Ni−Co−C alloy coatings with exceptional properties were fabricated via electrodeposition using an ammonium oxalate−ammonium citrate system.The optimized coatings exhibited dense crystallization with a distinct granula...Ni−Co−C alloy coatings with exceptional properties were fabricated via electrodeposition using an ammonium oxalate−ammonium citrate system.The optimized coatings exhibited dense crystallization with a distinct granular surface,where large particles were covered with nanoscale clusters.Additionally,C atoms primarily existed within the coatings as a solid solution,maintaining the FCC structures.Compared to binary Ni−Co coatings,the Ni−Co−C alloy coatings exhibited significantly improved hardness,wear resistance,and adhesion strength,which could be attributed to the potential strengthening effect of the C atoms.Specifically,the introduction of C atoms optimized the local charge density and electron distribution in the alloy,transforming local weak ionic bonds into strong covalent interactions,thereby enhancing the bonding capability between the corresponding atoms in the NiCo bulk.展开更多
Toughness is an important property for steels used in engineering applications. However, recent toughness testing has shown the existence of a significant fluctuation in toughness in a single rolled plate of titanium ...Toughness is an important property for steels used in engineering applications. However, recent toughness testing has shown the existence of a significant fluctuation in toughness in a single rolled plate of titanium micro-alloyed steel. The underlying causes of this fluctuation were investigated by fractography, analysis of microstructure and measurement of inclusions. Coarse and distributed TiN inclusions were responsible for the toughness variation, as they tended to act as the potential cleavage initiators to form micro-cracks. From a calculation of the local fracture stress, the critical size of coarse TiN inclusions for dominating micro-crack propagation was 4.93 μm, and similarly that of ferrite grains was 36.6μm. Under current casting and thermo-mechanically controlled processing schedules, the toughness fluctuation of rolled steel plates can be primarily attributed to the fraction of coarse TiN inclusions larger than 5μm. A corresponding relationship between impact energy and the proportion of coarse TiN inclusions was established. Finally, a normalizing treatment was applied to refine the ferrite grains of rolled steel plates. Despite the presence of coarse TiN inclusions, this refinement in ferrite grains minimized the toughness fluctuation and improved the uniformity of the impact properties of the steel plates.展开更多
Controlling the flow behavior in the mold in an appropriate way is the basis for realizing the billet ultra-high speed continuous casting.Based on the new proposed physical water modeling experiment considering the ef...Controlling the flow behavior in the mold in an appropriate way is the basis for realizing the billet ultra-high speed continuous casting.Based on the new proposed physical water modeling experiment considering the effects of solidified shell and hydrostatic pressure,the flow behavior in the mold with cross section of 160 mm 9160 mm during continuous casting of billet is regulated by optimizing the inner diameters and immersion depths of submerged entry nozzle at the ultra-high casting speeds of 5.0–6.5 m/min.The results show that under the premise of no slag entrainment,as well as uniform coverage and keeping good fluidity of liquid slag layer on the top free surface of the fluid in the mold,the appropriate parameters of submerged entry nozzle under the ultra-high casting speed of billet are 50 mm in inner diameter,95 mm in outer diameter and 180 mm in immersion depth.And on the basis of the obtained parameters of submerged entry nozzle,it can be known that the reasonable ranges of level fluctuation and impacting depth of the stream in the mold are about 0.82-1.11 and 593-617 mm,respectively.展开更多
A combined model to predict austenite grains growth of titanium micro-alloyed as-cast steel during reheating process was established.The model invoIves the behaviors of austenite grains growth in continuous heating pr...A combined model to predict austenite grains growth of titanium micro-alloyed as-cast steel during reheating process was established.The model invoIves the behaviors of austenite grains growth in continuous heating process and isothermal soaking process,and the variation of boundary pinning efficiency caused by the dissolution and coarsening kinetics of sec on d-phase particles was also con sidered into the model.Furthermore,the experimental verificatio ns were performed to examine the prediction power of the model.The results revealed that the mean austenite grains size increased with the increase in reheating temperature and soaking time,and the coarsening temperature of austenite grains growth was 1423 K under the current titanium content.In addition,the reliability of the predicted results in continuous heating process was validated by continuous heating experimenls.Moreover,an optimal regression expression of austenite grains growth in isothermal soaking process was obtained based on the experimental results.The compared results indicated that the combined model in conjunction with precipitates dissolution and coarsening kinetics had good reliability and accuracy to predict the austenite grains growth of titanium micro-alloyed casting steel during reheating process.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52274320,52074053)。
文摘Ni−Co−C alloy coatings with exceptional properties were fabricated via electrodeposition using an ammonium oxalate−ammonium citrate system.The optimized coatings exhibited dense crystallization with a distinct granular surface,where large particles were covered with nanoscale clusters.Additionally,C atoms primarily existed within the coatings as a solid solution,maintaining the FCC structures.Compared to binary Ni−Co coatings,the Ni−Co−C alloy coatings exhibited significantly improved hardness,wear resistance,and adhesion strength,which could be attributed to the potential strengthening effect of the C atoms.Specifically,the introduction of C atoms optimized the local charge density and electron distribution in the alloy,transforming local weak ionic bonds into strong covalent interactions,thereby enhancing the bonding capability between the corresponding atoms in the NiCo bulk.
基金This work was financially supported by the National Natural Science Foundation of China （NSFC, Grant Nos. 51374260, 51504048 and 51611130062）. The authors thank the members of Laboratory of Metallurgy and Materials, Chongqing University, for the support of this work.
文摘Toughness is an important property for steels used in engineering applications. However, recent toughness testing has shown the existence of a significant fluctuation in toughness in a single rolled plate of titanium micro-alloyed steel. The underlying causes of this fluctuation were investigated by fractography, analysis of microstructure and measurement of inclusions. Coarse and distributed TiN inclusions were responsible for the toughness variation, as they tended to act as the potential cleavage initiators to form micro-cracks. From a calculation of the local fracture stress, the critical size of coarse TiN inclusions for dominating micro-crack propagation was 4.93 μm, and similarly that of ferrite grains was 36.6μm. Under current casting and thermo-mechanically controlled processing schedules, the toughness fluctuation of rolled steel plates can be primarily attributed to the fraction of coarse TiN inclusions larger than 5μm. A corresponding relationship between impact energy and the proportion of coarse TiN inclusions was established. Finally, a normalizing treatment was applied to refine the ferrite grains of rolled steel plates. Despite the presence of coarse TiN inclusions, this refinement in ferrite grains minimized the toughness fluctuation and improved the uniformity of the impact properties of the steel plates.
基金financially supported by the National Science Foundation of China(NSFC)(Grant Nos.51874060 and 52074053).
文摘Controlling the flow behavior in the mold in an appropriate way is the basis for realizing the billet ultra-high speed continuous casting.Based on the new proposed physical water modeling experiment considering the effects of solidified shell and hydrostatic pressure,the flow behavior in the mold with cross section of 160 mm 9160 mm during continuous casting of billet is regulated by optimizing the inner diameters and immersion depths of submerged entry nozzle at the ultra-high casting speeds of 5.0–6.5 m/min.The results show that under the premise of no slag entrainment,as well as uniform coverage and keeping good fluidity of liquid slag layer on the top free surface of the fluid in the mold,the appropriate parameters of submerged entry nozzle under the ultra-high casting speed of billet are 50 mm in inner diameter,95 mm in outer diameter and 180 mm in immersion depth.And on the basis of the obtained parameters of submerged entry nozzle,it can be known that the reasonable ranges of level fluctuation and impacting depth of the stream in the mold are about 0.82-1.11 and 593-617 mm,respectively.
基金National Natural Science Foundation of China(Grant Nos.51504048,51874060,51874059 and 51611130062)The authors would like to acknowledge the members of Laboratory of Metallurgy and Materials,Chongqing University,for the support of this work.
文摘A combined model to predict austenite grains growth of titanium micro-alloyed as-cast steel during reheating process was established.The model invoIves the behaviors of austenite grains growth in continuous heating process and isothermal soaking process,and the variation of boundary pinning efficiency caused by the dissolution and coarsening kinetics of sec on d-phase particles was also con sidered into the model.Furthermore,the experimental verificatio ns were performed to examine the prediction power of the model.The results revealed that the mean austenite grains size increased with the increase in reheating temperature and soaking time,and the coarsening temperature of austenite grains growth was 1423 K under the current titanium content.In addition,the reliability of the predicted results in continuous heating process was validated by continuous heating experimenls.Moreover,an optimal regression expression of austenite grains growth in isothermal soaking process was obtained based on the experimental results.The compared results indicated that the combined model in conjunction with precipitates dissolution and coarsening kinetics had good reliability and accuracy to predict the austenite grains growth of titanium micro-alloyed casting steel during reheating process.
