Effects of Ti, Nb and Mischmetal on Creep Rupture Strength of 25Cr-20Ni Casting Steel
1979 Volume 65 Issue 7 Pages 985-993
Details
1979 Volume 65 Issue 7 Pages 985-993
Centrifugally casting steel HK40 (0.4C-25Cr-20Ni) is widely used for reformer tube in the steam reforming process or cracking tube in the equipment which produces ethylen. A study has been made on the effects of complex addition of a small amount of the Ti, Nb and Mischmetal on the creep ruptures trength of HK40.
By addition of Ti and Nb, (Ti, Nb) C is formed, and as a result of forming (Ti, Nb) C, precipitation of Cr carbides and their coarsening are retarded. Therefore, the strength and ductility of creep rupture are improved.
Mischmetal is effective to improve the creep rupture strength, if it is added by alone. However the effect of Mischmetal can not be found in complex addition with Ti and Nb, because the strong effect of Ti and Nb hides the effect of Mischmetal.
