Use material defines more

code/modules/materials/sheets/_sheets.dm

@@ -13,7 +13,7 @@
 		slot_r_hand_str = 'icons/mob/items/righthand_material.dmi',
 		)
 
-	var/default_type = DEFAULT_WALL_MATERIAL
+	var/default_type = MAT_STEEL
 	var/datum/material/material
 	var/perunit = SHEET_MATERIAL_AMOUNT
 	var/apply_colour //temp pending icon rewrite
@@ -26,7 +26,7 @@
 	randpixel_xy()
 
 	if(!default_type)
-		default_type = DEFAULT_WALL_MATERIAL
+		default_type = MAT_STEEL
 	material = get_material_by_name("[default_type]")
 	if(!material)
 		return INITIALIZE_HINT_QDEL

code/modules/materials/sheets/metals/metal.dm

@@ -1,7 +1,7 @@
 /obj/item/stack/material/steel
-	name = DEFAULT_WALL_MATERIAL
+	name = MAT_STEEL
 	icon_state = "sheet-refined"
-	default_type = DEFAULT_WALL_MATERIAL
+	default_type = MAT_STEEL
 	no_variants = FALSE
 	apply_colour = TRUE
 

code/modules/materials/sheets/metals/rods.dm

@@ -10,7 +10,7 @@
 	throw_range = 20
 	drop_sound = 'sound/items/drop/metalweapon.ogg'
 	pickup_sound = 'sound/items/pickup/metalweapon.ogg'
-	matter = list(DEFAULT_WALL_MATERIAL = SHEET_MATERIAL_AMOUNT / 2)
+	matter = list(MAT_STEEL = SHEET_MATERIAL_AMOUNT / 2)
 	max_amount = 60
 	attack_verb = list("hit", "bludgeoned", "whacked")