JP2018162516A - Nodular graphite cast iron alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-strength nodular graphite cast iron alloy which is excellent in the 0.2% yield strength, tensile strength and elongation at break in a cast state and does not require a separate heat treatment.SOLUTION: The nodular graphite cast iron alloy having a pearlitic-ferritic structure for cast iron products, contains: 2.8 to 3.7 mass% of C; 1.5 to 4 mass% of Si; 1 to 6.2 mass% of Ni; 0.02 to 0.05 mass% of P; 0.025 to 0.06 mass% of Mg; 0.01 to 0.03 mass% of Cr; 0.003 to 0.3 mass% of Al; 0.0005 to 0.012 mass% of S; 0.03 to 1.5 mass% of Cu; 0.1 to 2 mass% of Mn; and the balance of Fe and unavoidable impurities. The nodular graphite cast iron alloy in a cast state even without subsequent heat treatment achieves a high static strength of a 0.2% yield strength of at least 600 MPa and a tensile strength of at least 750 MPa as well as good ductility of an elongation at break A5 of 2 to 10%.SELECTED DRAWING: Figure 1

Description

  The present invention includes non-ferrous components C, Si, P, Mg, S, Mn, and Ni, and normal impurities, and already has 0.2% proof stress of ≧ 600 MPa and ≧≧ The present invention relates to a spheroidal graphite cast iron alloy having a pearlite-ferrite-like structure for cast iron products having a good ductility with a tensile strength of 750 MPa and a high elongation at break of 2% to 10%. Usability for automobile manufacture is for example chassis components such as wheel carriers, vehicle structural members, and crankshafts.

  Increasingly, in the manufacture of automobiles, the use of high-hard cast iron alloys that are superior to their relatively high strength to take advantage of the possibility of weight reduction is increasing. In this case, for cost reasons, the focus is on omitting all heat treatment processes as much as possible, and simply achieving the mechanical properties required with moderate alloy addition.

  From EP 1225239 (EP 1 225 239 A1), a high-hardness bainite spheroidal graphite cast iron alloy containing 2 to 4% by mass of Ni and 0.05 to 0.45% by mass of Mn is known as a non-ferrous component. This Ni-Mn span is used to adjust the ratio of changeable strength to elongation. For the practice of this invention, non-ferrous components C 3.1-4% by weight and Si 1.8-3% by weight are preferred. The raw material of this composition having this structure is superior in tensile elongation of 650 to 850 MPa and 0.2% proof stress of ≧ 500 MPa with a breaking elongation of 14.5 to 7%. These properties are achieved without heat treatment, but the achievable strength is limited by the alloy composition.

  From German Offenlegungsschrift 10 200 404 0056 (DE 10 2004 040 056 A1) another cast iron alloy is known which is described as being high tension and wear resistant and corrosion resistant. This cast iron alloy has C 3 to 4.2 mass%, Si 1 to 3.5 mass%, Ni 1 to 6 mass%, Cr ≦ 5 mass%, Cu ≦ 3 mass%, Mo ≦ 3 mass%, Mn ≦ 1 mass%, V ≦ 1 mass%, P ≦ 0.4 mass%, S ≦ 0.1 mass%, Mg ≦ 0.08 mass%, Sn ≦ 0.3 mass% and impurities resulting from the production. The This alternate alloy range includes a variety of> 50% acicular ferrite with various proportions of austenite (<20%), martensite (<30%), pearlite (<50%) and carbide (<15%). A matrix composition is produced, and the graphite formation is not limited to spherical graphite, but may be vermicular or piece-like. The bend fracture strength achievable for piston ring applications is> 1100 MPa, the hardness is 320 HB2.5, highlighting the high toughness / ductility not mentioned in detail. However, the elongation at break will obviously be reduced, especially in alloy variations with up to 15% carbide content in the structure. In the case of small wall thicknesses (module ≦ 1.5 cm), additional process steps in the form of tempering at temperatures <700 ° C. may also be necessary.

  From Canadian Patent Application No. 1224066 / US Pat. No. 4,484,953 (CA 122 40 66 A1 / US 448 49 53 A), a high-tensile spheroidal graphite cast iron alloy is known, and this spheroidal graphite cast iron alloy is known. Is C 3 to 3.6 mass%, Si 3.5 to 5 mass%, Ni 0.7 to 5 mass%, Mo 0 to 0.3 mass%, Mn 0.2 to 0.4 mass as a non-ferrous component %, P ≦ 0.06 mass%, and S ≦ 0.015 mass%. In this case, the ferrite-bainite structure is indispensable in order to achieve the stated tensile strength of ≧ 950 MPa, 0.2% proof stress of ≧ 550 MPa and 6-10% elongation at break. The disadvantage is that a heat treatment that completely ferritizes is absolutely necessary.

  From U.S. Pat. No. 3,702,269 (US 370 22 69 A), a high-strength, highly alloyed spheroidal graphite cast iron alloy is known, the non-ferrous component comprising C 2.6-4 mass%, Si 1 5-4 mass%, Ni 6-11 mass%, Co ≦ 7 mass%, Mo ≦ 0.4 mass%, Mn ≦ 1 mass%, and Cr ≦ 0.2 mass%. A high tensile strength of ≧ 1000 MPa is limited to a fine grained bainite structure, in which case this target structure must be adjusted by the necessary heat treatment in the form of tempering, which also requires an increase in cost. To do.

  U.S. Pat. No. 5,853,504 (US 585 35 04 A) describes a highly alloyed casting material based on iron, the non-ferrous component of which is C 0.8-3. 5 wt%, Si 1-7 wt%, Ni 5-15 wt%, Mn ≤1 wt%, Cr ≤2 wt%, at least one element of the group of Mg, Ca and Ce ≤0.1 wt%, and At least one element of the group of Mo, Nb, Ti and V ≦ 2% by mass. This raw material has a hardness of at least 250 HV with a martensite structure proportion of at least 30%, and the graphite formation is mainly spherical. As target product, wrapping discs are preferably known for use in the production of semiconductors. Despite the optional heat treatment, the elongation at break is too low based on the 5-10% carbides contained in the alloy and the too large portion of the martensitic matrix. For safety reasons, this excludes the use of dynamically cast automotive castings such as structural / chassis members.

  From US Pat. No. 3,549,430 (US 354 94 30 A), a high-tensile bainite-like spheroidal graphite cast iron alloy is known, and this spheroidal graphite cast iron alloy has C 2.9 to 3.9 as a non-ferrous component. Including mass%, Si 1.7-2.6 mass%, Ni 3.2-7 mass%, Mo 0.15-0.4 mass%, Cr ≦ 0.2 mass%, and Mn ≦ 1 mass% . This alloy is excellent with a high tensile strength of ≧ 820 MPa, a 0.2% proof stress of ≧ 520 MPa and an elongation at break of at least 2%. Heat treatment is required to achieve these properties, and for even larger wall thicknesses, locally used low temperature casting may be required.

  Furthermore, DE-A 1 808 515 (DE 180 85 15 A1) describes a high-tensile spheroidal graphite cast iron alloy, the non-ferrous component comprising C 2.9 to 3.9% by mass, Si 1.7-2.6 wt%, Ni 3.2-7 wt%, Mo 0.15-0.4 wt%, Mg ≤0.1 wt%, Mn 0-1 wt%, and max 0.5 It contains 0 to 0.25% by mass of Cr in the total content of Mo and Cr by mass%. This raw material has an elongation at break of at least 4% with a tensile strength of ≧ 1000 MPa and a 0.2% proof stress of ≧ 750 MPa. However, the main feature of this raw material is a heat treatment in the form of tempering at a temperature of 200-315 ° C. for several hours. This is because the described characteristic values cannot be achieved without tempering the matrix structure.

  From EP 1 384 005 (EP 1 834 005 B1), high tension, mainly pearlitic, spheroidal graphite cast iron alloys are known for use in automobile production. This spheroidal graphite cast iron alloy has a non-ferrous component of C 3.0 to 3.7% by mass, Si 2.6 to 3.4% by mass, P 0.02 to 0.05% by mass, Mg 0.025 to 0. 045% by mass, Cr 0.01-0.03% by mass, Al 0.003-0.017% by mass, S 0.0005-0.012% by mass, and B 0.0004-0.002% by mass, Cu 0.1-1.5 mass%, Mn 0.1-1.0 mass%, and an unavoidable impurity are included. Chassis components made with this composition already have a tensile strength of 600-900 MPa in a cast state without additional heat treatment, a 0.2% proof stress of 400-600, and a breaking elongation of 14-5%. .

  Starting from these prior arts, the central task of the present invention is that the requirements for 0.2% proof stress, tensile strength and elongation at break are already achieved in the cast state without other assistance, preferably In contrast to the known high-strength cast iron alloys, for example ADI raw materials (= Austempered Ductile Iron), it is to provide a high-tensile spheroidal graphite cast iron alloy which does not require a separate heat treatment.

  This subject is C 2.8-3.7 mass%, Si 1.5-4 mass%, Ni 1-6.2 mass%, P 0.02-0.05 mass%, Mg 0.025-0. 0.06 mass%, Cr 0.01-0.03% by mass, Al 0.003-0.3 mass%, S 0.0005-0.012 mass%, Cu 0.03-1.5 mass%, and Accomplished by a spheroidal graphite cast iron alloy according to the present invention comprising 0.1-2% by weight of Mn, the balance Fe and unavoidable impurities, this spheroidal graphite cast iron alloy is 0.2 ≧ 600 MPa in the cast state without subsequent heat treatment. A good ductility with a breaking elongation A5 of 2-10% is achieved simultaneously with a high static strength with a% yield strength and a tensile strength of ≧ 750 MPa.

  The matrix structure surrounding the spheroidal graphite deposit is in this case formed in a pearlite-ferrite form with> 50% pearlite, preferably the pearlite is in fine stripes and the ferrite is spherical. Also, thereby, the spheroidal graphite cast iron alloy according to the present invention has a partially overlapping Ni-alloy region except that the mechanical properties and carbide forming agents Mo, Nb, Ti and V are omitted. From US Pat. No. 5,853,504 (US 585 35 04 A) it is clearly distinguished from known alloys. In this respect as well, the difference from the known cast iron alloy is based on DE 10 2004 404 0056 A1 (DE 10 2004 040 056 A1). This is because the mechanical properties of acicular ferrite are clearly different from those of spherically formed ferrite.

  Preferably, the spheroidal graphite cast iron alloy is formed as a sand-type spheroidal graphite cast iron alloy.

  The central idea of the present invention is that in the manufacture of automobiles based on the combination of the appropriately adjusted composition of the spheroidal graphite cast iron alloy according to the invention and the resulting mechanical properties, for example, it is actually deformed in the event of an automobile collision. However, by providing a spheroidal graphite cast iron alloy that can be used for axle members and chassis members that must not break, as well as for structural members and crankshafts that are exposed to high dynamic loads. is there.

  It is worth mentioning that the spheroidal graphite cast iron alloy according to the present invention is already sufficient in terms of the addition of an appropriate alloy as compared with the austenitic spheroidal graphite cast iron alloy in view of its mechanical properties and availability.

  Ni and Si are known to increase the yield strength by 0.2%. This is on the one hand due to mixed crystal solidification (Si and Ni) and on the other hand due to pearlite refinement by lowering the austenite-ferrite transition temperature to a lower temperature (Ni). The alloy has the advantage of having as high a 0.2% proof stress as possible with a break elongation value not too low (possibility of a high weight-reducing structure). This is achieved firstly because the spheroidal graphite cast iron alloy has Ni 1-6.2% by mass, preferably Ni 2.5-5.2% by mass, particularly preferably Ni 4-5.2% by mass. Is done.

  Particularly good strength properties with a break elongation value not too low in relation to Si 1.5 to 4% by weight, preferably Si 2 to 3.5% by weight, particularly preferably Si 2.2 to 3.3% by weight Is achieved. For example, the pearlite-ferrite-like spheroidal graphite cast iron alloy of the present invention has a ≧ 600 MPa as compared with a bainite-like alloy known from EP 1225239 A1 which similarly does not require heat treatment. The 0.2% yield strength is clearly higher compared to ≧ 500 MPa (the tensile strength is somewhat higher as well). For example, the example described in EP 1225239 (EP 1 225 239 A1) does not include a 0.2% proof stress value exceeding 550 MPa.

  The maintenance of the upper and lower limits described for the non-ferrous components Si and Ni is important for the pearlite-ferritic target structure and thereby to achieve the mechanical properties of the spheroidal graphite cast iron alloy according to the invention.

