Compacted Iron Research Articles

Ultrasonic and magnetic analyses of porosity in iron compacts

This study showed that the tensile stress-strain behavior and ductility of porous iron compacts containing nearly spherical pores could be related solely to the initial poosity of the iron. Results are presented for these compacts on the use of ultrasonic wave propagation procedures for measuring porosity and on the effect on porosity on magnetic behavior, magnetization, and acoustic and magnetic Barkhausen signals. The successes, failures, and limitations of these nondestructive evaluation procedures for characterizing porosity and, therefore, the strength and ductility of porous iron are discussed. Wave velocity measurement techniques appear the most promising for characterizing porosity in porous iron compacts.

Quantitative Analysis of Anisotropic Shrinkage During Sintering of Cylindrical Nickel and Iron Compacts

Shrinkage of nickel and iron compacts has been measured continuously during isothermal sintering at 1423K under a stream of Ar–7 vol.-%H2. The results have been analysed to determine the quantitative agreement with phenomenological relationships given in the literature, with respect to both anisotropic and isotropic behaviour. These treatments are compared with the conventional treatment given in the literature. It is concluded that: (1) continuous measurement is necessary to follow shrinkage behaviour adequately; (2) quantitative description of the shrinkage is possible through suitable combination of several equations, each of which is applicable to a particular range of sintering. PM/0483

Anisotropic Shrinkage and Thermal Expansion During Sintering of Cylindrical Nickel and Iron Compacts

Anisotropic shrinkage and thermal expansion have been quantified for nickel and iron powder compacts during sintering at 1423 K following initial compaction at 200, 300, or 400 MPa. Shrinkage was greater in the radial direction of the cylindrical compacts than in the axial one. An anisotropy treatment is developed to describe the shrinkage in a quantitative manner. A similar approach to the thermal expansion results in quantitative relations that are specific to the individual powders. PM/0482

Fe-Ni-B母合金粉を用いた液相焼結法による鉄粉焼結体の緻密化と機械的性質の向上

Fe-Ni-B母合金粉を用いた液相焼結法による鉄粉焼結体の緻密化と機械的性質の向上

Picking Behaviour in Compacted Iron Powder Parts

An analysis has been performed on the selective removal of particles from the edges and thin lands on green iron powder compacts. The voids created as a result of this ‘picking’ are believed to be due to large (+ 125 μm (+ 120 mesh)) particles in the iron powder mix. Microscopic examinations indicated that in all cases picking occurred within isolated regions of large pore and particle size. Two possible independent causes for this problem have been advanced: segregation of large particles within the feed shoe during die filling; and an uneven load distribution across the face of a part due to the presence of tooling impressions on the upper punch. A series of follow up tests showed no change in the relative position of the large pore size region with upper punch orientation. Therefore, by deduction, particle segregation is advanced as the main cause of the observed picking. Suggestions are presented to alleviate this problem. PM/0495

鉄圧粉体の加圧拡散接合における寸法変化と接合強度

The dimensional change during bonding and the transverse rupture strength of joints of iron powder compacts were investigated. Most compacts were 10 mm regular cubes produced by pressing a reduced-ore powder with 0.7 mass% of zinc stearate as a lubricant under 600 MPa, and sintered and bonded at 1130°C for 35 min in a single cycle heating process in hydrogen. Some were sintered at 1130°C for 60 min before bonding.During bonding of green compacts on the pressed faces, the shrinkage increased in the pressing direction of bonding, while the expansion increased in the perpendicular one, with increase in the bonding pressure. The joint area and the transverse rupture strength increased with increasing bonding pressure in the low pressure range.During bonding of green compacts on the side faces, the shrinkage increased in the pressing direction of bonding, while the expansion increased in the perpendicular one, with increase in the bonding pressure. And the width of microcracks perpendicular to the pressing direction which had originally existed in green compacts grew larger. It caused a remarkable expansion in the pressing direction and a decrease of the transverse rupture strength.During bonding of sintered compacts on the side faces, the microcracks did not grow larger and the transverse rupture strength increased with increase in the bonding pressure.

焼結合金鋼の破壊靭性

Effects of alloying elements and heat treatment on the fracture toughness of sintered alloy steels have been investigated by means of three-point bending test, optical and scanning electron microscopies.The fracture toughness (KO) of sintered steels increased with an increase of carbon content. In Fe-Cu-1%C, the KO was somewhat increased by an addition of 1%Cu, but it was constant with Cu above 1%. This is explained in terms of the formation of pores at the original location of the Cu powders. On the other hand, the KO of Fe-Ni-1%C showed a peak with an addition of 3%Ni. This is attributed to the appearance of Ni rich martensitic phase with Ni above 3%, although Ni is effective to the densification of iron compacts. The KO of these compacts were also increased with yieled strength by heat treatment.A remarkable feature of the obtained results was that the KO increased simultaneously with the yield strength, which was contrary to the general behaviour of wrought materials. The origin of this mechanism is clarified from SEM observation, that is, the fracture process of sintered alloy steels is the necking down between the crack tip and adjacent pores.

Structure and some properties of austempered compacted iron (ACI)

Scanning electron microscopy on austempered compacted graphite cast irons is reported. Selected isothermal heat treatments at 300 and 400°C result in the formation of a bainitic microstructure which is responsible for the good properties of these materials.

On the properties and economics of sintered iron powder metallurgical extrudes

Cold Hooker extruded iron compacts have been evaluated for density, mechanical and metallurgical properties, in the as-extruded, annealed and re-sintered conditions and the results compared with those for an equivalent wrought composition. The extent of densification occurring due to cold deformation of the P/M compacts has also been examined. The commercial viability of the process of cold extruding a P/M preform has been analysed by considering the manufacture of a suitable component by the above process and comparing it with manufacture by the existing conventional process. This evaluation gives an indication of the economics of the Hooker extrusion process of P/M preforms for the manufacture of a similar family of products.

The evolution of damage and fracture in iron compacts with various initial porosities

This study evaluated the tensile and compressive mechanical properties of iron compacts of various initial porosities, and determined the effect of deformation on the evolution of porosity, pore size and pore shape. The loss in flow strength with porosity was considerably greater than predicted by Gurson's constitutive model for ductile porous materials, but it was in substantial agreement with recent modifications of that model. The modified models also give good agreement with observed porosity growth with increasing deformation. Pore growth in the tensile direction was somewhat less than that predicted from a model based on an isolated spherical pore and pore growth in the transverse direction was somewhat greater than that predicted from such a model. These discrepancies are probably a consequence of pore interactions during deformation. Observations on fracture behavior in the iron compacts showed that a localization model based on a band imperfection gave good predictions of ductility when the imperfection had a porosity about one and one-half to two times that of the bulk porosity. Dirichlet cell analyses give direct evidence that regions containing local area fractions of porosity up to 4–7 times the bulk porosity are present in the different iron compacts. These regions, however, are not in the form of bands of indefinite extent, and it is evident that further progress on the effect of pore distribution on fracture requires a more detailed theory.

Dielectromagnetics Containing Different Dielectrics

AbstractThe effects of dielectric type and method of incorporation in iron powder compacts on the structure and properties of dielectromagnetics are presented. The filling factor of a dielectromagnetic in iron, being the essential material parameter used in the design of magnetic circuits, is introduced and methods of calculating it are given. This enables both the establishment of a precise criterion for dividing dielectromagnetics and magnetodielectrics and the analysis of dielectric distribution inside the material, which influences dielectric and iron phase continuity. Theoretical considerations are presented concerning correlations between production and the structure and properties of dielectromagnetics, knowledge of which is essential for their wider application in magnetic cores for electrical converters. PM/0478

Void growth and failure in notched bars

Void growth and ductile failure in the nonuniform multiaxial stress fields of notched bars are studied numerically and experimentally. U-notched bars with different notch acuities are made from partially consolidated and sintered iron powder compacts with various residual porosities. The materials are modelled using an elastic-viscoplastic constitutive relation that accounts for strength degradation resulting from the growth of microvoids. The matrix stress-strain relation and the initial void volume fractions used in the calculations are determined experimentally. The remaining parameters in the constitutive equations are evaluated from micromechanical models. Comparisons of the calculations with experimental results indicate that the constitutive model can provide good estimates of the evolution of the void volume fraction and of the strength reduction induced by void growth under a variety of nonuniform stress histories.

