Production of ferroboron powders by solid boronizing method

Abstract

Ferroboron is an iron-boron alloy containing 10-20% of boron by weight. Commercial ferroboron production is made by two main processes: carbothermic reaction and aluminothermic reaction. Ferroboron also occurs in steel surfaces due to boronizing, which is applied to increase surface hardness in steel. Boronizing is a thermo-chemical surface hardening treatment. The ferroboron phases like Fe(2)B, FeB form by diffusing of boron element into iron. These phases are very hard, wear strengths are high, and friction coefficients are low. In this study, ferroboron powder was obtained by boronizing ASC 100.29 iron powder that was used widely in powder metallurgy area. Solid boronizing method was preferred due to its advantages in applications and Ekabor-HM powder was used as the boronizing agent. The 80% ASC 100.29 and 20% Ekabor HM were mixed homogeneously and subjected to boronizing at 850-950 degrees C for 1-6 h. Formation and development of ferroboron phase on the samples was determined by metallographic studies depending on various treatment conditions. The X-ray diffraction analysis revealed that the Fe(2)B phase did form but FeB phase did not. Micro hardness distributions were measured on the powder grains. Eighteen GPa hardness was measured at Fe(2)B phase obtained by boronizing while hardness of non-boronized iron powders was 1.06 GPa. The thickness of ferroboron layer formed by boronizing changed with boronizing conditions. The thickness of ferroboron layer increased with boronizing temperature or boronizing time. Depending upon processing parameters, ferroboron layers was formed partially or throughout ferrous powder structure. Since boronizing can be applied to iron powders having any size or shape, ferroboron production with required shape and size is possible. Finally, a new method, namely solid boronizing method, was developed in ferroboron powder production. (C) 2010 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.