摘要:

AbstractThere is a significant commitment by industry to understand the mechanism of the silicon induced modification of the Fe–Zn coating during batch galvanising. Considerable emphasis has been placed on solving this problem through investigation of substrate surface treatment. This article reviews pertinent literature dealing with surface effects associated with galvanising of silicon containing steels. Relevant observations were grouped together to help to establish the influence of crystallographic orientation, subsurface oxidation, strain energy, and topography on the formation of a reactive coating. This includes a critical discussion of the major factors and their interaction with thermodynamic instabilities informing reactive structure. It was found from the literature that subsurface oxidation and topographical effects had the greatest influence on the silicon reactivity phenomenon. However, these observations do not directly lead to economically viable solutions to the problem.MST/1173

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.8.681

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractThe thermodynamic properties and the phase diagram of the Nb–C system have been assessed using thermodynamic models for the Gibbs energy of all the stable phases. An optimum set of thermodynamic parameters reproducing consistently most of the available experimental information has been obtained.MST/1153

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.8.687

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractThe aging behaviour of quenched Zn–Al alloys containing small additions of copper was studied using metallography, hardness measurements, and quantitative X-ray diffraction. The kinetics of decomposition of supersaturatedα/α′andβphases were determined and related to structural changes. It was found that the Avrami or Johnson–Mehl equation may be used to analyse the kinetics of decomposition ofβphase with an acceptable degree of accuracy. However, the kinetics of zinc formation were more complex and did not obey any known rate equation.MST/1082

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.8.695

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractThe superplastic behaviour of nickel based superalloy NK17CDAT( Astroloy) has been studied using torsion testing. The evolutions of stress and average grain size are found to follow the same classical behaviour as other nickel based alloys under similar conditions. The superplastic flow is characterised by a strain rate sensitivity exponent of 0·5 and a grain size sensitivity exponent of 3. Modelling of this alloy can be considered using a combination of microscopic mechanisms, namely, those of Gittus, Coble, and dislocation glide–climb.MST/1135

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.8.705

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractThe microstructural evolution in (2–15)Cr–2W–0·1C (wt-%) firritic steels after quenching, tempering, and subsequent prolonged aging was investigated, using mainly transmission electron microscopy. The steels examined were low induced radioactivation ferritic steels for fusion reactor structures. With increasing Cr concentration, the matrix phase changed from bainite to martensite and a dual phase of martensite andδferrite. During tempering, homogeneous precipitation of fine W2C rich carbides occurred in bainite and martensite, causing secondary hardening between 673 and 823 K. With increasing tempering temperature, dislocation density decreased and carbides had a tendency to precipitate preferentially along interfaces such as bainite or martensite subgrain boundaries. During aging at high temperature, carbides increased in size and carbide reaction from W2C and M6C to stable M23C6occurred. No carbide formed inδferrite. The precipitation sequence of carbides was analogous to that in conventional Cr–Mo steels.MST/1049

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.8.714

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractThe effect of boron on the hardenability of steels depends on the contents of such elements as aluminium, titanium, nitrogen, and boron and on the austenitising temperature. An attempt has been made to calculate the solubility of boron in the presence of aluminium, titanium, and nitrogen in steels. Three systems, Ti–B–Al–N, Ti–B–N, and B–N, were derived according to the thermodynamic state of each steel and the soluble boron contents were calculated. It was found that the maximum boron factor was achieved at 0·0004–0·0005% soluble boron. The fact that aluminium content in the range 0·018–0·050 wt-% investigated in this study has little effect on the boron hardenability factor can be explained from the results of the thermodynamic calculation.MST/1025

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.8.724

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractThe evolution of dislocation structure in a quenched and tempered low carbon alloy steel with increasing number of fatigue cycles has been investigated using transmission electron microscopy. The changes in dislocation structure can be divided into three stages: the production of the dislocation structure having fatigue features, the formation of microscopic fatigue slip bands, and the initiation and propagation of wide fatigue deformation bands. Microscopic fatigue cracks are formed during the propagation of these bands.MST/1037

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.8.731

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractThe influences of thermal aging and environment on Paris-Erdogan regime fatigue crack growth rates and mechanisms in a high strength Cr–Ni steel (300M) have been investigated. Crack growth rates were measured in inert (vacuum) and aggressive (hydrogen) environments, for quenched and tempered material before and after thermal aging at 500°C. Aging induced an acceleration of crack growth in vacuum at low values of∆K, but a retardation at high values of∆K. The crack path was transgranular throughout, and followed carbide/matrix interfaces. These effects were associated with the embrittlement of carbide/matrix interfaces by phosphorus segregation, which facilitated transgranular crack growth at low∆K, but produced crack tip shielding by voids surrounding the crack at high∆K. Hydrogen acted synergistically with phosphorus to embrittle carbide/matrix interfaces, but it also localised slip deformation at crack tips, reducing void formation in surrounding material and associated crack tip shielding. This produced an enhancement of crack growth rates at all values of∆K significantly above the threshold regime. The role of carbide/matrix interface embrittlement constitutes a third mechanism of hydrogen embrittlement and temper embrittlement interaction in fatigue crack growth, additional to those of carbide precipitation and grain boundary embrittlement previously reported.MST/1142

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.8.735

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractThe high nitrogen 20Cr–10Ni–0·7N austenitic stainless steels were produced in a high pressure induction furnace and their hot workability was investigated. The results of torsion and drop hammer tests showed that the optimum temperature range for hot working was from 1350 to 1523 K, suggesting the difficulty in hot rolling. The precipitation of nitrides, which reduced the ductility; occurred below 1350 K. However, calcium treatment or reducing the oxygen and sulphur contents resulted in a marked improvement in hot workability and made hot rolling possible in these high nitrogen stainless steels.MST/1102

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.8.743

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractRapidly solidified Al–5Cr–2Zr, Al–6·43Cr–1·67Zr, and Al–4Cr–1Fe alloy powders were processed using cold compaction and hot extrusion. It was found that the iron containing alloy was more easily extruded than the zirconium containing alloys, and this was attributed to phase transformations occurring during deformation of the latter. By obtaining extrudates in the form of rectangular bars, mechanical properties could be studied for both the transverse and the longitudinal directions. Compared with the longitudinal direction, no significant decrease of strength was detected in the transverse direction for any of the alloys, whereas significant decreases of ductility were recorded, especially for Al–6·43Cr–1·67Zr alloy. Fracture was observed to occur along primary powder particle boundaries. The relationship between microstructure and mechanical properties was also investigated. Compared with the addition of iron, it was found that additions of zirconium are more beneficial in that they promote formation of fine intermetallic phases. In addition, between the Al–Cr–Zr alloys, a reduction of chromium content yields a more homogenous and fine microstructure, which combined with the beneficial effects of increased additions of zirconium results in superior properties.MST/1118

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.8.749

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor