Steel strip or sheet and method for producing same

Abstract

The present invention relates to cold rolled, annealed and hot dip galvanized or electrogalvanized bake hardenable steel strip or sheet and to a method for producing said steel strip or sheet.

Description

[Technical field]

[0001] The present invention relates to cold rolled, annealed and hot dip galvanized or electrogalvanized bake hardenable steel strip or sheet and to a method for producing said steel strip or sheet. [Background technology]

[0002] The ever-increasing demand for reduced steel weight in several applications, especially in transportation applications, has forced the steel industry to provide solutions to improve the mechanical properties of steel.

[0003] The various strengthening measures at the disposal of the steel industry include, but are not limited to, for example, increasing the temper rolling reduction after annealing, changing the chemical composition, modifying the processing conditions, e.g. the cold rolling reduction imposed on the strip or sheet, or changing the annealing conditions of the cold rolled steel strip or sheet.

[0004] The various measures may interact with each other and improve some properties while adversely affecting others, for example, increasing the temper rolling reduction improves the yield strength but decreases the uniform elongation value.

[0005] Any improvement must therefore be carefully balanced to improve those properties that are most important to a particular application while sacrificing, as little as possible, those properties that are less important.

[0006] A possible way to increase the strength without decreasing the relevant properties is to change the chemistry. It is known from the literature (e.g. S. Hoile in “Materials Science and Technology October 2000 Vol. 16, 1079) that the strength of ultra-low carbon steels, which are generally used for bake hardenable steel grades, depends on the alloy chemistry. The modification of the chemistry requires a careful balance between the mechanical properties as well as the processing parameters.

[0007] JP 06-322441 A discloses a method for producing a high strength cold rolled steel plate having formability and bake hardenability based on a steel having a composition with 0.003-0.010% C. Summary of the Invention [Problem to be solved by the invention]

[0008] It is an object of the present invention to provide a cold rolled, annealed and hot dip galvanized or electrogalvanized bake hardenable steel strip or sheet exhibiting a yield strength of at least 270 MPa / / RD.

[0009] It is also an object of the present invention to provide a cold rolled, annealed and hot-dip galvanized or electrogalvanized bake hardenable steel strip or sheet exhibiting a tensile strength of at least 360 MPa / / RD.

[0010] It is also an object of the present invention to provide a cold rolled, annealed and hot-dip galvanized or electro-galvanized bake hardenable steel strip or sheet exhibiting an elongation at 80 mm gauge length of at least 28% / / RD.

[0011] It is also an object of the present invention to provide a cold rolled, annealed and hot-dip galvanized or electro-galvanized bake-hardenable steel strip or sheet having a bake-hardening potential (BH2) of at least 30 MPa / / RD. [Means for solving the problem]

[0012] One or more of these objects may be achieved by the use of the following chemical composition (by weight): C: 0.0022~0.0042; Al_sol: 0.027~0.066; Nb: 0.004~0.028; B: 0.0004~0.0017; Ti: 0.004~0.014; N: 0.0004~0.0033; S: 0.022 or less; Cr:0.045 or less; V: 0.005 or less; Cu: 0.045 or less; Ni: 0.045 or less; Mo: 0.011 or less; Ca: 0~0.0100; Mn, P and Si: 1.445≦Mn(wt%)+10×P(wt%)+Si(wt%)≦1.925 Si: at least 0.148 wt.% and / or at most 0.248 wt.%; Fe and unavoidable impurities: balance A cold rolled, annealed and hot dip galvanized bake hardenable steel strip or sheet having Yield strength (Rp) / / RD is 270 to 330 MPa; Tensile strength (Rm) / RD is 360 to 460; Total strain (A80) / RD is at least 28%; n0 value is at least 0.13; The r value is at least 1.10; A bake-hardening index (BH2) of at least 30 MPa is achieved by said steel strip or sheet. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing a schematic manufacturing process. [Diagram 2] FIG. 2 is a diagram showing the value of Rp (MPa) versus Σ(Mn+Si+10×P) (wt %). [Diagram 3] FIG. 3 is a diagram showing U-shaped runout table cooling. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] All chemical compositions are expressed in weight % unless otherwise stated. The steel is preferably produced from molten steel produced by the Basic Oxygen Steelmaking (BOS) process, preferably also using vacuum degassing technology. The BOS process is preferred over the other commonly used steelmaking process, the Electric Arc Furnace (EAF) process, since it produces steel with a low level of impurities. While the EAF process is based on scrap molten steel, the BOS process starts from unused pig iron, and only small amounts of carefully selected scrap are added as coolant in the refining process from pig iron to molten steel, which is then cast into thick slabs (t: 150-350 mm) or thin slabs (t: 50-150 mm) in a continuous casting process, or into strips (t<20 mm) in a strip casting process. The cast slabs or strips are the material for the hot rolling process, and the hot rolled strips obtained in the hot rolling process are the material for the subsequent cold rolling process of the present invention.

[0015] The inventors have found that it is important to meet the following criteria for Mn, Si and P: 1.445 wt%≦(Mn(wt%)+10×P(wt%)+Si(wt%))≦1.925 wt%. High Mn levels lead to poor control of C levels and thus to large variations in mechanical properties, including bake hardening reactivity. High Si levels lead to unwanted oxide formation and thus coating adhesion problems. High P levels can cause casting problems due to expansion and can also lead to high rolling loads and severe wear of the rolling cylinders. High P can also lead to welding problems. If the values ​​are too low, the strength requirements are not met. Preferably, (Mn(wt%)+10×P(wt%)+Si(wt%)) is at most 1.825 wt% and / or at least 1.525 wt%.

[0016] The inventors have found that by using a careful balance between the elements Mn, Si and P in combination with a carefully balanced process it is possible to produce a titanium stabilized extra low carbon steel with a minimum yield strength of 270 MPa / / RD, a minimum tensile strength of 360 MPa / / RD, a minimum elongation A80 of at least 28% / / RD and a minimum bake hardenability BH2 (according to EN10325:2002) of at least 30 MPa / / RD. Despite the relatively high rolling loads in cold rolling, it is possible to produce rolled coils with widths of up to 2000 mm.

[0017] Rp, Rm, A80, n0, r0 as claimed are determined according to VDA239-100:2016 and BH2 is determined according to EN10325:2002. The notation / / RD means that the properties are measured on tensile specimens with the longitudinal direction parallel to the rolling direction. The 0 after n and r indicates the same thing (0 being at an angle of 0° to the rolling direction). For the avoidance of doubt, it should be noted that A80 is the total strain and is measured at a gauge length of 80 mm. BH2 was determined by measuring the increase in Rp after heating the cold rolled, annealed and hot dip galvanized material at 170°C in a 20 minute paint bake cycle according to EN10325:2006. Tensile tests were carried out according to EN10002-1:2001.

[0018] In one embodiment, A80 / / RD is at least 30%, preferably at least 32%. In one embodiment, n0 is at least 0.15, preferably at least 0.16. In one embodiment, r0 is at least 1.20, preferably at least 1.30. Good moldability is indicated when both parameters r0 and n0 exhibit high values.

[0019] In one embodiment, BH2 / / RD is at least 40 MPa, preferably at least 45 MPa. Preferably, Rp / / RD is at least 280 MPa, more preferably at least 290 MPa.

[0020] In the steel of the present invention, titanium (Ti) is added primarily to ensure that all N is precipitated as TiN. Free N adversely affects mechanical properties. Any excess Ti can precipitate as TiC or Ti4C2S2.

[0021] In the steel of the present invention, niobium (Nb) is added so that most of the C precipitates as NbC, however, a small amount of C in solid solution is essential to obtain the required BH response.

[0022] In the steel of the present invention, aluminum (Al) is used as a deoxidizer. However, Al is also added as an alloying element to promote the formation of aluminum nitride to improve deep drawability if not all N is precipitated as TiN. As a result, Al can be present in the steel as aluminum oxide (residual from deoxidation), metallic Al and AlN. Both Al and AlN are soluble in acid and are therefore collectively referred to as Al_sol. The total aluminum content of the steel is therefore given as Al_tot=Al_ox+Al_sol.