焼結鉄の靭性ならびに寸法変化の異方性に関する考察

Cylinders, d40 mm×h40 mm for small-sized Charpy specimens and d10 mm×h10 mm for electrical conductivity measurements during compacting, and 10 mm cubes for dilatometry were compacted. Electrolytic and reduced-ore iron powders were pressed by admixing 0.7 mass% of zinc-stearate, or by die-wall lubricating alone under 98-588 MPa, de-waxed at 600°C for 30 min, anc sin tered at 1100°C for 60 min in dissociated ammonia. Small-sized Charpy specimens were cut out from the 40 mm cylinders in the pressing or axial direction, and in the radial direction. The electrical conductivity was measured in the 10 mm diameter die lined with zirconia. Cubic compacts for the dilatometry were compressed slightly in the compacting direction after ejecting from the die.The toughness of the specimens with their length in the radial direction increased with test temperature, while those in the pressing direction remained almost constant, leading to an increased anisotropy of the toughness.The electrical conductivity decreased more in the elctrolytic iron powder compacts than in the reducedore ones, and during the ejecting rather than during the unloading.Re-pressing green compacts led to a decreased anisotropy of the toughness and decreased axial shrinkage during the sintering.

Microstructures and superplastic behavior of eutectic Fe-C and Ni-Cr white cast irons produced by rapid solidification

Superplastic behavior of two commercial grade white cast irons, eutectic Fe-C and Ni-Cr white cast irons, was investigated at intermediate temperatures (650 to 750 °C). For this purpose, rapidly solidified powders of the cast irons were fully consolidated by compaction and rolling at about 650 °C. The volume fractions of cementite in the eutectic cast iron and in the Ni-Cr cast iron were 64 pct and 51 pct, respectively, and both cast irons consisted of fine equiaxed grains of cementite (1 to 2 μm) and ferrite (0.5 to 2 μm). The cast iron compacts exhibited high strain-rate sensitivity (strain-rate-sensitivity exponent of 0.35 to 0.46) and high tensile ductility (total elongation of 150 pct to 210 pct) at strain rates of 10-4 to 10-3 s-1 and at 650 °C to 750 °C. Microstructure evaluations were made by TEM, SEM, and optical microscopy methods. The equiaxed grains in the as-compacted samples remained unchanged even after large tensile deformation. It is concluded that grain boundary sliding (e.g., along cementite grain boundaries in the case of the eutectic cast iron) is the principal mode of plastic deformation in both cast irons during superplastic testing conditions.

Magnetic properties of porous iron compacts

Magnetic hysteresis measurements, magnetoacoustic emission, and the Barkhausen effect have been used to investigate the magnetic properties of six porous iron compacts with porosities in the range 0.3–6.2% and pore sizes in the range 1.6–13.2 µm. Coercivity and maximum permeability varied with pore size, showing respectively a maximum and a minimum for pore areas in the range 50–100 (µm)2, corresponding to pore diameters 8–11 µm. Significant correlations were found between several of the magnetic parameters including a fundamental relationship between coercivity, initial permeability, and maximum differential permeability. There were also indications of a correlation between magnetic properties and the initial molding pressure, although these were not conclusive. However, none of the magnetic properties was found to vary in a progressive manner with percentage porosity, although it is conceivable that if all other variables, such as pore size and grain size, remained constant, that changes in magnetic properties with porosity could be detected from magnetic measurements.

Joining of iron powder compacts by an infiltration method

Joining of iron powder compacts by an infiltration method was attempted. The joining strength of the compacts was investigated with respect to variations in roughness of the surface, applied pressure, relative density of preforms, infiltration temperature and the time. The joining strength was found to be almost equal to those of monobloc ompacts by conventional infiltration when the joining was done under the optimum conditions. Joining of the iron powder compact and wrought steel samples such as S10C and S55C was also carried out and high strength could be obtained by this method. Samples with complicated shapes or with holes in the parts could be easily made with the infiltration technique proposed.

ＣＶＤ処理した多孔質鉄焼結体の特性

The sintered iron compacts will be able to be applied to selflubricating porous bearing, filter and metallic mold for casting, etc., because they have useful porosity. However, they do not have oxidation resistance, wear resistance and good mechanical properties. The chemical vapor deposition process (CVD process) is expected to give them good oxidation resistance and wear resistance. In this paper, the properties of the porous sintered iron compacts coated with TiC and Al2O3 by CVD process were investigated. The results obtained are as follows:The CVD coatings of the porous sintered iron compact are thinner from the surface forward the inside. The TiC coatings are smooth throughout the sintered compact, while the laminated coatings of TiC and Al2O3 are smooth in the surface part and granular toward the inside. The granular products on coatings are Al2O3. The hardness and the transverse rupture strength of the porous sintered iron compacts are remarkably increased and the intercommunicating porosity is decreased by the CVD treatment. The oxidation resistance is improved when the laminated coating of TiC and Al2O3 is repeated more than twice. The transverse rupture strength is not decreased and the intercommunicating porosity is decreased by oxidation.

圧延を施した焼結鉄ならびに鉛溶浸焼結鉄の内部摩擦について

For the purpose of estimating the damping capacity of composite structure type lead infiltrated iron compacts, the internal friction of them and of Fe sintered compacts for a comparison were measured, and influences of cold rolling and annealing on the internal friction were also studied. Results obtained were as follows:(1) The internal friction of Fe sintered compacts increased with an increase of porosity of compacts up to about 26%. Beyond that, the internal friction was retained almost constant value regardless of an increase of porosity of compacts. The internal friction of Fe sintered compacts could be enhanced remarkably by the rolling. But the enhanced internal friction was thermally unstable, and was reduced to the level of assintered condition after a short-time annealing.(2) The internal friction of Pb infiltrated Fe sintered compacts also increased with increasing both the Pb infiltration ratio and the rolling reduction. The internal friction of this material was thermally stable, i.e. the reduction ratio of internal friction was approximately one fifth after a prolonged annealing time. The damping mechanism of this material is thought to be mainly due to the absorption of vibration energy by the external friction at the interface between Fe skeleton and Pb infiltrant.

焼結鉄の気孔球状化に及ぼすＳの影響

The sintering process and the spheroidization of pores in the iron compacts having a small addition of sulfides such as ZnS or CaS and the gas sulfurizing treatment were investigated by means of photomicroscopic examination, DTA and EPMA. The mechanical properties of Fe-S compacts were also investigated and the correlation between the spherical pores and the properties was discussed.Upon sintering at above the eutectic temperature, a liquid phase of Fe-S was formed by the eutectic reaction of the Fe matrix and the FeS film formed at the pore surface and concentrated at the corners of sharp edged pores and at the interfaces between Fe particles. And the pore shape became more rounder without showing a remarkable shrinkage, which seemed to be due to the enhancement of neck growth between Fe particles by the surface diffusion mechanism. Because of the persistent presence of liquid phases connecting the pores during sintering, these pores were prone to coalesce easily.A small addition of sulfides to Fe compacts had little influence on tensile strength but decreased elongation. The reason for this could be attributed to the notch effect of the residual FeS found mainly at the edge of pores. The spheroidization of pores made the behaviour of ductile-brittle transition more distinctive and increased the impact strength at high temperatures.

High-temperature interaction of diffusion chromized iron-graphite materials in gaseous commercial-grade hydrogen

This work presents the results of investigations of the interaction of iron-base gas-permeable chromized materials with commercial-grade hydrogen at 870 degrees C. Specimens were prepared from PZh4M3 iron powder containing graphite with the addition of zinc sterate by pressing, which were diffusion chromized in a powder mixture at 1050 degrees C and then were annealed in a flow of type V commercial-grade hydrogen. Metallographic analysis of the iron and iron-graphite compacts showed through-impregnation with chromium through the pores. Figures show chromium distribution and kinetics of oxidation, and results show that pore formaiton and intergranular cracking accompanying hydrogen corrosion lead to sharp reduction in the heat resistance of the steel.