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Amitava Ray, S.K. Dhua, K.B. Mishra, S. Jha
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B.V. Krishna
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Yogesh Pathak, V. S. Aher
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Friedrich Karl Naumann, Ferdinand Spies
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Gudrun Urban
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Rodolfo Villa, Scot Roswurm
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Hardness distribution from periphery to core on transverse sections of non-...
Available to Purchase
in Worn Gears for Fuel Injection Pumps
> ASM Failure Analysis Case Histories: Automobiles and Trucks
Published: 01 June 2019
Fig. 7 Hardness distribution from periphery to core on transverse sections of non-worn areas of gears 1 and 2 and of the unused gear 3.
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Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.machtools.c0089534
EISBN: 978-1-62708-223-5
... by the hardness values (close to the maximum hardness values attainable) for the core. It was interpreted that the low tempering temperature used may have contributed to the brittleness. The procedures used for casting the jaws were recommended to be revised to eliminate the internal shrinkage porosity. Tempering...
Abstract
The specially designed sand-cast low-alloy steel jaws that were implemented to stretch the wire used in prestressed concrete beams fractured. The fractures were found to be macroscale brittle and exhibited very little evidence of deformation. The surface of the jaws was disclosed by metallographic examination to be case carburized. The case was found to be martensite with small spheroidal carbides while the core consisted of martensite plus some ferrite. The fracture was revealed to be related to shrinkage porosity. Tempering was revealed to be probably limited to about 150 deg C by the hardness values (close to the maximum hardness values attainable) for the core. It was interpreted that the low tempering temperature used may have contributed to the brittleness. The procedures used for casting the jaws were recommended to be revised to eliminate the internal shrinkage porosity. Tempering at a slightly higher temperature to reduce surface and core hardness was recommended.
Book Chapter
Metallurgical Investigation of a Prematurely Failed Roller Bearing Used in the Support and Tilting System of a Steel Making Converter Used in an Integrated Steel Plant
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.steel.c9001645
EISBN: 978-1-62708-232-7
... tempered martensite. Microhardness measurements revealed that. Although the core hardness of the roller and the inner-race samples were similar, the surface hardness of the roller was approximately 8.5 HRC units harder than that of the inner-race. SEM observations of the roller fracture surface revealed...
Abstract
An extensive metallurgical investigation was carried out on samples of a failed roller bearing from the support and tilting system of a basic oxygen furnace converter used in the steel melting shop of an integrated steel plant. The converter bearing was fabricated from low-carbon, carburizing grade steel and had failed in service within a year of fitting to a repaired shaft. Microscopic observations of both the broken roller and inner-race samples revealed subsurface cracking and preponderance of brittle oxide and other macroinclusions. Electron probe microanalysis studies confirmed that the brittle oxides that formed stringers were alumina, and the other macroinclusions were complex silicates. Both the alumina and silicate inclusions were deleterious to contact-fatigue properties. Microstructurally, the carburized regions of the broken roller and of inner-race samples contained high-carbon tempered martensite. Microhardness measurements revealed that. Although the core hardness of the roller and the inner-race samples were similar, the surface hardness of the roller was approximately 8.5 HRC units harder than that of the inner-race. SEM observations of the roller fracture surface revealed striations indicative of fatigue, and EDS analyses corroborated a high incidence of silicate inclusions at crack sites. The study suggests that the failure of the bearing occurred because the hardness difference between the roller bearing and the inner-race surfaces resulted in wear of the inner-race. The wear led to shaft misalignment and play during service. The misalignment, coupled with the presence of inclusions, caused fatigue failure of the roller bearing.
Book Chapter
Deformation of a Gas-Nitrided Drive-Gear Assembly
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.conag.c0092155
EISBN: 978-1-62708-221-1
..., of the case as a result of several factors. Recommendations included reducing the high local stresses at the pitch line to an acceptable level with a design modification. Also suggested was specification of a core hardness of 35 to 40 HRC to provide adequate support for the case and to permit attainment...
Abstract
Component slippage in the left-side final drive train of a tracked military vehicle was detected after the vehicle had been driven 13,700 km (8500 miles) in combined highway and rough-terrain service. The slipping was traced to the mating surfaces of the final drive gear and the adjacent splined coupling sleeve. Specifications included that the gear and coupling be made from 4140 steel bar oil quenched and tempered to a hardness of 265 to 290 HB (equivalent to 27 to 31 HRC) and that the finish-machined parts be single-stage gas nitrided to produce a total case depth of 0.5 mm (0.020 in.) and a minimum surface hardness equivalent to 58 HRC. Investigation (visual inspection, low-magnification images, 500X images of polished sections etched in 2% nital, spectrographic analysis, and hardness testing) supported the conclusion that the failure occurred by crushing, or cracking, of the case as a result of several factors. Recommendations included reducing the high local stresses at the pitch line to an acceptable level with a design modification. Also suggested was specification of a core hardness of 35 to 40 HRC to provide adequate support for the case and to permit attainment of the specified surface hardness of 58 HRC.
Book Chapter
Fatigue Failure of a Carburized Steel Bevel Pinion Because of Misalignment
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.mech.c0048273
EISBN: 978-1-62708-225-9
... Abstract Several teeth of a bevel pinion which was part of a drive unit in an edging mill failed after three months in service. Specifications required that the pinion be made from a 2317 steel forging and that the teeth be carburized and hardened to a case hardness of 56 HRC and a core...
Abstract
Several teeth of a bevel pinion which was part of a drive unit in an edging mill failed after three months in service. Specifications required that the pinion be made from a 2317 steel forging and that the teeth be carburized and hardened to a case hardness of 56 HRC and a core hardness of 250 HRB. Two teeth were revealed by visual examination to have broken at the root and fatigue marks extending across almost the entire tooth were exhibited by the surface of the fracture. Cracking in all the tooth was showed by magnetic-particle inspection. The pinion was concluded to have failed by tooth-bending fatigue. Spalling was also noted on the pressure (drive) side of each tooth at the toe end which indicated some mechanical misalignment of the pinion with the mating gear that caused the cyclic shock load to be applied to the toe ends of the teeth.
Book Chapter
Fatigue Fracture of a Cast Chromium-Molybdenum Steel Pinion
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.steel.c0047406
EISBN: 978-1-62708-232-7
... to 1045 steel. The pinion was annealed before flame or induction hardening of the teeth to a surface hardness of 363 HRB and a core hardness of 197 HRB. The broken pinion had a tooth which had failed by fatigue fracture through the tooth root because of the low strength from incomplete surface hardening...
Abstract
A cast countershaft pinion on a car puller for a blast furnace broke after one month of service; expected life was 12 months. The pinion was specified to be made of 1045 steel heat treated to a hardness of 245 HRB. The pinion steel was analyzed and was a satisfactory alternative to 1045 steel. The pinion was annealed before flame or induction hardening of the teeth to a surface hardness of 363 HRB and a core hardness of 197 HRB. The broken pinion had a tooth which had failed by fatigue fracture through the tooth root because of the low strength from incomplete surface hardening of the tooth surfaces. Contributing factors included uneven loading because of misalignment and stress concentrations in the tooth roots caused by tool marks. Greater strength was provided by oil quenching and tempering the replacement pinions to a hardness of 255 to 302 HRB. Machining of the tooth roots was revised to eliminate all tool marks. Surface hardening was applied to all tooth surfaces, including the root. Proper alignment of the pinion was ensured by carefully checking the meshing of the teeth at startup.
Book Chapter
Fatigue Fracture of AMS 6470 Steel Knuckle Pins
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.rail.c0046238
EISBN: 978-1-62708-231-0
... Abstract Within about one month, several knuckle pins (AMS 6470 steel failed, and required to have a minimum case hardness of 92 h15N, a case depth of 0.4 to 0.5 mm (0.017 to 0.022 in.), and a core hardness of 285 to 341 HRB) used in engines failed over a range of 218 to 463 h in operation...
