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The Critical Raw Materials (CRMs) list has been defined based on economic importance and supply risk by the European Commission. This review paper describes two issues regarding critical raw materials: the possibilities of their substitution in iron-based alloys and the use of iron-based alloys instead of other materials in order to save CRMs. This review covers strategies for saving chromium in stainless steel, substitution or lowering the amounts of carbide-forming elements (especially tungsten and vanadium) in tool steel and alternative iron-based CRM-free and low-CRM materials: austempered ductile cast iron, high-temperature alloys based on intermetallics of iron and sintered diamond tools with an iron-containing low-cobalt binder.

The stability of austenite is one of the most dominant factors affecting the toughness properties of high Co-Ni steels such as Aermet 100 and AF1410. Thus, the aim of this work was to get a deeper understanding on the impact of combined heat and cryogenic treatment on the stability of retained and reverted austenite. In order to characterize the evolution of the phase fraction of austenite during tempering at different temperatures and times, X-ray diffraction analyses were carried out. The stability of austenite, which was formed during tempering, was analyzed with dilatometric investigations by studying the transformation behavior of the austenite during cooling from tempering temperature down to −100°C. Additionally, transmission electron microscopy investigations were performed to characterize the chemical composition and phase distribution of austenite and martensite before and after tempering.

Three-dimensional electron backscatter diffraction, focused ion beam, transmission electron microscopy and energy filtered transmission electron microscopy were employed to investigate the structural information of primary Al{sub 3}(Sc,Zr) phase, i.e. size, shape, element distribution and orientation relationship with the α-Al matrix. It was found that (i) most primary Al{sub 3}(Sc,Zr) phases have a cubic three-dimensional morphology, with a size of about 6–10 μm, (ii) most primary Al{sub 3}(Sc,Zr) phases are located within the α-Al matrix, and exhibit a cube to cube orientation relationship with the α-Al matrix, and (iii) a layer by layer growth was observed within primary Al{sub 3}(Sc,Zr) phases. Al, Cu, Si and Fe are enriched in the α-Al matrix between the layers of cellular eutectic Al{sub 3}(Sc,Zr) phase, while Sc, Ti and Zr are enriched in small Al{sub 3}(Sc,Zr) phases. A peritectic reaction and subsequent eutectic reaction between Al{sub 3}Sc and Al was proposed to interpret the observed layer by layer growth. This paper demonstrates that the presence of impurities (Fe, Si, Cu, Ti) in the diffusion field surrounding the growing Al{sub 3}(Sc,Zr) particle enhances the heterogeneous nucleation of Al{sub 3}(Sc,Zr) phases. - Highlights: • Most fine cubic primary Al{sub 3}(Sc,Zr) phases were observed within the α-Al matrix.more » • A layer by layer growth within primary Al{sub 3}(Sc,Zr) phase was observed. • A peritectic and subsequent eutectic reaction between Al{sub 3}Sc and Al was proposed. • Impurities in diffusion fields enhance heterogeneous nucleation of Al{sub 3}(Sc,Zr)« less

The aim of this study was to analyze the influence of combined heat and cryogenic treatment on the evolution of martensite and reverted austenite in a high Co-Ni steel. To this end the evolution of phase fractions and lattice constants after thermal treatments were characterized by using X-ray diffraction (XRD) investigations and dilatometer analyses. The arrangement of phases and the element distribution in martensite, austenite and carbides were analyzed by using energy filtered transmission electron microscopy (EFTEM).

The presented X-ray diffraction techniques enable the simultaneous characterization of phase content, dislocation densities in the austenitic and the ferritic/bainitic/martensitic phases, or the tetragonal lattice distortion and the interstitial carbon content in martensite. The capability of the diffraction methods is demonstrated using the example of heat treatment of high speed steels.

Chromium nitride/titanium–titanium carbonitride multilayers composed of a 40 nm Cr interface followed by a 4.4 μm thick Cr2N layer, a 150 nm thick Ti layer, and a 1 μm thick TiCxNy top layer were deposited on silicon wafers by magnetron sputtering. The structural changes and the phase content changes of these multilayer samples were studied by means of high-temperature in-situ X-ray diffraction experiments at temperatures up to 550 °C. The lattice constants of the Cr phase as well as the Ti phase display an aberrant expansion behaviour during these experiments which is influenced by the defect structure, a nitrogen incorporation, and residual stress in the layers. The results were compared with structural data obtained by ex-situ transmission electron microscopy investigations of pristine and heated material, revealing phase separation and strong diffusion phenomena.

For the investigation of retained strains during hot forming, which are related to the dislocation structure, single and double hit compression tests were carried out at different temperatures and strain rates for a stainless steel. Using microhardness measurements the retained strains after the first and second pass were investigated as a function of the amount of deformation, temperatures as well as strain rates and dwell durations. In general, the retained strain decreases with increasing dwell durations in both the deformed and recrystallized grains, respectively. At a given total amount of deformation in a double hit compression, the retained strains for the as deformed unrecrystallized grains are reduced for a lower deformation in the first hit. For the recrystallized grains the retained strain increases, when comparing double hit with single hit compression.

Double-hit compression tests were carried out at different temperatures and strain rates for a nickel based alloy and a stainless steel. Using microhardness measurements the retained strains after the first and second pass were investigated as a function of the amount of deformation, temperatures as well as strain rates and dwell durations. In general, the retained strain decreases with increasing dwell durations. It is shown that at a given total amount of deformation, the retained strain is reduced for the as deformed grains that have not been recrystallized yet, but increased for the recrystallized grains, when comparing double hit with single hit compression tests.

For the application of Fe-Co-alloys in fuel-injection systems several physical properties as saturation magnetization, permeability, remanence and the electric resistivity are the predominant parameters to achieve an optimal functionality of coil formers. These properties are achievable by a process technology which starts at the vacuum melting and a vacuum arc remelting process and is continued at the blooming and the multi line rod rolling mill and ends finally at the finishing line. The above listed properties are associated with the low carbon ferrite structure, which can be achieved by the y/a- transformation and a subsequent ferritic recrystallization. Further the homogeneity and purity of the material take a dominant role in the thermo-mechanical controlled rolling process. To stabilize the deformed ferrite structure, the alloy has small additions of Vanadium, which is precipitated strain induced as vanadium-carbo-nitride in the deformed ferrite at 750 °C. Impurities as oxides or sulphides, which act as nucleation sites for this V(C,N)-precipitation reaction, consume therefore a part of the required nucleation potential. The second purpose of the small vanadium addition, associated with the precipitation, is to reduce the solute carbon content of the ferrite structure to achieve a low magnetic remanence. To investigate these interactions, several process steps were physically simulated on a "Gleeble 3800TM" system which has been extended by a "maxstrain" unit to simulate multistep deformation sequences below the γ/α- transformation temperature. Subsequently the achieved structures were investigated by transmission electron microscopy and electron back scatter diffraction analysis. The results have been successfully transmitted to the process and confirmed by the operational results.