A method is provided for preventing cracking along the surface at the inner hole of a hollow shaft during water quenching, including: a step of water-quenching the inner hole of the shaft placed horizontally, while the outer circle of the shaft is in a state of air cooling, in which the cooling time of the outer circle is selected to be not lower than its A.sub.r1 temperature so as to induce a compressive stress in the surface layer of the inner hole; and a step of water-quenching the outer circle and the inner hole of the shaft simultaneously, moreover, the quenching intensity of the inner hole is gradually reduced to cause a temperature rise in the surface layer of the inner hole to allow martensite in the surface layer to undergo self-tempering, which prevents the formation of quenching cracks along the surface of the inner hole.

The martensitic stainless steel material has a chemical composition, which contains: in mass %, C: 0.030% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.030% or less, S: 0.005% or less, Al: 0.010 to 0.100%, N: 0.0010 to 0.0100%, Ni: 5.00 to 6.50%, Cr: 10.00 to 13.40%, Cu: 1.80 to 3.50%, Mo: 1.00 to 4.00%, V: 0.01 to 1.00%, Ti: 0.050 to 0.300%, Co: 0.300% or less, Ca: 0.0006 to 0.0030%, and O: 0.0050% or less, and satisfies Formulae (1) and (2) in the description. An area of each intermetallic compound and each Cr oxide in the steel material is 5.0 μm.sup.2 or less, a total area fraction of intermetallic compounds and Cr oxides is 3.0% or less, and a maximum circle-equivalent diameter of Ca oxide is 9.5 μm or less.

The steel material according to the present disclosure contains a chemical composition consisting of, in mass %, C: 0.20 to 0.50%, Si: 0.05 to 0.50%, Mn: 0.05 to 1.00%, P: 0.030% or less, S: less than 0.0050%, Al: 0.005 to 0.050%, Cr: 0.10 to 1.50%, Mo: 0.25 to 1.80%, Ti: 0.002 to 0.050%, Nb: 0.002 to 0.100%, B: 0.0001 to 0.0050%, N: 0.0070% or less and O: less than 0.0050% with the balance being Fe and impurities. A yield strength is within a range of 655 to 1069 MPa, and a yield ratio is 85% or more. A proportion of KAM values of 1° or less is 30 area % or more.

The steel pipe according to the present disclosure contains a chemical composition consisting of, in mass %, C: 0.25 to 0.50%, Si: 0.05 to 0.50%, Mn: 0.05 to 1.00%, P: 0.025% or less, S: 0.0050% or less, Al: 0.005 to 0.100%, Cr: 0.30 to 1.50%, Mo: 0.25 to 3.00%, Ti: 0.002 to 0.050%, N: 0.0010 to 0.0100% and O: 0.0030% or less, with the balance being Fe and impurities. The steel pipe contains an amount of dissolved C within a range of 0.010 to 0.050 mass %. The tensile yield strength in the axial direction and the circumferential direction is 862 to 965 MPa, and the yield ratio in the axial direction is 90% or more. The tensile yield strength in the circumferential direction is 30 to 80 MPa higher than the compressive yield strength in the circumferential direction.

The steel material according to the present disclosure has a chemical composition consisting of, in mass %, C: 0.15 to 0.45%, Si: 0.05 to 1.00%, Mn: 0.01 to 1.00%, P: 0.030% or less, S: 0.0050% or less, Al: 0.005 to 0.100%, Cr 0.60 to 1.80%, Mo: 0.80 to 2.30%, Ti: 0.002 to 0.020%, V: 0.05 to 0.30%, Nb: 0.002 to 0.100%, B: 0.0005 to 0.0040%, Cu: 0.01 to 0.50%, Ni: 0.01 to 0.50%, N: 0.0020 to 0.0100% and O: 0.0020% or less, with the balance being Fe and impurities. The number density of BN in the steel material is 10 to 100 particles/100 μm.sup.2. The yield strength of the steel material is 758 MPa or more.

The steel material according to the present disclosure has a chemical composition consisting of, in mass %, C: 0.20 to 0.35%, Si: 0.05 to 1.00%, Mn: 0.01 to 1.00%, P: 0.025% or less, S: 0.0100% or less, Al: 0.005 to 0.100%, Cr 0.25 to 0.80%, Mo: 0.20 to 2.00%, Ti: 0.002 to 0.050%, B: 0.0001 to 0.0050%, N: 0.0020 to 0.0100% and O: 0.0100% or less, with the balance being Fe and impurities, and satisfying Formula (1). A number density of precipitates having an equivalent circular diameter of 400 nm or more is 0.150 particles/μm.sup.2 or less. The yield strength is within a range of 655 to 965 MPa. A dislocation density ρ is 7.0×10.sup.14 m.sup.−2 or less.

5×Cr—Mo-2×(V+Ti)≤3.00  (1)

The present invention relates to a tube product, namely a perforating gun hollow carrier, consisting of a steel alloy with martensitic matrix, characterized in that it has a yield strength Rp0,2 of at least 900 MPa, and that the steel alloy besides iron and impurities caused by melting has the following alloying elements: C 0.15-0.6% Si 1.4-2.6% Cr 2.0-4.0% Mn 0.15-2.0% Mo 0.2-0.6% N<0015% and at least one of the alloying elements Nb, V and Ti in sum of ≥0.01% and the tube product has been subjected to a quenching and partitioning heat treatment. Furthermore, the invention relates to a method of manufacturing such a tube product.

A process for manufacturing a high nitrogen stainless steel pipe material includes keeping an outside surface and/or an inside surface of an austenite stainless steel pipe material in contact with a substance that becomes a nitrogen (N) source, heating the steel pipe together with the nitrogen source substance at a temperature of 800° C. to 1100° C. in a range of temperatures not higher than the critical temperature for crystal grain enlargement of the steel pipe material to cause nitrogen to be absorbed into the surface of the pipe and diffused into the steel solid phase, and applying to the heat-treated pipe material annealing treatment in the range of temperatures in vacuum, inert gas including argon gas or an atmosphere of a gas with a reducing substance including H.sub.2 gas added thereto, to result in a decrease of nitrogen concentration gradient.

A corrosion resistant steel having a yield strength of at least 758 MPa is described. The corrosion resistant steel comprises in weight %: 0.005≤C<0.03, 14≤Cr≤17, 2.3≤Mo≤3.5, 3.2≤Ni≤4.5, Si≤0.6, 0.5≤Cu≤1.5, 0.4≤Mn≤1.3, 0.35≤V≤0.6, 3.2×C≤Nb≤0.1, W≤1.5, 0.5≤Co≤1.5, 0.02≤N≤0.05, Ti≤0.05, P≤0.03, S≤0.005, Al≤0.05, with the balance of the chemical composition of said corrosion resistant steel being constituted by Fe and inevitable impurities. A manufacturing method of such steel to obtain a quenched and tempered semi finished product is also described.

The invention deals with Steel for seamless pipes comprising the following chemical composition elements in weight percent: 0.04≤C≤ to 0.18, 0.10≤Si≤0.60, 0.80≤Mn≤1.90, P≤0.020, S≤0.01, 0.01≤Al≤0.06, 0.50≤Cu≤1.20, 0.10≤Cr≤0.60, 0.60≤Ni≤1.20, 0.25≤Mo≤0.60, B≤0.005, V≤0.060, Ti≤0.050, 0.010≤Nb≤0.050, 0.10≤W≤0.50, N≤0.012, where the balance is Fe and inevitable impurities. The steel of the invention can be used in offshore applications, line process pipes, structural and mechanical applications, especially where harsh environmental conditions and service temperatures down to −80° C. occur.