STEEL SHEET WITH A SACRIFICIAL CATHODIC PROTECTION COATING COMPRISING LANTHANE

Abstract

The invention relates to a steel sheet with a sacrificial cathodic protection coating comprising between 1 and 40% by weight of zinc, between 0.01 and 0.4% by weight of lanthanum, and optionally up to 10% by weight of magnesium, possibly up to 15% by weight of silicon, and optionally up to 0.3% by weight, in cumulative quantities, of additional components, the remainder being composed of aluminum and unavoidable impurities or residual elements. The invention also relates to a method for manufacturing parts by cold or hot die forging and the parts thus obtained.

Description

[0001] The present invention relates to a steel sheet with a sacrificial cathodic protection coating, more particularly intended for the manufacture of automotive parts, but not limited to it.

[0002] Indeed, to date, only zinc or zinc alloy coatings provide enhanced corrosion protection due to their dual barrier and cathodic protection. The barrier effect is achieved by applying the coating to the steel surface, thus preventing any contact between the steel and the corrosive environment and is independent of the coating type and substrate. Conversely, sacrificial cathodic protection is based on the fact that zinc is a less noble metal than steel and, in a corrosion situation, it is consumed preferentially to steel. This cathodic protection is particularly essential in areas where the steel is directly exposed to the corrosive atmosphere, such as cut edges or damaged areas where the steel is bare and the surrounding zinc will be consumed before any attack on the uncoated area.

[0003] However, due to its low melting point, zinc poses a problem when welding parts, as there is a risk of vaporization. To mitigate this issue, one possibility is to reduce the coating thickness, but this limits the duration of corrosion protection. Furthermore, when sheet metal is hardened under pressure, particularly by hot stamping, microcracks form in the steel and propagate from the coating. Similarly, painting certain parts that have been previously zinc-coated and hardened under pressure requires sandblasting before phosphating due to the presence of a fragile oxide layer on the surface of the part.

[0004] The other family of metallic coatings commonly used for automotive parts production is the family of aluminum-silicon-based coatings. These coatings do not generate micro-cracking in steel when deformed due to the presence of an Al-Si-Fe intermetallic layer and exhibit good paintability. While they provide barrier protection and are weldable, they do not, however, offer cathodic protection.

[0005] EP 1997927 describes corrosion-resistant steel sheets coated with a coating comprising more than 35% by weight of zinc and including a non-equilibrium phase with a specific heat measured by differential scanning calorimetry greater than or equal to 1 J / g, typically having an amorphous structure. Preferably, the coating comprises at least 40% by weight of zinc, 1 to 60% by weight of magnesium, and 0.07 to 59% by weight of aluminum. The coating may include 0.1 to 10% lanthanum to improve the coating's ductility and machinability. In addition, CN 103045980A discloses coatings of aluminum alloys with zinc and a minor contribution of rare earth elements. One of the objectives of this application is to remedy the disadvantages of prior art coatings by making available coated steel sheets with enhanced protection against corrosion, before and after processing by stamping, in particular.When sheets are intended to be hardened under pressure, particularly hot stamped, resistance to the propagation of microcracks in the steel is also sought, and preferably the widest possible window of use in time and temperature during the heat treatment preceding hardening under pressure.

[0006] In terms of sacrificial cathodic protection, the goal is to achieve an electrochemical potential at least 50 mV more negative than that of the steel, i.e., a minimum value of -0.78 V relative to a saturated calomel electrode (SCE). However, a value lower than -1.4 V is not desired, and even -1.25 V is not desirable, as this would lead to excessively rapid coating degradation and ultimately reduce the protection time of the steel.

[0007] For this purpose, the invention relates to a steel sheet defined according to claim 1 is provided with a sacrificial cathodic protection coating, the coating comprising from 1 to 40% by weight of zinc, from 0.01 to 0.4% by weight of lanthanum, and possibly up to 10% by weight of magnesium, possibly up to 15% by weight of silicon, and possibly up to 0.3% by weight, in cumulative contents, of possible additional elements, the remainder being made up of aluminium and residual elements or unavoidable impurities.

[0008] The sheet metal coating according to the invention may further incorporate the following characteristics, taken individually or in combination: the coating comprises between 1 and 40% by weight of zinc, in particular from 1 to 34% by weight of zinc, typically from 1 to 30% by weight of zinc, preferably from 2 to 20% by weight of zinc, the coating comprises from 0.05 to 0.4% by weight of lanthanum, typically from 0.1 to 0.4% by weight of lanthanum, preferably from 0.1 to 0.3% by weight of lanthanum, preferably again from 0.2 to 0.3% by weight of lanthanum, the coating comprises from 0 to 5% by weight of magnesium, the coating comprises from 0.5 to 10% by weight of silicon, preferably from 0.5 to 5% by weight of silicon, the coating has a thickness of 10 to 50 µm, preferably from 27 to 50 µm, the coating is obtained by hot dipping.

[0009] Coatings comprising, by weight: 2% silicon, 10% zinc, 0.2% lanthanum, and up to 0.3% by weight, in cumulative contents, of additional elements, the remainder being made up of aluminium and residual elements or unavoidable impurities, or 2% silicon, 4% zinc, 2% magnesium, 0.2% lanthanum, and up to 0.3% by weight, in cumulative contents, of additional elements, the remainder being made up of aluminium and residual elements or unavoidable impurities, are particularly preferred.

[0010] For the purposes of this application, the expression "between X and Y%" (e.g., between 1 and 40% by weight of zinc) implies that the values ​​X and Y are excluded, whereas the expression "from X to Y%" (e.g., from 1 to 40% by weight of zinc) implies that the values ​​X and Y are included.

[0011] The sheet metal coating according to the invention may include, in particular, 1 to 34% by weight of zinc, 0.05 to 0.4% by weight of lanthanum, 0 to 5% by weight of magnesium, 0.3 to 10% by weight of silicon, and up to 0.3% by weight, in cumulative amounts, of additional elements, the remainder being made up of aluminium and residual elements or unavoidable impurities.

[0012] Generally, the steel in sheet metal comprises, as a percentage by weight, 0.15% <C<0,5%, 0,5%<Mn<3%, 0,1%<silicium<0,5%, Cr<1%, Ni<0,1%, Cu<0,1%, Ti<0,2%, Al<0,1%, P<0,1%, S<0,05%, 0,0005%<B<0,08%, le reste étant constitué de fer et d'impuretés inévitables dues à l'élaboration de l'acier.

[0013] Another object of the invention is a method for manufacturing a steel part equipped with a sacrificial cathodic protection coating, comprising the following steps, taken in this order and consisting of: supply a steel sheet as defined above previously coated, then cut the sheet to obtain a blank, then heat the blank under a non-protective atmosphere to an austenitizing temperature Tm of 840 to 950°C, then maintain the blank at this temperature Tm for a time tm of 1 to 8 minutes, then hot stamp the blank to obtain a part which is cooled at a rate such that the microstructure of the steel includes at least one constituent chosen from martensite and bainite to obtain a steel part with a sacrificial cathodic protection coating, the temperature Tm, the time tm, the thickness of the previous coating and its lanthanum, zinc and possibly magnesium contents being chosen such that the final average iron content in an upper part of the coating of said steel part with a sacrificial cathodic protection coating is less than 75% by weight.

[0014] Another object of the invention is a part provided with a sacrificial cathodic protection coating which can be obtained by the process according to the invention or by cold stamping of a sheet according to the invention, and which is more particularly intended for the automotive industry.

[0015] The invention will now be described in more detail with reference to particular embodiments given by way of non-limiting examples.

[0016] The invention relates to a steel sheet with a coating comprising, in particular, lanthanum. Without wishing to be bound by any particular theory, it would appear that the lanthanum acts as a protective element for the coating.

[0017] The coating comprises 0.01 to 0.4% by weight of lanthanum, specifically 0.05 to 0.4% by weight, typically 0.1 to 0.3% by weight, and preferably 0.2 to 0.3% by weight. When the lanthanum content is less than 0.01%, the effect of increased corrosion resistance is not observed. The same is true when the lanthanum content exceeds 0.4%. Proportions of 0.1 to 0.3% by weight of lanthanum are particularly suitable for minimizing the appearance of red rust and thus for protecting against corrosion.

[0018] The sheet metal coating according to the invention comprises 5 to 40% by weight of zinc and optionally up to 10% by weight of magnesium. Without being bound by any particular theory, it would appear that these elements, in combination with lanthanum, reduce the electrochemical potential of the coating relative to the steel, in environments containing or not containing chloride ions. The coatings according to the invention thus provide sacrificial cathodic protection.

