Fractography and Porosity Analysis of Cr and Cr-Mo PM Steels

• Published in: Archives of metallurgy and materials Vol. 61; no. 3; pp. 1267 - 1276
• Main Authors: Kulecki, P., Lichańska, E., Radziszewska, A., Sułowski, M.
• Format: Journal Article
• Language: English
• Published: Warsaw De Gruyter Open 01.09.2016; Polish Academy of Sciences
• Subjects: alloying elements; fractography; mechanical properties; porosity; sintered steels
• ISSN: 2300-1909; 1733-3490; 2300-1909
• DOI: 10.1515/amm-2016-0263

The aim of the study was to evaluate the effect of processing variables on the porosity and fractography of Cr and Cr-Mo PM steels. The measurements were performed on sintered steels made from commercial Höganäs pre-alloyed powders: Astaloy CrA, Astaloy CrL and Astaloy CrM with two different carbon concentrations (0.2% and 0.6%) added in the form of ultra fine graphite powder grade C-UF. Following mixing in Turbula mixer for 30 minutes, green compacts were single-action pressed at 660 MPa according to PN-EN ISO 2740 standard. Sintering was carried out in a laboratory horizontal tube furnace at 1120°C and 1250°C for 60 minutes, in an atmosphere containing 5%H and 95%N . After sintering, the samples were tempered at 200°C for 60 minutes in air. For porosity evaluation computer software was employed. Hitachi S-3500M SEM equipped with EDS (made by Noran) was employed for fracture analysis. The steel based on Astaloy CrM pre-alloyed powder is characterized by fine pores and good mechanical properties. When sintered at 1250°C, it had area of pores approx. 7.12 μm , ultimate tensile strength (UTS) about 679 MPa and elongation about 4%. The steels were characterized by ductile/cleavage and ductile fractures.