Applicability of intercrital annealing heat treatments to low alloyed pure carbon powder metal steels and investigation their mechanical properties

In this study, the producibility of ferrite + martensite microstructures in low alloyed PM steels was investigated. For this purpose, PM specimens were prepared from iron-based powders (Ancorsteel 1000), admixed with different graphite contents (0.3 and 0.5 wt %) and also with 0.5 wt% Ni and 0.5 wt% Mn separately at a constant graphite content of 0.3 wt %. The mixed powders were cold pressed under a pressure of 700 MPa and sintered at 1120 °C for 30 minutes. The sintered specimens were then intercritically annealed at different temperatures (724, 735, 760 °C) and water-quenched. After sintering, porosities ferrite + pearlite microstructures formed in all specimens. The lowest porosity level was obtained in 0.5 % graphite and 0.3 % graphite + 0.5 % Mn-added specimens. Following intercritical annealing + water quenching heat treatments, ferrite + martensite were produced in 0.3 % graphite, 0.5 % graphite and 0.3 % graphite + 0.5 % Mn-added specimens but ferrite + Ni-rich martensite microstructures were obtained in 0.3 % graphite + 0.5 % Ni-added specimens. In addition, in order to produce fully martensite microstructure, specimens with 0.3 % and 0.5 % graphite content were austenitised at 890 °C and water- quenched. These specimens with fully martensite microstructure were then, again intercritically annealed and water-quenched. Following these heat treatments, fine grained ferrite + martensite microstructures were produced. In all specimens, martensite volume fraction increased with increasing intercritical annealing temperatures. Mechanical properties of 0.3 % and 0.5 % graphite added specimens were investigated. With increasing martensite volume fraction, strength and impact energy increased but elongation values decreased. It was seen that better mechanical properties were achieved in specimens with fine grained martensite microstructures.Key Words : P/M, Sintering, Dual phase steel, Porosity, Mechanical properties