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UNS G43400
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Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.usage.c9001539
EISBN: 978-1-62708-236-5
... grinding on high-strength steel; chromium should be stripped by electrochemical methods. Bolts Chromium plating Grinding cracks 4340 UNS G43400 Intergranular fracture During an overhaul, mechanics discovered a crack in a pivot bolt when they ground off the chromium plating. Investigation...
Abstract
Overhaul mechanics discovered a crack in an AISI 4340 Cr-Mo-Ni alloy steel pivot bolt when grinding off the chromium plating. The bolt had served for an estimated 10,000 h and was replated when last overhauled. On checking the bolt, several fine cracks were found on the surface. A 6500x micrograph revealed the intergranular nature of a crack. By trying different grinding procedures, investigators were able to reproduce this type of failure in the laboratory. It was concluded that grinding cracks initiated the failure. It should be noted that governing specifications prohibit grinding on high-strength steel; chromium should be stripped by electrochemical methods.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.aero.c9001538
EISBN: 978-1-62708-217-4
... gear 4340 UNS G43400 Intergranular fracture Stress-corrosion cracking Introduction Examination of a cracked nose landing gear cylinder proved that the part, AISI 4340 heat treated to the 260,000 to 280,000 psi tensile strength range, had started to fail on the inside diameter about 4 1...
Abstract
Examination of a cracked nose landing gear cylinder made of AISI 4340 Cr-Mo-Ni alloy steel proved that the part started to fail on the inside diam. When the nucleus of the stress-corrosion crack was studied in detail, iron oxide was found on the fracture surface. A 6500x micrograph revealed this area also displayed an intergranular texture. One of a group of small grinding cracks on the ID of the cylinder nucleated the failure. Other evidence indicated the cracks developed when the cylinder was ground during overhaul.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.aero.c9001540
EISBN: 978-1-62708-217-4
... overhaul. The specific source of hydrogen which produced failure was not ascertainable. Aircraft components Chromium plating Cylinders Landing gear 4340 UNS G43400 Intergranular fracture Hydrogen damage and embrittlement Introduction Ground maintenance personnel discovered hydraulic...
Abstract
Ground maintenance personnel discovered hydraulic fluid leaking from two small cracks in a main landing gear cylinder made from AISI 4340 Cr-Mo-Ni alloy steel. Failure of the part had initiated on the ID of the cylinder. Numerous cracks were found under the chromium plate. A 6500x electron fractograph showed cracking was predominantly intergranular with hairline indications. Leaking had occurred only 43 h after overhaul of the part. Total service time on the part was 9488 h. It was concluded that cracking on the ID was caused by hydrogen embrittlement which occurred during or after overhaul. The specific source of hydrogen which produced failure was not ascertainable.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.aero.c9001542
EISBN: 978-1-62708-217-4
... at this time ultimately resulted in pitting of the metal. The combination of surface pitting and stress concentration at the nearby inclusions resulted in stress-corrosion cracking. Aircraft components Cylinders Landing gear Nonmetallic inclusions Stress concentration 4340 UNS G43400 Pitting...
Abstract
A nose landing gear cylinder made from AISI 4340 Ni-Cr-Mo alloy steel was found cracked and leaking, causing partial depressurization. Investigation revealed the crack to be a stress-corrosion type, judging by the 6500x electron fractograph. It had started in a region of concentrated, large non-metallic inclusions near the chromium-plated ID of the cylinder. Also, there were breaks in the chromium plate and pits in the underlying base metal. The cylinder had been in service for 18,017 h, and 5948 h had passed since the first and only overhaul. Substandard plating of the ID at this time ultimately resulted in pitting of the metal. The combination of surface pitting and stress concentration at the nearby inclusions resulted in stress-corrosion cracking.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.usage.c0046366
EISBN: 978-1-62708-236-5
... or debris from an external source. No recommendations were made. Chromium plating Cylinders Scoring B850-T5 UNS A08500 4340 UNS G43400 Abrasive wear Several large chromium-plated 4340 steel cylinders were removed from service because of deep longitudinal score marks in the plating. One...
Abstract
Several large chromium-plated 4340 steel cylinders were removed from service because of deep longitudinal score marks in the plating. One of the damaged cylinders and a mating cast aluminum alloy B850-T5 bearing adapter that also exhibited deep longitudinal score marks were submitted for examination. Analysis (visual inspection, manual testing of the hardness and adherence of the chromium plating, 100x microscopic examination, and hardness testing) supported the conclusions that high localized loads on the cylinder had resulted in chipping of the chromium plating, particles of which became embedded in the aluminum alloy adapter. The sliding action of the adapter with embedded hard particles resulted in scoring of both the cylinder and the adapter. If the cylinder alone had been available for examination, it might have been concluded that the scoring had been caused by entrapped sand or debris from an external source. No recommendations were made.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.modes.c0006417
EISBN: 978-1-62708-234-1
... stainless steel was also recommended. Cadmium plating Corrosion prevention Corrosion products Energy dispersive x ray analysis Inhibitors Iron oxides Materials substitution Pipe bends Scanning electron microscopy 4340 UNS G43400 (Other, general, or unspecified) corrosion A cadmium...
Abstract
A cadmium-plated 4340 Ni-Cr-Mo steel ballast elbow assembly was submitted for failure analysis to determine the element or radical present in an oxidation product found inside the elbow assembly. Energy-dispersive x-ray analysis in the SEM showed that iron was the predominant species, presumably in an oxide form. The inside surface had the appearance of typical corrosion products. Hardness measurements indicated that the 4340 steel was heat treated to a strength of approximately 862 MPa (125 ksi). It was concluded that the oxide detected on the ballast elbow was iron oxide. The possibility that the corrosion products would eventually create a blockage of the affected hole was great considering the small hole diameter (4.2 mm, or 0.165 in.). It was recommended that a quick fix to stop the corrosion would be to apply a corrosion inhibitor inside the hole. This, however, would cause the possibility of inhibitor buildup and the eventual clogging of the hole. A change in the manufacturing process to include a cadmium plating on the hole inside surface was recommended. This was to be accomplished in accordance with MIL specification QQ-P-416, Type II, Class 1. A material change to 300-series stainless steel was also recommended.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.conag.c0047212
EISBN: 978-1-62708-221-1
... to fracture. No evidence of a defective design, improper microstructure, high inclusion count, or other stress-raising condition was observed. No recommendations were made. Earthmoving equipment Plastic deformation Shafts (power) 4340 UNS G43400 Fatigue fracture A steering knuckle used...
Abstract
A steering knuckle used on an earthmover failed in service. The component fractured into a flange portion and a shaft portion. The flange was 27.9 cm (11 in.) in diam around which there were 12 evenly spaced 16 mm diam bolt holes. The shaft was hollow with a 10.5 cm (4 in.) OD and a wall thickness of 17 mm. The steering knuckle was made of 4340 steel and heat treated to a hardness of about 415 HRB (yield strength of about 1069 MPa, or 155 ksi). The vehicle had been involved in a field accident six months before the steering knuckle failed. Several components, including portions of the frame, had been damaged and replaced, but there was no observed damage to the steering. Analysis supported the conclusion that the fracture was the result of the prior accident, the most likely explanation being that the shaft was bent and that continued use caused a crack to initiate and propagate to fracture. No evidence of a defective design, improper microstructure, high inclusion count, or other stress-raising condition was observed. No recommendations were made.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.conag.c9001495
EISBN: 978-1-62708-221-1
... and should have withstood normal operating conditions. The spacing of the gouge marks coincided with the spacing of the splines, indicative of careless assembly with the mating wheel gear. Assembling Axles Mining equipment Splines 4340 UNS G43400 Fatigue fracture One end of a broken axle...
Abstract
An axle shaft in an open-pit mining truck hauling overburden failed after operating for 27,000 h. Previous failures had resulted from longitudinal shear, but this had not, bringing material quality into question. Chemical analysis verified that the part was SAE4340 Ni-Cr-Mo alloy steel and thus met material specification. The failure was a result of torsional fatigue in the tensile plane, originating from one of several gouges around the splined radius of the shaft. The fatigue crack progressed for a large number of cycles before final fracture. The shaft met metallurgical requirements and should have withstood normal operating conditions. The spacing of the gouge marks coincided with the spacing of the splines, indicative of careless assembly with the mating wheel gear.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.aero.c0006444
EISBN: 978-1-62708-217-4
... in.). Protective Coatings Shot peening 4340 UNS G43400 Corrosion fatigue Pitting corrosion Several rotor blade components were received for laboratory analysis. These included the horizontal hinge pin and the associated nut the locking washer ( Fig. 1a , b , and c ). Fig. 1 Corrosion fatigue...
Abstract
Helicopter rotor blade components that included the horizontal hinge pin, the associated nut, and the locking washer were examined. Visual examination of the submitted parts revealed that the hinge pin, fabricated from 4340 steel, was broken and that the fracture face showed a flat beach mark pattern indicative of a preexisting crack. The threaded area of the pin had an embedded thread that did not appear to come from the pin. A chemical analysis was conducted on the embedded thread and on an associated attachment to determine the origin of the thread. Analysis showed that the thread and nut were 4140 steel. Scanning electron fractographic examination of the fracture initiation site strongly suggested that the fracture progressed by fatigue. It was concluded that the failure of the horizontal hinge pin initiated at areas of localized corrosion pits. The pits in turn initiated fatigue cracks, resulting in a failure mode of corrosion fatigue. It was recommended that all of the horizontal hinge pins be inspected. Those pins determined to be satisfactory for further use should be stripped of cadmium, shot peened, and coated with cadmium to a minimum thickness of 0.0127 mm (0.0005 in.).
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.aero.c9001552
EISBN: 978-1-62708-217-4
... plating Crankshafts Magnetic particle testing Nitriding Surface grinding 4340 UNS G43400 Fatigue fracture Metalworking-related failures Surface treatment related failures Fig. 1 illustrates a crankshaft of AISI 4340, heat treated and nitrided all over, which failed in bending fatigue...
Abstract
This report covers case histories of failures in fixed-wing light aeroplane and helicopter components. A crankshaft of AISI 4340 Ni-Cr-Mo alloy steel, heat treated and nitrided all over, failed in bending fatigue. The nitrided layer was ground too rapidly causing excessive heat generation which induced grinding cracks and grinding burn. Tensional stresses resulting from grinding developed in a thin surface layer. On another crankshaft, chromium plating introduced undesirable residual tensile stresses. Such plating is an unsatisfactory finish for crankshafts of aircraft engines. Aircraft engine manufacturers and aeronautical standards require magnetic particle inspection to detect grinding cracks after reconditioning. Renitriding after any grinding is needed also, regardless of the amount of undersize as it introduces beneficial residual compressive stresses.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.aero.c9001746
EISBN: 978-1-62708-217-4
... was inadequate procedure, which resulted in bending moments being applied to the bolt threads. Acid pickling Bolts Cadmium plating Landing gear Torque 4340 UNS G43400 Surface treatment related failures Hydrogen damage and embrittlement Fig. 1 shows a failed beam from a landing gear...
Abstract
Brittle intergranular fracture, typical of a hydrogen-induced delayed failure, caused the failure of an AISI 4340 Cr-Mo-Ni landing gear beam. Corrosion resulting from protective coating damage released nascent hydrogen, which diffused into the steel under the influence of sustained tensile stresses. A second factor was a cluster of non-metallic inclusions which had ‘tributary’ cracks starting from them. Also, eyebolts broke when used to lift a light aircraft (about 7000 lb.). The bolt failure was a brittle intergranular fracture, very likely due to a hydrogen-induced delayed failure mechanism. As for the factors involved, cadmium plating, acid pickling, and steelmaking processes introduce hydrogen on part surfaces. As a second contributing factor, both bolts were 10 Rc points higher in hardness than specified (25 Rc), lessening ductility and notch toughness. A third factor was inadequate procedure, which resulted in bending moments being applied to the bolt threads.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.usage.c0047823
EISBN: 978-1-62708-236-5
... UNS G43400 Fatigue fracture A plant utilized high-horsepower electric motors to drive large compressors required for a manufacturing process. Eight compressors had shafts made of 4340 steel quenched and tempered to a hardness of 35 to 39 HRC and gear-type couplings. The compressors operated...
Abstract
High-horsepower electric motors were utilized to drive large compressors (made of 4340 steel shafts and gear-type couplings) required in a manufacturing process. The load was transmitted by two keys 180 deg apart. Six of the eight compressor shafts were found cracked in a keyway and one of them fractured after a few months of operation. Visual examination of fractured shaft revealed that the cracks originated from one of the keyways and propagated circumferentially around the shaft. The shaft and coupling slippage was indicated by the upset keys and this type of fracture. The shaft surface both near and in the keyways indicated fretting which greatly reduced the fatigue limit of the shaft metal and initiated fatigue cracks. Fatigue marks were observed on the fractured key. Repetitive impact loading was responsible for propagation of the cracks. The high cyclic bending stresses were caused by misalignment between the electric motor and compressor and were transmitted to the shaft through the geared coupling. Flexible-disk couplings capable of transmitting the required horsepower were installed on the shafts as a corrective measure.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.modes.c0091096
EISBN: 978-1-62708-234-1
... groove in the shaft had performed its function, but at a lower overload level than intended. Recommendations included increasing the fatigue strength of the shaft by shot peening the shear groove to minimize chatter. Shafts (power) Shot peening Torsional fatigue 4340 UNS G43400 Fatigue...
Abstract
A 4340 steel shaft, the driving member of a large rotor subject to cyclic loading and frequent overloads, broke after three weeks of operation. The driving shaft contained a shear groove at which the shaft should break if a sudden high overload occurred, thus preventing damage to an expensive gear mechanism. The rotor was subjected to severe chatter, which was an abnormal condition resulting from a series of continuous small overloads occurring at a frequency of around three per second. Investigation (visual inspection, hardness testing, and hot acid etch images) supported the conclusion that the basic failure mechanism was fracture by torsional fatigue, which started at numerous surface shear cracks, both longitudinal and transverse, that developed in the periphery of the root of the shear groove. These shear cracks resulted from high peak loads caused by chatter. The shear groove in the shaft had performed its function, but at a lower overload level than intended. Recommendations included increasing the fatigue strength of the shaft by shot peening the shear groove to minimize chatter.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.machtools.c9001519
EISBN: 978-1-62708-223-5
... to change its cleaning practice from pickling to grit blasting. Bolts Pickling Vertical milling machines 4340 UNS G43400 Hydrogen damage and embrittlement Surface treatment related failures Problem The AISI 4340 alloy steel draw-in bolt and the collet from a vertical-spindle milling...
Abstract
An AISI 4340 Ni-Cr-Mo alloy steel draw-in bolt and the collet from a vertical-spindle milling machine broke during routine cutting of blind recesses after relatively long service life. Based on fracture surface features, it was suspected that the draw-in bolt was the first to fracture, followed by failure of the collet, which shattered one of its arms when it struck the work table. Scanning electron microscopy showed the presence of hairline crack indications along grain facets on the fracture surface of the bolt. This, coupled with stepwise cracking in the material, generally raised suspicion of hydrogen embrittlement. It appeared that fracture in service progressed transgranularly to produce delayed failure under dynamic loading. The pickling process used to remove heat scale was suspected to be the source of hydrogen on the surface of the bolt. The manufacturer was requested to change its cleaning practice from pickling to grit blasting.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.aero.c9001906
EISBN: 978-1-62708-217-4
... defects 4340 UNS G43400 Metalworking related failures Introduction Component: MS3314 general purpose bomb suspension lug Manufacturing defects: Forging laps and seams Background Two MS3314 suspension lugs fabricated from AISI 4340 steel are threaded into each 500- and 1000-lb general...
Abstract
Suspension lugs fabricated from AISI 4340 steel used to facilitate loading of bombs onto the underside of military aircraft could not sustain required loads during routine proof load testing. Three failed lugs underwent visual examination, chemical analysis, metallography, hardness testing, scanning electron microscopy, and energy-dispersive x-ray spectroscopy. It was determined that the failures were due to forging defects. Both forging laps and seams acted as stress concentrators when the lugs were loaded during proof testing.
Series: ASM Failure Analysis Case Histories
Volume: 2
Publisher: ASM International
Published: 01 December 1993
DOI: 10.31399/asm.fach.v02.c9001384
EISBN: 978-1-62708-215-0
... with bolts manufactured using controlled processes. Machine tools Milling cutters 4340 UNS G43400 Hydrogen damage and embrittlement Background The draw-in bolt and the collet from a vertical-spindle milling machine broke during routine cutting of blind recesses after a relatively long...
Abstract
The draw-in bolt and collet from a vertical-spindle milling machine broke during routine cutting of blind recesses after a relatively long service life. The collet ejected at a high rotational speed due to loss of its vertical support and shattered one of its arms upon impact with the work table. SEM fractography and metallographic examinations conducted on the bolt revealed hairline indications along grain facets on the fracture surface and stepwise cracking in the material, both indicating failure by hydrogen embrittlement. Similar draw-in bolts were discarded and replaced with bolts manufactured using controlled processes.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.process.c0049797
EISBN: 978-1-62708-235-8
... was thus attributed to the presence of the quench crack flaw caused by an improper machining sequence and heat treatment practice. Connecting rods Quench cracking Threads 4340 UNS G43400 Mixed-mode fracture An AISI 4340 threaded steel connecting rod was part of a connecting linkage used...
