Static creep and cyclic creep tests were carried out on a Cr-Mo rotor steel from 0.5 to 0.6 T_m. Cyclic creep retardation occurred under the test conditions.With an increase of stress frequency, cyclic creep strain ra...Static creep and cyclic creep tests were carried out on a Cr-Mo rotor steel from 0.5 to 0.6 T_m. Cyclic creep retardation occurred under the test conditions.With an increase of stress frequency, cyclic creep strain rate decreases and rupture time increases.The cyclic creep strain rate for the stress wave of a square shape is higher than that of a tri- angle shape.The apparent stress exponent of cyclic creep and the apparent activation energy of cyclic creep are both higher than those of static creep.The minimum strain rate is inversely proportional to rupture time for both static and cyclic creeps at dif- ferent stresses,temperatures,frequencies and wave shapes.The cyclic creep retardation mechanism was explored by the observation and analysis of the dis- location structure and fracture surface.展开更多
The effects of hydrogen atoms on behaviour of low cycle fatigue of 2.25Cr-1Mo steel have been investigated in present work. The results indicate that the cyclic softening rate and low cycle fatigue life are respective...The effects of hydrogen atoms on behaviour of low cycle fatigue of 2.25Cr-1Mo steel have been investigated in present work. The results indicate that the cyclic softening rate and low cycle fatigue life are respectively increased and reduced remarkably by hydrogen atoms. In addition, hydrogen atoms make the original stress amplitude of low cycle fatigue increase, which is because of the drag effect of hydrogen atoms on the moving dislocations. Analyses using electron microscopy show that hydrogen atoms accelerate crack initiation of low cycle fatigue from inclusion and transfer the source of low cycle fatigue crack from the surface of specimen to the inclusion, which results in the marked decrease of low cycle fatigue life. The increase of cyclic softening rate for hydrogen charged specimen is due to hydrogen atoms accelerating the initiating and growing of microvoids from the secondary phase particles in the steel. The reducing of the drag effect of hydrogen atoms on moving dislocations is also helpful to the increase of the cyclic softening rate.展开更多
Maraging steel (250) and 13-8 Mo stainless steel plates were joined by gas tungsten constricted arc welding(GTCAW) process in similar and dissimilar metal combinations using 13-8 Mo stainless steel filler wire. The si...Maraging steel (250) and 13-8 Mo stainless steel plates were joined by gas tungsten constricted arc welding(GTCAW) process in similar and dissimilar metal combinations using 13-8 Mo stainless steel filler wire. The similar and dissimilar metal welds made in solutionized condition were subjected to standard post weld hardening treatments direct ageing at 485 ℃, soaking for 31/2 hours followed by air cooling(ageing treatment of maraging steel) and direct ageing at 510 ℃, soaking for 4 h followed by air cooling(ageing treatment of 13-8 Mo stainless steel). The joint characterization studies include microstructure examination, microhardness survey across the weldments and transverse weld tensile test.Similar and dissimilar metal weldments responded to both the post weld ageing treatment. After post weld aging, increase in yield strength, UTS and slight reduction in % elongation of similar and dissimilar metal were observed. The observed tensile properties were correlated with microstructure and hardness distribution across the welds.展开更多
The mechanical and corrosive properties of 00Cr13Ni4Mo （S13 -4N） were tested and compared with those of 00Cr13Ni6Mo （S13 -6）. The effects of nitrogen on the properties of the steels were analyzed. The results of t...The mechanical and corrosive properties of 00Cr13Ni4Mo （S13 -4N） were tested and compared with those of 00Cr13Ni6Mo （S13 -6）. The effects of nitrogen on the properties of the steels were analyzed. The results of the tensile and corrosion tests show the strength,the ductility,and the pitting corrosion resistance of S13 -4N are higher, lower and poorer than those of S13 -6 respectively, when tempered at a temperature below 550 ℃and vice versa when the tempering temperature is higher than 550℃. The results of the X-ray diffraction （XRD） and the electron backscattered diffraction （EBSD） analyses reveal that inversed austenite appears at 550℃ and the amount of it peaks at 600 ℃ with the best ductility. And the total amount of the inversed austenite in S13 -6 is more than that in S13 -4N in different forms. Nitrogen performs better in terms of stabilizing inversed austenite while nickel is more favorable for forming inversed austenite, the amount and stability of which affect the ductility remarkably. The reason for the embrittlement of S13 -4N at 450℃ can be the result of carbide and nitride precipitating at grain boundaries.展开更多
Fused salt accelerated hot corrosion is quite common in gas turbines, fossil fuelled devices, waste inclinators, pyrochemical systems, etc. Presence of fused salt on metal surface dissolves their existing oxide layer....Fused salt accelerated hot corrosion is quite common in gas turbines, fossil fuelled devices, waste inclinators, pyrochemical systems, etc. Presence of fused salt on metal surface dissolves their existing oxide layer. This results in an increase in oxidation rate of the metal. Since, zirconia coating is well recognized for corrosion protection under high temperature oxidative environment, we have developed zirconia coating on 9Cr1Mo ferritic steel and their oxidation performance was evaluated in LiCl-NaCl and Na2SO4-K2SO4 salts deposit system in air atmosphere at 650?C and 850?C, respectively. Before coating development, zirconium based sol was synthesized using zirconium (IV) propoxide as a precursor. Oxidation test results indicated that the zirconia coated specimens shows more than two times higher corrosion resistance in LiCl-NaCl and three time higher corrosion resistance in Na2SO4-K2SO4 salt deposit, respectively.展开更多
DIN 1.2343 and 1.2367 steels are commonly used as die materials in aluminum extrusion, and single/duplex/multi-coatings enhance their surface properties. The design of an appropriate substrate/coating system is import...DIN 1.2343 and 1.2367 steels are commonly used as die materials in aluminum extrusion, and single/duplex/multi-coatings enhance their surface properties. The design of an appropriate substrate/coating system is important for improving the tribological performance of these steels under service conditions because the load-carrying capacity of the system can be increased by decreasing the plastic deformation of the substrate. In this study, the tribological behavior of CrN-coated Cr–Mo–V steels(DIN 1.2343, 1.2367, and 1.2999 grades) was investigated using different setups and tribological pairs at room and elevated temperatures. The aim of this study was to reveal the wear resistance of a suggested system(1.2999/CrN) not yet studied and to understand both the wear and the failure characteristics of coated systems. The results showed that(i) among the steels studied, the DIN 1.2999 grade steel exhibited the lowest friction coefficient because it had the highest load-carrying capacity as a result of secondary hardening at elevated temperatures;(ii) at room temperature, both abrasive tracks and adhesive layers were observed on the worn surfaces; and(iii) a combination of chemical reactions and progressive oxidation caused aluminum adhesion on the worn surface, and the detachment of droplets and microcracking were the characteristic damage mechanisms at high temperatures.展开更多
1.25Cr-0.5Mo steels with different Ti-B or Al-B treatment were exposed in 18 MPa hydrogen atmosphere at 480℃ fo f 100, 500 and 1000 h respectively. Tensile and bend properties of steels before and after hydrogen chan...1.25Cr-0.5Mo steels with different Ti-B or Al-B treatment were exposed in 18 MPa hydrogen atmosphere at 480℃ fo f 100, 500 and 1000 h respectively. Tensile and bend properties of steels before and after hydrogen changing were tested. The results show that the different mechanical properties of the steels with different B content have different responses to high temperature high pressure hydrogen charging processes.After hydrogen changing, more loss of ductility can be found in the steel not treated with B than those in the steels treated with B. Metallographic analyses indicated that decarburization occurred in all the steels. Furthermore, many methane bubbles were found by SEM analysis in the surface decarburization layer in the steel without B,while only a few bubbles, the number and size of which decreased with increasing B content, were found in steels with B treatment. In addition, hydrogen determination results manifested that after being exposed in hydrogen atmosphere the steel containing no B had higher hydrogen content than that of steels containing B. All this suggests that B treatment improved the HA resistance of 1.25Cgr-0.5Mo steel, and the more B the steel contained the more perceptible the effect.展开更多
The inclusion parameters,fracture surface morphology and void growth characteristics of ten- sile and fracture toughness specimens of 2.25Cr-1Mo steels with and without rare-earth (RE)additions have been investigated ...The inclusion parameters,fracture surface morphology and void growth characteristics of ten- sile and fracture toughness specimens of 2.25Cr-1Mo steels with and without rare-earth (RE)additions have been investigated by quantitative metaltography(QTM),scanning elec- tron microscopy(SEM)and energy dispersive spectroscopy(EDS).There is a substantially higher density of inclusions in the RE-treated steel,which has lower values of fracture proper- ties including critical values of COD and J integral(δ_c and J_(IC)),fracture strain(ε_f) and Charpy V-notch energy(CVN).The fracture surface of the RE-treated steel comprises equiaxed dimples of diameters comparable with its inclusion spacing,whereas for the non-RE-treated steels,a wide range of dimple sizes is found with average diameter much smaller than the corresponding inclusion spacing.The investigation indicates that the lower values of fracture properties for the steel with RE at room temperature may be ascribed to its large content of RE-containing inclusions.展开更多
Characteristic features of austenitic steel grades combine a good corrosion resistance with a low hardness, wear resistance and scratch resistance. An interesting possibility for improving the wear behaviour of these ...Characteristic features of austenitic steel grades combine a good corrosion resistance with a low hardness, wear resistance and scratch resistance. An interesting possibility for improving the wear behaviour of these steels without loss of their corrosion resistance lies in enriching the near surface region with nitrogen. The process of a solution nitriding allows the rise of the solution of nitrogen in the solid phase. On this state nitrogen increases the corrosion resistance and the tribilogical load-bearing capacity. The aim of the study was, to investigate the improvement of the pitting corrosion behaviour by solution nitriding. A special topic was to observe the effect of nitrogen by different molybdenum content. So austenitic stainless steels (18% Cr, 12% Ni, Mo gradation between 0.06 to 3.6%) had been solution nitrided. The samples could be prepared with various surface content of nitrogen from 0.04 to 0.45% with a step-by-step grinding. The susceptibility against pitting corrosion of these samples had been tested by determination of the stable pitting potential in 0.5M and 1M NaCl at 25°C. For the investigated steel composition and the used corrosion system there is no influence of molybdenum on the effectiveness of nitrogen. The influence of nitrogen to all of the determined parameters can be described well by PRE = Cr + 3,3 * Mo + 25 *N. XPS analysis of the sample surfaces support the results of the pitting corrosion tests.Additionally surface investigations with an acid elektolyte (0,1M HC1 + 0,4M NaCl) were performed. In this case the passivation effective nitrogen content increases markedly with rising molybdenum concentration of the steel. Obviously an interaction of Mo and N is connected with a strongly acid electrolyte.展开更多
The microstructure and hardness on and below the surface of Cr-Mo steel (SCM435) treated by water jet peening (WJP) were investigated using scanning electron microscopy and micro Vickers hardness measurements. The cha...The microstructure and hardness on and below the surface of Cr-Mo steel (SCM435) treated by water jet peening (WJP) were investigated using scanning electron microscopy and micro Vickers hardness measurements. The change of the surface residual stress caused by the WJP treatment influenced the surface microstructure and surface hardness of the SCM435 steel. Cementite in the pearlite phase tended to protrude as the duration of WJP was increased. Voids were formed in the area 0.5 - 1.0 mm below the surface and also at grain boundaries between ferrite and pearlite grains, whereas no voids were formed in the depth range from 2.0 to 3.0 mm below the surface.展开更多
文摘Static creep and cyclic creep tests were carried out on a Cr-Mo rotor steel from 0.5 to 0.6 T_m. Cyclic creep retardation occurred under the test conditions.With an increase of stress frequency, cyclic creep strain rate decreases and rupture time increases.The cyclic creep strain rate for the stress wave of a square shape is higher than that of a tri- angle shape.The apparent stress exponent of cyclic creep and the apparent activation energy of cyclic creep are both higher than those of static creep.The minimum strain rate is inversely proportional to rupture time for both static and cyclic creeps at dif- ferent stresses,temperatures,frequencies and wave shapes.The cyclic creep retardation mechanism was explored by the observation and analysis of the dis- location structure and fracture surface.
文摘The effects of hydrogen atoms on behaviour of low cycle fatigue of 2.25Cr-1Mo steel have been investigated in present work. The results indicate that the cyclic softening rate and low cycle fatigue life are respectively increased and reduced remarkably by hydrogen atoms. In addition, hydrogen atoms make the original stress amplitude of low cycle fatigue increase, which is because of the drag effect of hydrogen atoms on the moving dislocations. Analyses using electron microscopy show that hydrogen atoms accelerate crack initiation of low cycle fatigue from inclusion and transfer the source of low cycle fatigue crack from the surface of specimen to the inclusion, which results in the marked decrease of low cycle fatigue life. The increase of cyclic softening rate for hydrogen charged specimen is due to hydrogen atoms accelerating the initiating and growing of microvoids from the secondary phase particles in the steel. The reducing of the drag effect of hydrogen atoms on moving dislocations is also helpful to the increase of the cyclic softening rate.
基金Financial assistance from Defence Research and Development Organisation
文摘Maraging steel (250) and 13-8 Mo stainless steel plates were joined by gas tungsten constricted arc welding(GTCAW) process in similar and dissimilar metal combinations using 13-8 Mo stainless steel filler wire. The similar and dissimilar metal welds made in solutionized condition were subjected to standard post weld hardening treatments direct ageing at 485 ℃, soaking for 31/2 hours followed by air cooling(ageing treatment of maraging steel) and direct ageing at 510 ℃, soaking for 4 h followed by air cooling(ageing treatment of 13-8 Mo stainless steel). The joint characterization studies include microstructure examination, microhardness survey across the weldments and transverse weld tensile test.Similar and dissimilar metal weldments responded to both the post weld ageing treatment. After post weld aging, increase in yield strength, UTS and slight reduction in % elongation of similar and dissimilar metal were observed. The observed tensile properties were correlated with microstructure and hardness distribution across the welds.
文摘The mechanical and corrosive properties of 00Cr13Ni4Mo （S13 -4N） were tested and compared with those of 00Cr13Ni6Mo （S13 -6）. The effects of nitrogen on the properties of the steels were analyzed. The results of the tensile and corrosion tests show the strength,the ductility,and the pitting corrosion resistance of S13 -4N are higher, lower and poorer than those of S13 -6 respectively, when tempered at a temperature below 550 ℃and vice versa when the tempering temperature is higher than 550℃. The results of the X-ray diffraction （XRD） and the electron backscattered diffraction （EBSD） analyses reveal that inversed austenite appears at 550℃ and the amount of it peaks at 600 ℃ with the best ductility. And the total amount of the inversed austenite in S13 -6 is more than that in S13 -4N in different forms. Nitrogen performs better in terms of stabilizing inversed austenite while nickel is more favorable for forming inversed austenite, the amount and stability of which affect the ductility remarkably. The reason for the embrittlement of S13 -4N at 450℃ can be the result of carbide and nitride precipitating at grain boundaries.
文摘Fused salt accelerated hot corrosion is quite common in gas turbines, fossil fuelled devices, waste inclinators, pyrochemical systems, etc. Presence of fused salt on metal surface dissolves their existing oxide layer. This results in an increase in oxidation rate of the metal. Since, zirconia coating is well recognized for corrosion protection under high temperature oxidative environment, we have developed zirconia coating on 9Cr1Mo ferritic steel and their oxidation performance was evaluated in LiCl-NaCl and Na2SO4-K2SO4 salts deposit system in air atmosphere at 650?C and 850?C, respectively. Before coating development, zirconium based sol was synthesized using zirconium (IV) propoxide as a precursor. Oxidation test results indicated that the zirconia coated specimens shows more than two times higher corrosion resistance in LiCl-NaCl and three time higher corrosion resistance in Na2SO4-K2SO4 salt deposit, respectively.
文摘DIN 1.2343 and 1.2367 steels are commonly used as die materials in aluminum extrusion, and single/duplex/multi-coatings enhance their surface properties. The design of an appropriate substrate/coating system is important for improving the tribological performance of these steels under service conditions because the load-carrying capacity of the system can be increased by decreasing the plastic deformation of the substrate. In this study, the tribological behavior of CrN-coated Cr–Mo–V steels(DIN 1.2343, 1.2367, and 1.2999 grades) was investigated using different setups and tribological pairs at room and elevated temperatures. The aim of this study was to reveal the wear resistance of a suggested system(1.2999/CrN) not yet studied and to understand both the wear and the failure characteristics of coated systems. The results showed that(i) among the steels studied, the DIN 1.2999 grade steel exhibited the lowest friction coefficient because it had the highest load-carrying capacity as a result of secondary hardening at elevated temperatures;(ii) at room temperature, both abrasive tracks and adhesive layers were observed on the worn surfaces; and(iii) a combination of chemical reactions and progressive oxidation caused aluminum adhesion on the worn surface, and the detachment of droplets and microcracking were the characteristic damage mechanisms at high temperatures.
