Mechanical characterization and optimization of heat treatment parameters of manganese alloyed austempered ductile iron

Abstract

Austempered Ductile Iron (ADI) belongs to the family of cast irons whose mechanical properties are altered using austempering heat treatment process. The objective of this paper is to study the effects of heat treatment parameters on manganese alloyed ADI. Hence, austenitization temperature, austempering temperature and austempering time are taken as the control variables along with the manganese content in the material. The effects of heat treatment are studied by measuring the ultimate tensile strength and the hardness of the material. The regression equations are developed to relate the various parameters under study. The microstructures of the specimen reveal that retained austenite content increases with increase in manganese and results in decrease in hardness of the material. The statistical analyses indicate that the austempering temperature is the major factor affecting the variation in hardness and tensile strength with 74.5 % of contribution within the range of values whereas, variation in manganese content does not have significant effect on hardness within the investigated composition range in the material.

Effect of austempering temperature and manganese content on the impact energy of austempered ductile iron

“…This may be because of the higher amount of retained austenite obtained at this austempering temperature (Olawale & Oluwasegun, 2016). The ultimate tensile strength data is taken from the previously reported results from the same project by the same author (Hegde et al, 2019) for the comparison purpose. It may be seen that tensile strength obtained at the higher austempering temperature of 420°C is lower because of the coarser structure.…”

“…Statistical analysis is carried out to fit the regression model so that impact energy may be predicted for various austempering temperature. In the earlier study of the same project, it is reported about the tensile strength of ADI at various condition (Hegde et al, 2019). In the current study, with the additional results of impact energy and ductility, manganese content and austempering temperature are optimized in order to obtain superior combination of tensile strength and impact energy.…”

“…Specimens are then rapidly taken out and put in another salt bath comprising of sodium nitrate and sodium nitrite which is maintained at the pre-determined austempering temperature (320, 370 and 420°C). The test samples are kept at the asutempering temperature in the salt bath for the fixed duration of 2 h. The austenitization temperature, austenitization time and austempering time are not vaied, whose values are based on literature review (Hegde et al, 2019). Specimens are finally taken out from the salt bath and cooled in the air till it attains room temperature.…”

An Analysis of the Amount of Retained Austenite in Manganese Alloyed Austempered Ductile Iron

“…This justifies the variation in mechanical properties with the change in heat treatment parameters. Hardness and tensile strength values have been found to be decreasing with increasing austempering temperature [17][18][19] . These reduction in hardness and strength may be attributed to the coarser grains obtained at higher austempering temperature.…”

“…Amount of retained austenite has increased with the increase in the austempering temperature from 320 to 420ºC. This resulted in the lower hardness at the higher austempering temperature of 420ºC 17 .…”