  <No significant increase in yield strength is seen at Ni content of 1% by weight, and a content of> 6.2% by weight should be avoided based on increased risk of martensite formation. With regard to this risk of martensite formation, the spheroidal graphite cast iron alloy according to the invention is evident in comparison with alloys with similar Ni content limits from DE 10 2004 404 0056 (DE 10 2004 040 056 A1). For example, even in the case of a low wall thickness of about 8 mm, a martensite-free structure is reliably achieved without the need for subsequent tempering. In the case of a preferred embodiment of the spheroidal graphite cast iron alloy according to the invention, this is possible by maintaining a predetermined composition ratio with respect to Ni content, Si content and Mn content. For example, for the martensite-free pearlite-ferrite structure of the spheroidal graphite cast iron alloy according to the present invention in the cast state, the total content of Ni and Si is preferably ≦ 9% by mass, It is preferred that the ratio of Ni + 0.5 · Mn) / (1.5 · Si) does not exceed the value 1.5.

  A Si content of <1.5% by weight increases the risk of carbide formation and, in the worst case, can result in white solidification (Weisserstarrung). A Si content of> 4% by weight causes a clear decrease in the elongation at break and likewise increases the risk of martensite formation based on the reduced carbon solubility in austenite. Furthermore, the Si content must be limited because silicon shifts the austenite-ferrite transition temperature to higher temperatures, thereby adversely affecting the pearlite refinement that is to be achieved by nickel addition.

  The alloying of 0.03 to 1.5% by weight of Cu is intended to achieve mechanical properties with a low Ni content and at the same time a high Si content, especially with respect to the limits described for the spheroidal graphite cast iron alloy according to the invention In addition, it is performed mainly for securing a pearlite-like structure having pearlite> 50% and the balance ferrite, and in this case, the ferrite is preferably formed in a spherical shape.

  Mn becomes a scrap accompaniment when its proportion increases. In order to improve the yield strength, Mn up to an appropriate content is preferable. Furthermore, Mn can contribute to lowering the martensite start temperature and thereby reducing the risk of martensite formation in the thin walled member portion that is rapidly cooled. The upper limit of 2 mass% Mn for the spheroidal graphite cast iron alloy according to the present invention is due to significant embrittlement due to carbide formation, but at the same time, the increase in grain boundary carbide eluting at a relatively high Si content causes a low Mn content. Should already be recorded in case of rate.

  Alloy addition of 0.003 to 0.3 mass% Al can be performed in order to further improve the strength by mixed crystal solidification. However, the Al content should be limited to <0.3% by weight. This is because Al simultaneously acts as a ferrite stabilizer, thereby countering the formation of the main pearlitic structure with> 50% pearlite required for mechanical properties.

  Maintaining the stated upper limits for the non-ferrous components Mn, Cu, Mg, Cr, Al, P, S is important for achieving mechanical properties and workability of cast parts made of spheroidal graphite cast iron alloys according to the present invention It is. Excessively high contents for Cu, Mg, Al and S can have a detrimental effect on graphite formation, and the corresponding difference in the graphite shape from the spherical shape to be achieved is the elongation at break and the achievable strength. Cause obvious deterioration. Similarly, Cr acts to embrittle itself by promoting carbide formation.

  P must be limited based on the well-known embrittlement effect of the low melting P-rich phase (formerly P-rich residual melt region) that may form at grain boundaries.

  Preferably, the proportion of graphite immediately after the casting process is greater than 90% of the graphite present in the cast state, ie after casting and cooling in the mold.

  It is preferred if the matrix structure of the cast part is formed in a pearlite form immediately after the casting process, in the cast state, i.e. after casting and cooling in the mold.

In a preferred embodiment, the structure of the cast part has 200-1200 spherulites per mm ² immediately after the casting process, in the cast state, ie after casting and cooling in the mold.

  Preferably, the graphite particles have a size distribution of size 8 at least 5%, size 740% to 70%, size 6 up to 35% according to DIN EN ISO 945.

  Preferably, the cast part has a Brinell hardness of 260 to 320 HBW.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples, or is not limited to the following examples.

A Y2 sample was cast from a spheroidal graphite cast iron alloy according to the present invention in a sand mold. This chemical composition is C 2.87 mass%, Ni 5.12 mass%, Si 3.25 mass%, Cu 0.03 mass%, Mn 0.22 mass%, Mg 0.046 mass%, P 0. 037% by mass, 0.022% by mass of Cr, 0.013% by mass of Al, and 0.003% by mass of S, the balance being Fe and normal impurities. Therefore, the total content of Ni + Si is approximately 8.4 mass% (preferably ≦ 9 mass%), and the ratio (Ni + 0.5 · Mn) / (1.5 · Si) ≈1.1 (preferably ≦ 1 .5). This cast product was investigated in the cast state with respect to the number of spherulites, graphite content, graphite shape, and graphite size, pearlite content, characteristic values from tensile tests, Brinell hardness and impact work (impact energy). The number of spherulites is 218 spherulites per mm ² and the graphite content is 10.6%. 94% of the graphite shape according to DIN EN ISO 945 is shape VI. The size distribution according to DIN EN ISO 945 is size 88%, size 757%, and size 633%. The pearlite content of the matrix is 79% (see FIG. 1 for the structure image, remaining component: ferrite, formed in a spherical shape). The Brinell hardness is 310 ± 2 HBW5 / 750. The impact work of each sample was 30.1 J at room temperature and 12.5 J at −30 ° C., respectively. The room temperature tensile test according to DIN EN ISO 6892-1 yielded the following property values:
-0.2% yield strength: 658 to 663 MPa,
-Tensile strength: 884-889 MPa,
-Elongation at break: 6.2-7.9%,
-Modulus of elasticity (measured for regression within the range of 100-300 MPa): 175-186 GPa.

  A tensile test blank was also cast from the same melt as the above example of the spheroidal graphite cast iron alloy according to the present invention, and the cast wall thickness was about 8 mm in the test area. The 6 mm tensile specimen taken out of this passed the Y2 sample result and was able to achieve a breaking elongation of 6.9% with a 0.2% proof stress of 652 MPa and a tensile strength of 872 MPa.

  Therefore, the samples of these example variations of the spheroidal graphite cast iron alloy according to the present invention are already in the cast state with respect to the tensile test property values, by an extremely laborious heat treatment of ADI (= Austempered Ductile Iron). Of the higher-priced nodular cast iron raw material as expected, which can only be realized by the alloying of the produced Ni and / or Mo with a larger wall thickness and is standardized under EN 1564 in Europe In the grade.

  For the sake of illustration, FIG. 2 shows the yield strength Rp0.2 as a function of the breaking elongation A5. The examples described for the spheroidal graphite cast iron alloy according to the invention and representatives of the spheroidal graphite cast iron alloy standardized in DIN EN 1563 and DIN EN 1564 are plotted. The solid gray line in FIG. 2 connects the minimum values according to the DIN EN 1563 standard for cast iron with spheroidal graphite of the kind produced in the cast state. The consistent black solid line in FIG. 2 connects the minimum values according to the DIN EN 1564 standard for cast iron with heat-treated ADI type spheroidal graphite. Georg Fischer's patented spheroidal graphite cast iron alloys (EP 1834005 (EP 1 834 005 B1) and EP 1270747 (EP 1 270 747 B1)) are shown in black with dashed lines Has been.

Structure image of spheroidal graphite cast iron alloy according to the present invention Yield strength Rp0.2 is shown as a function of elongation at break A5 for various GJS alloys.

Claims (13)

As a non-ferrous component, it contains C, Si, Ni, Mn, Cu, Mg, Cr, Al, P, S and usual impurities, and already has high strength and good ductility and toughness in the cast state. In a spheroidal graphite cast iron alloy having a pearlite-ferrite-like structure for cast iron products, the spheroidal graphite cast iron alloy is:
C 2.8 to 3.7% by mass,
Si 1.5-4% by mass,
Ni 1-6.2 mass%,
P 0.02-0.05 mass%,
Mg 0.025-0.06 mass%,
Cr 0.01-0.03% by mass,
0.003 to 0.3% by mass of Al,
S 0.0005-0.012 mass%,
Cu 0.03-1.5 mass% and Mn 0.1-2 mass%,
The spheroidal graphite cast iron alloy containing the balance Fe and unavoidable impurities is not limited to 0.2% proof stress of 600 MPa or more and high static strength of 750 MPa or more at the same time without performing the subsequent heat treatment in the cast state. Spheroidal graphite cast iron alloy characterized in that good ductility with a breaking elongation A5 of 10% is achieved.   The alloy contains Si 2 to 3.5% by mass, particularly preferably Si 2.2 to 3.3% by mass, the total alloy content of Ni and Si is ≦ 9% by mass and simultaneously ( The ratio of Ni + 0.5 · Mn) / (1.5 · Si) is ≦ 1.5, and when cooling from high casting temperature to room temperature, more than 50% of pearlite, the pure pearlite-ferrite structure of the remaining ferrite The spheroidal graphite cast iron alloy according to claim 1, wherein the spheroidal graphite cast iron alloy is formed.   The alloy contains Ni 2.5-5.2% by weight, particularly preferably 4.0-5.2% by weight Ni, the total alloy content of Ni and Si is ≦ 9% by weight, and At the same time, the ratio of (Ni + 0.5 · Mn) / (1.5 · Si) is ≦ 1.5, and more than 50% of pearlite and the remaining ferrite pure pearlite-ferrite when cooling from high casting temperature to room temperature The spheroidal graphite cast iron alloy according to claim 1, wherein a structure is formed.   The alloy contains 0.2 to 0.5% by weight of Mn, particularly preferably 0.15 to 0.4% by weight of Mn, the total alloy content of Ni and Si is ≦ 9% by weight, and At the same time, the ratio of (Ni + 0.5 · Mn) / (1.5 · Si) is ≦ 1.5, and more than 50% of pearlite and the remaining ferrite pure pearlite-ferrite when cooling from high casting temperature to room temperature The spheroidal graphite cast iron alloy according to any one of claims 1 to 3, wherein a structure is formed.   The alloy contains 0.03-0.5 wt% Cu, particularly preferably 0.03-0.1 wt% Cu, the total alloy content of Ni and Si is ≤9 wt%, and At the same time, the ratio of (Ni + 0.5 · Mn) / (1.5 · Si) is ≦ 1.5, and more than 50% of pearlite and the remaining ferrite pure pearlite-ferrite when cooling from high casting temperature to room temperature 2. The spheroidal graphite cast iron alloy according to claim 1, wherein a texture is formed.   The alloy contains Al 0.003 to 0.25% by mass, particularly preferably Al 0.003 to 0.02% by mass, the total alloy content of Ni and Si is ≦ 9% by mass, and At the same time, the ratio of (Ni + 0.5 · Mn) / (1.5 · Si) is ≦ 1.5, and more than 50% of pearlite and the remaining ferrite pure pearlite-ferrite when cooling from high casting temperature to room temperature 2. The spheroidal graphite cast iron alloy according to claim 1, wherein a texture is formed.   7. The spheroidal graphite cast iron alloy according to claim 1, wherein more than 90% of the existing graphite is formed into a spherical shape immediately after casting and cooling.   The pearlite-ferrite-like matrix structure of the cast part is that 55-90% is formed pearlite immediately after casting and cooling, and the remaining ferrite is preferably spherical in this case. The spheroidal graphite cast iron alloy according to any one of claims 1 to 7, characterized in that it is characterized. 9. The spheroidal graphite cast iron alloy according to claim 1, wherein the structure of the cast part has 200 to 1200 spherulites per mm ² immediately after casting and cooling. .   The graphite particles according to DIN EN ISO 945, having a size distribution of at least 5% in size 8, from 740% to 70% in size 7, and up to 35% in size 6 The spheroidal graphite cast iron alloy according to any one of the above.   11. The spheroidal graphite cast iron alloy according to claim 1, wherein the cast part has a Brinell hardness of 260 to 320 HBW.   A chassis member in an automobile, preferably an automobile, having a good ductility with a breaking elongation A5 of 2 to 10% simultaneously with a 0.2% proof stress of 600 MPa or more and a high static strength with a tensile strength of 750 MPa or more Use of the spheroidal graphite cast iron alloy according to claim 1 for the manufacture of wheel carriers, universal bearings, axle guides, crankshafts and / or rear axle housings.   2. The method for producing a cast part comprising a spheroidal graphite cast iron alloy according to claim 1, wherein the cast part is not heat-treated after casting and cooling, and the cast part has a 0.2% yield strength of 600 MPa or more. And a good ductility with a breaking elongation A5 of 2 to 10% at the same time as a high static strength with a high tensile strength of 750 MPa or more.