Following three similar failures of load chains on manually operated geared pulley-blocks of 1-ton capacity, a portion of one of the chains was obtained for examination. The chain was made of mild steel and the links had been electrically butt-welded at one side. In the case of the sample obtained, the failure in service had resulted from fracture of one of the links in the plane of the weld. Six of the other links in the vicinity showed cracks in the welds in various stages of development. Microscope examination showed a crack in an early stage of development and also from an apparently sound link, the prepared surfaces lying in the planes of the links. This examination revealed that the welds were initially defective. Discontinuities were present in both cases adjacent to the insides of the links, of a type indicative of either inadequate fusion or incomplete expulsion of oxide, etc., at the time of the upset, i.e. the pressing together of the ends of the links to complete the welding. It was evident from the examination that the service failures were due to the use of chain that was initially defective.

Failure occurred by fatigue cracking of links from chains which were used to replace the ropes on grabs of the multirope type. In the first example, the links were made from high tensile steel rod. The fracture in the side of the link was duplex in appearance one half of the surface being discolored, indicative of a preexisting crack of the fatigue type, whilst the remaining portion was brightly crystalline, resulting from brittle fracture at the time of the mishap. In the second example, the fracture took place at a similar location adjacent to one of the butt welds situated at the mid-length of the sides. Brinell hardness values confirmed that the link was made from the higher tensile grade of material. The cracks were due to fatigue, there being no indications that the weld was initially defective.

A chain link which was part of the hoisting mechanism of a drop hammer broke after three or four months of service. It was reportedly manufactured of the heat resistant steel 30 Cr-Mo-V 9 (Material No. 1.7707). The fracture of the chain link had a conchoidal structure and ran along the austenitic grain boundaries. Such fractures are characteristic results of strong overheating. The coarse-grained, coarse acicular heat-treated structure of the chain link confirmed overheating. Because temperatures in excess of 1150 deg C are required for the solution of impurities, it is more probable that the real damage was done during the heat-up forging (drop-forging) and could not be removed during heat-treatment.

Three links of a chain showing unusually strong wear were examined. Corresponding to the stress, the wear was strongest in the bends of the links, but it was especially pronounced in the bend in which the butt weld seam was located. Investigation showed the links were manufactured from an unkilled carbon-deficient steel, and were case hardened to a depth of 0.8 to 0.9 mm. The peripheral structure at the places not showing wear consisted of coarse acicular martensite with a high percentage of retained austenite. The links therefore were strongly overheated, probably directly heated during case hardening. The butt weld seams were not tight and were covered with oxide inclusions. Given that wear occurred preferentially at the welds it may be concluded that this weld defect contributed to the substantial wear. This leaves unanswered whether these chains could have withstood the high operating stress if they had been welded satisfactorily and hardened correctly, and whether it made any sense to case harden highly stressed chains of this type.

While a chain sling was being used to lift a casting one of the links ruptured. The sling, reputed to be of the electrically-welded steel type, was at least eight years old and had been overhauled several times during its working life. Examination showed the links were scarf-welded. Furthermore, the welds were at the ends and not at the sides as is usual in the case of electrically-welded chains. A transverse section from one side of a link was examined microscopically. This showed the material to be wrought-iron of satisfactory quality. It was concluded this chain sling had been made from wrought-iron, forge welded in the usual manner, and that it was not electrically-welded steel as had been supposed. Failure was attributed to embrittlement in service of the surface material of the links. If it had been realized that the sling was made from wrought-iron then it would doubtless have been subjected to periodical annealing in accordance with Statutory requirements, which would have restored the ductility of the surface material.

A 10-cm (4-in.) chain link used in operating a large dragline bucket failed after several weeks in service. The link was made of cast low-alloy steel (similar to ASTM A487, class 10Q) that had been normalized, hardened, and tempered to give a yield strength of approximately 1034 MPa (150 ksi). A hydrogen flake approximately 5 cm (2 in.) in diam was observed at the center of the fracture surface. Beach marks indicative of fatigue encircled the hydrogen flake and covered nearly all of the remaining fracture surface. The failure of this linkways caused by an excessive hydrogen content. Two steps were taken to combat this type of failure. First, when service conditions did not require high hardness to combat wear, the links were produced of a steel having a yield strength of about 690 MPa (100 ksi) rather than 1034 M

The conveyor chain link failed by fracturing through a fabrication weld after some time in service. The link was made of cast low-alloy steel heat treated to a hardness of 285 HRB. The fabrication weld was made using E7018 electrodes. The fracture surfaces were almost entirely covered with beach marks, indicating fatigue cracking. The beach marks emanated from a 6.4 mm (1/4 in.) wide band of unusual appearance running across the center of the fracture. Saw cuts were made perpendicular to both of the fracture surfaces and across the unusual-looking bands. The cut surfaces were ground and etched with ammonium persulfate solution revealing that complete penetration had not been achieved at the weld root. The band observed in the fracture was apparently part of the unfused weld-preparation surface at the root of the weld. This failure was caused by fatigue that initiated at an incomplete penetration defect at the root of the fabrication weld. As a result of this failure, steps were taken to ensure that good welding practice (back-gouging) would be followed in the future fabrication of these links.

An ASTM A391 steel chain link of an over head hoist failed catastrophically, causing damage to both property and personnel. Macrofractography identified the sequence of fractures within the chain link. The first fracture occurred at the welded joint, a second occurred opposite the weld. SEM fractography and metallography indicated that the link failed in a ductile manner because of tensile overload, which occurred when the hoist hook contacted the hoist's housing and prevented uptake of the chain. It was recommended that a load-sensing device be installed to prevent future occurrences and that a dye penetrant inspection be performed on the renwinder of the chain.

The link which failed was a special long one connecting a grab chain to a swivel. It was made from En 14A steel and in continuous use for two years. On one of the fracture faces the chisel edge weld preparation was clearly visible and the crack progression markings present indicated failure was due to fatigue. Macro-etched cross sections showed a lack of penetration and fusion in the weld. Fatigue cracks developed and slowly progressed through the weld metal. Fracture occurred when the remaining area of sound metal was insufficient to support the load. Lack of penetration of this magnitude could be revealed by radiography or ultrasonics but it would be difficult to detect the presence of cracks in course of development from the defects. It would be more prudent to ensure that welded links of this type were free from internal cavities before being put into service.

Chain link, a part of a mechanism for transferring hot or cold steel blooms into and out of a reheating furnace, broke after approximately four months of service. The link was cast from 2% Cr austenitic manganese steel and was subjected to repeated heating to temperatures of 455 to 595 deg C (850 to 1100 deg F). Examination included visual inspection, macrograph of a nital-etched specimen from an as-received chain link 1.85x, micrographs of a nital-etched specimen from an as-received chain link 100x/600x, normal microstructure of as-cast standard austenitic manganese steel 100x, micrograph of a nital-etched specimen that had been austenitized 20 min at 1095 deg C (2000 deg F) and air cooled 315x, and micrograph of the same specimen after annealing 68 h at 480 deg C (900 deg F) 1000x). Investigation supported the conclusions that the chain link failed in a brittle manner, because the austenitic manganese steel from which it was cast became embrittled after being reheated in the temperature range of 455 to 595 deg C (850 to 1100 deg F) for prolonged periods of time. The alloy was not suitable for this application, because of its metallurgical instability under service conditions.

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.