US2477561A - Method of heat-treating metal parts with a bright finish - Google Patents
Method of heat-treating metal parts with a bright finish Download PDFInfo
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- US2477561A US2477561A US541281A US54128144A US2477561A US 2477561 A US2477561 A US 2477561A US 541281 A US541281 A US 541281A US 54128144 A US54128144 A US 54128144A US 2477561 A US2477561 A US 2477561A
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- bath
- temperature
- parts
- work
- heat
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Links
- 238000000034 method Methods 0.000 title description 7
- 229910052751 metal Inorganic materials 0.000 title description 6
- 239000002184 metal Substances 0.000 title description 6
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 27
- PUZPDOWCWNUUKD-UHFFFAOYSA-M sodium fluoride Chemical compound [F-].[Na+] PUZPDOWCWNUUKD-UHFFFAOYSA-M 0.000 description 16
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 description 15
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 14
- 229910000831 Steel Inorganic materials 0.000 description 13
- 239000010959 steel Substances 0.000 description 13
- 235000011121 sodium hydroxide Nutrition 0.000 description 9
- WCUXLLCKKVVCTQ-UHFFFAOYSA-M Potassium chloride Chemical compound [Cl-].[K+] WCUXLLCKKVVCTQ-UHFFFAOYSA-M 0.000 description 8
- 239000011775 sodium fluoride Substances 0.000 description 8
- 235000013024 sodium fluoride Nutrition 0.000 description 8
- 150000003839 salts Chemical class 0.000 description 7
- 239000011780 sodium chloride Substances 0.000 description 7
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 6
- 230000000717 retained effect Effects 0.000 description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 5
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 4
- KXZJHVJKXJLBKO-UHFFFAOYSA-N chembl1408157 Chemical compound N=1C2=CC=CC=C2C(C(=O)O)=CC=1C1=CC=C(O)C=C1 KXZJHVJKXJLBKO-UHFFFAOYSA-N 0.000 description 4
- 239000001103 potassium chloride Substances 0.000 description 4
- 235000011164 potassium chloride Nutrition 0.000 description 4
- 229910001104 4140 steel Inorganic materials 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 235000017550 sodium carbonate Nutrition 0.000 description 3
- 229910000029 sodium carbonate Inorganic materials 0.000 description 3
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- 238000007792 addition Methods 0.000 description 2
- 150000004649 carbonic acid derivatives Chemical class 0.000 description 2
- 238000011109 contamination Methods 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 2
- 150000004679 hydroxides Chemical class 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 229910052759 nickel Inorganic materials 0.000 description 2
- 238000010791 quenching Methods 0.000 description 2
- 230000000171 quenching effect Effects 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 241000756970 Artema Species 0.000 description 1
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical group [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 description 1
- 229910052783 alkali metal Inorganic materials 0.000 description 1
- 150000001340 alkali metals Chemical class 0.000 description 1
- 238000005279 austempering Methods 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 150000003841 chloride salts Chemical class 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- -1 ferrous metals Chemical class 0.000 description 1
- 150000004673 fluoride salts Chemical class 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 238000005272 metallurgy Methods 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 238000005554 pickling Methods 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 238000010301 surface-oxidation reaction Methods 0.000 description 1
- 230000008719 thickening Effects 0.000 description 1
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
- C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
- C21D1/607—Molten salts
Definitions
- the present invention relates to metallurgy and particularly to heat treatment liquid salt baths, more especially for use in heatin and quenching work pieces of steel, similar to austempering but with the variation that after the pieces of steel have been heated from 1350 F. to 1700 F. and quenched at a temperature of from 400 F. to 800 F., the work is held at this lower temperature for a substantial period of time, dependent upon the character of the metal and the size of the pieces comprising the work, and the work is then transferred to another bath operating at from 900 F. to 1100 F., and is finally quenched in cold water.
- the first or high temperature No. 1 bath in which the work is submerged comprises a molten bath of potassium chloride 34% to 50%, sodium chloride 45% to 65% and sodium fluoride to 8%, the preferred percentage being potassium chloride 43%, sodium chloride 55%, and sodium fluoride 2
- This No. 1 liquid bath may be operated from 1350 F. to 1700 F. Since the work pieces are covered with the molten salts of this bath as they are being transferred to the No. 2 bath, the work remains bright at this stage.
- the No. 2 bath or low temperature bath, comprises sodium hydroxide 30% to 70% and potassium hydroxide 30% to 70%; the preferred percentages being sodium hydroxide 50% and potassium hydroxide 50%.
- This second bath is adapted to be operated from 400 F. to 800 F.
- This No. 2 bath is preferably heated in a steel pot, with an electric electrode furnace using substantially pure nickel electrodes, that is, commercial nickel rods.
- No. 2 bath when heated as specified, are of a bright finish with no surface oxidation.
- the hydroxides are Work pieces coming from this gradually transformed into carbonates. This may be due to the bath taking up carbon dioxide from the surrounding atmosphere. Also, some of the No. 1 high temperature bath, comprising the chlorides and fluorides specified, is brought over into the No. 2 low temperature bath due to the transfer of work pieces from the No. 1 bath to the N0. 2 bath. This contamination of the No. 2 bath by additions from the No. 1 bath and the breakdown of the hydroxides to carbonates results in a thickening of the No. 2 bath which may continue to such extent that the materials of the No. 2 bath become too thick for satisfactory operation at the temperatures specified, at which time a portion or all of this bath is removed by bailing out, and is restarted with the proportions of the materials as previously herein specified.
- a No. 3 bath which is operated from 900 F. to 1100 F. and comprises the following chemicals: soda ash 20% to 30%, sodium chloride 5% to 15%, sodium cyanide 8% to 12%, sodium fluoride 10% to 15%, and caustic soda 30% to 50%, the preferred formula being soda ash 24%, sodium chloride 10%, sodium cyanide 10%, sodium fluoride 12%, and caustic soda 4.4%,
- soda ash 20% to 30% sodium chloride 5% to 15%
- sodium cyanide 8% to 12% sodium fluoride 10% to 15%
- caustic soda 30% to 50% the preferred formula being soda ash 24%, sodium chloride 10%, sodium cyanide 10%, sodium fluoride 12%, and caustic soda 4.4%
- the work when being carried from the No. 2 bath to the No. 3 bath, carries with it a small percentage of the chemicals of theNo. 2 bath which adhere to the work pieces, and, therefore, appropriate adjustments should be made from time to time in the N0. 3 bath to retain the same at approximately the percentages'
- the preferred percentages in the baths No. 1, No. 2, and No. 3 are the percentages of the mixtures when the baths are started, and when contamination reaches a point whereby the bath becomes thickened at the temperature at which the bath is supposed to be running, then it becomes necessary to bail out the thickened bath and replace the same with a mixture substantially the same as the proper mixture when the bath is started.
- the work When the work is removed from the No. 3 bath, it is of a bright finish and is immediately submerged in clear cold water for quenching, and the result is a clean bright surface thereby eliminating any major pickling or other treatment.
- the surface of the work is sufiiciently clean, after leaving the No. 3 bath, so that it may be electrolytically plated with any suitable finishing metal, tinned, brazed, or otherwise treated, without requiring any special treatment to remove oxides such as usually form when ferrous parts are heat treated.
- the three baths specified are adaptable for treatment of various metals, comprising stainless steels and other steels and non-ferrous metals.
- An example of use of the specified baths with a particular kind of steel comprises the treatment of SAE 4140 steel.
- This SAE 4140 steel was heated to'1550" F. in the No. 1 bath, and was quenched to a range between 600 F. and 700 F. in the No. 2 bath, then transferred to the No. 3 bath where it was heated to 900 F. and finally quenched in clear cold water.
- the No. 1 and No. 2 baths on] need to be used, and the No. 2 bath may be run from 600 F. to 1300 F.
- the improvement which comprises the first bath being potassium chloride 34% to 50%, sodium chloride 45% to 65% and sodium fluoride to 8% and the second bath being sodium hydroxide 30% to 70% and potassium hydroxide 30% to 70% heated in an electrode type electric furnace.
