Casting defects could largely affect the mechanical properties of casting products. A number of test pieces made of ductile iron (EN-GJS-400-18-LT) with different levels of shrinkage porosity were prepared and then te...Casting defects could largely affect the mechanical properties of casting products. A number of test pieces made of ductile iron (EN-GJS-400-18-LT) with different levels of shrinkage porosity were prepared and then tensile and fatigue tests were performed to investigate the impact of shrinkage porosity on their mechanical properties. The results showed that the tensile strength decreases linearly with increasing of the shrinkage porosity. The tensile elongation decreases sharply with the increase of the shrinkage porosity mainly due to the non-uniform plastic deformation. The fatigue life also dramatically declines with increasing of the porosity and follows a power law relationship with the area percentage of porosity. The existence of the shrinkage porosity made the fatigue fracture complex. The shrinkage pores, especially those close to the surface usually became the crack initiation sites. For test pieces with less porosity, the fatigue fracture was clearly composed of crack initiation, propagation, and overloading. While for samples with high level of porosity, multiple crack initiation sites were observed.展开更多
The effects of alloying elements on the as-cast microstructures and mechanical properties of heavy section ductile cast iron were investigated to develop press die material having high strength and high ductility. Mea...The effects of alloying elements on the as-cast microstructures and mechanical properties of heavy section ductile cast iron were investigated to develop press die material having high strength and high ductility. Measurements of ultimate tensile strength, 0.2% proof strength, elongation and unnotched Charpy impact energy are presented as a function of alloy amounts within 0.25 to 0.75 wt pct range. Hardness is measured on the broken tensile specimens. The small additions of Mo, Cu, Ni and Cr changed the as-cast mechanical properties owing to the different as-cast matrix microstructures. The ferrite matrix of Mo and Ni alloyed cast iron exhibits low strength and hardness as well as high elongation and impact energy. The increase in Mo and Ni contents developed some fractions of pearlite structures near the austenite eutectic cell boundaries, which caused the elongation and impact energy to drop in a small range. Adding Cu and Cr elements rapidly changed the ferrite matrix into pearlite matrix, so strength and hardness were significantly increased. As more Mo and Cr were added, the size and fraction of primary carbides in the eutectic cell boundaries increased through the segregation of these elements into the intercellular boundaries.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 °C and 135 min, and austempering temperature and time are 279 °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
Consistent mechanical and machining properties are essential in many applications where ductile irons offer the most cost-effective way to produce structural parts.In the production of hydraulic rotators,dimensional t...Consistent mechanical and machining properties are essential in many applications where ductile irons offer the most cost-effective way to produce structural parts.In the production of hydraulic rotators,dimensional tolerances are typically 20μm to obtain designated performance.For castings where intermediate strength and ductility is required,it is common knowledge that conventional ferritic-pearlitic ductile irons such as ISO 1083/500-7 show large hardness variations.These are mainly caused by the notoriously varying pearlite content,both at different locations within a part and between parts in the same or different batches.Cooling rate variations due to different wall thickness and position in the molding box,as well as varying amounts of pearlite-stabilizing elements,all contribute to detrimental hardness variations.The obvious remedy is to avoid pearlite formation,and instead obtain the necessary mechanical properties by solution strengthening of the ferritic matrix by increasing silicon content to 3.7wt%-3.8wt%.The Swedish development in this field 1998 resulted in a national standardization as SS 140725,followed in 2004 by ISO 1083/ JS/500-10.Indexator AB decided 2005 to specify JS/500-10 for all new ductile iron parts and to convert all existing parts.Improvements include reduction by 75%in hardness variations and increase by 30%in cutting tool life,combined with consistently better mechanical properties.展开更多
Cooling rate and inoculation practice can greatly affect the graphite morphology of ductile irons. In the present research, the effects of the cooling rate and antimony addition on the graphite morphology and mechanic...Cooling rate and inoculation practice can greatly affect the graphite morphology of ductile irons. In the present research, the effects of the cooling rate and antimony addition on the graphite morphology and mechanical properties of ductile irons have been studied. Three ductile iron castings were prepared through solidification under cooling conditions S (slow), M (medium) and F (fast). The cooling rates around the equilibrium eutectic temperature (1,150 ℃) for these cooling conditions (S, M and F) were set at 0.21 ℃.min1, 0.32℃.min1 and 0.37℃-min-1, respectively. In addition, four ductile iron castings were prepared by adding 0.01%, 0.02%, 0.03% and 0.04% (by weight) antimony, respectively under the slow cooling condition. The results show that the nodularity index, tensile strength and hardness of the ductile iron castings without antimony addition are all improved with the increase of cooling rate, while the ductile iron casting solidified under the medium cooling rate possesses the largest number of graphite nodules. Furthermore, for the four antimony containing castings, the graphite morphology and tensile strength are also improved by the antimony additions, and the effect of antimony addition is intensified when the addition increases from 0.01% to 0.03%. Moreover, the rare earth elements (REE)/antimony ratio of 2 appears to be the most effective for fine nodular graphite formation in ductile iron.展开更多
To improve the mechanical properties of heavy section ductile cast iron, bismuth(Bi) was introduced into the iron. Five castings with different Bi content from 0 to 0.014 wt.% were prepared; and four positions in the ...To improve the mechanical properties of heavy section ductile cast iron, bismuth(Bi) was introduced into the iron. Five castings with different Bi content from 0 to 0.014 wt.% were prepared; and four positions in the casting from the edge to the center, with different solidifi cation cooling rates, were chosen for microstructure observation and mechanical properties test. The effect of the Bi content on the graphite morphology and mechanical properties of heavy section ductile cast iron were investigated. Results show that the tensile strength, elongation and impact toughness at different positions in the fi ve castings decrease with a decrease in cooling rate. With an increase in Bi content, the graphite morphology and the mechanical properties at the same position are improved, and the improvement of mechanical properties is obvious when the Bi content is no higher than 0.011wt.%. But when the Bi content is further increased to 0.014wt.%, the improvement of mechanical properties is not obvious due to the increase of chunky graphite number and the aggregation of chunky graphite. With an increase in Bi content, the tensile fracture mechanism is changed from brittle to mixture ductile-brittle fracture.展开更多
The effects of sphere size on the microstructural and mechanical properties of ductile iron–steel hollow sphere(DI–SHS) syntactic foams were investigated in this study. The SHSs were manufactured by fluidized-bed ...The effects of sphere size on the microstructural and mechanical properties of ductile iron–steel hollow sphere(DI–SHS) syntactic foams were investigated in this study. The SHSs were manufactured by fluidized-bed coating via the Fe-based commercial powder–binder suspension onto expanded polystyrene spheres(EPSs). Afterwards, the DI–SHS syntactic foams were produced via a sand-mold casting process. The microstructures of specimens were investigated by optical microscopy, scanning electron microscopy(SEM), and energy-dispersive X-ray spectroscopy(EDS). The microscopic evaluations of specimens reveal distinct regions composed of the DI matrix, SHS shells, and compatible interface. As a result, the microstructures and graphite morphologies of the DI matrix depend on sphere size. When the sphere size decreases, the area fractions of cementite and graphite phases are observed to increase and decrease, respectively. Compression tests were subsequently conducted at ambient temperature on the DI–SHS syntactic foams. The results reveal that the compression behavior of the syntactic foams is enhanced with increasing sphere size. Furthermore, the compressed specimens demonstrate that microcracks start and grow from the interface region.展开更多
Ferritic spheroidal graphite irons with nodularity from 72%to 96%were prepared.The relationship between the nodularity and the mechanical properties of the ferritic spheroidal graphite iron was investigated.The effect...Ferritic spheroidal graphite irons with nodularity from 72%to 96%were prepared.The relationship between the nodularity and the mechanical properties of the ferritic spheroidal graphite iron was investigated.The effect of nodularity on the mechanical properties and tensile fracture of the cast iron were studied.Results showed that the tensile strength Rm,yield strength Rp0.2,elongation to failure A5,and impact energy KV2 of the cast iron had a good linear relationship with its nodularity.Nodularity and annealing treatment would obviously affect the fracture characteristics of ferritic spheroidal graphite iron.The annealed ferritic spheroidal graphite iron with 93%nodularity showed a completely ductile rupture.With the decrease of nodularity from 93%to 72%,the cleavage fracture area ratio increased gradually from 0%to 8.3%.Compared with as-cast ferritic spheroidal graphite iron,annealing treatment reduced the cleavage fracture area of the ferritic spheroidal graphite iron.展开更多
Semi-solid processing of metallic materials has been investigated for some time;however,this innovative production process has not fully established for ferrous alloys like ductile cast iron in the industry yet.Ferrou...Semi-solid processing of metallic materials has been investigated for some time;however,this innovative production process has not fully established for ferrous alloys like ductile cast iron in the industry yet.Ferrous alloys-specially ductile cast ironbecause of increasing complexity due to high temperature processing and some other limitations have been allocated a small share of this useful forming process to themselves.However,this work describes that thixo-forming of ductile iron despite all of the limitations is possible even for thin sections(less than 1 mm).Die temperature and injection velocity are the most effective parameters to thixo-forming particularly for high melting point materials such as ductile cast iron.Filling behavior,shape factor of graphites and fluidity of thixo-formed specimens were characterized.In addition,defects as well as shrinkage and cold laps were examined to achieve sound specimen.Subsequence to successful thixo-forming,two step austempering was performed to accomplish a uniform structure with minimum untransformed austenite volume(UAV).Following austempering,tensile test was carried out and the results show good combination of tensile strength and elongation for treated specimens(1 137 MPa strength and 12% elongation in best situation).展开更多
Impact toughness of ductile nodular cast iron loaded perpendicular to the austenitic dendrites is found to be 43% higher than that parallel to ones.Yet tensile strength and elongation of the former are 23% and 30% low...Impact toughness of ductile nodular cast iron loaded perpendicular to the austenitic dendrites is found to be 43% higher than that parallel to ones.Yet tensile strength and elongation of the former are 23% and 30% lower than the later respectively.It is belived that the dendritic segregation may cause such differences.展开更多
The aim of present work is to investigate the influencing factors on mechanical property stability of Cu-Mo-Ni alloyed austempered ductile iron (ADI). The results show that after austenitized at 900℃ for 2 h follow...The aim of present work is to investigate the influencing factors on mechanical property stability of Cu-Mo-Ni alloyed austempered ductile iron (ADI). The results show that after austenitized at 900℃ for 2 h followed by austempered at 370℃for another 2 h, the mechanical property of the alloyed ADI can reach the Germanite GGG-100 standard, i.e. σb≮1000 MPa,δ≮5%, at 95% confidence level. And the satisfactory mechanical properties were obtained when the alloyed ADI was austenitized at 850℃ to 1 000 ℃ for 1-4 h, and austempered at 355℃ to 400℃ for another 1 h to 4 h. The microstructures, including nodule number, white bright zone content (martensite-containing interdendritic segregation zone) and retained austenite content, can significantly influence the mechanical properties of the ADI. In order to obtain the good combinations of strength and ductility, the volume fraction of white bright zone should he less than 5%, and the retained austenite contents maintain hetween 30 % and 40%. The application of inoculation techniques to increase graphite nodule number can effectively reduce the white bright zone content in the structure.展开更多
It is important to improve the comprehensive performance of the ductile iron bars(DIBs)for the cylinder block of the extra high pressure hydraulic plunger pump and accelerate the industrial application.In this work,th...It is important to improve the comprehensive performance of the ductile iron bars(DIBs)for the cylinder block of the extra high pressure hydraulic plunger pump and accelerate the industrial application.In this work,the LZQT600-3 DIBs with the diameter of 145 mm were prepared by the horizontal continuous casting(HCC)process,that is,LZQT600-3 HCCDIBs.The microstructure and room temperature tensile properties of different sections[left-edge(surface layer),left-1/2R(left half of the radius),and the center of the HCCDIBs]were studied.The results show that the spheroidization of LZQT600-3 HCCDIBs matrix from the left-edge,left-1/2R to the center is at nodulizing grade II and above.As the cooling rate gradually decreases from surface to the center of the HCCIBs,the number of spheroidized graphite is gradually reduced,the size is gradually increased,the shape factor is decreased,and the pearlite content and lamellate spacing are increased.Along the horizontal direction of the section,the hardness of the material is distributed symmetrically around the center of the HCCDIBs.In the vertical direction,the hardness distribution in the center of the HCCDIBs is asymmetrical due to the gravity during the solidification process.Therefore,the microstructure in the lower part of the section solidifies relatively quickly.The left-edge has the best tensile mechanical properties,and the ultimate tensile strength,yield tensile strength and elongation are 597.3 MPa,418.5 MPa and 9.6%,respectively.The tensile fracture belongs to the ductile-brittle hybrid fracture.The comprehensive performances of LZQT600-3 HCCDIBs meet the actual application requirements of ultra-high pressure hydraulic plunger pump cylinder.展开更多
Effect of Cu. ni. Mn and,mo on the austemperability, Inicroslruclures and Inechanlcal properlies of auslempered duclile iron(ADI) weld metal have been investigated it has been demonslrated foal Mn and.Mo obviously enh...Effect of Cu. ni. Mn and,mo on the austemperability, Inicroslruclures and Inechanlcal properlies of auslempered duclile iron(ADI) weld metal have been investigated it has been demonslrated foal Mn and.Mo obviously enhance the austemperablity of weld metal. but a exdcess of Mn or Mo impairs the mechanical properties of ADI weld metal because of the formation or carbide at cell boundaries. Cu and Ni can improve the plasticity of ADI weld metal by suppressing the formation of carbide and by increaxsing the amount of austemite,.in order to obtain the weld having both the high austemperability and exceptional combination of mechanical properties. it is advantageous that welds is alloyed withe tWo Or more elements in relalivelv.small amounts.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
A foundry research project has been recently initiated at RTIT in order to better understand the fabrication of as-cast heavy section DI parts meeting high impact energy requirements at low temperatures.The experiment...A foundry research project has been recently initiated at RTIT in order to better understand the fabrication of as-cast heavy section DI parts meeting high impact energy requirements at low temperatures.The experimental castings have the following dimensions 180 mm x 180 mm x 190 mm.The achieved as-cast Charpy impact strengths were as follows:17 J (RT),16 J (-20℃) and 11 J (-40℃).The foundry process,the chemical composition and the microstructure of this experimental casting are compared to the ones of various examples in order to show the detrimental effects of residual elements,microshrinkage and microcarbide on the impact properties.Finally,quality index empirical models (based on casting chemical compositions) are used to analyse the impact tests results.This paper illustrates that an adequate nodule count can contribute to reducing the detrimental effects of the residual elements and microsegregation.展开更多
The erosion behavior of austempered ductile irons austenized at different temperatures was studied. The results indicate that the erosion rate well correlates with the mechanical properties. At high impact angles, inc...The erosion behavior of austempered ductile irons austenized at different temperatures was studied. The results indicate that the erosion rate well correlates with the mechanical properties. At high impact angles, increasing ductility and mechanical energy density results in decreasing erosion rate, whereas increasing hardness reduces the erosion rate at low impact angles. 2008 University of Science and Technology Beijing. All rights reserved.展开更多
Effect of Ce-Mg-Si (light RE) and Y-Mg-Si (heavy RE) nodulizers on the microstructures and mechanical properties of heavy section ductile iron was investigated to develop the material of spent-nuclear-fuel contain...Effect of Ce-Mg-Si (light RE) and Y-Mg-Si (heavy RE) nodulizers on the microstructures and mechanical properties of heavy section ductile iron was investigated to develop the material of spent-nuclear-fuel containers. Two as-casts were treated by the same quality percentage of light RE and heavy RE, respectively. Four positions were chosen to stand for different solidification cool-ing rates of specimens. The tensile strength, elongation and impact toughness of specimens treated by heavy RE were all higher than those of the specimens treated by light RE. With the decrease of cooling rate, the mechanical properties of two specimens decreased, and the fracture morphology changed from ductile fracture to brittle fracture. The improving effect of mechanical properties between heavy RE and light RE was obvious due to the better anti-degradation property of heavy RE. While the solidification process lasted for more than 250 min, the improving effect was not obvious due to serious spheroidalization decaying.展开更多
The microstructures and mechanical properties of the ductile cast iron (DI) specimens obtained by lost foam casting (LFC) with and without vibration were investigated. The results indicate that the number of the g...The microstructures and mechanical properties of the ductile cast iron (DI) specimens obtained by lost foam casting (LFC) with and without vibration were investigated. The results indicate that the number of the graphite nodule increases from 175 mm 2 of the specimens produced by LFC without vibration to 334 mm^-2 of the specimens produced by LFC with vibration, and the thickness of the ferrite shell increases. Meanwhile, the amount of the carbides decreases in the specimens produced by LFC with vibration and the granule structure then forms. These are mainly attributed to the "crystal shower" caused by the vibration. In addition, the tensile strength and elongation of DI specimens produced by LFC with vibration are improved due to the dispersion-strengthening of refined carbide and Dearlite colonv, uniform distribution of the graphite nodule, and increase of the amount of dimples and tearing edges.展开更多
Two gating systems namely stepped and tapered runners were used to cast strip samples with different thicknesses by CO2/silicate process using sand grain sizes of AFS 151 and 171. To assess the effect of mould coating...Two gating systems namely stepped and tapered runners were used to cast strip samples with different thicknesses by CO2/silicate process using sand grain sizes of AFS 151 and 171. To assess the effect of mould coating on the properties of thin wall ductile iron, half of the moulds were coated whilst the rest were not coated. Molten metal with the carbon equivalent of 4.29% was prepared and poured at 1 450 ℃. Microstructure of the specimens was analyzed by optical and scanning electron microscopes. Count, area fraction, roundness and diameter of the graphite nodules of the samples were measured by image analyzer. Brinell hardness and tensile tests of all the samples were also conducted. The results show that by using stepped runner gating system with uncoated and coarse sand mould, roundness and count of the graphite nodules decrease whereas diameter and area fraction increase. Although fine sand and coated mould cause longer distance of molten metal travel, hardness and strength of the samples decrease.展开更多
The influence of matrix structure on mechanical properties and dry rolling-sliding wear performance of alloyed ductile iron was examined. Four kinds of alloyed ductile irons with different matrix structures were produ...The influence of matrix structure on mechanical properties and dry rolling-sliding wear performance of alloyed ductile iron was examined. Four kinds of alloyed ductile irons with different matrix structures were produced through an adequate balance of alloying elements. Tensile tests and dry rolling-sliding wear tests were carried out at room temperature. The results show that yield strength and ultimate tensile strength increase, while elongation decreases until the matrix fully becomes pearlite. The lower matrix hardness results in more graphite emerging on the contact surface, which yields the decrease in friction coefficient. Besides, the wear rate decreases with the increase in matrix hardness among alloyed ductile irons except that with full pearlite matrix, the wear performance of which seems to be deteriorated due to poor fracture toughness. The main wear mechanism is delamination under an air-cooling condition. Based on the results of mechanical and wear tests, ductile iron with about 80% pearlite exhibits better wear performance as well as relatively reasonable mechanical properties.展开更多
基金supported by the Fund Project for Transformation of Science&Technology Achievements from Jiangsu Province(No.BA2009022)the National Innovation Fund for Small and Medium Technology Based Firms(No.10C26213204040)
文摘Casting defects could largely affect the mechanical properties of casting products. A number of test pieces made of ductile iron (EN-GJS-400-18-LT) with different levels of shrinkage porosity were prepared and then tensile and fatigue tests were performed to investigate the impact of shrinkage porosity on their mechanical properties. The results showed that the tensile strength decreases linearly with increasing of the shrinkage porosity. The tensile elongation decreases sharply with the increase of the shrinkage porosity mainly due to the non-uniform plastic deformation. The fatigue life also dramatically declines with increasing of the porosity and follows a power law relationship with the area percentage of porosity. The existence of the shrinkage porosity made the fatigue fracture complex. The shrinkage pores, especially those close to the surface usually became the crack initiation sites. For test pieces with less porosity, the fatigue fracture was clearly composed of crack initiation, propagation, and overloading. While for samples with high level of porosity, multiple crack initiation sites were observed.
文摘The effects of alloying elements on the as-cast microstructures and mechanical properties of heavy section ductile cast iron were investigated to develop press die material having high strength and high ductility. Measurements of ultimate tensile strength, 0.2% proof strength, elongation and unnotched Charpy impact energy are presented as a function of alloy amounts within 0.25 to 0.75 wt pct range. Hardness is measured on the broken tensile specimens. The small additions of Mo, Cu, Ni and Cr changed the as-cast mechanical properties owing to the different as-cast matrix microstructures. The ferrite matrix of Mo and Ni alloyed cast iron exhibits low strength and hardness as well as high elongation and impact energy. The increase in Mo and Ni contents developed some fractions of pearlite structures near the austenite eutectic cell boundaries, which caused the elongation and impact energy to drop in a small range. Adding Cu and Cr elements rapidly changed the ferrite matrix into pearlite matrix, so strength and hardness were significantly increased. As more Mo and Cr were added, the size and fraction of primary carbides in the eutectic cell boundaries increased through the segregation of these elements into the intercellular boundaries.
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 °C and 135 min, and austempering temperature and time are 279 °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Consistent mechanical and machining properties are essential in many applications where ductile irons offer the most cost-effective way to produce structural parts.In the production of hydraulic rotators,dimensional tolerances are typically 20μm to obtain designated performance.For castings where intermediate strength and ductility is required,it is common knowledge that conventional ferritic-pearlitic ductile irons such as ISO 1083/500-7 show large hardness variations.These are mainly caused by the notoriously varying pearlite content,both at different locations within a part and between parts in the same or different batches.Cooling rate variations due to different wall thickness and position in the molding box,as well as varying amounts of pearlite-stabilizing elements,all contribute to detrimental hardness variations.The obvious remedy is to avoid pearlite formation,and instead obtain the necessary mechanical properties by solution strengthening of the ferritic matrix by increasing silicon content to 3.7wt%-3.8wt%.The Swedish development in this field 1998 resulted in a national standardization as SS 140725,followed in 2004 by ISO 1083/ JS/500-10.Indexator AB decided 2005 to specify JS/500-10 for all new ductile iron parts and to convert all existing parts.Improvements include reduction by 75%in hardness variations and increase by 30%in cutting tool life,combined with consistently better mechanical properties.
基金supported by the Significant Science and Technology Project of Guangdong,China-Application and Demonstration of Energy Conservation and Emission Reduction Technology in Foundry Industry(2008A080800022)
文摘Cooling rate and inoculation practice can greatly affect the graphite morphology of ductile irons. In the present research, the effects of the cooling rate and antimony addition on the graphite morphology and mechanical properties of ductile irons have been studied. Three ductile iron castings were prepared through solidification under cooling conditions S (slow), M (medium) and F (fast). The cooling rates around the equilibrium eutectic temperature (1,150 ℃) for these cooling conditions (S, M and F) were set at 0.21 ℃.min1, 0.32℃.min1 and 0.37℃-min-1, respectively. In addition, four ductile iron castings were prepared by adding 0.01%, 0.02%, 0.03% and 0.04% (by weight) antimony, respectively under the slow cooling condition. The results show that the nodularity index, tensile strength and hardness of the ductile iron castings without antimony addition are all improved with the increase of cooling rate, while the ductile iron casting solidified under the medium cooling rate possesses the largest number of graphite nodules. Furthermore, for the four antimony containing castings, the graphite morphology and tensile strength are also improved by the antimony additions, and the effect of antimony addition is intensified when the addition increases from 0.01% to 0.03%. Moreover, the rare earth elements (REE)/antimony ratio of 2 appears to be the most effective for fine nodular graphite formation in ductile iron.
基金supported by the National Natural Science Foundation of China(Nos.51174068 and 51374086)
文摘To improve the mechanical properties of heavy section ductile cast iron, bismuth(Bi) was introduced into the iron. Five castings with different Bi content from 0 to 0.014 wt.% were prepared; and four positions in the casting from the edge to the center, with different solidifi cation cooling rates, were chosen for microstructure observation and mechanical properties test. The effect of the Bi content on the graphite morphology and mechanical properties of heavy section ductile cast iron were investigated. Results show that the tensile strength, elongation and impact toughness at different positions in the fi ve castings decrease with a decrease in cooling rate. With an increase in Bi content, the graphite morphology and the mechanical properties at the same position are improved, and the improvement of mechanical properties is obvious when the Bi content is no higher than 0.011wt.%. But when the Bi content is further increased to 0.014wt.%, the improvement of mechanical properties is not obvious due to the increase of chunky graphite number and the aggregation of chunky graphite. With an increase in Bi content, the tensile fracture mechanism is changed from brittle to mixture ductile-brittle fracture.
文摘The effects of sphere size on the microstructural and mechanical properties of ductile iron–steel hollow sphere(DI–SHS) syntactic foams were investigated in this study. The SHSs were manufactured by fluidized-bed coating via the Fe-based commercial powder–binder suspension onto expanded polystyrene spheres(EPSs). Afterwards, the DI–SHS syntactic foams were produced via a sand-mold casting process. The microstructures of specimens were investigated by optical microscopy, scanning electron microscopy(SEM), and energy-dispersive X-ray spectroscopy(EDS). The microscopic evaluations of specimens reveal distinct regions composed of the DI matrix, SHS shells, and compatible interface. As a result, the microstructures and graphite morphologies of the DI matrix depend on sphere size. When the sphere size decreases, the area fractions of cementite and graphite phases are observed to increase and decrease, respectively. Compression tests were subsequently conducted at ambient temperature on the DI–SHS syntactic foams. The results reveal that the compression behavior of the syntactic foams is enhanced with increasing sphere size. Furthermore, the compressed specimens demonstrate that microcracks start and grow from the interface region.
基金Fundamental Research Funds for the Central Universities,China(Grant No.2013B18020459).
文摘Ferritic spheroidal graphite irons with nodularity from 72%to 96%were prepared.The relationship between the nodularity and the mechanical properties of the ferritic spheroidal graphite iron was investigated.The effect of nodularity on the mechanical properties and tensile fracture of the cast iron were studied.Results showed that the tensile strength Rm,yield strength Rp0.2,elongation to failure A5,and impact energy KV2 of the cast iron had a good linear relationship with its nodularity.Nodularity and annealing treatment would obviously affect the fracture characteristics of ferritic spheroidal graphite iron.The annealed ferritic spheroidal graphite iron with 93%nodularity showed a completely ductile rupture.With the decrease of nodularity from 93%to 72%,the cleavage fracture area ratio increased gradually from 0%to 8.3%.Compared with as-cast ferritic spheroidal graphite iron,annealing treatment reduced the cleavage fracture area of the ferritic spheroidal graphite iron.
文摘Semi-solid processing of metallic materials has been investigated for some time;however,this innovative production process has not fully established for ferrous alloys like ductile cast iron in the industry yet.Ferrous alloys-specially ductile cast ironbecause of increasing complexity due to high temperature processing and some other limitations have been allocated a small share of this useful forming process to themselves.However,this work describes that thixo-forming of ductile iron despite all of the limitations is possible even for thin sections(less than 1 mm).Die temperature and injection velocity are the most effective parameters to thixo-forming particularly for high melting point materials such as ductile cast iron.Filling behavior,shape factor of graphites and fluidity of thixo-formed specimens were characterized.In addition,defects as well as shrinkage and cold laps were examined to achieve sound specimen.Subsequence to successful thixo-forming,two step austempering was performed to accomplish a uniform structure with minimum untransformed austenite volume(UAV).Following austempering,tensile test was carried out and the results show good combination of tensile strength and elongation for treated specimens(1 137 MPa strength and 12% elongation in best situation).
文摘Impact toughness of ductile nodular cast iron loaded perpendicular to the austenitic dendrites is found to be 43% higher than that parallel to ones.Yet tensile strength and elongation of the former are 23% and 30% lower than the later respectively.It is belived that the dendritic segregation may cause such differences.
文摘The aim of present work is to investigate the influencing factors on mechanical property stability of Cu-Mo-Ni alloyed austempered ductile iron (ADI). The results show that after austenitized at 900℃ for 2 h followed by austempered at 370℃for another 2 h, the mechanical property of the alloyed ADI can reach the Germanite GGG-100 standard, i.e. σb≮1000 MPa,δ≮5%, at 95% confidence level. And the satisfactory mechanical properties were obtained when the alloyed ADI was austenitized at 850℃ to 1 000 ℃ for 1-4 h, and austempered at 355℃ to 400℃ for another 1 h to 4 h. The microstructures, including nodule number, white bright zone content (martensite-containing interdendritic segregation zone) and retained austenite content, can significantly influence the mechanical properties of the ADI. In order to obtain the good combinations of strength and ductility, the volume fraction of white bright zone should he less than 5%, and the retained austenite contents maintain hetween 30 % and 40%. The application of inoculation techniques to increase graphite nodule number can effectively reduce the white bright zone content in the structure.
基金the support from the International Science and Technology Cooperation Program of Shaanxi Province(No.2023-GHZD-50)the Projects of Major Innovation Platforms for Scientific and Technological and Local Transformation of Scientific and Technological Achievements of Xi’an(No.20GXSF0003)+1 种基金the Projects of Major Scientific and Technological Achievements Local Transformation of Xi’an(No.2022JH-ZDZH-0039)the Higher Education Institution Discipline Innovation and Intelligence Base of Shaanxi Provincial(No.S2021-ZC-GXYZ-0011)。
文摘It is important to improve the comprehensive performance of the ductile iron bars(DIBs)for the cylinder block of the extra high pressure hydraulic plunger pump and accelerate the industrial application.In this work,the LZQT600-3 DIBs with the diameter of 145 mm were prepared by the horizontal continuous casting(HCC)process,that is,LZQT600-3 HCCDIBs.The microstructure and room temperature tensile properties of different sections[left-edge(surface layer),left-1/2R(left half of the radius),and the center of the HCCDIBs]were studied.The results show that the spheroidization of LZQT600-3 HCCDIBs matrix from the left-edge,left-1/2R to the center is at nodulizing grade II and above.As the cooling rate gradually decreases from surface to the center of the HCCIBs,the number of spheroidized graphite is gradually reduced,the size is gradually increased,the shape factor is decreased,and the pearlite content and lamellate spacing are increased.Along the horizontal direction of the section,the hardness of the material is distributed symmetrically around the center of the HCCDIBs.In the vertical direction,the hardness distribution in the center of the HCCDIBs is asymmetrical due to the gravity during the solidification process.Therefore,the microstructure in the lower part of the section solidifies relatively quickly.The left-edge has the best tensile mechanical properties,and the ultimate tensile strength,yield tensile strength and elongation are 597.3 MPa,418.5 MPa and 9.6%,respectively.The tensile fracture belongs to the ductile-brittle hybrid fracture.The comprehensive performances of LZQT600-3 HCCDIBs meet the actual application requirements of ultra-high pressure hydraulic plunger pump cylinder.
文摘Effect of Cu. ni. Mn and,mo on the austemperability, Inicroslruclures and Inechanlcal properlies of auslempered duclile iron(ADI) weld metal have been investigated it has been demonslrated foal Mn and.Mo obviously enhance the austemperablity of weld metal. but a exdcess of Mn or Mo impairs the mechanical properties of ADI weld metal because of the formation or carbide at cell boundaries. Cu and Ni can improve the plasticity of ADI weld metal by suppressing the formation of carbide and by increaxsing the amount of austemite,.in order to obtain the weld having both the high austemperability and exceptional combination of mechanical properties. it is advantageous that welds is alloyed withe tWo Or more elements in relalivelv.small amounts.
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.
文摘A foundry research project has been recently initiated at RTIT in order to better understand the fabrication of as-cast heavy section DI parts meeting high impact energy requirements at low temperatures.The experimental castings have the following dimensions 180 mm x 180 mm x 190 mm.The achieved as-cast Charpy impact strengths were as follows:17 J (RT),16 J (-20℃) and 11 J (-40℃).The foundry process,the chemical composition and the microstructure of this experimental casting are compared to the ones of various examples in order to show the detrimental effects of residual elements,microshrinkage and microcarbide on the impact properties.Finally,quality index empirical models (based on casting chemical compositions) are used to analyse the impact tests results.This paper illustrates that an adequate nodule count can contribute to reducing the detrimental effects of the residual elements and microsegregation.
基金the National Science Council(No.NSC 93-2216-E-006-034).
文摘The erosion behavior of austempered ductile irons austenized at different temperatures was studied. The results indicate that the erosion rate well correlates with the mechanical properties. At high impact angles, increasing ductility and mechanical energy density results in decreasing erosion rate, whereas increasing hardness reduces the erosion rate at low impact angles. 2008 University of Science and Technology Beijing. All rights reserved.
基金supported by National Natural Science Foundation of China(51174068,51374086)
文摘Effect of Ce-Mg-Si (light RE) and Y-Mg-Si (heavy RE) nodulizers on the microstructures and mechanical properties of heavy section ductile iron was investigated to develop the material of spent-nuclear-fuel containers. Two as-casts were treated by the same quality percentage of light RE and heavy RE, respectively. Four positions were chosen to stand for different solidification cool-ing rates of specimens. The tensile strength, elongation and impact toughness of specimens treated by heavy RE were all higher than those of the specimens treated by light RE. With the decrease of cooling rate, the mechanical properties of two specimens decreased, and the fracture morphology changed from ductile fracture to brittle fracture. The improving effect of mechanical properties between heavy RE and light RE was obvious due to the better anti-degradation property of heavy RE. While the solidification process lasted for more than 250 min, the improving effect was not obvious due to serious spheroidalization decaying.
基金Item Sponsored by National High Technology Research and Development Program(863Program)of China(2007AA03Z113)
文摘The microstructures and mechanical properties of the ductile cast iron (DI) specimens obtained by lost foam casting (LFC) with and without vibration were investigated. The results indicate that the number of the graphite nodule increases from 175 mm 2 of the specimens produced by LFC without vibration to 334 mm^-2 of the specimens produced by LFC with vibration, and the thickness of the ferrite shell increases. Meanwhile, the amount of the carbides decreases in the specimens produced by LFC with vibration and the granule structure then forms. These are mainly attributed to the "crystal shower" caused by the vibration. In addition, the tensile strength and elongation of DI specimens produced by LFC with vibration are improved due to the dispersion-strengthening of refined carbide and Dearlite colonv, uniform distribution of the graphite nodule, and increase of the amount of dimples and tearing edges.
文摘Two gating systems namely stepped and tapered runners were used to cast strip samples with different thicknesses by CO2/silicate process using sand grain sizes of AFS 151 and 171. To assess the effect of mould coating on the properties of thin wall ductile iron, half of the moulds were coated whilst the rest were not coated. Molten metal with the carbon equivalent of 4.29% was prepared and poured at 1 450 ℃. Microstructure of the specimens was analyzed by optical and scanning electron microscopes. Count, area fraction, roundness and diameter of the graphite nodules of the samples were measured by image analyzer. Brinell hardness and tensile tests of all the samples were also conducted. The results show that by using stepped runner gating system with uncoated and coarse sand mould, roundness and count of the graphite nodules decrease whereas diameter and area fraction increase. Although fine sand and coated mould cause longer distance of molten metal travel, hardness and strength of the samples decrease.
基金Funding was provided by National Natural Science Foundation of China (Grant No. U1760109).
文摘The influence of matrix structure on mechanical properties and dry rolling-sliding wear performance of alloyed ductile iron was examined. Four kinds of alloyed ductile irons with different matrix structures were produced through an adequate balance of alloying elements. Tensile tests and dry rolling-sliding wear tests were carried out at room temperature. The results show that yield strength and ultimate tensile strength increase, while elongation decreases until the matrix fully becomes pearlite. The lower matrix hardness results in more graphite emerging on the contact surface, which yields the decrease in friction coefficient. Besides, the wear rate decreases with the increase in matrix hardness among alloyed ductile irons except that with full pearlite matrix, the wear performance of which seems to be deteriorated due to poor fracture toughness. The main wear mechanism is delamination under an air-cooling condition. Based on the results of mechanical and wear tests, ductile iron with about 80% pearlite exhibits better wear performance as well as relatively reasonable mechanical properties.