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 prepar ed from low-alloy and low-carbon steels essentially containing Cr and/ or Mn as the major elements, Boronizing was done in a salt bath consis ting of borax, boric acid, and ferro-silicon. The temperature of the b ath was 940 degrees C and the boronizing was conducted at an atmospher ic pressure for 5-7 h. The presence of borides, e.g. Fe2B, was reveale d by X-ray diffractometry, SEM, and optical microscopy. The fracture t oughness 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 d epends strongly on chemical composition of substrate and boronizing ti me. Mn as an alloying element has a beneficial effect on fracture toug hness, and the longer boronizing time results in higher fracture tough ness. (C) 1997 Elsevier Science S.A.