Custom 450 (Type XM-25) stainless steel is a martensitic age-hardenable stainless steel that exhibits corrosion resistance similar to that of Type 304 but with three times higher yield strength. The alloy has a yield strength somewhat greater than 100 ksi in the annealed condition, but is easily fabricated. A single-step aging treatment develops higher strength with good ductility and toughness. The final mechanical properties will depend on the aging temperature selected. Custom 450 stainless has good resistance to atmospheric corrosion including seawater environments. Optimum corrosion resistance for this alloy is obtained in the annealed condition. However, age hardening results in only a slight reduction in corrosion resistance. For optimum corrosion resistance, surfaces must be free of scale, lubricants, foreign particles, and coatings applied for drawing and heading. After fabrication of parts, cleaning and passivation should be considered to optimize the corrosion resistance.