摘要:

AbstractAn analysis is given of the factors that determine the energy levels of impurity atoms segregated to grain boundaries, taking iron as the exemplary host metal. For an interstitial atom the energy level can be estimated by either the embedded atom method or the tight binding method. The first of these, which is appropriate for electron acceptor impurities, weakens the boundary and leads to intergranular brittleness. The second, which is appropriate for atoms which bond covalently, strengthens the boundary. The same factors apply to substitutional atoms, but an additional effect here is the loss of the coherency contributions of those host atoms which are replaced in the boundary by their impurity substitutes. The effects of various impurities in iron are discussed in terms of these three factors.MST/1189

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.4.325

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractStatic strain aging in steel of approximately eutectoid composition has been investigated using tensile testing and transmission electron microscopy for material in both low prestrain and drawn conditions. Two dominant modes of strain aging have been identified: (a) a low temperature mechanism dependent on interstitial solute diffusion and (b) a pseudo recovery mechanism which operates above 150°C. In the low temperature range, there exists a microstructure dependent transition temperature below which the kinetics of aging obeys a t1/3relationship and above which a rate exponent of approximately 1/2 is obtained. This has been attributed to a change from planar solute diffusion to dissolution of cementite as the rate limiting process.MST/1067

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.4.331

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractThe effects of precipitates formed by the addition of vanadium, nitrogen, and aluminium on the strength and toughness in 0·15%C steels were studied by cooling suitable steels at varying rates from temperatures giving a constant austenite grain size. Yield strength increments resulting from precipitation were derived from the experimental results. Similar increments were produced by vanadium carbide (VC) and vanadium carbonitride (V(C,N)) and in each case a reduction in cooling rate resulted in reduced strengthening because of increased particle coarsening. In the presence of aluminium rather less strengthening was obtained from V(C,N) precipitates. No strengthening resulted from the presence of aluminium nitride (AIN) particles. When the carbon content of the steel is greatly in excess of the stoichiometric quantity, the carbonitride formed is relatively low in nitrogen and the yield strength increments caused by low nitrogen V(C,N) and VC are similar. Impact transition temperature increments resulting from precipitation were also derived from the experimental data. These showed that V(C,N) precipitates are less detrimental to transition temperatures than are VC precipitates giving comparable yield strength increments. Shelf energies were also reduced to a greater extent by VC than by V(C,N). The presence of AIN particles had little effect on shelf energy, but had a detrimental effect on transition temperature. The high nitrogen V(C,N) precipitates are less detrimental to both impact transition temperatures and upper shelf energies of the steels than are low nitrogen V(C,N) or VC precipitates. Removal of soluble nitrogen in the form of nitrides has been confirmed as a means of improving the toughness of steels. Aluminium has been found to be more effective than vanadium in the removal of soluble nitrogen.MST/935

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.4.338

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractHigh purity 0·4C–Cr–Mo–Ni structural steel has been studied to determine the effect ?f the transformation microstructure on fracture toughness J1cof quenched and highly tempered low alloy steels. Martensitic and bainitic steels having a wide variation in the prior austenite grain size were investigated. In martensitic or lower bainitic steel, ductile fracture occurs at the crack tip and J1cis determined by intercarbide spacing. In upper bainitic steel having packets composed of well define blocks, brittle fracture occurs and J1cis controlled by block Size. In fully ductile fracture, J1ccan be correlated with carbide cracking in the process zone by which microvoids are created. Crack initiation occurs by interconnection of the crack tip and the microvoids, which are situated a characteristic distance from the crack tip. In fully brittle fracture, J1ccan be correlated with unstable cleavage cracks initiated at the boundary of a minimum microstructural unit in the process zone. Crack extension occurs by the combined action of the cleavage cracks and the main crack.MST/1012

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.4.349

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractA time dependent permeation method has been used to measure the diffusivity, permeability, and solubility of hydrogen in hot rolled low carbon steels. The measurements cover the temperature range 200–600°C which includes the onset of hydrogen trapping effects. The results have been interpreted using Oriani's model to explain the effects of microstructure on the trapping. The results show that the initial microstructure of the steel affects significantly the behaviour of the hydrogen atoms. Of the three possible trapping sites, namely, dislocations, interstitial atoms, and precipitated particles, it seems that the most effective traps are the interfaces between coarse particles and the matrix.MST/973

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.4.357

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractThe corrosion of high temperature alloys in a gas mixture (Ar-25H2–10HCl–5CO–1CO2, vol.-%), which is oxidising to chromium and aluminium, but reducing to the base metal and containing a high concentration of hydrogen chloride, has been studied under isothermal and thermal cycling conditions. The rates of attack were fairly low with Al2O3forming alloys, which were more resistant to attack than Cr2O3forming alloys. There was relatively little metal loss during isothermal exposures at 900°C, but, in some alloys, there were significant depths of internal corrosion. Some volatile chlorides were formed following penetration of chlorine containing species through the oxide scale to the alloy substrate: FeCl2was the major volatile species detected. The extent of corrosion was increased by thermal cycling, as a result of further disruption of the protective oxide scales. The corrosion processes can be accounted for in terms of the effectiveness or otherwise of the oxide scale as a barrier between the alloy substrate and the environment.MST/882

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.4.364

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractThe effect of high cutting speed and feed rate on the surface integrity of AISI 4340 steel during a finishing turning operation was investigated. The experimental work involved the determination of residual stress distribution in the surface region, microhardness variation of the surface region, and the examination of surface and subsurface using both optical and scanning electron microscopy. The residual stresses were found to be compressive. The microhardness in the surface region varied little and was the same as that of the bulk material. In general, the appearance of the surface was similar to those reported for low cutting speeds as recommended for machining the same type of steel.MST/998

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.4.371

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractMathematical and water models were used to study the flow behaviour of the gas bubbles and the molten steel in gas stirred ladles with and without an immersion hood. The mathematical model is based on a computatioal fluid dynamics technique which can handle the interactive, two phase (gas–liquid) flow problems and which allows the top surface of the melt to fluctuate. The water model is 1/10 scale of a 150 ton steel ladle. Water, a plexiglass container, and helium gas substitute for molten steel, the refractory ladle, and argon gas, respectively, in the actual steel ladle. The mathematical model developed was first tested under the same conditions used in the water model. Results of the analyses, including bubble pathlines and melt flow patterns, showed very good consistency with observations from the water model. The mathematical model was then used to study the phenomena in the steel ladle operations. The results showed that the flow behaviour in the steel ladle was very similar to that in the water model. However, the flow patterns of the molten steel with and without the addition of an immersion hood were considerably different. It was shown that the immersion hood not only can provide slag free surface and protective atmosphere inside the hood, for which it was originally designed, but also can produce a more favourable flow pattern for the molten steel in the ladle.MST/1031

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.4.376

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractThe grain coarsened tensile properties in the heat affected zone (HAZ) of medium strength (Rp0·2⋍330–470 MN m−2) low carbon microalloyed, C–Mn, and 2·25Cr–1Mo steels have been examined using the weld simulation technique. Very high values of yield and tensile strength (Rp0·2>900 MN m−2; Rm>1100 MN m−2) can be obtained for low heat input welding (E<1 MJ m−1;∆t8/510 s), however, a substantial reduction in the values of Rp0·2and Rmoccurs, with the exception of the 2·25Cr–IMo steel. Based on the empirical equations developed, and the Suzuki BL70 hardness formula, it is shown that the grain coarsened HAZ yield and tensile strength can be calculated to an accuracy of±50 MN m−2, while elongation at fracture and reduction in area can be predicted to an accuracy of±3% and±7%, respectively.MST/I077

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.4.383

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractThe process parameters and weld dimensions in consumable nozzle electroslag welding were calculated using the two dimensional heat flow condition based on Eregin's concept. The weld metal dilution under these operating variables was also computed. Experiments revealed that calculated parameters produce sound welded joints and that there is fairly good agreement between the calculated and observed results.MST/1103

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.4.390

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor