摘要:

AbstractA 0·4C–Cr–Mo–Ni steel has been studied to determine the major microstructural factor controlling the plane strain fracture toughnessKIcof desulphurised ultrahigh strength steel and to develop a method to improve the fracture toughness. For desulphurised steel containing 0·002 wt-%S, intergranular failure occurred during the fracture toughness test, so that there was little difference between the values ofKIcfor the desulphurised steel and those for steel containing sulphur at the commercial level (0·016 wt-%). This is attributed to the‘overheating phenomenon’, in which manganese and sulphur, which are taken into solution in the hot rolling temperature range, segregate to the grain boundaries and reprecipitate there asfine MnS. Reheating at high austenitising temperature followed by rapid quenching significantly improved the fracture toughness, but it had a detrimental effect on strength and Charpy impact energy. The addition of 0·0061 wt-% Ca (Ca/S=3) in the desulphurised melt just after vacuum degassing modified the morphology of the inclusions from fine MnS precipitated along grain boundaries to spheroidised CaS and consequently significantly improved the fracture toughness. This beneficial effect is briefly discussed in terms of metallography, fractography, and the crack extension model in the fibrous mode.MST1212

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.2.97

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractThe effect of steel cleanness, core hardenability, and microstructure after carburising on bending fatigue strength is described for the standard steel grade SS 2506. Examination of the fatigue fracture surfaces revealed that initiation had occurred at the surface where an internally oxidised layer was present. Differences in the inclusion content were not a major cause of fatigue failure. The highest fatigue strength was obtained for the smallest grain size material, but the effect of grain size is small in comparison with the base composition. An explanation for the variation in fatigue strength between heats is given with reference to the difference in case depth and core hardenability, and their effect on the compressive residual stresses within the case. Optimum fatigue strength was achieved for the shortest case depth and a low core hardenability. The results indicate the importance of close control over these two parameters in producing the optimum fatigue strength.MST/1239

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.2.105

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractThe grain boundary segregation of P and C in Ni–20Cr (wt-%) was investigated using Auger electron spectroscopy for specimens aged in the temperature range 500–700°C after fracture by a tensile test inside an ultra high vacuum chamber. At the grain boundaries, C segregates first and then is partly displaced by P; on continued aging, precipitation and growth of carbides occurs. High P contents initiate the formation of Cr23C6instead ofCr7C3. The correlation of these processes with the tensile strength is demonstrated and their influence on the stress corrosion cracking in a slow strain rate test during charging with hydrogen is examined.MST/1195

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.2.111

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractA procedure for computer aided calculation of the distribution of microstructure and mechanical properties of steel parts is outlined. The microstructural constitution in a certain position is calculated from the local cooling rate, grain size, and chemical composition by the Creusot–Loire regression model. The variation of mechanical properties is predicted from the microstructure and cooling rate distributions and the steel composition by empirical models. In the general case, numerical methods, e.g. the finite element method, must be applied to calculate the cooling rate at different positions of steel parts having complex geometrical form. Reasonable expressions for the temperature dependency of thermal properties, i.e. heat capacity and heat conductivity, of low alloy steels have been evaluated from literature data. An approximate expression for the calculation of cooling rates for air cooling of bars of small dimensions is derived. The procedure is used to predict microstructure and hardness after hot rolling and air cooling of steel bars.MST/1182

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.2.118

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractThe effect of intermediate reheating during tube piercing and rolling was studied by means of laboratory simulation. This was done by allowing the samples to cool below the Ar3and Ar1temperatures during torsion testing before reheating and applying the final passes. In the simulation, the process was divided into high and low temperature stages, separated by the reheating stage. The tests were performed on a plain C–Mn and five microalloyed steels (four Ti–V and one Nb–V grade). It is shown that the most effective grain refinement is produced when the sample is cooled below the Ar1temperature before reheating, i.e. when an on-line normalising concept is used. The largest grain size decrease was produced in the C–Mn steel and the smallest in the Ti–V grades. To retain such grain refinement, static recrystallisation must be inhibited during subsequent processing. A disadvantage of on-line normalising is that it reduces the precipitation strengthening produced in the ferrite in microalloyed steels.MST/1255

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.2.129

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractThe experimental results of an investigation of a chemical (alloying) and a physical (deformation) method for refining the microstructure of duplex stainless steels are described. The chemical technique involves alloying with copper. When 3 wt-%Cu is added to a 30Cr–8Ni steel, it was found that the copper precipitation (which is more rapid than that of austenite) takes place with a multitwinned morphology. The subsequent ferrite–austenite transformation nucleated on the finely dispersed copper particles results in a fine, homogeneously distributed, twinned austenite morphology. Copper particles also helped the refinement of the austenite by pinning the interphase interfaces. Another way of refining the microstructure is through cold deformation. As quenched fully ferritic steel with 30%Cr and 8%Ni was cold rolled by various amounts and aged at temperatures below 1000°C. On aging, partial recovery preceded the austenite transformation and nucleation occurred mainly on subgrain boundaries, thus resulting in a refined microstructure.MST/1221

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.2.137

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractA mechanical and microstructural evaluation of a weld mock-up was carried out for the same Cr–Mo–V rotor steel used in Part 1 of this study. The weldment was a submerged arc weld processed by a commercial fabricator; the welding parameters and heat treatments were not made available. One of the objectives of this study was to determine whether stresses associated with welding a large rotor section played a significant role in the development of reheat cracking. It was found that a butter weld layer was deposited before the multipass full thickness weld. This procedure led to significant grain refinement at the heat affected zone of the base metal, yielding excellent impact properties relative to the rotor base material. This welding technique and the selection of filler metal of lower strength than the rotor material apparently contributed to the elimination of reheat cracking. The Charpy impact energies of the full thickness and butter welds were much greater than those of the rotor steel; however, temper embrittlement resulted when full thickness weld specimens were subjected to thermal aging at 538°C or step cooled from 593°C. A second objective was the evaluation of the joint strength and its microstructure stability after high temperature exposure. It was determined that improvement in the impact properties of the weldment was obtained at the expense of poor room temperature tensile strengths and inferior stress rupture properties. However, it was determined that the weld metal used had not been intended for service at the high temperature end of a high pressure rotor.MST/1235

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.2.147

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractThe interfacial behaviour of a SiC fibre/CaO–MgO–Al2O3–SiO2glass ceramic matrix composite has been assessed by examining the shear properties of the interface. The room temperature (RT) frictional stress was measured after 12–164 h exposure in air at temperatures in the range 700–900°C. Compared with the as fabricated condition, the results reveal that the RT frictional stress increased after heat treatment at these temperatures and after long holding times at temperature. The thermodynamics of SiC fibres heat treated in air over the same range of temperatures and times is discussed.MST/1341

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.2.155

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractThe mechanical behaviour and microstructural evolution during high temperature compression were investigated in pure nickel and boron doped Ni3Al. Flow behaviour and microstructural development indicate the occurrence of dynamic recrystallisation. In Ni3Al the recrystallised microstructure is a typical‘necklace’structure at low deformation temperatures, but a uniformly recrystallised structure at high deformation temperatures. Pure nickel revealed a uniform structure at all temperatures. The dislocation arrangement of the deformed structure in Ni3Al showed a tendency to cell formation, although dislocation free cells were seldom observed. Locally, the formation of ordered dislocation networks was evident. The nuclei of dynamically recrystallised grains were always found at or close to prior grain boundaries, but the dislocation arrangement suggests that nucleation does not necessarily occur by bulging of grain boundaries. The relationships between flow behaviour, recrystallisation kinetics, and grain size have been analysed according to standard concepts and reveal substantial differences between nickel and Ni3Al. The results indicate that there may be a transition from dislocation glide to superplastic flow at high temperatures.MST/1282

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.2.158

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractDuring thermomechanical processing of aluminium alloy sheets, a strong anisotropy develops resulting from the presence of preferred orientations in the metal due to hot and cold deformation and recrystallisation. To date, little attention has been paid to the formation of deformation textures during hot rolling in the absence of recrystallisation. Some results obtained on two different aluminium alloys having high stacking fault energy are presented. Textures measured after hot and cold rolling, starting from the same initial texture, are analysed in detail. By contrast with other work, it is first shown that the starting textures are neither random nor orthotropic and it is demonstrated that assuming orthotropic symmetry can lead to somewhat erroneous conclusions. The principal results of the texture analysis are: the texture strength increases with increasing temperature; the orientations are more uniformly distributed along theβfibre after hot rolling than after cold rolling; and there is a significant increase of the brass component with increasing temperature. None of the actual texture predictions is in complete agreement with all these experimental observations.MST/1284

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.2.167

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor