Method of Making a High Strength, High Toughness, Fatigue Resistant, Precipitation Hardenable Stainless Steel and Product Made Therefrom

摘要

A process for making a precipitation hardenable stainless steel alloy is described. The process includes the step of melting a martensitic steel alloy having the following composition in weight percent, about Carbon 0.03 max. Manganese 1.0 max. Silicon 0.75 max. Phosphorus 0.040 max. Sulfur 0.020 max. Chromium 10-13 Nickel 10.5-11.6 Titanium 1.5-1.8 Molybdenum 0.25-1.5 Copper 0.95 max. Aluminum 0.25 max. Niobium 0.3 max. Boron 0.010 max. Nitrogen 0.030 max. and the balance being iron and usual impurities. The process also includes the step of adding calcium to the alloy while molten. The calcium combines with available sulfur and oxygen to form calcium base inclusions selected from the group consisting of calcium sulfides, calcium oxides, calcium oxysulfides, and combinations thereof. In a further step, the alloy is processed to remove at least a portion of the calcium base inclusions. The alloy is then solidified. As a result of the process, the alloy has a matrix containing a sparse dispersion of said calcium-based inclusions and substantially no rare-earth base inclusions.