by M9, do you mean 9 metric tons, so it is static casted (vs continuously cast)? if this is the case, the solidification will be slow, and hom process is almost a must to eliminate cast segregation. Hom could also dissolve ferrite for this alloy because Si is a ferrite former.
caution to be taken do not hold too long time to avoid sulfur and oxygen impurities rejected from austenite and diffused to grain boundaries, where they form weak, plastic films that can degrade hot workability. Grain growth worsens this effect.