ASME B31.3, Appendix F, F323.1 (2) states that " the
possible conversion of carbides to graphite during long time exposure to
temperatures above 427°C (800°F) of carbon steels, plain nickel steel, carbon-manganese
steel, manganese-vanadium steel, and Carbon-Silicon steel.
ASME B31.3, Appendix F, F323.1 (4) states that," the
advantages of silicon-killed carbon steel (0.1% silicon minimum) for
temperatures above 482°C (900°F)".
One statement says graphitisation of C-Si steel above 427°C (800°F) service and another clause says C-Si steel advantage above 482°C (900°F).I am confused!
My understanding is that, 'Si' Killing is a kind of de-oxidation process like 'Al' killing during steel making.So,the steels which I have mentioned in the above ASME B31.3 clauses have Silicon content.Then why one steel is prone to graphitisation above 427°C (800°F) service temperature and another can perform like a superman without graphitisation above 482°C (900°F)" service temperature?Could you throw some light on this matter?