A cast dragline bucket tooth failed by fracturing after a short time in service. The tooth was made of medium-carbon low-alloy steel heat treated to a hardness of 555 HRB. The fracture surface was covered with chevron marks. These converged at several sites on the surface of the tooth. A hardfacing deposit was located at each of these sites. Visual inspection of the hardfacing deposits revealed numerous transverse cracks, characteristic of many types of hardfacing. This failure was caused by cracks present in hardfacing deposits that had been applied to the ultrahigh-strength steel tooth. Given the small critical crack sizes characteristic of ultrahigh-strength materials, it is generally unwise to weld them. It is particularly inadvisable to hardface ultrahigh-strength steel parts with hard, brittle, crack-prone materials when high service stresses will be encountered. The operators of the dragline bucket were warned against further hardfacing of these teeth.

An investigation was conducted to determine the factors responsible for the occasional formation of cracks on the parting lines of medium plain carbon and low-alloy medium-carbon steel forgings. The cracks were present on as-forged parts and grew during heat treatment. Examination revealed that areas near the parting line exhibited a large grain structure not present in the forged stock. High-temperature scale was also found in the cracks. It was concluded that the cracks were caused by material being folded over the parting line. The folding occurred because of a mismatch in the forgings and from material flow during trimming and/or material flow during forging.

A cast dragline bucket tooth failed by fracturing after a short time in service. The tooth was made of medium-carbon low-alloy steel heat treated to a hardness of 555 HRB. The fracture surface was covered with chevron marks. These converged at several sites on the surface of the tooth. A hardfacing deposit was located at each of these sites. Visual inspection of the hardfacing deposits revealed numerous transverse cracks, characteristic of many types of hardfacing. This failure was caused by cracks present in hardfacing deposits that had been applied to the ultrahigh-strength steel tooth. Given the small critical crack sizes characteristic of ultrahigh-strength materials, it is generally unwise to weld them. It is particularly inadvisable to hardface ultrahigh-strength steel parts with hard, brittle, crack-prone materials when high service stresses will be encountered. The operators of the dragline bucket were warned against further hardfacing of these teeth.

This article introduces some of the general sources of heat treating problems with particular emphasis on problems caused by the actual heat treating process and the significant thermal and transformation stresses within a heat treated part. It addresses the design and material factors that cause a part to fail during heat treatment. The article discusses the problems associated with heating and furnaces, quenching media, quenching stresses, hardenability, tempering, carburizing, carbonitriding, and nitriding as well as potential stainless steel problems and problems associated with nonferrous heat treatments. The processes involved in cold working of certain ferrous and nonferrous alloys are also covered.

Graphitization, the formation of graphite nodules in carbon and low alloy steels, contributes to many failures in high-temperature environments. Three such failures in power-generating systems were analyzed to demonstrate the unpredictable nature of this failure mechanism and its effect on material properties and structures. In general, the more randomly distributed the nodules, the less effect they have on structural integrity. In the cases examined, the nodules were found to be organized in planar arrays, indicating they might have an effect on material properties. Closer inspection, however, revealed that the magnitude of the effect depends on the relative orientation of the planar arrangement and principle tensile stress. For normal orientation, the effect of embrittlement tends to be most severe. Conversely, when the orientation is parallel, the nodules have little or no effect. The cases examined show that knowledge is incomplete in regard to graphitization, and the prediction of its occurrence is not yet possible.

This article provides an overview of the effects of various material- and process-related parameters on residual stress, distortion control, cracking, and microstructure/property relationships as they relate to various types of failure. It discusses phase transformations that occur during heat treating and describes the metallurgical sources of stress and distortion during heating and cooling. The article summarizes the effect of materials and the quench-process design on distortion and cracking and details the effect of cooling characteristics on residual stress and distortion. It also provides information on the methods of minimizing distortion and tempering. The article concludes with a discussion on the effect of heat treatment processes on microstructure/property-related failures.

Several case-hardened and zinc-plated carbon-manganese steel wheel studs fractured in a brittle manner after very limited service life. The fracture surfaces of both front and rear studs showed no sign of fatigue beach marks or deformation in the form of shear lips that would indicate either a fatigue mechanism or ductile overload failure. SEM analysis revealed that the mode of fracture was intergranular decohesion, which indicates an environmental influence in the fracture mechanism. The primary fracture initiated at a thread root and propagated by environmentally-assisted slow crack growth until final fracture. The natural stress concentration at the thread root, when tightened to the required clamp load concomitant with the presence of cracks in the carburized case, was sufficient to exceed the critical stress intensity for hydrogen-assisted stress cracking (HASC). The zinc plating exacerbated the situation by providing a strong local corrosion cell in the form of a sacrificial anode region adjacent to the cracked thread. The enhanced generation of hydrogen in a corrosive environment subsequently lead to HASC of the wheel studs.

The defects observed along weldings of stainless steel pipelines employed in marine environments were evidenced by metallographic and electrochemical examination. A compilation of cases on the effect of defective weldings, in addition to improper choice of stainless steel for water pipelines, lead to the conclusion that intercrystalline corrosion in steels involved precipitation of a surplus phase at grain boundaries. Intercrystalline corrosion in austenitic stainless steels due to precipitation of chromium carbides during conditions generated due to welding and ways to avoid the precipitation (including reduction of carbon content, appropriate heat treatment, cold work of steel, reduction of austenitic grain size and stabilizing elements) were described. The presence of microcracks due to highly localized heat concentrations with consequent thermal expansion and considerable shrinkages during cooling was investigated. The specimens were taken from various sources including transverse and longitudinal welding seam, sensitized areas and it was concluded appropriate material selection with respect to medium could control some corrosion processes.

This study examines the role of calcium-precipitating bacteria (CPB) in heat exchanger tube failures. Several types of bacteria, including Serratia sp. (FJ973548), Enterobacter sp. (FJ973549, FJ973550), and Enterococcus sp. (FJ973551), were found in scale collected from heat exchanger tubes taken out of service at a gas turbine power station. The corrosive effect of each type of bacteria on mild steel was investigated using electrochemical (polarization and impedance) techniques, and the biogenic calcium scale formations analyzed by XRD. It was shown that the bacteria contribute directly to the formation of calcium carbonate, a critical factor in the buildup of scale and pitting corrosion on heat exchanger tubes.

Critical heat exchanger components are usually manufactured from durable steels, such as stainless steel, which exhibit good strength and corrosion resistance. Failure of a heat exchanger occurred due to specification of a plain carbon steel that did not survive service in the SO2 vapor environment. However, failure analysis showed that cavitation erosion was the responsible failure mechanism, not corrosion as might be expected.

This article describes the characteristics of tubing of heat exchangers with respect to general corrosion, stress-corrosion cracking, selective leaching, and oxygen-cell attack, with examples. It illustrates the examination of failed parts of heat exchangers by using sample selection, visual examination, microscopic examination, chemical analysis, and mechanical tests. The article explains corrosion fatigue of tubing of heat exchangers caused by aggressive environment and cyclic stress. It also discusses the effects of design, welding practices, and elevated temperatures on the failures of heat exchangers.

Failure of carbon-manganese steel wheel studs caused by improper tightening of the inner wheel nuts resulted in separation of a dual wheel assembly on a heavy truck. The benchmark pattern observed on the fracture surfaces of the studs evidenced fatigue cracks emanating from multiple origins around the circumference. There was no indication that any microstructural characteristics of the material contributed to the failure. Inclusions that were present were small and relatively few in number. Failure to check the torque of the inner wheel nuts as per the manufacturer's recommendation caused the inner wheel nuts to loosen during break-in and lose the required clamping force. The development and promotion of educational programs on proper wheel tightening procedures was recommended.

Corrosive wear is defined as surface damage caused by wear in a corrosive environment, involving combined attacks from wear and corrosion. This article begins with a discussion on several typical forms of corrosive wear encountered in industry, followed by a discussion on mechanisms for corrosive wear. Next, the article explains testing methods and characterization of corrosive wear. Various factors that influence corrosive wear are then covered. The article concludes with general guidelines for material selection against corrosive wear.

This article focuses on the mechanisms and common causes of failure of metal components in lifting equipment in the following three categories: cranes and bridges, particularly those for outdoor and other low-temperature service; attachments used for direct lifting, such as hooks, chains, wire rope, slings, beams, bales, and trunnions; and built-in members such as shafts, gears, and drums.

This article commences with a summary of fatigue processes and mechanisms. It focuses on fractography of fatigue. Characteristic fatigue fracture features that can be discerned visually or under low magnification are described. Typical microscopic features observed on structural metals are presented subsequently, followed by a brief discussion of fatigue in nonmetals. The article reviews the various macroscopic and microscopic features to characterize the history and growth rate of fatigue in metals. It concludes with a description of fatigue of polymers and composites.

Rollover accidents in light trucks and cars involving an axle failure frequently raise the question of whether the axle broke causing the rollover or did the axle break as a result of the rollover. Axles in these vehicles are induction hardened medium carbon steel. Bearings ride directly on the axles. This article provides a fractography/fracture mechanic approach to making the determination of when the axle failed. Full scale tests on axle assemblies and suspensions provided data for fracture toughness in the induction hardened outer case on the axle. These tests also demonstrated that roller bearing indentions on the axle journal, cross pin indentation on the end of the axle, and axle bending can be accounted for by spring energy release following axle failure. Pre-existing cracks in the induction hardened axle are small and are often difficult to see without a microscope. The pre-existing crack morphology was intergranular fracture in the axles studied. An estimate of the force required to cause the axle fracture can be made using the measured crack size, fracture toughness determined from these tests, and linear elastic fracture mechanics. The axle can be reliably said to have failed prior to rollover if the estimated force for failure is equal to or less than forces imposed on the axle during events leading to the rollover.

A fused-salt electrolytic-cell pot containing a molten eutectic mixture of sodium, potassium, and lithium chlorides and operating at melt temperatures from 500 to 650 deg C (930 to 1200 deg F) exhibited excessive corrosion after two months of service. The pot was a welded cylinder with 3-mm thick type 304 stainless steel walls and was about 305 mm (12 in.) in height and diam. Analysis (visual inspection and 500x micrographs etched with CuCl2) supported the conclusions that the pot failed by intergranular corrosion because an unstabilized austenitic stainless steel containing more than 0.03% carbon had been sensitized and placed in contact in service with a corrosive medium at temperatures in the sensitizing range. Recommendations included changing material for the pot from type 304 stainless steel to Hastelloy N (70Ni-17Mo-7Cr-5Fe). Maximum corrosion resistance and ductility are developed in Hastelloy N when the alloy is solution heat treated at 1120 deg C (2050 deg F) and is either quenched in water or rapidly cooled in air. An alternative, but less suitable, material for the pot was type 347 (stabilized grade) stainless steel. After welding, the 347 should be stress relieved at 900 deg C (1650 deg F) for 2 h and rapidly cooled to minimize residual stresses.

Fatigue failure of engineering components and structures results from progressive fracture caused by cyclic or fluctuating loads. Fatigue is an important potential cause of mechanical failure, because most engineering components or structures are or can be subjected to cyclic loads during their lifetime. This article focuses on fractography of fatigue. It provides an abbreviated summary of fatigue processes and mechanisms: fatigue crack initiation, fatigue crack propagation, and final fracture,. Characteristic fatigue fracture features that can be discerned visually or under low magnification are then described. Typical microscopic features observed on structural metals are presented subsequently, followed by a brief discussion on fatigue in polymers and polymer-matrix composites.

Persistent cracking in a forged 1080 steel turntable rail in a wind tunnel test section was investigated. All cracks were oriented transverse to the axis of the rail, and some had propagated through the flange into the web. Through-flange cracks had been repair welded. A section of the flange containing one through-flange crack was examined using various methods. Results indicated that the cracks had initiated from intergranular quench cracks caused by the use of water as the quenching medium. Brittle propagation of the cracks was promoted by high residual stresses acting in conjunction with applied loads. Repair welding was discontinued to prevent the introduction of additional residual stress., Finite-element analysis was used to show that the rail could tolerate existing cracks. Periodic inspection to monitor the degree of cracking was recommended.

This article commences with a discussion on the characteristics of stress-corrosion cracking (SCC) and describes crack initiation and propagation during SCC. It reviews the various mechanisms of SCC and addresses electrochemical and stress-sorption theories. The article explains the SCC, which occurs due to welding, metalworking process, and stress concentration, including options for investigation and corrective measures. It describes the sources of stresses in service and the effect of composition and metal structure on the susceptibility of SCC. The article provides information on specific ions and substances, service environments, and preservice environments responsible for SCC. It details the analysis of SCC failures, which include on-site examination, sampling, observation of fracture surface characteristics, macroscopic examination, microscopic examination, chemical analysis, metallographic analysis, and simulated-service tests. It provides case studies for the analysis of SCC service failures and their occurrence in steels, stainless steels, and commercial alloys of aluminum, copper, magnesium, and titanium.