Abstract
An AISI 4340 threaded steel connecting rod that was part of a connecting linkage used between a parachute and an instrumented drop test assembly fractured under high dynamic loading when the assembly was dropped from an airplane. A large flaw that originated from the root of a machined thread groove was visible on the fracture surface. Heavy oxidation at elevated temperatures was indicated as most of the surface of the flaw was black. Fine secondary cracks aligned transverse to the growth direction was revealed by scanning electron microscopy. It was established that intergranular cracking observed in this alloy was caused during heat treating as the thread root served as an effective stress concentration and induced quench cracking. It was found that fracture in the overload region occurred by a ductile void growth and coalescence process. Premature failure of the threaded rod was thus attributed to the presence of the quench crack flaw caused by an improper machining sequence and heat treatment practice.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.aero.c0046870
EISBN: 978-1-62708-217-4
...) was recommended as a standard maintenance procedure for shafts with long service lives. Aircraft components Shafts (power) Torsional fatigue AMS 6415 UNS G43400 Pitting corrosion Corrosion fatigue The hollow, splined alloy steel aircraft shaft shown in Fig. 1 cracked in service after more than...
Abstract
A hollow, splined alloy steel aircraft shaft (machined from an AMS 6415 steel forging – approximately the same composition as 4340 steel – then quenched and tempered to a hardness of 44.5 to 49 HRC) cracked in service after more than 10,000 h of flight time. The inner surface of the hollow shaft was exposed to hydraulic oil at temperatures of 0 to 80 deg C (30 to 180 deg F). Analysis (visual inspection, 15-30x low magnification examination, 4x light fractograph, chemical analysis, hardness testing) supported the conclusions that the shaft cracked in a region subjected to severe static radial, cyclic torsional, and cyclic bending loads. Cracking originated at corrosion pits on the smoothly finished surface and propagated as multiple small corrosion-fatigue cracks from separate nuclei. The originally noncorrosive environment (hydraulic oil) became corrosive in service because of the introduction of water into the oil. Recommendations included taking additional precautions in operation and maintenance to prevent the use of oil containing any water through filling spouts or air vents. Also, polishing to remove pitting corrosion (but staying within specified dimensional tolerances) was recommended as a standard maintenance procedure for shafts with long service lives.
Series: ASM Failure Analysis Case Histories
Volume: 2
Publisher: ASM International
Published: 01 December 1993
DOI: 10.31399/asm.fach.v02.c9001299
EISBN: 978-1-62708-215-0
... for cracks during periodic maintenance overhauls. Aerospace engines Airplanes Nonmetallic inclusions 4340 UNS G43400 Fatigue fracture Background A steel piston engine crankshaft in a transport aircraft failed catastrophically during flight. Applications The massive, complex-shaped...
Abstract
A 4340 steel piston engine crankshaft in a transport aircraft failed catastrophically during flight. The fracture occurred in the pin radius zone. Fractographic studies established the mode of failure as fatigue under a complex combination of bending and torsional stresses. SEM examination revealed that the fracture origin was a subsurface defect-a hard refractory (Al2O3) inclusion—in the zone close to the pin radius. Chemical analysis showed the crankshaft material to be of inferior quality. It was recommended that magnetic particle inspection using the dc method be used to cheek for cracks during periodic maintenance overhauls.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.mech.c9001619
EISBN: 978-1-62708-225-9
... of the splines. SEM examination revealed the splined shaft failed by fretting fatigue. Fretting fatigue Paper machines Shafts (power) 4340 UNS G43400 Fretting wear Fatigue fracture Wood chips can be efficiently turned into fiber for newsprint manufacture by the process of disc refining...
Abstract
A splined shaft on a wood chip-to-fiber refiner failed during equipment start-up. The shaft broke into two pieces at a location close to the end of the splined part of the shaft. The failed component showed the classical fatigue-cracking fracture face. The shaft had a diam of approximately 140 mm (5.5 in.) in the unsplined section and was made of 4340 Ni-Cr-Mo alloy steel heat treated to a uniform hardness of HRC 31. Cracks from at least seven different origins had coalesced to produce the single large crack that resulted in failure. The origins of these cracks were on the flanks of the splines. SEM examination revealed the splined shaft failed by fretting fatigue.
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