[0023] In one embodiment of the present invention, the P content is at least 0.054% by weight, preferably at least 0.065% by weight. The P content is preferably at most 0.099% by weight, more preferably at most 0.085% by weight. Thus, the preferred range is 0.065-0.085% by weight.

[0024] In one embodiment, the Mn content is at least 0.610 wt%, preferably at least 0.660 wt%. The Mn content is preferably equal to or less than 0.880 wt%, more preferably equal to or less than 0.800 wt%.

[0025] In the steel of the present invention, the Si-content is at least 0.148 wt.-%. In one embodiment, the Si-content is at least 0.165 wt.-%. In the steel of the present invention, the Si-content is at most 0.248 wt.-%. In one embodiment, the Si-content is at most 0.225 wt.-%.

[0026] In one embodiment of the present invention, the S content is at least 0.010 wt.%, more preferably at most 0.005 wt.%.

[0027] In a preferred embodiment, the maximum waviness Wsa(1-5) after 5% deformation (according to SEP 1941 and SEP 1942) is 0.37 μm. This value is obtained by a reproducible and robust method. The value of Wsa(1-5) depends to a large extent on the roughness of the work rolls in the last cold rolling stand of the cold rolling mill.

[0028] In one embodiment, the steel strip or sheet has a roughness value (Ra) of 0.80-1.50 μm and a waviness value after 5% deformation (Wsa(1-5)) of up to 0.37 μm.

[0029] Preferably, the waviness value Wsa(1-5) after 5% deformation is at most 0.35 μm, more preferably at most 0.34 μm and / or Ra is at most 1.45 μm.

[0030] In a further embodiment of the invention, the steel strip or sheet of the invention is provided, after cold rolling and annealing, with a metal coating layer, for example a zinc layer which may contain small amounts of Al, where Al is about 45% Al, about 35% Fe and about 20-35% Zn (FeAl 5-x Zinc x) and ensures proper adhesion of the zinc layer to the substrate. For this reason, 0.10-1.0 wt.% Al may be added to the zinc bath. The metal coating layer comprises 0.3-4.0 wt.% Mg, 0.3-6.0 wt.% Al, optionally up to 0.2 wt.% of one or more additional elements and unavoidable impurities, the balance being zinc. Preferably, the alloying elements in the zinc alloy coating layer comprise 1.0-2.0 wt.% magnesium, 1.0-3.0 wt.% aluminum, optionally up to 0.2 wt.% of one or more additional elements and unavoidable impurities, the balance being zinc. In an even more preferred embodiment, the zinc alloy coating layer comprises at most 1.0-2.0 wt.% Mg, 1.5-2.5 wt.% Al, optionally at most 0.2 wt.% of one or more additional elements, unavoidable impurities, and the balance being zinc.

[0031] The invention is also embodied by a method of providing a steel strip or sheet according to the invention, wherein the strip is successively annealed and then electrogalvanized according to the invention.

[0032] In another embodiment, the steel strip or sheet is provided with a metal coating layer, for example an (industrially pure) aluminum layer or an aluminum alloy layer. Industrially pure aluminum contains at least 99% by weight of Al (AA 1XXX series). A typical metal bath for hot-dip galvanizing with an aluminum alloy layer contains aluminum alloyed with silicon, for example 8-11% by weight of silicon, at most 4% by weight of iron, optionally at most 0.2% by weight of one or more additional elements (e.g. calcium), unavoidable impurities, the balance being aluminum. Silicon is present to prevent the formation of a thick iron-intermetallic compound layer, which reduces adhesion and formability. Iron is preferably present in an amount of 1-4% by weight, more preferably at least 2% by weight.

[0033] The thickness of the cold-rolled strip or sheet is not particularly limited, but it is more preferable that the thickness of the cold-rolled strip or sheet is 0.50 to 1.20 mm.

[0034] In one embodiment, the grain size of the ferrite grains in the cold rolled steel strip and sheet of the present invention is between 9 and 13 ASTM, preferably between 9.5 and 12 ASTM, and more preferably at least 10 ASTM.

[0035] Preferably, one, two or more or all of Cr, V, Cu, Ni and / or Mo are present only as unavoidable impurities in the steel of the present invention, more preferably one, two or more or all of Cr, V, Cu, Ni and / or Mo are completely absent.

[0036] According to a second aspect, the present invention also relates to a method for producing a cold rolled, annealed and hot dip galvanized bake hardenable steel strip or sheet having a chemical composition (in weight percent) comprising: The method comprises the steps of: The molten steel is prepared with the following chemical composition: C:0.0022~0.0042wt%; Al_sol:0.027~0.066wt%; Nb:0.004~0.028wt%; B:0.0004~0.0017% by weight; Ti:0.004~0.014wt%; N:0.0004~0.0033wt%; S: 0.022% by weight or less; Cr: 0.045% by weight or less; V: 0.005% by weight or less; Cu: 0.045% by weight or less; Ni: 0.045% by weight or less; Mo: 0.011% by weight or less; Mn, P and Si: 1.445 wt%≦Mn(wt%)+10×P(wt%)+Si(wt%)≦1.925 wt%; Si: at least 0.148 wt.% and / or at most 0.248 wt.%; Ca:0~0.0100wt%; Fe and inevitable impurities: balance continuously casting a slab or strip having the heating or reheating the slab to a temperature of at least 1050°C, hot rolling the slab to produce a hot rolled strip having a thickness of at most 5.0 mm, and cooling the hot rolled strip at a cooling rate of at least 40°C / sec to a coiling temperature of at least 650°C, wherein the finish rolling temperature of the hot rolling is higher than Ar3; post-treating the hot rolled strip by pickling; cold rolling the post-treated hot rolled strip at a cold rolling reduction of 65-90%; continuous annealing of the cold rolled strip to transform the microstructure of the cold rolled strip into a recrystallized microstructure and then forming a metallic coating on the annealed strip in a hot dip galvanizing step; temper rolling the hot-dip galvanized steel strip at a temper rolling reduction of at least 0.2%; Optionally, post-processing the temper rolled strip (e.g., coiling, cutting into sheets, forming) Including, When all of the following characteristics are measured with / / RD, The yield strength (Rp) is 270 to 330 MPa. Tensile strength (Rm) is 360 to 460; The total strain (A80) is at least 28%; n0 value is at least 0.13; The r value is at least 1.10; It is realised in a process where the bake hardenability index (BH2) is at least 30 MPa.

[0037] In one embodiment, the process conditions of the method of the present invention are the following process conditions: heating or reheating the slab to a temperature of at least 1100°C or at least 1150°C; The finish rolling temperature is 900-945℃; The coiling temperature of the central portion of the strip is 710°C or more and / or 750°C or less; The cold rolling reduction is at least 68%, preferably at least 70%, more preferably at least 75% and / or at most 90%; The hot-dip galvanized steel strip is temper rolled to 0.2-2.5%, preferably 1.25-2.10%. is selected from.

[0038] It should be noted that these process conditions may be selected independently of one another such that a process of the present invention embodies one, more than one or all of these process conditions.

[0039] It should also be noted that the coiling temperature at the front and rear ends can be higher than that at the center of the strip to compensate for the faster cooling rate at the front and rear ends after coiling. This compensation is important to promote certain metallurgical reactions, e.g., precipitation of AlN or NbC. In that case, a so-called U-shaped cooling can be used, where the front and rear ends are coiled at a higher temperature (see FIG. 3). The temperature difference between the front / end and the center during cooling, which needs to be compensated for the effect of the rear / front end, can be easily determined by a person skilled in the art, but as a general guide, the coiling temperature at the front and rear ends can be about 30° C. higher than the center of the strip. It should be noted that the front and rear ends are relatively short compared to the center. The optimum lengths of the front and rear ends compared to the center, the length of the transitions between the front / rear ends and the center, as well as the temperature difference over the entire length of the strip can be easily determined by thermal models that calculate the cooling of each point in the coil, and in combination with metallurgical models for e.g. precipitation of AlN, gives the optimum temperature path (Metallurgy for Hoogovens' new CA line for tin plate, Th.M. Hoogendoorn, AJ van den Hoogen, 1991 TMS Fall Meeting, Cincinnati (OH), October 22-24, 1991). EXAMPLES

[0040] The invention is further illustrated by the following non-limiting examples.

[0041] [Table 1]

[0042] Alloys A-J are in accordance with the present invention. Alloys O-T are outside the scope of the claimed invention and are presented to demonstrate the effects of chemistry and process.

[0043] All steels were produced in a basic oxygen steelmaking plant and continuously cast as thick slabs (~225mm). It should be noted that steels can also be produced by thin slab casting and direct hot rolling, in which case the thickness of the cast slabs is typically 50-100mm. This does not affect the properties of the final inventive product. A non-limiting production schematic is shown in Figure 1.

[0044] The steel slabs were reheated in a slab reheat furnace (SRF) to a temperature of at least 1050°C and then hot rolled to thicknesses of 2.8 mm, 3.1 mm and 3.5 mm. The finish hot rolling temperature (FRT) was higher than Ac3, so the hot rolling was performed in the austenitic state. A target FRT of about 910-930°C was used. After cooling the hot rolled strip on the run-out table (ROT), the strip was coiled at a target coiling temperature (CT) of 730°C. The hot rolled coils (HRC) were then pickled and cold rolled to a thickness of 0.70 mm, resulting in cold rolling reductions of 75%, 77% and 80% (depending on the HRC thickness). The cold rolled coils (CRC) were then successively annealed to fully recrystallize and temper rolled at 1.4-2.0%. Between annealing and temper rolling, the coil was subjected to a hot dip galvanizing treatment to provide the strip with a metallic coating layer and produce cold rolled metallic coated coil (CRCC).

[0045] The microstructure of the cold rolled metal coated coils shows a fully recrystallized microstructure with grain size of 10-10.5 ASTM. The mechanical properties are shown in Table 2.

[0046] [Table 2]

[0047] Analysis of the results shows that the strength is indeed dependent on the levels of Mn, Si and P. Coils with compositions outside the claimed ranges do not guarantee the required minimum strength of 270 MPa.

[0048] Further analysis of the tensile properties as a function of cold rolling reduction showed that Rp 02 It was revealed that Rp, Rm, Ag, A80 and n-values ​​were independent of the cold rolling reduction, and only the r-value was affected by the cold rolling reduction. The results in Table 2 show that the yield strength (Rp), tensile strength (Rm), elongation (A80) and r-values ​​were not or hardly affected by the temper mill settings, while the uniform elongation (Ag) and n-values ​​(strain hardening exponent) were somewhat decreased at high temper mill reductions. High temper mill reductions lead to further work hardening of the material, resulting in lower initial Ag and n-values. The increase in yield strength by increasing the temper mill reduction from 1.5% to 2.0% is only about 3 MPa.

[0049] Cold rolled metal coated coils were produced as standard file finish (FF: Full Finish). The roughness of the rolling cylinder in the last stand of the cold rolling mill (#5) was about 5.8 μm EDT. Roughness and waviness were measured in the center of the coil (with respect to the entire length) according to SEP 1941 (May 2012) after forming as described in SEP 1942 (May 2017 draft). The results are summarized in Table 3 together with the relevant process settings.

[0050] [Table 3]

[0051] BRIEF DESCRIPTION OF THE DRAWINGS The invention is further illustrated by the non-limiting figures shown below. Figure 1: Schematic manufacturing process. Figure 2: Value of Rp (MPa) versus Σ(Mn+Si+10×P) (weight%). Figure 3: U-shaped run-out table cooling.

[0052] In Figure 1 the manufacturing process of the steel of the invention is shown diagrammatically. The process starts with casting and ends with cold rolled galvanized coil (CRGC). Intermediate steps are shown diagrammatically.

[0053] Figure 2 shows the relationship of one of the mechanical properties (Rp, in MPa) as a function of Σ(Mn+Si+10×P) (in weight %), illustrating the improvement brought about by the steel and process according to the invention: the vertical dashed lines show the values ​​of 1.445 and 1.925 weight %, the horizontal dashed line shows Rp=270 MPa.

[0054] Figure 3 shows a schematic of the U-shaped cooling and identifies the leading, middle and trailing sections of the strip. The leading section is hot rolled first and therefore becomes the inner wrap in the "eye" of the coil, and the trailing section is hot rolled last and therefore becomes the outer wrap of the coil. The length of the middle section depends on the strip thickness, strip width and coil weight.

Claims

1. Chemical composition as follows: C: 0.0022 to 0.0042% by weight; Al_sol: 0.027-0.066% by weight; Nb: 0.004 to 0.028% by weight; B: 0.0004 to 0.0017% by weight; Ti: 0.004 to 0.014% by weight; N: 0.0004 to 0.0033% by weight; S: 0.022% by weight or less; Cr: 0.045% by weight or less; V: 0.005% by weight or less; Cu: 0.045% by weight or less; Ni: 0.045% by weight or less; Mo: 0.011% by weight or less; Mn, P and Si: 1.445 wt%≦Mn(wt%)+10×P(wt%)+Si(wt%)≦1.925 wt%; Si: at least 0.148 wt.% and / or at most 0.248 wt.%; Ca: 0 to 0.0100% by weight; Fe and unavoidable impurities: balance A cold rolled, annealed and hot-dip galvanized or electrogalvanized bake hardenable steel strip or sheet having a Yield strength (Rp) / / RD is 270 to 330 MPa; Tensile strength (Rm) / / RD is 360 to 460; Total strain (A80) / / RD is at least 28%; The n0 value is at least 0.13; The r value is at least 1.10; The bake hardening index (BH2) is at least 30 MPa; Rp, Rm, A80, n0 and r0 are determined in accordance with VDA239-100:2016; BH2 is determined in accordance with EN 10325:2002; / / The above steel strip or sheet, wherein RD means that the properties are measured on tensile specimens, in the longitudinal direction which is parallel to the rolling direction.

2. 2. The steel strip or sheet according to claim 1, having a roughness value (Ra) of 0.80 to 1.50 μm and a waviness after 5% deformation Wsa(1-5) as described in SEP 1941 and SEP 1942 of at most 0.37 μm.

3. 3. Steel strip or sheet according to claim 1 or 2, wherein the amount of P is at least 0.054 wt.% and / or at most 0.099 wt.%.

4. 3. Steel strip or sheet according to claim 1 or 2, wherein the amount of Mn is at least 0.610wt.% and / or at most 0.880wt.%.

5. 3. Steel strip or sheet according to claim 1 or 2, wherein Mn(wt%)+10*P(wt%)+Si(wt%) is at most 1.825wt% and / or at least 1.525wt%.

6. 3. The steel strip or sheet according to claim 1 or 2, wherein the galvanized layer is a metal coating layer, such as a zinc coating layer or a zinc alloy coating layer, or wherein the galvanized layer is a metal coating layer, such as a commercially pure aluminium layer or an aluminium alloy layer comprising at least 99% by weight of Al.

7. 7. The steel strip or sheet according to claim 6, wherein the zinc alloy coating layer comprises 0.3 to 4.0 wt.% Mg, 0.3 to 6.0 wt.% Al, optionally up to 0.2 wt.% of one or more additional elements, the balance being unavoidable impurities and zinc.

8. 3. The steel strip or sheet according to claim 1 or 2, wherein the thickness of the steel strip or sheet is between 0.50 and 1.20 mm.

