Abstract
The ferritic grains of SUS410L powder compacts with high green density abnormally grew during vacuum sintering at 1250°C. After the sintering, the size of super coarse grains reached to a few millimeter. In the cast and wrought SUS410L steels, the grain growth started as soon as they were held at high temperature, but in sintered steels, there was the incubation period for grain growth.
In order to explain the process of this abnormal grain growth, an expression based on Zener's equation was proposed.
fz=c(p/r'⋅an)
where fz is the restraining force for boundary migration by pore, p is the porosity, r' is the radius of the sphere which has the same volume of actual angular pore, a is the pore shape factor (a≤1) and c and n are the constants. As the sintering proceeds, the fz gradually decreases because the p decreases by densitication, r' increases by Ostwald ripening of pores and a approaches to 1 by spheroidization of pores. Therefore, some grains start to grow against the fz and result in forming the super coarse grains.
