Weld seam for joining ferrous materials

Abstract

Weld for joining two ferrous materials, wherein one ferrous material has a carbon content of more than 0.3 wt%, wherein the carbon content in the weld is between 1 wt% and 2 wt%, characterized in that the weld includes a filler material whose carbon content in wt% is matched to the materials to be welded such that the arithmetic mean between the carbon contents of the materials to be welded and the filler material lies within the concentration interval of 1 wt% and 2 wt% carbon, wherein the filler material is added in the form of a foil.

Description

[0001] The invention relates to a weld seam according to the preamble of claim 1.

[0002] When ferrous materials are to be joined by welding in a composite component, this generally leads to a limitation in the choice of materials, which is determined by the carbon content of the ferrous materials. The limit for materials that can be welded easily and reliably is approximately 0.2 wt% to 0.3 wt% carbon. Steels and cast iron materials with a higher carbon content harden under normal welding processes such as electric arc, MIG, or MAG welding, which leads to increased cracking and a resulting loss of weld strength.

[0003] In DE 10 2005 057 317 A1, a method for welding ferrous materials with different carbon contents is described, which is advantageous in itself.

[0004] Furthermore, US 2006 / 0237412 A1 discloses weld metal compositions intended to improve mechanical properties when welding cast iron. US 4,534,793 A discloses materials and a method for welding cast iron. US 3,466,422 A discloses an arc welding electrode.

[0005] GB 1 154 269 A also discloses arc welding electrodes. DE 10 2007 018 702 A1 discloses a method for producing a laser weld joint as known. DE 10 2005 057 317 A1 discloses a method for laser welding metallic materials. Furthermore, a weld metal is known from US 3 556 777 A.

[0006] The object of the invention is to improve the mechanical properties of a weld seam when welding ferrous materials with a higher carbon content, while simultaneously reducing process costs.

[0007] The solution to the problem consists of a weld seam with the features of claim 1.

[0008] The weld according to claim 1 is located between two ferrous materials, at least one of which has a carbon content of more than 0.3 wt.%. It has been found that a targeted increase in the carbon content of the weld to a value between 1 wt.% and 2 wt.% achieves a particularly good compromise between, on the one hand, the lowest possible hardness and, on the other hand, the highest possible ductility. The carbon content in the weld is preferably between 1.25 wt.% and 1.75 wt.%, and more preferably between 1.4 wt.% and 1.6 wt.%, and most preferably at 1.5 wt.%, whereby a technical inaccuracy of 0.2 wt.% in the representation of the weld must be taken into account.

[0009] Compared to special welding processes (e.g. hybrid processes), the weld described by claim 1 can be produced with low energy expenditure, it is environmentally friendly because nickel-containing filler materials can be dispensed with, and it can be produced by a technically relatively simple process control.

[0010] Furthermore, it is provided that the weld seam has a filler material whose carbon content in weight percent is matched to the materials to be welded in such a way that the arithmetic mean between the carbon content of the materials to be welded and the filler material lies in the concentration interval of 1 wt.% and 2 wt.% carbon, with the filler material being added in the form of a foil.

[0011] In a preferred embodiment, the weld seam exhibits at least a partial austenitic microstructure. Austenitic microstructure refers to γ-solid solutions in the iron-carbon phase diagram. These solid solutions form, for example, when the material is quenched from a temperature above 1000°C. Austenitic microstructures have a low yield strength but also high toughness. Preferably, at least remnants of an austenitic microstructure (residual austenite) are present in the weld seam, which contribute to its high toughness.

[0012] The weld seam is relatively narrow, namely 0.5 mm and 2 mm, preferably up to 1.1 mm. Such a narrow weld seam compensates for the often increased hardness in a transition zone between the material and the weld seam.

[0013] Further advantageous embodiments result from the remaining dependent claims.

[0014] The invention further relates to an arrangement of two components which can be joined by a weld seam as described above. It is particularly advantageous to chamfer one edge of each component at an angle of 45° in the joint area between the components, i.e., where the weld seam is to be applied between the components. The width of the chamfered area is ideally 0.2 to 0.4 mm. It is also particularly advantageous to insert the filler material in the form of a film into this joint area between the first and second components, wherein this filler material, in the form of a film, projects 0.4 to 0.6 mm beyond a surface of at least one component and 0.6 to 1 mm from a lower edge of a chamfered area of ​​at least one component. Such an arrangement enables the use of the device for controlling welding parameters in laser beam welding, as disclosed in DE 19716293 A1.The aforementioned patent application shall be deemed fully disclosed herein. The specified values ​​for the protrusion of the foil-shaped filler material are limited by the detectability of the material in the aforementioned control method. The lower limit is determined by the detectability of the filler material, and the upper limit by possible droplet formation due to heat buildup. In particular, this enables focus position control as well as penetration control.

[0015] The following section will examine individual, exemplary embodiments of the invention in more detail. These will demonstrate: Fig. 1 a cross-section through a weld, wherein Fig. 1 does not show an embodiment of the invention, and Fig. 2 a cross-section through a weld seam using a film as filler material. Fig. 3 a cross-section through an arrangement of two components with a foil-shaped additive material inserted in the joint area, which can be joined via a weld seam according to the invention. Example 1, Welding of cast iron with a heat-treated steel:

[0016] When welding a cast iron material 4, 4' with a heat-treated steel 6 according to Fig. For example, the following carbon contents in wt.% are present in the materials: Cast iron, GGG 60: 3.2 wt.% carbon (C) Tempered steel C 45: 0.45 wt.% C No additional material is used. (In this and the following calculations of the carbon content, it is always ideally assumed that the same volume of each material enters the weld.)

[0017] This yields an arithmetic mean carbon content (wt%) in the weld seam, of (3.2%+0.45%) / 2=1.85%.

[0018] While this carbon content of 1.85 wt.% lies within the desired range of 1 wt.% to 2 wt.%, the range of approximately 1.5 wt.% is particularly advantageous. To achieve this carbon content of 1.5 wt.%, it is advisable to offset the weld seam into the area of ​​the quenched and tempered steel. This results in the weld metal containing less than 50% by volume of cast material and more than 50% by volume of quenched and tempered steel, thus reducing the carbon content in the weld. Such a technique is already described in the aforementioned document.

[0019] The weld seam 2 is very narrow; according to Fig. 1. The weld seam is approximately 0.5 mm thick in a lower section and approximately 1.1 mm thick in an upper section. It tapers from a top surface 18 to a bottom surface 20. Such a weld seam can preferably be achieved using a laser welding process. Other possible welding processes include electron beam welding, plasma welding, and, in principle, hybrid welding processes as well as MAG, MIG, or TIG welding.

[0020] After welding, the weld is rapidly quenched from a temperature above 1000°C, resulting in the retention of an austenitic microstructure. This retained austenite, with a carbon content of approximately 1.5 wt%, exhibits high ductility for a microstructure with this carbon content, while its hardness is comparatively low. The combination of low hardness and high ductility, along with the very narrow weld seam, enables the weld to withstand dynamic stresses effectively. Example 2, Welding of cast iron and structural steel:

[0021] This example corresponds to Example 1 in its essential parameters. Only the carbon content in the steel is lower at 0.25 wt.% than in the heat-treated steel. The carbon concentrations in the weld are then as follows: Cast iron, GGG 60: 3.2 wt.% C Steel 25 Mo CR 4: 0.25 wt.% C No additional material is used.

[0022] This yields an arithmetic mean carbon content (wt%) in the weld seam, of (3.2%+0.25%) / 2=1.67%.

[0023] In this example as well, offsetting the weld seam into the steel layer is advantageous to further reduce the carbon content in the weld to 1.5 wt.%. Quenching is also performed here to achieve the advantageous austenitic microstructure. The mechanical properties of this weld are analogous to those in Example 1 and are based on the same mechanical properties. Another possible material combination for this example is GGG50 and 20MoCr4E.

[0024] Examples 1 and 2 have in common that no filler material is used in these welds. The desired carbon content of the weld, combined with the advantageous austenitic microstructure, can be achieved from the materials to be welded by the targeted offset of the weld (weld positioning method).

[0025] However, if the intention is to weld two heat-treated steels together, the correction through weld positioning cannot be successful, as neither of the materials to be welded has the desired 1.5 wt% carbon content. In this case, a filler material is required for welding. This is explained in the following example. Example 3, Welding of two heat-treated steels: Tempered steel C 45: 0.45 wt.% C Additive material (foil): 2.6 wt.% C

[0026] This yields an arithmetic mean carbon content (wt%) in the weld seam, of (0.45%+2.55%) / 2=1.5%.

[0027] To illustrate such a weld 14, a slide 16 is shown according to Fig. 2. A foil is placed as filler material between the workpieces 8 and 10, made of heat-treated steel, to be welded. The foil has a carbon content precisely matched to the carbon content of the heat-treated steels to be welded, in this case 2.55 wt.%, in order to achieve the preferred carbon content of 1.5 wt.% in the weld. Should other heat-treated steels with slightly varying carbon contents be welded, or should a value other than 1.5 wt.% from the advantageous range of 1 wt.% to 2 wt.% carbon content be desired, the carbon content of the foils is adjusted accordingly.

[0028] As an alternative to the foil-form filler material with 2.6 wt% C used here, a filler material made of spheroidal graphite cast iron (GJS) with a higher carbon content (3.4–3.8 wt% C) can also be selected for this material combination of C45 heat-treatable steel and C45 heat-treatable steel. This results in an overall higher carbon content in the weld. The thickness of the foil is variable and can, for example, be in the range of 0.3–0.4 mm.

[0029] Furthermore, weld 14 according to example 3 corresponds to weld 2 according to the Fig. 1 (Examples 1 and 2). Here too, the same mechanical results are achieved through rapid quenching, leading to at least a partially austenitic microstructure. The effect of this microstructure was already explained in more detail under Example 1. The same applies to the welding processes, which were also already mentioned in Examples 1 and 2.

[0030] In addition to the seam widths of at least 0.5 mm shown in the exemplary embodiments, the use of new laser technologies, in particular the introduction of single-mode lasers, makes it possible to focus the laser with increasing intensity and sharpness. These lasers deliver 5 kW of beam power into optical fibers with a diameter of 0.05 mm. This technology thus makes it conceivable to achieve significantly narrower seam widths in the range of 0.2 mm.

[0031] In general, all parameters must always be considered when carrying out the procedure. - Seam cross-section and - Carbon content as well as - The volumes of the components involved must be coordinated.

[0032] In this example, the use of a foil as filler material was described. However, it is also advantageous to apply the filler material in another form, for example, by means of a spray coating (plasma spray coating or arc wire spray coating) applied to the workpieces beforehand. Furthermore, for different workpieces, it is advantageous to continuously add the filler material to the welding process using a wire with the desired carbon content. The same can also be achieved by adding an ice powder that is precisely calibrated to the required carbon content.

[0033] Fig. Figure 3 shows an arrangement of a first component 100 and a second component 102, which can be joined via a weld seam as described above. In the joint area 104 between the first and second components 100, 102, a filler material 106 in the form of a foil is inserted. The thickness d1 of the filler material, and thus the gap between components 100, 102, is d1 = 0.4 mm. The edge area 108 of the first component 100 and the edge area 110 of the second component 102 are chamfered at an angle α = 45°. The width d4 of the chamfered area of ​​the first component 100 is 0.2 mm, and the width d5 ​​of the chamfered area 110 of the second component 102 is 0.4 mm.

[0034] The foil 106 extends beyond the surface 112 of the second component 102 by a length D2, with this overhang ideally being 0.4 to 0.6 mm. The overhang d3 of the foil 106 beyond the lower edge 114 of the chamfered area 110 of component 102, i.e., the deeper chamfered part, ideally ranges in length from 0.6 to 1 mm.

[0035] Such a workpiece geometry, as already described at the beginning, enables the use of a device for controlling welding parameters according to DE 19716293 A1. This is achieved by using a CCT camera and evaluating the weld pool geometry during welding of the... Fig. In the arrangement shown in Figure 3, such a device makes it possible to monitor and, if necessary, control the weld quality, in particular the weld position, the focus position of a laser beam, and the penetration depth.

[0036] Suitable components for welding include, among others, gearbox parts, shafts such as camshafts or crankshafts, as well as chassis components, engine parts and body parts.

Claims

[1] Weld for joining two ferrous materials, wherein one ferrous material has a carbon content of more than 0.3 wt%, wherein the carbon content in the weld is between 1 wt% and 2 wt%, characterized by , that the weld seam has a filler material whose carbon content in weight percent is matched to the materials to be welded such that the arithmetic mean between the carbon contents of the materials to be welded and the filler material lies within the concentration interval of 1 wt.% and 2 wt.% carbon, the filler material being added in the form of a foil. [2] Weld according to claim 1, characterized by that the weld contains austenitic microstructural components. [3] Weld according to claim 1 or 2, characterized by that the carbon content of the weld is between 1.25 wt.% and 1.75 wt.%. [4] Weld according to claim 3, characterized by , that the carbon content of the weld is between 1.4 wt.% and 1.6 wt.%, in particular 1.5 wt.%. [5] Weld according to any one of the preceding claims, characterized by that the seam width is between 0.2 mm and 2 mm. [6] Weld according to claim 5, characterized by that the seam width is between 0.5 mm and 2 mm. [7] Weld according to any one of the preceding claims, characterized by that the materials to be welded are cast iron and structural steel or heat-treated steel. [8] Weld according to any one of the preceding claims, characterized by that the materials to be welded are two heat-treated steels. [9] Arrangement of two metallic components (100, 102) which can be joined by a weld (2) according to one of the preceding claims, wherein in a joint area (104) between the first (100) and the second component (102) an additional material (106) in the form of a film is inserted between the first (100) and the second component (102). [10] Arrangement according to claim 9 characterized by , that the first (100) and the second component (102) in the joint area (104) each have at least one edge (108, 110) which is chamfered at an angle of 45°, the chamfered area extending over a length of 0.2 to 0.4 mm. [11] Arrangement according to claim 10, characterized by , that the filler material (106) in the form of a foil protrudes by 0.4 to 0.6 mm beyond a surface (112) of the first and / or the second component, and protrudes by a distance of 0.6 to 1 mm beyond a lower edge (114) of a chamfered area of ​​at least one of the components.

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