9. 1. A process for producing a cold rolled, annealed and hot dip galvanized or electrogalvanized bake hardenable steel strip or sheet having a chemical composition (wt.%) comprising: The method comprises the steps of: The molten steel was prepared having the following chemical composition: C: 0.0022 to 0.0042% by weight; Al_sol: 0.027-0.066% by weight; Nb: 0.004 to 0.028% by weight; B: 0.0004 to 0.0017% by weight; Ti: 0.004 to 0.014% by weight; N: 0.0004 to 0.0033% by weight; S: 0.022% by weight or less; Cr: 0.045% by weight or less; V: 0.005% by weight or less; Cu: 0.045% by weight or less; Ni: 0.045% by weight or less; Mo: 0.011% by weight or less; Mn, P and Si: 1.445 wt%≦Mn(wt%)+10×P(wt%)+Si(wt%)≦1.925 wt%; Si: at least 0.148 wt.% and / or at most 0.248 wt.%; Ca: 0 to 0.0100% by weight; Fe and unavoidable impurities: balance continuously casting a slab or strip having the heating or reheating the slab to a temperature of at least 1050°C, hot rolling the slab to produce a hot rolled strip having a thickness of at most 5.0 mm, and cooling the hot rolled strip at a cooling rate of at least 40°C / sec to a coiling temperature of at least 650°C, wherein the finish rolling temperature of the hot rolling is higher than Ar3; post-treating the hot rolled strip by pickling; cold rolling the post-treated hot rolled strip at a cold rolling reduction of 65-90%; continuous annealing of the cold rolled strip to transform the microstructure of the cold rolled strip into a recrystallized microstructure and then forming a metallic coating on the annealed strip in a galvanizing step; temper rolling the galvanized steel strip with a temper rolling reduction of at least 0.2%; Optionally, post-treating the temper rolled strip. Including, When all of the following characteristics are measured by / / RD, The yield strength (Rp) is 270 to 330 MPa; The tensile strength (Rm) is 360 to 460; A total strain (A80) of at least 28%; The n0 value is at least 0.13; The r value is at least 1.10; The process, wherein the bake hardening index (BH2) is at least 30 MPa.

10. 10. The method of claim 9, wherein the galvanizing step is a hot dip galvanizing step.

11. One, two or all of P, Mn and Si in the following amounts: P: at least 0.054% by weight and / or at most 0.099% by weight; Mn: at least 0.610 wt.% and / or at most 0.880 wt.%; Mn(wt%)+10×P(wt%)+Si(wt%): up to 1.825 wt% and / or at least 1.525 wt% 11. Steel strip or sheet produced by the method of claim 9 or 10, comprising:

12. The process conditions are as follows: Heating or reheating the slab to a temperature of at least 1100°C or at least 1150°C; The finish rolling temperature is 900-945°C; The coiling temperature is 710°C or more and / or 750°C or less; The cold rolling reduction is at least 75% and / or at most 83%; The hot dip galvanized steel strip is temper rolled to 0.2-2.5%, more preferably 1.25-2.10%. The method according to claim 9 or 10, wherein one, two or more or all of the following are satisfied:

13. The coiling temperature of the central portion of the strip is 710° C. or more and / or 750° C. or less; 11. The method according to claim 9 or 10, wherein the leading and trailing ends of the strip are wound at a higher temperature, preferably at least 10° C. and at most 50° C. higher than the winding temperature of the central portion of the strip, more preferably at least 20° C. and / or at most 40° C. higher than the winding temperature of the central portion of the strip.

14. 11. The method according to claim 9 or 10, wherein the galvanized layer is a metal coating layer, such as a zinc coating layer or a zinc alloy coating layer, or the galvanized layer is a metal coating layer, such as a commercially pure aluminum layer or an aluminum alloy layer containing at least 99% by weight of Al.

15. 15. The method according to claim 14, wherein the zinc alloy coating layer comprises 0.3-4.0 wt.% Mg, 0.3-6.0 wt.% Al, and optionally up to 0.2 wt.% of one or more additional elements, the balance being unavoidable impurities and zinc.

16. 11. Use of a steel strip or sheet produced by the method according to claim 9 or 10 for producing parts for automotive applications, for example car body parts, in particular exterior car body parts.

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