Alejandro Basso - Academia.edu (original) (raw)
Papers by Alejandro Basso
Frattura ed Integrità Strutturale
In this work, the effect of Ti addition and the cast part size on the solidification structure an... more In this work, the effect of Ti addition and the cast part size on the solidification structure and mechanical properties of a medium carbon, low alloy cast steel was analyzed. The experimental analysis involved the design of the melts by using Thermo-Calc® software, where different amounts of Ti added to a standard chemical composition of an AISI 13XX steel were simulated. Then, the solidification macrostructure (dendritic pattern and grain size) and microstructure were characterized by using conventional and specific metallographic techniques. Finally, the mechanical behavior in terms of hardness and tensile properties were evaluated. The results show that the addition of 0.12% of Ti promotes a fine dispersion of Ti nitrides and carbides, but when the Ti concentration raises to 0.2%, the size of the Ti nitrides and carbides increases while its amount decreases. Ti nitrides and carbides particles act as nucleation sites for the precipitation of ferrite from austenite, and it was fou...
Frattura ed Integrità Strutturale
The first stage of this study investigates the precipitation of free ferrite from the austenite o... more The first stage of this study investigates the precipitation of free ferrite from the austenite on fully austenitized ductile iron. Several sets of samples of low alloy ductile iron are fully austenitized and then cooled down to different temperatures and different times within the intercritical austenite-ferrite-graphite phase field. Based on these results, heat treatment cycles aimed at obtaining microstructures composed of free ferrite and ausferrite are carried out. Tensile, impact and toughness tests are performed to characterize the mechanical properties. The results show that, related to the high strength austempered ductile iron grades, the best combinations of properties were obtained from the mixed structures composed of 5% free ferrite and 95% ausferrite, resulting from the austempering at 280°C. These amounts of free ferrite allow obtaining an increase of the elongation (about 50%) and impact toughness (about 10%) while the tensile strength and fracture toughness decreas...
En los ultimos anos, se ha comenzado a estudiar una variante de las fundiciones esferoidales aust... more En los ultimos anos, se ha comenzado a estudiar una variante de las fundiciones esferoidales austemperizadas (ADI) denominada “ADI-Dual-Phase”, cuya matriz esta compuesta por ferrita libre y ausferrita [1-4]. La presencia de ferrita incrementa la elongacion y la fractotenacidad de las ADI, haciendola apta para aplicaciones de alto compromiso, como partes de suspension de automoviles. Un ciclo termico utilizado para obtener estructuras ADI-Dual-Phase, desarrollado por los autores del presente trabajo [4], consiste en someter a una FE a una austenizacion completa (etapa 1), seguida de un enfriamiento a una temperatura dentro del intervalo intercritico ?-?-grafito del diagrama Fe-C-Si y mantenimiento durante un determinado tiempo (etapa 2), seguido de un ciclo de austemperizado (etapa 3). Durante la etapa 2, se produce la transformacion austenita a ferrita: la ferrita nuclea y crece con una velocidad que depende de la temperatura y tiempo de mantenimiento dentro del intervalo intercrit...
International Journal of Cast Metals Research, 2020
High-silicon cast steels and proper heat treatment cycles were designed in order to obtain carbid... more High-silicon cast steels and proper heat treatment cycles were designed in order to obtain carbide-free bainitic microstructures. The design process allowed to obtain the desired microstructures after heat treatment cycles compatible with industrial practices and using low amounts of inexpensive alloying elements. The different chemical compositions and austempering temperatures tested resulted in ultra-high-strength steels showing remarkably total elongations. The obtained tensile properties satisfy the minimum requirements specified for AHSS in ASTM A1088 standard, and also the requirements for high-strength cast steels stated in ASTM A148. Moreover, many microstructures developed in this work reach the tensile performance of the very expensive maraging steels.
International Journal of Metalcasting, 2020
Three medium-carbon, high-silicon cast steels with different alloy contents were austempered at 3... more Three medium-carbon, high-silicon cast steels with different alloy contents were austempered at 330°C for different holding times in order to obtain carbide-free bainitic microstructures. Aiming at evaluating the influence of holding time and microstructural features on strength and ductility, tensile properties were measured for each steel at selected austempering times. The results obtained indicate that it is possible to adjust holding time in order to obtain the best strength/ductility combination at determined austempering temperature. Moreover, it has been shown that the mechanical stability of retained austenite is the key factor in controlling tensile performance. Short austempering times result in low carbon enrichment of the austenite (low stability) and promote higher ultimate tensile strength and lower ductility. For longer austempering times, steels present a slight decrease in ultimate tensile strength but a marked increase in ductility. This work shows that it is possible to obtain cast steels with ultimate tensile strength of 1682 MPa, yield strength of 1493 MPa and total elongation of 12.5% by means of bainitic reaction. This strength/ductility combination and others reported in this study are remarkable for cast steels.
International Journal of Cast Metals Research, 2018
This study investigates the effect of chemical composition and microsegregation on the bainitic t... more This study investigates the effect of chemical composition and microsegregation on the bainitic transformation of high Si cast steels at two different austempering temperatures. The advance of the bainite precipitation as a function of time and temperature was monitored through measurements of the amount of retained austenite by X-ray diffraction, the evolution of hardness and microstructural characterization. The results showed that the bainitic transformation starts preferentially at zones with lower contents of alloying elements but later covers the entire matrix. The austempering heat treatments resulted in an apparently homogeneous bainitic microstructure throughout the entire matrix after a short period of time. The results encourage the continuation of the development of high Si steels suitable to produce carbide-free austempered cast parts.
International Journal of Cast Metals Research, 2017
Abstract In this work the percent dimensional change (DC%) and its dispersion in high silicon Duc... more Abstract In this work the percent dimensional change (DC%) and its dispersion in high silicon Ductile Iron with ADI and Dual-Phase-ADI structures obtained through heat treatment starting from different as-cast microstructures, was studied. Specimens were obtained from three different melts with Si content ranging from 3.1 to 4.2%. Dual-Phase-ADI structures were obtained using special heat treatment, starting from as-cast structures. Regarding dimensional change, DC% in ADI and Dual-Phase-ADI decrease as Si% and the proportion of ferrite phase in as-cast specimens increased. On the other hand, DC% increased with austenitizing temperature and ausferrite content in the final microstructure. A fuzzy model to predict DC% in ADI parts was adapted to include DC% prediction in Dual-Phase-ADI. The fuzzy model allowed to predict the DC% for ADI and Dual-Phase-ADI parts with an root mean square <0.05%.
Materials Science and Technology, 2019
A high silicon, medium carbon cast steel was designed and heat-treated in order to develop micros... more A high silicon, medium carbon cast steel was designed and heat-treated in order to develop microstructures composed of carbide-free bainite and small amounts of free ferrite, with the aim of obtaining high strength cast steels with improved ductility. Because of microsegregation, it was observed that ferrite present in partially austenitised samples is mostly present at the highly alloyed zones, creating an interconnected network even for low proportions of this phase. Despite the coarse solidification structure and marked microsegregation in the cast steel, the mechanical properties obtained for both fully bainitic and bainitic-ferritic microstructures largely satisfy the minimum standard requirements for high strength cast steels and are similar to those reported for wrought steels of similar microstructures.
International Journal of Metalcasting, 2012
During the last few years, researchers have sought new ductile iron (DI) applications focusing on... more During the last few years, researchers have sought new ductile iron (DI) applications focusing on the development of mixed microstructures, such as ferritic-bainitic or ferritic-martensitic. These kinds of structures result in DI with a good combination of mechanical properties, compared to other conventional DI. The combination of properties offered by the mixed structure DI, particularly in "dual phase austempered ductile iron" (ADI) has opened new horizons for cast iron to replace steel castings and forgings in many engineering applications. This new DI has a particular microstructure composed of different amounts and morphologies of ausferrite and free ferrite. Dual phase ADI microstructures have afforded more opportunities for DI applications, acquiring better combinations of strength, ductility and toughness. This review describes the methodologies used to obtain this new kind of DI and the principal mechanical properties.
ISIJ International, 2015
This work deals with the feasibility of obtaining Austempered Ductile Iron with Dual Phase struct... more This work deals with the feasibility of obtaining Austempered Ductile Iron with Dual Phase structures (DPADI) through heat treatment, starting from different as-cast microstructures. The mechanical properties on these microstructures were evaluated. DPADI microstructures were obtained by adding different tenors of silicon (2.4% to 4.2%) to the melts and keeping the other alloying elements constant. The study focused on the determination of the time required to achieve the percentages of equilibrium phases (ferrite and austenite) at different temperatures in the intercritical temperature interval as a function of the starting as cast microstructure. The results showed that, as the silicon content increases, higher amount of ferrite is present in the as cast structure, and the time required to reach the thermodynamic equilibrium phases in the intercritical temperature interval is markedly reduced. Similarly, for a constant chemical composition, as the intercritical austenitizing temperature increases, the time required to reach the quantities of the equilibrium phases decreases. Regarding mechanical properties, the tests revealed that, as expected, as intercritical austenitising temperature increases so do tensile strength and hardness due to the higher ausferrite content in the DPADI matrix. These results indicate that high silicon Ductile Iron (with Si content higher than 3%) with a mostly ferritic microstructure in as cast conditions yields DPADI microstructures able to dispense with prior annealing heat treatments since the time required to reach the phase equilibrium percentages is compatible with the industrial practice and the mechanical properties are similar as compared to DPADI structures deriving from fully ferritic matrices.
Materials Science and Technology, 2009
The present work aims to evaluate and compare the influence that section size has on the microstr... more The present work aims to evaluate and compare the influence that section size has on the microstructure and properties of fully ferritic, fully ausferritic and dual phase ADI matrices. Samples taken from 'Y' blocks of 25, 50 and 75 mm thickness were used to perform metallographic studies and mechanical tests. Cooling rate differences arising from changes in section size promote different microsegregation characteristics affecting solid state transformations and, consequently, the final microstructure and properties. When the section size increases, some properties decrease. The strongest deleterious effect was ascribed to the elongation and impact of ADI samples, where drops of nearly 40% were reached when specimens taken from the thinnest 'Y' blocks were compared to those taken from the thickest ones. Regarding fracture toughness, ferritic matrices exhibited the most noticeable detrimental effect. Dual phase ADI samples, on the other hand, presented the least deleterious section size effect on all the studied properties.
Materials Science Forum, 2014
This work focuses on the study of the solid state transformations that take place during the aust... more This work focuses on the study of the solid state transformations that take place during the austempering of high silicon carbide-free bainitic cast steels with different chemical composition. In order to get this objective three cast steel melts with different chemical compositions were produced, evaluating the influence of Cr, Mn, Ni, Al and Co. For each of these steels, samples were subjected to an austempering heat treatment at 340 oC varying the austempering time from 5 sec to 120 sec. The results show that small regions of free ferrite were obtained during continuous cooling from the austenitising to the austempering temperatures in unalloyed high silicon cast steels. At short austempering time (5 sec), the presence of a small fraction of ausferrite was observed. Austempering for 60 sec showed a larger amount of ausferrite. However, the ausferritic reaction is incomplete, and some martensite also was present, mainly located in last to freeze (LTF) zones. After an austempering ...
Anales del Congreso Binacional …
Metals
Bainitic microstructures obtained in high-carbon (HC) and high-silicon (HSi) steels are currently... more Bainitic microstructures obtained in high-carbon (HC) and high-silicon (HSi) steels are currently of great interest. Microstructural evolution and the bainitic transformation kinetics of a high-carbon and high-silicon cast steel held at 280, 330, and 380 °C was analyzed using dilatometry, X-ray diffraction, optical and scanning electron microscopy, and electron backscatter diffraction (EBSD). It is shown that the heterogeneous distribution of silicon (Si), manganese (Mn), and chromium (Cr) associated to microsegregation during casting has a great impact on the final microstructure. The transformation starts in the dendritic zones where there is a lower Mn concentration and then expands to the interdendritic ones. As Mn reduces the carbon activity, the interdendritic areas with a higher Mn concentration are enriched with carbon (C), and thus, these zones contain a greater amount of retained austenite plus martensite, resulting in a heterogeneous microstructure. Higher transformation ...
Wear, 2018
In this work the rolling contact fatigue (RCF) behavior of dual-phase austempered ductile iron (A... more In this work the rolling contact fatigue (RCF) behavior of dual-phase austempered ductile iron (ADI) was studied and compared to that of conventional ADI. The effect of surface finishing (manual vs. automatic grinding) on the surface properties and RCF endurance was also analyzed. RCF tests were performed in a flat washer type testing rig and using lubricated pure rolling conditions. RCF tests results were analyzed using the two-parameter Weibull distribution and the Weibayes method. The results indicated that the dual-phase ADI metal matrix was composed of 94 % ausferrite and 6 % free allotriomorphic ferrite, approximately. The hardness of conventional ADI was higher than that of dual-phase ADI. The residual stresses were compressive in all the cases with similar average values for ADI and dual-phase ADI. Relative to manual grinding, the automatic process increased slightly the surface hardness and reduced by around a 50 % the 2 residual stresses of both ADI and dual-phase ADI. Regarding RCF, failures were characterized by the typical concentrated damage in the form of spalls. No significant differences in the RCF endurance of ADI and dual-phase ADI were observed. No differences in the RCF endurance attributable to the surface finishing method were identified in the current tests. Keywords: dual-phase austempered ductile iron, grinding, surface properties, rolling contact fatigue. Highlights RCF behavior of dual-phase ADI was compared to that of conventional ADI. The effect of surface finishing (manual polishing vs. grinding) on RCF endurance was analyzed. RCF, failures were characterized by the typical concentrated damage in the form of spalls. No significant differences in the RCF endurance of ADI and dual-phase ADI were observed. No differences in the RCF endurance attributable to the surface finishing method were identified.
RESUMEN En los últimos años las fundiciones nodulares austemperizdas (ADI) han mostrado una desta... more RESUMEN En los últimos años las fundiciones nodulares austemperizdas (ADI) han mostrado una destacable aptitud para reemplazar piezas de aceros aleados, templados y revenidos, tanto forjados como colados, merced a sus importantes ventajas técnicas y económicas. Una línea de investigación de gran interés actual tiene por objetivo lograr un aumento adicional de las ya notables propiedades de las ADI, buscando mejorar específicamente la ductilidad y la tenacidad mediante modificaciones en los ciclos de tratamiento térmico. En el presente trabajo se estudian las propiedades mecánicas de fundiciones ADI con matrices tipo "dual-phase" consistentes en ferrita alotriomórfica y ausferrita. Se analizan los efectos de distintas relaciones porcentuales de ambas fases, diferentes morfologías de ferrita y distintos tipos de ausferrita logradas para temperaturas de austemperizado de 300 y 330°C (distintos grados de ADI). Se reportan datos de resistencia y ductilidad para microestructuras...
Materials Science and Technology, 2007
Abstract The present work describes studies about the influence of processing variables on the mi... more Abstract The present work describes studies about the influence of processing variables on the microstructure and properties of dual phase austempered ductile iron (ADI). The upper and lower critical temperatures of conventional ductile iron melt were determined. Heat treatments involving austenitising within the intercritical interval, followed by austempering, allowed microstructures to be obtained composed of different combinations of free ferrite and ausferrite. Mechanical and fracture toughness tests performed on samples with mixed structures showed interesting combinations of strength and toughness, in comparison with fully ferritic and fully ausferritic matrices, particularly when austempering was carried out at 350°C. The results of the critical crack size, expressed by the relationship (K IC/σYS)2, which indicates the relative toughness of the material, showed the best values for ferritic matrices with ∼20% ausferrite. This effect is attributed to the location of the ausferrite in the last to freeze regions (the weakest areas in the matrix) where it acted as a reinforcing phase.
Tribology Transactions, 2013
ABSTRACT Similar to other mechanical properties, wear resistance is entirely dependent on a mater... more ABSTRACT Similar to other mechanical properties, wear resistance is entirely dependent on a material's microstructure, which, in turn, is related to the chemical composition and solidification rate, which controls the type of phase, size, amount, and dispersion. Depending on the tribosystem, the abrasive wear resistance of ductile iron (DI) may be improved by heat treatment as well as by reinforcing the matrix with hard particles such as carbides, typically obtained by alloying with elements such as chromium.The solidification rate mainly depends on wall thickness and mold characteristics. In DI, the solidification rate affects microstructural characteristics, such as nodule size, nodule count, carbide size and distribution, and matrix refinement, also including the last to freeze (LTF) amount, size, and distribution.This study evaluates the influence of the wall thickness (12.5, 25, 50, and 75 mm) on the abrasion resistance and impact toughness of DI with different matrices reinforced with carbides. Carbidic structures were obtained by alloying the melt with Cr, and the different types of matrices such as pearlitic, martensitic, and ausferritic (CADI) were obtained under as-cast conditions or by heat treatment.The results reflect the influence of cooling rate on the microstructural characteristics and its relationship with the mechanical properties, particularly the abrasive wear resistance. It was demonstrated that, under the present experimental conditions, the highest carbide content and matrix hardness, obtained from the 12.5-mm-thick part with a martensitic matrix, resulted in the highest abrasion resistance.
Key Engineering Materials, 2010
Austempered Ductile Iron (ADI) and fully ferritic ductile iron are frequently used to produce saf... more Austempered Ductile Iron (ADI) and fully ferritic ductile iron are frequently used to produce safety parts. A new kind of ductile iron (DI), usually referred to as “dual phase ADI” is currently under development. The matrix of this new material is composed of ausferrite (regular ADI microstructure) and free (or allotriomorphic) ferrite. This combined microstructure is obtained by subjecting DI to heat treatments comprising incomplete austenitization stages at temperatures within the intercritical interval (three phase α-γ-Gr field of the Fe-C-Si stable diagram) followed by an austempering step in a salt bath in order to transform the austenite into ausferrite. This work describes some alternatives to control morphologies and amounts of phases present in the final microstructure. A revision of the results obtained on this matter by the authors as well as by other researchers is also provided. A ductile iron melt was produced in a metal casting laboratory. Samples were heat treated fo...
Journal of Alloys and Compounds, 2011
ABSTRACT This work focuses on the influence exerted by the chemical composition on the characteri... more ABSTRACT This work focuses on the influence exerted by the chemical composition on the characteristics of the γ→α reaction occurring within the intercritical interval of the Fe–C–Si diagram, in order to produce a new “dual phase ADI” variant.Three ductile iron melts with different chemical compositions were used and several thermal cycles were performed. The results show a strong dependence between the alloy composition and the characteristics of the γ→α reaction, affecting the amount as well as the morphology of the precipitated allotriomorphic ferrite. Low alloy content promotes ferritic nucleation around graphite nodules and fast growth. Moreover, when the alloy content increases, the ferrite nucleates preferentially at the grain boundaries of the recrystallized austenite, and grows very slowly forming a continuous net. This novel microstructure is expected to enhance the mechanical properties of ductile cast iron.
Frattura ed Integrità Strutturale
In this work, the effect of Ti addition and the cast part size on the solidification structure an... more In this work, the effect of Ti addition and the cast part size on the solidification structure and mechanical properties of a medium carbon, low alloy cast steel was analyzed. The experimental analysis involved the design of the melts by using Thermo-Calc® software, where different amounts of Ti added to a standard chemical composition of an AISI 13XX steel were simulated. Then, the solidification macrostructure (dendritic pattern and grain size) and microstructure were characterized by using conventional and specific metallographic techniques. Finally, the mechanical behavior in terms of hardness and tensile properties were evaluated. The results show that the addition of 0.12% of Ti promotes a fine dispersion of Ti nitrides and carbides, but when the Ti concentration raises to 0.2%, the size of the Ti nitrides and carbides increases while its amount decreases. Ti nitrides and carbides particles act as nucleation sites for the precipitation of ferrite from austenite, and it was fou...
Frattura ed Integrità Strutturale
The first stage of this study investigates the precipitation of free ferrite from the austenite o... more The first stage of this study investigates the precipitation of free ferrite from the austenite on fully austenitized ductile iron. Several sets of samples of low alloy ductile iron are fully austenitized and then cooled down to different temperatures and different times within the intercritical austenite-ferrite-graphite phase field. Based on these results, heat treatment cycles aimed at obtaining microstructures composed of free ferrite and ausferrite are carried out. Tensile, impact and toughness tests are performed to characterize the mechanical properties. The results show that, related to the high strength austempered ductile iron grades, the best combinations of properties were obtained from the mixed structures composed of 5% free ferrite and 95% ausferrite, resulting from the austempering at 280°C. These amounts of free ferrite allow obtaining an increase of the elongation (about 50%) and impact toughness (about 10%) while the tensile strength and fracture toughness decreas...
En los ultimos anos, se ha comenzado a estudiar una variante de las fundiciones esferoidales aust... more En los ultimos anos, se ha comenzado a estudiar una variante de las fundiciones esferoidales austemperizadas (ADI) denominada “ADI-Dual-Phase”, cuya matriz esta compuesta por ferrita libre y ausferrita [1-4]. La presencia de ferrita incrementa la elongacion y la fractotenacidad de las ADI, haciendola apta para aplicaciones de alto compromiso, como partes de suspension de automoviles. Un ciclo termico utilizado para obtener estructuras ADI-Dual-Phase, desarrollado por los autores del presente trabajo [4], consiste en someter a una FE a una austenizacion completa (etapa 1), seguida de un enfriamiento a una temperatura dentro del intervalo intercritico ?-?-grafito del diagrama Fe-C-Si y mantenimiento durante un determinado tiempo (etapa 2), seguido de un ciclo de austemperizado (etapa 3). Durante la etapa 2, se produce la transformacion austenita a ferrita: la ferrita nuclea y crece con una velocidad que depende de la temperatura y tiempo de mantenimiento dentro del intervalo intercrit...
International Journal of Cast Metals Research, 2020
High-silicon cast steels and proper heat treatment cycles were designed in order to obtain carbid... more High-silicon cast steels and proper heat treatment cycles were designed in order to obtain carbide-free bainitic microstructures. The design process allowed to obtain the desired microstructures after heat treatment cycles compatible with industrial practices and using low amounts of inexpensive alloying elements. The different chemical compositions and austempering temperatures tested resulted in ultra-high-strength steels showing remarkably total elongations. The obtained tensile properties satisfy the minimum requirements specified for AHSS in ASTM A1088 standard, and also the requirements for high-strength cast steels stated in ASTM A148. Moreover, many microstructures developed in this work reach the tensile performance of the very expensive maraging steels.
International Journal of Metalcasting, 2020
Three medium-carbon, high-silicon cast steels with different alloy contents were austempered at 3... more Three medium-carbon, high-silicon cast steels with different alloy contents were austempered at 330°C for different holding times in order to obtain carbide-free bainitic microstructures. Aiming at evaluating the influence of holding time and microstructural features on strength and ductility, tensile properties were measured for each steel at selected austempering times. The results obtained indicate that it is possible to adjust holding time in order to obtain the best strength/ductility combination at determined austempering temperature. Moreover, it has been shown that the mechanical stability of retained austenite is the key factor in controlling tensile performance. Short austempering times result in low carbon enrichment of the austenite (low stability) and promote higher ultimate tensile strength and lower ductility. For longer austempering times, steels present a slight decrease in ultimate tensile strength but a marked increase in ductility. This work shows that it is possible to obtain cast steels with ultimate tensile strength of 1682 MPa, yield strength of 1493 MPa and total elongation of 12.5% by means of bainitic reaction. This strength/ductility combination and others reported in this study are remarkable for cast steels.
International Journal of Cast Metals Research, 2018
This study investigates the effect of chemical composition and microsegregation on the bainitic t... more This study investigates the effect of chemical composition and microsegregation on the bainitic transformation of high Si cast steels at two different austempering temperatures. The advance of the bainite precipitation as a function of time and temperature was monitored through measurements of the amount of retained austenite by X-ray diffraction, the evolution of hardness and microstructural characterization. The results showed that the bainitic transformation starts preferentially at zones with lower contents of alloying elements but later covers the entire matrix. The austempering heat treatments resulted in an apparently homogeneous bainitic microstructure throughout the entire matrix after a short period of time. The results encourage the continuation of the development of high Si steels suitable to produce carbide-free austempered cast parts.
International Journal of Cast Metals Research, 2017
Abstract In this work the percent dimensional change (DC%) and its dispersion in high silicon Duc... more Abstract In this work the percent dimensional change (DC%) and its dispersion in high silicon Ductile Iron with ADI and Dual-Phase-ADI structures obtained through heat treatment starting from different as-cast microstructures, was studied. Specimens were obtained from three different melts with Si content ranging from 3.1 to 4.2%. Dual-Phase-ADI structures were obtained using special heat treatment, starting from as-cast structures. Regarding dimensional change, DC% in ADI and Dual-Phase-ADI decrease as Si% and the proportion of ferrite phase in as-cast specimens increased. On the other hand, DC% increased with austenitizing temperature and ausferrite content in the final microstructure. A fuzzy model to predict DC% in ADI parts was adapted to include DC% prediction in Dual-Phase-ADI. The fuzzy model allowed to predict the DC% for ADI and Dual-Phase-ADI parts with an root mean square <0.05%.
Materials Science and Technology, 2019
A high silicon, medium carbon cast steel was designed and heat-treated in order to develop micros... more A high silicon, medium carbon cast steel was designed and heat-treated in order to develop microstructures composed of carbide-free bainite and small amounts of free ferrite, with the aim of obtaining high strength cast steels with improved ductility. Because of microsegregation, it was observed that ferrite present in partially austenitised samples is mostly present at the highly alloyed zones, creating an interconnected network even for low proportions of this phase. Despite the coarse solidification structure and marked microsegregation in the cast steel, the mechanical properties obtained for both fully bainitic and bainitic-ferritic microstructures largely satisfy the minimum standard requirements for high strength cast steels and are similar to those reported for wrought steels of similar microstructures.
International Journal of Metalcasting, 2012
During the last few years, researchers have sought new ductile iron (DI) applications focusing on... more During the last few years, researchers have sought new ductile iron (DI) applications focusing on the development of mixed microstructures, such as ferritic-bainitic or ferritic-martensitic. These kinds of structures result in DI with a good combination of mechanical properties, compared to other conventional DI. The combination of properties offered by the mixed structure DI, particularly in "dual phase austempered ductile iron" (ADI) has opened new horizons for cast iron to replace steel castings and forgings in many engineering applications. This new DI has a particular microstructure composed of different amounts and morphologies of ausferrite and free ferrite. Dual phase ADI microstructures have afforded more opportunities for DI applications, acquiring better combinations of strength, ductility and toughness. This review describes the methodologies used to obtain this new kind of DI and the principal mechanical properties.
ISIJ International, 2015
This work deals with the feasibility of obtaining Austempered Ductile Iron with Dual Phase struct... more This work deals with the feasibility of obtaining Austempered Ductile Iron with Dual Phase structures (DPADI) through heat treatment, starting from different as-cast microstructures. The mechanical properties on these microstructures were evaluated. DPADI microstructures were obtained by adding different tenors of silicon (2.4% to 4.2%) to the melts and keeping the other alloying elements constant. The study focused on the determination of the time required to achieve the percentages of equilibrium phases (ferrite and austenite) at different temperatures in the intercritical temperature interval as a function of the starting as cast microstructure. The results showed that, as the silicon content increases, higher amount of ferrite is present in the as cast structure, and the time required to reach the thermodynamic equilibrium phases in the intercritical temperature interval is markedly reduced. Similarly, for a constant chemical composition, as the intercritical austenitizing temperature increases, the time required to reach the quantities of the equilibrium phases decreases. Regarding mechanical properties, the tests revealed that, as expected, as intercritical austenitising temperature increases so do tensile strength and hardness due to the higher ausferrite content in the DPADI matrix. These results indicate that high silicon Ductile Iron (with Si content higher than 3%) with a mostly ferritic microstructure in as cast conditions yields DPADI microstructures able to dispense with prior annealing heat treatments since the time required to reach the phase equilibrium percentages is compatible with the industrial practice and the mechanical properties are similar as compared to DPADI structures deriving from fully ferritic matrices.
