On the correlation between electron structure and short range atomic order in iron-based alloys

Change in the electron structure caused by C, N and H atoms in iron and its effect on their interaction with dislocations

Effect of nitrogen on the electron structure and stacking fault energy in austenitic steels

The effect of nitrogen and carbon on the strengthening of the austenitic steel Cr18Ni16Mn10 by grain boundaries is studied. It is established in accordance with previous results that, in contrast to carbon, nitrogen markedly increases the coefficient k in the Hall-Petch equation. Because of a pronounced planar slip induced by nitrogen and the absence of any noticeable segregation of nitrogen atoms at the grain boundaries, nitrogen austenite presents an excellent object for testing different existing models of grain boundary strengthening (pile-up of dislocations, grain boundary dislocation sources, work hardening). Based on the analysis of available data and measurements of interaction between nitrogen or carbon atoms and dislocations it is shown that the nitrogen effect can be attributed to a strong blocking of dislocation sources in grains adjacent to those where the slip started.

Grain boundary strengthening in austenitic nitrogen steels

Diagnostic experimental results on the hydrogen embrittlement of austenitic steels

The effect of nitrogen and carbon on the electronic and magnetic properties of the iron-base Fe56Cr18Ni16Mn10 3d-alloy with f.c.c. lattice (austenite) is studied by means of the magnetic resonance. It is shown that the electron state density on the Fermi surface in the nitrogen austenite is one order of magnitude higher than that in the carbon one. Based on measurements of the temperature dependence of the g-factor the existence of superparamagnetic clusters is stated, the latter being obviously clusters of substitutional solutes. Signs and values of the exchange interaction between conduction electrons and other magnetic subsystems are obtained from the analysis of the temperature dependence of the paramagnetic susceptibilities. The exchange interaction between conduction electrons and isolated localised spins has antiferromagnetic character, while conduction electron—cluster interaction is ferromagnetic. The size of the clusters is markedly higher in the carbon austenite. This difference in structural homogeneity can be used for an explanation of the higher thermodynamic stability of the nitrogen austenite as compared to the carbon one.



Der Einflus von Stickstoff und Kohlenstoff auf die magnetischen Eigenschaften der Fe56Cr18Ni16Mn10 Eisenlegierung mit k.f.z. Gitter (Austenit) wird mit Hilfe der magnetischen Resonanz untersucht. Es wird gezeigt, das die Dichte der Elektronenzustande auf der Fermi-Oberflache im Stickstoffaustenit um eine Grosenordnung hoher als die im Kohlenstoffaustenit ist. Aus den Messungen der Temperatur-abhangigkeit des g-Faktors wird auf die Existenz von superparamagnetischen Clustern, d. h. Clustern von gelosten, substitutionellen Atomen, geschlossen. Vorzeichen und Werte der Austauschwechselwirkung zwischen freien Elektronen und anderen magnetischen Systemen werden aus der Analyse der Temperaturabhangigkeit der paramagnetischen Suszeptibilitat erhalten. Die Austauschwechselwirkung zwischen freien Elektronen und isolierten, lokalisierten Spins hat antiferromagnetischen Charakter, wahrend die Wechselwirkung zwischen freien Elektronen und Clustern ferromagnetisch ist. Die Grose der Cluster ist merklich hoher im Kohlenstoffaustenit. Dieser Unterschied in der strukturellen Homogenitat kann zur Erklarung der hoheren thermodynamischen Stabilitat des Stickstoffaustenits im Vergleich zum Kohlenstoffaustenit herangezogen werden.

Exchange interaction between electron subsystems in iron-based F.C.C. alloys doped by nitrogen or carbon

Relaxation and hysteretic phenomena caused by hydrogen in Crl8Ni15, Cr25Ni20, and Crl8Nil6Mn10 steels have been studied by using a low-frequency internal friction (IF) technique. Five IF peaks were observed in the temperature range of 80 to 450 K; three of them are of relaxation nature and two others have a hysteretic character. The enthalpies of activation have been evaluated by means of thermoactivation analysis. Short-range migration of hydrogen atoms has been found to be responsible for the relaxation peaks, while the hysteretic peaks have been attributed to the out-gassing processes accompanied by cracking. It follows from the data on orientation dependence of the relaxation strength and values of the activation enthalpies that relaxation has a Snoeklike nature and is caused by reorientation of complexes of hydrogen atoms with substitutional solutes causing noncubic defects, the symmetry of which is not higher than orthorhombic. Study of the composition effects has led to the conclusion that different substitutional solutes contribute to different compo-nents of the relaxation spectra in accordance with their influence on hydrogen diffusivity. Effect of electron irradiation on hydrogen-induced relaxation was studied and explained in terms of short-range atomic order. No indication of hydrogen-induced Snoek-Koster (SK) relaxation was observed in accordance with the data available evidencing absence of SK relaxation in face-centered cubic (fcc) metals having low values of stacking fault energy.

A. V. Tarasenko

Papers

Exchange interaction between electron subsystems in iron-based F.C.C. alloys doped by nitrogen or carbon

Internal friction in hydrogen-charged CrNi and CrNiMn austenitic stainless steels

The influence of nitrogen on the paramagnetic properties of the multicomponent d-element iron-based alloy