Papers by Keyword: Intragranular Ferrite

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Authors: Sheng Fu Yu, Yi Lei, Zhi Yuan Li
Abstract: Self refining grain behavior of X80 pipeline steel in the heat affected zone was studied systematically by physical simulation method. The sizes and distribution of the inclusions which promote intra-granular ferrite nucleation were measured using the automatic image analyzer, and the figures of the intra-granular ferrite which has self refining grain behavior were observed using transmission electron microscopes with energy dispersive X-ray spectroscopy, the fracture toughness values of the coarse grain zone in the HAZ were also measured. The results show that the welding thermal cycle has nearly no effect on the sizes and distribution of the inclusions in the HAZ. The reasons of self-refining grain in the HAZ are that the small non-metallic inclusions such as MnO、 TiO、MnS、CuS and (Mn,Cu)S in X80 pipeline steel ,which can induce the nucleation of intra-granular ferrite in the welding process, and sympathetic nucleation of intra-granular ferrite makes the coarse grains refined in the HAZ. First intra-granular ferrite has large boundary energy and high density dislocation, which induce the sympathetic nucleation of intra-granular ferrite.
741
Authors: Hai Bo Li, Hong Yu Liu, Yu Huang
Abstract: In order to study the effect of second phase precipitation on the refinement of microstructures during static recrystallization, the former researched non-quenched and tempered vanadium-nitrogen steel was chosen to conduct single and double-pass compression experiment by hot deformation simulator and the fraction of static recrystallization at different isothermal times was calculated. The precipitates were analyzed by TEM with accessories of EDS and energy filter. The results showed that precipitates in austenite during the pass isothermal times were mainly the (Ti, V) (C, N) with size varying from 55 to 140 nm, and during cooling and phase transformation were mainly vermicular VC with length in the range of 22-100nm and width 13-39nm. The key factor for refining the final structures: during short isothermal times is static recrystallization; during static recrystallization stagnation plateau is intragranular ferrites nucleated on precipitation phases; after stagnation plateau is intragranular ferrites promoted by the local solute-poor regions.
991
Authors: Stanislaw Zajac
Abstract: A brief summary is given of the desired effects of precipitation of microalloy nitrides and carbides in austenite and ferrite prior, during and after g−a transformation. Precipitation of microalloy compounds of Nb(C,N), TiC and V(C,N) is discussed in relation to several grain refinement and precipitation strengthening mechanisms. An improved understanding of the thermodynamics and kinetics of precipitation and phase transformations is presented using the approach based on the chemical driving force. Nucleation of intragranular polygonal ferrite on VN particles that grow in austenite and the formation of acicular ferrite inside the austenitic grains in Vsteels is described. The role of carbon in increasing the driving force for nucleation is elucidated and the benefits of using microalloy carbo-nitrides for precipitation strengthening of bainitic steels are reviewed. An expanded view on the role of microalloy carbo-nitrides in grain refinement and precipitation strengthening is presented.
75
Authors: Fan Zheng Bu, Xue Min Wang
Abstract: In order to make a more intuitive and easier analysis the influence of different inclusions on the formation of ferrite, a layer of high purity oxide powder was added in the two parts of the Q235 steel artificially. The effect of the inclusions Ti2O3MgOZrO2 and Al2O3 on the nucleation of intragranular ferrite were studied by means of the physical simulation method. The microstructure of the micro-zone adjacent to the inclusions was observed and the elements of the micro-zone adjacent were analyzed. The results showed that the inclusions Ti2O3 and Al2O3 can form the ferrite layers at the oxides-steels interface; the inclusions Ti2O3 has an ability to induce the nucleation of intragranular ferrite; the inclusions Ti2O3 can change the chemical composition of the metal micro-zone adjacent to the inclusions, where the Mn depletion area was observed.
3134
Authors: Zhi Gang Yang, Chi Zhang, T. Pan
Abstract: The intragranular ferrite, which renders fabrication of fine-microstructure and improves toughness of welds in ultra-fine grain steels, is often observed to nucleation on non-metallic inclusion. The mechanism of this nucleation is related to the interfacial energy between austenite, ferrite with inclusions, the solute depletion zone around the inclusions and the strain energy due to different thermal coefficients between matrix and inclusions, et al. The interfacial energy of iron with nitrides and carbides is crucial to promote the ferrite nucleation on such as VN. On the other hand, the composition change in local austenite is probably the control reason for ferrite on MnS and Ti2O3. The thermal strain energy is calculated to be far less than the driving force for phase transformation and not effective to promote ferrite nucleation unless at very small undercoolings.
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