Methods for forming-induced weld treatment

Abstract

Method for forming-induced weld treatment during gas metal arc welding with filler material for joining components, wherein a forming process of the weld (S) is carried out after the welding process by utilizing the heat input introduced during welding, characterized in that during the cooling of the weld, both the weld and the areas of the base material of the components (1) adjacent to the weld on both sides are subjected to forming, wherein the forming after welding is carried out at a temperature above the recrystallization temperature, so that a fine-grained microstructure is formed both in the weld down to a weld root and in the adjacent base material of the components (1) which was exposed to the welding temperature, wherein the forming is carried out by rolling and the weld of the planar weld is flattened by the rolling.- wherein the components (1) are longitudinally welded and are fed in a horizontally extending plane x / z via a transport device (2) in the form of a roller conveyor in the x-direction = feed direction to a welding and forming unit (3), which has a welding nozzle 4 and a forming unit (5), wherein the forming unit (5) has a substantially U-shaped upper frame (6) on which an upper work roll (7) and an upper support roll (8) arranged above the upper work roll (7) are each rotatably mounted about a horizontal axis and the work roll (7) is driven by means of a drive and the support roll (8) only rotates with it and - wherein the welding nozzle (4) as well as the upper work roll (7) and the upper support roll (8) are arranged height-adjustably on the upper frame (6) - and the welding nozzle (4) is attached to the upper frame (6) via an arm (4.1),wherein the arm (4.1) is bent at its lower region towards the upper work roll (7), so that a distance (a) between the welding nozzle (4) and the forming area of ​​the upper work roll (7) is maintained, and shielding gas and the electrode of the welding nozzle (4) are supplied via the arm (4.1), and wherein a lower frame 9 is arranged below the components (1) formed as sheets and aligned with the upper frame (6), which has a lower work roll (10) that rests against the underside of the components (1) and is supported by a lower backup roll (11), and wherein the outer diameter of the upper and lower work rolls (7, 10) is selected to be smaller than the diameter of the upper and lower backup rolls (8, 11), so that the welding nozzle (4) can reach as close as possible to the upper work roll (7).- wherein, by a feed movement of the components (1) in the x-direction under the work roll (7), the weld seam is leveled from a thickness (b1) to the sheet thickness (b), whereby an excess of material of the weld seam (S) is also displaced laterally, and thereby the area of ​​the components (1) adjacent to the weld seam on both sides is subjected to a deformation and structural change, and a structural change is produced in the weld seam (S) up to its weld seam root by the acting deformation.

Description

[0001] The invention relates to a method for forming-induced weld treatment according to the preamble of claim 1.

[0002] In the steel processing industry, the joining of sheets and other geometric components with suitable chemical, metallurgical, and physical properties is achieved, for example, through welding. This creates a permanent bond between two or more components, with welding fulfilling the specification of "creating an inseparable joint." The joining of the loose components is accomplished by applying heat and / or pressure, with or without filler material. Depending on the initial geometry and material, different welding processes are used. In most cases, the joining zone is partially liquefied, and if filler material is used, the material itself is also liquefied to achieve material cohesion. All welding processes involve heat input, which, especially in steel, leads to a transformation / change in the microstructure at the weld seam.In welded joints, the base material and the filler material differ in their chemical composition. In the molten state, the two materials mix to form a new steel composition. Depending on the welding process, a characteristically large heat-affected zone develops, marked by a significant temperature gradient. Gas welding, compared to arc welding, heats a much larger area of ​​the workpiece. This requires a greater amount of heat to be introduced into the workpiece, which consequently cools down more slowly. During solidification of the weld pool, in addition to the high temperature gradient (superheating of the weld pool) caused by the energy input from the heat source, rapid cooling rates also occur, leading to an irregular distribution of the microstructure (segregation and dendrites).The resulting "weld structure" thus resembles a globular cast structure, and the formation of the solid phase originates from nucleation followed by nucleation. The temperature-affected zone influences not only the weld properties but also those of the base material. Depending on its distance perpendicular to the weld bead, recrystallization phenomena, grain coarsening, porosity, or other microstructural alterations occur, leading to undesirable changes in strength (hardness sag). The joint therefore exhibits overall poorer fatigue strength properties than materials with a nearly constant / homogeneous microstructure. The areas with the greatest microstructural differences are the partially melted zone during welding and the coarse-grained zone.The first zone, only a few micrometers in size, adjoins the weld bead immediately, and depending on the alloy composition, impurities, and gases in the base material, these areas are most prone to melting. The subsequent zone is characterized by a very coarse-grained microstructure. Depending on the chemical composition of the base material, the coarseness of the grain increases, and the higher the carbon content of the steel, the greater the risk of hardening in this area, which in turn can lead to a loss of toughness and embrittlement.

[0003] Sheets, profiles, or other semi-finished products manufactured using forming processes possess a typical formed microstructure with grains of varying sizes. When these are welded, the welding filler material melts, resulting in a cast structure with more or less well-developed dendrites (depending on the cooling rate). In subsequent processing stages leading to the finished part, or when the welded component is subjected to stress in its operating environment, this microstructural difference can trigger potential material failure because the two microstructures exhibit diverse and significantly different mechanical properties (e.g., elongation, tensile strength). These phenomena are often further obscured by slag residues, oxides, and pores. As previously mentioned, the nature of the physical processes varies between different welding methods.Most untreated weld structures fail in the heat-affected zone because very coarse grain is present there, resulting in low strength. This invention disclosure relates to remelting welding processes, which differ in their method of electrode melting. In metal inert gas (MIG) welding, for example, a gas discharge, which ultimately leads to the formation of an electric arc, melts the filler material in the form of a wire. Depending on the shielding gas used, MIG welding can be classified as either MAG welding (using an active gas, e.g., CO2) or MIG welding (using an inert gas, e.g., Ar, He).In both processes, it is essential that the shielding gas supply with the required volume flow and the wire feed are coordinated to avoid side effects. Currently, the coexisting processes of welding and forming are combined by adjusting suitable process parameters. Both processes are characterized by different features, each of which influences the quality of the semi-finished products. It is already known from the literature that subsequent forming positively influences the mechanical properties.

[0004] From a technological perspective, the potential of conventional welding processes to improve service life is almost exhausted, which is why increasing research is now being conducted on weld post-treatment (targeted microstructure modification). For example, higher-frequency hammer blows can generate surface hardening and forming-induced compressive residual stresses, resulting in an increase in the stress range for the same number of load cycles. However, in this case, the forming of the weld does not occur immediately after the weld is formed. This is a cold working process that may require further thermal post-treatments (e.g., recrystallization annealing, etc.) and thus lengthens the process chain. The energy required for the final heating step incurs additional costs and is negatively impacted with regard to the overall resource efficiency of the process.

[0005] For example, it is known from German patent application DE 1 515 222 A to weld two components together in an overlapping area and then process them in a cold state by hammering or flattening. The flattening rollers also act on opposite surfaces of the overlap. This is intended to create a weld seam whose thickness corresponds to the thickness of the base material and which is free of waviness and distortion in both the weld zone and the surrounding material. However, in this process, in addition to the joined / chamfered base material, the material undergoes direct deformation. Therefore, after flattening, different microstructural features with varying mechanical properties are present in the component, which can only be homogenized by heat treatment.Resistance welding is also used, in which no filler material (a different material compared to the base material) is melted to join the components or semi-finished products.

[0006] In the publication DE 10 2010 033 929 A1, a welded joint of pipes is disclosed in which a seam post-treatment is also carried out in the cold state by hammering.

[0007] A disadvantage of this solution is the necessary heat treatment to initiate recrystallization processes in the cold-formed area and to relieve residual stresses. This process is not only time-consuming and expensive, but also reduces the mechanical properties due to grain coarsening in the base material.

[0008] German patent application DE 2 205 299 A describes a weld production process in which the weld metal is deformed during cooling by means of a welding forming process based on gas metal arc welding (GMAW) or submerged arc welding (SAW). The weld metal is deformed in one or more stages during cooling within a temperature range of 600–950 °C, preferably at 700–850 °C, by rolling, forging, drawing, or pressing. This is intended to remove the notches in the weld transition that affect the mechanical properties and to create a fine-grained microstructure, which, among other things, exhibits improved toughness.

[0009] A disadvantage is the required large weld cross-section. Another drawback is that the deformation only occurs in the weld area up to the weld notch. Too much heat is lost due to the distance between the welding nozzle and the deformation zone. Combined with the recommended deformation of a maximum of 50% (ideally less, but repeated several times), this prevents dynamic recrystallization from taking place in the areas of the heat-affected zone (HAZ) and the weld (including the weld root). Consequently, either the microstructure is not uniformly fine-grained, or a final heat treatment would be necessary to force recrystallization.

[0010] A method for thermally joining at least two metallic components is disclosed in German patent application DE 10 2009 006 304 A1. In this method, the components to be welded are plastically deformed by means of a mechanical pretreatment before the thermal energy input.

[0011] A disadvantage is that cold forming of the heat-affected zone (HAZ) is necessary before the actual joining process to force recrystallization in the HAZ through the welding heat during joining. Forming does not occur after the thermal energy input, which could result in the weld microstructure becoming a fine-grained material.

[0012] Solutions are also known in which a component is processed by weld overlay, whereby several weld layers are applied to a single component.

[0013] For example, DE 10 2011 087 A1 describes such a process in which, prior to the application of a new weld layer, the previously applied weld layer is at least partially plastically deformed by a forming process, thereby producing a fine-grained microstructure. The temperature of the weld layer during the forming process, which immediately follows the welding process, is preferably between 600°C and 800°C, so that the solidified molten material has not yet completely cooled. The forming process is preferably carried out using hammers, punches, or rollers. The disadvantage of this process is that it is a multi-layer welding process. Furthermore, the first weld layer is partially deformed (leading to low degrees of deformation), and only the heat from the subsequent weld layer is used to initiate recrystallization processes in the deformed first weld layer. Thus, the final layer does not undergo any recrystallization processes.

[0014] The object of the invention is to develop a method for forming-induced weld treatment with which, after gas metal arc welding, the weld seam and the base material in the heat-affected zone are improved with regard to their mechanical properties by direct forming.

[0015] This problem is solved by the characterizing features of the first patent claim.

[0016] Advantageous embodiments are set forth in the dependent claims. The method for forming-induced weld treatment is carried out particularly in welding with filler material for joining components, wherein, after the welding process, a forming treatment of the weld (also referred to as weld bead) is carried out by utilizing the heat input introduced during welding, and according to the invention, during the cooling of the weld, both the weld and the base material adjacent to the weld on both sides are subjected to a forming process.

[0017] The deformation of the weld seam and the area of ​​the base material adjacent to the weld seam is carried out after welding at a temperature above the recrystallization temperature, so that a fine-grained structure is formed both in the weld seam (up to the weld root) and in the adjacent base material of the components, which was exposed to the welding temperature.

[0018] The temperature should be at least 0.5 times, and in particular 0.6 times, the melting temperature of the base material, preferably 1000°C to 1100°C, particularly preferably 1050°C, e.g., for steel alloys, or preferably 850°C to 950°C, particularly preferably 900°C, e.g., for titanium alloys, at least in the area of ​​the weld seam and in the area of ​​the components adjacent to the weld seam (heat-affected zone) during the forming process following the welding process.

[0019] If the weld seam and the adjacent component material have cooled down too much between welding and forming, it is possible to additionally heat the component, at least in the weld seam area and the area adjacent to the weld seam, to a temperature above the recrystallization temperature. This can be achieved, for example, with an additional heating device (such as inductive heating) between the welding position and the forming position.

[0020] The forming process is preferably carried out by rolling, whereby the rolling process flattens the weld seam in the case of flat welds and provides a concave radius in the case of angled designs.

[0021] The process is preferably used for welding pipes, profiles or sheets, with gas metal arc welding being the preferred welding method.

[0022] With the solution according to the invention, it is possible to improve the mechanical properties of both the welds after metal inert gas welding and the base material in the heat-affected zone by direct deformation (utilizing the heat input) during the cooling of the weld bead. In the case of fillet welds, in addition to any welding defects, the notch effect and the existing hardness drop in the heat-affected zone are a decisive cause of failure, which is why a modified roller is used to create a rounded shape during hot forming. When joining heavy plates, the focus is primarily on leveling the weld bead and influencing the heat-affected zone through recrystallization.

[0023] This process is fundamentally of interest to steel construction companies with long welding lengths, e.g., in shipbuilding, heavy machinery manufacturing, beam and profile welding, structural engineering, bridge construction, large-diameter pipes, and pipeline construction. Advantages of the invention over current methods include the improvement of the weld structure with regard to strength and toughness properties (conversion from cast to formed structure) and the reduction of notch effects through optimized radius formation, thus increasing operational reliability. The tailored blanks can be dimensioned differently because the notch effect, which leads to over-dimensioning, can be minimized, making smaller and / or thinner welded structures conceivable for essentially similar component strengths.The increased efficiency achieved by eliminating necessary heat treatment measures shortens the process chain while simultaneously resulting in a more optimal property profile, representing a resource-saving feature. This new process, which can be used both during pre-assembly in automated welding processes and during on-site assembly, flattens the weld seam and, in the case of sheets joined at an angle, adds a radius (transforming the convex weld geometry into a concave one). This significantly reduces the notch effect in the joining zone, and additionally, the inhomogeneous microstructure in the heat-affected zone can be transformed into a fine-grained structure through recrystallization processes, resulting in improved mechanical properties. Possible welding processes include, among others...Gas welding processes are used for large cross-sections because the welding heat can remain in the material for a relatively long time, making hot forming easily achievable. Furthermore, this method results in little martensite formation, as cooling is slow in large volumes and thermal distortion is minimized. This reduces the need for additional heat treatment to homogenize the microstructure. In Germany, approximately 8% of annual steel production (equivalent to [missing information]) is produced using this method. Compared to seamless pipes, welded tubes offer the advantages of high dimensional accuracy (low to no eccentricity), very high surface quality, and thin walls (strip material as a semi-finished product), which is why many longitudinally welded precision tubes are used in the automotive industry.Currently, welded pipes made of unalloyed to low-alloy steels undergo multiple heat treatments and partial hammering after bending (U-0 bending of strips) and welding to ensure homogenization of the microstructure (coarse-grained structure with low strength) throughout the pipe and leveling of the weld reinforcement. This is intended to guarantee that these pipes can be further processed by drawing to final dimensions without damaging the drawing tools or the pipe itself due to differing cross-sectional geometries or brittle material properties. Alternatively, the currently used thermo-mechanically treated sheets with higher base strengths could be replaced, as the weld seam on these sheets requires subsequent cold forming (hammering, shot peening) for leveling, a process that also induces residual stresses through cold working.The new process utilizes a combination of welding (preferably a welding process with higher heat input, such as gas welding) and hot forming, thus shortening the process chain, which is primarily intended for the production of large-diameter pipes. In the solution according to the invention, leveling and microstructure homogenization through recrystallization effects (uniform grain sizes across the entire pipe cross-section) occur not only in the weld area but also in the base material adjacent to the weld, utilizing the heat from the welding process. This eliminates, among other things, the energy- and time-intensive heat treatments previously required under the prior art. The large-diameter pipes produced in this way can be directly processed or finished.Additionally, any defects that may occur in the weld (micro-voids or pores) are sealed and eliminated by the hot forming process, thus preventing the need to reject pipes previously rejected due to leakage problems and significantly reducing the scrap rate. Due to the high heat input and sufficiently large dimensions, the formation of weld martensite is avoided, making further heat treatment for microstructure and property homogenization unnecessary.

