Abstract: The relation between fatigue of the used weld metal and the quantity and morphology of residual austenite (Ar) are studied in the partial cold-welded metal on the 9Cr2Mo steel roll. Test result indicated that the block-like Ar was the main cause of early stage crack of the weld metal. The crack mechanism was that the block-like Ar fractured by plastic deformation and high stress induced to phase change twinning. As the quantity of strong carbide elements and carbon element accorded with the fixed-ratio theorem, the feeble carbide elements and non-carbide elements witch dissolved in base-phase affected the quantity and morphology of Ar.M1/Ar phase which was formed from thin film-like Ar and low carbon martensite can improve the anti-fatigue ability remarkably.

Key words: Residual austenite(Ar) Fatigue Hardfacing welding of rolls Cold-welding