Damage development during the strain induced phase transformation of austenitic stainless steels at low temperatures

Abstract

The strain-induced martensitic transformation greatly affects the plastic behavior of the metastable austenitic stainless steels. The martensitic transformation continuously changes the initially homogeneous material into a strongly heterogeneous bi-phase one. In addition to the hardening behavior, this phenomenon would influence the damage growth and load-carrying capacity of the material during the plastic deformation. In this study, plastic behavior of the material AISI 304 including the hardening and damage growth, has been examined at low temperature; where a high rate of martensitic transformation affects the microstructure strongly. Experimental analysis and microscopic observations have been performed for evaluating the martensite content and damage growth. In addition, based on the continuum damage mechanics, a simplified damage evolution model has been proposed to capture the effect of phase transformation on the damage growth rate explicitly. The results show that the damage initiates with a considerable rate in early stages of transformation, however at higher levels of transformation, damage growth rate decreases until a sudden fracture. The presented model properly predicts the observed damage behavior.

Constitutive Models for the Strain Strengthening of Austenitic Stainless Steels at Cryogenic Temperatures with a Literature Review

“…The model parameters of AISI304 steel were determined and corrected according to the results from the tensile test at −196 • C. The calculated results of the strain-induced phase transformation and damage propagation behaviors of AISI304 and AISI316L at −268.8 • C agree with the literature [56,[60][61][62][63], as shown in Figure 6.…”

“…The above models were transformed into a system constitutive model based on irreversible thermodynamics [55], in which dissipation phenomena are coupled through a dissipation potential. Lemaitre's isotropic model was modified to a form that clearly relies on the martensitic volume fraction generated after strain-induced phase transformation at cryogenic temperatures and the material coefficients that rely on the change in martensitic volume fraction during phase transformation, resulting in dramatic material damage [56]. In finite element analysis of other constitutive models of strain-induced phase transformation at cryogenic temperatures [57][58][59][60], the results of damage evolution and crack propagation in austenitic stainless steels are also matched well with the results of strain experiments at cryogenic temperatures to maintain reliable accuracy.…”

“…The experimental results show that the phase transformation of austenitic stainless steels begins simultaneously with the generation of damage initiation during strain at cryogenic temperatures, but the increase of martensitic volume fraction inhibits the increase of damage propagation [56]. By modifying the material parameters of the Lemaitre model, the damage potential function (φ D ) of austenitic stainless steel during strain-induced phase transformation at cryogenic temperatures is obtained [61], as shown in Equation (2).…”

“…The cumulative plastic strain ( . ε P ), another important problem during strain of stainless steels at cryogenic temperatures, is also determined according to the rotational plastic deformation rate [56], as shown in Equation ( 6).…”