Effect of carbon and nitrogen on chemical homogeneity of fcc iron-based alloys
- PDF / 193,457 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 10 Downloads / 183 Views
I.
INTRODUCTION
AUSTENITIC CrNi and CrNiMn steels have been widely applied owing to their excellent corrosion properties, but low strength is still considered to be one of the unsolved problems of their design. Alloying with interstitials seems to be the most effective way of improving their mechanical properties.[1] Although carbon and nitrogen atoms have nearly the same effective sizes in solid solutions and, therefore, produce similar stress fields, the corrosion resistance of carbon-containing austenitic steels is significantly lower than that of steels alloyed with nitrogen. Mo¨ssbauer spectroscopy[2–6] has allowed a difference between the distributions of carbon and nitrogen atoms in the fcc solid solution to be observed, and different values of C-C and N-N interaction energies in the first and second coordination spheres were derived from Mo¨ssbauer data using the Monte Carlo method.[7] On the basis of Mo¨ssbauer studies,[2] it has been suggested that carbon atoms show a tendency for clustering and nitrogen atoms for short-range atomic ordering in iron-based austenites. Thus, the question of how the distribution of interstitials affects that of substitutional solutes is of both scientific and practical significance. Mo¨ssbauer spectra are sensitive to the nearest environment of iron atoms (within the limits of the first two coordination spheres) and, therefore, do not enable one to obtain information about the size and structure of the chemical inhomogeneities. The technique of small angle neutron scattering (SANS), along with the neutron depolarization measurements, may be more informative for this purpose. Neutrons are uncharged, difficult to absorb, and also have a magnetic moment; thus, they allow one V.G. GAVRILJUK, Professor and Head, A.L. SOZINOV, Senior Science Researcher, and A.G. BALANYUK, Young Science Researcher, are with the Department of Alloyed Steels, Institute of Metal Physics, Kiev 252142, Ukraine. S.V. GRIGORIEV, Research Fellow, O.A. GUBIN, G.P. KOPITSA, Science Researchers, A.I. OKOROKOV, Professor, and V.V. RUNOV, Senior Science Researcher, are with the Condensed Matter Department, Petersburg Nuclear Physics Institute, Gatchina 188350, Russia. Manuscript submitted November 15, 1996. METALLURGICAL AND MATERIALS TRANSACTIONS A
(1) to study bulk phenomena in materials as well as surface effects; (2) to distinguish between the contributions of nuclear and magnetic scattering cross sections (using polarized neutrons); and (3) to make a deep contrast of an object studied using a wide spectrum of natural neutron scattering amplitudes for different elements, as well as an isotope substitution for nuclear scattering and the change of polarization of neutrons in the case of magnetic scattering. This study seeks to clarify the effects of carbon and nitrogen on the chemical homogeneity of the multicomponent iron-based fcc solid solutions, which could be used as a basis for the explanation of differences in the thermodynamical stability of carbon and nitrogen austenitic steels. II.
EXPERIMENTAL
Data Loading...
