Effect of microstructure on the wear resistance of borided Fe–Cr alloys

Abstract

Two boride layers were found to form at the interface between reacting phases in the course of boriding of Fe–Cr alloys (10, 15, 25 and 30% Cr) and chromium steels (13 and 25% Cr) in the temperature range of 850–950°C and reaction times 3600–43200 s (1–12 h). In the case of Fe-10%Cr and Fe-15%Cr alloys and 13% Cr steel, the outer boride layer bordering the boriding agent consists of the (Fe, Cr)B phase, whereas the inner boride layer adjacent to the solid substrate consists of the (Fe, Cr)2B phase. Each layer is thus a homogeneous phase (type I microstructure). In contrast, on the surface of Fe-25%Cr and Fe-30%Cr alloys and 25% Cr steel each of the two boride layers consists of two phases and has a peculiar network-platelet morphology. The outer boride layer comprises the (Fe, Cr)B and (Cr, Fe)B phases, while the inner consists of the (Fe, Cr)2B and (Cr, Fe)2B phases (type II microstructure). It is such boride layers that exhibit the highest wear resistance.