A method for manufacturing a high-strength steel bar can include the steps of: reheating a steel slab at a temperature ranging from 1000° C. to 1100° C., the steel slab including a certain amount of carbon (C), silicon (Si), manganese (Mn), phosphorus (P), sulfur (S), chromium (Cr), copper (Cu), nickel (Ni), molybdenum (Mo), aluminum (Al), vanadium (V), nitrogen (N), antimony (Sb), tin (Sn), and iron (Fe) and other inevitable impurities, The method can further include finish hot-rolling the reheated steel slab at a temperature of 850° C. to 1000° C., and cooling the hot-rolled steel to a martensite transformation start temperature (Ms (° C.)) through a tempcore process.

An example bushing has three portions along its radial direction including an inner portion most proximal to a central hole of the bushing, an outer portion most distal from the center hole, and a core portion between the inner portion and the outer portion. The core portion has a hardness that is less than the hardness of the inner portion or the outer portion of the bushing. The bushing may be formed using high carbon steel, which in some cases may be spheroidal cementite crystal structure. A rough bushing may be formed using the high carbon steel, followed by a direct hardening process, and an induction hardening process on the inner surface most proximal to the central hole of the bushing. The induction hardening on the inner surface may harden the outer portion while tempering the core portion of the bushing.

This invention generally relates to a method for producing parts of AHS steel via a controlled local cooling by a cooling medium and an interrupted cooling at a required temperature, without immersion in a cooling bath, to thereby create a multiphase microstructure. Typically, the steel part may be cooled by a jet of cooling medium so that, depending on the amount of heat which needs to be removed from the surface of the part, the locations from which a larger amount of heat needs to be removed are cooled at a higher intensity.

A steel plate to be heated is a blank having a first region and a second region adjacent to the first region. The blank is heated by direct resistance heating. A jet of cooling medium is applied to the first region during the direct resistance heating such that a temperature of the first region is kept lower than a quenching region while heating the second region to be equal to or higher than the quenching temperature. To provide a clear boundary between the first and second regions, the jet of cooling medium is applied along a slant direction such that the cooling medium expands along the boundary between the first and second regions. Alternatively, a partition member is provided along the boundary between the first and second regions. The heated blank is then press-formed and cooled in a press die to obtain a hot-pressed product.

The production method of a seamless steel pipe includes a heating step of heating an Nb-containing steel material to 800 to 1030 C., a pipe-making step of producing a hollow shell by performing piercing-rolling or elongation-rolling on the Nb-containing steel material, by using a piercing mill including a plurality of skewed rolls, a plug disposed between the plurality of skewed rolls, and a mandrel bar, and a cooling step immediately after rolling, of carrying out cooling using a cooling liquid on a hollow shell portion that passes between rear ends of the plurality of skewed rolls, in the hollow shell, so as to reduce an outer surface temperature of the hollow shell portion to 700 to 1000 C. within 15.0 seconds after the hollow shell portion passes between the rear ends of the plurality of skewed rolls.

A device for generating a microstructure with a structure gradient in an axisymmetric mechanical part having a hollow center and initially possessing a uniform structure with fine grains, the device including a first heater system defining a first shell for receiving the mechanical part and suitable for heating the outer periphery of the mechanical part to a first temperature higher than the solvus temperature. The device further includes a second heater system defining a second shell arranged inside the first shell and suitable for heating the inner periphery of the mechanical part to a second temperature lower than the solvus temperature, with the space between the first shell and the second shell defining a housing suitable for receiving the axisymmetric mechanical part having a hollow center.

A steel section has a web central portion connected on each side to a flange portion having a thickness of at least 100 mm. The steel section microstructure includes at least one kind of vanadium precipitates possibly comprising also one or more metal chosen among chromium, manganese and iron, the precipitates being chosen among nitrides, carbides, carbo-nitrides or any combination of them, more than 70% of such precipitates having a mean diameter below 6 nm. It also deals with a manufacturing method thereof.

The invention provides a method for preventing cracking along the surface at the inner hole of a hollow shaft during horizontal water quenching, including: step 1: transferring the shaft from heating furnace to quenching equipment; step 2: cooling the inner hole of the shaft, while the outer circle of the shaft is in the state of air cooling, and the cooling time on the outer circle is designed based on the temperature of the shaft being not lower than its A.sub.1 temperature, therefore, the compressive stress is formed at the surface layer of the inner hole, and small tensile stress is formed at the sub-surface layer; and step 3: cooling the outer circle and the inner hole of the shaft at the same time, wherein during the cooling, the cooling intensity of the inner hole is adjusted to gradually reduce so that sub-surface layer of the inner hole still exhibits low tensile stress while martensite formed in the surface layer experiences self-tempering, which effectively prevent the formation of quenching cracks along the surface of the inner hole. The invention solves the cracking problem during the horizontal water quenching for hollow shafts with large diameter and small hole-diameter.

A constant velocity universal joint is provided which includes an inner ring and an outer ring. A cage is disposed between an outer spherical surface of the inner ring and an inner spherical surface of the outer ring, and has windows in which respective balls are received. The cage has ball contact surface areas with which the balls come into contact, and includes soft portions that are lower in hardness than the ball contact surface areas. The soft portions are formed by local heat treatment at portions of the windows that are kept out of contact with the balls or surface portions around the windows.

A waterwall panel welding apparatus is provided. The apparatus includes an inlet assembly, a welding assembly, an outlet assembly, and a heating system. The inlet assembly is for receiving a plurality of tubes. The welding assembly is for receiving the tubes from the inlet assembly and for allowing the tubes to be welded together to form a waterwall panel. The outlet assembly is for receiving the waterwall panel from the welding assembly. The heating system heats the tubes and operates via magnetic induction.