Hardness measurements were then conducted across the face of the specimen in locations corresponding to the banded and nonbanded regions. These results(Fig. 7a)showed that the segregated region is considerably harder than the neighboring material The reason is that the increased carbon content of the segregated region, together with its higher alloy content, makes the region more responsive to what would have been normal heat treatment for this grade of tool steel The high-hardness material is also subject to microcracking on quenching; microcracks can act as nuclei for subsequent fatigue cracks. Examination of the fracture surface revealed that the fracture originated near the high-stress region of the die face; however, no indications of fatigue marks were found on either a macroscale or a microscale Conclusions. Failure of the die was the result of fracture that originated in an area of abnormally high hardness Ithough fatigue marks were not observed, the fact was that the fracture did not occur in a single cycle but required several cycles to cause failure Example 2: Fatigue Fracture that Originated on the Ground Surface of a Medium-Carbon Steel Forging with a Notch-Sensitive Band Structure. The broken connecting end of a forged medium-carbon steel rod used in an application in which it was subjected to severe low-frequency loading is illustrated in Fig. 8(a); the part shown from one of two identical rods that failed in service by fracture. In each instance fracture extended pletely through the connecting end in two places. The two fractured rods, together with two similar unused forged rods, were examined to determine the mechanism and cause of fracture Medium-cor bon steel 140 Bhn Fractured connecting Rough-ground area(typ Unetched fracture 2x both sides) Fracture (l of 2) surface (d) 80x Nital lOx g.8 Connecting end of forged rod, with banded structure from excessive segregation in the billet (Example 2).(a) Rod end showing locations of fractures at rough-ground areas at the parting line; in view A-A, dashed lines denote a rough-ground area, arrow points to a liquid-penetrant indication of an incipient crack, (b) Fracture surface, with beach marks indicating fracture origin at rough-ground surface.(c) Normal, homogeneous structure of an unused rod examined for comparison; this structure contains equal amounts of ferrite (light) and pearlite (dark).(d) Unsatisfactory structure of the fractured rod, which contains alternating bands of ferrite and pearlite. Thefileisdownloadedfromwww.bzfxw.comHardness measurements were then conducted across the face of the specimen in locations corresponding to the banded and nonbanded regions. These results (Fig. 7a) showed that the segregated region is considerably harder than the neighboring material. The reason is that the increased carbon content of the segregated region, together with its higher alloy content, makes the region more responsive to what would have been normal heat treatment for this grade of tool steel. The high-hardness material is also subject to microcracking on quenching; microcracks can act as nuclei for subsequent fatigue cracks. Examination of the fracture surface revealed that the fracture originated near the high-stress region of the die face; however, no indications of fatigue marks were found on either a macroscale or a microscale. Conclusions. Failure of the die was the result of fracture that originated in an area of abnormally high hardness. Although fatigue marks were not observed, the fact was that the fracture did not occur in a single cycle but required several cycles to cause failure. Example 2: Fatigue Fracture that Originated on the Ground Surface of a Medium- Carbon Steel Forging with a Notch-Sensitive Band Structure. The broken connecting end of a forged medium-carbon steel rod used in an application in which it was subjected to severe low-frequency loading is illustrated in Fig. 8(a); the part shown is from one of two identical rods that failed in service by fracture. In each instance, fracture extended completely through the connecting end in two places. The two fractured rods, together with two similar unused forged rods, were examined to determine the mechanism and cause of fracture. Fig. 8 Connecting end of forged rod, with banded structure from excessive segregation in the billet (Example 2). (a) Rod end showing locations of fractures at rough-ground areas at the parting line; in view A-A, dashed lines denote a rough-ground area, arrow points to a liquid-penetrant indication of an incipient crack. (b) Fracture surface, with beach marks indicating fracture origin at rough-ground surface. (c) Normal, homogeneous structure of an unused rod examined for comparison; this structure contains equal amounts of ferrite (light) and pearlite (dark). (d) Unsatisfactory structure of the fractured rod, which contains alternating bands of ferrite and pearlite. The file is downloaded from www.bzfxw.com