Maraging steel alloys are disclosed. The alloys are produced by microalloying of the maraging steel alloy to form carbides at prior austenite grain boundaries to increase Zener drag. A particular example alloy consists essentially of, by weight, 7.4 to 8.4 percent nickel, 7.6 to 8.6 percent chromium, 8.4 to 9.4 percent cobalt, 1.8 to 2.2 percent molybdenum, 2 to 2.6 percent tungsten, 1.6 to 2 percent aluminium, 0.05 to 0.08 percent carbon, a carbide former selected from the group consisting of: niobium at a concentration of 0.25 to 0.28 percent; titanium, at a concentration of 0.2 to 0.28 percent; and vanadium, at a concentration of 0.21 to 0.4 percent; the balance being iron and incidental impurities.