Papers by Keyword: Carbonitride

Abstract: NbC-xTi (C_0.7N_0.3)-10Ni-7.5VC (vol%) based cermets with 0, 5, 10, 15 or 25 vol% Ti (C_0.7N_0.3) were prepared by conventional pressureles liquid phase sintering at 1420°C in vacuum. Detailed microstructural investigation was performed by SEM, EPMA and XRD analysis. Sintering results indicated that the partial replacement of NbC by Ti (C_0.7N_0.3) had a significant effect on the carbide grain growth, microstructure, hardness as well as fracture toughness of the fully densified NbC-based cermets. The Ti (C_0.7N_0.3)-free NbC cermet was composed of homogeneous cubic (Nb,V)C solid solution grains, whereas core-rim structured NbC grains were observed in cermets with Ti (C_0.7N_0.3) addition. All sintered cermets with  15 vol% Ti (C_0.7N_0.3) were composed of a fcc solid solution Ni binder and a cubic core-rim solid solution (Nb,V,Ti)C phase with a Nb-rich core and a Ti-rich rim. 3.8 vol% of residual pristine Ti (C_0.7N_0.3) was present in the cermets with 25 vol% Ti (C_0.7N_0.3) addition. The 15 vol% Ti (C_0.7N_0.3) starting powder based cermet exhibited the finest average NbC grain size of 1.48 μm, with a core-rim structure and an interesting combination of hardness (1486 kg/mm²) and fracture toughness (8.7 MPa.m^1/2).

Abstract: By adding FeNCr6-A, K417G alloys with different nitrogen content from 4 to 32ppm were prepared by using the vacuum induction melting (VIM). The precipitation of the carbonitrides in the virgin alloys was studied. The results show that N mainly exists in Ti (N, C) phase which sometimes served as heterogeneous cores for the carbides in the alloy. Besides, a few isolated regular square blocky Ti (N,C) particles were also found in alloy with 10ppm N, and these isolated particles became larger in the alloy with 21ppm N. Moreover, as N level reaching 32ppm, the Ti (N,C) phase did not grown but these particles usually gathered together and formed many clusters. For the alloy with 4ppm N, the content of N in Ti (N,C) was lower, but for the alloys not less than 10ppm N, the N content of Ti (N,C) was higher and relatively stable.

Abstract: The paper analyzes the precipitation behavior of micro-alloy elements including Nb, V, Ti and its effect to ductility of the steel during thermal deformation process, study on relationship between Nb, C content and slab crack incidence rate, supply countermeasures to control crack incidence rate during continuous casting course from components adjustment and process discipline optimization.

Abstract: A thermodynamic model of the microalloy precipitation elements in austenite region for Fe-C-N-Al-Ti-Nb steel has been established. Through calculating the action of the microalloying element in austenite, it can be found that carbon in steel accelerates the precipitation of Nb greatly, Nb in solution decreases quickly and the precipitation of Nb increases quickly with the increase of carbon. When the C in steel is low, the main constituent of the precipitation is TiN in high temperature, and TiN guadually turns to be NbC with the decrease of tempertature. When the carbon in steel is high，the main constituent in the precipitation is NbC even though the temperature is higher. The nitrogen in steel has a slight effect on NbN precipitation.

Abstract: As for the techno -interface of CC-HR region, the precipitation and dissolution of carbonitride in Nb micro-alloyed steel E36 were studied during continuous casting, roller conveying, stack cooling, heat-preserved and heating units in typical slab process flow by hot simulation experiment based on study of heat transfer. The results are as follows: Ti(C,N), and (Ti,Nb)(C,N) precipitate in turn in continuous casting and conveying. A few (Ti,Nb)(C,N) particles are not solid solute completely after heating. The precipitation of carbonitride is effected significantly by different cooling rate in conveying. When slab conveied at the rate of 6.00 °C/min and then cooled down to 600°C, the distribution density of carbonitride particles is higher, and the average equivalent diameter of carbonitride particles is smaller, some carbonitride particles distribute along the austenitic grain boundaries and the generation elements of carbonitride particles are under over-saturation state. When slab conveyed at the rate of 0.30 °C/min or 0.15 °C/min and then cooled down to 400°C, the distribution density of carbonitride particles is lower, and the average equivalent diameter of carbonitride particles is bigger, the carbonitride particles precipitate fully. The behavior of carbonitride in slab are effected by different thermal history in heating. The status of carbonitride is effected insignificantly by different thermal history after heating.

Abstract: The carbonitrides precipitates in Nb-V micro-alloyed steels were investigated by 3DAP. Much difference in the composition and size of the precipitates were observed. It is proposed that the carbon atoms segregated first at the dislocation or vacancy, and the vanadium and niobium atoms diffused to these sites to form the V-C, V-Nb-C clusters, leading to the formation of (Nb,V)C complex phase. The composition becomes inhomogeneity as the precipitates grow up.

Abstract: Thermo-simulation test, transmission electron microscopy(TEM) and nanobeam EDS technique were used to investigate the strain induced precipitation behavior during relaxation process after deformed austenite in Mn-Mo-Nb-B low carbon multi-microalloyed Steel. The experiment results indicate that during isothermal held at 850 °Cand 900 °C after predeformation, the size of precipitates occurred in the Mn-Mo-Nb-B steel at different stage is smaller than that happened in the only Nb and Ti-bearing microalloyed steel. The ratio of Nb/Ti to precipitates increased with the relaxing time. After being held longer, Mo atoms would enter the lattice of (Nb,Ti)(C,N) precipitates and the amount in the precipitates increased with the relaxation as time prolonged.