Structural and strength characterization of steels subjected to bonding thermochemical process

Bonding is a thermomechanical process employed to obtain borided layers in metal alloy, especially steels, which are extremely hard and wear resistant. Formation kinetics of such layers has been extensively studied by carrying out the process in hermetic metallic vessels which contain the bonding agent, commonly a powder and the process packed together (D.M. Tsipas, J. Rus, H. Noguerra, The Institute of Metals, London, 5 (1988) 203–210; R. Chatterjee-Fischer, O. Schaaber, Metal Prog., (1986) 24–25, 27; R.D.T. Whitttle, V.D. Scott, Metals Technol., 11 (1984) 525–529). In this paper we analyze experimentally the influence of a high purity nitrogen atmosphere on the thickness, morphology and impact strength of the layers obtained in a 1018 low carbon steel, 9840 structural steel, W2 tool steel and 304 stainless steel using a paste as an alternative to powder. Using a total least square method to find the best regression analysis (which considers uncertainty in all variables) (C.M. Brakman, A.W. Gommers, E.J. Mittemeijer, The Institute of Metals, London, 5 (1988) 211–218), parabolic growing constants for FeB and Fe2B are determined, as well as wear and impact strength of the layers.