The corrosion resistance of boronized and unboronized steels against various chemicals has been investigated. The samples of SPCC, S15C, S35C and SPH were boronized at 950°C for 3hr or 6hr in the salt consisting of H3BO3: 40wt%, K2B4O7·5H2O: 20wt%, NaF: 15wt%, K2CO3: 15wt%, and Mg powder: 10wt%. As the corrosive media, water, NaCl, H2SO4, HCl, HNO3, H3PO4, HF, C3H6O8, NH4NO3 and HCO2H were used. The tests were performed at room temperature as well as at high temperatures (60 or 90°C). The results obtained were summarized as follows: The boronizing of steel remarkably increases the corrosion resistance against 0.5N-H2SO4, HCl, 60°C 85%-H3PO4, 47%-HF, 90°C 8%-C3H6O8, 60°C 50%-NH4NO3 and 60°C HCO2H. However, it does not improve the corrosion resistance against water, 10%-NaCl, 36N-H2SO4, 60°C 36N-H2SO4 and HNO3.
It is well known that the creep rupture behavior of rigid polyvinyl chloride (PVC) is brittle in conc. sulphuric acid. Although the mechanism of the fracture is not yet clarified well, the diffusion and the chemical reaction of sulphuric acid in PVC are considered important factors. In this paper the diffusion of sulphuric acid and the dehydrochlorination in a rigid PVC plate were studied under unloaded and loaded conditions at temperatures of 30°to 80°C. The concentration of sulphuric acid and residual chlorine in PVC were determined by the flaskcombustion method. The results obtained are as follows: (1) The concentration gradient of sulphuric acid near the surface of PVC plate increases with increasing temperature and the surface concentration tends to increase with immersion time. The concentration distribution has an anomalous peak below the depth of 0.1mm in the case of the immersion above 70°C. (2) The diffusion of sulphuric acid depends on both tensile and compressional stresses. Its dependence decreases with increasing temperature. (3) The dehydrochlorination of PVC plate following the diffusion of sulphuric acid occurs only near its surface as in the case of the diffusion.
The present work aims at the discussion about the influence of deformation twinning and basal- and pyramidal-slips on the stress-strain characteristics of zinc polycrystal specimens. For this purpose, the tensile tests have been made under 2000kg/cm2 hydrostatic pressure on two groups of specimens of cold-rolled zinc sheets; one group has the tensile axis coinciding with the rolling direction and the other perpendicular to that direction. The results are summarized as follows: (1) Hydrostatic pressure has no influence on the stress-strain behaviors of the specimens tested. Every specimen is ductile even under ordinary pressure, as expected from the grain size and texture of the specimen material. (2) The growth of deformation twinning raises the flow stress of a polycrystalline specimen. This is mainly due to the effect that each of the twins subdivides each grain. (3) Plastic flow in a zinc polycrystal is caused by both basal- and pyramidal slips. (4) The strain hardening behavior of a zinc polycrystal depends largely on pyramidal slips. (5) The flow stress is about 20% higher in the extension along the transverse direction than that along the rolling direction. (6) It seems that the low strain hardening rate of a zinc polycrystal results mainly from the dynamic recovery of dislocations in pyramidal slips. In addition to this, the stress relief due to the nucleation and growth of the twins should play an important role when a specimen has some extent of the preferred orientation of crystals.
Uni-axial compression tests of two plastics, polycarbonate (PC) and polyacetal (PA), were conducted at various strain rates from 2.2×10-4/sec up to the order of 103/sec by using short cylindrical specimens. Also the same tests were conducted under the static outer pressure of 200 or 400kg/cm2 applied to the circumferential surface of specimens. High strain rates of the order of 102∼103/sec were obtained by a Hopkinson pressure bar apparatus, and some discussions were made on the stress-strain relations obtained. As a result, the stress-strain relations for the materials used showed remarkable strain rate dependence. The ratio of the yield strength of PC without the static outer pressure at the high strain fate 360/sec to that at the low strain rate 2.2×10-4/sec was 1.65, and that of PA was 1.77 under almost the same condition as PC. The relation between the yield strength and the logarithmic strain rate for both PC and PA was found to be non-linear. The inclination in the relation was apt to increase as the strain rate increased. When the static outer pressure was applied to the specimen, the yield strength of the both materials at every strain rate was a little larger than that deduced from Tresca's or Mises' yield condition.
The crack growth rate of type 5056 aluminum alloy in reversed bending is much reduced in vacuum from that at atmospheric pressure, being independent of pressure in the range 10-4 to 10-6mmHg. On the contrary, the crack rate increases in high vacuum of 10-7mmHg under lower stress amplitude due to vacuum outgassing effect by prolonged exposure to high vacuum. The enhanced crack growth due to the vacuum outgassing appears more clearly in the ultra-high vacuum of 10-9mmHg irrespective of applied stresses. The plastic size generated at crack tips increases with the decrease of vacuum pressure, extraordinal plastic deformation being observed at 10-9mmHg. The acceleration of fatigue crack growth due to high vacuum outgassing can be remarkably observed on the surface crack extension of thin sheet specimens, which grows greater in the case of more prolonged exposure to higher vacuum.
Fatigue strength of tufftrided S15CK steel (smoothed specimen) was estimated using the change of temperature at the surface of a specimen during the rotating bending fatigue test. The results obtained are summarized as follows; (1) The relation between the mean temperature rise ΔTeq and the number of cycles to failure Nf can be described as ΔTeqmNf=C, and between ΔTeq and the stress amplitude σa it is ΔTeq=Aσan. (2) The fatigue strength for each of the three specimens with different diameters, and that under varying stress in the two level single block fatigue test can be approximately estimated from the change of temperature at the surface of a specimen during the fatigue test.
In the previous paper, the authors had discussed the effect of a high tensile load prior to stress cycling on fatigue strength. In the present study, in order to make clear the effect of a high tensile load during stress cycling on rotating bending fatigue strength, the following fatigue tests were carried out on smooth specimens of 0.33% carbon steel: a high tensile load was applied (i) during stress cycling in the ordinary fatigue test and (ii) at changing of stress amplitude in the two steps fatigue test. The conclusions obtained are summarized as follows: (1) The high tensile load σH=39.5kg/mm2, that is the lower yield stress, reduces the fatigue life. Especially, its effect is more pronounced at the lower stress level. This is due to non-uniformity of work hardening, as discussed in the previous paper. (2) The high tensile load σH=60.0kg/mm2 increases the fatigue life at the higher stress level, but decreases at the lower stress level. (3) There are two reasons to explain the effect of a high tensile load on fatigue life. One is the work hardening caused by the high tensile load. The other is the growth of cracks by the high tensile load to macro cracks from slip lines or micro cracks created during stress cycling. Therefore, the fatigue life is determined by the competitive process of both factors. It seems that the effect of residual stress caused by the high tensile load is very little.
The effect of phosphorus content in nickel film on the fatigue strength of electroless nickel plated steel was studied by a rotary bending method. In addition, the change in microstructure of the film during the fatigue test was examined by transmission electron microscopy. The results obtained are as follows; (1) The fatigue strength of steel is improved by electroless nickel plating regardless of phosphorus content in the plating film. The hardness of film and the degree of fatigue strengthening decrease with increasing phosphorus content in the film. (2) The baking at a temperature above 300∼350°C induces crystallization and grain-growth in the nickel film. The fatigue strength of plated steel after baking is lower than that of the non-plated one. (3) The electroless nickel film has a tendency to crystallize during the fatigue test under cyclic over-stress. (4) The fatigue damage of steel is suppressed by the electroless nickel film. Fatigue cracks initiate and propagate from a place just under the plating film, i. e., near the surface of substratum. (5) The nickel and phosphorus contents in plating films depend upon the pH value of the plating bath and show homogeneous distributions when the pH value in the plating bath is 5∼4.
The effect of solution pH on the corrosion fatigue behaviour of a low carbon steel (S15C) has been investigated in an aerated HCl-NaCl-NaOH aqueous solution environment, adjusted for a constant ionic strength of 0.5 at 25°C, over the range of pH0.5 to pH13.7. The main results obtained are as follows: (1) In the acidic range (pH<4), the corrosion fatigue strength decreased monotonically as solution pH was decreased. In the strongly alkaline range (pH>13) a marked increase in corrosion fatigue strength was observed. (2)In the middle pH range (pH4 to pH13) a maximum in corrosion fatigue strength was observed at pH5 to pH6, falling off to a local minimum at pH9 to pH12. This effect was most marked in the tests with a low cyclic stress amplitude, giving a large number of cycles to failure, and hence longer time for corrosion. The local minimum at pH9 to pH12 is thought to be due to a few deep corrosion pits, which were produced from localized pittings and acted as stress concentrators and crack initiation sites. (3) The corrosion fatigue fracture surface was predominantly intergranular in nature, although the specimens, fatigued in the passivating high pH (pH>13) region and in air, were both characterized by the fracture surface with fatigue striations and secondary cracks. (4) The fatigue lives obtained were compared with the results of corrosion tests in the identical corrosive environment under both flowing and stationary conditions.
In the previous paper, the authors studied the effects of hardness of samples and feed weight on grinding rate constants from the kinetic point of view. In the present paper, we studied their effects on rate constant of specific surface increase. The samples used were silica glass, borosilicate glass, soda glass, quartz, feldspar, limestone, marble, gypsum and talc. The pebble mill consisted of a 12.8cm-diameter by 13.2cm-long cylinder and 40 balls of 3cm diameter having the total weight of 1180g. The tests were done at the speed of 88.1% of critical one and with the feed size of -14+20mesh. Assuming that the shape factor is six, the specific surface of fine particles was measured by the permeability method and that of coarse particles was calculated from the size distribution. As the result, the following equation was obtained. Ks=17HV-0.58·Ws-1.5 where Ks is the rate constant of specific surface increase of zero order kinetics, HV the dimensionless Vickers hardness and Ws the dimensionless feed weight. To obtain Ks from the first order rate constant of feed size decrease K1, the following equation was derived. Ks=20HV-0.35(Ws/W1)-1.5·K1 where W1 is the dimensionless feed weight for the measurement of K1.
Brittle lacquer coating of air-drying type is superior in its applicability for experimental stress analysis to that of baking type, although on the former crazing often appears due to excessive internal tensile stress developed during the curing process at room temperature. Brittleness of the coating is markedly dominated, therefore, by the internal stress which is closely related to the basic ingredients, solvents and plasticizers used as the constituents of lacquer coating. Although previous studies have given informations about basic ingredients and solvents suitable for lacquer coating which displays high sensitivity and is of low toxicity and non-flammable, few studies have been made on plasticizers. Since it was expected that some neutral ingredients found in crude rosin might be useful as a plasticizer of the coating, a systematic study has been undertaken on the influence of these ingredients on both the brittleness and crazing. The results obtained are as follows. The lacquer coating employing β-sitosterol, which is most satisfactory among the ingredients tested, is not only free of crazing but also has an improved strain sensitivity of circ. 600 micro strain. The efficacy of β-sitosterol on the coating is attributable to the action that it relieves the overdeveloped internal stress effectively and increases adhesion between the coating and the top surface of the specimen. The glass transition temperature of the coating scarcely changes when a proper amount of β-sitosterol is used, so that the present lacquer coating can be applied even in summer.