Publications
Here you will find publications written and published by us on the subject of welding. If you have any questions about the respective publications, please do not hesitate to contact us.
Published May 2023
Abstract:
Title: 32nd Welding Technology Conference : May 11, 2023, Barleben Editor: Zinke, Manuela Schasse, René Kassawat, Adam Publication date: 2023 Type: Book Language: German Publisher: Otto von Guericke University Library, Magdeburg, Germany URN: urn:nbn:de:gbv:ma9:1-1981185920-1038840 Keywords: welding weld seam testing pollutants buildup welding cast iron repair Abstract: With exciting topics from welding and joining technology, the 32nd Welding Technology Conference will take place on May 11, 2023. May 2023, the 32nd Welding Technology Conference will be held as a joint event of the DVS District Association Magdeburg, the In-stitute for Materials and Joining Technology of the Ottovon Guericke University Magdeburg and the Welding Technology Training Institute Magdeburg. In steelmaking, the excess carbon is removed from the pig iron in hand by "freshening" it, formerly with air, nowadays usually with oxygen. Regardless of which process is used, both in the historical wind-freshing process and in the LD process, which represents the current state of the art, the oxygen forms a chemical compound with carbon and leaves the pig iron as CO or CO2 . Perhaps the discussion about the CO2 footprint and the increasing environmental awareness in general is helping to ensure that cast iron, which had in the meantime been regarded as "obsolete," is increasingly enjoying a renaissance as a material. It is well known that cast iron has a carbon content that is around 15 times greater than that of steel. This carbon is therefore bound and does not leave the pig iron during refining as the resulting CO or CO2 in the blast furnace in the direction of the atmosphere. [1] The fact that cast iron is used in modern components as a highly stressed structural material is shown, for example, by its use in Mercedes truck axles [2], in which cast iron is welded to steel, or in commercial vehicle construction in the "Flux 30" multi-way sideloader from Hubtex [3], in which the entire frame consists of a cast iron component. It is particularly worth mentioning that, in addition to the environmental aspect, the shorter process route of material production and vehicle manufacture (elimination of cutting, forming and joint welding work steps compared with a pure welded structure made of mild steel) results in economic advantages. The symbiosis of environmental and economic advantages of these industrial examples show why cast iron continues to be used as a modern material and why production and repair welding on cast iron must therefore also be constantly re-examined and re-evaluated from the current state of materials and process technology.
Authors: Dr. Django Baunack, Alexander Liehr, D. Janoschka, T. Niendorf
Published December 2022
Abstract:
SVS SCHWEIZERER VEREIN FÜR SCHWEISSTECHNIK: Schweisstechnik/Soudure magazine According to ISO 18265, hardness is a material parameter that can provide information about the mechanical properties of a material. Thus, if the hardness is known, statements can also be made about the structural condition of welds and heat-affected zones. https://www.svs.ch/de/unser-verein/fuer-unsere-mitglieder/vereinszeitschrift
Authors: Dr. Django Baunack, Christof Torrent, Alexander Liehr, T. Niendorf
Confirmed in tests and practice: Estimating material hardnesses for welders and welding supervisors
Published in December 2022
Abstract:
DVS Media; Der Praktiker; The magazine for welding technology and more Abstract: At the "DVS Congress" 2017, a new method for estimating the hardness of weld seam heat-affected zones was presented. Since this introduction, there have been repeated requests for practical presentations and queries about further areas of application. In a further study, the feasibility of using the hardness estimation method presented in 2017 with reference blocks for use on fine-grained structural steels in both the weld seam heat-affected zone and in the area of flame-cut edges was therefore examined. The article briefly introduces the method, briefly discusses the results of the new study and presents some practical examples.
Authors: Dr. Django Baunack, Alexander Liehr, T. Niendorf
www.derpraktiker.de Edition 12 (2022)
Confirmed in tests and practice: Estimating material hardnesses for welders and welding supervisors
Published in December 2022
Abstract:
Fachmagazin METALL; ÖSTERREICHISCHER WIRTSCHAFTSVERLAG Introduction: In welding technology, estimating the hardness of a material is of fundamental importance for both welders and welding supervisors, as it can provide information about the mechanical properties of a material. Derived from this, it is possible to make statements about the structural condition of weld seams and the heat-affected zone.
