On 15 March 2000, a National Railroad Passenger Corporation (Amtrak) train traveling from Chicago to Los Angeles derailed in Carbondale, KS. After the initial on-scene investigation, 12 pieces of rail were sent to the materials laboratory for examination. Ten of them were from the point of derailment (POD). A vertical crack was observed in the head of the rail (vertical split head). The crack was at least 233 in. (591 cm) long, continuing through the entire lengths of most pieces recovered from the POD. The vertical fracture surface had features consistent with overstress fracture with short-term exposure to an oxygen-rich environment. Fracture features emanated from longitudinally-aligned inclusions rich in aluminum.

An ASTM A 504 carbon steel railway car wheel that was used on a train in a metropolitan railway system failed during service, causing derailment. The wheel was completely fractured from rim to hub. Macrofractography of the fracture surface showed road grime, indicating that the crack had existed for a considerable time prior to derailment and initiated in the flange. Failure propagated from the flange across the rim and down the plate to the bore of the hub. Two zones that exhibited definite signs of heating were observed. The fracture initiation site was typical of fatigue fracture. No defects were found that could have contributed to failure. The wheel conformed to the chemical, microstructural, and hardness requirements for class A wheels. Failure was attributed to repeated severe heating and cooling of the rim and flange due to brake locking or misapplication of the hand brake. It was recommended that the brake system on the car be examined and replaced if necessary.

A failed spiral gear and pinion set made from 4320H Ni-Cr-Mo alloy steel operating in a high-speed electric traction motor gear unit driving a rapid transit train were submitted for analysis. The pinion was intact, but the gear had broken into two sections that resulted when two fractured areas went through the body of the gear. Wheel mileage of the assembly was 34,000 miles at the time of failure. All physical and metallurgical characteristics were well within specified standards, and both parts should have withstood normal loading conditions. The primary mode of failure was tooth bending fatigue of the gear from the reverse direction near the toe end. The cause of failure was a crossed-over tooth bearing condition that placed loads at the heel end when going forward and at the toe end when going in reverse. The condition was too consistent to be a deflection under load; therefore, it most likely was permanent misalignment within the assembly.

Three spur gears made from 8622 Ni-Cr-Mo alloy steel formed a straight-line train in a speed reducer on a rail-mounted overslung lumber carrier. The gears were submitted for nondestructive examination and evaluation, with no accompanying information or report. Two teeth on one of the gears were found to be pitted, one low on profile and the adjacent tooth high on profile. The mating gear had a similar characteristic, two adjacent teeth with evidence of pitting and the same difference in profile. It was correctly deduced that the pitting occurred because the gears were in a static position under a reverberating load for an extended period of time.

Personnel responsible for laboratory protection at some plants are required to participate in exercises simulating a breach of security at the site. This document reports a metallurgical investigation of blank firing adapters (BFA), one of which exploded during such a training exercise. Determination of the cause of the explosion was the primary objective of the examination. Metallographic studies included the examination of BFAs fabricated from two different types of alloys that were tested for shock reaction. Optical microscopy supported by electron microscopy and analytical methods were used. Our investigation supports the supposition that a live round of ammunition was inadvertently fired.

Following a freight train derailment, part of a fractured side frame was retained for study because a portion of its fracture surface exhibited a rock candy appearance and black scale. It was suspected of having failed, thereby precipitating the derailment. Metallography, scanning electron microscopy, EDXA, and x-ray mapping were used to study the steel in the vicinity of this part of the fracture surface. It was found to be contaminated with copper. Debye-Scherrer x-ray diffraction patterns obtained from the scale showed that it consisted of magnetite and hematite. It was concluded that some copper was accidentally left in the mold when the casting was poured. Liquid copper, carrying with it oxygen in solution, penetrated the austenite grain boundaries as the steel cooled. The oxygen reacted with the steel producing a network of scale outlining the austenite grain structure. When the casting fractured as a result of the derailment, the fracture followed the scale in the contaminated region thus creating the “rock candy” fracture.

A 60.3 mm (2.375 in.) diam drive shaft in the drive train of an overhead crane failed. The part submitted for examination was a principal drive shaft that fractured near a 90 deg fillet where the shaft had been machined down to 34.9 mm (1.375 in.) to serve as a wheel hub. A 9.5 mm (0.375 in.) wide x 3.2 mm (0.125 in.) deep keyway was machined into the entire length of the hub, ending approximately 1.6 mm (0.062 in.) away from the 90 deg fillet. A second shaft was also found to have cracked at a change in diameter, where it was machined down to serve as the motor drive hub. Investigation (visual inspection, inspection records review, optical and scanning electron microscopy, and fractography) supported the conclusion that the fracture mode for both shafts was low-cycle rotating-bending fatigue initiating and propagating by combined torsional and reverse bending stresses. Recommendations included replacing all drive shafts with new designs that eliminated the sharp 90 deg chamfers in favor of a more liberal chamfer, which would reduce the stress concentration in these areas.

Crane collapse due to bolt fatigue and fatigue failure of a crane support column, crane tower, overhead yard crane, hoist rope, and overhead crane drive shaft are described. The first four examples relate to the structural integrity of cranes. However, equipment such as drive and hoist-train components are often subject to severe fatigue loading and are perhaps even more prone to fatigue failure. In all instances, the presence of fatigue cracks at least contributed to the failure. In most instances, fatigue was the sole cause. Further, in each case, with regular inspection, fatigue cracks probably would have been detected well before final failure.

A pinion gear made of AMS 6470 steel, nitrided all over, lost internal splined teeth due to wear. Spline failure of the power turbine gear caused an engine overspeed and disintegration. Excessive spline wear resulted from a new coupling being mated during overhaul with a worn gear spline. Wear on the spline teeth flanks of the coupling was attributed to severe wear on the mating gear (internal) spline teeth. The assigned cause was an inadequate maintenance procedure which resulted in a wear-damaged component being retained in the power train during engine overhaul. To prevent reoccurrence, specific inspection criteria were issued defining maximum limits for spline wear. A procedure and requirements were specified for installing the coupling and pinion gear at the next overhaul.

Component slippage in the left-side final drive train of a tracked military vehicle was detected after the vehicle had been driven 13,700 km (8500 miles) in combined highway and rough-terrain service. The slipping was traced to the mating surfaces of the final drive gear and the adjacent splined coupling sleeve. Specifications included that the gear and coupling be made from 4140 steel bar oil quenched and tempered to a hardness of 265 to 290 HB (equivalent to 27 to 31 HRC) and that the finish-machined parts be single-stage gas nitrided to produce a total case depth of 0.5 mm (0.020 in.) and a minimum surface hardness equivalent to 58 HRC. Investigation (visual inspection, low-magnification images, 500X images of polished sections etched in 2% nital, spectrographic analysis, and hardness testing) supported the conclusion that the failure occurred by crushing, or cracking, of the case as a result of several factors. Recommendations included reducing the high local stresses at the pitch line to an acceptable level with a design modification. Also suggested was specification of a core hardness of 35 to 40 HRC to provide adequate support for the case and to permit attainment of the specified surface hardness of 58 HRC.

Work rolls made of indefinite chill double-poured (ICDP) iron are commonly used in the finishing trains of hot-strip mills (HSMs). In actual service, spalling, apart from other surface degeneration modes, constitutes a major mechanism of premature roll failures. Although spalling can be a culmination of roll material quality and/or mill abuse, the microstructure of a broken roll can often unveil intrinsic inadequacies in roll material quality that possibly accentuate failure. This is particularly relevant in circumstances when rolls, despite operation under similar mill environment, exhibit variations in roll life. The paper provides an insight into the microstructural characteristics of spalled ICED HSM work rolls, which underwent failure under similar mill operating environment in an integrated steel plant under the Steel Authority of India Limited. Microstructural features influencing ICDP roll quality, viz. characteristics of graphite, carbides, martensite, etc., have been extensively studied through optical microscopy, quantitative image analysis (QIA), and electron-probe microanalysis (EPMA). These are discussed in the context of spalling propensity and roll life.

Several elbow subassemblies comprising segments of oil-line assemblies that recycled aircraft-engine oil from pump to filter broke in service. The components of the subassemblies were made of aluminum alloy 6061-T6. Two subassemblies were returned to the laboratory to determine cause of failure. In one, the threaded boss had separated from the elbow at the weld. In the other, the failure was by fracture of the elbow near the flange. The separation of the threaded boss from the elbow was due to a poor welding procedure. Crack propagation was accelerated by fatigue caused by cyclic service stresses. The fracture of the second elbow near the flange was caused by overaging during repair welding of the boss weld. Satisfactory weld penetration was achieved by improved training of the welders plus more careful inspection. Repair welding was prohibited, to avoid recurrence of overaging from the welding heat. Additional support for the oil line was installed to reduce vibration and minimize fatigue of the elbow.

Failure occurred in a type 304 stainless steel leaf spring attached to the undercarriage assembly of an airport shuttle train. Failure analysis showed that the fracture was caused by low-cycle, reversed bending fatigue. The stresses leading to failure were imposed by poor alignment. It was recommended that improved assembly procedures be used and that, if another failure occurred, a steel of higher fatigue strength be used.

A sleeve-shaped fire shield that operates inside one of two burner trains in an oil and gas processing unit ruptured after 15 y of service. A detailed analysis was conducted to determine how and why the sleeve failed. The investigation included visual inspection, chemical and gas analysis, mechanical property testing, stereomicroscopy, and metallographic examination. The fire sleeves are fabricated from 3-mm thick plate made of Incoloy 800 rolled into 540-mm diam sections welded along the seam. Three such sections are joined together by circumferential welds to form a single 2.8 m sleeve. The findings from the investigation indicated that internal oxidation corrosion, driven by high temperatures, was the primary cause of failure. Prolonged exposure to temperatures up to 760 °C resulted in sensitization of the material, making it vulnerable to grain boundary attack. This led to significant deterioration of the grain boundaries, causing extensive grain loss (grain dropping) and the subsequent thinning of sleeve walls. Prior to failure, some portions of the sleeve were only 1.6 mm thick, nearly half their original thickness.

A hypoid pinion made from 4820 Ni-Mo alloy steel was the driving member of a power unit operating a rapid transit car. The pinion had been removed from service at the end of the initial test period because it showed undue wear. The mode of failure was severe abrasive wear. The cause of failure was insufficient surface hardness, resulting from improper heat treatment. A service recall for the remaining pinions was immediately initiated.

A 4340 steel shaft, the driving member of a large rotor subject to cyclic loading and frequent overloads, broke after three weeks of operation. The driving shaft contained a shear groove at which the shaft should break if a sudden high overload occurred, thus preventing damage to an expensive gear mechanism. The rotor was subjected to severe chatter, which was an abnormal condition resulting from a series of continuous small overloads occurring at a frequency of around three per second. Investigation (visual inspection, hardness testing, and hot acid etch images) supported the conclusion that the basic failure mechanism was fracture by torsional fatigue, which started at numerous surface shear cracks, both longitudinal and transverse, that developed in the periphery of the root of the shear groove. These shear cracks resulted from high peak loads caused by chatter. The shear groove in the shaft had performed its function, but at a lower overload level than intended. Recommendations included increasing the fatigue strength of the shaft by shot peening the shear groove to minimize chatter.