Melting,Processing, and Properties of Disordered Fe-Al and Fe-Al-C Based Alloys

This article presents a part of the research work conducted in our laboratory to develop lightweight steels based on Fe-Al alloys containing 7 wt.% and 9 wt.% aluminum for construction of advanced lightweight ground transportation systems, such as automotive vehicles and heavy-haul truck, and for civil engineering construction, such as bridges, tunnels, and buildings. The melting and casting of sound, porosity-free ingots of Fe-Al-based alloys was accomplished by a newly developed cost-effective technique. The technique consists of using a special flux cover and proprietary charging schedule during air induction melting. These alloys were also produced using a vacuum induction melting (VIM) process for comparison purposes. The effect of aluminum (7 wt.% and 9 wt.%) on melting, processing, and properties of disordered solid solution Fe-Al alloys has been studied in detail. Fe-7 wt.% Al alloy could be produced using air induction melting with a flux cover with the properties comparable to the alloy produced through the VIM route. This material could be further processed through hot and cold working to produce sheets and thin foils. The cold-rolled and annealed sheet exhibited excellent room-temperature ductility. The role of carbon in Fe-7 wt.% Al alloys has also been examined. The results indicate that Fe-Al and Fe-Al-C alloys containing about 7 wt.% Al are potential lightweight steels.     

Austenitic Die Steels and Alloys for Hot Deformation of Metals

Results of the development of highly heat-resistant austenitic precipitation-hardening die steels and alloys for the production of dies and pressing tools working at over 700°C are presented. Optimum heat treatment regimes for these steels and alloys are determined. Commercial grades of the new highly heat-resistant die steels and alloys are described.     

Hochlegierte nichtrostende Stähle und Nickelbasislegierungen im Chemie-Apparatebau

High alloy stainless steels and nickel-base alloys in chemical equipment construction The new ferritic chromium steels and ferritic-austenitic steels, high alloy special austenitic steels and nickel-base alloys presented in recent years have by now yielded some years' positive industrial experience in several applications. The group of austenitic steels containing 6 wt.-% molybdenum are at the threshold for large size application in chemical equipment construction. The results of the first comparative investigations with other high alloy steels are rather promising. The spectrum of nickel-base alloys will certainly be complemented by Hastelloy alloy C-22, so that this alloy will be used in addition to titanium alloys in contact with strongly oxidizing media.     

Thermodynamics,mechanisms and kinetics of metal dusting

A survey is given on recent research on “metal dusting” i.e. a catastrophic carburization or rather graphitization of metals and alloys occuring in carbonaceous atmospheres at carbon activities a_C>1. The thermodynamics are explained, the mechanisms for iron, low and high alloy steels, nickel and Ni-base alloys are described and the kinetics derived for iron and low alloy steels. Protection against metal dusting is possible by the presence of sulfur in the atmosphere, since adsorbed sulfur retards carbon transfer and hems graphite nucleation. Also dense oxide layers are protective, the preconditions for the formation of Cr-rich protectivee layers on steels and Ni-base alloys are shortly presenteed.     

Effect of Alloy Composition and Exposure Conditions on the Selective Oxidation Behavior of Ferritic Fe–Cr and Fe–Cr–X Alloys

Selective oxidation behavior of ferritic martensitic Fe–Cr base alloys, exposed in various atmospheres containing combinations of O₂, CO₂, and H₂O, were studied at various temperatures relevant to oxy-fuel combustion. This paper begins with a discussion of the required Cr content to form a continuous external chromia scale on a simple binary Fe–Cr alloy exposed in oxygen or air based on experiments and calculations using the classic Wagner model. Then, the effects of the exposure environment and Cr content on the selective oxidation of Fe–Cr alloys are evaluated. Finally, the effects produced by alloying additions of Si, commonly present in various groups of commercially available ferritic steels, are described. The discussion compares the oxide scale formation on simple binary and ternary Fe–Cr base model alloys with that on several commercially available ferritic steels.     

Synergistic abrasive—corrosive wear of chromium containing steels

Abstract

Commercial and experimental steels containing various chromium concentrations have been assessedfor their resistance to the combined effects of abrasion and corrosion. The degree of work hardening and macro- and microtoughness of low carbon martensite alloys, dual phase alloys, and metastable austenitic alloys provide good abrasion resistance, while chromium contents > 8% are required. Abrasion and corrosion are synergistic since the kinetics of corrosion are influenced by abrasion. The effects of the frequency of abrasion and corrosion are different for steels of different chromium contents. Low chromium steels perform better under lowfrequency conditions, whereas steels with higher chromium contents resist wear better when there are frequent abrasive periods.     

The role of molybdenum in the crevice corrosion of stainless steels

The paper starts with a literature review of Mo as an alloying element in stainless steels, with particular reference to crevice corrosion. Relevant aspects of the chemistry and electrochemistry of Mo are also summarized and used to discuss the possible role of soluble Mo species in corrosion inhibition. The need to examine solutions of low-valent Mo is indicated. Experiments are reported on stainless steels in the active range of corrosion potentials and the influence of soluble Mo^III and Mo^IV. No inhibitive effects are found; but inhibition is produced by films of insoluble Mo^IV oxide deposited on stainless steels. Such films can be produced by reduction of Mo^VI solutions, but not by oxidation of Mo^III. It is concluded that, in the corrosion of alloys, Mo probably passes directly from the metal into the protective film, and that soluble Mo compounds play no part in this process.     

Use of damping materials for increasing the quality and service properties of parts

Conclusion Type 04Kh11Yu chromium-aluminum steels are promising high-damping materials. They contain readily available alloy elements and are more corrosion- and scale-resistant than such high-damping alloys as magnesium and manganese-copper alloys and cast irons. In addition, they are more easily melted and hot worked by pressure than magnesium and manganese-copper alloys. Heat treatment of chromium-aluminum steels for high damping is simple.Broader use in industry of increased damping capacity type 120S2YuD graphitic steels is desirable. They are hardened significantly by heat treatment, are relatively inexpensive, and have recommended themselves positively during experimental production tests on reduction of the noise of mechanisms with gear drives. The use of them in place of 40Kh and 30KhGSA steels causes a reduction in noise of mechanisms with gear drives of 6 db. In addition, the wear resistance of the gears increases.Kirov Polytechnic Institute. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 12, pp. 3–4, December, 1987.     

Overview of Lightweight Ferrous Materials: Strategies and Promises

Reducing the density of steels is a novel approach for weight reduction of automobiles to improve fuel efficiency. In this overview article, strategies for the development of lightweight steels are presented with a focus on bulk ferrous alloys. The metallurgical principles of these steels and their mechanical properties of relevance to automotive applications are discussed. Some of the engineering aspects highlighting the possible problems related to mass production of these steels are also considered. Application prospects of these steels vis-à-vis standard automotive steels are shown.     

Thermodynamics of high-pressure melting

Great progress has been made in developing thermodynamic equations for high-nitrogen steels. Much of this work has centered on the effects of alloy composition on nitrogen concentration. Most of the currently produced high-nitrogen steels are formed by high-pressure melting. This joint U.S. Bureau of Mines, SRIM, and SIM study presents recent attempts to include the effects of pressure on the thermodynamic expressions used to determine the nitrogen concentration in Fe-Cr-Mn-Ni alloys.     

Microstructure and mechanical reliability of powder metallurgy (P/M) ferrous alloys

Because of their macroscopic brittle behavior, porous powder metallurgy (P/M) ferrous alloys are often not considered for structural applications. A statistical approach based on the evaluation and interpretation of the Weibull modulus was thus proposed to evaluate correctly and objectively the intrinsic structural reliability of these materials. In spite of their porosity, P/M ferrous alloys are as reliable as conventional wrought steels, provided that they are correctly produced and, if necessary, heat treated. In addition, the influence of density and the application of the method to the process optimization and control was highlighted. In all cases, the mechanical reliability of the materials was interpreted metallurgically.     

