Use of the GTAW method for surface hardening of cast-iron

Technologies which make it possible to improve the working properties of surface layers of castings, while utilising traditional materials, are increasingly being used in industrial applications. The life of fabrications can be extended as necessary. It is also possible to manufacture fabricates with working properties that are normally unobtainable in the case of traditional construction materials and technology.     

Optimisation of monolithic lining concepts of channel induction furnace

Abstract

For the possible energy savings and extension of the volume capacity, the monolithic lining of a channel induction furnace was optimised in the following manner. Orthogonal array method is utilised to systematically design the lining concepts, and the finite element simulations including the temperature dependent properties of monoliths are carried out to determine the temperatures and stresses during the preheating and holding. In terms of the main effect analysis materials for the monolithic lining are recommended. Moreover, a thickness–thickness–temperature isothermal map is provided to show the acceptable thickness range of working and insulating linings. Nevertheless, for the final decision the deliberate consideration for the cost effectiveness of a certain lining concept is also necessary.     

The strength properties of iron aluminides

For the development of Fe−Al alloys as structural materials, a deep understanding of slip and deformation properties is necessary. In particular, since mechanical properties of the iron aluminides are affected by excess vacancy strengthening as well as the positive-temperature dependence of yield stress, controlling these strength features is essential. In this article, the strength properties of iron aluminides are reviewed. Author’s Note: All compositions are provided in mole percent. Kyosuke Yoshimi earned his Ph.D. in materials science and engineering at Tohoku University in 1997. He is currently a research associate at Tohoku University. Shuji Hanada earned his Ph.D. in materials science and engineering at Tohoku University. He is currently a professor at Tohoku University. Dr. Hanada is also a member of TMS.     

Welding problems with thin brass plates and tungsten inert gas pulse welding

Abstract

Brass materials are widely used as engineering materials in industry because of their high strength, high corrosion resistance, and high electrical and thermal conductivity. They are easily shaped and they possess a pleasant appearance. However, it is difficult to weld brasses. The main problem with these alloys in fusion welding is the evaporation of zinc during the welding process. After welding, the weld metal becomes porous. Moreover, since the amount of zinc in the alloy is reduced due to evaporation, the brass material loses the physical and chemical properties which it normally possesses. Studies on weldability of brass materials are very few. There is very little information concerning the weldability of brass materials in the literature and general definitions are often seen. It is impossible to find studies on experimental investigations of the welding of brass materials apart for a few exceptions. There are virtually no studies to support experimental data about whether welding of brass materials is possible. The purpose of the present study is to determine suitable parameters by investigating the weldability of brass materials, and the difficulties involved. In order to enable low and controlled heat input into the welding bead, TIG pulse welding is used during experimental studies. The physical and chemical properties of welding beads (penetration, tensile strength, Erichsen deep drawing value, chemical composition of internal structure) have been determined and evaluations have been made.     

The stress corrosion cracking of high strength CrMnSiNi and CrMo steels

Practically all constructional steels are working under applied loads and environments. Below some stress levels the deterioriation of the material occurs by typical corrosion modes. Modern constructions are often loaded with enough high stresses to promote catastrophic failures due to stress corrosion crack propagation. Actually the whole range of metallic materials used in reliable constructions which are exposed to corrosive environments should be tested for their sensitivity to stress corrosion cracking. By measuring the material constant K_ISCC (critical stress intensity factor for stress corrosion cracking) it is possible to construct the reliable parts working in a safe range of stresses, which cannot be computed knowing yield strength of the material only. For measuring K_ISCC values of high strength CrMnSiNi and CrMo steels, original stands were built and long-term (> 10³h) tests applied by means of the cantilever beam method. Sensitivity of tested steels to stress corrosion cracking was expressed as a ratio K_ISCC:K_IC. Some other observations concerning kinetics of crack propagation and other properties of the materials have been carried out.     

Recent developments in ceramic nanocomposites

Ceramic nanocomposites are drawing considerable interest as processing methods are developed to enable these materials to go from the research laboratory scale to the commercial level. The potential benefits of ceramic nanocomposites can be substantial, but further research is needed. In-depth characterization is also needed in order to understand the novel physical and mechanical properties of these materials. In the literature dealing with mechanical properties, there are still many controversies to be resolved. S. Bhaduri earned her M.S. in metallurgical engineering at the University of Idaho in 1995. She is currently a doctoral candidate at the University of Idaho. S.B. Bhaduri earned his Ph.D. in materials science and engineering at the University of New York at Stony Brook in 1981. He is currently an associate professor at the University of Idaho. Dr. Bhaduri is also a member of TMS.     

Effect of the shield gas,working angles and displacement angles on the characteristics of fillet joints obtained via GMAW using a high-strength microalloyed steel

ABSTRACT

Fillet joints are one of the most commonly used joints in various industries, in particular for agricultural machinery. However, the complexity of the pieces that require welding often makes accessibility difficult for the welder for this kind of joint, and working and displacement angles are important aspects to be evaluated. In addition, in the GMAW process, the use of the Ar-20%CO₂ mixture as the shield gas has increased at the expense of 100% CO₂, generally requiring an adjustment of the electrical parameters. On the other hand, the incorporation of new materials with higher strength also involves optimizing the welding procedure. The aim of this study was to evaluate the effect of two shield gases (Ar-20% CO₂ and 100% CO₂), three working angles (30, 45 and 60°) and two displacement angles (45° using the push technique and 60° using the pull technique) on the dimensional characteristics of the seam and the mechanical strength of the fillet joint from a microalloyed steel with high strength welded using GMAW. The highest levels of penetration corresponded to the test specimens welded using the pull technique and with CO₂. The over thickness was smaller for conditions with the push technique and the gas mixture. The microhardness of the weld metal, for a similar working angle, was higher for the gas mixture in all cases. Indices of acceptability were developed, which graded geometric aspects and these were compared with the mechanical properties obtained on the welds, showing a good correlation.     

Formation and performance of an Fe-based amorphous-nanocrystalline composite coating by laser cladding and remelting

Abstract

A very important research topic in the area of the surface performance of engineering components, in particular their wear properties, recently has been the application of high quality surface layers on relatively cheap substrates. An Fe-based composite coating with both amorphous and nanocrystalline structures on a mild steel substrate offers a combination of high quality coating and low materials cost, at the same time extending the range of applications of traditional materials. The difficulties posed by preparation of Fe-based amorphous alloys have limited progress for many years. However, the recent development of high power lasers, and of laser material processing technology in general, has made the preparation of a Fe-based amorphous and nanocrystalline composite coatings over a large area a real possibility.     

Fatigue behavior in nickel-based superalloys: A literature review

In this literature review, the present understanding regarding the effects of microstructure, loading conditions, and environments on the fatigue behavior of nickel-based superalloys is reviewed. Authors' Note: Inconel, Incoloy, and Nicalon are registered trademarks. L. Garimella earned his M.S. in materials science and engineering at the University of Tennessee in 1997. He is currently working at an Internet company. Mr. Garimella is a member of TMS. P. K. Liaw earned his Ph.D. in materials science and engineering at Northwestern University in 1980. He is a professor and Ivan Racheff Chair of Excellence in the Department of Materials Science and Engineering at the University of Tennessee. Dr. Liaw is also a member of TMS. D.L. Klarstrom earned his Ph.D. in metallurgical engineering at the University of Wisconsin-Madison. He is currently director of Haynes International. Dr. Klarstrom is also a member of TMS.     

Refractory metal-intermetallic in-situ composites for aircraft engines

There has been substantial progress in the development of properties in high-temperature in-situ composites during the last five years. For example, fracture-toughness values in excess of 20 MPa √m have been reported in silicide-based composites toughened by niobium-based metallic solid solutions. These composites also have oxidation resistances and rupture lives comparable to those of single-crystal superalloys for temperatures up to 1,150°C. In this article, fracture toughness, oxidation characteristics, high-temperature mechanical behavior, and low-temperature fatigue properties of refractory metal-intermetallic composites (RMICs) are described and compared to air-craft-engine fundamental material property goals for the next millennium. Further avenues toward the pursuit of these goals are outlined. Author’s Note: All compositions are presented in atomic percent. B.P. Bewlay earned his Ph.D. in metallurgy and materials science at Oxford University in 1987. He is currently a metallurgist at General Electric Corporate R&D. Dr. Bewlay is also a member of TMS. J.J. Lewandowski earned his Ph.D. in metallurgical engineering and materials science at Carnegie Mellon University in 1983. He is currently director of the Mechanical Characterization Facility and professor of materials science and engineering at Case Western University. Dr. Lewandowski is also a member of TMS. M.R. Jackson earned his Ph.D. in metallurgy and materials engineering at Lehigh University in 1971. He is currently a metallurgist at General Electric Corporate R&D. Dr. Jackson is also a member of TMS.     

Ceramic-metal interfaces and the spreading of reactive liquids

A number of solid-state and liquid-state processing techniques are available for tailoring the properties of a ceramic-metal interface. While many of the techniques are successfully used in industry, the mechanisms for their microstructural formation are not well understood. For situations where a liquid metal is in contact with a solid ceramic substrate, the wetting and spreading behavior of the liquid is critical in determining the final microstructure and properties of the interface, which may control the properties of the component or system. Alan Meier earned his Ph.D. in metallurgical and materials engineering at the Colorado School of Mines in 1994. He is currently an assistant professor of metallurgy and materials engineering in the Ceramic Engineering and Materials Science Department, New York State College of Ceramics, Alfred University. Daniel A. Javernick is a Ph.D. candidate at the Colorado School of Mines. He is currently a graduate research assistant in the Department of Metallurgical and Materials Engineering, Colorado School of Mines. Glen R. Edwards earned his Ph.D. in materials science and engineering from Stanford University. He is a professor in the Department of Metallurgical and Materials Engineering and director of the Center for Welding, Joining and Coatings Research at Colorado School of Mines.     

Nanomaterials: Nomenclature,novelty, and necessity

Nanomaterials are on enabling component of the popularly labeled area of “nanotechnology,” but are generally not well understood in the materials community at large. The purpose of this article is to narrow this gap by framing nanomaterials in the traditional materials science and engineering context as well as discussing some potential implications to the materials enterprise. Editor’s Note: A hypertext-enhanced version of this article is available on-line at www.tms.org/pubs/journals/JOM/0410/Hunt-0410.html Warren H. Hunt, Jr. is technical consultant at TMS.     

Tribological and microstructural behaviour in coatings applied using GTAW and HVOF (thermal spraying process) and used to recover AISI/SAE D2 grade tool steels

ABSTRACT

Fe-Cr-Mo alloys are used in coatings for protecting components that are subjected to conditions involving wear and corrosion. The high velocity oxygen fuel (HVOF) method used for tool steel alloys for cold working with the use of Fe-Cr-Mo substrates has yielded good results in the field of spray coatings. HOVF is a great method for applying coatings and recovering diameters that become worn down during the operating process. New surfaces and materials can be provided without the distortion caused by conventional welding processes. It is a great method for materials that are susceptible to cracking due to the formation of hard and off-balance phases with compositions with high contents of carbon and chromium, due to the conditions of the process, which combine a relatively low flame temperature and a time of low exposure. The microstructure and characteristics of the coating are determined by the physical and chemical properties of the particles impregnated in the substrate which in turn depend on a lot of parameters such as the design of the spray gun, oxygen/fuel ratio, injection method, particle size and shape, among others. This study investigates the influence of the processing parameters on the mechanical and microstructural properties of the Diamalloy 1008 coating (mixed Fe-Cr-Mo alloy), which is applied using high velocity oxygen fuel (HVOF) and five different types of electrode applied using TIG (GTAW) welding in a tool steel for cold working. These coatings are usually used as a protection against corrosion and wear, but also have the ability to recover damaged areas as is the case with stamping dies in the automotive industry. The samples were characterised using optical microscopy and scanning electron microscopy in order to evaluate the quality of the material deposited on the substrate; Vickers microhardness and Pin-Ball Disc were used to quantify the mechanical properties of the coatings.     

The use of failure analysis as a preventative quality tool

The materials and processes used to fabricate electronic components have significant effects on their ul-timate reliability. By examining a small number of samples, high risk types of materials and poor work-manship can be flagged, either excluding them from production use,or using them to drive corrective actions. The tools of failure analysis are well suited to this approach, even though the sample components have technically not failed at all. Both nondestructive and destructive types of analysis can be used. By focusing on comparative device analysis between available suppliers, it is possible to find the best in class components for use in high- reliability applications such as automotive electronic modules.     

Failure analysis of some petrochemical plant components

Abstract

Failure analysis of five sections of plant (the cooling elbow of a chlorination reactor, electrolyte feed pipelines, tubes from an ethylene cracking furnace, the upper pressure cover of the chlorination reactor and heat exchanger tubing) in a petrochemical factory were investigated. Their microstructures were observed using optical and scanning electronic microscopy with compositional analysis measured using energy dispersive X-ray analysis. Mass loss experiments in the laboratory using selected materials and the working environment were also conducted. The main causes of the corrosion of the parts are discussed. Based on the results of the failure analysis, methods to improve the life of the parts are suggested. For example, by selection of suitable substitute alloys the working life of the parts may be increased.     

Expert system to choose coatings for flue gas desulphurisation plant

Abstract

The development and use of an expert system to recommend coatings for flue gas desulphurisation plant is described. The system ranks coatings by their material properties and experimental test and plant performance scores when the component to be coated and its working environment are specified. The user interface, the inference engine, the knowledge base, and the process used to implement the expert system are presented with comments on its suitability and application for corrosion consultations.     

The heredity of Al-Si-Mg-Mn before and after Remelting

This article reviews the heredity of metals and alloys that occurs in the casting process by studying the relationship of Al-Si-Mg-Mn alloy prior to and following a remelting process. The microstructure and mechanical properties of the samples are discussed. L. Xiangfa earned his Ph.D. in materials science and engineering at Shandong University of Technology in 1996. He is currently a staff member of the Liquid Metals and Heredity Engineering Laboratory (LMHEL) at Shandong University of Technology. B. Xifang earned his M.Sc. in materials science and engineering at Shandong University of Technology in 1983. He is currently a professor and president of the LMHEL. Q. Xiaogang earned his M.Sc. at Shandong University of Technology in 1997. He is currently a staff member of the LMHEL. M. Jiaji earned his Ph.D. in Russia in 1963. He is currently a staff member of the LMHEL.     

IFHTSE Global 21: Heat treatment and surface engineering in the twenty-first century Part 8 – Training in heat treatment and surface engineering

Abstract

It is well known that metallurgists, materials scientists and engineers all have some training in heat treatment and surface engineering (thermal processing) as an intrinsic part of their courses, irrespective of the qualification to which the course leads. However, for those who are going to work in the thermal processing industry or have responsibility for that area of their business, it has to be acknowledged that the level of training is not in sufficient depth to allow them to conduct the business in the best possible manner. In other words, additional training is required. How employees were trained some years ago is compared with the training that is available today, and measures to ensure that sufficient appropriately trained people are available to the industry in the future are proposed. Although the main thrust of this paper will be applicable to all businesses carrying out thermal processing, it is very much based on the author's experience of working for Bodycote, a major thermal processing service provider, for the past 31 years. My many discussions in both Europe and the USA with both colleagues and educators have led me to believe that the UK experience is far from unique.     

Practical Corrosion Problems in Relation to Welded Joints. I. Special Characteristics of the Welding Process Which can Cause Corrosion Problems

Abstract

The purpose of this paper is to explain very briefly how welding may lead to corrosion problems in structural engineering. A table is given summarising corrosion problems in welded joints of various materials possible causes of these problems and their remedies.     

Stress corrosion cracking and hydrogen embrittlement susceptibility studies on modified 9Cr-1Mo steel weldments in acidic and neutral media

Abstract

There is much scope for the development of new engineering materials for high temperature applications such as for tubing used in steam generation in fossil fuel and nuclear power plants and in petrochemical cracking units. The materials for such applications are often manufactured from mild steel and low alloy ferritic steels containing up to 9%Cr. Modified 9Cr-1Mo ferritic steel, prepared by incorporating vanadium and niobium, is one of the newer materials extensively used for high temperature applications. A study of weldments of this alloy and its susceptibility to stress corrosion cracking (SCC) and hydrogen embrittlement was carried out in acidic and neutral media. The anodic behaviour of modified 9Cr-1Mo under 90% proof stress was also examined. Mechanical properties of the material were assessed before and after SCC and hydrogen embrittlement tests. The SCC tests were made at various anodic potentials in 1M H₂SO₄ and showed that the welded alloy is not susceptible to SCC in all three critical zones. The alloy was, however, susceptible to SCC in chloride environments, namely a solution containing equal volumes of 1M NaCl and 1M MgCl₂. Fractographic analysis was carried out to determine the reasons for the failure of this alloy. The hydrogen embrittlement studies in 1M H₂SO₄ showed that the alloy is prone to delayed hydrogen cracking at more negative potentials. The fractographic examination using scanning electron microscopy revealed the presence of adsorbed hydrogen in microvoids which were responsible for the failure of the alloy. Other possible reasons for the failure of the alloy are also discussed.