Precipitation of Laves phase in a 28%Cr–4%Ni–2%Mo–Nb superferritic stainless steel

The main objective of the present work was to study the precipitation of the Laves phase in the X1 CrNiMoNb 28 4 2 (Werkstoff-Nr. DIN 1.4575) superferritic stainless steel employing several complementary techniques of microstructural analysis. The phase that precipitated in largest quantity in the DIN 1.4575 steel was the sigma (σ) phase. However, along grain boundaries, after aging at 850 °C, a Laves phase of the MgZn2 type, with a hexagonal C14 crystal structure and chemical composition (Fe,Cr,Ni)2(Nb,Mo,Si), was also identified. Growth of the Laves phase is curtailed by exhaustion of niobium of the matrix and by the presence of the sigma phase, which also precipitates in the vicinity of the grain boundaries, however in larger amounts. No chi (χ) or austenite phases were detected in the temperature range studied.