A nanocrystalline bainitic steel consisting of, by weight percentage: 0.3% to 0.6% carbon; 9.0% to 20.0% nickel; up to 10% cobalt; 1.0% to 4.5% aluminium; up to 0.5% molybdenum; up to 0.5% manganese; up to 0.5% tungsten; up to 3.0% chromium; and the balance being iron and impurities.

Provided is a ferritic stainless steel sheet. The steel sheet has a chemical composition containing, by mass %, C: 0.010% or less, Si: 1.0% or less, Mn: 1.0% or less, P: 0.040% or less, S: 0.030% or less, Cr: 17.0% or more and 18.5% or less, N: 0.015% or less, Nb: 0.40% or more and 0.80% or less, Ti: 0.10% or more and 0.40% or less, Al: 0.20% or less, Ni: 0.05% or more and 0.40% or less, Co: 0.01% or more and 0.30% or less, Mo: 0.02% or more and 0.30% or less, Cu: 0.02% or more and 0.40% or less, and the balance being Fe and inevitable impurities, in which expression (1) below is satisfied.

C %+N %: 0.018% or less(1)

In expression (1), C % and N % respectively denote the contents (mass %) of C and N.

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.

A method of hardening a surface of a ferro-alloy object, the method comprising at least partially gasifying a carbon-containing polymer to form a hardening material source; and exposing the object to the hardening material source, such that the hardening material source and the surface of the object react, thereby hardening the surface of the object.

The invention relates to a method for producing a high-strength ferritic austenitic duplex stainless steel with the TRIP (Transformation induced plasticity) effect with deformation. After the heat treatment on the temperature range of 950-1150 C. in order to have high tensile strength level of at least 1000 MPa with retained formability the ferritic austenitic duplex stainless steel is deformed with a reduction degree of at least 10%, preferably at least 20% so that with a reduction degree of 20% the elongation (A.sub.50) is at least 15%.

The invention relates to a method for producing a high-strength ferritic austenitic duplex stainless steel with the TRIP (Transformation induced plasticity) effect with deformation. After the heat treatment on the temperature range of 950-1150 C. in order to have high tensile strength level of at least 1000 MPa with retained formability the ferritic austenitic duplex stainless steel is deformed with a reduction degree of at least 10%, preferably at least 20% so that with a reduction degree of 20% the elongation (A.sub.50) is at least 15%.

A hollow screw and related process of making is provided, wherein the hollow screw is formed from a generally circular corrosion resistant stainless steel disk cut from flat roll stock. The hollow screw includes a head and an elongated and hollow shaft having a wall thickness between about 0.2 to about 0.7 millimeters extending therefrom and defining a shank portion and a threaded portion having a plurality of threads thereon with a rotational drive mechanism configured to facilitate tightening via the threads. The process involves annealing to soften the stamped hollow screw, followed by thread rolling, and then age hardening the hollow screw. As such, the resultant hollow screw is relatively lightweight, about 50% the mass of a solid core screw made from the same material, with a sufficient thread strength to meet most aerospace applications and contributes to important aircraft fuel economy.

A hollow screw and related process of making is provided, wherein the hollow screw is formed from a generally circular corrosion resistant stainless steel disk cut from flat roll stock. The hollow screw includes a head and an elongated and hollow shaft having a wall thickness between about 0.2 to about 0.7 millimeters extending therefrom and defining a shank portion and a threaded portion having a plurality of threads thereon with a rotational drive mechanism configured to facilitate tightening via the threads. The process involves annealing to soften the stamped hollow screw, followed by thread rolling, and then age hardening the hollow screw. As such, the resultant hollow screw is relatively lightweight, about 50% the mass of a solid core screw made from the same material, with a sufficient thread strength to meet most aerospace applications and contributes to important aircraft fuel economy.

Provided are a steel sheet which has a tensile strength of 900 MPa or higher and excellent weldability, and a method for producing the steel sheet. The steel sheet has a specific composition and a microstructure containing, in terms of area fraction, ferrite of 30% or less (including 0%), tempered martensite of 70% or more (including 100%), and the balance other than ferrite and the tempered martensite of 10% or less (including 0%) in total, the tempered martensite having an average grain size thereof is 5 m or lower, the tempered martensite having iron-based carbides, which have average particle sizes of 100 nm or less, precipitated on grain boundaries, and the tempered martensite containing, in terms of atomic concentration, 5 atom % or more in total of Si and Mn on the grain boundaries of the tempered martensite. The steel sheet has a tensile strength of 900 MPa or higher.

A tailored rolled blank in which a plate thickness changes in a tapered shape in a rolling direction, comprises a thick-wall portion, and a thin-wall portion that is thinner than the thick-wall portion. In the tailored rolled blank, a ratio of an average hardness H.sub.tmax of a thickest wall portion at which the plate thickness is thickest to an average hardness H.sub.tmin of a thinnest wall portion at which the plate thickness is thinnest is in a range of more than 1.0 to 1.5. For the tailored rolled blank, an average dislocation density of the thinnest wall portion is 110.sup.14 m.sup.2 or less, and a number density of fine Ti carbo-nitrides having a particle diameter of 10 nm or less is more than 210.sup.17 per cm.sup.3.