Compacted Iron Research Articles

INFLUENCE OF THIN OXIDE FILMS ON THE MECHANICAL PROPERTIES OF SINTERED METAL-POWDER COMPACTS

The influence of thin oxide films, in the range 200–1200Å thick, on the mechanical properties of sintered iron, copper, and nickel powder compacts has been investigated. As the thickness of the oxide film on the metal powders increased, the properties studied, namely, densification parameter, hardness, and tensile strength improved and attained a maximum at a critical oxide-film thickness, the value of which was ∼ 625 Å for iron and nickel and ∼ 500 Å for copper. Further increase in thickness to ∼ 1200 Å led to a gradual decline in the properties. The improvement in the properties obtained with powders having the optimum oxide thickness was independent of the sintering atmosphere. A probable explanation in terms of activated sintering is given.

Dimensional Change of Iron and Iron-Copper Powder Compacts during Sintering (Part I)

The densification during sintering of iron powder compacts with a small addition of phosphorus, antimony, boron, sulphur and copper respectively, was discussed. Specimens were prepared by mixing iron powder with additive powder, followed by compacting and sintering for 1 hr at 1150-1200°C in hydrogen.It has been shown from experimental results that the sintering of iron is accelerated by phosphorus or antimony addition, but not accelerated by boron, sulphur or copper addition. In the case of phosphorus or antimony addition, the crystal structure of iron alloy equilibrated at sintering temperature is α phase (bcc lattice) and in the other case that is γ phase (fcc lattice). The diffusion velocity in γ phase is much smaller than in α phase. Examining on the basis of the Kingery's equation, the ratio of the diffusion coefficient in α phase to that in γ phase was in the range of 140 to 250. These values are comparable with the ratio of the self-diffusion coefficient of α-iron to that of γ-iron at the sintering temperature (1150-1200°C). After all, whether or not the sintering of iron powder compact is accelerated by a additive powder depends upon the crystal structure of the sintering iron body equilibrated at the sintering temperature.According to Meechan's experimental results, the rate process of the sintering of α-iron might be the ring diffusion rather than the vacancy diffusion. However, when the α phase of iron of the sintering body is stabilized by the additives, the sintering process maybe proceed by the vacancy diffusion.

鉄系焼結体の焼結炉内調整雰囲気ガス

Since iron-graphite compacts are usually sintered in the furnace of atmosphere such as H2 gas or dissociated ammonia gas, the mechanical properties of sintered products are markedly deteriorated through decarburization of the compacts.Authors investigated, in this report, carbon potential of RX gas at sintering temperatures, carburizing and decarburizing reaction and bending strength of the iron, iron-graphite compacts sintered in the RX gas and hydrogen gas.Results of this experiment are as follows.1.Carbon potentials of RX gas in sintering furnace can be pre-estimated by extending the theory applicable to the gas carburizing of steel.2.When iron compacts are sintered in RX gas, the equilibrium carbon content can not be obtained and considerable differences in carbon content exist between surface and core structure of sintered products.3.When iron-graphite compacts are sintered in RX gas, uniform carbon contents in both surface and core structure of sintered parts can be produced by only controlling the dew point of RX gas.The mechanical strength obtained in such a process is superior to those of parts sintered in hydrogen.

Dimensional Changes of Iron and Iron-Copper Powder Compacts During Sintering (Part II)

Dimensional Changes of Iron and Iron-Copper Powder Compacts During Sintering (Part II)

SOME EFFECTS OF ATMOSPHERE ON THE SINTERING PROCESS OF IRON-CARBON COMPACTS

The sintering process of plain Iron compacts and Iron-Carbon compacts was investigated by thermal balance and dilatometer during thermal cycle. The effects of moisture contents in hydrogen atmosphere were observed ; A atmosphere with 1.7-1.9 mg/L moisture content, B with 0.2-0.3 mg/L. The Mechanical and physical properties of sintered compacts were measured. The results were as follows.1) Dimensional changeThe specimens containing graphite showed lower shrinkage than plain iron. The shrinkage was greater with A atmosphere than with B atmosphere.2) Weight changeThe weight continued to decrease up to about 900°C, owing to degassing, desorption of moisture and reduction of oxide on the surface of iron powder. Above that temperature, the gassification of graphite by hydrogen was observed.3) Mechanical propertiesHigher strength was obtained for specimens sintered in A atmosphere and their graphite contents were as high as 1%.4) CarburizationThe carburization rate was greatly influenced by the moisture content in hydrogen. In the A atmosphere, the formation of carbide was pronounced, with decarburized layer as thick as 1.6mm. On the contrary, in the B atmosphere, the decarburized layer was very thin and much carbon was left uncombined.

1 Sintering of Iron Powder Compacts. 1.3. Changes of Pores in Powder Compacts during Sintering

1 Sintering of Iron Powder Compacts. 1.3. Changes of Pores in Powder Compacts during Sintering

1 sintering of iron powder compacts

1 sintering of iron powder compacts

Sintering of iron powder compacts

In this paper, geometrical and chemical phenomenon in compacting and sintering processes of iron powders were investigated. Used powders were produced by various methods i.e. stamping, eddy milling and hydrogen reducing.Effect of shape factors of iron powders on such processes were observed through the characteristic feature when taping or compacting. As far as it was not sintered at high temperature, such a packing feature was remaind. But treatments of high pressure pressing, powder mixing between some shape or size, and high temperature sintering made to lose such a feature, especially the treatment of high temperature sintering made to progress the grain growth between each powder. So the geometrical characteristics of pore when produced by compacting were diminished.

Technical properties of iron powder magnets

Coercive force, remanence and maximum energy product of compacts of iron are measured as functions of density of packing (d/d0) and X-ray particle size (L). The iron is prepared by hydrogen reduction of ferric oxide and for the grade used optimum technical properties are: Br = 5200 gauss, (B. H)max = 0.82 × 106 gauss: oersted, and BHC = 400 oersted when L = 300 A and d/d0 = 0.5. Maximum coercive force obtained is 610 oersted when d/d0 = 0.3. For d/d0 fixed the three magnetic quantities increase with decreasing particle size, the increase being greatest with Br and (B. H)max. The increase in remanence is discussed in terms of its ratio to saturation magnetization and it is suggested that the observed increase is related to packing effects. Measurement of the influence of oxygen impurity indicates that the presence of a few per cent of oxide does not appreciably affect the quality of the magnets.

鉄粉焼結体の研究（第1報）粒度の相違が焼結体に及ぼす影響について

鉄粉焼結体の研究（第1報）粒度の相違が焼結体に及ぼす影響について

鉄粉焼結体の研究（第3報）成形圧力の相違が焼結体に及ぼす影響について

The crushed electrolytic iron powders were passed through a 325-mesh sieve, and annealed at 750° in H2. Then, these powders were pressed at 0∼20 t/cm2 and sintered at 350∼1450° for 2\frac12 hrs in H2. The same measurements as those in the 1st report were carried out with respect to the specimens thus obtained. The experimental results are summarized as follows:—(1) The stages of the sintering temperature may be classified into three groups such as “450∼750°”, “800∼1250°” and “above 1350°”. (2) At the first sintering stage, the increase of tensile strength is due to the remarkable increase of the bond between particles with rising temperatures and increasing pressures. (3) At the second sintering stage, the increase of elongation is due to the remarkable increase of the assimilation between particles with rising temperatures and increasing pressures. (4) At the third sintering stage, the properties of the sintered compacts approach to those of the molten iron, because of the marked increase of the grain-growth between crystal grains. Furthermore, it is noted the tensile strengths and the elongations of the sintered iron compacts pressed at over 12\frac12 t/cm2 and sintered at 1300∼1400° suddenly decrease and their fractured sections glitter.

鉄粉焼結体の研究（第2報）粉末の製造来歴の相違が焼結体に及ぼす影響について

鉄粉焼結体の研究（第2報）粉末の製造来歴の相違が焼結体に及ぼす影響について

Magnetic Properties of Iron Compacts in Relation to Sintering Temperature

Previous experiments have indicated that the magnetic permeability of sintered iron compacts is to a large extent determined by the final density of the compact. The permeability of five different iron powders has proved to be independent of the origin of the powder, if the compacts were sintered at the same temperature. The results were compared with the theory of Polder and Van Santen and agreed very well with their predicted curve, if the residual pores were assumed to be flat disks. It could be expected that at higher sintering temperatures, the disk-shaped pores would change into a more equiaxed or spherical shape. Experiments to check this theory have been made, and the results are in good agreement. Compared for identical densities, the permeability of different iron powders is appreciably higher if sintering is done at 1250–1350°C and for 24 hours, instead of at 1150°C for one hour. Different powders, however, now show quite different permeabilities, which could be explained by a different inclination of the powder to form spheroidal pores. It is shown that coining after high temperature sintering brings the permeability values back to the curve of the disk-shaped flat pores. The effect of the increase in permeability at higher temperature cannot, therefore, be due to a purification process, but must be attributed to a change in the pore shape.

Atomic Hydrogen Occluded in Iron Nitride

The author confirms the existence of atomic hydrogen in iron nitride: (1) By the presence of hydrogen when heating iron nitride above 430°C. at which iron nitride is found to decompose slowly. (2) By the measurement of the single potential of iron nitride in the normal ferrous sulphate solution. (3) By the oxidation of atomic hydrogen due to oxygen in the water in which iron nitride is immersed. (4) By the transformation of potassium ferricyanide into potassium ferrocyanide by atomic hydrogen occluded in iron nitride. By measuring the single potential of nitrided iron, he observed the change of compact iron into porous iron by nitriding. The influence of light on the single potential of iron nitride was tested and it was found that light produces no marked photo-chemical effect upon it.

窒化鐵に含まるゝ原子状水素に就て

The author confirms the existence of atomic hydrogen in iron nitride:(1) By tbe presence of hydrogen when heating iron nitride aboce 43°C. at which iron nitride is found to decompose slowly.(2) By the measurement of the single potential of iron nitride in the normal fargeus sulphate solution.(3) By the oxidation of atomic hydrogen due to oxygen in the water in which iron nitride is immersed.(4) By the transformation of potassium ferricyanide into potassium ferrocyanide by atomic hydrogen occluded in iron nitride.By measuring the single potential of nitrided iron, he observed the change of compact iron into porous iron by nitriding.The influence of light on the single potential of iron nitride was tested and it was found that light produces no marked photo-chemical effect upon it.

ATOMIC HYDROGEN OCCLUDED IN IRON NITRIDE

Abstract The author confirms the existence of atomic hydrogen in iron nitride: (1) By the presence of hydrogen when heating iron nitride above 430°C. at which iron nitride is found to decompose slowly. (2) By the measurement of the single potential of iron nitride in the normal ferrous sulphate solution. (3) By the oxidation of atomic hydrogen due to oxygen in the water in which iron nitride is immersed. (4) By the transformation of potassium ferricyanide into potassium ferrocyanide by atomic hydrogen occluded in iron nitride. By measuring the single potential of nitrided iron, he observed the change of compact iron into porous iron by nitriding. The influence of light on the single potential of iron nitride was tested and it was found that light produces no marked photo-chemical effect upon it.