Thermal fatigue tests of 18-8 stainless steel were carried out under two different conditions, using a testing equipment that has a property to produce the strain and temperature cycling either independently or under a certain predetermined co-relation. One condition was such that the specimens were subjected to tensile stress at higher temperature, and in the other, compressive stress was applied to the specimen at higher temperature. After the tests, the microstructures of the fractured specimens were examined carefully, and the test results were discussed in connection with the various features of the thermal fatigue phenomenon in detail. Conclusion are as follows: (1) Under 700-200°C temperature cycling, thermal fatigue life is shorter when the specimens are subjected to tensile stress at higher temperature, than when the specimens are subjected to compressive stress at the same temperature. But under 500-200°C temperature cycling, no marked difference can be seen. (2) The specimens subjected to compressive stress at higher temperature show a large bulging at the center of the testing portion, as the number of cycling increases, but the specimen subjected to tensile stress at the same temperature did not show much deformation. These phenomena seem to be due to the difference of the strain and temperature cycling combined with the different temperature distribution along the axis during the heating and cooling period, and also with the constraint of the straining at the fillet parts. (3) From the study of microstructure, the precipitation and corrosion were recognized especially in the specimens heated up to 700°C. It is assumed that corrosion has a large effect on the thermal fatigue life of the 18-8 stainless steel.
The authors has conducted some varying-constraint thermal fatigue experiments systematically, and found a conclusion that cycle maximum temperature Tmax as well as mechnical strain ε is the most sensitve factor in thermal fatigue. Based on this assumption, a criterion for thermal fatigue failure has been proposed. That is, the relationship ε2=ε02+Kexp(Q/Tmax)/N gives a good fit for thermal fatigue test results of stainless steel, where ε0 is endurance limit, K and Q are constant. In order to apply the criterion to practical design, the authors have introduced ε-Tmax-N curve. In addition, the relation between thermal fatigue in case constraint is constant and that in case constraint is varying is also discussed.
In order to study some characteristics of the impact tensile strength of rolled screw bolts, especially the aging effects after rolling, we have conducted impact tensile tests of 1"/4 and 3"/8 rolled screw bolts made of ordinary and high tension steels, at test temperatures from -190°C to +100°C. The results obtained are as follows: (I) The impact tensile strength of rolled screw bolts gets a little larger as test temperatures become lower than +100°C, and shows the maximum value between 0°C and -50°C, while the impact strength gets rapidly small within the temperature below -50°C, and screw bolts show brittle fracture. And the transition temperatures at which ductile fracture is changed into brittle one are below -60°C. (II) Though the impact tensile strength of cut screw bolts is smaller than that of rolled screw bolts, the effects of test temperatures on the impact tensile strength have nearly the same tendency with the case of rolled screw bolts. However, on cut screw bolts made of heat treated Cr-V alloy steel, the transition temperature seems to move toward lower temperature. (III) The effect of aging after rolling on the impact tensile strength of rolled screw bolts is recognized at low temperature as for ordinary steels. It makes the impact strength decrease and the transition temperature rise by about 10∼30°C. Therefore, we must be careful, in the use of rolled screw bolts in low temperature. But this effect does not appear in the rolled screw bolts made of heat-treated Cr-V steel and cut screw bolts.
The reduction of titanium aluminate (Al2O3·TiO2) heated at 1500°C in various reducing atmospheres containing hydrogene has been studied. The titanium aluminate is prepared by heating Al2O3-TiO2 compacts in air at 1650°C for four hours. For the identification of crystal structure in the specimens X-ray diffraction analysis is done with the Norelco type diffractometer, using Cu Kα radiation. As shown in Fig. 4, X-ray patterns of Al2O3·TiO2 heated in different reducing atmospheres containing H2 have shown observable shift in the (33.0) line and the evidence of α-Al2O3. Under the condition of more stronger reducing atmosphere X-ray patterns show the formations of free Ti2O3 and α-Al2O3. These data lead to the following conclusion for the reduction of Al2O3·TiO2; Al2O3·TiO2→(Al2-x·Tix)O3·TiO2+Al2O3→Al2O3+Ti2O3.
In this paper, we have investigated on the packing characteristics of the clay bodies which are affected by the burning shrinkage in the course of the sintering proces from ordinary temperature up to the temperature of 1000°C. Such clay bodies contain absorbed humidity, crystallization water, carbonlike or organic matters, and these combustible matters are gastified in the process of burning, and consequently these bodies are contracted remarkably. The change of the packing arrangement of clay bodies is intricate and some observations were made to analyze these phenomenon. First we took up the Kaolinite clays containing “sericite” as the components, only poor packing densities, comparing to their large contraction, were obtained when they were exposed on the burning schdule. When, on the other hand, we took up the Kaolinite clays containing no “sericite” as the components, the resulted packing properties were dense. The samples containing known amounts of carbon powder (graphite powder used) as the combustible constituent, were also observed, and their packing densities fell significantly in the burning process, and there were intimate relations between these carbon contents (Combustible constituent) and loosening characteristics of the packing arrengements. Consequently, we may say (εx-εmx) values1) for the clay bodies containing carbon were affected by the heating loss or contraction of the bodies and raw clay itself.
Using a high temperature X-ray diffractometer and differential thermal analysis, the thermal decomposition of tricalcium silicate has been investigated. The tricalcium silicate is prepared by heating the mixture of guaranteed reagents of calcium carbonate and silica. After heating the tricalcium silicate powder for a long time of about 24 days at high temperature such as 1000∼1250°C, sixteen per cent of free lime are formed by the thermal decomposition of tricalcium silicate. In order to predict and discuss the chemical equilibrium of the reaction 2CaO·SiO2+CaO→3CaO·SiO2 the entropy, enthalpy and free energy changes for the reaction have been calculated in the temperature range of 300∼2400°K.