The effect of niobium addition on the microstructure of cast AISI H13 hot work tool steel was evaluated by using EDX analyzer attached to the scanning electron microscope. The volume percent of eutectic area and eutec...The effect of niobium addition on the microstructure of cast AISI H13 hot work tool steel was evaluated by using EDX analyzer attached to the scanning electron microscope. The volume percent of eutectic area and eutectic cell size and also volume percent of different carbides of new steel, which is heat treated under different conditions, are also determined. The results show that the a niobium addition modifies the cast structure of Nb-alloyed hot work tool steel, and reduces the size and volume of eutectic cells, and increases the maximum hardness of the steel.展开更多
The effects of heat treatment on the microstructure of modified cast high chromium high carbon AISI D3 steel were studied. The modified AISI D3 steel was developed by replacing part of chromium with niobium and titani...The effects of heat treatment on the microstructure of modified cast high chromium high carbon AISI D3 steel were studied. The modified AISI D3 steel was developed by replacing part of chromium with niobium and titanium, in which chromium carbide was partially replaced with MC carbides. The cast samples produced by investment casting were heat treated under different conditions. The microstructures of the samples were studied by optical microscope and scanning electron microscope equipped with EDS analyzer. To determine the optimized homogenizing process, the effects of homogenizing treatment on the microstructure and the morphology of carbides were also studied. The results show that the MC carbides are not changed in shape and amounts during high temperature homogenizing, whereas the M3C carbides are reduced in amount and become semiglobular in shape, and the homogeneity of microstructure is improved.展开更多
The fatigue strength of a high V alloyed powder metallurgy tool steel with two different inclusion size levels, tempered at different temperatures, was investigated by a series of high cycle fatigue tests. It was show...The fatigue strength of a high V alloyed powder metallurgy tool steel with two different inclusion size levels, tempered at different temperatures, was investigated by a series of high cycle fatigue tests. It was shown that brittle inclusions with large sizes above 30μm prompted the occurrence of subsurface crack initiation and the reduction in fatigue strength. The fracture toughness and the stress amplitude both exerted a significant influence on the fish-eye size. A larger fish-eye area would form in the sample with a higher fracture toughness subjected to a lower stress amplitude. The stress intensity factor of the inclusion was found to lie above a typical value of the threshold stress intensity factor of 4 MPa.m^1/2. The fracture toughness of the sample with a hardness above HRC 56 could be estimated by the mean value of the stress intensity factor of the fish-eye. According to fractographic evaluation, the critical inclusion size can be calculated by linear fracture mechanics.展开更多
The characteristics of CrN coated martensitic H13 grade tool steels were studied. CrN coatings were depos- ited by the arc physical vapor deposition （PVD） before and after the pulse plasma nitriding of the samples. ...The characteristics of CrN coated martensitic H13 grade tool steels were studied. CrN coatings were depos- ited by the arc physical vapor deposition （PVD） before and after the pulse plasma nitriding of the samples. The PVD and plasma nitriding techniques were applied in relevant workshops by following the commercial practice parameters. Experimental results showed that CrN coating deposited on the nitrided surfaces exhibited superior scratch and wear resistances as compared to that deposited on the original martensitic surface.展开更多
Low temperature composite chromizing is a process composed of a plain ion-carbonitriding or ion-nitriding at 550-580℃,followed by a low-temperature chromizing in a salt-bath of 590℃.The microstructure and properties...Low temperature composite chromizing is a process composed of a plain ion-carbonitriding or ion-nitriding at 550-580℃,followed by a low-temperature chromizing in a salt-bath of 590℃.The microstructure and properties of the low temperature composite chromized layer on H13 tool steel were investigated using metallography,X-ray diffraction,microanalysis,hardness and wear tests.It was found that this low temperature process was thermo-dynamically and kinetically possible,and the composite chromized layer on H13 steel,with a thickness of 3-6μm,consisted of three sub-layers(bands),viz.the outer Cr-rich one,the intermediate(black)one,and the inner,original white layer.After chromizing,the former diffusion layer was thickened.The results of X-ray diffraction showed that the composite chromized layer contained such nitrides and carbides of chromium as CrN,Cr2N,(Cr,Fe)23C6,and(Cr,Fe)7C3,as well as plainα-(Fe,Cr).A high surface microhardness of 1450-1550 HV0.025,which is much higher than that obtained by the conventional ion carbonitriding and ion nitriding,was obtained.In addition,an excellent wear resistance was gained on the composite chromized layer.展开更多
The microstructure and the stability of carbides after heat treatments in an H23 tool steel were investigated. The heat treatments consisted of austenization at two different austenizing temperatures （1100℃ and 125...The microstructure and the stability of carbides after heat treatments in an H23 tool steel were investigated. The heat treatments consisted of austenization at two different austenizing temperatures （1100℃ and 1250℃）, followed by water quenching and double-aging at 650℃, 750℃, and 800℃with air cooling between the first and second aging treatments. Martensite did not form in the as-quenched micro- structures, which consisted of a ferrite matrix, M6C, M7C3, and MC carbides. The double-aged microstructures consisted of a ferrite matrix and MC, M6C, M7C3, and M23C6 carbides. Secondary hardening as a consequence of secondary precipitation of fine M2C carbides did not occur. There was disagreement between the experimental microstructure and the results of thermodynamic calculations. The highest double-aged hardness of the H23 tool steel was 448 HV after austenization at 1250℃ and double-aging at 650℃, which suggested that this tool steel should be used at temperatures below 650℃.展开更多
Wire+arc additive manufacturing(WAAM)is considered an innovative technology that can change the manufacturing landscape in the near future.WAAM offers the benefits of inexpensive initial system setup and a high deposi...Wire+arc additive manufacturing(WAAM)is considered an innovative technology that can change the manufacturing landscape in the near future.WAAM offers the benefits of inexpensive initial system setup and a high deposition rate for fabricating medium-and large-sized parts such as die-casting tools.In this study,AISI H13 tool steel,a popular die-casting tool metal,is manufactured by cold metal transfer(CMT)-based WAAM and is then comprehensively analyzed for its microstructural and mechanical properties.Location-dependent phase combinations are observed,which could be explained by nonequilibrium thermal cycles that resulted from the layer-by-layer stacking mechanism used in WAAM.In addition,remelting and reheating of the layers reduces welding anomalies(e.g.,pores and voids).The metallurgical characteristics of the H13 strongly correlate with the mechanical properties.The combinations of phases at different locations of the additively manufactured part exhibit a periodic microhardness profile.Martensite,Retained Austenite,Ferrite,and Carbide phases are found in combination at different locations of the part based on the part’s temperature distribution during additive deposition.Moreover,the tensile properties at elevated temperatures(23℃,300℃,and 600℃)are comparable to those from other WAAM and additive manufacturing(AM)processes.The X-ray diffraction results verify that the microstructural stability of the fabricated parts at high temperatures would allow them to be used in high temperatures.展开更多
A nanostructured surface layer has been fabricated on an AISI H13 tool steel by means of surface mechanical attrition treatment(SMAT).Strain-induced refinement processes of ferrite grains and carbide particles have be...A nanostructured surface layer has been fabricated on an AISI H13 tool steel by means of surface mechanical attrition treatment(SMAT).Strain-induced refinement processes of ferrite grains and carbide particles have been investigated by transmission electron microscopy(TEM)and scanning electron microscopy(SEM)in the SMAT surface layer.Grain refinement of ferrite is found to be dominated by dislocation activities and greatly facilitated by a large number of carbide particles at a depth〉20μm.The comparisons with microstructure refinement processes in other SMAT ferrite steels indicate that a larger volume fraction of carbide particles with a lower shear strength is expected to facilitate the refinement process of ferrite grains.展开更多
The effect of deep cryogenic treatment on the microstructure, hardness, and wear behavior of D2 tool steel was studied by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray diffracti...The effect of deep cryogenic treatment on the microstructure, hardness, and wear behavior of D2 tool steel was studied by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray diffraction （XRD）, hardness test, pin-on-disk wear test, and the reciprocating pin-on-fiat wear test. The results show that deep cryogenic treatment eliminates retained austenite, makes a better carbide distribution, and increases the carbide content. Furthermore, some new nano-sized carbides form during the deep cryogenic treatment, thereby increasing the hardness and improving the wear behavior of the samples.展开更多
The laser powder bed fusion(LPBF) process can integrally form geometrically complex and high-performance metallic parts that have attracted much interest,especially in the molds industry.The appearance of the LPBF mak...The laser powder bed fusion(LPBF) process can integrally form geometrically complex and high-performance metallic parts that have attracted much interest,especially in the molds industry.The appearance of the LPBF makes it possible to design and produce complex conformal cooling channel systems in molds.Thus,LPBF-processed tool steels have attracted more and more attention.The complex thermal history in the LPBF process makes the microstructural characteristics and properties different from those of conventional manufactured tool steels.This paper provides an overview of LPBF-processed tool steels by describing the physical phenomena,the microstructural characteristics,and the mechanical/thermal properties,including tensile properties,wear resistance,and thermal properties.The microstructural characteristics are presented through a multiscale perspective,ranging from densification,meso-structure,microstructure,substructure in grains,to nanoprecipitates.Finally,a summary of tool steels and their challenges and outlooks are introduced.展开更多
