Materials Chemistry and Physics 67 (2001) 66–71 Study of sinterability of bronze and phosphorus bronze steels N. Candela ∗ , A. Quesada, F. Velasco, J.M. Torralba Material Science and Engineering Department, Universidad Carlos III de Madrid, Av de la Universidad 30, 28911 Leganés Madrid, Spain Abstract The sinterability of different alloyed steels was studied by dilatometry at different temperatures. Iron and two amounts of graphite powders (0.3 and 0.7%) were used as raw materials for the base steels. Three levels (2, 5 and 8%) of bronze and phosphorus bronze (promoting liquid phase) were employed as alloying additions. All the materials were compacted at 700 MPa. The sintering study by dilatometry was made in 95%N 2 –5%H 2 atmosphere. Five different temperatures were: austenizing temperature, initial temperature of swelling, temperature of liquid phase forming, temperature at which maximum rate of deformation takes place, and initial temperature of shrinkage. With these temperatures, the optimum point of sinterability was determinated in each steel. Finally, all the materials were sintered at six different temperatures (910, 950, 990, 1030, 1070 and 1110 ◦ C) in the same atmosphere to obtain the sinterability plots (sintering density vs. temperature). © 2001 Elsevier Science B.V. All rights reserved. Keywords: Sintered steels; Bronze; Phosphorus bronze; Liquid phase sintering 1. Introduction Steels alloyed with bronze are used mainly for self- lubricated bearings, the open porosity facilitate the move- ment of the lubricant [1]. For this application the selected density is low, but other applications such as structural parts require higher density [2]. The properties of steels alloyed with bronze are superior to those alloyed with plain copper, due to the increase of tensile strength, the hardness, and the sintering behaviour because it promotes liquid phase. But brittle precipitates can appear. On the other hand, the addition of bronze with phospho- rus aids the sintering process because it increases the tran- sition temperature between  →  in the steels [3]. During sintering, the materials remain longer in -phase, increasing the sintering process, promoting shrinkage, with the pores being round. In industry, the phosphorus addition facilitates sintering at temperatures below 1120 ◦ C. The influence of bronze is to promote liquid-phase sintering, with properties otherwise obtained at higher temperatures [4–6]. An important im- provement is noticed in the tribological behaviour, but if the amount rises to 0.6%, of precipitates of Fe–P at the grain boundaries, it could cause embrittlement. ∗ Corresponding author. 2. Experimental procedure The characteristics of the powders used are shown in Table 1 and the compositions (wt.%) of the pre-alloyed pow- ders in Table 2. The materials studied are presented (wt.%) in Table 3. All the materials were compacted at 700MPa. The dilatometric study was made in 95%N 2 –5%H 2 atmo- sphere. The heating rate was 10 ◦ C min −1 up to 1300 ◦ C, the holding time was 30 min, and the cooling rate 15 ◦ C min −1 to 100 ◦ C. After determining the point of sinterability in each material, all were sintered at six different temperatures (910, 950, 990, 1030, 1070 and 1110 ◦ C) in 95%N 2 –5%H 2 atmo- sphere. This study was complemented with a microstructural study by optical and scanning electron microscopy. Sam- ples for dilatometry had the following dimensions: length, 28 mm; thickness, 3 mm; and width, 5 mm. 3. Results Fig. 1 shows the results obtained by dilatometry for all the materials with BZ additions and 0.7% graphite, with the change of the slope due to the  →  transformation and the final dimensional change. With an increased amount of additive (BZ) the shrinkage from ferrite to austenite is smaller, and the final dimensional changes are higher in all cases. The dilatometric trends (Fig. 1) are similar with PBZ and BZ. The main difference occurs when the additive is PBZ, and as a result the dimensional change is higher. This 0254-0584/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0254-0584(00)00421-1