A stainless steel comprises additives including at least one of rare earth elements and boron, so as to exhibit resistance to long term aging embrittlement. The stainless steel also contains balanced amounts of nickel and cobalt to minimize a ration of nickel to cobalt and optimize aging embrittlement resistance with as tempered toughness. The remainder of the stainless steel comprising, by weight percentage: ______________________________________ Carbon 0.08-0.15 Silicon 0.01-0.10 Chromium 8.00-13.00 At least one of Tungsten and Molybdenum 0.50-4.00 At least one Austenite stabilizer, 0.001-6.00 such as Nickel, Cobalt, Manganese and Copper Vanadium 0.25-0.40 Phosphorus 0.010 max. Sulfur 0.004 max. Nitrogen 0.060 max. Hydrogen 2 ppm max. Oxygen 50 ppm max. Aluminum 0.001-0.025 Arsenic 0.0060 max. Antimony 0.0030 max. Tin 0.0050 max. Iron Balance. ______________________________________