Authors: Dr. Django Baunack, Alexander Liehr, Christof Torrent, T. Niendorf
Estimation of material hardness for welders and welding supervisors
Published in September 2022
Abstract and Figures:
A new method for estimating the hardness of weld seam heat-affected zones was presented at the DVS Congress 2017 [1]. Since this introduction, there have been repeated requests for practical presentations and queries about further areas of application. In a further study, the feasibility of using the hardness estimation method presented in 2017 by means of reference blocks for use on fine-grained structural steels in the weld seam heat-affected zone as well as in the area of flame-cut edges was therefore examined. In this paper, the method is presented, the results of the new study are briefly described and discussed, and some practical examples are given. As is widely known, hardness is defined as the resistance of a body to the penetration of another, harder body. According to ISO 18265, this material parameter provides information about the local strength of a material. It also allows statements to be made about the structural condition of weld seams and heat-affected zones. For example, there are no known hardening cracks on steel weld seams whose heat-affected zone has a hardness lower than approx. 350 HV. Therefore, the maximum hardness of heat-affected zones for each material group (ISO 15608) is strictly limited in ISO 15614. If, for example, the maximum hardness values are exceeded on the test piece welded according to a preliminary welding procedure specification (pWPS), no certificate of qualification of the welding procedure (Welding Procedure Qualification Record, WPQR) can be issued by a corresponding testing body, as defects as a result of the welding cannot be ruled out. This article shows how the hardness can be estimated using the simplest means. The method presented uses a hardness comparison between the test piece and a reference piece of known hardness, based on the Mohs hardness test. This makes it possible, for example, to quickly and easily check whether the hardness of a supplied material is within the range of the ordered strength properties.
Authors: r. Django Baunack, Christof Torrent,Alexander Liehr, T. Niendorf,
Induction butt welding of black and white joints
Published in August 2022
Abstract:
It is shown that dissimilar welds (black and white welds) can be successfully welded with induction butt welding. The essential parameters for the quality of the welded joint are presented. Using a determined set of parameters, joints were produced whose mechanical properties corresponded to those of a welded structural steel. Hardness curves and microstructural images of the black and white joint were prepared and discussed. The residual stress curves offer the possibility to compare the trend between permeability, melting temperature and residual compressive stresses for any welded material pair.
Authors: Dr. Django Baunack, T. Niendorf, B. Scholtes
Influence of process variables in automated machining on the surface layer properties
Published in January 2022
Abstract:
About 80% of the components in machine construction are subjected to fatigued load. Components with inherent compressive residual stresses on the surface show the longest service lives under these stresses. Service life, compressive residual stresses at or at least below the surface are an important quality feature. A classic reason for the failure of shafts is a crack that spreads further and further, which finally leads to such a reduction of the cross-section that it leads violent fracture occurs. Shown is a fractured surface whose start of failure is at the machined surface. There is no other microscopically microscopically discernible microstructural defect in the interior. What parameters could have been changed during machine processing to prevent or at least delay this damage.
Authors: Dr. Django Baunack, Alexander Liehr, T. Niendorf
Cast iron repair: previously with nickel as an additive, now with bronze and using arc brazing?
Published in September 2021
Abstract and Figures:
Repair welding on cast iron can, as the welder says, be carried out "hot" or "cold". For a "hot" repair, a filler metal (SZW) is usually selected that largely corresponds to the base material. For a "cold" cast iron repair weld, a nickel-based filler metal is usually selected as the filler metal. [1] More recently, reports of successful cast iron repairs using MIG brazing can be read and heard online. [2, 3] A major problem with cast iron repair welding is possible hardening cracks. These are caused by the hardening that the weld metal undergoes during cooling when the carbon present as graphite in the base metal (cast iron) goes into solution. It is obvious that this problem could be avoided if the base material is not melted in the first place, as is usual in brazing. This problem does not exist to the same extent when repair welding with nickel-based SAW, as nickel can absorb significantly more carbon than iron or steel without hardening. With cast iron repairs in particular, however, it can happen that the optimum brazing or weld seam preparation has not taken place when grinding out a crack, for example, which can lead to the carbon melting and dissolving to an unintentionally high degree. This article shows the practical effects of the solubility of carbon in bronze, especially in aluminum bronze (the filler material for MIG brazing). A structure based on DIN 50129 and DVS data sheet 1004, which provokes high stresses in the weld seams due to self-loading, serves as a demonstrator. GJS600-3, i.e. cast iron with spheroidal graphite, was selected as the base material. The cast iron round specimens used were welded or brazed with a ferritic, a nickel-based SZW and a copper-based brazing filler as a reference. The results of the scope of testing (microfigures, hardness tests and EDX images) should show whether MIG brazing is generally superior to repair welding with nickel-based materials. https://www.dvs-media.eu/de/neuerscheinungen/4408/dvs-congress-2021-grosse-schweisstechnische-tagung-dvs-campus-inkl.-usb-card
Authors: Dr. Django Baunack, Wolfgang Zinn, Alexander Liehr, D. Janoschka, T. Niendorf
Published in September 2021
Abstract:
A representative case of damage to a welded construction made of high-strength fine-grained structural steel is presented. Such high production-related residual stresses were introduced that a component failed weeks after machining. As welding was carried out in the immediate vicinity, it was suspected that the welding had a significant influence on the cause of the damage. Such cases of damage are repeatedly investigated at the Institute of Materials Technology at the University of Kassel, where the cause of the damage is determined and remedial measures are developed. In order to make the material technology findings accessible to the public interested in welding technology despite confidentiality agreements, the circumstances were recreated. The identically occurring damage is presented as anonymized cases of damage. It is shown which test results (chemical composition, hardness curves, microfigures, etc.) can be used to draw conclusions about the cause of the damage, at which positions of a cold-formed (folded or round-rolled) sheet tensile or compressive residual stresses occur and under which circumstances a component can fail due to the induced tensile residual stresses. The aim of this article is to show ways of preventing such damage to your own components. In particular, it deals with the targeted elimination of residual tensile stresses and the introduction of residual compressive stresses in component areas close to the surface using the simplest manual means. Reference is made to current research results that were published in the previous DVS Congress (2020) [1] under the title "Residual stresses caused by hand-guided angle grinder machining with different grinding wheels (weld seam plastering)". These results are transferred to practice. https://www.dvs-media.eu/de/neuerscheinungen/4408/dvs-congress-2021-grosse-schweisstechnische-tagung-dvs-campus-inkl.-usb-card
Authors: Dr. Django Baunack, Wolfgang Zinn, Alexander Liehr, T. Niendorf
Published in May 2021
Abstract and Figures:
According to ISO 18265, hardness is a material parameter that can provide information about the mechanical properties of a material. If the hardness is known, it is therefore also possible to make statements about the structural condition of weld seams and heat-affected zones. For example, there are no known hardening cracks on steel weld seams whose heat-affected zone has a hardness lower than approx. 350 HV. Therefore, the maximum hardness of heat-affected zones for each material group (ISO 15608) is strictly limited in DIN EN ISO 15614. If, for example, the maximum hardness values are exceeded on the test piece welded according to a preliminary welding procedure specification (pWPS), no certificate of qualification of the welding procedure (Welding Procedure Qualification Record, WPQR) can be issued by a corresponding testing body, as defects as a result of the welding cannot be ruled out. For this reason, the hardness value is highly significant for the quality of a weld. As welding supervisors and welders rarely carry out regular hardness tests, it is often not possible to assess whether a hardness value is to be considered critical. In addition, both in vehicle and infrastructure technology (e.g. repairs to switches, rail joints, rail overlay welding, etc.), the increase in mobile applications with shorter time windows for decisions can increasingly be observed. This article shows how the hardness can be estimated using the simplest means. For this purpose, knowledge of the causes and positions of the hardness peaks to be expected on weld seams and the formation and associated dangers of hardness cracks is imparted. The method for estimating the hardness, which is explained in the article, uses a hardness comparison between the test piece of unknown hardness and a reference piece of known hardness, based on the Mohs hardness test. For this purpose, various everyday objects of comparison with known hardnesses are shown. By directly estimating the hardness, tests by testing laboratories on test pieces that are far outside the permissible range can be saved. The hardness of heat-affected zones on weld seams from the unregulated area, in which hardness tests by external testing laboratories are often dispensed with, can be estimated, thus reducing the risk of damage. Estimating the hardness of weld seams, as explained in this article, provides a hardness value that can be used to decide which further tests need to be carried out. Furthermore, this method is quick and uncomplicated.
Authors: Dr. Django Baunack, Alexander Liehr, Christof Torrent, T. Niendorf
Published in September 2020
Abstract:
Optimizing the mechanical properties of the weld root of a Laser Hyb-rid welded dissimilar joint by piercing the laser beam through the weld metal D. Baunack1, H. Picker2, A. Liehr1, T. Niendorf1, K. Grahner 1 University of Kassel, Institute for Materials Technology, 34125 Kassel 2 BPW Bergische Achsen Kommanditgesellschaft Ohlerhammer, 51674 Wiehl For joint welds on hollow steel profiles using laser hybrid welding, it is possible to adjust the laser power, the laser focus and the positioning in such a way that thermal energy is introduced on the opposite side of the hollow profile by means of the laser light and thus influence the temperature control of the welding process. With conventional methods, the energy input on the root side of the steel profile under investigation (round tube, diameter approx. 150 mm and wall thickness approx. 10 mm) is not possible due to accessibility. These process combinations therefore offer the possibility of carrying out a previously unknown process-integrated pre- and post-treatment of the heat-affected zone (HAZ). In this case, a mixed compound between an S355N and a BAH900+AR was investigated. G506MG2Ni2 was used as the welding filler material (SZW). It is well known that the strength of a construction material also increases its notch sensitivity, which is why the process-integrated pre- and post-treatment of the root is particularly relevant for future-relevant topics such as material substitution in terms of lightweight construction and resource conservation. This article uses the example of a welded truck axle to show which optimizations can be achieved using the piercing laser beam and what risks exist if the parameters are not selected accurately. The results of various radiographic residual stress (ES) measurements are presented. Among other things, a comparison of the residual stress curves measured with the new X-ray diffractometer µ-X360s from Pulstec (Debye ring, cos ) and measured with the (conventional) X-ray diffractometer X3000 from Stresstech (sin2 method) is made. This not only allows a statement to be made about the residual stress curve in the HAZ, but also provides comparative values for residual stress measurements with the new µ-X360s on weld seams. Furthermore, microstructural images and hardness curves through the HAZ are shown and discussed and the combined influence of notch (de)sharpening, hardness, microstructure and residual stress curve of the HAZ is explained.
Authors: Dr. Django Baunack, H. Picker, K. Grahner, Alexander Liehr, T. Niendorf
Published in September 2020
Abstract:
Residual stresses caused by hand-guided angle grinder machining with different grinding wheels (weld seam plastering) D. Baunack1, B. Alp2, W. Zinn1, A. Liehr1, T. Niendorf1 1 University of Kassel, Institute for Materials Technology, 34125 Kassel 2ULA Bebra Fahrzeuginstandsetzung GmbH & Co. KG , Kasseler Straße 28a, 36179 Bebra Hand grinding with an angle grinder is used in most specialist welding companies. Especially in welding companies with comprehensive quality requirements, it is known that the leveling of the weld seam elevation increases the fatigue strength of high-strength and therefore notch-sensitive materials. In everyday practice, this grinding is often carried out with hand-held angle grinders and fiber discs. In some machining processes (e.g. turning), the machining parameters can be selected so that the mechanical influence is greater than the thermal influence, allowing residual compressive stresses to be applied to the workpiece surface in a targeted manner. It is well known that the thermal influence usually predominates in uncooled grinding processes. This results in residual tensile stresses during hand-guided machining with angle grinders. The fatigue strength is negatively influenced by residual tensile stresses on the workpiece surface and positively influenced by residual compressive stresses. Furthermore, the residual stresses on the workpiece surface have a considerable influence on corrosion resistance. For example, tensile stresses on the surface are necessary for vibration corrosion cracking and stress corrosion cracking - two corrosion phenomena that are responsible for the majority of economic damage caused by corrosion. These types of corrosion cannot occur with compressive stresses on the surface. These examples show that the residual stresses caused by hand-guided angle grinder machining are not negligible. Nevertheless, there are only a few publications on which grinding wheels (roughing wheels, flap discs, fiber discs, wire brush attachments, etc.) and which grinding parameters (grinding direction, etc.) have which effect on the residual stresses that occur. As grinding wheels with tetrahedron-shaped abrasive media and very high removal rates (e.g. Cubitron II) have recently been increasingly used, the question arises as to whether the mechanical or thermal influence predominates in the generation of residual stresses in these grinding wheels, or which residual stresses occur in comparison to other types of grinding wheel. The presentation gives an overview of the residual stresses arising during manual grinding on structural steel with a special focus on the dependence of grinding wheel grain size and degree of wear on the residual stress formation. The residual stress depth curves were determined radiographically up to a depth of 80 µm in 10 µm steps and show how tensile residual stresses on the component surface can be avoided even with hand-guided angle grinder machining.
Authors: Dr. Django Baunack, Benjamin Alp, Alexander Liehr, Wolfgang Zinn, T. Niendorf
Published in January 2020
Abstract:
The present study focuses on induction butt welding of Fe–Mn–Al–Ni tubes. By comparing different processing routes, characterized by different temperatures and forces during welding, it was possible to find adequate process parameters for realization of defect-free joints. Moreover, it was feasible to fully reset the microstructure prevailing in the heat-affected zone by a subsequent cyclic heat treatment promoting abnormal grain growth. Tensile testing up to a maximum strain of 6% revealed excellent pseudoelastic properties of the final microstructural condition. The present study shows for the first time that welding with superimposed pressure is well suited for joining of Fe–Mn–Al–Ni shape memory alloys. Furthermore, it is revealed that abnormal grain growth induced by a cyclic heat treatment can be applied independently of the geometry of the component.
Induction butt welding of metallic mixed joints
Published in January 2018
Abstract:
The aim of the present work is to contribute to the development of a welding process in which joints that were previously welded with filler metal (SZW) or that were considered unsuitable for welding can be joined using other processes without SZW.
Autor: Dr. Django Baunack
Estimating hardness with the simplest means - practical tips for welders and welding supervisors
Published in September 2017
Abstract:
According to ISO 18265, hardness is a material parameter that can provide information about the mechanical properties of a material. Therefore, if the hardness is known, it is also possible to make statements about the structural condition of weld seams and heat-affected zones. For example, there are no known hardening cracks on steel weld seams whose heat-affected zone has a hardness lower than approx. 350 HV. For this reason, the maximum hardness of heat-affected zones for each material group (ISO 15608) is strictly limited in DIN EN 15614. If the maximum hardness values are exceeded, for example, on the test piece welded according to a preliminary welding procedure specification (pWPS), no certificate of qualification of the welding procedure (procedure qualification WPQR) can be issued by a certified body. As welding supervisors and welders rarely carry out regular hardness tests, it is often not possible to assess whether a hardness value is to be regarded as critical. This presentation shows how the hardness of weld seams can be estimated using the simplest means. For this purpose, knowledge of the causes and positions of the hardness peaks to be expected on weld seams and the development and associated dangers of hardness cracks will be imparted. The method for estimating the hardness, which is explained in the lecture, is based on a hardness comparison between the test piece of unknown hardness and a reference piece of known hardness, based on the Mohs hardness test. For this purpose, various everyday objects of comparison with known hardnesses are shown, e.g. screw 8.8 approx. 300 HV5, file approx. 860 HV5. This pre-estimation of the hardness during operation saves the need for examinations by test laboratories on test pieces that are far outside the permissible range. The hardness of heat-affected zones on weld seams from the unregulated range, in which hardness tests by external testing laboratories are often dispensed with, can be estimated, thus reducing the risk of damage. The estimation of hardness explained in this article shows a hardness value which can be used to decide which further tests should be carried out.
