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In elastic-plastic crystalline solids, intrinsic/extrinsic variables affect thecrack initiation and growth stages while dominating also the crack path habit. In thiscontext, the scale factor becomes highly important with further complexities that havebeen related to small volume components. Comprehensive overview on fracture physicsremains essential in order to develop better understanding that might reveal insightsinto the crack growth prediction refinements. The current study is centered on a subcriticalcrack extension case in iron-based single crystals. Pre-fatigued single edgesharp crack in mini-compact specimens have been exposed to deformation/environmentinteraction, enhancing as such a slow crack growth that could be tracked. In fact, thecurrent case consisted of a quasi-equilibrium crack extension, where in terms of crystalstability equation extremely tight crack stability margin prevailed. By utilizing variouscrack systems, anisotropic crack extension behavior was observed with significantchanges of the crack front. Based on a sound background, including slip traces analysisand low energy dislocation structures, the crack-tip mechanical environment wasestablished by a modified super-dislocation model. Simulation beside experimentalconfirmation defined the local crack-tip stress field by realizing plastic relaxation dueto dislocation shielding. Consequently a first order approximation attributed the crackgrowth to the role of the fracture surface energy. Following this view point, enabledsimulations to be pursued beside ultra fine features visualisation indicated consistentexperimental confirmation.