Kinetics of bonded AISI M2 high speed steel

Abstract

The present study reports on kinetics of bonded AISI M2 high speed steel. Boronizing thermochemical treatment was carried out in a solid medium consisting of EKabor powders at 850 degrees C, 900 degrees C and 950 degrees C for 2, 4, 6 and 8 h, respectively. The presence of borides FeB and Fe2B of steel substrate was confirmed by optical microscopy and scanning electron microscopy (SEM). The results of this study indicated that the morphology of the boride layer has a smooth and compact morphology, and its hardness was found to be in the range of 1600-1900 HV. Depending on process time and temperature the thickness of boride layer measured by a digital instrument attached to an optical microscope ranged from 3 to 141 mu m. Layer-growth kinetics were analyzed by measuring the extent of penetration of the FeB and Fe2B sublayers as a function of boronizing time and temperature. The fracture toughness of borides ranged from 4.80 to 5.21 MPa m(1/2). Moreover, an attempt was made to investigate the possibility of predicting the iso-thickness of boride layer variation and to establish an empirical relationship between process parameters and boride layer thickness. (C) 2011 Elsevier Ltd. All rights reserved.