Materials Science and Technology, 2009
The present work aims to evaluate and compare the influence that section size has on the microstr... more The present work aims to evaluate and compare the influence that section size has on the microstructure and properties of fully ferritic, fully ausferritic and dual phase ADI matrices. Samples taken from 'Y' blocks of 25, 50 and 75 mm thickness were used to perform metallographic studies and mechanical tests. Cooling rate differences arising from changes in section size promote different microsegregation characteristics affecting solid state transformations and, consequently, the final microstructure and properties. When the section size increases, some properties decrease. The strongest deleterious effect was ascribed to the elongation and impact of ADI samples, where drops of nearly 40% were reached when specimens taken from the thinnest 'Y' blocks were compared to those taken from the thickest ones. Regarding fracture toughness, ferritic matrices exhibited the most noticeable detrimental effect. Dual phase ADI samples, on the other hand, presented the least deleterious section size effect on all the studied properties.
Materials Science Forum, 2014
This work focuses on the study of the solid state transformations that take place during the aust... more This work focuses on the study of the solid state transformations that take place during the austempering of high silicon carbide-free bainitic cast steels with different chemical composition. In order to get this objective three cast steel melts with different chemical compositions were produced, evaluating the influence of Cr, Mn, Ni, Al and Co. For each of these steels, samples were subjected to an austempering heat treatment at 340 oC varying the austempering time from 5 sec to 120 sec. The results show that small regions of free ferrite were obtained during continuous cooling from the austenitising to the austempering temperatures in unalloyed high silicon cast steels. At short austempering time (5 sec), the presence of a small fraction of ausferrite was observed. Austempering for 60 sec showed a larger amount of ausferrite. However, the ausferritic reaction is incomplete, and some martensite also was present, mainly located in last to freeze (LTF) zones. After an austempering ...
Anales del Congreso Binacional …
Metals
Bainitic microstructures obtained in high-carbon (HC) and high-silicon (HSi) steels are currently... more Bainitic microstructures obtained in high-carbon (HC) and high-silicon (HSi) steels are currently of great interest. Microstructural evolution and the bainitic transformation kinetics of a high-carbon and high-silicon cast steel held at 280, 330, and 380 °C was analyzed using dilatometry, X-ray diffraction, optical and scanning electron microscopy, and electron backscatter diffraction (EBSD). It is shown that the heterogeneous distribution of silicon (Si), manganese (Mn), and chromium (Cr) associated to microsegregation during casting has a great impact on the final microstructure. The transformation starts in the dendritic zones where there is a lower Mn concentration and then expands to the interdendritic ones. As Mn reduces the carbon activity, the interdendritic areas with a higher Mn concentration are enriched with carbon (C), and thus, these zones contain a greater amount of retained austenite plus martensite, resulting in a heterogeneous microstructure. Higher transformation ...
Wear, 2018
In this work the rolling contact fatigue (RCF) behavior of dual-phase austempered ductile iron (A... more In this work the rolling contact fatigue (RCF) behavior of dual-phase austempered ductile iron (ADI) was studied and compared to that of conventional ADI. The effect of surface finishing (manual vs. automatic grinding) on the surface properties and RCF endurance was also analyzed. RCF tests were performed in a flat washer type testing rig and using lubricated pure rolling conditions. RCF tests results were analyzed using the two-parameter Weibull distribution and the Weibayes method. The results indicated that the dual-phase ADI metal matrix was composed of 94 % ausferrite and 6 % free allotriomorphic ferrite, approximately. The hardness of conventional ADI was higher than that of dual-phase ADI. The residual stresses were compressive in all the cases with similar average values for ADI and dual-phase ADI. Relative to manual grinding, the automatic process increased slightly the surface hardness and reduced by around a 50 % the 2 residual stresses of both ADI and dual-phase ADI. Regarding RCF, failures were characterized by the typical concentrated damage in the form of spalls. No significant differences in the RCF endurance of ADI and dual-phase ADI were observed. No differences in the RCF endurance attributable to the surface finishing method were identified in the current tests. Keywords: dual-phase austempered ductile iron, grinding, surface properties, rolling contact fatigue. Highlights RCF behavior of dual-phase ADI was compared to that of conventional ADI. The effect of surface finishing (manual polishing vs. grinding) on RCF endurance was analyzed. RCF, failures were characterized by the typical concentrated damage in the form of spalls. No significant differences in the RCF endurance of ADI and dual-phase ADI were observed. No differences in the RCF endurance attributable to the surface finishing method were identified.
