Masayoshi Tagaya

Observations of Dislocation Networks in an Alloy of Body-Centered Cubic Lattice by Electron Microscopy

Electron microscopic observations were made on dislocation networks in thin foils of 55%Cr–Fe alloy annealed at 720°C after cold working. Dislocation cross-grids, hexagonal networks and networks of irregular shape are observed. From the presence of three-fold nodes, it is suggested that Burgers vectors of type [100] may be stable as well as those of type \(\frac{1}{2}\)[111].

Surface Damage of Annealed Steel Subjected to Cyclic Straining in Plastic Range

It was found that the surface damage of annealed mild steel subjected to the cyclic straining in the plastic range is almost slip band cracks. A model is proposed to explain the fact that the slip band cracks are formed independently of the magnitude of stress if there are some large and strong obstacles in the microstructure, but only in the range of low stress if there are none such. With repeated cyclings, the screw parts of piled-up dislocations loops on the two neighboring parallel slip planes cross slip each other and annihilae themselves. As the result, an intrusion is formed, and the pile-up is made of edge dislocation loops enough to initiate a crack. Next, the intrusion is connected with the initiated crack, and hence a slip band crack is formed. Under high stress fatigue, no slip band crack is formed, if there is no large and strong obstacle, because the concentrated tensile stress is reduced by the pile-up of edge dislocations of opposite sign and the initiation of crack is thereby arrested.

The Stress-Corrosion of Austenitic Stainless Steels

We investigated the influence of cold drawing, heat treatment, presence of oxidizing agents and cathodic protection on the susceptibility to stress corrosion of austenitic stainless steel wires. As the corrosive solution, boiling 42% MgCl2 solution (154°C) was used in this test. The specimens were stressed in tention and measured the time to fracture. The results are as follows:1) Influence of cold drawing; When 70% of the 0.2% proof stress are applied, the life to failure of stainless steel wires (0.5mm) decreases with the increase in degree of cold working up to 20% reduction, then increases with the increase in degree of cold working up to 40% or 95% redustion.2) Effect of heat treatment; The specimens cooled rapidly after heating at 900°C in cracked NH3 gas atmosphere or 1000°C in air, were relatively immune from susceptibility to stress corrosion, but the specimens cooled rapidly after heating at 1150°C in cracked NH3 atmosphere, became remarkably susceptibile to stress corrosion. The times to fracture by stress corrosion of specimens annealed for one hour at 380°C after cold drawing were shorter than those of “as-cold drawn” specimens. The cold drawn specimens annealed at 650°C for 1.5 hours showed chromium carbide precipitation, but these specimens showed an improvement in stress corrosion resistance because of the stress relief by those heat treatment.3) Effect of oxidizing agent; When a small quantity of KNO3 as oxidizing agent was added to the corrosive solution, the fracture of these wires by stress corrosion did not occur.4) Effect of cathodic protection; The cathodically protected specimens did not fail for 24 hours in the corrosive solution, when the current density exceeded 30μA/cm2. The unprotected specimens failed within one hour.

Hot-dip Aluminum Coating on Steel

We investigated the corrosion resistance of aluminized steel, which had been diffusion heat-treated at 700-1000°C for 1/4-2 hours in atmosphere, in the solutions with pH value of 1-14 range at room temperature and 60°C. At the same time, we studied the effect of diffusion heat-treatment on tensile strength and repeated bending value of the steel.The thickness of diffused alloy layer grows remarkably with substantial increase of diffusion rate when the base metal is heated above Ac3, 900°C. The diffusion layer has almost nothing to do with heating time.The aluminized steels diffusion heat-treated at 700-800°C have lower tensile strength than that of the steel as hot-dip aluminum coated, and it is less than 52kg/mm2. The aluminized steels diffusion heat-treated at the temperature above 900°C become to have higher tensile strength than that of the steel as hot-dip aluminum coated due to the remarkable growth of hard and brittle diffused alloy layer. On the contrary, the repeated bending value of these steels decreases rapidly by diffusion heat-treatment at the temperature above 900°C.The corrosion resistance of aluminized steel in acidic, neutral and alkaline solution with pH value of 1-14 range at room temperature and 60°C can be much more improved by diffusion heat-treatment at high temperature, however, the embrittlement of these steels by the growth of diffused alloy layer should be kept in mind.For example, the diffused alloy layer of aluminized steel heat-treated at 1000°C is only attacked less than 10% in the thickness after 6 weeks immersion in the acidic and alkaline solutions with pH value of all range at room temperature, especially less than 2% in the thickness in the nearly neutral solutions. This diffused alloy layer is only attacked respectively 19% and 23% in the thickness after 24 hours immersion in the solutions with pH 1.25 and 13.6 at 60°C.Even if the diffusion heat-treatment is performed at the temperature of less than 850°C, the diffused alloy layer has remarkably superior corrosion resistance in the acidic and alkaline solutions than metal and alloy layer of steel as hot-dip aluminum coated not only at room temperature but even at 60°C.

Hot-dip Aluminium Coating on Steel

We compared the corrosion resistance of aluminized steel with that of galvanized steel in acidic, neutral and alkaline solutions with pH value of 2-14 range at room temperature and 60°C.At room temperature, aluminized steel has remarkably superior corrosion resistance in the neutral and acidic solutions with pH less than 8. Especially, this steel is not entirely attacked by immersion for more than one month in the solutions with pH 6-8, and maintains its initial metallic luster. But this steel is attacked remarkably by alkaline solutions with pH value of more than 8.5. Galvanized steel has rather superior corrosion resistance in alkaline solutions of narrow pH value range only from 11 to 13. The surface of this steel is easily attacked even by neutral solution and its color changes to black, of course, it is more easily attacked in the acidic solutions with pH value of less than 7.At 60°C, aluminized steel shows the weight loss by corrosion as follows; 2g/m2/day in neutral solution, 20g/m2/day in pH 3 solution and 60g/m2/day in pH 2 solution. But the corrosion resistance of aluminized steel in neutral and acidic solution at 60°C is still more superior to that of galvanized steel in the same solutions than at room temperature. Galvanized steel shows at 60°C good resistance only in the solution with pH value of 12. When the pH value of the solution is over 12, with even its slight change, the corrosion resistance of this steel becomes worse remarkably, and the steel is severely attacked at the same temperature.

ON THE DETERIORATION OF QUENCHING OILS (II): Mineral Oils@@@礦油の老化

Synopsis: The deterioration of mineral oils for quenching was studied under the same procedure as described in the 1st report (The Deterioration of Fatty Oils: Tetsu-to-Hagane No. 2, Feb. 1954 P . 103•`111). The properties of mineral oils vary with the blowing with air as follows: (1) The quenching ability of mineral oils increases at the beginning and then decreases slowly with the blowing time, and the time required to cool from 700•‹ to 350•Ž is given approximately as a function of the blowing time by the following formula:

The Role of Boundary Tensions in the Cooling Ability of Quenching Media

The authors formerly reported that the boundary tensions among solid, lipuid and gas were the important factors next to the volatility of liquid for the characteristic temperature, at which vapor film breaks down, of quenching media in the cooling process. Later the differences of cooling ability among various liquids were often explained by the boundary tensions in their reports, but these explanations were not sufficient for the lack of definite data.In this report, therefore, the views of the authors were complemented with appropriate data: that is, the difference of the characteristic temperature were explaind by the boundary tensions in such cases as aqueous solutions of NaCl, etc. (non-volatile solute), mineral oil containing some polar substances, and deteriorated oil. The difficulties to find suitable reagents which could improve the cooling ability of mineral oil were pointed out. In order to elevate the characteristic temperature the wettness is the important factcr next to the volatility of the liquid.

On the Mechanism of Rust Formation on the Surface of Steel and its Prevention

We investigated the mechanism of rust formation on the surface of carbon steel and low Cr-steel in atmosphere and researched its prevention. The results are as follows: 1) Rust particles formed on the polished surface of steel are classified as dotted, granular, thread-like and lumpy rusts in their appearance. The lumpy rusts are produced by a limited number among dew drops condensed on the steel surface and grow rapidly. This is the principal source of rusting. 2) Lumpy rust generally starts in the pearlite area of steel surface, therefore high carbon steels rust more rapidly than low carbon steels. 3) 0.6% C-steel is quenched from 800°C and tempered at various temperatures; the one which is tempered at 450°C is most resistive to rust. 4) About the action of dust adhered to the steel surface, soluble chloride and sulphate particles (NaCl, NH4Cl, MgCl2 and Na2SO4 etc, have strong accelerating action and lumpy rusts start at every particles of them; Fe2O3 particles have nearly the same action; contrary to this, SiO2, Al2O3, CaO particles show no action. 5) If the steel surface initially bears complete oxide film (invisible) it can resist rust; therefore steels finished by proper electrolytic treatment, held in dry air for a long period or immersed in 0.5% K2Cr2O, 1% Na2HPO4 solution show good resistivity. 6) The initial flowing current from the surface of steel wire bearing complete oxide film (that is, having good resistivity to rust) immersed in 1% H2SO4, increases slowly and it requires long time to reach constant current density. Accordingly we can find the resistance to rust formation by measuring the flowing current. 7) Waselin and animal oils have generally greater rust prevention effect than vegetable oils.

The Corrosion Resistance and Electrochemical Property of Dental Alloys

The corrosion resistace of some dental substitutional alloys now in uses in our country was testedd by dipping them in dil HCl-, lactic acid-, NaCl-, Na2S- solutions, etc. at 37° for 1 week. The results show that Cu-alloys and Acolite were corroded by any of the above solutions, Ni-Cr alloys by only acid solutions, while none of the solutions attacked 18-8 stainless steel and Ag-Pd alloys. The electrolytic potential of the, dental alloys in 1% NaCl and Ringers solution was then measured against N-calomel electrode. 18-8 stainless steel and some Ni-Cr alloys became much nobler with time, and the potential difference between them and 22 K gold was only 0.02-0.08 V after 24 hrs, while other metals and alloys became baser or slightly nobler under the same condition. The galvanic current between each substitutional alloy and 22 K gold in 1% NaCl and lactic acid solutions with electrodes o_??_ 1cm2 and 1cm appart was measured for 3 hrs by a milliammeter, microammeter or a mirror galvanometer in accordance with the amount of current, and the initial current in the instance of short circuiting two electrodes was measured with an oscllograph. The initial current instantaneously-decreases by polarization and alter 1/30-1/10 sec nearly horizontal value is attained and then the current decreases very slowly, taking after several minutes nearly steady-value. The steady galvanic current for several alloys, which is very small compared to the initial value, is as _??_ollows (10-6 A unit; Palladium-s (Ag-Pd alloys)=0.01), 18-8 Stainless steel=0.13, N-Cl (Ni-Cr alloy)=0.06, Ni=3, Cu-9.7 Randolf=14.5, Acolite=35 Amalgam=100 in 1%, NaCl solution.