Abstract: A vacuum carbonitriding method includes: performing a vacuum carburizing process on an object to be treated (a workpiece) in a heat treating furnace under reduced pressures by supplying a carburizing gas into the furnace that has been heated to a predetermined carburizing temperature; stopping supply of the carburizing gas while keeping the carburizing temperature so as to diffuse carbon in the workpiece under reduced pressures; and performing a nitriding process on the workpiece by supplying a nitriding gas into the furnace under reduced pressures after lowering the furnace temperature. Required heat treatment qualities such as surface hardness, effective case depth, toughness and the like can be achieved in a short time with reproducibility even in a case of workpiece made of low-grade steel or case-hardened steel.

Abstract: An apparatus and method of generating a carburizing atmosphere stably generate a reformed gas containing carbon monoxide of high concentration that is suitably used as a carburizing atmosphere. A first reforming furnace and a second reforming furnace are connected in series. A first cooler that removes moisture in an intermediate reformed gas from the first reforming furnace and a hydrocarbon adding section that adds hydrocarbon to the intermediate reformed gas are disposed between the first and second reforming furnaces. A raw material mixed gas with a low mixture ratio of hydrocarbon is introduced into the first reforming furnace to cause a catalytic reaction, thereby generating the intermediate reformed gas. Moisture contained in the intermediate reformed gas is removed. Hydrocarbon is added to the intermediate reformed gas. The intermediate reformed gas is introduced into the second reforming furnace to cause a catalytic reaction, to generate a carburizing atmosphere.

Abstract: In a first process of a method of gas carburizing, a steel treatment object in a carburizing atmosphere containing carburizing gas is heated to an initial set temperature which is not higher than a peritectic point at which ? iron and a liquid phase transform into ? iron and not less than a eutectic point at which the liquid phase transforms into ? iron and cementite, such that the surface carbon concentration thereof does not exceed a solid solubility limit. In a second process following the first process, the carburizing temperature is gradually decreased from the initial set temperature such that the surface carbon concentration of the treatment object increases without exceeding the solid solubility limit, and such that the carburized depth of the treatment object increases.

Abstract: An electric heater has multiple zones, wherein the multiple zones include at least one zone which is subject to high loading (e.g. bottom zone) and, at least one zone is a non-metal heating element, and the rest of the zones (e.g. middle zone and top zone) are metal resistance heating elements of light gauge overbent.

Abstract: A heating element (12) made of metal wire is installed at an internal circumferential surface of a cylindrical main thermal insulation body (11) of an electric heater according to the present invention. The heating element (12) comprises a plurality of resistance heat emitting portions (61)–(64) (71)–(74) (81)–(84) as segments along its length direction. The resistance heat emitting portions (61)–(64) (71)–(74) (81)–(84) are connected in parallel.

Abstract: In a first process of a method of gas carburizing, a steel treatment object in a carburizing atmosphere containing carburizing gas is heated to an initial set temperature which is not higher than a peritectic point at which ? iron and a liquid phase transform into ? iron and not less than a eutectic point at which the liquid phase transforms into ? iron and cementite, such that the surface carbon concentration thereof does not exceed a solid solubility limit. In a second process following the first process, the carburizing temperature is gradually decreased from the initial set temperature such that the surface carbon concentration of the treatment object increases without exceeding the solid solubility limit, and such that the carburized depth of the treatment object increases.

Abstract: In a first step of a method of gas carburizing, a steel treatment object is heated in a carburizing atmosphere comprising a carburizing gas until the surface carbon concentration of the treatment object reaches the final target value that is not higher than the solid solubility limit at a carburizing temperature that is not higher than the peritectic point, at which steel transforms from &dgr; iron and liquid phase to &ggr; iron, and is not less than the eutectic point, at which steel transforms from liquid phase to &ggr; iron and cementite. In a second step the gas carburizing is advanced after the first step so that the carburizing depth of the treatment object increases while the surface carbon concentration of the treatment object is kept at the final target value by reducing the carbon potential of the carburizing gas with the lapse of time.

Abstract: In a heat treating method and furnace used in this method which can prevent disturbance of an atmosphere gas inside a heat chamber, and can prevent deterioration of the processing quality and efficiency of work, a control section 4 first operates a vacuum pump VP to reduce the inner pressure of a purge chamber 3 to a predetermined pressure level, then manipulates a large and small caliber operating valve (13a, 13b) to supply the atmosphere from the interior of the heat chamber 1 to that of the purge chamber 3, and the control section 4 actuates transporting means 5 to transport the work W between the purge chamber 3 and the heat chamber 1 in a state wherein the inner pressures of the purge chamber 3 and the heat chamber 1 have been rendered substantially equal on the basis of detected values from first and second pressure sensors PS1, PS2.

Abstract: The present invention is a heat insulating material being a single unit having superior insulating performance as well as sufficient mechanical strength itself to constitute furnace walls, an electric heating unit having the heat insulating material and a method of manufacture of the heat insulating material and the electrical heating unit. The heat insulating material of the present invention includes an outer layer having mainly refractory inorganic fibers and a core layer supported within the outer layer. The outer layer has greater mechanical strength than the core layer. The core layer has a composition having a better insulating performance than the outer layer and extends in a plane substantially perpendicular to the thickness of the heat insulating material. The electrical heating unit of the present invention has a heating element embedded in the heat insulating material.