Fracture toughness of boride formed on low-alloy steels

In this study, we investigated the fracture toughness of boride layers formed on steel surfaces, The samples used for this study were prepared from low-alloy and low-carbon steels essentially containing Cr and/or Mn as the major elements, Boronizing was done in a salt bath consisting of borax, boric acid, and ferro-silicon. The temperature of the bath was 940 degrees C and the boronizing was conducted at an atmospheric pressure for 5-7 h. The presence of borides, e.g. Fe2B, was revealed by X-ray diffractometry, SEM, and optical microscopy. The fracture toughness of borided surfaces was measured via Vickers indenters with a load of 2 N. It was found that the fracture roughness of the borides ranged from 4 to 6 MPa m(1/2). The fracture toughness of the borides depends strongly on chemical composition of substrate and boronizing time. Mn as an alloying element has a beneficial effect on fracture toughness, and the longer boronizing time results in higher fracture toughness. (C) 1997 Elsevier Science S.A