At room temperature,dry sliding wear tests were carried out using pin-on-disc test rig,in which the pin is made of vermicular iron and the disc is made of 40 Cr steel.The microstructures of the frictional surfaces for...At room temperature,dry sliding wear tests were carried out using pin-on-disc test rig,in which the pin is made of vermicular iron and the disc is made of 40 Cr steel.The microstructures of the frictional surfaces for the pin specimens were investigated.Under the action of both frictional heat and frictional shearing stress,aplastic deformation layer under the frictional surface is formed.The morphology and properties of the plastic deformation layer depend on specimen material,contact pressure and frictional shearing stress.In the plastic deformation layer,the phosphorous mass percent varies at different depth and results in different hardness.On the outer side of surface,the hardness is the biggest and the phosphorous mass percent is the highest.They become gradually small from outer side to inner side of the surface.展开更多
Si-Mo vermicular iron is an ideal material for exhaust manifold that works in high temperature and thermal cycle conditions because its properties of thermal fatigue resistance and thermal distortion resistance are si...Si-Mo vermicular iron is an ideal material for exhaust manifold that works in high temperature and thermal cycle conditions because its properties of thermal fatigue resistance and thermal distortion resistance are significantly better than that of gray cast iron and nodular iron. This paper explains that the vermicularity of Si-Mo vermicular iron is better to be controlled approximately to 50% for the applications of exhaust manifold castings, and generalizes the successful experience of vermicularizing technique that uses sandwich (pour over) process combining with cored-wire injection in trough process together, and uses rare earths-magnesium-silicon as vermicularizing alloy in Disa high speed molding line and automatic plug rod air pressure pouring furnace. In addition, this paper also describes the method to solve the shrinkage hole and porosity defects in the exhaust manifold production.展开更多
In China, the research and development of vermicular graphite cast iron (VGCI) as a new type of engineering material, were started in the same period as in other developed countries; however, its actual industrial app...In China, the research and development of vermicular graphite cast iron (VGCI) as a new type of engineering material, were started in the same period as in other developed countries; however, its actual industrial application was even earlier. In China, the deep and intensive studies on VGCI began as early as the 1960s. According to the incomplete statistics to date, more than 600 papers on VGCI have been published by Chinese researchers and scholars at national and international conferences, and in technical journals. More than ten types of production methods and more than thirty types of treatment alloy have been studied. Formulae for calculating the critical addition of treatment alloy required to produce VGCI have been put forward, and mechanisms for explaining the formation of dross during treatment were brought forward. The casting properties, metallographic structure, mechanical and physical properties and machining performance of VGCI, as well as the relationships between them, have all been studied in detail. The Chinese Standards for VGCI and VGCI metallographic structure have been issued. In China, the primary crystallization of VGCI has been studied by many researchers and scholars. The properties of VGCI can be improved by heat treatment and addition of alloying elements enabling its applications to be further expanded. Hundreds of kinds of VGCI castings have been produced and used in vehicles, engines, mining equipment, metallurgical products serviced under alternating thermal load, machinery, hydraulic components, textile machine parts and military applications. The heaviest VGCI casting produced is 38 tons and the lightest is only 1 kg. Currently, the annual production of the VGCI in China is about 200 000 tons. The majority of castings are made from cupola iron without pre-treatment, however, they are also produced from electric furnaces and by duplex melting from cupola-electric furnaces or blast furnace-electric furnace. Examples of typical applications for VGCI castings are introduced in this paper. In China, the technologies such as rapid testing of the molten metal and non-destructive testing of casting microstructure still need to be improved. Several proposals are put forward in this paper in order to improve the production of VGCI. Generally speaking, in China, the research, production, and application of vermicular graphite cast iron are at the same level as in other developed countries and in some fields China even takes lead. (332 references and 5 Tables)展开更多
The relationships of cooling rate with microstructure and thermal conductivity of vermicular graphite cast iron(VGI) cylinder block were studied, which are important for design and optimization of the casting process ...The relationships of cooling rate with microstructure and thermal conductivity of vermicular graphite cast iron(VGI) cylinder block were studied, which are important for design and optimization of the casting process of VGI cylinder blocks. Cooling rates at different positions in the cylinder block were calculated based on the cooling curves recorded with a solidification simulation software. The metallographic structure and thermal conductivity were observed and measured using optical microscopy(OM), scanning electrical microscopy(SEM) and laser flash diffusivity apparatus, respectively. The effects of the cooling rate on the vermicularity, total and average areas of all graphite particles, and the pearlite fraction in the VGI cylinder block were investigated. It is found that the vermicularity changes in parabola trend with the increase of cooling rate. The total area of graphite particles and the cooling rate at eutectoid stage can be used to predict pearlite fraction well. Moreover, it is found that the thermal conductivity at room temperature is determined by the average area of graphite particles and pearlite fraction when the range of vermicularity is from 80% to 93%. Finally, the quantitative models are established to calculate the vermicularity, pearlite fraction, and thermal conductivity of the VGI cylinder block.展开更多
The initiation and propagation of thermal fatigue cracks in gray cast iron and vemicular graphite cast iron were investigated by Uddeholm method to reveal the complex thermal fatigue behaviors of cast iron.Differences...The initiation and propagation of thermal fatigue cracks in gray cast iron and vemicular graphite cast iron were investigated by Uddeholm method to reveal the complex thermal fatigue behaviors of cast iron.Differences of thermal fatigue behaviors of gray cast iron and vemicular graphite cast iron were observed and analyzed.It is found that the observed differences are related to the combination of graphite morphology and the oxidization of matrix.More oxidized matrix is observed in gray cast iron due to its large specific surface area.The brittle oxidized matrix facilitates the propagation of microcracks along the oxidization layer.By contrast,the radial microcracks are formed in vermicular graphite at the edge of graphite due to fewer oxidization layers.It indicates that the thermal fatigue resistance of gray cast iron is dominated by graphite content and morphology while that of vermicular graphite cast iron strongly relates to the strength of the matrix.展开更多
The 25 years’ production and application have proved that vermicular graphite iron cylinder heads with vermicularity ≥50% satisfy the machinability and performance demand of diesel engine. The method, in which using...The 25 years’ production and application have proved that vermicular graphite iron cylinder heads with vermicularity ≥50% satisfy the machinability and performance demand of diesel engine. The method, in which using cupola-induction furnace duplex melting and pour-over process with rare earth-ferrosilicon or rare earth-silicon compound as vermicularizing alloy plus rare earth-magnesium-ferrosilicon as stirring alloy, is an optimal vermicularizing process for obtaining satisfied vermicularity. Using top kiss risers, enlarging kissing areas and expanding covering width and making ingates to freeze earlier are the effective measures to eliminate shrinkage, blowhole and oxide inclusions in the vermicular graphite iron cylinder heads.展开更多
In this research, a vermicular graphite cast iron brake drum was produced by cored wire injection in a one-step method. Silica sand and low-density alumina-silicate ceramic were used as molding materials in order to i...In this research, a vermicular graphite cast iron brake drum was produced by cored wire injection in a one-step method. Silica sand and low-density alumina-silicate ceramic were used as molding materials in order to investigate the effect of cooling rate on percentage of vermicular graphite and mechanical properties of the brake drum casting. Several thermocouples were inserted into the casting in the desired positions to measure the temperature change. By means of one-step cored wire injection, the two residual concentrations of Mg and RE were effectively controlled in the ranges of 0.013%-0.017% and 0.019%-0.025%, respectively, which are crucial for the production of vermicular graphite cast iron and the formation of vermicular graphite. In addition, the cooling rate had a significant effect on the vermicular graphite percentage. In the case of the silica mold brake drum casting, there was an obvious difference in the cooling rate with the wall change, leading to a change in vermicular graphite percentage from 70.8% to 90%. In the low-density alumina-silicate ceramic mold casting, no obvious change in temperature was detected by the thermocouples and the percentage of the vermicular graphite was stable at 85%. Therefore, the vermicular graphite cast iron brake drum with a better combination of mechanical properties could be obtained.展开更多
基金Item Sponsored by Provincial Outstanding Youth Science Foundation of Henan in China(04120002100)Opening Foundationof State Key Laboratory of Solid Lubrication
文摘At room temperature,dry sliding wear tests were carried out using pin-on-disc test rig,in which the pin is made of vermicular iron and the disc is made of 40 Cr steel.The microstructures of the frictional surfaces for the pin specimens were investigated.Under the action of both frictional heat and frictional shearing stress,aplastic deformation layer under the frictional surface is formed.The morphology and properties of the plastic deformation layer depend on specimen material,contact pressure and frictional shearing stress.In the plastic deformation layer,the phosphorous mass percent varies at different depth and results in different hardness.On the outer side of surface,the hardness is the biggest and the phosphorous mass percent is the highest.They become gradually small from outer side to inner side of the surface.
文摘Si-Mo vermicular iron is an ideal material for exhaust manifold that works in high temperature and thermal cycle conditions because its properties of thermal fatigue resistance and thermal distortion resistance are significantly better than that of gray cast iron and nodular iron. This paper explains that the vermicularity of Si-Mo vermicular iron is better to be controlled approximately to 50% for the applications of exhaust manifold castings, and generalizes the successful experience of vermicularizing technique that uses sandwich (pour over) process combining with cored-wire injection in trough process together, and uses rare earths-magnesium-silicon as vermicularizing alloy in Disa high speed molding line and automatic plug rod air pressure pouring furnace. In addition, this paper also describes the method to solve the shrinkage hole and porosity defects in the exhaust manifold production.
文摘In China, the research and development of vermicular graphite cast iron (VGCI) as a new type of engineering material, were started in the same period as in other developed countries; however, its actual industrial application was even earlier. In China, the deep and intensive studies on VGCI began as early as the 1960s. According to the incomplete statistics to date, more than 600 papers on VGCI have been published by Chinese researchers and scholars at national and international conferences, and in technical journals. More than ten types of production methods and more than thirty types of treatment alloy have been studied. Formulae for calculating the critical addition of treatment alloy required to produce VGCI have been put forward, and mechanisms for explaining the formation of dross during treatment were brought forward. The casting properties, metallographic structure, mechanical and physical properties and machining performance of VGCI, as well as the relationships between them, have all been studied in detail. The Chinese Standards for VGCI and VGCI metallographic structure have been issued. In China, the primary crystallization of VGCI has been studied by many researchers and scholars. The properties of VGCI can be improved by heat treatment and addition of alloying elements enabling its applications to be further expanded. Hundreds of kinds of VGCI castings have been produced and used in vehicles, engines, mining equipment, metallurgical products serviced under alternating thermal load, machinery, hydraulic components, textile machine parts and military applications. The heaviest VGCI casting produced is 38 tons and the lightest is only 1 kg. Currently, the annual production of the VGCI in China is about 200 000 tons. The majority of castings are made from cupola iron without pre-treatment, however, they are also produced from electric furnaces and by duplex melting from cupola-electric furnaces or blast furnace-electric furnace. Examples of typical applications for VGCI castings are introduced in this paper. In China, the technologies such as rapid testing of the molten metal and non-destructive testing of casting microstructure still need to be improved. Several proposals are put forward in this paper in order to improve the production of VGCI. Generally speaking, in China, the research, production, and application of vermicular graphite cast iron are at the same level as in other developed countries and in some fields China even takes lead. (332 references and 5 Tables)
文摘The relationships of cooling rate with microstructure and thermal conductivity of vermicular graphite cast iron(VGI) cylinder block were studied, which are important for design and optimization of the casting process of VGI cylinder blocks. Cooling rates at different positions in the cylinder block were calculated based on the cooling curves recorded with a solidification simulation software. The metallographic structure and thermal conductivity were observed and measured using optical microscopy(OM), scanning electrical microscopy(SEM) and laser flash diffusivity apparatus, respectively. The effects of the cooling rate on the vermicularity, total and average areas of all graphite particles, and the pearlite fraction in the VGI cylinder block were investigated. It is found that the vermicularity changes in parabola trend with the increase of cooling rate. The total area of graphite particles and the cooling rate at eutectoid stage can be used to predict pearlite fraction well. Moreover, it is found that the thermal conductivity at room temperature is determined by the average area of graphite particles and pearlite fraction when the range of vermicularity is from 80% to 93%. Finally, the quantitative models are established to calculate the vermicularity, pearlite fraction, and thermal conductivity of the VGI cylinder block.
文摘The initiation and propagation of thermal fatigue cracks in gray cast iron and vemicular graphite cast iron were investigated by Uddeholm method to reveal the complex thermal fatigue behaviors of cast iron.Differences of thermal fatigue behaviors of gray cast iron and vemicular graphite cast iron were observed and analyzed.It is found that the observed differences are related to the combination of graphite morphology and the oxidization of matrix.More oxidized matrix is observed in gray cast iron due to its large specific surface area.The brittle oxidized matrix facilitates the propagation of microcracks along the oxidization layer.By contrast,the radial microcracks are formed in vermicular graphite at the edge of graphite due to fewer oxidization layers.It indicates that the thermal fatigue resistance of gray cast iron is dominated by graphite content and morphology while that of vermicular graphite cast iron strongly relates to the strength of the matrix.
文摘The 25 years’ production and application have proved that vermicular graphite iron cylinder heads with vermicularity ≥50% satisfy the machinability and performance demand of diesel engine. The method, in which using cupola-induction furnace duplex melting and pour-over process with rare earth-ferrosilicon or rare earth-silicon compound as vermicularizing alloy plus rare earth-magnesium-ferrosilicon as stirring alloy, is an optimal vermicularizing process for obtaining satisfied vermicularity. Using top kiss risers, enlarging kissing areas and expanding covering width and making ingates to freeze earlier are the effective measures to eliminate shrinkage, blowhole and oxide inclusions in the vermicular graphite iron cylinder heads.
基金financially supported by the Foundation of Heilongjiang Educational Committee(Grant No.12531116)the Harbin Special Funds for Creative Talents in Science and Technology(Grant No.2013RFQXJ102)
文摘In this research, a vermicular graphite cast iron brake drum was produced by cored wire injection in a one-step method. Silica sand and low-density alumina-silicate ceramic were used as molding materials in order to investigate the effect of cooling rate on percentage of vermicular graphite and mechanical properties of the brake drum casting. Several thermocouples were inserted into the casting in the desired positions to measure the temperature change. By means of one-step cored wire injection, the two residual concentrations of Mg and RE were effectively controlled in the ranges of 0.013%-0.017% and 0.019%-0.025%, respectively, which are crucial for the production of vermicular graphite cast iron and the formation of vermicular graphite. In addition, the cooling rate had a significant effect on the vermicular graphite percentage. In the case of the silica mold brake drum casting, there was an obvious difference in the cooling rate with the wall change, leading to a change in vermicular graphite percentage from 70.8% to 90%. In the low-density alumina-silicate ceramic mold casting, no obvious change in temperature was detected by the thermocouples and the percentage of the vermicular graphite was stable at 85%. Therefore, the vermicular graphite cast iron brake drum with a better combination of mechanical properties could be obtained.
