Death of the Inflexible

The Death of the Inflexible was an Imperial excoriation campaign carried out by the entirety of the Sons of Iron Space Marine Chapter against an unnamed, metallic race of mutants that ravaged several Imperial sectors. The Sons of Iron willingly the call-to-arms, and helped seek out and purge the mutant presence from the system, though at the cost of their Chapter Master's life.

Background
On the world of Hyborea, near the Somnium Stars, the creation of the Cicatrix Maledictum, led to the birth of innumerable mutants which ate metal. Those ravenous colossus, faster, stronger and deadlier than their human parents, overrun the world, and only one bastion, the Retreat of Saint-Belit the Radiant, endured, behind heavy stone walls. When Rauth received their call for help, he brought the full might of his Chapter on this cursed world. The Sons of Iron fought with their cold fury, and in mere months, all the mutants had been slaughtered. Alas, Kardan Rauth fell early in the campaign, when a surprise assault by thousands of the monsters reached his command center. Even as he was devoured alive, he managed to slay dozens of mutants and preserved Foesgrinder and Rempart of the Imperium.