[0019] Zinc is preferred because its protective effect is greater than that of magnesium and it is simpler to use as it is less prone to oxidation. Therefore, zinc is preferred in concentrations of 1 to 40% by weight, specifically 1 to 34% by weight, and preferably 2 to 20% by weight, sometimes combined with 1 to 10%, or even 1 to 5% by weight, of magnesium.

[0020] The sheet coatings according to the invention also comprise up to 15% by weight of silicon, in particular from 0.1 to 15%, typically from 0.5 to 10% by weight of silicon, preferably from 0.5 to 5% by weight of silicon, for example from 1 to 3% silicon. Silicon, in particular, provides the sheets with high resistance to oxidation at high temperatures. The presence of silicon thus allows their use up to 650°C without risk of coating spalling. Furthermore, silicon prevents the formation of a thick iron-zinc intermetallic layer during hot-dip coating, an intermetallic layer that would reduce the coating's adhesion and formability. The presence of a silicon content greater than 0.5% by weight makes them particularly suitable for press hardening and, in particular, for forming by hot stamping. For this purpose, it is preferable to use an amount of 0.5 to 15% silicon.A content greater than 15% by weight is not desirable because primary silicon is then formed which could degrade the properties of the coating, in particular the corrosion resistance properties.

[0021] The sheet metal coatings according to the invention may also comprise, in cumulative amounts, up to 0.3% by weight, preferably up to 0.1% by weight, or even less than 0.05% by weight, of additional elements such as Sb, Pb, Ti, Ca, Mn, Cr, Ni, Zr, In, Sn, Hf, or Bi. These various elements can, among other things, improve the coating's corrosion resistance, its brittleness, or its adhesion, for example. Those skilled in the art, who are familiar with their effects on the coating's characteristics, will know how to use them according to the desired additional purpose, in the appropriate proportion, which will generally be from 20 ppm to 50 ppm. It has also been verified that these elements do not interfere with the principal properties sought within the scope of the invention.

[0022] The sheet metal coatings according to the invention may also include residual elements and unavoidable impurities originating, in particular, from the contamination of hot-dip galvanizing baths by the passage of steel strips, or from impurities originating from the ingots used to feed these baths or from the ingots used to feed vacuum deposition processes. Iron, in particular, may be mentioned as a residual element, as it can be present in quantities of up to 5% by weight and generally from 2 to 4% by weight in hot-dip coating baths. The coating may therefore contain from 0 to 5% iron by weight, for example, from 2 to 4% by weight.

[0023] The sheet metal coatings according to the invention ultimately comprise aluminum, the content of which can range from approximately 29% to nearly 99% by weight. This element provides corrosion protection for the sheets through a barrier effect. It increases the melting and evaporation temperatures of the coating, thus facilitating its application, particularly by hot stamping, over a wide range of time and temperature conditions. This can be especially advantageous when the steel composition of the sheet metal and / or the desired final microstructure of the part necessitate high-temperature austenitizing and / or prolonged processing times. Generally, the coating comprises more than 50%, and preferably more than 80% by weight, aluminum.

[0024] The sheet metal coatings according to the invention do not include an amorphous phase. The presence or absence of an amorphous phase can be verified, in particular, by differential scanning calorimetry (DSC). The amorphous phase is generally difficult to form. It is usually formed by significantly increasing the cooling rate. Document EP 1 997 927 describes obtaining an amorphous phase by adjusting the cooling rate, said rate being dependent on the cooling method and the coating thickness.

[0025] Preferably, the coating's microstructure comprises: an interfacial layer comprising two layers: (i) a very thin layer of FeAl 3 / Fe 2 Al 5 and (ii) a layer of FeSiAl intermetallic, for example 5 µm thick, a top layer, consisting of a solid Al-Zn solution and Si-rich needles.

[0026] Lanthanum is also present in the microstructure of the coating.

[0027] When the zinc content is greater than 20%, the top layer may also contain Al-Zn binary.

[0028] The coating thickness is preferably between 10 and 50 µm. Below 10 µm, the corrosion protection of the strip may be insufficient. Above 50 µm, the corrosion protection exceeds the required level, particularly in the automotive sector. Furthermore, if a coating of this thickness is subjected to a significant temperature increase and / or prolonged exposure, it may melt on the upper surface and drip onto furnace rollers or into stamping dies, causing damage. A thickness of 27 to 50 µm is particularly suitable for manufacturing press-hardened parts, especially those produced by hot stamping.

[0029] As regards the steel used for the sheet according to the invention, its nature is not critical as long as the coating can adhere to it sufficiently.

[0030] However, for certain applications requiring high mechanical strength, such as for structural parts for automobiles, it is preferred that the steel have a composition that allows the part to achieve a tensile strength of 500 to 1600 MPa, depending on the conditions of use.

[0031] In this range of resistances, it is particularly preferable to use a steel composition comprising, as a percentage by weight: 0.15% <C<0,5%, 0,5%<Mn<3%, 0,1%<Si<0,5%, Cr<1%, Ni<0,1%, Cu<0,1%, Ti<0,2%, Al<0,1%, P<0,1%, S<0,05%, 0,0005%<B<0,08%, le reste étant du fer et des impuretés inévitables issues de l'élaboration de l'acier. Un exemple d'un acier disponible dans le commerce est le 22MnB5.

[0032] When the required strength level is around 500 MPa, a steel composition is preferred, comprising: 0.040% ≤ C ≤ 0.100%, 0.80% ≤ Mn ≤ 2.00%, Si ≤ 0.30%, S ≤ 0.005%, P ≤ 0.030%, 0.010% ≤ Al ≤ 0.070%, 0.015% ≤ Nb ≤ 0.100%, 0.030% ≤ Ti ≤ 0.080%, N ≤ 0.009%, Cu ≤ 0.100%, Ni ≤ 0.100%, Cr ≤ 0.100%, Mo ≤ 0.100%, Ca ≤ 0.006%, the remainder being iron and unavoidable impurities from steelmaking.

[0033] Steel sheets can be manufactured by hot rolling and can optionally be cold-rolled, depending on the final thickness sought, which can vary, for example, from 0.7 to 3 mm.

[0034] Sheet metal can be coated by any suitable method, such as electrodeposition or by vacuum or near-atmospheric pressure deposition, such as magnetron sputtering, cold plasma, or vacuum evaporation, for example. However, hot-dip coating in a molten metal bath is preferred. Indeed, surface cathodic protection is observed to be greater for hot-dip coatings than for coatings obtained by other methods.

[0035] When the hot-dip coating process is carried out, after the coating has been applied, the coating is cooled until it solidifies completely at a cooling rate advantageously between 5 and 30°C / s, preferably between 15 and 25°C / s, for example by blowing inert gas or air. The cooling rate of the present invention does not allow for the formation of an amorphous phase in the coating. The sheets according to the invention can then be shaped by any process adapted to the structure and shape of the parts to be manufactured, such as, for example, cold drawing.

[0036] However, the sheets according to the invention are more particularly suited to the manufacture of hardened parts under pressure, in particular by hot stamping.

[0037] This process consists of supplying a steel sheet according to the invention, previously coated, and then cutting the sheet to obtain a blank. This blank is then heated in a furnace under a non-protective atmosphere to an austenitizing temperature Tm of 840 to 950°C, preferably of 880 to 930°C, and then maintaining the blank at this temperature Tm for a time tm of 1 to 8 minutes, preferably of 4 to 6 minutes.

[0038] The temperature Tm and the holding time tm depend on the type of steel, but also on the thickness of the sheets to be drawn, which must be entirely within the austenitic range before forming. The higher the temperature Tm, the shorter the holding time tm, and vice versa. Furthermore, the rate of temperature rise also influences these parameters; a high rate (greater than 30°C / s, for example) also reduces the holding time tm.

[0039] The blank is then transferred to a hot stamping tool and stamped. The resulting part is then cooled either in the stamping tool itself or after transfer to a specific cooling tool.

[0040] The cooling rate is in all cases controlled according to the composition of the steel, so that its final microstructure after hot stamping includes at least one constituent chosen from martensite and bainite, in order to achieve the desired level of mechanical resistance.

[0041] Controlling the temperature (Tm), time (tm), thickness of the pre-coating, and / or its lanthanum, zinc, and possibly magnesium content, such that the final average iron content in the upper part of the coating is less than 75% by weight, preferably less than 50% by weight, or even less than 30% by weight, generally ensures that the hot-stamped and coated part provides sacrificial cathodic protection. This upper part has a thickness of at least 5 µm and is generally less than 13 µm. The iron content can, for example, be measured by glow discharge spectrometry (GDS).

[0042] Indeed, when heated to the austenitizing temperature Tm, iron from the substrate diffuses into the pre-coating and increases its electrochemical potential. Therefore, to maintain satisfactory cathodic protection, it is necessary to limit the average iron content in the upper part of the final coating.

[0043] To achieve this, it is possible to limit the temperature Tm and / or the holding time tm. It is also possible to increase the thickness of the initial coating to prevent the iron diffusion front from reaching the coating surface. In this regard, it is preferable to use a sheet with a initial coating thickness greater than or equal to 27 µm, preferably greater than or equal to 30 µm, or even 35 µm.

[0044] To limit the loss of cathodic power of the final coating, the lanthanum and / or zinc and possibly magnesium content of the previous coating can also be increased.

[0045] The person skilled in the art is certainly able to play on these different parameters, also taking into account the nature of the steel, to obtain a hardened coated steel part under pressure, and in particular, hot stamped, exhibiting the qualities required by the invention.

[0046] The following examples and figures illustrate the invention.

[0047] The figure represents the spread of red rust as a function of time in hours for each of the 6 coatings tested in the tests.

[0048] Implementation tests were carried out to illustrate certain embodiments of the invention. Tests

[0049] Tests were carried out with 4 three-layer samples, each consisting of a 5 mm thick cold-rolled 22MnB5 sheet (1st layer), with a 1 mm thick hot-dip coating whose composition is specified below (2nd layer), itself covered with a second 5 mm thick cold-rolled 22MnB5 sheet (3rd layer).

[0050] The 6 coatings tested and comprised the following percentages by weight: 2% silicon, 10% zinc, the remainder being aluminum and residual elements or unavoidable impurities, 2% silicon, 10% zinc, 0.2% lanthanum, the remainder being aluminum and residual elements or unavoidable impurities, 2% silicon, 10% zinc, 0.5% lanthanum, the remainder being aluminum and residual elements or unavoidable impurities, 2% silicon, 4% zinc, 2% magnesium, the remainder being aluminum and residual elements or unavoidable impurities, and 2% silicon, 4% zinc, 2% magnesium, 0.2% lanthanum, the remainder being aluminum and residual elements or unavoidable impurities. 2% silicon, 4% zinc, 2% magnesium, 0.5% lanthanum, the remainder being made up of aluminium and residual elements or unavoidable impurities.

[0051] Various corrosion tests were carried out on this batch of samples: An accelerated corrosion test, simulating atmospheric corrosion (VDA 233-102 cyclic corrosion test); static tests in a climate chamber at 35°C or 50°C and 90% or 95% relative humidity (RH). The samples were sprayed with 1% NaCl solution (pH 7) once a day for a total of 15 days.

[0052] For each of these tests, red rust extension and electrochemical measurements were carried out and are provided in the tables below. Al-2Si-10Zn Al-2Si-10Zn-0.2La Al-2Si-10Zn-0.5La Al-2Si-4Zn-2Mg Al-2Si-4Zn-2Mg-0.2La Al-2Si-4Zn-2Mg-0.5La N-VDA test, red rust No protection Partial protection No protection No protection Partial protection No protection Average surface area over which red rust has spread under static conditions (%) 25 5 38 28 6 24 N-VDA, 35°C / 95% RH, average galvanic current (nA) -700 1862 240 N-VDA, 50°C / 90% RH, average galvanic current (nA) -120 1400 250

[0053] The figure shows that the spread of red rust is smaller: with a coating of 2% silicon, 10% zinc, 0.2% lanthanum, the remainder being aluminum and residual elements or unavoidable impurities compared to: a coating of 2% silicon, 10% zinc, 0.5% lanthanum, the remainder being aluminum and residual elements or unavoidable impurities, or to a coating of 2% silicon, 10% zinc, the remainder being aluminum and residual elements or unavoidable impurities, with a coating of 2% silicon, 4% zinc, 2% magnesium, 0.2% lanthanum, the remainder being aluminum and residual elements or unavoidable impurities compared to: a coating of 2% silicon, 4% zinc, 2% magnesium, 0.5% lanthanum, the remainder being aluminum and residual elements or impurities inevitable, or to a coating of 2% silicon, 4% zinc, 2% magnesium, the remainder being made up of aluminum and residual elements or inevitable impurities.

