Mechanisms and kinetics of tempering in weldments of 9Cr-1Mo steel

The microstructural mechanisms and the kinetics of the tempering process in an MMA welded 9Cr-1Mo steel have been studied in detail. Based on the micr ostructural studies of the various regions of the weldment tempered at diff erent temperatures, three distinct mechanisms could be identified for the g radual softening observed in the weldments. A classification scheme has bee n proposed based on which the temperature regimes over which tempering proc eeds through different mechanisms, have been rationalised. The kinetics of the tempering process have been studied using the temperature dependence of the rate of softening. The apparent activation energy of the tempering pro cess is evaluated using an Arrhenius analysis and the corresponding rate-co ntrolling process is identified as the diffusion of carbon in alpha-ferrite . (C) 2000 Elsevier Science B.V. All rights reserved.