Method for providing implants in the surface of a substrate, roll formed using this method, and flat material using such roll

Abstract

The invention relates to a method for providing implants in the surface layer of a substrate, wherein a layer of particles is deposited on the surface of the substrate, and the layer of particles is exposed to pulses of an energy beam to form the implants in the surface layer of the substrate. According to the invention a further layer of particles is deposited on the substrate in which implants are formed, and the further layer of particles is exposed to pulses of an energy beam to form additional implants in the surface layer of the substrate. The invention also relates to a roll, such as a skin pass roll formed using this method, and to flat material rolled using such a roll.

Description

[0001] METHOD FOR PROVIDING IMPLANTS IN THE SURFACE OF A SUBSTRATE, ROLL FORMED USING THIS METHOD, AND FLAT MATERIAL USING SUCH ROLL

[0002] 5 The invention relates to a method for providing implants in the surface layer of a substrate, wherein a layer of particles is deposited on the surface of the substrate, and the layer of particles is exposed to pulses of an energy beam to form the implants in the surface layer of the substrate. The invention also relates to a roll, such as a skin pass roll formed using this method, and to flat material rolled using such a roll.

[0003] A method for providing implants in the surface layer of a substrate is known. This method is for instance known from: K. Hilgenberg and K. Steinhoff, Texturing of skin-pass rolls by pulsed laser dispersing, Journal of Materials Processing Technology 225 (2015), pages 84 - 92.

[0004] Skin-pass rolling is a method that is known in the art of rolling especially steel strip.

[0005] 15 Skin-pass rolling is the final forming step in the production of steel strip and has two main purposes: to produce a defined surface condition with a calibrated strip thickness together with a defined surface condition. The surface condition is for instance needed to improve the formability in deep drawing operations for automotive surfaces. To provide the surface condition of the strip, the skin-pass roll needs a defined texture.

[0006] 20 It is already know for decades that a texture can be provided by either shot blast texturing (SBT), electron discharge texturing (EDT) or electron beam texturing (EBT). Nowadays also laser texturing is used to texture skin-pass rolls. All these known techniques remove material from the surface of the roll. However, such surfaces wear during skin-passing of steel strip.

[0007] 25 To improve the lifetime of the rolls Hilgenberg and Steinhoff suggest to provide implants in the surface layer of a substrate such as a skin-pass roll. This can be done by providing a coating on a substrate, consisting of hard powder particles with a high melting point that are held together by a binder. After complete drying of the coating, a focused laser beam creates a melt pool in the surface layer of the substrate, where the hard powder particles mix with the locally molten substrate. After the laser pulse these hard powder particles become embedded or are dissolved within the re-solidified substrate, forming an implant that protrudes from the surface of the substrate. This implantation method can be iterated by repositioning the laser beam or by adjusting the position of the substrate relative to the laser beam. Finally, the surface of the substrate must be cleaned to remove the coating that is still present on the

[0008] 35 surface of the substrate.

[0009] However, experiments have shown that when the coating with the particles is exposed to high laser intensities not only the substrate melts. It also results in a loss (or lack) of powder

[0010] 1

[0011] Sensitivity: general surrounding the implant, because the absorbed laser energy generates a crater in the coating with a diameter that is typically two times and up to four times as large as the diameter of the implant.

[0012] The consequence of the large craters in the coating is that implants can only be formed

[0013] 5 at a relatively large distance or pitch, because each implant needs an (almost) intact coating for each laser pulse. The minimum pitch between the implants is thus also about two to four times the diameter of the implants.

[0014] It is an object of the invention to provide a method for providing implants in the surface layer of a substrate using pulses of an energy beam, such as a laser beam, with which an improved pattern of implants can be achieved.

[0015] It is another object of the invention to provide a method for providing implants in the surface layer of a substrate using pulses of an energy beam, such as a laser beam, with which the location of the implants in the surface layer of the substrate can be easily varied.

[0016] It is a further object of the invention to provide a roll, such as a skin-pass roll, having a

[0017] 15 surface layer with an improved pattern of implants that is suitable for rolling flat material, such as steel strip, and that has an improved lifetime.

[0018] It is still another object of the invention to provide flat material, such as steel strip material, that is rolled using such a roll.

[0019] According to a first aspect of the invention one or more of these objects is reached by

[0020] 20 using a method for providing implants in the surface layer of a substrate, wherein a layer of particles is deposited on the surface of the substrate, and the layer of particles is exposed to pulses of an energy beam to form the implants in the surface layer of the substrate, wherein a further layer of particles is deposited on the substrate in which implants are formed, and the further layer of particles is exposed to pulses of an energy beam to form additional implants

[0021] 25 in the surface layer of the substrate.

[0022] By providing a further layer of particles on the substrate, it is possible to form additional implants that can for instance be situated between the implants formed from the first layer of particles. Thus, a pattern of implants can be formed being more densely packed in comparison to using only one layer of particles. It is even possible to provide a third layer of particles, from

[0023] 30 which even more implants in the surface layer of the substrate can be formed.

[0024] It is also possible to form the additional implants on top of the implants formed from the first layer of particles. In this way the implants are formed that protrude a larger distance above the surface of the substrate in comparison to the use of only one layer of particles. By using three or more layers of particles it is of course possible to form both a pattern of implants

[0025] 35 that is more densely packed then when only one layer of particles is used, and also to form implants that protrude a larger distance above the surface of the substrate.

[0026] 2

[0027] Sensitivity: general Preferably at least part of the remainder of the layer of particles is removed from the surface of the substrate before the further layer of particles is deposited on the substrate. By removing the layer of particles that was deposited on the surface to form the first implants, it is possible to provide an new layer of particles with the required thickness. It is also easier to

[0028] 5 form a homogeneous layer, because there are no craters in the layer of particles that have to be filled.

[0029] According to a preferred embodiment the particles have a melting point that exceeds the melting point of the substrate. When the particles have a melting point that is higher than the melting point of the substrate, the particles can remain intact in the implant and thus provide a high hardness to the implant. It is also possible that (part of) the particles are dissolved in the melt pool, thus forming an implant that has a hardness that is higher than that of the substrate, but lower than that of the particles that are imbedded in the solidified melt pool.

[0030] Preferably, the particles mainly or fully consist of ceramic material, having a mean size

[0031] 15 between 1 and 100 micron, preferably a mean size between 2 and 30 micron. Ceramic particles are hard and have a high melting point, which is often required for implants. The size should be suitable for the required thickness of the layer of particles.

[0032] More preferably, the ceramic material consists of a carbide, a nitride, a boride or an equivalent ceramic material, preferably titanium carbide or tungsten carbide or a suchlike

[0033] 20 ceramic material. Carbides, nitrides and borides are the ceramic materials that are most often used, and titanium carbide and tungsten carbides are suitable ceramics that are used to form particles having the right size.

[0034] According to a preferred embodiment the particles in the further layer of particles mainly or fully consist of a ceramic material that is different from the ceramic material of the

[0035] 25 particles in the layer of particles that is deposited before the further layer of particles is deposited. In this way, two (or more, if more than two layers of particles are used) different implants are formed that can have different properties, such as a different hardness and / or a different chemical composition.

[0036] According to a preferred method for providing implants in the surface layer of a substrate the energy beam is a laser beam that is generated using a laser source having a wavelength in the range of 300 nanometre to 50 micrometre, preferably providing a laser spot on the substrate having a diameter of 10 - 500 micron, preferably a diameter of 50 - 200 micron, more preferably providing a laser pulse with a duration of 1 - 100 ms, preferably a duration of 2 - 20 ms, most preferably the laser pulse having a pulse power of 10 - 1000 W,

[0037] 35 preferably a pulse power of 40 - 250 W.

[0038] By using such a laser beam for providing a laser pulse, it is possible to form the implants in the surface layer of the substrate from any layer of suitable (ceramic) particles. For

[0039] 3

[0040] Sensitivity: general different substrates and / or different particles and / or layer thicknesses thereof laser pulses having a different diameter, duration and / or pulse power can be used.

[0041] According to another method for providing implants in the surface layer of a substrate the energy beam is an electron beam, preferably providing a electron beam spot on the

[0042] 5 substrate having a diameter of 10 - 500 micron, preferably a diameter of 50 - 200 micron, more preferably providing an electron beam pulse with a duration of 1 - 100 ms, most preferably the electron beam pulse having a pulse power of 10 - 1000 W, preferably a pulse power of 40 - 250 W.

[0043] By using such an electron beam for providing an electron beam pulse, it is possible to form implants in the surface layer of the substrate from any layer of suitable (ceramic) particles. For different substrates and / or different particles and / or layer thicknesses thereof electron beam pulses having a different diameter, duration and / or pulse power can be used.

[0044] Preferably the layer of particles that is deposited on the substrate contains a binder, preferably comprising a polymer such as polyvinyl butyral. Using a binder makes it easier to

[0045] 15 provide the layer of particles on the substrate in a required thickness. Furthermore, the layer adheres better to the substrate.

[0046] It is preferred when the layer of particles that is deposited on the substrate has a thickness between 1 and 500 micron, preferably between 30 and 200 micron. The thickness of the layer has a significant influence on the size of the implants that are formed in the surface

[0047] 20 layer of the substrate.

[0048] According to a preferred method the substrate that is used is a roll for rolling flat material, such a metal strip material, preferably steel strip material. By using the method according to the invention the implants can be provided in the surface layer in any required arrangement, and if so required with implants having a different shape and / or dimensions

[0049] 25 an / or hardness, which makes the method very suitable to provide a roll for rolling flat material having the right texture and right hardness of the protrusions thereof.

[0050] Preferably the roll that is used is a skin pass roll for rolling steel strip. For a skin pass roll the arrangement and size of the implants is of special importance to skin pass steel strip.

[0051] According to a special method for providing implants in the surface layer of a substrate, the substrate is a roll for rolling metal strip material, for instance a skin pass roll, the layers of particles have a thickness between 50 - 120 micron and the particles are TiC particles having a mean size of 4 - 7 micron and use a binder of polyvinyl butyral, and the laser provides pulses having a duration between 6 - 8 ms and has a pulse power between 80 and 120 W, preferably 100 W, providing a laser spot on the substrate having a diameter between 50 - 120 micron,

[0052] 35 wherein the laser pulses are provided to form implants having a pitch or distance between the implants of 200 - 1000 micron.

[0053] 4

[0054] Sensitivity: general In this way a roll for rolling metal strip material, such as a skin pass roll for skin pass rolling of steel strip is provided that has implants having a suitable size and hardness to form the texture of the roll so as to be able to roll steel strip during a long lifetime.

[0055] Preferably the roll, for instance a the skin pass roll, is provided with implants that are

[0056] 5 formed from the further layer which are offset in relation to the implants that are formed before.

[0057] According to a second aspect of the invention a roll, for instance a skin pass roll, is provided with implants using the method according to the first aspect of the invention. Such a roll or skin pass roll can have the required texture to roll or skin pass roll flat material, such as metal strip material, preferably steel strip material.

[0058] According to a third aspect of the invention flat material is provided that is rolled using a roll, for instance a skin pass roll, according to the second aspect of the invention, the flat material being metal strip material, preferably steel strip material. This flat material has the right texture for further processing, such as deep drawing or forming.

[0059] The invention will be elucidated referring to the attached figures.

[0060] 15 Figure 1 shows the steps in the method for providing implants in the surface layer of a substrate in accordance with the prior art.

[0061] Figure 2 shows the steps in the method for providing implants in the surface layer of a substrate in accordance with the present invention.

[0062] Figure 1 shows a substrate (1) on which a layer (2) of particles (3) is deposited using

[0063] 20 a mask (20) and a knife (21), see Fig. 1(a). Using a mask and a knife results in a layer of particles having a constant thickness. The thickness is typically around 100 micrometre, but can be thicker or thinner. Usually the particles are suspended in a binder (4), so that the particles adhere to each other and to the substrate. The deposition of the particles on the substrate is also shown schematically in Fig. 1(d).

[0064] 25 The substrate material used is AISI A2 (X100CrMoV5) tool steel (procured from Uddeholm, Sweden). Its chemical composition is listed in Table 1. Slabs measuring 30x 30 mm2with a thickness of 6 mm were polished using a increasing grid to achieve a final surface roughness value of Ra= 0.2 m. Additionally, the slabs were heat-treated, by vacuum hardening and annealing to a base hardness of 600 Hv ±30 which is typical for roll steel. The material

[0065] 30 properties are listed in Table 2.

[0066] C Si Mn Cr Mo V

[0067] 1% 0.3% 0.16% 5.3% 1.1% 0.2%

[0068] 35 Table 1 : Chemical composition substrate

[0069] 5

[0070] Sensitivity: general Substrate AISI A2 Particles (TiC) Binder

[0071] Material X100CrMoV5 TiC PVB

[0072] Density [kg / m3] 7860 4930 1080

[0073] Melting point [°C] 1424 3160 165

[0074] Hardness [Hv] 600 3200

[0075] Measured d50 [pm] - 5.49

[0076] Table 2: Material properties substrate, particles and binder

[0077] Titanium carbide (TiC) ceramic powder particles are used as implantation particles. These particles have a high melting point, exceeding that of the substrate. This powder shows

[0078] 5 a low proportion of particles below 1 m and exceeding 30 pm. From SEM micrographs it is concluded that the particles are irregularly shaped with sharp edges and no uniform size distribution. From the measured size distribution of the TiC particles it is concluded that the size of the particles is equal to d50= 5.49 pm. The powder paste is formed by mixing the TiC powder with a polyvinyl butyral (PVB) binder (4) and ethanol solvent. The mixing ratio was 94%wt TiC powder to 6%wt binder. This paste is then applied to substrates to create a smooth layer of 100 pm thickness, with a measured maximum thickness deviation of 5%. After application the applied layer is air dried for six hours, resulting in a complete evaporation of the ethanol.

[0079] When the layer (2) of particles (3) and binder (4) is dried, the layer is exposed to pulses

[0080] 15 of a laser beam (5). This is schematically shown in Fig. 1(b) and Fig 1(e). The laser beam is provided by a Nd:YAG fiber laser source (JK100FL of JK Lasers Ltd., UK) emitting a 1080 nm wavelength laser beam which is transported through a single mode fibre. The laser beam exiting the single mode fibre the beam is collimated by a collimator lens with a focal length of fc= 7Q mm. The laser beam is focused on to the substrate using a focus lens (JK Lasers, UK)

[0081] 20 with a focal length of ft = 300 mm. The substrate is positioned 2.75 mm below the focus to achieve a spot diameter of 105 pm on the substrate. The focus beam has a Gaussian intensity profile with a beam quality of M2= 1.23 (measured with a MSM+ spot monitor of Primes GmbH, Germany). Additionally, to prevent oxidation during laser-processing, argon is supplied through a nozzle (with a diameter of 6 mm) at a rate of 10 l / min positioned approximately 20

[0082] 25 mm laser implantation zone, angled at 45 degrees with the surface of the substrate. The laser pulse power is 100 W, and the laser pulse duration is 7 ms.

[0083] The laser pulse results in the evaporation of the binder (4) at the spot where the laser beam impinges the layer (2), thereby causing a crater in the layer (2), see Fig. 1 (f). The evaporation of the binder results in the removal of a portion of the particles from the crater. In

[0084] 30 the middle of the crater, in the laser-material interaction zone, the substrate melts, and

[0085] 6

[0086] Sensitivity: general remaining particles (2) will mix with the molten substrate. Together the molten substrate and the particles form a melt pool (6), consisting of molten substrate, dissolved particles and undissolved particles. Because the particles are added to the molten substrate, the melt pool protrudes above the surface of the substrate. When the substrate cools, the melt pool forms

[0087] 5 the implant (7) in the substrate. The implant (7) is embedded in a heat affected zone (8) of the substrate (1), see Fig 1 (g).

