US3698943A - Protective coating - Google Patents
Protective coating Download PDFInfo
- Publication number
- US3698943A US3698943A US69439A US3698943DA US3698943A US 3698943 A US3698943 A US 3698943A US 69439 A US69439 A US 69439A US 3698943D A US3698943D A US 3698943DA US 3698943 A US3698943 A US 3698943A
- Authority
- US
- United States
- Prior art keywords
- coating
- temperature
- workpiece
- ingot
- alumina
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/68—Temporary coatings or embedding materials applied before or during heat treatment
-
- 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
- C23D—ENAMELLING OF, OR APPLYING A VITREOUS LAYER TO, METALS
- C23D5/00—Coating with enamels or vitreous layers
Definitions
- Another object of the invention is to provide a protective coating, particularly suited for use on high-speed tool steel workpieces, that gives the required protection against scaling and decarburization at the high temperatures incident to billet production, and yet will adhere to the workpiece at the substantially lower temperatures of the ingots at the time the coating is applied.
- Another object of the invention is to provide a protective coating for high-speed tool steel workpieces that will adhere to an ingot at a temperature on the order of 1000 F. and protect the workpiece from oxidation and decarburization during the long, high-temperature heating cycles to temperatures above 2000 F. incident to the hot working of the tool steel ingot to a billet product.
- Another more particular object of the invention is to provide a protective coating for use on highspeed tool steel ingots to protect the same against oxidation and decarburization during processing to billets that will not impair the hot-working operations due to any reduction in the friction between the workroll surfaces and the workpiece surfaces.
- FIG. 1 is a graphic presentation of data relating to the adherence properties of the coating of the present invention
- FIG. 2 is a graphic presentation of data relating to the properties of the coating in protecting tool steel workpieces against high temperature oxidation and carburization;
- FIG. 3 is a graphic presentation of data relating to the amount of alumina required in the coating to provide the viscosity necessary for the purpose of the invention.
- the protective coating in the practice of the invention the protective coaing comprises an admixture of sodium borate (Na B O- silica (SiO and alumina (A1 0 Silica is present in the coating within the range of 10 to 55 percent by weight and preferably Within the range of 25 to 45 percent by weight.
- the total coating constituents are limited to provide an adherence ratio, which term will be defined hereinafter, of at least 0.2 and preferably at least 0.3.
- the protection rating and the adherence rating of the coating which are defined hereinafter, must be at least 3 for the purpose of achieving the objects of the invention.
- Boric acid in anhydrous powder form may be substituted for a minor portion of the sodium borate in the coating material.
- the sodium borate in the coating which may be regarded as a low-temperature melting constituent and a [flux that lowers the melting point of the other constituents of the coating, functions in the coating to adhere the coating to the workpiece, such as a tool steel ingot, at an intermediate temperature on the order of for example 1000 F.
- the silica and the alumina, which remain unmelted at these relatively low ingot temperatures, are consequently bonded to the ingot at such temperatures by the action of the sodium borate.
- boric acid anhydrous powder may be substituted for a minor portion of the sodium borate; the substitution of the boric acid, which at a low melting temperature, e.g. about 700 F., will serve to lower the melting temperature of the low-temperature melting constituents and thus enable it to adhere to workpieces, such as ingots, at relatively lower temperatures, e.g., less than for example 1000 F.
- the previously unmelted silica and alumina fluxed by the sodium borate will melt to provide a continuous coating over the workpiece surface to be protected.
- the desired protection against oxidation and decarburization is provided by the silica of the coating material, which at the high temperatures incident to billet production forms an adherent, dense continuous surface layer over the metal workpiece. This surface layer prevents exposure of the metal surface to the oxidizing atmosphere and thereby prevents surface oxidation or scaling.
- decarburization of the workpiece surface is prevented by shielding the surface against any carbon reaction with the surrounding oxygen-containing atmosphere.
- the aluminum content of the coating serves a dual function. First, it acts as a viscosity-promoting agent to reduce the fluidity of the coating and thus prevents it from running off the vertical surfaces of the workpiece during processing. Also, the alumina serves to increase the friction between the coated workpiece surface and the workrolls used in reducing the ingot to billet form during hot-working. In the absence of alumina, there is not sufiicient friction between the coated workpiece surface and the workrolls and, consequently, slippage occurs during rolling, which detracts from the efficiency of the rolling operation.
- the coating of the invention is particularly adapted for use in the production of tool steel billets in that it adheres to the ingot at intermediate temperatures of about 1000 F. when initially applied and subsequently protects the ingot from oxidation and decarburization during the long heating cycles to hot-working temperatures of 2000" F. and higher, while not inhibiting the hot-working of the material by reducing the friction between the workpiece surfaces and the workroll surfaces.
- the coating of the invention upon completion of processing from a tool steel ingot to billet form, the coating of the invention is readily removed by the metal flow incident to hotworking.
- the coating may, if desired, be formed in situ by first applying a quantity of sodium borate substantially continuous over the workpiece surface to be protected.
- the silica and alumina may then be deposited thereover.
- the fused sodium borate will serve to bond the alumina and silica to the workpiece surfaces at the intermediate temperature. It is the preferred practice, however, to provide the sodium borate, silica and alumina in admixture and apply the admixture to the surface of the ingot while at typical intermediate temperature.
- the coating of the invention to properly function in its intended application for preventing oxidation and decarburization of tool steel ingots during high-temperature processing to billet form, it must adhere to the ingot surface at the relatively low, intermediate, temperature and provide the required protection against the ambient oxygen-containing atmosphere during the high-temperature processing cycle incident to hot-working.
- the coating material coating does not adhere at the low temperatures so that areas of the workpiece surface are exposed to the oxidizing atmosphere during high-temperature processing, then no matter what the otherwise protective properties of the coating may be, the exposed areas of the workpiece will be subjected to oxidation and decarburization when processed at elevated temperature.
- the coating will not be useful if it provides complete adherence and yet does not serve to protect the workpiece surface against the high-temperature oxidizing atmosphere during processing to billet form.
- the adherence of the coating has been found to be governed by the total surface area of the sodium borate (low-temperature melting constituent), which will melt at the application temperature, divided by the total surface area of the silica and alumina (high-temperature melting constituents), which will remain unmelted at the application temperature.
- This function which may be termed the adherence ratio, may be expressed as follows:
- silica For the purpose of providing protection of the workpiece against oxidation and decarburization by providing a continuous barrier at high temperature against the surrounding oxygen-containing atmosphere, silica must be present within the range of 10 to 55 percent by weight and preferably within the range of 25 to percent by weight.
- T 0 provide a coating with viscosity sufficient to prevent it from running off the vertical surfaces of the workpiece during processing, alumina should be present in an amount of at least about 25 percent by weight. An upper limit for alumina would be about 60' percent by weight. It is understood that it is necessary in combination with this silica limitation to have an adequate adherence ratio so that the coating remains continuous over must serve both of these functions to be useful. If the workpiece surface to be protected.
- the coating compositions as listed in Table I were produced. To determine the adherence properties of the coatings reported in Table I, they were subjected to the following test conditions. The quantity of each of the coating materials was applied to a ten-pound tool steel ingot, which was heated for one hour to a temperature of 1200 F. A single horizontal surface of the heated ingot was coated, and the coated surface was positioned horizontally for five seconds. The coated surface was then turned vertically and the ingot was struck on the adjacent, uncoated surface to disturb the coating. The coated ingot surface was then examined to determine the extent to which the coating was removed during the above-described testing operation. An adherence rating was then given for each of the coating materials tested:
- the coatings as listed in Table I were also tested to determine their properties in protecting the coated workpiece surfaces against oxidation and decarburization.
- each of the coating materials listed in Table I were applied on four sides of a ten-pound tool steel ingot previously heated to a temperature of 1200 F. for one hour.
- Each coated ingot was heated for six hours at a temperature of 2100 F. in an atmosphere containing 4 percent excess oxygen.
- the ingots were then cross sectioned and etched with a solution of nitric acid. The cross sections were evaluated to determine the extent of oxidized scale and decarburized surface layer present.
- the coating it is necessary that the coating have a minimum protection rating of 3, and preferably 3.5 or above.
- the coating must have a silica content within the range of 10 to 55 percent by weight, and preferably within the range of 25 to 45 percent by weight.
- the adherence ratio as described hereinabove, be maintained at least at 0.2 and preferably at least 0.3. Otherwise, the coating will not be continuous and the exposed areas of the workpiece surface will be subjected to oxidation and decarburization to an extent rendering the coating ineffective for its intended use.
- a method for protecting a metal workpiece against scaling and decarburization during elevated-temperature processing comprising coating said workpiece, while said workpiece is at an intermediate elevated temperature, with a coating material comprising sodium borate, 10 to 55 weight percent silica and at least 25 weight percent alumina, with the constituents of said coating material being limited to provide an adherence ratio of at least 0.2, thereafter increasing the temperature of said workpiece to permit hot-working thereof and hot-working said workpiece while at said increased temperature.
Abstract
Description
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US6943970A | 1970-09-03 | 1970-09-03 |
Publications (1)
Publication Number | Publication Date |
---|---|
US3698943A true US3698943A (en) | 1972-10-17 |
Family
ID=22088983
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US69439A Expired - Lifetime US3698943A (en) | 1970-09-03 | 1970-09-03 | Protective coating |
Country Status (1)
Country | Link |
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US (1) | US3698943A (en) |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3950575A (en) * | 1973-01-23 | 1976-04-13 | Nippon Steel Corporation | Heat treatment of metals in a controlled surface atmosphere |
US4310574A (en) * | 1980-06-20 | 1982-01-12 | The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration | Method of protecting a surface with a silicon-slurry/aluminide coating |
US4720419A (en) * | 1982-07-14 | 1988-01-19 | United Kingdom Atomic Energy Authority | Substrates for electronic devices |
EP0498028A1 (en) * | 1990-07-26 | 1992-08-12 | Rockwell International Corporation | Protection of gamma titanium aluminides with aluminosilicate coatings |
-
1970
- 1970-09-03 US US69439A patent/US3698943A/en not_active Expired - Lifetime
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3950575A (en) * | 1973-01-23 | 1976-04-13 | Nippon Steel Corporation | Heat treatment of metals in a controlled surface atmosphere |
US4310574A (en) * | 1980-06-20 | 1982-01-12 | The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration | Method of protecting a surface with a silicon-slurry/aluminide coating |
US4720419A (en) * | 1982-07-14 | 1988-01-19 | United Kingdom Atomic Energy Authority | Substrates for electronic devices |
EP0498028A1 (en) * | 1990-07-26 | 1992-08-12 | Rockwell International Corporation | Protection of gamma titanium aluminides with aluminosilicate coatings |
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Legal Events
Date | Code | Title | Description |
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AS | Assignment |
Owner name: COLT INDUSTRIES OPERATING CORP. Free format text: MERGER AND CHANGE OF NAME;ASSIGNOR:CRUCIBLE CENTER COMPANY (INTO) CRUCIBLE INC. (CHANGED TO);REEL/FRAME:004120/0308 Effective date: 19821214 |
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Owner name: CRUCIBLE MATERIALS CORPORATION, PENNSYLVANIA Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:COLT INDUSTRIES OPERATING CORP.;REEL/FRAME:004194/0621 Effective date: 19831025 Owner name: CRUCIBLE MATERIALS CORPORATION, A DE CORP. Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:COLT INDUSTRIES OPERATING CORP.;REEL/FRAME:004194/0621 Effective date: 19831025 |
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AS | Assignment |
Owner name: MELLON BANK, N.A. FOR THE CHASE MANHATTAN BANK (NA Free format text: SECURITY INTEREST;ASSIGNOR:CRUCIBLE MATERIALS CORPORATION, A CORP. OF DE.;REEL/FRAME:004490/0452 Effective date: 19851219 Owner name: CHASE MANHATTAN BANK, THE (NATIONAL ASSOCIATION) A Free format text: SECURITY INTEREST;ASSIGNOR:CRUCIBLE MATERIALS CORPORATION, A CORP. OF DE.;REEL/FRAME:004490/0452 Effective date: 19851219 Owner name: MELLON FINANCIAL SERVICES CORPORATION Free format text: SECURITY INTEREST;ASSIGNOR:CRUCIBLE MATERIALS CORPORATION, A CORP. OF DE.;REEL/FRAME:004490/0410 Effective date: 19851219 Owner name: MELLON BANK, N.A. AS AGENT FOR MELLON BANK N.A. & Free format text: SECURITY INTEREST;ASSIGNOR:CRUCIBLE MATERIALS CORPORATION, A CORP. OF DE.;REEL/FRAME:004490/0410 Effective date: 19851219 |