Technological changes are expected in steel production in the future, as governments are calling for a reduction in CO2 emissions from crude steel production. One option is to operate with higher scrap rates. This will generally result in higher requirements for scrap in terms of both quantity and quality. The production of automotive-grade steel from post-consumer automotive scrap imposes specific requirements on scrap quality, which must be considered within the framework of closed-loop recycling. End-of-life vehicles consist of various materials that must be separated during recycling. For steel recycling, separation is particularly important because certain elements, such as Cu and other tramp elements, must be present at low concentrations to enable the production of new automotive steel grades from scrap, especially in the flat steel sector. An increasing share of electric vehicles is entering the recycling stream. These vehicles contain higher amounts of Cu, which negatively affects scrap composition for steelmaking. This study addresses this challenge by first identifying the critical influences and tramp elements in automotive steel scrap. Vehicles with different drive systems (internal combustion, hybrid, and electric) were shredded, and the resulting steel fractions were analysed for tramp elements including Cu, Ni, Mo, Cr, Mn, Al, and Si. A sorting concept was developed to separate fractions with high Cu content. The results reveal varying proportions of bound and loose Cu across different steel fractions. Finally, post-consumer automotive steel scrap from the Car2Car project was used to manufacture various automotive components, such as B-pillar reinforcements and door outer panels.

This study investigated powder mixtures composed of recycled eroded particles (REP) from electro discharge machining (EDM) and H11 powder, with a focus on their use in laser beam direct energy deposition. The compositions of H11 and REP are close, with difference being their carbon content due to an uptake during EDM. Mixtures with varying carbon contents were created to minimize crack formation, and analyzed for particle size distribution, chemistry and usability for coatings. By this, a secondary powder supply is ensured. Powders were deposited on a low-carbon substrate, and layers evaluated through image analysis and hardness testing. Thermal analyses were performed to investigate microstructural transformations. Metallographic investigations were employed to study the microstructure. The deposition resulted in crack-free layers on preheated substrates, with targeted dilution ratios ranging from 10 % to 24 %. Developed microstructures were complex, exhibiting phases as M7C3 carbide, M3C carbide, martensite, and austenite. Carbon loss and phase transformations were observed and could be controlled by adjusting the feed material mixture (0 %, 15 %, 30 %, 45 %, 60 %, 100 % REP). Hardness testing showed that pure H11 layers have lower microhardness (660 HV10) compared to pure REP layers (790 HV10), with the hardness of coatings varying based on REP content and present phases (365-510 HV10). Thermal analysis confirmed the presence of observed phases, and electron backscatter diffraction proved austenite and martensite along with carbide precipitates, further elucidating the complexity of material systems.

In this study, an austenitic CrMnNi–N steel is examined with regard to its solidification behavior of the weld metal. For this purpose, the cooling rate of the weld metal at different welding speeds is determined for tungsten inert gas welding without filler metal. The relationship between secondary dendrite arm spacing () and cooling rate () can be described using . Moreover, the microstructure is characterized by a scanning electron microscope using energy‐dispersive X‐ray spectroscopy (EDS). Based on the EDS measurement, it is possible to describe the microsegregation of Cr, Ni, Mn, Mo, and N. The detected microsegregation behavior is compared with the results obtained from Thermo‐Calc calculations. The microsegregation varies depending on the present phase during solidification and correlate well with microstructure observations. By using the software Thermo‐Calc, the theoretical description of solidification is based on the classical Scheil model with fast diffusion of N. A primary ferritic solidification is calculated, which correlates with the experimental findings.

This study focuses on the effect of pre-deformation on hydrogen diffusion and hydrogen embrittlement of the high alloy austenitic TRIP steel X3CrMnNiMo17-8-4. Different cold-rolled steel sheets with thicknesses of ≤400 µm were electrochemically charged on both sides in 0.1 M sodium hydroxide with hydrogen for two weeks. Comparative measurements on uncharged and immersed samples prove that hydrogen causes embrittlement in this steel for all investigated states. The embrittlement increases with increasing pre-deformation and is accompanied by deformation-induced martensite formation. The corresponding fractured surfaces were examined using electron microscopy and compared to modelled hydrogen distributions with previously determined diffusion coefficients. For this purpose, various diffusion coefficients are determined using the Devanathan–Stachurski permeation test and hot extraction in order to describe the diffusion process. The hydrogen concentration profiles and the fractographic analyses show a good agreement, so this study provides a basis for estimating the embrittlement behaviour for later application.

To obtain a successful product during additive manufacturing, the powder as a raw material must have the high quality. The purpose of this work is to investigate CrMnNi steel powders obtained by inert gas atomization with nickel content: 3, 6, and 9 wt% and to identify dependencies between the powder size and morphology, solidification structure, and change in chemical composition and thermophysical properties. Particle size distribution is measured by a laser scattering analyzer: d50 value are 82.02, 69.32, and 75.54 μm for powders with 3, 6, and 9 wt%, respectively. Surface tension (ST) measurements are made by maximum bubble pressure method: for steels with 3, 6, and 9 wt% at temperature 1500 °C, ST is 1.01, 1.07, and 1.15 mN m−1, respectively. It is found that the change in particle size affects the chemical composition, the content of the ferromagnetic phase and secondary dendritic arm‐spacing. Changes in the content of elements such as S, O, N, and Mn are determined, depending on the diameter of the particles. The influence of changes in content of S, O, and N on the thermophysical properties such as ST is investigated.

The grain size of austenitic-stainless-cast steels is usually coarse and may be several hundred microns to millimeters, depending on solidification conditions and ingot geometry. During solidification, dendritic crystals grow into the supercooled melt and stop growing when they touch each other, which is accompanied by the formation of high-angle grain boundaries. Further cooling of metastable austenitic steels with a martensite start temperature above room temperature can partially transform them into martensite. During subsequent heating above the austenite start temperature, also known as austenite reversion treatment (ART), the martensite transforms back into austenite. The resulting austenitic microstructure is thus significantly refined, leading to an even finer martensitic microstructure during subsequent cooling. To reduce the martensite formation capability, partitioning is carried out to enrich the austenite with C and N and thus improve the formability. In the present work, the temperature-dependent phase transformation behavior of the martensitic-austenitic stainless X16CrNiMnN15-3-1 transformation-induced-plasticity-cast steel is determined by means of dilatometry. The influence of a single or multiple ART on the resulting austenite grain size, the microstructure and the tensile properties are described. It is demonstrated that ultrahigh-strength steels with good ductility can be achieved by using partitioning after ART. The effect of austenite reversion treatment (ART) on the phase transformation behavior and the mechanical properties of the martensitic-austenitic stainless X16CrNiMnN15-3-1-transformation-induced-plasticity-cast steel is investigated. It is further shown that an ultrahigh-strength steel with good ductility can be achieved by subsequent partitioning at 450 degrees C for 180 s after ART.image (c) 2024 WILEY-VCH GmbH

Different waste streams from electro discharge machining (EDM) were investigated for an upcycled usage in processes for additive manufacturing (AM). These erosion sludges accumulate in filter cartridges and at the bottom of machining basins. The enclosed particles were extracted, sieved and investigated via laser diffraction, dynamic image analysis, scanning electron microscopy, optical emission spectroscopy, elemental analysis and flowability measurements. Additionally, thermal, crystallographic and metallographic investigations as well as X-ray micro-computed tomography (µ-CT) were utilized for the characterization of particle and material properties. In general, eroded powders fulfill the requirements for AM regarding particle size and shape very well, which is confirmed in morphological investigations and powder flow characteristics showing similar properties as the H11 AM reference material. The chemical composition of the powders is equal to the machined H11 alloy, except for the high carbon content. Carbon is entrapped in the iron lattice originating from pyrolysis of the present dielectric fluid and the graphite electrode during rapid solidification, which leads to a transition from martensite to cementite structures. This change is observed in the microstructure of powders, in which acicular primary cementite and austenite are present. After remelting with slow heating and cooling rates the microstructure changed to ledeburite II with retained austenite and martensitic phases. The pore size and shape distributions obtained by µ-CT measurements showed a pore formation in the compact sample. These results provide a fundament of major properties as well as handling and recycling suggestions for eroded particles enclosed in waste sludges. Graphical Abstract

The plastic deformation and martensite evolution of austenitic CrMnNi–N stainless steel with 8.6 wt% Mn and 4 wt% Ni is investigated in a temperature range of −40 to 100 °C. Martensite evolution is determined by in situ magnetic measurements during tensile test. The triggering stress and strain for martensite formation decrease with decreasing temperature. Ex situ volumetric magnetic measurements are used to determine the strain‐induced α′‐martensite volume fractions. The characterization of the microstructure is carried out with scanning electron microscope. Using electron backscatter diffraction, strain‐induced α′‐martensite is detected within deformation bands in the austenite. The strain hardening curve at −40 °C shows a typical progression for metastable austenitic stainless steels with pronounced strain‐induced α′‐martensite formation and can be divided into four hardening stages. At this temperature, the studied steel achieves the highest strain hardening rate. The amount of martensite increases with decreasing test temperature and reaches a maximum volume fraction of 76 vol% at −40 °C. The highest ductility of 83% is achieved at 40 °C, accompanied by a tensile strength of 732 MPa. The in situ magnetic measurement confirms that the inflection point in the strain hardening curve coincides with the maximum martensite formation rate.

The study evaluates the effect of electrochemical hydrogen charging on the tensile properties and fracture behavior of the plasma tungsten inert gas weld of the high‐alloy austenitic steel X3CrMnNiMoN17‐8‐4 in comparison to the pure base metal (BM). The weld metal exhibits a higher susceptibility to hydrogen embrittlement than the BM, which is mainly expressed by a loss in ductility. Based on the performed electron backscatter diffraction and X‐ray diffraction examinations, this is attributed to the higher amount of δ‐ferrite and the higher dislocation density in the weld zone. Furthermore, fractographic analyses reveal a change in the manner of fracture mode from ductile to brittle fracture starting from the edge in the hydrogen charged samples. The wider area of brittle fracture in the weld seam in relation to the BM indicates that hydrogen penetrates deeper into the material. Consequently, the diffusivity of hydrogen in the weld seam is determined to be significantly higher than in the BM.

The present study deals with the pitting and repassivation behavior of a nickel‐reduced austenitic stainless steel with different nitrogen contents. While nitrogen promoted the resistance to pitting, no significant effect on repassivation was found. The study also aims to address the experimental difficulties in determining repassivation potentials owing to the occurrence of crevice corrosion. Furthermore, the mechanism of the ongoing reactions was investigated, indicating that pitting was initiated in regions where manganese sulfide inclusions were present next to the remaining δ‐ferrite.

In this study, a Ni-reduced austenitic stainless TRIP/TWIP steel with < 5 vol.% δ-ferrite was investigated before and after plasma arc welding and gas tungsten arc welding. The 4-mm-thick hot-rolled sheet was produced as hot-rolled heavy plate on an industrial scale and manufactured as longitudinally welded pipes without filler metal. Microstructural characterization was done using light optical microscope and scanning electron microscope with electron backscatter diffraction (EBSD). The microstructure consisted of non-recrystallized austenite with a small amount of δ-ferrite. The welds exhibited skeletal and lacy δ-ferrite morphologies. ε-martensite and α´-martensite were found in the weld seam after pipe expansion. Further, the mechanical properties were evaluated using tensile test. The results showed a tensile strength of 823 MPa with a uniform elongation of 69% at room temperature. The change of hardness in the weld seam was studied for welded pipe, welded expanded pipe and welded, post-weld heat-treated (PWHT) pipe with Vickers hardness testing. The lowest hardness was achieved after PWHT. The corrosion resistance tests were conducted in chloride containing environment. The results showed that the susceptibility to pitting corrosion increased with the degree of deformation. Furthermore, the weld metal and heat-affected zone exhibited local attack whereas the base metal seemed unaffected.

