Austempered ductile iron(ADI)is composed of an ausferritic matrix with graphite nodules and has a wide range of applications because of its high mechanical strength,fatigue resistance,and wear resistance compared to o...Austempered ductile iron(ADI)is composed of an ausferritic matrix with graphite nodules and has a wide range of applications because of its high mechanical strength,fatigue resistance,and wear resistance compared to other cast irons.The amount and size of the nodules can be controlled by the chemical composition and austenitizing temperature.As the nodules have lower stiffness than the matrix and can act as stress concentrators,they influence crack propagation.However,the crack propagation mechanism in ADI is not yet fully understood.In this study,we describe a numerical investigation of crack propagation in ADIs subjected to cyclic loading.The numerical model used to calculate the stress intensity factors in the material under the given conditions is built with the aid of Abaqus commercial finite element code.The crack propagation routine,which is based on the Paris law,is implemented in Python.The results of the simulation show that the presence of a nodule generates a shear load on the crack tip.Consequently,even under uniaxial tensile loading,the presence of the nodule yields a non-zero stress intensity factor in mode II,resulting in a deviation in the crack propagation path.This is the primary factor responsible for changing the crack propagation direction towards the nodule.Modifying the parameters,for example,increasing the nodule size or decreasing the distance between the nodule and crack tip,can intensify this effect.In simulations comparing two different ADIs with the same graphite fraction area,the crack in the material with more nodules reaches another nodule in a shorter propagation time(or shorter number of cycles).This suggests that the high fatigue resistance observed in ADIs may be correlated with the number of nodules intercepted by a crack and the additional energy required to nucleate new cracks.In summary,these findings contribute to a better understanding of crack propagation in ADIs,provide insights into the relationship between the presence of nodules and the fatigue resistance of these materials,and support studies that associate the increased fatigue resistance with a higher number of graphite nodules.These results can also help justify the enhanced fatigue resistance of ADIs when compared to other cast irons.展开更多
Austempered ductile iron(ADI) parts have a unique combination of high strength and toughness with excellent design flexibility and low cost. These excellent properties are directly related to its microstructure called...Austempered ductile iron(ADI) parts have a unique combination of high strength and toughness with excellent design flexibility and low cost. These excellent properties are directly related to its microstructure called "ausferrite" that is the result of austempering heat treatment applied to ductile irons. Alloying elements increase ADI austemperability and change speeds of austempering reactions. Thus, they can affect ADI resultant microstructure and mechanical properties. In this paper, the effects of alloying elements on ADI mechanical properties, microstructural changes, two-stage austempering reactions, processing windows, austemperability, and other aspects are reviewed.展开更多
In the present research, the orthogonal experiment was carried out to investigate the influence of different austempering process parameters （i.e. austenitizing temperature and time, and austempering temperature and ...In the present research, the orthogonal experiment was carried out to investigate the influence of different austempering process parameters （i.e. austenitizing temperature and time, and austempering temperature and time） on microstructure and mechanical properties of LZQT500-7 ductile iron dense bars with 172 mm in diameter which were produced by horizontal continuous casting （HCC）. The results show that the major factors influencing the hardness of austempered ductile iron （ADI） are austenitizing temperature and austempering temperature. The fraction of retained austenite increases as the austenitizing and austempering temperatures increase. When austenitizing temperature is low, acicular ferrite and retained austenite can be efifciently obtained by appropriately extending the austenitizing time. The proper austmepering time could ensure enough stability of retained austenite and prevent high carbon austenite decomposition. The optimal mechanical properties of ADI can be achieved with the fol owing process parameters： austenitizing temperature and time are 866 ＆#176;C and 135 min, and austempering temperature and time are 279 ＆#176;C and 135 min, respectively. The microstructure of ADI under the optimal austempering process consists of ifne acicular ferrite and a smal amount of retained austenite, and the hardness, tensile strength, yield strength, elongation and impact toughness of the bars are HBW 476, 1670 MPa, 1428 MPa, 2.93%and 25.7 J, respectively.展开更多
This study focused on the development of austempered ductile iron(ADI)with desirable combination of mechanical properties for crankshaft applications by the combined effect of vanadium(V)alloying and an optimized heat...This study focused on the development of austempered ductile iron(ADI)with desirable combination of mechanical properties for crankshaft applications by the combined effect of vanadium(V)alloying and an optimized heat treatment process.The produced unalloyed GGG60,0.15%V-alloyed GGG60(V-15),and 0.30%V-alloyed GGG60 samples were subjected to austenitizing at 900℃for 1 h and subsequent austempering processes at 250,300,and 350℃for 15,30,60,90,and 180 min.As a result of these austempering processes,different bainitic structures were obtained,which led to the formation of diverse combinations of mechanical properties.The mechanical properties of the austempered samples were tested comprehensively,and the results were correlated with their microstructures and the stability of the retained austenite phases.From the microstructural observations,the V-alloyed samples exhibited a finer microstructure and a more acicular ferrite phase than unalloyed samples.The V addition delayed the coarsening of the acicular ferrite structures and considerably contributed to the improvement of the mechanical properties of GGG60.Moreover,the X-ray diffraction results revealed that the retained austenite volume and the carbon enrichment of austenite phases in ADI samples were remarkably affected by the addition of vanadium.The increase in volume fraction of retained austenite and its carbon content provided favorable ductility and toughness to V-15,as confirmed by the elongation and impact test results.Consequently,the dual-phase ausferrite microstructure of V-15 that was austempered at 300℃for 60 min exhibited high strength with substantial ductility and toughness for crankshaft applications.展开更多
文摘Austempered ductile iron(ADI)is composed of an ausferritic matrix with graphite nodules and has a wide range of applications because of its high mechanical strength,fatigue resistance,and wear resistance compared to other cast irons.The amount and size of the nodules can be controlled by the chemical composition and austenitizing temperature.As the nodules have lower stiffness than the matrix and can act as stress concentrators,they influence crack propagation.However,the crack propagation mechanism in ADI is not yet fully understood.In this study,we describe a numerical investigation of crack propagation in ADIs subjected to cyclic loading.The numerical model used to calculate the stress intensity factors in the material under the given conditions is built with the aid of Abaqus commercial finite element code.The crack propagation routine,which is based on the Paris law,is implemented in Python.The results of the simulation show that the presence of a nodule generates a shear load on the crack tip.Consequently,even under uniaxial tensile loading,the presence of the nodule yields a non-zero stress intensity factor in mode II,resulting in a deviation in the crack propagation path.This is the primary factor responsible for changing the crack propagation direction towards the nodule.Modifying the parameters,for example,increasing the nodule size or decreasing the distance between the nodule and crack tip,can intensify this effect.In simulations comparing two different ADIs with the same graphite fraction area,the crack in the material with more nodules reaches another nodule in a shorter propagation time(or shorter number of cycles).This suggests that the high fatigue resistance observed in ADIs may be correlated with the number of nodules intercepted by a crack and the additional energy required to nucleate new cracks.In summary,these findings contribute to a better understanding of crack propagation in ADIs,provide insights into the relationship between the presence of nodules and the fatigue resistance of these materials,and support studies that associate the increased fatigue resistance with a higher number of graphite nodules.These results can also help justify the enhanced fatigue resistance of ADIs when compared to other cast irons.
文摘Austempered ductile iron(ADI) parts have a unique combination of high strength and toughness with excellent design flexibility and low cost. These excellent properties are directly related to its microstructure called "ausferrite" that is the result of austempering heat treatment applied to ductile irons. Alloying elements increase ADI austemperability and change speeds of austempering reactions. Thus, they can affect ADI resultant microstructure and mechanical properties. In this paper, the effects of alloying elements on ADI mechanical properties, microstructural changes, two-stage austempering reactions, processing windows, austemperability, and other aspects are reviewed.
基金financially supported by the fund of the Key Projects of Shaanxi Provincial International Technology Cooperation Plan(2013KW16)the Scientific Research Program funded by Shaanxi Provincial Education Department(2013JK0914)+2 种基金the State Key Laboratory of Solidifi cation Processing in NWPU(SKLSP201115)the Scientific Research Project of Xi'an University of Technology(2013CX004)the fund of the Key Laboratory of Electrical Materials and Infi ltration Technology of Shaanxi Province,China(2014)
文摘In the present research, the orthogonal experiment was carried out to investigate the influence of different austempering process parameters （i.e. austenitizing temperature and time, and austempering temperature and time） on microstructure and mechanical properties of LZQT500-7 ductile iron dense bars with 172 mm in diameter which were produced by horizontal continuous casting （HCC）. The results show that the major factors influencing the hardness of austempered ductile iron （ADI） are austenitizing temperature and austempering temperature. The fraction of retained austenite increases as the austenitizing and austempering temperatures increase. When austenitizing temperature is low, acicular ferrite and retained austenite can be efifciently obtained by appropriately extending the austenitizing time. The proper austmepering time could ensure enough stability of retained austenite and prevent high carbon austenite decomposition. The optimal mechanical properties of ADI can be achieved with the fol owing process parameters： austenitizing temperature and time are 866 ＆#176;C and 135 min, and austempering temperature and time are 279 ＆#176;C and 135 min, respectively. The microstructure of ADI under the optimal austempering process consists of ifne acicular ferrite and a smal amount of retained austenite, and the hardness, tensile strength, yield strength, elongation and impact toughness of the bars are HBW 476, 1670 MPa, 1428 MPa, 2.93%and 25.7 J, respectively.
文摘This study focused on the development of austempered ductile iron(ADI)with desirable combination of mechanical properties for crankshaft applications by the combined effect of vanadium(V)alloying and an optimized heat treatment process.The produced unalloyed GGG60,0.15%V-alloyed GGG60(V-15),and 0.30%V-alloyed GGG60 samples were subjected to austenitizing at 900℃for 1 h and subsequent austempering processes at 250,300,and 350℃for 15,30,60,90,and 180 min.As a result of these austempering processes,different bainitic structures were obtained,which led to the formation of diverse combinations of mechanical properties.The mechanical properties of the austempered samples were tested comprehensively,and the results were correlated with their microstructures and the stability of the retained austenite phases.From the microstructural observations,the V-alloyed samples exhibited a finer microstructure and a more acicular ferrite phase than unalloyed samples.The V addition delayed the coarsening of the acicular ferrite structures and considerably contributed to the improvement of the mechanical properties of GGG60.Moreover,the X-ray diffraction results revealed that the retained austenite volume and the carbon enrichment of austenite phases in ADI samples were remarkably affected by the addition of vanadium.The increase in volume fraction of retained austenite and its carbon content provided favorable ductility and toughness to V-15,as confirmed by the elongation and impact test results.Consequently,the dual-phase ausferrite microstructure of V-15 that was austempered at 300℃for 60 min exhibited high strength with substantial ductility and toughness for crankshaft applications.
