A 13/16-in. hex socket failed while in use. Analysis (hardness testing, optical and scanning electron microscopy, and EDS) revealed that the socket was made of low carbon steel formed in a powder metallurgy process. A number of flaws were found including nonuniform wall thickness, poor geometric design with sharp corners as stress raisers, and incomplete sintering evidenced by unsintered particles. These were determined to be the primary cause of failure, although inclusions on the fracture surface containing S and Al may have played a role as well.

A maintenance worker was injured when his 3/4 in. (19 mm) open-ended wrench failed, fracturing in overload fashion along the jaw. The failed wrench was unavailable for testing, but an identical one that failed in the same manner was acquired and subjected to hardness, chemistry, SEM, and metallurgical analyses. SEM imaging revealed microvoid coalescence within the fracture zone. The microvoids were flat and smooth edged indicating insufficient bonding. In addition, a cross sectional sample, mounted and etched using alkaline chromate, revealed an oxygen-rich zone in the jaw. It was concluded that the failures stemmed from forging laps in the jaw that broaching failed to remove.

An impact breaker bar showed signs of rapid wear. The nominal composition of this chromium alloy cast iron was Fe-2.75C-0.75Mn-0.5Si-0.5Ni-19.5Cr-1.1Mo. The measured hardness of this bar was 450 to 500 HRB. The desired hardness for this material after air hardening is 600 to 650 HRB. The microstructure consisted of eutectic chromium carbides (Cr7C3) in a matrix of retained austenite and martensite intermingled with secondary carbides. Analysis (visual inspection and 500x view of sections etched with Marble's reagent) supported the conclusion that the low hardness resulted from an excessive amount of retained austenite. This caused reduced wear resistance and thus rapid wear in service. Recommendations included avoiding an excessive austenitizing temperature and excessive cooling rates from the austenitizing temperature and controlling the chemical composition to avoid excessive hardenability for the section size involved.

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.

Two slitting saw blades were delivered for the purpose of determining the cause of damage. One had cracked while the other one came from a prior sheet delivery, that had less tendency to crack formation according to the manufacturer. The blades were supposed to have been stamped out of a sheet made from a 55 kp/sq mm strength steel. The saw blades were used for separating steel profiles at high rotational speeds. The cracks in question were located at the base of the teeth, i.e. at the point of highest operating stress. Metallographic examination showed that all cracks were non-decarburized and were free of chromium deposits. Therefore they could not have existed before heat treatment and chrome plating. It was concluded that the damage was due neither to poor quality of the sheet nor to defective stamping or heat treatment, but had occurred later either during surface treatment or during operation.

A sledge hammer chipped during use. The chip struck a by stander in the eye, leading to its loss. The hammerhead surface was examined visually, nondestructively (magnetic particle method), and stereo microscopically, and a microstructural analysis of a cross section of the head was conducted using optical microscope. Chemical composition of the hammerhead was determined by emission spectrometry. The chemical compositions of the chip and hammer head were compared using energy-dispersive analysis. Microhardness versus distance from the striking face was also determined. The hammerhead material was UNS G10800 (AISI/SAE grade 1080). Excessive hardnesses were measured in the first 3 mm (0. 12 in.) below the striking surface, indicating that there was lack of control during the final tempering operation.