The main objective of this work was to obtain information about the hydrogen diffusion behaviour in a cold-worked austenitic stainless steel (X3CrMnNiMoN17-8-4) in which deformation-induced martensite formation occurs during mechanical deformation. Three different states of pre-deformation (31 %, 39 % and 49 %) that showed induced phase transformation from austenite to α’martensite as well as the solution-annealed material were part of this study. All samples were charged with hydrogen in a 0.1 M NaOH solution. This charging took place electrolytic with 10 mA cm-2 at three different temperatures (50 °C; 65 °C and 80 °C) in the double cell according to Devanathan and Stachurski. Due to the very slow diffusion of hydrogen through austenite, the samples were not charged until the equilibrium state was reached. To find out the necessary diffusion parameters, the data were fitted with numerical optimisation. Using this method, the effective diffusion coefficients of charging could be determined for all material states. The study also contains microscopic analyses to visualize the effect of cold working on the microstructure of the material. The appearance of α’-martensite significantly contributes to the susceptibility to hydrogen uptake leading to increasing diffusion coefficients in relation to higher pre-deformation.

Austenitic steels are known to exhibit a low hydrogen diffusion coefficient and hence a good resistance to hydrogen embrittlement. Therefore, it is an experimental challenge to investigate their hydrogen diffusion properties. In this study, the electrochemical perme-ation technique is used to determine the hydrogen diffusion coefficients in different pre -deformed states (4 = 0, 0.32, 0.39, 0.49) of the high-alloy austenitic TRIP steel X3CrMnNiMoN17-8-4 in a temperature range of 323 K-353 K. In combination with micro -structural analysis, a correlation between phase transformation from g-austenite to a'- martensite and dislocation density is shown. As a result of the lattice transformation from fcc to bcc, the diffusion rate of hydrogen is significantly increased (Dapp, 4 = 0-= 3.6 x 10-12 cm2 s-1, Dapp, 4 = 0.32 = 1.6 x 10-11 cm2 s-1at 323 K). With higher degrees of deformation, the dislocation density also increased in the martensite islands, resulting in a degressive growth of the diffusion coefficient (Dapp, 4 = 0.39 = 5.3 x 10-11 cm2 s-1, Dapp, 4 = 0.49 = 1.1 x 10-10 cm2 s-1at 323 K). Moreover, detailed calculations are performed to describe the way of hydrogen trapping and to give a possible mechanism of diffusion.(c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

In this study, the type of solidification of an austenitic stainless steel during plasma tungsten inert gas (TIG) welding was investigated. The stainless steel Fe-17Cr-7Mn-4Ni-(0.12–0.19)N, concentration in wt.%, was studied in hot-rolled condition with a δ-ferrite fraction less than 5 vol.%. The investigated steel could be successfully welded without filler metal. The steel had an increased Mn content and a lowered Ni content to reduce alloying costs. To verify the solidification type after welding, microstructural investigations are performed using light optical microscopy, scanning electron microscopy, and hardness measurements. Moreover, the microstructure was characterized by scanning electron microscope using electron backscatter diffraction (EBSD). Based on the EBSD measurements, it was possible to elucidate the solidification process. In the present alloy system, the primary solidification of the weld seam according to Scheil-Gulliver model was calculated, taking the fast diffusing N into account. The Scheil-Gulliver model predicted primary ferritic (body-centered cubic, BCC) solidification. After solidification of approx. 84% solid phase, the austenite (face-centered cubic, FCC) is formed via eutectic reaction and the residual melt solidified as austenite. The theoretically determined solidification type agrees with the experimentally observed microstructure. In addition, susceptibility to solidification cracking was investigated, for which no evidence was found in the studied microstructure.

In this study, the influence of various nitrogen contents (0.12-0.23 wt.%) on the mechanical properties, especially the strain-induced alpha'-martensite formation behavior, of the austenitic stainless steel X3CrMnNiMoN17-8-4 was investigated by temperature dependent in situ tensile tests. With the aid of in situ magnetic measurements during tensile test, the correlation between the strain-induced alpha'-martensite formation and the inflection points in the true stress-strain curve could be verified. In addition, a connection between the in situ measured alpha'-martensite formation rate and the strain hardening curve was established. As the temperature decreases, the formation of a large strain-induced alpha'-martensite fraction allows a strong increase in strength accompanied by a simultaneous decrease in elongation. The alpha'-martensite volume fraction increase and the triggering stress for the strain-induced martensite formation decreases with decreasing nitrogen content from to 0.23 wt.% to 0.12 wt.%. The deformation mechanisms taking place at various temperatures during tensile test were analyzed by microstructure analysis. As expected, a transition from Transformation Induced Plasticity to Twinning Induced Plasticity behavior was observed with increasing temperature. Compared to the other examined steels, the steel with 0.19 wt.% nitrogen has the highest tensile strength of 856 MPa accompanied by an excellent total elongation of 75 % at RT.

Herein, considerable insight is provided into the evolution of strain‐induced martensite and mechanical properties of Fe–19Cr–4Ni–3Mn–0.15N–0.15C wt% austenitic stainless steel (in short Cr19NC15.15) during deformation at room temperature and cryogenic temperatures. In situ magnetic measurements of the martensite evolution during tensile tests at various temperatures are conducted. The triggering stress required for strain‐induced martensite formation is determined at the minimum in the strain hardening curve. It is found that with reducing deformation temperature in the range from 0 to –20 °C slightly decreases, whereas the triggering stress increases with further reduction of deformation temperature to −70 °C. The relation between the formed α′‐martensite fraction and the strain applied during tensile test is established. The results demonstrate that a reduced deformation temperature from room temperature (RT) to −70 °C significantly enhances the transformation rate and the total volume fraction of strain‐induced α′‐martensite. The yield and tensile strength increase whereas elongation continuously decreases due to an increasing α′‐martensite volume fraction with decreasing tensile test temperature. The α′‐martensite formation kinetic follows Olson and Cohen's model and are in good agreement between the in situ experiment and theoretical calculations.

In this study, the effect of interstitial contents on the mechanical properties and strain-induced martensite formation in an austenitic stainless steel was investigated. The mechanical properties of solution annealed Fe-15Cr-7Mn-4Ni-0.5Si-(0.01-0.2)N-(0.01-0.2)C concentrations in weight percent stainless steels were studied using room temperature tensile tests. All three alloys used in the present study have a sum content of C + N of about 0.2 wt.%. To verify the influence of C and N on deformation behavior, microstructural investigations are performed using light optical microscopy, scanning electron microscopy, and magnetic and hardness measurements. Moreover, strain-induced α′-martensite nucleation was characterized by scanning electron microscope using EBSD. In the present alloy system, carbon provides a stronger austenite stabilizing effect than nitrogen. Hence, the smallest amount of strain-induced α′-martensite was formed in the steel alloyed with 0.2 wt.% C. It also exhibited the optimal mechanical properties, including the highest ultimate tensile strength (1114 MPa), uniform elongation (63%), and total elongation (68%). Moreover, the interstitial content influences the occurrence of dynamic strain aging (DSA), which was only observed in the steel alloyed with carbon. With increasing C content, the triggering strain for DSA decreases, which can be confirmed by in situ magnetic measurements during tensile testing.