This paper studies a compound treatment. i. e. liquid S , N,C co-diffusing with rare earth (RE) and then oxidization , for hot-working die steels , and the effect of RE on thermal fatigue behavior of the diffused laye...This paper studies a compound treatment. i. e. liquid S , N,C co-diffusing with rare earth (RE) and then oxidization , for hot-working die steels , and the effect of RE on thermal fatigue behavior of the diffused layer. XRD and SEM energy spectrum prove that trace RE element actually penetrates into the surface layer of steels. The result shows that RE can reduce the gradient of change of hardness in diffused layer, improve the morphology and distribution of compounds , and reduce the degree of surface alligator crack for thermal fatigue. The behavior of thermal fatigue of hot-working die steels is raised by 70% or so after the application of RE. The effect of RE is analysed according to the theory.展开更多
The characteristics and microstructural changes of cyclic softening in hot-working die steels 5CrNiMo and 5Cr2NiMoVSi were studied under strain controlled low-cycle fatigue.The re- sults show that the cyclic softening...The characteristics and microstructural changes of cyclic softening in hot-working die steels 5CrNiMo and 5Cr2NiMoVSi were studied under strain controlled low-cycle fatigue.The re- sults show that the cyclic softening is featured in both steels hardened in different conditions under the strain controlled amplitude range of Δε_t/2=0.6-1.8×10^(-2).The softening effect mainly occurs in some initial cycles and the stress amplitude varies slightly in the sequential cycles,i.e.the softening effect is minified.No obvious stress saturation phenomenon was ob- served during the whole cyclic deformation.The TEM analysis shows that the cyclic softening is related to heterogenity of plastic deformation.The softening of the tested steels is caused by the formation of the dislocation cell structure with low density and low internal stress,and by the fragmentation and redissolution of fine carbides into matrix.展开更多
ERH end-quenching method was used to determine the hardenability of four kinds hot-forging die steels with deep-hardening and hence the order of their hardenability was given.The tempering hardness of the steels was m...ERH end-quenching method was used to determine the hardenability of four kinds hot-forging die steels with deep-hardening and hence the order of their hardenability was given.The tempering hardness of the steels was measured and the tempering resistance was studied.It was approved that ERH method is effective for the determination of hardenability of deep-hardening steel and the beginning of hardness drop in the ERH specimen is caused by bainite occurring.展开更多
Nitrogen can increase the strength of steels without weakening the toughness and improve the corrosion resistance at the same time. Compared with conventional nitrogen-free die steels, a new type of nitrogen-containin...Nitrogen can increase the strength of steels without weakening the toughness and improve the corrosion resistance at the same time. Compared with conventional nitrogen-free die steels, a new type of nitrogen-containing die steel was developed with many superior properties, such as high strength, high hardness, and good toughness. This paper focused on the effects of heat treatment on the microstruc- tures and mechanical properties of the new type of nitrogen-containing die steel, which were investigated by the optimized deformation process and heat treatment. Isothermal spheroidal annealing and high-temperature quenching as well as high-temperature tempering were ap- plied in the experiment by means of an orthogonal method after the steel was multiply forged. The mechanical properties of nitro- gen-containing die steel forgings are better than the standard of NADCA #207-2003.展开更多
The influence of prior austenite deformed at different temperature on the subsequent continuous cooling bainitic transformation has been investigated in an C-Ma-Cr-Ni-Mo plastic die steel. The results show that the pr...The influence of prior austenite deformed at different temperature on the subsequent continuous cooling bainitic transformation has been investigated in an C-Ma-Cr-Ni-Mo plastic die steel. The results show that the prior deformation in low temperature region of austenite retards significantly the bainitic transformation. For the same continuous cooling schedule, as austenite deformed at lower temperature, the quantity of the classical sheaf-like bainite becomes less. The present results show that severe deformation leads to mechanical stabilization of austenite and causes the difficulty of bainitic ferrite propagation into the austenite.展开更多
The effects of RE modification on structure and the properties of a new cast hot work die (CHD) steel were investigated. The grains of the CHD steel are refined by RE modification. With the increase of RE addition, b...The effects of RE modification on structure and the properties of a new cast hot work die (CHD) steel were investigated. The grains of the CHD steel are refined by RE modification. With the increase of RE addition, both grain size and inclusion amount are reduced. Appropriate amount of RE results in decrease in inclusion amount and formation of spheroidal inclusions uniformly-distributed in steel, so that the morphology and distribution of inclusions are improved. RE composite modification favors the formation of bainite, austenite and fine lath martensite with dense dislocation. When the residual RE content reaches 0.02%, no obvious changes in strength and hardness are found, while fracture toughness and threshold of fatigue crack growth are increased. The impact toughness, elongation and reduction of cross sectional area are increased by a factor of two, and thermal fatigue resistance is also improved.展开更多
Taking the hot working die steel （HWDS） 4Cr3Mo2NbVNi as an example, the phase electron structures （PES） and the biphase interface electron structures （BIES） of Mo2C and V4 C3 , which are two kinds of important c...Taking the hot working die steel （HWDS） 4Cr3Mo2NbVNi as an example, the phase electron structures （PES） and the biphase interface electron structures （BIES） of Mo2C and V4 C3 , which are two kinds of important carbides precipitated during tempering in steel were calculated, on the basis of the empirical electron theory of solids and molecules and the improved TFD theory. The influence of Mo2 C and V4 C3 on the mechanical properties of HWDS has been analyzed at electron structure level, and the fundamental reason that the characteristic of the PES and the BIES of carbides decides the behavior of them has been revealed.展开更多
An approach was presented to characterize the stress response of workpiece in hard machining, accounting for the effect of the initial workpiece hardness in addition to temperature, strain and strain rate on flow stre...An approach was presented to characterize the stress response of workpiece in hard machining, accounting for the effect of the initial workpiece hardness in addition to temperature, strain and strain rate on flow stress in this paper. AISI H13 die steel was chosen to verify this methodology. The proposed flow stress model demonstrates a good agreement with experimental data. Therefore, the proposed model can be used to predict the corresponding flow stress-strain response ofAISl H13 die steel with variation of the initial workpiece hardness in hard machining.展开更多
The effect of magnesium addition on the number, morphology, composition, size, and density of inclusions in H13 die steel was studied. The results show that the total oxygen content in the steel can be significantly d...The effect of magnesium addition on the number, morphology, composition, size, and density of inclusions in H13 die steel was studied. The results show that the total oxygen content in the steel can be significantly decreased to 0.0008wt%. Al2O3 and Mn S inclusions are changed into nearly spherical Mg O·Al2O3 spinel and spherical Mg O·Mg S inclusions, respectively. The number of inclusions larger than 1 μm decreases and the number of inclusions smaller than 1 μm increases with increasing magnesium content. V（N,C） precipitates around Mg O·Al2O3 and Mg O·Mg S inclusions during solidification of liquid steel. The densities of Mg O·Al2O3 spinel inclusions are lower than that of alumina inclusions. With increasing magnesium content in the Mg-containing inclusions, the density of inclusions decreases, leading to the improvement of inclusion removal efficiency.展开更多
Thermo-Calc software package (TCP+DICTRA) was used to simulate the carbide transformation process in die steel for plastic. Combined with TEM analysis, the calculated result confirms that the carbide in equilibrium st...Thermo-Calc software package (TCP+DICTRA) was used to simulate the carbide transformation process in die steel for plastic. Combined with TEM analysis, the calculated result confirms that the carbide in equilibrium state is M_7C_3 carbide. The dissolution of M_7C_3 carbide in steel is predicted by DICTRA program. It was shown that the temperature remarkably affects the dissolution process of M_7C_3 carbide, but the influence of alloy elements such as manganese and molybdenum can be neglected in this steel.展开更多
The fatigue behavior of cemented carbide die under service load in the multistage cold forging of steel was investigated. It was found that the fatigue cracks do not initiate at the stress concentration position and t...The fatigue behavior of cemented carbide die under service load in the multistage cold forging of steel was investigated. It was found that the fatigue cracks do not initiate at the stress concentration position and the crack initiation position can be classified to three types. The crack initiation position can be predicted by FEM only when the plastic deformation of the die is considered.展开更多
