It's a little confusing to have 'Refined Iron' when it would be simpler to call it 'Steel' since that is what refined iron actually is.
A suggested simple adjustment to the process to make it that small bit more realistic (and more complex) for all us OCD types would be this:
Smelting 'Coal dust' = 'Coke' (purified Coal with double or more EU output when burned)
Combine 02 x 'Iron ingots' (simulating molten iron) with 01 x 'Coke' = 02 x 'Steel chunks' (include 'Limestone' along with 'Coke' here as well to make it perfect)
Smelting 'Steel chunk' = 'Steel ingot' (basically renamed with no need to change block ID or image)
You could also have 'steel' equipment with higher durability then Bronze.
Maybe if you do find a way to include 'Limestone' as a new block that is common as 'Gravel', crushed/maceratored to 'Limestone dust' it can be used in the 'Steel' recipe as mentioned above with 'Coke'
Another part it could be used is to combine with 'Sand' and 'Gravel' to make 'Cement powder'. Combine 'Cement powder' with a 'Bucket of water' to make 'Cement blocks' (smooth whitish blocks) and then used much the same as 'Stone' for building/construction and vanilla recipes. When broken (by pickaxe) it turns back into 'Cement powder'.
PS love your work, makes a whole new world of MC coupled with Buildcraft and RP plus submods. Full complex industries ftw!