Effects of Aging Treatment on High Temperature Strength of Nb Containing Ferritic Stainless Steels

摘要

Effects of aging treatment at 700deg C on high temperature strength of Nb containing ferritic stainless steels were compared with those of Nb free steels. Hot tensile tests were carried out at 700 deg C after the aging for different aging times using Gleeble 1500. The high temperature strength of Nb free steels decreased with increasing aging time mainly due to grain growth. However, the reduction of the high temperature strength in Nb (0.38 wt percent) containing steels occurred by Nb precipitation. It was observed that Fe_2Nb (Laves phase), NbC, NbN and Fe_3Nb_3C were precipitated out in 0.01C-0.38Nb steel, while only NbC, NbN was formed in 0.03C-0.38Nb steel during the aging at 700 deg C. This was well agreed with the calculated equilibrium fraction of precipitates. The coarsening rate of Fe_2Nb was measured faster than that of NbC. Coarse Fe_2Nb particles formed during the aging were very detrimental to high temperature strength. However, fine Fe_2Nb precipitates formed during the tensile test contributed to high temperature strength in 0.01C-0.38Nb steel.