摘要:

AbstractThe main features of the stress-corrosion failure of glass-reinforced plastic tanks and vessels are described. Model experiments using a modified double cantilever beam test have been made on aligned composite materials tested in 0·6M HCI. The rate of crack growth normal to the fibre direction depends on stress intensity. The crack-tip fracture processes for cracks growing in the velocity range 10−9to 2×10−8m S−lhave been determined using fractographic techniques. The stresses in the fibres before fracture at the crack tip have been estimated from the size of the mirror zones. A major feature of stress corrosion is the planar nature of the crack surface and, at low stress intensities, fracture occurs without interface cracking or debonding. An estimate of the strain energy release rate has been made from an analysis of the stress fields at the crack tip and the mechanisms of crack growth. The results are in reasonably good agreement with experimentally determined values.MST/64

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.3.177

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractThe mechanisms responsible for strengthening a series of high-strength cold-rolled steels with tensile strengths up to 800 MN m−2have been investigated. The magnitude of precipitation strengthening in the annealed steels is shown to be in agreement with the Orowan-Ashby model for non-deforming particles. Strengthening depends only upon the volume fraction and diameter of the precipitates, and is not influenced by their chemical composition, nor by whether the precipitation-hardening elements are added singly or in combination. Manganese alone is a weak solid-solution-strengthening agent, but has a synergistic effect in combination with titanium or niobium, which is attributed to its depression of the austenite-ferrite transformation and precipitation temperatures. Vanadium is a much less efficient strengthening element than titanium or niobium in annealed steel, owing to the rapid coarsening rate of vanadium carbonitride precipitates and the considerable loss in strength on processing from hot-rolled coil to annealed sheet. Sulphur acts to reduce the strength of the annealed steels and tends to coarsen the grain structure. The physical basis of this effect is not known, but it is suggested that it may be associated with the partial solution of managanese sulphide during slab reheating and its subsequent re-precipitation during hot rolling. Phosphorus and nitrogen are the most efficient strengthening agents up to tensile strengths of 450 MN m−2, but stronger materials require a combination of strengthening modes, depending upon the application.MST/111

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.3.183

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractThe effect of cooling from temperatures in the range 1100-1400°C at 2 K min−1and air cooling on the overheating behaviour of a low-alloy Ni–Cr–Mo steel (A 508 Class 2) containing ~ 10 ppm S at two levels of manganese, i.e. 0.01 and 0·2 wt-% is described. A third steel which contained 80 ppm S and 0·2 wt-%Mn was also investigated. The results show that by decreasing the levels of manganese and sulphur the tendency to overheating can be reduced. However, unless the levels of aluminium and nitrogen are also controlled in the high-purity steel, high-temperature treatments lead to an even greater decrease in toughness as a result of the precipitation of AIN on the prior austenite grain boundaries. By increasing the manganese content, which has been found to lower the solubility temperature of A IN, and/or by air cooling from the high preheat temperatures, any deleterious effects caused by the precipitation of AIN may be reduced. In the steel of high sulphur content, intergranular fracture was observed after heat treating at temperatures above 1250°C. Manganese sulphides were identified on the intergranular facets. A decrease in toughness for this steel occurred after cooling at 2 K min−1from the highest preheat temperatures; this decrease appears to be related to the rod-shaped morphology of the sulphides.MST/137

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.3.192

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractA study has been made of the susceptibility to hydrogen attack of a newly developed 3Cr–1 Mo–1Ni pressure-vessel steel, intended for use in coal-conversion vessels, following long-term exposure to high-pressure (14-17 MPa) gaseous hydrogen at 550 and 600°C; the results are compared to the behaviour of 2·25Cr–1Mo steel. To simulate the condition of both surface and mid-section locations of thick-section (400 mm) plate during commercial normalizing, oil quenched and slowly cooled (8 K min−1) structures were examined after tempering at 650 and 700°C, with respect to their strength, ductility, and impact toughness properties. Compared to unexposed samples, structures exposed to hydrogen were observed to show some softening (up to 20% reduction in yield stress) and‘embrittlement’(up to 22% reduction in upper-shelf Charpy energies and increases in the transition temperatures by 65–100 K), although there were no visible signs of major microstructural damage. Moreover, the behaviour of the oil-quenched and slow-cooled structures was largely similar. In comparison to 2·25Cr–1 Mo steel, which can become highly susceptible to hydrogen damage in the very slowly cooled state, the present 3Cr–1Mo–1Ni steel was found to have far superior resistance to hydrogen attack. This was attributed primarily to two factors: namely, the increased hardenability, which resulted from the absence of pro-eutectoid ferrite in as-cooled microstructures, and the accelerated kinetics in the carbide precipitation sequence, which resulted in the more rapid replacement of M3C by more stable, higher-alloyed carbides, such as M23C6.MST/95

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.3.198

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractThe deformation behaviour of Cu–P alloys has been investigated by torsion and tensile testing over a range of strain rates and temperatures. The torsion flow curves are interpreted in terms of dynamic softening processes, and the curves obtained during interrupted testing are used to examine static-restoration behaviour. Constitutive equations relating flow strength to strain rate and temperature are deduced, with allowance made for the effect of deformation heating, and implications of the equation constants are discussed. It is shown from tensile results that a state of superplasticity can be achieved in alloys containing 3·8 and 6·8 wt-%P. Superplasticity can occur only if the smallαgrain size is stable and if the temperature and strain rate fall within certain limits. The activation energy associated with superplastic flow has been determined.MST/52

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.3.209

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractTransmission electron microscopy studies have been carried out on the structures of chips formed during the high-speed machining of steel. The chip bodies, which reached temperatures of ~300°C during machining, had a pearlitic-ferritic structure with very fine, elongated, parallel-sided ferrite cells. The structure of the flow zone, which attained a maximum temperature of ~900°C, consisted, in all cases, of equiaxed ferritic cells, 0·5–1·5μm dia., with dislocation tangles in many cell boundaries, but few internal dislocations. No pearlite was observed in the flow zone, but initially pearlitic areas showed cementite networks at cell boundaries and very small cementite particles. Coarse cementite particles in spheroidized steel remained largely intact in the flow zone. Textures developed in the flow zone and in the chip body were ferrite shear textures. The flow zone is a thermoplastic instability, and this work suggests that the observed fine, equiaxed cell structures have the characteristic of permitting unlimited strain in thermoplastic instabilities in steel, and probably also in other metals and alloys.MST/105

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.3.220

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractThe interfacial structures between 2·25Cr–1Mo steel and Inconel 182 weld metal have been studied after post-weld heat treatments (PWHTs) at 700°C and subsequent aging at 630°C. This aging temperature accelerates the changes in interfacial structure that occur during power-station operation, and thus provides a method of studying the effects of the initial PWHT. The paper shows that during PWHT for≤8 h at 700°C, arrays of carbide particles develop in the ferritic steel, parallel and very close to the weld metal interface, and that these arrays continue to grow during aging at 630°C for 6000 h. However, the precipitate sizes after PWHT are small compared with those developed during the subsequent aging. For longer heat treatments, up to 100 h at 700°C, the I interfacial precipitates develop to significant sizes, but growth then ceases because of the limited carbon migration from the 2·25Cr–1Mo steel. Aging at 630°C then causes carbon redistribution in the heat-affected zone, resulting in an incubation period before further interfacial precipitate growth can occur. The net result is that after aging for≥500 h at 630°C, PWHTs of 2–100 h at 700°C have negligible effects on the interfacial-precipitate sizes and distributions, compared with those found in similarly aged as-welded specimens.MST/119

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.3.227

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractThe microstructure and mechanical properties of a single-bead ferritic weld metal were studied in the as-welded and artificially strain-aged condition. It was found that the phenomena by which artificial strain aging increases hardness and strength, but decreases toughness, are caused by an increased dislocation density and the formation of precipitates at dislocations within the ferrite grains. These differences on a submicrometre scale are responsible for the observed changes in mechanical properties upon strain aging the ferritic weld metal.MST/123

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.3.234

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractAs the number of layers on multilayer printed-circuit boards increases, the interlayer bonding requirements become progressively more stringent. One way of easing interlayer stresses is to reduce the preheat-soldering temperature interval. To do this by raising the preheat temperature is damaging to both board and components, and one alternative is to choose a solder alloy with a lower melting point than conventional Sn-Pb solders. In this paper, a study is described of the wetting characteristics of a range of near-eutectic Sn-Bi alloys, whose melting points fall near 139°C, ~46 K lower than Sn-Pb solders, making possible a reduction of 55 K in soldering temperature. The effect of divergence of composition from the 42Sn-58Bi eutectic composition on wetting, wetting speed, and spread area is described for two flux systems on plain copper, immersiontinned copper, and palladium-coated substrates. Additionally, the effects of various impurity levels of Sb, As, Cu, Fe, Pb, Ni, and Pd on solderability are investigated, the type of defects which each produces being listed. Some difficulties involved in contamination investigations on Al and S are also discussed. Finally, the effects of these impurities on Sn-Pb and Sn-Bi eutectic solder alloys are compared.MST/88

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.3.240

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.3.249

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor