Sigurd Berg

Surface chemical analysis of prealloyed water atomised steel powder

Abstract Prealloyed water atomised steel powder was investigated regarding composition, morphology and thickness of the surface oxide. The materials were two varieties of Cr alloyed and one Mo alloyed. The oxides formed on powder surfaces were studied by means of the surface analytical techniques X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy, in combination with high resolution electron microscopy and X-ray microanalysis. On all powder surfaces, the oxide formed contained strong oxide forming elements such as Cr, Mn and Si. Still, the dominant oxide on the powder surface was Fe oxide, the relative cation concentration in the surface being about 80%. The surface morphology showed a heterogeneous structure with particulate compounds supposed to be rich in strong oxide formers and an Fe rich thin oxide layer. This heterogeneous surface oxide morphology was more pronounced for the Mo alloyed powder compared with the Cr alloyed varieties. For this alloy, the average thickness of the oxide layer was somewhat larger (7–87·5 nm for fraction , <63 μm and 63–106 μm) compared with that of Cr alloyed powder (6–7 nm in all cases for fraction , <63 μm and 63–106 μm). An interesting observation was that Cr oxide also appeared on the nominally Cr free Mo alloyed powder, which indicates selective oxidation of Cr also when this element is present in low quantities. Although the alloying elements are enriched by a factor of 40–50 in the surface oxide, there is little effect on depletion of them from the steel matrix. From a sintering point of view, the particulate oxide compounds should play a minor role, since the most probable contacts between individual metal particles are Fe oxide/Fe oxide.

Carbon control in PM sintering: industrial applications and experience

Abstract The challenges in controlling carbon potential during sintering of steel powder have been discussed in many experimental and theoretical studies. The main issues lie within the complex thermodynamics and kinetics of processing atmosphere chemistry in continuous sintering furnaces. Although many models have been proposed to address the problem, these have rarely come to reality and entered industry practice. The purpose of this article is to summarise these discussions and investigate the interaction of the atmosphere constituents with the sintered compact within a sintering furnace. An important aim is to provide the PM industry with a fresh understanding of furnace operations and to provide recommendations to improve the control of furnace conditions. A case study is given of an existing furnace installation using Sinterflex technology which allows continuous monitoring and/or control of the furnace atmosphere. The reduction of oxides and carbon potentials to optimise the production parameters is described.

Manufacturing of Valve Bridge Component Utilizing Lean Alloyed Powders and Vacuum Sintering

Abstract Increasing the application area of powder metallurgy (PM) steels for manufacturing of high-performance structural components results in material saving, reduction in energy consumption, etc. In this study, feasibility of the manufacturing of valve bridge component for heavy duty engine utilizing lean alloyed powders and novel vacuum sintering approach, followed by low pressure carburizing, is studied. Three low alloyed steel powders were processed by conventional uniaxial pressing and sintering at 1120 and 1250°C in industrial vacuum furnace. The components were tested under high cycle fatigue testing, simulating real conditions of operation. Fatigue properties did not show significant dependence on the sintering temperature and were comparable to currently used reference cast material. Fracture surfaces of broken samples were analyzed to detect crack initiations and fracture mechanisms as well as quality of sintering. Results showed preferentially ductile failure, well developed sintering necks and clean pore surfaces, indicating good sintering. Tested material in combination with novel vacuum sintering process show to be an attractive alternative for manufacturing of this type of components for heavy duty engine applications.

Application Experiences in Powder Compaction of Iron Powder - Influence of Tool Material on Tool Life

Tool steels for powder pressing are normally heat treated to a high hardness to counteract plastic deformation during the compacting process. Ductility and wear resistance of the die punch or core rod are determined by the type, size, amount, hardness and distribution of the hard phase in the martensitic matrix. Thus, tool steels can be designed and optimized for specific powder pressing application. To be able to utilize the full potential of the tool steel, also the design, heat treatment and eventual surface coating of the steel must be taken into account. In this paper new low-friction tool steel is investigated in PM manufacturing for a number of applications. An increase of tool life of more than two times compared to ordinary tool steels is found. Furthermore, the new low friction tool steel shows a potential for sintered parts with higher densities through the applicability of increased compaction pressure or minimized lubricant amount.

Low alloy powders may point way to cost-effective high performance

With automotive customers demanding more performance at lower cost, metal powder makers have a real interest in optimising product performance…