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The current work presents a new test method to evaluate liquid metal embrittlement (LME) susceptibility of zinc-coated steels in arc processes under application-oriented conditions. The procedure is based on the programmable deformation cracking test (PVR test). The PVR test is a variation of a controlled tensile test for hot cracking investigations in arc welding processes. Two dual-phase steels (DP600, DP980) and five transformation-induced plasticity steels (TRIP690, TRIP700, TRIP700, TRIP1100, TRIP1200) were used. The investigations showed that comparable thermo-mechanical loading conditions can be guaranteed for materials of different sheet thicknesses in the PVR test through a targeted adjustment of the heat input per unit length of weld. Furthermore, it was shown that the critical deformation rate $${v}_{cr}$$ v cr (used for assessing hot cracking susceptibility) may also be used to assess the LME susceptibility of a particular steel. Furthermore, another LME susceptibility parameter, the relative reduction in load-bearing ability $$\Delta\Sigma$$ Δ Σ could be derived, which may be used to understand how LME cracking affects materials’ mechanical and fracture properties.

Wire + arc additive manufacturing (WAAM®) is a versatile, low-cost, energy-efficient technology used in metal additive manufacturing (AM). This process uses arc welding to melt a wire and form a three-dimensional (3D) object using a layer-by-layer deposit. In the present study, the effect of heat input and shielding gas during CMT-WAAM welding on cooling time, mechanical properties at room temperature, and macro- and microstructure was investigated based on different part geometries (wall, block) using two S Ni 7718 wire batches. The heat input and consequently the cooling rate were varied by changing the wire feed and the travel speed. As expected, increasing the heat input leads to higher cooling times. Due to the 2D-heat conduction, the thin walls cool significantly slower than the multi-pass block welds. Nevertheless, the influence on mechanical properties is only marginal. Both the AM batch of S Ni 7718 with the lower Nb/C and the multi-pass block welds with the higher thermomechanical reactions exhibit a high susceptibility to unacceptable seam defects, such as hot cracks or lacks of fusion. But even the standard batch causes hot cracks. An influence of the shielding gas on microstructure, mechanical properties, and occurrence of the seam defects cannot be detected.

Due to their mechanical and corrosive properties, nickel-based alloys are very important in several industrial sectors like power stations, chemical apparatus, and the oil industry. While flux-cored arc welding (FCAW) of carbon steels often uses flux-cored wires (FCW), the use of Ni-based flux-cored wires is industrially less common. The reasons for this include the lower degree of recognition and the higher material costs compared to solid wires. In comparison to solid wires, flux-cored wires have some technological benefits such as the possibility of welding without pulsed arc technology using low-cost standard mixed gases, which has a much lower tendency to weld defects due to high penetration depth. Depending on the slag, the flux-cored wires have a good weldability and excellent mechanical properties. Based on the self-stressed and externally stressed hot crack tests, the basic FCW showed a higher hot cracking susceptibility, contrary to the original assumption. Even if the causes have not yet been finally clarified, a negative influence of the comparatively high sulfur and oxygen contents in the basic FCW is suspected. The weld metal of the solid wires showed the highest hot crack resistance.

The influence of arc energy and different filler metal composition on the mechanical properties and macro- and microstructure of additively welded thin-walled structures of Ni-based alloy were investigated using four different variants commercially available solid wire electrodes of type S Ni 6625. As the welding process, the Cold Metal Transfer (CMT) process was used. The heat input and cooling rate were varied by adjusting wire feed and travel speed. The results show that an increase in arc energy leads to longer t10/6 cooling times. This leads to an increase in the dendrite arm spacing and thus to a reduction in the strength values and hardness of the thin-walled structures. The higher Fe-containing variant of S Ni 6625 produces the highest strength and hardness values, while the W-alloyed solid wire electrode produces the lowest values. The porosity in the walled structures was very low, and unacceptable weld defects, hot cracks and lack of fusion did not occur. Segregations occur in all weld metal specimens. While niobium, molybdenum and titanium are the preferred segregations in the Nb-alloyed Ni 6625 type weld metal, only Mo is present in the W-alloyed Ni 6660 type weld metal.

When dissimilar metal welding of high-manganese (Fe-Mn) steels with low-alloyed steels, martensite may form in the weld metal. Current constitution diagrams for weld metal microstructure prediction cannot be used for Fe-Mn steels since the influence of the high manganese content in those steels is not sufficiently considered in the Ni equivalent. This paper concentrates on the development of a new constitution diagram for reliable weld metal microstructure prediction when dissimilar metal welding of Fe-Mn steels with low-alloyed ferritic and martensitic steel grades. For developing the constitution diagram a specially designed arc melting technique was used to experimentally simulate dissimilar weld metals in different dilutions and compositions. The resulting samples were evaluated regarding the type and quantity of the microstructural phases by means of hardness and ferrite number measurements as well as light-optical microscopy. Using this dataset it was possible to determine functional correlations between the chemical composition and the weld metal microstructures. By means of statistical analysis, a new constitution diagram was developed. Actual GMAW welds of different material combinations were performed to validate the applicability of the diagram. The new constitution diagram has a very high prediction accuracy and also distinguishes between the different types of martensite (e and α’).

This paper presents an arc melting technique that allows simulating dissimilar weld metal of high manganese steels with ferritic and martensitic steel grades. The objective of this initial study was to conceive a melting technique that produces dissimilar metal welds using a GTA process in a water-cooled copper crucible under welding adequate cooling conditions and with homogeneous mixing. For this purpose, the sample size, the shape of the crucible, and the melting parameters have been optimized. Using the developed arc melting technique avoids the time-consuming and expensive process of iteratively producing actual welds. It is demonstrated that the dissimilar weld metal microstructure and properties can be easily evaluated for a wide range of dilutions. For an industrially relevant material combination of an austenitic high manganese steel and a ferritic low-alloy steel, the effect of dilution on the weld metal microstructure, the hardness, and the measured ferrite number are shown utilizing the developed arc melting technique. Determining the effect of dilution for a wide range material combination is the basis for the development of a constitutional diagram and will be part of a subsequent paper.

When welding super duplex stainless steels, a non-admissible pore formation can occur even if recommended processing guidelines are strictly followed. To investigate this phenomenon and to determine the influencing factors, different bead-on-plate welds were produced using gas metal arc welding and submerged arc welding. The welding consumables, the shielding gas, and the welding flux were varied. Additionally, the influences of heat input and interpass temperature were examined. The studies have shown that the shielding gas, the welding flux, and the filler metal have great influence on the pore formation. Even small variations in the chemical composition of the welding consumables lead to different results. In addition, the ferrite number and the chemical composition of the bead-on-plate welds strongly depend on the used shielding gases and filler metals. Furthermore, it became clear that the porosity of the weld metal can be affected by the welding speed.

Ductility-dip cracking (DDC) in the base metal heat-affected zone (HAZ) of NiCr15Fe-type alloys was studied using the programmable-deformation-crack (PVR) and the strain-to-fracture (STF) test. This paper concentrates on the correlation of the different cracking criteria used in both tests for DDC susceptibility assessment. Full temperature-strain curves were developed for three base metal NiCr15Fe-alloy variants using the STF test. The results were compared to a previous material ranking obtained by PVR testing. To determine a local cracking criterion for base metal DDC in the PVR test, a finite element analysis (FEM) was conducted on the thermomechanical aspects of crack initiation during PVR testing. The local temperature and strain conditions associated with DDC in the PVR base metal HAZ were observed and discussed with regard to the comparability and transferability of the cracking criteria used in the PVR and STF test.

Carrier gas hot extraction (CGHE) technique was used for measurement of hydrogen in press-hardened (and as delivered) condition of 22MnB5 steel primarily coated with a thin layer of Al-Si. The CGHE technique was applied using different temperature programs: isothermal heating, tempera- ture step, and linear heating in solid state. The effusing hy- drogen was measured using thermal conductivity device (TCD) and high resolution mass spectroscopy (MS). Single isothermal heating at 400 and 900 °C allowed determining absolute value of effusing hydrogen. The linear heating, also known as thermal desorption analysis (TDA), revealed tem- perature dependent hydrogen effusion peaks. The deconvolution of the TDA spectra by peak fitting allowed the calculation of hydrogen desorption energies for each peak. The results showed good agreement between hydrogen con- centrations measured with MS and TCD. In addition, the as- received ferrite-perlite microstructure showed only hydrogen effusion above 400 °C. The subsequent press hardening pro- cess leads to hydrogen uptake in the microstructure. In gener- al, the press-hardened 22MnB5 revealed a hydrogen concen- tration of 0.4 to 0.5 ppm. The biggest concentration was released at isothermal holding at 400 °C indicating reversibly trapped hydrogen. TDA results with different heating rates confirmed mostly diffusible and reversible trapped hydrogen due to calculated activation energies in the range from 4 to 20 kJ mol −1 ;i t was ascertained that nearly 90 %o f the hydrogen left the specimens below 400 °C. Melt extraction (ME) was performed to measure the total hydrogen amount (including the diffusible and trapped hydrogen) and showed that above 900 °C up to 1 ppm hydrogen is trapped.

Over the last decades, press hardening or hot forming has become all pervasive for automotive body-in-white design. Press-hardened boron-microalloyed steels are widely used in modern body structure for high safety standard and lightweight achievement. Considering the welding of press-hardened components, some special considerations have to be taken into account compared to conventional deep-drawing steel grades. The welding process results in a significant hardness drop in the heat-affected zone (HAZ) which may lead to a change in failure mode or premature failure. Furthermore, the mechanical properties of the welded joints are influenced by the weld metal hydrogen content. Hydrogen pickup of press-hardened steel may result from the heat treatment or the welding process. Due to the martensitic microstructure and the high strength level, a critical hydrogen content may cause hydrogen embrittlement or hydrogen-assisted cold cracking (HACC). This paper contributes to the determination of the diffusible hydrogen content in resistance spot-welded and gas metal arc-welded joints of press-hardened boron-microalloyed steel. It also promotes the understanding of the effect of diffusible hydrogen on the mechanical properties of those joints. Hydrogen was deliberately introduced during welding by wetting of the sheet surface with hydrogenated fluids. The hydrogen content in the weld metal was quantified by thermal desorption mass spectrometry (TDMS) technique. Finally, the influence on the mechanical properties of the welded joints was determined based on a simple component test. A GMA-welded component was set under a constant static load and evaluated for delayed hydrogen-assisted cracking.

The corrosion behavior of duplex stainless steels is strongly affected by the austenite–ferrite ratio. With regard to corrosion resistance as well as mechanical properties a balanced ratio between these two microstructural components is desired. Weld seams manufactured by electron beam welding (EBW) generally exhibit very high amounts of ferrite due to a strong loss of nitrogen during the welding process and a very high cooling rate, which can affect the corrosion behavior adversely. Significant improvements can be reached by varying the electron beam guidance and applying multi-beam technology. This paper considers the pitting corrosion as well as selective corrosion behavior of the welds as a function of the chosen process parameters during EBW. Comparisons with the corrosion performance of manual metal arc and tungsten inert gas welds are also made.

The use of commercially available filler metals for wire and arc additive manufacturing (WAAM) of duplex stainless steel components results in a microstructure with a very low ferrite content. The ferrite&ndash, austenite ratio in the duplex stainless steel weld metal depends on both the cooling rate and particularly on the chemical composition. However, the research and testing of special filler metals for additive deposition welding using wire and arc processes is time-consuming and expensive. This paper describes a method that uses an additional cold wire feed in the gas metal arc welding (GMAW) process to selectively vary the alloy composition and thus the microstructure of duplex stainless steel weld metal. By mixing different filler metals, a reduction of the nickel equivalent and hence an increase in the ferrite content in additively manufactured duplex stainless steel specimens was achieved. The homogeneous mixing of electrode and cold wire was verified by energy dispersive spectroscopy (EDS). Furthermore, the addition of cold wire resulted in a significant increase in sample height while the sample width remained approximately the same.

The main problem of electron beam welding of duplex stainless steels (DSS) is the degradation of the mechanical properties and the corrosion resistance due to an unfavourable ferrite content in the weld metal. This occurs because of the high cooling rate and the effusion of nitrogen from the weld pool, which is characteristic for this welding process. To guarantee the necessary mechanical and technological properties and the corrosion resistance, the DSS are welded with filler material and afterwards undergo a post-weld heat treatment. The present work shows the results of investigations concerning the development of an electron multi-beam technology for welding the thick-walled components of DSS without a filler material and post-weld heat treatment. The electron multi-beam technique allows the formation of many weld pools at the same time, which might achieve slower cooling rates and influence the austenite–ferrite formation of the DSS welds. Based on the results of previous studies, in which the optimum cooling rate and number of weld pools were determined, different electron multi-beam techniques were developed and applied to produce the bead on plates of these steels. The studies were performed on standard duplex stainless steel of type X2CrNiMoN22-5-3 and on lean duplex stainless steel of type X2CrNiN23-4. The resulting austenite formation, mechanical properties and the corrosion resistance of the electron multi-beam welds were investigated and are presented in this work.

Thick-walled components made of duplex stainless steels are used in the semi-finished products as well as in machinery, apparatus and plant construction. Electron beam welding (EBW) of these components may be recommended for economic and quality reasons. To guarantee the necessary mechanical and technological properties and the corrosion resistance, the duplex stainless steels are welded with filler material and afterwards undergo a post-weld heat treatment. The present work shows interim results of investigations concerning the development of an electron beam multi-process technology for welding these steels without filler material and post-weld heat treatment. The studies were performed on standard duplex stainless steel of type 1.4462 (X2CrNiMoN22-5-3). When welding duplex stainless steels, the cooling rate and the chemical composition have a crucial influence on the final result. Based on fundamental investigations relating to the influence of the process parameters on the effusion of nitrogen and the cooling rates, the resulting austenite formation, mechanical properties and the corrosion resistance were taken into account to develop appropriate electron beam multi-process techniques. The ferrite content was measured metallographically and by magnetic induction, the impact toughness was measured at −40 °C and the determination of critical pitting temperatures was performed using electrochemical noise measurements.

In this study, the hot cracking susceptibility of centrifugal and sand cast nickel base alloys was evaluated compared to the wrought products. Three solid-solution strengthened nickel base alloys—alloy 59, alloy 625 and alloy 617—were studied with respect to the formation and propagation of hot cracking in the cast and wrought microstructure. Hot cracking tests were performed by PVR (programmable deformation crack) test to rank the cracking susceptibility of the cast base metals against the wrought equivalents. Further investigation on the crack susceptible region in the base metal heat-affected zone (HAZ) of cast and wrought alloy 625 was conducted by hot ductility testing using a Gleeble® system. PVR testing indicates a considerably higher hot cracking susceptibility of the cast nickel base alloys compared to the wrought forms of the same composition. The much more severe HAZ liquation cracking of the cast alloys is attributed to the presence of low melting constituents or constitutional liquation of constituents in the large grained and very segregated cast microstructure. Results of hot ductility testing showed that the brittle temperature range (BTR) of the cast alloy 625 is almost three times as wide as for the wrought equivalent. Indicating a much higher hot cracking susceptibility of the cast alloy, this is in good correlation to the PVR test results. Metallurgical and fractographic evaluation of hot ductility samples revealed that in the cast microstructure severe liquation initiates in the vicinity of MC (NbC) carbides. This carbide constitutional liquation reaction leads to the formation of grain boundary liquid films providing a strong driving force for HAZ liquation cracking in cast alloy 625.

Due to their good corrosion resistance in high-temperature and wet corrosive environments, nickel-based alloys are widely used as construction materials in the chemical industry, as well as in offshore applications and other energy and environmental technologies. Their outstanding corrosion performance, however, is often accompanied by a limited weldability due to a high hot cracking sensitivity. This paper presents a comparative overview of the hot cracking susceptibility of iron and nickel-based alloys type 1.4958 (alloy 800 H), 2.4663 Q (alloy 617), 2.4816 (alloy 600 H), 2.4856 (alloy 625) and 2.4605 (alloy 59). Hot cracking tests are performed by PVR test (deformation crack test), using GTA-welded externally loaded specimens to rank the hot cracking sensitivity of the base metals. In order to gain further knowledge regarding formation and propagation of the hot cracks, optical microscopy and EDX-analyses were performed. In addition to a ranking of materials and processes, interim results regarding the crack types and the metallurgical causes of cracking are discussed.

High-Mn austenitic steels with TWIP and TRIP effect are characterized by an exceptional combination of high plasticity and high strength making them ideal for use in crash-relevant automobile components. At this point, European and international steel producers are facing the market launch of these steels, without detailed information regarding their weldability. This paper presents results from a publicly funded research project concerning the weldability of different systems of uncoated Fe-Mn alloys for gas metal arc welding. The different alloying concepts were produced by the Max Planck Institute for Iron Research GmbH in Dusseldorf specifically for this research project. For gas metal arc welding some newly developed metal cored wires were used and the heat input was varied by using different arc welding processes (short arc, cold metal transfer, cold metal transfer + pulsed arc). In addition to the metallurgical characteristics of the base metals and welds (segregation behaviour, grain size) the paper presents results on the quality of the welds depending on welding process and filler material.

As important factors for high corrosion resistance and good mechanical-technological properties of welds of super duplex stainless steels made with over-alloyed filler metals, the minimization of the dilution with the base metal as well as the avoidance of excessive heat input must be taken into consideration. On the one hand, there exists the risk of occurrence of unfavourable alloy compositions, on the other hand, too many undesirable secondary phases can be precipitated in the weld metal which can also lead to a noticeable reduction of the hot-crack resistance of the joints. This was the reason for systematically examining and determining relations between hot crack sensibility, corrosion resistance and impact strength of over-alloyed weld metals in dependence on dilution level (number of layers) and heat input (welding process) for four different over-alloyed filler metals. On the base of our results we recommend the over-alloyed filler metal Nicrofer S 5020 (DIN EN 18274 — S Ni 6650) for welding of SDS, because it offers the best compromise. It has likewise a lower Ni-content, which has an important influence of the material price.

Due to their excellent high-temperature behaviour and corrosion-resistance properties, as well as to their equally good high-temperature strength and long time strength, high-temperature resistant fully austenitic Ni-base alloys are widely employed in industrial branches for especially demanding and exacting use. The outspoken tendency of the weld metal to hot cracking, however, considerably restricts the outstanding working-life properties of this group of materials. In our research project is investigated systematically the metallurgical effect of nitrogen for avoidance of hot cracks in fully austenitic weld metal. As objects of the investigation, were selected hot-crack sensitive fully austenitic high-temperature Ni- and Fe-base alloys (alloy 602 CA, alloy 601 H, alloy 617, alloy 690, alloy 800), which were processed with GTAW and pulsed GMAW procedures under the use of suitable weld filler materials as applied in practical use. The element nitrogen was added as gaseous component with the weld shielding gas. The hot-crack behaviour of the base metals and of the welds was evaluated by the Programmed Deformation Rate-Test. As results of the hot cracking tests, the positive effect of nitrogen was shown at first and foremost only with the primary carbide containing Ni-base alloy 602 CA and slightly with alloy 601 H. The reasons for this effect are metallurgical. Starting from the presented results and the experience meanwhile gained in practice in matched arc welding the high-temperature resistant Ni-base alloy 602 CA, nitrogen additions between 1 and 3 % for the GTAW process and between 5 and 12% for the pulsed GMAW process are recommended.

Increasing demands on safety and environment require the production of complex components with high strength and reduced weight. To this purpose, a great variety of steel concepts was developed in the past 30 years. Novel austenitic Fe-Mn-steels with high manganese levels ranging from 15 to 25%, which are characterised by an exceptional combination of high plasticity and high strength, show a great potential for innovative lightweight designs. The excellent mechanical properties of these steels are based on the TWIP-effect (twinning induced plasticity), generating a high energy absorption capability through work hardening. At this point, European and international steel producers are facing the market launch of these steels without statements regarding their weldability. While the newly developed materials offer a high potential for use in car bodies, they also demand high production technology standards. This paper introduces the first fundamental investigations on the hot cracking behaviour of four different high manganese TWIP-Steels. The TWIP-steels were produced by the Max-Planck Institut fur Eisenforschung GmbH (MPIE) Dusseldorf especially for this project and are characterized by different alloying concepts concerning the contents of carbon, manganese, silicon and aluminium. The investigations include the measurement of the thermo-physical properties (solidification temperature range, thermal expansion, thermal diffusivity, specific heat capacity) of the TWIP-steels. Hot cracking tests are performed by PVR-test (deformation crack test), using TIG-welded externally loaded specimens to rank the hot cracking sensitivity with respect to other already assessed Cr-Ni-Steels and Ni-Base Alloys. Furthermore, a special self-restraint testing procedure for arc welding processes tailored to a real weldment geometry was investigated and the results were compared to those of the PVR-test. In order to gain further knowledge regarding formation and propagation of the hot cracks, optical microscopy, SEM-microscopy and EDX-analyses were performed. In conclusion, the experimental results are discussed with respect to their significance for the welding suitability of these TWIP-steels.