Some Preventive methods for corrosion cracking were studied for 80 kg/mm² high strength steel (HT 80) in an accelerated corrosion cracking environment (liquid ammonia saturated with NH₄CO₂NH₂) at 30°C and in field liquid ammonia by means of a constant load or strain method using quenched specimens. The results obtained are as follows:
(1) In the accelerated environment, corrosion cracking of HT 80 is prevented when the specimen is in contact with Mg or Zn, but accelerated when it is in contact with Al. However, it is difficult to prevent the corrosion cracking of WOL-type specimens in liquid ammonia in a field pipe line, even if they are in contact with Mg or Zn. In this case Mg and Zn are covered with corrosion products.
(2) Corrosion cracking of HT 80 is prevented by the addition of more than 0.01 wt% refrigerator oil or more than 0.0005 wt% rape seed oil to the accelerated environment.
(3) Corrosion cracking of HT 80 is prevented by keeping the temperature of the accelerated environment below 10°C. Anodic polarization curves of HT 80 in the above-mentioned environment show that the passive current density decreases and the width of passive region increases as the temperature drops. These experimental results suggest that the field liquid ammonia tanks should be kept at low temperatures. The number of corrosion cracks in the tanks is certainly decreased markedly by keeping the storage temperature at 5°C.
(4) Recently corrosion cracking of many ammonia storage tanks has been found out in Japan. This phenomenon seems to come from the decrease of the amount of machine oil entrained by the ammonia. The decrease of the oil amount is due to the change of compressor’s types employed in ammonia manufacturing plants.

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Effects of water and air on the anodic polarization and the stress corrosion cracking (SCC) of a quenched high strength steel in liquid ammonia saturated with NH₄CO₂NH₂ (about 0.9 wt%) were investigated by using the potentiodynamic and constant strain methods. The results obtained are as follows:
(1) In the above-mentioned environment without water, the steel showed different anodic polarizations and SCC behaviors in the same content of air, according to the kind of gases (N₂, Ar or NH₃) with which the air in the test vessel was replaced before filling it with liquid ammonia. SCC of the steel was observed and the air inhibited corrosion and SCC in those environments.
(2) The critical current density of anodic polarization curves increased with increases in water content and temperature and decreased with an increase in air content, respectively. The passive current density decreased with water content and increased with temperature. SCC of steel tended to occur when the critical current density and the passive current density of the anodic polarization curves were high.
(3) In the liquid with more than 0.3 wt% water, the steel showed a passive potential and did not corrode in presence of air. On the other hand, the steel showed an active potential in the presence of a small amount of air.
(4) In the liquid with water (maximum 1.0 wt%), SCC of specimens showing an active potential was prevented by addition of 1.0 wt% water, but it was liable to occur when the contents of air and water were low. And the test results of SCC of specimens showing a passive potential were lacking in reproducibility.
(5) The amount of water neccessary to prevent SCC in a liquid ammonia tank seems to vary with CO₃⁻⁻ and O₂ contents in the liquid ammonia and its temperature.

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Wear properties of ion nitrided low alloyed steels (SCM3 and SACM1) and a mild steel (S15C) were studied in comparison with the cases of conventional gas nitriding and tufftriding processes.
Rolling wear tests were done under dry and wet conditions with 9% slip ratio, using a Nishihara type rolling wear testing machine. The contact stresses were 60 or 50 kg/mm².
The results obtained were as follows.
(1) In the case of low alloyed steels, the difference in wear properties tested under dry condition was hardly recognized.
(2) Under wet condition, the ion nitriding was superior in both initial wear loss and wear ratio to the other processes.
(3) As for the ion nitriding, there was little difference in wear properties with regard to the nitriding conditions.
(4) The wear properties with nitriding condition were considered to be caused by the difference in morphology of the compound layer. The compound layers formed by ion nitriding were solid, whereas those by gas nitriding and tufftriding were porous.
(5) In the case of mild steel, the endurance against pitting was more important than the wear loss.

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X-ray pseudo-Kossel patterns, which are certain diffraction patterns obtained from irradiating divergent characteristic X-rays to a single crystal plate, are analyzed and represented in a few expressions.
After Imura who was the first to analyze these patterns in a complicated equation, only two points of each pattern have been adopted in some experimental analysis.
In this paper new simple sinusoidal equations of a pseudo-Kossel pattern are expressed in correspondance to the film with diffracting points on th specimen surface. Every part of the diffracted pattern as well as every point of the specimen surface can be available for analytical purposes. As an example, the equations of pseudo-Kossel patterns are applied to determine the lattice constant of pure aluminium and the sensitivity of each variable is examined.

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The metal cutting mechanism is affected by both the plasticity and fracture properties of crystals. The zinc crystal has the large plasticity or the cleavage in accordance with the crystal orientation, and moreover there exists only the limited slip system, (0001)⟨11\bar20⟩. This experiment was conducted under the two-dimensional cutting using the large zinc crystals of known orientation.
The main results obtained are as follows:
(1) In the grain having the (0001) plane which inclines towards the inside of the workpiece from the cutting edge, the cleavage crack occurs passing through the entire grain.
(2) In the grain having the (0001) plane which inclines towards the free surface of the workpiece from cutting edge, the following cutting process is repeated: The chip thickness increases gradually with the advance of cutting, and the cleavage fracture occurs suddenly along the secondary cleavage plane {10\bar10}. Then the chip is removed owing to the cleavage fracture which occurs along the (0001) plane in succesion. As a result of the above-mentioned cutting process, the cut surface becomes coarse in appearance.
(3) In the grain with the (0001) plane almost perpendicular to the cut surface and almost parallel with the cutting direction, the cutting process is stable and continuous ribbon-like chips are formed.
(4) In the stable cutting, the shear angle (φ₁) is slightly smaller than the angle between the cut surface and the slip direction which inclines towards the free surface of the workpiece from the cutting edge (φ₂).
(5) In the stable cutting, the shear stress on the shear plane (τ) is independent of the shear strain (γ), taking the values of 18 to 22 kg/mm².

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Metallographic observations are made to study the difference in kinetics of the two types of discontinuous precipitation appearing in Pb-1.5 wt%Cd alloy. Volume fraction (P) and growth rate (G) of discontinuous precipitation cell, and interlamellar spacing (S) in the cell are determined with the specimens aged at temperatures ranging from −25 to 150°C for various times. The T-T-T diagram shows a double C-curve which is separated into two C-curves by a temperature of about 70°C. The G and S remain almost constant (G₀ and S₀) in the initial stage of isothermal aging, and then the G decreases while the S increases with further aging. Dependences of G₀ and S₀ upon aging temperature (T_A) differ between the two types of discontinuous precipitation.
Zener’s volume diffusion model and Turnbull’s interface diffusion model are shown to be applicable respectively for the G₀ of each discontinuous precipitation above and below 70°C. The lattice volume diffusivity (D_V) and the grain-boundary diffusivity (D_b) are estimated from G₀ and S₀. It is shown that the temperature 70°C agrees approximately with the T_A, above which the D_b⁄D_V is smaller than S₀⁄λ. Where λ is the thickness of the cell boundary. This result suggests that the type of discontinuous precipitation observed at a given T_A gives a higher growth rate. Substitution of S₀ into Zener’s equation for S yields the result that the interfacial energy between solid Pb and Cd for the discontinuous precipitation of D_b-control is about 3 times larger than the value for that of D_V-control. This suggests that the equilibrium state cannot be established within the cell of the discontinuous precipitation of D_b-control.

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An ultra-high temperature microscope was newly designed and constructed, and it has three noticeable advantages as follows. Firstly, the maximum temperarture of specimens is available more than 2500°C by the electron beam heating. Secondary, the exchange procedures of specimens become easier by using an air-lock mechanism, so called the side-entry goniostage. Thirdly, the image contrast even under high temperatures is kept as high as that at room temperature, as the direct radiation from the heating specimen is cut off from the imaging ray by means of narrow band pass filters.
In addition, an infrared pyrometer was ready to use any programming of heating and cooling of specimens, in combination with the electron beam gun. The expected functional features were attained very successfully and some preliminary applications were also obtained.

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The mechanical properties of a molybdenum sheet of 1 mm thickness prepared by rolling a boat-shape ingot of EB-melted molybdenum have been examined for its industrial application. The results obtained were as follows.
(1) By melting a compact of metal molybdenum powder, to which 0.06% carbon was added with a supply of the electric power of 21 kW hr/kg, a cast ingot containing 0.026% carbon and 0.001% oxygen was obtained.
(2) The above-mentioned ingot could easily be rolled into a sheet about 1 mm thick at a processing temperature of 1200°C.
(3) The recrystallizing temperature is between 1050 and 1200°C. Even at 1050°C there already occurs a partial recrystallization.
(4) The ductile brittle transition temperature of the sheet sample, tentatively defined as the temperature at which the elongation in the tensile test was 5%, was −15°C in the “as rolled” state and it was −40, −20, −20, −20, 0°C respectively for the annealing temperatures of 900, 1050, 1200, 1350 and 1500°C.
(5) From a comparison between the room-temperature tensile properties of a sheet recrystallized at 1200°C and those previously reported on EB-molybdenum, the present results with a tensile strength of 46 kg/mm² and a 25% elongation were indicated that the sample investigated is of the softest kind.
(6) The tensile specimen of recrystallized sheet, into which a fusion bead was introduced by EB in the middle of gauge length for intending the simulation of welding, did not break at the bead part in a tensile test at room temperature and 100°C, but it broke at the base material sufficiently away from the bead. The refinement of carbides in the fusion bead is considered to be the cause of the strengthening at the bead part.

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Creep tests have been carried out on Hastelloy X alloy at 900°C in air and in helium containing similar impurities to those in the coolant of the high temperature gas cooled reactor. (HTGR)
The results indicate that creep lives and rates strongly depend on the grain size, that is, the creep rate increases linearly with (grain size)⁻¹ and the time to 20% creep, T₂₀ is proportional to (grain size)^0.86.
The difference between the creep behaviour in air and in helium is discussed on the base of the creep property corrected with the grain size, and the metallurgical examination and analysis of carbon content are carried out on specimens tested in air and in helium. It is suggested that there is little deterioration in the creep property of Hastelloy X alloy under the simulated HTGR atmosphere at 900°C.

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Stress corrosion cracking (SCC) tests of Al-4%Cu single crystals cold-reduced up to 30% were carried out under applied stresses, σ_a=0.3σ_f and 0.4σ_f (σ_f: tensile strength), respectively, in 5.4%NaCl+0.6%H₂O₂ solution. The characteristics of crack growth in SCC were analysed by a mechanochemical mechanism previously presented.
In this system, SCC always occurs owing to preferential attack at (100) traces. The number of cracks was independent of the level of applied stress and cold reduction. The time to fracture was nearly constant, i.e. about 10³ minutes under the applied stress mentioned above, despite the difference in the degrees of cold reduction. Where as the crack induction period (t_i) decreased with increasing cold reduction, the propagation period (t_c) increased. There were the following relations: c^1⁄2∝t_c between crack length (c) and t_c, c∝ε between c and srtain (ε), c^1⁄2⁄t_c decreased and c⁄ε increased with increasing cold reduction. The results suggest the validity of the mechanochemical mechanism for SCC of this system.

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Synthetically produced FeCr₂O₄ was reduced isothermally and non-isothermally with graphite powder in flowing (300 cc/min) and suspended Ar gas atmospheres. The rates of reduction were measured by means of a thermobalance using a silica glass spring.
The results are as follows:
(1) In the first stage of reduction, the FeO component was reduced preferentially and Cr₂O₃ was precipitated, following which Cr₂O₃ began to be reduced.
(2) The metallic products changed with proceeding reduction in the following order: Austenite\dashrightarrowaustenite+(Fe, Cr)₃C\dashrightarrow(Fe, Cr)₃C+(Cr, Fe)₇C₃\dashrightarrow(Cr, Fe)₇C₃.
(3) After the reduction of the FeO component, the rate of reduction decreased for a while and then increased. It seemed that the intermediate decrease in the rate of reduction was due to carburization with the reduction, because the carburization increased the P_CO2⁄P_CO ratio of the gas phase.
(4) The rate of reduction in the gaseous flow of Ar at 300 cc/min was considerably lower than in the suspended Ar, for the total pressure (P_CO+P_CO2) was decreased by flowing Ar.
(5) Above about 70% reduction, the rate of reduction decreased rapidly. It seemed that the reaction was controlled by the counter-current diffusion of CO and CO₂ through a relatively compact layer of (Cr, Fe)₇C₃.

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In order to study the crack propagation mode of lenticular martensitic steel fractured at a low temperature, the fracture surfaces were observed by means of optical and scanning electron microscopies using Fe-26%Ni-0.4%C alloy (Ms=−54°C). This alloy transformed into typical lenticular martensites and contained about 13% residual austenite by cooling into liquid nitrogen. Despite the fact that specimens were fractured at liquid nitrogen temperature, a ductile fracture was sometimes observed in addition to brittle fracture (clevage fracture and intergranular fracture along the austenite grain boundary), because the alloy contained a considerable amount of retained austenite and the martensite itself was somewhat ductile due to high Ni content.
The observed crack propagation pathes in relation to the microstructure can be classified into the following four modes as shown schematically in Fig. 1. The probability of each mode is also shown in the brackets. Type 1: intergranular brittle fracture along prior austenite grain boundary (38%). Type 2: fracture along the interface of martensite plate (11%). Type 3: fracture across the martensite plate. This is furthere subdivided into two types. Type 3(a): clevage fracture (26%). Type 3(b): ductile fracture (10%). Type 4: ductile fracture passing through the coexisting region of retained austenites and martensites (15%).
Fracture modes of Type 2 and Type 3 were mainly observed in relatively large martensite plates which were formed at the early stages of transformation. On the other hand, Type 4 was generally observed in the region of small martensite plates mixed with retained austenites. The results of the present observations show that, in the case of lenticular martensite, the crack propagation path is generally governed by large martensite plates and is entirely different from that observed in lath martensite.

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An improved method for the determination of nitrogen in powdered tantalum without using the metal bath was established, which involves pelleting of powdered tantalum at a pressure of 300 kg/cm² and at room temperature with the addition of one mole ratio of powdered graphite and the extraction of gases at 2250∼2350°C.
From the study in a graphite crucible of changing the thickness of the tantalum pellet and gas extraction temperature, it was found that extraction of nitrogen was quantitatively completed only when the pellet was as thin as 0.2 mm and the extraction temperature was as high as 2300°C.
The analyses of tantalum pellet with a thickness of 0.2 mm which had been extracted of gases showed a gravimetrical increase of one mole carbon per mole of the tantalum and the X-ray diffraction of the sample showed the formation of TaC.
It was considered that carbon played an important role in the release of nitrogen; extraction of nitrogen was enhanced by the addition of carbon. From the above finding an addition of one mole ratio of powdered graphite to the sample was attempted. With this procedure the extraction of gases was accomplished in a short gas collection time compared with the one without the addition of graphite, independent of the thickness of the samples.
The results of determination were in agreement with those obtained by Kjeldahl method. The gas collection time for a 1∼2 g of powdered tantalum containing 0.004∼0.007% by weight of nitrogen was within 30∼60 min with the precision of variation coefficient of less than 5%.

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Magnetic behavior of Fe-Al alloys with the composition in the neighborhood of 25 at%Al has been investigated by means of magnetic and Mössbauer measurements. A reliable phase constitution is determined for the atomic and magnetic ordering. Magnetic anomalies observed in this system can be satisfactorily interpreted in terms of our phase relationship. The variation of magnetization with quenching temperature shows a rapid increase in the intermediate temperature range owing to the appearance of the ferromagnetic disordered α phase. The so-called “double Curie point” phenomenon is primarily caused by the coexistence of the ferromagnetic phase with the paramagnetic one. The ratio of the phases, ferromagnetic α to paramagnetic B2, determines the magnetic intensity of the alloy depending on the composition and the cooling rate.

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In a 3%Si-Fe alloy with mean grain sizes from 13.6 to 80.9 μ, a new yielding accompanied by a prominent yield drop was observed when it was pulled only under a certain test condition at high temperatures. The characteristics of this high-temperature yielding phenomenon were studied by tensile tests at various temperatures from room temperature to 800°C with strain rates varying from 1 to 10⁻⁵ l/sec. The results were as follows: (1) The relation between the yield stress and grain size was approximately represented by the Hall-Petch equation from room temperature to 800°C. (2) In the region where the high-tmperature yielding was observed, the grain size effect K_y. D^−1⁄2, was nearly independent of temperature and strain rate, but the friction stress, σ₀, was strongly sensitive to them. The yielding phenomenon was observed in the region of lower temperature and higher strain rate in this thermal deformation range or only in the region of friction stress between an upper bound and a lower bound, independent of the actual temperature or strain rate. At the lower temperatures and higher strain rates furthermore, friction stress was nearly independent of temperature and strain rate, indicating the athermal deformation behaviour. (3) Friction stress, σ₀, in the thermal deformation range can be correlated with temperature, T, and strain rate, \dotε, approximately by the follwing deformation equation.
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\ oindentwhere τ₀=1⁄2·σ₀, ΔH₀^′ is 93.5 kcal/mol and the values of exponent m decrease from 5.1 to 4.0 with increasing temperature. ΔH decreases from 93.5 kcal/mol to 79.5 kcal/mol with increasing τ₀ from 1 kg/mm² to 9 kg/mm² and the activation area calculated using the above equation decreases from about 140 b² to 35 b² with increasing τ₀ from 2 kg/mm² to 9 kg/mm². (4) The heterogeneous deformation related to this yielding phenomenon was not observed and the density of etch-pit which was considered to be related to each dislocation increased rapidly at the yielding.
From these experimental results it is considered that the values and strain rate dependence of friction stress in the region where the high-temperature yielding occurs are sufficiently large and mobile dislocations multiply rapidly at the yielding and therefore this phenomenon may be interpreted as arising from the mechanism proposed originally by Johnston. The yield deformation in this region is likely to be controlled by the process based on a short range interaction between gliding dislocations and localized obstacles.

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Frequency response of a passive iron electrode was studied in a neutral solution (pH 8.39) at various potentials. An electronic potentiostat with a sinusoidal wave generator was used to control both d.c. and superposed a.c. potential of the electrode. The impedance was determined by measuring the amplitude and the phase shift of a.c. voltage and current on a two-channel osciloscope and recorder. The measurement was made in a frequency range from 10⁻² to 2×10⁴ Hz. The frequency response diagrams obtained were classified into three categories according to the corresponding potential regions. In a complate passive state, the frequency response was similar to that of an ideal capacitor, and the electrode behaved as an ideal polarizable electrode, because of the absence of any possible reaction. In the pre-passive and the trans-passive state, however, the frequency responses were simulated by that of a cascade connection of two circuits of capacitor and resistor in parallel connection. It is readily seen that one of the parallel circuits corresponds to the impedance at solution/passive film interface, which represents the transfer resistance and double layer capacitance. Only when the transfer resistance was deduced by the existence of electrochemical adsorption or dissolution, the impedance of the passive film became appreciable. The potential profile across the passive film was discussed and it was concluded that the major part of potential drop exist at the solution/passive film interface.

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In order to account for the excellent ductility of a ausformed steel, the tensile properties of ausformed martensite were compared with those of deformed austenite using an Fe-25%Ni-0.4%C alloy. The results obtained were as follows.
(1) Although the size of martensite plate became smaller by ausforming, there were still lenticular martensite plates in the ausformed steel as large as in the non-ausformed one. In such a large ausformed martensite which showed a characteristic morphology, there were several islands or layers of retained austenite in the plate.
(2) The elongation of martensite was hardly effected by the amount of ausforming, while that of austenite decreased with an increase in the amount of prior-deformation. The elongation of deformed austenite, therefore, became smaller than that of ausformed martensite, when the prior-deformation (ausforming) was more than about 30%. The heavily deformed austenite was enhanced in strength and elongation by subzero-cooling to produce martensite.
(3) In the fractured surfaces of austenitic specimens, some kinds of large or elongated dimples were observed and their number increased with the degree of prior-deformation, while the size and shape of dimples were hardly changed by the degree of prior-deformation (ausforming) in martensitic specimens.

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