Abstract: A sintering furnace can include an outer shell defining an internal volume a reactive agent inlet configured to introduce a reactive agent into the internal volume; an insulation chamber within the outer shell; and a retort configured to retain an object. A method of operating a sintering furnace can include sintering a part precursor within a retort arranged within a chamber, wherein the chamber defines an intermediate volume between the retort and the chamber, wherein a sintering byproduct is oxidized within the intermediate volume.

Abstract: Disclosed are a high-pressure liquid-state or supercritical-state quenching apparatus, comprising a working chamber, a heating device, a cooling device, a vacuum pump set, a storage tank, a buffer tank, a gas booster, a first pressure gauge, and a temperature controller. According to the Invention, vacuum liquid-state or supercritical-state quenching is implemented, which satisfies a quenching requirement of a large workpiece, and can also achieve an effect of high-pressure gas quenching. In addition, clean heat treatment is implemented, which avoids waste gas and waste water pollution, and is energy-saving and environmentally-friendly heat treatment.

Abstract: An air hardenable steel alloy is disclosed comprising, in percent by weight: 0.18 to 0.26 carbon; 3.50 to 4.00 nickel; 1.60 to 2.00 chromium; 0 to 0.50 molybdenum; 0.80 to 1.20 manganese; 0.25 to 0.45 silicon; 0 to less than 0.005 titanium; 0 to less than 0.020 phosphorus; 0 up to 0.005 boron; 0 up to 0.003 sulfur; iron; and impurities. The air hardenable steel alloy has a Brinell hardness in a range of 352 HBW to 460 HBW. The air hardenable steel alloy combines high strength, medium hardness and toughness, as compared with certain known air hardenable steel alloys, and finds application in, for example, any of a steel armor, a blast-protective hull, a blast-protective V-shaped hull, a blast-protective vehicle underbelly, and a blast-protective enclosure.

Abstract: A non-scaling heat-treatable steel with particular suitability for producing hardened or die-hardened components is disclosed, characterized by the following chemical composition in % by weight: C 0.04-0.50; Mn 0.5-6.0; Al 0.5-3.0; Si 0.05-3.0; Cr 0.05-3.0; Ni less than 3.0; Cu less than 3.0; Ti 0.010-?0.050; B 0.0015-?0.0040; P less than 0.10; S less than 0.05; N less than 0.020; remainder iron and unavoidable impurities. Further disclosed is a method for producing a non-scaling hardened component from the steel and a method for producing a hot strip from a steel.

Abstract: A method for manufacturing high-Si cold rolled steel sheets includes heating a cold rolled steel sheet with a direct flame burner (A) having an air ratio of not more than 0.89 when the temperature of the cold rolled steel sheet that is being increased is in the temperature range of not less than 300° C. and less than Ta° C., subsequently heating the cold rolled steel sheet with a direct flame burner (B) having an air ratio of not less than 0.95 when the temperature of the cold rolled steel sheet is in the temperature range of not less than Ta° C. and less than Tb° C., and subsequently soak-annealing the cold rolled steel sheet in a furnace having an atmospheric gas composition which has a dew point of not more than ?25° C. and contains 1 to 10 volume % of H2 and the balance of N2.

Abstract: A method for controlling microbial growth in potable water stored in a vessel having a metallic surface includes heating the metallic surface to a temperature between about 480° C. (900° F.) and about 870° C. (1600° F.), exposing the metallic surface to oxygen during heating to oxidize potential reduction sites on the metallic surface and charging potable water containing silver ions to the vessel. A vessel having a metallic surface is prepared for long-term storage of potable water containing silver ions by heating the metallic surface to a temperature between about 480° C. (900° F.) and about 870° C. (1600° F.) and exposing the metallic surface to oxygen during heating to oxidize electropositive metals on the metallic surface or by treating the metallic surface with an aqueous solution containing on oxidizing agent to oxidize potential reduction sites on the metallic surface.

Abstract: A method for the manufacturing of high strength cold rolled steel sheets includes continuously annealing a cold rolled steel sheet that has a composition containing C: 0.05-0.3% mass, Si: 0.6-3.0% mass, Mn: 1.0-3.0% mass, P: ?0.1% mass, S: ?0.02% mass, Al: 0.01-1% mass, N: ?0.01% mass, and Fe and inevitable impurities: balance, in a manner such that the cold rolled steel sheet is heated in a furnace using an oxidizing burner to a steel sheet temperature of ?700° C., then soak-annealed in a reducing atmosphere furnace at 750-900° C., then cooled so the average cooling rate between 500° C. and 100° C. is ?50° C./s. High-Si cold rolled steel sheets with high strength and good phosphatability while containing Si?0.6% are obtained without controlling conditions so as to increase the dew point in the reducing atmosphere in the soaking furnace or to increase the vapor hydrogen partial pressure ratio.

Abstract: For regulating process gases for heat treatments of metal materials/workpieces in industrial furnaces (1), which have at least one treatment chamber (2), at least one burnoff point (4) having at least one first valve (4.1), and a regulator (5) having pressure meter (5.1), the burnoff point (4) is only to be opened as a function of requirements related to the process gas. For this purpose, in a first step, with open first valve (4.1), a quantity of a flushing gas (6.1) of the gas mixture (6) of the respective process gas is supplied in a controlled manner to the industrial furnace (1) and then burned off, in a second step, the valve (4.1) is closed, the industrial furnace (1) is regulated to a preset furnace pressure and this is permanently detected via the pressure meter (5.1), in a third step, with the target pressure of the industrial furnace achieved, this pressure is detected via the pressure meter (5.1) and maintained, the first valve (4.1) further remaining closed.

Abstract: A processing method is provided integrating hot stamping and controllable subsequent heat treatment in the technical field of hot working for steels. It includes the steps of selecting and preparing a steel blank, hot stamping treatment, controllable temperature quenching, adjusting the temperature of the steel blank to a tempering temperature and fine stamping at the same time. The invention combines the hot stamping and controllable heat treatment to improve the strength of material with precise plastic deformation and save energy as well. The tensile strength of the processed steel is greater than 1900 Ma.

Abstract: In a method and with a device for preparing process gases (3) for heat treatments of metallic materials/workpieces, the respective process gas (3) is to be fed into at least one treatment chamber (1.1) in an industrial furnace (1) having been practically fully prepared, homogenised and heated, and the method is to be carried out both with newly built and particularly with already existing installations of industrial furnaces (1) with the aid of the device, wherein the process gas (3) is prepared with compression at temperatures uncoupled from the temperature in the treatment chamber (1.1), in a process separate from the heat treatment process in the treatment chamber (1.1), and in a temperature range up to about 1250° C., and is rendered usable for economical and low-emission heat treatment (FIG. 3).

Abstract: A continuous annealing and pickling process of flat cold-rolled products, such as stainless steel strips, to obtain a high surface quality product at high production rates and with a low environmental impact. It comprises the following steps: heating, up to a temperature comprised in the range 650-1050° C., in an atmosphere with an oxygen content comprised in the range from 0.5 to 12%; heating for a time comprised from 10 to 200 sec up to a temperature comprised in the range from 650 to 1200° C. in presence of oxidizing agents and/or inert agents; cooling down to temperatures comprised in the range from 650° C. to ambient temperature in presence of oxidizing agents and/or inert agents; thermochemical or electrolytic descaling and finally possible pickling and/or passivation, by means of the use of pickling baths consisting of mineral acid solutions.

Abstract: An apparatus for thermally treating and coloring a plurality of curved suture needles. The apparatus includes a conveyer for transferring the plurality of curved suture needles from a source of curved suture needles to a receiver, a housing positioned adjacent the conveyer, the housing having a first end, a second end, and an opening running from the first end to the second end, the opening aligned with the conveyer to enable the plurality of curved suture needles to pass therethrough, a heat source located within the housing for heating the plurality of curved suture needles as the plurality of curved suture needles are transferred by the conveyer from the first end of the housing to the second end of the housing and a system for providing a gas mixture containing a fractional concentration of oxygen to oxidize and colorize the surfaces of the plurality of curved suture needles as the plurality of suture needles pass through the housing.

Abstract: A method is described for batchwise heat treatment of goods to be annealed which are heated in a heating chamber after scavenging air with a scavenging gas under protective gas to a predetermined treatment temperature, with the protective gas being conveyed through the heating chamber depending on the occurrence of impurities in different quantities. In order to enable the economic use of protective gas, it is proposed that the protective gas which is withdrawn from the heating chamber after the main occurrence of impurities and which is loaded with a residual quantity of impurities is conveyed, optionally after intermediate storage, into the heating chamber during the main occurrence of impurities of a subsequent batch before non-loaded protective gas is introduced into the heating chamber.

Abstract: A continuous annealing and pickling process of flat cold-rolled products, such as stainless steel strips, to obtain a high surface quality product at high production rates and with a low environmental impact. It comprises the following steps: heating, up to a temperature comprised in the range 650-1050° C., in an atmosphere with an oxygen content comprised in the range from 0.5 to 12%; heating for a time comprised from 10 to 200 sec up to a temperature comprised in the range from 650 to 1200° C. in presence of oxidizing agents and/or inert agents; cooling down to temperatures comprised in the range from 650° C. to ambient tempera in presence of oxidizing agents and/or inert agents; thermochemical or electrolytic descaling and finally possible pickling and/or passivation, by means of the use of pickling baths consisting of mineral acid solutions.

Abstract: A method of heat treating stainless steel in the form of blanks, piping, tubing, strip, or wire-like material, after rolling the material, and in a heat treatment furnace at a temperature higher than about 900° C. The material is subjected to a preheating stage and a final heating stage, wherein in the preheating stage flames from burners are directed toward the surface of the material to impinge on the surface. Burners situated in the preheating stage are supplied with a fuel that burns with the aid of an oxidizing gas that contains gaseous oxygen. The material is held in the preheating stage long enough to obtain at least some degree of oxidation on the surface of the material, and the material is heated further in a following, final heating stage by burners situated in a furnace and that are supplied with a fuel and an oxidizing gas.

Abstract: A heating system includes a furnace configured to receive a product to be thermally treated within the furnace, where the furnace includes at least one burner to generate combustion gases from a source of oxygen and a carbon-based fuel source provided to the burner, and the combustion gases provide heat to the product disposed within the furnace. A gas pipeline delivers a heated inert gas into the furnace at a location proximate the product so as to at least partially surround and protect a surface of the product and minimize or prevent the product from chemically reacting with other gases within the furnace.

Abstract: A thermodynamic metal treating apparatus and process describes utilizing a quenchant mixture of liquid and gas in a cell. Heated metal is passed over the heated quenchant mixture which contains a liquid and a gas such as air bubbled through the liquid at a desired rate. The process is particularly suited for improving the breaking, tensile strength and ductility of steel wire as is used in belted vehicle tires. A series of quenching cells allow for fast, uniform treatment of the metal wire.

Abstract: The present invention provides a process to treat steels, preferably carbon steel to reduce the tendency of the steel to form coke when in contact with hydrocarbons at elevated temperatures. The steel may be first reduced then treated with a mixture of compounds which further modify the reduced surface and finally the treated steel surface is cured. The treated steel has a reduced propensity to form coke when in contact with hydrocarbons particularly at higher temperatures.

Abstract: A method of heat treating tool steel by using a high intensity infrared heating source, said source being tungsten halogen heat lamps which operate in air, non-air and/or vacuum environments, and a tool steel heat treat system which includes a furnace containing said tungsten halogen lamp means, a lining of a reflective metal and, preferably, support structure for the tool steel workpieces which are composed of ceramic or other high melting point material.

Abstract: In a rolling bearing put under a working circumstance in which water tends to intrude into lubricants, it has been known such a phenomenon that hydrogen ions formed by decomposition of the lubricants are adsorbed to raceway surfaces and accumulated as hydrogen atoms in highly strained sites (in the vicinity of the position for maximum shearing stress), to cause stress corrosion cracking type peeling. The present invention provides a rolling bearing in which an oxide layer of an iron/chromium oxide series is formed at a thickness of from 1 to 1000 nm to at least one of raceway surfaces of bearing rings or rolling contact surfaces of rolling elements and a manufacturing method thereof.

Abstract: A process of production of a compressor shoe superior in durability and reduced in manufacturing cost, wherein a process of quenching the shoe is performed in a vacuum, inert gas, or modified gas so as to prevent oxidation of the chrome and manganese of the surface of the material or the quenching process is performed after forming an antioxidation film on the surface of the material to prevent the oxidation of the chrome and manganese.

Abstract: The present invention relates to a low alloy, low to medium carbon content, high strength, and high ductility steel composition. The present invention contains relatively low nickel content, yet exhibits high performance characteristics and is manufactured at a substantially lower cost than alloy compositions containing high levels of nickel.

Abstract: The present invention provides a process to treat steels, preferably carbon steel to reduce the tendency of the steel to form coke when in contact with hydrocarbons at elevated temperatures. The steel may be first reduced then treated with a mixture of compounds which further modify the reduced surface and finally the treated steel surface is cured. The treated steel has a reduced propensity to form coke when in contact with hydrocarbons particularly at higher temperatures.

Abstract: The invention concerns the modification of the thermal profile developed by a product during treatment, in particular in a reheating furnace. The invention is characterised in that it consists in decreasing the treating time of the products, while increasing the available heating power, thereby enabling to reduce the thickness of the decarburized layer and/or the thickness of the calamine layer, hence decreasing melting losses.

Abstract: Method of making safe a heat treatment enclosure operating under a gas atmosphere, the said enclosure comprising a cooling chamber for rapidly cooling a metal strip running from an upstream chamber to a downstream chamber by means of a plurality of guide rollers, wherein said rapid cooling chamber is filled with a controlled atmosphere with a high hydrogen content and said strip is confined within said rapid cooling chamber by means of at least one pressure-balancing duct and of a plurality of gas locks placed between the various chambers, the pressures of the gas atmospheres between the chambers being balanced by means of ducts controlling the flow rates of the gas flowing through the said gas locks.

Abstract: The present invention provides a rolling bearing in which an oxide layer of an iron/chromium oxide series is formed at a thickness of from 1 to 1000 nm to at least one of raceway surfaces of bearing rings or rolling contact surfaces of rolling elements and a manufacturing method thereof. The oxide layer can inhibit hydrogen formed by decomposition of water incorporated in the lubricants from intruding into the matrix of the bearing members, thereby preventing early peeling for the raceway surfaces of the bearing rings or the rolling contact surfaces of the rolling elements and, thus, greatly improving the rolling life. The oxide layer can be formed simply by merely tempering the bearing member and then applying a re-heating treatment in air at a temperature lower than the tempering temperature.

Abstract: The film boiling state of a refrigerant is maintained for a time longer than in the prior art by t to lower the nuclear boiling start temperature to a temperature at which the material proof strength of a work exceeds thermal stress, thereby lowering the cooling rate of the work. In addition, by controlling the cooling rate in hardening, the film boiling state of the refrigerant is maintained to a temperature at which the material proof strength exceeds thermal stress, thereby cooling the work at a temperature equal to or higher than the critical cooling rate of the work.

Abstract: To be able to satisfactorily bright-anneal metals having a high affinity to oxygen in a hood-type furnace or the like under a protective gas, a rather pure inert gas such as argon, neon or helium, which is mixed with not more than 50 vol-% of a reducing gas, for instance hydrogen, is used as protective gas in cooperation with an oxygen binder, preferably titanium.

Abstract: A protective atmosphere for the heat-treatment of metals is obtained by heating a reactor containing a Nickel-based catalyst to a temperature of between 1000.degree. C. and 1200.degree. C., feeding to the reactor a flow of nitrogen having an oxygen content of between 0.1% and 9% and a flow of hydrocarbons that is substantially stoichiometric to the content of oxygen in the flow of nitrogen to obtain CO and H.sub.2, and sending the gas from the catalytic reactor (2) to a heat-treatment furnace (1). The flow of hydrocarbons is interrupted periodically or by command while maintaining the flow of nitrogen, and is resumed after a preset or calculated time.

Abstract: Fe--Ni alloy with improved etch factors for electronic parts are provided which are characterized by the composition consisting of, all by weight, 30-55% Ni, 0.8% or less Mn, 0.0030-0.0100% N, or 0.02% less Al, and the balance Fe and unavoidable impurities, preferably with 0.01% or less C, 0.003% or less Si, 0.005%, or less S, 0.005% or less P, and 0.0100% or less O. There is provided Fe--Ni alloy materials for electronic parts which have high etch factors and produce favorably etched surfaces without blister generation, by restricting the N and Al contents within specified ranges and preferably limiting C, Si, P, S, and O contents below specified levels.

Abstract: An apparatus for the treatment of components by means of a gas mixture, comprising mainly a first light gas and minor amounts of a second gas being heavier than the first gas, has a treatment chamber (10) in which the treatment occurs and a concentration, and purification device (19, 29, 30) in which the gas mixture is concentrated and purified to increase the concentration of the first gas. The treatment chamber (10) comprises an outlet member (19) provided in an upper part of the treatment chamber (10) and means (14, 15) being arranged to move the gas mixture upwardly and out through the outlet member (19). Said means may comprise an inlet member (14) provided in a lower part of the treatment chamber (10) and arranged to supply additional gas and to admit a laminar inward flow of said additional gas.

Abstract: A method of quenching a metal object having steps of: (a) providing a liquid coolant having a temperature from about 100.degree. F. to about 180.degree. F. and containing about 0.01 to about 0.1 standard cubic feet of carbon dioxide gas per gallon of water dissolved therein; and (b) spraying the liquid coolant on the metal object to quench the metal object.

Abstract: There is disclosed a process for forming aluminide diffusion coatings containing reactive elements on metal substrates such as iron, nickel or cobalt based alloys for protection against high temperature oxidation or corrosive environments. The process includes depositing a mixed metal coating containing aluminum and at least one reactive element onto the metal substrate and heat treating the coated substrate to induce interdiffusion of elements between the substrate and the deposited metal coating. In one aspect of the invention, the reactive element is yttrium and the metal coating is deposited by ion plating yttrium-aluminum by thermal evaporation from a yttrium-aluminum source. The coated substrate is heat treated between 500.degree.-1200.degree. C. to form a reactive element modified-aluminide diffusion coating having a thin outer Al.sub.2 O.sub.3 coating formed thereon.

Abstract: Process for the continuous heat treatment of a metal strip, the latter travelling through a furnace, which is thermally insulated, and in a protective atmosphere; the said furnace consisting of at least one section, for heating, for temperature hold and for cooling; the said strip being guide by a plurality of rollers arranged especially in the lower part and in the upper part of the said sections, so as to form a plurality of runs, wherein the strip passes through at least one partial or total isolating device positioned within at least one section or between two sections, so as to ensure different heat transfer properties on the strip compared with at least one other adjacent section having a different atmosphere, by adjusting the composition of the atmosphere consisting of a gas mixture whose hydrogen or helium content exceeds 5% and more particularly 15%, in order to allow differentiation of the thermomechanical properties of the atmosphere.

Abstract: The present invention is directed to a method for forming a heat treating atmosphere in which a nitrogen rich gas containing small amounts of oxygen is preheated. An oxygen-reactive gas, such as a hydrocarbon gas, is combined with the nitrogen rich gas and the mixture is reacted outside of the furnace at temperatures above which substantial sooting does not occur. The resulting heat treating atmosphere is then forwarded to the furnace for conducting the heat treating process.

Abstract: Annealing is performed in the annealing chamber (2) of the annealing furnace (1) under a protective gas atmosphere. A partial-stream cleaning device (3) for the protective gas is connected to the annealing chamber. The protective gas can be cooled, the condensate forming from water vapour and rolling oil residues is then separated and/or undesirable gas components are removed by adsorption. Once the cleaning process has been running for so long that the protective gas essentially no longer contains any rolling oil residues, the protective gas may be passed through a hot reaction chamber (4) in which oxygen is removed from it so that the dew point drops and easily oxidised alloying components of the annealing charge are protected against oxidation.

Abstract: A method of quenching a metal object comprising: (a) providing a reservoir of liquid coolant containing gas that has been dissolved therein; and (b) immersing the metal object in the reservoir to quench the metal. The gas is selected from the group consisting of nitrogen and carbon dioxide and is preferably carbon dioxide. The gas is preferably maintained within the range of 0.001 to 0.2 standard cubic feet of gas per gallon of coolant. The liquid coolant is preferably water. In a preferred embodiment, the reservoir of liquid coolant is open to ambient pressure and temperature.

Abstract: Method for heat treating a metal in which argon gas is selectively injected into the cooling zone of a heat treating apparatus when the temperature therein is above the level at which significant nitriding will occur.

Abstract: Martensitic steel components of apparatus for magnetic conditioning of liquids which are subjected to cathodic reaction and degradation are treated prior to use to form a barrier of iron-chromium oxide and a uniform level of hardness throughout by heating the steel to a temperature near the grain boundary temperature of the steel, maintaining that temperature for a specified period and then rapidly quenching the steel.

Abstract: A method of annealing of siderurgical products comprised of carbon steel having a chromium content in the range 0.15-1.5 wt. % and a manganese content also in the range 0.15-1.5 wt. %, whereby said products are held in an annealing furnace under nitrogen atmosphere to bring about globulization of the perlite; characterized in that oxygen is added to this atmosphere, in an amount greater than or equal to 0.5 vol. %.

Abstract: A new class of ductile iron is formed by the hot isostatic pressing of a ductile iron casting, followed by austempering of the ductile iron casting. Hot isostatic pressing can be carried out at a pressure in the range of 10,000 to 17,000 psi at a temperature above 1600.degree. F., and usually in the range of 1850.degree. F. to 2050.degree. F. Austempering of the material is carried out by heating to the austenitizing temperature (about 1500.degree. F. to 1800.degree. F.), maintaining the austenitizing temperature for a suitable time period, and rapidly cooling to an austempering temperature (about 400.degree. F. to 750.degree. F.) to form ausferrite within the sample.

Abstract: A method of quenching metals, in particular steel alloys includes treatment of the article being quenched in a boiling aqueous solution of sodium tetraborate, with gas being additionally introduced into the quench bath. The supply of gas enables a continuous operation in a wide range of application and avoids the use of conventional less environmentally friendly quenching media (oils).

Abstract: A heat treatment process in a roll type furnace for metal articles, in which the articles are heated in stages up to 800.degree.-850.degree. C. in several pre-heating zones with atmospheres containing free oxygen; the articles are heated in a high temperature zone in a reducing atmosphere containing no free oxygen and run through this zone relatively quickly; the burners of the high temperature zone are timed with high and low power periods, depending on the quantity of articles supplied and the amount of heat to be transmitted; rolls of the furnace are set in the high temperature zone at a short distance from each other; and baffle plates between the zones are set at the smallest possible distance from the rolling track or the articles on the rolling track. The burners are located above and below the rolling track.

Abstract: A process for producing low-cost atmospheres suitable for decarburize annealing carbon steels from non-cryogenically generated nitrogen containing up to 1.54 residual oxygen by catalytically deoxygenating a non-cryogenically generated nitrogen stream at low temperatures with a hydrocarbon gas and mixing the deoxygenated stream with an economical amount of hydrogen prior to introduction into the furnace for annealing. The process includes the use of 1) hydrocarbon gas to convert residual oxygen to a mixture of carbon dioxide and moisture at low temperatures and 2) mixing the deoxygenated stream with a sufficient amount of hydrogen to maintain a pH.sub.2 /pH.sub.2 O ratio of at least 2 in the furnace.

Abstract: A process to prevent the formation of adhesives when annealing a steel band having a low carbon content uses an inert gas consisting of nitrogen and hydrogen and includes the phases of heating up, holding time and cooling. The process is characterized in that during the holding time, the steel band is coated by oxidation with a thin coating which is then completely removed by reduction during the cooling phase.

Abstract: A sliding member is sulphonitride by heating at 480.degree.-600.degree. C. in the presence of both 10-500 ppm of a hydrogen sulfide gas and a 20-70 vol % ammonia gas, or by a method which comprises performing a primary heat treatment on the sliding member at 450.degree.-540.degree. C. in the presence of 50-200 ppm of a hydrogen sulfide gas and a 10-70 vol % ammonia gas, then ceasing the supply of the ammonia gas, slowly reducing the temperature to a level of 200.degree.-350.degree. C., and performing a secondary heat treatment at that temperature level. By the either method, the sliding member having a FeS.sub.2 on its topmost surface can be obtained.

Abstract: Increased cooling rate of an article heated to an elevated temperature is achieved by flowing an inert gas mixture of helium and another inert gas over the article under conditions of turbulent flow.

Abstract: For the annealing of steel in continuously operating units, the formation of so-called white dust is almost completely eliminated by subjecting the steel to a deoxidizing pretreatment before the annealing sequence so as to at least largely remove the oxygen adsorbed on the surface of the steel, as well as any oxygen compounds also present on the surface.

Abstract: Process for heat treating articles by hardening them in a recirculating gas medium which is in contact with the treated articles, the hardening gas being cooled by means of a heat exchanger, of the type in which helium is used as hardening gas, and is stored under holding pressure in a buffer container, wherein at the end of a hardening operation, a helium load is extracted from the treatment enclosure, in final phase by means of pump until a primary vacuum is obtained, the extracted helium is brought to purifying pressure by means of a compressor associated to a mechanical filter, and the helium under purifying pressure is sent to a purifier in which impurities are removed, after which it is transferred, if desired, after recompression in the buffer container.