Dilatometry study of the sintering behavior of boron-alloyed Fe-1.5 pct Mo powder
- PDF / 1,126,299 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 85 Downloads / 128 Views
I. INTRODUCTION
THE effect of boron on the sintering of iron and iron alloys has been studied by several authors. Boron presents many favorable characteristics for the activation of the sintering process, as demonstrated by a quantitative approach based on the figures of merit for activated sintering.[1,2,3] Boron, which may also promote the stabilization of the a phase (ferrite),[4] thus further enhancing sintering, has beneficial effects on the hardness of iron and on the hardenability of steels, with further positive effects on the technological properties of the sintered components. These aspects have been demonstrated by previous investigations on iron and steels,[5,6] iron-molybdenum,[7] and martensitic[8] and austenitic stainless steels.[9,10] Boron can be added under different forms, mostly as a compound.[11,12,13] In a few investigations only, elemental boron was used.[9,10,14] German et al.,[14] as an example, used elemental boron and molybdenum powders to investigate the microstructural and mechanical characteristics of FeMo-B alloys with compositions in the Fe-rich corner of the ternary system. Care must be used, however, in the selection of the sintering atmosphere. Owing to the high affinity of boron to nitrogen and oxygen, in fact, very pure and dry H2 is recommended.[14,15] On the other hand, the high affinity of boron to oxygen may be exploited during sintering, since it may effectively contribute to the reduction of oxides present on the metallic grains of powder.[15] In the present investigation, elemental boron was added, to different extents, to a prealloyed Fe-1.5 pct Mo powder. Then, sintering experiments were carried out in a dilatometer in order to follow the relevant dimensional changes. The effect of three different heating rates was also investigated. A. MOLINARI, Associate Professor, and S. GIALANELLA and G. STRAFFELINI, Senior Researchers, are with the Department of Materials Engineering, University of Trento, 38050, Mesiano-Trento, Italy. T. PIECZONKA, Senior Researcher, is with the Academy of Mining and Metallurgy, Cracow, Poland. J. KAZIOR, Associate Professor, is with the Cracow University of Technology, Cracow, Poland. Manuscript submitted July 7, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS A
A microstructural characterization of the final products was carried out in order to identify the transformations occurring during sintering. II. EXPERIMENTAL PROCEDURE The specimens were produced by mixing together a prealloyed Fe-1.5 pct Mo powder (Ho¨ganas-grade AstaloyMo, average particle size of 50 mm) with three different percentages (0.2, 0.4, and 0.6 pct, in wt pct) of an elemental boron powder (Goodfellows product, average particle size of 2 mm and purity of 99.99 pct). Boron-free specimens were also produced for a comparison. The specimens for dilatometry were 14 3 4 3 4 mm3 prisms, uniaxially compacted at 600 MPa with die-wall lubrication. The compaction pressure was applied normally to the dilatometry direction, i.e., the direction along which dimensional changes were measure
Data Loading...
