摘要:

AbstractThe influence of tempering temperature in the range 200–600°C on the monotonic and cyclic response of a high-strength, low–alloy steel used for haulage chains has been investigated. Static properties are little affected by tempering up to 400°C, with a small loss of strength arising from carbide coarsening. At higher tempering temperatures, dislocation annihilation is substantial and the strength falls markedly. On undergoing high–strain fatigue, the alloy exhibits cyclic softening at all tempering temperatures, but with a maximum of about 25% after a 400°C temper. The microstructural changes producing this are difficult to detect directly, but it is thought that dislocation unpinning has an important role. For tempering temperatures in excess of 400°C, the reduced softening can clearly be equated with a dislocation redistribution and the formation of cell substructure within the ferrite grains. Estimations of the magnitude of the various components of strength are made.MST/199

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.8.577

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractThe effect of 0·003–0·050 wt-%C additions on strain aging and carbide precipitation in batch-annealed aluminium–killed steels has been investigated. The low–carbon steels exhibited unusual strain–aging characteristics: steels containing 0·020–0·040 wt–%C strain aged at 160 but not at 50°C, whereas those containing 0.007–0·020 wt–%C aged at both temperatures. This behaviour is due to the presence of fine carbide particles, which form as a result of the supersaturation of carbon in the matrix during cooling and which raise the carbon solubility by the Thomson-Freundlich effect. Expressions are derived which give the carbon supersaturation as a function of temperature during cooling, and of the precipitation temperature of each class of carbide. Carbide precipitation alternates between the nucleation of new particles and the growth of existing ones, depending upon the particle spacing and the cooling rate. Strain aging in the 0·05 wt–%C steel is negligible up to 225°C, but then rises to a peak at 325°C, which has been attributed to effects of partition in the dislocation matrix.MST/141

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.8.583

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractThe effect of discrete operations during thermomechanical processing on the earing behaviour of two aluminium alloys (AA 5052 and AA 5454) has been investigated. In the homogenized condition AA 5454 contained a fine dispersoid distribution while AA 5052 was dispersoidfree. It was found that for the dispersoid-containing material the hot-rolling process was less dominant. Nevertheless, for both alloys the earing quality could be adjusted by suitable modifications to hot-rolling, cold-reduction, and annealing cycles. Pole-figure analysis indicated differences in hot-rolled texture caused by variations in processing, which became more significant as the total hot reduction was increased.MST/41

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.8.593

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractEnthalpy calculations, based on Miedema's model for alloy formation, show theδ–hydride (ZrH~1·6) to be the most stable hydride in the Zr–H system. Theγ–hydride (ZrH) is the least stable and, as suggested in the literature, is quite probably metastable. In addition, theε–hydride (ZrH2±x) is shown to be the last hydride formed in the Zr–H system. TiH1·38is shown to be the most stable hydride in the Ti–H system corresponding to theγ–hydride phase on the equilibrium phase diagram.MST/187

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.8.600

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.8.603

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractAn introduction from a customer's viewpoint is provided for a series of papers on the repair and refurbishment of superalloy components. The nature of superalloy components in use worldwide is used to demonstrate the size of the potential market for repair and the possible return for both the repairer and the user. The design features which make superalloy components expensive are illustrated. The considerations in determining the real value and cost effectiveness of a repair in terms of cost per operating hour are reviewed. Post–repair inspection requirements are often neglected. The importance of developing suitable inspection methods concurrently with the repair process so that maximum advantage can be taken in using it by ensuring the integrity of the repair parts is discussed. Similarly, the importance of demonstrating and maintaining process control in order to guarantee good repair where inspection is impractical is illustrated.MST/99

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.8.604

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractIn this paper, the different types of damage occurring in components of the hot section of gas turbines and the techniques used in their restoration are described. Brazing as a repair technique and its use on typical types of damage is discussed and illustrated. Welding is reported to be useful only when the damage is limited to small areas of blades or vanes, because of the composition of super alloys and the deformation caused by the local heat input. Brazing is discussed with respect to brittleness, erosion, corrosion resistance, and the size and shape of the defects to be repaired. Examples of slurry brazes are illustrated by pictures and micrographs and the parameters for such brazing are discussed briefly to show the interaction of brazing with the various steps in a repair and heat-treatment procedure.MST/100

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.8.608

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractRepair procedures for stationary gas–turbine blades, both established practices and techniques which have yet to find wide application, are described. Special attention is paid to quality assurance–making sure that repaired parts do not reduce reliability. Of the various repair techniques, only regenerative heat treatment (including hot isostatic pressing, or hipping) and recoating can be performed as standard procedures. Machining (e.g. grinding) changes the geometry of the blade and requires an exact knowledge of design tolerances. Straightening has to be done very carefully and should be followed by a hipping treatment. The greatest number of restrictions apply when fusion and deposition techniques such as brazing, welding, inserting, sintering, and plasma deposition are used. These techniques are used at present only if it is absolutely necessary to restore heavily worn blades.MST/101

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.8.613

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractThe design life for blades of large stationary gas turbines is at least 100000 h in creep terms. Typical damage occurring within the lifetime of gas-turbine blading may be hot corrosion and/or erosion, foreign-object damage, tip rubbing, and cracking caused by low-cycle fatigue, thermocycle fatigue, high-cycle fatigue, and creep crack growth. When applying refurbishing procedures both technical and economic aspects should be considered. The repair procedures available are welding, brazing, plasma spraying, recoating, combined with special heat treatment cycles, and occasionally intermediate hot isostatic pressing. The limiting factors for repair procedures are the mechanical properties and the hot corrosion behaviour of the refurbished parts. Examples are given of results from metallographic and laboratory tests on refurbished Kraftwerk Union (KWU) test specimens and blades in relation to the material, design, and stressing of the components. Typical examples of the refurbished parts are also presented. Service experience with refurbished blades in stationary gas turbines is limited at present. Therefore, KWU can only consider these procedures in the light of the growing knowledge of refurbishing processes and the operating experience of refurbished parts as well as the economic aspects.MST/102

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.8.620

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractThe general procedures for repairing aero gas-turbine hot-section components are described. A number of examples are given in order to illustrate particular repair processes: (i) the welding of nozzle guide vanes made from high–strength, nickelbase alloy, demonstrating the effect of microstructural refinement and welding techniques; (ii) the brazing of similar nozzle guide vanes, with emphasis on the advantages of using a halide cleaning process and of modifying the braze alloy by adding a powder having a composition close to that of the parent metal; (iii) the use of an improved coating system to upgrade components; (iv) the possibility of using MCr AlY coatings applied by low–pressure plasma spraying; and (v) hot isostatic pressing as a method of restoring creep life.MST/103

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.8.629

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor