Volume 12 - Fractography Part 9 ppsx

[...]... medium-carbon steel forging occurred after 2 years of operation on a crane serving an open-hearth furnace Fig 2 39: Spalled section of tread Fatigue crack originated at a forging defect (arrow) 3× Fig 240: Close-up of failure origin 0.75× Fig 241: Oblique lighting reveals texture of fracture surface (compare with Fig 240) Note beach marks associated with fatigue crack Fatigue fracture of 90 -mm (3.6-in.)... bearing diameter The part was broken in the laboratory Fig 228: Fracture surface with chevrons in casehardened zone pointing to single origin at top Fine- and coarse-grained structures in case and core regions, respectively, indicate that heat treatment was properly performed Fig 2 29: Side view of fractured axle shaft in Fig 228 (Z Flanders, Packer Engineering Associates, Inc.) In-service rotary bending... fatigue-crack origin (at right), which is at a second seam 10× Cause of brittle behavior in a small percentage of flat spring parts made of annealed AISI 1070 was traced to a nitrided/nitrogenized layer, 0.25 mm (0.010 in.) thick, produced during heat treating The heat-treating operation included a 5-min stay in a shaker hearth furnace having a dissociated ammonia atmosphere However, some of the parts... history of fractured shafts This particular grate had jammed twice before, and each time a new key had to be machined due to twisting of the shaft Mechanical properties at surface of shaft: yield strength, 348 MPa (50.5 ksi); tensile strength, 556 MPa (80.6 ksi); elongation, 31% Core properties: yield, 300 MPa (43.5 ksi); tensile, 620 MPa ( 89. 9 ksi); elongation, 25% Fig 2 49 and 250: One half of broken... (3.6-in.) diam medium-carbon steel axle housing (217 to 2 29 HB) The part was subjected to unidirectional bending stresses normal for the application Fig 243: Fracture surface showing four major fatigue crack origins (arrows) Cracks progressed up both sides of the tube and joined at the small final rupture area at top Note increasing coarseness of fracture surface as cracks grew Fig 244: Higher-magnification... of axle failure in Fig 220 and 221 Fig 225: Case-core transition zone SEM, 50× Fig 226 (Core structure at transition zone (see Fig 225) showing primarily cleavage fracture SEM, 1000× Fig 227: Same as Fig 226, but at higher magnification SEM, 2000× (General Motors Research Laboratories) Classic bending overload fracture of automotive axle shaft (direct-on bearing design) Material and heat treatment:... keyways are visible) and its fracture surface (note twisting and smearing) All at ~0.5× (Z Flanders, Packer Engineering Associates, Inc.) Ferrite at prior-austenite grain boundaries and spheroidized pearlite characterize microstructure of drive shaft in Fig 2 49, 250, 251, and 252 All etched in 2% nital Fig 253 and 254: Structure at surface of shaft (radial orientation) 100× and 400× Fig 255 and 256: Transverse... view of fractured axle shaft in Fig 228 (Z Flanders, Packer Engineering Associates, Inc.) In-service rotary bending fatigue fracture of automotive axle shaft (direct-on bearing design) due to improper heat treatment The modified AISI 1050 part was induction hardened and tempered to 60 HRC min at the bearing diameter However, the hardened zone did not extend into the flange fillet radius Fig 230: Fracture... significant surface damage These defect were probably caused by mechanical action or lubrication breakdown during strip production while the material was in the annealed condition Fig 2 79: SEM, 25× Fig 280: Same as Fig 2 79, but at higher magnification SEM, 100× (J.H Maker, Associated Spring, Barnes Group Inc.) ... The extended heating time, plus the presence of a small amount of undissociated ammonia, led to formation of the embrittling layer Fig 274 and 275: Grainboundary damage at surface of AISI 1070 spring part SEM, 1000× and 2000× Fig 276 and 277: Nitrides (or carbonitrides) in grain boundaries SEM, 1000× and 5000× (J.H Maker, Associated Spring, Barnes Group Inc.) Power spring made of tempered AISI 1074 . case- hardened zone pointing to single origin at top. Fine- and coarse-grained structures in case and core regions, respectively, indicate that heat treatment was properly performed. Fig. 2 29: . Associates, Inc.) In-service rotary bending fatigue fracture of automotive axle shaft (direct-on bearing design) due to improper heat treatment. The modified AISI 1050 part was induction hardened. automotive axle shaft (direct-on bearing design). Material and heat treatment: modified AISI 1050, induction hardened and tempered to 60 HRC at the bearing diameter. The part was broken in the laboratory.