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Case hardening
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Image
Published: 01 January 2002
Fig. 75 Geometric models of carbides formed during case hardening. (a) Massive carbide grain, 4000×. (b) Film carbide, 2000×. (c) Intergranular carbide, 4000×. Source: Ref 30
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Series: 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
... 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...
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
Published: 01 January 2002
Fig. 92 Effect of hardening by plastic deformation. (a) Case-hardened surface. (b) Non-case-hardened surface. Both 243×. Source: Ref 30
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Published: 15 January 2021
Image
Published: 01 January 2002
Fig. 89 Micrograph of grinding cracks in case-hardened 8620 steel showing small cracks (see small arrows) that passed through the hardened case to the core, and the burned layer on the surface (dark band with arrow at the left) that resulted in grinding burns. (Note: Nital and acidic ferric
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Image
Published: 01 December 1992
Fig. 7 Scanning electron micrograph of case-hardened core fracture boundary of second fracture surface. 235×.
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Image
Published: 01 December 1992
Fig. 8 Scanning electron micrograph of case-hardened fracture surface where local cleavage occurred. 2000×.
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Image
Published: 01 December 1993
Fig. 12 Microstructure of the case-hardened gear teeth, consisting of martensite and dispersed carbides along with a few manganese sulfide inclusions. The average hardness is 55 HRC. Nital etchant. (a) 154×(b) 616×
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in Failure Analysis of Gears and Reducers
> Analysis and Prevention of Component and Equipment Failures
Published: 30 August 2021
Fig. 18 Cross sections of through- and case-hardened metallurgies. In practice, depending on the alloy, the through-hardened tooth hardness may vary slightly across the section.
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in Failure Analysis of Gears and Reducers
> Analysis and Prevention of Component and Equipment Failures
Published: 30 August 2021
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in Failure Analysis of Gears and Reducers
> Analysis and Prevention of Component and Equipment Failures
Published: 30 August 2021
Fig. 42 The origin of the fatigue cracks on this case-hardened pinion indicate there was a misalignment, and the red dye shows that it was present when the unit was manufactured.
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in Failures of Structures and Components by Metal-Induced Embrittlement
> Handbook of Case Histories in Failure Analysis
Published: 01 December 2019
Fig. 27 Macroscopic view of failed case-hardened steel planetarygear from a centrifugal gear-box. Note the blackened inside diameter and temper colours at the end surface
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in Brittle Fracture of a Case-Hardened Component Because of Low Impact Resistance and Grinding Burns
> ASM Failure Analysis Case Histories: Processing Errors and Defects
Published: 01 June 2019
Fig. 1 Main-clutch stop arm of 8620 steel on which the case-hardened latch tip failed in service from brittle fracture because of low impact resistance and grinding burns. (a) View of stop arm showing location of fracture in latch tip, and detail showing original and improved designs of latch
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Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.process.c0046028
EISBN: 978-1-62708-235-8
... in service were sent to the metallurgical laboratory for determination of the cause of failure. Fig. 1 Main-clutch stop arm of 8620 steel on which the case-hardened latch tip failed in service from brittle fracture because of low impact resistance and grinding burns. (a) View of stop arm showing...
Abstract
The 8620 steel latch tip, carburized and then induction hardened to a minimum surface hardness of 62 HRC, on the main-clutch stop arm on a business machine fractured during normal operation when the latch tip was subjected to intermittent impact loading. Fractographic examination 9x showed a brittle appearance at the fractures. Micrograph examination of an etched section disclosed several small cracks. Fracture of the parts may have occurred through similar cracks. Also observed was a burned layer approximately 0.075 mm (0.003 in.) deep on the latch surface, and hardness at a depth of 0.025 mm (0.001 in.) in this layer was 52 HRC (a minimum of 55 HRC was specified). Thus, the failure was caused by brittle fracture in the hardness-transition zone as the result of excessive impact loading. The burned layer indicated that the cracks had been caused by improper grinding after hardening. Redesign was recommended to include reinforcing the backing web of the tip, increasing the radius at the relief step to 1.5 x 0.5 mm (0.06 x 0.02 in.), the use of proper grinding techniques, and a requirement that the hardened zone extend a minimum of 1.5 mm (0.06 in.) beyond the step.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.aero.c0047793
EISBN: 978-1-62708-217-4
... Abstract Failure of a case hardened steel shaft incorporated fuel pump in a turbine-powered aircraft resulted in damage to the aircraft. The disassembled pump was found to be dry and free of any contamination. Damage was exhibited on the pressure side of each spline tooth in the impeller...
Abstract
Failure of a case hardened steel shaft incorporated fuel pump in a turbine-powered aircraft resulted in damage to the aircraft. The disassembled pump was found to be dry and free of any contamination. Damage was exhibited on the pressure side of each spline tooth in the impeller and the relatively smooth cavities and undercutting of the flank on this side indicated that the damage was caused by an erosion or abrasion mechanism. A relatively smooth worn area was formed at the center of each tooth due to an abrasive action and an undulating outline with undercutting was observed on the damaged side. Particles of sand, paint, or plastic, fibers from the cartridge, brass, and steel were viewed in the brown residue on the filter cartridge under a low power microscope and later confirmed by chemical analysis. Large amount of iron was identified by application of a magnet. It was concluded that the combined effect of vibration and abrasive wear by sand and metal particles removed from the splines damaged the shaft. Case hardened spline teeth surface was recommended to increase resistance to wear and abrasion.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.matlhand.c9001209
EISBN: 978-1-62708-224-2
... 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...
Abstract
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.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.mech.c0046195
EISBN: 978-1-62708-225-9
... and microstructural investigation supported the conclusion that the bushing fractured in fatigue because of a highly stressed case-hardened surface of unsatisfactory microstructure and subsurface nonmetallic inclusions. Cracks initiated at the highly stressed surface and propagated across the section as a result...
Abstract
A pilot-valve bushing fractured after only a few hours of service. In operation, the bushing was subjected to torsional stresses with possible slight bending stresses. A slight misalignment occurred in the assembly before fracture. The bushing was made of 8617 steel and was case hardened to a depth of 0.13 to 0.4 mm (0.005 to 0.015 in.) by carbonitriding. Specifications required that the part be carbonitrided, cooled, rehardened by quenching from 790 deg C (1450 deg F), then tempered at about 175 deg C (350 deg F). Visual examination, hardness testing, and metallographic and microstructural investigation supported the conclusion that the bushing fractured in fatigue because of a highly stressed case-hardened surface of unsatisfactory microstructure and subsurface nonmetallic inclusions. Cracks initiated at the highly stressed surface and propagated across the section as a result of cyclic loading. The precise cause of the unsatisfactory microstructure of the carbonitrided case could not be determined, but it was apparent that heat-treating specifications had not been closely followed. Recommendations included that inspection procedures be modified to avoid the use of steel containing nonmetallic stringer inclusions and that specifications for carbonitriding, hardening, and tempering be rigorously observed.
Series: ASM Failure Analysis Case Histories
Volume: 1
Publisher: ASM International
Published: 01 December 1992
DOI: 10.31399/asm.fach.v01.c9001094
EISBN: 978-1-62708-214-3
... were singular and intergranular with little branching. Secondary subsurface cracks suggested possible hydrogen embrittlement. The 410 screws had been introduced to replace conventional case-hardened carbon steel screws that conform to SAE specification J78. Carbon steel screws had a proven record...
Abstract
Cadmium-coated type 410 martensitic stainless steel 1 4 -14 self-drilling tapping screws fractured during retorquing tests within a few weeks after installation. The screws were used to assemble structural steel frames for granite panels that formed the outer skin of a high-rise building. Fractographic and metallographic examination showed that the fractures occurred in a brittle manner from intergranular crack propagation. Laboratory and simulated environmental tests showed that an aqueous environment was necessary for the brittle fracture/cracking phenomenon. The cracks were singular and intergranular with little branching. Secondary subsurface cracks suggested possible hydrogen embrittlement. The 410 screws had been introduced to replace conventional case-hardened carbon steel screws that conform to SAE specification J78. Carbon steel screws had a proven record of acceptable performance for the intended application. It was recommended that use of the 410 screws be discontinued in preference to the case-hardened carbon steel screws.
Series: ASM Failure Analysis Case Histories
Volume: 2
Publisher: ASM International
Published: 01 December 1993
DOI: 10.31399/asm.fach.v02.c9001300
EISBN: 978-1-62708-215-0
... Abstract A bull gear from a coal pulverizer at a utility failed by rolling-contact fatigue as the result of continual overloading of the gear and a nonuniform, case-hardened surface of the gear teeth. The gear consisted of an AISI 4140 Cr-Mo steel gear ring that was shrunk fit and pinned onto...
Abstract
A bull gear from a coal pulverizer at a utility failed by rolling-contact fatigue as the result of continual overloading of the gear and a nonuniform, case-hardened surface of the gear teeth. The gear consisted of an AISI 4140 Cr-Mo steel gear ring that was shrunk fit and pinned onto a cast iron hub. The wear and pitting pattern in the addendum area of the gear teeth indicated that either the gear or pinion was out of alignment. Beach marks observed on the fractured surface of the gear indicated that fatigue was the cause of the gear failure. Similar gears should be inspected carefully for signs of cracking or misalignment. Ultrasonic testing is recommended for detection of subsurface cracks, while magnetic particle testing will detect surface cracking. Visual inspection can be used to determine the teeth contact pattern.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.conag.c9001248
EISBN: 978-1-62708-221-1
... Abstract Failure occurred in the teeth of a case-hardening Ni-Cr-Mo alloy steel spur gear in the transmission system of heavy duty tracked vehicles. The defects were in the nature of seizure on the involute profile. Scrutiny of the transmission system showed there might be choking...
Abstract
Failure occurred in the teeth of a case-hardening Ni-Cr-Mo alloy steel spur gear in the transmission system of heavy duty tracked vehicles. The defects were in the nature of seizure on the involute profile. Scrutiny of the transmission system showed there might be choking in the lubricating oil line. Such would cause seizure of the gears and damage. The incidence of such defects stopped after corrective measures were taken.
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