ULTRA LOW CARBON STEEL FREE OF INTERSTITIALS

Abstract

The invention relates to an ultra-low carbon, interstitial-free steel with an improved composition, wherein Ti+Nb+V is at most 0.10% by weight. This steel has very good ductility.

Description

ULTRA LOW CARBON COMPOSITE-FREE STEEL FIELD OF INVENTION The invention relates to an ultra-low carbon interstitial-free steel. BACKGROUND OF THE INVENTION Interstitial-free steel (IF steel) is a mild steel with excellent formability because all the interstitial elements—carbon, nitrogen, and boron—are bonded, for example, by titanium, niobium, or aluminum, to form carbides, nitrides, and borides. Therefore, the interstitial elements do not impede the movement of dislocations within the iron crystal grain. Due to the stabilization of carbon, nitrogen, and boron, IF steels can be stored for an almost unlimited time, unlike furnace-hardenable steels. Due to its high formability, IF steel is primarily used in the automotive industry for manufacturing blank body parts, which are often difficult to form by pressing. Therefore, high formability is a requirement. Because of its low carbon content, IF steels are mild steels with a low yield strength and high ductility. IF steels are standardized, for example, according to EN 10346:2015. In this standard, low-carbon steels for cold forming are listed in Tables 1 and 7. They are designated as DX51–DX57, where higher numbers indicate better formability. DX57 offers the highest formability. According to the standard, these IF steels contain a maximum of 0.30% titanium by mass. The German standard VDA 239-100 (2016) also provides cold-rolled mild steels in Tables 6 and 24. These steels are designated as CR1–CR5 and have a composition and mechanical properties almost identical to the DX types of EN 10346:2015. A cold-rolled mild steel CR6 with improved ductility was introduced as a draft standard in the May 2019 revision of VDA 239-100. It is known that it is advantageous to use very low carbon (ULC) steels as IF steels because the lower the amount of carbon (and nitrogen) in the steel, the less titanium or niobium is needed to bind the carbon and nitrogen. Therefore, in practice, quantities of elements lower than the maximum amounts specified in the standards are used. On the other hand, ULC steels need to have a reasonable yield strength and tensile strength, as prescribed by the standards. This means that sufficient strength-providing elements, such as manganese, phosphorus, and / or silicon, must be present. BRIEF DESCRIPTION OF THE INVENTION It is an objective of the present invention to provide a strip, sheet or die-cut piece of ultra-low carbon IF steel having improved formability. Another objective of the invention is to provide a strip, sheet, or die-cut piece of ultra-low carbon IF steel having an improved plastic deformation rate. An additional objective of the invention is to provide a steel strip, sheet, or die-cut piece. ultra-low carbon IF that has an improved strain hardening exponent. An additional objective of the invention is to provide an ultra-low carbon IF steel strip, sheet, or die-cut piece that meets the requirements mentioned in draft standard VDA 239-100 (May 2019). DETAILED DESCRIPTION OF THE INVENTION The invention relates to a strip, sheet or stamped piece of interstice-free, ultra-low carbon steel, wherein the steel has, in % by weight, a composition of the following elements: C: max0.005 Mn: max0.20 Yes: max0.10 Al: 0.01 - 0.20 Ti: max0.10 Nb: max0.10 V: max0.10 P: max0.02 S: max0.02 N: max0.01 where Ti+Nb+V together, max 0.10 and optionally: Cr: max 0.10 Ni: max. 0.10 B: max 0.0005 Ca: max0.01 Cu: max0.10 Me: max0.10 Sn: max0.05 the rest is Fe and unavoidable impurities, the steel has a yield strength in the transverse direction between 110 and 170 MPa, a tensile strength in the transverse direction between 250 and 330 MPa, an elongation A80 in the transverse direction of at least 42%, an average plastic strain ratio r of at least 2.00 and a strain hardening exponent n90 in the transverse direction of at least 0.22. The average plastic strain ratio r or average r value is defined as: (r0+2*r45+r90) / 4, where rO is the plastic strain ratio in the rolling or longitudinal direction, r45 is the plastic strain ratio in the diagonal direction, and r90 is the plastic strain ratio in the transverse direction. 007AΩη / 77Ω7 / B / YILI Since measurements of the elongation A80, plastic strain ratio ry, and strain hardening exponent n (in all three directions) can be inaccurate, and all measured values ​​may differ slightly across hot-rolled strips from a heat, the A80 and ryn values ​​used in the claims are the average of at least three measurements taken from at least three different strips of a heat. This statistically reduces the inaccuracies. The inventors have discovered that a strip, sheet, or die-cut piece of interstitial-free, ultra-low carbon steel with this composition can have the mechanical properties described above, where especially the elongation A80, the average plastic strain ratio r, and the strain hardening exponent n90 in the transverse direction provide a good indication of the required ductility of IF steel. The inventors have also discovered that it is especially necessary to limit the sum of Ti, Nb, and V to 0.10% by weight to obtain the required mechanical properties and ductility. Carbon is usually present to provide strength to steel, but when there is too much carbon, more carbides form, which impair ductility. Therefore, carbon is present in a maximum amount of 0.005% by weight, and preferably in a maximum of 0.003% by weight. More preferably, the maximum amount is 0.0022% by weight. Since some carbon is unavoidable and necessary for strength, the minimum amount is preferably 0.0001% by weight, and more preferably 0.0005% or even 0.0010% by weight. Manganese is present in IF steel to provide strength, but also formability. The A80 and r-values ​​decrease with increasing Mn content. Therefore, the maximum amount is preferably 0.20% by weight, and more preferably 0.18% by weight, or even 0.15% by weight. A minimum amount is preferably 0.01% by weight, and more preferably 0.04% by weight, depending also on the amount of other elements in the IF steel. Silicon can also be used to improve the strength of IF steel, but at the same time, formability, or the A80 and r-values, decrease as the Si content increases. For this reason, the maximum amount of silicon is preferably 0.10 wt%. Since silicon reduces the ductility of the steel, it is preferable for the maximum amount of silicon to be 0.05 wt, and more preferably 0.03 wt. An even more preferable maximum amount of silicon is 0.015 wt or even 0.013 wt. A preferable minimum amount of silicon is 0.001 wt or even 0.002 wt, taking into account the strength requirements. Aluminum is used to deoxidize steel, that is, to bond with nitrogen, in the same way that titanium does. For this reason, steel contains between 0.01 and 0.20% aluminum by weight. Preferably, the maximum amount of aluminum is 0.10% by weight, and more preferably 0.08% by weight, to avoid compromising the ductility of IF steel. Phosphorus can be used to improve the strength of IF steel, but at the same time, it will reduce formability and is detrimental to steelmaking. It can also cause an increase in the ductile-to-brittle transformation temperature (DBTT). Therefore, phosphorus should be present in very low quantities, preferably a maximum of 0.02% by weight, and more preferably a maximum of 0.015% or even a maximum of 0.013% by weight. The minimum quantity is preferably 0.001% by weight, and more preferably 0.002% by weight, considering the required strength. Sulfur and nitrogen are detrimental to steelmaking and to the steel itself, so they must be present in very low quantities, preferably a maximum of 0.02% and 0.01% by weight, respectively. More preferably, the maximum quantities of sulfur are 0.015 or even 0.013% by weight, and those of nitrogen are 0.008 or even 0.006% by weight, and more preferably 0.004% by weight. Nitrogen, in particular, must be present in low quantities because it must bind to form nitrides in IF steel. In the case of sulfur, the minimum preferred quantity is 0.001 or even 0.003% by weight, and for nitrogen, the minimum preferred quantity is 0.001%. These minimum quantities are derived from steelmaking requirements. Preferably, the sum of Mn + Si + 10*P is at most 0.30% by weight, more preferably at most 0.25% by weight, more preferably at most 0.20% by weight to achieve the required strength. The minimum of this sum is preferably 0.06%, more preferably 0.07% by weight. Titanium, niobium, and / or vanadium are added to bind the carbon and nitrogen. Nitrogen can also be bound with aluminum or boron. Together, they must be sufficient to ensure that no carbon or nitrogen remains in the solid solution. However, these elements should not be present in excessive amounts, also considering their cost. Therefore, the Ti+Nb+V combination is preferably maximized to 0.10 wt%. More preferably, each of the elements Ti, Nb, and V is present in a maximum amount of 0.09 wt, and the sum is also maximized to 0.09 wt. Even more preferably, the amount of vanadium and / or niobium is maximized to 0.01 wt. In another preferred embodiment, neither vanadium nor, preferably, niobium is added to the IF steel, meaning that these elements are present only as unavoidable impurities. Titanium is preferably present in an amount of at least 0.01% by weight, more preferably in an amount of at least 0.03% by weight, and most preferably in an amount of at least 0.05% by weight, especially when neither vanadium nor niobium is added to the IF steel. Optional elements may be present in the quantities indicated above. Preferably, the maximum limits for these elements are even lower, for example, a maximum of 60% of the quantities indicated above for each additional element, and more preferably these optional elements are not added to IF steel at all, meaning that these elements are present only as unavoidable impurities. The elastic limit Rp0,2 in the transverse direction and the tensile strength Rm in the transverse direction preferably have a minimum and a maximum value to be used commercially according to the standards. The transverse elongation A80 of at least 42% and the mean plastic strain ratio r of at least 2.0 are some of the most important factors in determining the QQZAnn / zznz / E / YiAi Ductility of IF steel. The total elongation, in this case given as A80, provides a measure of the deformation that can be achieved when the steel is stretched to fracture. Therefore, a high A80 elongation is an indication of the deformability of IF steel. The r-value is a measure of the steel's resistance to thinning when used for deep drawing. The higher the r-value, the better the IF steel is suitable for deep drawing. Therefore, these parameters provide a measure for achieving one or more of the objectives of the invention. The steps for achieving these parameters are explained below. Additionally, IF steel has a strain hardening exponent n90 in the transverse direction of at least 0.22. The n value is a measure of IF steel's response to cold working. The higher the n value, the more ductile the steel. To evaluate the steel's ductility, the elongation A80, the y value, and the n90 value must be considered. According to a preferred embodiment, the steel has an A80 elongation in the transverse direction of at least 44%, preferably at least 46%, more preferably at least 48%, even more preferably at least 50%, and most preferably at least 52%. The inventors have discovered that it is possible to achieve these high A80 elongation values ​​in combination with a high ry value / n value. It is also preferred when the steel has a strain hardening exponent n90 in the transverse direction of at least 0.23, preferably at least 0.24. These high numbers for the n value are very important to provide a highly ductile IF steel. Additionally, the steel preferably has an average plastic strain ratio r of at least 2.15, preferably at least 2.20, more preferably at least 2.25, even more preferably at least 2.30 or even 2.35, most preferably at least 2.4. Furthermore, the high figures for the average value of r indicate that the ductility of IF steel has improved. On the other hand, the steel preferably has a plastic strain ratio in the diagonal direction r45 of at least 1.8 or at least 1.9, preferably at least 2.0, more preferably at least 2.1, even more preferably at least 2.2, and most preferably at least 2.3. By providing an IF steel with a high r45 value in the diagonal direction, an additional measure of the steel's ductility is provided. In practice, the r values ​​in all three directions must be sufficiently high to provide an IF steel that is sufficiently ductile for deep drawing complex automotive parts. Preferably, a low-carbon, interstice-free steel strip, sheet, or stamped piece is provided, wherein one or more of the steel elements are present in the following ranges: C: 0.0001 -0.003 Mn: 0.01 - 0.20, preferably 0.04 - 0.18 Yes: 0.001 - 0.05, preferably 0.002 - 0.015 Al: 0.01-0.10 Ti: 0.01-0.09 Nb: max. 0.09, preferably max. 0.01 V: max. 0.09, preferably max. 0.01 P: max. 0.015 S: max. 0.015 N: max. 0.008 where Ti+Nb+V in total, max. 0.09 and optionally: Cr: max. 0.06 Ni: max. 0.06 B: max. 0.0004 Ca: max. 0.005 Cu: max. 0.06 Mo: max. 0.06 Sn: max. 0.03. These more restricted ranges provide an IF steel particularly well-suited for high formability, as is often required. According to a preferred embodiment, a strip, sheet or stamped piece of ultra-low carbon interstice-free steel is provided having, % by weight, a composition of: QozAnn / zznz / E / YiAi C: 0.0001 - 0.0022 Mn: 0.01 - 0.15 Si: 0.001 - 0.013 Al: 0.02 - 0.08 Ti: 0.03 - 0.09 P: 0.001 - 0.013 S: 0.001 - 0.013 N: 0.001 - 0.006 and optionally: Nb: max. 0.003 V: max. 0.005 Cr: max. 0.05 Ni: max. 0.05 B: max. 0.0003 Ca: max. 0.002 Cu: max. 0.05 Mo: max. 0.04 Sn: max. 0.02. This preferred composition is very suitable for achieving the mechanical properties as previously explained. According to an additional preferred embodiment, a strip, sheet or stamped piece of ultra-low carbon interstitial-free steel is provided having, % by weight, a composition of: C: 0.0010- 0.0022 Mn: 0.04-0.13 Yes: 0.002-0.013 Al: 0.03 - 0.07 Ti: 0.05 - 0.09 P: 0.002-0.013 S: 0.003-0.013 N: 0.001 - 0.004 and optionally: Nb: max. 0.002 V: max. 0.004 Cr: max. 0.04 Ni: max. 0.04 B: max. 0.0002 Ca: max. 0.001 Cu: max. 0.04 Mo: max. 0.02 Sn: max. 0.01. This preferred composition can be used to achieve maximum ductility, as required in the automotive industry. The upper and / or lower limit of each element in the two preferred embodiments above can also be used to limit the respective element in the main embodiment of the invention as provided above. As an indication of the ductility of IF steel according to the invention, it is preferred when the ratio of mean plastic strain r to the strain hardening exponent n90 in the transverse direction is at least 0.44, preferably at least 0.48, more preferably at least 0.52, and more preferably 0.56. This combination of mean r value and transverse n value provides a good indication of the ductility of IF steel, together with the elongation A80. For another indication of the ductility of IF steel according to the invention, it is preferred when the ratio of plastic deformation in the diagonal direction r45 to the strain hardening exponent n90 in the transverse direction is at least 0.40, preferably at least 0.44, more preferably at least 0.48, and most preferably at least 0.52. This combination of the value r in the diagonal direction and the value n in the transverse direction provides a different indication of the ductility of IF steel, together with the elongation value A80. QQZAnn / zznz / E / YiAi In a further indication of the ductility of IF steel according to the invention, the ratio of plastic strain in the transverse direction r90 to the strain hardening exponent in the transverse direction n90 is at least 0.50, preferably at least 0.55, more preferably at least 0.58 or even at least 0.60, even more preferably at least 0.62, more preferably at least 0.64 or even 0.66. The combination of the transverse ryn values ​​provides an indication of the transverse ductility, which is usually greater than in the diagonal direction. A different indication of the ductility of IF steel according to the invention is provided by the combination of the ratio of plastic strain in the diagonal direction r45 and the strain hardening exponent in the diagonal direction n45, wherein the ratio of plastic strain in the diagonal direction r45 to the strain hardening exponent in the diagonal direction n45 is at least 0.35, preferably at least 0.40, more preferably at least 0.45, even more preferably at least 0.48, and most preferably at least 0.50. Since both the r value and the n value in the diagonal direction are usually smaller than in the transverse and rolling directions, this combination provides a valuable measure of the steel's ductility. According to a special preferred embodiment of IF steel according to the invention, the yield strength Rp0.2 in the transverse direction is between 110 and 155 MPa. A lower yield strength of IF steel provides better formability. Typically, IF steel according to the invention is coated with a metallic coating, preferably an aluminum alloy or a zinc alloy coating. This type of coating is frequently required in the automotive industry. These coatings are known to those skilled in the art and are usually applied to the steel strip by hot-dip galvanizing. The steps of the method that can be used to obtain the inventive IF steel will be clarified later. The inventors have discovered that the ductility of IF steel according to the invention is greatly influenced by the cold rolling reduction during the cold rolling of the steel. It has been found that a cold rolling reduction of between 80% and 85% is required to obtain a high r-value. Additionally, the reduction of the roll box thickness of the applied IF steel strip, for example, after hot-dip galvanizing, also has a significant effect on the strip's strength and ductility. The roll box reduction should be limited to <1.0%, preferably between 0.4% and 0.7%. Furthermore, the inventors have discovered that the temperature of the steel strip in the last box of the hot rolling mill finishing train should preferably be between 900 and 950°C, and the cooling rate on the exit table should preferably be between 60°C / s and 90°C / s, and therefore preferably between 25°C / s and 150°C / s. The winding temperature of the hot-rolled strip is preferably approximately 700°C, and therefore preferably between 600°C and 750°C. QozAnn / zznz / E / YiAi These values ​​are valid for the center of the winding; the values ​​at the top and back may be slightly different. These parameters are particularly advantageous for IF steel containing more than 0.05% titanium by weight. Therefore, in a method for producing a low-carbon, interstice-free steel strip, as described above, molten steel of the specified composition is cast and, after being cut into slabs, is hot-rolled at a hot-rolling finish temperature between 900 and 950°C, preferably between 900°C and 940°C, more preferably between 900 and 930°C, and cooled on the drawtable at a cooling rate between 25°C / s and 150°C / s, preferably between 60°C / s and 90°C / s. The winding temperature ranges from 600°C to 750°C, preferably between 675°C and 725°C. After cooling and pickling, the coils are cold rolled with a reduction of between 78% and 88%, preferably a reduction of between 80% and 85%, and are continuously annealed at a temperature of approximately 810°C (between 800°C and 820°C).After standard hot-dip galvanizing to provide a Gl coating, the strips were placed in a rolling mill with a roll box and reduced by between 0.4% and 0.7%, preferably approximately 0.6%. Further steps of the method are known to those skilled in the art and are more or less standard. The invention will be described with reference to the following examples. Tables 1a and 1b show the composition of 16 examples of cast, hot-rolled, cold-rolled, hot-dip galvanized coils placed in a rolling mill with a roll stand. Table 1a indicates elements that are significant, deliberately added, or present in larger quantities. Table 1b lists elements present in small quantities or as unavoidable impurities. All elements in Tables 1a and 1b are given in milliweight percent. Alzo means acid-soluble aluminum. All examples are inventive examples, as can be seen from Table 2, which shows the elastic limit Rp0.2, the tensile strength Rm, the elongation A80, the plastic strain ratio r (the r value) and the strain hardening exponent n (the n value) in three directions: the longitudinal direction (in the rolling direction of the winding), the diagonal direction (less than 45 degrees with the rolling direction) and the transverse direction (less than 90 degrees with the rolling direction). At the end of Table 2, the average r value (r_AVG) is also provided, which is calculated as (r0+2*r45+r90) / 4, where r0 is the plastic strain ratio in the rolling or longitudinal direction, r45 is the plastic strain ratio in the diagonal direction, and r90 is the plastic strain ratio in the transverse direction. οαζΑπη / ζζηζ / Ε / γίΛΐ Table 1a E¡- IDENTIFICACIÓN DE LA COLADA CN Mn Si Al AlZo Ti Cu Cr Ni 1 M0737 1.3 2.7 107 4 56 54 67 13 21 18 2 M1886 1.4 2.6 87 4 57 55 66 13 15 20 3 M2790 1.9 2.3 66 3 52 50 64 13 14 21 4 M8642 1.3 2.1 64 4 57 54 69 11 14 21 5 N0499 1.4 2.9 95 5 56 54 68 16 31 24 6 N6718 1.5 2.7 83 2 48 46 65 16 17 18 7 N6719 1.3 2.5 121 3 58 54 68 17 21 18 8 N6982 1.4 2.4 103 4 50 48 66 16 20 19 9 N6987 1.4 2.0 98 3 52 50 67 17 22 21 10 N6995 1.1 3.2 90 4 49 47 66 11 17 19 11 N6997 1.1 3.4 102 3 52 50 66 13 17 18 12 N8428 1.4 2.8 65 5 48 46 67 14 16 18 13 N9832 1.0 3.0 64 4 42 41 59 17 22 21 14 P1887 1.3 1.9 94 4 56 54 65 15 16 19 15 P2198 1.3 2.9 95 4 57 55 70 18 22 26 16 P2200 1.3 2.3 99 4 54 51 69 14 23 23 Tabla 1b E¡- MASH IDENTIFICATION PS Nb BV Mo Sn Ca 1 M0737 5 6 0 0.1 2 3 3 - 2 M1886 3 5 0 0.0 2 2 2 - 3 M2790 4 8 0 0.0 2 3 3 - 4 M8642 4 9 0 0.0 2 4 3 - 5 N0499 6 6 0 0.1 2 5 2 - 6 N6718 6 6 0 0.0 2 4 2 0 7 N6719 7 6 0 0.0 2 2 2 0 8 N6982 7 8 0 0.0 2 2 1 1 9 N6987 6 4 0 0.1 2 3 2 0 10 N6995 7 6 0 0.0 2 3 1 0 11 N6997 6 6 0 0.0 2 3 2 0 12 N8428 6 7 0 0.0 2 3 6 0 13 N9832 7 6 0 0.0 2 4 2 0 14 P1887 7 6 0 0.0 2 3 2 0 15 P2198 6 6 0 0.0 2 7 2 0 16 P2200 7 8 0 0.0 2 5 1 0 All windings, examples of which are shown in Tables 1a, 1b and 2, were cast with the composition indicated in Tables 1a and 1b and hot-rolled at a finishing temperature between 920°C and 930°C. The cooling rate in the output table was approximately 60°C / s, and the winding temperature was approximately 710°C. All these values ​​are valid for the center of the winding; the values ​​at the top and bottom may be slightly different. After cooling and pickling, the coils were cold rolled with an 82% reduction and subjected to continuous annealing at a temperature of approximately 810°C. After standard hot-dip galvanizing to provide a Gl coating, the strips were placed in a rolling box rolling mill with a reduction of 0.6%. Table 2 οαζΑπη / ζζηζ / Ε / γίΛΐ Example- Identification of casting Longitudinal Rp Rm A80 Value Value rrn MPa MPa % diagonal η η λοα Value Value Rp Rm A80 rrn MPa MPa % transverse η η λ da Value Value Rp Rm A80 rrn MPa % rrn MPa 290 48 2.20 0.24 146 296 48 1.95 0.23 144 288 44.5 2.75 0.23 2.21 10 N6995 143 294 46.5 2.15 0.24 148 2947 2.70 0.23 148 291 44 2.60 0.23 2.19 6 N6718 146 296 45.5 2.25 0.23 150 298 45.5 2.00 0.22 149 295 47 2.05 2.26 166 N67 143 290 51 2.15 0.24 148 294 51.5 2.00 0.23 147 288 46.5 2.85 0.23 2.25 8 N6982 139 292 47 2.15 0.40 2.24 4.495 0.23 142 290 47.5 2.95 0.23 2.33 9 N6987 140 292 46 2.30 0.24 146 299 44.5 2.00 0.23 143 290 49 2.25 2.27 269 N6 141 294 46 2.30 0.24 145 299 44.5 2.15 0.23 144 292 47.5 2.75 0.23 2.34 8 N6982 140 289 47 2.30 0.42 2.495 1495 0.23 143 286 48.5 2.85 0.23 2.26 11 N6997 149 288 47.5 2.20 0.23 155 295 45.5 1.85 0.22 152 285 46.5 2.21 .21 . N6997 140 287 46 2.25 0.23 144 291 45.5 2.15 0.23 144 287 45.5 2.95 0.23 2.38 2 M1886 127 288 48 2.20 0.24 132 292 46.5 2.20 0.23 130 287 47.5 2.90 0.24 2.38 2 M1886 132 292 45 2.35 0.24 138 299 42 1.95 0.23 136 291 45.5 2.90 0.24 2.29 2 M1886 125 288 46 2.20 0.24 130 292 45 2.05 0.23 129 287 46.5 2.80 0.24 2.28 4 M8642 136 286 44 2.35 0.24 140 290 45.5 2.00 0.22 136 282 46 2.65 0.23 2.25 4 M8642 135 282 49 2.30 0.23 137 286 50.5 2.10 0.22 135 280 54 2.70 0.23 2.30 4 M8642 133 283 49 2.30 0.24 138 287 48.5 2.15 0.22 135 282 50.5 2.70 0.24 2.33 4 M8642 136 288 41 2.15 0.24 142 294 41.5 1.85 0.23 139 287 48 2.70 0.23 2.14 1 M0737 133 285 48.5 2.40 0.24 140 293 42.5 1.85 0.23 136 283 46.5 2.65 0.24 2.19 7 N6719 144 292 48.5 2.25 0.24 150 294 46 2.20 0.22 149 290 46.5 3.00 0.23 2.41 12 N8428 145 294 46 2.05 0.23 140 291 48 2.05 0.24 144 288 47.5 2.60 0.23 2.19 5 N0499 138 289 49.5 2.30 0.23 143 294 50 2.20 0.22 141 289 48.5 3.05 0.23 2.44 15 P2198 139 293 47.5 2.00 0.24 143 297 45.5 1.90 0.23 142 292 48.5 2.60 0.23 2.10 16 P2200 145 289 47 2.15 0.24 151 292 48.5 2.10 0.23 149 288 50.5 2.80 0.23 2.29 16 P2200 142 288 47 2.15 0.24 149 291 47 2.25 0.23 145 285 52 2.60 0.24 2.31 14 P1887 145 293 49 2.00 0.24 150 296 50 1.95 0.23 148 290 49.5 2.60 0.23 2.13 14 P1887 143 290 48 2.05 0.24 148 293 48.5 2.00 0.23 148 289 52 2.60 0.23 2.16 15 P2198 145 291 49.5 2 0.24 149 295 48.5 1.95 0.23 148 289 49.5 2.6 0.23 2.13 15 P2198 145 291 47 2.05 0.24 151 295 45 2.1 0.22 149 290 50.5 2.5 0.23 2.19 16 P2200 141 286 50.5 2.05 0.24 147 289 48.5 1.95 0.23 144 286 48.5 2.75 0.23 2.18 14 P1887 146 294 47 2 0.24 150 297 45 2 0.23 149 292 49 2.55 0.23 2.14 15 P2198 145 289 47 2.1 0.24 151 291 48 2.15 0.23 151 288 51.5 2.8 0.23 2.30 13 N9832 140 282 49.5 2.15 0.24 148 291 49.5 1.8 0.23 142 281 48.5 2.55 0.24 2.08. The relatively low Rp0.2 and high A80 levels, values ​​ry and n, and their combinations can be attributed to a relatively high amount of Ti and Mn, in combination with a relatively low amount of C and Si. Of course, the indicated process steps are preferred to achieve these values. For the expert in the technique, it is clear that the process steps may vary to achieve the values ​​specified in the claims. The protection sought is not limited by the examples; in this respect, only the limitations of the claims count.