Abstract
Within about one month, several knuckle pins (AMS 6470 steel failed, and required to have a minimum case hardness of 92 h15N, a case depth of 0.4 to 0.5 mm (0.017 to 0.022 in.), and a core hardness of 285 to 341 HRB) used in engines failed over a range of 218 to 463 h in operation. Visual examination revealed beach marks typical of fatigue cracks that had nucleated at the base of the longitudinal oil hole. Micrographs of sections revealed a remelt zone and an area of untempered martensite within the region of the cracks. However, review of inspection procedures disclosed the pins had been magnetic-particle inspected by inserting a probe into the longitudinal hole. Evidence found supports the conclusions that the knuckle pins failed by fatigue fracture. The circular cracks at the longitudinal holes were the result of improper technique in magnetic-particle inspection. Thermal transformation of the metal also causes a stress concentration that may lead to fatigue failure. Recommendations included insulating the conductor to prevent arc burning at the base of the longitudinal oil hole. Also, a borescope or metal monitor could be used to inspect the hole for evidence of arc burning from magnetic-particle inspection.
Book Chapter
Hydrogen Induced Cracking of a Tappet Adjusting Screw
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.process.c9001613
EISBN: 978-1-62708-235-8
...-0.40%, Mn-1.0-1.3%, P&S-0.035% max, Cr-0.8-1.1% Mechanical Properties: Core Strength — 1000–1200 MPa Core hardness — 310–370 HV Surface hardness in cup portion — 600–750 HV Case depth — 0.15–0.20 mm The Analysis Visual inspection of the fracture surface revealed a dull...
Abstract
The electroplated tappet adjusting screws used in diesel engines failed during initial bend testing. The analysis of the failure showed that the fracture was nucleated from the subsurface of the screw. The fracture surface was intergranular at the ID and OD region and microvoid coalescence in the center. The improper baking after electroplating of the screw led to H2-induced blistering/cracking. The high strength of the threaded region of the adjusting screw increased the failure propensity.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.modes.c9001503
EISBN: 978-1-62708-234-1
... in hardness throughout the case, which influenced the effective depth. Also, the midprofile had been affected more severely than the root radius. And the core hardness, 38 HRC, is typical of a good quenching and tempering process for the tooth root but is about three hardness points low for what would have...
Abstract
A hypoid pinion made from 4820 Ni-Mo alloy steel was the driving member of a power unit operating a rapid transit car. The pinion had been removed from service at the end of the initial test period because it showed undue wear. The mode of failure was severe abrasive wear. The cause of failure was insufficient surface hardness, resulting from improper heat treatment. A service recall for the remaining pinions was immediately initiated.
Book Chapter
Analysis of Bearing Cup Assembly Failure in Drive Shaft Assembly
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Volume: 3
Publisher: ASM International
Published: 01 December 2019
DOI: 10.31399/asm.fach.v03.c9001759
EISBN: 978-1-62708-241-9
... tempered martensite. Core microstructure is hardened and tempered structure with upper transformation product. Figure 6 shows micrograph at X100 magnification. Fig. 6 Microstructure of SAE 1117 carburized and hardened specimen Nital 3% ×100 Hardness Measurements Hardness was measured...
Abstract
A bearing cup in a drive shaft assembly on an automobile was found to have failed. A detailed analysis was conducted using the QC story approach, which begins by proposing several possible failure scenarios then following them to determine the main root cause. A number of alternative solutions were identified and then validated based on chemical analysis, endurance and hardness tests, and microstructural examination. The investigation revealed that carbonitriding can effectively eliminate the type of failure encountered because it prevents through hardening of the bearing cup assembly.
Series: ASM Failure Analysis Case Histories
Volume: 1
Publisher: ASM International
Published: 01 December 1992
DOI: 10.31399/asm.fach.v01.c9001092
EISBN: 978-1-62708-214-3
... in.). The core hardness specified was 33 to 38 HRC. Specimen Selection A transverse slice of circular cross section was cut from the shaft, intersecting undamaged, burnished, and surface-spalled zones. The section was metallographically prepared and used for microscopic study and microhardness testing...
Abstract
An AISI 4320 H transfer gear shaft that was part of a transmission sustained severe surface damage after 12 h of dynamometer testing at various gearing and torque loads. The damage was characterized by generalized wear and spalling. Examination of a cross section of the shaft that intersected undamaged, burnished, and surface-spalled zones revealed no anomalies in the chemistry, microstructure, or hardness that could have caused the damage. The physical evidence suggested that the operable mechanism was contact fatigue caused by misalignment of the shaft in the assembly.
Book Chapter
Failure of Carburized Steel Impeller Drive Gears Due to Pitting and a Wear Pattern
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.modes.c0048253
EISBN: 978-1-62708-234-1
... Abstract Two intermediate impeller drive gears (made of AMS 6263 steel, gas carburized, hardened, and tempered) exhibited evidence of pitting and abnormal wear after production tests in test-stand engines. The gears were examined for hardness, case depth, and microstructure of case and core...
Abstract
Two intermediate impeller drive gears (made of AMS 6263 steel, gas carburized, hardened, and tempered) exhibited evidence of pitting and abnormal wear after production tests in test-stand engines. The gears were examined for hardness, case depth, and microstructure of case and core. It was found that gear 1 had a lower hardness than specified while the case hardness of gear 2 was found to be within limits. Both the pitting and the wear pattern were revealed to be more severe on gear 1 than on gear 2. Surface-contact fatigue (pitting) of gear 1 (cause of lower carbon content of the carburized case and hence lower hardness) was found to be the reason for failure. It was recommended that the depth of the carburized case on impeller drive gears be increased from 0.4 to 0.6 mm to 0.6 to 0.9 mm to improve load-carrying potential and wear resistance. A minimum case-hardness requirement was set at 81 HRA.
Image
Examples of tooling features used to cool deep cores or hard-to-reach areas...
Available to PurchasePublished: 15 May 2022
Book Chapter
Investigation of a Case Hardened Sleeve
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.process.c9001214
EISBN: 978-1-62708-235-8
... had specified a 2 mm case depth and a hardness of at least HRC 55 at a depth of 1.5 mm. An etched cross section of the cracked end showed that the case layer had a depth of 2.3 mm, so that the sleeve was almost through-hardened at the flat ends. While the core material with the full wall thickness had...
Abstract
A case-hardened sleeve made of C 15 (Material No. 1.0401) was flattened at two opposing sides and had cracked open at these places, the crack initiating at a face plane. The wall of the sleeve was 9 mm thick, but the flat ends were machined down to 5.5 mm from the outside. The customer had specified a 2 mm case depth and a hardness of at least HRC 55 at a depth of 1.5 mm. An etched cross section of the cracked end showed that the case layer had a depth of 2.3 mm, so that the sleeve was almost through-hardened at the flat ends. While the core material with the full wall thickness had the quench structure of low-carbon steel, the structure of the flattened area consisted of coarse acicular martensite with a small amount of pearlite (quench troostite) and ferrite. Therefore the sleeve was overheated and probably quenched directly from case. To prevent damage, it would have been necessary to have a lower case depth, carburize less deeply, and prevent overheating that causes brittleness and leads also to increased case depth, or else use a fine-grained steel of lower hardenability.
Image
Gas-nitrided 4140 steel (27–31 HRC) drive-gear assembly in which gear teeth...
Available to PurchasePublished: 15 January 2021
Fig. 13 Gas-nitrided 4140 steel (27–31 HRC) drive-gear assembly in which gear teeth deformed because of faulty design and low core hardness. Details A and B show deformed areas on drive-gear teeth and mating internal splines. Dimensions given in inches
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Image
Gas-nitrided 4140 steel (27–31 HRC) drive-gear assembly in which gear teeth...
Available to PurchasePublished: 01 January 2002
Fig. 13 Gas-nitrided 4140 steel (27–31 HRC) drive-gear assembly in which gear teeth deformed because of faulty design and low core hardness. Details A and B show deformed areas on drive-gear teeth and mating internal splines. Dimensions given in inches
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Image
Gas-nitrided 4140 steel (27–31 HRC) drive-gear assembly in which gear teeth...
Available to Purchase
in Deformation of a Gas-Nitrided Drive-Gear Assembly
> ASM Failure Analysis Case Histories: Construction, Mining, and Agricultural Equipment
Published: 01 June 2019
Fig. 1 Gas-nitrided 4140 steel (27–31 HRC) drive-gear assembly in which gear teeth deformed because of faulty design and low core hardness. Details A and B show deformed areas on drive-gear teeth and mating internal splines. Dimensions given in inches
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Series: ASM Failure Analysis Case Histories
Volume: 1
Publisher: ASM International
Published: 01 December 1992
DOI: 10.31399/asm.fach.v01.c9001129
EISBN: 978-1-62708-214-3
... compared with the core hardness of 20 HRC. The martensite formed when the area adjacent to the weld metal was heated above the transformation temperature and was “self-quenched” via thermal conduction by the mass of the casting. Unwanted martensite is considered detrimental and represents improper welding...
Abstract
The failure of a 45 Mg (50 ton) rail crane bolster was investigated. Spectrochemical analysis indicated that the material was a 0.25C-1.24Mn-0.62Cr-0.24Mo cast steel. SEM examination revealed the presence of fatigue, as well as intergranular and ductile fractures. Microstructural analysis focused on an area where an antisway device had been welded to the structure and revealed the presence of coarse, untempered martensite that had resulted from faulty weld repair techniques. It was suggested that the use of proper welding procedures, including preheating and postheating, would have prevented the failure.
Book Chapter
Broken Milling Machine Arbors Made of 16 Mn Cr 5 E
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.machtools.c9001155
EISBN: 978-1-62708-223-5
...–60. The hardness of core should be HR C 33; HR C 40 was measured. Thus the surface and core hardnesses of both arbors were too high. The case depth should have been 0.6 to 0.7 mm. The hardness curves, which were normal, showed a case depth of 0.7 mm for the limiting hardness value of HV = 550 kgf...
Abstract
Milling machine arbors were inserted with satellite spindles having a maximum speed of 1500 rpm, and broke out between the groove and the flange. The appearance of the fracture surface was the same on both arbors. The pronounced scan lines characterized the fractures as fatigue fractures. The appearance of the fracture in the arbors indicated ductile fatigue fracture which had its origin in the radii between groove and flange. These radii of 0.15 and 0.2 mm were too small for the load on the milling machine. In addition there were grooves at the base of the radii which had an unfavorable effect on the life of the component by acting as notches with their resulting stress concentration. Considering the great hardness of the case, the small radii would have been critical even without grooves. Measures were taken so that the critical radius of the milling machine was increased and the surface roughness measured more precisely.
Book Chapter
Failure Analysis of a Jet Engine Gearbox Drive Gearshaft Ball Bearing
Available to PurchaseSeries: ASM Failure Analysis Case Histories
Volume: 3
Publisher: ASM International
Published: 01 December 2019
DOI: 10.31399/asm.fach.v03.c9001754
EISBN: 978-1-62708-241-9
... the Vicker’s scale (1 kg load). The average results were converted to Rockwell C per ASTM E140 [ 1 ]. The average core hardness of the OR, IR and one rolling element was 65, 64 and 62 HRC, respectively. Surface to core microhardness testing was also performed during the investigation. A comparison...
Abstract
The case study presented in this article details the failure investigation of an M50 alloy steel bearing used in a jet engine gearbox drive assembly. It discusses the investigative steps and analytic tools used to determine the root cause, highlighting the importance of continuous, thorough questioning by the investigating activity. The combined analyses demonstrated that the bearing failed by a single event overload as evidenced by bulk deformation and traces of foreign material on the rolling elements. The anomalous transferred metal found on the rolling elements subsequently led to the discovery of overlooked debris in an engine chip detector, and thus resulted in a review of several maintenance practices.
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