In this work,the effects of temperature and cooling rate on the precipitation of carbides in nickel-saving metastable austenitic stainless steel were studied.The test results show that the temperature range of carbide...In this work,the effects of temperature and cooling rate on the precipitation of carbides in nickel-saving metastable austenitic stainless steel were studied.The test results show that the temperature range of carbide precipitation in the test steel was 500-950℃,and 750℃was the most sensitive temperature.However,when completely solution treated samples were cooled from high to room temperature at a cooling rate of more than 50 K/s,no carbides precipitated.The carbide precipitates increased the yield strength but decreased the corrosion resistance of the steel,with little impact on toughness.展开更多
The properties of heat-resistant steel 309S at elevated properties were investigated.The results revealed a rapid decrease in the short-time tensile strength at elevated temperatures.At 1 000 ℃,the yield strength and...The properties of heat-resistant steel 309S at elevated properties were investigated.The results revealed a rapid decrease in the short-time tensile strength at elevated temperatures.At 1 000 ℃,the yield strength and tensile strength are 14% and 7% of their respective values at room temperature,respectively.The creep rupture strength was inferred in terms of the relationship between stress and duration time at high temperatures.After 1 000 h,the creep rupture strength is 37.98 MPa at 800 ℃,12.63 MPa at 900 ℃,and 7.27 MPa at 1 000 ℃.The fractures occurring at these high temperatures were intergranular in nature.Under the experimental condition,the fatigue limit stress is 25 MPa.The number of fatigue cycles and crack growth time decrease with increasing stress.Fracture morphology analysis shows that the fatigue cracks initiate on the surface of the sample and propagate through transgranular expansion.展开更多
Along with strict environmental regulation, new-energy vehicles are becoming increasingly popular due to their low emissions, and they will inevitably replace existing fossil-fuel-based buses in China. To achieve a li...Along with strict environmental regulation, new-energy vehicles are becoming increasingly popular due to their low emissions, and they will inevitably replace existing fossil-fuel-based buses in China. To achieve a lightweight bus body ,high-strength steels are commonly used for the bus frame,but these grades are susceptible to corrosion. From the perspective of ＂lower life-cycle cost＂, high-strength stainless steel is a better bus structure choice than high-strength carbon steels, since stainless steel bus frames last 10-15 years without requiring any maintenance. The low-cost high-strength stainless steels developed by Baosteel are introduced,the yield and tensile strengths of which can be controlled to within the range of 350-700 MPa and 900-1 200 MPa,respectively, and the elongation values are above 30%. Measurements of the toughness and fatigue resistance of these high-strength stainless steels and their joints indicate that the structural integrity requirements for bus frames can be met. The results of salt spray corrosion studies indicate that stainless steels will substantially increase the service life of bus frames in wet and icy winter conditions where deicing with CaC12 is necessary for road safety. The results of our investigation clearly indicate that high-strength stainless steel is a potential bus-frame material that makes it possible to achieve substantial weight savings, excellent corrosion resistance, and prolonged operational life.展开更多
In recent years, with attention paid to global environmental problems, there have been requirements for continuous improvement of automobile fuel economy and exhaust gas purification rate. The properties of the ferrit...In recent years, with attention paid to global environmental problems, there have been requirements for continuous improvement of automobile fuel economy and exhaust gas purification rate. The properties of the ferritic stainless steels （FSS） used to make automobile parts have been improved. This paper introduces the construction of automotive exhaust systems and describes their main failure behaviors and corrosion evaluation procedures.展开更多
This study investigates the corrosion properties of 0Cr11Ti and 0Cr11NbTi ferritic stainless steels （FSS） for automotive exhaust systems. The results indicate that the base metal and weld seam of 0Cr11NbTi steel exh...This study investigates the corrosion properties of 0Cr11Ti and 0Cr11NbTi ferritic stainless steels （FSS） for automotive exhaust systems. The results indicate that the base metal and weld seam of 0Cr11NbTi steel exhibit better intergranular and condensate corrosion resistant properties because carbon and nitrogen are stabilized by Nb and Ti, and the precipitation of Cr carbide is retarded in grain boundaries.展开更多
The kinetic curves of the high-temperature oxidation of austenitic heat resistant stainless steel 1. 4828 at 1 050 ℃ were measured using a weighing method. It is shown that the oxidation curves at 1 050 ℃ followed t...The kinetic curves of the high-temperature oxidation of austenitic heat resistant stainless steel 1. 4828 at 1 050 ℃ were measured using a weighing method. It is shown that the oxidation curves at 1 050 ℃ followed the parabolic line law, and after 250 h of oxidation, the mass gain was about 80 g/m2. The surface morphology and structure of the oxide layers were studied by scanning electron microscopy and X-ray diffraction. A complicated oxide layer obtained at 1 050 ℃ was mainly composed, from inner to outer, of （FeSi） 3 04, Cr2 03, Fe2 03, and spinel oxides FeCr204 and NiMn204.展开更多
Non-metallic inclusion is the main reason for the presence of surface defects in cold-rolled steel strip. In this study, the composition, morphology, and size of the non-metallic inclusion in hot-rolled 304 stainless ...Non-metallic inclusion is the main reason for the presence of surface defects in cold-rolled steel strip. In this study, the composition, morphology, and size of the non-metallic inclusion in hot-rolled 304 stainless steel strips are analyzed. Cold-rolled 304 stainless steel strips with different cold-rolling reduction have been prepared, and the morphology and size of inclusion in these cold-rolled strips are also analyzed. Furthermore, the deformation behavior of a non-metallic inclusion during the cold-rolling process is studied. The results show that CaO-SiO2- MgO-Al2 O3, a kind of brittle compound oxide,is the main type of inclusion in hot-rolled 304 stainless steel strips. During the cold-rolling process, ductile deformation of this type of inclusion is not obvious, where large inclusions are crushed, and the average size of inclusions in cold-rolled strips decreased while the cold-rolling reduction increased.展开更多
Austenitic stainless steel Cr20 Ni12 Si2 RE was developed for use in hot-end components of automobile exhaust systems,especially in automobiles designed according to the China VI emission standard. The hightemperature...Austenitic stainless steel Cr20 Ni12 Si2 RE was developed for use in hot-end components of automobile exhaust systems,especially in automobiles designed according to the China VI emission standard. The hightemperature oxidation kinetic curve of Cr20 Ni12 Si2 RE at 1 050 ℃ was obtained using the weighting method. The oxidation curves exhibit the parabolic law at 1 050 ℃; after 250 h of oxidation,the mass gain was 22 g/m^2. The morphology,structure,and composition of the oxide film were examined using scanning electron microscopy and Xray diffraction methods. A thin,stable,and dense spinel oxide film obtained after 250 h of oxidation at 1 050 ℃ was mainly composed of( Mn_(0.87)Fe_(0.13))( Mn_(0.13)Fe_(0.87)Cr) O_4 and Cr_2 O_3 with a silicon-containing oxide underneath. The addition of rare earth elements was found to restrict further diffusion of metallic atoms from the austenite toward the oxide film,and consequently,led to a low growth rate of the oxide film. The inner silicon-containing oxide was produced by the diffusion of oxygen atoms and enhanced the coherent strength of the oxide film.展开更多
18CrNbTi ferritic stainless steel is a low-cost material mainly used for the fabrication of manifolds, which usually work at temperatures below 950℃. With the development of engine technology, exhaust manifolds tend ...18CrNbTi ferritic stainless steel is a low-cost material mainly used for the fabrication of manifolds, which usually work at temperatures below 950℃. With the development of engine technology, exhaust manifolds tend to work above 1 000 ℃ and this may be even higher in the future. For developing a new kind of steel to satisfy these requirements,the effects of tungsten （W）addition on the high-temperature strength and oxidation resistance of 18CrNbTi ferritic stainless steel are discussed in this study. The test results show that W enhances high-temperature strength at 1 000 ℃ and significantly improves oxidation resistance. However, W addition tends to degrade oxide layer adhesion,causing spalling during alternate hot and cold conditions.展开更多
An improved three-dimensional （3-D） experimental visualization methodology is presented tor evaluating the fracture mechanisms of ferritic stainless steels by in-situ tensile testing with an environmental scanning e...An improved three-dimensional （3-D） experimental visualization methodology is presented tor evaluating the fracture mechanisms of ferritic stainless steels by in-situ tensile testing with an environmental scanning electron microscope （ESEM）. The samples were machined with a radial notched shape and a sloped surface. Both planar surface deformation and sloping surface deformation-induced microvoids were observed during dynamic tension experiments, where a greater amount of information could be obtained from the sloping surface. The results showed that microvoids formed at the grain boundaries of highly elongated large grains. The microvoids nucleated in the severely deformed regions grew nearly parallel to the tensile axis, predominantly along the grain boundaries. The microvoids nucleated at the interface of particles and the matrix did not propagate due to the high plasticity of the matrix. The large microvoids propagated and showed a zigzag shape along the grain boundaries,seemingly a consequence of the fracture of the slip bands caused by dislocation pile-ups. The final failure took place due to the reduction of the load-beating area.展开更多
In order to better understand the relation between grain boundary characteristic distribution （GBCD） and the brittle cracking of ferritic stainless steel, the GBCD, impact test and bend test were investigated using ...In order to better understand the relation between grain boundary characteristic distribution （GBCD） and the brittle cracking of ferritic stainless steel, the GBCD, impact test and bend test were investigated using scanning electron microscopy （SEM） and the electron backscatter diffraction （EBSD） technique. The results show that a crack occurs preferentially at high angle boundaries, and that low angle and low-∑ coincidence site lattice（CSL） boundaries can offer resistance to the propagation of cracks. It is suggested that an optimum GBCD, i.e. a high frequency of low angle or low-∑ CSL boundaries and discontinuous high angle boundaries network can offer the potential for decreasing the ductile-to-brittle transition temoerature （DBTT） of ferritic stainless steels.展开更多
Based on a 00Cr11NbTi ferritic stainless steel plate produced by Baosteel,the plasma arc welding was performed without filler wire. The mechanical properties of the welded joints were tested,as a result,the transverse...Based on a 00Cr11NbTi ferritic stainless steel plate produced by Baosteel,the plasma arc welding was performed without filler wire. The mechanical properties of the welded joints were tested,as a result,the transverse tensile strength of the welded joints decreased to a certain extent in comparison with that of the base metal,but the bending performance and plasticity of the welded joint were good.展开更多
The thermal fatigue behavior of 441 ferritic stainless steel was investigated in air and synthetic automotive exhaust gas by the cyclic tests under 100℃-800℃ and 900℃ conditions.After the fracture failure,the micro...The thermal fatigue behavior of 441 ferritic stainless steel was investigated in air and synthetic automotive exhaust gas by the cyclic tests under 100℃-800℃ and 900℃ conditions.After the fracture failure,the microstructure,oxide film,and precipitated phases were analyzed using optical microscopy,X-ray diffraction,scanning electron microscopy,and transmission electron microscopy.In both atmospheres,increasing the maximum temperature from 800℃ to 900℃ results in lower strength and fatigue life and higher elongation and grain size.At the same maximum temperature,the thermal fatigue life of the specimen is lower in the synthetic exhaust gas than in the air.Both the higher maximum temperature and the synthetic exhaust gas facilitate fatigue failure.The failure mechanism is discussed according to the grain size,thermal stress,high-temperature oxidation rate,and the precipitation of secondary phases.Some precipitated carbides play an important role in the rapid fatigue failure of specimens in the synthetic exhaust gas.展开更多
文摘In this work,the effects of temperature and cooling rate on the precipitation of carbides in nickel-saving metastable austenitic stainless steel were studied.The test results show that the temperature range of carbide precipitation in the test steel was 500-950℃,and 750℃was the most sensitive temperature.However,when completely solution treated samples were cooled from high to room temperature at a cooling rate of more than 50 K/s,no carbides precipitated.The carbide precipitates increased the yield strength but decreased the corrosion resistance of the steel,with little impact on toughness.
文摘The properties of heat-resistant steel 309S at elevated properties were investigated.The results revealed a rapid decrease in the short-time tensile strength at elevated temperatures.At 1 000 ℃,the yield strength and tensile strength are 14% and 7% of their respective values at room temperature,respectively.The creep rupture strength was inferred in terms of the relationship between stress and duration time at high temperatures.After 1 000 h,the creep rupture strength is 37.98 MPa at 800 ℃,12.63 MPa at 900 ℃,and 7.27 MPa at 1 000 ℃.The fractures occurring at these high temperatures were intergranular in nature.Under the experimental condition,the fatigue limit stress is 25 MPa.The number of fatigue cycles and crack growth time decrease with increasing stress.Fracture morphology analysis shows that the fatigue cracks initiate on the surface of the sample and propagate through transgranular expansion.
基金sponsored by Shanghai Committee of Science and Technology with the project No.15XD1520100
文摘Along with strict environmental regulation, new-energy vehicles are becoming increasingly popular due to their low emissions, and they will inevitably replace existing fossil-fuel-based buses in China. To achieve a lightweight bus body ,high-strength steels are commonly used for the bus frame,but these grades are susceptible to corrosion. From the perspective of ＂lower life-cycle cost＂, high-strength stainless steel is a better bus structure choice than high-strength carbon steels, since stainless steel bus frames last 10-15 years without requiring any maintenance. The low-cost high-strength stainless steels developed by Baosteel are introduced,the yield and tensile strengths of which can be controlled to within the range of 350-700 MPa and 900-1 200 MPa,respectively, and the elongation values are above 30%. Measurements of the toughness and fatigue resistance of these high-strength stainless steels and their joints indicate that the structural integrity requirements for bus frames can be met. The results of salt spray corrosion studies indicate that stainless steels will substantially increase the service life of bus frames in wet and icy winter conditions where deicing with CaC12 is necessary for road safety. The results of our investigation clearly indicate that high-strength stainless steel is a potential bus-frame material that makes it possible to achieve substantial weight savings, excellent corrosion resistance, and prolonged operational life.
文摘In recent years, with attention paid to global environmental problems, there have been requirements for continuous improvement of automobile fuel economy and exhaust gas purification rate. The properties of the ferritic stainless steels （FSS） used to make automobile parts have been improved. This paper introduces the construction of automotive exhaust systems and describes their main failure behaviors and corrosion evaluation procedures.
文摘This study investigates the corrosion properties of 0Cr11Ti and 0Cr11NbTi ferritic stainless steels （FSS） for automotive exhaust systems. The results indicate that the base metal and weld seam of 0Cr11NbTi steel exhibit better intergranular and condensate corrosion resistant properties because carbon and nitrogen are stabilized by Nb and Ti, and the precipitation of Cr carbide is retarded in grain boundaries.
文摘The kinetic curves of the high-temperature oxidation of austenitic heat resistant stainless steel 1. 4828 at 1 050 ℃ were measured using a weighing method. It is shown that the oxidation curves at 1 050 ℃ followed the parabolic line law, and after 250 h of oxidation, the mass gain was about 80 g/m2. The surface morphology and structure of the oxide layers were studied by scanning electron microscopy and X-ray diffraction. A complicated oxide layer obtained at 1 050 ℃ was mainly composed, from inner to outer, of （FeSi） 3 04, Cr2 03, Fe2 03, and spinel oxides FeCr204 and NiMn204.
文摘Non-metallic inclusion is the main reason for the presence of surface defects in cold-rolled steel strip. In this study, the composition, morphology, and size of the non-metallic inclusion in hot-rolled 304 stainless steel strips are analyzed. Cold-rolled 304 stainless steel strips with different cold-rolling reduction have been prepared, and the morphology and size of inclusion in these cold-rolled strips are also analyzed. Furthermore, the deformation behavior of a non-metallic inclusion during the cold-rolling process is studied. The results show that CaO-SiO2- MgO-Al2 O3, a kind of brittle compound oxide,is the main type of inclusion in hot-rolled 304 stainless steel strips. During the cold-rolling process, ductile deformation of this type of inclusion is not obvious, where large inclusions are crushed, and the average size of inclusions in cold-rolled strips decreased while the cold-rolling reduction increased.
