Stainless steel powders (303L, 304L, 310L and 316L) were formed into tensile test bars using the “press and sinter” process. Most processing parameters, except heating rate, were kept constant. During the heating of the experimental specimens from 700°C to the sintering temperature of 1300°C, heating rates were varied, e.g., 2.5, 5.0, and 10.0°C/min. Experimental results showed that a material heated with a low heating rate tended to have higher sintered density and tensile strength. However, the low heating rate caused grain growth in the sintered material. These results are in contradiction with the improved densification of some ceramics by ultra rapid heating. The reasons for contradiction are as follows. First, the heating rates employed in this work are not very different. The second is attributed to small thermal gradients generated in the thin metal powder compacts. Because of these reasons, densification of the sintered stainless steels series 300 is controlled by an isothermal condition. The low heating rate allows longer time for atomic diffusion, which is an important sintering factor. This means more atoms move to points of contact between powder particles to form necking and to cause necking growth. This results in better sintering. However, the low heating rate means that the materials are exposed to heat for longer time and thus their grains have a tendency to grow.
