US1961520A - Method of case hardening steel - Google Patents

Method of case hardening steel Download PDF

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Publication number
US1961520A
US1961520A US596567A US59656732A US1961520A US 1961520 A US1961520 A US 1961520A US 596567 A US596567 A US 596567A US 59656732 A US59656732 A US 59656732A US 1961520 A US1961520 A US 1961520A
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Prior art keywords
steel
bath
case
cyanide
steels
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US596567A
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Vincent T Malcolm
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Chapman Valve Manufacturing Co
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Chapman Valve Manufacturing Co
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    • 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
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/40—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using liquids, e.g. salt baths, liquid suspensions
    • C23C8/42—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using liquids, e.g. salt baths, liquid suspensions only one element being applied
    • C23C8/48—Nitriding
    • C23C8/50—Nitriding of ferrous surfaces

Definitions

  • This invention r'elates to improvements in steel manufacture and is directed more particularly to improvements in methods of providing steel with hardened surfaces and the products thereof. 5
  • the principal objects of the invention are directed to the provision of improvements in aethods for treating steels to provide hardened surfaces, therefore and according to special fea- .tures of the invention, steel may be treated in the novel way to bring about the hardening effect at low cost.
  • steels of various compositions may be treated.
  • ordinary cold rolled and cold drawn steels,class S. A. E. 1010, 1020, 1030, 1040, with or without high manganese, nickel steels of any particular composition up to and including 5 nickel, chromiumnickel steels of practically any composition, chrome-tungsten, chrome-molybdenum, chromevanadium and others may be treated by the novel process.
  • Steels of the types above mentioned may be fabricated or formed into objects of various sizes and shapes, such as castings, forgings, tubes, rods, bars, sheets, etc., and. the objects may either be finished ground or they may be hardened previous to the finish grind.
  • the steel to be treated is immersed in a bath of nitrogen containing salts which is heated to a temperature ranging from 1400 to 1750 degrees F. or
  • Sodium cyanide; potassium cyanide. ammonium carbonate and ammonium nitrate have been found to be satisfactoryfor the purpose of the invention, but no single salts such as cyanides, particularly sodium and potassium, are suitably adapted for the novel method. It is therefore preferable to use a combination of salts rather than asingle salt.
  • Certain mixtures of salts containing nitrogen are heated within the range stated and during the process of treatment ammonia gas is passed through the bath.
  • the decomposition of the ammonia in the bath isbelieved to impart to the steel nitrogen in the nascent form.
  • the nitrogen penetrates into the steel thus readily forming a solid solution of iron-nitrogen.
  • the hydrogen from the decomposition of the ammonia breakup passes upwardly to the top of the bathwhere it burns with a brilliant flame.
  • the process should be carefully regulated on account of the possibility of the hydrogen and air forming an explosive compound, and requires complete knowledge of the subject.
  • Nitrogen has heretofore been considered as having a harmful effect upon steel in that it lowers in particular the elongation value and re-" sistance to shock.
  • Nitrogen has heretofore been considered as having a harmful effect upon steel in that it lowers in particular the elongation value and re-" sistance to shock.
