Critical Aspects of Alloying of Sintered Steels with Manganese
- PDF / 2,242,145 Bytes
- 18 Pages / 593.972 x 792 pts Page_size
- 56 Downloads / 177 Views
UCTION
POWDER metallurgy (PM) is a technology for the large-scale manufacturing of precision parts for the automotive industry, for example. The profitable PM manufacturing route for structural parts manufacture consists of compaction and sintering stages and gives high productivity with low energy consumption and high material utilization. However, residual porosity is an inalienable feature of the pressed and sintered PM parts. Hence, the resulting mechanical properties (yield and tensile strength, fatigue endurance, etc.) are usually inferior in comparison with the same parts produced by machining of wrought material and precision casting. To tailor the mechanical properties of PM steels, the addition of various alloying elements is required. The choice of alloying element (and its quantity) depends on the properties that have to be improved. Traditionally, PM high-strength steels are alloyed with Cu, Ni, and Mo, whereas conventional low alloy structural steels contain mostly Cr, Mn, and Si along with some addition of carbide formers like V and Mo. The price of currently employed PM alloying elements like Mo and Ni is EDUARD HRYHA, Assistant Professor, and LARS NYBORG, Professor, are with the Department of Materials and Manufacturing Technology, Chalmers University of Technology, Ra¨nnva¨gen 2A, SE - 412 96 Gothenburg, Sweden. Contact e-mail: [email protected] EVA DUDROVA, Associate Professor, is with the Institute of Materials Research, Slovak Academy of Science, Watsonova 47, 043 53 Kosˇ ice, Slovakia. Manuscript submitted March 13, 2010. Article published online July 9, 2010 2880—VOLUME 41A, NOVEMBER 2010
dozens of times higher in comparison with that of Cr or Mn.[1] This situation creates a strong economical stimulation to introduce cheaper and more efficient alloying elements to improve the competitiveness of PM structural parts. In the last three decades, the potential in using manganese in PM for the realization of precision structural parts with high static and dynamic properties has been addressed extensively.[2–24] However, the issue periodically has amounted to how to obtain high-quality manganese containing PM steels, or in other words, what type of alloying method is better to use? Different approaches of alloying with manganese have been proposed (e.g., prealloying or admixing), but none of them have been adopted widely in industry. Powder systems admixed with manganese were proposed first and have been scrutinized for the last 30 years.[5–21] The driving force for possible sintering of such highly oxygen-sensitive powder systems was the so-called ‘‘self-cleaning’’ effect discovered by Sˇalak.[6–11] The effect is related to the high volatility of manganese that leads to significant manganese sublimation at elevated temperatures. The manganese vapor then is supposed to prevent the specimen from subsequent oxidation. Manganese sublimates at relatively low temperatures, and its partial pressure reaches about 103 Pa at 973 K (700 C) (Figure 1) when thermodynamic conditions also favor its oxidation. The manga
Data Loading...