[0054] The figure also shows that the 0.2% lanthanum coating exhibits a much higher galvanic coupling current with the steel than the coating without lanthanum or with 0.5% lanthanum. These results indicate that the 0.2% lanthanum coating is active and sacrificial, and consequently provides better cathodic protection to the steel.

Claims

1. Steel sheet provided with a coating providing sacrificial cathodic protection, the coating comprising 1 to 40 weight % zinc, from 0.01 to 0.4 weight % lanthanum, and optionally up to 10 weight % magnesium, optionally up to 15 weight % silicon and optionally up to 0.3 weight %, in accumulated weight, of possible additional elements selected from among Sb, Pb, Ti, Ca, Mn, Cr, Ni, Zr, In, Sn, Hf and Bi, the remainder being formed of aluminium and residual elements, among which iron at a content of 0 to 5 weight %, or unavoidable impurities derived in particular from pollution of hot dip galvanising baths through the passing of steel strips, or impurities derived from the ingots feedings these same baths or from ingots feeding vacuum deposit processes.

2. The steel sheet provided with a coating providing sacrificial cathodic protection according to claim 1, the coating comprising 1 to 34 weight % of zinc.

3. The steel sheet provided with a coating providing sacrificial cathodic protection according to claim 2, the coating comprising 2 to 20 weight % of zinc.

4. The steel sheet provided with a coating providing sacrificial cathodic protection according to any one of claims 1 to 3, the coating comprising 0.1 to 0.3 weight % of lanthanum.

5. The steel sheet provided with a coating providing sacrificial cathodic protection according to any one of claims 1 to 4, the coating comprising 0.2 to 0.3 weight % of lanthanum.

6. The steel sheet provided with a coating providing sacrificial cathodic protection according to any one of claims 1 to 5, the coating comprising from 0 to 5 weight % of magnesium.

7. The steel sheet provided with a coating providing sacrificial cathodic protection according to any one of claims 1 to 6, the coating comprising from 0.5 to 10 weight % of silicon.

8. The steel sheet provided with a coating providing sacrificial cathodic protection according to any one of claims 1 to 7, the steel having a weight content of 0.15%<C<0.5%, 0.5%<Mn<3%, 0.1%<silicon<0.5%, Cr<1%, Ni<0.1%, Cu<0.1%, Ti<0.2%, Al<0.1%, P<0.1%, S<0.05%, 0.0005%<B<0.08%, the remainder being formed of iron and unavoidable impurities due to steel processing.

9. The steel sheet provided with a coating providing sacrificial cathodic protection according to any one of claims 1 to 8, wherein said coating has a thickness of 10 to 50 µm.

10. The steel sheet provided with a coating providing sacrificial cathodic protection according to claim 9, wherein the said coating has a thickness of 27 to 50 µm.

11. The steel sheet provided with a coating providing sacrificial cathodic protection according to any one of claims 1 to 10, the coating being obtained by hot dip.

12. A process to manufacture a part in steel provided with a coating providing sacrificial cathodic protection comprising the following steps taken in this order and consisting of: - Providing a steel sheet according to any one of claims 1 to 11 previously coated , then - Cutting said sheet to obtain a blank, then - Heating said blank in a non-protective atmosphere up to an austenitisation temperature Tm of 840 to 950°C, then - Holding said blank at this temperature Tm for a time tm of 1 to 8 minutes, then - Hot drawing said blank to obtain a part that is cooled at a rate such that the microstructure of said steel comprises at least one constituent selected from among martensite and bainite to obtain a steel part provided with a coating providing sacrificial cathodic protection, - the temperature Tm, time tm, thickness of the prior coating and the lanthanum, zinc and optionally magnesium contents thereof being selected so that the final mean iron content in an upper portion of the coating of said steel part provided with a coating providing sacrificial cathodic protection is lower than 75 weight %.

13. A steel part provided with a coating providing sacrificial cathodic protection obtained using the hot drawing process according to claim 12.

14. The steel part provided with a coating providing sacrificial cathodic protection obtained by cold drawing a sheet according to any one of claims 1 to 11.