To provide a steel for bolts with excellent delayed fracture resistance and cold forgeability while maintaining the strength as a steel material, and also to provide a bolt producing from such a steel for bolts.

The steel for bolts according to the present invention includes, in percent by mass: 0.20 to 0.40% of C; 1.5 to 2.5% of Si; 0.20 to 1.5% of Mn; more than 0% and 0.03% or less of P; more than 0% and 0.03% or less of S; 0.05 to 1.5% of Cr; 0.01 to 0.10% of Al; 0.0003 to 0.01% of B; 0.002 to 0.020% of N; and one or two elements selected from the group consisting of 0.02 to 0.10% of Ti and 0.02 to 0.10% of Nb, with the balance being iron and inevitable impurities.

A fastener for connecting a first housing part of a steam or gas turbine to a second housing part of the turbine which is made of a parent metal with a high degree of stress relaxation.

The invention relates to steel with a specific composition of the following elements: 0.25%≤C≤0.35%, 0.80%≤Cr≤1.50%, 0.50%≤Ni≤1.50%, 0.0010%≤B≤0.0050%, 0.010%≤Ti≤0.060%, 0.40%≤Mn≤1.00% and 0.003%≤N≤0.0150%, whereby after being subjected to a quench and tempering treatment, the characteristics required by the ISO 898-1 standard for class 10.9 and class 12.9 bolts, screws and studs are achieved, while at the same time achieving high fatigue strength values. The use of this steel allows achieving the mentioned characteristics in large-sized parts or elements (up to a diameter of 75 mm), considerably reducing the alloying costs compared with the steels used today.

A bolt of the present invention is a high-strength bolt of high-carbon steel having a tempered martensite structure, wherein the composition of the bolt comprises: 0.50 mass % or more and 0.65 mass % or less of carbon (C); 1.5 mass % or more and 2.5 mass % or less of silicon (Si); 1.0 mass % or more and 2.0 mass % or less of chromium (Cr); 0.2 mass % or more and 1.0 mass % or less of manganese (Mn); and 1.5 mass % or more and 5.0 mass % or less of molybdenum (Mo); a total content of impurities being phosphor (P) and sulfur (S) is 0.03 mass % or more; and the remaining is iron (Fe). Furthermore, the carbon concentration satisfies the following Formula (1): 0.75≤X<1 . . . Formula (1) wherein, in Formula (1), X represents surface carbon concentration/inner carbon concentration. Therefore, the bolt of the present invention has low quench cracking susceptibility and excellent delayed fracture resistance, because an increase in temperature at which martensite transformation occurs (Ms point) on the surface side is held down.

The invention relates to a device for water spray quenching that includes (i) a quenching chamber designed and set up to receive metallic workpieces, with a batch of volume V.sub.0 of 0.045 to 3.5 m.sup.3 and (ii) at least one atomizer which is configured to atomize water in air or nitrogen and is fluidically connected to the quenching chamber; in which the at least one atomizer and the device are designed and set up to generate a spray mist with a water content of 2.5 to 40 vol. % and a Sauter mean diameter of 20 to 2000 m and also a spray mist flow through the batch volume V.sub.0 of 0.05 to 25 m.sup.3/s.

A method for producing a threaded nut of a threaded drive, includes the following steps: a sleeve is produced from a steel sheet which is suitable for case-hardening; a rolling profile for a rolling contact with rolling bodies is molded on the inner circumference of the sleeve, said rolling profile being wound in a helical manner about the longitudinal axis of the sleeve; a flange is welded to the end face of the sleeve; the flange is provided with a welding surface on the flange end face facing away from the sleeve for welding to a machine part; the welding surface initially has a diffusion-inhibiting layer which inhibits the penetration of carbon; and the welding surface is exposed by removing the diffusion-inhibiting layer after case-hardening the threaded nut. A threaded nut produced according to the method can be part of a ball screw drive, the flange of which can be welded to a provided machine part by the user.

The present disclosure provides a wire rod for cold heading that can shorten the spheroidizing heat treatment time, processed products using the same, and manufacturing method thereof. A wire rod for cold heading according to an embodiment of present disclosure includes, in percent (%) by weight of the entire composition, C: 0.15 to 0.5%, Si: 0.1 to 0.4%, Mn: 0.3 to 1.5%, Cr: 0.1 to 1.5%, Al: 0.02 to 0.05%, N: 0.004 to 0.02%, at least one selected from the group consisting of Nb: 0.001 to 0.03%, V: 0.01 to 0.3%, Mo: 0.01 to 0.5%, Ti: 0.001 to 0.03%, and the remainder of iron (Fe) and other inevitable impurities, and the microstructure has a long and short axis ratio of cementite present in pearlite colonies of 200:1 or less.

An NPR non-magnetic steel material for rock bolt and a production method thereof are disclosed. The NPR non-magnetic steel material for rock bolt has a composition, in weight percent, consisting of: C: 0.4-0.7%, MN: 15-20%, Cr: 1-18%, Si: 0.3-3%, Ca: 0.05-0.15%, Cu: ≤0.03%, Ni: ≤0.02%, S: ≤0.001%, P: ≤0.001%, and the rest being Fe and unavoidable impurity elements. The NPR non-magnetic steel material for rock bolt and the production method thereof effectively solve the problems of steel materials for rock bolt in the prior art such as strong magnetism, low tensile strength and low effective elongation. The NPR non-magnetic steel material for rock bolt has a fully-austenitized structure and is non-magnetic, its yield strength is adjustable in the range of 600-1000 MPa, and its elongation is adjustable in the range of 20-60%.

Provided is a heat treatment apparatus (1), including: a conveying device (10), which is configured to convey a rod-shaped workpiece (W) at a predetermined velocity along an axial direction of the workpiece (W); and a heating device (2) including a heating coil (3) configured to inductively heat the workpiece (W) being conveyed to a quenching temperature, wherein the heating coil (3) includes a first heating section (3A) and a second heating section (3B), which are coupled to each other in series along the axial direction of the workpiece (W), and is electrically connected to a single high-frequency power supply (4), and wherein a coil pitch (D2) of the second heating section (3B) arranged relatively on a front side in a conveying direction for the workpiece (W) is larger than a coil pitch (D1) of the first heating section (3A) arranged relatively on a rear side in the conveying direction.

High-strength screw (1), with a head (2) with a tool engagement contour (4), a shank (3) with a free end (5) pointing away from the head (2), a threaded section (6) with a thread (7) being arranged on the shank (3), the thread (7) being formed as a metric ISO thread or inch thread, the head (2) and the shank (3) being designed as materially separate parts, the head (2) having a coupling recess (8) arranged radially inside with an axial force transmission element (9) and a torque transmission element (10), the shank (3) having a coupling element (11) arranged radially outside on its outer circumference with an axial force transmission counter element (12) and a torque transmission counter element (13), the coupling element (11) engaging in the coupling recess (8), the axial force transmission element (9) and the axial force transmission counter element (12) being designed and arranged to positively interlock in such a way that an axial translatory movement of the head (2) relative to the shank (3) in the direction away from the free end (5) of the shank (3) is prevented or will be prevented, in particular non-releasably, and the torque transmission element (10) and the torque transmission counter element (13) being designed and arranged to interlock in such a way that a rotational movement of the head (2) relative to the shank (3) in the tightening direction of the thread (7) is or will be prevented.