Sinter-Hardening

Bainite morphologies in sintered steels: influence of materials and process conditions

“…Then, the internal cooling speed of a porous part with ε porosity is proportional to the ratio (1 - nε)/(1-ε) 2/3 , which, for ε > 0, is always > 1. n is a factor linked to porosity and > 1. By calculation it is possible to find that at 7.0 g/cm 3 density – other conditions being equal – the cooling speed inside a porous body can increase more than 5%with respect to a fully dense part, equally shaped [25]. These considerations explain why, in this research, the porosity fraction has been considered irrelevant.…”

“…In this regard, it must be borne in mind that the beliefs spread up more than 30 years ago [20] were disproved by experimental researches conducted by Saaritas et al [21] and, shortly afterwards, by Bocchini et al [22][23][24], Those researches demonstrated that the cooling speed within a sintered PM part is higher than that of an analogous part, made of fully dense steel, and increases as density decreases. According to Bocchini [25] the explanation is as follows:…”

“…[21] and, shortly afterwards, by Bocchini et al [22–24], Those researches demonstrated that the cooling speed within a sintered PM part is higher than that of an analogous part, made of fully dense steel, and increases as density decreases. According to Bocchini [25] the explanation is as follows: … the heat flux from the cooling part – other conditions being equal – occurs through the outer surface. This surface, in the case of a porous part with ε porosity, is larger than that of a corresponding fully dense part (equal shape and mass) by the [1/(1 – ε)] 2/3 factor, where ε is the porosity.…”