The trial-and-error method is widely used for the current optimization of the steel casting feeding system, which is highly random, subjective and thus ineff icient. In the present work, both the theoretical and the e...The trial-and-error method is widely used for the current optimization of the steel casting feeding system, which is highly random, subjective and thus ineff icient. In the present work, both the theoretical and the experimental research on the modeling and optimization methods of the process are studied. An approximate alternative model is established based on the Back Propagation(BP) neural network and experimental design. The process parameters of the feeding system are taken as the input, the volumes of shrinkage cavities and porosities calculated by simulation are simultaneously taken as the output. Thus, a mathematical model is established by the BP neural network to combine the input variables with the output response. Then, this model is optimized by the nonlinear optimization function of the genetic algorithm. Finally, a feeding system optimization of a steel traveling wheel is conducted. No shrinkage cavities and porosities are induced through the optimization. Compared to the initial design scheme, the process yield is increased by 4.1% and the volume of the riser is decreased by 5.48×10~6 mm3.展开更多
This paper expatiates on domestic status of heavy steel casting production, with a special focus on hydraulicturbine castings for Three Gorges Project. In China, there is magnificent demand for heavy castings with the...This paper expatiates on domestic status of heavy steel casting production, with a special focus on hydraulicturbine castings for Three Gorges Project. In China, there is magnificent demand for heavy castings with the rapidgrowth of the national economy in recent years and the expected high growth in the coming 10 to 20 years. Someheavy and large castings such as mill housing and hydraulic turbine runner crown, blade and band for Three GorgesProject have been successfully made. However, the domestic production capability is still far from meeting the giganticrequirements. The domestic capability still lags behind the world class level, and a lot of heavy castings still dependon import. The paper also gives a particular introduction of the key technologies in the manufacturing of heavy steelcastings like metal melting, foundry technology, heat treatment technology and numerical simulation technique, etc.In addition, several case studies on the application of numerical simulation in the production of heavy steel castingsare presented.展开更多
EVA plastic film is the key material for V-process. Through decades of research, special EVA film for V-process has been produced. The film has adequate elongation; its maximum is about 800% in longitudinal direction ...EVA plastic film is the key material for V-process. Through decades of research, special EVA film for V-process has been produced. The film has adequate elongation; its maximum is about 800% in longitudinal direction and 750% in transversal direction. The single width of the film is 2.8 m and the double width is 5.6 m, which is the widest sheet film for V-process in China. Sheets with different thickness ranging from the thickest 0.35 mm to the thinnest 0.08 mm can meet different demands in China. The film can be used not only for V-process of iron castings, but also for the manganese steel railway frog, steel rocking support and side frame castings for train and the steel bridge box for engine truck.展开更多
The key manufacturing technologies associated with composition, microstructure, mechanical properties, casting quality and key process control for large martensitic stainless steel castings are involved in this paper....The key manufacturing technologies associated with composition, microstructure, mechanical properties, casting quality and key process control for large martensitic stainless steel castings are involved in this paper. The achievements fully satisfeid the technical requirements of the large 700 MW stainless steel hydraulic turbine runner for the Three Gorges Hydropower Station, and become the major technical support for the design and manufacture of the largest 700 MW hydraulic turbine generator unit in the world developed through our own efforts. The characteristics of a new high yield to tensile strength (R p0.2/R m ) ratio and high obdurability martensitic stainless steel with ultra low carbon and high cleanliness are also described. Over the next ten years, the large martensitic stainless steel castings and advanced manufacturing technologies will see a huge demand in clean energy industry such as nuclear power, hydraulic power at home and abroad. Therefore, the new high yield o tensile strength (R p0.2/R m ) ratio and high obdurability martensitic stainless steel materials, the fast and flexible manufacturing technologies of large size castings, and new environment friendly sustainable process will face new challenges and opportunities.展开更多
In steel squeeze casting process, the working condition of a punch was very rigorous. The abnormal failure models of an H13 punch, such as plastic rubbed damnification, could not be avoided easily. Based on the analys...In steel squeeze casting process, the working condition of a punch was very rigorous. The abnormal failure models of an H13 punch, such as plastic rubbed damnification, could not be avoided easily. Based on the analysis of the flow stress and the friction-shearing stress of an H13 punch in steel squeeze casting process, the following results were obtained： if the flow stress of an H13 punch was smaller than its friction-shearing stress, these abnormal failures could not be avoided; and if there were some protection measures that enable the flow stress to have a greater value than its friction-shearing one, the abnormal failures would not occur. In the production of 45^# steel valves and catenary system components, the flow stress of a lateral H13 punch without any protection measure was about 29 MPa and its friction-shearing stress was about 51 MPa, then, the abnormal failures occurred; however, when the protection measures of the punch enabled its working temperature to have a value below 682 ℃ its flow stress was greater than its friction-shearing stress, and the abnormal failures were avoided.展开更多
Pure magnesia filter and periclase-spinel filter were prepared using porous MgO powder and Al2O3 micro-powder as raw materials.The filtration efficiency and purification mechanism of the two sets of filters on molten ...Pure magnesia filter and periclase-spinel filter were prepared using porous MgO powder and Al2O3 micro-powder as raw materials.The filtration efficiency and purification mechanism of the two sets of filters on molten steel were investigated through steel casting tests.The results show that on the basis of surviving the thermal shock of molten steel,both filters can significantly reduce the number of non-metallic inclusions and total oxygen content of steel,thereby improving the cleanliness of the molten steel.After the thermal shock of molten steel,cracks were found in the microstructure of pure magnesia filter.Via the diffusion of non-metallic inclusions from steel into MgO grains of the filter to form solid solution,the inclusions were adsorbed to the internal and external surfaces of the pure magnesia filter.The number of inclusions was reduced by 62.5%,and the total oxygen content decreased from 0.892 to 0.265 wt.%after filtration,achieving a filtration efficiency of 70.3%.Compared with the pure magnesia filter,no cracks were found in the microstructure of the periclase-spinel filter.The mass transfer rate was accelerated due to the diffusion of inclusions from steel into MgO and MgAl2O4 grains of the filter,as well as the higher high-temperature liquid content and smaller pore structure of the filter.More non-metallic inclusions were able to enter the interior of the filter,which made the periclase-spinel filter more capable of adsorbing inclusions from steel and reducing total oxygen content.The periclase-spinel filter reduced the number of inclusions in steel by 84.4%and decreased the total oxygen content of the steel from 0.892 to 0.119 wt.%,with a filtration efficiency of 86.7%,demonstrating excellent comprehensive performance.展开更多
The present study designed two kinds of Fe-18Mn-1.3C-2Cr-(4,11)Al(wt.%)low-density steels.Tensile and impact tests were carried out to evaluate the work hardening and impact toughness properties via aluminum(Al)alloyi...The present study designed two kinds of Fe-18Mn-1.3C-2Cr-(4,11)Al(wt.%)low-density steels.Tensile and impact tests were carried out to evaluate the work hardening and impact toughness properties via aluminum(Al)alloying control.Meanwhile,microstructure evolution and fracture morphology were investigated by X-ray diffraction(XRD),a scanning electron microscope(SEM)equipped with electron backscatter diffraction(EBSD),a transmission electron microscope(TEM),and a stereo-optical microscope(OM).It is found that the Al addition obviously promotes the dislocation planar slipping,resulting in cleavage and brittle impact fracture in 11wt.%Al steel.Besides,the microband-induced plasticity(MBIP)mechanism is found in 4wt.%Al containing steel,introducing considerable work hardening capacity and impact toughness of 156.8±17.4 J.The present study provides a direct illustration of the relationship between work hardening and impact toughness behaviors of these two low-density steels for potential application as impact-resistant components.展开更多
It is of great significance to investigate effect of multiple heat treatments on fracture property of centrifugal casting stainless steels Z3CN20.09M cut from pump casing with long-term thermal aging degradation for n...It is of great significance to investigate effect of multiple heat treatments on fracture property of centrifugal casting stainless steels Z3CN20.09M cut from pump casing with long-term thermal aging degradation for nuclear power plants to consider actual operation of nuclear power plants.Both multiple heat treatments and accelerated thermal aging experiment at the same temperature of 400℃ for different time were successively carried out on centrifugal casting stainless steels Z3CN20.09M in order to examine the metallographic modification and impact properties.Finally,an additional investigation on the related fracture properties was carried out,in which the critical initial fracture toughness Ji was determined by stretch zone width and 0.2 mm offset line methods.These results indicated that the multiple heat treatments led to the dispersed distribution of ferrite phases in austenite matrix and thus microhardness increased,but impact energy exhibited a decreasing tendency significantly.After long-term aging,the metallographic structure remained almost unchanged,but the size of ferrite phases showed a slight increasing trend because of spinodal decomposition in ferrite phases and G-phase precipitation.In addition,centrifugal casting stainless steels Z3CN20.09M with multiple heat treatments exhibited the higher microhardness,Charpy impact toughness,critical initial fracture toughness J_(IC)(J-integral determined by 0.2 mm offset line method),and J_(SZW)(J-integral determined by stretch zone width method)than those with primary heat treatment,while the specific number of the heat treatment had a low influence on fracture toughness.展开更多
A novel Nb–V–Ce multi-microalloyed low-alloy cast steel for offshore platform nodes was investigated to achieve the properties similar to X80 pipeline steel,including high yield strength and low-temperature impact e...A novel Nb–V–Ce multi-microalloyed low-alloy cast steel for offshore platform nodes was investigated to achieve the properties similar to X80 pipeline steel,including high yield strength and low-temperature impact energy.The experimental results demonstrate that the addition of elements such as Nb,V and Ce can markedly improve the strength of the low-alloy cast steel.Maintaining a constant level of elements such as Nb,V and Ce,while reducing the content of Si to 0.28 wt.%,leads to substantial enhancements in impact energy at−40℃,meeting the mechanical properties criteria of X80 pipeline steel.The excellent mechanical properties of the multi-microalloyed low-alloy cast steel result from the reason that the multi-addition of microalloying elements refines the grains and facilitates the formation of nanoprecipitates like NbC.Moreover,decreasing Si content can enhance the recovery of martensitic laths in cast steel during the tempering process,reducing stress from dislocation movement and improving plasticity.展开更多
New discovery in whisker growth on Cr-Al-B MAB phase,which was formed during hot-dip aluminizing and subsequent thermal diffusion treatment of Fe-Cr-B cast steel,after cultivation under 400℃,was found.Specifically,al...New discovery in whisker growth on Cr-Al-B MAB phase,which was formed during hot-dip aluminizing and subsequent thermal diffusion treatment of Fe-Cr-B cast steel,after cultivation under 400℃,was found.Specifically,along with the growth of Sn whiskers on the whitened Cr-Al-B MAB phase,Al whiskers also formed,mainly attributed to the thermal activation of whisker cultivation at 400℃and promotion effect of Sn in the Cr-(Al,Sn)-B MAB phase solid solution.Partial Al whiskers,interspersed with small amounts of Sn,exhibited transparency under the scanning electron microscopy image.These whiskers underwent random growth and sucking back into the matrix simultaneously.The temperature during whisker cultivation had a significant effect on the whisker growth.展开更多
The study aimed to address the issue of elevated residual stress levels in dissimilar girth welds of cast steel joints.To achieve this,the hybrid welding technology,which yields high welding speeds while simultaneousl...The study aimed to address the issue of elevated residual stress levels in dissimilar girth welds of cast steel joints.To achieve this,the hybrid welding technology,which yields high welding speeds while simultaneously reducing residual stresses,has been introduced.This study utilizes a numerical simulation method to investigate the temperature and residual stress field in the hybrid welding of G20Mn5 casting-Q355 low-alloy steel welded pipe.A com-parison of the findings of this study with those of other welding processes revealed the technological advantages of hybrid welding.The research outcomes show that due to geometric discontinuities and material differences,the temperature field of the joint exhibits uneven distribution characteristics,and the peak temperatures on the Q355 steel side exceeds those on the G20Mn5 steel side.An evident stress gra-dient is present in the residual stress field of the joint post-welding,with peak stress located at the weld root on the Q355 steel.Compared with arc welding,the hybrid welding leads to decreased residual stresses and deformation,with high stress outside the heat-affected zone diminishing rapidly.Furthermore,it significantly improves the welding efficiency.This study elucidates the distribution and underlying causes of thermal and residual stress fields in dissimilar girth welds.This serves as a foundation for the application of hybrid welding technology in welded cast steel joints.展开更多
To study the distribution law and random characteristics of casting defects in steel castings,24 civil engineering structural cast steel joints were divided into two groups:simple cast steel joints and complex cast st...To study the distribution law and random characteristics of casting defects in steel castings,24 civil engineering structural cast steel joints were divided into two groups:simple cast steel joints and complex cast steel joints.Three kinds of nondestructive testing(NDT)methods,namely,visual,magnetic particle,and ultrasonic inspections,were used to detect the macroscopic defects in joints.The NDT results were then statistically analyzed.The results show that the unfused core support is a common defect of complex cast steel joints,and the defect can be seen visually,so excavation and repair welding should be carried out before castings leave factories.Casting cracks are extremely likely to occur in the intersection area of tubes,which is called the ultrasonic inspection blind zone.The occurrence probability of gas pores on simple cast steel joints is the largest,and the occurrence probability of core support incomplete fusions on complex cast steel joints is the largest.However,when cast steel joints are counted as a whole sample,the occurrence probability of gas pores is larger than that of core support incomplete fusions.Therefore,it is the most common defect in cast steel joints.展开更多
To replace metal padding by insulation padding for castings can save the melt and reduce cleaning work of castings. The design of insulation padding was investigated. The equation of the modulus extension factor for i...To replace metal padding by insulation padding for castings can save the melt and reduce cleaning work of castings. The design of insulation padding was investigated. The equation of the modulus extension factor for insulation padding and the ratio of its thickness over the modulus of a casting were improved to deter- mine the thickness of insulation padding. The insulation padding was designed for a turbine guide vane casting weighing 3.5 t. A sound casting was obtained with 750 kg steel saved. On the other side, the cast- ing obviously expanded at the interface with the insulation padding, which is perhaps the reason that the use of insulation padding has been suspended for many years. To avoid the expansion of insulation pad- ding, a shielding layer made of a kind of material of good fire resistance was adopted to prevent the insula- tion layer from touching the melt. The shielding layer serves as a cushion of heat and expansion during so- lidification process so as to resist the expansion of castings and guarantee the feeding effect at the same time. Furthermore, insulation padding can be placed by a certain offset into the mold cavity so as to coun- teract the expansion of castings.展开更多
The static recrystallization kinetics of low carbon steel cast strip was investigated by means of interrupted hot tensile tests. As-cast strip was reheated and soaked and its austenite grain size was similar to the wi...The static recrystallization kinetics of low carbon steel cast strip was investigated by means of interrupted hot tensile tests. As-cast strip was reheated and soaked and its austenite grain size was similar to the width level of the as-cast columnar structure. The tests were carried out on Gleeble-3500 thermomechanical simulator. The deformation temperature is in the range of 800 to 1 200 ℃ with strain rate of 0.01 to 1 s ^-1. The prestrain is fixed at 0. 04 to 0.12, and the inter-hit delay time varies from 1 to 3 000 s. Effect of deformation conditions and initial microstructure on static recrystallization behavior was investigated. The activation energy （Qsrx） and Avrami exponent （n） of static recrystallization were determined to have 241 kJ/mol and 0.54 respectively by linear regression of the experimental results. A kinetics model was proposed to describe the static recrystallization kinetics in low-carbon steel cast strip. The predicted softening fractions are in good agreement with the experimental results, indicating that the proposed equations can give an accurate estimate of the softening behaviors for the low-carbon steel cast strip.展开更多
The alloying design of cast hot-forging die steels was analyzed. The relationship of the life of cast hot-forging dies with the failure patterns was studied. The thermal wear resistance was believed to be the key prop...The alloying design of cast hot-forging die steels was analyzed. The relationship of the life of cast hot-forging dies with the failure patterns was studied. The thermal wear resistance was believed to be the key property for the alloying design of cast hot-forging die steels. The alloying design parameters were selected and optimized for the cast hot-forging die steel with high wear resistance. The wear resistance of the optimized cast die steel was evaluated in comparison with commercial H13 steels and 3Cr2WSV steel. In the new cast hot-forging die steel, VC is predominant carbide with Cr and Mo as the main solution elements in α-Fe. It is found that the cast die steel has significantly lower wear rate than normal H13 steel and 3Cr2W8V steel, almost the same as that of high purity H13 steel. The high wear resistance of the new cast hot-forging die steel can be attributed to its reasonable alloying design and nonsensibility to the detrimental function of S and P.展开更多
The influence of microalloying additions on the mechanical properties of a low-carbon cast steel containing combinations of V, Nb, and Ti in the as-cast condition was evaluated. Tensile and hardness test results indic...The influence of microalloying additions on the mechanical properties of a low-carbon cast steel containing combinations of V, Nb, and Ti in the as-cast condition was evaluated. Tensile and hardness test results indicated that good combinations of strength and ductility could be achieved by V and Nb additions. While the yield strength and UTS （ultimate tensile strength） increased up to the range of 378-435 MPa and 579- 590 MPa, respectively in the microalloyed heats, their total elongation ranged from 18% to 23%. The presence of Ti, however, led to some reduction in the strength. Microstructural studies including scanning electron microscopy （SEM） and optical microscopy revealed that coarse TiN particles were responsible for this behavior. The Charpy impact values of all compositions indicated that microalloying additions significantly decreased the impact energy and led to the dominance of cleavage facets on the fracture surfaces. It seems that the increase in the hardness of coarse ferrite grains due to the precipitation hardening is the main reason for brittle fracture.展开更多
The effect of main alloying elements on thermal wear of cast hot-forging die steels was studied. The wear mechanism was discussed. The results show that alloying elements have significant influences on the thermal wea...The effect of main alloying elements on thermal wear of cast hot-forging die steels was studied. The wear mechanism was discussed. The results show that alloying elements have significant influences on the thermal wear of cast hot-forging die steels. The wear rates decrease with an increase in chromium content from 3% to 4% and molybdenum content from 2% to 3%, respectively. With further increase of chromium and molybdenum contents, chromium slightly reduces the wear resistance and molybdenum severely deteriorates the wear resistance with high wear rate. Lower vanadium/carbon ratio （1.5-2.5） leads to a lower wear resistance with higher wear rate. With an increase in vanadium/carbon ratio, the wear resistance of the cast steel substantially increases. When vanadium/carbon ratio is 3, the wear rate reaches the lowest value. The predominant mechanism of thermal wear of cast hot-forging die steels are oxidation wear and fatigue delamination. The Fe2O3 and Fe3O4 or lumps of brittle wear debris are formed on the wear surface.展开更多
In the present paper, a new type of austempered boron alloyed high silicon cast steel has been developed, and its microstructures and mechanical properties at different temperatures were investigated. The experimental...In the present paper, a new type of austempered boron alloyed high silicon cast steel has been developed, and its microstructures and mechanical properties at different temperatures were investigated. The experimental results indicate that the boron alloyed high silicon cast steel comprises a dendritic matrix and interdendritic eutectic borides in as-cast condition. The dendritic matrix is made up of pearlite, ferrite, and the interdendritic eutectic boride is with a chemical formula of M2B （M represents Fe, Cr, Mn or Mo） which is much like that of carbide in high chromium white cast iron. Pure ausferrite structure that consists of bainitic ferrite and retained austenite can be obtained in the matrix by austempering treatment to the cast steel. No carbides precipitate in the ausferrite structure and the morphology of borides remains almost unchanged after austempering treatments. Secondary boride particles precipitate during the course of austenitizing. The hardness and tensile strength of the austempered cast steel decrease with the increase of the austempering temperature, from 250℃ to 400 ℃. The impact toughness is 4-11 J.cm^-2 at room temperature and the impact fracture fractogragh indicates that the fracture is caused by the brittle fracture of the borides.展开更多
The toughness of 31Mn2SiRE wear-resistance cast steel were increased by means of RE compound modification and high temperature austenitizing. The results show that the microstructures can be refined, needle and networ...The toughness of 31Mn2SiRE wear-resistance cast steel were increased by means of RE compound modification and high temperature austenitizing. The results show that the microstructures can be refined, needle and network ferrite are eliminated, the dislocation density and the quantity of dislocated martensite are increased remarkably, and the shape and distribution of inclusions are improved by the addition of RE. Therefore, the mechanical properties of the modified steel can be greatly increased, especially the toughness (αK) by 44%, yield strength (σs) by 10%, and elongation (δ5) by 42%.展开更多
With the help of solidification kinetics, precipitation and growth of TiNhave been studied theoretically and the effect of cooling rate on the growth of TiN has beendiscussed. Through induction electric furnace experi...With the help of solidification kinetics, precipitation and growth of TiNhave been studied theoretically and the effect of cooling rate on the growth of TiN has beendiscussed. Through induction electric furnace experiment and electroslag remelting experiment withdifferent cooling rates, the distribution and particle size of TiN were investigated. It is provedthat the higher cooling rate is, the smaller the final size of TiN is and the more TiN particles canbe found in the steel. That TiN can restrain the growth of columnar crystal and enhance theproportion of equiaxed crystals to refine solidification structure as the heterogeneous nucleationsites of δ-ferrite is confirmed preliminarily. A new method to reduce macrosegregation incontinuous cast steel is provided.展开更多
基金financially supported by the Program for New Century Excellent Talents in University(Nos.NCET-13-0229,NCET-09-0396)the National Science&Technology Key Projects of Numerical Control(Nos.2012ZX04010-031,2012ZX0412-011)the National High Technology Research and Development Program("863"Program)of China(No.2013031003)
文摘The trial-and-error method is widely used for the current optimization of the steel casting feeding system, which is highly random, subjective and thus ineff icient. In the present work, both the theoretical and the experimental research on the modeling and optimization methods of the process are studied. An approximate alternative model is established based on the Back Propagation(BP) neural network and experimental design. The process parameters of the feeding system are taken as the input, the volumes of shrinkage cavities and porosities calculated by simulation are simultaneously taken as the output. Thus, a mathematical model is established by the BP neural network to combine the input variables with the output response. Then, this model is optimized by the nonlinear optimization function of the genetic algorithm. Finally, a feeding system optimization of a steel traveling wheel is conducted. No shrinkage cavities and porosities are induced through the optimization. Compared to the initial design scheme, the process yield is increased by 4.1% and the volume of the riser is decreased by 5.48×10~6 mm3.
文摘This paper expatiates on domestic status of heavy steel casting production, with a special focus on hydraulicturbine castings for Three Gorges Project. In China, there is magnificent demand for heavy castings with the rapidgrowth of the national economy in recent years and the expected high growth in the coming 10 to 20 years. Someheavy and large castings such as mill housing and hydraulic turbine runner crown, blade and band for Three GorgesProject have been successfully made. However, the domestic production capability is still far from meeting the giganticrequirements. The domestic capability still lags behind the world class level, and a lot of heavy castings still dependon import. The paper also gives a particular introduction of the key technologies in the manufacturing of heavy steelcastings like metal melting, foundry technology, heat treatment technology and numerical simulation technique, etc.In addition, several case studies on the application of numerical simulation in the production of heavy steel castingsare presented.
文摘EVA plastic film is the key material for V-process. Through decades of research, special EVA film for V-process has been produced. The film has adequate elongation; its maximum is about 800% in longitudinal direction and 750% in transversal direction. The single width of the film is 2.8 m and the double width is 5.6 m, which is the widest sheet film for V-process in China. Sheets with different thickness ranging from the thickest 0.35 mm to the thinnest 0.08 mm can meet different demands in China. The film can be used not only for V-process of iron castings, but also for the manganese steel railway frog, steel rocking support and side frame castings for train and the steel bridge box for engine truck.
文摘The key manufacturing technologies associated with composition, microstructure, mechanical properties, casting quality and key process control for large martensitic stainless steel castings are involved in this paper. The achievements fully satisfeid the technical requirements of the large 700 MW stainless steel hydraulic turbine runner for the Three Gorges Hydropower Station, and become the major technical support for the design and manufacture of the largest 700 MW hydraulic turbine generator unit in the world developed through our own efforts. The characteristics of a new high yield to tensile strength (R p0.2/R m ) ratio and high obdurability martensitic stainless steel with ultra low carbon and high cleanliness are also described. Over the next ten years, the large martensitic stainless steel castings and advanced manufacturing technologies will see a huge demand in clean energy industry such as nuclear power, hydraulic power at home and abroad. Therefore, the new high yield o tensile strength (R p0.2/R m ) ratio and high obdurability martensitic stainless steel materials, the fast and flexible manufacturing technologies of large size castings, and new environment friendly sustainable process will face new challenges and opportunities.
文摘In steel squeeze casting process, the working condition of a punch was very rigorous. The abnormal failure models of an H13 punch, such as plastic rubbed damnification, could not be avoided easily. Based on the analysis of the flow stress and the friction-shearing stress of an H13 punch in steel squeeze casting process, the following results were obtained： if the flow stress of an H13 punch was smaller than its friction-shearing stress, these abnormal failures could not be avoided; and if there were some protection measures that enable the flow stress to have a greater value than its friction-shearing one, the abnormal failures would not occur. In the production of 45^# steel valves and catenary system components, the flow stress of a lateral H13 punch without any protection measure was about 29 MPa and its friction-shearing stress was about 51 MPa, then, the abnormal failures occurred; however, when the protection measures of the punch enabled its working temperature to have a value below 682 ℃ its flow stress was greater than its friction-shearing stress, and the abnormal failures were avoided.
基金supported by the Key Project of the National Natural Science Foundation of China(Grant No.U21A2058 and U1860205)the Natural Science Funds of Hubei Province for Distinguished Young Scholars(Grant No.2020CFA088).
文摘Pure magnesia filter and periclase-spinel filter were prepared using porous MgO powder and Al2O3 micro-powder as raw materials.The filtration efficiency and purification mechanism of the two sets of filters on molten steel were investigated through steel casting tests.The results show that on the basis of surviving the thermal shock of molten steel,both filters can significantly reduce the number of non-metallic inclusions and total oxygen content of steel,thereby improving the cleanliness of the molten steel.After the thermal shock of molten steel,cracks were found in the microstructure of pure magnesia filter.Via the diffusion of non-metallic inclusions from steel into MgO grains of the filter to form solid solution,the inclusions were adsorbed to the internal and external surfaces of the pure magnesia filter.The number of inclusions was reduced by 62.5%,and the total oxygen content decreased from 0.892 to 0.265 wt.%after filtration,achieving a filtration efficiency of 70.3%.Compared with the pure magnesia filter,no cracks were found in the microstructure of the periclase-spinel filter.The mass transfer rate was accelerated due to the diffusion of inclusions from steel into MgO and MgAl2O4 grains of the filter,as well as the higher high-temperature liquid content and smaller pore structure of the filter.More non-metallic inclusions were able to enter the interior of the filter,which made the periclase-spinel filter more capable of adsorbing inclusions from steel and reducing total oxygen content.The periclase-spinel filter reduced the number of inclusions in steel by 84.4%and decreased the total oxygen content of the steel from 0.892 to 0.119 wt.%,with a filtration efficiency of 86.7%,demonstrating excellent comprehensive performance.
基金This work was financially supported by the Guangdong Province Key Area R&D Program(Grant No.2020B0101340004)the International Science and Technology Cooperation Project of Guangdong Province(Grant No.2021A0505030051)+2 种基金the Innovation and Technology Fund(ITF)(Grant No.ITP/020/21AP)the Young Talent Support Project of Guangzhou Association for Science and Technology(Grant No.QT20220101075)the GDAS'Project of Science and Technology Development(Grant No.2022GDASZH-2022010103).
文摘The present study designed two kinds of Fe-18Mn-1.3C-2Cr-(4,11)Al(wt.%)low-density steels.Tensile and impact tests were carried out to evaluate the work hardening and impact toughness properties via aluminum(Al)alloying control.Meanwhile,microstructure evolution and fracture morphology were investigated by X-ray diffraction(XRD),a scanning electron microscope(SEM)equipped with electron backscatter diffraction(EBSD),a transmission electron microscope(TEM),and a stereo-optical microscope(OM).It is found that the Al addition obviously promotes the dislocation planar slipping,resulting in cleavage and brittle impact fracture in 11wt.%Al steel.Besides,the microband-induced plasticity(MBIP)mechanism is found in 4wt.%Al containing steel,introducing considerable work hardening capacity and impact toughness of 156.8±17.4 J.The present study provides a direct illustration of the relationship between work hardening and impact toughness behaviors of these two low-density steels for potential application as impact-resistant components.
基金supported by the National Key Research and Development Program of China(No.2017YFB0702200)the Natural Science Foundation of Jiangsu Province(No.BK20171223 and BK20170383).
文摘It is of great significance to investigate effect of multiple heat treatments on fracture property of centrifugal casting stainless steels Z3CN20.09M cut from pump casing with long-term thermal aging degradation for nuclear power plants to consider actual operation of nuclear power plants.Both multiple heat treatments and accelerated thermal aging experiment at the same temperature of 400℃ for different time were successively carried out on centrifugal casting stainless steels Z3CN20.09M in order to examine the metallographic modification and impact properties.Finally,an additional investigation on the related fracture properties was carried out,in which the critical initial fracture toughness Ji was determined by stretch zone width and 0.2 mm offset line methods.These results indicated that the multiple heat treatments led to the dispersed distribution of ferrite phases in austenite matrix and thus microhardness increased,but impact energy exhibited a decreasing tendency significantly.After long-term aging,the metallographic structure remained almost unchanged,but the size of ferrite phases showed a slight increasing trend because of spinodal decomposition in ferrite phases and G-phase precipitation.In addition,centrifugal casting stainless steels Z3CN20.09M with multiple heat treatments exhibited the higher microhardness,Charpy impact toughness,critical initial fracture toughness J_(IC)(J-integral determined by 0.2 mm offset line method),and J_(SZW)(J-integral determined by stretch zone width method)than those with primary heat treatment,while the specific number of the heat treatment had a low influence on fracture toughness.
基金supported by the National Natural Science Foundation of China(No.52071195)Key Project of the National Natural Science Foundation of China(No.52130109).
文摘A novel Nb–V–Ce multi-microalloyed low-alloy cast steel for offshore platform nodes was investigated to achieve the properties similar to X80 pipeline steel,including high yield strength and low-temperature impact energy.The experimental results demonstrate that the addition of elements such as Nb,V and Ce can markedly improve the strength of the low-alloy cast steel.Maintaining a constant level of elements such as Nb,V and Ce,while reducing the content of Si to 0.28 wt.%,leads to substantial enhancements in impact energy at−40℃,meeting the mechanical properties criteria of X80 pipeline steel.The excellent mechanical properties of the multi-microalloyed low-alloy cast steel result from the reason that the multi-addition of microalloying elements refines the grains and facilitates the formation of nanoprecipitates like NbC.Moreover,decreasing Si content can enhance the recovery of martensitic laths in cast steel during the tempering process,reducing stress from dislocation movement and improving plasticity.
基金financial support from the National Natural Science Foundation of China(Grant Nos.42066003 and 51701053)Hainan Province Science and Technology Special Fund(Grant No.ZDYF2023GXJS148)+1 种基金General Program of Natural Science Foundation of Hainan Province(Grant Nos.420RC522 and 517076)Evaluation Project of Guangdong Provincial Key Laboratory(Grant No.2023B1212060043).
