Abstract
The disclosure relates to a method for welding sheets provided with an aluminum silicon anti-corrosion coating, wherein chronologically before the welding, the aluminum silicon layer on the sheets in the region of the weld joint and the underlying intermetallic interlayer between the base material and the anti-corrosion coating is passed over with a laser and as a result, on the one hand, material of the aluminum silicon layer and the underlying intermetallic interlayer is vaporized and aspirated and on the other hand, a reaction with the base material extending into the base material is produced so that a metallic reaction ablation layer or alloying ablation layer is produced, which has iron and possibly alloying elements from the base material and aluminum silicon from the aluminum silicon layer and the intermetallic interlayer, the reaction layer reaching a thickness of 5 m to 100 m.
Claims
1. A method for welding preparation of steel sheets comprising: providing at least one steel sheet composed of a hardenable steel material with an aluminum silicon anti-corrosion coating, wherein an alloying ablation is performed; passing a laser beam over aluminum silicon layer on the sheets, the underlying intermetallic interlayer and the underlying base material, in the region of a desired welding edge of the at least one sheet; vaporizing and aspirating the material of the aluminum silicon layer and the underlying intermetallic interlayer; producing a reaction with the base material extending into the base material; producing a metallic reaction ablation layer or alloying ablation layer having iron and alloying elements from the base material and aluminum silicon from the aluminum silicon layer and the intermetallic interlayer; and wherein, the reaction layer reaching a thickness of 5 m to 100 m whereby the aluminum content of the metallic reaction layer after the welding preparation is >2% and does not exceed 11.3% (in % by mass).
2. The method according to claim 1, wherein the advancing speed V.sub.abl is between 4 m/min and 30 m/min, the laser is operated in a pulsing fashion, with pulse durations between 20 to 150 ns, and at frequencies of 1 to 100 kHz, at average ablation powers of 500 W to 5000 W.
3. The method according to claim 1, wherein the method is carried out so that the aluminum content of the metallic reaction layer after the welding preparation does not exceed 10% (in % by mass).
4. The method according to claim 1, wherein the method is carried out so that the aluminum content of the metallic reaction layer after the welding preparation is >1% (in % by mass).
5. The method according to claim 1, wherein the base material is a steel, which is a boron manganese steel that can be hardened by means of an austenitization and quench hardening process.
6. The method according to claim 1, wherein a steel of the general alloy composition (in % by mass) is: TABLE-US-00004 carbon (C) 0.03-0.6 manganese (Mn) 0.8-3.0 aluminum (Al) 0.01-0.07 silicon (Si) 0.01-0.8 chromium (Cr) 0.02-0.6 titanium (Ti) 0.01-0.08 nitrogen (N) <0.02 boron (B) 0.002-0.02 phosphorus (P) <0.01 sulfur (S) <0.01 molybdenum (Mo) <1 and residual iron and smelting-related impurities is used as the base material.
7. The method according to claim 1, wherein a steel of the general alloy composition (in % by mass) is: TABLE-US-00005 carbon (C) 0.03-0.30 manganese (Mn) 1.00-3.00 aluminum (Al) 0.03-0.06 silicon (Si) 0.01-0.20 chromium (Cr) 0.02-0.3 titanium (Ti) 0.03-0.04 nitrogen (N) <0.007 boron (B) 0.002-0.006 phosphorus (P) <0.01 sulfur (S) <0.01 molybdenum (Mo) <1 and residual iron and smelting-related impurities is used as the base material.
8. The method according to claim 1, wherein a steel of the alloy composition C=0.20, Si=0.18, Mn=2.01, P=0.0062, S=0.001, Al=0.054, Cr=0.03, Ti=0.032, B=0.0030, M=0.0041, residual iron, and smelting-related impurities is used as the base material, with all of the above indications expressed in % by mass.
9. The method according to claim 1, wherein the width of the reaction ablation layer or alloying ablation layer from the joint or butt joint is 0.4 to 2.4 mm.
10. The method according to claim 1, wherein the vapor and molten particles produced are conveyed away from the weld joint by means of suitable blowing nozzles in the pressure range from 0.1 to 20 bar and aspiration devices.
11. A sheet bar that is produced and prepared for welding with a method according to claim 1.
12. The method according to claim 5, wherein the base material a steel from the group of 22MnB5 steels is used.
13. A welded component made of sheet bars according to claim 11.
14. The method according to claim 10, wherein the vapor and molten particles produced are conveyed away from the weld joint by means of suitable blowing nozzles in the pressure range from 0.3 to 5 bar and aspiration devices.
15. A welded component made of sheet bars, the sheet bars each having been produced and prepared for welding with the method of claim 1, wherein the sheet bars are placed against one another with ablated joints and are welded by means of laser.
16. The welded component made of sheet according to claim 15, wherein during the welding, a filler rod is introduced into the welding seam.
17. The method according to claim 1, wherein the reaction layer has a thickness of 20 m to 50 m.
18. The method according to claim 2, wherein the advancing speed V.sub.abl is between 7 m/min and 15 m/min, the laser is operated in a pulsing fashion, with pulse durations between 30 to 100 ns, and at frequencies of 10 to 30 kHz, at average ablation powers of 1000 W to 2000 W.
19. The method according to claim 3, wherein the aluminum content of the metallic reaction layer after the welding preparation does not exceed 8% (in % by mass).
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) A detailed description of various aspects, features, and embodiments of the subject matter described herein is provided with reference to the accompanying drawings, which are briefly described below. The drawings are illustrative and are not necessarily drawn to scale, with some components and features being exaggerated for clarity. The drawings illustrate various aspects and features of the present subject matter and may illustrate one or more embodiment(s) or example(s) of the present subject matter in whole or in part.
(2) FIG. 1: shows a complete ablation according to the prior art;
(3) FIG. 2: shows a partial ablation according to the prior art;
(4) FIG. 3: shows the alloying ablation according to the disclosure;
(5) FIG. 4: shows an electron microscope image of an aluminum silicon coating on a steel sheet before a heat treatment;
(6) FIG. 5: shows an electron microscope image of a steel sheet with an aluminum silicon coating and a partial ablation track in the non-hardened state;
(7) FIG. 6: shows an electron microscope image and light microscope image of the partial ablation track according to FIG. 5;
(8) FIG. 7: shows a detail from the non-hardened partial ablation layer according to FIG. 6;
(9) FIG. 8: shows a light microscope image of a complete ablation track;
(10) FIG. 9: shows an enlarged image of the complete ablation track according to FIG. 8;
(11) FIG. 10: shows complete ablation track according to FIG. 9 in the hardened state;
(12) FIG. 11: shows the alloying ablation according to the disclosure in the non-hardened state in a comparison between an electron microscope image and a light electron microscope;
(13) FIG. 12: shows the alloying ablation track in the non-hardened state in an enlarged light microscope depiction;
(14) FIG. 13: shows an enlarged electron microscope image in the non-hardened state;
(15) FIG. 14: shows the alloying ablation track in the hardened state in a light microscope image and an electron microscope image with element identification;
(16) FIG. 15: shows a component that has undergone welding preparation according to the disclosure, in the welded and non-hardened state;
(17) FIG. 16: shows the component according to FIG. 16 after the hardening;
(18) FIG. 17: shows the parameters of the ablation and the welding;
(19) FIG. 18: shows a detail in the region of the welding seam edge of the component that has undergone welding pretreatment according to the disclosure in the non-hardened state;
(20) FIG. 19: shows the component according to FIG. 19 in the hardened state;
(21) FIG. 20: shows the test parameters for the complete ablation, partial ablation, and alloying ablation according to the disclosure.
DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT
(22) It is known to provide hardenable steels with an anti-corrosion layer and in particular with an anti-corrosion layer that is intended to protect the steel from corrosion during hardening. This hardening usually takes place in such a way that the steel material is austenitized and then quench hardened so that the austenite is partially or completely converted into martensite and this brings about a hardening. The usual temperatures for this are much higher than 800 C. At such temperatures, surface oxidation and decarburization of the steel material occur if it has not been provided with a layer to protect it from decarburization and oxidation.
(23) For example, typical hardenable steels have the following general alloy composition (all indications in % by mass):
(24) TABLE-US-00001 carbon (C) 0.03-0.6 manganese (Mn) 0.8-3.0 aluminum (Al) 0.01-0.07 silicon (Si) 0.01-0.8 chromium (Cr) 0.02-0.6 titanium (Ti) 0.01-0.08 nitrogen (N) <0.02 boron (B) 0.002-0.02 phosphorus (P) <0.01 sulfur (S) <0.01 molybdenum (Mo) <1
residual iron and smelting-related impurities.
(25) Particularly suitable steels are those of the following alloy composition:
(26) TABLE-US-00002 carbon (C) 0.03-0.30 manganese (Mn) 1.00-3.00 aluminum (Al) 0.03-0.06 silicon (Si) 0.01-0.20 chromium (Cr) 0.02-0.3 titanium (Ti) 0.03-0.04 nitrogen (N) <0.007 boron (B) 0.002-0.006 phosphorus (P) <0.01 sulfur (S) <0.01 molybdenum (Mo) <1
residual iron and smelting-related impurities.
(27) A particularly suitable steel is one with the following alloy composition:
(28) TABLE-US-00003 C Si Mn P S Al Cr Ti B N [%] [%] [%]a [%] [%] [%] [%] [%] [%] [%] 0.20 0.18 2.01 0.0062 0.001 0.054 0.03 0.032 0.0030 0.0041
residual iron and smelting-related impurities.
(29) Such steels are expressly also suitable for use in the disclosure.
(30) FIG. 1 shows a complete ablation according to the prior art. It depicts a base material to which an aluminum silicon layer has been applied; between the aluminum silicon layer and the base material, an intermetallic zone or intermetallic interlayer has formed, which inevitably occurs due to reactions of the base material with the aluminum silicon coating at the elevated temperatures that occur during the hot-dip coating process. The thickness of the intermetallic interlayer in this case is approximately 3 to 10 m and that of the aluminum silicon layer is 25 to 30 m. Typical total layer thicknesses are thus 19 to 35 m in a conventional coating run of 60 g aluminum silicon per m2. The overall layer analysis of this layer consists of aluminum with 8 to 11% silicon and 2 to 4% iron. In the complete ablation, both blowing nozzles and extractors in the vicinity of the incident laser beam are used to aspirate the metal vapor and molten droplets being generated.
(31) FIG. 2 shows a so-called partial ablation process. Here, the aluminum silicon layer on the base material and the intermetallic interlayer between them are once again visible; in this case, though, the laser beam is guided so that the intermetallic interlayer is left behind and only the aluminum silicon layer is vaporized by the laser beam and correspondingly aspirated.
(32) FIG. 3 shows the reaction or alloying ablation according to the disclosure. Here once again, the aluminum silicon layer on the base material is present with the intermetallic interlayer between the two. Here, too, blowing nozzles and an extractor are used, but the laser beam influences both the aluminum silicon layer and the intermetallic zone as well as the base material and after the laser beam has removed the aluminum silicon layer and the intermetallic interlayer in their initial form, a metallic reaction layer has formed, which can extend into the base material, and in which an aluminum silicon layer or an intermetallic interlayer can no longer be detected. Thus according to the disclosure, the laser beam has produced an entirely separate metallic reaction layer, which has taken place based on metallic reactions in the reaction zone under the influence of the laser beam. In this case, the reaction layer itself can extend 5 to 50 m into the base material from the surface of the original base material and can have an overall layer thickness of 5 m to 100 m and preferably 20 m to 50 m.
(33) FIG. 20 shows the parameters for the partial ablation, the complete ablation, and the reaction ablation or alloying ablation. The partial ablation was performed with a speed of 8.5 m/min and a pulse duration of 56 nanoseconds. The average ablation power is 923 Watt, the ablation frequency is 10 kHz, and the blowing nozzle pressure is 0.5 bar of positive pressure. The complete ablation was performed with the same ablation speed of 8.5 m/min, but with a pulse duration of 64 nanoseconds at a frequency of 12 kHz and an average ablation power of 1191 Watt. The blowing nozzle pressure in this case is identical to that of the partial ablation.
(34) The alloying ablation is performed with the same ablation speed, but by contrast with the partial ablation and complete ablation, the pulse duration is increased to 91 nanoseconds and an ablation power of 1702 Watt is used at a frequency of 18 kHz. Here, too, the blowing nozzle pressure is 0.5 bar of positive pressure.
(35) FIG. 4 shows a typical aluminum silicon coating of the kind used on steel sheets in large industrial-scale applications. The aluminum silicon coating shown therein is depicted in the initial state, i.e. in the as-delivered state of a coated sheet of this kind, before this sheet has been heat treated. It should be noted here that the heat treatment of these conventional sheets, which are used for structural components in automobile manufacture, consists of austenitizing and quench hardening these sheets, which means that in the heat treatment, a sheet temperature of 900 is usually exceeded, but at least a temperature above the Ac3 point of the respective steel alloy. Here, a total layer thickness of 31 m is shown, with a layer thickness of the intermetallic interlayer of 6 m. The intermetallic interlayer consists of a composition that obeys the general formula FexAlySiz and FexAly. In the intermetallic zone, the EDX analysis reveals an aluminum content of 55.8%, an iron content of 33.5%, and a silicon content of 10.3%. The base material is usually a so-called boron manganese steel, which is highly hardenable. In particular, the base material is a so-called 22MnB5, which is one of the customary steels used for producing such components. The group of boron manganese steels that are suitable for this, however, is significantly larger and is expressly not limited to 22MnB5.
(36) FIG. 5 shows a coating like the one in FIG. 4, but which has a partial ablation track according to the prior art, in the non-hardened state. In the left region of FIG. 5 is an uninfluenced aluminum silicon coating with the intermetallic zone, as shown in FIG. 4. In the right region, a partial ablation track is shown in which the intermetallic interlayer is only still present with a layer thickness of approx. 5 m. Interposed between the partially ablated region and the coating region, a transition region is visible in which the coating is altered due to the influence of the heat of the laser beam.
(37) For comparison purposes, FIG. 6 shows the same state again, compared to a light microscope image of the same region that clearly shows the partially ablated region, the transition region between ablation and coating, and the aluminum silicon coating region.
(38) FIG. 7 once again shows the partial ablation region with an enlarged detail of the remaining intermetallic interlayer approx. 5 m thick and the underlying base material. The partial ablation has also altered the intermetallic interlayer somewhat because now, the iron content is 68.7%, the aluminum content is 26.7%, the silicon content is 3.9%, and the manganese content is 0.7%. It is thus clear that a further reaction under the influence of the laser beam heat has taken place so that the aluminum content is reduced in favor of the iron content and silicon content. In addition, the increased manganese content indicates that a reaction with the boron manganese steel has taken place.
(39) FIG. 8 shows a micrograph of a non-hardened, completely ablated region; in the region of the complete ablation, a heat influence zone of the ablation process is visible, while spaced apart from this, the aluminum silicon layer and the intermetallic interlayer are visible. Ablation residue is present on top of this and under it is the base material. The enlargement of this region in FIG. 9 shows the transition region in which the aluminum silicon layer is once again altered due to the influence of the heat of the laser.
(40) FIG. 10 then shows the hardened state, i.e. a state that has been produced by subjecting the sheet, which has previously undergone complete ablation, to an austenitization and quench hardening. The hardening has also altered the aluminum silicon coating on the intermetallic interlayer; in particular, the latter now consists of the general composition AlxFey, AlxFeySiz, and -Fe. In the region of the complete ablation, a scale layer is visible on a decarburized zone, i.e. in this case, the hardening and in particular the heat treatment for the hardening, namely the austenitization, has resulted in the fact that the base material is oxidized on the surface (scale), i.e. essentially consists of iron oxides and oxides of the alloying elements, whereas in the upper region, the carbon that is intrinsically required for the hardening has been reduced in the steel by the heat treatment and removed through oxidation.
(41) In the alloying or reaction ablation according to the disclosure (FIG. 11), in the non-hardened state, it is clear that instead of an intermetallic interlayer and/or a pure base material layer, a white reaction layer has been left behind, which is visible on the right side in FIG. 12. An element analysis in this white metallic reaction layer shows that in it, the iron content is 91.3%, the aluminum content is 6%, the silicon content is 1.2%, the manganese content is 1.2%, and the chromium content is 0.2%. The comparatively high manganese and chromium contents show how powerful a reaction with the base material has taken place. The remaining contents of 6% aluminum and 1.2% silicon have turned out to be absolutely non-critical with regard to the load-bearing capacity of a welding seam produced with such a sheet.
(42) In FIG. 12 once again shows a light microscope image of the corresponding region.
(43) FIG. 13 once again shows an enlarged region of the reaction layer and the transition region to the aluminum silicon coating.
(44) In the hardened state, the extreme superiority of the reaction layer according to the disclosure compared to all known prior welding preparations for such sheets is identifiable (FIG. 14). In the hardened state, the reaction layer is present in a very clearly defined way, while the base material is not influenced at all and in particular, exhibits no decarburization or scale underlying it. After the hardening, it is clear that in the reaction layer (FIG. 15, bottom), the iron content has further increased at the expense of the aluminum and silicon contents and once again, the manganese content and chromium content have also increased slightly. Nevertheless, this reaction layer has provided a powerful anti-corrosion effect.
(45) If a component that is prepared in this way according to the disclosure is welded to another component of this kind, this yields the non-hardened state shown in FIG. 15. FIG. 16 shows the hardened state. Here once again, it is very clear how reliably the reaction ablation zone or alloying ablation zone, which appears white therein, has protected the underlying material. FIG. 17 shows the parameters; in this case, an ablation speed of 8.5 m/min and an average ablation power of 1702 Watt were used at a frequency of 18 kHz and with a blowing nozzle pressure of 1.5 bar of positive pressure. Welding was likewise performed at a speed of 8.5 m/min with a welding power of 4920 Watt and a gas flushing of 15 l argon per minute.
(46) FIG. 18 shows the transition to the welding seam in the non-hardened region, showing the aluminum silicon layer plus the intermetallic interlayer at the far left, the reaction layer in the middle region, and the welding seam at the far right. In the hardened state (FIG. 19), an aluminum silicon layer, which has been converted by the heat treatment, is visible on the intermetallic interlayer at the far right, the clearly defined reaction layer that is formed is visible in the middle region, and next to it, the welding seam.
(47) The hardening took place at a furnace temperature of 930 C. and with a furnace dwell time of 5 minutes and 10 seconds. The transfer time to the cooling was 8 seconds, with the cooling taking place in a water-cooled sheet die.
(48) The ablation laser used was the type i1600E-60 laser produced by the company Powerlase. The ablation laser optics has a focus geometry of 2.40.4 mm2, with the 0.4 mm being oriented in the ablation advancing direction. The focal length of the focus lens was approximately 150 mm; the laser optics can be ordered from the company Andritz Soutec with the order number 62-515781. The suitable extraction hood that was used in the tests is also produced by the company Andritz Soutec and can be ordered from Andritz Soutec under the name Souspeed ablation extraction hood with the order number 64-515460. The result according to the disclosure can be reliably reproduced with the given parameters and the above-mentioned equipment.
(49) With the disclosure, it is therefore advantageous that the inventors have discovered a way on the one hand to inhibit scale formation and edge decarburization and on the other hand to preclude the formation of intermetallic or soft ferritic phases without rendering the method excessively complex. In addition, the load-bearing cross-sections are not reduced.
