Retained Austenite Control for the Soft Machining of High-Hardness Tool Steels

Most high-hardness tool steels comprising forming dies require expensive finish machining operations to compensate for the dimensional distortion and surface oxidation caused by the die heat treatment. Precipitation-hardening (PH) tool steels allow for soft finish machining followed by an aging treatment without major deformation or oxidation in the die, but exhibit poor wear performance owing to the lack of carbides in their structure. This drawback can be overcome by combining laser cladding technology, austenite retention, and cryogenic treatments. Hence, an alternative die manufacturing route based on laser cladding was explored. The forming surface of a modified chemistry tool steel die was subjected to cladding. The martensite finish (M-f) temperature of the steel was tuned to enhance austenite retention at room temperature. The cladded surface was then machined in a reduced-hardness condition resulting from retained austenite formation. Subsequent deep cryogenic treatment of the die favoured the retained-austenite-to-martensite transformation, thereby increasing the die hardness without major distortion or oxidation. This process combined the advantages of high-carbide-bearing tool steels and PH steels, allowing for a die with hardness exceeding 58 HRC to be finish machined at <52 HRC. Controlling the occurrence of retained austenite represents an effective strategy for achieving new manufacturing scenarios.The authors gratefully acknowledge the funding provided by the Department of Research and Universities of the Basque Government under Grant No. IT947-16 and the University of the Basque Country UPV/EHU under Program No. UFI 11/29

Reconstrucción de la vegetación asociada al depósito tobáceo fluvial Holoceno del Nogal de El Batán, Las Parras del Martín, Cordillera Ibérica

El desarrollo de edificios tobáceos de origen fluvial se asocia a menudo con fases cálidas y húmedas cuaternarias y son comúnmente empleados como indicadores climáticos. En el presente trabajo se estudia el depósito tobáceo fluvial Holoceno del Nogal de El Batán, situado en el valle del río Las Parras (Cordillera Ibérica, NE España), bajo una perspectiva cronológica, estratigráfica y palinológica. La acumulación tobácea de 8, 2 m de espesor, intercala gravas, facies de rudstones de fitoclastos, boundstones de tallos, limos y arenas de composición carbonatada, además de margas, lime mud y niveles turbosos. La acumulación tobácea se emplaza en el Holoceno temprano final (ca. 8400 cal BP) y se correlaciona con los cambios ambientales ocurridos en la región, identificando tres fases principales. Los análisis polínicos señalan un paisaje dominado por coníferas en la base de la secuencia, esencialmente Pinus nigra/sylvestris tipo y Juniperus, mientras que localmente se desarrolla un bosque ripario donde destacan Corylus, Alnus, Salix, Populus, Celtis, Fraxinus, Tamarix y Rosaceae. En el Holoceno medio (ca. 8000-5000 cal BP) se produce la máxima expansión de las quercíneas, junto con taxones termófilos como Pistacia, Rhamnus, Arbutus y Olea. El incremento de taxones herbáceos y ruderales, y en especial la aparición de esporas coprófilas, marca la expansión agro-pastoril a lo largo del valle fluvial durante el Holoceno tardío (ca. 4300 cal BP). Development of Quaternary fluvial tufa buildings are often associated with warm and humid phases and are commonly used as climate indicators. El Nogal de El Batán Holocene fluvial tufa buildup, located in Las Parras River valley (Iberian Range, NE Spain), is investigated, following radiocarbon dating, stratigraphic description and palynological analysis. The studied deposit, 8.2 m-thick, is formed of gravels, phytoclast rudstones, calcite-coated stem boundstones and fine carbonate deposits (sands, silts and marls) with peaty horizons and carbonaceous debris. It has been dated within the upper early Holocene (ca. 8400 cal BP) and correlated with the environmental changes reconstructed for the region, identifying at least, three main phases. Pollen results highlight the existence of a conifer landscape, mainy dominated by Pinus nigra/sylvestris type and Juniperus, and locally dense riparian woodland with Corylus, Alnus, Salix, Populus, Celtis, Fraxinus, Tamarix and Rosaceae. Deciduous and evergreen oaks were the main spread regional forests accompanied by many warm-loving taxa like Pistacia, Rhamnus, Arbutus and Olea during the middle Holocene (ca. 8000-5000 cal BP). The transition towards the late Holocene (ca. 4300 cal BP) is evidenced by the rise of herbs and ruderal taxa, and especially the presence of coprophilous fungi, which are linked to the spread of agricultural and grazing practices along the river valley. © 2021, Asociacion Espanola para el Estudio del Cuaternario (AEQUA). All rights reserved

Microstructural Tuning of a Laser-Cladding Layer by Means of a Mix of Commercial Inconel 625 and AISI H13 Powders

The aim of this work is to evaluate the microstructural evolutions developed by mixing a corrosion-resistant and high-performance material with a high-hardness material in a coating obtained by laser-cladding technology. In this paper, five different mixtures of Inconel 625 alloy and AISI H13 steel powders have been deposited on a plate of 42CrMo4 steel using a 2.2 kW diode pumped Nd:YAG laser. The effect of adding tool steel to a Ni-based superalloy has been analyzed by the characterization of each cladded sample using optical microscopy and scanning electron microscopy (SEM). The precipitates observed in the samples have been analyzed by energy dispersive X-ray spectroscopy (EDS X-ray). SEM micrographs and EDS analysis indicate the existence of Laves phase. It has been observed that the presence of these precipitates is stabilized in a certain range of AISI H13 addition

Microstructural and micromechanical characterization of Ti-6Al-4V samples produced by laser cladding

Additive manufacturing of metals is an innovative technology that stimulates much interest. In the particular case of titanium alloys, this technology is nowadays used to produce components, mainly for the aeronautic industry, achieving important weight and cost reduction. This paper deals with the microstructural and micromechanical characterization of small size samples of Ti-6Al-4V manufactured by direct energy deposition. Specifically, the technology employed to produce those samples was laser cladding, with powder as a raw material. The main aim behind this research is to analyze the influence of several manufacturing parameters, such as the laser power and the deposition speed, on the geometrical aspect and the microstructural characteristics of the different samples produced. Also, nano-indentacion and micro-hardness tests have been performed to extract the nano- and the micromechanical response in terms of hardness of the samples.Postprint (published version

Reconstrucción de la vegetación asociada a depósitos tobáceos fluviales holocenos del sistema ibérico.

Fluvial tufa build- ups located in the Queiles, Val and Las Parras del Martín river valleys (Iberian Range, NE Iberia), are investigated following radiocarbon dating, palynological and anthracological analyses. The studied tufa deposits have been framed within the Early-Mid Holocene (ca. 9500 to 4000 cal yr BP) in agreement with regional palaeoenvironmental evidences. The obtained palaeobotanical results highlight the existence of dense riparian woodland where diverse broadleaved trees defined the main vegetation features in the river valleys. Deciduous and evergreen oaks were the main spread regional forests accompanied by many warm-loving taxa. Pinewoods were usually confined to high-altitude elevations, although their presence is also relevant around El Batán deposit (in Las Parras del Río Martín) during the Early Holocene. The transition towards the Late Holocene is evidenced by the rise of nitrophilous and ruderal taxa, which are linked to the spread of agricultural and grazing practices along the river valleys

Escenarios, tempo e indicadores paleoambientales para la identificación del Antropoceno en el paisaje vegetal del Pirineo Central (NE Iberia)

The Anthropocene is related to the origin of current landscape configuration, and in terms of vegetation, with the consideration of human action as main forcing of clear, intense and permanent changes through time. In this paper we compile and compare data from palynological sequences, microcharcoal records, archaeological sites and radiocarbon dates from palaeofires located in the Central Pyrenees besides historical documents, and we argue that some evidences related to early deforestation processes and use of human fire are not so clear than some authors point. Conversely, indicators of unequivocal human use and the origin of cultural landscapes are located only a few centuries and not a few millennia ago. In fact, high temporal and spatial variability is recorded until the Middle Ages (last 700 years, 1300 AD), when a series of consistent and permanent changes suggest the onset of the Anthropocene.El Antropoceno puede considerarse como el origen de la configuración paisajística actual, y en relación a la vegetación, como el periodo en el que la intervención humana es el agente principal de los cambios que se producen de forma clara, intensa y permanente en el tiempo. En este trabajo se recopilan y comparan datos de secuencias palinológicas y de microcarbones, ocupaciones de yacimientos arqueológicos y dataciones de paleoincendios localizados en el Pirineo Central, además de información documental, exponiendo una reflexión sobre las supuestas evidencias que promulgan una deforestación temprana y el uso del fuego de origen antrópico como señal inequívoca de intervención humana y surgimiento de los paisajes culturales desde hace milenios. En realidad, lo que se constata es una alta diversidad temporal y espacial entre todos los indicios, y sólo a partir de la Baja Edad Media (últimos 700 años, 1300 AD), los indicadores y valores de los mismos ofrecen auténtico consenso sobre el inicio de cambios consistentes y duraderos que marcarían el inicio del Antropoceno

Environmental and climate change in the southern Central Pyrenees since the Last Glacial Maximum: A view from the lake records

In this contribution we compile and summarize the available paleo-environmental lacustrine data for the last 20,000 years from the southern Central Pyrenees (from west to east: El Portalet, Tramacastilla, Basa de la Mora, Estanya, Redon, Montcortès and Marcelino lakes) and present a new sequence from mid altitude (Holocene record of Lake Estanya). Multiproxy analyses of lake records have identified large vegetation and hydrological changes during last glacial, deglaciation and the Holocene periods at millennial, centennial and even decadal scales and documented their timing, intensity and varied nature. The review indicates that landscape dynamics in the Pyrenees have been greatly controlled by both long term and abrupt climate changes and, since the Middle Holocene, and particularly since Medieval times, by human activities as new transforming agent. Although high internal variability characterized every site, common temporal trends are evidenced, as well as a suggestive western–eastern gradient superimposed to the expected altitudinal one (highlands versus lowlands). Thus, the long-term Central Pyrenees environmental history presents a relatively high degree of internal coherence across space and provides some past scenarios of landscape-climate interactions to evaluate the expected impacts of current and future Global Change.CICYTOrganismo Autónomo de Parques NacionalesGobierno VascoDepto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEpu