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Grain growth
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in Problems Associated with Heat Treated Parts
> Analysis and Prevention of Component and Equipment Failures
Published: 30 August 2021
Fig. 9 Austenite grain growth in a fine-grained 0.5% C hypoeutectoid steel (aluminum deoxidized). 0.43C-0.23Si-0.75Mn (wt%). (a) Austenitized for 1 h at 850 °C, cooled at 300 °C/h. Austenite grain size: ASTM No. 7, 180 HV. Picral. 100x. (b) Austenitized for 1 h at 900°C, cooled at 300 °C/h
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in Problems Associated with Heat Treated Parts
> Analysis and Prevention of Component and Equipment Failures
Published: 30 August 2021
Fig. 11 Overheated surface on SAE 1045 steel showing excessive grain growth and cracking. Hardness at a depth of 250 μm was HRC 59. Source Ref 7
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Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.steel.c9001598
EISBN: 978-1-62708-232-7
... Abstract The metallurgical condition of a cylindrical induction melter (CIM) vessel was evaluated after approximately 375 h of operation over a two-year span at temperatures between 1400 to 1500 deg C. Wall thinning and significant grain growth was observed in the lower portion of the conical...
Abstract
The metallurgical condition of a cylindrical induction melter (CIM) vessel was evaluated after approximately 375 h of operation over a two-year span at temperatures between 1400 to 1500 deg C. Wall thinning and significant grain growth was observed in the lower portion of the conical section and the drain tube. No through-wall penetrations were found in the cylindrical and conical sections of the CIM vessel and only one leak site was identified in the drain tube. Failure of the drain tube was associated with localized overheating and creep. The observed degradation resulted from cumulative service at elevated temperature. A recommendation was made to implement a support for the conical section of the CIM and to increase the wall thickness of the drain tube. Thus, the possibility of drain tube misalignment in the induction coils and localized over heating will be minimized. In addition, the use of grain stabilized Pt/Rh alloy should be evaluated as a method to prevent grain growth.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.process.c9001443
EISBN: 978-1-62708-235-8
... 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. Butt welds Conductors (devices) Grain growth Weld defects Copper Joining-related...
Abstract
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.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.aero.c9001717
EISBN: 978-1-62708-217-4
... an alternative material with a lower notch sensitivity. In addition, the temperature at which this alloy is treated must be monitored to prevent coarse grain growth. As a result of this investigation and in an effort to eliminate future failures, ARL assisted in developing a cadmium brush plating procedure...
Abstract
The US Army Research Laboratory performed a failure investigation on a broken main landing gear mount from an AH-64 Apache attack helicopter. A component had failed in flight, and initially prevented the helicopter from safely landing. In order to avoid a catastrophe, the pilot had to perform a low hover maneuver to the maintenance facility, where ground crews assembled concrete blocks at the appropriate height to allow the aircraft to safely touch down. The failed part was fabricated from maraging 300 grade steel (2,068 MPa [300 ksi] ultimate tensile strength), and was subjected to visual inspection/light optical microscopy, metallography, electron microscopy, energy dispersive spectroscopy, chemical analysis, and mechanical testing. It was observed that the vacuum cadmium coating adjacent to the fracture plane had worn off and corroded in service, thus allowing pitting corrosion to occur. The failure was hydrogen-assisted and was attributed to stress corrosion cracking (SCC) and/or corrosion fatigue (CF). Contributing to the failure was the fact that the material grain size was approximately double the required size, most likely caused from higher than nominal temperatures during thermal treatment. These large grains offered less resistance to fatigue and SCC. In addition, evidence of titanium-carbo-nitrides was detected at the grain boundaries of this material that was prohibited according to the governing specification. This phase is formed at higher thermal treatment temperatures (consistent with the large grains) and tends to embrittle the alloy. It is possible that this phase may have contributed to the intergranular attack. Recommendations were offered with respect to the use of a dry film lubricant over the cadmium coated region, and the possibility of choosing an alternative material with a lower notch sensitivity. In addition, the temperature at which this alloy is treated must be monitored to prevent coarse grain growth. As a result of this investigation and in an effort to eliminate future failures, ARL assisted in developing a cadmium brush plating procedure, and qualified two Army maintenance facilities for field repair of these components.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.mech.c9001483
EISBN: 978-1-62708-225-9
... in between the bolt and the hole in the strip. The bolt end adjacent to the fracture had been subjected to intense local heating. The extent of the grain-growth indicating that the temperature had been in the region of 1200 deg C (2192 deg F). When the temperature reached the melting-point of copper, 1083...
Abstract
A steel bolt had been used to join the copper connecting strips between the poles of a 10-pole, series-connected, rotating field rotor of a synchronous motor. The exciting current was 155 amps. Failure of the bolt resulted in severe damage to the stator windings by the loosened ends of the strips. The bolt had fractured near the head, a location which probably coincided with the junction of the strips. A portion of the fracture surface was covered with copper that had been deposited in the molten state, while some was also present along the shank of the bolt, having apparently run in between the bolt and the hole in the strip. The bolt end adjacent to the fracture had been subjected to intense local heating. The extent of the grain-growth indicating that the temperature had been in the region of 1200 deg C (2192 deg F). When the temperature reached the melting-point of copper, 1083 deg C (1981 deg F), molten metal came into contact with the bolt, into which it penetrated along the grain boundaries, culminating in rupture.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.process.c0047080
EISBN: 978-1-62708-235-8
... the conclusions that bending of the connector tubes in the annealed condition induced critical strain near the neutral axis of the tube, which resulted in excessive growth of individual grains during the subsequent solution treatment. Recommendations included bending the connector tubes in the T4 temper as early...
Abstract
Several of the aluminum alloy 6061-T6 drawn seamless tubes (ASTM B 234, 2.5 cm (1.0 in.) OD with wall thickness of 1.7 mm (0.065 in.)) connecting an array of headers to a system of water-cooling pipes failed. The tubes were supplied in the O temper. They were bent to the desired curvature, preheated, then solution treated, water quenched, and then aged for 8 to 10 h. Analysis (visual inspection, slow-bend testing, 65x macrographic analysis, macroetching, spectrographic analysis, hardness tests, microhardness tests, tension tests, and microscopic examination) supported the conclusions that bending of the connector tubes in the annealed condition induced critical strain near the neutral axis of the tube, which resulted in excessive growth of individual grains during the subsequent solution treatment. Recommendations included bending the connector tubes in the T4 temper as early as possible after being quenched from the solution temperature. The tubes should be stored in dry ice after the quench until bending can be done. The tubes should be aged immediately after being formed. Flattening and slow-bend tests should be specified to ensure that the connector tubes had satisfactory ductility.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.process.c0091048
EISBN: 978-1-62708-235-8
...) Metallographic profile of the weld near the cracking, showing melt-through, grain growth, and precipitation. 8.9×. (d) Grain-boundary precipitates in the weld zone. 119×. (c) and (d) were etched with Vilella's reagent followed by electrolytic etching in 10% oxalic acid. Investigation Examination...
Abstract
A welded ferritic stainless steel heat exchanger cracked prior to service. The welding filler metal was identified as an austenitic stainless steel and the joining method as gas tungsten arc welding. Investigation (visual inspection, SEM images, 5.9x images, and 8.9x/119x images etched with Vilella's reagent followed by electrolytic etching in 10% oxalic acid) supported the conclusion that the heat exchanger cracked due to weld cold cracking or postwelding brittle overload that occurred via flexure during fabrication. The brittle nature of the weld was likely due to a combination of high residual stresses, a mixed microstructure, inclusions, and gross grain coarsening. These synergistic factors resulted from extreme heat input during fillet welding. Recommendations included altering the welding variables such as current, voltage, and travel speed to substantially reduce the heat input.
Series: ASM Handbook
Volume: 11A
Publisher: ASM International
Published: 30 August 2021
DOI: 10.31399/asm.hb.v11A.a0006816
EISBN: 978-1-62708-329-4
... growth or overall grain growth Increases hardenability May cause variations in local hardenability May reverse normalization and increase local segregation or banding Preheat Behaves as stress relief Relieves prior stresses Machining Grinding Cold working/forming...
Abstract
This article introduces some of the general sources of heat treating problems with particular emphasis on problems caused by the actual heat treating process and the significant thermal and transformation stresses within a heat treated part. It addresses the design and material factors that cause a part to fail during heat treatment. The article discusses the problems associated with heating and furnaces, quenching media, quenching stresses, hardenability, tempering, carburizing, carbonitriding, and nitriding as well as potential stainless steel problems and problems associated with nonferrous heat treatments. The processes involved in cold working of certain ferrous and nonferrous alloys are also covered.
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in Weld Cracking of a Stainless Steel Heat Exchanger
> ASM Failure Analysis Case Histories: Processing Errors and Defects
Published: 01 June 2019
Fig. 1 Cracking of a welded ferritic stainless steel heat exchanger. (a) Diagram showing the heat-exchanger weld joint design. (b) The transverse crack that occurred through the weld. 5.9×. (c) Metallographic profile of the weld near the cracking, showing melt-through, grain growth
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Published: 01 January 2002
growth, and precipitation. 8.9×. (d) Grain-boundary precipitates in the weld zone. 119×. (c) and (d) were etched with Vilella's reagent followed by electrolytic etching in 10% oxalic acid.
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Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.steel.c0046998
EISBN: 978-1-62708-232-7
... in Fig. 1 (labeled 0.012 to 0.017 in.), showed no grain coarsening. The metal near the outer surface (which was exposed to soot and to the endothermic atmosphere), before being overheated, had apparently undergone sufficient grain-boundary carburization to prevent subsequent grain growth in the outer...
Abstract
One of 14 vertical radiant tubes (RA 333 alloy) in a heat-treating furnace failed when a hole about 5 x 12.5 cm (2 x 5 in.) corroded completely through the tube wall. The tube measured 183 cm (72 in.) in length and 8.9 cm (3 in.) in OD and had a wall thickness of about 3 mm (0.120 in.). Failure occurred where the tube passed through the refractory hearth (floor) of the furnace. Although the furnace atmosphere was neutral with respect to the work, it had a carburizing potential relative to the radiant tubes. Analysis (visual inspection, 250x spectroscopic examination of specimens etched with mixed acids, metallographic examination, and chemical analysis) supported the conclusions that the premature failure of the tube by perforation at the hearth level resulted from (1) corrosion caused by sulfur contamination from the refractory cement in contact with the tube and (2) severe local overheating at the same location. Recommendations included replacing all tubes using a low sulfur refractory cement in installation and controlling burner positioning and regulation more closely to avoid excessive heat input at the hearth level.
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in Metallurgical Evaluation of a Five Inch Cylindrical Induction Melter
> ASM Failure Analysis Case Histories: Steelmaking and Thermal Processing Equipment
Published: 01 June 2019
Fig. 4 Photomicrograph of the sample sectioned from the CIM drain tube showing significant grain growth
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Image
Published: 01 January 2002
Fig. 33 Examples of the microstructure of AISI M2 high-speed steel. (a) Desired quenched-and-tempered condition: 1200 °C (2200 °F) for 5 min in salt, oil quench, double temper at 595 °C (1100 °F). Etched with 3% nital. 500×. (b) Grain growth caused by reaustenitizing without annealing: 1220 °C
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Image
Published: 15 January 2021
near the cracking, showing melt-through, grain growth, and precipitation. Original magnification: 8.9×. (d) Grain-boundary precipitates in the weld zone. Original magnification: 119×. (c) and (d) were etched with Vilella’s reagent followed by electrolytic etching in 10% oxalic acid.
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Image
Published: 30 August 2021
Fig. 33 Examples of the microstructure of AISI M2 high-speed steel. (a) Desired quenched-and-tempered condition: 1200 °C (2200 °F) for 5 min in salt, oil quench, double temper at 595 °C (1100 °F). Etched with 3% nital. Original magnification: 500×. (b) Grain growth caused by reaustenitizing
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in Metallurgical Evaluation of a Five Inch Cylindrical Induction Melter
> ASM Failure Analysis Case Histories: Steelmaking and Thermal Processing Equipment
Published: 01 June 2019
Fig. 7 Composite photomicrograph showing microstructure of the conical section from the CIM. Note significant grain growth and the lack of voids throughout the cross section. Molten glass attack is visible on ID surface, but no wall thinning occurred.
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Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.bldgs.c9001135
EISBN: 978-1-62708-219-8
... higher than specified by the ASTM standards. The fatigue crack growth rate through this area was much faster than expected. All of these property changes resulted from increased carbon levels, higher yield strength, and larger than normal grain size. Bridges (structural) Grain size Segregation...
Abstract
In 1979, during a routine bridge inspection, a fatigue crack was discovered in the top flange plate of one tie girder in a tied arch bridge crossing the Mississippi River. Metallographic analysis indicated a banding or segregation problem in the middle of the plate, where the carbon content was twice what it should have been. Based on this and results of ultrasonic testing, which revealed that the banding occurred in 24-ft lengths, it was decided to close the bridge and replace the defective steel. The steel used in the construction of this bridge was specified as ASTM A441, commonly used in structural applications. Testing showed an increase in hardness and weight percent carbon and manganese in the banded region. Further testing revealed that the area containing the segregation and coarse grain structure had a lower than expected toughness and a transition temperature 90 deg F higher than specified by the ASTM standards. The fatigue crack growth rate through this area was much faster than expected. All of these property changes resulted from increased carbon levels, higher yield strength, and larger than normal grain size.
Series: ASM Failure Analysis Case Histories
Volume: 2
Publisher: ASM International
Published: 01 December 1993
DOI: 10.31399/asm.fach.v02.c9001270
EISBN: 978-1-62708-215-0
... was not present in the forged stock and was not typical of the forging process. The suspected cause was uneven flow of material during the forging process, which resulted in stagnant areas where grain growth occurred. Microscopic examination of the parts revealed large grain areas near the parting line. The rest...
Abstract
An investigation was conducted to determine the factors responsible for the occasional formation of cracks on the parting lines of medium plain carbon and low-alloy medium-carbon steel forgings. The cracks were present on as-forged parts and grew during heat treatment. Examination revealed that areas near the parting line exhibited a large grain structure not present in the forged stock. High-temperature scale was also found in the cracks. It was concluded that the cracks were caused by material being folded over the parting line. The folding occurred because of a mismatch in the forgings and from material flow during trimming and/or material flow during forging.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.machtools.c9001574
EISBN: 978-1-62708-223-5
... of the used punch. Presence of a yellow porous layer was clearly evident between the nitrided layer and the coating, in case of the used punch. Cracks were observed to propagate from the outer surface into the bulk (see Figure 1a ). Oxidation was evident along the cracks. Also, extensive grain growth...
Abstract
A CrN coated restrike punch was made of WR-95 (similar to H-11), which was fluidized bed nitrided. The coated punch was used on hot Inconel at about 1040 deg C (1900 deg F). However, a water-soluble graphite coolant was used to maintain the punch temperature at 230 deg C (450 deg F). Visual and binocular inspection at 64+ revealed presence of cracks and complete washout of coating in the working area of the failed punch. Comparison of metallographic cross sections of used and unused punches revealed a significant microstructural transformation in case of the used punch. Presence of a yellow porous layer was clearly evident between the nitrided layer and the coating, in case of the used punch. Cracks were observed to propagate from the outer surface into the bulk. Oxidation was evident along the cracks. The microstructural transformation observed in the case of the used punch was a clear indication of high temperature exposure (due to insufficient cooling) during application. The most probable cause of failure was thermal fatigue.
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