Charpy impact property related to {100} cleavage fracture in 15CrODS steel

Abstract

Based on the former results that delamination along {100} cleavage fracture leads to the improved absorbed energy, {100} cleavage plane was formed in parallel to the rolled plate by recrystallisation and cold roll processing in 15CrODS steel plate. Charpy impact properties were investigated in terms of notch direction against {100} cleavage plane. Notch with normal direction against {100} cleavage plane induced delamination fracture, but provided similar absorbed energy to that of conventional extruded bar. The transverse notch direction against {100} cleavage plane served higher absorbed energy at low temperature. Higher upper shelf energy and lower DBTT were attained in conventional hot extruded bar, which contains any crystallographic planes rotated around <110> axis at the transverse direction. The delamination fracture leading to high absorbed energy is significantly affected by a crystallographic morphology of the {100} cleavage plane perpendicular to transverse plane.

On delamination toughening of a 14YWT nanostructured ferritic alloy

“…For example, Junceda et al [29] and Kimura et al [23] reported that the grains are oriented in <110> along the hot extrusion direction in 14YWT ODS steel, and in a tempered martensitic steel, respectively. Ukai et al [15] also reported {100}<110> textured grains in parallel to rolling planes and rolling directions in a hot extruded, recrystallized and cold-rolled 15YWT ODS alloy leading to a lower cleavage BDTT in Charpy impact tests, due to delamination. Bourell [30] also found a similar texture component in warm-rolled low carbon steel.…”

“…NFAs are typically processed by ball milling Fe-Cr-Ti-Wand Y2O3 powders to mechanically alloy Y and O into solid solution [2,5,[7][8][9][10][11][12][13][14][15]35]. However, in the case of NFA-1, Y was included in the melt prior to gas atomization and rapid solidification.…”

“…While enjoying a host of outstanding properties, NFAs often have poor fracture toughness and high brittle-to-ductile transition temperatures (BDTT), as well as properties that are highly anisotropic [7][8][9][10][11][12][13][14][15]. NFA toughness is lower when the crack propagates parallel to the principal deformation (e.g., extrusion) direction, but is usually significantly higher in transverse orientations.…”

“…Delaminations/splitting are sometimes observed in Al-Li alloys [16][17][18] and structural steels [15,[19][20][21][22][23][24][25][26][27][28][29][30][31], leading to what is sometimes called delamination toughening.…”

Why Do Secondary Cracks Preferentially Form in Hot-Rolled ODS Steels in Comparison with Hot-Extruded ODS Steels?

“…Therefore at low temperatures, the tensile stresses arising from the plane strain condition cleave the {100} planes, aligned parallel to rolling plane (Figure 5a). As the secondary crack planes (LT planes in Figure 2a) are parallel to the cleavage planes, secondary cracks appear [37].…”