A broken cross-recessed die was examined. Examination of the unetched, polished section for impurities revealed several coarse streaks of slag. The purity did not therefore correspond to the requirements set for a high speed tool steel of the given theoretical quality DMo 5. After etching with 5% nital the polished surface exhibited a pronounced, easily-visible, fibrous structure. Microscopic examination revealed that this etch pattern was produced by marked segregation bands. The very unfavorable structure for a high speed steel tool of these dimensions and subject to such stresses together with the low purity favored the fracture of the tool.

A cooler of an ammonia synthesis plant was destroyed after three years of service due to the rupture of a distribution manifold. Synthesis gas under high pressure and at about 300 deg C, consisting of 10% NH3 and unconverted gas of 25% N2 and 75% H2 content, was water-cooled externally to room temperature in this unit. The fracture had the typical flat-gray fibrous structure of a material destroyed by hydrogen. Specimens for the metallographic investigation showed that the structure appeared to have been loosened by intergranular separations. DVM notched impact specimens from the affected area yielded low specific impact energy values. These are the significant characteristics of hydrogen attack. The attack penetrated to a depth of 13 to 16 mm. It was recommended that the manifolds be made of hydrogen-resistant steel instead of the unalloyed steel used.

The head of a socket spanner made of heat-treated 0.40C-0.34Cr steel cracked in service. The pronounced fibrous structure of the component became evident as soon as it was etched with 2% nital. Folds in the material originating from the shaping process were visible, and the micrograph showed that cracks ran along these folds oriented according to the fiber. The fissures, with the exception of the hardening crack, were partly filled with oxide and showed signs of decarburization at the edges. From this it could be assumed that parts of the external skin had been forced into the folds during forging. This evidence supported the conclusion that even through there was some indication of chemical segregation, the folds made during forging initiated the main crack. Furthermore, even if the steel had been more homogeneous, hardening cracks would probably have been promoted by the coarse fissures at the fold zones.

A 1-in. diam pump spindle fractured within the length covered by the boss of the impeller which was attached to the spindle by means of an axial screw. The pump had been in use in a chemical plant handling mixtures of organic liquids and dilute sulfuric acid having a pH value of 2 to 4 at temperatures of 80 to 90 deg C (176 to 194 deg F). The fracture was unusual in that it was of a fibrous nature, the fibers-which were orientated radially-were readily detachable. The surface of the spindle adjacent to the fracture had an etched appearance and the mode of cracking in this region suggested that failure resulted from an intergranular attack. Subsequent microscope examination confirmed the generally intergranular mode of failure. A macro-etched section near the fracture revealed a radial arrangement of columnar crystals, indicating that the spindle was a cast and not a wrought product as had been presumed. Spectroscope examination showed this particular composition (Fe-23Cr-18Ni-1.8Mo-1.2Si) did not conform to a standard specification and is apparently a proprietary alloy. It was evident that the particular mode of failure was related to the inherent structure of the material.

Two bolts from the stressed structure of a church building that had broken during stressing were examined to establish the cause of fracture. The fracture of one of the first bolt occurred in a double-vee groove weld whose root was not completely welded. The second bolt had cracked outside of the weld seam closely under the head. Neither one had been particularly deformed before fracture. The composition of the head pieces corresponded approximately to manganese steel (Material No. 1 0845), a weldable construction steel with increased yield point and strength, while the shafts were made from Cr-Mo steel (Material No. 1.7225) according to DIN 17200. It was found that the bolts were not made from a suitable alloy steel, but were welded together from two unsuitable steels, one of which lacked sufficient strength. The austenitic weld seams showed hot tears and were not welded through to the root. Also, the pieces were not preheated before welding, so that stress cracks occurred in the transition zones. The second bolt was overstressed during the impact caused by the breaking of the first bolt.

The specified elongation of 10% could not be achieved in several hollow pinion gear shafts made of cast Cr-Mo steel GS 35 Cr-Mo 5 3 that were heat treated to a strength of 90 kp/sq mm. The steel was melted in a basic 3 ton arc furnace and deoxidized in the furnace and in the pan with a total of 7 kg aluminum. Fracture of a tensile specimen occurred with low elongation and, apparently, also with low reduction of area. In some places it was coarse grained conchoidal. It was found that the exceptionally low elongation of the cast specimens was due to excessive deoxidation by aluminum.

Ball joints made from carburized En 353 (BS970:815A16) steel failed after several hours of being fitted into vehicles. The parts were forged, machined, and thread rolled. The threads were copper plated to prevent carburization. The heat treatment consisted of carburizing in a cyanide bath for 12 hours at 930 deg C. After tempering for 2 h at 170 to 175 deg C, the copper plate was removed by immersing in an acid bath for 45 min. The investigations found the microstructure, hardness, and chemistry all met the specification. The case depth was approximately 0.75 mm to 1.0 mm. The SEM studies showed that it was a brittle fracture and completely intergranular to a depth of about 2.5 mm. It was concluded that the failure was due to hydrogen embrittlement for the following reasons: (i) failure did not occur immediately after loading, (ii) the fracture was intergranular to a depth of two to three times the case depth, (iii) secondary cracks were observed at the surface. The hydrogen was introduced during copper plate removal by acid dipping. If the tempering operation was performed after the acid dip operation, the hydrogen would have been driven out.

A steel valve spring meeting Steel-Iron-Test 1570 fractured during the high-stress condition of the operation of its valve. Metallographic examination of a transverse section adjacent to the fracture and a longitudinal section through the crack showed the steel was free of major defects and was of high purity, although a number of minor surface defects such as rolling laps were found. The spring was heat treated and its surface strengthened by shot-peening, but the surface was also decarburized to a depth of approximately 0.03 mm which resulted in a lowering of the surface hardness. The fracture of this valve spring is therefore primarily due to surface defects, and secondly perhaps also to weak surface decarburization. No recommendation resulted from the investigation except to note that comparatively minor effects suffice to cause fractures in highly stressed springs.

The paper discusses the analysis of a coating defect on a high phosphorus electroless nickel (Ni-11 wt. % P) deposit plated on an aluminum alloy substrate. Preliminary investigations had indicated that the elongated defects were possibly caused by the entrapment of long fibers or particles during the plating. The possible sources of fibers were identified. The SEM/EDS analysis of fibers collected from the air duct filters correlated very well with the defect shape and the EDS profile collected from under the defect site. It appears that the fibers from air duct filters directly above the plating line were blown into the plating tank and getting co-deposited. The paper describes the step-by-step analysis of the defect that led to successful identification of the root cause of the defect.

An anchorage plate which fractured was one of a pair used as intermediate members through which the boom suspension ropes were attached to the jury-mast of an excavator. Failure of the plate released the ropes on one side of the boom, resulting in extensive damage to the latter and also bending of the other anchorage plate. The anchorage plates were 23 x 9 in. and had been flame-cut from mild steel plate. Collars were fillet-welded on each side at both ends to provide extra bearing area for the pins. Holes had then been flame-cut slightly under size and bored to final dimensions. The plates were given a slight set after flame-cutting to provide a more direct line of pull for the ropes. The fracture surface was bounded by narrow lips, indicative of shear failure. Failure of the anchorage plate was attributed to cracks present at the junctions of the fillet welds, and deficient notch-ductility of the material from which the plates were made.

This article provides a description of the microscale models and mechanisms for deformation and fracture. Macroscale and microscale appearances of ductile and brittle fracture are discussed for various specimen geometries and loading conditions. The article reviews the general geometric factors and materials aspects that influence the stress-strain behavior and fracture of ductile metals. It highlights fractures arising from manufacturing imperfections and stress raisers. The article presents a root cause failure analysis case history to illustrate some of the fractography concepts.

This article focuses on characterizing the fracture-surface appearance at the microscale and contains some discussion on both crack nucleation and propagation mechanisms that cause the fracture appearance. It begins with a discussion on microscale models and mechanisms for deformation and fracture. Next, the mechanisms of void nucleation and void coalescence are briefly described. Macroscale and microscale appearances of ductile and brittle fracture are then discussed for various specimen geometries (smooth cylindrical and prismatic) and loading conditions (e.g., tension compression, bending, torsion). Finally, the factors influencing the appearance of a fracture surface and various imperfections or stress raisers are described, followed by a root-cause failure analysis case history to illustrate some of these fractography concepts.

Alloy steel forgings used as structural members of a ski chair lift grip mechanism were identified to have contained forging laps (i.e., sharp-notched discontinuities) during an annual magnetic particle inspection of all chair lift grip structural members at a mountain resort. The material was confirmed to be 34Cr-Ni-Mo6. A heavy oxide on the dark area of one of the broken-open laps was revealed by scanning electron microscopy in conjunction with EDS. A bright area that contained ductile dimple rupture was observed adjacent to the dark area. The oxidized portion of the fracture was established to be the preexisting forging lap while the bright area was created during the breaking-open process. As a corrective action all forgings showing laps were recommended to be removed from service. Critical review and revision of the forging process and revisions to the nondestructive evaluation procedures at the forging supplier was recommended.

The failure of HP turbine blades in a low bypass turbofan engine was analyzed to determine the root cause. Forensic and metallurgical investigations were conducted on all failed blades as well as failed downstream components. It was found that one of the blades fractured in the dovetail region, causing extensive damage throughout the turbine. Remedial measures were suggested to prevent such failures in the future.

Six wrist pins in a high-performance six-cylinder automotive engine failed after 4800 km (3000 mi) of normal operation. The pins were made of low-carbon steel that had been carburized both inside and outside. Two failed pins were examined. One had fractured into three pieces. The other had not fractured, but exhibited circumferential cracks on the surface of the central zone. Visual surface examination and metallographic and chemical analyses were performed on the specimens. Cracking was attributed primarily to poor heat treatment, resulting in a brittle grain-boundary network of cementite, and to a design that had a raised central section of the inner diameter whose fillets were locations of high stress concentration. Rough machining of the inner diameter and an excessively deep case also contributed to failure. A double type of heat treatment after carburizing and change of the design to eliminate the raised central section were recommended.

An ASTM A391 steel chain link of an over head hoist failed catastrophically, causing damage to both property and personnel. Macrofractography identified the sequence of fractures within the chain link. The first fracture occurred at the welded joint, a second occurred opposite the weld. SEM fractography and metallography indicated that the link failed in a ductile manner because of tensile overload, which occurred when the hoist hook contacted the hoist's housing and prevented uptake of the chain. It was recommended that a load-sensing device be installed to prevent future occurrences and that a dye penetrant inspection be performed on the renwinder of the chain.

The fan used to cool a diesel engine fractured catastrophically after approximately 100 h of operation. The fan failed at a spider, which was resistance spot welded to a shim placed between two circular spiders of 3 mm thickness. The detailed analysis of the fracture indicated that the premature failure of the fan was due to inadequate bonding between the sheets at the weld nugget. The fracture was initiated from the nugget-plate interface. The inadequate penetration and lack of fusion between the steel sheets during resistance spot welding led to poor weld strength and the fracture during operation. The propensity to crack initiation and failure was accentuated by improper cleaning of the surfaces prior to welding and to inadequate nugget-to-sheet edge distance.

An AISI D2 tool steel insert from a forming die used in the manufacture of automotive components failed prematurely during production. Results of various analyses and simulation tests indicated fatigue failure resulting from improper heat treatment. The fatigue fracture originated because of a highly stressed condition produced by a sharp corner combined with low toughness from ineffective tempering. It was recommended that 25 other inserts that belonged to the same die be double tempered.

Sudden and unexplained bearing cap bolt fractures were experienced with reduced-shank design bolts fabricated from 42 CrMo 4 steel, quenched and tempered to a nominal hardness of 38 to 40 HRC. Fractographic analysis provided evidence favoring stress-corrosion cracking as the operating transgranular fracture failure mechanism. Water containing H7S was subsequently identified as the aggressive environment that precipitated the fractures in the presence of high tensile stress. This environment was generated by the chemical breakdown of the engine oil additive and moisture ingress into the normally sealed bearing cap chamber surrounding the bolt shank. A complete absence of fractures in bolts from one of the two vendors was attributed primarily to surface residual compressive stresses produced on the bolt shank by a finish machining operation after heat treatment. Shot cleaning, with fine cast shot, produced a surface residual compressive stress, which eliminated stress-corrosion fractures under severe laboratory conditions.

Music wire springs used in a printer return mechanism failed near the bend in the hook portion of the spring during qualification testing. Samples were examined in a scanning electron microscope equipped with an energy-dispersive x-ray microprobe. Fatigue fractures originated at rub marks on the inside edge of the spring. An investigation of loads encountered in service indicated that the springs had been loaded to a large fraction of the yield strength. Redesign of the spring mechanism was recommended.