Effect of M-C (M valence Mo, Mn, and Cr) Atomic Pairs on Creep Properties of Fe-M-C Ternary Alloys

摘要

Effects of solute elements, Mo, Mn, and Cr, on thecreep strength were examined by Fe-M-C (M valence Mo, Mn,and Cr) and Fe-C alloys in view of M-C atomic pairs. Thelargest strengthening effect was obtained by the addition of Moto the Fe-C alloy, and Mn, and Cr showed almost the samestrengthening effects in creep tests at 773K. Measurements ofinstantaneous elongation and contraction as a fraction of stresschange revealed the existence of instantaneous plastic strainduring steady state creep in all alloys. This indicates that thesteady state creep is controlled by recovery as in pure metals.For all alloys, the values of about 230GPa were obtained as thecoefficient of strain hardening by the method proposed by Ishidaand McLean. The recovery rate, r, the coefficient of strainhardening, h, and the steady state creep strain rate, r, satisfiedthe Bailey-Orowan relationship in all alloys. These resultsindicate that the alloying element affects mainly the recoveryrate. From analysis by the model proposed by Sandstrom, it isconcluded that M-C pair reduces the climb velocity ofdislocations due to large interaction energies with dislocations.The magnitude of the reduction can be estimated from thebinding energy between M and C atoms and the diffusioncoefficient of M atom. The co-segregation of M and C atoms onedge dislocations is predicted by thermodynamic analysis, and itis pointed out that this may result in the apparent reduction ofthe dislocation climb velocity even in alloys containing verylimited amount of alloying elements.