Thee!ectofmicrostructuralchangeduringisothermalheattreatmentonstructure-sensitivemagneticpropertieshasbeeninvestigatedfor1Cr}1Mo}0.25Vsteel.Magneticpermeabilityincreased,butcoerciveforceandVickershardnessdecreasedasageingtimeincreased.Duringtheisothermalheattreatment,Mn23C6and(Cr2.5Fe4.3Mo0.1)C3carbideswerefoundatgrainboundaries.These