摘要:

AbstractThe relationships between hardness and the volume fraction of martensite for continuously cooled steels containing 0·1–0·3%C, 1·6%Mn, 0–0·3% V (all wt-%), which are used to measure the hardenability expressed by the ideal critical diameter, have been established. It has been shown that for steels transformed to a fine mixture of lath martensite and lath bainite it is not possible to measure the volume fraction of martensite by means of quantitative optical metallography and therefore the volume fraction of martensite was determined from dilatometric records of continuously cooled specimens. The continuous cooling transformation diagrams were determined and microstructures of the dilatometric specimens were examined by optical and transmission electron microscopy. The values of the 50% martensite hardness established for the steels containing vanadium were found to be outside the range given by the widely used Hodge and Orehoski relationship. The relevance of the results to the assessment of hardenability by means of the ideal critical diameter concept is discussed.MST/484

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.11.1016

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.11.1065

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractA study has been made of the effect of thermal spiking on the strength and thermomechanical behaviour of Fibredux 914C/T300 and Fibredux 914C/XAS carbon fibre reinforced plastic materials. The unidirectional material was aged in a hot humid atmosphere before thermally spiking up to 130°C. The thermomechanical behaviour was measured using the torsion pendulum technique and interlaminar shear, compression, and transverse tensile tests at room temperature and 120°C. Shear strength was measured by short beam bending. The static and dynamic values obtained were found to be independent of the spiking cycle but strongly dependent on the amount of absorbed moisture. At the test temperature of 120°C, the interlaminar shear strength slightly decreased as spiking was done at 130°C. Microcracking and/or some unknown effects could be responsible for the observed small decrease in interlaminar shear values.MST/432

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.11.1081

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractExisting models for plastic hole growth have been re-evaluated in terms of their applicability to superplastic flow. The Cocks and Ashby model is modified to include more properly the effect of void shape, and the effect of simultaneous strain hardening is also discussed. Some new experimental data on the growth of artificial holes drilled in a sheet sample of Coronze 638 are presented and compared with data on the development of general cavitation damage in the same material without artificial holes. The difference between the two sets of results is explained in terms of a coalescence effect during general damage. Cavitation rates are found to be independent of strain in both sets of experiments. This result is explained by including the effect of strain hardening (brought about by strain enhanced grain growth) in the models.MST/461

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.11.1086

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractNecking development and fracture strain of superplastic material under tensile load are analysed by introducing a model of cavity growth into the long wavelength approximation analysis which can describe the external neck development of specimens during deformation. The results show that both strain rate sensitivity m and cavity growth rateηhave an important influence on the fracture strain of superplastic material. According to these results, a fracture diagram is presented in m–ηcoordinates, which is divided into three: a region in which material fails by macroscopic external necking, a region where cavity growth is predominant leading to fracture without pronounced external necking, and an intermediate region where both fracture modes occur. The prediction of fracture strain for various superplastic alloys exhibiting cavity growth during deformation is in good agreement with experimental results. The present analysis thus enables quantitative prediction of the effects of both strain rate sensitivity and cavity growth on superplastic fracture under uniaxial tension.MST/491

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.11.1093

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractThe influence of grain size on the hot ducility of microalloyed steels (C–Mn–Al, C–Mn–V–Al, and C–Mn–Nb–Al) has been determined by heating them above their solution temperatures and cooling to the test temperature of 850°C. The C–Mn–Al steel showed excellent hot ductility which was independent of grain size. Dynamic recrystallization readily occurred and there was no evidence for AlN precipitation. Marked dynamic precipitation occurred during the tensile test for vanadium- and niobium-containing steels but this did not vary significantly with reheating temperature, provided complete dissolution of the precipitates had occurred. Isolating the influence of grain size from that of precipitation in these steels showed that a change in grain size from 150 to 300μm reduced the reduction of area values by 15–20%. Precipitate distribution was also varied by heating to temperatures in the range 850–1330°C and tensile testing at 850°C. When present before testing at theγgrain boundaries in the form of a fine grain-refining precipitate, AlN reduced the hot ductility in the C–Mn–Al steel and delayed the onset of dynamic recrystallization. Coarser precipitates produced by raising the reheating temperature allowing dynamic recrystallization to occur gave improved ductility. For the niobium- and vanadium-containing steels, precipitate distributions which were in a coarse randomly precipitated form gave the best hot ductility. These occurred with the niobium-containing steel when heated to 1100°C and more generally in the vanadium-containing steel throughout a wide temperature range. The worst precipitate distribution occurred in the niobium containing steel when the NbCN was taken into solution before testing and reprecipitated in a fine form at theγgrain boundaries and within the matrix during the test.MST/490

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.11.1099

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractHigh-strength steels offer fuel savings in automotive components through weight reduction and when high strength is achieved in low-alloy steels, an economical material is produced, suitable for a wide range of applications.‘Formable and strengthenable’(FS) steels have been developed as an alternative to present high-strength low-alloy (HSLA) steels, and are produced in a manner different from the conventional alloys. The FS steel is formed in the soft, fully annealed condition, and the final strength is developed by a nitriding heat treatment. The present paper describes the microstructure and properties of an FS steel containing titanium as the nitride-forming element. Annealed and nitrided Fe–Ti alloys are extremely hard and brittle but cold working before nitriding greatly improves ductility. The replacement of boundaries on cold working by a fine subcell structure eliminates embrittlement, and added strength is obtained by the stabilization of the cell structure by Ti–N clusters or TiN particles. Cold worked and nitrided alloys have a microstructure which varies with depth from the nitrided surface into the component, producing a complex structure which prevents detailed analysis of the strengthening process. However, the present work demonstrates the value of FS steels as a useful addition to the range of HSLA steels.MST/379

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.11.1106

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractCreep tests have been carried out at 600°C on type 316 pipe and bar material, some of which was pre-aged to accelerate metallurgical changes. Solute concentrations were assessed by determining the lattice parameters and analyzing extract solutions. A transient strain-induced strengthening of ~3×104h duration was observed for material containing>0·025 wt-% dissolved carbon before testing; this was ascribed to a Mo–C interaction which progressively pinned dislocations. When the transient had decayed, a steady creep rate was achieved. The transient strain induced strength could be eliminated by pre-aging to reduce the dissolved carbon, and this occurred more rapidly in finer-grained material. In the steady creep regime viscous drag was rate controlling, but the effect of dissolved molybdenum was observed to become saturated in the range 0·8–2·0%. There is some evidence that this was because molybdenum acts in conjunction with nitrogen in the steady creep regime.MST/489

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.11.1123

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractThe decomposition of deformed ferrite in a duplex stainless steel (U44L) has been examined using transmission electron microscopy. During annealing, austenite precipitation was extremely rapid and pinned the developing ferritic subgrain structure. Hence, the ferrite recrystallized via a continuous mechanism. Deformation of the ferrite, and to a lesser extent the austenite during growth/coarsening of the austenite, led to a‘secondary recovery’process. Subgrain coalescence, within the‘primary’ferrite subgrain structure and in the austenite particles, was observed after long term anneals: this process took place by the dissolution of the sub-boundaries formed during the secondary recovery process. In addition to the formation of austenite, M23C6,σ, and martensite were also observed.MST/311

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.11.1131

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractThe microstructures of two austenitic stainless steels after cathodic charging of hydrogen and room temperature out gassing have been examined in the transmission electron microscope. The charging and aging cycle results in a considerable degree of faulting and transformation toα′- andε-martensites. Although the extent of hydrogen induced transformation is atypical of the material behaviour after deformation at the same temperature, the morphology of the transformation products is similar. Observations have indicated that the surface cracking commonly encountered in austenitic stainless steels after cathodic hydrogen charging is associated primarily with the hydrogen inducedε-martensite. In an alloy which did not transform as a result of deformation, the defect structures resulting from prior cold work did not appreciably reduce the extent of faulting, twinning, andε-martensite formation after hydrogen charging and aging.MST/430

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.11.1140

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor