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Abstract
The present study investigates the effects of intercritical austenitising, tempering time and martensite volume fraction on the tensile properties of ferritic ductile iron with a dual matrix structure. The results showed that a structure having proeutectoid ferrite plus martensite (the dual matrix structure) has been developed and that the volume fraction of proeutectoid ferrite and martensite can be controlled to influence the strength and ductility. Specimens quenched from the (α+γ) temperature range exhibited significantly greater ductility than conventionally heat treated specimens. By changing only the intercritical austenitising time and keeping the rest of the heat treatment conditions constant it was observed that specimens intercritically austenitised for 30 s exhibited higher strength and ductility than those intercritically austenitised for 20 min. This was considered to result from carbon enrichment of the austenite depending on the time for carbon diffusion during intercritical austenitising. The specimens intercritically austenitised for 30 s and having ∼49% martensite volume fraction exhibited the best combination of high strength and ductility. The tensile and proof stresses of this material are much higher than pearlitic and ferritic grades and ductility is significantly lower than ferritic grades.