摘要:

AbstractThe present state of understanding of surface cracking in low C low alloy steel slabs in the continuous casting (CC) and direct rolling (DR) processes is outlined. Hot cracking of the CC slab surface can be explained in terms of carbide and/or nitride precipitation behaviour. In addition toγgrain boundary precipitation, the matrix strengthening owing to dynamic precipitation and the existence of softer layers along the boundaries such as grain boundary allotriomorphs of ferrite or precipitate free zones play animportant role in intergranular ductile fracture. The origin of hot cracking during the DR process lies also in the precipitation of carbides and/or nitrides, and is not related to the severe embrittlement caused by a similar mechanism with dynamic precipitation of sulphides, which is observed usually in the high strain rate deformation after reheating at higher temperatures. Furthermore, a well known effect of C on hot cracking susceptibility in both CC and DR processes, attaining a maximum in the range 0·10–0·15 wt.–%C, is found to arise mainly fromγgrain growth during solidification in the mould. Some methods to prevent surface cracking are also discussed.MST/1226

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.9.793

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractThe ideas of the electron theory of chemisorption are applied to the behaviour of H, B, C, N, and 0 atoms segregated on and in iron. The general theory can be divided naturally into two branches depending on whether the valence levels of the embedded atoms‘float’at the Fermi level, as in the case of B, C, and N; or‘sink’to a level below the bottom of the d band, as with Hand O. In the former, the valence states take on the cationic role when they hybridise with nearby d states and a predominantly covalent bond is formed, which increases grain boundary cohesion. In the latter, the atoms form screened negative ions, with little covalent interaction, and thereby decrease cohesion, so promoting intergranular brittleness.MST/1267

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.9.806

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractA theoretical model has been developed to describe the grain growth process during recrystallisation of metals. The theory has been tested on various experimental results presented previously in the literature. It has been found that the effect of grain orientation and the effect of alloying elements on the process can be explained by the new theory.MST/1120

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.9.811

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractHot deformation within the steady state regime of commercial purity aluminium has been carried out under wide ranges of deformation parameters: temperature, strain, and strain rate. The microstructure developed after deformation exhibited dynamically formed grains having volume fraction increasing with strain and of size inversely dependent on flow stress. The effects of the parameters of deformation and of the annealing temperature after deformation on statically recrystallised grain size and on the rate of grain boundary migration during recrystallisation were studied and can be satisfactorily described by equations in which each of the variables is considered to act independently. The effects of the deformation parameters on the grafnsize produced after static recrystallisation are interpreted in terms of their influence on the number of dynamically formed grains that can act as pre-existing nuclei. A decrease in the final recrystallised grain size with an increase in annealing temperature, which may be related to the number of dynamically formed grains that become viable nuclei, was observed. The growth rate during recrystallisation was found to decrease with increasing time, probably as a result of the distribution of stored energy within the deformed structure.MST/1169

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.9.819

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractThe precipitation hardening behaviour owing to orderedδ′Al3Li in an Al–3Li–12Si–3Mg (wt-%) based alloy was investigated during aging between room temperature and 523 K after quenching from between 723 and 823 K. The induced radioactivity level of this alloy is very low, suitable for fusion reactor structures. Effects of aging temperature, solutionising temperature, and pretreatments on precipitation hardening were examined in detail. Tensile properties were also examined in the as quenched condition as a function of testing temperature between room temperature and 673 K. Yield stress exhibited a positive temperature dependence between room temperature and 523 K and decreased abruptly above 523k with increasing test temperature. The precipitation behaviour ofδ′and the strengthening mechanisms owing toδ′were discussed.MST/1100

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.9.829

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractPrecipitation of NbC inferrite has been examined in a low C (0·03 wt-%) steel in which the austenite-ferrite transformation kinetics has been slowed down substantially by the combined addition of 2%Mn and 4%Cr. This has enabled the carbide precipitation sequence at 700°C to be defined more precisely, starting with precipitation on dislocations, followed by interphase precipitation and, finally, carbide free ferrite. At 650°C the formation at theγ/αinterface of V-shaped carbides and also the growth of carbide fibres have been related to the morphology of the interfaces. The retardation of theγ–αtransformation by alloying additions encouraged the growth of these alternative carbide morphologies.MST/1158

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.9.838

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractThe low temperature mechanical properties of 0·4C–Cr–Mo–Ni steel can be improved significantly by thefollowing treatments. Modified oil quenching (MOQ): interrupt quenching at 573 K just below the martensitic transformation temperature followed by short time tempering at 673 K (up-quenching) before oil quenching and subsequently 473 K tempering (after conventional 1133 K austenitisation). Modified austempering (MA): the same up-quenching treatment followed by austempering at 673 K and subsequently water cooling. Each modified treatment was compared with its corresponding conventional treatment. The MOQ treatment significantly improved the notched tensile strength of the steel with slightly increased 0·2%PS and UTS, owing to an increase infracture ductility over the temperature range 123–203 K and also improved the Charpy impact energy of the steel over the temperature range 203–373 K. As a result of the MA treatment, the 0·2%PS and UTS and the notched tensile strength were developed remarkably with little change of fracture ductility over the temperature range 123–293 K. This treatment also improved the Charpy impact energy of the steel over the temperature range 203–293 K. The beneficial effect of the modified heat treatments on the mechanical properties is briefly discussed in terms of a modified law of mixtures, fibre loading theory, and fracture profiles.MST/1157

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.9.843

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractThe fracture behaviour and JIcfracture toughness of a commercial Al–Zn–Mg–Cu alloy plate has been investigated. Based on the experimental results and available theoretical analyses, the following results were obtained. Secondary grain boundary cracks appeared ahead of the main crack, which served as a triggering mechanism for small scale shearing. Shear failure facets on the fracture surface of single edge notched bend specimens represent the same type of fracture as the fast shear failure that occurred during tensile tests on notched specimens. The grain boundary cracking–small scale shearing mechanism is essentially a type of shielding event that not only makes the fracture appearance obviously anisotropic, but also, to a considerable extent, accounts for the strong anisotropy of fracture toughness.MST/1111

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.9.850

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractThe relationship between microstructure and mechanical properties of composites of squeeze cast Al–Cu and Al–Cu–Mg reinforced with 25 vol.-%SiC whiskers was investigated. Tensile test results were compared with values calculated using a modified rule of mixtures (ROM). The results were found to be in good agreement for the Al–Cu matrix composite, whereas a relatively large discrepancy was observed for the Al–Cu–Mg matrix composite. It was concluded from microstructural observations that this difference resulted from a reduction of the whisker strength due to more pronounced decoration of the interfaces by oxides and spinels. For the Al–Cu–Mg composite, the effect of interfacial phases on the composite strength must betaken into account when the modified ROM is applied.MST/1242

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.9.857

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractOver seventy compounds of transition metals with B group elements were prepared and oxidised in air to determine the temperature for a weight increase of 1mg cm−1over 4 h, which is a measure of the onset of terminal oxidation and has been designated Tp. A vast majority of the compounds was found to be highly resistant to thermal oxidation and to be stable up to temperatures of the order of their melting point. The results have been classified using the concept of a periodic table divide and its associated zone of influence.MST/1228

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.9.863

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor