Quantitative Analysis of Precipitate in Vanadium-microalloyed Medium Carbon Steels Using Small-angle X-ray and Neutron Scattering Methods

Abstract

The microstructures and chemical composition of nano-precipitates in vanadium (V) steels were investigated by the alloy contrast variation method (ACV) using small-angle X-ray scattering (SAXS) coupled with small-angle neutron scattering (SANS) at holding temperatures ranging between 600 and 700°C. Both the SAXS and SANS profiles exhibited clear scattering, depending on the holding temperature, due to the presence of nano-precipitates. The scattering profiles of the precipitates are characteristic of spherical or disc-like particles. The average diameters of these precipitates increased from 0.5 nm at 600°C to 23 nm at 700°C, whereas the number density of the precipitates decreases with increased holding temperature. Therefore, the increasing holding temperature results in an increase in the growth rate of the precipitates. ACV analysis revealed that the chemical composition of the precipitates corresponds to NaCl-type vanadium carbide (VC) at 675 and 700°C, and as VC0.9 at 625 and 650°C. The formation of a different heterogeneity, non-NaCl type, was found in the sample at a holding temperature of 600°C. This probably corresponds to a precursor of the NaCl phase in the initial process of precipitation.

Practical applications of small-angle neutron scattering

“…If an external magnetic field is applied, the magnetic neutron scattering 127 is most pronounced perpendicular to the field and tends to zero in the parallel direction. 125 This can provide a way to remove the additional SANS arising from magnetic scattering, 128 but can also be used to select data arising from just the magnetic structure. To do this, measurements of the detected scattering in both positions are subtracted from one other to give the SANS from magnetic scattering alone.…”

“…This can be compared to the values calculated for expected precipitates. Systems studied using the ACV method include oxide clusters, 133 sulfide inclusions 134 and carbide precipitates 128 in a variety of different steels. This attractive method has advantages over TEM and even atom probe analysis, mainly in that it requires no sample perturbation, and could clearly be applied to other systems to gain insights into composition and crystallinity.…”

Intermediate-angle Neutron Scattering Instrument for Quantitative and Non-destructive Characterization of Nanostructures in Steels and Other Alloys

“…16) For the V added steels, Oba et al reported that nanoscale VC has off-stoichiometry in the early stage of precipitation. 15) Coakley et al reported partitioning of constituent elements to nanoscale ω precipitation in the titanium alloys. 17) As these examples show, the ACV technique is particularly useful when partitioning of the main constituent element occurs.…”

“…[8][9][10] Odetta et al reported detailed microstructural analysis of oxide dispersed strengthened (ODS) steels using a combination of SANS, ATP and TEM. 11,12) SANS studies of nanoscale carbides such as TiC, 13) NbC 14) and VC 15) has been reported by different groups. In addition to these basic SAS applications, one of the authors (MO) proposed a new way to determine phase by the combining SANS and SAXS methods.…”

Quantitative Analysis of Inclusions in Low Carbon Free Cutting Steel Using Small-angle X-ray and Neutron Scattering

“…3 using SANS and SAXS. [13][14][15][16][17] Most of them analyzed for nanoscale precipitates with a size of < 100 nm. Since SAS covers the analysis of quite a wide size range, from < 1 nm to > 1 μm, it is also useful for inclusions, which typically have sizes > 1 μm.…”