Abstract: A method is proved for hot pressing hot rolled steel sheet, cold rolled steel sheet, Al-based plated steel sheet or Zn-based plated steel sheet, where the hot pressed sheet can exhibit a strength of at least about 1200 Mpa, and my be prevented from exhibiting hydrogen embrittlement. The steel sheet may include between about 0.05 to 0.5 wt % C, and/or it may be plated with an Al-based or Zn-based plating material. The steel sheet may be heating to a temperature greater than an Ac3 temperature and not more than about 1100° C. before pressing. An atmosphere can be provided during heating which contains not more than about 6 vol % of hydrogen and a dew point of not more than about 10° C. The exemplary methods may be used to form high strength parts which may be used, e.g., in automobiles.

Abstract: A base plate of a stainless-steel body material formed by pressing is polished and cleared of burrs by means of an abrasive material that consists mainly of Fe2O3 in a polishing process. The polished base plate is heated to a heat treatment temperature for solid solution in a reducing atmosphere in a heat treatment process. In this heat treatment process, an oxide in the constituents of minute fragments of the abrasive material in the surface of the body material of the base plate is reduced to leave iron, which is dispersed into the body material.

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: 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: In composition of a Fe-Ni alloy used for television shadow masks and containing in, Co, Mn, Si and Cr as the major components, additional inclusion of Be assures high deformation resistance and easy pore formation via etching without impairing its inherent low thermal expansion. Introduction of annealing at 800.degree. to 1200.degree. C. temperature into production process sufficiently lowers proof stress of the product without causing any noticeable crystal coarseness. Increased mechanical strength enables production of a thin shadow mask material well suited for pore formation via etching, thereby assuring high grade screen display.

Abstract: This disclosure is concerned with a method for treating a stainless steel surface by high temperature oxidation. The surface of a stainless steel article is cleaned, TiO.sub.2 and SiO.sub.2 are mixed in microparticles to form a coating agent, and water is added to the mixture to make a slip. The slip is coated on the steel surface to form a coating having a uniform thickness. The coating is dried and the article is subjected to a heat-treatment to form an oxide film. This treatment is performed in an oxidizing atmosphere for a time and a temperature suitable for the color tone to be produced. A desirable temperature for the heat-treatment is between 350.degree. C. to 700.degree. C. When a coating agent is used, it is later removed by washing, etc. after cooling the article.

Abstract: An aperture mask comprised of a nickel-iron alloy having a low thermal expansion for a color CRT is produced by combining a first annealing to produce a low coercive force and mechanical properties desirable for a warm forming operation during which a desired profile of the mask is produced with minimized springback and a second annealing after forming to provide a stress free low coercive force mask also having an oxidized high thermal emissivity surface. Wherein the process requires control of the atmospheres and oxidizing potentials in the two annealing steps.

Abstract: A method for bonding silicone rubber to a metal member is shown in which the metal member is first treated by heating the metal member to a temperature and for a time sufficient to form an oxide layer on the outer surface of the metal member. The treated metal member is then contacted with an uncured silicone rubber composition, and the silicone rubber composition is cured to bond the treated metal member to the silicone rubber composition.

Abstract: Process for applying a protective coating to a metal substrate which provides a thermal barrier and a barrier against oxidation of the substrate. The coating material is a mixture of (1) zirconium and/or hafnium and (2) a metal such as nickel which does not form a stable oxide at a high temperature in an atmosphere having a very low concentration of oxygen. The coating is subjected to such conditions to produce an outer oxide layer of metal zirconium and/or hafnium and an inner metal layer of the second metal alloyed with one or more components of the substrate. The oxide layer provides thermal and oxidation protection and the inner layer bonds the coating to the substrate.

Abstract: The present invention concerns a process for preparing ferrous parts of a color television tube and a furnace for operating such a process.According to the invention, each ferrous part behind the base of the television tube, is prepared in a single furnace and undergoes successively an annealing, a reduction and an oxidation in three parts of the furnace 3, 4 and 5, in such a way as to eliminate the mechanical stresses, remove the rust and deposit homogeneous and adhesive layers of iron oxides I and II.

Abstract: A heat process for producing corrosion resistant steel articles, comprising a first step during which the articles placed in a furnace are nitrided in a gaseous atmosphere to produce on their surface a first layer consisting essentially of epsilon type iron nitride, followed by a second stage during which the articles are exposed to an oxidizing atmosphere to form a second, oxide-rich layer on the surface of the articles. According to the invention, during the first step, an atmosphere comprising 20 to 70% by volume of ammonia NH.sub.3, 1 to 5% by volume of nitrous oxide N.sub.2 O and 25 to 79% by volume of nitrogen N.sub.2 is introduced into the furnace, the concentration ratio of ammonia to nitrous oxide [NH.sub.3 ]/[N.sub.2 O] in the introduced atmosphere being greater than 5 so that the furnace atmosphere is not oxidizing, and during the second step, an atmosphere comprising 0 to 25% by volume NH.sub.3, 0 to 5% by volume N.sub.2 O and 70 to 100% by volume N.sub.

Abstract: A compacted knitted wire seal and a method of forming the seal. The method comprises the steps of knitting a flattened wire to form a tubular sock, rolling the sock on itself, heating the rolled sock in an atmosphere containing oxygen to anneal the wire in the sock and to form oxides on the surfaces of the wire, and compressing the annealed and oxidized ring to form a compacted wire ring seal of preferably V-shaped cross section. The seal made by the method has sufficient flexibility to permit it to compensate for minor irregularities in the configurations of elements with which it is positioned in engagement, and the oxides on the surfaces of the wire in the seal improve the leak-rate qualities of the seal. The seal is particularly effective for use in automotive catalytic converters, wherein it is utilized for sealing between monolith and housing portions of converters.

Abstract: Electrical shorting between dense arrangements of electrical lead-ins having a normal operating potential difference therebetween in an arc sustaining atmosphere is substantially avoided by providing the lead-ins with an adherent, flexible, oxide coating. The lead-ins are preferably formed from a nickel-iron alloy.

Abstract: A method for hardening a selected region of a steel bearing surface of an earth boring bit using the steps of stretching a rubber protector over a seal region to be protected from treatment (the rubber being selected from the group consisting of silicone, neoprene and nitrile), exposing the bearing surface and protector to a medium (selected from the group consisting of carburizing, nitriding, carbonitriding, siliconizing, chromizing and boronizing) of the type for altering the chemical composition of the steel to be hardened, heating the medium and bearing surface, cooling the bearing and protector, and removing and cleaning the surface.

Abstract: The present invention pertains to zirconium base alloys containing about 0.1 to 0.6 weight percent tin; about 0.07 to 0.24 weight percent iron; about 0.05 to 0.15 weight percent chromium; and up to about 0.05 weight percent nickel. The balance of the alloy is zirconium with incidental impurities. The levels of the incidental impurity, oxygen, is controlled to a level of less than about 350 ppm. These alloys have been designed to minimize the adverse effects of pellet-clad interaction, when they are used as a liner bonded to the inside surface of water reactor nuclear fuel cladding. Specific cladding and fuel element designs according to the present invention are described.

Abstract: This disclosure is concerned with a method for treating a stainless steel surface by high temperature oxidation. The surface of a stainless steel article is cleaned. TiO.sub.2 and SiO.sub.2 are mixed in microparticles to form a coating agent, and water is added to the mixture to make a slip. The slip is coated on the steel surface to form a coating having a uniform thickness. The coating is dried and the article is subjected to a heat-treatment to form an oxide film. This treatment is performed in an oxidizing atmosphere for a time and a temperature suitable for the color tone to be produced. A desirable temperature for the heat-treatment is between 350.degree. C. to 700.degree. C. When a coating agent is used, it is later removed by washing, etc. after cooling the article.

Abstract: A ferritic stainless steel alloy is provided which is hot workable and is resistant to thermal cyclic oxidation and scaling at elevated temperatures. The iron-chromium-aluminum alloy contains cerium, lanthanum and other rare earths and is suitable for forming thereon an adherent textured aluminum oxide surface. Also provided are an oxidation resistant catalytic substrate made from the alloy and a method of making the steel article and products having a textured aluminum oxide surface. The method includes steps of heat treating the cold worked steel article to form the adherent textured oxide surface and, optionally, pretreatment heating of the cold worked article before the texture heat treatment.

Abstract: A paint priming method which forms, on the surface part of a ferrous material to be treated, a nitride layer with an adequate depth and preferably .epsilon. phase as a main phase thereof, and with no carbon adhesion to the surface thereof, by carrying out a gas soft nitriding treatment with gas components which generate no free carbon. The nitride layer formed on the surface part of the material is used as a presubstrate on which direct painting is possible, thereby providing a simplified and improved presubstrate treatment for painting.

Abstract: A process is provided for boriding metals and metal alloys in a fluidized bed at a temperature of from about 580.degree. to about 1300.degree. C. As a boriding agent, there was used a granular material comprising essentially spherical particles having a particle size of from about 0.025 to about 5.00 mm, which granular material was manufactured by spray drying a preferably aqueous suspension or dispersion based on materials that yield boron, and which can contain fillers, extenders and binders.

Abstract: A method is set forth of passivating at least a portion of a surface of a stainless steel member to retard buildup of radioactive materials on such surface portion. The surface portion is preferably polished until it is substantially featureless at 100 times magnification. The polished surface is exposed to a gaseous oxygen source at a temperature of 150.degree. C. to 450.degree. C. for at least about five hours. When a pipe passivated as set forth above is utilized in a water system of a light water nuclear reactor, radioactive buildup on the surface is significantly reduced as compared to pipes which have been passivated by exposure to liquid during the passivating process.

Abstract: A process and apparatus for surface coating of workpieces in fluidized beds under atmospheric or slightly higher pressure is disclosed. The process comprises submerging the workpiece(s) in the fluidized bed, mixing a metal halide with an inert gas to form the fluidizing gas, feeding to the fluidized bed another gas which is capable of reacting with the metal halide in the fluidized bed and coating the workpiece(s). The workpiece(s) are maintained at a temperature in the range of from 1600.degree. F. to 2000.degree. F. until it is evenly coated. The apparatus comprises a saturator vessel for saturating the inert gas with the metal halide and a fluid bed reactor. There are several advantages that the present invention offers over the prior art, namely, the coating can be performed in a relatively short period of time, 4 to 5 hours and that atmospheric pressure can be used, eliminating the need for a costly vacuum system.

Abstract: A method of manufacturing a picture tube shadow mask wherein a thin metal plate containing iron and nickel as major components is first etched to form a plurality of mask apertures, then, annealing of the metal plate is performed and, after being cooled in a reducing atmosphere, a darkened oxide layer is formed on the surface of the annealed metal plate by subjecting the metal plate at first to a relatively weak oxidizing steam atmosphere and then to a relatively strong oxidizing steam atmosphere.

Abstract: Improved adherence of oxide wear layers on hard metal or cemented carbide substrates is attained by providing a thin surface-oxidized bonding layer comprising a carbide or oxycarbide of at least one of tantalum, niobium or vanadium, optionally adding aluminum to the bonding layer, and finally providing an outer oxide wear layer.

Abstract: Cobalt-free ferromagnetic particles are disclosed. The particles are comprised of ferromagnetic metal inner cores and an outer oxidized layer. The particles have a saturation magnetization of 60 to 100 emu/g and a coercive force of 500 Oe or more. The outer layer provides a means for stabilizing the magnetic characteristics of the particles at temperatures not higher than 80.degree. C. in air. The particles are produced by gradually oxidizing ferromagnetic metal particles containing no cobalt in oxygen-containing gas such that the surface-oxidized metal particles have a saturation magnetization of 60 to 100 emu/g. The particles provided have good magnetic characteristics which are maintained with the passage of time even when the particles are subjected to adverse temperature and humidity conditions.

Abstract: In aluminum-containing stainless steel foil, the presence of magnesium impurity in an amount greater than about 0.002 weight percent has been found to inhibit formation of a preferred oxide surface layer characterized by multitudinous oxide whiskers of a type suitable for tightly bonding an applied coating. A method for purifying magnesium-contaminated foil comprises heating the foil to selectively vaporize the magnesium while avoiding incipient melting of the base alloy, preferably between about 1000.degree. C. and 1150.degree. C. The magnesium vapors escape into a suitable ambient phase such as a vacuum or a dry hydrogen gas. Thereafter, the foil is oxidized under conditions effective to produce the desired whiskers. A preferred steel is composed of an iron-base alloy comprising about 15 to 25 weight percent chromium and 3 to 6 weight percent aluminum, and optionally may contain cerium or yttrium in an amount effective to promote oxide adherence.

Abstract: A method for cleaning and removing iron oxide deposits from the internal heat transfer surfaces of boiler tubes, which consists in purging the tubes with superheated steam and oxygen driven at a speed of 20 to 80 m/sec. The oxygen content is 0.3 to 1.0 kg per ton of steam. The process both cleans and passivates the metal surfaces of the tubes.

Abstract: Metal surfaces are protected from corrosion by reaction with a silane. In the case of a clean metal surface, reaction with the silane produces an intermetallic compound that is subsequently oxidized to yield a surface layer of, for example, silicon oxide. In the situation where the metal has an oxide coating, the silane reacts directly with this coating to produce the protective surface.

Abstract: A hard corrosion resistant surface is provided on a ferrous substrate by first overlay welding onto the substrate surface a chromium containing ferrous material. The deposited overlay can then be machined. It is thereafter subjected to a carburization treatment at a temperature and for a time sufficient to cause the overlay to become converted to an austenitic material containing iron chromium carbides. After cooling, the carburized overlay material is heated for a time and at a temperature sufficient to cause the austenitic matrix material to precipitate secondary carbides and convert to a martensite matrix material upon cooling. It is also contemplated to initiate the aforesaid treatment with a suitably selected chromium containing ferrous material that thereby is not overlay welded.

Abstract: A method for preparing cores and the like such as magnetic recording head cores. They are made from metallic alloy oxides such as ferrite and used as electric, electronic, or magnetic elements of electric appliances such as tape recorders and televisions. The method is characterized by covering alloy compacts in part or as whole by silver and then baking them in an oxygen atmosphere for a predetermined time and at a predetermined temperature, whereby constituents of the alloy compacts are converted to oxides under strict control. Silver converging baked cores may be utilized for attaching terminals.

Abstract: A method is proposed to attenuate hydrogen diffusion through fusion reactor components via controlled oxidation of prealloyed surfaces. Alloys of zirconium, vanadium, titanium, niobium, tantalum, tungsten, nickel and iron may be protected from hydrogen isotope permeation by using vanadium as an intermediate layer and either chromium, nickel-chromium, silicon or aluminum as the oxide forming component. This method may also be used to prevent hydrogen embrittlement of metals from external hydrogen environments and is applicable to the majority of alloy systems exhibiting hydrogen embrittlement phenomena.

Abstract: Disclosed herein is a method for protecting a metal surface against carbon accumulation wherein the metal surface is one which is susceptible to carbon accumulation when exposed to an environment in which carbon-containing gases are undergoing decomposition which method comprises providing a coating on the metal surface which coating is comprised of a metal oxide selected from the group consisting of Ti.sub.4 O.sub.7, NbO.sub.2, and VO.

Abstract: A catalyst comprising a metallic carrier having a catalytically active metal-containing surface layer, the catalytic metal being other than a noble metal, whereby the catalytically active surface layer is formed out of a homogeneous metallic carrier by oxidizing in an oxidizing gas such as air and subsequently reducing with hydrogen the surface of the metallic carrier at a temperature at which the active metal is substantially not sintered, characterized in that the carrier is a web or felt of fibers with a diameter between 4 and 100 microns.

Abstract: The process of forming a composite with an alloy having an alloy component of about 0.5 to 12% aluminum and a matrix selected from a material of the group consisting of copper, iron or nickel. The alloy is heated in an oxygen-rich atmosphere to form a material oxide-rich layer on a surface of the alloy. The alloy is then heated in a reducing atmosphere to reduce the material oxide-rich layer to form an aluminum oxide on the surface of the alloy and a material-rich layer on the aluminum oxide layer.

Abstract: There is disclosed a method of making a solar energy collector element which comprises the step of forming a carbon containing film on at least the sunlight receiving surface of a substrate which is made of an iron metal material, and then heat-treating at least the sunlight receiving surface in an oxidizing atmosphere. The solar energy collector element made by the method of the present invention is superior in selective absorption characteristics for the solar energy and inexpensive in manufacturing.

Abstract: A batch process for the halogenation of solid polymeric or metallic material comprising the following steps:(a) providing a closed system comprising a chamber containing air at about atmospheric pressure and having inlet and outlet means, a heat exchanger, and a circulation pump, all connected in series;(b) introducing the material into the chamber;(c) heating the chamber and the material to a selected temperature in the range of about 100.degree. F. to about 200.degree. F. by recirculating the air through the heat exchanger;(d) evacuating the system;(e) introducing a halogen into the system in an amount (i) of up to about 10 percent in excess of the theoretical amount of halogen required to halogenate the polymeric material to a desired depth and (ii) sufficient to provide a partial pressure in the system in the range of about 0.

Abstract: Process for applying a protective coating to a metal substrate which provides a thermal barrier and a barrier against oxidation of the substrate. The coating material is a mixture of two metals M.sub.1 and M.sub.2, e.g., cerium (M.sub.1) and cobalt (M.sub.2), one of which when exposed to an atmosphere containing a low partial pressure of oxygen and at a high temperature forms a stable oxide, the other of which does not form a stable oxide under such conditions. A coating consisting of such a metal alloy or mixture is subjected to such conditions to produce an outer oxide layer of metal M.sub.1 and an inner metal layer of M.sub.2 alloyed with one or more components of the substrate. The oxide layer provides thermal and oxidation protection and the inner layer bonds the coating to the substrate.

Abstract: Aluminium is coated on steel strip. The steel strip is heated in hydrogen to reduce surface oxides to iron, and is then sprayed at 400.degree. C. with nitrogen-atomized molten aluminium to a depth of 150 microns. Still in nitrogen/hydrogen, at 350.degree. C., the coated strip is rolled. Under these conditions, the aluminium is subjected to very high compressive stress (compared with its yield stress) while the steel does not even reach its yield stress.

Abstract: Method for the manufacturing of deformation-resistant oxide coatings on metallic workpieces, in which fissures are induced in the oxide layer formed on the surface of the workpiece as a result of severe deformations in the base material. The fissures are subsequently healed by filling the interstices with subsequently produced oxide resulting from a post-oxidation process. Repeating the process several times controls the natural stress condition of the surface layer such that the effective elastic deformation range is extended.

Abstract: The invention concerns an abrasion resistent coating for steel and a method which makes it possible to obtain such a coating.The coating comprises two surface layers. The first surface layer, the outer layer, is formed of the phase (Cr, Fe).sub.2 B and possibly the phase M.sub.23 C.sub.6, while the second surface layer, the inner one, is formed of the phase (Fe, Cr).sub.2 B. In order to obtain this coating, a boriding is effected on steels at a temperature less than or equal to 950.degree. C. for a period of time greater than or equal to four hours, followed by a chromizing at a temperature less than or equal to 950.degree. C. for a period of time greater than or equal to 10 hours.Application to all steels in order to increase their resistance to wear is possible.

Abstract: A gaseous mixture of nitrogen and water vapor (dew point of about -8.degree. to 32.degree. C.), heated to 550.degree. to 750.degree. C., contacts the surfaces of a steel part for a sufficient time to produce adherent, deep-black layers on the part. Steel aperture masks and support frames for color television picture tubes may be blackened by the novel method.

Abstract: A semi-conducting, stable polychelate coating is manufactured in situ on a conducting substrate providing metal coordination centers, by carrying out a controlled chelating reaction and thermal treatment on the substrate surface with a predetermined specific amount (X.sub.o) of tetranitrile compound per unit substrate area. The temperature and duration as well as this specific amount (X.sub.o) are selected from given ranges to form a uniform polychelate coatingbonded to the substrate surface.Titanium electrodes are provided with such polychelate coatings for different purposes. Electrodes with other metal substrates are further provided with such polychelate coatings.

Abstract: An object of the present invention is a method for the anti-wear treatment of the surface of steel parts having a carbon content of at least 0.15% and the coating obtained thereby. The method is characterized by the fact that an addition of sulfur, by depositing of a metal sulfide for example, and a vapor-phase chromizing are carried out in sucession on the surface to be treated.The coating obtained is characterized by the presence of a layer of chromium sulfide on the surface and by the partial recrystallization of the underlying M.sub.7 C.sub.3 chromium carbide layer.The invention can be applied to any moving mechanical system which is subject to abrasion. The invention has importance because it increases the resistance to wear and the life of the system treated while limiting the wear of the untreated opposing part as a result of friction.

Abstract: This invention is directed to an improved process for treating steel carrier core surfaces which comprises providing a steel carrier core composition, oxidizing in the air stream the surface of the carrier core at a temperature of from about 500 degrees Fahrenheit to about 1,000 degrees Fahrenheit, adding water to the air stream prior to accomplishing the oxidation reaction, at a partial pressure of water in excess of 20 millimeters of mercury, thereby resulting in carrier cores having a resistance of from about 10.sup.5 ohm-cm to about 10.sup.12 ohm-cm.

Abstract: A process for stabilizing pyrophoric acicular metal particles consisting essentially of iron, by reaction with oxygen-containing gases in two stages, wherein, in the first stage, up to 1/3 of the passivating layer present in the final state is formed at from 25.degree. to 45.degree. C. and, in a subsequent second stage, the remainder of the passivating layer is formed at from 50.degree. to 70.degree. C.

Abstract: A process is disclosed herein in which the inner surface of a ferritic steel tube is subjected to relatively high temperature steam for a period of time, thereby resulting in the formation of a duplex scale layer of steam-grown oxide at the inner surface. As also disclosed herein, the steel tubing is pretreated so as to form a diffusion barrier at the center of the duplex layer. This barrier serves to retard the rate at which the duplex layer forms, thereby reducing the chances that the scale will grow to sufficient thickness that it will spall in response to thermal stress as the tube is placed into and taken out of service.

Abstract: The apparatus and method for processing steel strand wire cable and the like for use in prestressed concrete is disclosed in which the outer surface of the cable produced has a substantial pure rust or hydrated oxide coating thereon enabling the cable to be utilized immediately in concrete configurations to thereby produce substantially higher flexural strengths in prestressed concrete than heretofore in the prior art. The apparatus and method specifically encompasses the use of ultrasonic cleaning equipment which causes cavitation cleaning effects in the liquid medium through which the cable passes during its cleaning process. In effect, the ultrasonic cleaning "catalyzes" the chemical redox reactions by removing all surface inhibitors and reducing reactant diffusion barriers thus accelerating surface wetting of the strand cable with H.sub.2 O and O.sub.2, such that the rusting chemical reactions can occur spontaneously. The dominant bond developed between the steel and concrete is chemical.

Abstract: The invention is addressed to preventing full reduction of oxides and enabling nitriding temperature through the oxidized layer to be raised which leads in a relatively shorter time, to formation of thicker and harder superficial layers, diffusion saturated with nitrogen.This aim has been achieved by carrying on the tool oxidation process advantageously for the whole time of the gas nitriding process, the said oxidation process accompanying the gas nitriding process being carried on in steam consisting 5 to 0.5 percent by volume of the whole gas atmosphere, the atmosphere of dissociated ammonia being obtained by the dissociation of ammonia at the presence of steam, the process of a simultaneous nitriding and oxidation of tools being carried on for an arbitrary period of time.

Abstract: Tubing, pump cylinders and tank vessels, and similar tubular apparatus for containing and conveying from a supply thereof a highly erosive composition slurry comprising fine particulates in a liquid medium and free of gross particulates along a predetermined path extending from a slurry supply is provided, and method therefor, the apparatus comrising a steel wall of elongated tubular configuration defining an interior surface confining the slurry on the predetermined path, the surface tending to erode though passing contact with the slurry, and an erosion resistant diffusion coating on the surface having an inner layer comprising intimately dispersed iron carbide and an outer layer consisting essentially of iron boride, in erosion blocking relation during conveyance of the slurry through the tubular apparatus.

Abstract: Protection of cast austenitic stainless steel tubes is provided against initiation of carburization by (a) cold-working the inner surfaces of said tubes to deform the surface to such a degree that upon the subsequent heat treatment of step (b) below, dissolution of the M.sub.23 C.sub.6 carbides in the deformed region is accompanied by recrystallization resulting in a refined micrograin structure in the deformed regions to a substantially uniform minimum depth of about 20 microns; and (b) heating the cold-worked inner surfaces of said tubes, for an effective amount of time, at a temperature between its recrystallization temperature and its melting temperature, in an atmosphere of which the oxygen partial pressure is at least oxidizing with respect to chromium.

Abstract: A thin corrosion protective film of an iron oxide can be formed on the inner surface of a condenser tube made of a copper alloy by first applying on the inner surface a thin layer of an acidic suspension containing iron powder and then exposing the thus-coated inner surface to an atmosphere of an oxidizing gas. The above method can be carried out in a relatively short period of time and also in a relatively simple fashion. The resultant protective film is uniform and hardly reduces the thermal conductivity of the condenser tube, thus ideal as a protective film for condenser tubes of a heat exchanger.