Effects of cold working on the mechanical properties, precipitation hardening, transformation temperature and texture formation have been investigated in a Co-free W-containing maraging steel(W-250). The alloy has a composition of Fe-19.5Ni-5.2W-1.3Ti-0.1Al and is strengthened by $Ni_3W$ and $\eta-Ni_3Ti$ precipitates in a bcc martensitic matrix.
The strength and hardness of cold worked maraging steel W-250 increased continuously with increasing amount of cold reduction. The cold working resulted in increases in tensile strength from 1847MPa to 2116MPa and yield strength from 1799MPa to 2098MPa at 90% cold reduction. However, the elongations for the maraging steel revealed a slight decrease with increasing amount of cold reduction.
Double step cold working treatment with a solution treatment between the cold-working resulted in an improvement in tensile strength, yield strength, elongation and notch toughness. The increase of the strength was a result of the refinement of the microstructure; a more refined structure in the double step cold working showed higher values of tensile properties, compared with single step cold working.
The cold worked maraging steel exhibited an anisotropy in mechanical properties; the tensile and yield strength in the transverse to rolling direction were higher than those in the rolling direction. On the other hand, the elongation and notch toughness showed lower values in the transvers direction. A texture study showed that the recrystallized texture of $\{112\}$<110> transformed into $\{100\}<110>$ deformation texture via $\{554\}$<225> texture with the increasing coldworking ratio.
The microstructure of the maraging steel W-250 consisted of lath martensite with dislocation cells, and the sizes of dislocation cells were decreased with increasing the degree of the cold deformation. The tensile fracture surfaces of the all cold worked samples showed ductile fracture mode. The sizes of dimples decreased by double step cold working and with increasing amount of cold reduction. The transformation temperature($P_s$, $A_s$, $A_f$) of cold worked specimens also decreased with the increase of cold reduction. On the other hand, $A_s\simA_f$ interval increased.
Recrystallization of austenite in the cold worked alloy occurred above $A_f$ temperature. The recrystallized grain size decreased with the increasing the number of reverse transformation cycle and amount of cold reduction.
