The effects of austenitizing temperature(1223,1303,and 1373 K)and holding time(1-1500 s)on the microstructure,mechanical properties,and precipitation behavior of the H13 hot work die steel were investigated.The result...The effects of austenitizing temperature(1223,1303,and 1373 K)and holding time(1-1500 s)on the microstructure,mechanical properties,and precipitation behavior of the H13 hot work die steel were investigated.The results indicate a softening phenomenon when H13 steel is austenitized at 1303 K beyond 900 s and 1373 K beyond 600 s,respectively.For the sample held for 1200 s,the tensile strength is found capable of reaching up to 2.2 GPa when quenched from a temperature above 1303 K.Meanwhile,prior-austenite grain size increases with the increase in austenitizing temperature.The kinetic behavior of the precipitates(mainly MC-type carbides)in H13 steel could be elaborated through the principles set forth by the Arrhenius and Avrami equations.Finally,the comprehensive strengthening of the H13 steel was discussed in detail.The results show that the activation energy of the transformed fraction of carbides is higher than that of the diffusion process for common alloying elements(Cr,V,Mo,and Ni)found in the austenite.This suggests that it would be difficult for precipitates to dissolve into the matrix when H13 steel is austenitized at high temperatures.With the increasing austenitizing temperature,the precipitation fraction decreases,and the dislocation density increases.The dislocation strengthening is regarded as the dominant strengthening contributed to yield strength in as-quenched H13 steel.展开更多
SA508Gr.4 N steel is commonly used in nuclear pressure vessels. The current study discloses the impact of austenitizing temperature on its martensitic transformation. Various austenitizing temperatures were employed t...SA508Gr.4 N steel is commonly used in nuclear pressure vessels. The current study discloses the impact of austenitizing temperature on its martensitic transformation. Various austenitizing temperatures were employed to examine the martensitic transformation at different experimental conditions. The characteristics of grain boundaries, microstructure, transformation kinetics, and crystallography of the martensitic phase following the austenitizing process and martensitic transformation were analyzed. Austenitizing temperatures had minimal effects on the critical temperature of the austenitizing phase transition. However, an increase in austenitizing temperature resulted in larger grain sizes. The phase composition primarily consisted of lath martensite, accompanied by a small amount of residual austenite (RA). As the austenitizing temperature increased, the temperature of martensite-start temperature (Ms) initially decreased and then increased. On the other hand, the temperature of martensite-finish (Mf) showed no significant sensitivity to changes in the austenitizing temperature. Moreover, the average size of the lath martensite structure was increased, and there was an increased tendency for variant selection as the austenitizing temperature increased, and the combination of specific orientation relationships appeared. This study is very valuable for revealing the microstructure evolution at different temperatures.展开更多
To address the inhomogeneous microstructure and improve the mechanical properties of DT300 ultra-high strength steel specimens fabricated by laser powder bed fusion,different post-heat treatment schedules are performe...To address the inhomogeneous microstructure and improve the mechanical properties of DT300 ultra-high strength steel specimens fabricated by laser powder bed fusion,different post-heat treatment schedules are performed.With the increase in austenitizing temperature and time,the migration rate of austenite grain boundaries continuously increases with the dissolution of nano-carbides,and the formation of nano-oxides and twin martensite is also inhibited accordingly.The rapid growth in the size of prior austenite grains and martensite laths,as well as the decrease in the content of nano-oxides and twin martensite,led to a rapid decrease in the strength(yield strength and ultimate tensile strength)from HT2 to HTF specimens.The HT1 specimens(austenitizing at 830℃for 30 min,then oil quenching and tempering at 300℃for 120 min and finally air cooling)display excellent mechanical properties of yield strength of 1572 MPa,ultimate tensile strength of 1847 MPa,elongation of 9.84%,and fracture toughness of 106 MPa m^(1/2),which are counterparts to those of conventional DT300 steel forgings after heat treatment.展开更多
The influence of austenitizing temperature on the microstructure and corrosion resistance of 55Cr18MolVN high-nitrogen plastic mould steel was investigated. The microstructure, elemental distribution and Cr-depleted z...The influence of austenitizing temperature on the microstructure and corrosion resistance of 55Cr18MolVN high-nitrogen plastic mould steel was investigated. The microstructure, elemental distribution and Cr-depleted zone of different heat-treated samples were investigated by X-ray diffraction, electron probe microanalyzer analysis, and trans- mission electron microscopy. The corrosion resistance was evaluated using electrochemical measurements, and the analysis of passive film was carded out by X-ray photoelectron spectroscopy. The results indicated that the volume fraction of precipitates decreased, and the homogeneity of elements was improved with increasing austenitizing temperature. The degree of Cr-depleted zone around coarse M23C6 was severer than that around M2N, and pitting corrosion initiated preferentially around M23C6. The corrosion resistance of the samples increased with the austenitizing temperature. With the increase in austenitizing temperature, the passive film was thickened and Cr（III）cr2O3 in the inner layer of passive film was enriched, which enhanced the corrosion resistance of the steel. The higher content of nitrogen in solid solution at higher austenitizing temperature contributed to the increased intensity of CrN and NH3, leading to the increase in pH value in the pit, and promoting the repassivation of 55Cr18Mo1N steel.展开更多
The microsturctural transformation of austenite grain, pearlite interlamellar spacing, and lamellar cement ite thickness of spring steel 60Si2MnA for railway were studied in the hot-rolled and reheated states. Further...The microsturctural transformation of austenite grain, pearlite interlamellar spacing, and lamellar cement ite thickness of spring steel 60Si2MnA for railway were studied in the hot-rolled and reheated states. Furthermore, the effect of microstructural characterization on its final mechanical properties was discussed. The results showed that as far as 60Si2MnA, the pearlite interlamellar spacing determined the hardness, whereas, the austenite grain determined the toughness. Compared with microstructure and mechanical properties in the hot rolled state, after reheating treatment at 950 ℃, its average grain sizes are apparently fine and the pearlite interlamellar spacing and lamellar cementite thickness coarsen to some extent, but both hardness and impact toughness increase to HRC 48 and 8.5 J, respectively. In the course of making spring, the optimum reheating austenitizing temperature for the 60Si2MnA steel is 950 ℃.展开更多
By continuous quenching process, the effect of austenitizing temperature and time on the structure and hardness of bainiteductile cast iron was studied. It was found that (l) low austenitizing temperature would result...By continuous quenching process, the effect of austenitizing temperature and time on the structure and hardness of bainiteductile cast iron was studied. It was found that (l) low austenitizing temperature would result in scrap ferrite existing in matrix, whichreduces the macro-hardness of bainite ductile cast iron; (2) high austenitizing temperature would make carbide decomposed, which alsoinduces the macro-hardness of bainite cast iron, and (3) austenitizing time has little effect on the structure of bainite ductile cast iron, butas it increases, the macro-hardness ofbainite ductile cast iron and micro-hardness of bainite increases. To the ductile cast iron, as a result,the suitable austenitizing temperature and time are recommended as 880 and 120 min respectively.展开更多
The effect of austenitizing temperature on segregation of impurities along grain boundaries in steel 4330M has been examined by AES.The impurity segregation was computed quantitatively.Results showed that the quantity...The effect of austenitizing temperature on segregation of impurities along grain boundaries in steel 4330M has been examined by AES.The impurity segregation was computed quantitatively.Results showed that the quantity of impurity segregation changed with the austenitizing temperature.The limitation of the McLean′s expression for equilibrium segrega- tion was discussed.展开更多
The change of inclusions and microstructure of 16Mn steel treated by Ce were observed,and the effect of austenitizing temperature on the microstructure was also examined.The results show that the inclusions are transf...The change of inclusions and microstructure of 16Mn steel treated by Ce were observed,and the effect of austenitizing temperature on the microstructure was also examined.The results show that the inclusions are transformed from Si-Mn-Al composite oxide and MnS into AlCeO3,Ce2O2S,and MnS composite inclusions after being treated by Ce.Plenty of intragranular ferrites are formed in 16Mn steel containing～0.017wt% Ce.A large amount of intragranular acicular ferrites are formed after being austenitized for 20min at 1473 K.The prior austenite grain size fit for the formation of intragranular acicular ferrites is about 120μm.展开更多
Microstructural evolution of GCr15 steels with different C and Cr contents during austenitizing and quenching was studied. Thermodynamic analysis of cementite dissolution was implied to obtain the critical temperature...Microstructural evolution of GCr15 steels with different C and Cr contents during austenitizing and quenching was studied. Thermodynamic analysis of cementite dissolution was implied to obtain the critical temperature. The coordination number x in Fe_xCr_(3-x)C and the volume fraction of undissolved cementite were computed according to element conservation and equilibrium phase diagram. The M_S(martensite transformation temperature) was calculated by using empirical formula. The retained austenite content was calculated with further consideration of quenching temperature. The results showed that the coordination number and the undissolved cementite content were promoted by the austenitizing temperature and carbon content of the steel. Increasing Cr element reduced the coordination number.GCr15 steels with different components had nearly the same M_S when austenitization at 830 °C to 860 °C. The interaction of C and Cr complicated the evolution of M_S and retained austenite content. The results were in good agreement with the literature, which could guide to obtain specified retained austenite and/or carbides.展开更多
The Fe-0.21C 2.2Mn 0.49Si-1.77A1 transformation induced plasticity （TRIP） aided steel was heat trea- ted at various austenitizing temperatures under both TRiP-aided polygonal ferrite type （TPF） and an- nealed mart...The Fe-0.21C 2.2Mn 0.49Si-1.77A1 transformation induced plasticity （TRIP） aided steel was heat trea- ted at various austenitizing temperatures under both TRiP-aided polygonal ferrite type （TPF） and an- nealed martensite matrix （TAM） processes. The microstructure evolution and their effects on mechanical properties were systematically investigated through the microstructure observation and dilatometric analysis. The microstructure homogeneity is improved in TPF steel heated at a high temperature due to the reduced banded martensite and the increased bainite. Compared with the mechanical properties of the TPF steels, the yield strength and elongation of the TAM steels are much higher, while the tensile strength is lower than that of TPF steels. The stability of intercritical austenite is affected by the heating tempera- ture, and thus the following phase transformation influences the mechanical properties, such as the bain- ite transformation and the precipitation of polygonal ferrite. Obvious dynamic bainite transformation occurs at TAM850, TAM900 and TAM950, More proportion of polygonal ferrite is found in the sample heated at 950 ℃. The bainite transformation beginning at a higher temperature results in the wider bainitic ferrite laths. The more proportion of polygonal ferrite and wide bainitic ferrite laths commonly contribute to the lower strength and better elongation. The uniform microstructure with lath-like morphology and retained austenite with high average carbon content ensures a good mechanical property in TAM850 with the product of strength and elongation of about 28 GPa ·%,展开更多
This investigation studies the impact strength, tensile strength, hardness, and wear behavior of thin wall austempered and intercritically austempered ductile iron samples with a chemical composition of 3.37% C, 2.7% ...This investigation studies the impact strength, tensile strength, hardness, and wear behavior of thin wall austempered and intercritically austempered ductile iron samples with a chemical composition of 3.37% C, 2.7% Si, 0.30% Mn, 0.01% S, and 0.01% P. The austempered samples were austenitized at 900?C for 1 h and rapidly quenched in a salt bath furnace at 375?C for 1 h. The intercritically austempered samples were sub-austenitized at 810?C for 1 h and rapidly quenched in a salt bath furnace at 375?C for 1 h. The properties of the austempered and intercritically austempered thin wall plates of 5, 10, and 15 mm thickness were evaluated and compared to the as-cast samples. Austempering process affects greatly the tensile properties of all cast thicknesses where ultimate strength reached 1004 MPa for 5-mm thickness. Optimum impact toughness of 40 J was obtained for the austempered samples of 10- and 15-mm thicknesses. The intercritically austempered samples showed properties between the austempered and as-cast samples. Maximum wear resistance was also reported for the austempered samples due to containing retained austenite in the structure which in turn transformed into martensite that increases well the wear resistance. Maximum ultimate strength (1056) MPa and hardness (396 HV) were obtained for 5 mm ADI sample. Maximum impact toughness (43 J) was achieved for 15 mm IADI sample due to existing of pro-eutectoid ferrite in matrix. For all As-cast, ADI and IADI irons, wear resistance decreased with increasing sample thickness. Minimum wear rate (2.22 × 10?6 g/s) was reported for 5-mm ADI sample and maximum one (15.8 × 10?6 g/s) was registered for 15-mm as-cast DI sample, at a sliding speed of 2 m/s.展开更多
In 316L austenitic stainless steel,the presence of ferrite phase severely affects the non-magnetic properties.316L austenitic stainless steel with low-alloy type(L-316L)and high-alloy type(H-316L)has been studied.The ...In 316L austenitic stainless steel,the presence of ferrite phase severely affects the non-magnetic properties.316L austenitic stainless steel with low-alloy type(L-316L)and high-alloy type(H-316L)has been studied.The microstructure and solidification kinetics of the two as-cast grades were in situ observed by high temperature confocal laser scanning microscopy(HT-CLSM).There are significant differences in the as-cast microstructures of the two 316L stainless steel compositions.In L-316L steel,ferrite morphology appears as the short rods with a ferrite content of 6.98%,forming a dual-phase microstructure consisting of austenite and ferrite.Conversely,in H-316L steel,the ferrite appears as discontinuous network structures with a content of 4.41%,forming a microstructure composed of austenite and sigma(σ)phase.The alloying elements in H-316L steel exhibit a complex distribution,with Ni and Mo enriching at the austenite grain boundaries.HT-CLSM experiments provide the real-time observation of the solidification processes of both 316L specimens and reveal distinct solidification modes:L-316L steel solidifies in an FA mode,whereas H-316L steel solidifies in an AF mode.These differences result in ferrite and austenite predominantly serving as the nucleation and growth phases,respectively.The solidification mode observed by experiments is similar to the thermodynamic calculation results.The L-316L steel solidified in the FA mode and showed minimal element segregation,which lead to a direct transformation of ferrite to austenite phase(δ→γ)during phase transformation after solidification.Besides,the H-316L steel solidified in the AF mode and showed severe element segregation,which lead to Mo enrichment at grain boundaries and transformation of ferrite into sigma and austenite phases through the eutectoid reaction(δ→σ+γ).展开更多
The microstructural evolution of a cold-rolled and intercritical annealed medium-Mn steel(Fe-0.10C-5Mn)was investigated during uniaxial tensile testing.In-situ observations under scanning electron microscopy,transmiss...The microstructural evolution of a cold-rolled and intercritical annealed medium-Mn steel(Fe-0.10C-5Mn)was investigated during uniaxial tensile testing.In-situ observations under scanning electron microscopy,transmission electron microscopy,and X-ray diffraction analysis were conducted to characterize the progressive transformation-induced plasticity process and associated fracture initiation mechanisms.These findings were discussed with the local strain measurements via digital image correlation.The results indicated that Lüders band formation in the steel was limited to 1.5%strain,which was mainly due to the early-stage martensitic phase transformation of a very small amount of the less stable large-sized retained austenite(RA),which led to localized stress concentrations and strain hardening and further retardation of yielding.The small-sized RA exhibited high stability and progressively transformed into martensite and contributed to a stably extended Portevin-Le Chatelier effect.The volume fraction of RA gradually decreased from 26.8%to 8.2%prior to fracture.In the late deformation stage,fracture initiation primarily occurred at the austenite/martensite and ferrite/martensite interfaces and the ferrite phase.展开更多
Multistage heat treatment involving quenching(Q),lamellarizing(L),and tempering(T)is applied to marine 10Ni5CrMoV steel.The microstructure and mechanical properties were studied by multiscale characterizations,and the...Multistage heat treatment involving quenching(Q),lamellarizing(L),and tempering(T)is applied to marine 10Ni5CrMoV steel.The microstructure and mechanical properties were studied by multiscale characterizations,and the kinetics of reverse austenite transformation,strain hardening behavior,and toughening mechanism were further investigated.The lamellarized specimens possess low yield strength but high toughness,especially cryogenic toughness.Lamellarization leads to the development of film-like reversed austenite at the martensite block and lath boundaries,refining the martensite structure and lowering the equivalent grain size.Kinetic analysis of austenite reversion based on the JMAK model shows that the isothermal transformation is dominated by the growth of reversed austenite,and the maximum transformation of reversed austenite is reached at the peak temperature(750℃).The strain hardening behavior based on the modified Crussard-Jaoul analysis indicates that the reversed austenite obtained from lamellarization reduces the proportion of martensite,significantly hindering crack propagation via martensitic transformation during the deformation.As a consequence,the QLT specimens exhibit high machinability and low yield strength.Compared with the QT specimen,the ductile-brittle transition temperature of the QLT specimens decreases from-116 to-130℃due to the low equivalent grain size and reversed austenite,which increases the cleavage force required for crack propagation and absorbs the energy of external load,respectively.This work provides an idea to improve the cryogenic toughness of marine 10Ni5CrMoV steel and lays a theoretical foundation for its industrial application and comprehensive performance improvement.展开更多
In the present study,a simple but effective two-step annealing processing strategy via manipulating the austenite reversion path is proposed to obtain a large fraction of retained austenite in low-Mn medium-Mn steels....In the present study,a simple but effective two-step annealing processing strategy via manipulating the austenite reversion path is proposed to obtain a large fraction of retained austenite in low-Mn medium-Mn steels.Initially,the Fe-3Mn-0.2C-1.5Si(wt%)steel is intercritically annealed to form Mn-enriched lamellar martensite precursors.Subsequently,the austenite reversion transformation is manipulated to occur within the martensite lamellae during the second annealing process,resulting in an ultra-fine duplex microstructure of laminated austenite and ferrite.This process can not only allow a large fraction of austenite to be retained in low-Mn medium-Mn steels,but also increase the elongation by up to 41%without sacrificing the strength level compared to the conventional annealing.展开更多
In this study, novel reconstruction methods, including grain graph and variant graph, were established to reconstruct parent austenite on the basis of electron backscatter diffraction (EBSD) data. The evaluation indic...In this study, novel reconstruction methods, including grain graph and variant graph, were established to reconstruct parent austenite on the basis of electron backscatter diffraction (EBSD) data. The evaluation indicators included boundary identification and variant distribution. Moreover, an innovative variant pair analysis method was proposed. The results indicated that the Kurdjumov-Sachs orientation relationship was the most appropriate because it had the smallest refinement error and deviation. In addition, the variant graph reconstruction was more effective in reducing mis-indexing areas than the grain graph, exhibiting a robust capacity to accurately identify austenite grain boundaries. Additionally, the variant graph reconstruction induced the transformation of variants, variant pairs, close-packed plane (CP) groups, and Bain groups. Moreover, various reconstructed datasets (calc-grain data and EBSD data) affected the distribution of variants. The austenite grains reconstructed from the calc-grain data featured two or more variants clustered within the same region due to the preprocessing (calculating, filtering, and smoothing) of the EBSD data. These variations did not impede the microstructural analysis when consistent original data and reconstruction methods were used. The reconstruction of parent austenite grains holds promise for providing a fresh perspective and a deeper understanding of strengthening and toughening mechanisms in the future.展开更多
The hardenability of steel is crucial for its durability and performance in engineering applications,significantly influencing mechanical properties such as hardness,strength,and wear resistance.As the engineering fie...The hardenability of steel is crucial for its durability and performance in engineering applications,significantly influencing mechanical properties such as hardness,strength,and wear resistance.As the engineering field continuously demands higher-performance steel materials,a deep understanding of the key influencing factors on hardenability is crucial for developing quality steel that meets stringent application requirements.The effects of some specific elements,including carbon(C),vanadium(V),molybdenum(Mo),and boron(B),as well as heat treatment process parameters such as austenitizing temperature,austenitizing holding time,and cooling rate,were examined.It aims to elucidate the interactions among these factors and their influence on steel hardenability.For each influencing factor,the heat treatment procedure,characteristic microstructure resulting from it,and corresponding Jominy end quench curves were discussed.Furthermore,based on the continuous development of big data technology in the field of materials,the use of machine learning to predict the hardenability of steel and guide the design of steel material was also introduced.展开更多
A cyclic quenching treatment(CQT)succeeded in turning a 2.3 GPa maraging steel with a Charpy impact energy of 9 J into a new grade with the same strength but a Charpy impact energy of 20 J upon 4 cyclic treatments.The...A cyclic quenching treatment(CQT)succeeded in turning a 2.3 GPa maraging steel with a Charpy impact energy of 9 J into a new grade with the same strength but a Charpy impact energy of 20 J upon 4 cyclic treatments.The improvement of mechanical properties is attributed to the refinement and increased chemical heterogeneity of the martensitic substructure,rather than the refinement of prior austenite grain(PAG),as well as the Transformation-Induced Plasticity(TRIP)effect facilitated by small austenite grains.The role of local segregation of Ni during CQT in the formation of Ni-rich austenite grains,Ni-rich martensite laths and Ni-poor martensite laths,was investigated and verified by DICTRA simulations.This study highlights the important influence of Ni partitioning behavior during CQT,providing insights into microstructural evolution and mechanical properties.展开更多
Medium-manganese steel exhibits excellent strength and toughness,which are essential features in wear resistance applications.This study examines the impact of annealing temperature on impact abrasive wear.The results...Medium-manganese steel exhibits excellent strength and toughness,which are essential features in wear resistance applications.This study examines the impact of annealing temperature on impact abrasive wear.The results have indicated that samples annealed at different temperatures display plowing and fatigue wear effects.In the initial wear stage,the hightemperature annealed steel outperforms samples annealed at a lower temperature in terms of anti-plowing wear performance.This phenomenon is mainly due to the lower initial hardness of the samples subjected to low-temperature annealing.However,with prolonged wear time,the low-temperature annealed samples exhibit improved plowing wear performance,which is ascribed to a refinement of the lamellar microstructure and an increased residual austenite(RA),which enhances the work hardening effect,improving the hardness of the worn surface.The low-temperature annealed samples consistently delivered superior fatigue wear performance when compared with samples annealed at the higher temperature.The latter effect may be attributed to two factors.Firstly,the finer lamellar microstructure in the low-temperature annealed samples,coupled with greater RA,results in transformation-induced plasticity or twin-induced plasticity effect that hinders crack formation and propagation.Secondly,the low-temperature annealed samples form nanoscale equiaxed grains near the worn surface during the wear process.These grains can withstand crack driving forces in fine-grained regions,suppressing the formation and propagation of cracks.展开更多
Liquefied natural gas storage and transportation as well as space propulsion systems have sparked inter-est in the martensitic transformation and behaviours of 316 L stainless steels(SS)under ultra-cryogenic deformati...Liquefied natural gas storage and transportation as well as space propulsion systems have sparked inter-est in the martensitic transformation and behaviours of 316 L stainless steels(SS)under ultra-cryogenic deformation.In this study,high-resolution transmission electron microscopy(HRTEM)and molecular dy-namics(MD)simulations were used to investigate the atomic arrangements and crystalline defects of deformation-induced γ-austenite→ε-martensite→α'-martensite and γ→α'martensitic transforma-tions in 316 L SS at 15 and 173 K.Theγ→εtransformation involves the glide of Shockley partial dislocations on(111)γplanes without a change in atomic spacing.The formation of anα'inclusion in a singleε-band is achieved by a continuous lattice distortion,accompanied by the formation of a tran-sition zone ofα'and the expansion of the average atomic spacings due to dislocation shuffling.Asα'grows further intoγ,the orientation relationship(OR)of theα'changes by lattice bending.This pro-cess follows the Bogers-Burgers-Olson-Cohen model despite it not occurring on intersecting shear bands.Stacking faults and twins can also serve as nucleation sites forα'at 173 K.We also found that direct transformation of γ→α'occurs by the glide of √6aγ[11(2)]/12 dislocations on every(111)γplane with misfit dislocations.Overall,this study provides,for the first time,insights into the atomic-scale mech-anisms of various two-step and one-step martensitic transformations induced by cryogenic deformation and corresponding local strain,enhancing our understanding of the role of martensitic transformation under ultra-cryogenic-temperature deformation in controlling the properties.展开更多
基金This research is financially supported by the China Scholarship Council under Grant No.201806935054the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi,China,under Grant No.201802035.
文摘The effects of austenitizing temperature(1223,1303,and 1373 K)and holding time(1-1500 s)on the microstructure,mechanical properties,and precipitation behavior of the H13 hot work die steel were investigated.The results indicate a softening phenomenon when H13 steel is austenitized at 1303 K beyond 900 s and 1373 K beyond 600 s,respectively.For the sample held for 1200 s,the tensile strength is found capable of reaching up to 2.2 GPa when quenched from a temperature above 1303 K.Meanwhile,prior-austenite grain size increases with the increase in austenitizing temperature.The kinetic behavior of the precipitates(mainly MC-type carbides)in H13 steel could be elaborated through the principles set forth by the Arrhenius and Avrami equations.Finally,the comprehensive strengthening of the H13 steel was discussed in detail.The results show that the activation energy of the transformed fraction of carbides is higher than that of the diffusion process for common alloying elements(Cr,V,Mo,and Ni)found in the austenite.This suggests that it would be difficult for precipitates to dissolve into the matrix when H13 steel is austenitized at high temperatures.With the increasing austenitizing temperature,the precipitation fraction decreases,and the dislocation density increases.The dislocation strengthening is regarded as the dominant strengthening contributed to yield strength in as-quenched H13 steel.
基金financially supported by the Yunnan Fundamental Research Projects(Grant No.202101AU070152)the Yunnan Ten Thousand Talents Plan Young&Elite Talents Project(Grant No.YNWR-QNBJ-2020-020)+2 种基金the Key Research&Development Program of Yunnan Province(Grant Nos.202103AA080017 and CBN21281004A)the Natural Science Research Foundation of Kunming University of Science and Technology(Grant No.KKZ3202051043)supported via funding from Prince Sattam bin Abdulaziz University project No.PSAU/2023/R/1444.
文摘SA508Gr.4 N steel is commonly used in nuclear pressure vessels. The current study discloses the impact of austenitizing temperature on its martensitic transformation. Various austenitizing temperatures were employed to examine the martensitic transformation at different experimental conditions. The characteristics of grain boundaries, microstructure, transformation kinetics, and crystallography of the martensitic phase following the austenitizing process and martensitic transformation were analyzed. Austenitizing temperatures had minimal effects on the critical temperature of the austenitizing phase transition. However, an increase in austenitizing temperature resulted in larger grain sizes. The phase composition primarily consisted of lath martensite, accompanied by a small amount of residual austenite (RA). As the austenitizing temperature increased, the temperature of martensite-start temperature (Ms) initially decreased and then increased. On the other hand, the temperature of martensite-finish (Mf) showed no significant sensitivity to changes in the austenitizing temperature. Moreover, the average size of the lath martensite structure was increased, and there was an increased tendency for variant selection as the austenitizing temperature increased, and the combination of specific orientation relationships appeared. This study is very valuable for revealing the microstructure evolution at different temperatures.
基金funded by the Science and Technology Project of Guangdong Province (2020B090923001)Guangdong Basic and Applied Basic Research Foundation (2023A1515010384)The Fundamental Research Funds for the Central Universities (2023ZYGXZR005).
文摘To address the inhomogeneous microstructure and improve the mechanical properties of DT300 ultra-high strength steel specimens fabricated by laser powder bed fusion,different post-heat treatment schedules are performed.With the increase in austenitizing temperature and time,the migration rate of austenite grain boundaries continuously increases with the dissolution of nano-carbides,and the formation of nano-oxides and twin martensite is also inhibited accordingly.The rapid growth in the size of prior austenite grains and martensite laths,as well as the decrease in the content of nano-oxides and twin martensite,led to a rapid decrease in the strength(yield strength and ultimate tensile strength)from HT2 to HTF specimens.The HT1 specimens(austenitizing at 830℃for 30 min,then oil quenching and tempering at 300℃for 120 min and finally air cooling)display excellent mechanical properties of yield strength of 1572 MPa,ultimate tensile strength of 1847 MPa,elongation of 9.84%,and fracture toughness of 106 MPa m^(1/2),which are counterparts to those of conventional DT300 steel forgings after heat treatment.
基金financially supported by National Natural Science Foundation of China (Grant Nos.51304041, 51434004 and U1435205)Fundamental Research Funds for the Central Universities (Grant No. N150204007)
文摘The influence of austenitizing temperature on the microstructure and corrosion resistance of 55Cr18MolVN high-nitrogen plastic mould steel was investigated. The microstructure, elemental distribution and Cr-depleted zone of different heat-treated samples were investigated by X-ray diffraction, electron probe microanalyzer analysis, and trans- mission electron microscopy. The corrosion resistance was evaluated using electrochemical measurements, and the analysis of passive film was carded out by X-ray photoelectron spectroscopy. The results indicated that the volume fraction of precipitates decreased, and the homogeneity of elements was improved with increasing austenitizing temperature. The degree of Cr-depleted zone around coarse M23C6 was severer than that around M2N, and pitting corrosion initiated preferentially around M23C6. The corrosion resistance of the samples increased with the austenitizing temperature. With the increase in austenitizing temperature, the passive film was thickened and Cr（III）cr2O3 in the inner layer of passive film was enriched, which enhanced the corrosion resistance of the steel. The higher content of nitrogen in solid solution at higher austenitizing temperature contributed to the increased intensity of CrN and NH3, leading to the increase in pH value in the pit, and promoting the repassivation of 55Cr18Mo1N steel.
基金Item Sponsored by Science Council of Beijing of China(D0404001040221)
文摘The microsturctural transformation of austenite grain, pearlite interlamellar spacing, and lamellar cement ite thickness of spring steel 60Si2MnA for railway were studied in the hot-rolled and reheated states. Furthermore, the effect of microstructural characterization on its final mechanical properties was discussed. The results showed that as far as 60Si2MnA, the pearlite interlamellar spacing determined the hardness, whereas, the austenite grain determined the toughness. Compared with microstructure and mechanical properties in the hot rolled state, after reheating treatment at 950 ℃, its average grain sizes are apparently fine and the pearlite interlamellar spacing and lamellar cementite thickness coarsen to some extent, but both hardness and impact toughness increase to HRC 48 and 8.5 J, respectively. In the course of making spring, the optimum reheating austenitizing temperature for the 60Si2MnA steel is 950 ℃.
文摘By continuous quenching process, the effect of austenitizing temperature and time on the structure and hardness of bainiteductile cast iron was studied. It was found that (l) low austenitizing temperature would result in scrap ferrite existing in matrix, whichreduces the macro-hardness of bainite ductile cast iron; (2) high austenitizing temperature would make carbide decomposed, which alsoinduces the macro-hardness of bainite cast iron, and (3) austenitizing time has little effect on the structure of bainite ductile cast iron, butas it increases, the macro-hardness ofbainite ductile cast iron and micro-hardness of bainite increases. To the ductile cast iron, as a result,the suitable austenitizing temperature and time are recommended as 880 and 120 min respectively.
文摘The effect of austenitizing temperature on segregation of impurities along grain boundaries in steel 4330M has been examined by AES.The impurity segregation was computed quantitatively.Results showed that the quantity of impurity segregation changed with the austenitizing temperature.The limitation of the McLean′s expression for equilibrium segrega- tion was discussed.
基金supported by the National Natural Science Foundations of China (No.50734008)the Fundamental Research Funds for the Central Universities (No.FRF-AS-11-003A)
文摘The change of inclusions and microstructure of 16Mn steel treated by Ce were observed,and the effect of austenitizing temperature on the microstructure was also examined.The results show that the inclusions are transformed from Si-Mn-Al composite oxide and MnS into AlCeO3,Ce2O2S,and MnS composite inclusions after being treated by Ce.Plenty of intragranular ferrites are formed in 16Mn steel containing～0.017wt% Ce.A large amount of intragranular acicular ferrites are formed after being austenitized for 20min at 1473 K.The prior austenite grain size fit for the formation of intragranular acicular ferrites is about 120μm.
基金Project(51575414)supported by National Natural Science Foundation of ChinaProject(IRT13087)supported by the Innovative Research Team Development Program of Ministry of Education of ChinaProject(2015AAA005)supported by the project of Important Science and Technology Innovation Program of Hubei Province,China
文摘Microstructural evolution of GCr15 steels with different C and Cr contents during austenitizing and quenching was studied. Thermodynamic analysis of cementite dissolution was implied to obtain the critical temperature. The coordination number x in Fe_xCr_(3-x)C and the volume fraction of undissolved cementite were computed according to element conservation and equilibrium phase diagram. The M_S(martensite transformation temperature) was calculated by using empirical formula. The retained austenite content was calculated with further consideration of quenching temperature. The results showed that the coordination number and the undissolved cementite content were promoted by the austenitizing temperature and carbon content of the steel. Increasing Cr element reduced the coordination number.GCr15 steels with different components had nearly the same M_S when austenitization at 830 °C to 860 °C. The interaction of C and Cr complicated the evolution of M_S and retained austenite content. The results were in good agreement with the literature, which could guide to obtain specified retained austenite and/or carbides.
基金funded by National Natural Science Foundation of China(51574028)
文摘The Fe-0.21C 2.2Mn 0.49Si-1.77A1 transformation induced plasticity （TRIP） aided steel was heat trea- ted at various austenitizing temperatures under both TRiP-aided polygonal ferrite type （TPF） and an- nealed martensite matrix （TAM） processes. The microstructure evolution and their effects on mechanical properties were systematically investigated through the microstructure observation and dilatometric analysis. The microstructure homogeneity is improved in TPF steel heated at a high temperature due to the reduced banded martensite and the increased bainite. Compared with the mechanical properties of the TPF steels, the yield strength and elongation of the TAM steels are much higher, while the tensile strength is lower than that of TPF steels. The stability of intercritical austenite is affected by the heating tempera- ture, and thus the following phase transformation influences the mechanical properties, such as the bain- ite transformation and the precipitation of polygonal ferrite. Obvious dynamic bainite transformation occurs at TAM850, TAM900 and TAM950, More proportion of polygonal ferrite is found in the sample heated at 950 ℃. The bainite transformation beginning at a higher temperature results in the wider bainitic ferrite laths. The more proportion of polygonal ferrite and wide bainitic ferrite laths commonly contribute to the lower strength and better elongation. The uniform microstructure with lath-like morphology and retained austenite with high average carbon content ensures a good mechanical property in TAM850 with the product of strength and elongation of about 28 GPa ·%,
文摘This investigation studies the impact strength, tensile strength, hardness, and wear behavior of thin wall austempered and intercritically austempered ductile iron samples with a chemical composition of 3.37% C, 2.7% Si, 0.30% Mn, 0.01% S, and 0.01% P. The austempered samples were austenitized at 900?C for 1 h and rapidly quenched in a salt bath furnace at 375?C for 1 h. The intercritically austempered samples were sub-austenitized at 810?C for 1 h and rapidly quenched in a salt bath furnace at 375?C for 1 h. The properties of the austempered and intercritically austempered thin wall plates of 5, 10, and 15 mm thickness were evaluated and compared to the as-cast samples. Austempering process affects greatly the tensile properties of all cast thicknesses where ultimate strength reached 1004 MPa for 5-mm thickness. Optimum impact toughness of 40 J was obtained for the austempered samples of 10- and 15-mm thicknesses. The intercritically austempered samples showed properties between the austempered and as-cast samples. Maximum wear resistance was also reported for the austempered samples due to containing retained austenite in the structure which in turn transformed into martensite that increases well the wear resistance. Maximum ultimate strength (1056) MPa and hardness (396 HV) were obtained for 5 mm ADI sample. Maximum impact toughness (43 J) was achieved for 15 mm IADI sample due to existing of pro-eutectoid ferrite in matrix. For all As-cast, ADI and IADI irons, wear resistance decreased with increasing sample thickness. Minimum wear rate (2.22 × 10?6 g/s) was reported for 5-mm ADI sample and maximum one (15.8 × 10?6 g/s) was registered for 15-mm as-cast DI sample, at a sliding speed of 2 m/s.
基金support of the Research Project Supported by Shanxi Scholarship Council of China(2022-040)"Chunhui Plan"Collaborative Research Project by the Ministry of Education of China(HZKY20220507)+2 种基金National Natural Science Foundation of China(52104338)Applied Fundamental Research Programs of Shanxi Province(202303021221036)Shandong Postdoctoral Science Foundation(SDCX-ZG-202303027,SDBX2023054).
文摘In 316L austenitic stainless steel,the presence of ferrite phase severely affects the non-magnetic properties.316L austenitic stainless steel with low-alloy type(L-316L)and high-alloy type(H-316L)has been studied.The microstructure and solidification kinetics of the two as-cast grades were in situ observed by high temperature confocal laser scanning microscopy(HT-CLSM).There are significant differences in the as-cast microstructures of the two 316L stainless steel compositions.In L-316L steel,ferrite morphology appears as the short rods with a ferrite content of 6.98%,forming a dual-phase microstructure consisting of austenite and ferrite.Conversely,in H-316L steel,the ferrite appears as discontinuous network structures with a content of 4.41%,forming a microstructure composed of austenite and sigma(σ)phase.The alloying elements in H-316L steel exhibit a complex distribution,with Ni and Mo enriching at the austenite grain boundaries.HT-CLSM experiments provide the real-time observation of the solidification processes of both 316L specimens and reveal distinct solidification modes:L-316L steel solidifies in an FA mode,whereas H-316L steel solidifies in an AF mode.These differences result in ferrite and austenite predominantly serving as the nucleation and growth phases,respectively.The solidification mode observed by experiments is similar to the thermodynamic calculation results.The L-316L steel solidified in the FA mode and showed minimal element segregation,which lead to a direct transformation of ferrite to austenite phase(δ→γ)during phase transformation after solidification.Besides,the H-316L steel solidified in the AF mode and showed severe element segregation,which lead to Mo enrichment at grain boundaries and transformation of ferrite into sigma and austenite phases through the eutectoid reaction(δ→σ+γ).
基金supported by the National Key R&D Program of China(No.2017YFB0304402)。
文摘The microstructural evolution of a cold-rolled and intercritical annealed medium-Mn steel(Fe-0.10C-5Mn)was investigated during uniaxial tensile testing.In-situ observations under scanning electron microscopy,transmission electron microscopy,and X-ray diffraction analysis were conducted to characterize the progressive transformation-induced plasticity process and associated fracture initiation mechanisms.These findings were discussed with the local strain measurements via digital image correlation.The results indicated that Lüders band formation in the steel was limited to 1.5%strain,which was mainly due to the early-stage martensitic phase transformation of a very small amount of the less stable large-sized retained austenite(RA),which led to localized stress concentrations and strain hardening and further retardation of yielding.The small-sized RA exhibited high stability and progressively transformed into martensite and contributed to a stably extended Portevin-Le Chatelier effect.The volume fraction of RA gradually decreased from 26.8%to 8.2%prior to fracture.In the late deformation stage,fracture initiation primarily occurred at the austenite/martensite and ferrite/martensite interfaces and the ferrite phase.
基金financially supported by the National Key K&D Program of China(No.2023YFE0200300)the National Natural Science Foundation of China(Nos.52174303and 51874084)the Program of Introducing Talents of Discipline to Universities(No.B21001)。
文摘Multistage heat treatment involving quenching(Q),lamellarizing(L),and tempering(T)is applied to marine 10Ni5CrMoV steel.The microstructure and mechanical properties were studied by multiscale characterizations,and the kinetics of reverse austenite transformation,strain hardening behavior,and toughening mechanism were further investigated.The lamellarized specimens possess low yield strength but high toughness,especially cryogenic toughness.Lamellarization leads to the development of film-like reversed austenite at the martensite block and lath boundaries,refining the martensite structure and lowering the equivalent grain size.Kinetic analysis of austenite reversion based on the JMAK model shows that the isothermal transformation is dominated by the growth of reversed austenite,and the maximum transformation of reversed austenite is reached at the peak temperature(750℃).The strain hardening behavior based on the modified Crussard-Jaoul analysis indicates that the reversed austenite obtained from lamellarization reduces the proportion of martensite,significantly hindering crack propagation via martensitic transformation during the deformation.As a consequence,the QLT specimens exhibit high machinability and low yield strength.Compared with the QT specimen,the ductile-brittle transition temperature of the QLT specimens decreases from-116 to-130℃due to the low equivalent grain size and reversed austenite,which increases the cleavage force required for crack propagation and absorbs the energy of external load,respectively.This work provides an idea to improve the cryogenic toughness of marine 10Ni5CrMoV steel and lays a theoretical foundation for its industrial application and comprehensive performance improvement.
基金support from the National Natural Science Foundation of China(Grant Nos.52321001 and 52071322).
文摘In the present study,a simple but effective two-step annealing processing strategy via manipulating the austenite reversion path is proposed to obtain a large fraction of retained austenite in low-Mn medium-Mn steels.Initially,the Fe-3Mn-0.2C-1.5Si(wt%)steel is intercritically annealed to form Mn-enriched lamellar martensite precursors.Subsequently,the austenite reversion transformation is manipulated to occur within the martensite lamellae during the second annealing process,resulting in an ultra-fine duplex microstructure of laminated austenite and ferrite.This process can not only allow a large fraction of austenite to be retained in low-Mn medium-Mn steels,but also increase the elongation by up to 41%without sacrificing the strength level compared to the conventional annealing.
基金the National Natural Science Foundation of China(Grant Nos.52325406,52374331,and U1960203)the Program of Introducing Talents of Discipline to Universities(Grant No.B21001).
文摘In this study, novel reconstruction methods, including grain graph and variant graph, were established to reconstruct parent austenite on the basis of electron backscatter diffraction (EBSD) data. The evaluation indicators included boundary identification and variant distribution. Moreover, an innovative variant pair analysis method was proposed. The results indicated that the Kurdjumov-Sachs orientation relationship was the most appropriate because it had the smallest refinement error and deviation. In addition, the variant graph reconstruction was more effective in reducing mis-indexing areas than the grain graph, exhibiting a robust capacity to accurately identify austenite grain boundaries. Additionally, the variant graph reconstruction induced the transformation of variants, variant pairs, close-packed plane (CP) groups, and Bain groups. Moreover, various reconstructed datasets (calc-grain data and EBSD data) affected the distribution of variants. The austenite grains reconstructed from the calc-grain data featured two or more variants clustered within the same region due to the preprocessing (calculating, filtering, and smoothing) of the EBSD data. These variations did not impede the microstructural analysis when consistent original data and reconstruction methods were used. The reconstruction of parent austenite grains holds promise for providing a fresh perspective and a deeper understanding of strengthening and toughening mechanisms in the future.
基金supported by the National Natural Science Foundation of China(Nos.52122408 and 52071023)Hong-hui Wu also thanks the financial support from the Fundamental Research Funds for the Central Universities(University of Science and Technology Beijing,Nos.FRF-TP-2021-04C1 and 06500135)supported by USTB MatCom of Beijing Advanced Innovation Center for Materials Genome Engineering.
文摘The hardenability of steel is crucial for its durability and performance in engineering applications,significantly influencing mechanical properties such as hardness,strength,and wear resistance.As the engineering field continuously demands higher-performance steel materials,a deep understanding of the key influencing factors on hardenability is crucial for developing quality steel that meets stringent application requirements.The effects of some specific elements,including carbon(C),vanadium(V),molybdenum(Mo),and boron(B),as well as heat treatment process parameters such as austenitizing temperature,austenitizing holding time,and cooling rate,were examined.It aims to elucidate the interactions among these factors and their influence on steel hardenability.For each influencing factor,the heat treatment procedure,characteristic microstructure resulting from it,and corresponding Jominy end quench curves were discussed.Furthermore,based on the continuous development of big data technology in the field of materials,the use of machine learning to predict the hardenability of steel and guide the design of steel material was also introduced.
基金sponsored by the National Natural Science Foun-dation of China(Grant Nos.52271122,52203384).
文摘A cyclic quenching treatment(CQT)succeeded in turning a 2.3 GPa maraging steel with a Charpy impact energy of 9 J into a new grade with the same strength but a Charpy impact energy of 20 J upon 4 cyclic treatments.The improvement of mechanical properties is attributed to the refinement and increased chemical heterogeneity of the martensitic substructure,rather than the refinement of prior austenite grain(PAG),as well as the Transformation-Induced Plasticity(TRIP)effect facilitated by small austenite grains.The role of local segregation of Ni during CQT in the formation of Ni-rich austenite grains,Ni-rich martensite laths and Ni-poor martensite laths,was investigated and verified by DICTRA simulations.This study highlights the important influence of Ni partitioning behavior during CQT,providing insights into microstructural evolution and mechanical properties.
基金financial support to the Application Foundation Frontier Project of the Major Program(JD)of Hubei Province(2023BAA019-4)the National Natural Science Foundation of China(U20A20279,12072245,52071238)+2 种基金the Science and Technology Program of Guangxi Province(AA22068080)the Key Research and Development Program of Hubei Province(2021BAA057)the Taishan Industry-Leading Talent Project Special Funding and Subject Innovation and Talent Introduction Program in Colleges and Universities(111 programs No.D18018)。
文摘Medium-manganese steel exhibits excellent strength and toughness,which are essential features in wear resistance applications.This study examines the impact of annealing temperature on impact abrasive wear.The results have indicated that samples annealed at different temperatures display plowing and fatigue wear effects.In the initial wear stage,the hightemperature annealed steel outperforms samples annealed at a lower temperature in terms of anti-plowing wear performance.This phenomenon is mainly due to the lower initial hardness of the samples subjected to low-temperature annealing.However,with prolonged wear time,the low-temperature annealed samples exhibit improved plowing wear performance,which is ascribed to a refinement of the lamellar microstructure and an increased residual austenite(RA),which enhances the work hardening effect,improving the hardness of the worn surface.The low-temperature annealed samples consistently delivered superior fatigue wear performance when compared with samples annealed at the higher temperature.The latter effect may be attributed to two factors.Firstly,the finer lamellar microstructure in the low-temperature annealed samples,coupled with greater RA,results in transformation-induced plasticity or twin-induced plasticity effect that hinders crack formation and propagation.Secondly,the low-temperature annealed samples form nanoscale equiaxed grains near the worn surface during the wear process.These grains can withstand crack driving forces in fine-grained regions,suppressing the formation and propagation of cracks.
基金supported by the Henry Royce Institute for Advanced Materials,funded through Engineering and Physical Sciences Research Council(EPSRC)grants EP/R00661X/1,EP/S019367/1,EP/P025021/1,and EP/P025498/1.
文摘Liquefied natural gas storage and transportation as well as space propulsion systems have sparked inter-est in the martensitic transformation and behaviours of 316 L stainless steels(SS)under ultra-cryogenic deformation.In this study,high-resolution transmission electron microscopy(HRTEM)and molecular dy-namics(MD)simulations were used to investigate the atomic arrangements and crystalline defects of deformation-induced γ-austenite→ε-martensite→α'-martensite and γ→α'martensitic transforma-tions in 316 L SS at 15 and 173 K.Theγ→εtransformation involves the glide of Shockley partial dislocations on(111)γplanes without a change in atomic spacing.The formation of anα'inclusion in a singleε-band is achieved by a continuous lattice distortion,accompanied by the formation of a tran-sition zone ofα'and the expansion of the average atomic spacings due to dislocation shuffling.Asα'grows further intoγ,the orientation relationship(OR)of theα'changes by lattice bending.This pro-cess follows the Bogers-Burgers-Olson-Cohen model despite it not occurring on intersecting shear bands.Stacking faults and twins can also serve as nucleation sites forα'at 173 K.We also found that direct transformation of γ→α'occurs by the glide of √6aγ[11(2)]/12 dislocations on every(111)γplane with misfit dislocations.Overall,this study provides,for the first time,insights into the atomic-scale mech-anisms of various two-step and one-step martensitic transformations induced by cryogenic deformation and corresponding local strain,enhancing our understanding of the role of martensitic transformation under ultra-cryogenic-temperature deformation in controlling the properties.