文摘New discovery in whisker growth on Cr-Al-B MAB phase,which was formed during hot-dip aluminizing and subsequent thermal diffusion treatment of Fe-Cr-B cast steel,after cultivation under 400℃,was found.Specifically,along with the growth of Sn whiskers on the whitened Cr-Al-B MAB phase,Al whiskers also formed,mainly attributed to the thermal activation of whisker cultivation at 400℃and promotion effect of Sn in the Cr-(Al,Sn)-B MAB phase solid solution.Partial Al whiskers,interspersed with small amounts of Sn,exhibited transparency under the scanning electron microscopy image.These whiskers underwent random growth and sucking back into the matrix simultaneously.The temperature during whisker cultivation had a significant effect on the whisker growth.
基金The SEU Innovation Capability Enhancement Plan for Doctoral Students(No.CXJH_SEU 24115)Marine Economic Development Project of Guangdong Province(No.GDNRC[2022]25).
文摘The study aimed to address the issue of elevated residual stress levels in dissimilar girth welds of cast steel joints.To achieve this,the hybrid welding technology,which yields high welding speeds while simultaneously reducing residual stresses,has been introduced.This study utilizes a numerical simulation method to investigate the temperature and residual stress field in the hybrid welding of G20Mn5 casting-Q355 low-alloy steel welded pipe.A com-parison of the findings of this study with those of other welding processes revealed the technological advantages of hybrid welding.The research outcomes show that due to geometric discontinuities and material differences,the temperature field of the joint exhibits uneven distribution characteristics,and the peak temperatures on the Q355 steel side exceeds those on the G20Mn5 steel side.An evident stress gra-dient is present in the residual stress field of the joint post-welding,with peak stress located at the weld root on the Q355 steel.Compared with arc welding,the hybrid welding leads to decreased residual stresses and deformation,with high stress outside the heat-affected zone diminishing rapidly.Furthermore,it significantly improves the welding efficiency.This study elucidates the distribution and underlying causes of thermal and residual stress fields in dissimilar girth welds.This serves as a foundation for the application of hybrid welding technology in welded cast steel joints.
基金The National Key R&D Program of China(No.2017YFC0805100)the National Natural Science Foundation of China(No.51578137)+1 种基金the Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutionsthe Open Research Fund Program of Jiangsu Key Laboratory of Engineering Mechanics。
文摘To study the distribution law and random characteristics of casting defects in steel castings,24 civil engineering structural cast steel joints were divided into two groups:simple cast steel joints and complex cast steel joints.Three kinds of nondestructive testing(NDT)methods,namely,visual,magnetic particle,and ultrasonic inspections,were used to detect the macroscopic defects in joints.The NDT results were then statistically analyzed.The results show that the unfused core support is a common defect of complex cast steel joints,and the defect can be seen visually,so excavation and repair welding should be carried out before castings leave factories.Casting cracks are extremely likely to occur in the intersection area of tubes,which is called the ultrasonic inspection blind zone.The occurrence probability of gas pores on simple cast steel joints is the largest,and the occurrence probability of core support incomplete fusions on complex cast steel joints is the largest.However,when cast steel joints are counted as a whole sample,the occurrence probability of gas pores is larger than that of core support incomplete fusions.Therefore,it is the most common defect in cast steel joints.
基金funded by National Basic Research Program of China(No.2011CB012900)
文摘To replace metal padding by insulation padding for castings can save the melt and reduce cleaning work of castings. The design of insulation padding was investigated. The equation of the modulus extension factor for insulation padding and the ratio of its thickness over the modulus of a casting were improved to deter- mine the thickness of insulation padding. The insulation padding was designed for a turbine guide vane casting weighing 3.5 t. A sound casting was obtained with 750 kg steel saved. On the other side, the cast- ing obviously expanded at the interface with the insulation padding, which is perhaps the reason that the use of insulation padding has been suspended for many years. To avoid the expansion of insulation pad- ding, a shielding layer made of a kind of material of good fire resistance was adopted to prevent the insula- tion layer from touching the melt. The shielding layer serves as a cushion of heat and expansion during so- lidification process so as to resist the expansion of castings and guarantee the feeding effect at the same time. Furthermore, insulation padding can be placed by a certain offset into the mold cavity so as to coun- teract the expansion of castings.
基金Item Sponsored by National Natural Science Foundation of China (50801046)Key Project of Science and Technology of Shanghai of China (07DZ11003)Research Fund for Doctoral Program of Higher Education of China (200802481138)
文摘The static recrystallization kinetics of low carbon steel cast strip was investigated by means of interrupted hot tensile tests. As-cast strip was reheated and soaked and its austenite grain size was similar to the width level of the as-cast columnar structure. The tests were carried out on Gleeble-3500 thermomechanical simulator. The deformation temperature is in the range of 800 to 1 200 ℃ with strain rate of 0.01 to 1 s ^-1. The prestrain is fixed at 0. 04 to 0.12, and the inter-hit delay time varies from 1 to 3 000 s. Effect of deformation conditions and initial microstructure on static recrystallization behavior was investigated. The activation energy （Qsrx） and Avrami exponent （n） of static recrystallization were determined to have 241 kJ/mol and 0.54 respectively by linear regression of the experimental results. A kinetics model was proposed to describe the static recrystallization kinetics in low-carbon steel cast strip. The predicted softening fractions are in good agreement with the experimental results, indicating that the proposed equations can give an accurate estimate of the softening behaviors for the low-carbon steel cast strip.
基金Item Sponsored by Hi-Tech Research and Development Program of China (2002AA331180)State Key Laboratory of Materials Modification by Laser,Ion and Electron Beams(0708)
文摘The alloying design of cast hot-forging die steels was analyzed. The relationship of the life of cast hot-forging dies with the failure patterns was studied. The thermal wear resistance was believed to be the key property for the alloying design of cast hot-forging die steels. The alloying design parameters were selected and optimized for the cast hot-forging die steel with high wear resistance. The wear resistance of the optimized cast die steel was evaluated in comparison with commercial H13 steels and 3Cr2WSV steel. In the new cast hot-forging die steel, VC is predominant carbide with Cr and Mo as the main solution elements in α-Fe. It is found that the cast die steel has significantly lower wear rate than normal H13 steel and 3Cr2W8V steel, almost the same as that of high purity H13 steel. The high wear resistance of the new cast hot-forging die steel can be attributed to its reasonable alloying design and nonsensibility to the detrimental function of S and P.
文摘The influence of microalloying additions on the mechanical properties of a low-carbon cast steel containing combinations of V, Nb, and Ti in the as-cast condition was evaluated. Tensile and hardness test results indicated that good combinations of strength and ductility could be achieved by V and Nb additions. While the yield strength and UTS （ultimate tensile strength） increased up to the range of 378-435 MPa and 579- 590 MPa, respectively in the microalloyed heats, their total elongation ranged from 18% to 23%. The presence of Ti, however, led to some reduction in the strength. Microstructural studies including scanning electron microscopy （SEM） and optical microscopy revealed that coarse TiN particles were responsible for this behavior. The Charpy impact values of all compositions indicated that microalloying additions significantly decreased the impact energy and led to the dominance of cleavage facets on the fracture surfaces. It seems that the increase in the hardness of coarse ferrite grains due to the precipitation hardening is the main reason for brittle fracture.
基金Item Sponsored by Early-Term Key Technology of Industrialization and Whole Set Equipment From Plan Committee of China(1999317) ,863 Project of China (2002AA331180) ,and Project of Key Lab of Universities in Jiangsu Province of China(Kjsmcx04004)
文摘The effect of main alloying elements on thermal wear of cast hot-forging die steels was studied. The wear mechanism was discussed. The results show that alloying elements have significant influences on the thermal wear of cast hot-forging die steels. The wear rates decrease with an increase in chromium content from 3% to 4% and molybdenum content from 2% to 3%, respectively. With further increase of chromium and molybdenum contents, chromium slightly reduces the wear resistance and molybdenum severely deteriorates the wear resistance with high wear rate. Lower vanadium/carbon ratio （1.5-2.5） leads to a lower wear resistance with higher wear rate. With an increase in vanadium/carbon ratio, the wear resistance of the cast steel substantially increases. When vanadium/carbon ratio is 3, the wear rate reaches the lowest value. The predominant mechanism of thermal wear of cast hot-forging die steels are oxidation wear and fatigue delamination. The Fe2O3 and Fe3O4 or lumps of brittle wear debris are formed on the wear surface.
基金supported by the National Natural Science Foundation of China(No.50974080)
文摘In the present paper, a new type of austempered boron alloyed high silicon cast steel has been developed, and its microstructures and mechanical properties at different temperatures were investigated. The experimental results indicate that the boron alloyed high silicon cast steel comprises a dendritic matrix and interdendritic eutectic borides in as-cast condition. The dendritic matrix is made up of pearlite, ferrite, and the interdendritic eutectic boride is with a chemical formula of M2B （M represents Fe, Cr, Mn or Mo） which is much like that of carbide in high chromium white cast iron. Pure ausferrite structure that consists of bainitic ferrite and retained austenite can be obtained in the matrix by austempering treatment to the cast steel. No carbides precipitate in the ausferrite structure and the morphology of borides remains almost unchanged after austempering treatments. Secondary boride particles precipitate during the course of austenitizing. The hardness and tensile strength of the austempered cast steel decrease with the increase of the austempering temperature, from 250℃ to 400 ℃. The impact toughness is 4-11 J.cm^-2 at room temperature and the impact fracture fractogragh indicates that the fracture is caused by the brittle fracture of the borides.
基金Project supported by the Innovation Fund for Outstanding Scholar of Henan Province (0621000600)
文摘The toughness of 31Mn2SiRE wear-resistance cast steel were increased by means of RE compound modification and high temperature austenitizing. The results show that the microstructures can be refined, needle and network ferrite are eliminated, the dislocation density and the quantity of dislocated martensite are increased remarkably, and the shape and distribution of inclusions are improved by the addition of RE. Therefore, the mechanical properties of the modified steel can be greatly increased, especially the toughness (αK) by 44%, yield strength (σs) by 10%, and elongation (δ5) by 42%.
基金This work was financially supported by the National Basic Research on New Generation Steel (973) (No.J1998061511-3)
文摘With the help of solidification kinetics, precipitation and growth of TiNhave been studied theoretically and the effect of cooling rate on the growth of TiN has beendiscussed. Through induction electric furnace experiment and electroslag remelting experiment withdifferent cooling rates, the distribution and particle size of TiN were investigated. It is provedthat the higher cooling rate is, the smaller the final size of TiN is and the more TiN particles canbe found in the steel. That TiN can restrain the growth of columnar crystal and enhance theproportion of equiaxed crystals to refine solidification structure as the heterogeneous nucleationsites of δ-ferrite is confirmed preliminarily. A new method to reduce macrosegregation incontinuous cast steel is provided.
