Abstract
The effect of alloying element such as C, B, Ti and Nb, and heat treatment on the high temperature strength and micro structure of 18Cr-12Ni-3Mo austenitic heat resisting steels containing boron were investigated.
In B addition, creep rupture strength increased with increasing B content, whereas in C addition, tit reached maximum at 0.2%C. These effects were ascribed mainly to a precipitation hardening duevto M23C6 occurring during creep. The effects of Ti and Nb additions on creep rupture strength were given as a function of (Ti+Nb)/C (atomic percent ratis) irrespective of C contents, and gave a maximum effect at (Ti+Nb)/C=0.4-0.8. Therefore, these effects of Ti and Nb additions were ascribed partly to a change in morphology and growth rate of M23C6, into which Ti and Nb were dissolved.
Moreover, creep rupture strength increased with increasing solution temperature, up to 1250°C. Surprisingly, the eutectic structures had no negative effect upon creep rupture strength of the steels.
Also, the complex borides in these alloys were identified by X ray and chemical analyses. The relation between the sort of borides and eutectic temperature was also discussed.
