Mechanical and magnetic properties as well as their relationship in the reduced activation martensitic （RAM） steel were investigated in the temperature range from -90℃ to 20℃. Charpy impact tests show that the duc...Mechanical and magnetic properties as well as their relationship in the reduced activation martensitic （RAM） steel were investigated in the temperature range from -90℃ to 20℃. Charpy impact tests show that the ductile-to-brittle transition temperature （DBTT） of the RAM steel is about -60℃. Low-temperature tensile tests show that the yield strength, ultimate tensile strength and total elongation values increase as temperature decreases, indicating that the strength and plasticity below the DBTT are higher than those above the DBTT. The coercive field （Hc） in the scale of logarithm decreases linearly with the increasing temperature and the absolute value of the slope of InHc versus temperature above the DBTT is obviously larger than that below the DBTT, also confirmed in the T91 steel. The results indicate that the non-destructive magnetic measurement is a promising candidate method for the DBTT detection of ferromagnetic steels.展开更多
Microstructure and mechanical properties of GN9 Ferritic/Martensitic steel for sodium-cooled fast reactors have been investigated through orthogonal design and analysis.Scanning electron microscopy(SEM),transmission e...Microstructure and mechanical properties of GN9 Ferritic/Martensitic steel for sodium-cooled fast reactors have been investigated through orthogonal design and analysis.Scanning electron microscopy(SEM),transmission electron microscopy(TEM),differential scanning calorimeter(DSC),tensile and impact tests were used to evaluate the heat treatment parameters on yield strength,elongation and ductile-to-brittle transition temperature(DBTT).The results indicate that the microstructures of GN9 steel after orthogonal heat treatments consist of tempered martensite,M23C6,MX carbides and MX carbonitrides.The average prior austenite grains increase and the lath width decreases with the austenitizing temperature increasing from 1000°C to 1080°C.Tempering temperature is the most important factor that influences the dislocation evolution,yield strength and elongation compared with austenitizing tempera-ture and cooling methods.Austenitizing temperature,tempering temperature and cooling methods show interactive effects on DBTT.Carbide morphology and distribution,which is influenced by austenitizing and tempering tempera-tures,is the critical microstructural factor that influences the Charpy impact energy and DBTT.Based on the orthogo-nal design and microstructural analysis,the optimal heat treatment of GN9 steel is austenitizing at 1000°C for 0.5 h followed by air cooling and tempering at 760°C for 1.5 h.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
In order to explore the eff ect of a small amount of rare earth addition in ultra-cleaned pipeline steel and the influence of the cooling process on the tensile and impact properties,three API X80 pipeline steels were...In order to explore the eff ect of a small amount of rare earth addition in ultra-cleaned pipeline steel and the influence of the cooling process on the tensile and impact properties,three API X80 pipeline steels were fabricated by varying RE addition and the cooling process at the same time.Three microstructures with different features for a low C high Nb microalloyed high-strength pipeline steel and the corresponding mechanical properties were investigated.The results showed that even in the ultra-cleaned steel with O and S contents less than 10 ppm,the addition of RE would still cause an increase in the volume fraction of inclusions consisting of complicated RE oxysulfide and RE sulfide.More inclusions formed in the 112 ppm RE steel were harmful to the low temperature toughness,while few inclusions formed in the 47 ppm RE steel had almost no influence on the low temperature toughness.The two RE additions had no effect on strength of the steels.As the finishing cooling temperature was increased and the cooling rate was decreased within a certain range,the volume fractions of polygonal ferrite and quasi-polygonal ferrite as well as the number density and size of martensite–austenite islands were increased.Under such combined effect,the strength of the steels had almost no change.As the finishing cooling temperature was increased from 481 to 584℃and the cooling rate was reduced from 20 to 13℃/s,for the steel with 112 ppm addition of RE,there was an obvious decrease in the low temperature toughness.The reduced value(about 33 J)of the USE of steel consisted of two parts including the influence(about 18 J)of more inclusions formed due to 112 ppm addition of RE and the eff ect(about 15 J)of the lower high-angle grain boundaries.展开更多
