US2537035A - Method of coating stainless steel - Google Patents
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- US2537035A US2537035A US596593A US59659345A US2537035A US 2537035 A US2537035 A US 2537035A US 596593 A US596593 A US 596593A US 59659345 A US59659345 A US 59659345A US 2537035 A US2537035 A US 2537035A
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- 238000000576 coating method Methods 0.000 title description 38
- 229910001220 stainless steel Inorganic materials 0.000 title description 30
- 239000010935 stainless steel Substances 0.000 title description 29
- 239000011248 coating agent Substances 0.000 title description 24
- 238000000034 method Methods 0.000 title description 12
- KMUONIBRACKNSN-UHFFFAOYSA-N potassium dichromate Chemical compound [K+].[K+].[O-][Cr](=O)(=O)O[Cr]([O-])(=O)=O KMUONIBRACKNSN-UHFFFAOYSA-N 0.000 claims description 18
- 150000003839 salts Chemical class 0.000 claims description 14
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 13
- 229910052760 oxygen Inorganic materials 0.000 claims description 13
- 239000001301 oxygen Substances 0.000 claims description 13
- JHWIEAWILPSRMU-UHFFFAOYSA-N 2-methyl-3-pyrimidin-4-ylpropanoic acid Chemical compound OC(=O)C(C)CC1=CC=NC=N1 JHWIEAWILPSRMU-UHFFFAOYSA-N 0.000 claims description 10
- 239000007789 gas Substances 0.000 claims description 10
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims description 6
- 229910052804 chromium Inorganic materials 0.000 claims description 6
- 239000011651 chromium Substances 0.000 claims description 6
- 239000000047 product Substances 0.000 description 43
- 229910052751 metal Inorganic materials 0.000 description 17
- 239000002184 metal Substances 0.000 description 17
- 238000007654 immersion Methods 0.000 description 14
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 8
- 238000005260 corrosion Methods 0.000 description 8
- 230000007797 corrosion Effects 0.000 description 8
- 229910000831 Steel Inorganic materials 0.000 description 7
- 230000008569 process Effects 0.000 description 7
- 239000010959 steel Substances 0.000 description 7
- 238000005498 polishing Methods 0.000 description 6
- 230000001464 adherent effect Effects 0.000 description 5
- 239000002253 acid Substances 0.000 description 4
- 230000008901 benefit Effects 0.000 description 4
- SOCTUWSJJQCPFX-UHFFFAOYSA-N dichromate(2-) Chemical compound [O-][Cr](=O)(=O)O[Cr]([O-])(=O)=O SOCTUWSJJQCPFX-UHFFFAOYSA-N 0.000 description 4
- 229910052742 iron Inorganic materials 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- 230000001590 oxidative effect Effects 0.000 description 4
- 238000005554 pickling Methods 0.000 description 4
- 229910000851 Alloy steel Inorganic materials 0.000 description 3
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 3
- 229910001882 dioxygen Inorganic materials 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 2
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- 238000007792 addition Methods 0.000 description 2
- 229910045601 alloy Inorganic materials 0.000 description 2
- 239000000956 alloy Substances 0.000 description 2
- 230000005587 bubbling Effects 0.000 description 2
- 239000003086 colorant Substances 0.000 description 2
- 150000001875 compounds Chemical class 0.000 description 2
- 239000000470 constituent Substances 0.000 description 2
- 238000000354 decomposition reaction Methods 0.000 description 2
- 238000007598 dipping method Methods 0.000 description 2
- 239000003792 electrolyte Substances 0.000 description 2
- 239000002421 finishing Substances 0.000 description 2
- VLTRZXGMWDSKGL-UHFFFAOYSA-N perchloric acid Chemical compound OCl(=O)(=O)=O VLTRZXGMWDSKGL-UHFFFAOYSA-N 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 229910000975 Carbon steel Inorganic materials 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 1
- 229910001209 Low-carbon steel Inorganic materials 0.000 description 1
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 238000005452 bending Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000010962 carbon steel Substances 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000001311 chemical methods and process Methods 0.000 description 1
- 229910017052 cobalt Inorganic materials 0.000 description 1
- 239000010941 cobalt Substances 0.000 description 1
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- MCWXGJITAZMZEV-UHFFFAOYSA-N dimethoate Chemical compound CNC(=O)CSP(=S)(OC)OC MCWXGJITAZMZEV-UHFFFAOYSA-N 0.000 description 1
- 230000008030 elimination Effects 0.000 description 1
- 238000003379 elimination reaction Methods 0.000 description 1
- 239000003517 fume Substances 0.000 description 1
- 239000004519 grease Substances 0.000 description 1
- 238000000227 grinding Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 1
- WPBNNNQJVZRUHP-UHFFFAOYSA-L manganese(2+);methyl n-[[2-(methoxycarbonylcarbamothioylamino)phenyl]carbamothioyl]carbamate;n-[2-(sulfidocarbothioylamino)ethyl]carbamodithioate Chemical compound [Mn+2].[S-]C(=S)NCCNC([S-])=S.COC(=O)NC(=S)NC1=CC=CC=C1NC(=S)NC(=O)OC WPBNNNQJVZRUHP-UHFFFAOYSA-L 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000010297 mechanical methods and process Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 239000011733 molybdenum Substances 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 239000010955 niobium Substances 0.000 description 1
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 239000003973 paint Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
- 238000005488 sandblasting Methods 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- 239000011734 sodium Substances 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 229910021653 sulphate ion Inorganic materials 0.000 description 1
- 235000011149 sulphuric acid Nutrition 0.000 description 1
- 239000001117 sulphuric acid Substances 0.000 description 1
- 230000000153 supplemental effect Effects 0.000 description 1
- 239000010936 titanium Substances 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
- 239000010937 tungsten Substances 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
- GPPXJZIENCGNKB-UHFFFAOYSA-N vanadium Chemical compound [V]#[V] GPPXJZIENCGNKB-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C22/70—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using melts
- C23C22/72—Treatment of iron or alloys based thereon
Definitions
- stainless steel is defined as a low-carbon steel comprising 10% to 35% chromium, with or Without nickel, and with or without supplemental additions of manganese, silicon,
- the coatings obtained often lack uniformity from portion to portion of the treated product, fail to meet hardness or toughness requirements or are insufficiently resistant to corrosion. Where unequal thicknesses of a given coating occur, interference colors due to refraction of light through unequal or unduly thin coatings commonly are encountered.
- the coatings obtained by certain conventional methods often are porous and as such are inadequatefor protecting the underlying metal from
- An outstanding object of my invention are the provision of a method for producing black-coated stainless steel products, which coating is stable, durable and corrosion resistant under a wide variety of conditionsand even is adherent wl en the metal is bent, which coating is hard and tough and uniform both in texture and appearance, and which, being dense and substantially free of chalkiness, does not rub off or wear away during extended use.
- I provide stainless steel articles, for example. with black oxide coatings of exceptional quality by immersion treatment of; the steel in an oxidizing bath of molten sodium i a dichromate and/or potassium dichromate while passing oxygen, illustratively in the form of air or commercial oxygen, through the bath, during the period of immersion.
- the quality and thickness of black coating which I thus obtain on the articles depend upon such factors as time of immersion and temperature of the treating bath. I find that surface condition of the article or roduct when immersion treatment is begun, generally influences the actual appearance of black coating imparted by the bath.
- a dull gray unpolished stainless steel piece for example, possesses a dull black appearance, while, a, polished.
- stainless steel articles to be coated preferably are preliminarily cleansed such as by pickling, to eliminate substantially all scale, oxide film, grease, dirt or the like often present on the prod-- uct surfaces as a result of earlier treatment or fabrication.
- mechanical cleansing methods such as sandblasting or grinding, with or without pickling.
- pickling the stainless steel products quick dipping in an aqueous solution of 20% nitiic acid. and 1% hydrofluoric acid usually is adequate.
- O strofslry entitled Polishing Stainless Iron and Steel, that is by making the products the anode of an aqueous electrolyte comprising an aliphatic-carboxylie acid such ascitric acid and a sol-- uble compound having a sulphate radical such as sulphuric acid; or by anodio treatment of the same in an aqueous solut on of concentrated perchloric acid as covered copending application, Serial to. 319, 35? entitled Electrolytic Polishing of Stainless Iron and Steel, now abandoned; or by subjecting the products to alternating current treatment in a concentrated acid bath including a substantial amount of nitric acid as set forth in the copending application Serial No.
- the bath itself consists of or comprises substantial amounts of sodium dichromate and/or potassium dichromate.
- constituents -ntageously are heated; at temperature substantially below decomposition temperature of the final melt.
- a bath con- The products subsequently are dried and taming either substantially all sodium dichromate or a predominance thereof is preferable, for this salt displays strong oxidizing eifects. Additions of somewhat less active potassium dichromate to the bath on the other hand afford the advantage of higher bath decomposition temperatures.
- I employ a coating treatment which requires the circulation of oxygen illustratively in the form of air or commercial oxygen through the molten salt bath.
- the oxygen supply conveniently initiates from a pressure tank or gas pump and thence is brought into the dichromate as by means of suitable tubing connecting as through the side or bottom of the bath vat or container.
- the bath Before commencing the coating operations I find it desirable to adjust the bath to full treating temperature, usually to within the approximate range of 615 F. to 850 F., or even up to about 930 F. Preferably the temperature is maintained between 730 F. and approximately 800 F; Atthese temperatures, the bath is capable of exerting a. highly oxidizing effect and is ready for receiving the product to be coated.
- the treating bath temperature preferably is within the range of treating temperatures throughout the immersion perio'cLand the oxygen supply advantageously is continuous from beginning to end of the immersion treatment.
- a limit on gas supply usually is imposed only by such factors as undue splashing set up by the rising bubbles in the instance of employing an open vat, and by bath cooling effect of the gas. I find. it convenient to leave the product immersed in the bath: as on a rack or in a holder throughout the entire treatment, or to immerse the product repeatedly as by dipping.
- the blackening bath exerts an extremely powerful oxidizing actionon the immersed product and rapidly causes a black coating or film to' form on the metal body, which surfacing,- in the instance of stainless steeL is rich in oxides of iron and chromium.
- I withdraw the coated stain less product or other metal article from the blackening bath Wash the coated surface and cool the metal to room temperature.
- the resulting stainless steel product has the many beneficial characteristics of stainless steel such as its corrosion" resistance, hardness and strength, yet possesses a durable and beautiful black oxide finish which in no manner impairs the rustless or corrosionresisting properties of the underlying metal.
- Articles blackened in accordance with my treatment possess a black coating which generally is more intense than those treated in a still bath; the coating usually displays an intense black hue throughout, and interference colors due to' refraction of light on or through the coatings obtained are at a minimum;
- thebubbling gas agitates the bath and is thought to' afford oxygen which contributes in making chemical blackening action on the immersed metal more positive and more complete, although I do; not wish to be bound by this explanation.
- the stirring effect achieved by the gas is of special value'irr the processing of large quantities of articles, particularly small intricately shaped pieces which when piled together inhibit a ready flow of chemical to all their parts.
- the black oxide film or coating which I provide is dense, hard, tough and corrosion resistant and thus does not wear away or readily wipe off and, moreover, is highly adherent and flexible and does not crack, chip or spall ofi even upon being subjected to flexing or bending stresses.
- the coating whether dull or lustrous black in appearance, depending upon initial finish of the metal before dichromate bath treatment, is uniform and of stable quality. In products which I achieve, the coatings often are relied upon for superior corrosion resistance as compared with the underlying metal.
- the art which includes, treating the alloy steel articles or products by immersing the same in a molten salt bath consisting of potassium dichromate in substantial amount and a predominating amount by weight of sodium dichromate, and circulating gas containing free oxygen through said bath during the immersion treatment.
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- Chemical & Material Sciences (AREA)
- General Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Chemical Treatment Of Metals (AREA)
Description
Patented Jan. 9, 1955i METHOD OF QCOATIN G STAINLESS STEEL Irvine C. Clingan, Baltimore, Md., assignor, by
mesne assignments, to Armco Steel Corporation, a corporation of Ohio N 0 Drawing. Application May 29, 1945, Serial No. 596,593
'7 Claims. (01. lie-cal) l V This application is a continuation-in-part of my copending application, Serial No. 470,853, filed December 31, 1942 and entitled Stainless Steel and Method of Coating Same, now Patent 2,- 394,899 of February 12, 1946, and the invention relates to a process of blackening metallic products, more especially products of stainless steel. Among the objects of my invention is the provision of ,a simple, economical and thoroughly practical process for the blackening of stainless steel or other metal or alloy products, such as machine and equipment parts, implements, trim, finishings, and the like, giving a black coating which is dense and adherent and of high quality,
durability and resistance to corrosion.
Other-objects in part will be obvious and in part pointed out hereinafter.
The invention, accordingly, consists in the several operational steps and the relation of each of the same to-one or more of the others, as described herein, the scope ofthe application of which is indicated in the claims following the description.
As conducive to a clearer understandingof certainfeatures of my invention, it may be noted at this point that stainless steel is defined as a low-carbon steel comprising 10% to 35% chromium, with or Without nickel, and with or without supplemental additions of manganese, silicon,
cobalt, copper, molybdenum, tungsten, vanadium,
columbium, titanium, and the like, for special purposes, and a balance which is substantially all iron.
There is a growing demand for blackened metal products, including those of stainless steel, which differ in appearance from the usual metallic appearance. In meeting this demand, a number of coating or blackening processes of the prior art are employed which in the instance of stain-' less steel afford a finish differing from the unpolished dull gray or briliantly polished natural finish. The more popular coatings among those heretofore obtained are chemical compounds of the metal, which coatings differ from paint or the like in that they aremore adherent, and durable.
The heretofore known chemical processes of black-coating stainless steel have, for the most part, been of limited success, one reason beingthat the steel is characteristically stable under treatment or that the time of processing required is too long for practical purposes. oftentimes, the processes necessarily create dangerous or obnoxious fumes .or other working conditions which are objectionable. Certain of the known proo corrosive effects.
chemicals which deteriorate or are spent in a short while. A considerable expenditure, therefore, usually is entailed in effecting replacement of the treating materials for maintaining standards of treatment.
Among the heretofore known processes are those Whichare wholly incapable of giving satisfactory coatings on stainless steel'products or, as suggested hereinbefore, are not easily controlled to give an expected quality of coating in a consistent manner. Experience with certain methods of blackening stainless steel has shown that some grades blacken less readily than others.
The coatings obtained often lack uniformity from portion to portion of the treated product, fail to meet hardness or toughness requirements or are insufficiently resistant to corrosion. Where unequal thicknesses of a given coating occur, interference colors due to refraction of light through unequal or unduly thin coatings commonly are encountered.
The coatings obtained by certain conventional methods often are porous and as such are inadequatefor protecting the underlying metal from There are also soft coatings as for example the heretofore known hydroxide coatings which are chalky and rub off or wear away too readily to be of practical use. They also undergo change in the presence of moisture.
Other known coatings are not sufiiciently adherent to the underlying metal. Tlfev crack, chip, or spall off, especially where stressingsuch as flexing or binding are encountered. Another class of coatings heretofore achieved on stainless steel as well as on other metals or alloys are thick, and materially affect the final dimensions of finished products, and are to be avoided when close dimensional tolerances are required in production.
An outstanding object of my invention, accordingly, are the provision of a method for producing black-coated stainless steel products, which coating is stable, durable and corrosion resistant under a wide variety of conditionsand even is adherent wl en the metal is bent, which coating is hard and tough and uniform both in texture and appearance, and which, being dense and substantially free of chalkiness, does not rub off or wear away during extended use.
Referring now more particularly to the practice of my invention, I provide stainless steel articles, for example. with black oxide coatings of exceptional quality by immersion treatment of; the steel in an oxidizing bath of molten sodium i a dichromate and/or potassium dichromate while passing oxygen, illustratively in the form of air or commercial oxygen, through the bath, during the period of immersion. The quality and thickness of black coating which I thus obtain on the articles depend upon such factors as time of immersion and temperature of the treating bath. I find that surface condition of the article or roduct when immersion treatment is begun, generally influences the actual appearance of black coating imparted by the bath. A dull gray unpolished stainless steel piece, for example, possesses a dull black appearance, while, a, polished.
piece displays a lustrous black, surfacing, after immersion in the bath for an effective period of time.
As illustrative of the practise of my invention, stainless steel articles to be coated preferably are preliminarily cleansed such as by pickling, to eliminate substantially all scale, oxide film, grease, dirt or the like often present on the prod-- uct surfaces as a result of earlier treatment or fabrication. At times, I find advantage in resorting to mechanical cleansing methods such as sandblasting or grinding, with or without pickling. In pickling the stainless steel products, quick dipping in an aqueous solution of 20% nitiic acid. and 1% hydrofluoric acid usually is adequate. Thereafter, I prefer to rinse the products in clean Water, finally obtaining a passivated, scale-free and otherwise clean metal surface which usually is of dull gray or satin-like a pearance. then are ready for coating especially Where a dull blacl; finish is desired.
In the production of products-having a lustrous black finish, I prefer to introduce one or more polishing operations as after pickling but before black coating trea 'nent. A satisfactory polish at times is accomplished in this connection by buifing or by other mechanical methods. I find, however, that a better polish is achieved electrolytically as for example inaccordance with the rocess described and claimed in the recent United States Patent 2,335,354 of James N. O strofslry, entitled Polishing Stainless Iron and Steel, that is by making the products the anode of an aqueous electrolyte comprising an aliphatic-carboxylie acid such ascitric acid and a sol-- uble compound having a sulphate radical such as sulphuric acid; or by anodio treatment of the same in an aqueous solut on of concentrated perchloric acid as covered copending application, Serial to. 319, 35? entitled Electrolytic Polishing of Stainless Iron and Steel, now abandoned; or by subjecting the products to alternating current treatment in a concentrated acid bath including a substantial amount of nitric acid as set forth in the copending application Serial No. iGOjZQG entitled Electrolytic Polishing of Stainless Steel, now U. S. Patent 2,442,591, date-d June 1, 1948. After electrolytically polishing the steel products, I wash them in clean water so as to remove traces of the electrolyte employed. The products are ready for coating treatment.
It is conveniem to provide my treating bath for coating stainless steel articles and products, or other products as of carbon steel, in a melting vat or the like, equipped with a suitable heating unit. The bath itself consists of or comprises substantial amounts of sodium dichromate and/or potassium dichromate. In preparation and use constituents -ntageously are heated; at temperature substantially below decomposition temperature of the final melt. A bath con- The products subsequently are dried and taming either substantially all sodium dichromate or a predominance thereof is preferable, for this salt displays strong oxidizing eifects. Additions of somewhat less active potassium dichromate to the bath on the other hand afford the advantage of higher bath decomposition temperatures.
As indicated hereinbefore I employ a coating treatment which requires the circulation of oxygen illustratively in the form of air or commercial oxygen through the molten salt bath. The oxygen supply conveniently initiates from a pressure tank or gas pump and thence is brought into the dichromate as by means of suitable tubing connecting as through the side or bottom of the bath vat or container.
Before commencing the coating operations I find it desirable to adjust the bath to full treating temperature, usually to within the approximate range of 615 F. to 850 F., or even up to about 930 F. Preferably the temperature is maintained between 730 F. and approximately 800 F; Atthese temperatures, the bath is capable of exerting a. highly oxidizing effect and is ready for receiving the product to be coated.
I immerse a stainless steel product, for exam-= ple, in the coating bath for a period of time usually ranging from about two to thirty minutes or more. The treating bath temperature preferably is within the range of treating temperatures throughout the immersion perio'cLand the oxygen supply advantageously is continuous from beginning to end of the immersion treatment. In bubbling oxygen through the molten dichromate a limit on gas supply usually is imposed only by such factors as undue splashing set up by the rising bubbles in the instance of employing an open vat, and by bath cooling effect of the gas. I find. it convenient to leave the product immersed in the bath: as on a rack or in a holder throughout the entire treatment, or to immerse the product repeatedly as by dipping. At times at least I find advantage in extending the immersion time sufficiently to enable the product to assume a temperature equal to or near that of the moltenbath. In any event, the blackening bath" exerts an extremely powerful oxidizing actionon the immersed product and rapidly causes a black coating or film to' form on the metal body, which surfacing,- in the instance of stainless steeL is rich in oxides of iron and chromium. After treatment, I withdraw the coated stain less product or other metal article from the blackening bath, Wash the coated surface and cool the metal to room temperature. The resulting stainless steel product has the many beneficial characteristics of stainless steel such as its corrosion" resistance, hardness and strength, yet possesses a durable and beautiful black oxide finish which in no manner impairs the rustless or corrosionresisting properties of the underlying metal.
Articles blackened in accordance with my treatment possess a black coating which generally is more intense than those treated in a still bath; the coating usually displays an intense black hue throughout, and interference colors due to' refraction of light on or through the coatings obtained are at a minimum; During treatment thebubbling gas agitates the bath and is thought to' afford oxygen which contributes in making chemical blackening action on the immersed metal more positive and more complete, although I do; not wish to be bound by this explanation. The stirring effect achieved by the gas is of special value'irr the processing of large quantities of articles, particularly small intricately shaped pieces which when piled together inhibit a ready flow of chemical to all their parts. By elimination of agitatin mechanisms and the labor required to agitate products such as small parts, which usually is permissible with my process, the coating operations are simple and all the more economical.
The black oxide film or coating which I provide is dense, hard, tough and corrosion resistant and thus does not wear away or readily wipe off and, moreover, is highly adherent and flexible and does not crack, chip or spall ofi even upon being subjected to flexing or bending stresses. The coating whether dull or lustrous black in appearance, depending upon initial finish of the metal before dichromate bath treatment, is uniform and of stable quality. In products which I achieve, the coatings often are relied upon for superior corrosion resistance as compared with the underlying metal.
Thus it will be seen that there is provided in this invention an art in which the various objects hereinbefore noted, together with many thoroughly practical advantages, are successfully achieved. It will be seen that the product is strong, durable and corrosion resistant, and that it is given an attractive black oxide finish in a direct and thoroughly reliable manner without in any way impairing the rustless and corrosion resistant characteristics of the metal. Moreover, it will be seen that in the practice of my process, highly efiective and readily available treating constituents are combined for the purpose at hand to give unusually satisfactory results.
I claim:
1. In the blackening of articles and products containing at least chromium, the art which includes, treating the articles or products in a molten salt bath essentially consisting of salts of the group consisting of sodium dichromate and potassium dichromate, and circulating gas containing free oxygen through the bath during such treatment.
2. In the blackening of stainless steel articles and products, the art which includes, immersing the stainless steel articles or products for a period ranging from about two to thirty minutes time in a molten salt bath consisting of salts of the group consisting of sodium dichromate and potassium dichromate at a temperature of 615 F. to 930 F., and circulating gas containing free oxygen through the bath during such immersion.
3. In the blackening of alloy steel articles and products containing at least 10% chromium, the art which includes, treating the alloy steel articles or products by immersing the same in a molten salt bath consisting of potassium dichromate in substantial amount and a predominating amount by weight of sodium dichromate, and circulating gas containing free oxygen through said bath during the immersion treatment.
4. In the blackening of alloy steel articles and products containing at least 10% chromium, the art which includes, polishing such articles or products, immersing the same in polished condition in a molten salt bath consisting of salts of the group consisting of sodium dichromate and potassium dichromate, and circulating gas containing free oxygen through said bath during the immersion treatment.
5. In the blackening of stainless steel articles and products, the art which includes electropolishing such articles or products, immersing the same in polished condition in a molten salt bath consisting of salts of the group consisting of sodium dichromate and potassium dichromate, and circulating oxygen gas through said bath during the immersion treatment.
6. In blackening stainless steel articles and products, the art which includes, treating the stainless steel articles or products by immersing the same in a molten salt bath essentially consisting of sodium dichromate at a temperature in the range of about 615 F. to 850 F., and hubbling oxygen gas through said bath during the immersion treatment.
7. In blackening stainless steel articles and products, the art which includes, treating the stainless steel articles or products by immersing the same in a molten salt bath essentially consisting of sodium dichromate at a temperature in the range of about 730 F. to 800 F., and bubbling oxygen gas through said bath during the immersion treatment.
IRVINE C. CLINGAN.
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS Number Name Date 1,541,778 Agricola June 16, 1925 2,394,899 Clingan Feb. 12, 1946 FOREIGN PATENTS Number Country Date 688,812 Germany Mar. 2, 1940 OTHER REFERENCES Irvine Clingan, Black Oxide Coatings on Stainless Steels, Metal Finishing, March 1944, pages 139-140.
Claims (1)
1. IN THE BLACKENING OF ARTICLES AND PRODUCTS CONTAINING AT LEAST 10% CHROMIUM, THE ART WHICH INCLUDES, TREATING THE ARTICLES OR PRODUCTS IN A MOLTEN SALT BATH ESSENTIALLY CONSISTING OF SALTS OF THE GROUP CONSISTING OF SODIUM DICHROMATE AND POTASSIUM DICHROMATE, AND CIRCULATING GAS CONTAINING FREE OXYGEN THROUGH THE BATH DURING SUCH TREATMENT.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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US596593A US2537035A (en) | 1945-05-29 | 1945-05-29 | Method of coating stainless steel |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
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US596593A US2537035A (en) | 1945-05-29 | 1945-05-29 | Method of coating stainless steel |
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US2537035A true US2537035A (en) | 1951-01-09 |
Family
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Family Applications (1)
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US596593A Expired - Lifetime US2537035A (en) | 1945-05-29 | 1945-05-29 | Method of coating stainless steel |
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Cited By (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2618578A (en) * | 1950-10-13 | 1952-11-18 | Armco Steel Corp | Blackening stainless steel |
US3963530A (en) * | 1974-01-08 | 1976-06-15 | Coral Chemical Company | Stainless steels coated with black oxides |
US4255213A (en) * | 1978-04-24 | 1981-03-10 | Amax Inc. | Method for producing solar collector plates |
FR2525637A1 (en) * | 1982-04-23 | 1983-10-28 | Stephanois Rech Mec | PROCESS FOR TREATING FERROUS METAL PARTS IN OXIDIZING SALT BATTERS TO IMPROVE CORROSION RESISTANCE, PARTS CONTAINING SULFUR |
US4905695A (en) * | 1984-07-19 | 1990-03-06 | Ethicon, Inc. | Sterile surgical needle having dark non-reflective surface |
US4959068A (en) * | 1984-07-19 | 1990-09-25 | Ethicon, Inc. | Sterile surgical needle having dark non-reflective surface |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US1541778A (en) * | 1923-11-17 | 1925-06-16 | Karl A Agricola | Apparatus for refining metal |
DE688812C (en) * | 1934-11-01 | 1940-03-02 | Degussa | all and their alloys |
US2394899A (en) * | 1942-12-31 | 1946-02-12 | American Rolling Mill Co | Stainless steel and method of coating same |
-
1945
- 1945-05-29 US US596593A patent/US2537035A/en not_active Expired - Lifetime
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US1541778A (en) * | 1923-11-17 | 1925-06-16 | Karl A Agricola | Apparatus for refining metal |
DE688812C (en) * | 1934-11-01 | 1940-03-02 | Degussa | all and their alloys |
US2394899A (en) * | 1942-12-31 | 1946-02-12 | American Rolling Mill Co | Stainless steel and method of coating same |
Cited By (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2618578A (en) * | 1950-10-13 | 1952-11-18 | Armco Steel Corp | Blackening stainless steel |
US3963530A (en) * | 1974-01-08 | 1976-06-15 | Coral Chemical Company | Stainless steels coated with black oxides |
US4255213A (en) * | 1978-04-24 | 1981-03-10 | Amax Inc. | Method for producing solar collector plates |
FR2525637A1 (en) * | 1982-04-23 | 1983-10-28 | Stephanois Rech Mec | PROCESS FOR TREATING FERROUS METAL PARTS IN OXIDIZING SALT BATTERS TO IMPROVE CORROSION RESISTANCE, PARTS CONTAINING SULFUR |
US4448611A (en) * | 1982-04-23 | 1984-05-15 | Centre Stephanois De Recherches Mecaniques Hydromecanique Et Frottement | Process for improving the corrosion resistance of ferrous metal parts |
US4905695A (en) * | 1984-07-19 | 1990-03-06 | Ethicon, Inc. | Sterile surgical needle having dark non-reflective surface |
US4959068A (en) * | 1984-07-19 | 1990-09-25 | Ethicon, Inc. | Sterile surgical needle having dark non-reflective surface |
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