Mechanical Behavior of Iron Boride Formed in the Surface of an AISI W2

Abstract

The present study reports the growth of layers formed in the surface of the boride steel AISI W2; by the application of the dehydrated paste-pack boriding process and using three different temperatures at 1173, 1223 and 1273 K, with 2, 4, 6 and 8 h of exposure. The substrate and the boride Fe2B were analysed quantitatively and qualitatively. The growth of the boride layer Fe2B was examined using optical microscopy (OM), scanning electron microscopy (SEM-EDS) and X-ray diffraction (XRD). The properties were mechanically evaluated, using a Vickers indenter with loads of 0.5 and 1 N, with a constant distance of 15 μm and 30 μm. To determine the fracture toughness (Kc) and the adherence of the boride layer Fe2B, the Rockwell C test method (VDI 3198) was used. The morphology present in the boride Fe2B layer showed a smooth flat, whit ranged thickness from 13.96 ± 1.61 μm to 79.86 ± 4.13 μm. The presence of boride Fe2B layers of steel substrate was confirmed by XRD and the distribution of alloying elements by Energy Disperses for Spectroscopy (EDS). The hardness of the boride layers Fe2B ranged from 157 9± 17 to 1875 ± 25 HV. The fracture toughness of boride Fe2B layer observed ranged from 4.15 to 4.75 MPam1/2. The boride layer has a scale delamination H3 to H6. The boride layers formed in the surface have the function to increase the service life of W2 steels used in the industry.