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revealed"woody"fracture features(Fig. 12b), as a result of decohesion between a high volume fraction of manganese sulfide stringers and the matrix(Fig. 13). The matrix fracture features showed ductile dimple rupture Fig. 12 Crack (a) and broken-open fracture surface(b)of failed wedge-shaped middle tapered ring.6× Fig. 13 Higher-magnification view of fracture surface shown in Fig. 12 at origin of cracking arrows indicate large manganese sulfide inclusion at origin Chemical analysis of the material revealed a resulfurized grade of carbon steel (Sae type 1144, UNS G11440),as required by the manufacturer. This type of steel is marketed as having a rather unusual combination of high strength and high machinability. The source of the high strength is in the carbon content and the cold-drawing process used to produce the bar material, giving rise to enhanced longitudinal tensile properties. The high volume fraction of manganese sulfide inclusions(Fig. 14)impart the high machinability properties, due to the well-documented enhancement to chipmakingrevealed “woody” fracture features (Fig. 12b), as a result of decohesion between a high volume fraction of manganese sulfide stringers and the matrix (Fig. 13). The matrix fracture features showed ductile dimple rupture. Fig. 12 Crack (a) and broken-open fracture surface (b) of failed wedge-shaped middle tapered ring. 6× Fig. 13 Higher-magnification view of fracture surface shown in Fig. 12 at origin of cracking. Arrows indicate large manganese sulfide inclusion at origin. Chemical analysis of the material revealed a resulfurized grade of carbon steel (SAE type 1144, UNS G11440), as required by the manufacturer. This type of steel is marketed as having a rather unusual combination of high strength and high machinability. The source of the high strength is in the carbon content and the cold-drawing process used to produce the bar material, giving rise to enhanced longitudinal tensile properties. The high volume fraction of manganese sulfide inclusions (Fig. 14) impart the high machinability properties, due to the well-documented enhancement to chipmaking
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