Describe the metallurgy of 15-7 MO stainless steel and its specific benefits for high-load retaining rings.

15-7 MO (PH 15-7 Mo) is a semi-austenitic precipitation-hardening stainless steel. By replacing 2% of the Chromium in 17-7PH with Molybdenum, it achieves higher strength and better resistance to softening at elevated temperatures. In the CH900 condition, it can reach a UTS of over 1700 MPa. For retaining rings, this translates to the highest possible thrust load capacity per unit of thickness. Its resistance to 'set' and its high fatigue limit make it the preferred choice for heavy-duty retaining rings in landing gear and high-pressure hydraulic cylinders where space is at a premium and the environment is mildly corrosive.