The Impact Toughness and Fracture Behavior of Ni-Containing Powder Metal Steels

The toughness of powder metal (PM) steel is always inferior due to the presence of pores. An alloying element is typically found to improve the tensile strength, while sacrificing toughness. These issues prohibit the development of high-strength PM steels with satisfactory toughness. To formulate high-strength PM steels with superior toughness, the effects of Cr and Mo on the impact toughness and fracture behaviors of Ni-containing PM steels were investigated. The results indicated that both 1.5wt% Cr and 1.5 wt% Mo additives can improve the microstructures and tensile strengths of Ni-containing PM steels. However, while 1.5 wt % Mo apparently impairs the toughness, 1.5 wt % Cr does not. The addition of 1.5 wt% Cr results in the formation of Ni-rich martensite, which is strong and tough, thereby improving the tensile strength by 150% without sacrificing toughness.