[0088] The pulse of the laser beam (5) is repeated by moving the laser and the substrate relative to each other, to form a pattern of implants. After the remainder of the layer (2) of particles (3) and binder (4) is removed, the substrate contains a pattern of implants (7) protruding from the substrate, as shown in Fig. 1 (c). The implants have a height between 10 m and 15 m above the surface of the substrate.

[0089] The method for providing implants in accordance with the invention is schematically shown in Figure 2. In a first stage, implants are formed in the substrate (1) as in the prior art. This is shown in Fig. 2(a) to 2(d). Due to the forming of craters in the layer (2) of particles (3)

[0090] 15 and binder (4), it is impossible to create closely spaced implants. After a laser pulse insufficient particles are left around the implant to allow an implant to be formed close to the first implant. Therefore, after the first series of implants with a relatively large pitch, the substrate is cleaned and provided with another layer of particles.

[0091] The second layer of particles is to be applied on top of the first pattern of implants. Fig.

[0092] 20 2(e) shows the steps involving the application of the second layer (12) of particles (13) and binder (14). The height of the first series of implants textures (ranging form 10 m to 15 pm) is significantly lower than the thickness of the powder layer (100 pm). The second powder layer can be applied uniformly with the same thickness as the first layer namely 100 pm. Thereafter, in the same way as with the first layer (2), using the second layer a second pattern

[0093] 25 of second implants (17) can be formed using a laser beam (15).

[0094] Fig. 2(f) to 2(h) show that the second implants (17) are formed in between the first implants (7) formed from the first layer. This provides an overall pattern of first implants (7) and second implants (17) having a much smaller pitch between the implants than possible using the method according to the prior art, using only one layer of particles to form implants.

[0095] 30 The above shows that by using the method according to the invention, it is possible to achieve densely packed patterns of implants by using two layers of particles that are exposed to laser pulses one after the other.

[0096] However, it is also possible that the second pattern of implants (17) is placed on top of the first pattern of implants (7). Also other variations are possible in relation to the position of

[0097] 35 the second implants relative to the first implants.

[0098] To assess the geometric properties of the implants, a Scanning Electron Microscope (JSM-7200F, JEOL, Japan) was employed. Confocal microscopy (S neox, Sensofar, Spain)

[0099] 7

[0100] Sensitivity: general was utilized to determine the diameter of the craters. In the case of elliptical shaped crater, the diameter was calculated by averaging the lengths of the major and minor axes of the crater.

[0101] It will be clear to the skilled person that instead of a laser beam another type of energy

[0102] 5 beam could be used to generate pulses to form the implants, such as an electron beam.

[0103] It will also be clear that it is not necessary to remove the remainder of the first layer before the second layer is applied, though it is preferred that the remainder of the first layer is removed before the second layer is applied to get a layer with constant thickness.

[0104] It is also clear that after a second layer is applied and second implants are formed, a third layer or even further layers can be used to form further implants.

[0105] Furthermore, the particles of the second or further layer can be different from the particles in the first layer, and so can be the thickness of the layers. Also the laser processing conditions of the laser beam or the processing parameters of another energy beam used for the first implants can be different from those for the second or further implants.

[0106] 15 Moreover, apart from using a mask and a knife to provide a layer of particles on a substrate, other deposition methods are known to the person skilled in the art.

[0107] The particles used in the method according to the invention are usually made of ceramic material, such as TiC, but other material is also possible. Ceramic material is used because it has a melting point that is higher than most substrates, in any case higher than that

[0108] 20 of steel.

[0109] The method according to the invention is particularly suitable to provide implants in the surface layer of a roll for rolling metal material, in particular steel strip. The method can very well be used for providing implants in skin pass rolls for skin pass rolling steel strip, where a dense pattern of implants is often required. The implants provided by the method according to

[0110] 25 the invention also provide a long lifetime to the skin pass roll and a suitable texture to the steel strip.

[0111] The scope of protection is not limited by the above description of the method according to the invention, but is determined by the following claims only.

[0112] 8

[0113] Sensitivity: general

Claims

CLAIMS1. Method for providing implants in the surface layer of a substrate, wherein a layer of particles is deposited on the surface of the substrate, and the layer of particles is exposed to pulses of an energy beam to form the implants in the surface layer of the substrate, characterised in that a further layer of particles is deposited on the substrate in which implants are formed, and the further layer of particles is exposed to pulses of an energy beam to form additional implants in the surface layer of the substrate.

2. Method for providing implants in the surface layer of a substrate according to claim 1 , wherein at least part of the remainder of the layer of particles is removed from the surface of the substrate before the further layer of particles is deposited on the substrate.

3. Method for providing implants in the surface layer of a substrate according to claim 1 or 2, wherein the particles have a melting point that exceeds the melting point of the substrate.

4. Method for providing implants in the surface layer of a substrate according to any of the preceding claims, wherein the particles mainly or fully consist of ceramic material, having a mean size between 1 and 100 micron, preferably a mean size between 2 and 30 micron.

5. Method for providing implants in the surface layer of a substrate according to claim 4, wherein the ceramic material consists of a carbide, a nitride, a boride or an equivalent ceramic material, preferably titanium carbide or tungsten carbide or a suchlike ceramic material.

6. Method for providing implants in the surface layer of a substrate according to claim 4 or 5, wherein the particles in the further layer of particles mainly or fully consist of a ceramic material that is different from the ceramic material of the particles in the layer of particles that is deposited before the further layer of particles is deposited.

7. Method for providing implants in the surface layer of a substrate according to any of the preceding claims 1 - 6, wherein the energy beam is a laser beam that is generated using a laser source having a wavelength in the range of 300 nanometre to 509micrometre, preferably providing a laser spot on the substrate having a diameter of 10 - 500 micron, preferably a diameter of 50 - 200 micron, more preferably providing a laser pulse with a duration of 1 - 100 ms, preferably a duration of 2 - 20 ms, most preferably the laser pulse having a pulse power of 10 - 1000 W, preferably a pulse power of 40 - 250 W.

8. Method for providing implants in the surface layer of a substrate according to any of the preceding claims 1 - 6, wherein the energy beam is an electron beam, preferably providing a electron beam spot on the substrate having a diameter of 10 - 500 micron, preferably a diameter of 50 - 200 micron, more preferably providing an electron beam pulse with a duration of 1 - 100 ms, most preferably the electron beam pulse having a pulse power of 10 - 1000 W, preferably a pulse power of 40 - 250 W.

9. Method for providing implants in the surface layer of a substrate according to any of the preceding claims, wherein the layer of particles that is deposited on the substrate contains a binder, preferably comprising a polymer such as polyvinyl butyral.

10. Method for providing implants in the surface layer of a substrate according to any of the preceding claims, wherein the layer of particles that is deposited on the substrate has a thickness between 1 and 500 micron, preferably between 30 and 200 micron.

11. Method for providing implants in the surface layer of a substrate according to any of the preceding claims, wherein the substrate that is used is a roll for rolling flat material, such a metal strip material, preferably steel strip material.

12. Method for providing implants in the surface layer of a substrate according to claim 11 , wherein the roll that is used is a skin pass roll for rolling steel strip.

13. Method for providing implants in the surface layer of a substrate according any of the preceding claims 1 - 7, wherein the substrate is a roll for rolling metal strip material, for instance a skin pass roll, the layers of particles have a thickness between 50 - 120 micron and the particles are TiC particles having a mean size of 4 - 7 micron and use a binder of polyvinyl butyral, and the laser provides pulses having a duration between 6 - 8 ms and has a pulse power between 80 and 120 W, preferably 100 W, providing a laser spot on the substrate having a diameter between 50 - 120 micron, wherein the laser pulses are provided to form implants having a pitch or distance between the implants of 200 - 1000 micron.1014. Method for providing implants in the surface of a substrate according to claim 13, wherein the implants formed from the further layer are offset in relation to the implants that are formed before.

15. Roll, for instance a skin pass roll, provided with implants using the method according to one of the method claims 1 - 14.

16. Flat material rolled using a roll, for instance a skin pass roll, according to claim 15, the flat material being metal strip material, preferably steel strip material.11

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