The hardness and microstructure evolution of a 8%Cr cold work tool steel during tempering for 40 h were investigated.Transmission electron microscope examinations showed that M_(3)C carbides precipitated from supersat...The hardness and microstructure evolution of a 8%Cr cold work tool steel during tempering for 40 h were investigated.Transmission electron microscope examinations showed that M_(3)C carbides precipitated from supersaturated martensite after tempering at 350℃.When the tempering temperature was higher than 520℃,the M_(23)C_(6)carbides precipitated to substitute for M_(3)C carbides.After ageing at the temperature of 520℃for 40 h,it was observed that very fine and dense secondary Mo_(2)C precipitates were precipitated.Thus,it can be concluded that the early stage of Mo_(2)C-carbide precipitation is like to be Gunier-Preston(G-P)zone formed by[Mo-C]segregation group which is responsible for the secondary hardening peak at 520℃.Overageing at 700℃resulted in recovery of martensitic microstructure and precipitation of M_(23)C_(6)carbides.When ageing at 700℃for more than 20 h,recrystallization occurred,which resulted in a change of the matrix morphology from martensitic plates to equiaxed ferrite.It was noticed that the size of recrystallized grain/subgrain was very fine,which was attributed to the pinning effect of M_(23)C_(6)precipitates.展开更多
The effect of deep cryogenic treatment on the mechanical properties of 80CrMo 12 5 tool steel was investigated. Moreover, the effects of stabilization （holding at room temperature for some periods before deep cryogen...The effect of deep cryogenic treatment on the mechanical properties of 80CrMo 12 5 tool steel was investigated. Moreover, the effects of stabilization （holding at room temperature for some periods before deep cryogenic treatment） and tempering before deep cryogenic treatment were studied. The results show that deep cryogenic treatment can eliminate the retained austenite, making a better carbide distribu- tion and a higher carbide amount. As a result, a remarkable improvement in wear resistance of cryogenically treated specimens is observed. Moreover, the ultimate tensile strength increases, and the toughness of the sample decreases. It is also found that both stabilization and tem- pering before deep cryogenic treatment decrease the wear resistance, hardness, and carbides homogeneity compared to the deep cryogeni- cally treated samples. It is concluded that deep cryogenic treatment should be performed without any delay on samples after quenching to reach the highest wear resistance and hardness.展开更多
Both wear and crack due to heat checking in hot work tool steel are major failure modes.It is desirable to find amethod to lengthen the tool life while reducing manufacturing cost.This paper suggests a method to impro...Both wear and crack due to heat checking in hot work tool steel are major failure modes.It is desirable to find amethod to lengthen the tool life while reducing manufacturing cost.This paper suggests a method to improve toollife for hot work tool steel(SKD6)with crack by laser-melting process.The method has been evaluated using theimpact and fatigue test results.It is demonstrated that a repair of the crack by a laser-melting process is effectivefor life extension of the damaged tool.展开更多
AISI H13 （4Cr5MoSiV1） is one of the commonly used materials for extrusion tool, and it suffers from fatigue-creep damage during the hot extrusion process. Stress-controlled fatigue and creep-fatigue interaction test...AISI H13 （4Cr5MoSiV1） is one of the commonly used materials for extrusion tool, and it suffers from fatigue-creep damage during the hot extrusion process. Stress-controlled fatigue and creep-fatigue interaction tests were carried out at 500℃ to investigate its damage evolution. The accumulated plastic strain was selected to define the damage variable due to its clear physical meaning. A new fatigue-creep interaction damage model was proposed on the basis of continuum damage mechanics. A new equivalent impulse density for fatigue-creep tests was proposed to incorporate the holding time effect by transforming creep impulse density into fatigue impulse density. The experimental results indicated that the damage model is able to describe the damage evolution under these working conditions.展开更多
The characteristics and generation mechanism of（Ti,Nb,V）（C,N） precipitates larger than 2 μm in Nb-containing H13 bar steel were studied. The results show that two types of（Ti,Nb,V）（C,N） phases exist—a Ti-V-r...The characteristics and generation mechanism of（Ti,Nb,V）（C,N） precipitates larger than 2 μm in Nb-containing H13 bar steel were studied. The results show that two types of（Ti,Nb,V）（C,N） phases exist—a Ti-V-rich one and an Nb-rich one—in the form of single or complex precipitates. The sizes of the single Ti-V-rich（Ti,Nb,V）（C,N） precipitates are mostly within 5 to 10 μm, whereas the sizes of the single Nb-rich precipitates are mostly 2–5 μm. The complex precipitates are larger and contain an inner Ti-V-rich layer and an outer Nb-rich layer. The compositional distribution of（Ti,Nb,V）（C,N） is concentrated. The average composition of the single Ti-V-rich phase is（Ti_（0.511）V_（0.356）Nb_（0.133））（CxNy）, whereas that for the single Nb-rich phase is（Ti_（0.061）V_（0.263）Nb_（0.676））（C_xN_y）. The calculation results based on the Scheil–Gulliver model in the Thermo-Calc software combining with the thermal stability experiments show that the large phases precipitate during the solidification process. With the development of solidification, the Ti-V-rich phase precipitates first and becomes homogeneous during the subsequent temperature reduction and heat treatment processes. The Nb-rich phase appears later.展开更多
Single-edged notched tension （SENT） specimen is used to study the fatigue crack growth rate （FCGR） behavior of AISI 50100 steel using MTS 810. Calibration tests are run to get plots of crack mouth opening displace...Single-edged notched tension （SENT） specimen is used to study the fatigue crack growth rate （FCGR） behavior of AISI 50100 steel using MTS 810. Calibration tests are run to get plots of crack mouth opening displacement （CMOD） vs. load and CMOD vs. crack length-to-width ratio with the known crack lengths. Numerical simulation is also done to try to establish a relation between crack length and CMOD. FCGR of welded and un-welded specimens are plotted against stress intensity factor range to show the effect of welding on fatigue crack growth rate of AISI 50100 steel. The experimentally obtained CMOD values are compared with values obtained by numerical simulation using ABAQUS/StandardTM software package. Results show that numerical values are in good agreement with experimental data for small crack lengths and lower values of applied load,展开更多
Repair welding of cold-work tool steels in cold is very risky and almost impossible by conventional processes. The application of pulse shaping in laser cladding with wire to avoid the solidification problems in relev...Repair welding of cold-work tool steels in cold is very risky and almost impossible by conventional processes. The application of pulse shaping in laser cladding with wire to avoid the solidification problems in relevant steel is demonstrated. The results show that sound remelting and/or cladding can be achieved by the right selection of laser parameters and pulse shape, i.e. long pulse duration, moderate pulse peak powers and ramped-down pulse shape. Despite the defects and softening in the cladding due to the formation of retained austenite, the cladding shows better wear resistance at lower loads compared to the heat-treated base material.展开更多
The high cycle fatigue response of a high V-alloyed powder metallurgy tool steel （AISI 11） with different inclusion sizes was studied. Two materials of this grade at a similar hardness of about HRC 60 were subjected...The high cycle fatigue response of a high V-alloyed powder metallurgy tool steel （AISI 11） with different inclusion sizes was studied. Two materials of this grade at a similar hardness of about HRC 60 were subjected to axial loading fatigue tests, tensile tests and fracture toughness measurements to investigate their mechanical properties. Large inclusion above 70 ~rn is indicated to be responsible for the tensile fracture which happens before yielding. The fatigue strength obtained up to 107 cycles is found to decrease from approximately 1 538 MPa to 1000 MPa with the inclusion size increasing above 30 Izm. The internally induced crack initiation is mainly attributed to the surface compressive residual stress of 300-450 MPa. Fractographic evaluation demonstrates that the crack initiation and propagation controlling factors of the two materials are almost the same, indicating that the two factors would be insignificantly affected by the inclusion size level. Paris sizes of the two materials both show a tendency to decrease as the ratio of stress intensity factor of crack origin to factor of fish-eye increases. The investigation into the relationship between stress intensity factors and fatigue life of the two materials further indicates that the high cycle fatigue behavior of AISI 11 is controlled by crack propagation.展开更多
Laboratory-scale experiments were performed to investigate the deoxidation of H13 tool steel with CaF_(2)-MgO-Al_(2)O_(3)-CaO-SiO_(2) slags at 1873 K.The calculation of thermodynamics and kinetics was also verified th...Laboratory-scale experiments were performed to investigate the deoxidation of H13 tool steel with CaF_(2)-MgO-Al_(2)O_(3)-CaO-SiO_(2) slags at 1873 K.The calculation of thermodynamics and kinetics was also verified through the experimental results.The results show that[Si]-[O]reaction is the control reaction,and with the increase of basicity of slag,the limitation of deoxidation was decreased.The limitation of deoxidation is the lowest for the slag with basicity of 2.0.Under the conditions of the basicity of 2.0 and the content of CaF_(2) more than 50%,the limitation of deoxidation is less than 10×10^(−6),and it does not depend on the contents of Al_(2)O_(3) and CaF_(2) in slags.The mass transport of oxygen in the metal phase is the rate-controlling step,and the slag composition has no effect on the equilibrium time of deoxidation.Based on this finding,the optimized slag composition is designed and it contains the following components:51.5%CaF_(2),20.3%MgO,16.2%Al_(2)O_(3),8.2%CaO and 3.8%SiO_(2).In the case of the optimized deoxidizing slag,the total oxygen content in H13 steel can be reduced from 25×10^(−6) to 6×10^(−6).展开更多
