Materials Science Forum Vol. 672

Abstract: 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.

Abstract: Powder Injection Moulding (PIM) is a fast-growing manufacturing method, providing a cost efficient production route to complicated steel parts in highly stressed mechanical applications, but also to polished steel and ceramic parts fulfilling the most stringent aesthetical demands of design-dominated consumer products. The marriage between the two technologies plastic injection moulding and powder sintering is providing a valuable synergy, leading to a very efficient production of high density sintered steel and ceramic parts with a complex geometry. Reliable sources for PIM granulate; the use of standard injection moulding machines and the availability of mature furnace technology have each contributed to the credibility of in particular the Metal Injection Moulding (MIM) technology and have enabled in recent years the launch of mobile phone and automotive mass productions. While typical MIM parts in mobile phones are small and weigh around 1 g, the number of parts required is impressive and may reach several millions of parts per month. MIM parts in engineering applications, including automotive, are typically 5 - 50 g and have the advantage of long-lasting production runs, in some cases already approaching 10 years. Ceramic Injection Moulding (CIM) is not yet in the same stage of development as MIM due to the niche character of ceramic materials. Complex ceramic parts are not yet very common, but are also starting to appear in all segments.

Abstract: The present paper is focused on the wear characteristic of vacuum sintered Cr-Mo-[Mn]-[Cu] steels. The effect of chemical composition and the processing conditions in a vacuum furnace were evaluated. In such furnaces the cooling rate is generally determined by the pressure of the gas (N2) introduced into the chamber, the average cooling rates were calculated in the range of 1240°C to 400°C. The wear characteristics were analyzed as function of the processing and microstructures of the tested alloys through pin on disk test. Sintering of specimens in vacuum together with rapid cooling resulted in the formation of dominant martensitic microstructures with some small bainitic areas. The effect of both surface hardness and microstructure on the wear behaviour of the investigated steels shows the relation between the hardness and the wear rate. The influence of processing condition on the amount of martensite is also presented.

Abstract: In this work, the gigacycle fatigue response of several tool steel grades has been studied using an ultrasonic resonance testing device. It showed that both with ingot metallurgy (IM) and powder metallurgy (PM) tool steels, a true fatigue limit does not exist up to 10E10 cycles. PM steels resulted in significantly higher endurance strength levels than IM grades. However, there was virtually no effect of the composition and hardness of the materials, both for PM and IM grades cold work tool steels and high speed steels exhibiting virtually the same S-N curves. In the IM tool steel grades, crack initiation started at large primary carbides or carbide clusters, while in the PM grades, nonmetallic inclusions were the critical sites. In any case it is very important to avoid introducing residual stresses into the specimen surfaces during preparation, which would markedly shift the endurance strength levels.

Abstract: The effect of high temperature sintering and high cooling rate on shifting the microstructural composition to the favourably of martensite-bainite structures and thus effective improvement of mechanical properties of sintered steels based on Astaloy CrL powder with an addition of 1 and 2% Cu or 50% Distaloy AB powder and 0.65% C was investigated. All the systems were processed by both sinter-hardening and conventional sintering. The vacuum sintering at high-temperature of 1240 0C and at common temperature of 1180 0C were integrated with high (6 0C/s), medium (3 0C/s) and slow (0.1 0C/s) cooling rates; conventional sintering at 1180 0C with cooling rate of ~0.17 0C/s was carried out in a N2+10%H2 atmosphere. In dependence on chemical composition, the yield and tensile strengths of 890-1150 MPa and 913-1230 MPa respectively and impact energy of 10-15 J were achieved by sinter-hardening. The yield and tensile strengths are approximately double than those resulting from conventional sintering.

Abstract: Powders metallurgy route was used to produce foams from pure Al powders and pre-alloyed Al alloy powders (Alumix 231) with or without reinforcing elements addition. Both classical Al foam and spherical Al foam were produced with various production parameters and the results obtained have been discussed. SiC particles were used as reinforcing elements and TiH2 powders were used as foaming agent. Prior to compaction process, Al powders, reinforcing element and foaming agent were mixed in a three dimensional turbula for 30 min. Mixed powders were compacted, sintered and deformed and then foamed at 690 oC for spherical foam and 710 oC for classical foam. Effect of volume fraction of reinforcing elements, foaming temperatures and foaming agent amounts on the foaming behavior, pore structure, pore distribution, linear expansion rate, density and wall thickness of the cell were investigated. Experimental studies have shown that 1% foaming agent and 4 % SiC addition was found to be the most suitable for foaming. In general foam produced from Alumix 231 powders exhibited more homogenous pore structure compared to the ones produced from pure Al powders.

Abstract: The paper presents the main stages of the development of Romanian international relations in powder metallurgy, especially regarding its beginnings at the Technical University of Cluj-Napoca, with a tradition of almos51t 60 years.

Abstract: Mechanical properties, microstructure and fracture of Fe-3Cr-0.5Mo-xMn steels sintered laboratory at 1250°C and industrially at 1180°C, and of Fe-3Cr-0.3Mo-0.3V-xMn steels laboratory sintered at 1200°C are presented; all steels with 0.24% C. The highest tensile strength of 806 and 856 MPa attained the steels with 2% Mn based on Fe-3Cr-0.5Mo powder and of 929 MPa the Fe-3Cr-0.3Mo-0.3V-1.5Mn-0.24C steels. Linear increase of hardness and relatively linear decrease of impact energy in dependence on Mn addition was recorded. Tested steels exhibited lower heterogeneity of the microstructures. The fracture of steel containing vanadium with 2% Mn showed more metallic inclusions adversely affecting the strength properties.

Abstract: The effect of three iron powder grades and three manganese carrier types on mechanical and tribological characteristics of sintered 1 -5% Mn steels was investigated. The different effect of iron powder grades in dependence on manganese addition expressed oneself in strength and in wear. The highest strength and highest wear attained the steels with 3% Mn added as high carbon ferromanganese. The components – rollers - prepared from manganese steel exhibited lower wear than that from Fe-4Ni-1.5Cu-0.5Mo powder. The gears for hydrogenerator prepared from Fe-3.5Mn-0.5Mo-0.3C steel exhibited longer life time at increased oil pressure compared with that from through hardened sintered Fe-4Ni-1C steel.