Effect of Alloying Elements on Creep Rupture Strength of 25Cr-20Ni Casting Steel

Abstract

Centrifugally casting steel HK40 (0.4C-25Cr-20Ni) is used for reformer tube in the steam reforming process or cracking tube in the equipment which produces ethylene. A study has been made of the effects of constituent elements such as C, Cr, Ni and adding elements such as Ti, Nb, Mo on the creep rupture strength of HK40.
The results obtained are summarized as follows:
1. C, Cr and Ni are effective to improve the creep rupture strength, where Si is sligtly effective and Mn is ineffective. With increasing Ni content, the slope of the rupture time-stress curve becomes gently and long time creep rupture strength increases.
2. By adding Ti, Mo, V and Nb, known as carbide former, the creep rupture strength is still improved at high temperature of 982°C. Mischmetal is effective and N is ineffective.