TTT diagrams,CCT diagrams and critical points of steels H13,S7,S5 for annealing were measured and investigated by means of Formastor-Digital full-automatic phase transformation dilatometer in order to make their annea...TTT diagrams,CCT diagrams and critical points of steels H13,S7,S5 for annealing were measured and investigated by means of Formastor-Digital full-automatic phase transformation dilatometer in order to make their annealing technology reasonable and scientific.The basis is provided for making a new annealing technology scientifically.The new technology improves the quality of annealed materials,saves energy and increases productivity.展开更多
文摘The effect of niobium addition on the microstructure of cast AISI H13 hot work tool steel was evaluated by using EDX analyzer attached to the scanning electron microscope. The volume percent of eutectic area and eutectic cell size and also volume percent of different carbides of new steel, which is heat treated under different conditions, are also determined. The results show that the a niobium addition modifies the cast structure of Nb-alloyed hot work tool steel, and reduces the size and volume of eutectic cells, and increases the maximum hardness of the steel.
文摘The effects of heat treatment on the microstructure of modified cast high chromium high carbon AISI D3 steel were studied. The modified AISI D3 steel was developed by replacing part of chromium with niobium and titanium, in which chromium carbide was partially replaced with MC carbides. The cast samples produced by investment casting were heat treated under different conditions. The microstructures of the samples were studied by optical microscope and scanning electron microscope equipped with EDS analyzer. To determine the optimized homogenizing process, the effects of homogenizing treatment on the microstructure and the morphology of carbides were also studied. The results show that the MC carbides are not changed in shape and amounts during high temperature homogenizing, whereas the M3C carbides are reduced in amount and become semiglobular in shape, and the homogeneity of microstructure is improved.
基金financially supported by the National Key Technologies Research and Development Program of China (No. 2007BAE51B05)
文摘The fatigue strength of a high V alloyed powder metallurgy tool steel with two different inclusion size levels, tempered at different temperatures, was investigated by a series of high cycle fatigue tests. It was shown that brittle inclusions with large sizes above 30μm prompted the occurrence of subsurface crack initiation and the reduction in fatigue strength. The fracture toughness and the stress amplitude both exerted a significant influence on the fish-eye size. A larger fish-eye area would form in the sample with a higher fracture toughness subjected to a lower stress amplitude. The stress intensity factor of the inclusion was found to lie above a typical value of the threshold stress intensity factor of 4 MPa.m^1/2. The fracture toughness of the sample with a hardness above HRC 56 could be estimated by the mean value of the stress intensity factor of the fish-eye. According to fractographic evaluation, the critical inclusion size can be calculated by linear fracture mechanics.
文摘The characteristics of CrN coated martensitic H13 grade tool steels were studied. CrN coatings were depos- ited by the arc physical vapor deposition （PVD） before and after the pulse plasma nitriding of the samples. The PVD and plasma nitriding techniques were applied in relevant workshops by following the commercial practice parameters. Experimental results showed that CrN coating deposited on the nitrided surfaces exhibited superior scratch and wear resistances as compared to that deposited on the original martensitic surface.
基金This work was financially supported by the Research Fund for the Doctoral Program of High Education of China(No.20030561001)by the National Natural Science Foundation of China(Grant No.50371028).
文摘Low temperature composite chromizing is a process composed of a plain ion-carbonitriding or ion-nitriding at 550-580℃,followed by a low-temperature chromizing in a salt-bath of 590℃.The microstructure and properties of the low temperature composite chromized layer on H13 tool steel were investigated using metallography,X-ray diffraction,microanalysis,hardness and wear tests.It was found that this low temperature process was thermo-dynamically and kinetically possible,and the composite chromized layer on H13 steel,with a thickness of 3-6μm,consisted of three sub-layers(bands),viz.the outer Cr-rich one,the intermediate(black)one,and the inner,original white layer.After chromizing,the former diffusion layer was thickened.The results of X-ray diffraction showed that the composite chromized layer contained such nitrides and carbides of chromium as CrN,Cr2N,(Cr,Fe)23C6,and(Cr,Fe)7C3,as well as plainα-(Fe,Cr).A high surface microhardness of 1450-1550 HV0.025,which is much higher than that obtained by the conventional ion carbonitriding and ion nitriding,was obtained.In addition,an excellent wear resistance was gained on the composite chromized layer.
