Influence of pre-existing martensite on the wear resistance of metastable austenitic stainless steels

The effect of pre-existing martensite on the sliding wear behavior of a commercial metastable austenitic stainless steel was investigated. Two different steel conditions were considered: annealed (with a fully austenitic microstructure) and cold rolled, consisting of mixtures of austenite and martensite. Wear tests were carried out using ball on disc technique at constant velocity and different sliding distances. Correlation between microstructure and wear mechanisms was performed by X-ray diffraction, electron back-scattered diffraction and focus ion beam. Results show that wear resistance decreases at increasing the amount of pre-existing martensite. In this sense, more strain-induced martensite developed for cold rolled samples, hardening the surface and consequently reducing wedge formation, which induced material removal from the surface. The detailed analysis of the wear track demonstrated the formation of an ultrafine-grain layer just below the surface, not only for annealed but also for cold rolled steel.Peer ReviewedPreprin

Martensitic transformation during fatigue testing of an AISI 301LN stainless steel

The plastic deformation accumulated during fatigue testing can induce the transformation of austenite to martensite in metastable austenitic stainless steels. To analyze this issue, a metastable austenitic stainless steel grade AISI 301 LN was studied in two different conditions, i.e. annealed and cold rolled. In the first case, the steel was fully austenitic, whereas cold rolled material had almost 30% of martensite. High cycle fatigue tests at a stress ratio of 0.8 were carried out on flat specimens from both steel conditions. Several characterization techniques, including optical microscopy, X-ray diffraction (XRD) and electron back scattered diffraction (EBSD), were used to detect and quantify the martensite induced by the cyclic deformation.Postprint (published version

Una auténtica escuela internacional de ingeniería: la EEIGM

El presente artículo presenta algunas estadísticas sobre la movilidad internacional de estudiantes universitarios en los últimos años. En ese contexto, es reseñable dar a conocer que existe una titulación que fue pionera, pues celebró ya su vigésimo año de funcionamiento el pasado mes de septiembre de 2011. Dicha titulación es la EEIGM, siglas que corresponden a su denominación en francés: Ecole Européenne d’Ingénieurs en Génie des Matériaux. Se trata de una escuela de Ingeniería de Materiales creada en 1991 a partir de la colaboración de universidades de tres países europeos: Francia, Alemania y España, a las que poco después se unió una institución sueca. En la actualidad, otras tres universidades integran también el consorcio de la EEIGM: una de Polonia, otra de Rusia y una segunda universidad española. Además existen acuerdos activos para intercambios de estudiantes con centros de Marruecos, Túnez, China, Brasil, Japón y Rumanía. La EEIGM ofrece a sus titulados una sólida formación en el ámbito de la ciencia e ingeniería de los materiales, pero además, y no menos importante, es que durante su vida como estudiantes habrán aprendido al menos tres idiomas y descubierto diferentes culturas. Esta formación es altamente valorada por las empresas. No es casualidad que el tiempo necesario para que un ingeniero de la EEIGM encuentre su primer empleo sea de apenas dos meses.Peer Reviewe

Una auténtica Escuela Internacional de Ingeniería: EEIGM

En el contexto actual del Espacio Europeo de Educación Superior (EEES), merece la pena destacar que existe una titulación pionera en este sentido, pues celebró ya su vigésimo año de funcionamiento en septiembre de 2011. Esta original titulación es la EEIGM (Ecole Européenne d’Ingénieurs en Génie des Matériaux). Se trata de una escuela de ingeniería de materiales creada en 1991 a partir de la colaboración de tres universidades de diferentes países: Institut National Polytechnique de Lorraine (Francia), Universität des Saarlandes (Alemania) y Universitat Politècnica de Catalunya, a las que en 1994 se les unió una cuarta institución de educación superior, Luleå Tekniska Universitet (Suecia). Más recientemente, en concreto en el año 2009, dos universidades más se adhirieron al EEIGM: AGH University of Science and Technology (Polonia) y Universitat Politècnica de Valencia. Y la expansión continua, pues el próximo curso 2012-13 una nueva universidad se integrará en el consorcio: la prestigiosa National University of Science and Technology (MISIS) de Moscú. Pero además la EEIGM cuenta actualmente con una apertura internacional que desborda el marco de las universidades europeas asociadas. Así, existen acuerdos activos de intercambios de estudiantes con universidades en Marruecos, Túnez, China, Brasil, Japón y Rumanía. La EEIGM permite a sus titulados adquirir una sólida formación en el ámbito de la ciencia e ingeniería de los materiales. Pero además, y no menos importante, es que durante su vida como estudiantes habrán aprendido al menos tres idiomas y descubierto diferentes culturas. Esta formación es altamente valorada por las empresas. Por ello el tiempo necesario para encontrar un primer empleo se sitúa en menos de 6 meses y el salario medio supera los 32000 € anuales.Postprint (published version

Effect of laser surface texturing on Schmid factor and plastic deformation mechanisms on AISI 301LN steel

In this comprehensive study, the multifaceted impact of laser surface texturing (LST) on AISI 301LN stainless steel is explored. Changes in the microstructure, mechanical properties, and grain characteristics are examined. The dynamic relationship between Schmid factor evolution and plastic deformation in this stainless steel alloy is unveiled through the analysis of grain statistics and individual grain scrutiny. It is revealed that LST initiates the formation of strain-induced a’-martensite, grain refinement, and substantial hardness enhancements. Notably, an a’-martensite crystalline size of 2.05 Å is induced by LST. Furthermore, a 12% increase in tensile strength is observed after LST along with an 11% boost in yield strength. However, reductions of 19% in elongation to fracture and 12% in the area reduction are experienced.This research was funded by AGAUR, Agency for Administration of University and Research (Agència de Gestió d’Ajuts Universitaris i de Recerca), grant number FI-SDUR 2020.Peer ReviewedPostprint (published version

Exploring the effects of laser surface modification on AISI 301LN steel: a micro-mechanical study

This article investigates the surface hardening capability of a metastable austenitic TRansformation Induced Plasticity (TRIP) stainless steel, particularly on AISI 301LN, by laser texturing. This technology produces microstructural surface changes in terms of both phase transformation and grain size modification and, as a direct consequence, the laser influences the surface characteristics, mainly hardness and roughness. In this sense, the key parameters (laser power, scanning speed and position of the focal length) were investigated by using a Design of Experiments (DoE) in detail to better understand the correlation between texturing parameters, microstructural and mechanical changes, always at the superficial level. From all the aforementioned information, the results show that the maximum surface hardening is obtained by increasing the laser power and decreasing the scanning speed. Furthermore, by reducing the focal distance, the depth of the microstructural evolution layer is more significant, while the width is less affected. Finally, a suitable model was developed to correlate the processing parameters here investigated with the resulting surface integrity, in terms of mechanical properties, by means of a regression equation.This research was funded by AGAUR, Agency for Administration of University and Research (Agència de Gestió d’Ajuts Universitaris i de Recerca), grant number FI-SDUR 2020.Peer ReviewedPostprint (published version

Fatigue propagation of long cracks in metastable austenitic stainless steels

Fatigue crack growth of a metastable austenitic stainless steel was investigated in thin specimen under positive stress ratio. Annealed and Co l d rolled conditions were used to test the influence of the microstructure. The influence of load ratio and load history on propagation behavior was analyzed using the Elber`s closure approach, the Donald and Paris partial crack closure and the empirical Kujawski (∆K•Kmax) α parameter. Results show that load ratio effects could be explained by two parameters concepts . It see ms that the amount of martensite transformation is responsible for the observed differences in fatigue crack growth resistance.Postprint (published version

Phase transformation and residual stresses after laser surface modification of metastable austenitic stainless steel

Laser surface modification treatments have been applied to samples of a metastable austenitic stainless steel AISI 301LN. The amount of residual stresses and the presence of induced a´-martensite phase on the surface and subsurface of the samples, as a consequence of laser modification, have been investigated in this study. X-ray diffraction has been used to measure these values, which is a non-destructive method. Laser modification has been applied as parallel lines at a distance of 40 µm, using a laser intensity of 4 A and scanning speeds of 1, 3, and 5 bits/ms, frequency had a constant value of 1000 Hz. The results of the phase analysis show an increase in the a´-martensite present in the surface modified by the laser and that the sample corresponding to the lowest laser speed has the highest martensite fraction. Also, high tensile residual stresses were generated, more pronounced for the lowest laser scanning speed.Peer ReviewedPostprint (published version