H2, CO, H2+CO, or a gas consisting mainly of CO and H2 are used as reducing agent of the iron ores. It is well known that various manufacturing methods of metallic iron, treated iron ores with gases have been recently investigated in Japan as well as abroad. As a fundamental experiment of manufacturing of iron powder, studies were made on the reduction of hematite powder with H2, NH3 cracking, and C3H8 cracking gases. The results obtained are as follows; 1) The determining step of the reduction with H2 gas is a chemical reaction between H2 gas and iron oxide. 2) In the reduction processes, the reduction velocity is reduced when the Wustite phase appeared. 3) When the iron oxide is cracked, the reduction velocity is accelerated. 4) The use of the temperature range of 550-560°C is advantageous, when the iron oxide powder is reduced with H2 gas. 5) The reduction behaviour with NH3 cracking gas is almost the same as with H2 gas, but the reduction velocity is rather slower. 6) The reduction velocity at the early period is different from that at the later period, during which it becomes faster. 7) The reduction velocity with C3H8 cracking gas is the slowest among those of all the methods used here. 8) When fine hematite powder is sintered at above 800°C, it is necessary to increase the flow rate of reducing gas and to reduce it at about 800°C by the reduction with C3H8 cracking gas.
The fluidized bed reduction of powdery iron ores has become the object of the authors' attention in view of special localized conditions in Japan and making practical use of domestic materials. In this experiment, fluidized bed reduction by hydrogen gas of one sample of hematite and magnetite was carried out on a laboratory scale. The apparatus was designed so as to fluidize powdery iron are by flat perforated grids or funnel type grids in a stainless steel pipe. Samples were extracted through a sampling tube at proper time intervals to investigate the effects of various factors on the reduction rate. The results obtained were as follows: (1) The rate of reduction of hematite are under atmospheric pressure reached 90% in 20 minutes at 600°C, and over 90% in only 10 minutes at 700°C and 800°C. (2) In the case of magnetite ore, the rate of reduction under atomospheric pressure reached 80% in 15 minutes at 600°C Contrary to the former case, it became more dificult to reduce the ore at above 600°C (3) No distinct relation between the ore size and the reduction rate was observed. (4) When the hydrogen gas amount was slightly over the minimum value enough to complete fluidization, the reduction rate was increased remarkably. But the effect of hydrogen gas amount was a little even when it was more increased. (5) Using funnel type grids, the reduction time was shortend, therefore ore-treating capacities was increased. When the same quantity of ores was reduced, the rate of reduction with those grids reached the same as with flat perforated grids by using nearly one half of hydrogen gas amount. (6) In fluidized bed reduction under increased pressure, the reduction rate reached nearly twice as much as under atmospheric pressure when a gauge pressure of 2kg/cm2 was adopted at lower temperature.
In previous studies of other authors, it has been shown that the so-called A-type deflection (as classified by Kaplan) observed in steam-turbine rotors during the heat-indication test (H. YOSHIDA, et ib., Vol. 47 (1961), 591-599) is caused by non-uniformity in heat aborbability of the rotor surface and the heat absorbability is a function of the degree of roughness of the machined surface. Also it has been shown that non-uniformity in the heat absorbability is a result of non-uniformity in heat-treatment of the material, which can be shown by hardness testing. In the present investigation, by using an apparatus designed by the anthor, measurements of the heat-absorbability of a Cr-Mo-V steel, a Ni-Mo-V steel and a plain carbon steel tempered under various conditions were carried out to establish a quantitative relationship between the heat-absorbability and the tempering conditions. The results obtained are as follows: (1) In the same steel, the heat absorbability has a linear relationship to the hardness of the machined surface: Hard surface shows a low absorbability. (2) Relation between the heat absorbability and the hardness depends on the kind of steel, and it is found that the carbon steel is the most sensitive to non-uniformity in the heat absorbability, while Cr-Mo-V steel and Ni-Mo-V steel are less sensitive. (3) The heat absorbability at between room temperature and 380°C depends mainly on the surface roughness, while at above 380°C oxide layers make a large effect on the absorbability.
The corrosion resistance of 13% Cr stainless steel as deformed in the metastable austenite state prior to martensite transformation was qualitatively compared with that of the same steel as quenched conventionally. As corrosive environment, 40% HNO3 in boiling state and 5% H2SO4 at room temperature were chosen. It was observed that, compared with undeformed steel, deformed steel at 450°C did not show a poorer resistance to both acid solutions when steel was austenitized at 950°C or 1000°C. However, the corrosion resistance of the steel became worse by deformation at 650°C, especially in 5% H2SO4. It seemed that this poorer corrosion resistance by deformation at 650°C was due to a heterogeneity of structure induced by the product of accelerated isothermal transformation.
Thirteen kinds of austenitic 18-12·stainless steels containing zirconium up to 2·81% were melted in vacuum. The behaviors of carbide, nitride and some other phases in the forged specimens of these steels during heat treatments were studied by examining the austenite grain size, hardness and microscopic structures. At the same time, these phases were extracted from these specimens electrolytically and identified by the X-ray analyses or electron-diffraction method. Results obtained are as follows; (1) Austenite grain size of 18-12 stainless steel is refined by the addition of a small amount of zirconium such as 0·02%. (2) The microstructures of each ingot containing zirconium shows the precipitation of ZrC and the quantity of ZrC is increased as the content of zirconium is increased. An intermetallic compound Fe2Zr is found in the steels containing zirconium higher than 1·15%. In addition to these phases, some zirconium nitrides of cubic structure are found in each steel. (3) In the specimens solution-treated at 1100°C for 3h, M23C6 dissolves into the matrix, but, even. in steels containing a small amount of zirconium. a part of ZrC remains as the undissolved carbide. Though the solution treatment at higher temperature such as 1300°C causes the austenite grain growth and decreases hardness, it is impossible to dissolve ZrC completely. (4) Burning structures are found on the austenite grain boundaries. and the intermetallic compound Fe2Zr is dissolved by the solution treatment at 1300°C for 3h. (5) The precipitation of M23C6 is observed in the specimens containing a small amount of zirconium by annealing at 600°C for 100h, but the quantity of this precipitant is decreased as the content of zirconium is increased, and this carbide is not observed microscopically in the specimen containing 0·87% zirconium. (6) The precipitation of M23C6 is accelerated by annealing at 900°C and the carbide is already observed at this annealing temperature within 5h. (7) M23C6 cannot be observed in the specimens annealed at 1000°C while ZrC seems to be precipitated at this temperature within 100h. (8) This carbides M23C6 is identified to be (Fe·Cr) 23C6 from the results of electrondiffraction pattern.
In the previous reports, the author introduced the age-hardenable characteristics and high temperature load-carrying ability of the various gamma-prime precipitated alloys varied from Ni-base alloys to Fe-base alloys In this investigation, the author studied the precipitation process during aging of these alloys by X-ray diffraction tests and electron metallography. By the X-ray diffraction tests on the electrolytic extracts from the various specimens after up to 1, 000h aging, MC, M7C3, M23C6, γ′, σ and β phases were identified. High-Ni alloys precipitated M7C3 besides MC, M23C6 and γ′ phase. On the other hand, high-Fe alloys precipitated the massive β phases. The matrix, γ′ lattice parameters and γ′-matrix lattice mismatch of the alloys comprizing no β phase were hardly changed in the precipitation process during 1, 000h aging. The γ′-matrix lattice mismatches were increased with the Co contents, and were decreased with the Fe contents. γ′ particle sizes were increased with aging time, but the growth of γ′ particles were retarded as the Co and Fe contents of matrix composition were enhanced. The amount of γ′ particles were increased with the aging time and the Co contents, but were decreased as the Fe content of matrix composition was raised. It was presumed that these precipitated β phases changed as follows by aging: γ′→γ′+β→β