The influences of microstructural parameters on the lower yield point σ were investigated, in the microstructure containing tempered martensite patches in free ferrite matrix. The results obtained are as follows: (1) σ is not affected by the difference of hardness in the tempered martensite patches. (2) σ rises with the increasing of f, the volume ratio of total tempered martensite, when the ferrite grain size α1 is kept at a constant value. However, σ does not vary, when the mean free path between the tempered martensite patches α2 is kept at a constant value. (3) There is an approximately linear relationship between (α1)-1/2 and σ in the presence of tempered martensite patches. And the sensitivity of σ to α1 increases with the increasing of f. (4) There is a linear relationship between (α2)-1/2 and σ, and better correlation is demonstrated compared with the relationship between (α1)-1/2 and σ. Furthermore, when the values of f are with in the range of 15 to 40%, the values of σ are plotted on a straight line irrespective of f. (5) These results can be understood under the consideration that, in the propagation of Lüders band, α2 is the effective length of slip band to produce the stress concentration for forcing a dislocation out from a boundary of free ferrite and tempered martensite patch, when the tempered martensite patches are contained.
The room and elevated temperature mechanical properties as well as the aging characteristics after various heat-treatment have been investigated on commercial 21-4N valve steel. The results obtained are as follows: (1) Solution temperature of 1200°C is suitable for this steel. (2) In aging the sufficiently solution treated steel at 900∼1000°C, both general and lamellar precipitation occur, but in the steel aged at temperatures below 800°C only general precipitates appear. In the insufficiently solution treated steel at the temperatures below 1150°C, however, only general precipitation takes place regardless of the aging temperature. (3) This steel shows high strength and toughness even in solution treated state. The aging causes only slight improvement of strength, but the toughness at room temperature decreases remarkably by aging, particularly by high temperature aging in which the lamellar precipitation occurs.
The fatigue tests under the pulsating tension were performed of the threaded joints made of the steel bars entirely hardened by the high frequency induction heating and tempered to the various values of ultimate tensile strength. The threading was made by means of cold rolling after the heat treatment. The results obtained are as follows: (1) The relationship of the static tensile strength of steel bar and the fatigue strength of the threaded joint made of the bar varies with the difference of mean tensile stress in the fatigue test. Under the low mean tensile stress, the increase of the static tensile strength of the bar contributes to the increasing of the fatigue strength of the threaded joint. Under the high mean tensile stress, the fatigue strength of the threaded joint does not vary with the difference of the static strength of the bar. (2) It has been said that the fatigue strength of the threaded joint does not vary with the difference of mean tensile stress. However, the effect of mean tensile stress is apparent in the threaded joint made of the steel bar having the high static strength.
We have already reported on the effect of intermetallic compound CrAl7 on the fatigue strength of extruded 7075-T6 aluminium alloy when the compound (about less than 2mm wide) is situated at the central part of the surface of unnotched specimen. This study was performed on the fatigue strength of the alloy specimens having square or hole-type artificial defects at their central surface, and compared with the above mentioned results. The Schenck's plane-vibrating fatigue tester has been used for fatigue experiments and the measurements of fatigue strengths have been made at 107 cycles. The shape, size and depth of artificial defects are shown in Fig. 2, Tables II and III. The square-type defects are made by electric-discharge method and hole-type defects are made by drilling process. The bottom of each defect is flattened. The fatigue strengths and fatigue strength reduction factors are shown in Figs. 6, 7, 9 and 10, respectively, and the fatigue strength of the specimen having an intermetallic compound is also indicated in Table IV. The fatigue strengths of the specimen having intermetallic compounds approximately correspond to the values of square-type 0.1mm depth and the fatigue strengths of hole-type defect specimens are higher than that of square-type defect specimens. Accordingly, the intermetallic compound may be acceptable as a square-type artificial defect, and the depth of the defect affects the fatigue strength more than the width of defect.
