摘要:

AbstractPhases formed by isothermal diffusion in the Al–Zn–Sn ternary system have been studied at 270, 280, and 290°C for the three couples (Zn–10Sn)–Al, (Zn–28Al)–Sn, and (Al–10Sn)–Zn. The present work completes an earlier study using direct together with differential thermal analysis, and provides better understanding of isothermal equilibria. Comparing the results allows different possible diffusion paths to be proposed, and microprobe analysis of phases in isothermal equilibrium gives detailed information on the Al–Zn–Sn phase diagram.MST/378

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.4.241

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractFerrite grain refinement by accelerated cooling has been studied in a carbon steel. The size of ferrite grains dαformed by continuous cooling transformation from polygonal austenite has been measured as a function of cooling rate and austenite grain size dγ. In the cooling rate range studied (q= 0·05–5 K s−1), dαwas found to be proportional to q−0·26dγ0·46. The mechanism of grain refinement by accelerated cooling is discussed, and it is shown that this occurs in the transformation where the ratio of nucleation to growth rate increases with a decrease in temperature. The austenite grain size dependence of ferrite grain size is shown to become progressively large as the nucleation mode changes from homogeneous to grain surface to edge to corner. A theoretical estimation of ferrite grain size formed by continuous cooling transformation was attempted on the basis of nucleation and growth rates. In the alloy studied, ferrite grain size was theoretically estimated to be proportional to q−0·17dγ0·33. This was in close agreement with the dependence obtained in the present experiment.MST/466

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.4.249

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractThe effects of manganese and silicon on the mechanical properties of the 5 wt-%Cr secondary hardening steel H-11 have been investigated. This steel normally contains about 0·5 wt-%Mn and 1wt-%Si. Two other steels were also considered, both identical to H-11, except that one contained no manganese and the other neither manganese nor silicon. The room temperature hardness and impact toughness were determined for the three steels for tempering temperatures ranging from 200 to 600°C. The results indicate that manganese has no influence on the tempering response or toughness of H-11, but that silicon significantly influences both.MST/506

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.4.256

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractThe mechanical properties of directly sintered T6 high-speed steel in the temperature range 20–600°C were generally comparable to those of concurrently heat-treated wrought material of similar composition. For the hardness range 860–940 HV30 macroscopic ductility was detected at 200°C and 450°C in the wrought and sintered materials, respectively; failure strains, however, did not exceed 2%. The value of Young's modulus dropped from ~240 to ~120 GNm−2as the temperature was raised to 600°C, yield strength dropped from 2·2 to 1·0 GNm−2, but the fracture strengths showed a maximum, ~2·1 GNm−2at ~400°C for the wrought steel and ~1·4 GNm−2at ~450°C for the sintered steel. Microcracking preceded yielding and/or failure and was mainly through carbides, which were generally below the critical size to cause catastrophic fracture. The second stage of the failure process involved the linking through the matrix of such microcracks until conditions for fast fracture were satisfied (stage three). A quantitative model for carbide cracking in high-speed steels is absent as is the correlation of fracture strength with fracture toughness via the critical defect size, since, for example, the failure originating zones in wrought samples identified by scanning electron microscopy were generally larger than those predicted by linear elastic fracture mechanics (LEFM). It is suggested that there may be some analogies between failure in monotonic loading of high-speed steels and of ceramics with small defects; the behaviour in fatigue of short cracks in alloys and microscopic crack growth in delayed fracture of ceramics where LEFM analyses developed as a result of studying artificial long cracks appear not to hold.MST/606

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.4.260

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractThe effects of microstructural variations arising from the casting conditions on the creep performance of alloy IN939 have been assessed in order to determine the structural features having the greatest influence on creep properties. The results of creep tests at 850°C show that while grain size has an effect, the dendrite spacing is a more significant parameter in influencing performance. In particular, the life-to-rupture was greatest in specimens with fine dendrites as a consequence of the improved ductility with this type of structure. Thus the optimum combination of creep properties was obtained for material with fairly coarse grain size (~1mm) and fine dendrites (~20μm). The structural changes associated with the various stages of the commercial heat treatment have been determined by optical metallography and electron microscopy of thin foils, and evidence has been found of dislocation bowing and shearing ofγ′particles in fractured creep specimens. The creep results are discussed in the context of the microstructural changes observed and the relevance of mechanisms of deformation involving dislocation–particle interactions.MST/537

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.4.268

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractThe development of texture during the cold rolling of Cu–12·5Ni and Cu–27Ni (wt-%) alloys has been studied using X-ray analysis and transmission electron microscopy (TEM). Pole figures and diffractometer intensity measurements from rolling sections confirm that the texture is of the‘copper’type, although the preferred orientation develops more slowly and is consequently less sharp than in the pure metal at equivalent strains. The microstructures were consistent with deformation by slip, no evidence of mechanical twinning being found despite the greater hardness of the alloys compared with copper. However, the presence of nickel in solid solution was found to alter the deformation sequence observed by TEM. Beyond 80% reduction (ε=2·0), the cell structure characteristic of deformed copper, both at low and high strains, was almost entirely replaced by an assembly of small, slightly elongated crystallites whose boundaries often lay at ~±35°to the rolling direction. Long microbands, associated with fine scale rippling in the optical microstructure, appeared after only ~90% reduction (ε=2·5), there being a much reduced tendency for such lamellae to group into transition bands than in copper. Compared with the pure metal, the macroscopic deformation of cupronickels thus proceeds more homogeneously, although larger orientation differences, e.g. of ~10;°, as measured by a precision convergent beam technique, existed between adjacent crystallites, adjacent microbands, and across crystallite/microband boundaries. Possible causes of these differences of behaviour in the alloys are discussed and related to the higher hardness and work hardening rates of Cu–Ni alloys.MST/499

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.4.275

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractThe structures after solution soaking of five copper-bearing alloys (two falling within the AA 2014 specification) have been examined and related to the structures after extrusion. Variations along the length and radially are documented, and it is shown that the indirect process yields a more homogeneous structure. The factors affecting peripheral recrystallization are discussed and it is shown that variations in the preheat practice, the extrusion mode and process parameters, and the container temperature may each be used as a means of producing the desired structure.MST/508

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.4.285

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractAn investigation has been undertaken into the relationships between surface roughness, surface heat transfer coefficients, and thermal stress and strain generated during the quenching of 30 mm thick steel plates in water. Variation in surface roughness influenced the length of the vapour blanket stage and the magnitude of the surface heat transfer coefficient during subsequent nucleate boiling. The latter increased as the surface became smoother, but the former was shorter at intermediate levels of roughness (400 grade) than with specimens that were either smoother (600 grade) or rougher (120 grade). The effect of variations in the duration of the vapour blanket stage had little effect on the residual strain at the end of the quench, although the increase in quenching rate during nucleate boiling produced by a decrease in the surface roughness significantly increased this strain at all points in the plate. In contrast, neither effect produced a significant change to the stress distribution at the end of the quench, which always showed a maximum tensile stress of about 300 MN m−2just below the surface and a maximum compressive stress of−200 MN m−2at the centre. The results indicate that minor damage to a component surface during the hardening of low-alloy steels will not cause serious modifications to the residual stress distribution, although significant and unexpected changes to the residual strain distribution might be produced by such effects. The removal of the vapour blanket aids the formation of martensite as opposed to decomposition products produced by diffusion processes. The results indicate that such a procedure would not seriously impair the residual stress distribution.MST/531

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.4.291

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractChip segmentation and the tool forces involved during cutting of hardened steel are discussed. AISI 4340 steel was machined on an engine lathe to study chip morphology, tool forces, and the surface generated. It was found that chip segmentation occurs when the hardness of the steel exceeds a certain value, and that the tool forces associated with chip segmentation are very high. A transformed layer of untempered martensite and retained austenite was produced when the cutting conditions were severe.MST/469

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.4.299

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractA three-dimensional axisymmetric model of the fluid flow and heat transfer in a laser-melted pool is developed. The model corresponds to the limiting case when the scanning velocity is small compared with the recirculating velocity. This model is also valid for spot welding. Non-dimensional forms of the governing equations are derived, from which four dimensionless parameters are obtained: the Marangoni number, the Prandtl number, the dimensionless melting temperature, and the radiation factor. Their effects and significance are discussed, and numerical solutions are obtained. The position and shape of the solid/liquid interface are obtained by an iterative scheme. The quantitative effects of the dimensionless parameters on pool shape are presented. In the presence of the flow field, the heat transfer becomes convection dominated. The effect of convection on isotherms within the molten pool is discussed, and experimental results are presented.MST/535

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.4.306

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor