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In this work, a high-performance maraging steel M300 was processed by laser powder bed fusion, where the layer thickness and the laser emission mode were modified. As-built microstructures were studied by considering the metallurgical phenomena taking place during printing: melting of the material deposited over previous layers; rapid solidification of the melt pool; and martensite-to-austenite reversion and precipitation of intermetallic phases induced by the combined effects of repeated heating and cooling cycles in the process. After printed, parts were subjected to ageing treatments at temperatures ranging from 480 to 540 °C. Microstructural characterization results evidenced the importance of layer thickness as a key parameter to modify the solidification cell size of the as-built samples. Two different phases were identified from the X-ray diffraction patterns in the microstructure: BCT martensite and FCC austenite. It was found that the tetragonality of martensite remained constant across different layers for all as-built conditions regardless of the successive reheating cycles, which are experienced during subsequent melting passes. No significant effect of the studied printing parameters was observed on the evolution of the microstructure during ageing. Finally, it was observed that the hardness of aged microstructures is comparable to that obtained by conventional manufacturing methods.

La actividad desarrollada por nuestro centro en sus 60 años de existencia convierte al CENIM en el primer centro integral de investigación del sector metalúrgico español. En este período, en sintonía con los objetivos del CSIC, se ha potenciado nuestra capacidad para transferir resultados a la industria, basados en la realización de una Ciencia de Excelencia. Nuestro objetivo para el futuro es consolidar esta posición e incrementar nuestra visibilidad tanto a nivel nacional como internacional, respondiendo a la creciente demanda de innovación y desarrollo en este ámbito, así como a los nuevos retos como es la tarea de hacer sostenibles las aleaciones estructurales y sus productos. Ahora, en la aceleración de la fase del Antropoceno, sus grandes ventajas en términos de disponibilidad, producción en masa y bajo precio también se han convertido en una carga ambiental. La sostenibilidad de los materiales metálicos estructurales requiere una visión holística que englobe desde las etapas iniciales de su producción y fabricación; la comprensión de la relación entre su estructura y propiedades; la funcionalidad del producto y su vida en servicio (longevidad); eficiencia de recursos naturale

Grade 316L is one of the most versatile austenitic stainless-steel products whose potential in laser powder bed fusion has been recently evaluated. This process allows manufacturing parts with complex shapes to be used in fields such as power generation, oil and gas, water treatment, petrochemical, and construction. The way of improving its properties is to promote dispersion hardening and to control texture. In this work, the effect of dispersion hardening and texture on the behavior at high temperature of a 316L steel was evaluated. Two 316L samples were manufactured by laser powder bed fusion, where the powder of one of them was inoculated with TiC nanoparticles. Advanced characterization proved that inoculation did not affect the solidification structure or the grain size, although it did modify the bulk texture.

Steel is the main structural material to our modern society. To guarantee the supply of sustainable steel, the steelmaking industry must achieve net-zero CO2 emissions by 2050. Besides the replacement of coal-based energy carriers to lower the CO2 emissions, the substitution of primary raw materials with scrap is essential to promote energy and resource efficiency in the circular economy strategy. Steel production via the scrap-based electric arc furnace (EAF) route reduces the CO2 emissions by 80% with respect to the blast furnace-basic oxygen furnace (BF-BOF) route. Nowadays, most of the overall scrap steel is fabrication and post-consumer scrap. Scrap utilization at higher rates poses a challenge for the steel industry due to the increasing content of tramp elements (Cu, Sn, Cr, Ni and Mo) in steel since the 1990. Some steel qualities demand very strict composition requirements, as either the absences or the controlled content of tramp elements. Improving scrap processing and classification methods is essential to ensure better scrap quality for new steel.

Alumina-forming austenitic stainless steels (AFA) [1] are designed for applications where corrosion and creep resistance are of paramount importance. However, they suffer from stress corrosion cracking and, due to their FCC crystalline structure, show poor resistance to volume swelling under irradiation. The motivation of our work is to take advantage of the knowledge acquired in the last 40 years of service of heat-resistance ferritic-martensitic steels [2-4], combined with the exceptional corrosion resistance properties offered by a protective layer of alumina. For this reason, in this research, alumina-forming martensitic steels have been designed. Extensive thermodynamic calculations have been performed under the approach proposed by Olson and Cohen where the stacking fault energy is estimated in order to optimize the martensitic transformation, coupled with the precipitation of strengthening MX precipitates. A compositional window with enough content of Cr and Al in order to obtain protective layers, but yet allowing the martensite formation, has been defined. The approach considers a single thermal treatment step (austenization + alumina forming) in order to make these alloys commercially viable. Several alloys have been produced and characterized. The transformation from austenite to martensite has been evaluated using high resolution dilatometry, while the obtained microstructures and the capacity to form an alumina layer have been characterised using X-ray diffraction, optical and scanning electron microscopy. For a deeper characterisation of the alumina layer, scanning transmission electron microscopy, two-dimensional EDS maps (elemental mapping) as well as point and linear EDS were carried out to evaluate the distribution and proportion of elements in the alumina layer. The results presented pave the way to develop alumina forming martensitic steels for energy applications.

Understand how critical varying printing parameters such as the laser emission mode and the layer thickness can be to modify mechanical properties of maraging steel M300 manufactured by LPBF. Obtain improved properties compared to the ones achieved in conventionally processed parts.

The deployment of Press Hardened Steels (PHSs) in the Body-In-White structures that took place during the two last decades is at the origin of a breakthrough weight saving on vehicles while guaranteeing the safety requirements of the automotive industry. The production of parts with complex shapes and a high strength between 1500-2000MPa was made possible by taking advantage of the hot rheology of austenite combined with the fast cooling obtained by in-die quenching leading to auto-tempered martensitic microstructures. In the present work, PHS1500 was hot stamped with different thermomechanical processes to promote different lath-like microstructures (bainite, tempered martensite¿). An innovative approach is proposed to link the complex microstructures formed between thermoregulated dies to the mechanical behaviour and local ductility of these materials during crash-like solicitations. The microstructure has been characterised through a multi-characterization technique approach including light optical microscopy, scanning electron microscopy and X-ray diffraction. The local ductility is assessed with a combination of crack initiation tests (bending, notch tensile test) and crack propagation resistance tests (Essential work of fracture). Despite similar microstructural crystallographic features, lower bainite and auto-tempered martensite can lead to very different strength ¿ local ductility compromise.

Press hardening offers a better dimensional control of formed parts, gives higher process stability and also offers the possibility to tailor mechanical properties in a component. The technology evolution and the market penetration rate allow estimating that the share of press hardened parts in future car bodies will be in excess of 45%, thanks to the current and future developments of the technology. - Actual B-steels allows forming complex geometries and obtaining very high strength (from 1200 to 2000 MPa). However, new materials and developments are needed to keep pushing the technology and explore new applications, i.e. smart distribution of soft and hard areas, in onestep operations through a smart control of the process thermal history. - Nevertheless, all these new developments depend on the ability of the scientific community to integrate different phase-transformation models for the microstructure and to predict engineering properties.

El Consejo Superior de Investigaciones Científicas (CSIC), en colaboración con la Plataforma Aeroespacial Española PAE y el Centro para el Desarrollo Tecnológico e Industrial (CDTI), organiza el próximo viernes, 16 de diciembre, una jornada sobre nuevos materiales e hidrógeno en la industria aeronáutica. Especialistas en el sector procedentes de distintos ámbitos científicos y de la industria debatirán sobre los nuevos desafíos que implica el empleo del hidrógeno como combustible, así como su interacción con nuevos materiales, en el campus central del CSIC en Madrid., Presentaciones disponibles en : https://plataforma-aeroespacial.es/jornada-materiales-e-h2-en-las-aeronaves/presentaciones

Additive manufacturing is becoming a support tool for teching-learning processes, especially for theoretial-practical content in technical teaching, and particularly in distance learning education. This work shows its potential as a tool for understanding basic concepts that require spatial vision, as is the case of Bravais crystal lattices, The methodology can be extrapolated to any other field of knowledge.

Press Hardened Steels (PHS), with tensile strength in the range 1300 and 1800 MPa, are fundamental elements in the body-in-white of automotive structures. Developed in the late 90’s, the idea of a 22MnB5 blank hardened by austenitization treatment and die quenching made its way to become a breakthrough discovery such as the development of commercial steel Usibor® 1500AS. The simplicity of its alloy design combined with a cost-efficient hot stamping process allow for achieving the technical requirements for anti-intrusion parts during crash. In this work, the chemical composition of a PHS1500 steel has been adjusted by different silicon and aluminium additions to ensure some bainite formation during press hardening process combined with isothermal transformation. This strategy is expected to lead to the formation of different combinations of tempered martensite and/or bainite with different morphologies here examined through a multi-characterization technique approach, including light optical microscopy, scanning electron microscopy, and X-ray diffraction. Silicon and aluminium additions allowed the formation of lathlike ferritic microstructures with certain amount of austenite after conventional hot stamping practices. Mechanical properties seem promising in terms of local ductility and fracture strain for automotive applications.

La industria siderúrgica necesita reducir drásticamente su huella de carbono para asegurar el bienestar social, económico y medioambiental de nuestra sociedad en el futuro [1]. En el año 2020, por cada tonelada de acero producido, se emitieron 1,85 toneladas de gas dióxido de carbono (CO2), lo que supone alrededor del 8% de las emisiones de CO2 en todo el mundo [2]. Esto se debe al uso extendido de la ruta del alto horno convertidor (de aquí en adelante referida como BF-BOF, del inglés blast furnace-basic oxygen furnace), que supone un 71 % de la producción mundial de acero y se basa en una tecnología dependiente del consumo de combustibles fósiles. Para alcanzar los objetivos fijados desde el Acuerdo de Paris (2015), la Unión Europea (UE) lidera el cambio hacia la neutralidad climática impulsando el uso eficiente de recursos, las energías renovables y la movilidad limpia [3].

Among the materials that might be manufactured with laser powder bed fusion (LPBF), one can highlight maraging steels, with excellent weldability, strength and fracture toughness. However, the effects of the processing parameters and the mechanisms governing the as-built texture are not clear yet. A recent publication showed a low texture index in the prior austenite, in contrast to other alloys subjected to LPBF with the same strategy. Authors suggested several hypotheses, although no conclusions were drawn. This work aims to investigate these findings by using a 300 maraging steel processed under different conditions, i.e. different printer, powder layer thickness and laser emission mode. To do so, X-Ray Diffraction, Electron Backscattered Diffraction and Scanning Electron Microscopy have been used. Results show that the heat treatment intrinsic to the LPBF process does not affect the prior austenite grains, whose texture and morphology remain unchanged throughout the process. Also, for the studied ranges, the microstructure texture is not related to the powder layer thickness or to the laser emission mode, although it could be affected by the laser power or the scan strategy. Finally, a low degree of variant selection has been observed, where the selected variants are those that contribute to a martensite cubic rotated texture.

There is a need worldwide to develop materials for advanced power plants with steam temperatures of 700 °C and above that will achieve long-term creep-rupture strength and low CO2 emissions. The creep resistance of actual 9-12Cr steels is not enough to fulfil the engineering requirements above 600 °C. In this paper, the authors report their advances in the improvement of creep properties of this type of steels by the microstructural optimization through nano-precipitation using two methodologies. 1) Applying a high temperature austenitization cycle followed by an ausforming step (thermomechanical treatment, TMT) to G91 steel, to increase the martensite dislocation density and, thus, the number density of MX precipitates (M = V,Nb; X = C,N) but at the expense of deteriorating the ductility. 2) Compositional adjustments, guided by computational thermodynamics, combined with a conventional heat treatment (no TMT), to design novel steels with a good ductility while still possessing a high number density of MX precipitates, similar to the one obtained after the TMT in G91. The microstructures have been characterized by optical, scanning and transmission electron microscopy, EBSD and atom probe tomography. The creep behaviour at 700 °C has been evaluated under a load of 200 N using small punch creep tests.

