The Oceanykan red soil is very rich in iron, with traces of copper, bluetrite, carbon, and a number of other impurities. As such, in the late medieval era, some very inventive Oceanykans discovered that much of the "gunk" could be melted away carefully, leaving behind a... metal...
Munition steel is an indescript alloy made out of processed soil. The result is a cheap, light, malleable, conductive and tough metal. However, its actual and exact properties are unreliable to say the least. Due to its ease of manufacturing, it is a popular alternative to standard steel in armours, weapons and tools, but use in hulls and firearms has proven too unreliable.
The name refers to the historical concept of munition armour. In the European medieval era, warriors would buy their own protection, but raised troops could be issued cheaper (and lower quality) munition armour. In the Oceanykan medieval era, these stockpiled armours would commonly be made from munition steel.