Investigation of Aluminum Effect on the KIC and ac of Hadfield Hypereutectoid Steel By Using Impact Test Results

In this study, effect of aluminum alloying element on KIC and ac of Hadfield hypereutectoid steel was investigated by using the impact test results. For this purpose, initially 2 casting blocks were prepared from Hadfield steel (without addition of Al and with 1.68 wt% Al) by using coreless induction furnace. After casting, all blocks were austenitized in 1100C for 2 hours and immediately quenched in pure water. In the next step, uniaxial tensile test, Vickers hardness test and Charpy impact test were applied on specimens at room temperature. Evaluation of microstructures were conducted by optical microscopy and the fractured surfaces were observed by scanning electron microscope. The results of impact tests and fracture toughness empirical relationships were used to evaluate the KIC and ac of the Hadfield steel. The optical microscopy images indicated that by increasing the amount of aluminum in the chemical composition of Hadfield manganese austenitic steel, austenite grains size increased from 111.9 to 142.5 micrometer. The results of tensile test, hardness test and impact test represents an increase in yield strength and hardness, and reduction of failure strain and impact energy of Hadfield steel because of adding aluminum to its composition. Calculations of fracture toughness and critical crack length for Hadfield steel showed that the addition of aluminum to steel leads to reduction of fracture toughness from 163.7 to 104.5 Mpa.(m)1/2 and reduced the critical crack length at surface from 0.014 to 0.007m.