Effect of Nitriding Process on Wear Behavior of Dual Phase (Ferrite+Martensite) Ductile Cast Iron

Abstract

In this study, it was aimed to improve the surface hardness by applying gas nitriding treatment to dual-phase ductile cast iron and to produce ductile cast irons with a good strength-ductility combination. Thus, it has been tried to develop a ductile cast iron with high wear resistance, strength, and ductility. Ductile cast iron specimens with a dual-phase microstructure consisting of ferrite + martensite were produced by oil quenching at 70 °C after intercritical austenitizing at 800 ⁰C in the ferrite + austenite zone. Instead of the tempering process, nitriding treatment was applied to the dual-phase ductile cast iron specimens at 560 °C for 540 minutes. The tempering process required to be applied to the martensitic structure was also performed by the nitriding process and a hard 10 µm thick nitride layer was obtained on the surface. Optical microscope and XRD analysis were performed for microstructural characterization of nitrided dual-phase ductile cast iron specimens. The wear properties were tested with a tribometer. For comparison reasons, microstructural characterization and wear tests were also performed on non-nitrided dual-phase ductile cast iron. In ductile cast iron, microstructures consist of a hard nitride layer (10 µm white layer) on the surface and a ferrite + tempered martensite (43% martensite volume fraction) structure in the center can be produced by oil quenching from intercritical austenitizing and nitriding treatment. Surface hardness of 510 HV in nitrided dual-phase ductile cast iron, 193 HV in dual-phase ductile cast iron, and 353 HV in austempered KGDD were obtained. The lowest weight loss and coefficient of friction were obtained in nitrided dual-phase ductile cast iron. The highest weight loss and friction coefficient values with wear were obtained in dual-phase ductile cast iron. The wear resistance of nitrided dual-phase ductile cast iron is 2 times higher than that of dual-phase ductile cast iron and austempered ductile cast iron.

Keywords

• dual phase ductile cast iron
• ferrite+martensitic structure
• nitriding
• wear behavior
• ductile cast iron