The effects of plastic deformation and H2 S on fracture toughness of high strength casing steel(C110 steel) were investigated. The studied casing specimens are as follows: original casing, plastic deformation(PD)...The effects of plastic deformation and H2 S on fracture toughness of high strength casing steel(C110 steel) were investigated. The studied casing specimens are as follows: original casing, plastic deformation(PD) casing and PD casing after being immersed in NACE A solution saturated with H2S(PD+H2S). Instrumented impact method was employed to evaluate the impact behaviors of the specimens, meanwhile, dynamic fracture toughness(JId) was calculated by using Rice model and Schindler model. The experimental results show that dynamic fracture toughness of the casing decreases after plastic deformation. Compared with that of the original casing and PD casing, the dynamic fracture toughness decreases further when the PD casing immersed in H2 S, moreover, there are ridge-shaped feature and many secondary cracks present on the fracture surface of the specimens. Impact fracture mechanism of the casing is proposed as follows: the plastic deformation results in the increase of defect density of materials where the atomic hydrogen can accumulate in reversible or irreversible traps and even recombine to form molecular hydrogen, subsequently, the casing material toughness decreases greatly.展开更多
Metals have been mankind’s most essential materials for thousands of years.In recent years,however,innovation-driven development of major national security strategy and core areas of the national economy is highly im...Metals have been mankind’s most essential materials for thousands of years.In recent years,however,innovation-driven development of major national security strategy and core areas of the national economy is highly impeded by a shortage of advanced higher-strength-toughness metals.One of the main reasons is that metals inherently exhibit the inverted-relationship of strength-toughness.The emergence of two types of disordered metals:amorphous alloys and high entropy alloys,provides a fully-fresh strategy for strength-toughening by tailoring the topological and/or chemical disorder.In this paper,we first briefly review the history of strength-toughening of metals,and summarize the development route-map.We then introduce amorphous alloys and high entropy alloys,as well as some case studies in tailoring disorder to successfully achieve coexisting high strength and high ductility/toughness.Relevant challenges that await further research are summarized in concluding remarks.展开更多
Laser shock peening(LSP) is a widely used surface treatment technique that can effectively improve the fatigue life and impact toughness of metal parts.Cr5Mo1 V steel exhibits a gradient hardened layer after a LSP p...Laser shock peening(LSP) is a widely used surface treatment technique that can effectively improve the fatigue life and impact toughness of metal parts.Cr5Mo1 V steel exhibits a gradient hardened layer after a LSP process.A new method is proposed to estimate the impact toughness that considers the changing mechanical properties in the gradient hardened layer.Assuming a linearly gradient distribution of impact toughness,the parameters controlling the impact toughness of the gradient hardened layer were given.The influence of laser power densities and the number of laser shots on the impact toughness were investigated.The impact toughness of the laser peened layer improves compared with an untreated specimen,and the impact toughness increases with the laser power densities and decreases with the number of laser shots.Through the fracture morphology analysis by a scanning electron microscope,we established that the Cr5Mo1 V steel was fractured by the cleavage fracture mechanism combined with a few dimples.The increase in the impact toughness of the material after LSP is observed because of the decreased dimension and increased fraction of the cleavage fracture in the gradient hardened layer.展开更多
Three kinds of high Co Ni secondary hardening steels with different Ni contents were studied. The nanoscale austenite layers formed at the interface of matensite laths were observed. Both observation and diffusion kin...Three kinds of high Co Ni secondary hardening steels with different Ni contents were studied. The nanoscale austenite layers formed at the interface of matensite laths were observed. Both observation and diffusion kinetic simulation results showed that both Ni and Co did not obtain enough time to get the equilibrium content in this system. The Ni content in austenite layers decreased significantly, and Co content increased slightly with the decrease of Ni content in overall composition. The austenite stability was estimated by Olson-Cohen model, in which both chemical and mechanical driving force could be calculated by equilibrium thermodynamic and Mohr's circle methods, respectively. Simulation and mechanical test results showed that The decrease of Ni content in austenite layers would cause the change of austenite stability and decrease the fracture toughness of the steels. When the Ni content in the overall composition was lower than 7 wt. %, the Ni content in y phase would be lower than 20 wt.%. And the simulation value of M; (stress induced critical martensite transformation temperature) would be up to 80 ℃, which was about 60℃ higher than room temperature. Based on the analysis, the Ni content in the overall composition of high Co Ni secondary hardening steels should be higher than 8 wt. % in order to obtain a good fracture toughness.展开更多
基金Funded by the Construction of Key Disciplines for Young Teacher Science Foundation of the Southwest Petroleum University(No.P209)the Research Fund for the Doctoral Program of Higher Education(No.20105121120002)the National Natural Science Foundation of China(Nos.51004084 and 51374177)
文摘The effects of plastic deformation and H2 S on fracture toughness of high strength casing steel(C110 steel) were investigated. The studied casing specimens are as follows: original casing, plastic deformation(PD) casing and PD casing after being immersed in NACE A solution saturated with H2S(PD+H2S). Instrumented impact method was employed to evaluate the impact behaviors of the specimens, meanwhile, dynamic fracture toughness(JId) was calculated by using Rice model and Schindler model. The experimental results show that dynamic fracture toughness of the casing decreases after plastic deformation. Compared with that of the original casing and PD casing, the dynamic fracture toughness decreases further when the PD casing immersed in H2 S, moreover, there are ridge-shaped feature and many secondary cracks present on the fracture surface of the specimens. Impact fracture mechanism of the casing is proposed as follows: the plastic deformation results in the increase of defect density of materials where the atomic hydrogen can accumulate in reversible or irreversible traps and even recombine to form molecular hydrogen, subsequently, the casing material toughness decreases greatly.
基金This work was supported by the National Outstanding Youth Science Fund Project of National Natural Science Foundation of China(NSFC)(No.12125206)the NSFC Basic Science Center for“Multiscale Problems in Nonlinear Mechanics”(No.11988102)the NSFC(Nos.11972345 and 11790292).
文摘Metals have been mankind’s most essential materials for thousands of years.In recent years,however,innovation-driven development of major national security strategy and core areas of the national economy is highly impeded by a shortage of advanced higher-strength-toughness metals.One of the main reasons is that metals inherently exhibit the inverted-relationship of strength-toughness.The emergence of two types of disordered metals:amorphous alloys and high entropy alloys,provides a fully-fresh strategy for strength-toughening by tailoring the topological and/or chemical disorder.In this paper,we first briefly review the history of strength-toughening of metals,and summarize the development route-map.We then introduce amorphous alloys and high entropy alloys,as well as some case studies in tailoring disorder to successfully achieve coexisting high strength and high ductility/toughness.Relevant challenges that await further research are summarized in concluding remarks.
基金supported by the National Natural Science Foundation of China (Grants 11002150,11332011,and 11402277)the Basic Research Equipment Project of the Chinese Academy of Sciences (YZ200930) for financia support
文摘Laser shock peening(LSP) is a widely used surface treatment technique that can effectively improve the fatigue life and impact toughness of metal parts.Cr5Mo1 V steel exhibits a gradient hardened layer after a LSP process.A new method is proposed to estimate the impact toughness that considers the changing mechanical properties in the gradient hardened layer.Assuming a linearly gradient distribution of impact toughness,the parameters controlling the impact toughness of the gradient hardened layer were given.The influence of laser power densities and the number of laser shots on the impact toughness were investigated.The impact toughness of the laser peened layer improves compared with an untreated specimen,and the impact toughness increases with the laser power densities and decreases with the number of laser shots.Through the fracture morphology analysis by a scanning electron microscope,we established that the Cr5Mo1 V steel was fractured by the cleavage fracture mechanism combined with a few dimples.The increase in the impact toughness of the material after LSP is observed because of the decreased dimension and increased fraction of the cleavage fracture in the gradient hardened layer.
基金financially supported by National Basic Research Programs of China (No.2015CB654802 and No.2015GB118001)National Natural Science Foundation of China(Grant No.51471094)
文摘Three kinds of high Co Ni secondary hardening steels with different Ni contents were studied. The nanoscale austenite layers formed at the interface of matensite laths were observed. Both observation and diffusion kinetic simulation results showed that both Ni and Co did not obtain enough time to get the equilibrium content in this system. The Ni content in austenite layers decreased significantly, and Co content increased slightly with the decrease of Ni content in overall composition. The austenite stability was estimated by Olson-Cohen model, in which both chemical and mechanical driving force could be calculated by equilibrium thermodynamic and Mohr's circle methods, respectively. Simulation and mechanical test results showed that The decrease of Ni content in austenite layers would cause the change of austenite stability and decrease the fracture toughness of the steels. When the Ni content in the overall composition was lower than 7 wt. %, the Ni content in y phase would be lower than 20 wt.%. And the simulation value of M; (stress induced critical martensite transformation temperature) would be up to 80 ℃, which was about 60℃ higher than room temperature. Based on the analysis, the Ni content in the overall composition of high Co Ni secondary hardening steels should be higher than 8 wt. % in order to obtain a good fracture toughness.