[0024] The invention is explained in more detail below with reference to exemplary embodiments and accompanying drawings. These show:

[0025] Fig. 1 a three-dimensional representation of a system for carrying out the process,

[0026] Fig. 2 a side view of the plant according to Fig. 1,

[0027] Fig. 3 a representation of the radius in the area of ​​the weld seam,

[0028] Fig. 4 A schematic representation in side view with positions AA and BB indicated.

[0029] Fig. 5 micrographs of the weld seam before and after forming.

[0030] In Fig. 1 is a three-dimensional representation and in Fig. 2 A side view of a system for carrying out the process is shown, which here is used for the material-bonded joining of components. 1 It is installed in the form of two sheets of metal by longitudinal seam welding. The two sheets / components 1 They lie in a horizontally extending plane x / z and are transported via a transport device. 2 (only in Fig. (shown in 1) in the form of a roller belt in the x-direction = feed direction to the welding and forming unit 3 supplied. This has a welding nozzle. 4 and a forming unit 5 up. The forming unit 5 It has an essentially U-shaped upper frame6 , on which an upper work roller 7 and one above the upper working roller 7 arranged upper support roller 8 each is rotatably mounted about an unnamed horizontal axis, wherein the work roller 7 is driven by means of a drive not shown and the support roller 8 only runs with this one. The welding nozzle 4 as well as the upper work roller 7 and the upper support roller 8 are preferably height-adjustable on the upper frame 5 arranged.

[0031] The welding nozzle 4 is over an arm 4.1 on the upper frame 5 attached, with the arm 4.1 at its lower area towards the upper work roller 7 is bent, so that a relatively small distance a (preferably about 100 mm, especially less than 300 mm) of the welding nozzle 4 to the forming area of ​​the upper work roll7 is present. Over the arm 4.1 Shielding gas and the electrode (not shown) of the welding nozzle 4 supplied. Below the sheets / components 1 and aligned with the upper frame 5 is a lower frame 9 arranged, which is a lower working roller 10 exhibits features on the underside of the sheets / components 1 is located and is supported by a lower support roller 11 is supported.

[0032] It is also possible to use the lower working roller. 10 to drive, alternatively this can be achieved by the feed of the components. 1 also run along with it. Also the lower support roller. 11 runs with the lower working roller 10 with.

[0033] The outer diameter of the upper and lower work rollers 7 , 10 is chosen to be smaller than the diameter of the upper and lower support rollers 8 , 11, so that the welding nozzle 4 as close as possible to the upper working roller 7 can reach.

[0034] The highest point of the outer diameter of the lower work roller lies essentially at the level of the support of the transport device. 2 , so that the underside 1.1 the components on the lower work roll 10 is attached. The upper work roller 7 is the amount of the sheet thickness b of the components 1 from the lower working roller 10 spaced apart. The one with the welding nozzle 4 generated weld seam S, the height of which in the area in front of the work roll 7 a thickness b1 (thickness in the area of ​​the weld before forming) is observed, which is higher than the sheet thickness b (see. Fig. 2) is caused by the feed movement of the components 1 in the x-direction under the working roller 7through and is thereby leveled to the sheet thickness b, whereby the "excess material" of the weld seam S is also displaced laterally, and the area of ​​the components adjacent to the weld seam on both sides is subjected to deformation and thus to a previously described change in microstructure. A change in microstructure is also produced in the weld seam S, extending to its root, by the deformation. In the solution according to the invention, microstructure homogenization through recrystallization effects occurs by utilizing the welding heat in the area of ​​the weld seam and also in the base material adjacent to the weld seam. The temperatures of the weld seam and the base material heated by the weld seam (heat-affected zone) should be between 950 and 1150 °C, preferably 1050 °C, for steel materials, depending on the alloy composition, and at least the following temperatures for the base materials listed below.The temperatures mentioned above should preferably apply to all steels. However, it is also possible to apply the method to non-ferrous metals, although the temperatures must be chosen differently. In principle, a minimum of 0.5 times the melting temperature could apply, and in particular, a minimum of 0.6 times the melting temperature.

[0035] Fig. Figure 3 shows two components 1 , which were welded together at a 90° angle. The upper work roller 7 It tapers in diameter on both sides and has a radius in its middle. 7.1 up, so that the upper working roller 7 can flatten the weld seam S.

[0036] Fig. Figure 4 shows a schematic representation of the process flow in a side view with sections AA after welding with the weld seam S and before forming, and BB after forming and flattening the weld seam S down to the thickness b of the welded components. 1using an upper working roller 7 and a lower working roller 10 .

[0037] In Fig.Figure 5 shows the micrographs of the weld seam in the area of ​​positions AA and BB. In the area of ​​position AA, Figure 1 (top left) shows the microstructure of the weld seam in the surface area, and Figure 2 (bottom left) shows the unformed weld seam microstructure in the core area. It is evident that the microstructure of the unformed weld seam is cast-like, both on its surface and in its core (root) area. Figure 3 (top right) shows a micrograph of the formed weld seam microstructure in the surface area from position BB, and Figure 4 (bottom right) shows a micrograph of the core area of ​​the formed weld seam. It is evident that in position BB, and thus after forming the weld seam, a far-grained microstructure is present.

[0038] The size or dimensioning of the weld seam and the degree of deformation to be achieved by rolling, which also ensures deformation of the material of the component areas adjacent to the weld seam, is determined, for example, in preliminary tests. Reference symbol list 1 component 2 Transport device 3 Welding and forming unit 4 welding nozzles 5 Conversion unit 6 upper rack 7 upper work roller 7.1 Radius 8 upper support roller 9 lower rack 10 lower work roller 11 lower support roller a distance b sheet thickness b1 Thickness in the area of ​​the weld before forming S weld seam QUOTES INCLUDED IN THE DESCRIPTION

[0039] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0040] DE 1515222 A

[0005] DE 102010033929 A1

[0006] DE 2205299 A

[0008] DE 102009006304 A1

[0010] DE 102011087 A1

[0013]

Claims

[1] Methods for forming-induced weld treatment, especially in welding with filler material for joining components, wherein a forming treatment of the weld seam / weld bead is carried out after the welding process by utilizing the heat input introduced during welding, characterized by that during the cooling of the weld, both the weld and the base material adjacent to the weld on both sides are subjected to deformation. [2] Method according to claim 1, characterized by that the deformation of the weld seam and the area of ​​the base material adjacent to the weld seam takes place after welding at a temperature above the recrystallization temperature. [3] Method according to claim 1 or 2, characterized by that between welding and forming, the component is heated to a temperature above the recrystallization temperature. [4] Method according to any one of claims 1 to 3, characterized by that the temperature during forming is at least 0.5 × the melting temperature of the base material of the components. [5] Method according to any one of claims 1 to 4, characterized by that the forming process is carried out by rolling. [6] Method according to any one of claims 1 to 5, characterized by that the rolling process flattens the weld seam in the case of flat welds and provides a concave radius in the case of angled designs. [7] Method according to any one of claims 1 to 6, characterized by that it is used for welding pipes, profiles or sheets, [8] Method according to any one of claims 1 to 7, characterized by that a gas metal arc welding process is used.

Images