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Showing papers in "Materials Science and Technology in 1994"


Journal ArticleDOI
TL;DR: In this article, the methods for producing magnesium are briefly described and its alloying behaviour is discussed with particular reference to the roles of individual alloying elements, and current and future trends in the use of magnesium alloys are considered together with examples of recent applications.
Abstract: The methods for producing magnesium are briefly described and its alloying behaviour is discussed with particular reference to the roles of individual alloying elements. Cast and wrought alloys are considered separately and particular attention is paid to microstructure–property relationships and corrosion behaviour. Alloys produced via new processing techniques are treated separately and mention is made of metal matrix composites and the use of rapid solidification to produce amorphous and other novel materials. Finally, current and future trends in the use of magnesium alloys are considered together with examples of recent applications.MST/2023

741 citations


Journal ArticleDOI
TL;DR: In this paper, a quantitative interpretation of these observations is achieved by modelling the mechanical properties of bainite and martensite in their tempered states, and it is found that the peak in the curve of the strength as a function of the volume fraction of Martensite can be attributed to two factors.
Abstract: Recently published experimental data demonstrate that the strength of mixed microstructures of tempered bainite and martensite can peak at an intermediate volume fraction of martensite. In the present work, a quantitative interpretation of these observations is achieved by modelling the mechanical properties of bainite and martensite in their tempered states. It is found that the peak in the curve of the strength as a function of the volume fraction of martensite can be attributed to two factors. When bainite forms it enriches the residual austenite with carbon, so that the strength of the subsequent martensite increases. In addition, during its deformation, the strength of the bainite is enhanced via plastic constraint by the surrounding stronger martensite. Taking these effects into account, it is possible to predict accurately both the trends and the absolute values of published experimental data on the strength of mixed microstructures.MST/1901

188 citations


Journal ArticleDOI
TL;DR: High wear resistance is an attribute frequently ascribed to metal matrix composites and is of clear importance to the designer is considering both the use of these materials in some applications an....
Abstract: High wear resistance is an attribute frequently ascribed to metal matrix composites and is of clear importance to the designer is considering both the use of these materials in some applications an...

133 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that a small addition of Mn significantly accelerates the homogenising process (transformation of the brittle plate-like β-AlFeSi phase to the more rounded α-Al FeSi phase) which results in superior hot formability and ductility.
Abstract: The hot deformation of AA 6063 and AA 6005 Al alloys has been related to chemical composition and the microstructural evolution occurring during the various heat treatment procedures before extrusion. It was shown that a small addition of Mn significantly accelerates the homogenising process (transformation of the brittle platelike β-AlFeSi phase to the more rounded α-AlFeSi phase) which results in superior hot formability and ductility. The mechanical behaviour of Al–Mg–Si alloys during hot deformation can be explained in terms of a model of dislocations climbing around particles. Large β phase particles increase initial work hardening rate and flow stress and impair hot ductility. The hot ductility of the material investigated via tensile testing was found to correlate with the density of particles covering grain boundaries. It was also shown that grain refinement in the billet leads to more uniform distribution of intermetallic constituents, which accelerates the homogenising process and improv...

112 citations


Journal ArticleDOI
TL;DR: In this paper, the authors presented a model to calculate the time at which the catastrophic breakaway oxidation for a given component occurs, where the calculated data are presented as oxidation diagrams in which the time to breakaway is plotted as a function of component wall thickness.
Abstract: The long term oxidation resistance of most high temperature alloys depends on the ability to form protective alumina or chromia surface scales during service. Scale growth and scale rehealing after spalling leads to depletion of the scale forming element, aluminium or chromium, in the bulk alloy. If the concentration of this element decreases below a critical level, oxidation of the base elements, e.g. iron, nickel, or cobalt, occurs leading to catastrophic oxidation and destruction of the metallic component. Using iron based, alumina forming, oxide dispersion strengthened alloys as an example, a model is presented which allows the calculation of the time at which the catastrophic breakaway oxidation for a given component occurs. The calculated data are presented as oxidation diagrams in which the time to breakaway is plotted as a function of component wall thickness. Experimental data for the oxidation of the oxide dispersion strengthened alloys MA 956, PM 2000 and ODM 751 in air in the temperat...

