The present work aims to investigate the effect of heating temperature(400,600 and 800°C)and inoculating elements(Ca,Ca-Ba,Ca-RE)on oxidation behavior of ductile irons containing 5.25%Si and 4.8%Si-2.3%Mo in dry ...The present work aims to investigate the effect of heating temperature(400,600 and 800°C)and inoculating elements(Ca,Ca-Ba,Ca-RE)on oxidation behavior of ductile irons containing 5.25%Si and 4.8%Si-2.3%Mo in dry air and combustion gas containing water vapour(natural gas burning).The oxidation is influenced by the gas atmosphere type,the iron alloying system,and the inoculating elements depending on the heating temperature.The weight gain increases from 0.001%-0.1%(400°C)to 0.05%-0.70%(600°C)and up to 0.10%-2.15%(800°C).No particular effects of the considered influencing factors are found when heating at 400°C,while at 600°C,mainly the oxidation gas atmosphere type shows a visible influence.At the highest heating temperature of 800°C,a limited increase of the weight gain is found for dry air atmosphere(up to 0.25%),but it drastically increases for combustion atmospheres(0.65%-2.15%).The water vapour presence in the combustion atmosphere is an important oxidising factor at 600-800°C.The alloying system appears to influence the oxidation behavior mainly at a heating temperature of 800°C in the combustion atmosphere,as evidenced by the lower weight gain in 5.25%silicon cast iron.Positive effects of inoculating elements increase with the heating temperature,with Ca and Ba-FeSi inoculation generally showing better performance.Irons inoculated with CaRE-FeSi exhibit a higher degree of oxidation.These results are in good relationship with the previous reported data:Ca-Ba-inoculation system appears to be better than simple Ca for improving the graphite parameters,while RE-bearing inoculant negatively affects the compactness degree of graphite particles in high-Si ductile irons.As the lower compactness degree is typical for graphite nodules in high-Si ductile irons,which negatively affects the oxidation resistance,it is necessary to employ specific metallurgical treatments to improve nodule quality.Inoculation,in particular,is a potential method to achieve this improvement.展开更多
The effect of addition of 0.05wt.% to 0.25 wt.% Ca,Zr,Al-FeSi alloy on in-ladle and in-mould inoculation of grey cast irons was investigated.In the present paper,the conclusions drawn are based on thermal analysis.For...The effect of addition of 0.05wt.% to 0.25 wt.% Ca,Zr,Al-FeSi alloy on in-ladle and in-mould inoculation of grey cast irons was investigated.In the present paper,the conclusions drawn are based on thermal analysis.For the solidification pattern,some specific cooling curves characteristics,such as the degree of undercooling at the beginning of eutectic solidif ication and at the end of solidifi cation,as well as the recalescence level,are identif ied to be more influenced by the inoculation technique.The degree of eutectic undercooling of the electrically melted base iron having 0.025% S,0.003% Al and 3.5% Ce is excessively high(39-40℃),generating a relatively high need for inoculation.Under these conditions,the in-mould inoculation has a more signif icant effect compared to ladle inoculation,especially at lower inoculant usage(less than 0.20 wt.%).Generally,the eff iciency of 0.05wt.% -0.15wt.% of alloy for in-mould inoculation is comparable to,or better than,that of 0.15wt.% -0.25wt.% addition in ladle inoculation procedures.In order to secure stable and controlled processes,representative thermal analysis parameters could be used,especially in thin wall grey iron castings production.展开更多
Flake graphite iron, compacted graphite iron and spheroidal graphite iron with various tensile strengths were cast. They were selected and grouped according to roughly the same tensile strength, and then the main cutt...Flake graphite iron, compacted graphite iron and spheroidal graphite iron with various tensile strengths were cast. They were selected and grouped according to roughly the same tensile strength, and then the main cutting force in each group was measured and compared. The microstructures of different cast irons were characterized. The relationship between the cutting force and microstructure was established. Results show that the graphite morphology in cast irons determines the strength. In order to obtain the same strength of the cast iron with sharply edged graphite, more or finer pearlite in the matrix is needed. Graphitic cast irons with high pearlite content and smaller pearlite interlamellar spacing have higher hardness. For the cast irons with different graphite morphologies, but almost the same tensile strength, the main cutting force is obviously different, along with the hardness. Harder cast irons have a greater cutting force, but the difference in cutting force is not proportional to hardness.展开更多
The objective of this investigation is to study the influence of vanadium（5.0wt%–10.0wt%） and chromium（0–9.0wt%） on the microstructure and hardness of Cr-V-Mn-Ni white cast irons with spheroidal vanadium carbide...The objective of this investigation is to study the influence of vanadium（5.0wt%–10.0wt%） and chromium（0–9.0wt%） on the microstructure and hardness of Cr-V-Mn-Ni white cast irons with spheroidal vanadium carbides. The alloys＇ microstructural features are presented and discussed with regard to the distribution of phase elements. The structural constituents of the alloys are spheroidal VC, proeutectoid cementite, ledeburite eutectic, rosette-shaped carbide eutectic（based on M7C3）, pearlite, martensite, and austenite. Their combinations and area fraction（AF） ratios are reported to be influenced by the alloys＇ chemical composition. Spheroidized VC particles are found to be sites for the nucleation of carbide eutectics. Cr and V are shown to substitute each other in the VC and M7C3 carbides, respectively. Chromium alloying leads to the formation of a eutectic（γ-Fe ＋ М7С3）, preventing the appearance of proeutectoid cementite in the structure. Vanadium and chromium are revealed to increase the total carbide fraction and the amount of austenite in the matrix. Cr is observed to play a key role in controlling the metallic matrix microstructure.展开更多
Full factorial design was used to evaluate the two-body abrasive resistance of 3wt%C–4wt%Mn–1.5wt%Ni spheroidal carbide cast irons with varying vanadium（5.0wt%–10.0wt%） and chromium（up to 9.0wt%） contents. The ...Full factorial design was used to evaluate the two-body abrasive resistance of 3wt%C–4wt%Mn–1.5wt%Ni spheroidal carbide cast irons with varying vanadium（5.0wt%–10.0wt%） and chromium（up to 9.0wt%） contents. The alloys were quenched at 920℃. The regression equation of wear rate as a function of V and Cr contents was proposed. This regression equation shows that the wear rate decreases with increasing V content because of the growth of spheroidal VC carbide amount. Cr influences the overall response in a complex manner both by reducing the wear rate owing to eutectic carbides（M7C3） and by increasing the wear rate though stabilizing austenite to deformation-induced martensite transformation. This transformation is recognized as an important factor in increasing the abrasive response of the alloys. By analyzing the regression equation, the optimal content ranges are found to be 7.5wt%–10.0wt% for V and 2.5wt%–4.5wt% for Cr, which corresponds to the alloys containing 9vol%–15vol% spheroidal VC carbides, 8vol%–16vol% M7C3, and a metastable austenite/martensite matrix. The wear resistance is 1.9–2.3 times that of the traditional 12wt% V–13wt% Mn spheroidal carbide cast iron.展开更多
This study aims to clarify the influence of external notch on impact characteristics of high toughness ductile cast irons prepared by austempering heat treatment. We produced ductile cast irons samples with various ma...This study aims to clarify the influence of external notch on impact characteristics of high toughness ductile cast irons prepared by austempering heat treatment. We produced ductile cast irons samples with various matrix microstructure tested by Charpy impact within five kinds of external notches whose stress concentration factors (α), with values taken from 1.0 (Un-notched) to 4.8. In addition, to clarify the initiation process of impact characteristics, we observed the evolution of microstructure surface during bending tests with a slow loading speed for the un-notched and the notched impact samples. The results showed that the impact fracture energy decreases strongly in the range of α from 1 to 2.3 but decreases slightly for α larger than 3. Moreover, the impact value of samples with austempered microstructure is sensitive to the external notch shape. The impact transition temperature increases with increasing the stress concentration factor. The fracture energy is decreasing with the external notch from the impact test since the crack initiation energy is directly affected by this later. This work contributes to get a better understanding in the basic theories of external notch effect on impact characteristics of austempered spheroidal graphite cast irons (ADI).展开更多
The paper reviews original data obtained by the present authors,revealed in recent separate publications,describing specific procedures for high quality grey irons,and reflecting the forecast needs of the worldwide ir...The paper reviews original data obtained by the present authors,revealed in recent separate publications,describing specific procedures for high quality grey irons,and reflecting the forecast needs of the worldwide iron foundry industry.High power,medium frequency coreless induction furnaces are commonly used in electric melting grey iron foundries.This has resulted in low sulphur(<0.05wt.%)and aluminium(<0.005wt.%)contents in the iron,with a potential for higher superheating(>1,500°C),contributing to unfavourable conditions for graphite nucleation.Thin wall castings are increasingly produced by these electric melt shops with a risk of greater eutectic undercooling during solidification.The paper focused on two groups of grey cast irons and their specific problems:carbides and graphite morphology control in lower carbon equivalent high strength irons(CE=3.4%-3.8%),and austenite dendrite promotion in eutectic and slightly hypereutectic irons(CE=4.1%-4.5%),in order to increase their strength characteristics.There are 3 stages and 3 steps involving graphite formation,iron chemistry and iron processing that appear to be important.The concept in the present paper sustains a threestage model for nucleating flake graphite[(Mn,X)S type nuclei].There are three important groups of elements(deoxidizer,Mn/S,and inoculant)and three technological stages in electric melting of iron(superheat,pre-conditioning of base iron,final inoculation).Attention is drawn to a control factor(%Mn)x(%S)ensuring it equals to 0.03–0.06,accompanied by 0.005wt.%–0.010wt.%Al and/or Zr content in inoculated irons.It was found that iron powder addition promotes austenite dendrite formation in eutectic and slightly eutectic,acting as reinforcement for the eutectic cells.But,there is an accompanying possible negative influence on the characteristics of the(Mn,X)S type graphite nuclei(change the morphology of nuclei from polygonal compact to irregular polygonal,and therefore promote chill tendency in treated irons).A double addition(iron powder+inoculant)appears to be an effective treatment to benefit both austenite and graphite nucleation,with positive effects on the final structure and chill tendency.展开更多
The physical metallurgy underlying the development of cast microstructures in abrasion resistant high chromium cast irons, and their structural modification by thermal treatments is relatively complex. Structural char...The physical metallurgy underlying the development of cast microstructures in abrasion resistant high chromium cast irons, and their structural modification by thermal treatments is relatively complex. Structural characterisation via electron microscopy therefore has a key role to play in furthering our understanding of the phase transformations that control the microstructures and hence the service performances of these irons as wear parts. This paper shows how both scanning and especially transmission electron microscopy can provide valuable information on the nature of eutectic and secondary carbides and on the matrix structures in these irons. Particular attention is given to current characterisation research on conventionally cast 30%Cr irons that are used for applications involving corrosive wear e.g. slurry pumps and on a semi-solid cast 27%Cr iron that has a potential for applications in industry.展开更多
Recent studies revealed that in eutectic to slightly hypereutectic grey irons （CE = 4.3%-4.5%） the presence of austenite dendrites provides an opportunity to improve the cast iron properties, as a high number of eut...Recent studies revealed that in eutectic to slightly hypereutectic grey irons （CE = 4.3%-4.5%） the presence of austenite dendrites provides an opportunity to improve the cast iron properties, as a high number of eutectic cells are ＂reinforced＂ by austenite dendrites. An iron powder addition proved to be important by promoting dendritic austenite in hypereutectic irons, but was accompanied by adverse effect on the characteristics of potential nuclei for graphite. The purpose of the present paper is to investigate the solidification pattern of these irons. Chill wedges with different cooling moduli （CM = 0.11 - 0.43 cm） were poured in resin bonded sand and metal moulds. Relative clear / mottled / total chill measurement criteria were applied. Iron powder additions led to a higher chill tendency, while single inoculation showed the strongest graphiUzing effect. The various double treatments show an intermediate position, but the inoculant added after iron powder appears to be the most effective in reducing base iron chill tendency, for all cooling moduli and chill evaluation parameters. This performance reflects the improved properties of （Mn,X）S polygonal compounds as nucleation sites for graphite, especially in resin bonded sand mould castings. Both austenite and graphite nucleation benefit from a double addition of iron powder ＋ inoculant, with positive effect on the final structure and chill tendency.展开更多
This study aimed at optimizing impact toughness and abrasion wear resistance of 15%Cr-2%Mo hypereutectic abrasion-resistant white irons. The effects of dynamic solidification, niobium addition, combined action of them...This study aimed at optimizing impact toughness and abrasion wear resistance of 15%Cr-2%Mo hypereutectic abrasion-resistant white irons. The effects of dynamic solidification, niobium addition, combined action of them and heat treatment have been investigated. Investigations were performed by means of the image analyzer, scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS) and X-ray diffraction. Impact toughness and abrasion wear resistance tests were conducted. Fracture and worn surfaces were studied. Results indicated that microstructural control during solidifciation is the most valuable tool to attain the optimum combination between impact toughness and wear resistance in hypereutectic iron. Combined action of Nb addition and dynamic solidifciation improves impact toughness and wear resistance even more than the action of each individual factor. In the as-cast condition, impact toughness and abrasion resistance were increased after dynamic solidification compared to statically solidified one by 71.4% and 10%, respectively. This enhancement was increased to 114.3 % and 28.8 % by adding 2% Nb. Lower tempering temperature of 260°C exhibits better impact and abrasion resistance than the sub-critical tempering temperature of 500°C.展开更多
The novel cast irons of chemical composition(wt%)0.7C-5W-5Mo-5V-10Cr-2.5Ti were invented with the additions of 1.6wt%B and 2.7wt%B.The aim of this work was to study the effect of boron on the structural state of the a...The novel cast irons of chemical composition(wt%)0.7C-5W-5Mo-5V-10Cr-2.5Ti were invented with the additions of 1.6wt%B and 2.7wt%B.The aim of this work was to study the effect of boron on the structural state of the alloys and phase elemental distribution with respect to the formation of wear-resistant structural constituents.It was found that the alloy containing 1.6wt%B was composed of three eutectics:(a)“M_(2)(C,B)_(5)+ferrite”having a“Chinese Script”morphology(89.8vol%),(b)“M_(7)(C,B)_(3)+Austenite”having a“Rosette”morphology,and(c)“M_(3)C+Austenite”having a“Ledeburite”-shaped morphology(2.7vol%).With 2.7wt%of boron content,the bulk hardness increased from HRC 31 to HRC 38.5.The primary carboborides M_(2)(C,B)_(5) with average microhardness of HV 2797 appeared in the structure with a volume fraction of 17.6vol%.The volume fraction of eutectics(a)and(b,c)decreased to 71.2vol%and 3.9vol%,respectively.The matrix was“ferrite/austenite”for 1.6wt%B and“ferrite/pearlite”for 2.7wt%B.Both cast irons contained compact precipitates of carbide(Ti,M)C and carboboride(Ti,M)(C,В)with a volume fraction of 7.3%-7.5%.Based on the energy-dispersive X-ray spectroscopy,the elemental phase distributions and the appropriate phase formulas are presented in this work.展开更多
Application of rare earths in cast iron is a traditional applied field of rare earths in industry. The consumption of rare earths on cast iron is the first rank in all applied fields in China. The affinity between rar...Application of rare earths in cast iron is a traditional applied field of rare earths in industry. The consumption of rare earths on cast iron is the first rank in all applied fields in China. The affinity between rare earths and O,S and other elements in cast iron is strong enough,which is the foundation to improve microstructures and properties of cast iron. But dynamics of reaction of rare earths in cast iron is disappointed. Therefore,effects of application of rare earths in cast iron always fluctuate. The good effects can be got when dynamics of reaction of rare earths on cast iron is controlled and improved. It is proved by practice that microstructures and properties of cast iron,such as ductile iron,vermicular graphite cast iron,gray cast iron,white cast iron and so on,are improved with amonnt of rare earths incrtasing. There is 'double peaks effect' for strength of cast iron vs. addition of rare earths in cast iron. The application of rare earths in cast iron still possesses bright prospects nowadays and future.展开更多
The corrosion behavior of spheroidal graphite and flake graphite cast irons was studied in oxidizing and sulfidizing atmospheres between 600 and 800℃ for 50 h. The corrosion rate in the sulfidizing atmosphere was fas...The corrosion behavior of spheroidal graphite and flake graphite cast irons was studied in oxidizing and sulfidizing atmospheres between 600 and 800℃ for 50 h. The corrosion rate in the sulfidizing atmosphere was faster than that in air above 700℃, due to the formation of the Fe0.975S sulfide. The corrosion rate of the spheroidal graphite cast iron was similar to that of the flake graphite cast iron.展开更多
A jet type erosion-corrosion tester was developed for the erosion-corrosion investigation of high-chromium cast irons. During tests the size and the shape of particles in the slurry can be maintained stable. The jet v...A jet type erosion-corrosion tester was developed for the erosion-corrosion investigation of high-chromium cast irons. During tests the size and the shape of particles in the slurry can be maintained stable. The jet velocity and attack angle can be accurately controlled. The repeatability and ranking consistency of the test results are satisfactory. The test parameters can be adjusted in a wide range, so that the tester can simulate various practical working conditions. Electrochemical test data can be automatically collected and processed. Dynamic polarization curves can be obtained during erosion-corrosion test, which can be used to study the dynamic corrosion characteristics.Two high chromium cast irons were studied in hot concentrated alkaline slurry. The results show that the erosioncorrosion mass loss rate and dynamic corrosion rate of 295Cr26 iron is lower than that of 185Cr13 under the conditions similar to alumyte processing. The mechanism of erosion-corrosion of 295Cr26 and 185Cr13 was studied by using the tester. The interaction between erosion and corrosion was also quantitatively evaluated.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
The relationship between the retained austenite content of the matrix in16Cr-3C white irons and the abrasion resistance was investigated. The results show that: (1) theabrasion resistance can be improved by sub-critic...The relationship between the retained austenite content of the matrix in16Cr-3C white irons and the abrasion resistance was investigated. The results show that: (1) theabrasion resistance can be improved by sub-critical heat treatment, which could be attributed to thedecrease of the retained austenite content; (2) both the abrasion resistance and hardness can beimproved by controlling the retained austenite content below 20 percent-30 percent and arrive at themaximum when the retained austenite content is reduced to about 10 percent; (3) the abrasionresistance decreases abruptly once the retained austenite content is lower than 10 percent, whichstems from both the in situ transformation of (Fe, Cr)_(23)C_6 to M_3C carbides and the formation ofpearlitic matrix.展开更多
The austenitizing temperature controls the carbon content of the austenite which,in turn,influences the structure and properties of cast irons after subsequent cooling to room temperature.In this paper,for a cast iron...The austenitizing temperature controls the carbon content of the austenite which,in turn,influences the structure and properties of cast irons after subsequent cooling to room temperature.In this paper,for a cast iron with known silicon content,a formula of calculating austenite carbon content at a certain austenitizing temperature was developed.This relationship can be used to more accurately select carbon content of austenite or austenitizing temperature to produce desired properties after subsequent cooling to room temperature.展开更多
The influences of copper on microstructure and the hardening behavior of high chromium cast irons subjected to sub-critical treatment were investigated. The results show that the microstructure of the as-cast high chr...The influences of copper on microstructure and the hardening behavior of high chromium cast irons subjected to sub-critical treatment were investigated. The results show that the microstructure of the as-cast high chromium cast irons consists of retained austenite, martensite and M1C3 type eutectic carbide. When copper is added into high chromium cast irons, austenite and carbide contents are increased. The increased addition of copper content from 0% to 1.84% leads to the increase of austenite and carbide from 15.9% and 20. 0% to 61.0% and 35.5% , respectively. In the process of sub-critical treatment, the retained austenite in the matrix can be precipitated into secondary carbides and then transforms into martensite in cooling process, which causes the secondary hardening of the alloy under sub-critical treatment. High chromium cast irons containing copper in sub-critical treatment appear the second hardening curve peak due to the precipitation of copper from supersaturated matrix.展开更多
Because of the excellent performance of ductile irons and the unique superiority of investment casting, thepreparation of complicated and thin-wall ductile iron castings by investment casting shows a good developmentp...Because of the excellent performance of ductile irons and the unique superiority of investment casting, thepreparation of complicated and thin-wall ductile iron castings by investment casting shows a good developmentprospect. In this present work, combined with the actual product experiments, the characteristics of shell making,spheroidization, inoculation and defect prevention are presented, and some suggestions are given for investmentcasting of ductile iron.展开更多
基金supported by a grant from National Program for Research of the National Association of Technical Universities-GNAC ARUT 2023.
文摘The present work aims to investigate the effect of heating temperature(400,600 and 800°C)and inoculating elements(Ca,Ca-Ba,Ca-RE)on oxidation behavior of ductile irons containing 5.25%Si and 4.8%Si-2.3%Mo in dry air and combustion gas containing water vapour(natural gas burning).The oxidation is influenced by the gas atmosphere type,the iron alloying system,and the inoculating elements depending on the heating temperature.The weight gain increases from 0.001%-0.1%(400°C)to 0.05%-0.70%(600°C)and up to 0.10%-2.15%(800°C).No particular effects of the considered influencing factors are found when heating at 400°C,while at 600°C,mainly the oxidation gas atmosphere type shows a visible influence.At the highest heating temperature of 800°C,a limited increase of the weight gain is found for dry air atmosphere(up to 0.25%),but it drastically increases for combustion atmospheres(0.65%-2.15%).The water vapour presence in the combustion atmosphere is an important oxidising factor at 600-800°C.The alloying system appears to influence the oxidation behavior mainly at a heating temperature of 800°C in the combustion atmosphere,as evidenced by the lower weight gain in 5.25%silicon cast iron.Positive effects of inoculating elements increase with the heating temperature,with Ca and Ba-FeSi inoculation generally showing better performance.Irons inoculated with CaRE-FeSi exhibit a higher degree of oxidation.These results are in good relationship with the previous reported data:Ca-Ba-inoculation system appears to be better than simple Ca for improving the graphite parameters,while RE-bearing inoculant negatively affects the compactness degree of graphite particles in high-Si ductile irons.As the lower compactness degree is typical for graphite nodules in high-Si ductile irons,which negatively affects the oxidation resistance,it is necessary to employ specific metallurgical treatments to improve nodule quality.Inoculation,in particular,is a potential method to achieve this improvement.
文摘The effect of addition of 0.05wt.% to 0.25 wt.% Ca,Zr,Al-FeSi alloy on in-ladle and in-mould inoculation of grey cast irons was investigated.In the present paper,the conclusions drawn are based on thermal analysis.For the solidification pattern,some specific cooling curves characteristics,such as the degree of undercooling at the beginning of eutectic solidif ication and at the end of solidifi cation,as well as the recalescence level,are identif ied to be more influenced by the inoculation technique.The degree of eutectic undercooling of the electrically melted base iron having 0.025% S,0.003% Al and 3.5% Ce is excessively high(39-40℃),generating a relatively high need for inoculation.Under these conditions,the in-mould inoculation has a more signif icant effect compared to ladle inoculation,especially at lower inoculant usage(less than 0.20 wt.%).Generally,the eff iciency of 0.05wt.% -0.15wt.% of alloy for in-mould inoculation is comparable to,or better than,that of 0.15wt.% -0.25wt.% addition in ladle inoculation procedures.In order to secure stable and controlled processes,representative thermal analysis parameters could be used,especially in thin wall grey iron castings production.
基金supported by the China’s National Overseas Study Fund(CSC201808180001)the National Natural Science Foundation of China(U1804146)the Program for Science and Technology Innovation Talents in Universities of the Henan Province(17HASTIT026)
文摘Flake graphite iron, compacted graphite iron and spheroidal graphite iron with various tensile strengths were cast. They were selected and grouped according to roughly the same tensile strength, and then the main cutting force in each group was measured and compared. The microstructures of different cast irons were characterized. The relationship between the cutting force and microstructure was established. Results show that the graphite morphology in cast irons determines the strength. In order to obtain the same strength of the cast iron with sharply edged graphite, more or finer pearlite in the matrix is needed. Graphitic cast irons with high pearlite content and smaller pearlite interlamellar spacing have higher hardness. For the cast irons with different graphite morphologies, but almost the same tensile strength, the main cutting force is obviously different, along with the hardness. Harder cast irons have a greater cutting force, but the difference in cutting force is not proportional to hardness.
基金the Muroran Institute of Technology for funding this project
文摘The objective of this investigation is to study the influence of vanadium（5.0wt%–10.0wt%） and chromium（0–9.0wt%） on the microstructure and hardness of Cr-V-Mn-Ni white cast irons with spheroidal vanadium carbides. The alloys＇ microstructural features are presented and discussed with regard to the distribution of phase elements. The structural constituents of the alloys are spheroidal VC, proeutectoid cementite, ledeburite eutectic, rosette-shaped carbide eutectic（based on M7C3）, pearlite, martensite, and austenite. Their combinations and area fraction（AF） ratios are reported to be influenced by the alloys＇ chemical composition. Spheroidized VC particles are found to be sites for the nucleation of carbide eutectics. Cr and V are shown to substitute each other in the VC and M7C3 carbides, respectively. Chromium alloying leads to the formation of a eutectic（γ-Fe ＋ М7С3）, preventing the appearance of proeutectoid cementite in the structure. Vanadium and chromium are revealed to increase the total carbide fraction and the amount of austenite in the matrix. Cr is observed to play a key role in controlling the metallic matrix microstructure.
文摘Full factorial design was used to evaluate the two-body abrasive resistance of 3wt%C–4wt%Mn–1.5wt%Ni spheroidal carbide cast irons with varying vanadium（5.0wt%–10.0wt%） and chromium（up to 9.0wt%） contents. The alloys were quenched at 920℃. The regression equation of wear rate as a function of V and Cr contents was proposed. This regression equation shows that the wear rate decreases with increasing V content because of the growth of spheroidal VC carbide amount. Cr influences the overall response in a complex manner both by reducing the wear rate owing to eutectic carbides（M7C3） and by increasing the wear rate though stabilizing austenite to deformation-induced martensite transformation. This transformation is recognized as an important factor in increasing the abrasive response of the alloys. By analyzing the regression equation, the optimal content ranges are found to be 7.5wt%–10.0wt% for V and 2.5wt%–4.5wt% for Cr, which corresponds to the alloys containing 9vol%–15vol% spheroidal VC carbides, 8vol%–16vol% M7C3, and a metastable austenite/martensite matrix. The wear resistance is 1.9–2.3 times that of the traditional 12wt% V–13wt% Mn spheroidal carbide cast iron.
文摘This study aims to clarify the influence of external notch on impact characteristics of high toughness ductile cast irons prepared by austempering heat treatment. We produced ductile cast irons samples with various matrix microstructure tested by Charpy impact within five kinds of external notches whose stress concentration factors (α), with values taken from 1.0 (Un-notched) to 4.8. In addition, to clarify the initiation process of impact characteristics, we observed the evolution of microstructure surface during bending tests with a slow loading speed for the un-notched and the notched impact samples. The results showed that the impact fracture energy decreases strongly in the range of α from 1 to 2.3 but decreases slightly for α larger than 3. Moreover, the impact value of samples with austempered microstructure is sensitive to the external notch shape. The impact transition temperature increases with increasing the stress concentration factor. The fracture energy is decreasing with the external notch from the impact test since the crack initiation energy is directly affected by this later. This work contributes to get a better understanding in the basic theories of external notch effect on impact characteristics of austempered spheroidal graphite cast irons (ADI).
文摘The paper reviews original data obtained by the present authors,revealed in recent separate publications,describing specific procedures for high quality grey irons,and reflecting the forecast needs of the worldwide iron foundry industry.High power,medium frequency coreless induction furnaces are commonly used in electric melting grey iron foundries.This has resulted in low sulphur(<0.05wt.%)and aluminium(<0.005wt.%)contents in the iron,with a potential for higher superheating(>1,500°C),contributing to unfavourable conditions for graphite nucleation.Thin wall castings are increasingly produced by these electric melt shops with a risk of greater eutectic undercooling during solidification.The paper focused on two groups of grey cast irons and their specific problems:carbides and graphite morphology control in lower carbon equivalent high strength irons(CE=3.4%-3.8%),and austenite dendrite promotion in eutectic and slightly hypereutectic irons(CE=4.1%-4.5%),in order to increase their strength characteristics.There are 3 stages and 3 steps involving graphite formation,iron chemistry and iron processing that appear to be important.The concept in the present paper sustains a threestage model for nucleating flake graphite[(Mn,X)S type nuclei].There are three important groups of elements(deoxidizer,Mn/S,and inoculant)and three technological stages in electric melting of iron(superheat,pre-conditioning of base iron,final inoculation).Attention is drawn to a control factor(%Mn)x(%S)ensuring it equals to 0.03–0.06,accompanied by 0.005wt.%–0.010wt.%Al and/or Zr content in inoculated irons.It was found that iron powder addition promotes austenite dendrite formation in eutectic and slightly eutectic,acting as reinforcement for the eutectic cells.But,there is an accompanying possible negative influence on the characteristics of the(Mn,X)S type graphite nuclei(change the morphology of nuclei from polygonal compact to irregular polygonal,and therefore promote chill tendency in treated irons).A double addition(iron powder+inoculant)appears to be an effective treatment to benefit both austenite and graphite nucleation,with positive effects on the final structure and chill tendency.
文摘The physical metallurgy underlying the development of cast microstructures in abrasion resistant high chromium cast irons, and their structural modification by thermal treatments is relatively complex. Structural characterisation via electron microscopy therefore has a key role to play in furthering our understanding of the phase transformations that control the microstructures and hence the service performances of these irons as wear parts. This paper shows how both scanning and especially transmission electron microscopy can provide valuable information on the nature of eutectic and secondary carbides and on the matrix structures in these irons. Particular attention is given to current characterisation research on conventionally cast 30%Cr irons that are used for applications involving corrosive wear e.g. slurry pumps and on a semi-solid cast 27%Cr iron that has a potential for applications in industry.
文摘Recent studies revealed that in eutectic to slightly hypereutectic grey irons （CE = 4.3%-4.5%） the presence of austenite dendrites provides an opportunity to improve the cast iron properties, as a high number of eutectic cells are ＂reinforced＂ by austenite dendrites. An iron powder addition proved to be important by promoting dendritic austenite in hypereutectic irons, but was accompanied by adverse effect on the characteristics of potential nuclei for graphite. The purpose of the present paper is to investigate the solidification pattern of these irons. Chill wedges with different cooling moduli （CM = 0.11 - 0.43 cm） were poured in resin bonded sand and metal moulds. Relative clear / mottled / total chill measurement criteria were applied. Iron powder additions led to a higher chill tendency, while single inoculation showed the strongest graphiUzing effect. The various double treatments show an intermediate position, but the inoculant added after iron powder appears to be the most effective in reducing base iron chill tendency, for all cooling moduli and chill evaluation parameters. This performance reflects the improved properties of （Mn,X）S polygonal compounds as nucleation sites for graphite, especially in resin bonded sand mould castings. Both austenite and graphite nucleation benefit from a double addition of iron powder ＋ inoculant, with positive effect on the final structure and chill tendency.
文摘This study aimed at optimizing impact toughness and abrasion wear resistance of 15%Cr-2%Mo hypereutectic abrasion-resistant white irons. The effects of dynamic solidification, niobium addition, combined action of them and heat treatment have been investigated. Investigations were performed by means of the image analyzer, scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS) and X-ray diffraction. Impact toughness and abrasion wear resistance tests were conducted. Fracture and worn surfaces were studied. Results indicated that microstructural control during solidifciation is the most valuable tool to attain the optimum combination between impact toughness and wear resistance in hypereutectic iron. Combined action of Nb addition and dynamic solidifciation improves impact toughness and wear resistance even more than the action of each individual factor. In the as-cast condition, impact toughness and abrasion resistance were increased after dynamic solidification compared to statically solidified one by 71.4% and 10%, respectively. This enhancement was increased to 114.3 % and 28.8 % by adding 2% Nb. Lower tempering temperature of 260°C exhibits better impact and abrasion resistance than the sub-critical tempering temperature of 500°C.
基金This work was financially supported by Ministry of Edu-cation and Science of Ukraine under the project No 0119U100080.
文摘The novel cast irons of chemical composition(wt%)0.7C-5W-5Mo-5V-10Cr-2.5Ti were invented with the additions of 1.6wt%B and 2.7wt%B.The aim of this work was to study the effect of boron on the structural state of the alloys and phase elemental distribution with respect to the formation of wear-resistant structural constituents.It was found that the alloy containing 1.6wt%B was composed of three eutectics:(a)“M_(2)(C,B)_(5)+ferrite”having a“Chinese Script”morphology(89.8vol%),(b)“M_(7)(C,B)_(3)+Austenite”having a“Rosette”morphology,and(c)“M_(3)C+Austenite”having a“Ledeburite”-shaped morphology(2.7vol%).With 2.7wt%of boron content,the bulk hardness increased from HRC 31 to HRC 38.5.The primary carboborides M_(2)(C,B)_(5) with average microhardness of HV 2797 appeared in the structure with a volume fraction of 17.6vol%.The volume fraction of eutectics(a)and(b,c)decreased to 71.2vol%and 3.9vol%,respectively.The matrix was“ferrite/austenite”for 1.6wt%B and“ferrite/pearlite”for 2.7wt%B.Both cast irons contained compact precipitates of carbide(Ti,M)C and carboboride(Ti,M)(C,В)with a volume fraction of 7.3%-7.5%.Based on the energy-dispersive X-ray spectroscopy,the elemental phase distributions and the appropriate phase formulas are presented in this work.
文摘Application of rare earths in cast iron is a traditional applied field of rare earths in industry. The consumption of rare earths on cast iron is the first rank in all applied fields in China. The affinity between rare earths and O,S and other elements in cast iron is strong enough,which is the foundation to improve microstructures and properties of cast iron. But dynamics of reaction of rare earths in cast iron is disappointed. Therefore,effects of application of rare earths in cast iron always fluctuate. The good effects can be got when dynamics of reaction of rare earths on cast iron is controlled and improved. It is proved by practice that microstructures and properties of cast iron,such as ductile iron,vermicular graphite cast iron,gray cast iron,white cast iron and so on,are improved with amonnt of rare earths incrtasing. There is 'double peaks effect' for strength of cast iron vs. addition of rare earths in cast iron. The application of rare earths in cast iron still possesses bright prospects nowadays and future.
文摘The corrosion behavior of spheroidal graphite and flake graphite cast irons was studied in oxidizing and sulfidizing atmospheres between 600 and 800℃ for 50 h. The corrosion rate in the sulfidizing atmosphere was faster than that in air above 700℃, due to the formation of the Fe0.975S sulfide. The corrosion rate of the spheroidal graphite cast iron was similar to that of the flake graphite cast iron.
文摘A jet type erosion-corrosion tester was developed for the erosion-corrosion investigation of high-chromium cast irons. During tests the size and the shape of particles in the slurry can be maintained stable. The jet velocity and attack angle can be accurately controlled. The repeatability and ranking consistency of the test results are satisfactory. The test parameters can be adjusted in a wide range, so that the tester can simulate various practical working conditions. Electrochemical test data can be automatically collected and processed. Dynamic polarization curves can be obtained during erosion-corrosion test, which can be used to study the dynamic corrosion characteristics.Two high chromium cast irons were studied in hot concentrated alkaline slurry. The results show that the erosioncorrosion mass loss rate and dynamic corrosion rate of 295Cr26 iron is lower than that of 185Cr13 under the conditions similar to alumyte processing. The mechanism of erosion-corrosion of 295Cr26 and 185Cr13 was studied by using the tester. The interaction between erosion and corrosion was also quantitatively evaluated.
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.
文摘The relationship between the retained austenite content of the matrix in16Cr-3C white irons and the abrasion resistance was investigated. The results show that: (1) theabrasion resistance can be improved by sub-critical heat treatment, which could be attributed to thedecrease of the retained austenite content; (2) both the abrasion resistance and hardness can beimproved by controlling the retained austenite content below 20 percent-30 percent and arrive at themaximum when the retained austenite content is reduced to about 10 percent; (3) the abrasionresistance decreases abruptly once the retained austenite content is lower than 10 percent, whichstems from both the in situ transformation of (Fe, Cr)_(23)C_6 to M_3C carbides and the formation ofpearlitic matrix.
基金supported by the scientific and technological project of China Textile Industry Association
文摘The austenitizing temperature controls the carbon content of the austenite which,in turn,influences the structure and properties of cast irons after subsequent cooling to room temperature.In this paper,for a cast iron with known silicon content,a formula of calculating austenite carbon content at a certain austenitizing temperature was developed.This relationship can be used to more accurately select carbon content of austenite or austenitizing temperature to produce desired properties after subsequent cooling to room temperature.
文摘The influences of copper on microstructure and the hardening behavior of high chromium cast irons subjected to sub-critical treatment were investigated. The results show that the microstructure of the as-cast high chromium cast irons consists of retained austenite, martensite and M1C3 type eutectic carbide. When copper is added into high chromium cast irons, austenite and carbide contents are increased. The increased addition of copper content from 0% to 1.84% leads to the increase of austenite and carbide from 15.9% and 20. 0% to 61.0% and 35.5% , respectively. In the process of sub-critical treatment, the retained austenite in the matrix can be precipitated into secondary carbides and then transforms into martensite in cooling process, which causes the secondary hardening of the alloy under sub-critical treatment. High chromium cast irons containing copper in sub-critical treatment appear the second hardening curve peak due to the precipitation of copper from supersaturated matrix.
文摘Because of the excellent performance of ductile irons and the unique superiority of investment casting, thepreparation of complicated and thin-wall ductile iron castings by investment casting shows a good developmentprospect. In this present work, combined with the actual product experiments, the characteristics of shell making,spheroidization, inoculation and defect prevention are presented, and some suggestions are given for investmentcasting of ductile iron.
