Abstract
Yielding behaviors of sintered iron compacts were investigated through the microscopic observations and the tensile tests at both room and high temperatures with different strain rates.
Yield drop, named as pseudo yield point, in a stress-strain curve is observed in various iron compacts, pressed at 3-7 t/cm2 and sintered in hydrogen for 1 hr at 1200°C. This behavior, which differs from that of mild steel as to the existence of plastic strain before yield point, may be due to the yielding of matrix and subsequently to the stress relaxation by nucleation and propagation of the crack from residual pores. The pseudo yield point and tensile strength of sintered compacts may depend en the strain rate (10-5-10-2/sec) as in the case of mild steel.
The strength increment due to strain aging and the serrated stress-strain curves known as blue brittleness are clearly observed in iron compacts sintered even in hydrogen. Furthermore, this phenomenon is remarkable in the high nitrogen iron compacts sintered in dissociated ammonia.
