Investigation of Mechanical Properties of Powder Metallurgy Parts with Control of Microstructure
In the present work, two kinds of steel powder were (Distaloy HP-1 & Ultrapac-LA) selected and subjected to powder metallurgy processing. For Ultrapac-LA, a heterogeneous microstructure consisting of tempered martensite, nickel-rich ferrite, divorced pearlite and nickelrich regions surrounding pores was observed. For Distaloy HP-1 in slow cooling rates (0.4 °C.s-1), the amounts of martensite and bainite varied between 50-60% and 30-40%. However, for fast cooling rates (1.2 °C.s-1), the variation was between 70-80% and 10-20%. The mechanical properties of the prepared samples were studied with controlled production conditions such as cooling rate and heat treatment. The increasing porosity was found to play an important role in the tensile stress and fatigue strength. The ultimate tensile strength and fatigue strength were more than 1000 MPa and 400 MPa in this research (for Distaloy HP-1, 7.2 g.cm-3, 0.5% carbon content and fast cooling rates). Macroscopic examination of the fracture surfaces for all specimens revealed that fatigue crack growth and final fracture regions were brittle and without noticeable permanent deformation. The final fracture regions for all tests were very similar, and the final fracture in these two material conditions revealed brittle macrobehavior and ductile microbehavior.
Duk Yong Yoon, Suk-Joong L. Kang, Kwang Yong Eun and Yong-Seog Kim
H. Khorsand and S.M. Habibi, "Investigation of Mechanical Properties of Powder Metallurgy Parts with Control of Microstructure ", Materials Science Forum, Vols. 534-536, pp. 297-300, 2007