Ausfferit transformation in making the austempered ductile iron (ADI)

  • Nguyễn Hữu Dũng

Abstract

For traditional ductile iron, the mechanical properties can exhibit: the ultimate tensile stress UTS = 700 - 750 MPa; elongation  δ= 2 - 5 %. To achieve higher mechanical propertiesand therefore, the reliability of the product, variables such as chemical composition of the alloy, casting quality, graphite structure and heat treatment process (austenitising and austempering time and temperature) should be controlled. This paper presents a method by which the austempered ductile iron (ADI) was made. For ADI, the obtained microstructure consisting of acicular ferrite (AF) and retained austenite, yields the best combination of mechanical properties, i.e.,:UTS: 1200 MPa; elongation: 7 - 8 %. The dilatometric results were also used to calculate n and k in the Johnson-Mehl-Avrami equation and to derive the time-temperature-transformation diagrams. The processing window is established to be austempering temperature 380oC for 2 houres. 

điểm /   đánh giá
Published
2016-01-18
Section
Articles