The present work has dealt with the torsion creep behavior and the torsion creep strength at moderate temperatures of quenched and tempered hot-work die steel (SKD5), high speed steel (SKH2) and JIS spring steel (SUP6) which were used for high-temperature spring material. Torsion creep test were carried out on 5mmφ solid cylindrical specimen at 15°, 300° and 400°C under a stress of 12∼45% of static torsional strength. In the case of 150°C of SUP6 and 300°C of SKD5, creeping did not proceed after about 300 hours, but at 300°C of SUP6 and SKH2 and 400°C of SKD5 and SKH2 creeping was continued even after 400 hours with decreasing the creep rate. The torsion creep strength for a strain of 0.03% in 100 hours of 300°C of SKD5 was 28kg/mm2, and for 400°C was 23kg/mm2. For 300°C of SKH2 was 41kg/mm2, and 18kg/mm2 for 400°C. And also, for 150°C and 300°C of SUP6 were 34kg/mm2 and 16kg/mm2, respectively.
A series of fatigue tests were made on high pre-stressed notched specimens. A specimen was stretched statically, and thereafter fatigue load (completely reversed axial stress, pulsating tensile stress or rotating bending stress) was applied on it. The schedule of experiments are shown in Table I. The fatigue test results show that when a considerably high pre-stress is applied on a notched specimen, the specimen is possible of improvement in fatigue strength, but the extent of the improvement will be influenced by the kind of material, the shape and size of the notch, and the extent of pre-stress.
In order to study the development of the fatigue strength of steel due to the induction hardening, it is necessary to investigate the effect of tempering upon the fatigue limits σw1, σw2 and the condition of crack propagation. This paper contains the experimental results and the considerations concerning the induction hardened steel specimens (0.16%C) with V-notch, tempered at several kinds of temperatures. The data and considerations may be summarized as follows; (1) The fatigue limit σw1 has little change, while σw2 decreases rapidly with increase of tempering temperature. This fact shows the fact that the initial crack of specimens tempered at high temperature develops easily to final fracture. This is closely related with the experimental results concerning the residual compressive stress-release due to the tempering at the V-notch root. (2) At σ=30kg/mm2 stress level the curves of crack depths to stress cycles of specimens with two different tempering conditions (no-tempered and tempered at 300°C) completely coincide. At higher stress level σ=50kg/mm2, however, the rate of the crack propagations of the tempered specimens is larger than that of the non-tempered ones, while the stress cycles before crack formation remain almost the same under both conditions. (3) Based upon the above facts, the effects of the residual compressive stress at the crack tip upon the crack propagation have been discussed.
In the previous report the fatigue deformation limit diagram at room temperature was studied experimentally on the coiled springs of 0.82% C-steel wire. In the present paper the same limit diagram on that of 0.44% C-steel wire is investigated at room temperature and 100°C. The results obtained are as follows; (1) The fatigue deformation limit at 100°C is remarkably lower than that at room temperature. This may be the result mainly from the over-ageing due to both heating and repeated stress. (2) From the above result, it is undesirable to use these coiled springs at elevated temperature, even at 100°C. If these springs must be used at 100°C they should be used under the repeated stress condition below the fatigue deformation limit obtained in this investigation.
The propellers of ships have often been observed as damaged as a result of cavitation erosion. Although several investigations have been made on the problem of cavitation erosion of coatings by way of prevention against damage of propellers, the cavitation tests have been conducted under different test conditions with different test methods. This is the report of test conducted of 6 coatings (neoprene, polyurethane, electro nickel plating, electrochromium plating, flame sprayed colmonoy (fused) and welded high Al-bronze) with a view to determining their comparative efficacy for cavitation erosion resistance. A magnetostrictive cavitation test apparatus, a rotating-blade cavitation test apparatus and a water-tunnel cavitation test apparatus were used for the purpose. These coatings were applied to base Al-bronze. The results obtained are summarized as follows: (1) In the magnetostrictive cavitation test, the electrochromium plating shows superior cavitation erosion resistance, but the flame sprayed colmonoy (fused) shows cavitation erosion 3 times as large as that in the electrochromium plating. (2) In the rotating-blade cavitation test, the electrochromium plating shows superior cavitation erosion resistance, but the welded high Al-bronze shows cavitation erosion 10 times as large as that in the electrochromium plating. (3) The ranking of cavitation erosion resistance of coatings in the water-tunnel cavitation test is the same as in the magnetostrictive cavitation test.
The effect of the minor components added to 3CaO·SiO2 on the thermal decomposition of 3CaO·SiO2 has been studied by the methods of X-ray diffraction, differential thermal analysis and thermogravimetric analysis. The tricalcium silicate is prepared by heating the mixture of guaranteed reagents of calcium carbonate and silica, and also the guaranteed reagents used for the additives. The results obtained are summarized as follows; (1) The minor components, i.e., B2O3, Cr2O3, CoO, CuO, BaO, NaCl and CaF2 accelerate the thermal decomposition of 3CaO·SiO2 in the mixture of 3CaO·SiO2 1mol+the minor component 0.05mol heated at 1200°C for 5 or 10hr, as shown in Table I. (2) The mixtures of 3CaO3·SiO2+additives, i.e., Cr2O3, MnO2, NiO, CoO, ZnO and CuO are influenced by the heating atmosphere. (3) It seems that the ions of nearly the same size as Si4+ or having smaller size and larger ions than Ca2+ are possible to stabilize β or α' form of 2CaO·SiO2 and accordingly these ions are effective for the thermal decomposition of 3CaO·SiO2.
To express the linear viscoelastic properties of plastics, the author proposes the use of new spectra, G1(τ) and F1(τ) defined by Eqs. 4 and 7 as substitutes for the retardation and relaxation spectra, F(τ) and F(τ). These new spectra, implying the viscosity term and not being normalized, little differ from the Schwarzl-Staverman's 1st approximation for F(τ), F(τ) derived from creep and relaxation functions. The author attaches importance to the G1(τ) and F1(τ) as the functions expressing the nature of plastics in stead of treating them only as the derivatives from the 1st approximations for F(τ) and F(τ). As given in Eqs. 3, 4, 6, 7 and 9, the computings of these new spectra from the data of creep, relaxation and constant strain rate tensile tests are carried out exactly and easily, and the reverse is the same. The transformation between G1(τ) and F1(τ) is also very easily carried out by Eq. 10 using the electronic computer. The fact that not every continuous function arbitrarily given for the creep or relaxation curves can be expressed by F(τ) or F(τ), but that they can always, be expressed by G1(τ) or F1(τ) is a distinguished feature of using these new spectra, apart from the discussion whether the feature is necessary for the description of the nature of plastics or not. The derivations of viscoelastic relations expressed by G1(τ) and F1(τ), the discussion on the benefits of using these spectra and the examples of G1(τ)&F1(τ) transformations are given below.