基金the Directorate of Higher Education, Indonesian Government and to the Institut Teknologi Nasional (Itenas), Bandung, Indonesia for their financial support
文摘The microstructure and the stability of carbides after heat treatments in an H23 tool steel were investigated. The heat treatments consisted of austenization at two different austenizing temperatures （1100℃ and 1250℃）, followed by water quenching and double-aging at 650℃, 750℃, and 800℃with air cooling between the first and second aging treatments. Martensite did not form in the as-quenched micro- structures, which consisted of a ferrite matrix, M6C, M7C3, and MC carbides. The double-aged microstructures consisted of a ferrite matrix and MC, M6C, M7C3, and M23C6 carbides. Secondary hardening as a consequence of secondary precipitation of fine M2C carbides did not occur. There was disagreement between the experimental microstructure and the results of thermodynamic calculations. The highest double-aged hardness of the H23 tool steel was 448 HV after austenization at 1250℃ and double-aging at 650℃, which suggested that this tool steel should be used at temperatures below 650℃.
基金support of the Korea Institute of Industrial Technology as a project on the development of metal 3D printing materials and process optimization technology for medium-and large-sized transportation part mold manufacturing(KITECH JE200008)。
文摘Wire+arc additive manufacturing(WAAM)is considered an innovative technology that can change the manufacturing landscape in the near future.WAAM offers the benefits of inexpensive initial system setup and a high deposition rate for fabricating medium-and large-sized parts such as die-casting tools.In this study,AISI H13 tool steel,a popular die-casting tool metal,is manufactured by cold metal transfer(CMT)-based WAAM and is then comprehensively analyzed for its microstructural and mechanical properties.Location-dependent phase combinations are observed,which could be explained by nonequilibrium thermal cycles that resulted from the layer-by-layer stacking mechanism used in WAAM.In addition,remelting and reheating of the layers reduces welding anomalies(e.g.,pores and voids).The metallurgical characteristics of the H13 strongly correlate with the mechanical properties.The combinations of phases at different locations of the additively manufactured part exhibit a periodic microhardness profile.Martensite,Retained Austenite,Ferrite,and Carbide phases are found in combination at different locations of the part based on the part’s temperature distribution during additive deposition.Moreover,the tensile properties at elevated temperatures(23℃,300℃,and 600℃)are comparable to those from other WAAM and additive manufacturing(AM)processes.The X-ray diffraction results verify that the microstructural stability of the fabricated parts at high temperatures would allow them to be used in high temperatures.
基金supported by the National Natural Science Foundation of China(Nos.50621091,50701044and 50890171)the Ministry of Science and Technology(No.2005CB623604)the National High Technology Research and Development Program of China(No.2007AA03Z352)
文摘A nanostructured surface layer has been fabricated on an AISI H13 tool steel by means of surface mechanical attrition treatment(SMAT).Strain-induced refinement processes of ferrite grains and carbide particles have been investigated by transmission electron microscopy(TEM)and scanning electron microscopy(SEM)in the SMAT surface layer.Grain refinement of ferrite is found to be dominated by dislocation activities and greatly facilitated by a large number of carbide particles at a depth〉20μm.The comparisons with microstructure refinement processes in other SMAT ferrite steels indicate that a larger volume fraction of carbide particles with a lower shear strength is expected to facilitate the refinement process of ferrite grains.
文摘The effect of deep cryogenic treatment on the microstructure, hardness, and wear behavior of D2 tool steel was studied by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray diffraction （XRD）, hardness test, pin-on-disk wear test, and the reciprocating pin-on-fiat wear test. The results show that deep cryogenic treatment eliminates retained austenite, makes a better carbide distribution, and increases the carbide content. Furthermore, some new nano-sized carbides form during the deep cryogenic treatment, thereby increasing the hardness and improving the wear behavior of the samples.