The casting specimens are made of copper-zinc alloy (i.e. brass). Of the latter there are seven sorts according to zinc ingredient ratio in the range of 10∼40%. Turning and drilling tests have been experimented. Research has been conducted of the correlation between the chemical composition or the microscopic structure and the machinability in the viewpoint of the cutting resistance, the unit net horsepower, the surface roughness, and the torque or the drilling time under constant load drilling among others. The results are as follows; With the α-phase alloy with zinc ingredient in the range of 10∼30%, the cutting resistance and the unit net horsepower decrease with the rise of zinc content, but, when the alloy changes from α-single phase to (α+β)-phase with zinc content in the range of 30∼40%, the cutting resistance and the unit net horsepower increase, and this inclination is especially distinct in the case of the small side rake angle. In this experiment, the surface roughness is generally well, and there is not so much difference by the alloyed zinc content. To be precise, however, the rough surface gets improved with the rise of the zinc content and increase in side rake angle. In drilling under constant load, the torque corresponding to the zinc content is not so changeable and the inclination is not so distinct, but, the drilling time changes clearly according to zinc content in α-single phase and increases again if the alloy becomes in (α+β)-phase with increase of zinc content.
The failure of glass envelope of miniature electron tubes in the thermal shock tests are discussed in the present paper to control the quality. It is pointed out that the factors of failure are the stress of the glass, the degree of the glass heating, the final shape of the sealed electron tube and the stiffness of the outer pin of the stem. In addition, we have classified the thermal shock test defects of glass envelope according to the above mentioned results. This report is mainly discussed on various methods of thermal shock testing. Their summary runs as follows: (1) If in making the stem the stem glass is strongly tempered, strong radial compression stress is set up, and crack occurs radially across the stem through the pin in the seal-in process. If on the other hand, the stem glass is lightly tempered, strong radial tension stress is set up, and crack occurs tangentially on the circle of the pin through the pin in the seal-in process. The test of upward thermal shock has been introduced by inserting the stem into the electric oven to examine the thermal resistivity against the crack of the stem. The crack of the stem in this test has correlation with the crack of the stem in the seal-in process of the stem and the bulb. (2) In order to make sure of the result of the thermal shock test of the electron tube it is recommended that both upward and downward thermal shock tests will be performed, and it is very important that failure in thermal shock will be avoided by carefully observing the difference in temperature between the upward and the downward testing.
We discussed mainly the various methods of thermal shock testing of glass envelope of electron tubes in our previous report. In this paper, it is pointed out that the stiffness of the stem pin, the firing condition of stem molding and the seal-in process have a great deal to do with the thermal shock cracking. It is intended in the present paper to clear up the causes of thermal shock failure based on these results. (1) If the glass base of the electron tube is strongly tempered in the seal-in process, strong radial compression stress is set up and crack occurs radially across the base through the pin on the downward thermal shock test. On the other hand, if the base is lightly tempered, strong radial tension stress is set up and crack occurs radially across the base through the pin or the crack tangentially on the circle of the pin through the pin in the upward thermal shock test. (2) The relation between the test of stiffness of the Ni outer pin of the stem (annealing treatments of the Ni outer pin) and the thermal shock test with deflexion cone has been examined, and if the pin is too stiff, crack occurs tangentially on the circle of the pin through the pin in the thermal shock testing. (3) Crack occurs radially across the base between the pins in the thermal shock test when the temperature of stem molding is too low. It appears that laps are formed between the stem beads, and they act as the cause of the fracture. (4) If the final shape of the sealed electron tube is deformed, crack occurs tangentially on the seal in the thermal shock test. (5) The cracks of the glass base are classified into four types, that is, Type A: Crack radially across the base through the pin Type B: Crack tangentially on the circle of the pin through the pin Type C: Crack radially across the base between the pins Type D: Crack tangentially on the seal.
The environmental stress-crack behavior of acetal copolymer Duracon was studied by the immersion method in HCl aq. solution, using a test specimen of 1mm thick Duracon sheet attached to a quarter section of an elliptical jigs. It was found that among the several variables affecting the stress-cracking of acetal copolymer, such as acid concentration, immersion time and immersion temperature, the acid concentration had the greatest effect on the critical strains. It was also found that at any concentration of HCl tested a state of equilibrium of critical strain was reached in the time between 30 and 60 minutes at 16.5°C in immersion, but at the higher immersion temperature this equilibrium of critical strain was not attained within 60 minutes for the dilute acid solution. These results were used to discuss the method of estimating the critical stress from the critical strain data.