The large steel ring produced for a nuclear application from a billet of 8822 steel was inspected. The large billet was first forged into a doughnut preform in a large press, and then formed into the ring by ring rolling. A straight-beam ultrasonic inspection was instituted and calibrated using the back-surface-reflection method to determine whether adequate ultrasonic penetration was available. Areas of indications were noted at approximately midheight and adjacent to the bore area. An axial angle-beam inspection from the outside was performed, mainly in the area of indications to reveal detectable indications. The indications were not considered serious enough to reject the forgings. A few small indications in the areas tested were revealed by magnetic particle inspection. The area was conditioned by grinding and polishing to obtain an additional inspection at a greater depth from the inside surface. A much more severe condition was revealed after the test. The indications were classified as areas of chemical segregation and nonmetallic inclusions. The ring was considered unsatisfactory for the application and replacement of the defective ring from an acceptable billet was the most economical solution.

A recurring piston shaft failure problem on the billet-loading tray of an extrusion press was investigated. Two shafts fractured within a period of 10 days. The shaft was machined from normalized EN3 (AISI C1022) steel stock without further treatment. Visual, microstructural, chemical, and mechanical (hardness and tensile properties) analyses of failed shaft specimens were conducted. The examinations showed that the shafts had failed by fatigue. It was recommended that a low-alloy steel (e.g., 3% Ni-Cr) in the hardened and tempered condition and subjected to shot-peening surface-hardening treatment be used. The provision of a stop to reduce bending stresses was also recommended.

During the lifting of a piece of machinery by means of an overhead travelling crane the hook fractured suddenly. The load was attached to the hook by means of fiber rope slings and rupture occurred in a plane which appeared to coincide with the sling loop nearest to the back of the hook. The rated capacity of the crane was 15 tons. At the time of the mishap it was being used to lift one end of a hydraulic cylinder with a total weight of about 27 tons. Fracture was of the cleavage type throughout. There was no evidence of any prior deformation of the material in the vicinity, nor was there any indication of a pre-existing crack or major discontinuity at the point of origin. A sulfur print suggested the hook had been forged from a billet cogged down from an ingot of semi-killed steel. Failure of this hook was attributed to strain-age embrittlement of the material at the surface of the intrados.

A resistance-welded chain link made from 16 mm diam 4615 steel failed while lowering a 9070 kg load of billets into a rail car after being in service for 13 months. Beach marks, typical of fatigue were found to have originated at the inside of the link which broke at the weld. Cracks in the weld zone (up to 1.2 mm deep) were revealed during metallographic examination of a section through the fracture surface. The cracks were filled with scale which indicated that they had formed during resistance welding of the link. The defect was thus attributed to the weld defects which initiated the fatigue failure by acting as stress raisers. The welding method was changed by the manufacturer and all chains were replaced with defect free chains.

Several thousands of new 16 mm diam alloy steel sling chains used for handling billets failed by chain-link fractures. No failures were found to have occurred before delivery of the new chains. It was observed that the links had broken at the weld. It was found that all failures had occurred in links having hardness values in the range of 375 to 444 HRB. It was revealed by the supplier that the previous hardness level of 302 to 375 HRB was increased to minimize wear which made the links were made notch sensitive and resulted in fractures that initiated at the butt-weld flash on the inside surfaces of the links. A further reduction in ductility was believed to have been caused by lower temperatures during winter months. Thus, the failure was concluded to have been caused in a brittle manner caused by the notch sensitivity of the high hardness material at lower temperatures. The chains were retempered to a hardness of 302 to 375 HRB as a corrective measure and subsequently ordered chains had this hardness as a requirement.

Several failed dies were analyzed and the results were used to evaluate fatigue damage models that have been developed to predict die life and aid in design and process optimization. The dies used in the investigation were made of H13 steels and fractured during the hot extrusion of Al-6063 billet material. They were examined to identify critical fatigue failure locations, determine corresponding stresses and strains, and uncover correlations with process parameters, design features, and life cycle data. The fatigue damage models are based on Morrow’s stress and strain-life models for flat extrusion die and account for bearing length, fillet radius, temperature, and strain rate. They were shown to provide useful information for the analysis and prevention of die failures.

The primary purpose of this article is to describe general root causes of failure that are associated with wrought metals and metalworking. This includes a brief review of the discontinuities or imperfections that may be common sources of failure-inducing defects in the bulk working of wrought products. The article addresses the types of flaws or defects that can be introduced during the steel forging process itself, including defects originating in the ingot-casting process. Defects found in nonferrous forgings—titanium, aluminum, and copper and copper alloys—also are covered.

Results of failure analyses of two aircraft crankshafts are described. These crankshafts were forged from AMS 6414 (similar composition to AISI 4340) vacuum arc remelted steels with sulfur contents of 0.003% (low sulfur) and 0.0005% (ultra-low sulfur). A grain boundary sulfide precipitate was caused by overheat of the low sulfur steel, and an incipient melting of grain boundary junctions was caused by overheat of the ultra-low sulfur steel. The precipitates and incipient melting in these two failed crankshafts were observed during the examination. As expected, impact fractures from the low sulfur steel crankshaft contained planar dimpled facets along separated grain boundaries with a small spherical manganese sulfide precipitates within each dimple. In contrast, planar dimpled facets along separated grain boundaries of impact fractures from the ultra-low sulfur crankshaft steel contained a majority of small spherical particles consisting of nitrogen, boron, iron, carbon, and a small amount of oxygen. Some other dimples contained manganese sulfide precipitates. Fatigue samples machined from the ultra-low sulfur steel crankshaft failed internally at planar grain boundary facets. Some of the facets were covered with nitrogen, boron, iron, and carbon film, while other facets were relatively free of such coverage. Results of experimental forging studies defined the times and temperatures required to produce incipient melting overheat and facets at grain boundary junctions of ultra-low sulfur AMS 6414 steels.

The connecting end of two forged medium-carbon steel rods used in an application in which they were subjected to severe low-frequency loading failed in service. The fractures extended completely through the connecting end. The surface hardness of the rods was found to be lower than specifications. The fractures were revealed to be in areas of the transition regions that had been rough ground to remove flash along the parting line. The presence of beach marks, indicating fatigue failure, was revealed by examination. The fracture origin was confirmed by the location and curvature of beach marks to be the rough ground surface. An incipient crack 9.5 mm along with several other cracks on one of the fractured rods was revealed by liquid penetration examination. Metallographic examination of the fractured rods indicated a banded structure consisting of zones of ferrite and pearlite. It was established that the incipient cracks found in liquid-penetrant inspection had originated at the surface in the banded region, in areas of ferrite where this constituent had been visibly deformed by grinding. Closer control on the microstructure, hardness of the forgings and smooth finish in critical area was recommended.

Splined rotor shafts (constructed from 1151 steel) used on small electric motors were found to miss one spline each from several shafts before the motors were put into service. Apparent peeling of splines on the induction-hardened end of each rotor shaft was revealed by visual and stereo-microscopic examination. One tooth on each shaft was found to be broken off. It was revealed by metallographic examination of an unetched section through the fractured tooth that the fracture surface was concave and had an appearance characteristic of a seam. Partial decarburization of the surface was revealed after etching with 1% nital. The presence of a crack, with typical oxides found in seams at its root, was disclosed by an unetched section through the shaft in an area unaffected by induction heating. The etched samples revealed similar decarburization as was noted on the fracture surface of the tooth. It was concluded that the seam had been present before the shaft was heat treated and these seams acted as stress raisers during induction hardening to cause the shaft failure. It was recommended that the specifications should specify that the shaft material should be free of seams and other surface imperfections.

This article describes the general root causes of failure associated with wrought metals and metalworking. This includes a brief review of the discontinuities or imperfections that may be the common sources of failure-inducing defects in bulk working of wrought products. The article discusses the types of imperfections that can be traced to the original ingot product. These include chemical segregation; ingot pipe, porosity, and centerline shrinkage; high hydrogen content; nonmetallic inclusions; unmelted electrodes and shelf; and cracks, laminations, seams, pits, blisters, and scabs. The article provides a discussion on the imperfections found in steel forgings. The problems encountered in sheet metal forming are also discussed. The article concludes with information on the causes of failure in cold formed parts.

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.

Following the fusing of one of the copper leads in the choke circuit of an electric welder, a piece of the affected lead was obtained for examination. The sample had large internal cavities and surface bulges. It is remarkable that a wire containing defects of the magnitude present in this case could have been drawn without failure. Failure in service was due to overheating resulting from the inability of the conductor to carry the current where its cross section was reduced by the presence of a cavity. Another failure of a conductor occurred in one of the field coils of a direct-current motor. The mode of failure and the changes in the microstructure showed that fracture was due to a defective resistance butt-weld which had been made when the wire was in process of drawing. A further example of a conductor failure occurred in a 12 SWG copper connection between the rotor contactor and the resistance in a starter. A transverse section through the zone of failure showed an oxide layer extended almost completely across the plane of a weld, and also the grain growth that had occurred in this region.

A valve stem made of 17-4 PH (AISI type 630) stainless steel, which was used for operating a gate valve in a steam power plant, failed after approximately four months of service, during which it had been exposed to high-purity water at approximately 175 deg C (350 deg F) and 11 MPa (1600 psi). The valve stem was reported to have been solution heat treated at 1040 +/-14 deg C (1900 +/-25 deg F) for 30 min and either air quenched or oil quenched to room temperature. The stem was then reportedly aged at 550 to 595 deg C (1025 to 1100 deg F) for four hours. Investigation (visual inspection, 0.7x/50x images, hardness testing, reheat treatment, and metallographic examination) supported the conclusion that failure was by progressive SCC that originated at a stress concentration. Also, the solution heat treatment had been either omitted or performed at too high of a temperature, and the aging treatment had been at too low of a temperature. Recommendations included the following heat treatments: after forging, solution heat treat at 1040 deg C (1900 deg F) for one hour, then oil quench; to avoid susceptibility to SCC, age at 595 deg C (1100 deg F) for four hours, then air cool.