Juan Asensio-Lozano

The construction sector is presently among the most resource-intensive industries, driving a substantial body of research dedicated to the development of more sustainable materials to address these demands. A particularly promising approach within the framework of the circular economy is the repurposing of waste as a principal raw material for the creation of new construction products. Within this context, the primary aim of this study is to engineer ceramic materials for brick production using 100% waste-derived inputs, specifically aggregate washing sludge and manganese mining by-products. To evaluate the potential of these sustainable ceramic materials, an extensive investigation was conducted, encompassing both physical and mechanical testing, as well as a thorough characterisation of the waste inputs. For this purpose, a series of ceramic specimens were fabricated with varying proportions of mining residues and aggregate washing sludge, adhering to the conventional protocols employed in the manufacture of ceramic bricks. The results demonstrate that these sustainable ceramics exhibit a linear shrinkage reduction of up to 5% compared to traditional clay-based ceramics. Furthermore, they show water absorption levels—whether via capillarity, cold water, or hot water absorption—that are up to twice those observed in conventional clay ceramics, while maintaining comparable density values. This increased absorption, however, correlates with a reduction in mechanical strength at higher concentrations of manganese waste, yet the material continues to meet the minimum strength requirements as specified by industry standards for such products. In conclusion, this research introduces a novel, sustainable ceramic material that not only reduces economic and environmental costs but also adheres to the required performance criteria for construction applications.

Hypoeutectic white cast irons with a high chrome content are commonly used in the industrial mining sector where there is a demand for both high resistance to adhesive wear and an acceptable toughness for the absorption of impacts and falls of diverse materials. Through the application of a design of experiment (DoE) technique, factors related to thermal treatment are analyzed with respect to resistance to sliding wear, maximum rupture stress and toughness. The results show that, in order to increase resistance to adhesive wear, it is convenient to use destabilization temperatures of 1050 °C and tempering of two hours at 400 °C. This foments a very hard martensite and a high proportion of highly alloyed retained austenite, which, with low tempering, achieves a precipitation of carbides from this austenite with hardly any loss of hardness of the martensite. In order to increase the energy which this material is capable of absorbing until breakage, furnace cooling set at 150 °C followed by tempering at 550 °C would be favorable. Slower cooling implies a greater quantity of conditioned retained austenite, so that, following this, it may be transformed into lower bainite with a high density of finely dispersed precipitated carbides. Furthermore, this tempering also allows the transformation of martensite into ferrite with finely dispersed carbides.

Hypoeutectic high chromium white cast irons are commonly used in the mining and cement industries, where high resistance to abrasive wear is demanded. Through the application of a Design of Experiment technique (DoE), different factors related to thermal industrial treatments are analysed with regard to resistance to abrasive wear and impact response. Abrasion tests were carried out in accordance with the ASTM G065-16 standard. The provisional results show that to increase wear resistance, high destabilisation temperatures (1050 °C) followed by slow cooling to room temperature (RT) and subsequent tempering at 400 °C are most favourable. This is because these conditions are favourable to maintaining a certain tetragonality of the martensite after tempering and also, because of the presence of a high density of mixed carbides M₇C₃, through a secondary precipitation during cooling. Oil quenching and a high tempering temperature (550 °C) with long dwell times of 6 h were found to increase impact toughness. These conditions favour a lack of retained austenite. The presence of retained austenite was found unfavourable for both wear resistance and toughness, whereas tempering at 400 °C has been shown to be insufficient to transform martensite on tempering, which in turn seemed to increase the hardness of the matrix constituent.

In this article, the effects of an ionic nitriding treatment are analysed, together with deliberate variation of different thermal parameters associated with the destabilisation of austenite, on erosive wear resistance of white cast irons with 25% Cr. The methodology followed in this research was an experimental design, where six factors were analyzed by performing eight experiments. The thickness of the nitrided layer is much smaller than in white cast iron with lower percentages in Cr, never reaching 20 microns. The nitriding treatment entails considerable softening of the material underneath the nitriding layer. This softening behaviour becomes partially inhibited when the destabilisation temperature of austenite is 1100 °C and dwell times at such temperature are prolonged. This temperature seems to play a significant role in the solubilization of non-equilibrium eutectic carbides, formed during industrial solidification. The nitriding treatment leads to additional hardening, which, in these cases, favours a second destabilisation of austenite, with additional precipitation of secondary carbides and the transformation of retained austenite into martensite. Despite softening of the material, the nitriding treatment, together with air-cooling after destabilisation of the austenite, allows a noticeable increase in resistance to erosive wear.

Hypoeutectic white cast irons containing 25% Cr are used in ore-processing industries due to their high resistance to erosive wear. Applying a Design of Experiments (DoE), the aim of this study is to analyse the influence of thermal processing factors on the microstructural variation of a white cast iron containing 25% Cr and 0.6% Mo. The carbides present in the as-cast state are of the M₇C₃, M₂C, and M₃C types. M₂C carbides precipitate on the eutectic M₇C₃ carbides favoured by heterogeneous nucleation conditions. Two kinetics compete during the destabilisation of austenite. One dissolves those eutectic carbides precipitated as a result of non-equilibrium solidification (M₇C₃ and M₂C), while the other enables the precipitation of secondary M₇C₃ and M₂₃C₆ carbides. The M₇C₃ carbides begin to precipitate first. Low destabilisation temperatures and short dwell times are insufficient to dissolve the precipitated eutectic carbides from non-equilibrium conditions, thus favouring the presence of M₂C carbides, which are associated with Mo. The factor that has the greatest influence on hardness is the tempering temperature. The optimal tempering temperature is found to be 500 °C. Short tempering times maintain the distortion of the ferrite unit cell. The precipitation of Cr carbides during tempering requires a temperature of 500 °C and the prior dissolution of the carbon precipitated during the initial stages of said tempering. With short tempering times, the Cr atoms still remain dissolved in the ferrite, distorting its unit cell and increasing the hardness of the matrix constituent of the alloy.

In the as-cast state, Al–Mg–Si alloys are not suitable for hot forming. They present low ductility due to the presence of intermetallic β-AlFeSi particles that form in the interdendritic regions during the solidification process. Homogenization treatments promote the transformation of these particles into α-(FeMn)Si particles, which are smaller in size and more rounded in shape, thus improving the ductility of the material. This paper analyses the influence of various solution treatments on the transformation of β-AlFeSi particles into α-(FeMn)Si particles in an Al 6063 alloy. Their effect on different ageing treatments in the 150–180 °C temperature range is also studied. An increase in the solution temperature favours greater transformation of the β-AlFeSi particles into α-(FeMn)Si, dissolving a greater amount of Si, thereby having a significant effect on subsequent ageing. We found that as the dwell time at a temperature of 600 °C increases, the rate of dissolution of the Fe atoms from α-(FeMn)Si particles exceeds the rate of incorporation of Mn atoms into said particles. This seems to produce a delay in reaching the peak hardness values in ageing treatments, which warrants further research to model this behaviour. The optimal solution treatment takes place at around 600 °C and the highest obtained peak hardness value is 104 HV after a 2 h solution treatment at said temperature and ageing at 160 °C for 12 h.

Hypoeutectic white cast irons containing 25% Cr are used in very demanding environments that require high resistance to erosive wear, for instance, the crushing and processing of minerals or the manufacture of cement. This high percentage in Cr, in turn, favors corrosion resistance. The application of a Design of Experiments (DoE) allows the analysis of the effects of modifying certain factors related to the heat treatments applied to these alloys. Among these factors, the influence of prior softening treatment to facilitate the machining of these cast irons and the influence of the factors related to the destabilization of austenite, during both quenching and tempering, were analyzed. The precipitated phases were identified by X-ray diffraction (XRD), while the Rietveld structural refinement method was used to determine their percentages by weight. Erosive wear resistance was calculated using the ASTM G76 standard test method. It is concluded that the thermal softening treatment, consisting of 2 h at 1000 °C and 24 h at 700 °C, does not result in additional softening of the material compared to its as-cast state. Furthermore, it is observed that not only eutectic carbides influence wear resistance, but that the influence of the matrix constituent is also significant. It is also verified that the tempering treatment plays a decisive role in wear resistance. Temperatures of 500 °C and tempering times of 6 h increase the wear resistance and hardness of the aforementioned matrix constituent. Tempering temperatures of 200 °C lead to an increase in retained austenite content and the presence of M₃C carbides versus mixed M₇C₃ and M₂₃C₆ carbides. The quench cooling medium is not found to have a significant influence on the hardness or wear resistance.

High-Cr hypo-eutectic white cast irons are used in very demanding environments that require high resistance to erosive wear. The influence on the microstructural variation and erosive wear resistance of several fundamental factors related to the thermal treatments of these cast irons was analysed by means of a fractional Design of Experiments (DoE). These factors included the ones related to the destabilization of austenite. The precipitated phases were identified by X-ray diffraction (XRD), while the Rietveld structural refinement method was used to determine their percentages by weight. Erosion wear resistance was calculated using the test defined by ASTM G76. It was concluded that the quench cooling medium does not significantly influence either erosive wear resistance or the proportion of martensite or retained austenite. The destabilization temperature is a key factor with respect to the percentage of retained austenite. In order to increase the amount of martensite and decrease the amount of retained austenite, temperatures not exceeding 1000 °C are required. An increase of 100 °C in the destabilization temperature can lead to a 25% increase in retained austenite. Moreover, tempering temperatures of around 500 °C favour an additional increase in the percentage of martensite. Erosive wear commences on the matrix constituent without initially affecting the eutectic carbides. Once the deterioration of the matrix constituent surrounding these carbides occurs, they are released. High tempering times provide an increase in resistance to erosive wear due to a second destabilization of austenite during the said tempering.

Vanadis 10 steel is a powder metallurgy (PM) processed tool steel. It is a ledeburitic steel with 8% Cr and 10% V. By deliberately varying the process parameters related to the quenching, tempering, and nitriding of these steels, the aim of this study is to determine which of these parameters have a significant influence on its adhesive wear resistance. The research methodology employed was a Design of Experiments (DoE) with six factors and two levels for each factor. The tempering temperature, number of temperings, and carrying out of a thermochemical nitriding treatment were found to have a significant effect. To increase adhesive wear resistance, austenitization at 1100 °C with air cooling is recommended, followed by three temperings at 500 °C and a subsequent nitriding treatment. It should be noted that the quench cooling medium does not have a significant influence on wear resistance. Furthermore, (Fe,Cr)₇C₃ (M₇C₃ carbides) are transformed into carbonitrides during nitriding. However, (Fe,V)C (MC carbides) are not affected by this nitriding process.

Vanadis 10 steel is a powder metallurgy processed tool steel. The aim of the present study is to analyze the microstructural variation in this steel that takes place when the process variables related to the heat treatments of quenching and tempering are modified. Specifically, the destabilization of austenite, the precipitation of secondary carbides and the amount of retained austenite were analyzed. The research methodology employed was a Design of Experiments (DoE). The percentage and types of precipitated crystalline phases were determined by XRD, while the microstructure was revealed by means of SEM-energy-dispersive X-ray spectroscopy (EDX). The destabilization of austenite was favored by tempering at 600 °C for at least 4 h. These same conditions stimulated the removal of the retained austenite and the precipitation of M₇C₃ secondary carbides. For the precipitation of MC secondary carbides, it was necessary to maintain the steel at a temperature of 1100 °C for at least 8 h. The highest hardness values were obtained when the tempering temperature was lower (500 °C). Tempering in air or oil did not have a significant influence on the hardness of the steel after double or triple tempering at 500 or 600 °C. These results allow the manufacturers of industrial tools and components that use this type of steel in the annealed state as a material to define the most suitable quenching and tempering heat treatment to optimize the in-service behavior of these steels.