Authors: Dr. Django Baunack
Estimating hardness from a welder's perspective
Published in September 2015
Abstract:
Almost 200 years ago, Mohs published what was probably the first attempt to classify the hardness of materials. This was followed by Martens, Brinell, Rockwell as well as Smith and Sandland with the Vickers hardness test, named after their employer - Vickers Ltd. Although this is the test method with the highest accuracy and the largest measuring range, like all other test methods it is not easy to integrate into a welder's daily work routine. This article shows how welders can estimate the hardness that is important to them - before carrying out a procedure qualification or in the unregulated area - without much effort and without a testing device.
Author: Dr. Django Baunack
Materials engineering principles of bend straightening
Published in February 2015
Abstract:
This paper addresses key material science aspects of bending straightening. First, the basics of the bending test and the occurring inhomogeneous distributions of stresses and deformations are described. Then, using the example of the steel 42CrMoS4 in different heat treatment states, the development of residual stresses is discussed, whereby both the effect of different degrees of deformation and the microstructure state are shown. Macro and micro residual stresses are generated in steels by bending straightening. In conjunction with the permanent deformations introduced, they lead to characteristic changes in the deformation behavior when subjected to further stress. It is important to know whether the stress is equal or opposite to the deformation during straightening. In the latter case, there is a pronounced Bauschinger effect, which leads to significantly reduced strength. It is shown that the loss of strength depends both on the extent of pre-deformation during straightening and on the microstructure and is more pronounced than with uniaxial homogeneous tension-compression loading. In states containing residual austenite, bending straightening can cause stress-induced phase transformations that depend on the sign of the stress. Finally, some special aspects are addressed that are present in case-hardened components with inhomogeneous microstructures.
Damage and repair: Welding sequence, residual stress state and high-strength aluminium: Determination of the cause of damage and resulting production process optimization
Published in September 2023
Abstract:
A case of damage to a welded prototype construction made of high-strength aluminum is presented. Cracks were detected next to weld seams during the test phase. Due to the known problem of loss of
strength in the HAZ of high-strength aluminum, the question arose as to whether welding had a significant influence on the damage. As a publicly appointed and sworn expert for investigations and
damage analyses in welding and materials technology by the relevant Chamber of Industry and Commerce, I repeatedly investigate such cases of damage and determine the cause of the damage. Once the
cause of the damage has been determined, research and advice on how to avoid the damage in the future is often requested. In order to make the material technology findings understandable to the
public interested in welding technology, despite confidentiality agreements, the circumstances were recreated. The identical cases of damage are presented as fictitious or anonymized cases of
damage. Especially when it comes to court, it is still sometimes necessary, after the cause of the damage has been found, to recreate the (supposedly) causal circumstances for the damage and to
compare the artificially created damage pattern with the original damage pattern in order to be able to explain the circumstances to a more or less technology-enthusiastic lawyer. In the welded
aluminum construction, both the welding sequence and the subsequent surface treatment had a significant influence on the premature component failure. This is demonstrated by means of residual
stress measurements, chemical analyses, hardness curves and micrographs. The hypothesis on the cause of damage developed on the basis of these results is verified by recreating the environmental
influences on an identically welded component. Finally, the advantages and disadvantages of various remedial measures are discussed and it is shown why the remedial measures were chosen. The
article is the second part of a series on complex damage investigations that was started with the article "Damage to fine-grained structural steel attributable to residual stresses: Causes,
effects and simple remedial measures" in DVS Congress 2021.
Authors: Dr. Django Baunack and Dr. Alexander Liehr
