Nondestructive evaluation of microstructure of wear resistance Ni-hard4 cast iron by eddy current technique

In this paper, the nondestructive eddy current test method was used for evaluation of microstructure and hardness of Ni-Hard4 wear resistant alloyed cast iron. For the purpose, the destabilizing heat treatment at 750, 800, 850 and 900ºC for 1 to 5h were done and then tempering heat treatment were applied on Ni-Hard4 cast iron blocks at 300ºC for 3 hours. Microstructure characteristics were evaluated by optical microscopy (OM) equipped with the image analysis software and scanning electron microscopy (SEM). Hardness measurements were done by Vickers method. Then eddy current technique was applied at several frequencies. To achieve an optimum situation for evaluation, relation between eddy current outputs (such as inductive reactance and electrical resistance indexes) and microstructural parameters and hardness values were analyzed. Results show that a good relation exists between eddy current outputs and retained austenite amount and hardness and 150kHz and 170kHz are optimal frequencies for investigation of retained austenite and hardness, respectively. This shows eddy current technique has a high potential for prediction of metallurgical properties and could be used as an in-line inspection and quality control systems.