John J. Moore

Study of precipitation and growth of γ′ and dislocation structure in Inconel X-750

Abstract The precipitation of the γ′ (Ll 2 ) phase in Inconel X-750 has been studied in the 704–871°C ageing temperature range using transmission electron microscopy. The morphology of γ′ was observed to be cuboidal for all ageing temperatures, deviating from this only at long ageing times. The loss of coherency of γ′ precipitate occurred by nucleation of dislocation loops at and around the precipitate, interaction of dislocations at the interface, and the attraction of dislocations toward the particle/matrix interface.

Precipitation of M23C6 carbides in an aged Inconel X-750

Abstract A study was made of the precipitation of M23C6 carbides in Inconel X-750 aged in the temperature range of 704–871°C. Direct evidence was found that this precipitation occurred on grain boundaries, noncoherent twin boundaries, and dislocations.

Fabrication of formable metal-metal composites

Abstract Composite fabrication techniques were developed for the reinforcement of a precipitation-hardening aluminium alloy (Duralumin) with stainless steel and maraging steel and for the reinforcement of titanium alloys with high strength steel using an in situ ausforming (hot-cold working) operation. Both sheet and rod composites were produced using roll-bonding and hot-pressing techniques. Maximum permissible levels of rolling deformation in the direction of reinforcement were determined for these composites during both their fabrication and the subsequent rolling sequences using the previously developed formability criteria. Owing to the large difference in flow strengths between the Duralumin and steel reinforcement under the conditions of fabrication and cold rolling there was an upper limit of deformation achievable in the Al-steel composites. No such limit was found on using continuous “hot-cold”-rolling techniques for Ti-steel composites between the steel austenitizing temperature and 400°C. However, cold rolling of the Ti-steel composites was not possible because of the large difference in flow strengths between the matrix and reinforcement and the poorly sustained work-hardening rate of the ausformed steel reinforcement. Nevertheless, Al-steel and Ti-steel composites were produced which are capable of competing with the high strength light metals in terms of their specific strength and, at the same time, are capable of undergoing a certain amount of rolling deformation in the direction of reinforcement alignment.

Formability limits of metal-metal composites on rolling in the direction of fiber alignment

Abstract Hot-pressed composites were produced using superpure aluminum, a work-hardening aluminum alloy (7%MgAl) and a precipitation-hardening aluminum alloy (Duralumin) as matrix materials, each reinforced with wires of stainless steel, high carbon (0.9% C) steel, low carbon (0.2% C) steel and copper. The composites were deformed by cold rolling in the direction of wire alignment to determine the limit of reduction achievable prior to the onset of plastic instability of the reinforcement. In each case an increased strain to fracture was achieved with the composite compared with that of the reinforcement alone. A simplified model was developed to explain the increased formability of the composites which dependend on the relative flow strengths of the matrix and reinforcement and the rate of work hardening of the reinforcement.

Application of Plasma Technology in Iron and Steelmaking

The potential for the application of plasma technology in metal oxide reduction and in iron and steelmaking is outlined and discussed. Recent evolution and developments in the plasma-based reactors employed in the production of iron, steel, and ferroalloys have been reviewed; the current status is outlined in terms of process control, flexibility in the raw materials consumed, product quality, and energy conservation. The advantages and limitations of thermal plasma-based reactors have been critically outlined and their potential to seriously challenge the blast furnace/basic oxygen furnace steelmaking route is considered.

Evaluation of formable light metal-alloy steel composites

Abstract Al-steel and Ti-steel and rod composites were fabricated by hot-pressing or roll-bonding techniques in line with previously developed formability criteria for the production of formable metal-metal composites. The composite materials produced were in the form of roll-bonded laminates, hot-pressed sheet and roll-bonded rod composites. Each of these composite systems was evaluated with respect to the optimum fabrication process developed, the bond strength produced between the matrix and reinforcement, and the resultant mechanical properties. Precipitation-hardened aluminium alloy reinforced with either stainless steel or maraging steel and Ti 318 alloy reinforced with an ausforming (hot-cold worked) steel produced promising composite materials. Both these materials provided a range of mechanical properties which could compete with the high strength light metals.

Influence of inclusions and heat treated microstructure on hydrogen assisted fracture properties of aisi 316 stainless steel

Abstract An attempt has been made to assess the influence of nonmetallic inclusions and heat treated microstructure on hydrogen assisted cracking of AISI 316 austenitic steel. The steel obtained in two levels of cleanliness was given solution annealing treatment in the temperature range of 1173–1473 K, and additional sensitization treatment of 973 K for 26 hours. Hydrogen embrittlement of this steel has been studied by charging Charpy and Compact Tension specimens of ASTM specification, with hydrogen through cathodic polarization. It is found that hydrogen embrittlement susceptibility increases with the presence of large size inclusions, larger grain and sensitized microstructure.

In-Flight Plasma Reduction of Domestic Chromite

This paper explains the principle of the new sustained shockwave plasma (SSP) reactor, which achieves in-flight reduction of minerals. Initial research is described in which an open 40 kW SSP reactor is used to assess the feasibility of in-flight reduction of a low-grade, domestic chromite concentrate. The effect of feed and operating conditions are discussed and a reduction mechanism based on both conventional theory and conditions thought to exist within the sustained shockwave plasma is postulated. In conclusion, the ongoing research program at the Mineral Resources Research Center (MRRC) and the potential for plasma processing of minerals are outlined.

Application of thermodynamic and kinetic principles in the reduction of metal oxides by carbon in a plasma environment

The application of plasma technology to metal oxide reduction is discussed with reference to established thermodynamic and kinetic principles. ΔG°-T diagrams for the corresponding metal oxide, metal carbide, and C-CO reactions are presented and the important role played by thepCO/PCO2 ratio examined. On the basis of these theoretical considerations, supported by some earlier experimental results conducted on the reduction of iron and chromium oxide concentrates in the form of taconite and chromite by carbon within a plasma reactor, the tendency to form either elemental metals or carbides is discussed. It is also suggested that the reduction of taconite by carbon takes place in two stages within the plasma medium. In the first stage, ferric oxide is reduced to wustite by carbon, and in the second stage wustite is reduced to metal. It is also postulated that in the first stage of reduction, ferric oxide may also be reduced to wustite through an exchange reaction between ferric oxide and iron, without CO evolution. The rate controlling step for the first stage of taconite reduction is thought to lie at the gas/slag interface generated within the plasma environment, while the second stage of reduction is controlled by carbon gasification by CO2.

INFLUENCE OF AGE-TREATED FINE-SCALE MICROSTRUCTURE ON THE FRACTURE BEHAVIOUR OF INCONEL X-750

ABSTRACT Age-hardening nickel-base alloy Inconel X-750, which is used extensively in PWR and BWR components, has exhibited intergranular fracture under service conditions due to improper heat treatment. At present there seems to be no recognized standard aging treatment for this alloy, but the usual process is to use a triple heat treatment which comprises solution treatment at 1149°C/2 hours, air cool, + 843°C/24 hours, air cool, + 704°C/20 hours, air cool. The present study investigates the influence on the fracture behaviour of varying microstructural features produced by single aging between 704-871°C after solution annealing at 1075°C for two hours. Inconel X-750 obtained by electroslag refining has been subjected to single aging treatments ranging from 704 to 871°C for times of 2 hours to 200 hours. The fine-scale microstructures were well documented using optical microscopy, TEM and SEM. Fracture studies were carried out using notched charpy specimens given the treatment mentioned above and the fracture surfaces were examined using scanning electron microscopy.