  • experiments show that the impact value of the steel is not lowered to any appreciable. extent, if at all.
  • the time for treatment in the specified bath indicates that the time of immersion of the steel to develop the proper case depends largely on the size of the work, the temperature of operation and the depth of the case required. It has been discovered when steel is immersed in the bath and heated within the temperature range mentioned,:that it will have a case depth and an extremely hard surface fully as deep 11* not deeper, than that obtained by the so-called nitriding process where a special nitriding steel is used. At the same time, the hardened surface is decidedly less brittle than that obtained by the nitriding or any similar processes.
  • the surface hardness ranges from 600 to 1000 Brinnell hardness as determined by the well-known Monotrom apparatus, varying somewhat on the particular treatment.
  • carbon does not enter into the hardening of the surface layer as it does in the ordinary salt bath treatment and the action is quite unlike case carburizing which is the process of adding carbon to the surface and then hardening by heating the work above the critical point and quenching.
  • carburizing operation parts are usually packed in a granular compound which is mostly carbon and heated to a temperature between 1500 and 1800 degrees for hours. The carbon is taken up or absorbed by the surface of the steel so that when parts are later quenched the surface behaves like a high carbon steel that has been hardened.
  • an object containing from .15 to .25% carbon and from .1 to 1.5% manganese was immersed in a salt bath containing 15 to 40% calcium-cyanide, 20% to 40% sodium nitrate, 10 to 15% barium-carbonate and 5 to 10% sodium-chloride and subjected to a temperature some higher than the melting point of the combination.
  • a salt bath containing 15 to 40% calcium-cyanide, 20% to 40% sodium nitrate, 10 to 15% barium-carbonate and 5 to 10% sodium-chloride and subjected to a temperature some higher than the melting point of the combination.
  • a case 7 of extreme hardness having a depth of at least .020 was produced.
  • ammonia gas was used the time was reduced and it was only necessary to heat the bath to a point above the melting point.
  • the case produced is approximately .020 deep and at least more than one-half of this case 'is of extreme hardness and is clearly visible in a fractured specimen wherein the hardness decreases gradually until the case merges with the core.
  • the case obtained by my novel method, is harder than anything previously known in case hardened steels and will readily cut glass. The resistance to wear is very great, amounting to considerably more than carburized and quenched steels.
  • the core has toughness, strength and impact resistance, all of which is desirable.
  • the hardness of the surface may bemeasured in different ways. It may be tried qualitatively with a-file or by means of the Monotron or Vickers testing machines. pressions show the surface of the specimens to be satisfactorily ductile, but the Rockwell point may puncture the case and should not be used to measure this particular result. Using the two machines previously described is preferred.
  • the process. of the invention gives surface hardness with very little if any material distortion and the physical properties of the core of the material is not injurious lyaected or materially changed.
  • the hardness and wear resistance is extremely great and the hardness is not injured by tempering, within reasonable limits while the material is rust-resistant to a desirable extent.
  • the process may be adapted for various requirements and may be readily accomplished by selecting the proper steel of the proper composition for the purpose for which it is to be used. According to the invention it is possible to quench from the bath in either oil, brine, water or air and include in this various salt combinations as may be required for quenching media.

Description

Patented June 5, 1934 UNITED STATES reunion or case HARDENING s'rmn. Vincent "r. Malcolm, Springfield, Mass., assignor to Chapman Valve Manufacturing Company, Indian Orchard, Mass, a corporation of Massachusetts No Drawing. Application March 3, 1932,
Serial No. 596,567
2 Claims. (Cl. 148-15) This invention r'elates to improvements in steel manufacture and is directed more particularly to improvements in methods of providing steel with hardened surfaces and the products thereof. 5 The principal objects of the invention are directed to the provision of improvements in aethods for treating steels to provide hardened surfaces, therefore and according to special fea- .tures of the invention, steel may be treated in the novel way to bring about the hardening effect at low cost.
The ever increasing demands for better and less costly materials of all kinds in order to produce mechanisms to meet the requirements for strong- 2 and higher unit pressures have created problems overcome by the method hereinafter described.
With prior art processes certain specific steels must be treated in certain ways wherefore the results are limited. In carburizing as well as in nitriding processes the time, element is an important consideration because the cost is dependent more or less on the time consumed in treatment. According to the novel features of this invention it is possible to treat a wide range of materials, at least, itis not necessary to confine the treatment to a particular steel or to make it necessary to provide a special steel which will be particularly adapted for the novel treatment. Not only by means of the invention is it possible to treat. various steels in a relatively short time as compared with nitriding and carburlzing operations but the treatment provides a non-brittle hardened surface of desirable depth which is tough while at the same time the core of the material is tough and of desirable tensile strength.
According to this invention, steels of various compositions may be treated. For instance ordinary cold rolled and cold drawn steels,class S. A. E. 1010, 1020, 1030, 1040, with or without high manganese, nickel steels of any particular composition up to and including 5 nickel, chromiumnickel steels of practically any composition, chrome-tungsten, chrome-molybdenum, chromevanadium and others may be treated by the novel process. Steels of the types above mentioned may be fabricated or formed into objects of various sizes and shapes, such as castings, forgings, tubes, rods, bars, sheets, etc., and. the objects may either be finished ground or they may be hardened previous to the finish grind.
According to the method of this invention, the steel to be treated is immersed in a bath of nitrogen containing salts which is heated to a temperature ranging from 1400 to 1750 degrees F. or
thereabouts. Steel may be treated withpure er, faster, lighter and safer equipment have resulted in great efforts to meet the needs. These in the metallurgical art which have been largelyeutectic mixtures of various salts containing to the maximum temperature of-1750 degrees mentioned.
Sodium cyanide; potassium cyanide. ammonium carbonate and ammonium nitrate have been found to be satisfactoryfor the purpose of the invention, but no single salts such as cyanides, particularly sodium and potassium, are suitably adapted for the novel method. It is therefore preferable to use a combination of salts rather than asingle salt.
Certain mixtures of salts containing nitrogen are heated within the range stated and during the process of treatment ammonia gas is passed through the bath. The decomposition of the ammonia in the bath isbelieved to impart to the steel nitrogen in the nascent form. The nitrogen penetrates into the steel thus readily forming a solid solution of iron-nitrogen. The hydrogen from the decomposition of the ammonia breakup passes upwardly to the top of the bathwhere it burns with a brilliant flame. The process should be carefully regulated on account of the possibility of the hydrogen and air forming an explosive compound, and requires complete knowledge of the subject.
Nitrogen has heretofore been considered as having a harmful effect upon steel in that it lowers in particular the elongation value and re-" sistance to shock. In the method of this invention however experiments show that the impact value of the steel is not lowered to any appreciable. extent, if at all.
No measurements of vaporpressure of these salts have been made but-it has been definitely established that the operation can be carried out with no undesirable results without a hood over the bath but for general application a hood may be desirable.
The time for treatment in the specified bath indicates that the time of immersion of the steel to develop the proper case depends largely on the size of the work, the temperature of operation and the depth of the case required. It has been discovered when steel is immersed in the bath and heated within the temperature range mentioned,:that it will have a case depth and an extremely hard surface fully as deep 11* not deeper, than that obtained by the so-called nitriding process where a special nitriding steel is used. At the same time, the hardened surface is decidedly less brittle than that obtained by the nitriding or any similar processes.
It has been demonstrated that the surface hardness ranges from 600 to 1000 Brinnell hardness as determined by the well-known Monotrom apparatus, varying somewhat on the particular treatment.
In the method of this invention, carbon does not enter into the hardening of the surface layer as it does in the ordinary salt bath treatment and the action is quite unlike case carburizing which is the process of adding carbon to the surface and then hardening by heating the work above the critical point and quenching. In the carburizing operation, parts are usually packed in a granular compound which is mostly carbon and heated to a temperature between 1500 and 1800 degrees for hours. The carbon is taken up or absorbed by the surface of the steel so that when parts are later quenched the surface behaves like a high carbon steel that has been hardened.