基金financial supports provided by the China Scholarship Council(Nos.202206 290061 and 202206290062)。
文摘The laser powder bed fusion(LPBF) process can integrally form geometrically complex and high-performance metallic parts that have attracted much interest,especially in the molds industry.The appearance of the LPBF makes it possible to design and produce complex conformal cooling channel systems in molds.Thus,LPBF-processed tool steels have attracted more and more attention.The complex thermal history in the LPBF process makes the microstructural characteristics and properties different from those of conventional manufactured tool steels.This paper provides an overview of LPBF-processed tool steels by describing the physical phenomena,the microstructural characteristics,and the mechanical/thermal properties,including tensile properties,wear resistance,and thermal properties.The microstructural characteristics are presented through a multiscale perspective,ranging from densification,meso-structure,microstructure,substructure in grains,to nanoprecipitates.Finally,a summary of tool steels and their challenges and outlooks are introduced.
基金Item Sponsored by National Key Technologies Research and Development Program of China(2007BAE510B04)
文摘The hardness and microstructure evolution of a 8%Cr cold work tool steel during tempering for 40 h were investigated.Transmission electron microscope examinations showed that M_(3)C carbides precipitated from supersaturated martensite after tempering at 350℃.When the tempering temperature was higher than 520℃,the M_(23)C_(6)carbides precipitated to substitute for M_(3)C carbides.After ageing at the temperature of 520℃for 40 h,it was observed that very fine and dense secondary Mo_(2)C precipitates were precipitated.Thus,it can be concluded that the early stage of Mo_(2)C-carbide precipitation is like to be Gunier-Preston(G-P)zone formed by[Mo-C]segregation group which is responsible for the secondary hardening peak at 520℃.Overageing at 700℃resulted in recovery of martensitic microstructure and precipitation of M_(23)C_(6)carbides.When ageing at 700℃for more than 20 h,recrystallization occurred,which resulted in a change of the matrix morphology from martensitic plates to equiaxed ferrite.It was noticed that the size of recrystallized grain/subgrain was very fine,which was attributed to the pinning effect of M_(23)C_(6)precipitates.
文摘The effect of deep cryogenic treatment on the mechanical properties of 80CrMo 12 5 tool steel was investigated. Moreover, the effects of stabilization （holding at room temperature for some periods before deep cryogenic treatment） and tempering before deep cryogenic treatment were studied. The results show that deep cryogenic treatment can eliminate the retained austenite, making a better carbide distribu- tion and a higher carbide amount. As a result, a remarkable improvement in wear resistance of cryogenically treated specimens is observed. Moreover, the ultimate tensile strength increases, and the toughness of the sample decreases. It is also found that both stabilization and tem- pering before deep cryogenic treatment decrease the wear resistance, hardness, and carbides homogeneity compared to the deep cryogeni- cally treated samples. It is concluded that deep cryogenic treatment should be performed without any delay on samples after quenching to reach the highest wear resistance and hardness.
文摘Both wear and crack due to heat checking in hot work tool steel are major failure modes.It is desirable to find amethod to lengthen the tool life while reducing manufacturing cost.This paper suggests a method to improve toollife for hot work tool steel(SKD6)with crack by laser-melting process.The method has been evaluated using theimpact and fatigue test results.It is demonstrated that a repair of the crack by a laser-melting process is effectivefor life extension of the damaged tool.
文摘AISI H13 （4Cr5MoSiV1） is one of the commonly used materials for extrusion tool, and it suffers from fatigue-creep damage during the hot extrusion process. Stress-controlled fatigue and creep-fatigue interaction tests were carried out at 500℃ to investigate its damage evolution. The accumulated plastic strain was selected to define the damage variable due to its clear physical meaning. A new fatigue-creep interaction damage model was proposed on the basis of continuum damage mechanics. A new equivalent impulse density for fatigue-creep tests was proposed to incorporate the holding time effect by transforming creep impulse density into fatigue impulse density. The experimental results indicated that the damage model is able to describe the damage evolution under these working conditions.
文摘The characteristics and generation mechanism of（Ti,Nb,V）（C,N） precipitates larger than 2 μm in Nb-containing H13 bar steel were studied. The results show that two types of（Ti,Nb,V）（C,N） phases exist—a Ti-V-rich one and an Nb-rich one—in the form of single or complex precipitates. The sizes of the single Ti-V-rich（Ti,Nb,V）（C,N） precipitates are mostly within 5 to 10 μm, whereas the sizes of the single Nb-rich precipitates are mostly 2–5 μm. The complex precipitates are larger and contain an inner Ti-V-rich layer and an outer Nb-rich layer. The compositional distribution of（Ti,Nb,V）（C,N） is concentrated. The average composition of the single Ti-V-rich phase is（Ti_（0.511）V_（0.356）Nb_（0.133））（CxNy）, whereas that for the single Nb-rich phase is（Ti_（0.061）V_（0.263）Nb_（0.676））（C_xN_y）. The calculation results based on the Scheil–Gulliver model in the Thermo-Calc software combining with the thermal stability experiments show that the large phases precipitate during the solidification process. With the development of solidification, the Ti-V-rich phase precipitates first and becomes homogeneous during the subsequent temperature reduction and heat treatment processes. The Nb-rich phase appears later.
基金supported by University of Engineering and Technology, Taxila
文摘Single-edged notched tension （SENT） specimen is used to study the fatigue crack growth rate （FCGR） behavior of AISI 50100 steel using MTS 810. Calibration tests are run to get plots of crack mouth opening displacement （CMOD） vs. load and CMOD vs. crack length-to-width ratio with the known crack lengths. Numerical simulation is also done to try to establish a relation between crack length and CMOD. FCGR of welded and un-welded specimens are plotted against stress intensity factor range to show the effect of welding on fatigue crack growth rate of AISI 50100 steel. The experimentally obtained CMOD values are compared with values obtained by numerical simulation using ABAQUS/StandardTM software package. Results show that numerical values are in good agreement with experimental data for small crack lengths and lower values of applied load,
文摘Repair welding of cold-work tool steels in cold is very risky and almost impossible by conventional processes. The application of pulse shaping in laser cladding with wire to avoid the solidification problems in relevant steel is demonstrated. The results show that sound remelting and/or cladding can be achieved by the right selection of laser parameters and pulse shape, i.e. long pulse duration, moderate pulse peak powers and ramped-down pulse shape. Despite the defects and softening in the cladding due to the formation of retained austenite, the cladding shows better wear resistance at lower loads compared to the heat-treated base material.
基金Project(2007BAE51B05)supported by the National Key Technologies Research and Development Program of China
文摘The high cycle fatigue response of a high V-alloyed powder metallurgy tool steel （AISI 11） with different inclusion sizes was studied. Two materials of this grade at a similar hardness of about HRC 60 were subjected to axial loading fatigue tests, tensile tests and fracture toughness measurements to investigate their mechanical properties. Large inclusion above 70 ~rn is indicated to be responsible for the tensile fracture which happens before yielding. The fatigue strength obtained up to 107 cycles is found to decrease from approximately 1 538 MPa to 1000 MPa with the inclusion size increasing above 30 Izm. The internally induced crack initiation is mainly attributed to the surface compressive residual stress of 300-450 MPa. Fractographic evaluation demonstrates that the crack initiation and propagation controlling factors of the two materials are almost the same, indicating that the two factors would be insignificantly affected by the inclusion size level. Paris sizes of the two materials both show a tendency to decrease as the ratio of stress intensity factor of crack origin to factor of fish-eye increases. The investigation into the relationship between stress intensity factors and fatigue life of the two materials further indicates that the high cycle fatigue behavior of AISI 11 is controlled by crack propagation.
基金Project(18SYXHZ0069)supported by the Science and Technology Program of Sichuan Province,ChinaProjects(51974139,51664021)supported by the National Natural Science Foundation of China。
文摘Laboratory-scale experiments were performed to investigate the deoxidation of H13 tool steel with CaF_(2)-MgO-Al_(2)O_(3)-CaO-SiO_(2) slags at 1873 K.The calculation of thermodynamics and kinetics was also verified through the experimental results.The results show that[Si]-[O]reaction is the control reaction,and with the increase of basicity of slag,the limitation of deoxidation was decreased.The limitation of deoxidation is the lowest for the slag with basicity of 2.0.Under the conditions of the basicity of 2.0 and the content of CaF_(2) more than 50%,the limitation of deoxidation is less than 10×10^(−6),and it does not depend on the contents of Al_(2)O_(3) and CaF_(2) in slags.The mass transport of oxygen in the metal phase is the rate-controlling step,and the slag composition has no effect on the equilibrium time of deoxidation.Based on this finding,the optimized slag composition is designed and it contains the following components:51.5%CaF_(2),20.3%MgO,16.2%Al_(2)O_(3),8.2%CaO and 3.8%SiO_(2).In the case of the optimized deoxidizing slag,the total oxygen content in H13 steel can be reduced from 25×10^(−6) to 6×10^(−6).
基金Item Sponsored by Provincial Natural Science Foundation of Inner Mongolia of China(9610E22)
文摘TTT diagrams,CCT diagrams and critical points of steels H13,S7,S5 for annealing were measured and investigated by means of Formastor-Digital full-automatic phase transformation dilatometer in order to make their annealing technology reasonable and scientific.The basis is provided for making a new annealing technology scientifically.The new technology improves the quality of annealed materials,saves energy and increases productivity.