RESUMEN En los últimos años las fundiciones nodulares austemperizdas (ADI) han mostrado una desta... more RESUMEN En los últimos años las fundiciones nodulares austemperizdas (ADI) han mostrado una destacable aptitud para reemplazar piezas de aceros aleados, templados y revenidos, tanto forjados como colados, merced a sus importantes ventajas técnicas y económicas. Una línea de investigación de gran interés actual tiene por objetivo lograr un aumento adicional de las ya notables propiedades de las ADI, buscando mejorar específicamente la ductilidad y la tenacidad mediante modificaciones en los ciclos de tratamiento térmico. En el presente trabajo se estudian las propiedades mecánicas de fundiciones ADI con matrices tipo "dual-phase" consistentes en ferrita alotriomórfica y ausferrita. Se analizan los efectos de distintas relaciones porcentuales de ambas fases, diferentes morfologías de ferrita y distintos tipos de ausferrita logradas para temperaturas de austemperizado de 300 y 330°C (distintos grados de ADI). Se reportan datos de resistencia y ductilidad para microestructuras...
Materials Science and Technology, 2007
Abstract The present work describes studies about the influence of processing variables on the mi... more Abstract The present work describes studies about the influence of processing variables on the microstructure and properties of dual phase austempered ductile iron (ADI). The upper and lower critical temperatures of conventional ductile iron melt were determined. Heat treatments involving austenitising within the intercritical interval, followed by austempering, allowed microstructures to be obtained composed of different combinations of free ferrite and ausferrite. Mechanical and fracture toughness tests performed on samples with mixed structures showed interesting combinations of strength and toughness, in comparison with fully ferritic and fully ausferritic matrices, particularly when austempering was carried out at 350°C. The results of the critical crack size, expressed by the relationship (K IC/σYS)2, which indicates the relative toughness of the material, showed the best values for ferritic matrices with ∼20% ausferrite. This effect is attributed to the location of the ausferrite in the last to freeze regions (the weakest areas in the matrix) where it acted as a reinforcing phase.
Tribology Transactions, 2013
ABSTRACT Similar to other mechanical properties, wear resistance is entirely dependent on a mater... more ABSTRACT Similar to other mechanical properties, wear resistance is entirely dependent on a material's microstructure, which, in turn, is related to the chemical composition and solidification rate, which controls the type of phase, size, amount, and dispersion. Depending on the tribosystem, the abrasive wear resistance of ductile iron (DI) may be improved by heat treatment as well as by reinforcing the matrix with hard particles such as carbides, typically obtained by alloying with elements such as chromium.The solidification rate mainly depends on wall thickness and mold characteristics. In DI, the solidification rate affects microstructural characteristics, such as nodule size, nodule count, carbide size and distribution, and matrix refinement, also including the last to freeze (LTF) amount, size, and distribution.This study evaluates the influence of the wall thickness (12.5, 25, 50, and 75 mm) on the abrasion resistance and impact toughness of DI with different matrices reinforced with carbides. Carbidic structures were obtained by alloying the melt with Cr, and the different types of matrices such as pearlitic, martensitic, and ausferritic (CADI) were obtained under as-cast conditions or by heat treatment.The results reflect the influence of cooling rate on the microstructural characteristics and its relationship with the mechanical properties, particularly the abrasive wear resistance. It was demonstrated that, under the present experimental conditions, the highest carbide content and matrix hardness, obtained from the 12.5-mm-thick part with a martensitic matrix, resulted in the highest abrasion resistance.
Key Engineering Materials, 2010
Austempered Ductile Iron (ADI) and fully ferritic ductile iron are frequently used to produce saf... more Austempered Ductile Iron (ADI) and fully ferritic ductile iron are frequently used to produce safety parts. A new kind of ductile iron (DI), usually referred to as “dual phase ADI” is currently under development. The matrix of this new material is composed of ausferrite (regular ADI microstructure) and free (or allotriomorphic) ferrite. This combined microstructure is obtained by subjecting DI to heat treatments comprising incomplete austenitization stages at temperatures within the intercritical interval (three phase α-γ-Gr field of the Fe-C-Si stable diagram) followed by an austempering step in a salt bath in order to transform the austenite into ausferrite. This work describes some alternatives to control morphologies and amounts of phases present in the final microstructure. A revision of the results obtained on this matter by the authors as well as by other researchers is also provided. A ductile iron melt was produced in a metal casting laboratory. Samples were heat treated fo...
Journal of Alloys and Compounds, 2011
ABSTRACT This work focuses on the influence exerted by the chemical composition on the characteri... more ABSTRACT This work focuses on the influence exerted by the chemical composition on the characteristics of the γ→α reaction occurring within the intercritical interval of the Fe–C–Si diagram, in order to produce a new “dual phase ADI” variant.Three ductile iron melts with different chemical compositions were used and several thermal cycles were performed. The results show a strong dependence between the alloy composition and the characteristics of the γ→α reaction, affecting the amount as well as the morphology of the precipitated allotriomorphic ferrite. Low alloy content promotes ferritic nucleation around graphite nodules and fast growth. Moreover, when the alloy content increases, the ferrite nucleates preferentially at the grain boundaries of the recrystallized austenite, and grows very slowly forming a continuous net. This novel microstructure is expected to enhance the mechanical properties of ductile cast iron.