Segregation of Boron to Grain Boundaries in Iron and a Stainless Steel

The effects of boron on the grain boundary and surface energies in iron at 900 and 1000 OC and AISI 316 stainless steel in the temperature range 950-1 250 OC were investigated. It was found that boron reduced these energies in a manner typical of an element with low solubility in the matrix. It has been found that boron improves the grain boundary strength of iron at low temperatures [I] and increases the creep rupture life and ductility of austenitic steels and nickel alloys at high temperatures [2]. Measurements of grain boundary and surface energies were used to determine whether equilibrium segregation of boron to these interfaces occurs in iron and AISI 316 stainless steel. The techniques used were the standard ones of measuring the ratios of twin and grain boundary energies to the surface energy from the profiles formed during vacuum annealing at the intersections of these boundaries with the surface. By assuming that the boron content of the materials did not affect the twin boundary energy, its effect on the relative surface and grain boundary energies was assessed. The multiphase equilibration technique [3] was used to obtain a value of surface energy for one of the steels and this and a literature value of surface energy for boron free iron were used to estimate the absolute values of all the interfacial energies. Details of the energy measurements are given elsewhere [4]. Figure 1 shows the effect of boron additions on