- the parts are heated in a first molten salt bath operated at a temperature of from 1350 F. to 1700 F., the parts being retained in the bath until heated to the temperature of the bath; the parts then being transferred to a second molten salt bath without substantial loss of temperature to the parts during said transfer, the second bath being operated at a temperature of from 400 F. to 800 F., the parts being retained in the second bath until they have acquired the temperature of said bath; the parts then being removed from the second bath and transferred to a third bath, the third bath being operated at .a temperature of from 900 F. to 1100 F., the first molten salt bath operated at a temperature of from 1350 F. to 1700 F., the parts being retained in the bath until heated to the temperature of the bath; the parts then being transferred to a second molten salt bath without substantial loss of temperature to the parts during said transfer, the second bath being operated at a temperature of from 400 F. to 800 F., the parts being retained in the second bath until they have acquired the temperature of said bath; the parts then
- the parts being retained in the third bath until they have acquired the temperature of said third bath; the parts then being removed from the third bath and quenched in water: the improvement which comprises the first bath being potassium chloride 34% to 50%, sodium chloride 45% to and sodium fluoride /2 to 8%, the second bath being sodium hydroxide 30% to and potassium hydroxide 30% to 70% heated in an electrode type electric furnace, and the third bath consisting substantially of soda ash 24%, sodium chloride 10%, sodium cyanide 10%, sodium fluoride 12% and sodium hydroxide 44%.
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
Description
Patented Aug. 2, 1949 METHOD OF HEAT-TREATING METAL PARTS WITH A BRIGHT FINISH Artemas F. Holden, New Haven, Conn.
No Drawing.
Application June 20, 1944,
Serial No. 541,281
4 Claims. 1
The present invention relates to metallurgy and particularly to heat treatment liquid salt baths, more especially for use in heatin and quenching work pieces of steel, similar to austempering but with the variation that after the pieces of steel have been heated from 1350 F. to 1700 F. and quenched at a temperature of from 400 F. to 800 F., the work is held at this lower temperature for a substantial period of time, dependent upon the character of the metal and the size of the pieces comprising the work, and the work is then transferred to another bath operating at from 900 F. to 1100 F., and is finally quenched in cold water.
In accordance with the present invention, the first or high temperature No. 1 bath in which the work is submerged, comprises a molten bath of potassium chloride 34% to 50%, sodium chloride 45% to 65% and sodium fluoride to 8%, the preferred percentage being potassium chloride 43%, sodium chloride 55%, and sodium fluoride 2 This No. 1 liquid bath may be operated from 1350 F. to 1700 F. Since the work pieces are covered with the molten salts of this bath as they are being transferred to the No. 2 bath, the work remains bright at this stage.
The No. 2 bath, or low temperature bath, comprises sodium hydroxide 30% to 70% and potassium hydroxide 30% to 70%; the preferred percentages being sodium hydroxide 50% and potassium hydroxide 50%. This second bath is adapted to be operated from 400 F. to 800 F.
This No. 2 bath is preferably heated in a steel pot, with an electric electrode furnace using substantially pure nickel electrodes, that is, commercial nickel rods. No. 2 bath, when heated as specified, are of a bright finish with no surface oxidation.
It was found that where this No. 2 bath was heated in a steel pot in a gas fired furnace, that the work came from the pot with a blue oxide finish. The reason why the work comes from a gas fired furnace with a blue oxide finish, and comes from the electric electrode furnace with a bright non-oxidized finish, may perhaps be due to electrical decomposition of the salts in the electric furnace, thereby producing a small amount of metallic alkali metals which act to prevent the formation of any oxide on the surface of the Work. This suggestion is merely a possible theory and is not put forward as a definite explanation, but the fact remains, however, that the results are as stated.
In the course of the operation of the low temperature hydroxide No, 2 bath, the hydroxides are Work pieces coming from this gradually transformed into carbonates. This may be due to the bath taking up carbon dioxide from the surrounding atmosphere. Also, some of the No. 1 high temperature bath, comprising the chlorides and fluorides specified, is brought over into the No. 2 low temperature bath due to the transfer of work pieces from the No. 1 bath to the N0. 2 bath. This contamination of the No. 2 bath by additions from the No. 1 bath and the breakdown of the hydroxides to carbonates results in a thickening of the No. 2 bath which may continue to such extent that the materials of the No. 2 bath become too thick for satisfactory operation at the temperatures specified, at which time a portion or all of this bath is removed by bailing out, and is restarted with the proportions of the materials as previously herein specified.
After the temperature of the work has been reduced to the temperature of the No. 2 bath, it is desirable, in most cases, to again raise the temperature of the work pieces in a No. 3 bath which is operated from 900 F. to 1100 F. and comprises the following chemicals: soda ash 20% to 30%, sodium chloride 5% to 15%, sodium cyanide 8% to 12%, sodium fluoride 10% to 15%, and caustic soda 30% to 50%, the preferred formula being soda ash 24%, sodium chloride 10%, sodium cyanide 10%, sodium fluoride 12%, and caustic soda 4.4%, The work, when being carried from the No. 2 bath to the No. 3 bath, carries with it a small percentage of the chemicals of theNo. 2 bath which adhere to the work pieces, and, therefore, appropriate adjustments should be made from time to time in the N0. 3 bath to retain the same at approximately the percentages'specified, more especially by the addition of sodium cyanide and sodium fluoride.
The preferred percentages in the baths No. 1, No. 2, and No. 3 are the percentages of the mixtures when the baths are started, and when contamination reaches a point whereby the bath becomes thickened at the temperature at which the bath is supposed to be running, then it becomes necessary to bail out the thickened bath and replace the same with a mixture substantially the same as the proper mixture when the bath is started.
When the work is removed from the No. 3 bath, it is of a bright finish and is immediately submerged in clear cold water for quenching, and the result is a clean bright surface thereby eliminating any major pickling or other treatment. The surface of the work is sufiiciently clean, after leaving the No. 3 bath, so that it may be electrolytically plated with any suitable finishing metal, tinned, brazed, or otherwise treated, without requiring any special treatment to remove oxides such as usually form when ferrous parts are heat treated.
The three baths specified are adaptable for treatment of various metals, comprising stainless steels and other steels and non-ferrous metals. An example of use of the specified baths with a particular kind of steel comprises the treatment of SAE 4140 steel. This SAE 4140 steel was heated to'1550" F. in the No. 1 bath, and was quenched to a range between 600 F. and 700 F. in the No. 2 bath, then transferred to the No. 3 bath where it was heated to 900 F. and finally quenched in clear cold water. The physical properties of this SAE 4140 steel after the treatment, in accordance with the present method, was found to be: reduction in cross-sectional area of from 45% to 59%; and elongation of from 13% to 16% under the application of a pull of from 160,000 pounds to 170,000 pounds, on a standard a testing machine.
When it is desired to merely anneal the work, the No. 1 and No. 2 baths on]; need to be used, and the No. 2 bath may be run from 600 F. to 1300 F.
What I claim is:
1. In the method of heat treating steel parts and providing a non-oxide bright finish thereon, wherein the parts are heated in a first molten salt bath operated at a temperature of from 1350 F. to 1700 F., the parts being retained in the bath until heated to the temperature of the bath; the parts then being transferred to a second molten salt bath without substantial loss of temperature to the parts during said transfer, the second bath being operated at a temperature of from 600 F. to 1300 F., the parts being retained in the second bath until they have acquired the temperature of said bath; the parts then being removed from the second bath and. quenched in water: the improvement which comprises the first bath being potassium chloride 34% to 50%, sodium chloride 45% to 65% and sodium fluoride to 8% and the second bath being sodium hydroxide 30% to 70% and potassium hydroxide 30% to 70% heated in an electrode type electric furnace.
2. The method of heat treating steel parts with a non-oxide bright finish thereon according to claim 1, and wherein the second bath comprises substantially 50% sodium hydroxide and 50% potassium hydroxide.
3. In the method of heat treating steel parts and providin a non-oxide bright finish thereon,
wherein the parts are heated in a first molten salt bath operated at a temperature of from 1350 F. to 1700 F., the parts being retained in the bath until heated to the temperature of the bath; the parts then being transferred to a second molten salt bath without substantial loss of temperature to the parts during said transfer, the second bath being operated at a temperature of from 400 F. to 800 F., the parts being retained in the second bath until they have acquired the temperature of said bath; the parts then being removed from the second bath and transferred to a third bath, the third bath being operated at .a temperature of from 900 F. to 1100 F., the
parts being retained in the third bath until they have acquired the temperature of said third bath; the parts then being removed from the third bath and quenched in water: the improvement which comprises the first bath being potassium chloride 34% to 50%, sodium chloride 45% to and sodium fluoride /2 to 8%, the second bath being sodium hydroxide 30% to and potassium hydroxide 30% to 70% heated in an electrode type electric furnace, and the third bath consisting substantially of soda ash 24%, sodium chloride 10%, sodium cyanide 10%, sodium fluoride 12% and sodium hydroxide 44%.
4. The method of heat treating steel parts with a non-oxide bright finish thereon according to claim 3, and wherein the second bath comprises substantially 50% sodium hydroxide and 50% pctassium hydroxide.
ARTEMAS F. HOLDEN.
REFERENCES CITED The following referenlces are of record in the file of this patent:
UNITED STATES PATENTS Number Name Date 2,237,434 Holden Apr. 8, 1941 2,309,745 Bergin Feb. 2, 1943 2,370,959 Holden Mar. 6, 1945 FOREIGN PATENTS Number Country Date 12,816 Great Britain June 7, 1905 OTHER REFERENCES Fuels and Furnaces, pages 1169, 1173-1174, Sept. 1927.
Iron Age, page 721 and advertising page 16, Nov. 10. 1932; ibid.. pages 62-69, Feb. 10, 1944,
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US541281A US2477561A (en) | 1944-06-20 | 1944-06-20 | Method of heat-treating metal parts with a bright finish |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US541281A US2477561A (en) | 1944-06-20 | 1944-06-20 | Method of heat-treating metal parts with a bright finish |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| US2477561A true US2477561A (en) | 1949-08-02 |
Family
ID=24158931
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| US541281A Expired - Lifetime US2477561A (en) | 1944-06-20 | 1944-06-20 | Method of heat-treating metal parts with a bright finish |
Country Status (1)
| Country | Link |
|---|---|
| US (1) | US2477561A (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2644775A (en) * | 1950-07-01 | 1953-07-07 | Hooker Electrochemical Co | Method of bright annealing and cleaning |
| US2738294A (en) * | 1951-09-13 | 1956-03-13 | Diamond Alkali Co | Salt bath system and method for treating metals |
| US2859029A (en) * | 1955-06-06 | 1958-11-04 | Holcroft & Co | Apparatus for treating metal parts |
| US3137752A (en) * | 1958-12-10 | 1964-06-16 | Ankersen Borge Richard | Rotary salt bath furnaces |
| FR2306268A1 (en) * | 1975-04-02 | 1976-10-29 | Degussa | SALT BATH FOR SOAKING BUILDING ELEMENTS NITRIDES IN BATH |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2237434A (en) * | 1937-11-30 | 1941-04-08 | Holden | Heat treatment bath |
| US2309745A (en) * | 1940-10-14 | 1943-02-02 | American Steel & Wire Co | Method of processing wire |
| US2370959A (en) * | 1942-03-04 | 1945-03-06 | Artemas F Holden | Method of heat treatment for wire drawing |
-
1944
- 1944-06-20 US US541281A patent/US2477561A/en not_active Expired - Lifetime
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2237434A (en) * | 1937-11-30 | 1941-04-08 | Holden | Heat treatment bath |
| US2309745A (en) * | 1940-10-14 | 1943-02-02 | American Steel & Wire Co | Method of processing wire |
| US2370959A (en) * | 1942-03-04 | 1945-03-06 | Artemas F Holden | Method of heat treatment for wire drawing |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2644775A (en) * | 1950-07-01 | 1953-07-07 | Hooker Electrochemical Co | Method of bright annealing and cleaning |
| US2738294A (en) * | 1951-09-13 | 1956-03-13 | Diamond Alkali Co | Salt bath system and method for treating metals |
| US2859029A (en) * | 1955-06-06 | 1958-11-04 | Holcroft & Co | Apparatus for treating metal parts |
| US3137752A (en) * | 1958-12-10 | 1964-06-16 | Ankersen Borge Richard | Rotary salt bath furnaces |
| FR2306268A1 (en) * | 1975-04-02 | 1976-10-29 | Degussa | SALT BATH FOR SOAKING BUILDING ELEMENTS NITRIDES IN BATH |
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