The understanding of oxidation behaviors on H13 steel was helpful to improve the service life and performance of hot work moulds and dies. Thermal-Calc Software was performed to calculate the oxidation phases on H13 s...The understanding of oxidation behaviors on H13 steel was helpful to improve the service life and performance of hot work moulds and dies. Thermal-Calc Software was performed to calculate the oxidation phases on H13 steel along with different partial oxygen pressures in the interesting temperature range of 500-700 ℃. In this range H13 steel samples were treated respectively in different atmosphere including flowing water vapor (0.2 MPa), normal pressure air (0.1 MPa) and low pressure air (0.001 MPa). The different oxidation films were detected with optical microscopy and X-ray diffraction. The microstructures and phase constitutions of the films formed in low pressure air were similar to those of the films formed in water vapor, and obviously different to those of the films formed in normal pressure air. The oxidation mechanisms of H13 steel in different atmosphere were also discussed.展开更多
Thermal fatigue test has been carried out on widely used hot work steel 4Cr5MoSiV1and a low alloyed steel 3Cr3MoV in temperature range of 200to 700℃.Tempering resistance,as well as high temperature hardness/strength ...Thermal fatigue test has been carried out on widely used hot work steel 4Cr5MoSiV1and a low alloyed steel 3Cr3MoV in temperature range of 200to 700℃.Tempering resistance,as well as high temperature hardness/strength of steel specimens,works as a dominating material parameter on thermal fatigue resistance.During the heating period,high hardness can depress the inelastic deformation.This deformation is the origination of tensile stress,which acts as the driving force of heat checking during the cooling period.The cyclic strain-oxidation interaction can speed up the damage on surface defects,which plays an obvious role in initiation of thermal cracks.On4Cr5MoSiV1steel specimens,borders between the matrix and inclusions such as titanium compounds,or lager carbides such as primary carbides,are focused by strain and attacked by oxidation,and are main initiating places of cracks.While on 3Cr3MoV steel specimens,larger strain causes plastic deformation concentrating around grain boundaries.Then the following oxidation accelerates this grain boundary damage and creates cracks.展开更多
A new hot-work die steel for hot stamping was developed, and used the die for mass production. The produced die showed good performance owing to its high heat conductivity and wear-resistant characteristics. Two diffe...A new hot-work die steel for hot stamping was developed, and used the die for mass production. The produced die showed good performance owing to its high heat conductivity and wear-resistant characteristics. Two different benchmarking hot-work die steels were investigated, and then compared in terms of their impact ductility,temper characteristics, heat conductivity, and thermal stability. The result of the high-temperature friction wear test indicated that oxidative wear was the main mode in high temperature. On the basis of the comparison and test results, the alloying composition of the new hot-work die steel was especially designed. The new die steel showed good performance with good wear-resistant quality, as well as temper hardness and heat conductivity of HRC 50 and34.3 W/(m·K), respectively. Furthermore,without surface plasma nitriding, the die made of the new steel had no obvious galling with 6142 strokes. After surface plasma nitriding, the die completed 40000 strokes with good surface. The die life is expected to exceed 200000 strokes.展开更多
The restoration mechanisms for static recrystallization of work-hardened austenite were investigated by using double-pass compression tests performed on medium-carbon steel containing chromium and molybdenum. The soft...The restoration mechanisms for static recrystallization of work-hardened austenite were investigated by using double-pass compression tests performed on medium-carbon steel containing chromium and molybdenum. The softening fraction was defined by 2% offset method. The results show that Avrami exponent of about 0.21 is insensitive to deformation temperature, indicating that the action of steel grade should be considered. The time of 50% recrystallization (t0.5) decreases noteworthily with the increase of deformation temperature. Apparent activation energy for static recrystallization of 195 kJ/mol, which is close to that of vanadium microalloyed steel, is obtained by calculating. The increasing trend of the driving force for recrystallization is opposite to that of the deformation temperature, which is attributed to the number of operative slip system increasing as temperature increasing.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 V4C3, which are two kinds of important car...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 V4C3, 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 Mo2C and V4C3 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
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, bo...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
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 steels5CrNiMo and 5Cr2NiMoVSi were studied under strain controlled low-cycle fatigue.The re-sults show that the cyclic softening i...The characteristics and microstructural changes of cyclic softening in hot-working die steels5CrNiMo 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 conditionsunder the strain controlled amplitude range of Δε<sub>t</sub>/2=0.6-1.8×10<sup>-2</sup>.The softening effectmainly occurs in some initial cycles and the stress amplitude varies slightly in the sequentialcycles,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 softeningis related to heterogenity of plastic deformation.The softening of the tested steels is caused bythe formation of the dislocation cell structure with low density and low internal stress,and bythe fragmentation and redissolution of fine carbides into matrix.展开更多
H13 hot work steel samples and surface water vapor oxidized H13 samples were immersed into molten ADC 12 alloy under static resting or dynamic rotating conditions. Weigh-losing method was used to discover the influenc...H13 hot work steel samples and surface water vapor oxidized H13 samples were immersed into molten ADC 12 alloy under static resting or dynamic rotating conditions. Weigh-losing method was used to discover the influences of temperature, time and surface conditions on the erosion resistance of H13 steel. The interfaces between the steel and the molten alloy were studied with optical microscopy to compare the different erosion resistance behaviours. The results show that the composite layer outside of the compounds layers changes obviously with increasing temperature, lasting time or sample movement. The better erosion resistance of H13 steel can be endowed with the oxide films, which would gradually decrease along with the dissolve of the films.展开更多
A hot-working AISI H13 tool steel was subjected to a combined process consisting of surface nanocrystallization(SNC)and chromizing treatment successively.The composition,microstructure,hardness and wear resistance of ...A hot-working AISI H13 tool steel was subjected to a combined process consisting of surface nanocrystallization(SNC)and chromizing treatment successively.The composition,microstructure,hardness and wear resistance of the chromized layer were characterized by using the scanning and transmission electron microscopy,a nano-indenter and a tribo-meter.It was shown that a continuous chromized layer of approximately 30 μm in thickness was formed on the SNC specimen after a dual chromizing treatment at both 600℃ and 1050℃ consecutively,as thick as about 3 times of that on the coarse-grained specimen after the same chromizing treatment.In addition,the wear resistance of the SNC-chromized specimen was enhanced significantly,due to a smaller grain size and a higher hardness,as well as smoother gradient variations of the microstructure,composition and hardness across a greater depth in the formed chromized surface layer.展开更多
基金ItemSponsored by Science and Technology Development Fund of Shanghai Municipality (015211010)ASSABTooling Technology (Shanghai) Co Ltd
文摘The understanding of oxidation behaviors on H13 steel was helpful to improve the service life and performance of hot work moulds and dies. Thermal-Calc Software was performed to calculate the oxidation phases on H13 steel along with different partial oxygen pressures in the interesting temperature range of 500-700 ℃. In this range H13 steel samples were treated respectively in different atmosphere including flowing water vapor (0.2 MPa), normal pressure air (0.1 MPa) and low pressure air (0.001 MPa). The different oxidation films were detected with optical microscopy and X-ray diffraction. The microstructures and phase constitutions of the films formed in low pressure air were similar to those of the films formed in water vapor, and obviously different to those of the films formed in normal pressure air. The oxidation mechanisms of H13 steel in different atmosphere were also discussed.
基金Sponsored by National Key Technology Research and Development Program in 11th Five-Year Plan of China(2007BAE51B04)funded by the Chinese Scholarship Committee(CSC)under document No.20093004
文摘Thermal fatigue test has been carried out on widely used hot work steel 4Cr5MoSiV1and a low alloyed steel 3Cr3MoV in temperature range of 200to 700℃.Tempering resistance,as well as high temperature hardness/strength of steel specimens,works as a dominating material parameter on thermal fatigue resistance.During the heating period,high hardness can depress the inelastic deformation.This deformation is the origination of tensile stress,which acts as the driving force of heat checking during the cooling period.The cyclic strain-oxidation interaction can speed up the damage on surface defects,which plays an obvious role in initiation of thermal cracks.On4Cr5MoSiV1steel specimens,borders between the matrix and inclusions such as titanium compounds,or lager carbides such as primary carbides,are focused by strain and attacked by oxidation,and are main initiating places of cracks.While on 3Cr3MoV steel specimens,larger strain causes plastic deformation concentrating around grain boundaries.Then the following oxidation accelerates this grain boundary damage and creates cracks.
文摘A new hot-work die steel for hot stamping was developed, and used the die for mass production. The produced die showed good performance owing to its high heat conductivity and wear-resistant characteristics. Two different benchmarking hot-work die steels were investigated, and then compared in terms of their impact ductility,temper characteristics, heat conductivity, and thermal stability. The result of the high-temperature friction wear test indicated that oxidative wear was the main mode in high temperature. On the basis of the comparison and test results, the alloying composition of the new hot-work die steel was especially designed. The new die steel showed good performance with good wear-resistant quality, as well as temper hardness and heat conductivity of HRC 50 and34.3 W/(m·K), respectively. Furthermore,without surface plasma nitriding, the die made of the new steel had no obvious galling with 6142 strokes. After surface plasma nitriding, the die completed 40000 strokes with good surface. The die life is expected to exceed 200000 strokes.
文摘The restoration mechanisms for static recrystallization of work-hardened austenite were investigated by using double-pass compression tests performed on medium-carbon steel containing chromium and molybdenum. The softening fraction was defined by 2% offset method. The results show that Avrami exponent of about 0.21 is insensitive to deformation temperature, indicating that the action of steel grade should be considered. The time of 50% recrystallization (t0.5) decreases noteworthily with the increase of deformation temperature. Apparent activation energy for static recrystallization of 195 kJ/mol, which is close to that of vanadium microalloyed steel, is obtained by calculating. The increasing trend of the driving force for recrystallization is opposite to that of the deformation temperature, which is attributed to the number of operative slip system increasing as temperature increasing.
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 V4C3, 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 Mo2C and V4C3 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.
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.
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 steels5CrNiMo 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 conditionsunder the strain controlled amplitude range of Δε<sub>t</sub>/2=0.6-1.8×10<sup>-2</sup>.The softening effectmainly occurs in some initial cycles and the stress amplitude varies slightly in the sequentialcycles,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 softeningis related to heterogenity of plastic deformation.The softening of the tested steels is caused bythe formation of the dislocation cell structure with low density and low internal stress,and bythe fragmentation and redissolution of fine carbides into matrix.
基金support of Shanghai Science and Technology Development Fund.
文摘H13 hot work steel samples and surface water vapor oxidized H13 samples were immersed into molten ADC 12 alloy under static resting or dynamic rotating conditions. Weigh-losing method was used to discover the influences of temperature, time and surface conditions on the erosion resistance of H13 steel. The interfaces between the steel and the molten alloy were studied with optical microscopy to compare the different erosion resistance behaviours. The results show that the composite layer outside of the compounds layers changes obviously with increasing temperature, lasting time or sample movement. The better erosion resistance of H13 steel can be endowed with the oxide films, which would gradually decrease along with the dissolve of the films.
基金supported by the National High-Tech.R&D Program(the National 863 plans projects,Grant No.2007AA03Z352)the National Science Foundation of China(Grant No.50701044 and 50890171)
文摘A hot-working AISI H13 tool steel was subjected to a combined process consisting of surface nanocrystallization(SNC)and chromizing treatment successively.The composition,microstructure,hardness and wear resistance of the chromized layer were characterized by using the scanning and transmission electron microscopy,a nano-indenter and a tribo-meter.It was shown that a continuous chromized layer of approximately 30 μm in thickness was formed on the SNC specimen after a dual chromizing treatment at both 600℃ and 1050℃ consecutively,as thick as about 3 times of that on the coarse-grained specimen after the same chromizing treatment.In addition,the wear resistance of the SNC-chromized specimen was enhanced significantly,due to a smaller grain size and a higher hardness,as well as smoother gradient variations of the microstructure,composition and hardness across a greater depth in the formed chromized surface layer.