Claims

1. A low-carbon, interstice-free steel strip, sheet, or stamped piece, characterized in that the steel has, by weight %, a composition of the following elements: C: 0.0010-0.0022 Mn: 0.04-0.13 Si: 0.002-0.013 Al: 0.03-0.07 Ti: 0.05-0.09 Nb: max. 0.002 V: max. 0.004 P: 0.002-0.013 S: 0.003-0.013 N: 0.001-0.004 where Ti+Nb+V together, max. 0.10 and optionally: Cr: max. 0.04 Ni: max. 0.04 B: max. 0.0002 Ca: max. 0.001 Cu: max. 0.04 Mo: max. 0.02 Sn: max. 0.01 the remainder is Fe and unavoidable impurities, the steel has a yield strength in the transverse direction between 110 and 170 MPa, a tensile strength in the transverse direction between 250 and 330 MPa, an elongation A80 in the transverse direction of at least 42%, an average plastic strain ratio r of at least 2.00, and a strain hardening exponent n90 in the transverse direction of at least 0.22; and a plastic strain ratio in the diagonal direction r45 of at least 1.8, wherein the values ​​of A80, ry n90 are the average values ​​of at least three measurements made on at least three different strips of a mold, wherein the steel is coated with a zinc alloy coating and wherein the steel is standardized to EN 10346:2015.

2. The low-carbon, gap-free steel strip, sheet, or die-cut piece according to claim 1, further characterized in that the steel has a transverse elongation A80 of at least 44%, preferably at least 46%, more preferably at least 48%, even more preferably at least 50%, and more preferably at least 52%.

3. The interstice-free, low-carbon steel strip, sheet, or die-cut piece according to any of the preceding claims, further characterized in that the steel has a cross-sectional strain-hardening exponent n90 of at least 0.23, preferably at least 0.

24.

4. The low carbon steel interstice-free strip, sheet or die-cut piece according to any of the preceding claims, further characterized in that the steel has an average plastic strain ratio r of at least 2.15, preferably at least 2.20, more preferably at least 2.25, even more preferably 2.30 or even 2.35, more preferably at least 2.

40.

5. The interstice-free, low-carbon steel strip, sheet, or die-cut piece according to any of the preceding claims, further characterized in that the steel has a plastic deformation ratio in the diagonal direction r45 of at least 1.9, preferably at least 2.0, more preferably at least 2.1, even more preferably at least 2.2, and more preferably at least 2.

3.

6. The interstice-free, low-carbon steel strip, sheet, or die-cut piece according to any of the preceding claims, further characterized in that the average plastic strain ratio r multiplied by the strain hardening exponent n90 in the transverse direction is at least 0.44, preferably at least 0.48, even more preferably at least 0.52, and most preferably at least 0.

56.

7. The interstice-free, low-carbon steel strip, sheet, or die-cut piece according to any of the preceding claims, further characterized in that the ratio of plastic deformation in the diagonal direction r45 to the strain hardening exponent n90 in the transverse direction is at least 0.40, preferably at least 0.44, more preferably at least 0.46, even more preferably at least 0.48, and more preferably at least 0.

52.

8. The interstice-free, low-carbon steel strip, sheet, or die-cut piece according to any of the preceding claims, further characterized in that the ratio of transverse plastic deformation r90 to transverse strain hardening exponent n90 is at least 0.50, preferably at least 0.55, more preferably at least 0.58 or even at least 0.60, even more preferably at least 0.62, more preferably at least 0.64 or even 0.

66.

9. The interstice-free, low-carbon steel strip, sheet, or die-cut piece according to any of the preceding claims, further characterized in that the ratio of plastic deformation in the diagonal direction r45 multiplied by the strain hardening exponent in the diagonal direction n45 is at least 0.35, preferably at least 0.40, more preferably at least 0.45, even more preferably at least 0.48, and more preferably at least 0.

50.

10. The interstice-free, low-carbon steel strip, sheet, or die-cut piece in accordance with any of the preceding claims, further characterized in that the elastic limit Rp0,2 in the transverse direction is between 110 and 155 MPa.