A bar-shaped steel product extends unidirectionally and has a chemical composition including, by mass %, 0.001 to 0.20% of C, 0.01 to 3.0% of Si, 0.01 to 2.0% of Mn, 0.01 to 5.0% of Ni, 7.0 to 35.0% of Cr, 0.01 to 5.0% of Mo, 0.01 to 3.0% of Cu, 0.001 to 0.10% of N, 0.2 to 2.0% of Nb, optional element(s), and a balance consisting of Fe and inevitable impurities, and has 0.5 or less of a rolling-direction-crystal-orientation RD//<100> fraction (an area ratio of crystal having 20 degrees or less of an orientation difference between a <100> orientation and a rolling direction).

This high-frequency hardening apparatus is provided with: an induction heating coil which has a U-shaped part that sandwiches a turbine blade, a pair of linear parts, and a connection part connecting the U-shaped part and the linear parts; a temperature detection unit which detects, in a non-contact manner, temperature around the induction heating coil; a moving mechanism which relatively moves the turbine blade and the induction heating coil in the direction of blade height; an electrical current supply unit which supplies a high-frequency electrical current to the induction heating coil; and a control device which has an electrical current control unit that, on the basis of a detection value provided by the temperature detection unit, controls the magnitude of the high-frequency electrical current supplied from the electrical current supply unit such that the detection value will not exceed a predetermined temperature.

A method for producing a motor vehicle component with at least two regions of different strengths and a protective layer, consisting of the following process steps: —providing precoated blanks made of a steel alloy, which can be hardened, —homogeneously heating to a heating temperature, which is at least greater than or equal to the AC1 temperature, preferably greater than or equal to the AC3 temperature, —holding the heating temperature, so that the precoating alloys with the blank, —homogeneously intercooling the alloyed blank to an intercooling temperature between 450 deg. C. and 700 deg. C., partially heating the blank from the intercooling temperature to at least the AC3 temperature in regions of the first type and holding regions of the second type at substantially intercooling temperature, —hot forming and press hardening the partially tempered blank so as to form the motor vehicle component, wherein a tensile strength of greater than 1400 MPa is produced in regions of the first type, a tensile strength of less than 1050 MPa is produced in regions of the second type, and a transition region is produced between said regions.

A piercer plug with increased life and a method of manufacturing it are provided. The piercer plug 1 includes a tip portion 2 and a trunk portion 3 made of the same material as the tip portion 2 and continuous to the tip portion 2. The trunk portion 3 includes a cylindrical portion 5 having a hole used for attaching a bar. The tip portion 2 is harder than the cylindrical portion 5.

A piercer plug with increased life and a method of manufacturing it are provided. The piercer plug 1 includes a tip portion 2 and a trunk portion 3 made of the same material as the tip portion 2 and continuous to the tip portion 2. The trunk portion 3 includes a cylindrical portion 5 having a hole used for attaching a bar. The tip portion 2 is harder than the cylindrical portion 5.

The present invention relates to a steel for a mold including: on % by mass basis, 0.55% ≤ C ≤ 0.70%; 0.30% ≤ Si ≤ 0.60%; 0.55% ≤ Mn ≤ 1.2%; 5.7% ≤ Cr ≤ 6.9%; 1.2% ≤ Mo + W/2 ≤ 1.6%; 0.55% ≤ V ≤ 0.79%; and 0.005% ≤ N ≤ 0.1%, with the remainder being Fe and inevitable impurities including, Al ≤ 0.020%, Ni ≤ 0.20%, S ≤ 0.0015%, and Cu ≤ 0.10%, and satisfying P1 ≥ 24 and 4.9 ≤ P2 ≤ 7.3, P1 and P2 being a value obtained based on the following formula (1) and (2), respectively, P1 = 45 - 13.6[Si] - 7.0([Mo]+[W]/2) - 12.9[Ni] (1), P2 = 7.4[V] + 15.8[N] + 38.6[Al] (2) in which [M] represents a content of an element M in % by mass basis, and relates to a mold including the steel for a mold.

The present invention relates to a steel for a mold including: on % by mass basis, 0.55% ≤ C ≤ 0.70%; 0.30% ≤ Si ≤ 0.60%; 0.55% ≤ Mn ≤ 1.2%; 5.7% ≤ Cr ≤ 6.9%; 1.2% ≤ Mo + W/2 ≤ 1.6%; 0.55% ≤ V ≤ 0.79%; and 0.005% ≤ N ≤ 0.1%, with the remainder being Fe and inevitable impurities including, Al ≤ 0.020%, Ni ≤ 0.20%, S ≤ 0.0015%, and Cu ≤ 0.10%, and satisfying P1 ≥ 24 and 4.9 ≤ P2 ≤ 7.3, P1 and P2 being a value obtained based on the following formula (1) and (2), respectively, P1 = 45 - 13.6[Si] - 7.0([Mo]+[W]/2) - 12.9[Ni] (1), P2 = 7.4[V] + 15.8[N] + 38.6[Al] (2) in which [M] represents a content of an element M in % by mass basis, and relates to a mold including the steel for a mold.

A decompression heat-insulating pipe structure that can exhibit the desired heat-insulating performance and is easy to assemble. In the structure, a space between ends of inner and outer tubes is decompressed. The outer tube includes a first flange, which extends radially inward from an axially one end thereof, and a second flange, which extends radially outward from the axially other end thereof. The inner tube includes a third flange, which extends radially inward from an axially one end thereof and is opposed to the first flange at an axially inward position of the first flange, and a fourth flange, which extends radially outward from the axially other end thereof and being opposed to the second flange at an axially outward position of the second flange. First and second elastic seal members are disposed between the first and third flanges and between the second and fourth flanges, respectively.

Disclosed are a case hardened steel which is suitable as a material for producing mechanical structural parts having high rotating bending fatigue strength and impact fatigue strength at a relatively low cost, and a method of producing the same. The case hardening steel has a chemical composition containing, by mass %, C, Si, Mn, P, S, Cr, Mo, B, Ti, N, and O within a range satisfying a predetermined relationship, and Al in at least a predetermined amount in relation to the B, N, and Ti contents, with the balance being Fe and inevitable impurities, wherein √I≤80 is satisfied, where I represents an area in μm.sup.2 of an oxide-based inclusion located at the center of a fish-eye on a fracture surface of the case hardening steel after being subjected to carburizing-quenching and tempering and subsequently to a rotating bending fatigue test.

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.