Secondary hardening and fracture behavior in the high Co-Ni steels containing W, has been studied in terms of severe deformation, Cr addition, and austenite condition. Two kinds of Co-Ni steels, containing the only W(W steel), and the W and Cr(WCr steel), were severely rolled and followed by direct quenching(DQ). In comparison with undeformed. specimens, re-austenitizing(RA) was performed. DQ specimens exhibited higher impact toughness as well as higher hardness, as compared to RA specimens. The aging kinetics of the WCr steel was accelerated due to the Cr addition. While the W steel showed the intergranular embrittlement in the high temperature RA condition, in addition, the WCr steel exhibited the transgranular mode of mostly dimple type.