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.

During a routine inspection, cracks were discovered in several aluminum alloy (similar to either 2014 or 2017) coupling nuts on the fuel lines of a missile. The fuel lines had been exposed to a marine atmosphere for six months while the missile stood on an outdoor test stand near the seacoast. A complete check was then made, both visually and with the aid of a low-power magnifying glass, of all coupling nuts of this type on the missile. Investigation (visual inspection, spectrographic and chemical analysis, and metallographic examination) supported the conclusion that the cracking of the aluminum alloy coupling nuts was caused by stress corrosion. Contributing factors included use of a material that is susceptible to this type of failure, sustained tensile stressing in the presence of a marine (chloride-bearing) atmosphere, and an elongated grain structure transverse to the direction of stress. The elongated grain structure transverse to the direction of stress was a consequence of following the generally used procedure of machining this type of nut from bar stock. Recommendations included changing the materials specification for new coupling nuts for this application to permit use of only aluminum alloys 6061-T6 and T651 and 2024-T6, T62, and T851.

Extra high strength zinc-coated 1080 steel welded wire was wound into seven-wire cable strands for use in aerial cables and guy wires. The wires and cable strands failed tensile, elongation, and wrap tests, with wires fracturing near welds at 2.5 to 3.5% elongation and through the welded joints in wrap tests. The welded wire was annealed by resistance heating. The wire ends had a chisel shape, produced by the use of sidecutters. Tests of the heat treatment temperatures showed that the wire near the weld area exceeded 775 deg C (1425 deg F). Metallographic examination revealed martensite present in the weld area after the heat treatment. The test failures of the AISI 1080 steel wire butt-welded joints were due to martensite produced in cooling from the welding operation that was not tempered adequately in postweld heat treatment, and to poor wire-end preparation for welding that produced poorly formed weld burrs. The postweld heat treatment was standardized on the 760 deg C (1400 deg F) transformation treatment. The chisel shape of the wire ends was abandoned in favor of flat filed ends. The wrap test was improved by adopting a hand-cranked device. Under these conditions, the welded joints withstood the tensile and wrap tests.

The cause of fracture of two piston rods of hammers of a drop forge was determined. The first rod of 180 mm diam consisted of an unalloyed steel with 0.37% C and 0.67% Mn and had a strength of 56 kp/sq mm at 26% elongation. Fatigue fractures propagated from several points which could be recognized as flaky cracks already in the fracture, and which later were united. No material defects could be detected in the cross section parallel to the fracture plane except for these very short cracks. These comparatively insignificant defects were sufficient to cause the fracture during high impact fatigue stresses in the drop forge. The second piston rod of 120 mm diam consisted of a steel with 0.25% C and 1.00% Mn. It allegedly had 57 kp/sq mm tensile strength and 26% elongation. The basic structure of the 120 mm piston rod was ferritic-pearlitic and hardness of 155 Brinell was accordingly low, corresponding to approximately 53 kp/sq mm tensile strength. The incipient fractures had no connection with the material defects in this shaft and therefore the fracture could not have been caused by them. Probably the low strength of the piston rod was insufficient for the high stresses.

A failure analysis was conducted in late 1996 on two rolls that had been used in the production of iron and steel powder. The rolls had elongated over their length such that the roll trunnions had impacted with the furnace wall refractory. The result was distortion and bowing of the roll bodies which necessitated their removal from service. The initial analysis found large quantities of nitrogen had been absorbed by the roll shell. Further research indicated nitrogen pickup accounted for 3% volumetric growth for every 1% by weight nitrogen absorption. This expansion was sufficient to account for the dimensional change observed in the failed rolls. This paper details the failure analysis and resulting research it inspired. It also provides recommendations for cast material choice in highly nitriding atmospheres.

A steel galvanizing vat measuring 3 x 1.2 x 1.2 m (10 x 4 x 4 ft) and made of 19 mm thick carbon steel plate (ASTM A285, grade B)) at a shipbuilding and ship-repair facility failed after only three months of service. To verify suspected failure cause, two T joints were made in 12.5 mm thick ASTM A285, grade B, steel plate. One joint was welded using the semiautomatic submerged arc process with one pass on each side. A second joint was welded manually by the shielded metal arc process using E6010 welding rod and four passes on each side. The silicon content of the shielded metal arc weld was 0.54%, whereas that of the submerged arc weld was 0.86%. After being weighed, the specimens were submerged in molten zinc for 850 h. Analysis (visual inspection, chemical analysis, 100x 2% nital-etched micrographs) supported the conclusions that the vat failed due to molten-zinc corrosion along elongated ferrite bands, possibly because silicon was dissolved in the ferrite and thus made it more susceptible to attack by the molten zinc. Recommendations included rewelding the vat using the manual shielded metal arc process with at least four passes on each side.

Deformation, surface cracking, and spalling on the raceway of the outer ring (made of 4140 steel) of a large bearing caused it to be replaced from a radar antenna. The raceway surfaces were to be flame hardened to 55 HRC minimum and 50 HRC 3.2 mm below the surface, according to specifications. Samples from both the inner and outer rings were examined. A much lower hardness (25.2 to 18.9 HRC) was indicated during a vertical traverse 4.1 cm from the outer surface of the outer ring while slightly lower hardness values (46.8 to 54.8 HRC) were seen on the hardness traverse on the inner ring raceway. The lower hardness values were attributed to improper flame hardening. It was confirmed by metallographic examination of a 3% nital etched sample that the inner ring (tempered martensite and ferrite) and the outer ring (ferrite, scattered patches of pearlite, and martensite) were not properly austenitized. Displacement of metal on the outer raceway was revealed by elongation of grain structure. It was concluded that the failure of the raceway surface was due to incomplete austenitization caused by the improper heat treatment during flame hardening process.