Effects of copper and malleablizing time on mechanical properties of austempered malleable iron

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Physical metallurgy and materials science, 2007-10, Vol.38 (10), p.2419-2427
• Main Authors: HSU, Cheng-Hsun, LU, Jung-Kai, CHEN, Fan-Shiong
• Format: Article
• Language: English
• Subjects: Alloys; Applied sciences; Carbides; Carbon monoxide; Copper; Exact sciences and technology; Impact tests; Matrix; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metallurgy; Metals. Metallurgy; Scanning electron microscopy
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-007-9282-7

In this study, both the unalloyed and 1 wt pct copper alloyed white irons were successively treated with a duplex heating process consisting of malleablizing and austempering, and then the effects of copper and processing variables on micro structure and mechanical properties of the austempered malleable iron (AMI) were investigated. The results showed that AMI could effectively shorten malleablizing time to obtain the constituents of irregular graphite, acicular ferrite, and retained austenite in the microstructure. Moreover, 1 pct Cu-AMI had a higher retained austenite content than unalloyed AMI. This is because copper is an austenite stabilizer and acts to delay the start of the transformation into ausferrite. In the case of mechanical properties, AMI increased tensile strength (1083 to 1190 MPa) and impact toughness (16 to 22 J) by 2 to 3 times after 930 °C-20 hours malleablizing treatment as compared to as-cast (572 to 580 MPa and 5 to 6 J). In particular, 1 pct Cu-AMI had better performance than unalloyed AMI except for hardness. In comparison with conventional malleable irons, AMI was found to possess better tensile and impact properties. [PUBLICATION ABSTRACT]