摘要:

AbstractExperimental steels similar in composition to structural grades were prepared from weld metal deposits to study the formation of acicular ferrite under conditions experienced in the heat affected zone for a range of welding processes. The formation of acicular ferrite under these conditions is found to be dependent on the presence of a suitable distribution of oxide inclusions>0·4μm in size. The characteristics and proportion of acicular ferrite in the microstructure also depend on the prior austenite grain size and cooling rate. The relationship between these factors is presented in a simplified quantitative model, which is supported by data from limited welding trials. Metallographic observations suggest that acicular ferrite forms in two stages. The first involves the formation of relatively large primary acicular ferrite plates by multiple nucleation at intragranular inclusion sites, and the second involves the formation of many smaller acicular ferrite grains that grow sympathetically from the primary plates.MST/1027

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.11.1057

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractSintered and precipitation hardened Cu–25Cr (wt-%) contact alloys were prepared and their properties related to those of a precipitation and strain hardened reference alloy. The evolution of microstructure during sintering, solution heat treatment, and precipitation hardening was studied, in particular with respect to precipitate morphology and growth. The influence of microstructure on the hardness, strength, and electrical conductivity of Cu–25Cr alloys was evaluated. The relative importance of precipitation and strain hardening has been clarified, and it is shown that the contribution of the precipitation effect is dominant. The importance of monitoring the evolution of microstructure with respect to long term stability of Cu–Cr contact alloys is emphasised.MST/999

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.11.1069

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractMilled lead sheet exhibits a recrystallised microstructure, the grain size of which decreases with increasing copper content; copper is present as particles of ~1–5μm in length, formed from the initial needles or plates of the cast billet by spheroidisation, or by particle break-up during rolling. A comparison of materials produced by several manufacturers indicates that the copper distribution and final grain size are dependent on the thermomechanical history of the sheet. Direct method sheet exhibits a cast cellular structure within grains which usually extend through the full thickness of the cast sheet; copper is present as a fine dispersion (particles ~0·5μm dia.) at cell boundaries. The copper distribution in both materials was stable with prolonged heating (100 h at 200°C), but some grain growth occurred in the milled sheet. It was not possible to obtain a fully dispersed eutectic microstructure at the eutectic composition; primary lead dendrites (or cells) were always present. This is thought to be a result of the difficulty of nucleating a copper particle in the very low copper concentration alloys used in this work.MST/1065

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.11.1074

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractA new approach is suggested whereby the mechanical properties of commercially available 0·4C–Cr–Mo–Ni ultrahigh strength steel can be significantly improved whether the testing orientation is longitudinal or transverse. The new approach consists of combining the decreased hot rolling reduction treatment with a short time isothermal transformation treatment. This approach, compared with conventional heat treatment, resulted in significant improvements of the plane strain fracture toughness KIcat increased strength and of the Charpy V-notch impact energy, for either testing orientation. Steel treated using the new approach also had an improved combination of mechanical properties compared with steels treated using high austenitisation and controlled rolling, which are possible approaches to improving the values of KIcor other mechanical properties of steels. The favourable effect on the mechanical properties is discussed in terms of metallography, X-ray measurements, and fractography.MST/984

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.11.1084

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe micromechanisms of ductile fracture have been studied in a commercial AISI 316 austenitic stainless steel. Tensile, Charpy impact, and ductile fracture toughness testing have been performed on unaged material and samples aged at 700°C for times up to 4380 h. Examination of the specimens after testing has shown that the microstructural changes occurring at grain boundaries are responsible for the observed losses of ductility and crack growth resistance. The relative magnitude of the observed changes in mechanical properties has been explained using a simple model to describe the ductile fracture process.MST/1001

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.11.1090

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractWeld heat affected zone microstructures have been simulated in a niobium microalloyed C–Mn steel. These structures have been Charpy impact tested and examined metallographically. Troughs were observed in the plots of Charpy energy against post-weld heat treatment time at 600°C. The explanation for this behaviour is shown to be associated with non-equilibrium segregation of phosphorus to lath boundaries in the steel. Mathematical modelling of non-equilibrium segregation, together with high spatial resolution analytical electron microscopy results, support this contention. Using the predictions of the model, several suggestions are made concerning the alleviation of phosphorus segregation to boundaries and hence the reduction of cracking susceptibility during post-weld heat treatment of the steel.MST/994

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.11.1095

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThis investigation has examined intergranular fracture during heat treatment and deformation of an Al–Li–Cu–Mg alloy and of an Al–Li–Cu alloy. When solution treatment of the Al–Li–Cu–Mg alloy was initiated by rapid heating to temperatures≥545°C, non-equilibrium eutectic melting of a grain boundary precipitate phase occurred and the liquid spread along grain boundaries as a thin film. On quenching, intergranular cracks were observed at grain boundaries into which a liquid film had penetrated during solution treatment. For less rapid heating rates, non-equilibrium eutectic melting did not occur and no intergranular cracks were observed after quenching. No evidence of non-equilibrium eutectic melting was observed in the Al–Li–Cu alloy irrespective of the rate of heating to 550°C. During tensile testing of as quenched and quenched and aged specimens of the two alloys, intergranular fracture occurred in most specimens, whether or not non-equilibrium eutectic melting had taken place during solution treatment, indicating that at least one additional mechanism of intergranular fracture was initiated by deformation.MST/947

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.11.1102

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThis investigation deals with superplastic deformation and cavitation behaviour of a 7475 high strength aluminium alloy in uniaxial tension. Intergranular cavitation increases sharply with strain as a result of continuous nucleation, thus limiting the ductility to relatively small strains in the superplastic range and affecting the room temperature service properties. To reduce the overall cavitation, several processes have been carried out. They involve treatments of the material with or without superimposed hydrostatic pressure and they can be applied before, during, or after deformation. The results of these processes are presented and compared. It is concluded that cavitation can be significantly reduced and even eliminated. Such a result can increase the use of superplastic forming for industrial applications in aeronautics and aerospace technology.MST/985

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.11.1109

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractControl of earing behaviour at the hot band stage is a critical requirement for successful manufacture of aluminium alloy sheet for beverage cans. The present study has combined production scale experiments with laboratory examinations to investigate the effect of various material and process parameters on microstructure, texture, and earing of the resulting products. It is shown that optimisation of the product is strongly dependent on (i) iron content of the alloy, (ii) ingot homogenisation temperature, (iii) finish hot rolling temperature, and (iv) heating rate during hot band annealing. Earing level after annealing is shown to depend on the balance between cube (+ Goss) texture intensity and the volume of material having almost randomly spread orientations. Pronounced 0/90°earing tendency is usually associated with coarse and elongated grain structures. A model is shown which represents the microstructure–texture evolution as a competition between cube/Goss grains, which nucleate systematically within transition bands, and randomly oriented grains, which nucleate in the vicinity of coarse second phase particles.MST/1032

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.11.1118

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractTo clarify the physical and mechanical properties of nickel based alloys (Alloy 600 and 690), the effects of chromium carbides on the electrical resistivity and hardness were examined after low temperature aging following cold working. In Alloy 600, chromium carbide precipitates were dispersed at grain boundaries and within the grains and the electrical resistivity and hardness increased markedly after short time aging. In Alloy 690, chromium carbides precipitated mainly at grain boundaries and the increases in electrical resistivity and hardness were relatively small, even after long aging times. The most probable mechanism causing the large increases in electrical resistivity in Alloy 600 is the segregation of solute atoms, such as carbon and nitrogen atoms, to dislocation loops around chromium carbides introduced by cold working.MST/939

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.11.1128

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor