The invention is directed to a method for improving the mechanical behavior of a metallic body (4) comprising an internal volume for a fluid and at least one threaded connecting port (6, 8) to said internal volume, the method comprising a step of treatment by autofrettage of the internal volume by applying a pressure to a liquid inside said volume. The autofrettage step comprises closing the internal volume by screwing a plug (28) to each the at least one threaded connecting port (8), so that the thread(s) of said port(s) is/are also subject to the autofrettage treatment. The invention is also directed to a body (4) resulting from such a treatment, with compressive stresses at the root of one of the most carrying turns of the thread of each of the connecting ports. The compressive stresses improve the fatigue behavior of the body.

The invention is directed to a method for improving the mechanical behavior of a metallic body (4) comprising an internal volume for a fluid and at least one threaded connecting port (6, 8) to said internal volume, the method comprising a step of treatment by autofrettage of the internal volume by applying a pressure to a liquid inside said volume. The autofrettage step comprises closing the internal volume by screwing a plug (28) to each the at least one threaded connecting port (8), so that the thread(s) of said port(s) is/are also subject to the autofrettage treatment. The invention is also directed to a body (4) resulting from such a treatment, with compressive stresses at the root of one of the most carrying turns of the thread of each of the connecting ports. The compressive stresses improve the fatigue behavior of the body.

A method for producing a steel material for line pipes including heating a steel having a specific composition to a temperature of 1000? C. to 1200? C.; performing hot rolling such that a cumulative rolling reduction ratio in a non-recrystallization temperature range is 60% or more, a cumulative rolling reduction ratio in a temperature range of (a rolling finish temperature +20? C.) or less is 50% or more, and a rolling finish temperature is the Ar.sub.3 transformation point or more and 790? C. or less; subsequently performing accelerated cooling from a temperature of the Ar.sub.3 transformation point or more, at a cooling rate of 10? C./s or more, to a cooling stop temperature of 200? C. to 450? C.; and then performing reheating such that the temperature of a surface of the steel plate is 350? C. to 550? C. and the temperature of the center of the steel plate is less than 550? C.

A method of generating compressive residual stresses through a thickness of a metal component comprising the steps: receiving a metal base component (10), which in use is subjected to applied pressure and applying by thermal deposition cladding (16) to one or more surfaces (14) of the base component. The cladding (16) comprises one or more layers of metal or metal alloy. The method also includes, subsequent to the cladding step, applying autofrettage to the clad component thereby generating compressive residual stresses through the one or more layers of metal or metal alloy (16) and at least part way through the base component.

A method of generating compressive residual stresses through a thickness of a metal component comprising the steps: receiving a metal base component (10), which in use is subjected to applied pressure and applying by thermal deposition cladding (16) to one or more surfaces (14) of the base component. The cladding (16) comprises one or more layers of metal or metal alloy. The method also includes, subsequent to the cladding step, applying autofrettage to the clad component thereby generating compressive residual stresses through the one or more layers of metal or metal alloy (16) and at least part way through the base component.

A method for producing a tube of a stainless steel alloy tube which comprises the steps of hot working a stainless steel casting into a pretubular shaped workpiece or into a cylindrical bar, trepanning the cylindrical bar or machining an inner diameter of the pretubular shaped workpiece to obtain a tubular workpiece, and cold working the workpiece. The hot working comprises one of: rolling, forging, and a combination thereof. The cold working comprises flow forming or pilgering. The stainless steel tube produced with the method comprises an outer diameter greater than or equal to 152 mm, an average wall thickness greater than or equal to 2.8 mm and less than or equal to 70 mm, and a length greater than 5 m.

A value stream process or method for forming vehicle rails from extruded aluminum tubes includes the steps of extruding an aluminum tube and hydroforming the extruded aluminum tube into a vehicle rail. More specifically, the method includes extruding the aluminum tube, bending the aluminum tube, preforming the aluminum tube, hydroforming the aluminum tube into a vehicle rail, trimming the vehicle rail to length and then artificially aging the rail followed by batch chemical pretreatment. In an alternative embodiment the artificial aging and batch chemical pretreatment processes are performed in reverse order. In either of the embodiments, localized induction annealing to recover formability may be performed between bending and preforming, between preforming and hydroforming or both.

A value stream process or method for forming vehicle rails from extruded aluminum tubes includes the steps of extruding an aluminum tube and hydroforming the extruded aluminum tube into a vehicle rail. More specifically, the method includes extruding the aluminum tube, bending the aluminum tube, preforming the aluminum tube, hydroforming the aluminum tube into a vehicle rail, trimming the vehicle rail to length and then artificially aging the rail followed by batch chemical pretreatment. In an alternative embodiment the artificial aging and batch chemical pretreatment processes are performed in reverse order. In either of the embodiments, localized induction annealing to recover formability may be performed between bending and preforming, between preforming and hydroforming or both.

Steel material for composite pressure vessel liners that, when used as raw material for manufacturing a composite pressure vessel liner, yields a liner having sufficient strength and a high fatigue limit and enables the manufacture of an inexpensive composite pressure vessel is provided. Steel material for composite pressure vessel liners comprises: a chemical composition containing, in mass %, C: 0.10% to 0.60%, Si: 0.01% to 2.0%, Mn: 0.1% to 5.0%, P: 0.0005% to 0.060%, S: 0.0001% to 0.010%, N: 0.0001% to 0.010%, and Al: 0.01% to 0.06%, with a balance being Fe and incidental impurities; and a metallic microstructure in which a mean grain size of prior austenite grains is 20 m or less, and a total area ratio of martensite and lower bainite is 90% or more.

The invention relates to a high-alloy steel, in particular for producing pipes shaped by means of internal high pressure, having high cold formability, TRIP and/or TWIP properties, a partially or completely austenitic microstructure having at least 5% residual austenite, and having the following chemical composition (in wt %): Cr: 7 to 20; Mn: 2 to 9; Ni: up to 9; C: 0.005 to 0.4; N: 0.002 to 0.3; the remainder being iron including unavoidable, steel-accompanying elements, with optional addition of the following elements (in wt %): Al: 0 to 3; Si: 0 to 2; Mo: 0.01 to 3; Cu: 0.005 to 4; V: 0 to 2; Nb: 0 to 2; Ti: 0 to 2; Sb: 0 to 0.5; B: 0 to 0.5; Co: 0 to 5; W: 0 to 3; Zr: 0 to 2; Ca: 0 to 0.1; P: 0 to 0.6; S: 0 to 0.2. The invention further relates to a method for producing pipes from this steel, said pipes being shaped by means of internal high pressure.