文摘1.25Cr-0.5Mo steels with different Ti-B or Al-B treatment were exposed in 18 MPa hydrogen atmosphere at 480℃ fo f 100, 500 and 1000 h respectively. Tensile and bend properties of steels before and after hydrogen changing were tested. The results show that the different mechanical properties of the steels with different B content have different responses to high temperature high pressure hydrogen charging processes.After hydrogen changing, more loss of ductility can be found in the steel not treated with B than those in the steels treated with B. Metallographic analyses indicated that decarburization occurred in all the steels. Furthermore, many methane bubbles were found by SEM analysis in the surface decarburization layer in the steel without B,while only a few bubbles, the number and size of which decreased with increasing B content, were found in steels with B treatment. In addition, hydrogen determination results manifested that after being exposed in hydrogen atmosphere the steel containing no B had higher hydrogen content than that of steels containing B. All this suggests that B treatment improved the HA resistance of 1.25Cgr-0.5Mo steel, and the more B the steel contained the more perceptible the effect.
文摘The inclusion parameters,fracture surface morphology and void growth characteristics of ten- sile and fracture toughness specimens of 2.25Cr-1Mo steels with and without rare-earth (RE)additions have been investigated by quantitative metaltography(QTM),scanning elec- tron microscopy(SEM)and energy dispersive spectroscopy(EDS).There is a substantially higher density of inclusions in the RE-treated steel,which has lower values of fracture proper- ties including critical values of COD and J integral(δ_c and J_(IC)),fracture strain(ε_f) and Charpy V-notch energy(CVN).The fracture surface of the RE-treated steel comprises equiaxed dimples of diameters comparable with its inclusion spacing,whereas for the non-RE-treated steels,a wide range of dimple sizes is found with average diameter much smaller than the corresponding inclusion spacing.The investigation indicates that the lower values of fracture properties for the steel with RE at room temperature may be ascribed to its large content of RE-containing inclusions.
基金The DFG(Deutsche Forschungsgemeinschaft)is gratefully acknowledged for the financial support(DFG No.PA 699/3-1 and FR 1603/1-2).
文摘Characteristic features of austenitic steel grades combine a good corrosion resistance with a low hardness, wear resistance and scratch resistance. An interesting possibility for improving the wear behaviour of these steels without loss of their corrosion resistance lies in enriching the near surface region with nitrogen. The process of a solution nitriding allows the rise of the solution of nitrogen in the solid phase. On this state nitrogen increases the corrosion resistance and the tribilogical load-bearing capacity. The aim of the study was, to investigate the improvement of the pitting corrosion behaviour by solution nitriding. A special topic was to observe the effect of nitrogen by different molybdenum content. So austenitic stainless steels (18% Cr, 12% Ni, Mo gradation between 0.06 to 3.6%) had been solution nitrided. The samples could be prepared with various surface content of nitrogen from 0.04 to 0.45% with a step-by-step grinding. The susceptibility against pitting corrosion of these samples had been tested by determination of the stable pitting potential in 0.5M and 1M NaCl at 25°C. For the investigated steel composition and the used corrosion system there is no influence of molybdenum on the effectiveness of nitrogen. The influence of nitrogen to all of the determined parameters can be described well by PRE = Cr + 3,3 * Mo + 25 *N. XPS analysis of the sample surfaces support the results of the pitting corrosion tests.Additionally surface investigations with an acid elektolyte (0,1M HC1 + 0,4M NaCl) were performed. In this case the passivation effective nitrogen content increases markedly with rising molybdenum concentration of the steel. Obviously an interaction of Mo and N is connected with a strongly acid electrolyte.
文摘The microstructure and hardness on and below the surface of Cr-Mo steel (SCM435) treated by water jet peening (WJP) were investigated using scanning electron microscopy and micro Vickers hardness measurements. The change of the surface residual stress caused by the WJP treatment influenced the surface microstructure and surface hardness of the SCM435 steel. Cementite in the pearlite phase tended to protrude as the duration of WJP was increased. Voids were formed in the area 0.5 - 1.0 mm below the surface and also at grain boundaries between ferrite and pearlite grains, whereas no voids were formed in the depth range from 2.0 to 3.0 mm below the surface.
