Correlation of the Effects of Alloying Elements on the Hardenability of Steels to the Diffusion Coefficients of Elements in Fe

Abstract

Abstract:The effects of various alloying elements on the hardenability of steels are known experimentally, but the reasons for these effects are not well understood. In this work, the upper critical cooling rate was selected as the index of hardenability. Changes in the upper critical cooling rate of steel caused by the presence of alloying elements and the diffusion coefficients of those elements in the ã-phase of Fe, plotted on thermal conductivity-Young's modulus diagrams, showed similar patterns. The correlation between these factors was studied. Good correlation was found: the upper critical cooling rate decreased linearly with increasing diffusion coefficient of the alloying element in the ã-phase, i.e., the hardenability increased. It is considered that a large diffusion coefficient of an alloy element in the ã-phase increases its entropy and, on cooling, thermodynamically stabilizes the ã-phase, thereby preventing its transformation to the á-phase and retaining the ã-phase at a lower temperature, which consequently favors martensitic transformation even at low cooling rates.

Peculiarity of Zr in the Neutron Absorption Cross-section and Corrosion Resistance in Water

“…Formerly, the author showed that the corrosion resistance of Zircaloy was provided by the precipitates in the alloy matrix through the mechanism of the anodic protection [1]. Recently, the author introduced the diagram with thermal conductivity on the abscissa and Young's modulus on the ordinate to explain the various properties of elements [2][3][4][5][6]. This diagram will be called "TC-YM diagram" or "diagram".…”