Abstract: Steel alloys having high yield and ultimate tensile strengths in combination with high toughness based on medium carbon secondary hardening steel compositions having low cobalt content. Nickel is added to the medium carbon secondary hardening steel compositions to increase the yield and tensile strengths and fracture toughness. Applications of a steel alloy of the present disclosure include structural applications requiring high strength and high fracture toughness, such as aircraft landing gear.

Abstract: An ultra-high strength stainless steel alloy with enhanced toughness includes in % by weight: 0 to 0.06% carbon (C); 12.0 to 18% chromium (Cr); 16.5 to 31.0% cobalt (Co); 0 to 8% molybdenum (Mo); 0.5 to 5.0% nickel (Ni); 0 to 0.5% titanium (Ti); 0 to 1.0% niobium (Nb); 0 to 0.5% vanadium (V); 0 to 16% tungsten (W); balance iron (Fe) and incidental deoxidizers and impurities. The heat treating method includes the steps of austenitizing at least once followed by quenching, tempering and sub-zero cooling to obtain no more than about 6-8% retained austenite in the finished alloy.

Abstract: Steel alloys having high yield and ultimate tensile strengths in combination with high toughness based on medium carbon secondary hardening steel compositions having low cobalt content. Nickel is added to the medium carbon secondary hardening steel compositions to increase the yield and tensile strengths and fracture toughness. Applications of a steel alloy of the present disclosure include structural applications requiring high strength and high fracture toughness, such as aircraft landing gear.

Abstract: A secondary hardening steel alloy substantially lacking Cobalt is disclosed. In spite of the substantial lack of Cobalt, a steel alloy of the present disclosure has a low Stage II crack growth, and a high fracture toughness. Applications of a steel alloy of the present disclosure include structural applications, including aircraft landing gear.

Abstract: A secondary hardening steel alloy substantially lacking Cobalt is disclosed. In spite of the substantial lack of Cobalt, a steel alloy of the present disclosure has a low Stage II crack growth, and a high fracture toughness. Applications of a steel alloy of the present disclosure include structural applications, including aircraft landing gear.

Abstract: An ultra-high strength stainless steel alloy with enhanced toughness includes in % by weight: 0 to 0.06% carbon (C); 12.0 to 18% chromium (Cr); 16.5 to 31.0% cobalt (Co); 0 to 8% molybdenum (Mo); 0.5 to 5.0% nickel (Ni); 0 to 0.5% titanium (Ti); 0 to 1.0% niobium (Nb); 0 to 0.5% vanadium (V); 0 to 16% tungsten (W); balance iron (Fe) and incidental deoxidizers and impurities. The heat treating method includes the steps of austenitizing at least once followed by quenching, tempering and sub-zero cooling to obtain no more than about 6-8% retained austenite in the finished alloy.

Abstract: An ultra-high strength stainless steel alloy with enhanced toughness includes in % by weight: 0 to 0.06% carbon (C); 12.0 to 18% chromium (Cr); 16.5 to 31.0% cobalt (Co); 0 to 8% molybdenum (Mo); 0.5 to 5.0% nickel (Ni); 0 to 0.5% titanium (Ti); 0 to 1.0% niobium (Nb); 0 to 0.5% vanadium (V); 0 to 16% tungsten (W); balance iron (Fe) and incidental deoxidizers and impurities. The heat treating method includes the steps of austenitizing at least once followed by quenching, tempering and sub-zero cooling to obtain no more than about 6-8% retained austenite in the finished alloy.

Abstract: An ultra-high strength stainless steel alloy with enhanced toughness includes in % by weight: 0 to 0.06% carbon (C); 12.0 to 18% chromium (Cr); 16.5 to 31.0% cobalt (Co); 0 to 8% molybdenum (Mo); 0.5 to 5.0% nickel (Ni); 0 to 0.5% titanium (Ti); 0 to 1.0% niobium (Nb); 0 to 0.5% vanadium (V); 0 to 16% tungsten (W); balance iron (Fe) and incidental deoxidizers and impurities. The heat treating method includes the steps of austenitizing at least once followed by quenching, tempering and sub-zero cooling to obtain no more than about 6-8% retained austenite in the finished alloy.

Abstract: A duplex strengthened structural steel that is particularly suitable for demanding applications which require both high yield strength and fatigue properties is provided. The preferred steel alloys of this invention are characterized by both the presence of intermetallic strengthening precipitates like maraging steels, as well as alloy carbide strengtheners as is common with secondary hardening steels. Titanium is substantially absent from the preferred steel alloys of this invention. Thus the formation of nonmetallic inclusions, such as titanium carbonitrides, are alleviated which correspondingly enhances the fatigue properties of the preferred alloys. To compensate for the lack of titanium strengthening precipitates within the alloy, additions of aluminum are provided such that the aluminum forms intermetallic strengthening precipitates with nickel.

Abstract: A high strength vacuum melted ferrous alloy having enhanced fracture toughness comprising not more than about 0.01% by weight sulfur, not more than about 0.1% manganese, and titanium in an amount in atomic percent of not less than about twice the atomic percentage of sulfur present in the alloy. Other detailed limits of titanium, zirconium, and niobium are also disclosed.

Abstract: A secondary hardening alloy steel composition consisting essentially of about 0.25-0.5% carbon, about 0.5-1.0% manganese, about 1.5-3.0% nickel, about 0-1.0% chromium, about 1.75-2.5% molybdenum, about 0-0.4% vanadium, and an additive selected from about 1-3% aluminum and a combination of at least about 1% aluminum and at least about 1% silicon for a combined Al+Si content of about 2-4%, the balance being iron and impurity elements. The present steel composition has the following characteristics: it exhibits a flat tempering response, it is hardenable upon tempering to a Rockwell C hardness of at least 50, and it has an improved combination of hardness vs. toughness properties after tempering in the secondary hardening range. A method of preparation is also described.