welding a fireplace grate?

hey guys
i got a nice big fire pit outside, and i picked up a few grates for a last year
i got both of the grates butted up against each other, which creates a high spot in the center

so thought it would work better if there wasnt a high spot, so i thought i might cut the backs of both of em, and weld them together

now, im pretty sure these are cast iron grates, and all i got is a fluxcore welder
ive been told this may not work because cast iron likes to get brittle when hot, but these are grates made to get hot, so who knows