The alteration of the strength, hardness and impact ductility of 5CrNiMo steel using three different additions of RE La element is studied in this paper. The mechanical properties of 5CrNiMo steel with RE La additions...The alteration of the strength, hardness and impact ductility of 5CrNiMo steel using three different additions of RE La element is studied in this paper. The mechanical properties of 5CrNiMo steel with RE La additions are be compared with that of the 5CrNiMo steel on the same heat-treatment condition without RE La element addition. The results show that the strength, hardness and impact ductility of 5CrNiMo steel will be improved obviously when the content of RE La element is proper, and as the content of RE La element is 0.033%(mass fraction), the 5CrNiMo steel has the best mechanical properties.展开更多
The differential etching methods of carbides M_6C, MC and M_(23)C_6 in die steel havebeen studies by volt-ampere method and potentioastatic method. It can be used for the observation ,identification and quantitative a...The differential etching methods of carbides M_6C, MC and M_(23)C_6 in die steel havebeen studies by volt-ampere method and potentioastatic method. It can be used for the observation ,identification and quantitative analysis of carbides.展开更多
An optimization strategy for high speed machining of hardened die/mold steel based on machining feature analysis was studied. It is a further extension of the previously presented study on the thermal mechanism of end...An optimization strategy for high speed machining of hardened die/mold steel based on machining feature analysis was studied. It is a further extension of the previously presented study on the thermal mechanism of end milling and constant cutting force control. An objective function concerning machining cost and associated optimization algorithm based on machining time and cutting length calculation was proposed. Constraints to satisfy specific machining strategies when high speed machining the hardened die/mold steel, trochoid tool path pattern in slot end milling to avoid over-heat and feed rate adaptation to avoid over-load, were also discussed. As a case study, the tool selection problem when machining a die part with multiple machining features was investigated.展开更多
Larger-sized primary carbides lead to stress concentration during the application of H13 hot-work die steel,resulting in microcracks and fatigue failure.Rare earth was usually added to modify the carbides and inclusio...Larger-sized primary carbides lead to stress concentration during the application of H13 hot-work die steel,resulting in microcracks and fatigue failure.Rare earth was usually added to modify the carbides and inclusions.The existing literature is reviewed on the effect of rare earth on primary carbides in H13 steel.A comprehensive review on the effect of rare earth on the characteristics of primary carbides,i.e.,number,size,morphology,and thermal stability in H13 steel,was done.The precipitation mechanism and nucleation of primary carbides with rare earth were summarized.The position and form of rare earth in steel and their effects on alloying elements segregation were reviewed.The addition techniques of rare earth in H13 steel were compared,and the prospects for other uncommon rare earth and emerging technology were present.Based on the current references,it can be known that adding rare earth facilitated refined and dispersed primary carbides.The size of primary carbides would be reduced,and their morphology would be improved because the rare earth inclusions formed in H13 steel can act as nucleation cores forγ-Fe orδ-Fe,refining the dendritic structure.Besides,the number of primary carbides at grain boundaries would be significantly reduced.However,rare earth had little impact on thermal stability.The nucleation of primary carbides tended to be inhibited due to the modification of inclusions by rare earth which were likely to be nucleation cores for primary carbides.Rare earth had been reported to affect the mechanism and process of primary carbide precipitation.Additionally,the addition of rare earth can inhibit the segregation of alloying elements and carbon diffusion by calculation.Thus,laboratory experiments and theoretical calcu-lations need to be conducted to study the states and evolution of rare earth steels.展开更多
The effects of heat treatment on the precipitates and strengthening mechanism in AISI H13 steel were investigated. The results showed that the presence of nanoscale precipitates favorably affected grain refinement and...The effects of heat treatment on the precipitates and strengthening mechanism in AISI H13 steel were investigated. The results showed that the presence of nanoscale precipitates favorably affected grain refinement and improved the yield strength. The volume fraction of precipitates increased from 1.05% to 2.85% during tempering, whereas the average precipitate size first decreased then increased during tempering. Contributions to the yield strength arising from the various mechanisms were calculated quantificationally, and the results demonstrated that grain refinement and dislocation density most strongly influenced the yield strength. In addition, under the interaction of average size and volume fraction, precipitates＇ contribution to the yield strength ranged from 247.9 to 378.5 MPa. Finally, a root-mean-square summation law of σ = σg ＋ σs ＋（σd^2 ＋ σp^2）^1/2, where σg, σs, σd, and σp represent the contributions of fine-grain strengthening, solid-solution strengthening, dislocation strengthening, and precipitation strengthening, respectively, was confirmed as the most applicable for AISI H13 steel, which indicates a strong link between precipitates and dislocations in AISI H13 steel.展开更多
The morphology and amount of the retained austenite in the duplex microstructure of martensite and tower bainite of a tow,alloy cold die steel(it is called GD steel for short) with high strength and high toughness hav...The morphology and amount of the retained austenite in the duplex microstructure of martensite and tower bainite of a tow,alloy cold die steel(it is called GD steel for short) with high strength and high toughness have been investigated.The thermal and mechanical stabilities of the retained austenite were analyzed.Furthermore the effects of retained austenite on the mechanical properties of the steel were studied.The results show that the morphology and amount of retained austenite vary with silicon content in the steel.Retained austenite with high stability was responsible for the simultaneous increase in strength and toughness of the steel.The duplex microstructure of martensite and abnormal lower bainite of the steel with the maximum silicon content exhibits a relatively good strength-toughness combination.展开更多
Suggestions have been put forward speeding up the development of high-level tool steel and mold steel in China based on the analysis of products and development status of special steel home and abroad. Feasibility and...Suggestions have been put forward speeding up the development of high-level tool steel and mold steel in China based on the analysis of products and development status of special steel home and abroad. Feasibility and necessity to produce high-level tool steel and mold steel by applying the spray forming method in future have been put forward.展开更多
Compared with H13 steel, the influences of different heat treatment process on the microstructure and properties of the new type of hot working die steel H13MOD were studied. The results show that the complete aus ten...Compared with H13 steel, the influences of different heat treatment process on the microstructure and properties of the new type of hot working die steel H13MOD were studied. The results show that the complete aus tenitizing temperature of H13MOD is around 1030 ℃ and the quenching hardness achieves the maximum value at this temperature. While for H13, the complete austenitizing temperature is above 1100 ℃ and the quenching hardness rise constantly with the quenching temperature increasing. In quenching process, the undissolved MC carbides can prevent the coarsening of grain in both steels. With the rise of quenching temperature, when MC carbides dissolve completely, the grain grows quickly. The hardness and strength of H13MOD at higher tempering temperature （above 570 ℃） are nearly the same as those of H13, but its toughness is higher than that of H13. Mo2C carbide is the main strengthening phase in H13MOD, which is attributed to the higher content of Mo. The quantity of VC eutectic car- bides is reduced because of lower content of V in H13MOD, which plays an important role in enhancing the impact toughness of H13MOD. Under a certain strength condition, H13MOD steel can be used in the environment that higher toughness is required and the service life of die casting mold can be improved.展开更多
The effect of cryogenic treatment on the properties of Cr8-type cold work die steel was investigated. The results show that cryogenic treatment increases hardness by decreasing retained austenite, but the degree depen...The effect of cryogenic treatment on the properties of Cr8-type cold work die steel was investigated. The results show that cryogenic treatment increases hardness by decreasing retained austenite, but the degree depends on the austenitizing temperature. When quenching at lower austenitizing temperature, the steel can obtain higher tough- ness by cryogenic treatment substituting conventional treatment process. Cryogenic time has little effect on cryogenic treatment. Conversely, cryogenic temperature has a great effect on cryogenic treatment and the effect of cryogenic treatment is more obvious with decreasing cryogenic temperature. In addition, deep cryogenic treatment improves the wear resistance by precipitating more homogeneous specific carbides.展开更多
文摘This paper studies a compound treatment. i. e. liquid S , N,C co-diffusing with rare earth (RE) and then oxidization , for hot-working die steels , and the effect of RE on thermal fatigue behavior of the diffused layer. XRD and SEM energy spectrum prove that trace RE element actually penetrates into the surface layer of steels. The result shows that RE can reduce the gradient of change of hardness in diffused layer, improve the morphology and distribution of compounds , and reduce the degree of surface alligator crack for thermal fatigue. The behavior of thermal fatigue of hot-working die steels is raised by 70% or so after the application of RE. The effect of RE is analysed according to the theory.
