Sintered Iron Compacts Research Articles

Electroplating of Sintered Iron Compacts

SummaryIron compacts, sintered to nominal porosities of 5, 10 and 15%, have been electroplated with copper, nickel and zinc in single and multilayered coating systems from several types of solution. Porosity measurements were made using a modified Lea and Nurse gas permeability technique before and after plating. Compacts having nominal porosities less than 10% can be coated satisfactorily but above this pore closure is incomplete. Multilayer systems improve the ability to fill pores and thicker coatings are more effective. For single layer coating a complexed cyanide solution of high throwing power offers best pore closure but using multilayer systems acid solutions can be almost as effective. The cleaning and pickling pretreatments prior to electroplating may affect the initial permeability and care must be taken to note this effect.

Fatigue Strength of Copper-Infiltrated Sintered Iron Compacts

This study was undertaken to examine the influence of filling pore with copper on the fatigue strength of copper-infiltrated sintered iron compacts by means of microscopical observation of the aspects of its fatigue fracture under low and high cycles.The following conclusions are obtained from the investigation.1) The tensile strength of copper-infiltrated sintered iron compacts exhibits the same value irrespective of green porosity by filling pore with copper in the same sintering condition.2) In copper-infiltrated sintered iron compacts, the inflection point of the S-N curve is not clearly observed, and the curve is similar to that in cast iron, and the fatigue strength for the time rises differently from S-N curve of sintered iron compacts.3) The fatigue strength of copper-infiltrated sintered iron compacts is not influenced by the green porosity under low cycles.Under high cycles, the fatigue strength of the test pieces with the green porosity of 15% has the same value, but for the specimens with the green porosity over 15%, it falls as well as the sintered iron compacts, due to the difference in the shape of infiltrated copper.

The Relationship between the Pore Structure and the Mechanical Properties of the Sintered Iron Compacts

Sintered iron compacts have many pores, which seem to reduce the mechanical properties of them. The pore structure is very complex, and its influences on the mechanical properties are also complicated.Then, authors analyzed the pore structure, particularly size, shape, and distribution, quantitatively, and its effects on the mechanical properties were investigated.The following conclusions are obtained:1) The size of pore becomes large in proportion as the porosity increases, and in a case of the same porosity, the pore size becomes large as the particle size of iron powder is large.The shape of pore becomes irregular in proportion as the porosity increases.2) Tensile strength decreases with increasing porosity, but in a case of the same porosity, the strength is not much influenced with particle size of iron powder.On the other hand, fatigue strength varies not only with the porosity but also the particle size. This is considered to be caused by the characteristics of the mechanism of fatigue fracture.

A Quantitative Assessment of the Mechanical Preparation of Sintered Iron Micrographic Specimens

Abstract The examination of P/M microstructures by automated image analysis requires a reproducible high level of surface finish from the section of the specimen under investigation. The preparation of mechanically polished sections involves a number of procedures each susceptible to variation. The effect of variations taken together can be large, resulting in erroneous information. A quantitative assessment of each procedure for polishing specimens from an iron P/M system has been conducted using automated polishing machines. The porosity of sintered iron compacts was measured using an automated image analysing computer. The ‘measured’ porosities were compared with the ‘true’ bulk porosity in each case to assess the variation due to each polishing parameter. Although a universal set of polishing conditions cannot be given, the results enable a set of optimized polishing conditions to be derived.

On the Fatigue Behavior of Sintered Iron

Completely reversed plane bending fatigue tests were carried out using sintered iron compacts made from five different iron powders. The fatigue specimens with sintered densities in the range of 6.2-7.0g/cm3 were prepared by single compacting and sintering at 1200°C for 1 hr in hydrogen. The fatigue limits of various specimens were measured, and the fatigue microcracks were observed by optical microscopy.The patterns of fractured surfaces were also investigated in a scanning electron microscope.Results were summarized as follows;1) The type of S-N curves for sintered irons showed no difference between iron powders, snd the endurance limits of them increased with increasing sintered densities.In comparison with the same sintered densities of them, the fatigue strengths of electrolytic and reduced ore iron powder compacts were higher than that of atomized powder. The fatigue ratios were found to be in the range of 0.40-0.47.2) Fatigue microcracks were initiated at the edge of the specimen, small pores or non-metallic inclusions with porosity of the specimen surface, and then the main fatigue crack for final failure was formed and grew from pore to pore in mixed transgranular-intergranular mode.3) At the early period of fatigue life, the pattern was partly the grain boundary fracture, and at the final period, it was mainly the ductile dimple pattern by the shearing fracture.

Process of Initiation and Propagation of Fatigue Craks in Medium and Low-Density Sintered Iron Compacts

Medium and low-density sintered iron compacts usually have many pores, which size and shape are various. In the present paper the influence of these pores upon the fatigue strength has been investigated.For the fatigue fracture of the medium and low-density sintered iron compacts, the following conclusions were obtained from microscopic observations.1) Cracks generate from the pores with sharp edges and from the pseudo boundaries, without generation of slip bands in a crystal grain.2) These cracks generate later than in the case with high density sintered iron compacts and once the cracks generate, they grow rapidly.This tendency becomes stronger, in the case of fatigue fracture under low stress.

Process of Initiation and propagation of Fatigue Cracks in High-density Sintered Iron Compact

The sintered iron compacts generally have many pores. The author investigated how the amount and shape of pores affect the fatigue fracture of sintered iron compacts and observed microscopically the aspects of its fatigue fracture under low cycle.The following conclusions are obtained from the above microscopical observations.1) Firstly slip bands generate in grains and they grow into fatigue crack, and the crack appeared to propagate from pore to pore through in grain or along grain boundary.2) Fatigue cracks generate from all pores. But, fatigue crack grows generally from medium or fine pores and scarcely from larger pores.

Relation between the Tensile Strength and the Fatigue Strength of Sintered Iron Compacts

Although many investigations have been made on the mechanical properties of sintered iron compacts, few have been made on the fatigue behaviour. The fatigue strength of sintered iron compacts is one of the most important factors when it is used under repeated stress. Since the sintered iron compacts generally have many pores; the purpose of the present work are as follows; to investigate the notch effect caused by the stress concentration arising from pores at the tensile and fatigue tests, and then, to further investigate the relation between the tensile and fatigue strength.The following conclusions are obtained from the above investigations:1) As the porosity of sintered iron compacts is increased, the tensile and fatigue strength are reduced. But when the porosity is constant, the pore size and its shape have influence on the tensile and the fatigue r strength-particulary, stronger influence on the latter than the former.2) Most of sintered iron compacts have the fatigue ratio (the ratio of the endurance limit to the tensile strength) in the range of 0.23-0.6, and the fatigue ratio decreases with increasing porosity.

On the Yielding Behavior in Tension of Sintered Iron

Yielding behaviors of sintered iron compacts were investigated through the microscopic observations and the tensile tests at both room and high temperatures with different strain rates.Yield drop, named as pseudo yield point, in a stress-strain curve is observed in various iron compacts, pressed at 3-7 t/cm2 and sintered in hydrogen for 1 hr at 1200°C. This behavior, which differs from that of mild steel as to the existence of plastic strain before yield point, may be due to the yielding of matrix and subsequently to the stress relaxation by nucleation and propagation of the crack from residual pores. The pseudo yield point and tensile strength of sintered compacts may depend en the strain rate (10-5-10-2/sec) as in the case of mild steel.The strength increment due to strain aging and the serrated stress-strain curves known as blue brittleness are clearly observed in iron compacts sintered even in hydrogen. Furthermore, this phenomenon is remarkable in the high nitrogen iron compacts sintered in dissociated ammonia.

The Effects of Silicon on Mechanical Properties of Sintered Iron Compacts

In order to investigate the effect of silicon on the mechanical properties of sintered iron compacts, 1-4%Si were added to iron compacts, and W and Mo were also added to Fe-3%Si compacts, which showed the improved mechanical properties. They were compacted and sintered by the single-press and sinter techniques, by the double-press and sinter techniques and studied of various mechanical properties. The results were summarized as follows.(1) Generally, the addition of Si to iron compacts increased the hardness and the tensile strength, however decreased the elongation of the compacts sintered at 1120°C.(2) In the case of sintering at 1220 and 1300°C, their densification was remarkably accelerated above 2%Si, and therefore gave not only a high tensile strength, but also a high elongation. But the elongation decreased at 4%Si.(3) The sintered Fe-3%Si compacts, when W and Mo were added, showed the improved mechanical properties. The elongation, however, decreased above 7%W and 5%Mo because of the precipitation of the compounds, namely Fe2W and Fe2Mo.(4) The double-press and sinter techniques generally gave higher strengths than the single-press and sinter techniques, although at high temperatures there were only slight differences between both techniques.

On the Magnetic Properties of Sintered Iron Compacts Containing Phosphorus

This report relates to magnetic properties of sintered iron containing phosphorus. The effects, on sintered iron compacts, of forming pressure, the amount of hydrogen loss of iron powders, sintering temperature and times were investigated.The iron powders used are made by reduction of iron ore. The amount of adding phosphorus, forming pressure, amount of hydrogen loss of iron powders are 0-2.5 (wt)%, 2-8 T/ cm2, 0.4-1.6 (wt)%, respectively.Magnetic properties are improved by adding phosphorus, and the optimum ratio of it was 0.8-1.0 (wt)%b and are superior when sintered at 1, 300°C in hydrogen for 3hr. Maximum permeability and magnetic induction B 25, both increase with the sintered density, but maximum permeability of sintered iron containing much phosphorus tend to decrease. The quantities of phosphorus that produce maximum sintered density and maximum permeability are different for each forming pressure and the amout of hydrogen loss of used iron powder.

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

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.

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.