US2226403A - Manufacture of veneered articles - Google Patents

Description

Dec. 24, 1940. HOPKlNs 2,226,403

TUBE OF VENEERED ARTICLES Filed July 23, 1938 \JWFQ 159m ATTORNEY Patented Dec. 24, 1940 UNITED STATES PATENT OFFICE 4 Claims.

This invention relates to the manufacture of coated or veneered articles, more particularly the invention relates to the conversion of thick, coated or veneered, metal bodies into thinner worked 5 bodies.

In my prior Patents. No. 2,151,194 of March 28, 1939, and No. 2,191,469 of February 27, 1940, are disclosed new methods for making coated articles. The new methods briefly, include the deposition of fusing metal on the surface of a base metal under a blanket of flux of substantially nongassing character and of a sufficient thickness to protect the metal depositing operation from the r atmosphere. The fusing metal is deposited by means of electric current discharge beneath the flux blanket through a gap, or gaps, between one or more electrodes and the base metal. The current discharge is effective to fuse metal of the electrode, or electrodes, and a depth of the metal of the base so that these metals commingle to form the coating or veneer. The'penetration into the base metal and the analysis of the metal deposited from the electrode, or electrodes, are so chosen and controlled that the final coating or veener is of the required analysis.

The coating or veneer is deposited in the form of comparatively wide bands of substantially uniform penetration and analysis. The entire surface of the base metal to be coated or veneered is 30 covered by depositing the necessary number of I have found that in the commercial production of coated or veneered worked articles. in accordance with the method briefly described above, and especially steel articles coated or veneered with corrosion resistant alloys such as chrome steels, chrome nickel steels, etc., perfect articles are not invariably produced but imperfections are sometimes developed during the working operations. Aside from the usual imperfections such as snakes, bursts, etc., which are more or less inherent in working operations, particularly roll-working operations, and which may appear on either side of v the metal worked, there appear from time to time I closely spaced, short, narrow checks or cracks, 1 which are found only on the alloy side of the article. The closely spaced checks or cracks are usually quite shallow but occasionally they extend completely through the alloy coating or veneer.

Also, the checks or cracks if they appear at all, either cover the whole alloy surface of the article or cover a well defined part of it; isolated checks or cracks are seldom if ever found.

The usual imperfections can, as a rule be repaired economically; this is seldom true of these unusual cracks or checks. Because of the nature of the cracks or checks it is dangerous to employ articles showing them in the manufacture of apparatus, such as pressure vessels for the petroleum refining industry, that are to be subjected to extreme pressures and temperatures in the presence of corrosive media.

A careful study of the problem leads to the conclusion that theclosely spaced checks and cracksdo not result from the coating or veneering operation but are developed during the working operation. Thus, identical slabs have been coated with substantially identical veeners under the same conditions and these coated slabs rolled under nonidentical conditions. Perfect plate was obtained from some of these slabs and plate of varying degrees of imperfection attained from others of the slabs.

It is the primary object of this invention to provide a novel method for working metal bodies having a coating of veneer metal of different com+ position integrally united to them throughout, in which the metal bodies are work deformed into the final articles without producing closely spaced checks and cracks in the surface of the veneer metal.

It is a further object of this invention to provide a method for heat treating metal bodies having a coating of veneer metal of diiferent composition integrally united to them throughout, by means of which the full thickness of the metal bodies are brought to such a degree of plasticity that they can be work deformed into final articles without producing closely spaced checks and cracks in the surface of the veneer metal.

The further objects and advantages of the invention will be better appreciated from a consideration of the following detailed description of present preferred modes for carrying it out in practice, taken with the accompanying drawing, in which:

Fig. 1 is a schematic view partly in section illustrating the manner in which the coating or veneer is applied to the base metal,

Figs. 2 and 3 are schematic views, in section, 11-

lustratin g roll working of coated or veneered bodies, and

Fig. 4 is a fragmentary view on a larger scale of the subject matter of Fig. 2.

The invention is of general application and may be used in the working of coated or veneered metal bodies of a wide range of compositions, however, since steel, either plain carbon steel or carbon steel that includes low percentages of alloying elements such as chromium, manganese, molybdenum, nickel, etc., is the most common of the metals used as base metal for coated or veneered articles, and the corrosion resisting alloys such as chrome steel, chrome nickel steel, etc., are the most common metals used to form the coating or veneer, the invention will be described in connection with the manufacture of coated or veneered articles that include a steel base and a corrosion resisting coating or veneer. Also, while a wide variety of coated or veneered articles may be manufactured by various working operations the invention will be described in connection with roll working for the manufacture of fiat articles such as plates, sheets, etc.

The workpiece employed in the manufacture of the flat article just mentioned is preferably a thick steel slab coated with a correspondingly thick veneer of the chosen analysis, thus, the slab may range in thickness from six inches, or less, to twenty-four inches or more, and the coating may range from one-half an inch, or less, to several inches or more depending on the thickness of the final desired article and the reduction desired.

To form the workpiece, a steel slab I0 is positioned beneath a suitable welding head I I. Welding head Il may be of any preferred type and construction but should include arrangements for supplying electric current at controllable voltages and amperages, and arrangements for automatically feeding, either independently or in parallel, electrodes l2 (two being shown but a lesser or greater number may be employed) to maintain electrical discharge of predetermined characteristics. Head ll may include a current generator or may be provided with current connections to an outside source. Current is supplied to work ill by cable l5 and to contact devices l4, through which electrodes I! pass, by cable l3.

Electrode or electrodes I2 may be solid or hollow, of any preferred cross section, and may include all of the constituents necessary to form the desired alloy coating or veneer, when the metal fused from the electrodes and the work intermingle, or they may include only some of the constituents and the remainder supplied from an external source such as flux blanket I 6, a metal bar, etc. At present, I prefer to employ a plurality of electrodes that includes one or more hollow electrodes and supply the remainder of the required constituents through the. hollow electrodes. When the chosen coating or veneer is chrome steel, the hollow electrode is preferably of mild steel and the required chromium is supplied as ferro-chrome through the hollow electrode; when the chosen coating is chrome-nickel steel the chromium is supplied as ferro-chrome as before and the nickel is supplied as powder, pellets, etc. With some alloys, as for instance chrome-nickel steel, it is sometimes preferable to make one or more of the hollow electrodes and/or one or more of the other electrodes of a metal other than steel, as for instance nickel as all of the iron required, may sometimes be supplied by the base and the remainder of the electrodes.

The electrodes l2 are fed until they almost touch work l0 and are starters placed between them and base Ill. The surface of work ID to be coated or veneered is then covered with a blanket of flux Iii of sufficient depth to submerge the coating or veneering operation and to protect it as well as the fused metal from the atmosphere. Flux blanket Hi may be from an inch to six inches, or more, deep and is confined at the area to be coated by dams I'I.

The flux should be such that it will not liberate deleterious gas, either as to quantity or kind, and will not add substantial quantities of undesirable ingredients to or remove substantial quantitles of desirable ingredients from the molten metal but will flux out impurities. A wide variety of fluxes may be used satisfactorily. Silicates, simple or compound or a mixture of these, aluminates, titanates, and the like, are satisfactory. The flux may be prefused or it may be made up of dried or calcined components. At present, silicates of the alkaline] earth metals (calcium and magnesium being preferred), manganese and iron are preferred fluxes.

After flux blanket I6 is laid, the electric energy circuit is closed and the operation started, the

, tween the electrodes and the surface of the work.

The heat generated by the discharges will fuse a depth of metal of work I0, metal of the electrodes, and any metal passed to the gaps between the electrodes and the work with the result that an alloy pool will be formed of substantially uniform analysis that is integrally united to work Ill. The heat generated will also fuse some of the flux and thus provide a molten blanket that protects the operation from the atmosphere. The electrodes are moved relative to the work to deposit the alloy in the form of a wide band l8. A band I8 of desired composition is obtained by so controlling the operation that there is continuously fused predetermined proportions of the metal of base I0 and metal from electrodes l2 and metal from other sources. The desired portion of the surface of work Ill is coated or veneered by laying a suflicient number of bands 18. In order to obtain a continuous alloy coating bands l8 are overlapped somewhat.

After the coating operation is completed the coated slab is roll worked to form it into the finished article. The working operations comprise the heating of the slab to a rolling temperature and the actual rolling.

While coated slab i0 is primarily a steel slab, since the greater proportion of its thickness and volume is of steel, the heating and rolling practice ordinarily employed for comparable steel slabs will generally produce a finished article that shows the objectionable cracks in the surface of the coating This results from the fact that coating l8, which while it may only be a minor proportion of the slab behaves differently than the steel and requires different treatment.

If a, coated slab is heated and rolled under the conditions ordinarily employed in the rolling of steel slabs, the coated slab will deform as shown in Figs. 2 and 4. Fig. 2 shows diagrammatically the manner in which the surface metal of the slab is acted upon by the rollers. It is obvious from examination of this figure that if a coated slab were heated in accordance with the practice usually employed with all steel slabs the central portion of the coated slab would not be as plastic as the remainder of the slab and would, therefore, not be susceptible to the same rate of deformation as the remainder of the s1ab.- Because of this fact, the central portion of the slab would not be elongated solely by the decrease in thickness caused by the setting oi the rollers, but partly by high tensile stresses set up in the surface of the slab and the material between the surface and the center. These high tensile stresses cause the metal of the coating to pullapart and therefore produce checks onthe surface oi the finished plate. This is illustrated in his. ti wherein the dotted lines are intended to illustrate the crystals or grains of metal it. The reason the coated sur face checks and the carbon steel suriace on the other side does not check is partly due tothe dendrites existing in the res-cast alloy material and to the tenderness oi this type oi alloy as com: pared to the partially worked and inherently tougher carbon steel. Since coating metals such as chrome-steels, chrome=niclsel steels do not pressure weld readily, it at all, the cracks and checks are not eliminated by subsequent passes through the rolls but as a matter at fact more oi them are produced.

I have found that in order to invariably pro" duce coated worked articles that are tree, or sub= stantially free, of the objectionable cracks and checks it is necessary that the be heated so it is at a substantially uniiorru temperature throughout its thickness and extent. The temperature should be such that the coating mate rial will be sufificiently plastic to deform without -"'rlotlceable slippage between its grains. The tom perature, furthermore, should be such that the steel portion of the slab will be suwcientiy plastic to deform, under the pressure applied. uniformly throughout its thickness so that a minimum oi stress will be set up in the coating material.

When coated slabs heated in accordance with this invention, are rolled as in the ordinary prac ties, the deformation is substantially uniform throughout the slab, see i ls". so that a mini mum of stresses are set up that tend to crack or check'tlie surface oi the coatinu metal [18.

The optimum roiling temperature will vary with the analysis oi the steel base it and the coating metal to and in each particular case can best he arrived at by experiment. The desired re suits have becn'obtalned with coated steel slabs having'a base made oi plain sea carbon steel and a coating made of lt-l5% chrome steel by rolling at a temperature oi 23cc it. Satisfactory results can generally be obtained with plain carbon steel slabs, or carbon steel slabs that in clude low percentages of alloyinc constituents such as nickel, manganese, molybdenum etc... that are coated with; chromium steel or chromcmlclrel steel by rolling at temperatures that initially range from moo-24cc" F. The optimum temperature will generally be substantially the lowest temperature that will give the desired plasticity to both the base and the coating. The use of higher temperatures, is not desirable. The heating to higher temperatures, while it increases the piss ticity, not only increases the cost of the operation but oftentimes produces defects in the metal.

To heat the coated slab to the selected rolling temperature, so that all of the metal between its surfaces. is at a substantially uniform temperature and yet deleterlously efi'ect the metal of the slab to a.minlmum degree, a special technique is required. I have found that best results are obtained by initially heating the slab in a pit, turnace, etc., to a surface temperature in the vicinity of the upper critical temperature of the steel base metal. The temperature of the furnace or pit is then raised until the temperature of the exposed surfaces of the slab attain a temperature that is at or approaches the lower limit or the plastic range of the metals of the slab. The heat input into the furnace or pit is then controlled to maintain the surface temperature substantially constant for a period of time required to bring the whole of the metal to the surface temperature. This condition will be closely approximated though never quite attained as there is of niecessity a temperature gradient from the surface of the slab, the place oi entrance of the heat, to the metal at the center of the slab. The holding time necessary for uniform temperature throughout the slab depends on many factors such as the luminosity of the heat source, the furnace or pit design, the thickness of the metals oi the slab, their difiusivities, their conductivities, their specific heats, densities, etc. The holding time can be calculated from formulae that are known, or at least readily available to the workers in the art and, consequently, need not be set forth here. With coated slabs oi the character set forth above, a holding time in the neighborhood or"- 15 minutes per inch of thickness oi the slab will, in general, be satisfactory.

After the whole of the slab hasbeen brought to the selected temperature, at or approaching the plastic range of the metals of the slab the heat lrnput to the furnace or pit is increased to raise the surface temperature of the slab to the predetermined rolling" temperature. The heat iniput to the iurnace or pit is then controlled to maintain the surface metal at the predetermined temperature for the length of time required for the whole slab to attain a uniform temperature. The holding time is a function of the factors stated above, and may be calculated from known and available formulae. With coated slabs of the character set tor-tit above, a holding time in the neighborhood of 26 minutes per inch oi thickness of the slab will give the desired results. After this treatment the slab is passed to the rolls whereat it is worked to increase its area and reduce its thickness. The working operations convert the coating metal from metal havins the characteristics of cast metal into worlr refined metal.

