a higher percentage of martensite and a higher degree of recrystallization.

[0043] 1A-B show Klemm etch micrographs of (FIG. 1A) Nb and (FIG. 1B) NbTi. Martensite appears as bright spots on the micrographs. The samples were annealed at 800°C. FIG. 1C-D show Nital etch micrographs of (FIG. 1C) Nb and (FIG. 1D) NbTi, showing the presence of polygonal ferrite (recrystallized + unrecrystallized), acicular ferrite, and pearlite and cementite precipitates in the sample annealed at 800°C.

[0044] As shown in Figure 1, in the micrographs of the etched samples, the martensite appears as white spots. Etching was performed by standard Klemm etching (polishing the surface of the sample to optical grade and etching the surface for a few seconds with Klemm etchant (a solution of saturated aqueous sodium thiosulfate and 1 g of potassium metabisulfite) followed by washing with ethanol). These spots were analyzed using ImageJ (https: / / imagej.nih.gov), an open source software for processing and analyzing scientific images, to determine the percentage of martensite precipitates and their average size. The etched image is converted to a black and white image and the software determines the distribution of martensite in the micrograph of the Klemm etched steel Nb sample (annealing temperature = 820 °C) (see Figure 2A). Figure 2B is the size distribution of the martensite after processing by the ImageJ software, and Figure 2C is the size distribution of the martensite.

[0045] Optical characterization of the microstructure of the steel according to the invention reveals that the high degree of recrystallization of the microstructure is a key contributor for the realization of balanced properties. EBSD measurements confirmed the accuracy of the optical measurements. SEM conditions were 15 kV, 120 μm aperture, high current on. EBSD conditions were 16 mm working distance and 100 fps scan speed. 300 × 1000 μm 2 (step size 0.5 μm) and 200 × 200 μm 2 Scanning (step size 0.2 μm) gave similar results.

[0046] [Table 1]

[0047] [Table 2]

[0048] Hot stamping The steel according to the invention is also suitable for hot stamping applications. This is demonstrated by subjecting Nb and NbTi compositions to a direct hot stamping process. A typical tT schedule is as follows: the sample is heated in a reheat furnace to 900°C for 5-7 minutes. It is then cooled in air for 5-10 seconds during the transfer between the furnace and the hot press before it is removed from the furnace and cooled. A typical experimental heating and cooling curve is shown in Figure 3. In such a curve, the hot pressing is performed at approximately 800°C.

[0049] After hot pressing, the NbTi grades have mechanical properties comparable to various commercial grades (see Tables 4 and 5). These results highlight the versatility of the steel grades according to the invention, which is the result of a balanced composition and microstructure.

[0050] [Table 3]

[0051] [Table 4]

Claims

1. In weight percent, C: 0.050-0.090, Nb: 0.030 to 0.060, Mn: 1.000-1.800, S: maximum 0.015, Si: 0.050 to 0.300, P: maximum 0.015, Al_sol: 0.020 to 0.080, N: 0.002 to 0.008, Ca+REM: maximum 0.0050, Optionally, B:0.0001~0.0010 Ti: maximum 0.050 and Remainder: Iron and unavoidable impurities A hybrid high strength low alloy (HSLA) cold rolled and annealed steel strip consisting of: the steel has a tensile strength Rm of 520 to 680 MPa and a yield strength Rp of 460 to 580 MPa, Rp / Rm is 0.70 to 0.80, The microstructure of the steel is a precipitation-strengthened ferrite matrix containing polygonal and / or acicular ferrite; a second phase comprising cementite, 2-10% martensite, and optionally one or more of pearlite and bainite; Including, The steel strip, wherein the recrystallization rate of the ferrite matrix is ​​at least 85%.

2. The steel strip of claim 1 , wherein the ferritic matrix comprises unrecrystallized ferrite.

3. 3. Steel strip according to claim 1 or 2, wherein the recrystallization fraction of the ferritic matrix is ​​at least 85%, preferably at least 87%.

4. 3. Steel strip according to claim 1 or 2, wherein the average grain size of the ferrite matrix at the position 1 / 10 of t is between 4 and 8 μm.

5. 3. Steel strip according to claim 1 or 2, wherein the steel contains at least 0.001% by weight of titanium, preferably at least 0.005% by weight of titanium, and / or at most 0.035% by weight, preferably at most 0.020% by weight of titanium.

6. 3. Steel strip according to claim 1 or 2, wherein the steel contains at least 0.0002% and / or at most 0.0008% by weight of boron, preferably at most 0.0006% by weight of boron.

7. 3. Steel strip according to claim 1 or 2, wherein the steel contains max. 0.010% by weight of S, preferably max. 0.005% by weight of S.

8. 3. Steel strip according to claim 1 or 2, wherein the steel contains max. 0.085 wt.% C, preferably max. 0.080 wt.% C.

