Lots of work has been done to investigate slab surface microstructure evolution during continuous casting in order to improve hot ductility and avoid transverse cracks.The slab surface microstructure after continuous ...Lots of work has been done to investigate slab surface microstructure evolution during continuous casting in order to improve hot ductility and avoid transverse cracks.The slab surface microstructure after continuous casting was characterized by optical microscopy,and the precipitation behavior was investigated by transmission electron microscopy.At the same time,the mechanical properties of the slabs were measured using a Gleeble 1500 Dthermal simulator and the transformation temperatures were examined by means of a thermal dilatometer.The experimental results show that homogeneous microstructure without film-like ferrites and chain-like precipitates at grain boundary can be obtained through surface intensive cooling and transverse cracks do not occur on the slab surface.For the experimental steel,fine ferrite can form at slab surface when the water flow rate is larger than 1560L/min at vertical section.As the distance to surface increases,microstructure turned to ferrite and pearlite.Moreover,nano-size carbonitrides precipitated in the ferrite grain and the size was larger at the junction of the dislocations.The mechanical experiment results show that the hot ductility of the sample deformed at 650°C was better than that of the sample deformed at 750°C.The reason is that filmlike ferrite formed at the grain boundary in the sample deformed at 750°C.Thus,the slab must be cooled quickly below Ar3 to prevent the occurrence of film-like ferrite and transverse cracks on the slab surface during casting.展开更多
The oxidation behavior of Fe-based amorphous ribbons was tested by annealing at 380℃ in air for different time with heat treatment furnace and analyzed by X-ray photoelectron spectroscopy （XPS） and scanning electro...The oxidation behavior of Fe-based amorphous ribbons was tested by annealing at 380℃ in air for different time with heat treatment furnace and analyzed by X-ray photoelectron spectroscopy （XPS） and scanning electron micros- copy （SEM）. The mechanism of oxides formation of the amorphous ribbons was discussed in detail. The results showed that the oxides were mostly B2O3 , SiO2 and Fe2O3 or FeO. With the increase of annealing time and holding temperature, the fraction of the oxides on the ribbon surface increased and the size of the oxides became larger due to the generation of new oxides and the coalescence of small oxides. The oxides have different shapes, such as round, rod and needle-shaped. Experimental results also showed that the oxides nucleated at fish scale, air pocket and impu-rities in priority, and the growth of the oxides was controlled by the diffusion of atoms. With the increase of the distance to the ribbon surface, the oxygen concentration decreased dramatically. Due to the low binding energy of B2O3 and the large diffusion coefficient of B atom, the B elemaent was oxidized firstly compared with other elements. More- over, the oxidation deoths of the B2O3 and SiO2 were larger than that of Fe2O3.展开更多
文摘Lots of work has been done to investigate slab surface microstructure evolution during continuous casting in order to improve hot ductility and avoid transverse cracks.The slab surface microstructure after continuous casting was characterized by optical microscopy,and the precipitation behavior was investigated by transmission electron microscopy.At the same time,the mechanical properties of the slabs were measured using a Gleeble 1500 Dthermal simulator and the transformation temperatures were examined by means of a thermal dilatometer.The experimental results show that homogeneous microstructure without film-like ferrites and chain-like precipitates at grain boundary can be obtained through surface intensive cooling and transverse cracks do not occur on the slab surface.For the experimental steel,fine ferrite can form at slab surface when the water flow rate is larger than 1560L/min at vertical section.As the distance to surface increases,microstructure turned to ferrite and pearlite.Moreover,nano-size carbonitrides precipitated in the ferrite grain and the size was larger at the junction of the dislocations.The mechanical experiment results show that the hot ductility of the sample deformed at 650°C was better than that of the sample deformed at 750°C.The reason is that filmlike ferrite formed at the grain boundary in the sample deformed at 750°C.Thus,the slab must be cooled quickly below Ar3 to prevent the occurrence of film-like ferrite and transverse cracks on the slab surface during casting.
基金Item Sponsored by National Natural Science Foundation of China(51374080)
文摘The oxidation behavior of Fe-based amorphous ribbons was tested by annealing at 380℃ in air for different time with heat treatment furnace and analyzed by X-ray photoelectron spectroscopy （XPS） and scanning electron micros- copy （SEM）. The mechanism of oxides formation of the amorphous ribbons was discussed in detail. The results showed that the oxides were mostly B2O3 , SiO2 and Fe2O3 or FeO. With the increase of annealing time and holding temperature, the fraction of the oxides on the ribbon surface increased and the size of the oxides became larger due to the generation of new oxides and the coalescence of small oxides. The oxides have different shapes, such as round, rod and needle-shaped. Experimental results also showed that the oxides nucleated at fish scale, air pocket and impu-rities in priority, and the growth of the oxides was controlled by the diffusion of atoms. With the increase of the distance to the ribbon surface, the oxygen concentration decreased dramatically. Due to the low binding energy of B2O3 and the large diffusion coefficient of B atom, the B elemaent was oxidized firstly compared with other elements. More- over, the oxidation deoths of the B2O3 and SiO2 were larger than that of Fe2O3.