Homogenität und Korrosionsbeständigkeit hochlegierter Stähle

Homogeneity and corrosion resistance of high alloy steels A major number of case histories in the chemical industry are due to local corrosion the origin of which can be attributed to the inhomogeneity of the steels produced according to conventional melting process. Special processes such as electro slag remelting may give rise to a considerable increase in structural homogeneity of corrosion resistant alloys. Typical examples are increased resistance to nitric acid, Streicher's solution, seawater or reaction mixtures of urea synthesis. These results clearly demonstrate the superiority of the material which is largely free from inhomogeneities such as segregations which give rise to local corrosion phenomena.     

Allgemeine Beständigkeit von Schweißnähten unter Berücksichtigung der Spannungs- und Schwingungsrißkorrosion

General resistance of weld seams with a view to stress corrosion cracking and corrosion fatigue The corrosion of welds is due to thermal effects during welding which give rise to structural changes and, frequently, compositional changes in the transition zone. The welded material is rapidly cooled and may thus be heterogeneous and may present residual stresses resulting in increased susceptibility to selective and stress corrosion. The manganese content is of high importance in low alloy steels, as well as residual martensite or austenite embedded in a ferrite matrix. Low ferrite contents are generally beneficial because they counteract high temperature cracking; however, ferrite contents should be hept below 10% in order to prevent the formation of a continuous network giving rise to selective corrosion. Corrosion susceptibility may also be produced by carbide or carbonitride precipitation in austenitic and ferritic steels and nickel base alloys. Weld zones in aluminium alloys are attacked in rare cases (e.g. by HNO₃) and the susceptibility of Ta, Zr and Ti depends from the properties of the protective atmospheres.     

材料在青岛地区的大气腐蚀及防护对策

在青岛地区对碳钢、低合金钢、不锈钢、铝及铝合金、钛及钛合金以及涂镀层进行了８年大气腐蚀暴露。得到了各种材料在青岛海洋大气中的腐蚀数据及相应的环境数据。８年暴露腐蚀主耐侯钢我为０．０１４６ｍｍ／ａ,碳钢约为０．０６２２ｍｍ／ａ,其腐蚀失重发展符合指数函数规律Ｄ＝ＡＴ＾ｎ。钛合金,高铬不锈钢在大气中完全耐蚀。金属名热喷涂加封闭是保护钢结构最有效的方法。     

Fe---Cr---Ni---Mo---C alloys produced by laser surface alloying

Several Fe---Cr---Ni---Mo---C alloys were produced by laser alloying on plain carbon steel substrates, using the blown powder technique. It was found that a careful selection of the laser treatment parameters results in alloyed layers free of defects and with a homogeneous chemical composition. The structures were martensitic, fully austenitic and austenitic-ferritic, depending on the chemical composition. The high cooling rates were found to affect the austenitic-ferritic structures, which showed a larger quantity of δ ferrite than that predicted by the Shaeffler diagram. Surface alloys produced by laser processing, with chemical composition similar to that of conventional austenitic stainless steels, showed better pitting corrosion resistance than their bulk counterparts produced by conventional techniques, despite their higher carbon content.     

Special Features of Steels Alloyed with Nitrogen

The role of nitrogen as an alloying element that stabilizes austenite in steels and makes it possible to replace nickel, manganese, and other austenization promoters without deterioration of mechanical and special properties of the metal is considered. Put into practice this could reduce the volume of mining of the mentioned elements. Methods for introducing nitrogen into iron alloys are described. The mechanical properties of nitrogen-bearing steels are considered. It is shown that such steels with a structure of nitrogen martensite possess a specific strength under static and cyclic loads no worse than the strength of light structural alloys and have better fracture toughness and technological properties than the latter. The replacement of light alloys by such steels should reduce the consumption of energy in the production.     

A comparison of material removal mechanism under low stress abrasive condition of steel and hardfacing alloys

The low stress abrasive wear behavior of two types of steels commonly used for making a number of commonly used engineering components has been compared with the composition of a few hardfacing alloys that can be overlayed on the steels to impart a wear-resistant surface. The mechanism of material removal as studied by the scanning electron micrographs of the worn and transverse sections is different for the steels and hardfacing alloys. An attempt has been made to explain the mechanism of material removal for the steels and hardfacing alloys.     

Corrosion of nickel-base and iron-base alloys in a simulated fluidized-bed coal-combustion environment

The modes of initiation and propagation of corrosion attack on a series of high-temperature alloys were studied in synthetic gas mixtures at 900°C. The gas mixtures were intended to simulate the oxygen and sulfur partial pressures experienced in reducing zones in a coal-fired fluidized-bed combustor and comprised mixtures of CO, CO₂, and SO₂. The alloys studied were candidates for in-bed heat exchanger tubing for an air-heater cycle operating at 843°C and 300–500 psig and so ranged from type 300-series stainless steels to nickel-base alloys. With the exception of two FeCrAlY alloys and types 304 and 347 stainless steels, it was found that sulfidation corrosion could be initiated on all the alloys within 0.25 hr; the rate of propagation of the corrosive attack depended on the flux of SO₂ in the environment and on the nickel content of the alloys. The presence of iron in the alloys appeared to slow the initiation of sulfidation, by forming a continuous iron oxide layer. The effects of various alloying additions are discussed, and a schematic model for the initiation of sulfidation is proposed.     

Über die transpassive Auflösung von Nickel-Basis-Legierungen und Edelstählen in sauerstoff- und chloridhaltigem Hochtemperatur-Wasser

Transpassive dissolution of nickel-base alloys and stainless steels in oxygen and chloride containing high-temperature water The corrosion behaviour of different nickel base alloys and stainless steels (2.4605 [alloy 59; NiCr23Mol6Al], 2.4633 [alloy 602 CA; NiCr25FeAlY], 2.4819 [alloy C-276; NiMol6Crl5W], 2.4856 [alloy 625; NiCr22Mo9Nb], 2.4606 [alloy 686; NiCr20Mu16], 2.4646 [alloy 214; NiCrl6AlFe] and 1.4401 [UNS S 31600; X5CrNiMol7122]) was investigated in oxygen and chloride containing high-temperature water (temperatures up to 600°C; pressures up to 38 MPa; oxygen concentration 0.48 mol/kg; chloride concentrations up to 0. 1 mol/kg). All alloys show a similar corrosion behaviour, depending on temperature. At temperatures below about 150°C, only slight intergranular corrosion was observed. At higher temperatures (between about 150 and 300°C) pitting was detected. Most of the original surface in this temperature range remained unattacked. At higher temperatures, morphology of pitting changed towards shallow pitting and the whole surface is penetrated. The high general corrosion observed in these areas can be attributed to transpassive dissolution of the alloys' protecting chromium oxide layers with following dissolution of the alloy. At supercritical temperatures, corrosion decreased drastically, and only transpassive intergranular corrosion was detected. The observed decrease of ion-induced corrosion phenomena can he attributed to the change of physical and chemical properties of water (solubility of ions). Corrosion in neutral and alkaline solution was significantly less. Both pitting and transpassive dissolution shifted towards higher temperatures or were not detected respectively.     

Microstructure and Mechanical Properties of Direct Quenched Versus Conventional Reaustenitized and Quenched Plate

Direct quench processing of steels may be employed as a more cost efficient mechanism to produce low-carbon martensitic plate steels. However, the strengthening mechanisms of direct-quenched (DQ) steels, which can include grain size, dislocation density, and precipitation, are not well understood. Three experimental alloys containing 0.19 wt.% carbon with microalloy additions of Nb and V were developed to compare direct-quench processed steels to steels processed through reaustenitizing and quenching, the more conventional method to produce martensitic plate steels. Two different direct quench processing routes, conventional controlled rolling and recrystallization controlled rolling, with variations in the amount of final rolling reduction were investigated with two of the alloys. The third alloy was processed through reaustenitizing and quenching. The microstructures were quantified using light optical microscopy, scanning electron microscopy, and electron backscattered diffraction and correlated with tensile test results to assess the strengthening mechanisms in each of the conditions. The strength of the DQ steels was similar and matched that of the reaustenitized and quenched steel. It was found that the martensite block size was constant across the experimental conditions, and might play a major role in strengthening the DQ plates.