Tensile flow and work hardening behaviour of 9Cr–1Mo ferritic steel in the frame work of Voce relationship

Comparative tensile flow and work hardening behaviour of thin section and forged thick section 9Cr–1Mo ferritic steel in the framework of Voce equation and Kocks–Mecking approach

“…8) and hr-r and in the variations of work hardening parameters associated with Voce equation (Figs. 9-11) and K-M approach with temperature observed for plate and tubeplate forging are in agreement with those reported for ferritic and austenitic steels [11][12][13][14][15]24].…”

“…Marginal difference in the respective work hardening parameters with increase in temperature obtained for plate and tubeplate forging at room and intermediate temperatures suggests that the dislocation substructural behaviour in its totality are not very different in the two temperature regimes. Therefore, as suggested [15,28], long range stress field due to dislocation multiplication and its interaction is expected to play a major role at room and intermediate temperatures.…”

“…Recent investigation on P9 steel for wrapper applications in future sodium cooled fast reactors has demonstrated that a combination of Ludwigson and Hollomon equations provide the best description of tensile r-e behaviour with the lowest v 2 values [24]. Alternately, Voce equation as a single relationship can describe tensile flow behaviour with marginally higher v 2 values in the range of temperatures of interest for useful engineering applications [15,24]. v 2 values less than 10 obtained for both plate and tubeplate forging in the range 300-873 K ( Table 2) (Fig.…”

“…12) with increasing temperature can be ascribed to change in controlling deformation mechanism from cross-slip to climb of dislocations and subboundary migration at high temperatures. It has been reported that at low and intermediate temperatures, where crossslip is dominant, n V,Voce is expected to have a low absolute value [14,15,39]. A change in controlling mechanism from cross-slip to dislocation climb and subboundary migration at high temperatures leads to high n V,Voce and h 0,K-M values .…”

“…n V describes the rate at which the stress from its initial value tends to reach steady state or saturation stress value [6]. The applicability of Voce relationship for describing stress-strain behaviour useful for engineering applications has been demonstrated for ferritic, pearlitic-ferritic and austenitic stainless steels [11][12][13][14][15]. In the Kocks-Mecking phenomenological approach [7,8], the evolution of dislocation structure with strain at constant strain rate is assumed as a single structural parameter responsible for plastic flow.…”