Formation of L12-ordered precipitation in an alumina-forming austenitic stainless steel via Cu addition and its contribution to creep/rupture resistance

Addition of 2.8 wt.% Cu to an alumina-forming austenitic (AFA) stainless steel promotes formation of a L12-ordered phase with the dominating elements Ni, Cu and Al, instead of B2-NiAl and Cu-rich phases as predicted by the phase equilibrium calculation. At 700 °C/150 MPa, the creep/rupture life of the AFA steel increases from 1537 h to 2047 h with the occurrence of the L12-ordered phase. The nano-size L12-ordered Ni–Cu–Al precipitates are uniformly distributed in the austenitic matrix with an average diameter of 35 ± 7 nm even after 2047 h creep/rupture testing.

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