Deformation of steel powder compacts during sintering: Correlation between macroscopic measurement and in situ microtomography analysis

The SC 100.26 iron powder and the PASC 60 powder (with a P content of 0.6 wt%) were mixed with graphite and copper powders. The blended powder mixtures were compacted, sintered and the P-containing sintered alloys were then induction-hardened. Experimental results show that the microstructure of sintered Fe–C–Cu alloys varies with the copper content. The proeutectoid ferrite becomes refined and decreases in volume when the copper content is increased. The ferritic phase is markedly hardened by the dissolved copper. The P-containing specimens exhibit marked volume expansion following sintering. The volume dilation increases with increasing compacting pressure. The hardness of sintered Fe–C–Cu–P alloys increases with increasing compacting pressure and carbon content. Further strengthening is resulted from the strong solution hardening effect of phosphorus in iron. Hardness variation of sintered alloys, with the carbon content, is dependent on the compacting pressure. Following induction hardening the surface hardness also increases with increasing carbon content and compacting pressure, but by a different mode from that in the as-sintered state. This is promoted by the phosphorus addition.

Effect of alloying elements and processing factors on the microstructure and hardness of sintered and induction-hardened Fe-C-Cu alloys

Modelling of swelling of Fe-Cu compacts sintered at temperatures above the copper melting point

Up to 5% each of copper and nickel powders as well as 0.35 or 0.65 wt.-% graphite were added to sponge iron powder grade SC 100.26. Tensile specimens prepared from the mixes were sintered in endogas in a belt furnace at 1120°C for 1 h. Dimensional change, hardness, and tensile properties were measured. The results show that the tensile strength increases with increasing copper and nickel additions at each carbon content level and that copper has the greatest influence. Since plain copper additions cause considerable growth during sintering, it is advantageous to combine the two elements. Conditions for ‘zero growth’ have been established. The highest strength for a ‘zero growth’ material was achieved with an alloy containing 4.0% Ni, 2·5% Cu, and 0.6% C, with a density of 7.1 g/cm3. Retention of austenite seems to limit the strengthening effect of nickel at this carbon content. Addition of molybdenum counteracts this effect and raises the strength. With a partially prealloyed powder containing 4% ...

The effect of copper and nickel additions to high-compressibility sponge iron powder on the sintered properties of materials with 0·3 and 0.60% carbon

Since low alloyed sintered steels were introduced in the market of the structural parts, we have followed the evolution of a material with poor mechanical properties and any uniformity (in the sense of reproducibility) to materials that today are produced with high reliability and performance. The working efficiency could be equivalent in many cases with the best wrought steel, and maintaining a good margin in terms of cost and competitively. In this paper a complete review of the topic is accomplished, from the early times when the first parts were made by plain iron or iron-carbon, going through the different alloying systems: Fe-Cu, Fe-P, Fe-Cu-Ni-Mo, and more recently Fe-Cr-Mo and Fe-Mn. The development in processing routes has been considered too. The main milestones in the field of new alloying systems have been: 1) the introduction of Cu in 60-70’s, 2) the new complex systems with Cu-Ni-Mo in the 80’s and 3) the introduction of alloying elements with high oxygen affinity (in the late 90’s). Regarding the milestones in processing could be considered: 1) the development of new mixing procedures, 2) the warm compaction and high velocity compaction, 3) the improvements in sintering control and high temperature sintering. Several decades of research and innovation, acting on the processing system (mixing, pressing, sintering, post-sintering operations,…) and on the alloying system (from the earliest times with plain iron to complex systems used today), has allowed us to have a highly competitive materials, in terms of performance, and processes in terms of cost. The future is still open to new developments.

/pdf/from-sintered-iron-to-high-performance-pm-steels-2qily00vce.pdf

From sintered iron to high performance PM steels

Three grades of iron powder-an atomized steel powder, a sponge iron powder reduced from magnetite with carbon, and a powder reduced from mill scale with hydrogen were mixed with 3% of copper powder and pressed into compacts. The diametral dimensional changes of the compacts during sintering below and above the melting point of copper were measured, their microstructures examined, and both related to the characteristics of the powders, particularly their specific surface. During sintering below the melting point of copper, compacts of all three powders shrank. Micrographic examination showed that the copper is transported by solid-state diffusion along the surfacesand grain boundaries of the iron powder particles. During sintering above the melting point of copper, compacts of the atomized and the MH-100 sponge iron powders grew while those of the hydrogen reduced mill-scale powder shrank. This phenomenon is related to the different mode of penetration of liquid copper in the compacts from the thre...

F. V. Lenel

Papers

Observations on the sintering of compactsfrom a mixture of iron and copper powders