Following the previous work on the Charpy impact test on multi-run mild steel welds, the results of the NRL drop weight test on the same welds are reported in this paper. Much has been known about the NRL drop weight test on the base plate, but very little attention has been directed to the welds. Therefore, in this study, not only to test the specimens taken from the welds in different orientations, but also to clarify the significance of the NRL drop weight test, the experiment was carried out to record the load-time curve during impact as in the Charpy test.
No difference in NDT was observed between the base plate and the welds. The effects of specimen orientation and welded structures that were observed in the Charpy test did not appear in the NRL drop weight test. Furthermore, evaluation of the fracture toughness or stress intensity parameter, K_IC, was made by recording the load-time curve: and it was found that NDT corresponded to the temperature at which the yield point fracture occurred.

抄録全体を表示

The transition phase, ω, which was formed during the decomposition of the quenched Ti-8%Mn alloys was directly observed by means of transmission electron microscopy, using its thin foils. Three phases were observed in the specimen: a retained β phase, a diffuse-ω or (ω′) phase and a face-centered cubic martensite (α″). Of these phases, the fcc martensite is a new phase which cannot be expected from the equilibrium diagram of the Ti-Mn system, its lattice parameter being approximatly 4.3 Å. This martensite includes many microtwins in it. If the quenching temperature is higher than 1000°C, the fcc martensite cannot be observed in the alloy.

抄録全体を表示

In the Ti-8%Mn alloy brine quenched from 950°C, ω′ (which gives diffuse diffraction spots at the same positions as ω) and α″ (fcc martensite) phases besides retained β phase were observed by electron microscopy. In this report, the authors studied the structure change of these phases by aging treatment at 450°C and the structure of the precipitated ω. According to the result of the electron microscopic observation on the aged materials, ω′ grows to ω and α″ decomposes into α and β. The crystal structure of the ω phase is hexagonal and its c axis is parallell to ⟨111⟩_β. It is observed that the precipitated ω phase has a rod shape which elongates along ⟨111⟩_β and its longitudinal size is approximately 300 Å. The α phase is observed in the specimen aged for 60 min and it has Widmansttaten structure. The orientation relationship between β phase and α phase is [0001]_α\varparallel[110]_β.

抄録全体を表示

The etch figures were observed on 3% silicon iron sheets which were cold rolled to over 3% reduction, recrystallized, and then etched with 35% aqueous solution of FeCl₃ or with 10% aqueous solution of HNO₃. We observed that a few to several hundred etch figures crowded about annealing twins, the density of these crowds of etch figures being maximum (10 groups/cm²) approximatly at 5% rolling. A twin crystallite with a cross-section thiner than 1μ×0.1μ and the length over 20 μ was found to correspond to an etch figure by transmission electron microscope observations. It seems, however, that the etch figures were formed by the effect of etching twin boundaries, and it is difficult to interpret the formation of such annealing twins by the conventional models.

抄録全体を表示

With regard to fixed-, moving- and fluidised-bed reactors treating with non-catalytic gas-solid reactions, seven operational models which consist of the mass-balance equations and boundary conditions under an isothermal condition are established. These models are analytically solved to give both the fractional conversion of solid particles and the exit concentration of the gaseous reactant.
When the fractional conversion of solid particles is specified with a given particle diameter, inlet gas concentration and reaction temperature, the reactor performances on the solid particles-output in the continuous reaction operation as compared with batch-wise fixed-bed operation can be estimated by means of the evaluation of a dimensionless ratio such as δτ⁄\varphi(=Sθ⁄(1−ε)Lρ_p). Calculated results indicate that among the three types of the reactor, the moving-bed reactor has the highest performance capacity. The co-current operation is superior to the counter-current operation within a range of α=0.1∼10, whereas the latter to the former at α<0.1. Both the operations have a nearly equal capacity under the condition of α>10. Also, the reactor performance on the output of particles of the continuous fluidised-bed reactor is inferior to that of the fixed-bed reactor.
With increasing fractional conversion of solid particles, the reaction or retention time of the particles is prolonged. In this sense, the continuous fluidised-, counter-current moving-, co-current moving- and fixed-bed reactors become lower in efficiency in its order. In case of the continuous fluidised-bed reactor of the lowest efficiency, the feed rate of solid particles at \barf₁=0.98 should be held as small as one-twentieth of the value at \barf₁=0.7.

抄録全体を表示

The thermally-activated process of deformation of age-hardened aluminium alloys is studied by the differential mechanical test. The alloys studied are Al-3.92%Cu alloy, 24 S-T₄ and 75S-T₆. All specimens are pre-strained at 293°K and deformed again under various conditions. The work-hardening behaviours at the pre-strained condition of those alloys are analyzed by comparing the thermal component of flow stress corresponding to an activation energy with the athermal component. The main results obtained are as follows:
(1) The difference between the flow stress at 293°K and that at 78°K of the Al-Cu alloy containing GP I zone decreases with strain, but that of the alloy containing GP II zone+θ′, θ′ or θ phase increases with strain.
(2) The 0.07% offset stress of GP II zones+θ′ alloy has neither temperature nor strain-rate dependence, but the flow stress at strains higher than 0.6% has such a temperature and strain rate dependence corresponding to the athermal component of flow stress as flow stress of pure aluminium.
(3) The flow stress of either θ′ or θ alloy is determined by the same mechanism of deformation process as that of pure aluminium, and from the relation between σ_a and σ_t (0.2 eV) it is concluded that the increase of flow stress with strain or due to precipitates can be attributed to the increase of piled-up dislocations, where σ_a and σ_t are the athermal and the thermal components of flow stress respectively.
(4) From the result of the measurement of work hardening at pre-yield micro strain, the yield (0.07% offset) stress of GP II+θ′ alloy is thought to be the sum of the back stress of dislocations surrounded by zones and the resistance of zone itself.
(5) In the case of GP I alloy, the short range interaction between the zone and dislocation determines the thermal component of flow stress. This holds also for the case of for 24 S-T₄ alloy.
(6) On the other hand, the condition of 75 S-T₆ resembles that of pure aluminium just as in the case of the Al-Cu alloy containing θ′ or θ phase. The strengthening seems due to the increase of dislocation density caused by the presence of precipitates.

抄録全体を表示

Mechanical and electrical properties in various aged states of Cu-Cr-Hf alloys containing about 0.6%Cr and 0.14∼0.90%Hf were studied in comparison with those of Cu-Cr-Zr and Cu-Cr alloys. The relations between properties and microstructures were also studied by using the transmission electron microscope. The specimens were cast, hot-worked, solution-treated at 950°C for 1 hr, quenched and finally cold-reduced about 83% to 0.5 mm thick sheets.
The results obtained were as follows. (1) Cu-Cr-Hf alloys were remarkably age-hardened in the temperature range of 400°∼450°C. (2) The age-hardenability was shown to be caused by the precipitation of two sorts of precipitates, i.e., Cr-rich phase and Cu-Hf compound. The Cu-Hf compound precipitated on the {111} habit plane of the matrix. (3) The alloys containing about 0.6%Cr and 0.2∼0.6%Hf exhibited properties of more than 60 kg/mm² in strength and about 80% IACS in electrical conductivity, when aged at 400°∼450°C for about 3∼20 hr. (4) Therefore, the above alloys were considered to be superior to Cu-Cr alloys and equivalent or somewhat inferior to Cu-Cr-Zr alloys.

抄録全体を表示

Structual changes in copper single crystals during high temperature creep deformation were investigated. Creep tests were performed in argon atmosphere at 745°C=0.75T_m and 880°C=0.85T_m (T_m: the melting temperature in Kelvin). After creep deformation, various observation surfaces were prepared by cutting the deformed crystals parallel to (1) the primary slip plane (111), (2) the (\bar101) plane on which deformation bands due to the primary slip are formed, and (3) the (1\bar21) plane normal to the lattice rotation axis in the deformation band. Substructures were examined by means of the Berg-Barrett method using micro-focused Cu-K_α radiation.
The results obtained are as follows: In the transient creep region, pillar-like subgrains elongating in the direction of [1\bar21] have been observed. They are surrounded by sub-boundaries parallel to (111) and to (\bar101), which are twist and tilt boundaries, respectively. Spacings between the subboundaries were about 50∼100 μ at 880°C and 30∼50 μ at 745°C, and remained almost constant throughout the steady-state creep region. In the examination on the (111) plane, the crystal-lattice twisting about the [1\bar21] axis was found with a period of about 10 μ. The increase of the twisting was the most remarkable structual change during creep deformation.
In specimens crept for more than 50 hr at 880°C, very large subgrains (300∼500 μ) having small lattice misorientation were observed in some places. They may correspond to the regions where dynamical recovery occurred more conspicuously than their neighbourhood. This fact suggests that the high temperature creep is a heterogeneous process.

抄録全体を表示

Dislocation distribution and substructure formation in copper single crystals due to high temperature creep were investigated by means of the etch-pit technique and transmission electron microscopy. Etch-pit observation was made on the surfaces parallel to the primary slip plane, (111), and to the critical slip plane, (\bar111). Thin foil specimens made parallel to the primary slip plane were examined by transmission electron microscopy.
In an early stage of transient creep, subgrains elongating in the direction of the deformation band (10∼20 μ×50∼200 μ in size) have been found on the (111) plane. Cell structures (∼100 μ in size) have also been found in the region next to that of the long subgrains. With the progress of transient creep, however, the width of the long subgrains increased. At the same time, the cell structures changed into well-developed subgrain structures, decreasing in their size. In the steady-state creep region, little change was observed in the shape and the size of the substructure. The width of the long subgrains was 20∼40 μ, while the size of subgrains originating from the cell structures was ∼50 μ. This fact indicates that these two types of structures tend to become similar with the advance of creep deformation.
By the etch-pit technique, many primary dislocations were observed within the subgrains and cells in the transient creep region. The primary dislocations, which are generated during instantaneous elongation, decreased in the transient creep region and increased again in the steady-state region.
In transmission electron microscopy, random distribution of sub-boundaries of about 10 μ in length and parallel to the (\bar101)-trace was observed with a spacing of several microns perpendicular to the (\bar101)-trace, in addition to the dislocation networks lying nearly parallel to the (111) plane. The lattice distortion about the [1\bar21] axis may be ascribed to the existence of the former.

抄録全体を表示

Lead selenide single crystals whose composition slightly deviated from stoichiometry were grown from a vapour phase under controlled selenium pressure. The number of nucleus was controlled, and growth conditions of the single crystals were obtained.
It was revealed to be efficacious for the growth of large single crystal to adopt a “nucleus elimination method”; namely, a few nucleus were at first grown under relatively large temperature differences, ΔT, between the growth chamber and the source chamber and then these nucleus were eliminated into one or two nucleus by reversing the temperature gradient. In order to obtain the single crystals at 800°C by the usual method, the temperature gradient is required to be lower than 3°C. However, it was about 7°C when the “nucleus elimination method” was adopted. The growth rate of the single crystals with this method could be about five times as much as that by the usual method at 800°C.
By selecting a suitable growth condition, large single crystals of lead selenide with dimensions about 8×5×3 mm³ were obtained.
The shape of the grown crystals changed from cubic-like to platelet, columnar and needle-like with increasing ΔT.

抄録全体を表示

Defects of vapour grown crystals were investigated and compared with those of melt grown crystals by means of chemical etching, the Berg-Barrett method, and Hall effect and electrical conductivity measurements.
Controlling the partial pressure in the gas phase during crystal growth, we have been able to obtain single crystals of various compositions with small deviations from stoichiometry.
It was found that the vapour grown crystals had a smaller defects concentration than the melt grown crystals in the as-grown state. After heat treatment under controlled selenium pressure, both crystals showed similar electrical properties in carrier concentration (min. value at 77°K was p: 2×10¹⁶/cm³) and Hall mobility (μ_p; 5×10⁴ cm²/V·sec at 77°K). But significant differences were found in etch pit density (V.G.; 1×10⁶/cm², M.G.; 3×10⁶/cm²) and average misorientation (V.G.; 1.3°/cm, M.G.; 2.3°/cm) even after heat treatment.
It was known that the vapour grown crystals had smaller structural defects than the melt grown ones, but both crystals were estimated to be similar in electrically sensitive defects concentration.

抄録全体を表示

The precipitation hardening process in Cu-4.5, 6.5 and 7.4 wt%Ag alloys has been investigated principally by optical microscope observations and the hardness test. The age hardening of these alloys can be attributed to the general precipitation and the grain boundary reaction type precipitation. The age hardening in coarse grain specimens is almost controlled by the general precipitation, but in fine grain specimens it is controlled by the grain boundary reaction type precipitation. The softening in these alloys originates from the coalescening of general precipitates or from the second grain boundary reaction which produces nodules of very coarse interlamellar spacing. The maximum hardness obtained by ageing is higher in coarse grain specimens than in fine grain specimens. The interlamellar spacing in nodules of the first grain boundary reaction with the degree of undercooling can be expressed by the equation: l=2.1×10⁻³⁄(T_E−T) cm. The 0.2% yield strength of the alloy wholly covered with nodules is inverse proportional to the interlamellar spacings.

抄録全体を表示

The diffusion coefficients of silver in molten silver-antimony and silver-tin alloys were measured by the capillary reservoir method with Ag¹¹⁰ as the radioactive tracer within the temperature ranges 623°∼1070°C and 627°∼1015°C, respectively. The results obtained are as follows:
(This article is not displayable. Please see full text pdf.)
The activation energies of silver in various liquid metals and alloys were found to be directly proportional to the surface tensions of those within the experimental errors. This relation seems to support Frenkel’s model on the activation energy of diffusion. On the alloys containing silver as the solute, the ratios between the diffusion coefficients of solute and solvent calculated by the Swalin’s fluctuation model were compared with the experimental values.

抄録全体を表示

To make clear factors influencing the structure of columnar dendrite, especially the dendrite element size and the dendrite arm spacing, of primary solid solution in a polycomponent system, the authors have investigated the effect of freezing condition and solute elements on the structure of columnar dendrite in Al-Cu-Si aluminum-base ternary alloys. The relationship between freezing variables and the structure in the ternary alloys is similar to that for aluminum-base binary alloys. That is, the dendrite element size and the dendrite arm spacing are inversely proportional to the square root and the forth root, respectively, of the cooling rate in the solid-liquid coexisting region. In order to know the behavior of the solute elements in the ternary alloys during freezing, it is necessary to consider the gross distribution coefficient and gross solute content which correspond to the distribution coefficient and solute content in a binary system. By taking these two, the effect of solute elements in the ternary alloys on the structure of columnar dendrite can be determined as in the case of binary alloys. When the sum of solute contents is constant, the larger the ratio of silicon content to copper content becomes the larger the dendrite element size, and the smaller the dendrite arm spacing. This may be attributed to the decrease of the gross distribution coefficient with increasing ratio of silicon content to copper content.

抄録全体を表示

The authors have investigated the structure of unidirectionally frozen metastable iron-carbon alloys with less than 1 wt% third elements, such as silicon, manganese, phosphorus and sulfur. The results obtained are as follows: (1) The width between the stalks of cellular dendrite of primary austenite in the hypo-eutectic alloys is inversely proportional to the square root of the cooling rate at the beginning of crystallization of primary austenite, as in the case of iron-carbon binary alloys. The presence of silicon and phosphorus as third elements increases the width between the stalks of cellular dendrite. (2) The dendrite arm spacing of primary austenite is not changed in the hypo-eutectic alloys containing the above mentioned elements as third elements. (3) The width of ledeburite colony in the nearly eutectic alloys with silicon, phosphorus or sulfur as a third element is inversely proportional to the square root of the cooling rate at the beginning of crystallization of ledeburite and increases as the content of the third element increases. The third element which may segregate stronger during the eutectic freezing seems to increase the ledeburite colony size to a greater extent. (4) The presence of manganese as a third element does not hold the relationship between the colony size and the cooling rate, described in (3). (5) Dendritic growth of ledeburite is promoted by containing phosphorus and sulfur rather than containing silicon and manganese as third elements.

抄録全体を表示

The effect of small amounts of elements was studied on the corrosion resistance of 316L stainless steel in boiling 5% sulphuric acid solution by weight loss and polarization measurements. It was found that the presence of P, S, As, Sb, or Pd increased the corrosion rate, while Cu or Sn decreased it. However, in the presence of Cu, not only Sn but S, As and Sb also improved slightly the corrosion resistance.
Cathodic polarization curves measured by the rapid method (galvanostatic method) revealed that there was a close relationship between corrosion rate and hydrogen overvoltage in acid solution. The larger hydrogen overvoltage was observed for the higher corrosion-resistant steel.
After the corrosion experiments, Pd, Cu and Sn were observed to be enriched in the surface film on the specimens by electron diffraction or spectroscopic analysis. The results suggest that these minor elements affected the corrosion resistance of steel by increasing or decreasing the hydrogen overvoltage as the result of deposition of such elements in the form of metal or sulphide in the surface film.

抄録全体を表示

Carbide reactions were studied in a steel containing 1.31%C, 0.65%Cr and 4.59%W, which had been previously annealed into a meta-stable equilibrium state, on isothermal austenitizing at a temperature of 850° to 1000°C by means of an X-ray diffraction method and chemical analysis of the residues after electrolytic separation.
The carbide change from a meta-stable to a stable equilibrium state can be expressed by the reactions, M₂₃C₆→M₂₃C₆+M₆C→M₂₃C₆+M₆C+WC→Fe₃C+WC (below 900°C) or WC (above 950°C). The M₆C appears as soon as the specimen is austenitized and the concentration of tungsten in the M₆C increases with the holding time. Nucleation of tungsten carbide crystals takes place after a incubation period which becomes shorter with increasing austenitizing temperature, and the crystals grow larger due to both the precipitation of carbon and tungsten on them from the austenite matrix and the dissolution of the M₂₃C₆ and M₆C, accompanied by the decrease in concentration of tungsten in the M₂₃C₆.

抄録全体を表示

To make clear the origin of the invar characteristics, some physical properties of fcc (Fe_1−xCo_x)_0.89Cr_0.11 alloys which are most typical invar alloys in the Fe-Co-Cr system (stainless invar) have been studied so far. In the present experiment, the temperature and composition dependences of thermal expansions of the alloys were measured and the following results were obtained:
It has been ascertained that these alloys have the same remarkable invar characteristics as reported by Masumoto. Measurements of the thermal expansions at sufficiently high temperatures made it clear that the invar characteristics are caused by the effect of the spontaneous volume magnetostriction in the temperature range below the Curie point of short range magnetic ordering. And the spontaneous volume magnetostriction at 0°K has been estimated from normal thermal expansion curves (only lattice vibration), compared with the thermal expansion of Ni. The value obtained on an alloy of x=0.6 was 12±1×10⁻³, about three times the value in Fe-Ni invar alloys.
The microscopic mechanism or the cause of this large spontaneous volume magnetostriction may be ascribed to (1) the magnetic mechanism due to the characteresitic electronic state of invar alloys and (2) the elastic mechanism due to peculiar lattice properties of invar alloys associated with the α\ ightleftharpoonsγ martensitic transformation process which is common in each system having the invar region.

抄録全体を表示

Masumoto et al. discovered previously that alloys near the composition to Ni₃Mn exhibit high permeability when these alloys have an optimum degree of order. These alloys were named “Nimalloy”. Much subsequent work has been followed to investigate the effect of additions of various elements on the properties of nickel-manganese alloys, and the highest initial permeability of 76000 and the highest maximum permeability of 441000 have been obtained.
The results obtained by chromium additions to nickel-manganese alloys show that the optimum cooling rate to attain the highest permeability in each alloy decreases rapidly in general with increasing chromium content. Therefore, the alloys were baked for a long time at various temperatures below the order-disorder transformation point after slow cooling from 900°C. With increasing chromium content, the permeabilities of nickel-manganese alloys gradually increase at the beginning and then rapidly to a maximum value, after which it decrease sharply. The alloy consisting of 80.93%Ni, 17.13%Mn and 1.94%Cr exhibits the highest initial permeability of 17000 when cooled at a rate of 5°C/hr from 900°C, followed by reheating at 380°C for 600 hr, while the alloy of 80.47%Ni, 17.30%Mn and 2.23%Cr shows the highest maximum permeability of 103000 when cooled at a rate of 5°C/hr from 900°C, followed by reheating at 400°C for 400 hr. The latter alloy shows a magnetic hysteresis loss of 22.64 erg/cm³/cycle and a coercive force of 0.0168 Oe for the maximum magnetic induction of 4000 G, an intrinsic magnetic induction of 4550 G at an effective field of 900 Oe and an electrical resistivity of 73.8 μΩ-cm at 20°C.

抄録全体を表示

The present work was conducted to know whether impedance measurement of stainless steel under potentiostatic polarization is possible or not. A semi-conductor type potentiostat and an a.c. bridge were used, and a series equivalent circuit was employed. Converting the obtained data into the parallel equivalent circuit, both parallel capacity and resistance were obtained. The results suggest that the passive film of iron or stainless steel is decreased in thickness or becomes porous before oxygen evolution or transpassive dissolution takes place.

抄録全体を表示

For a rapid and simple determination of small amounts of In and Ga in wertz slags of zinc ores and related materials, a spectrographic method, with only one series of standards and a constant analytical condition, was studied. An optica plane grating spectrograph B-5 was used. To reduce the difference of matrix effects of the diverse sample compositions, investigations were carried out on various factors, such as pretreatment of the sample, spectroscopic buffer, type of electrode, arc current, exposure time, internal standards, and correction to the line interferrence. As a result, the following method was established: A sample is treated with a mixture of sulfuric acid and nitric acid, oxidized in a furnace and mixed with two parts of an internal standard-buffer mixture (Na₂CO₃+C+Tl₂O₃). The mixture (30 mg) is then placed in the bottom of a graphite cup (I.D.4.8 mm, depth 7 mm) and excited in a d.c. arc at 12 A for 60 sec. Tl is used as an internal standard element for spectroscopic analysis. Correction to the interferrence of the Fe line is carried out, if necessary. By this method, In and Ga in various wertz slags of zinc ores and related materials can be simultaneously determined to 0.0005% within the errors of 8% and 12% in terms of the variation coefficient, respectively. But when a medium type quartz spectrograph Qu-24 is used, the analytical sensitivity decreases to 0.002%, within the errors of 9% for In and 16% for Ga. Analysis of 10 various samples requires about 7 hours. This method is also applicable to other ores and related materials.

抄録全体を表示

The two dimentional diffusion of solute in the liquid ahead of solid-liquid interface having periodic projection has been treated mathematically under a condition of steady state unidirectional solidification.
The shape of a solid-liquid interface, the solute distribution and the micro-segregation at the top and bottom of the projection have been computed for various conditions of solidification.
From these considerations, the optimum condition for growth of columnar crystal is derived as follows:
(This article is not displayable. Please see full text pdf.)
l is the spacing of columnar crystal, V is the freezing velocity, D is the diffusion coefficient of solute in the melt and k₀ is the equilibrium distribution coefficient.
Comparison of the relations between V and l obtained from the above equation with experimental data for steady state solidification of Pb-Sn alloy and Sn-Pb alloy have been made. Satisfactory agreement with experiment was found.

抄録全体を表示

The Structure of maraging stainless steels containing molybdenum and cobalt in the subzero-treated condition were examined by X-ray diffraction and optical microscope, and the results were represented graphically. Also, the age-hardening characteristics of these steels were studied by hardness measurements, electron microscope and calorimetric analysis. All the martensitic steels hardened in two distinct stages by isothermal aging at 500°C: In the early stage, the hardness increases very rapidly and approaches to a constant value within 0.2 hr: in the later stage, the hardness increases slowly and changes by a typical nucleation and growth process, followed by overaging, which is due to the formation of austenite in part at least. It is thought that the early stage hardening corresponds to the low temperature aging where clusters or rich zones of solute grow on the parent lattice, and the later stage hardening to the high temperature aging where Laves phase (Fe Cr)₂ Mo forms at dislocations in martensite crystals. These precipitates look finer and greater in number when steel contains more cobalt. On the other hand, the specific heat versus temperature curves clearly show that heat is evolved at a low temperature where the clusters and rich zones are formed during the low-temperature aging, but it is absorbed at an intermediate temperature where the aging products formed at a lower temperature are redissolved, and evolved again during the high temperature aging where the precipitate phase is formed.

抄録全体を表示

The low temperature aging behavior in the substitutional iron base martensite of ternary and quaternary alloys containing chromium, nickel, cobalt and molybdenum has been investigated by means of calorimetric analysis and the hardness test. Specific heat versus temperature curves were obtained by reheating the specimens at approximately 1°C/min from room temperature to about 700°C. The results are useful in providing information on the low temperature aging and its reversion, and the high temperature aging. Although the age-hardenability is consistently promoted by the increase of molybdenum, the behavior of the heat evolution due to the low temperature aging are scarcely affected by the molybdenum content in both series of 13%Cr-16%Co-Mo steels and 13%Cr-8%Ni-Mo steels. As the cobalt content in chromium-cobalt stainless steels increases, however, the amount of this evolution increases definitely. Heat evolution due to the low temperature aging is also clearly observed in 18%Ni-8%Co steel. These results obtained by calorimetric analysis support the conclusion that the cluster or rich zones of nickel and cobalt are mainly responsible for the heat evolution in the low temperature aging. From the variation in both behaviors of the heat evolution and the reversion dehardening with preaging at 500°C, it is suggested that a part of the slow reaction of the low temperature aging is maintained in the precipitation hardening stage of the isothermal aging. The activation energy for the reaction of the low temperature aging is about 34 kcal per mole from the heat evolution in the specific heat versus temperature curve.

抄録全体を表示

In the operation of anodic peotection for a chemical apparatus, an accident of a potential controller is a fatal blow. As a counter-measure for such an accident, the galvanic coupling of a chemical apparatus with a platinum-oxygen electrode was examined using a model cell.
The electrode system studied was composed of a SUS 32 stainless steel electrode and a platinum-oxygen electrode in 50% sulfulic acid solution at 50°∼90°C. Three kinds of platinum, that is, bright platinum, platinized platinum and platinized platinum sintered by flame, were used.
The effectiveness of coupling with these platinum-oxygen electrodes on the maintenance of passivity of the stainless steel depended on the cathodic polarization characteristics of the oxygen electrodes, and the effectiveness decreased in the order of platinized platinum>platinized platinum sintered>bright platinum. It was also confirmed that these platinum-oxygen electrodes became poisoned with the lapse of time, and this tendency decreased in the order of bright platinum>platinized platinum sintered>platinized platinum. Therefore, the stainless steel coupled with platinized platinum, showed a stable and high passive potential for many hours.
But a platinized platinum electrode has a serious defect, that is, platinum black is liable to fall off. After all, it appears that a bright platinum-oxygen electrode is best suited to practical use despite the lower reduction efficiency.

抄録全体を表示

The strain rate and grain size dependence of the lower yield stress of polycrystalline iron containing 0.002 to 0.05 wt% carbon has been investigated by compression tests at room temperature over strain rates ranging from 3.3×10⁻⁵ to 4×10³ sec⁻¹. The results obtained are as follows:
(1) Under high strain rate deformation twinning occurs and the larger the grain size of the specimen becomes, the more frequently it is observed.
(2) The strain rate dependence of the lower yield stress (∂σ_ly⁄∂ln\dotε) increases with increasing strain rate and is independent of the grain size and carbon content. The relation between the lower yield stress and the strain rate can be expressed as
(This article is not displayable. Please see full text pdf.)
\ oindentover the range of strain rate tested. The value of m turns out to be 10.5∼18 and tends to increase with decreasing grain size.
(3) The relation between the effective stress and the activation volume agrees well with the previous results obtained from the tests at low strain rates for varying temperatures. Therefore, it is concluded that the deformation at high strain rates and room temperature is controlled by the same thermally activated process as for the deformation at low strain rates and low temperatures. This process is presumed to be the overcoming of the Peierls-Nabarro barrier by the moving dislocations.
(4) The value of k_y in Petch’s equation for slowly cooled specimens turns out to be 2.4∼2.8 kg/mm^3⁄2 for the low strain rate range and is a little greater for the high strain rate range, being independent of carbon content. On the other hand, the value for rapidly cooled specimens is 1.0 kg/mm^3⁄2 for the low strain rate range and 2.6∼2.7 kg/mm^3⁄2 for the high strain rate range.

抄録全体を表示