Search Results for iron-copper graphite

Door-closer cylinder castings manufactured of class 30 gray iron were breaking during machining. The manufacturing source reported that a random sampling of castings from this lot had hardnesses from 180 to 210 HRB. Based on the color of the components, heat treatment of these castings was suspected. Metallurgical examination on two representative castings supported the conclusions that the cracks in these gray iron door closers that were present either before or during the heat treatment were attributed to a substandard microstructure of the wrong type of graphite combined with excessive ferrite. This anomalous structure is caused by shortcomings in the foundry practice of chemical composition, solidification, and inoculation control. Judging from the microstructure, the strength of the material was lower than desired for class 30 gray iron, and the suspected heat treatment further reduced the strength. Recommendations included that the chemistry and inoculation should be controlled to produce type A graphite structure. The chemistry control should aim for a carbon equivalent close to 4.3% to achieve adequate fluidity for thin sections and to alleviate gas defects.

The information provided in this article is intended for those individuals who want to determine why a casting component failed to perform its intended purpose. It is also intended to provide insights for potential casting applications so that the likelihood of failure to perform the intended function is decreased. The article addresses factors that may cause failures in castings for each metal type, starting with gray iron and progressing to ductile iron, steel, aluminum, and copper-base alloys. It describes the general root causes of failure attributed to the casting material, production method, and/or design. The article also addresses conditions related to the casting process but not specific to any metal group, including misruns, pour shorts, broken cores, and foundry expertise. The discussion in each casting metal group includes factors concerning defects that can occur specific to the metal group and progress from melting to solidification, casting processing, and finally how the removal of the mold material can affect performance.

Cast iron bearing caps in tractor engines fractured repeatedly after only short operating periods. The fracture originated in a cast-in groove and ran approximately radially to the shaft axis. The smallest cross section was at the point of fracture. The core structure of the caps consisted of graphite in pearlitic-ferritic matrix. Casting stresses did not play a decisive role because of the simple shape of the pieces that were without substantial cross sectional variations. Two factors exerted an unfavorable effect in addition to comparatively low strength. First, the operating stress was raised locally by the sharp-edged groove, and second, the fracture resistance of the cast iron was lowered at this critical point by the existence of a ferritic bright border. To avoid such damage in the future it was recommended to observe one or more of the following precautions: 1) Eliminate the grooves; 2) Remove the ferritic bright border; 3) Avoid undercooling in the mold and therefore the formation of granular graphite; 4) Inoculate with finely powdered ferrosilicon into the melt for the same purpose; and, 5) Anneal at lower temperature or eliminate subsequent treatment in consideration of the uncomplicated shape of the castings.

This article addresses the forms of corrosion that contribute directly to the failure of metal parts or that render them susceptible to failure by some other mechanism. It describes the mechanisms of corrosive attack for specific forms of corrosion such as galvanic corrosion, uniform corrosion, pitting and crevice corrosion, intergranular corrosion, and velocity-affected corrosion. The article contains a table that lists combinations of alloys and environments subjected to selective leaching and the elements removed by leaching.

Three sprinkler system dry pipe valve castings (class 30 gray iron), two that had failed in service and one that had been rejected during machining because of porosity, were submitted for examination. The two failures consisted of cracks in a seating face. All three were from the same heat. Visual examination showed that the casting had cracked through a thin area in the casting sidewall. Evidence of a sharply machined corner at the fracture site was also discovered. Tensile testing and metallographic analysis revealed no metallurgical cause for the failure. It was recommended that the manufacturer work with the foundry to evaluate the criticality of core placement and to eliminate the undesired thin section.

Corrosion is the electrochemical reaction of a material and its environment. This article addresses those forms of corrosion that contribute directly to the failure of metal parts or that render them susceptible to failure by some other mechanism. Various forms of corrosion covered are galvanic corrosion, uniform corrosion, pitting, crevice corrosion, intergranular corrosion, selective leaching, and velocity-affected corrosion. In particular, mechanisms of corrosive attack for specific forms of corrosion, as well as evaluation and factors contributing to these forms, are described. These reviews of corrosion forms and mechanisms are intended to assist the reader in developing an understanding of the underlying principles of corrosion; acquiring such an understanding is the first step in recognizing and analyzing corrosion-related failures and in formulating preventive measures.

This paper describes an investigation on the failure of a large leaded bronze bearing that supports a nine-ton roller of a plastic calendering machine. At the end of the normal service life of a good bearing, which lasted for seven years, a new bearing was installed. However the new one failed catastrophically within a few days, generating a huge amount of metallic wear debris and causing pitting on the surface of the cast iron roller. Following the failure, samples were collected from both good and failed bearings. The samples were analyzed chemically and their microstructures examined. Both samples were subjected to accelerated wear tests in a laboratory type pin-on-disk apparatus. During the tests, the bearing materials acted as pins, which were pressed against a rotating cast iron disk. The wear behaviors of both bearing materials were studied using weight loss measurement. The worn surfaces of samples and the wear debris were examined by light optical microscope, SEM, and energy-dispersive x-ray microanalyzer. It was found that the laboratory pin-on-disk wear data correlated well with the plant experience. It is suggested that the higher lead content ~18%) of the good bearing compared with 7% lead of the failed bearing helped to establish a protective transfer layer on the worn surface. This transfer layer reduced metal-to-metal contact between the bearing and the roller and resulted in a lower wear rate. The lower lead content of the failed bearing does not allow the establishment of a well-protected transfer layer and leads to rapid wear.

This article focuses on the general root causes of failure attributed to the casting process, casting material, and design with examples. The casting processes discussed include gravity die casting, pressure die casting, semisolid casting, squeeze casting, and centrifugal casting. Cast iron, gray cast iron, malleable irons, ductile iron, low-alloy steel castings, austenitic steels, corrosion-resistant castings, and cast aluminum alloys are the materials discussed. The article describes the general types of discontinuities or imperfections for traditional casting with sand molds. It presents the international classification of common casting defects in a tabular form.

This article aims to identify and illustrate the types of overload failures, which are categorized as failures due to insufficient material strength and underdesign, failures due to stress concentration and material defects, and failures due to material alteration. It describes the general aspects of fracture modes and mechanisms. The article briefly reviews some mechanistic aspects of ductile and brittle crack propagation, including discussion on mixed-mode cracking. Factors associated with overload failures are discussed, and, where appropriate, preventive steps for reducing the likelihood of overload fractures are included. The article focuses primarily on the contribution of embrittlement to overload failure. The embrittling phenomena are described and differentiated by their causes, effects, and remedial methods, so that failure characteristics can be directly compared during practical failure investigation. The article describes the effects of mechanical loading on a part in service and provides information on laboratory fracture examination.

The various methods of furnace, torch, induction, resistance, dip, and laser brazing are used to produce a wide range of highly reliable brazed assemblies. However, imperfections that can lead to braze failure may result if proper attention is not paid to the physical properties of the material, joint design, prebraze cleaning, brazing procedures, postbraze cleaning, and quality control. Factors that must be considered include brazeability of the base metals; joint design and fit-up; filler-metal selection; prebraze cleaning; brazing temperature, time, atmosphere, or flux; conditions of the faying surfaces; postbraze cleaning; and service conditions. This article focuses on the advantages, limitations, sources of failure, and anomalies resulting from the brazing process. It discusses the processes involved in the testing and inspection required of the braze joint or assembly.

This article discusses the classification of sliding bearings and describes the major groups of soft metal bearing materials: babbitts, copper-lead bearing alloys, bronze, and aluminum alloys. It provides a discussion on the methods for fluid-film lubrication in bearings. The article presents the variables of interest for a rotating shaft and the load-carrying capacity and surface roughness of bearings. Grooves and depressions are often provided in bearing surfaces to supply or feed lubricant to the load-carrying regions. The article explains the effect of contaminants in bearings and presents the steps for failure analysis of sliding bearings. It also reviews the factors responsible for bearing failure with examples.

To determine the effect of severe service on cast 357 aluminum pistons, a metallurgical evaluation was made of four pistons removed from the engine of the Hawk-Offenhauser car which had been driven by Rich Muther in the first Ontario, California 500 race. The pistons were studied by visual inspection, hardness traverses, radiography, dye penetrant inspection, chemical analysis, macrometallography, optical microscopy, and electron microscopy. The crown of one piston had a rough, crumbly deposit, which was detachable with a knife. Two pistons had remains of carbonaceous deposits. The fourth was severely hammered. It was concluded that the high temperatures developed in this engine created an environment too severe for 357 aluminum. Surfaces were so hot that the low-melting constituent melted. Then, the alloy oxidized rapidly to form Al2O3, an abrasive which further aggravated problems. The temperature in much of the piston was high enough to cause softening by overaging, lowering strength.

This article explains the main types and characteristic causes of failures in boilers and other equipment in stationary and marine power plants that use steam as the working fluid with examples. It focuses on the distinctive features of each type that enable the failure analyst to determine the cause and suggest corrective action. The causes of failures include tube rupture, corrosion or scaling, fatigue, erosion, and stress-corrosion cracking. The article also describes the procedures for conducting a failure analysis.

Overload failures refer to the ductile or brittle fracture of a material when stresses exceed the load-bearing capacity of a material. This article reviews some mechanistic aspects of ductile and brittle crack propagation, including a discussion on mixed-mode cracking, which may also occur when an overload failure is caused by a combination of ductile and brittle cracking mechanisms. It describes the general aspects of fracture modes and mechanisms. The article discusses some of the material, mechanical, and environmental factors that may be involved in determining the root cause of an overload failure. It also presents examples of thermally and environmentally induced embrittlement effects that can alter the overload fracture behavior of metals.

High temperature corrosion may occur in numerous environments and is affected by factors such as temperature, alloy or protective coating composition, time, and gas composition. This article explains a number of potential degradation processes, namely, oxidation, carburization and metal dusting, sulfidation, hot corrosion, chloridation, hydrogen interactions, molten metals, molten salts, and aging reactions including sensitization, stress-corrosion cracking, and corrosion fatigue. It concludes with a discussion on various protective coatings, such as aluminide coatings, overlay coatings, thermal barrier coatings, and ceramic coatings.

A gray cast iron (ASTM 247 type A) gate valve in an oleum and sulfuric acid piping loop at a chemical process plant fractured catastrophically after approximately 10 years of service. The valve was a 150 mm (6 in.) bolted flange type rated to conform to ANSI B16.1 for service at 1034 kPa (150 psi) and 120 deg C (250 deg F) maximum in 93 to 99% sulfuric acid. The fracture originated at stress-corrosion cracks that occurred in a high-stress transition region at the valve body-to-flange juncture. The mechanical properties of the failed valve were below those of the manufacturer's cited specification, and the wall thickness through which the fracture occurred exceeded the minimum 9.5 mm (38 in.) thickness cited by the manufacturer The valve flange had been unbolted and rebolted to a maintenanced piping coil immediately prior to failure. It was recommended that the flange-to-valve body juncture be redesigned to reduce stress levels. A method of maintenance and inspection in concert with a criterion for life prediction for this and other valves and components in the system was also recommended.

Impact or percussive wear is defined as the wear of a solid surface that is due to percussion, which is a repetitive exposure to dynamic contact by another body. Impact wear, however, has many analogies to the field of erosive wear. The main difference is that, in impact wear situations, the bodies tend to be large and contact in a well-defined location in a controlled way, unlike erosion where the eroding particles are small and interact randomly with the target surface. This article describes some generic features and modes of impact wear of metals, ceramics, and polymers. It discusses the processes involved in testing and modeling of impact wear, and includes two case studies.

This article focuses on the mechanisms of microbiologically influenced corrosion as a basis for discussion on the diagnosis, management, and prevention of biological corrosion failures in piping, tanks, heat exchangers, and cooling towers. It begins with an overview of the scope of microbial activity and the corrosion process. Then, various mechanisms that influence corrosion in microorganisms are discussed. The focus is on the incremental activities needed to assess the role played by microorganisms, if any, in the overall scenario. The article presents a case study that illustrates opportunities to improve operating processes and procedures related to the management of system integrity. Industry experience with corrosion-resistant alloys of steel, copper, and aluminum is reviewed. The article ends with a discussion on monitoring and preventing microbiologically influenced corrosion failures.

Failure of AISI 1015 steel brake discs used in power transmissions in emergency winches was investigated using various testing methods. The failed discs were stampings that had replaced cast discs. Residual stresses in the fillets of new cast and new stamped brake discs were measured by x-ray diffraction. The results indicated that the stamped brake discs had failed by fatigue caused by a tensile residual stress pattern in the fillet. The residual stress pattern was attributed to the change in manufacturing process from casting to stamping. Use of a manufacturing process that yields a compressive residual stress in the fillet, appropriate heat treatment of stamped discs, or redesign of the disc and/or transmission assembly was recommended.