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grain boundary segregation
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in Failure Analysis of a Set of 1CrMoV Studs From a Steam Turbine and Techniques for Its Assessment
> ASM Failure Analysis Case Histories: Power Generating Equipment
Published: 01 June 2019
Series: ASM Failure Analysis Case Histories
Volume: 3
Publisher: ASM International
Published: 01 December 2019
DOI: 10.31399/asm.fach.v03.c9001833
EISBN: 978-1-62708-241-9
... indicated that the boiler failure was caused by grain-boundary segregation of phosphorous, tin, and nitrogen and the in-service formation of carbide films and granules on the grain boundaries. steam chest fracture high-temperature oxidation chromium alloy steel grain boundary defects scanning...
Abstract
The failure of a boiler operating at 540 °C and 9.4 MPa was investigated by examining material samples from the near-failure region and by thermodynamic analysis. A scanning Auger microprobe, SEM, and commercial thermodynamic software codes were used in the investigation. Results indicated that the boiler failure was caused by grain-boundary segregation of phosphorous, tin, and nitrogen and the in-service formation of carbide films and granules on the grain boundaries.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c9001004
EISBN: 978-1-62708-229-7
... of grain boundary phosphorus segregation exhibited a good relationship with ambient temperature Charpy data. The electrochemical polarization kinetic reactivation, EPR, approach, however, proved disappointing in that the overlapping scatter in the minimum current density, Ir, for an embrittled and a non...
Abstract
The results of a failure analysis of a series of Cr-Mo-V steel turbine studs which had experienced a service lifetime of some 50,000 h are described. It was observed that certain studs suffered complete fracture while others showed significant defects located at the first stress bearing thread. Crack extension was the result of marked creep embrittlement and reverse temper embrittlement (RTE). Selected approaches were examined to assess the effects of RTE on the material toughness of selected studs. It was observed that Auger electron microscopy results which indicated the extent of grain boundary phosphorus segregation exhibited a good relationship with ambient temperature Charpy data. The electrochemical polarization kinetic reactivation, EPR, approach, however, proved disappointing in that the overlapping scatter in the minimum current density, Ir, for an embrittled and a non-embrittled material was such that no clear decision of the toughness properties was possible by this approach. The initial results obtained from small punch testing showed good agreement with other reported data and could be related to the FATT. Indeed, this small punch test, combined with a miniature sample sampling method, represents an attractive approach to the toughness assessment of critical power plant components.
Series: ASM Failure Analysis Case Histories
Volume: 3
Publisher: ASM International
Published: 01 December 2019
DOI: 10.31399/asm.fach.v03.c9001775
EISBN: 978-1-62708-241-9
... dispersive x-ray analysis (EDXA) indicated significant segregation of sulfur and chlorine along the grain boundaries. Failure was attributed to hypochlorous-acid (HClO)-induced stress-corrosion cracking (SCC). The HClO was formed by the reaction of HCl with atmospheric O 2 that entered the tube during...
Abstract
A bent Ni-Cu Monel 400 alloy tube, which operated as part of a pipeline in a petrochemical distillery, failed by through-thickness cracking. The pipeline was used to carry a stream of gaseous hydrocarbons containing hydrochloric acid (HCl) into a reaction tower. The tower provided a caustic solution (NaOH) to remove HCl from the stream, before the latter was directed to a burner. Metallographic examination showed that the cracks were intergranular and were frequently branched. Although nominal chemical composition of the component was found within the specified range, energy dispersive x-ray analysis (EDXA) indicated significant segregation of sulfur and chlorine along the grain boundaries. Failure was attributed to hypochlorous-acid (HClO)-induced stress-corrosion cracking (SCC). The HClO was formed by the reaction of HCl with atmospheric O 2 that entered the tube during shutdowns and startups. Residual stresses, originating from in situ bend forming of the tube during assembly of the line, provided a driving force for crack growth, and the segregation of sulfur on grain boundaries made the material more susceptible to cracking.
Image
Published: 01 December 1993
Fig. 8 Micrograph of section of hardened case from rail flange. Microstructure is tempered martensite, as expected from specified heat treatment. Nital etch. Note that no anomalies, such as grain boundary segregation, are extant. 268×
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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.c9001062
EISBN: 978-1-62708-214-3
... to a decrease in grain-boundary cohesion resulting from sulfur segregation. Addition of molybdenum proved effective in preventing cracking. The molybdenum promoted MnS precipitation in the grain and preferentially segregated to the interfaces. Brittle fracture Casting defects Castings Molybdenum...
Abstract
The causes of internal cracking that occurred in 9% Ni steel castings during manufacture were investigated using a series of eight laboratory castings containing varying amounts of molybdenum. The effect of mold thickness was also investigated. The laboratory castings were subjected to three-point bend testing, and fracture surfaces were examined using SEM fractography, metallography, and depth analysis (SIMS) of the fracture surface. The cracks were found to originate at austenitic grain boundaries that coincided with primary dendrite interfaces. The cracking was attributed to a decrease in grain-boundary cohesion resulting from sulfur segregation. Addition of molybdenum proved effective in preventing cracking. The molybdenum promoted MnS precipitation in the grain and preferentially segregated to the interfaces.
Series: ASM Handbook Archive
Volume: 11
Publisher: ASM International
Published: 01 January 2002
DOI: 10.31399/asm.hb.v11.a0003540
EISBN: 978-1-62708-180-1
... alterations. Grain boundaries are thus the preferential region for congregation and segregation of impurities. Weakening or embrittlement can also occur by preferential phase precipitation or absorption of environmental species in the grain boundaries. In addition, the grain-boundary regions are also weakened...
Abstract
This article briefly reviews the various metallurgical or environmental factors that cause a weakening of the grain boundaries and, in turn, influence the occurrence of intergranular (IG) fractures. It discusses the mechanisms of IG fractures, including the dimpled IG fracture, the IG brittle fracture, and the IG fatigue fracture. The article describes some typical embrittlement mechanisms that cause the IG fracture of steels.
Series: ASM Handbook
Volume: 11
Publisher: ASM International
Published: 15 January 2021
DOI: 10.31399/asm.hb.v11.a0006777
EISBN: 978-1-62708-295-2
... cracking steam generator tubes INTERGRANULAR FRACTURE is decohesion that occurs along a grain boundary. Intergranular fracture is often associated with the presence of an embrittlement mechanism or the presence of precipitates and segregates at the grain boundary, which make the grain boundary...
Abstract
This article briefly reviews the factors that influence the occurrence of intergranular (IG) fractures. Because the appearance of IG fractures is often very similar, the principal focus is placed on the various metallurgical or environmental factors that cause grain boundaries to become the preferred path of crack growth. The article describes in more detail some typical mechanisms that cause IG fracture. It discusses the causes and effects of IG brittle cracking, dimpled IG fracture, IG fatigue, hydrogen embrittlement, and IG stress-corrosion cracking. The article presents a case history on IG fracture of steam generator tubes, where a lowering of the operating temperature was proposed to reduce failures.
Series: ASM Failure Analysis Case Histories
Volume: 1
Publisher: ASM International
Published: 01 December 1992
DOI: 10.31399/asm.fach.v01.c9001123
EISBN: 978-1-62708-214-3
... was different from that specified. The presence of excess aluminum and lead impurities that had segregated to the grain boundaries, coupled with an inadequate amount of magnesium, resulted in intergranular corrosion and subsequent intergranular failure. Corrosion was accelerated by storage in a humid...
Abstract
Extensive cracking was found in a batch of die-cast ZAMAK 3 solenoid valve seats during commissioning of the system in which they were installed. Scanning electron microscopic and chemical analyses conducted on one of the failed valve seats showed that the composition of the alloy was different from that specified. The presence of excess aluminum and lead impurities that had segregated to the grain boundaries, coupled with an inadequate amount of magnesium, resulted in intergranular corrosion and subsequent intergranular failure. Corrosion was accelerated by storage in a humid environment in a coastal area. It was recommended that proper chemical analysis of the zinc-aluminum alloy be carried out as a quality control procedure.
Series: ASM Failure Analysis Case Histories
Volume: 3
Publisher: ASM International
Published: 01 December 2019
DOI: 10.31399/asm.fach.v03.c9001838
EISBN: 978-1-62708-241-9
.... pipe hot cracking grain boundary segregation stainless steel tear ridges melt bridging microfractography induction heating frequency X6CrNiMoTi17-12-2 (titanium-stabilized austenitic stainless steel) UNS S31635 Introduction Large austenitic stainless steel piping used for manifolds...
Abstract
Stainless steel pipe (273-mm OD x 8-mm wall thickness) used in the fabrication of large manifolds developed crack-like decohesions during a routine inductive bending procedure. The imperfections, which were found near the outside diameter, were around 3 mm in length oriented in the circumferential direction and penetrated nearly 2 mm into the pipe wall. The pipes were made of titanium-stabilized austenitic stainless steel X6CrNiMoTi17-12-2. Six hypotheses were considered during the investigation, which ultimately concluded that the failure was caused by liquation cracking due to overheating.
Series: ASM Failure Analysis Case Histories
Volume: 2
Publisher: ASM International
Published: 01 December 1993
DOI: 10.31399/asm.fach.v02.c9001308
EISBN: 978-1-62708-215-0
... with the specified material requirements. No material anomalies, such as segregation at the grain boundaries, were observed. Fig. 8 Micrograph of section of hardened case from rail flange. Microstructure is tempered martensite, as expected from specified heat treatment. Nital etch. Note that no anomalies...
Abstract
Persistent cracking in a forged 1080 steel turntable rail in a wind tunnel test section was investigated. All cracks were oriented transverse to the axis of the rail, and some had propagated through the flange into the web. Through-flange cracks had been repair welded. A section of the flange containing one through-flange crack was examined using various methods. Results indicated that the cracks had initiated from intergranular quench cracks caused by the use of water as the quenching medium. Brittle propagation of the cracks was promoted by high residual stresses acting in conjunction with applied loads. Repair welding was discontinued to prevent the introduction of additional residual stress., Finite-element analysis was used to show that the rail could tolerate existing cracks. Periodic inspection to monitor the degree of cracking was recommended.
Series: ASM Failure Analysis Case Histories
Volume: 3
Publisher: ASM International
Published: 01 December 2019
DOI: 10.31399/asm.fach.v03.c9001837
EISBN: 978-1-62708-241-9
...–CrMoV steel is transgranular, but in this case, the fracture was found to be brittle intergranular which indicates that the grain boundaries were weakened due to some reason [ 5 ]. Main source of grain boundary weakening in low alloy steels is segregation of P, S, As, Sb, Sn, etc., to the prior...
Abstract
This case study describes the failure analysis of a steel nozzle in which cracking was observed after a circumferential welding process. The nozzle assembly was made from low-carbon CrMoV alloy steel that was subsequently single-pass butt welded using gas tungsten arc welding. Although no cracks were found when the welds were visually inspected, X-ray radiography showed small discontinuous surface cracks adjacent to the weld bead in the heat affected zone. Further investigation, including optical microscopy, microhardness testing, and residual stress measurements, revealed that the cracks were caused primarily by the presence of coarse untempered martensite in the heat affected zone due to localized heating. The localized heating was caused by high welding heat input or low welding speed and resulted in high transformation stresses. These transformation stresses, working in combination with thermal stresses and constraint conditions, resulted in intergranular brittle fracture.
Series: ASM Failure Analysis Case Histories
Volume: 2
Publisher: ASM International
Published: 01 December 1993
DOI: 10.31399/asm.fach.v02.c9001335
EISBN: 978-1-62708-215-0
.... Discussion Many polycrystalline metals can become brittle and fail along grain boundaries when a low stress is applied. The brittleness has been attributed to intergranular weakness caused by the precipitation or segregation of impurities to grain boundaries. For example, Auger electron spectroscopy...
Abstract
The causes of cracking of an as-drawn 90-10 cupronickel tube during mechanical working were investigated to determine the source of embrittlement. Embrittlement was sporadic, but when present was typically noted after the first process anneal. Microstructural and chemical analyses were performed on an embrittled section and on a section from a different lot that did not crack during forming. The failed section showed an intergranular fracture path. Examination of the fracture surfaces revealed the presence of tellurium at the grain boundaries. The source of the tellurium was thought to be contamination occurring in the casting process that became concentrated in the recycled skimmings. It was recommended that future material specifications for skimmings and for externally obtained scrap copper include a trace analysis for tellurium.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.process.c9001253
EISBN: 978-1-62708-235-8
... spots in the fibrous fracture ( Fig. 2 ). Microscopic observation showed that the separations were short cracks that ran along the primary grain boundaries marked by ferrite and sulfide segregations ( Fig. 3 ). The formation of Such cracks is favored by segregations of various kinds 1 , 2 , 3...
Abstract
Octagonal cast ingots weighing 6.5 tons and made of unalloyed heat treated steel CK 45 according to DIN 17200, and crankshafts forged from these ingots showed internal separations during ultrasonic testing. To determine the cause of defect, an ingot slice and a crank arm were examined metallographically. Investigation showed this was a case where flaky forgings were made from cast ingots with primary grain boundary cracks. This parallelity supports the often expressed opinion that both occurrences have the same origin, i.e. that hydrogen precipitation was the driving force in the formation of primary grain boundary cracks in cast ingots.
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in Influence of Microstructure on the Premature Failure of a Second-Intermediate Sendzimir Mill Drive Roll
> ASM Failure Analysis Case Histories: Steelmaking and Thermal Processing Equipment
Published: 01 June 2019
Fig. 5 Villela-etched roll microstructure showing inhomogeneous carbide distribution in tempered martensite. (a) Carbide segregation at grain boundaries. (b) Massive carbide segregate with skeleton-like appearance. 500×
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Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.med.c0048399
EISBN: 978-1-62708-226-6
... and had segregations in the microstructure and gas holes and precipitates in the grain boundaries ( Fig. 1c ). The nut was not specifically loaded and did not fail. The other broken pin was made from a cold-worked cobalt-chromium alloy. The grain boundaries contained few precipitates, but lines...
Abstract
Two of four adjustable Moore pins, which had been used to stabilize a proximal femur fracture, were found to be broken and deformed at their threads. The pins were made from a cobalt-chromium alloy and were not in the same condition. Brittle precipitates in the grains and grain boundaries were seen in one of the pins and hence the fracture was revealed to have occurred along the grain boundaries. The other pin made from cold-worked cobalt-chromium alloy was observed to have randomly lines of primary inclusions. Intermingled dimples and fatigue striations were exhibited on the fracture surface of this pin. Thus, the effect of different conditions of cobalt-chromium alloys on failure behavior was demonstrated as a result of this study.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.steel.c9001535
EISBN: 978-1-62708-232-7
...×. It is clearly evident from Fig. 5 that the carbide segregations have occurred preferentially along grain boundary contours. The massive carbide network depicted in Fig. 5 reveals a skeleton-like morphology, presumably indicative of its eutectic origin, i.e., genesis at the ingot solidification stage...
Abstract
Although a precise understanding of roll failure genesis is complex, the microstructure of a broken roll can often unravel intrinsic deficiencies in material quality responsible for its failure. This is especially relevant in circumstances when, even under a similar mill-operating environment, the failure involves a particular roll or a specific batch of rolls. This paper provides a microstructural insight into the cause of premature breakage of a second-intermediate Sendzimir mill drive roll used at a stainless steel sheet rolling plant under the Steel Authority of India Limited. Microstructural issues influencing roll quality, such as characteristics of carbides, tempered martensite, retained austenite, etc., have been extensively studied through optical and scanning electron microscopy, electron-probe microanalysis, image analysis, and x-ray diffractometry. These are discussed to elucidate specific microstructural inadequacies that accentuated the failure. The study reveals that even through retained austenite content is low (6.29 vol%) and martensite is non-acicular, the roll breakage is a consequence of intergranular cracking caused by improper carbide morphology and distribution.
Book Chapter
Series: ASM Handbook Archive
Volume: 11
Publisher: ASM International
Published: 01 January 2002
DOI: 10.31399/asm.hb.v11.a0003507
EISBN: 978-1-62708-180-1
... postforming processes Process Possible defects Electroplating Hydrogen embrittlement, galvanic corrosion Heat treatment Excessive grain growth, burning of grain boundaries, brittle structure, carburization, decarburization, quench cracks Electrolytic cleaning Pitting Surface hardening...
Abstract
This article describes the general root causes of failure associated with wrought metals and metalworking. This includes a brief review of the discontinuities or imperfections that may be the common sources of failure-inducing defects in bulk working of wrought products. The article discusses the types of imperfections that can be traced to the original ingot product. These include chemical segregation; ingot pipe, porosity, and centerline shrinkage; high hydrogen content; nonmetallic inclusions; unmelted electrodes and shelf; and cracks, laminations, seams, pits, blisters, and scabs. The article provides a discussion on the imperfections found in steel forgings. The problems encountered in sheet metal forming are also discussed. The article concludes with information on the causes of failure in cold formed parts.
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in Intergranular Corrosion Failure in Zn-Al Alloy Solenoid Valve Seats
> Handbook of Case Histories in Failure Analysis
Published: 01 December 1992
Fig. 3 Scanning electron micrograph showing lead segregation (indicated by arrows) at grain boundaries.
More
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.steel.c9001255
EISBN: 978-1-62708-232-7
... responsible for the scaly fracture and the formation of primary grain boundary cracks. Fig. 7 Micro-shrinkage cavity with carbon segregation (ledeburite). Etched in picral. 50 × Fig. 8 Primary grain boundary with precipitates of ledeburite and secondary cementite. Etched in picral. 200...
Abstract
Several back up rolls of 1400 mm barrel diam from a broad strip mill broke after a relatively short operating time as a result of bending stresses when the rolls were dismantled. The fracture occurred in the conical region of the neck at about 600 mm diam. The rolls were shaped steel castings with 0.8 to 1.0% C, 1% Mn, 1% Cr, 0.5% Mo and 0.4% Ni and were heat treated to a tensile strength of 950 N/sq mm. Because the bending stress on mounting was only 42 N/sq mm in the fracture cross section, it was evident at the outset that material defects had promoted the fracture. In the case of this roll and the other broken rolls, the cracking and fracture were promoted by various casting defects. Investigation of the rolls showed that both the breaking off of the neck and the disintegration of the barrel edges was caused by material defects, more exactly casting defects. The fractures on the other rolls examined were so badly rusted or contaminated that they were incapable of yielding any information.
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