On the significance to use dislocation-density-related constitutive equations to correlate strain hardening with microstructure of metallic alloys: The case of conventional and austempered ductile irons

The Role of Microstructure on Tensile Plastic Behavior of Ductile Iron GJS 400 Produced through Different Cooling Rates, Part I: Microstructure

“…Angella et al [19] shows that the dislocation-density-related Voce equation describes properly the correlations between strain hardening and microstructure of metallic alloys. From published literature [19][20][21][22][23][24], there is limited information on the effect of microstructure on tensile plastic behavior of ductile iron in terms of the strain hardening effect and micro-mechanisms occurring during deformation of its microstructure. Hence, the tensile flow curves modeling associated with an explicit correlation between plastic behavior and some microstructure parameters have not yet been clearly disclosed.…”

Validation of a New Quality Assessment Procedure for Ductile Irons Production Based on Strain Hardening Analysis

“…Firstly, the Voce equation has been proved to be more reliable on fitting tensile flow curves and determining the uniform elongations [8,19,20]. In Reference [8], it has been reported that theoretical uniform strains ε u,p and the experimental ε u,exp matched very well in IDIs and ferritic-pearlitic DIs with errors between experimental and theoretical values between 1% and 4%, if Voce formalism was used, in opposition to other constitutive equations, like Hollomon and Hollomon-type equations, where deviations between 50 and 100% were found. Secondly, in the here-proposed approach, the e r,mdf is calculated by the Voce parameters found from the tensile flow curve itself, by replacing e u (see Equations (4) and (5)) to e r,mdf .…”

“…where σ is the true flow stress, ε p the true plastic strain, σ V is the saturation stress that is achieved asymptotically with straining, ε c is the characteristic transient strain that defines the rate with which σ V is approached, and σ o is the back-extrapolated stress to ε p = 0. Voce equation has been successfully applied to a wide number of metallic materials, like copper [18,19], austenitic stainless steels [21,22], aluminum alloys [13][14][15][16], ferritic-pearlitic DIs, IDIs, and ADIs [8,9,11,12], and also solid solution and precipitation strengthened nickel based superalloys [23]. The differential form of the Voce equation is used to investigate the strain hardening behavior of IDIs:…”

“…Due to the demand of improving mechanical properties, new chemical compositions and production routes of Ductile Irons (DIs) have been explored to obtain different microstructures. Thus, new classes of advanced DIs have been produced, that are, for instance, the alloyed SiBoDur [1] and High Silicon Strengthened (HSiS) DIs, i.e., with silicon content above 3.5-4.0 wt% [2][3][4], and the Austempered DIs (ADIs) [5][6][7][8] and Isothermed DIs (IDIs) [8] that are produced through heat treatments. The current international standards were originally produced for classifying conventional DIs, where silicon content is almost constant (1.8-2.8 wt%) and the pearlite to ferrite ratio, changing because of alloying elements like copper, is the key microstructure parameter that increases yield and tensile strengths, and reduces elongations to rupture.…”

The Role of Microstructure on the Tensile Plastic Behaviour of Ductile Iron GJS 400 Produced through Different Cooling Rates—Part II: Tensile Modelling

“…At strain ε P = 0, σ G was assumed to be nil because of the negligible initial dislocation density of GJS 400 in the cast conditions. The total dislocation-density ρ increases because of straining, according to the mechanistic evolution equation by Kocks-Mecking-Estrin [22][23][24][25][26][27][28]:…”