As a specific example, a coated slab made up oi a plain carbon steel base (0.20% carbon) 17.25 inches thick to which has been integrally united throughout, to one of the major faces thereof, a coating of 13-15% chrome steel 0.75 inch thick, is charged at ordinary temperature into a lur nace and heated until the surface metal attains a temperature oi 1600" F. The furnace and slab may be raised in temperature together or the furnace may be up to temperature when the slab is charged. The furnace employed was of the type usually employed in steel mills for heatins slabs prior to rolling operations. The heat source was such as to fall within the technical classification oi highly luminous flame. After the i600 Etemperature was attained, the heat imput was increased to raise the surface ternperature of the slab to 2000 F. it required. one and. one-half hours to obtain thistemperature increase. Theheat imput was then adjusted to maintain the surface temperature of the slab substantially constant tor the length of time (5.5 hours) required to substantially secure this temperature throughout the depth of the slab. From fill calculations it had been determined that a holding time of 15 minutes per inch of thickness of the slab was necessary. At the end of the 5.5 hours holding time the heat imput was again increased to raise the surface temperature to 2300 F., the temperature determined by experiment to be the satisfactory rolling temperature. This temperature increase required one hour. The heat imput was then adjusted to maintain this new surface temperature for the length of time (6 hours) necessary to substantially secure this temperature throughout the metal of the slab. It has also been determined from calculations that a holding time of 20 minutes per inch of thickness of the slab was required for this purpose. Calculations indicated that at the end of this holding time the metal at the center of the slab would attain a temperature of 2277 F. The 23 F. temperature gradient could be reduced by increasing the holding time but the added cost as well as the deleterious effects on the metals of the slab, would outweigh any advantages that could be obtained by the small increase in plasticity of the center of the slab.

The thus heated slab was then passed to the rolls and converted into a plate 1.5 inches thick. The plate was free from checks and cracks on its alloy surface.

I claim:

1. The method of manufacturing worked composite metal articles, which comprises, heating a composite workpiece, made up or" a ferrous metal base to which is integrally united a protective alloy coating, to the critical rangeof the ferrous base metal, raising the temperatureof the surface metal of said workpiece to substantially the lower limit of the plastic ranges of the metals of said workpiece, maintaining said surface temperature for a time interval suiiicient to raise substantiallyall of the metal of said workpiece to said surface temperature, further raising the temperature of the surface metal of said work piece to a selected working temperature within alloy coating, to the critical range of the ferrous base metal, raising the temperature of the surface metal of said workpiece to substantially the lower limit of the plastic ranges of the metals of said workpiece, maintaining said surface temperature for a time interval equivalent to substantially 15 minutes per inch thickness of said workpiece based on a highly luminous heat source,

further raising the temperature of the surface metal of said workpiece to the selected working temperature within the plastic ranges of the metals, maintaining said surface temperature for a time interval equivalent to substantially 20 minutes per inch of thickness of said workpiece based on a highly luminous heat source, and work deforming the said heated workpiece to form the desired worked article.

3. The method of manufacturing worked composite metal articles which comprises, heating a composite workpiece, made up of a ferrous metal base to which is integrally united a corrosion resistant chromium containing alloy coating, to substantially the upper critical point of the ferrous metal base, raising the temperature of the surface metal of said workpiece to substantially 2000 F., maintaining said surface temperature for a time interval equivalent to substantially 15 minutes per inch thickness of said workpiece based on a highly luminous heat source, further raising the temperature of the surface metal to a selected working temperature between 2100 and 2400 F., maintaining the surface at said working temperature for a period of time substantially equal to 20 minutes per inch of thickness of said workpiece based on ahighly luminous heat source, and work deforming the said heated workpiece to form the desired worked article.

4. The method of manufacturing worked composite metal articles which comprises, heating a composite workpiece, made up of a carbon steel base to which is integrally united a chrome steel coating, to 1600 F., raising the temperature of the surface of said metal to 2000 F., maintaining said surface temperature for a period of time substantially equal to 15 minutes per inch of thickness of said workpiece based on a highly luminous of-said workpiece based on a highly luminous heat 1 source, and work deforming the said heated workpiece to form the desired worked article.

ROBERT K. HOPKINS.

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