Effect of Copper Addition on Mechanical Properties of Nodular Indefinite Chilled Iron (NICI)

Abstract

Nodular infinite chilled iron (NICI) material with high content of nickel (~4.00%) was usually used as work roll in hot strip rolling mill. Microstructure of NICI was consists with nodular graphite and cementite with matrix phase consist of pearlite, martensite and ausferrite that depend on the alloying content. The introduction of copper was successfully increasing the hardenability of NICI by only using low nickel content (~2.50 %) with small addition of copper (0.52%). The development of NICI was done by hot shakeout of CO2 sand mold of as-cast iron and then isothermal heating in muffle furnace in temperature 300 oC in 6 hours to achieve ausferritic transformation. By achieving the martensite and ausferrite phase in as-cast condition, the sample will not need austenitizing and quenching process and the sample that will be free of quenching crack and thermal stress that usually occurred austenitizing and quenching process. It was confirmed by optical microscope and scanning electron microscope (SEM) observations that with the small addition of copper (0.52%), the amount of pearlite was very small (~1.00%), but with further addition of copper (2.02%), the amount of martensite was significantly increase the hardness until 51.56 HRC but the tensile strength was significantly dropped into 442 Mpa from previously 571 Mpa without copper addition. From hardness and tensile strength data it can be seen that the optimum content of copper is 1.45 % that have good combination of hardness (47.75 HRC) and moderate tensile strength (508 Mpa).