WO2010086146A1 - Method for joining at least two metal components - Google Patents

Abstract

A description is given of a method for joining at least two metal components involving the introduction of thermal energy to form a welded region connecting the two components to each other, in the form of a weld seam and/or a weld spot. The invention is characterised in that, before the thermal energy is introduced, at least one component undergoes a plastic deformation in a region of the component that is directly adjacent to the welded region forming during the course of the introduction of thermal energy, resulting in the introduction of flaws within the metallic microstructure of the respective component that are starting points for recrystallization processes initiated by the introduction of thermal energy during the subsequent welding operation.

Description

 Method for joining at least two metallic components

Technical area

The invention relates to a method for joining at least two metallic components by thermal energy input for forming a welding area connecting the two components in the form of a weld seam and / or a spot weld.

State of the art

The load limits of components consisting of metallic materials are essentially determined by the microstructure of the materials, their residual stresses and their structural design. If two components made of metallic materials are joined together by means of thermal energy input to form a weld joint in the form of a weld and / or a welding point, the strength of the joint connection also depends on the quality of the so-called heat-affected zone forming during the welding which corresponds to that component region which in each case directly adjoins the weld seam or at the welding point and undergoes a metallographically visible influencing of the structural state in the metallic material due to the thermal energy input. The properties of the formed by the welding process heat affected zones are essentially determined by the nature of the base material and the amount of heat input and the dependent thereon thermal heating and Abkühlverläläufen that the respective structural areas of the base material during the thermal energy input or during Thus, the extent of the changes to the metallic material within the heat affected zone depends on many factors, such as the welding parameters, the component dimensions, the geometry of the weld area, for example the width, depth and shape of a weld concerning the residual stress states of the components involved in the joining process, and of the chemical compositions of both the component material as well as the additional materials required for the joining process.

In particular, as a result of the high input of thermal energy within the joining region for the formation of a melt, a pronounced grain growth often develops in the material areas of the components involved close to the melting point. However, as the grain size of the metallic structure of the so-called "coarse grain zone" forming within the heat-affected zone increases, the mechanical quality values, such as toughness, become significantly less favorable the heat-affected zone and thus the component behavior in the joined state can be adversely affected, whereby just those immediately adjacent to the welding area component area is a starting point for failure of the entire welded joint.

In order to meet this known, problematic phenomenon of the formation of a coarse grain zone weakening the welded joint within the heat-affected zone, different efforts have hitherto been made. One possibility is to optimize the welding parameters, in particular the dynamics as well as the amount of thermal energy deposited in the welding area. However, the optimization of the welding parameters with respect to the formation of the heat affected zone clear limits set, especially as an exclusive focus on the optimization of the selection of welding parameters, eg. With the aim of forming a spatially smallest possible and fine-grained heat affected zone, others for the training of Welding connection would completely ignore important aspects. So it is the welding parameters also with regard to a maintained geometry of the weld area, vote on any existing residual stress and distortion in the respective components to be joined together as well as on the most error-free weld metal, just to name a few joining technology relevant aspects.

Another alternative to meeting the formation of a quality of the welded connection detrimentally affecting heat affected zone is the thermal treatment of the welded joint. Thus, with the help of the heat affected zone tuned annealing process may well under certain conditions, for example, a subsequent reduction in residual stress in the heat affected zone, however, affect it associated annealing temperatures inevitably also the strength properties of all other areas of the welded joint, such as the weld metal, which are adjacent to the coarse grain zone remaining areas of the heat affected zone and adjacent to the heat affected zone metallic material of the component. In addition, a thermal aftertreatment lead to distortion of the respective components, to a scaling of the component surfaces and to a change, usually in the form of a decrease in the strength properties of the components. Grain refining within the coarse grain zone of the heat affected zone is not possible in this way or only to a very small extent.

In addition, attempts have been made by the coarseness caused structural weakening within the heat affected zone by a To reduce mechanical mechanical treatment or eliminate, for example by means of shot blasting, hammering, rolling or the like in the heat affected zone. Such measures lead to plastic deformation and a concomitant near-surface solidification of the component material and to the formation of residual compressive stresses. However, the latter are often degraded by fatigue operations when the assembled components vibrate. However, such a mechanical aftertreatment can by no means significantly reduce the coarseness within the heat-affected zone.

The above-mentioned problem occurring in particular in welded joints can, of course, fundamentally be avoided by using alternative joining methods, such as clinching, riveting or gluing, but other disadvantages are associated with these alternatives, such as, for example, much lower joining strengths, higher weight according to necessary material overlaps of two components etc.

It remains therefore to be noted that so far no satisfactory measures are known with which a weakening due to the formation of the coarse grain zone described above within the heat affected zone can be effectively counteracted in welded joints between metallic components.

Presentation of the invention

The invention is based on the object of specifying a method for joining at least two metallic components by means of thermal energy input for forming a weld region connecting both components in the form of a weld seam and / or a weld point such that a connection weakening is based on a coarse grain zone forming within the heat affected zone , is to be effectively countered. The measures to be taken in this case should weaken neither the components nor the forming joint compound, but it is a grain refinement in the Joining joint weakening coarse grain zone within the heat affected zone to bring about.

The solution of the problem underlying the invention is specified in claim 1. The concept of the invention advantageously further features are the subject of the dependent claims and the further description with reference to the exemplary embodiments.

The method according to the invention is based on a grain refining in metallic materials by a conversion-related grain new formation or a grain new formation by recrystallization. Thus, it has been recognized in accordance with the solution that a uniform grain structure adapted to the metallic base material of the respective component is obtainable in the critical region of the coarse grain zone of the heat affected zone, if the heat affected zone, and in particular the coarse grain zone, ie. H. that component region immediately adjacent to the melting region forming in the course of the thermal joining process is plastically deformed prior to the thermal energy input.

By a targeted plastic deformation of forming in the way of the thermal energy input heat affected zone defects within the metallic structure of the respective component are introduced, which in turn are starting points for Rekristallisationsvorgänge that are triggered by the thermal energy input in the subsequent welding process. Between the plastic deformation and the welding process, no additional heat treatment is interposed. The recrystallization processes result in grain remodeling with a much smaller grain size than is the case in the case described above for the coarse grain zone within the heat affected zone which forms in conventional welding techniques, above all gas welding, arc welding, inert gas welding or resistance welding. The plastic deformation, which can preferably be brought about by processes such as shot blasting, hammering or laser shock treatment, but also in the context of a mechanical processing of the parts to be joined parts, for example. By means of bending, grinding, milling, etc., can be performed limited in the sense of the sense exclusively on those part of the area that is detected by the thermal energy input and within which the metallic material of the component undergoes a metallographically visible influence on the microstructure state.

If, for example, it is necessary to connect two rod-shaped components along their end faces by means of a welding operation, the heat-influencing zone forming by the welding process extends in each case orthogonally to the end face into the interior of the component. For an effective plastic deformation of this component area, it is the end face of a surface plastic deformation, for example, to undergo by way of a shot peening process and this with a depth effect that corresponds at least to the depth of the coarse grain forming zone. In the case of the above-described rod-shaped components thus the surface treatment takes place exclusively along the end faces of both components.

On the other hand, if, for example, it is necessary to add two sheet-like components in overlap by welding, the plastic deformation upstream of the welding process takes place exclusively at the overlapping surface areas of both components to be joined.

An optimization with regard to the selection of the component areas which are to be subjected to plastic deformation and the expression of the depth effect associated with the plastic deformation is determined in preliminary tests on the respective component or component-like samples depending on the respective materials and the welding techniques used. Thus, it is necessary to perform the plastic deformation on the corresponding component areas in such a way that the entire surface layer of the component, which corresponds to the coarse grain zone forming in the course of the welding process, is detected decrease the crystallographic defects within the metallic microstructure caused by the plastic deformation with increasing component depth in terms of their severity and number. In this way, the refinement contributing effect due to recrystallization processes is provided with a gradient, so that the expression of the refinement concentrates on the particularly vulnerable region near the melting region, for example in the form of a fusion seam or a melting point, and As a consequence, the effect of the refinement decreases with increasing distance to the welding area, so that the component areas not affected by the heat input do not experience any crystallographic irritations due to flaw formation.

Only by means of the solution-based, locally limited, mechanical pretreatment of the component in the region of the heat-influencing zone forming by way of the thermal joining process can it be ensured that a largely continuous adaptation of the grain size forming within the heat-affected zone to the grain size of the thermally uninfluenced metallic material of the respective component will be produced. Preferably, the plastic deformation of the component is carried out at room temperature or temperatures below room temperature. Basically, however, that the temperature level in the plastic deformation of the respective component area should be below the softening temperature of the metallic material of the component.

To illustrate the komverfeinenden effects that can be achieved with the method according to the solution, reference is made to an illustrated in Figures 1 and 2 embodiment. To demonstrate the grain-refining effect associated with the pretreatment for a weld joining process according to the invention, tests were carried out on round specimens of a 23MnB4 steel. On the round samples, of which a pictorial representation of a round sample 1 is shown in FIG. 1, welding spots 2 were applied by means of a welding laser. Subsequently, the microstructure of the heat affected zone of these welds was examined metallographically. One of the round samples was plastically deformed at 8 bar before spot welding on the surface by means of shot peening with glass beads of grain size 70 to 100, a second sample was provided with a spot weld in the undeformed starting state.

FIG. 2 shows the result of the metallographic investigations in the region of the heat-affected zone HZ and the basic structure 3 of the metallic material of the round sample which adjoins on the right in each case. The heat affected zone WEZ is marked in each case by two lines. In the left-hand pictorial representation in FIG. 2, the micrograph of an undeformed weld sample is shown, whereas the right-hand illustration in FIG. 2 illustrates the micrograph of a sample prepared in accordance with the solution. In both cases, it is assumed that the respective left edge of the microstructure corresponds to the edge region of the weld region.

In the micrographs, the line-shaped transformation into bainitic-martensitic microstructure in the heat-affected zone is recognizable in both cases. In the case of the untreated round sample (left-hand micrograph according to FIG. 2), the lines of the uninfluenced basic microstructure 3 of the metallic material are exactly imaged within the heat-affected zone WEZ and appear macroscopically significantly coarser. In contrast, in the solution-pretreated round sample according to the right-hand micrograph image within the rows of the basic structure 3 within the heat-affected zone WEZ grain new formations and thus grain fines become visible. Macroscopically, the appearance within the heat-affected zone WEZ is finer than the line structure of the thermally uninfluenced basic structure of the metallic material of the round sample.

With the method according to the solution, a number of important advantages thus arise. Structural improvement of the heat affected zone by reducing the grain size in the coarse grain zone of the heat affected zone of welded joints. This results in better mechanical properties of the entire welded joint by avoiding caused by the coarse structure structural weakening of the heat affected zone.

Avoidance of the need for thermal aftertreatments, which can negatively affect all areas of the welded joint (weld metal, base material of the component, other HAZ zones).

Easy to carry out pre-treatment, even of large components that can not be subsequently heat treated.

Preservation of the optimized properties even with oscillating stresses or after high degrees of deformation.

The possibility of additional mechanical and thermal treatment remains intact.

LIST OF REFERENCE NUMBERS

WEZ heat affected zone

1 round sample

2 welding point

3 basic structure

Claims

claims 1. A method for joining at least two metallic components by means of thermal energy input for forming a two components interconnecting welding area in the form of a weld and / or a weld point, characterized in that at least one component before the thermal energy input in a directly to the in the way the thermal energy input forming welding area adjacent component area undergoes a plastic deformation are introduced through the defects within the metallic structure of the respective component, the starting points for recrystallization processes are triggered by the thermal energy input in the subsequent welding process. 2. The method according to claim 1, characterized in that the plastic deformation takes place by one of the following processes or by a combination of these processes: shot peening, hammering, rolling, laser shock treatment, mechanical surface processing with or without local material removal, such as grinding, milling or folding. 3. The method according to claim 1 or 2, characterized in that the plastic deformation is carried out exclusively in the component area corresponding to a detected by the thermal energy input area, the so-called heat affected zone, within the metallic material of the component a metallographically visible influence on the microstructure state experiences. 4. The method according to any one of claims 1 to 3, characterized in that the plastic deformation is performed such that form within the metallic material of the component defects in the metallic microstructure. 5. The method according to claim 4, characterized in that the plastic deformation is performed such that the number and the expression of crystallographic defects from the surface of the component decrease with increasing component depth. 6. The method according to any one of claims 1 to 5, characterized in that the degree of plastic deformation with respect to a component surface deformation and an associated extending into the component depth effect selected depending on the metallic material of the component and the type and amount of thermal energy input becomes. 7. The method according to any one of claims 1 to 6, characterized in that the plastic deformation is carried out at temperatures below the softening temperature of the metallic material, in particular at room temperature or at temperatures below room temperature.