The infamous type Ⅳ failure within the fine-grained heat-affected zone (FGHAZ) in G115 steel weldments seriously threatens the safe operation of ultra-supercritical (USC) power plants.In this work,the traditional the...The infamous type Ⅳ failure within the fine-grained heat-affected zone (FGHAZ) in G115 steel weldments seriously threatens the safe operation of ultra-supercritical (USC) power plants.In this work,the traditional thermo-mechanical treatment was modified via the replacement of hot-rolling with cold rolling,i.e.,normalizing,cold rolling,and tempering (NCT),which was developed to improve the creep strength of the FGHAZ in G115 steel weldments.The NCT treatment effectively promoted the dissolution of preformed M_(23)C_(6)particles and relieved the boundary segregation of C and Cr during welding thermal cycling,which accelerated the dispersed reprecipitation of M_(23)C_(6) particles within the fresh reaustenitized grains during post-weld heat treatment.In addition,the precipitation of Cu-rich phases and MX particles was promoted evidently due to the deformation-induced dislocations.As a result,the interacting actions between precipitates,dislocations,and boundaries during creep were reinforced considerably.Following this strategy,the creep rupture life of the FGHAZ in G115 steel weldments can be prolonged by 18.6%,which can further push the application of G115 steel in USC power plants.展开更多
The service performance of heat resistance steels is largely determined by the precipitation kinetics.The nucleation-growth-coarsening behaviors of precipitates in G115 martensitic heat resistance steel during long-te...The service performance of heat resistance steels is largely determined by the precipitation kinetics.The nucleation-growth-coarsening behaviors of precipitates in G115 martensitic heat resistance steel during long-term aging at 650℃ have been systemically investigated.The microstructural characteristics,precipitate morphology and alloying element distribution were studied by scanning electron microscopy,transmission electron microscopy and scanning transmission electron microscopy.The lognormal distribution fitting combined with the multiple regression analysis was adopted to evaluate the precipitate size distributions.Laves phase has longer incubation time,and its coarsening rate is almost one order of magnitude higher in comparison with that of M_(23)C_(6) carbide.Furthermore,the nucleation rate,number density,average radius,and volume fraction of two precipitates are simulated based on the classical nucleation theory and the modified Langer-Schwartz model.The precipitation behavior of Laves phase can be well explained with the Fe-W system as the interfacial energy takes 0.10 J/m^(2).In contrast,the simulation results of M_(23)C_(6) carbide in the Fe-Cr-C system are significantly overestimated,which results from the inhibitory effect of boron on coarsening.展开更多
The effects of annealing before normalizing and different cooling ways, i.e., air cooling, quenching, and water mist cooling after normalizing on the toughness of G115 steels were investigated. The impact tests showed...The effects of annealing before normalizing and different cooling ways, i.e., air cooling, quenching, and water mist cooling after normalizing on the toughness of G115 steels were investigated. The impact tests showed that the annealed samples had better toughness compared to the unannealed samples for three cooling ways. Microstructure observations revealed that the annealed samples had a more uniform grain distribution, smaller size and area fraction of M_(23)C_(6) particles along the grain boundaries, and lower dislocation density than those in the unannealed samples, which performed together for good toughness. Among three cooling ways, air cooling gave the best toughness due to the smallest occupancy of M23C6 particles in the grain boundaries. Thus, the combination of annealing conducted before normalizing and air cooling selected after normalizing can improve the toughness a lot of G115 steels.展开更多
基金financially supported by the National Key R&D Program of China(No.2022YFB3705300)the National Natural Science Foundation of China(Nos.U1960204 and 51974199)the Postdoctoral Fellowship Program of CPSF(No.GZB20230515)。
文摘The infamous type Ⅳ failure within the fine-grained heat-affected zone (FGHAZ) in G115 steel weldments seriously threatens the safe operation of ultra-supercritical (USC) power plants.In this work,the traditional thermo-mechanical treatment was modified via the replacement of hot-rolling with cold rolling,i.e.,normalizing,cold rolling,and tempering (NCT),which was developed to improve the creep strength of the FGHAZ in G115 steel weldments.The NCT treatment effectively promoted the dissolution of preformed M_(23)C_(6)particles and relieved the boundary segregation of C and Cr during welding thermal cycling,which accelerated the dispersed reprecipitation of M_(23)C_(6) particles within the fresh reaustenitized grains during post-weld heat treatment.In addition,the precipitation of Cu-rich phases and MX particles was promoted evidently due to the deformation-induced dislocations.As a result,the interacting actions between precipitates,dislocations,and boundaries during creep were reinforced considerably.Following this strategy,the creep rupture life of the FGHAZ in G115 steel weldments can be prolonged by 18.6%,which can further push the application of G115 steel in USC power plants.
基金financially supported by the National Key Research and Development Program of China(Grant Nos.2020YFB0311000 and 2017YFB0305201)the Fund of Key Laboratory of Advanced Materials of Ministry of Education(ADV22-12)the Jiangsu Funding Program for Excellent Postdoctoral Talent.
文摘The service performance of heat resistance steels is largely determined by the precipitation kinetics.The nucleation-growth-coarsening behaviors of precipitates in G115 martensitic heat resistance steel during long-term aging at 650℃ have been systemically investigated.The microstructural characteristics,precipitate morphology and alloying element distribution were studied by scanning electron microscopy,transmission electron microscopy and scanning transmission electron microscopy.The lognormal distribution fitting combined with the multiple regression analysis was adopted to evaluate the precipitate size distributions.Laves phase has longer incubation time,and its coarsening rate is almost one order of magnitude higher in comparison with that of M_(23)C_(6) carbide.Furthermore,the nucleation rate,number density,average radius,and volume fraction of two precipitates are simulated based on the classical nucleation theory and the modified Langer-Schwartz model.The precipitation behavior of Laves phase can be well explained with the Fe-W system as the interfacial energy takes 0.10 J/m^(2).In contrast,the simulation results of M_(23)C_(6) carbide in the Fe-Cr-C system are significantly overestimated,which results from the inhibitory effect of boron on coarsening.
基金supported by the National Natural Science Foundation of China(Grant No.5177io97)the China Postdoctoral Science,Foundation,(Grant_No.035-043201106)the_Tsinghua University Initiative_Scientific Research Program,and the Science Challenge Project(Grant No.TZ2018004).
文摘The effects of annealing before normalizing and different cooling ways, i.e., air cooling, quenching, and water mist cooling after normalizing on the toughness of G115 steels were investigated. The impact tests showed that the annealed samples had better toughness compared to the unannealed samples for three cooling ways. Microstructure observations revealed that the annealed samples had a more uniform grain distribution, smaller size and area fraction of M_(23)C_(6) particles along the grain boundaries, and lower dislocation density than those in the unannealed samples, which performed together for good toughness. Among three cooling ways, air cooling gave the best toughness due to the smallest occupancy of M23C6 particles in the grain boundaries. Thus, the combination of annealing conducted before normalizing and air cooling selected after normalizing can improve the toughness a lot of G115 steels.