Synchrotron Investigation on the Precipitation Behaviour of Niobium Microalloyed Steel

Abstract

The precipitation and dissolution behavior of niobium carbo-nitrides is of particular interest for many technical applications. Niobium-microalloyed high strength low alloy (HSLA) steels are widely used in civil construction, automobile and line pipe applications. These steels rely on thermomechanical processing. In this context, coupled processes like thin slab casting and thermomechanical rolling of microalloyed steel grades require most precise information on the precipitation state at the individual processing steps. Reasonable equations for the solubility product at thermal equilibrium can be taken from literature but kinetics is largely unknown. Conventional X-ray technology is not able to detect small volume fractions below 0.1% of nanoscale precipitates. Investigation of nanoscale niobium precipitates by transmission electron microscopy (TEM) analysis or chemical extraction methods is common practice. However, TEM suffers from statistical relevance and chemical extraction will not give information on particle distribution and orientation. Investigation by high energy synchrotron X-ray of about 100 keV offers statistical relevance as volumes of several cubic millimeters are regarded. This large reflecting sample volume allows to detect nanometer-sized particles and provides very high angular resolution leading to an exact determination of the reflection peaks. The wavelength of around 0.12 Å is able to analyze nanometer-sized particles. Due to the high energy of the applied synchrotron radiation, precipitation and dissolution reactions could be observed during thermal treatment inside a soaking furnace. The results establish this technology for analysis of nanoscale niobium carbo-nitride precipitates

Revealing Precipitate Development During Hot Rolling and Cooling of a Ti–Nb Micro‐Alloyed High Strength Low‐Alloy Steel through X‐Ray Scattering

“…In this context, it has previously been shown that with high‐energy synchrotron X‐ray scattering, the increase of precipitates when annealing above 500 °C was detectable in micro‐alloyed Nb steels with volume fractions below 0.1%. [ 7,8 ]…”

“…In this context, it has previously been shown that with high-energy synchrotron X-ray scattering, the increase of precipitates when annealing above 500 °C was detectable in micro-alloyed Nb steels with volume fractions below 0.1%. [7,8] The primary objective of this work was to study precipitate development in a commercial Ti-Nb micro-alloyed steel in thermomechanically treated samples and to assess if high-energy synchrotron SAXS could be used to study mm-thick samples and to detect very small volume fractions of <10 nm sized particles. The high-energy synchrotron X-ray beamline P21.2 at DESY was used to track even minor changes of very small volume fractions of nanosized particles.…”

Precipitate number density determination in microalloyed steels by complementary atom probe tomography and matrix dissolution

“…Precipitate number densities cannot be determined via two-dimensional electron microscopy investigations on carbon extraction replicas and/or metallographically prepared cross sections of bulk samples. Further, the small volume fraction of precipitates (below 0.1%) limits the precipitate number density determination to high-resolution tomographic techniques such as X-ray diffraction in synchrotrons [22] or small-angle neutron scattering [5,23].…”

Fast X-ray diffraction crystal size distribution analysis

“…using EXPGUI (Toby, 2001) which is a graphical user interface for GSAS (Larson & Von Dreele, 2000) Such a non-ambient environment may for example be a halogen lamp furnace with a protective atmosphere, equipped with windows for X-rays diffraction measurements (e.g. Klinkenberg & Klein, 2016). In case of measurements in any sort of container, one of course always has to measure a reference sample in the same environment (yet usually at ambient conditions) to account for the likely attenuation effects e.g.…”