Method for conditioning the surfaces of heat-treated galvanised steel sheets

Abstract

The invention relates to a method for conditioning the surfaces of heat-treated, galvanised or alloy-galvanised sheet steel components, wherein either at least regions of a sheet steel are heated for the purpose of austenitisation and subsequently formed into a sheet steel component and cooled at a rate above the critical cooling rate, or a sheet steel is first formed into a sheet steel component and subsequently heated at least in regions for the purpose of austenitisation and, after austenitising at least regions thereof, the sheet steel component is cooled at a rate above the critical cooling rate and, in both cases, the surface of the sheet steel component is subsequently subjected to wheel blasting, characterised in that the wheel blasting is carried out with an Almen intensity of between 0.05 mm N and 0.20 mm N.

Description

[0001] Process for conditioning the surfaces of heat-treated, galvanized steel sheets

[0002] The invention relates to a method for conditioning the surfaces of heat-treated, galvanized steel sheets or steel sheet components.

[0003] It is known to produce components, such as car body components, from galvanized steel sheets in particular. For this purpose, a steel material is first melted and typically cast in a continuous casting process. The slab produced in the continuous casting process is then hot-rolled into a steel strip in a conventional manner. This type of steel strip is also referred to as hot-rolled strip.

[0004] At the end of the hot rolling process, the hot strip rolled from the slab is typically wound into a coil. For cold rolling, this coil is unwound and rolled out in a cold rolling mill to produce the cold-rolled strip.

[0005] The cold-rolled steel strip is then coated with a zinc layer in a hot-dip galvanizing or electrolytic galvanizing process.

[0006] In both hot rolling and cold rolling, the material is reduced from the original slab thickness to a desired target thickness, for example, a target thickness of 0.5 to 2 mm. This significantly elongates the material, so that the original slab, after cold rolling, results in a steel strip with a length of, for example, 2.7 km. This cold-rolled strip is wound into a steel coil, unwound for galvanizing, and rewound into a steel coil after galvanizing.

[0007] Whenever a forming process or a forming step is mentioned below, this expressly does not mean the reduction in thickness during rolling.

[0008] It is also known to produce such steel strips from steel grades that are quench-hardenable. During quench-hardening, a steel material is heated to at least a temperature at which austenitization, i.e., the transformation of iron into gamma iron, occurs. If this steel phase is cooled in a subsequent step at a cooling rate above the critical cooling rate, martensite is formed from the gamma iron. Due to a difference in carbon solubility compared to gamma iron, a martensitic microstructure has a distorted structure, which leads to high residual stress and thus hardness.

[0009] It is also known that the effect of quench hardening can also be used in the production of sheet steel components and in particular automotive components, such as body parts or structural components.

[0010] Two basic procedures have been established for this purpose.

[0011] In the first process, a steel blank is cut or cut from a steel strip. This flat steel blank is heated to the aforementioned austenitizing temperature and then placed into a forming tool, in which the hot steel blank is formed into a component in a single stroke. As the hot sheet rests against the relatively cooler forming tool at the end of the forming process, with the tool closed, the heat from the sheet is dissipated into the tool at a rate exceeding the critical hardening rate. Thus, a hardened steel component is obtained from the hot blank through hot forming combined with hardening.

[0012] The second method involves cutting or cutting a flat steel sheet blank from a steel strip and forming this steel sheet blank into a sheet steel pre-component in a conventional, in particular multi-stage forming process, usually mainly through a combination of deep drawing, trimming and / or post-forming. This pre-component is then heated to the austenitizing temperature and the heated pre-component is placed in a tool, wherein the tool has the contour of the pre-component or the final component. In this tool, while maintaining the shape of the pre-component or largely maintaining the shape of the pre-component, the pre-component is quench-hardened with the tool closed by the tool surfaces resting against the pre-component and the heat is dissipated into the tool. A hardened sheet steel component is thus obtained from the hot pre-component through hardening.The first process is also called press hardening or direct process, the second process is also called die hardening or indirect process.

[0013] In both processes, coated steel sheets can be processed into hardened steel components. In particular, it is known to use galvanized steel sheets in both processes. Zinc-based alloys, i.e., with zinc as the element with the highest weight percent in the coating, can be particularly advantageous. For example, zinc can be alloyed with aluminum, copper, chromium, nickel, or other elements. It is also known to use aluminum-based coatings, such as aluminum-silicon alloys, in the first process, i.e., press hardening.

[0014] Whenever the following text refers to "galvanized" or "galvanized steel sheets," this always includes a zinc-based alloy.

[0015] In the case of galvanized steel sheets, during heat treatment for the purpose of press hardening or during heat treatment for the purpose of form hardening, alloying reactions occur between the zinc and the steel substrate on the one hand, but on the other hand, changes in the surface can also occur, in which oxides of zinc or layered alloying elements, such as aluminum, or elements contained in the steel, such as iron or manganese, can form on the surface.

[0016] Such surfaces, in this case oxide layers, can also be glass-like.

[0017] It is common practice for such surfaces to be conditioned and, in particular, cleaned before delivery and before further processing steps.

[0018] For this purpose, various conditioning processes have been developed in the state of the art, which are usually blasting processes in which the surface is blasted with, for example, dry ice or other blasting media such as solids.

[0019] This is done in particular to ensure product properties with regard to welding, painting, bonding and corrosion.

[0020] Currently, wheel blasting (SRS) is most commonly used to condition these surfaces, although other methods are also known, particularly dry ice cleaning, but also vibratory grinding, honing, and others. To test the conditioning effect of these processes on the surface as part of quality assurance, it is common practice to test the surface using direct, destructive, and also complex and time-consuming testing procedures. These include, for example, paint adhesion tests, welding tests, corrosion tests, adhesive adhesion tests, and others.

[0021] In addition, non-destructive, indirect and more cost-effective testing methods are also known, some of which can even be performed during series production. These include, for example, measuring the contact resistance value, comparing the surface with optical limit samples, comparing the results of an adhesive tape peel test with limit samples, or conducting a wipe test.

[0022] However, when it comes to assessing the effect of conditioning processes on the surface, these indirect, more cost-effective testing methods are significantly less informative than direct, destructive, and complex methods. For example, surfaces of hardened components may exhibit low contact resistance values ​​equivalent to those of conditioned surfaces without the surface conditioning required to ensure component quality having taken place. This can be the case, for example, if the surfaces of blanks or prefabricated components were exposed to short to medium furnace dwell times for the purpose of austenitization.

[0023] DE 40 36 568 C2 discloses a system for blasting and matting sheet metal, in particular for blasting and matting large-format, thin-walled sheets using a blasting medium such as sand, glass beads, metal, or the like. At least two blasting devices are provided, with which the sheets to be processed, located in a vertical processing plane, are blasted section by section. The blasting devices apply the blasting medium equally to both opposite surfaces of the vertically arranged sheets, each on exactly opposite partial surfaces.

[0024] EP 1 630 244 B2 discloses a press-hardened product and a manufacturing method therefor. The product has a zinc-based coating layer on its surface, which comprises an iron-zinc solid solution phase and has a thickness of at least 1 μm and at most 50 μm. A zinc oxide layer with an average thickness of at most 2 μm is to be present thereon, which layer is to be reduced in one process step. The thickness of the zinc oxide layer is to be reduced by shot blasting and liquid honing.From DE 10 2007 022 174 B3 a method is known for producing and removing a temporary protective layer for a cathodic coating, in particular for producing a hardened steel component with a surface that is easy to paint, wherein this is a zinc layer which is present on the surface of the steel sheet and in this zinc layer oxygen-affine elements are contained in an amount of 0.1 - 15 wt.%, which during austenitization form a thin skin of the oxide of the oxygen-affine elements on the surface of the cathodic protective layer and this oxide layer is blasted off after hardening by irradiating the sheet component with dry ice particles.

[0025] From DE 10 2010 037 077 B4 a method for conditioning the surface of hardened corrosion-protected components made of sheet steel is also known, wherein vibratory grinding is carried out to condition the surface of the metallic coating, i.e. the corrosion protection layer, wherein the corrosion protection coating is a zinc-based coating and the surface conditioning is carried out in such a way that oxides lying on or adhering to the corrosion protection layer are ground off and zinc-iron phases present in the corrosion protection layer are ground off and their microporosity is exposed, but the corrosion protection coating is not substantially ground off.

[0026] EP 2 233 598 B1 discloses a method for producing a coatable and / or joinable sheet metal part with a corrosion protection coating, wherein, after carrying out a curing process during which a temporary protective layer is formed on the corrosion protection coating, this temporary protective layer is at least partially removed from the sheet metal part by cleaning blasting with an abrasive blasting agent and / or by mechanical cleaning, wherein the corrosion protection coating is to be substantially retained.

[0027] From DE 10 2020 105 046 B4 a method for producing a flat steel product and the use of such a flat steel product are known, wherein the flat steel product is to be shot blast treated, wherein the flat steel product is continuously moved relative to a shot blast treatment system which directs a blasting agent jet against at least one surface of the flat steel product over a blasting duration of 0.03 minutes to 2 minutes, wherein the blasting agent of the blasting agent jet consists of particles with an average diameter of 0.05 - 4 mm and the impact speed of the particles is at least 50 m / sec, so that after the flat steel product has passed the impact length, predetermined roughness values ​​apply to the surface exposed to the blasting agent jet.The problem with the surfaces of galvanized steel sheets, especially with the oxide layers that form during heat treatment for the purpose of austenitization and especially with medium to long furnace residence times, is that these are not always present in an optimal form, whereby loosely adhering oxides in particular must be safely removed or their adhesion must be increased.

[0028] In addition, there are no simple testing methods that provide sufficient information on surface conditions with regard to conditioning quality, e.g., under the microscope in surface plan view or in cross-section. Current methods that provide more or less reliable information are destructive, complex, and time-consuming procedures that are unsuitable for testing during series production. In contrast, the known non-destructive testing methods for quality assurance are not sufficiently precise or meaningful. For example, components with sufficiently low contact resistances can still produce negative results, for example in corrosion tests, paint adhesion tests, potentiostatic-cathodic polarization, or galvanostatic-cathodic polarization. Furthermore, unwanted limitations in the processing, e.g., a reduced welding process window, can occur.

[0029] The object of the invention is to provide a method for conditioning the surface of a heat-treated, galvanized material, which achieves high surface quality and reproducible results and which can be used cost-effectively.

[0030] The problem is solved by a method having the features of claim 1.

[0031] Advantageous further training is indicated in the dependent subclaims.

[0032] According to the invention, during wheel blasting, a specific blasting intensity is set by the blasting medium used, also called blasting material, and / or by system parameters such as turbine speed and / or throughput speed. The grain size distribution of the blasting material used is determined by sieve analysis or adjusted to a specific value range. Furthermore, the success of the process can be clearly demonstrated by assessing a cross-section of an irradiated sample; in addition, a specific degree of coverage can also be determined, preferably by top-down surface analysis under a reflected light microscope. By determining and adjusting the aforementioned parameters, surface conditioning can be optimized and adapted to the respective technical and production-related conditions.It has been found that setting the beam intensity to certain values ​​has a significant impact on success.

[0033] It is known to determine the beam intensity using so-called Almen test strips. The Almen test strips are made of spring steel and are available in three different thicknesses as "N", "A" and "C" strips. The "N" strips are 0.79 mm, the "A" strips 1.29 mm and the "C" strips 2.39 mm thick. The Almen test strips are clamped in a holder which is attached to the test sheet or test component at the position to be tested, for example by welding, and are blasted on one side together with the test sheet or test component using the settings to be tested. The Almen test strips bend towards the blasted side. The resulting bend height of the strip is measured with a dial indicator and specified as the beam intensity as a value in mm. The Almen measuring strip used must always be specified, e.g. intensity = 0.25 mm A.

[0034] In the state of the art, comparatively low blasting intensities of less than 0.04 mm N Almen are achieved for heat-treated coated body components made of sheet steel during wheel blasting due to comparatively high throughput speeds selected for economic reasons in combination with suboptimal settings.

[0035] The Almen intensity according to the invention is above 0.05 mm N, preferably greater than 0.10 mm N, and more preferably greater than 0.15 mm N, but less than 0.2 mm N. Accordingly, the Almen type "N" is used here in Class 1, with a strip thickness of 0.79 mm in the case of the invention. Class 1 therefore defines the pre-bending to + / - 0.025 mm maximum. The length and width of the strip are 76.1 x 19.0 mm, and the hardness for type "N" is 72.5-76 HRA, with the measurement being carried out according to SAE AMS 2430.

[0036] The beam intensity should not be set too low, so that surface areas with no or poor oxide adhesion are reliably reduced and pronounced cavities spanned by oxides, so-called domes, which occur particularly during medium to long furnace residence times, are reliably broken up. For economic reasons, this should also be achieved at the highest possible throughput speeds.

[0037] However, the blasting intensity should not be set too high, as otherwise the grains of the blasting material would wear away too quickly and / or the components would be deformed beyond the specified dimensional accuracy requirements and / or the zinc-iron coating would be damaged. According to the invention, it was found that both requirements are met very well at blasting intensities between 0.05 mm N Almen and 0.20 mm N Almen.

[0038] Regarding the blasting material used, it is advantageous if 50% of the grains have a grain size greater than or equal to 0.30 mm, and the maximum grain size is less than 0.70 mm. Regular sieve analysis is beneficial to maintain a high proportion of coarse grain. It has been shown that a proportion of > 50% of the grains with a grain size greater than or equal to 0.30 mm is preferable. This can further improve surface conditioning.

[0039] Round grit is preferred over square grit for blasting. It has been found that round grit wears down more slowly and the system wears less quickly.

[0040] In principle, any grain material can be used as long as the hardness of the grain is adjusted and preferably lies between 450 and 520 HV.

[0041] It was found that with these settings the blasting material consumption over time can be significantly lower than with the state of the art.

[0042] In a preferred embodiment, for example, it can be provided that the turbine speed can be in a range between 1200 and 2500 rpm. Particularly preferably, the speed can be between 1500 and 2000 rpm. The blade shape of the turbines with which the blasting material is projected onto the component surfaces to be conditioned can preferably be flat. This can offer advantages in terms of the durability of the turbine blades, as their wear can be reduced.

[0043] In a preferred embodiment, the throughput speed of the components through the blasting process can be, for example, 4 to 16 m / min. A high throughput speed can increase the yield.

[0044] The inventors surprisingly discovered that, for example, by appropriately selecting the blasting material, a sufficiently high alumina intensity can still be achieved even at comparatively low turbine speeds and comparatively high throughput speeds. The conditioning success of blasted samples and / or components can be verified, for example, by cross-section. This allows, on the one hand, the percentage of areas with non-adhering or non-bonding oxides to be determined over the length of the section, and, on the other hand, the height of the voids spanned by oxides to be measured. If one of the two values ​​is too high, or both values ​​are too high, this can be problematic, particularly for paint adhesion in subsequent processes.

[0045] Preferably, in the cross-section on the surface, the proportion of areas with cavities under the oxide layer, i.e. areas with non-adjacent oxides, can be at most 35%, particularly preferably at most 15% of the surface.

[0046] Preferably, the proportion of adhering oxides can be at least 65%, particularly preferably at least 85% of the surface.

[0047] In addition or alternatively to the percentage of non-attached oxides, preferably at the surface of the cross-section there should be no more than one pronounced cavity higher than 10 pm under the oxide layer for every 400 pm of section length.

[0048] The preparation of the cross sections must be carried out carefully, i.e. the oxide structure should be essentially preserved and any existing cavities should not be filled or removed during the preparation of the cross sections, as otherwise the previously mentioned values ​​could be falsified.

[0049] The conditioning success of blasted samples and / or components can be verified by the degree of coverage, i.e., the proportion of the surface exposed to blasting grit during blasting relative to the total surface. The degree of coverage can be determined alternatively or additionally using light microscopy or scanning electron microscopy (SEM) in a top view of the surface.

[0050] The invention is explained by way of example with reference to a drawing. It shows:

[0051] Figure 1: Almen N jet intensities of different combinations of turbine speed and flow velocity according to the prior art and according to the invention;

[0052] Figure 2: Grain size distributions of the blasting material according to the invention and the prior art; Figure 3: The loss rate of blasting material depending on the number of blasting cycles according to the invention and the prior art;

[0053] Figure 4: a cross section showing a heat-treated surface with percentage

[0054] Evaluation of areas with non-adherent oxides outside the tolerance;

[0055] Figure 5: a cross section showing a heat-treated surface with percentage

[0056] Evaluation of areas with non-adherent oxides within tolerance;

[0057] Figure 6: a cross-section showing a heat-treated surface without areas of non-adhering oxides within tolerance and with filled cavities;

[0058] Figure 7: a cross-section showing a heat-treated surface with pronounced cavities spanned by oxides, so-called domes;

[0059] Figure 8: a comparison of microscopic top views showing a suitable coverage of 64% according to the invention and an unsuitable coverage of 35%;

[0060] Figure 9: a section showing a galvanized steel 22MnB5 with a zinc coating

[0061] Z140 before hardening;

[0062] Figure 10: A comparison of surface images showing a galvanized steel 22MnB5 with a Z140 zinc coating, heat-treated, conditioned, and coated using cathodic dip painting (KTL); with suitable conditioning after 10 weeks of VDA-old treatment without rust spots and with unsuitable conditioning after 10 weeks of VDA-old treatment with rust spots caused by crater formation in the KTL paint; Figure 11: A crater in the KTL paint layer (10 weeks before VDA-old treatment) in plan view and in profile;

[0063] Figure 12: a crater in the KT paint layer (VDA-old 10 weeks ago) in cross section;

[0064] Surprisingly, it has been shown that, contrary to conventional assumptions, complete removal of the oxides is not necessary to ensure good surface quality for subsequent processes. Surprisingly, it has also been shown that pushing and compacting oxides together in surface cavities is not detrimental; on the contrary, leveling the surface by wheel blasting in this way is beneficial, as it also reduces the tendency for craters to form in the short-circuit paint layer.

[0065] According to the invention, this is achieved if the beam intensity is precisely selected between 0.05 mm N and 0.20 mm N as the Almen intensity.

[0066] Furthermore, it is advantageous if the grain size of the blasting material is adjusted by means of sieve analysis so that at least 50% of the grains have a size of at least 0.3 mm to a maximum of 0.7 mm.

[0067] As a result, the cross-section of the blasted sample should show an image in which areas with non-adhering oxides amount to a maximum of 35% of the section length, and at most a single distinct cavity spanned by oxides with a total height of more than 10 pm is present on the section length of 400 pm.

[0068] A coverage of at least 50% is advantageously aimed for. The coverage is defined as the proportion of the component's surface that was actually exposed to blasting medium relative to the total surface. Surprisingly, it has been found that a coverage of 100% is disadvantageous, and that the optimum coverage lies between 60% and 90%. Figure 2a shows grain size distributions according to the invention, with the proportion of grains with a diameter of 0.3 mm to 0.6 mm being more than 50%. Accordingly, the worn grains must be removed and fresh grains added to maintain this proportion during operation.

[0069] Figure 3 shows the loss rates of the blasting material from laboratory tests. It can be seen that in the prior art (right), the loss rates, shown here as the fine fraction (grain size < 0.15 mm) separated during the process, which results from wear of the blasting material, are significantly higher than in the invention (left), which clearly has increased stability against wear due to the choice of blasting material. The test was carried out until 100% of the original blasting material had been used up, i.e. the original application weight had been used up. For the test, the used blasting material was replaced with fresh blasting material after 500 cycles. It can be seen that in the example according to the invention, 6000 cycles could be carried out until 100% of the original blasting material was used up, whereas in the test according to the prior art, this value was reached after just 4500 cycles.This corresponds to an extension of the deployment time by 1 / 3.

[0070] This is also due to the preferred use of a round grain according to the invention.

[0071] Figure 4 shows a cross-section of a steel substrate with a zinc-iron layer on top, with areas of both adherent and non-adherent oxides above it, and an overall comparatively rugged surface. In the areas with non-adherent oxides, marked by black blocks in the lower part of the image for the purpose of percentage analysis, pronounced cavities beneath the oxides, so-called domes, can be seen. The areas with non-adherent oxides total 51% of the section length, and thus more than 35% of the section length. Such a surface is not suitable for subsequent processing steps.

[0072] Figure 5 shows a comparable micrograph, in which significantly fewer areas with non-adhering oxides are visible, so that such a surface would be acceptable. Figure 6 shows a surface optimized and conditioned according to the invention. It can be seen that this surface is very little fissured. The wheel blasting process, adjusted according to the invention, pushed oxides, which may have been detached or loosely attached by the wheel blasting, into cavities and fissures in the surface and compacted them there, thus creating a smooth or comparatively smooth surface.

[0073] In Figure 7, the cross section shows pronounced cavities covered by oxides, so-called domes.

[0074] Figure 8a shows a microscopic top view of a surface with a coverage of 63%, meaning that 63% of the surface was hit by the grit. This is a good surface similar to the one shown in Figure 6 (cross-section).

[0075] In Figure 8b, however, the microscopic top view shows a surface that was only 33% hit by blasting material, which is insufficient for good performance. It is clearly visible that the proportion of areas that were not hit at all is very high (67%). If components with such surfaces are subjected to a KT paint, the paint adhesion in these areas may be poor, either because aluminum oxides are present there, which are difficult to phosphate, and / or because the oxides are not bonded to the metallic layer, causing the paint to detach along with these oxides. In addition, the tendency for crater formation in the KT paint may be increased in these areas.

[0076] Figure 9 shows a cross-section in which a galvanized, hardenable steel, which is provided with a zinc coating Z140, can be seen before hardening.

[0077] If the treatment is not carried out according to the invention, as previously described, poorly adhering oxides may remain on the surface or craters may form in the cathodic dip-paint layer, weakening it locally. The consequences of such craters or other surface defects are shown in Figures 10a and 10b. It can be seen that corrosion begins first at these locations if the conditioning was not carried out according to the invention. Figure 10a shows the surface appearance after a VDA 621-415 corrosion test without rust spots for a sheet metal in which the conditioning was carried out according to the invention.

[0078] In contrast, Figure 10b shows the surface appearance after the same corrosion test for a sheet that was not conditioned according to the invention. It is clear that without appropriate surface conditioning, significantly increased damage from rust spots occurs.

[0079] Figures 11 to 12 show corresponding craters that locally weaken the e-coat layer and that occur without adequate surface conditioning. A corresponding cross-section is shown in Figure 12 in a micrograph.

[0080] This shows the necessity of conditioning the surface, whereby the surface conditioning according to the invention improves the surface independently of the furnace residence time in such a way that the disadvantages shown do not occur in subsequent processing steps or in the case of corrosive exposure.

[0081] It has been shown that conditioning the surface with wheel blasting within the specified parameters leads to a high degree of flexibility, as conditioning is always reliably achieved without damaging the surface, regardless of the furnace residence time. This is particularly important because in practice, furnace residence times vary due to delays or stops that occur in real processes.

[0082] Thus, the invention provides a method for conditioning surfaces which is reliable, simple and cost-effective and leads to a significant reduction in rejects and to higher quality.

Claims

Claims Method for conditioning the surfaces of heat-treated, galvanized or alloy-galvanized sheet steel components, wherein either a steel sheet is heated at least in part for the purpose of austenitizing and then formed to a sheet steel component and cooled at a rate above the critical cooling rate, or a steel sheet is first formed to a sheet steel component and then heated at least in part for the purpose of austenitizing and after the at least partial austenitizing the sheet steel component is cooled at a rate above the critical cooling rate and in both cases the surface of the sheet steel component is subsequently subjected to centrifugal wheel blasting, characterized in that the centrifugal wheel blasting is carried out with an air intensity between 0.05 mm N and 0.20 mm N.Method according to claim 1, characterized in that greater than or equal to 50% of the blasting material has a grain size greater than or equal to 0.30 mm. Method according to claim 1, characterized in that a round grain is used as the grain of the blasting material. Method according to claim 1 or 2, characterized in that a grain with a hardness of between 400 HV and 550 HV, in particular between 450 HV and 520 HV, is used as the grain of the blasting material.

5. Method according to one of the preceding claims, characterized in that blasting is carried out with an intensity of between 0.1 mm N and 0.15 mm N.

6. Method according to one of the preceding claims, characterized in that the degree of coverage, i.e. the proportion of the surface exposed to blasting material during blasting, is between 50% and 95%, preferably between 60% and 90%, based on the total blasted surface.

7. Method according to one of the preceding claims, characterized in that the blasting is carried out in such a way that the areas visible in the cross-section in which the oxide layer does not adhere amount to at most 35%, preferably 15%, of the section length.

8. Method according to one of the preceding claims, characterized in that the proportion of adhering oxides is at least 65%, preferably at least 85% of the surface.

9. Method according to one of the preceding claims, characterized in that the blasting is carried out in such a way that at most one single cavity under the oxide layer higher than 10 pm is present on the surface of the cross-section for every 400 pm of section length.

10. Method according to one of the preceding claims, characterized in that the blasting material does not contain any grains larger than 0.7 mm in diameter.

11. Method according to one of the preceding claims, characterized in that the turbine speed is in a range from 1200 rpm to 2500 rpm, preferably in a range from 1500 rpm to 2000 rpm.

12. Method according to one of the preceding claims, characterized in that the throughput speed of the components through the blasting process is 4 m / min to 16 m / min. Method according to one of the preceding claims, characterized in that the sheet steel component or the sheet steel blank is used with the following composition (all data in wt.%): Carbon up to 0.4, preferably 0.15 to 0.3 Silicon up to 1.9, preferably 0.11 to 1.5 Manganese up to 3.0, preferably 0.8 to 2.5 Chromium up to 1.5, preferably 0.1 to 0.9 Molybdenum up to 0.9, preferably 0.1 to 0.5 Nickel up to 0.9, Titanium up to 0.2 preferably 0.02 to 0.1 Vanadium up to 0.2 Tungsten up to 0.2, Aluminum up to 0.2, preferably 0.02 to 0.07 Boron up to 0.01, preferably 0.0005 to 0.005 Sulphur max. 0.01, preferably max. 0.008 Phosphorus max. 0.025, preferably max. 0.01 The remainder is iron and impurities. A hardened steel component with a zinc-based coating, wherein the steel component has a surface conditioned by wheel blasting according to any one of the preceding claims.

15. Hardened steel component according to claim 14, wherein on the cross section there is at most one single cavity under the oxide layer higher than 10 pm per 400 pm of section.

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