In this work, different heat treatments were performed in order to study two different bainite morphologies, granular and lath-like, obtained at different cooling rates in a low carbon microalloyed steel. For that purpose, advanced crystallographic characterization and quantitative metallography using SEM, EBSD and TEM were carried out. The evolution of the volume percentage, size, aspect ratio, retained austenite volume percentage and crystallography of the M/A constituents was studied as a function of the cooling rate and classified according to a machine learning algorithm. For the characterization of the crystallography and morphology of the bainitic ferrite matrix, two microstructures were selected as representative of granular and lath-like bainite. The results show that the main differences between granular and lath-like bainite are the size and shape of the M/A constituents, that change progressively from a mixture of large grains, coarse blocks and fine roughly equiaxed grains at low cooling rates to short and long films at high cooling rates. The crystallographic and morphological differences between both microstructures can be explained based on the different driving force and amount of bainitic ferrite formed at the different temperature ranges. These results confirm that the mechanisms by which granular bainite forms are not different from the transformation mechanisms of lath-like bainite.

There is a need worldwide to develop materials for advanced power plants with steam temperatures of 700°C and above that will achieve long-term creep-rupture strength and low CO2 emissions. The creep resistance of actual 9-12Cr steels is not enough to fulfil the engineering requirements above 600°C. In this paper, the authors report their advances in the improvement of creep properties of this type of steels by the microstructural optimization through nano-precipitation using two methodologies. 1) Applying a high temperature austenitization cycle followed by an ausforming step (thermomechanical treatment, TMT) to G91 steel, to increase the martensite dislocation density and, thus, the number density of MX precipitates (M = V ,Nb; X = C ,N) but at the expense of deteriorating the ductility. 2) Compositional adjustments, guided by computational thermodynamics, combined with a conventional heat treatment (no TMT), to design novel steels with a good ductility while still possessing a high number density of MX precipitates, similar to the one obtained after the TMT in G91. The microstructures have been characterized by optical, scanning and transmission electron microscopy, EBSD and atom probe tomography. The creep behaviour at 700°C has been evaluated under a load of 200 N using small punch creep tests.

A developed electrical system enables power to be generated at key locations and distributed widely. To realize such a system requires means of generation, distribution and utilization. Electrical steels play a key role in an electrical system; alongside copper conductors, they make the whole system feasible. This chapter reviews the production and recent developments, with special attention to coating technologies, of the two main groups of electrical steels, i.e. the grain-oriented electrical steels and the non grain-oriented grain electrical steels.

There is a worldwide need to develop materials for advanced power plants with steam temperatures of 700°C and above which have the capacity to achieve high efficiency and low CO2 emissions. This request involves the development of new grades of 9-12Cr heat-resistant steels, with a nanostructured martensite, mainly focusing on the long-term creep rupture strength of base metal and welded joints, creep-fatigue properties, and microstructure evolution during exposure at such elevated temperatures. The main shortcomings of actual 9-12Cr high-chromium steels are that the creep resistance is not enough to fulfill the engineering requirements at temperatures higher than 600°C and the material undergoes a cyclic softening. Creep strength at high temperature could be improved by a microstructural optimization through nano-precipitation, guided by computational thermodynamics, and thermomechanical control process optimization.

Steel remains as one of the most successful and cost-effective material; it is recyclable, possesses great durability and requires low amounts of energy to be produced compared to other materials. During the early 20th century, it was discovered accidentally that alloying steel with high quantities of chromium could make carbon steels corrode less. The addition of chromium promotes the formation of a chromium oxide, (Fe,Cr)2O3, passive surface film of a few nanometers, which protects it of staining, rusting, corroding or oxidizing in environments where normal low alloyed carbon steels are susceptible. Since the production of the first stainless steel, attributed to Harry Brearly (1913, Sheffield, UK), their production has increased, being currently of 48 million and growing at a rate of 5.8 % per year. A wide variety of stainless steel grades is produced and new ones are developed every year to meet the increasing and more severe industrial demands. The use of stainless steels ranges from the low-end products such as water buckets or cutlery, to the very high-end ones, like power plants, spacecraft or surgical implants/tools. The omnipresence of stainless steels in our daily life makes it impossible to enumerate all their applications.