105 citations


Journal ArticleDOI
TL;DR: In this paper, X-ray pole figures were measured and the orientation distribution function was calculated using optical microscopy to investigate the microstructure of pure Ta and explained by dislocation glide on {110, 111, 112, and 123 systems.
Abstract: Pure Ta has been cold rolled and annealed at various temperatures. The crystallographic textures were studied by measuring X-ray pole figures and subsequently calculating the orientation distribution function. The microstructure was investigated via optical microscopy. The rolling textures were explained by dislocation glide on {110}〈111〉, {112}〈111〉 and {123}〈111〉 glide systems. Corresponding simulations were carried out using relaxed constraints Taylor theory. Interpretation of the annealing textures was carried out via continuous recrystallisation in the case of weak deformations and temperatures and via discontinuous recrystallisation for higher rolling degrees and temperatures, respectively.MST/1886

92 citations


Journal ArticleDOI
TL;DR: In this article, the transformation kinetics of ferrous weld metals have been investigated as a function of austenite grain size, alloy content, and inclusion characteristics, and the results imply that different types of inclusion have different free energy barriers to ferrite nucleation.
Abstract: The transformation kinetics of ferrous weld metals has been investigated as a function of austenite grain size, alloy content, and inclusion characteristics. Two series of weld metals were studied, designated low and high B–Ti content. Aluminium and calcium additions were made to each weld series to change the inclusion characteristics. Austenite grain size variations were achieved by thermally cycling in a dilatometer to different peak temperatures. The transformation temperature and microstructural changes, and the soluble boron levels of the thermally cycled weld metals, have been quantified. The factors influencing the competing processes of grain boundary and intragranular ferrite nucleation at selected austenite grain sizes have been assessed. The results imply that different types of inclusion have different free energy barriers to ferrite nucleation. The balance of nucleation is shifted from the austenite grain boundaries to the intragranular regions and acicular ferrite formation is great...

88 citations


Journal ArticleDOI
TL;DR: A series of highly ductile, high strength steels exhibiting transformation induced plasticity due to retained austenite was developed by varying the carbon content in the range 0·01 − 0·4 wt-% in 5 wt −%Mn based steel as mentioned in this paper.
Abstract: A series of highly ductile, high strength steels exhibiting transformation induced plasticity due to retained austenite was developed by varying the carbon content in the range 0·01–0·4 wt-% in 5 wt-%Mn based steel. For up to 0·l%C the mechanical properties are insensitive to cooling rate after intercritical heating, but afurther increase in carbon content causes a large sensitivity to the cooling rate, owing to carbide precipitation occurring during slow cooling. By suppressing this carbide precipitation with water quenching after the intercritical holding, an excellent combination of tensile strength (1580 MN m−2) and uniform elongation (21%) was attained at 0·3%C in this series.MST/1964

83 citations


Journal ArticleDOI
TL;DR: In this paper, the assumption of a planar interface made by Jackson and Hunt is relaxed and the boundary element method is used to calculate the solute distribution for a curved interface.
Abstract: Extensive interlamellar spacing measurements on directionally solidified Al–CuAl2 eutectic alloys show that in this system the eutectic exhibits a limited range of spacings rather than a unique spacing during steady state growth at a constant velocity. The minimum spacing observed corresponds to the extremum spacing predicted by the Jackson–Hunt model. However, the maximum observed spacing is much less than the maximum spacing predicted by the theory. In this paper the assumption of a planar interface made by Jackson and Hunt is relaxed and the boundary element method is used to calculate the solute distribution for a curved interface. An iterative technique is used to calculate the maximum spacing for which a selfconsistent interface shape can be calculated for a range of velocities. This maximum selfconsistent spacing shows much closer agreement with the maximum observed spacing than that calculated on the assumption of a planar interface. The deepest point on the selfconsistent interface shape ...

78 citations


Journal ArticleDOI
TL;DR: In this paper, a 0·lC −5Mn (wt-%) steel was examined to ascertain whether a considerable amount of retained austenite is formed after simple thermal treatment consisting of heating, holding at temperatures in the intercritical range, and cooling.
Abstract: To develop a high strength, high ductility steel, making use of transformation induced plasticity due to retained austenite, a 0·lC–5Mn (wt-%) steel was examined to ascertain whether a considerable amount of retained austenite is formed after simple thermal treatment consisting of heating, holding at temperatures in the intercritical range, and cooling. The amount of retained austenite passes through a peak with increasing holding time and is virtually insensitive to cooling rate. The maximum amount that can be retained is about 30 vol.-%. The ductility of the specimens tested is almost proportional to the amount of retained austenite.MST/1921

74 citations


Journal ArticleDOI
TL;DR: In this article, the creation of wear resistant surface metal matrix composites in both aluminium alloys and titanium via the incorporation of pre-placed SiCp has been successfully undertaken by using a 5 kW CO2 laser.
Abstract: The creation of wear resistant surface metal matrix composites in both aluminium alloys and titanium via the incorporation of preplaced SiCp has been successfully undertaken by using a 5 kW CO2 laser. The problems associated with the production of a metal matrix composite layer freefrom porosity, cavities, and cracks, with a satisfactory distribution of ceramic were considered. Optimum laser processing conditionsfor Al–SiCp gave a well distributed ceramic withfew defects, but limited to 35 μm thickness. This was increased to 250 μm using a preplaced mixture of Al powder and SiCp. A prep laced SiCp layer on commercially pure Ti resulted in a dissolution of SiCp and precipitation of TiC, or the partial dissolution of SiCp and agglomeration into a hard layer (1400 HV). Pin on disc wear tests indicated that surfaces could be produced via laser surface melting associated with preplaced SiCp which showed a similar wear resistance to bulk metal matrix composite Al alloy–SiCp, and an improvement of an or...

Journal ArticleDOI
TL;DR: In this paper, the thermal and thermomechanical behaviour of the relaxation of the residual stresses of a shot peened Astroloy superalloy under tensile cyclic loads has been evaluated by X-ray diffraction and investigated.
Abstract: The thermal and thermomechanical behaviour of the relaxation of the residual stresses of a shot peened Astroloy superalloy under tensile cyclic loads has been evaluated by X-ray diffraction and investigated. The stress relaxation under purely thermal conditions (550 and 650°C) and thermomechanical conditions (pulsating tensile loading at 650°C) as afunction of the exposure time is presented. The purely thermal relaxation is interpreted by annihilation and reorganisation of the crystalline defects induced by shot peening, whereas the mechanical relaxation is linked to cyclic plasticity of materials. In consequence, the thermomechanical relaxation is essentially due to the complex mechanism of the concurrent thermal and mechanical effects. A model is used to predict the residual stresses induced by the specified shot peening conditions and their relaxation under the specified thermal/thermomechanical conditions.MST/1963

Journal ArticleDOI
TL;DR: In this article, the hot working and microstructural behaviour of a 15 vol.-%SiC particle reinforced Al 6061 composite is discussed, and the average size of the SiC particles is 18 μm.
Abstract: Hot working and microstructural behaviour of a 15 vol.-%SiC particle reinforced Al 6061 composite is discussed in this paper. The average size of the SiC particles is 18 μm. The hot torsion test te...

Journal ArticleDOI
TL;DR: In this paper, extensive studies have been undertaken of cementite composition changes as a function of time and temperature in a 2·25Cr 1Mo steel with a fully bainitic microstructure.
Abstract: The microstructure of a power plant steel changes during elevated temperature service. These changes in effect provide a built in time–temperature recorder which can be used in remanent life assessments. Hence, extensive studies have been undertaken of cementite composition changes as a function of time and temperature in a 2·25Cr–1Mo steel with a fully bainitic microstructure. The results are interpreted theoretically using a model for the enrichment of carbides as a function of heat treatment and steel chemistry. The results confirm the validity of the model, although further work is needed to predict the onset of alloy carbide formation at the expense of cementite.MST/1895

Journal ArticleDOI
TL;DR: In this paper, it was shown that retrogression and reaging produces coarsening of grain boundary precipitates and thereby improves resistance to stress corrosion cracking, while it causes pronounced heterogeneous precipitation on dispersoids of E (Al18Cr2Mg3) phase inside the grain of 7075 alloy.
Abstract: Retrogression and reaging produces coarsening of grain boundary precipitates and thereby improves resistance to stress corrosion cracking. At the same time it causes pronounced heterogeneous precipitation on dispersoids of E (Al18Cr2Mg3) phase inside the grain of 7075 alloy. Such heterogeneous precipitation does not occur on the coherent dispersoids of Al3Zr phase in 7050 alloy and its absence leads to higher strength compared with 7075 alloy. Supplementary examination of laboratory alloys 7075-Zr and 7075-Cr differing only in transition metal content supports the above result. This effect is probably the reason why retrogression and reaging (T77 heat treatment) is recommended for alloys containing zirconium but not for those containing chromium.MST/1898

Journal ArticleDOI
TL;DR: In this paper, an accelerated aging response was detected in AA 6061 based metal matrix composites, in age hardening curves via microstructural observations, and the influence of vacancies on the precipitation processes of AA 60 61 alloy and its composites was also considered.
Abstract: An accelerated aging response, detected in AA 6061 based metal matrix composites, in age hardening curves was examined via microstructural observations. The influence of vacancies on the precipitation processes of AA 6061 alloy and its composites was also considered. In the composites, after peak aging, a higher density of dislocations and a higher density of intermediate β′ precipitates was observed. It is thought that the dislocation assisted nucleation processes reduce the apparent activation energy for precipitation, and a higher nucleation density of precipitates in the composites, compared with that in the AA 6061 alloy, leads to an earlier attainment of the peak aging condition.MST/1906

Journal ArticleDOI
TL;DR: In this article, the effects of strain induced martensite formation and grain size on the room temperature low cycle fatigue behavior of AISI 304LN austenitic stainless steel were considered.
Abstract: The effects of strain induced martensite formation and grain size on the room temperature low cycle fatigue behaviour of AISI 304LN austenitic stainless steel were considered. Two grain sizes, namely, 60 and 350 μm, were developed via suitable solution annealing treatments. Microstructural changes before and after low cycle fatigue testing were identified. The martensitic transformation was studied using aferritescope, X-ray diffractometry, and optical microscopy. The mechanical response was correlated with the microstructural changes. Secondary hardening as well as a crossover in the strain–life plots for the two grain sizes resulted from martensite formation. Dislocation configurations depended on the strains imposed.MST/1902

Journal ArticleDOI
TL;DR: In this paper, the thermodynamic driving force necessary to stimulate the nucleation of acicular ferrite and bainite was investigated for a series of high strength weld metals, using a combination of dilatometry, scanning electron microscopy, and thermodynamic calculations.
Abstract: The thermodynamic driving force necessary to stimulate the nucleation of acicular ferrite and bainite is investigated for a series of high strength weld metals, using a combination of dilatometry, scanning electron microscopy, and thermodynamic calculations. The results indicate that the nucleation of acicular ferrite and bainite can be represented by the same thermodynamic model. It therefore appears that the nucleation mechanism of acicular ferrite on non-metallic inclusions in weld metals is essentially similar to that of bainite at the austenite grain boundaries. Metallographic observations confirm the notion that acicular ferrite is essentially intragranularly nucleated bainite.MST/1897

Journal ArticleDOI
TL;DR: In this article, the first transformation product to be formed is M23C6, having a cube-cube orientation with the parent γ grain, is found only on certain γ/α boundaries and its nucleation is shown to be strongly dependent on the γ boundary plane.
Abstract: The decomposition of a duplex stainless steel during aging at 600°C has been investigated using analytical transmission electron microscopy with the intention of elucidating the nucleation sites of the new phases arising from ferrite decomposition. The first transformation product to be formed is M23C6. This carbide, having a cube–cube orientation relationship with the parent γ grain, is found only on certain γ/α boundaries and its nucleation is shown to be strongly dependent on the γ boundary plane of the γ/α interface. Chromium depletion in the vicinity of γ/α boundaries caused by M23C6 precipitation initiates the α→γ transformation by migration of existing γ/α boundaries. Another mechanism for this bcc→fcc phase change is observed through the growth of Widmanstatten γ plates into α. Precipitation of σ begins after M23C6 formation has stopped. The existence of M23C6 on γ/α boundaries is crucial to σ formation because the majority of σ particles are found to nucleate on nodes in migrating γnew/α ...

Journal ArticleDOI
TL;DR: In this article, the textures of austenite and ferrite in a duplex steel X2CrNiMoN225 were studied via X-ray and electron diffraction.
Abstract: The textures of austenite and ferrite in a duplex steel X2CrNiMoN225 were studied via X-ray and electron diffraction. This latter method was also used to determine the orientation difference distribution of grains and phase boundaries. The mechanical properties, e.g. hardness, microhardness, ultimate tensile strength, etc. were also measured. It was found that the hot rolled material was only partially recrystallised. Even after annealing at 1030°C the austenitic phase was not fully recrystallised. In addition, no change in texture was observed after aging in the two embrittlement ranges. Tensile deformation changed both textures due to plastic deformation in the two phases. During deformation at 45° to the rolling direction, rigid rotation of the phase particles may have contributed to the observed texture changes. The grain boundary distribution function revealed a large amount of low angle boundaries in both phases.MST/1396

Journal ArticleDOI
TL;DR: In this article, the influence of temperature and time of austempering on a nodular cast iron austenitised for 30 min at 900°C has been investigated using optical and transmission electron microscopy.
Abstract: The influence of temperature and time of austempering on a nodular cast iron austenitised for 30 min at 900°C has been investigated using optical and transmission electron microscopy. The carbon content of the austenite has been evaluated by measuring the lattice parameter via X -ray diffraction. The structure consisted of bainite containing retained austenite, the amount of which increased, and the carbon content of which decreased, with increasing austempering temperature. No carbides were detected in the materials austempered at 300 and 370°C for up to 2 h, which contained only bainite and austenite. After austempering at 410°C and cooling to room temperature a certain amount of martensite was always detected. After long times at this temperature the austenite decomposed to ferrite and complex carbides. Martensite formation seems to be promoted by the decrease in the carbon content of austenite due to the precipitation of ɛ carbide homogeneously within it. During long austempering treatments at...

Journal ArticleDOI
TL;DR: The phase equilibria between the titanium aluminides, Ti3Al and TiAl, and V have been investigated in the temperature range 1473-873 K as mentioned in this paper.
Abstract: The phase equilibria between the titanium aluminides, Ti3Al and TiAl, and V have been investigated in the temperature range 1473–873 K. Microstructures were characterised using light, scanning electron, and transmission electron microscopy and the nature of the phases present was established via X-ray diffractometry, electron diffraction, and energy dispersive X-ray analysis. A series of isothermal sections have been determined and are compared with those obtained in earlier studies. Ordering of the high temperature bcc β phase to a simple cubic B2 (β2) structure was observed: the ordering temperature was found to decrease with increasing V content, whereas the opposite effect was observed with Al. The effect of oxygen is to stabilise the α phase and to shift the α2+β2+γ field in the V rich direction. The lattice parameters of α2 and β phases decrease with additions of Al and V: empirical equations have been developed to predict these changes.MST/1881

Journal Article
TL;DR: In this article, extensive studies have been undertaken of cementite composition changes as a function of time and temperature in a 2.25Cr-1Mo steel with a fully bainitic microstructure.
Abstract: The microstructure of a power plant steel changes during elevated temperature service. These changes in effect provide a built in time-temperature recorder which can be used in remanent life assessments. Hence, extensive studies have been undertaken of cementite composition changes as a function of time and temperature in a 2.25Cr-1Mo steel with a fully bainitic microstructure. The results are interpreted theoretically using a model for the enrichment of carbides as a function of heat treatment and steel chemistry. The results confirm the validity of the model, although further work is needed to predict the onset of alloy formation at the expense of cementite

Journal ArticleDOI
TL;DR: In this paper, the structure and mechanical properties of model functionally gradient materials consisting of two discrete layers are compared with those of composites of homogeneous composition, and the strengths of the functionally gradient material and composites have been determined via three point bend tests and the fracture toughness properties assessed using single edge notch bend ty...
Abstract: Functionally gradient materials exhibit a progressive change in composition, structure, and properties as a function of position within the material. Functionally gradient materials and conventional metal matrix composites have been manufactured from gas atomised aluminium alloy 2124 powders (matrix) and particulate silicon carbide (reinforcement) by mechanical mixing followed by hot pressing at 500°C at a pressure of 1·5 GN m−2. In this work the structure and mechanical properties of model functionally gradient materials consisting of two discrete layers are compared with those of composites of homogeneous composition. A careful microstructural investigation has revealed a uniform distribution of the reinforcing SiC and defect free interfaces between adjacent layers of the functionally gradient materials. The strengths of the functionally gradient materials and composites have been determined via three point bend tests and the fracture toughness properties assessed using single edge notch bend ty...

Journal ArticleDOI
TL;DR: In this article, the influence of strain rate on the formation of deformation induced ferrite was explored, and it was found that the strain to peak stress decreased with decreasing temperature in the range 750-610°C.
Abstract: Compression testing was used to explore the influence of strain rate on the formation of deformation induced ferrite. Samples of a 0·4%C–1·4%Mn plain C–Mn steel were heated to 1225°C, cooled to test temperatures in the range 1100–610°C, and then given a true strain of 0·6, at strain rates of3 × 10−2, 3 × 10−3, and 3 × 10−4 S−1. At the lowest strain rate it wasfound that the strain to peak stress decreased with decreasing temperature in the range 750–610°C. This behaviour is related to the formation of thin films of the softer deformation induced ferrite at the γ grain boundaries at the higher temperatures, and spheroidisation at the lower temperatures. More normal stress–strain curves were observed at the higher strain rates, as raising the strain rate prevents the formation of deformation induced ferrite and delays spheroidisation. The strain rate was also found to have an important influence on the extent of recovery in the deformation induced ferrite; the lowest strain rate enabling full recov...

Journal ArticleDOI
TL;DR: In this article, powder mixtures of Al and Ti-6Al-4V(wt-%) alloy were used with a Ti substrate of commercial purity to produce several discrete layers of increasing Al content.
Abstract: Laser surface alloying and cladding have been used with the aim of producing functionally gradient materials based on the Ti–Al system. A continuous powder feed into a laser generated melt pool produced several fully overlapping layers of increasing Al content. Alloying involved feeding powdered Al onto a near-α Ti alloy substrate. For cladding, powder mixtures of Al and Ti–6Al–4V(wt-%) alloy were used with a Ti substrate of commercial purity. Cladding involving low dilutions provides a better approach to producing several discrete layers of increasing Al content than does alloying which is associated with higher dilutions. Structural and compositional data are reported for samples containing up to four layers having Al contents of up to approximately 34·5 wt-% (48 at.-%).MST/1913

PatentDOI
TL;DR: In this paper, a pre-weld overageing heat treatment for nickel-based superalloys was proposed, where the alloy is heated to solutionization temperature for a time sufficient to dissolve the gamma prime phase of the alloy microstructure, then slowly cooled with periods of intermittent heating.
Abstract: The present invention is directed to a pre-weld overageing heat treatment for nickel-based superalloys, where the alloy is heated to solutionization temperature for a time sufficient to dissolve the gamma prime phase of the alloy microstructure, then slowly cooled with periods of intermittent heating, so that the gamma prime phase reprecipitates as coarse equiaxed particles, and the presence of fine sized gamma prime phase particles is substantially avoided. The present invention is also directed to a welding method wherein said pre-weld overageing treatment is used.

Journal ArticleDOI
TL;DR: In this paper, the authors present a methodology for evaluating materials in design, with the aim of linking MMCs to applications, using performance indices and materials selection charts for specific design goals.
Abstract: Applications for metal matrix composites (MMCs) have not emerged at the rate needed to justify the development costs. A reason for this may be that material developments have not been adequately linked to identified commercial needs. It is certainly true that some of the expectations raised about the potential offered by MMCs have been misguided. As the MMC business contracts, there is an ever greater need for a systematic method of linking material properties to the needs of engineering designers. This paper presents a methodology for evaluating materials in design, with the aim of linking MMCs to applications. The methodology has two main components: first, the use of performance indices and materials selection charts for specific design goals, to compare existing MMCs with competing materials; and secondly, the conceptual design of new MMC systems guided by those design goals. A selection of case studies illustrates that in mechanical applications the gains in using MMCs are frequently margina...

Journal ArticleDOI
TL;DR: In this paper, the effects of tempering temperature on the hydrogen diffusivity and hydrogen assisted cracking, without external stress, were investigated, and the critical microstructural sites for hydrogen induced cracking were found to nucleate at MnS interfaces.
Abstract: The hydrogen embrittlement of Cr–Mo steel has been studied. The effects of tempering temperature on the hydrogen diffusivity and hydrogen assisted cracking, without external stress, are investigated. Hydrogen permeation and trapping, for the various microstructural conditions, were measured using electrochemical equipment. The microprecipitate distribution in the steel was observed using transmission electron microscopy. The steel, which was heat treated to give a variety of microstructures, was cathodically hydrogen charged and the critical microstructural sites for hydrogen induced cracking examined. Cracks initiated by the charging treatments were found to nucleate at MnS interfaces. Hydrogen diffusivity and trapping are strongly dependent on the tempering parameters.MST/1947

Journal ArticleDOI
TL;DR: In this article, an unalloyed nodular cast iron has been studied after heat treating in the bainite temperature range, and the microstructure produced for austempering times up to 3 h was typical of ductile iron, consisting of carbide free upper bainitic ferrite together with a stable, high carbon enriched retained, reacted, austenite.
Abstract: An unalloyed nodular cast iron, in which the conventional addition of silicon has been replaced by aluminium, has been studied after heat treating in the bainite temperature range. Specimens were austenitised at 950°C for 2 h and then austemperedfor times up to 5 h at either 300 or 400°C. At 400°C the microstructure producedfor austempering times up to 3 h was typical of austempered ductile iron, consisting of carbide free upper bainitic ferrite together with a stable, high carbon enriched retained, reacted, austenite. For longer times, transition carbides are precipitated, initially η carbide in the ferrite, and after 5 h, χ carbide at the austenite/ferrite interfaces by decomposition of the high carbon austenite. Austempering at 300°C produced e carbide in a lower bainitic ferrite together with stable, high carbon retained austenite, for all heat treatment conditions: χ carbide precipitated at the ferrite/austenite interfaces after 5 h austempering. The fracture behaviour of samples austempered ...