文摘Austenitic stainless steel Cr20 Ni12 Si2 RE was developed for use in hot-end components of automobile exhaust systems,especially in automobiles designed according to the China VI emission standard. The hightemperature oxidation kinetic curve of Cr20 Ni12 Si2 RE at 1 050 ℃ was obtained using the weighting method. The oxidation curves exhibit the parabolic law at 1 050 ℃; after 250 h of oxidation,the mass gain was 22 g/m^2. The morphology,structure,and composition of the oxide film were examined using scanning electron microscopy and Xray diffraction methods. A thin,stable,and dense spinel oxide film obtained after 250 h of oxidation at 1 050 ℃ was mainly composed of( Mn_(0.87)Fe_(0.13))( Mn_(0.13)Fe_(0.87)Cr) O_4 and Cr_2 O_3 with a silicon-containing oxide underneath. The addition of rare earth elements was found to restrict further diffusion of metallic atoms from the austenite toward the oxide film,and consequently,led to a low growth rate of the oxide film. The inner silicon-containing oxide was produced by the diffusion of oxygen atoms and enhanced the coherent strength of the oxide film.
文摘18CrNbTi ferritic stainless steel is a low-cost material mainly used for the fabrication of manifolds, which usually work at temperatures below 950℃. With the development of engine technology, exhaust manifolds tend to work above 1 000 ℃ and this may be even higher in the future. For developing a new kind of steel to satisfy these requirements,the effects of tungsten （W）addition on the high-temperature strength and oxidation resistance of 18CrNbTi ferritic stainless steel are discussed in this study. The test results show that W enhances high-temperature strength at 1 000 ℃ and significantly improves oxidation resistance. However, W addition tends to degrade oxide layer adhesion,causing spalling during alternate hot and cold conditions.
文摘An improved three-dimensional （3-D） experimental visualization methodology is presented tor evaluating the fracture mechanisms of ferritic stainless steels by in-situ tensile testing with an environmental scanning electron microscope （ESEM）. The samples were machined with a radial notched shape and a sloped surface. Both planar surface deformation and sloping surface deformation-induced microvoids were observed during dynamic tension experiments, where a greater amount of information could be obtained from the sloping surface. The results showed that microvoids formed at the grain boundaries of highly elongated large grains. The microvoids nucleated in the severely deformed regions grew nearly parallel to the tensile axis, predominantly along the grain boundaries. The microvoids nucleated at the interface of particles and the matrix did not propagate due to the high plasticity of the matrix. The large microvoids propagated and showed a zigzag shape along the grain boundaries,seemingly a consequence of the fracture of the slip bands caused by dislocation pile-ups. The final failure took place due to the reduction of the load-beating area.
文摘In order to better understand the relation between grain boundary characteristic distribution （GBCD） and the brittle cracking of ferritic stainless steel, the GBCD, impact test and bend test were investigated using scanning electron microscopy （SEM） and the electron backscatter diffraction （EBSD） technique. The results show that a crack occurs preferentially at high angle boundaries, and that low angle and low-∑ coincidence site lattice（CSL） boundaries can offer resistance to the propagation of cracks. It is suggested that an optimum GBCD, i.e. a high frequency of low angle or low-∑ CSL boundaries and discontinuous high angle boundaries network can offer the potential for decreasing the ductile-to-brittle transition temoerature （DBTT） of ferritic stainless steels.
文摘Based on a 00Cr11NbTi ferritic stainless steel plate produced by Baosteel,the plasma arc welding was performed without filler wire. The mechanical properties of the welded joints were tested,as a result,the transverse tensile strength of the welded joints decreased to a certain extent in comparison with that of the base metal,but the bending performance and plasticity of the welded joint were good.
基金supported by the National Natural Science Foundation of China and Baowu Steel Group Co.,Ltd.(Grant No.U1660205)。
文摘The thermal fatigue behavior of 441 ferritic stainless steel was investigated in air and synthetic automotive exhaust gas by the cyclic tests under 100℃-800℃ and 900℃ conditions.After the fracture failure,the microstructure,oxide film,and precipitated phases were analyzed using optical microscopy,X-ray diffraction,scanning electron microscopy,and transmission electron microscopy.In both atmospheres,increasing the maximum temperature from 800℃ to 900℃ results in lower strength and fatigue life and higher elongation and grain size.At the same maximum temperature,the thermal fatigue life of the specimen is lower in the synthetic exhaust gas than in the air.Both the higher maximum temperature and the synthetic exhaust gas facilitate fatigue failure.The failure mechanism is discussed according to the grain size,thermal stress,high-temperature oxidation rate,and the precipitation of secondary phases.Some precipitated carbides play an important role in the rapid fatigue failure of specimens in the synthetic exhaust gas.