9. 3. Steel strip according to claim 1 or 2, wherein the steel comprises at least 1.200% by weight of Mn, preferably at least 1.350% by weight of Mn, and / or at most 1.600% by weight of Mn, preferably at most 1.550% by weight of Mn.

10. 3. Steel strip according to claim 1 or 2, wherein the steel strip is provided with a metallic coating, preferably a hot-dip metallic coating.

11. In weight percent, C: 0.050-0.080, Nb: 0.030 to 0.050, Mn: 1.200 to 1.550, S: maximum 0.010, Si: 0.050 to 0.300, P: maximum 0.010, Al_sol: 0.020 to 0.050, N: 0.002 to 0.005, Ca: maximum 0.0050, Optionally, B:0.0001~0.0010 Ti:0.001~0.020 and Remainder: Iron and unavoidable impurities 3. The steel strip according to claim 1 or 2, comprising: the steel has a tensile strength Rm of 520 to 680 MPa and a yield strength Rp of 460 to 580 MPa, Rp / Rm is 0.70 to 0.80, The microstructure of the steel is a precipitation-strengthened ferrite matrix containing polygonal and / or acicular ferrite; a second phase comprising cementite, 2-10% martensite, and optionally one or more of pearlite and bainite; Including, The steel strip, wherein the recrystallization rate of the ferrite matrix is ​​at least 85%.

12. 10. A method for producing hybrid dual-phase steel strip according to claim 1, comprising the steps of: - continuously casting a steel slab or steel strip and hot rolling said slab or said steel strip into a hot rolled steel strip, The hot-rolled steel strip comprises, in weight percent: C: 0.050-0.090, Nb: 0.030 to 0.060, Mn: 1.000-1.800, S: maximum 0.015, Si: 0.050 to 0.300, P: maximum 0.015, Al_sol: 0.020 to 0.080, N: 0.002 to 0.008, Ca: maximum 0.0050, Optionally, B:0.0002~0.0006 Ti:0.001~0.050 and Remainder: Iron and unavoidable impurities having a composition consisting of The hot-rolled steel strip has a thickness of 2.0 to 4.5 mm, the step of finish rolling being performed while the steel strip has an austenitic microstructure; cooling the hot rolled steel strip after finish rolling, preferably at a cooling rate of at least 30°C / s; - coiling the cooled steel strip at a coiling temperature CT of 500-660°C and cooling the coiled steel strip to ambient temperature; - after uncoiling the coiled steel strip, pickling and cold rolling with a reduction of at least 40% and at most 80%; -Continuous annealing of the cold rolled steel strip, i. heating the steel strip; ii. Annealing the steel strip in a dual-phase condition; iii. Cooling the intercritically annealed steel strip to an intermediate temperature; iv. Optionally, holding the steel strip at the intermediate temperature for a time t_oa between 5 and 100 seconds; v. Optionally, hot dip coating the steel strip; vi) further cooling the steel strip to a post-annealing coiling temperature at a cooling rate sufficient to induce martensite formation in the annealed steel strip; vii. Winding the steel strip a step of performing wherein said steel strip is optionally provided with a metal coating by a) hot dip coating in step v or b) by cold application techniques after step vii; Optionally, temper rolling the coated steel strip at a reduction of 0.05 to 3.00%; wherein said optionally coated and optionally temper rolled steel strip has a tensile strength Rm of 520 to 680 MPa and a yield strength Rp of 460 to 580 MPa, with Rp / Rm being 0.70 to 0.80; - coiling the coated steel strip or cutting the coated steel strip into steel plates or blanks; Optionally, thereafter shaping said coated steel strip, sheet or blank by cold forming operations such as stamping, bending, deep drawing, or by warm or hot press forming. The method comprising:

13. 13. The method according to claim 12, wherein the temper rolling reduction is at most 2.50%, preferably at most 1.30%, more preferably at most 0.80% and / or the temper rolling reduction is at least 0.10%, preferably at least 0.20%.

14. 14. A method according to claim 12 or 13 for producing the hybrid high strength low alloy (HSLA) cold rolled and annealed steel strip according to claim 1, comprising: The steel strip comprises, in weight percent: C: 0.050-0.080, Nb: 0.030 to 0.050, Mn: 1.200 to 1.550, S: maximum 0.010, Si: 0.050 to 0.300, P: maximum 0.010, Al_sol: 0.020 to 0.050 N: 0.002 to 0.005, Ca: maximum 0.0050, Optionally, B:0.0001~0.0010 Ti:0.001~0.020 and Remainder: Iron and unavoidable impurities It consists of The method, wherein the recrystallization rate of the ferrite matrix is ​​at least 85%.

15. 14. Use of a steel according to claim 1 producible or produced by the method according to claim 12 or 13 in automotive applications.

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