Metallurgical Tests Research Articles

A Study on Corrosion of Cast-On-Strap Alloys

The effects of different Sn or Se content on the corrosion behavior of lead-Sn or Pb-Sn_Se alloy in sulfuric acid solutions were investigated by metallurgical microscope, SEM, and weight loss tests. It was found that the addition Sn acts as grain coarser, but Se acts as grain refiner and Pb-Sn-Se alloys feature smaller grains. SEM for the corrosion layer indicated that the intergranular corrosion occurs on the surface of alloys with high Sn content (>1.wt%), but the general corrosion occurs on the surface of Pb-Sn alloys with low Sn content (<1.wt%) and all Pb-Sn-Se alloys. And The structure of corrosion layer and the eroded degree are relative to the height of the strap alloys above the plate. And the 1cm strap alloy above the plate was cathodically protected and almost no corrosion problems appeared. The corrosion rate of alloys containing Se is lower than Pb-Sn binary alloys. And the higher of Se content, the lower of corrosion rate. The results demonstrated that Pb-Sn-Se alloys show the potential for application as the negative strap in VRLA batteries.

Performance of weldments in advanced 9%Cr steel–‘FB2’

The improvement of tensile and creep rupture strength, achieved by the development of martensitic-ferritic 9–12%Cr creep-resistant steels, known as creep strength enhanced ferritic (CSEF) steels, is attractive to designers who want to take advantage of them to improve power plant efficiency and reduce component wall thickness. However, although parent alloy developments have been making good progress, weldment performance has been of increasing concern. In particular, the cross-weld creep performance for CSEF steels is an issue, with Type IV cracking characterised by rupture in the outer region of the heat affected zone (HAZ) and low strain to failure being the typical features of failure in cross-weld tests. In this investigation, narrow gap TIG welding, flux-cored arc welding (FCAW) and reduced pressure electron beam (RPEB) welding were employed to produce a series of butt welds in a new European steel–FB2–a wrought, boron-containing 9%Cr steel. These welds were subjected to metallurgical examination and mechanical testing, including toughness and cross-weld creep rupture tests. Results are compared with the well known steel grades 91 and 92. Welding process was found to have a marked effect on weld metal toughness, but not on the long term cross-weld creep rupture performance. FB2 weldments were found to out-perform those of grades 91 and 92 in long term creep tests, but they did suffer from type IV cracking and reduced rupture strength, compared with the parent steel. The paper draws conclusions on the performance of the welded joints, and makes recommendations for further work and possible application within the power industry.

A new fixture for FSW processes of titanium alloys

FSW of titanium alloys is nowadays one of the most challenging welding operations, even with a solid state process, due to the thermo-mechanical and thermo-chemical characteristics of such materials. Due to the relevant application of titanium alloys in the aeronautic and aerospace industries, in the recent years few attempts were carried out to develop FSW processes aimed to maximize the mechanical performances of the welded parts. In the paper a new fixture is presented allowing obtaining effective FSW joints of titanium blanks, which were investigated through mechanical and metallurgical tests highlighting the peculiarities of FSW of titanium alloys.

Mineralogical signature of nonsulfide zinc ores at Accha (Peru): A key for recovery

The Accha deposit in Southern Peru is the first case in which an integrated study between mineralogy, petrography and metallurgical characteristics of a nonsulfide Zn orebody has been carried out. The Accha–Yanque Zinc Belt is located in a major zinc-rich metallogenic province hosting a number of economic mineral deposits, which extends in a zone peripheral to the edge of the Oligocene–Miocene Yauri–Apurímac granite batholith. This belt is comprised of a number of weathering-derived nonsulfides occurrences, showings and mineral deposits. A thorough mineralogical and petrographic study has been carried out on the MET 1, MET 2, MET 3 and MET 4 cores, drilled between 2006 and 2007 for metallurgical purposes. The nonsulfides mineral association in the deposit consists mainly of smithsonite and hemimorphite replacing both primary ore minerals and carbonate host rocks. Smithsonite occurs in zoned concretions with goethite, Mn(hydr)oxides and Zn-clays. One of the most peculiar nonsulfide Zn mineral at Accha is a sauconite-like Zn-smectite, which can be locally very abundant (up to 30%). Differences in mineralogy of the ore and gangue minerals, as well as the composition of the host rock can have a profound impact on zinc recovery and reagent consumption in any extraction process. The Accha nonsulfide ore minerals are intimately intergrown with the limestone host and therefore difficult to separate with traditional methods, this rendering the economic recovery of the metal through the acid leaching process difficult. This is further complicated by the abundance of sauconite in the deposit. It was therefore necessary to envisage a flowsheet development, derived from a thorough metallurgical test work program on various ore types, which could result in an economically viable treatment route in the light of both the carbonate host rock and the peculiar mineralogical association. Several careful processing steps comprised of comminution, dense media separation and flotation before acid leaching, and including precise acid leaching conditions to prevent the formation of deleterious ‘gels’ that would interfere with subsequent solid–liquid separation processes, have been tested for Accha as part of the development of an economic processing flowsheet.

Failure Analysis of a High-Pressure Component

Martensitic stainless steel nuts were received for failure analysis. A few of these nuts cracked at the immediate stress loading while the others fractured after 2 years of service. These nuts were subjected to different metallurgical tests such as visual examination, optical microscopy, chemical analysis, hardness testing, and fractography. It was concluded that improper heat treatment weakened the structure and subsequently fractured on the application of load.

Bainitic steel grade for solid wheels: metallurgical, mechanical, and in-service testing

Bainitic steel grades generally have superior rolling contact and thermal fatigue resistances, but poorer wear characteristics when compared with ‘conventional’ pearlitic steel wheels. To improve the wear characteristics, the manufacturing process of bainitic materials needs to be carefully controlled. In this article, the manufacturing process of the ‘MICRALOS’ bainitic steel grade has been described. The main focus is on metallurgical testing activities performed in order to compare the new steel grade with standard pearlitic steels and to predict the service behaviour of the solid bainitic wheels. Further, on-going field tests on the iron ore line between Luleå and Narvik have been reported, with details about measurement methods and results. The performance of the wheels is reviewed and compared with the current scientific knowledge of bainitic steel grades and the deterioration of heavy haul wheels. Finally, benefits of and challenges for bainitic wheels in general and for the MICRALOS grade wheels in particular will be discussed.

Techniques and applications for predictive metallurgy and ore characterization using optical image analysis

Optical image analysis (OIA) as a predictive metallurgical tool has been advanced by work completed at SGS Mineral Services by integrating a standard image analysis system with innovative preparation methods and measurement techniques. The preparation of sized material into non-touching particle polished sections as well as the selective coating of epoxy facilitates the recognition of non-opaque minerals, thus correctly identifying locked and complex particles. Advanced data analysis enables the preparation of predictive metallurgical data. Test cases were compared to metallurgical test results including size distribution, mineral release and grade/recovery data for various ore deposits. The limiting factor in direct optical image analysis is the discrimination between minerals with similar reflective properties. Advances made at the University of Liege have made it possible to optically distinguish these minerals using multispectral imaging. Integrating these technologies will enable OIA to be an affordable and viable alternative for gathering process mineralogical data.

Medium-temperature pressure leaching of copper concentrates — Part II: Development of direct electrowinning and an acid-autogenous process

Part I in this series of papers considered the chemistry of medium-temperature pressure leaching of copper sulfide concentrates and reviewed the metallurgical testing and initial process development for this technology. This initial work resulted in the development of a process flowsheet utilizing superfine grinding (to a P98 of 12 to 15 µm and P80 of 6 to 7 µm), pressure leaching at 160° to 170°C, followed by conventional solution extraction (SX) and electrowinning (EW) for the recovery of copper. However, this process required a significant amount of concentrated acid to be fed to the pressure leach vessel to meet the reaction requirements, representing a cost of between $0.03 and 0.05/lb copper (2006 basis) produced by the process. It was immediately recognized that the development of a process that did not require such a large acid addition would be advantageous. This paper, which is Part II in the series, describes the development of a process that incorporates medium-temperature pressure leaching and direct electrowinning (DEW) in a novel and innovative process flowsheet. Phelps Dodge (a subsidiary of Freeport-McMoRan Copper & Gold Inc.) refers to this as the “MT-DEW-SX” process. Part III in this series covers the large-scale demonstration of the MT-DEW-SX process at Bagdad, Arizona; and Part IV addresses the development and design of a full-scale commercial application at Morenci, Arizona.

Cyclic Void Growth Model to Assess Ductile Fracture Initiation in Structural Steels due to Ultra Low Cycle Fatigue

A new model is proposed to simulate ductile fracture initiation due to large amplitude cyclic straining in structural steels, which is often the governing limit state in steel structures subjected to earthquakes. Termed the cyclic void growth model (CVGM), the proposed technique is an extension to previously published models that simulate ductile fracture caused by void growth and coalescence under monotonic loading. The CVGM aims to capture ultra low cycle fatigue (ductile fracture) behavior, which is characterized by a few (generally, less than 20) reverse loading cycles to large inelastic strain amplitudes (several times the yield strain). The underlying mechanisms of low-cycle fracture involve cyclic void growth, collapse, and distortion, which are distinct from those associated with more conventional fatigue. The CVGM represents these underlying fracture mechanisms through plastic strain and stress triaxiality histories that can be modeled at the material continuum level by finite-element analyses. Development and validation of the CVGM is substantiated by about 100 notched bar tests, with accompanying finite-element analyses, metallurgical tests, and fractographic examinations of seven varieties of structural steels.

Effect of Cooling History on Cladding Ductility under LOCA Conditions

In a Loss-of-Coolant Accident of LWRs, heated and oxidized fuel cladding is slowly cooled and then quenched by re-flooding water. Effects of cooling rate during the slow-cooling process and quench temperature were investigated on post-quench ductility of the oxidized cladding. Unirradiated Zircaloy-4 cladding specimens were oxidized in steam at 1,373 or 1,473 K, cooled at a rate from 2 to 7 K/s, and finally quenched from temperatures ranging 1,073 to 1,373 K. Post-quench ductility was evaluated by ring-compression test, and microscopic properties were examined by metallurgical examination, hardness test, and oxygen analysis. Morphology of oxygen-rich α phase in the metallic prior-β phase layer changed depending on the cooling history. Area fraction of α phase region in the cross section obviously increased and post-quench ductility reduced with decrease in the quenching temperature. Since α phase region with low ductility can be preferential path for crack propagation, increase in area fraction of α phase region possibly decreases resistance for fracture, which results in ductility reduction. On the other hand, the area fraction was nearly constant irrespective of the rate of the slow cooling, and consequently, effect of the cooling rate on the post-quench ductility was negligible.

Pitting failure of truck spiral bevel gear

Spiral bevel gears are some of the most important elements used in truck differential. In this study, the fracture of spiral bevel gear for truck differential produced from case hardening steel is investigated. In order to study the causes of the failure, specimens prepared from the damaged spiral bevel gears were subjected to experiments, such as visual inspection, hardness, chemical analysis and metallurgical tests. Pitting occurrence on gear surfaces was observed. The effect of microstructure on the fracture was considered. Low surface hardness values were found. The calculated contact stress was higher than the allowable contact stress which is emphasized in literature.

Marine Accident Investigation Techniques: Finding the Root Causes

A vessel that has been damaged by a fire and/or explosion, suffered a mechanical failure, or had some sort of accident that resulted in injuries or property loss is almost always the subject of an investigation to determine the root cause and significant contributing factors. This paper describes the investigation process, including the skills and special knowledge that is often required for a complete investigation. Using several case investigations, the synergy of combining marine/mechanical and metallurgical testing and analyses is also discussed. Several engineering disciplines typically are required to recreate the sequence of events, components involved, and most probable causes. Such issues as maintenance, controls, design, and fail-safe performance are the domain of the marine/mechanical specialist. Determination of the failure mode, role of corrosion, thermal degradation, and materials selection issues are typically evaluated by a metallurgist. Design, materials selection, and component fabrication methods can become significant issues.

Failure study of pneumatic rock drill piston

In this study, the fracture of piston for rock drill produced from case hardening steel is investigated. In order to study the causes of the fracture, specimens prepared from the damaged pistons were subjected to experiments such as hardness, chemical analysis and metallurgical tests. The effect of microstructure on the fracture was also considered. The detailed metallurgical analysis was conducted on the fractured pistons and compared with the unfailed pistons in service. Results showed that the obtained pistons hardness values were lower than the values stated in the literature. Geometrical analysis of the pistons revealed that early failure of the structure started from a notch by which stress concentrations are created at the end of the threaded region.

Fracture analysis of gear pump used for polymer production

In this study, the fracture of gears for polymer injection pumps fabricated via P/M (powder metallurgy) is investigated. In order to study the causes of the fractures, specimens prepared from the damaged gears were subjected to hardness, chemical analysis and metallurgical tests. The effect of microstructure on the fracture was also considered. Detailed metallurgical analysis was conducted on the fractured gears and compared with the unfailed gears in service. Results showed that gears hardness values were higher than values stated in the literature. Geometrical analysis of the gears revealed that early failure of the structure started from a sharp corner radius by which stress concentrations are created in the gear keyway.

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Reliability Investigation of Gallium Nitride HEMT

III-N HEMT is one of the most promising transistor for the next generation of RF power devices. Despite the impressive results on power density obtained using discrete devices and total output power for GaN-based amplifier announced in 2003, reliability demonstration is the key issue before devices can be fielded in practical applications. In this article test procedures and samples are described and the last results concerning storage and DC life tests are presented. Schottky barrier degradation was observed as a key factor for the metallurgical tests. DC life-tests showed a slow and steady drain current drop followed by stabilization as a function of time.

Control de procesos de temple con láser mediante dispositivos pirométricos

In this work, a detailed description of an on-line control system for laser heat treatments based on pyrometric monitorization, is presented. The study includes full details concerning monitorization devices and comprehensive description of the control loop, based on a direct synthesis regulator. The system validation and exportable character of the proposed method are also discussed. Finally, results obtained for CO 2 laser transformation hardening of F-114 steel are analyzed, including parametric analysis of control variables through metallurgical testing of the treated material.

Fitness for Service Evaluation of Ring Joint Groove Cracking

Cracking of ring joint style flanges has been a recurring problem in the petrochemical industry, particularly in high-pressure hydrogen processing vessels. The cracking of the ring joint groove region is an inherent problem with the design. The ring groove is subjected to high stresses from the wedging action of the gasket and the ring groove radii are not substantial enough to effectively reduce the stress concentrating effect. A fitness for service assessment was conducted for a hydrogen processing vessel containing cracks in the ring groove radius region of a ring joint style flange. The flange was forged 2-1/4Cr-1Mo material with a Type 347 SS overlay. Results of an elastic-plastic numerical fracture mechanics assessment showed that the driving force for crack propagation was high for a very localized region near the ring groove radius. However, the driving force decreased significantly for deeper cracks as the crack tip became removed from the very localized high stress region of the ring groove. The assessment also showed that the highest stresses occurred during the bolt-up operation. Metallurgical tests were performed on a small sample removed from the flange. The chemistry, grain size, microstructure, and hardness of the material indicated that the probability that this material had very low resistance to hydrogen-assisted crack growth during downtime was quite small and that the resistance to crack advance during service was good. Therefore, the combined results of the fracture assessment and metallurgical testing were used to justify continued operation without repair of the cracks present in the flange. [S0094-9930(00)01901-6]

Damage caused while dissembling the retainer rings of a generator of the Piratininga power plant

The inspection was undertaken of the retaining rings of a generator of the Piratininga Power Plant in Sao Paulo, Brazil. The generators are of the General Electric Co. type ATB, 3600 rpm, hydrogen-cooled, each one of 136 MVA, and were installed in 1960. The retaining rings were made to support the centrifugal load of the copper end windings. Normally, evaluation of these rings is recommended by most manufacturers of generators due to the high stress condition during operation and stress corrosion cracking in the material (18Mn 5Cr or 18Mn 18Cr, according to ASTM 289 class B and C). During the dissembly of the rings using electric induction, it was found that electric discharges, i.e. arcing, had occurred between the coil cabling and the surface of the rings, causing damage to all the rings. After metallurgical replication tests near the affected surfaces, the manufacturers condemned two of the four dissembled rings and determined that the other two rings should be machined to a certain maximum admissible ...