effect of austempering heat treatment on strength properties and hardness of aluminum grey cast iron

in the present work, the effect of aluminum content, austenitizing temperature and austempering time and temperature on the mechanical properties and hardness of fe-c-al grey cast iron was investigated. for this purpose, three alloys containing 1, 2 and 4 weight percent of aluminum were provided. the tensile samples were austenitized at 850?c and 900?c for 120 min, followed by austempering process at 275 ?c, 325 ?c and 375 ?c for 1-120 min. the ultimate strength and hardness of samples with tensile and hardness tests were investigated. the results showed that the samples without aluminum had the maximum strength. when amount of aluminum increased to 2 wt% ultimate strength decreased and while the amount of aluminum increased to 4 wt% the ultimate strength improved somewhat. the increase of austenitizing temperature from 850 ?c to 900?c in the samples not containing aluminum and containing 4 wt% aluminum increases ultimate tensile strength and hardness. in the alloys with 1 wt% and 2 wt% aluminum, the increase in the austenitizing temperature leads to decrease in the ultimate tensile strength and hardness. the results also indicate that in the samples not containing aluminum and/or containing 4 wt% aluminum, the first stage of transformation is completed after 30 minutes. between 30 and 60 minutes, the second stage of transformation starts and the increase of austempering time to over 60 minutes leads to the beginning of the third stage of transformation. in the alloy with 1 wt% of aluminum maximum elongation was seen after 30 minutes but more austempering time caused the decrease of the elongation. in the alloy containing 2 wt% aluminum, using low austempering temperature (275 ?c, 325 ?c) and increasing the austempering time leads to the rising of elongation. in the high austempering temperature (375 ?c), the third stage of transformation begin after 30 minutes and the elongation decreases.