2D RVE based micro-mechanical modeling with real microstructures of heat-treated 20MnMoNi55 steel

Effect of microstructural constituents and morphological characteristics on low cycle fatigue behaviour of inter-critically annealed 20MnMoNi55 steel

“…M represents the Taylor factor as mentioned earlier. It was shown in the previous literature 1,2 that as-received 20MnMoNi55 steel shows a yield point elongation phenomenon, whereas the heat-treated 20MnMoNi55 steels (DP steels) exhibit continuous yielding behaviour during the uniaxial monotonic deformation. The yield point elongation behaviour is an aftermath of the Cottrell atmosphere, where the interstitial carbon atoms hindrances in dislocation mobility so the critical stress required to overcome the dislocation barrier is much higher than the stress required to maintain its mobility during deformation.…”

“…Hence to transform it into ferrite and martensite with a range of fractional variation, a proper design of heat treatment schedules was established based on critical temperatures obtained from the dilatometric test as discussed in a previous article. 2 A 4 mm diameter and 10 mm long cylindrical specimen was used for dilatometric testing where it was heated up to 1100 °C with a heating rate of 1 °C/s. Thus, the obtained temperature versus dilation curve from the experimental result shows the A c1 and A c3 temperatures of about 758 °C and 825 °C, respectively.…”

“…(a) Dilation versus temperature diagram and (b) a schematic representation of heat treatment schedules. 2 …”

“…In this context, reactor pressure vessel (RPV) steel 20MnMoNi55 was transformed through a series of inter-critical heat treatment procedures to achieve a variation of martensite fraction in the ferrite matrix as reported in the literature. 1,2 The purpose of such transformation in its constituent phases was to achieve higher specific strength and fatigue durability without sacrificing much in its total elongation. Previously to improve the impact toughness of bainitic RPV steel MnMoNi, Xie et al 3 have already proposed an inter-critical heat treatment procedure to introduce martensite and austenite as its constituent phases.…”

“…So, to introduce RVEs considering actual microstructures obtained from OM, a python scripting interface is utilized in an ABAQUS FE environment for mapping coordinates of grain boundaries as already discussed in the previous literature. 2 Introduction of a Gurson–Tvergaard–Needleman damage model along with a constitutive flow rule of individual phases in RVE-based FE simulation was also proposed by Uthaisangsuk et al 30–33 for predicting the micromechanical failure mechanism. In contrary to the observed deformation behaviour as homogeneous in a macroscopic viewpoint, multiphase material actually experiences deformation inhomogeneity through strain partitioning among the constituent phases.…”