文摘The characteristics and microstructural changes of cyclic softening in hot-working die steels 5CrNiMo and 5Cr2NiMoVSi were studied under strain controlled low-cycle fatigue.The re- sults show that the cyclic softening is featured in both steels hardened in different conditions under the strain controlled amplitude range of Δε_t/2=0.6-1.8×10^(-2).The softening effect mainly occurs in some initial cycles and the stress amplitude varies slightly in the sequential cycles,i.e.the softening effect is minified.No obvious stress saturation phenomenon was ob- served during the whole cyclic deformation.The TEM analysis shows that the cyclic softening is related to heterogenity of plastic deformation.The softening of the tested steels is caused by the formation of the dislocation cell structure with low density and low internal stress,and by the fragmentation and redissolution of fine carbides into matrix.
基金Project sponsored by Research Fund for Doctoral Program of Higher Education(9514509)
文摘ERH end-quenching method was used to determine the hardenability of four kinds hot-forging die steels with deep-hardening and hence the order of their hardenability was given.The tempering hardness of the steels was measured and the tempering resistance was studied.It was approved that ERH method is effective for the determination of hardenability of deep-hardening steel and the beginning of hardness drop in the ERH specimen is caused by bainite occurring.
基金supported by the National Natural Science Foundation of China (Nos.50974014 and 51174026)
文摘Nitrogen can increase the strength of steels without weakening the toughness and improve the corrosion resistance at the same time. Compared with conventional nitrogen-free die steels, a new type of nitrogen-containing die steel was developed with many superior properties, such as high strength, high hardness, and good toughness. This paper focused on the effects of heat treatment on the microstruc- tures and mechanical properties of the new type of nitrogen-containing die steel, which were investigated by the optimized deformation process and heat treatment. Isothermal spheroidal annealing and high-temperature quenching as well as high-temperature tempering were ap- plied in the experiment by means of an orthogonal method after the steel was multiply forged. The mechanical properties of nitro- gen-containing die steel forgings are better than the standard of NADCA #207-2003.
文摘The influence of prior austenite deformed at different temperature on the subsequent continuous cooling bainitic transformation has been investigated in an C-Ma-Cr-Ni-Mo plastic die steel. The results show that the prior deformation in low temperature region of austenite retards significantly the bainitic transformation. For the same continuous cooling schedule, as austenite deformed at lower temperature, the quantity of the classical sheaf-like bainite becomes less. The present results show that severe deformation leads to mechanical stabilization of austenite and causes the difficulty of bainitic ferrite propagation into the austenite.
文摘The effects of RE modification on structure and the properties of a new cast hot work die (CHD) steel were investigated. The grains of the CHD steel are refined by RE modification. With the increase of RE addition, both grain size and inclusion amount are reduced. Appropriate amount of RE results in decrease in inclusion amount and formation of spheroidal inclusions uniformly-distributed in steel, so that the morphology and distribution of inclusions are improved. RE composite modification favors the formation of bainite, austenite and fine lath martensite with dense dislocation. When the residual RE content reaches 0.02%, no obvious changes in strength and hardness are found, while fracture toughness and threshold of fatigue crack growth are increased. The impact toughness, elongation and reduction of cross sectional area are increased by a factor of two, and thermal fatigue resistance is also improved.
基金ItemSponsored by National Natural Science Foundation of China (50271030) Provincial Natural Science Foundation ofLiaoning Province of China (972072)
文摘Taking the hot working die steel （HWDS） 4Cr3Mo2NbVNi as an example, the phase electron structures （PES） and the biphase interface electron structures （BIES） of Mo2C and V4 C3 , which are two kinds of important carbides precipitated during tempering in steel were calculated, on the basis of the empirical electron theory of solids and molecules and the improved TFD theory. The influence of Mo2 C and V4 C3 on the mechanical properties of HWDS has been analyzed at electron structure level, and the fundamental reason that the characteristic of the PES and the BIES of carbides decides the behavior of them has been revealed.
基金the Natural Science Foundation of Jiangxi Province(No.550067)the National Natural Science Foundation of China(No.50465003)Foundation of the State Key Laboratory of Plastic Forming Simulation and Die & Mould Technology(No.06-3)
文摘An approach was presented to characterize the stress response of workpiece in hard machining, accounting for the effect of the initial workpiece hardness in addition to temperature, strain and strain rate on flow stress in this paper. AISI H13 die steel was chosen to verify this methodology. The proposed flow stress model demonstrates a good agreement with experimental data. Therefore, the proposed model can be used to predict the corresponding flow stress-strain response ofAISl H13 die steel with variation of the initial workpiece hardness in hard machining.
基金financially supported by the National Natural Science Foundation of China(No.51374022)China Postdoctoral Science Foundation(No.2014M560047)
文摘The effect of magnesium addition on the number, morphology, composition, size, and density of inclusions in H13 die steel was studied. The results show that the total oxygen content in the steel can be significantly decreased to 0.0008wt%. Al2O3 and Mn S inclusions are changed into nearly spherical Mg O·Al2O3 spinel and spherical Mg O·Mg S inclusions, respectively. The number of inclusions larger than 1 μm decreases and the number of inclusions smaller than 1 μm increases with increasing magnesium content. V（N,C） precipitates around Mg O·Al2O3 and Mg O·Mg S inclusions during solidification of liquid steel. The densities of Mg O·Al2O3 spinel inclusions are lower than that of alumina inclusions. With increasing magnesium content in the Mg-containing inclusions, the density of inclusions decreases, leading to the improvement of inclusion removal efficiency.
文摘Thermo-Calc software package (TCP+DICTRA) was used to simulate the carbide transformation process in die steel for plastic. Combined with TEM analysis, the calculated result confirms that the carbide in equilibrium state is M_7C_3 carbide. The dissolution of M_7C_3 carbide in steel is predicted by DICTRA program. It was shown that the temperature remarkably affects the dissolution process of M_7C_3 carbide, but the influence of alloy elements such as manganese and molybdenum can be neglected in this steel.
文摘The fatigue behavior of cemented carbide die under service load in the multistage cold forging of steel was investigated. It was found that the fatigue cracks do not initiate at the stress concentration position and the crack initiation position can be classified to three types. The crack initiation position can be predicted by FEM only when the plastic deformation of the die is considered.
文摘The alteration of the strength, hardness and impact ductility of 5CrNiMo steel using three different additions of RE La element is studied in this paper. The mechanical properties of 5CrNiMo steel with RE La additions are be compared with that of the 5CrNiMo steel on the same heat-treatment condition without RE La element addition. The results show that the strength, hardness and impact ductility of 5CrNiMo steel will be improved obviously when the content of RE La element is proper, and as the content of RE La element is 0.033%(mass fraction), the 5CrNiMo steel has the best mechanical properties.
文摘The differential etching methods of carbides M_6C, MC and M_(23)C_6 in die steel havebeen studies by volt-ampere method and potentioastatic method. It can be used for the observation ,identification and quantitative analysis of carbides.
文摘An optimization strategy for high speed machining of hardened die/mold steel based on machining feature analysis was studied. It is a further extension of the previously presented study on the thermal mechanism of end milling and constant cutting force control. An objective function concerning machining cost and associated optimization algorithm based on machining time and cutting length calculation was proposed. Constraints to satisfy specific machining strategies when high speed machining the hardened die/mold steel, trochoid tool path pattern in slot end milling to avoid over-heat and feed rate adaptation to avoid over-load, were also discussed. As a case study, the tool selection problem when machining a die part with multiple machining features was investigated.
基金supported by the National Natural Science Foundation of China(Grant Nos.52064011 and 52274331)Guizhou Provincial Basic Research Program(Natural Science)(Nos.ZK[2021]258 and ZK[2022]Zhongdian 023)+1 种基金Guizhou Provincial Program on Commercialization of Scientific and Technological Achievements(No.[2022]089)Natural Science Research Project of Guizhou Provincial Department of Education(No.[2022]041).
文摘Larger-sized primary carbides lead to stress concentration during the application of H13 hot-work die steel,resulting in microcracks and fatigue failure.Rare earth was usually added to modify the carbides and inclusions.The existing literature is reviewed on the effect of rare earth on primary carbides in H13 steel.A comprehensive review on the effect of rare earth on the characteristics of primary carbides,i.e.,number,size,morphology,and thermal stability in H13 steel,was done.The precipitation mechanism and nucleation of primary carbides with rare earth were summarized.The position and form of rare earth in steel and their effects on alloying elements segregation were reviewed.The addition techniques of rare earth in H13 steel were compared,and the prospects for other uncommon rare earth and emerging technology were present.Based on the current references,it can be known that adding rare earth facilitated refined and dispersed primary carbides.The size of primary carbides would be reduced,and their morphology would be improved because the rare earth inclusions formed in H13 steel can act as nucleation cores forγ-Fe orδ-Fe,refining the dendritic structure.Besides,the number of primary carbides at grain boundaries would be significantly reduced.However,rare earth had little impact on thermal stability.The nucleation of primary carbides tended to be inhibited due to the modification of inclusions by rare earth which were likely to be nucleation cores for primary carbides.Rare earth had been reported to affect the mechanism and process of primary carbide precipitation.Additionally,the addition of rare earth can inhibit the segregation of alloying elements and carbon diffusion by calculation.Thus,laboratory experiments and theoretical calcu-lations need to be conducted to study the states and evolution of rare earth steels.
基金financially supported by the National Natural Science Foundation of China(No.51274031)
文摘The effects of heat treatment on the precipitates and strengthening mechanism in AISI H13 steel were investigated. The results showed that the presence of nanoscale precipitates favorably affected grain refinement and improved the yield strength. The volume fraction of precipitates increased from 1.05% to 2.85% during tempering, whereas the average precipitate size first decreased then increased during tempering. Contributions to the yield strength arising from the various mechanisms were calculated quantificationally, and the results demonstrated that grain refinement and dislocation density most strongly influenced the yield strength. In addition, under the interaction of average size and volume fraction, precipitates＇ contribution to the yield strength ranged from 247.9 to 378.5 MPa. Finally, a root-mean-square summation law of σ = σg ＋ σs ＋（σd^2 ＋ σp^2）^1/2, where σg, σs, σd, and σp represent the contributions of fine-grain strengthening, solid-solution strengthening, dislocation strengthening, and precipitation strengthening, respectively, was confirmed as the most applicable for AISI H13 steel, which indicates a strong link between precipitates and dislocations in AISI H13 steel.
文摘The morphology and amount of the retained austenite in the duplex microstructure of martensite and tower bainite of a tow,alloy cold die steel(it is called GD steel for short) with high strength and high toughness have been investigated.The thermal and mechanical stabilities of the retained austenite were analyzed.Furthermore the effects of retained austenite on the mechanical properties of the steel were studied.The results show that the morphology and amount of retained austenite vary with silicon content in the steel.Retained austenite with high stability was responsible for the simultaneous increase in strength and toughness of the steel.The duplex microstructure of martensite and abnormal lower bainite of the steel with the maximum silicon content exhibits a relatively good strength-toughness combination.
文摘Suggestions have been put forward speeding up the development of high-level tool steel and mold steel in China based on the analysis of products and development status of special steel home and abroad. Feasibility and necessity to produce high-level tool steel and mold steel by applying the spray forming method in future have been put forward.
文摘Compared with H13 steel, the influences of different heat treatment process on the microstructure and properties of the new type of hot working die steel H13MOD were studied. The results show that the complete aus tenitizing temperature of H13MOD is around 1030 ℃ and the quenching hardness achieves the maximum value at this temperature. While for H13, the complete austenitizing temperature is above 1100 ℃ and the quenching hardness rise constantly with the quenching temperature increasing. In quenching process, the undissolved MC carbides can prevent the coarsening of grain in both steels. With the rise of quenching temperature, when MC carbides dissolve completely, the grain grows quickly. The hardness and strength of H13MOD at higher tempering temperature （above 570 ℃） are nearly the same as those of H13, but its toughness is higher than that of H13. Mo2C carbide is the main strengthening phase in H13MOD, which is attributed to the higher content of Mo. The quantity of VC eutectic car- bides is reduced because of lower content of V in H13MOD, which plays an important role in enhancing the impact toughness of H13MOD. Under a certain strength condition, H13MOD steel can be used in the environment that higher toughness is required and the service life of die casting mold can be improved.
基金Item Sponsored by National Key Technologies Research and Development Program of China (2007BAE510B04)
文摘The effect of cryogenic treatment on the properties of Cr8-type cold work die steel was investigated. The results show that cryogenic treatment increases hardness by decreasing retained austenite, but the degree depends on the austenitizing temperature. When quenching at lower austenitizing temperature, the steel can obtain higher tough- ness by cryogenic treatment substituting conventional treatment process. Cryogenic time has little effect on cryogenic treatment. Conversely, cryogenic temperature has a great effect on cryogenic treatment and the effect of cryogenic treatment is more obvious with decreasing cryogenic temperature. In addition, deep cryogenic treatment improves the wear resistance by precipitating more homogeneous specific carbides.
