The holy grail of materials science; plasteel can take heat like Tungsten, is as hard as Iridium, can bend like plastic, and won't corrode with basically anything. Many precursor machines, weapon and artifacts are manufactured from this alloy, but its production process is entirely alien to humanity. Forging things out of recovered plasteel is almost impossible, and requires either cutting-edge equipment or a decades-experienced bluemetal-specialised blacksmith.