The effects of 0.01–0.11 wt.%Zr on the inclusions,microstructure,tensile properties,and impact toughness of the China low activation martensitic steel were investigated.Results showed that Zr exhibits good deoxidatio...The effects of 0.01–0.11 wt.%Zr on the inclusions,microstructure,tensile properties,and impact toughness of the China low activation martensitic steel were investigated.Results showed that Zr exhibits good deoxidation and desulfurization abilities.The scanning electron microscope was used to examine the inclusions in the ingots.The main inclusions in the alloys were Zr–Ta–O,Zr–O,and Zr–O–S.However,some blocky Zr-rich inclusions appeared in Zr-2 and Zr-3 alloys.Typical martensitic structures were observed in the alloys,and average prior austenite grain sizes of 21.1,15.7,and 14.8µm were obtained for Zr-1,Zr-2,and Zr-3 steels,respectively.However,increasing Zr content of the steels deteriorated their mechanical property,owing to the blocky inclusions.The alloy with 0.01%Zr resulted in excellent mechanical properties due to the fine inclusions and the precipitation of Zr3V3C carbides.Values of 576 and 682 MPa were obtained for the yield strength and ultimate tensile strength of Zr-1 alloy,respectively.Furthermore,the ductile–brittle transition temperature of the alloy decreased to−85℃.展开更多
The Charpy impact properties of 15Cr12MoVWN ferritic/martensitic steel for sodium-cooled reactors with variation in heat treatment factors and parameters are reported.The results show that the ductile-to-brittle trans...The Charpy impact properties of 15Cr12MoVWN ferritic/martensitic steel for sodium-cooled reactors with variation in heat treatment factors and parameters are reported.The results show that the ductile-to-brittle transition temperature(DBTT)increased and the upper shelf energy(USE)decreased with increase in normalizing temperature.However,the variation tendency of DBTT and USE was the opposite with increase in tempering temperature.The tempering temperature showed a greater influence on USE than the normalizing temperature,and normalizing and tempering temperatures had the equally significant effects on DBTT,but the cooling method was not a significant factor for DBTT and USE.The prior austenite grain and M_(23)C_(6) size were the main influences on DBTT,and the dislocation density was the main factor affecting the variation of USE.The heat-treatment regime recommended for 15Cr12MoVWN steel was composed of normalizing at 1000-1050℃ for 0.5 h followed by water quenching or air cooling and tempering at 760℃ for 1.5 h.展开更多
文摘Mechanical and magnetic properties as well as their relationship in the reduced activation martensitic （RAM） steel were investigated in the temperature range from -90℃ to 20℃. Charpy impact tests show that the ductile-to-brittle transition temperature （DBTT） of the RAM steel is about -60℃. Low-temperature tensile tests show that the yield strength, ultimate tensile strength and total elongation values increase as temperature decreases, indicating that the strength and plasticity below the DBTT are higher than those above the DBTT. The coercive field （Hc） in the scale of logarithm decreases linearly with the increasing temperature and the absolute value of the slope of InHc versus temperature above the DBTT is obviously larger than that below the DBTT, also confirmed in the T91 steel. The results indicate that the non-destructive magnetic measurement is a promising candidate method for the DBTT detection of ferromagnetic steels.
基金Supported by Natural Science Foundation Guidance Plan of Liaoning Province of China(Grant No.2019-ZD-0362)CAS Key Laboratory of Nuclear Materials and Safety Assessment,Institute of Metal Research,Chinese Academy of Sciences(Grant No.2021NMSAKF02).
文摘Microstructure and mechanical properties of GN9 Ferritic/Martensitic steel for sodium-cooled fast reactors have been investigated through orthogonal design and analysis.Scanning electron microscopy(SEM),transmission electron microscopy(TEM),differential scanning calorimeter(DSC),tensile and impact tests were used to evaluate the heat treatment parameters on yield strength,elongation and ductile-to-brittle transition temperature(DBTT).The results indicate that the microstructures of GN9 steel after orthogonal heat treatments consist of tempered martensite,M23C6,MX carbides and MX carbonitrides.The average prior austenite grains increase and the lath width decreases with the austenitizing temperature increasing from 1000°C to 1080°C.Tempering temperature is the most important factor that influences the dislocation evolution,yield strength and elongation compared with austenitizing tempera-ture and cooling methods.Austenitizing temperature,tempering temperature and cooling methods show interactive effects on DBTT.Carbide morphology and distribution,which is influenced by austenitizing and tempering tempera-tures,is the critical microstructural factor that influences the Charpy impact energy and DBTT.Based on the orthogo-nal design and microstructural analysis,the optimal heat treatment of GN9 steel is austenitizing at 1000°C for 0.5 h followed by air cooling and tempering at 760°C for 1.5 h.
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.
基金financially supported by the National Key Research and Development Program of China(Grant No.2017YFB0304901)。
文摘In order to explore the eff ect of a small amount of rare earth addition in ultra-cleaned pipeline steel and the influence of the cooling process on the tensile and impact properties,three API X80 pipeline steels were fabricated by varying RE addition and the cooling process at the same time.Three microstructures with different features for a low C high Nb microalloyed high-strength pipeline steel and the corresponding mechanical properties were investigated.The results showed that even in the ultra-cleaned steel with O and S contents less than 10 ppm,the addition of RE would still cause an increase in the volume fraction of inclusions consisting of complicated RE oxysulfide and RE sulfide.More inclusions formed in the 112 ppm RE steel were harmful to the low temperature toughness,while few inclusions formed in the 47 ppm RE steel had almost no influence on the low temperature toughness.The two RE additions had no effect on strength of the steels.As the finishing cooling temperature was increased and the cooling rate was decreased within a certain range,the volume fractions of polygonal ferrite and quasi-polygonal ferrite as well as the number density and size of martensite–austenite islands were increased.Under such combined effect,the strength of the steels had almost no change.As the finishing cooling temperature was increased from 481 to 584℃and the cooling rate was reduced from 20 to 13℃/s,for the steel with 112 ppm addition of RE,there was an obvious decrease in the low temperature toughness.The reduced value(about 33 J)of the USE of steel consisted of two parts including the influence(about 18 J)of more inclusions formed due to 112 ppm addition of RE and the eff ect(about 15 J)of the lower high-angle grain boundaries.
基金National Natural Science Foundation of China(Nos.51874081 and 51574063)Fundamental Research Funds for the Central Universities(N150204012)Liaoning Province Doctoral Research Initiation Fund Guidance Project(No.20170520079).
文摘The effects of 0.01–0.11 wt.%Zr on the inclusions,microstructure,tensile properties,and impact toughness of the China low activation martensitic steel were investigated.Results showed that Zr exhibits good deoxidation and desulfurization abilities.The scanning electron microscope was used to examine the inclusions in the ingots.The main inclusions in the alloys were Zr–Ta–O,Zr–O,and Zr–O–S.However,some blocky Zr-rich inclusions appeared in Zr-2 and Zr-3 alloys.Typical martensitic structures were observed in the alloys,and average prior austenite grain sizes of 21.1,15.7,and 14.8µm were obtained for Zr-1,Zr-2,and Zr-3 steels,respectively.However,increasing Zr content of the steels deteriorated their mechanical property,owing to the blocky inclusions.The alloy with 0.01%Zr resulted in excellent mechanical properties due to the fine inclusions and the precipitation of Zr3V3C carbides.Values of 576 and 682 MPa were obtained for the yield strength and ultimate tensile strength of Zr-1 alloy,respectively.Furthermore,the ductile–brittle transition temperature of the alloy decreased to−85℃.
基金supported by the Natural Science Foundation Guidance Plan of Liaoning Province(No.2019-ZD-0362).
文摘The Charpy impact properties of 15Cr12MoVWN ferritic/martensitic steel for sodium-cooled reactors with variation in heat treatment factors and parameters are reported.The results show that the ductile-to-brittle transition temperature(DBTT)increased and the upper shelf energy(USE)decreased with increase in normalizing temperature.However,the variation tendency of DBTT and USE was the opposite with increase in tempering temperature.The tempering temperature showed a greater influence on USE than the normalizing temperature,and normalizing and tempering temperatures had the equally significant effects on DBTT,but the cooling method was not a significant factor for DBTT and USE.The prior austenite grain and M_(23)C_(6) size were the main influences on DBTT,and the dislocation density was the main factor affecting the variation of USE.The heat-treatment regime recommended for 15Cr12MoVWN steel was composed of normalizing at 1000-1050℃ for 0.5 h followed by water quenching or air cooling and tempering at 760℃ for 1.5 h.
