The hydrogen trapping characteristics at the grainboundaries of iron-phosphorus and iron-boron alloys were investigated by the thermal analysis technique using gas chromatograph.
All the alloys were heat treated to give a grainboundary segregation, particularly the grainboundary concentration of phosphorus of the constant bulk phosphorus content was controlled by varing the time of aging at 500℃.
In case of iron-phosphorus alloys, aged at 500℃ for the same time, the amounts of hydrogen trapped at grainboundaries were decreased with the increase of the phosphorus concentration. And increasing the time of aging at 500℃ for a given bulk phosphorus concentration, the grain sizes are nearly equal and the amount of hydrogen trapped at grainboundaries were decreased.
These results are mainly ascribed to the change of the lattice hydrogen solubility with phosphorus content, and may be the site competition effects between the segregated phosphorus and hydrogen.
In contrast to the iron-phosphorus alloys, in iron-boron systems, the amounts of hydrogen at grainboundaries were increased with the increase of the bulk boron concentration when the samples were austenized and aged at 700℃. This is mainly attributed to the grain size refinement by the boron, i.e.,the lattice hydrogen solubility change with the boron content and site competition effect between boron and hydrogen are the minor effect on the hydrogen trapped at grainboundaries.