It has been known for many years that heating steel in cyanide has been used extensively under the heading of cyanide dip, cyanide wash and cyanide reheat. In the first two operations work is preheated in the furnace and then treated in the cyanide bath from 15 seconds to four minutes before quenching. In the cyanide reheat, cold work is placed in the cyanide bath and treated from 10 to 40 minutes. 'These treatments provide a mixed nitrogen-carbon case which more or less increases the wear of the piece, but the case obtained is very light and can only be used where the piece has been thoroughly hardened before casing.
According to this invention a case has been produced having a depth averaging .020 while a .030 maximum has been obtained by the action of decomposition of the nitrogen compound. It is believed that the hardness is considerably greater than a nitrided case.
As an example an object containing from .15 to .25% carbon and from .1 to 1.5% manganese was immersed in a salt bath containing 15 to 40% calcium-cyanide, 20% to 40% sodium nitrate, 10 to 15% barium-carbonate and 5 to 10% sodium-chloride and subjected to a temperature some higher than the melting point of the combination. In approximately an hours time a case 7 of extreme hardness having a depth of at least .020 was produced. In a similar'demonstration where ammonia gas was used the time was reduced and it was only necessary to heat the bath to a point above the melting point.
The economies involved in connection with the invention have a direct bearing on the plant scale operation and the cost is considerably lower than by the use of the so-called nitriding or carburizing operations."
Experiments? have demonstrated that steels treated by this process have extreme hardness, wear-and abrasion resistance as well as chemical stability, in combination with a tough core having very high impact value.
The case produced, as previously explained, is approximately .020 deep and at least more than one-half of this case 'is of extreme hardness and is clearly visible in a fractured specimen wherein the hardness decreases gradually until the case merges with the core. The case, obtained by my novel method, is harder than anything previously known in case hardened steels and will readily cut glass. The resistance to wear is very great, amounting to considerably more than carburized and quenched steels. At the same time, the core has toughness, strength and impact resistance, all of which is desirable.
The hardness of the surface may bemeasured in different ways. It may be tried qualitatively with a-file or by means of the Monotron or Vickers testing machines. pressions show the surface of the specimens to be satisfactorily ductile, but the Rockwell point may puncture the case and should not be used to measure this particular result. Using the two machines previously described is preferred.
The process. of the invention gives surface hardness with very little if any material distortion and the physical properties of the core of the material is not injurious lyaected or materially changed.
The hardness and wear resistance is extremely great and the hardness is not injured by tempering, within reasonable limits while the material is rust-resistant to a desirable extent. The process may be adapted for various requirements and may be readily accomplished by selecting the proper steel of the proper composition for the purpose for which it is to be used. According to the invention it is possible to quench from the bath in either oil, brine, water or air and include in this various salt combinations as may be required for quenching media.
Examination of Rockwell im- By means of the novel method described it is treat steel and provide a case which is equal in hardness, toughness, depth and ductility equal to that produced by prior art methods in a much less time and the process is not limited to any particular steel wherefore economy in manufacture results.
Various changes and modifications may be made in the practice of the invention without departing from the spirit and scope thereof.
What I desire to secure and claim by Letters Patent of the United States is;
1. The process of treating steel to form ironnitrogen and provide a hardened case which consists in, immersing the steel in a fused salt bath, said bath including from 15 to 40% of calcium cyanide, from 20 to 40% of sodium nitrate, from 10 to 15% of barium carbonate and from 5 to 10% of sodium chloride, heating said bath to within a temperature range of from 1400 to 1750 F., and leading ammonia gas into the bottom of said bath whereby said gas dissociates to supply nitrogen to the bottom of .said bath and hydrogen to the top thereof.
2. The process of treating steel to form ironnitrogen and provide a hardened case which consists in, immersing the steel in a fused salt bath, said bath including from 15 to 40% of calcium cyanide, from 20 to 40% of sodium nitrate, from 10 to 15% of barium carbonate and from 5 to 10% of sodium chloride, heating said bath to within a temperature range of from 1400 to 1750 F., and leading ammonia gas into said bath whereby said gas dissociates to supply substantially free nitrogen and hydrogen to said bath.
VINCENT T. MALCOLM.
US596567A 1932-03-03 1932-03-03 Method of case hardening steel Expired - Lifetime US1961520A (en)

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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2454020A (en) * 1946-09-16 1948-11-16 Armco Steel Corp Ferrochrome process and product
US3136084A (en) * 1962-03-09 1964-06-09 Smith And Wesson Inc Gas cutting prevention in revolver firearms
US3475291A (en) * 1964-05-28 1969-10-28 Jacques Jean Caubet Method of electrolytically sulfiding ferrous parts in a thiocyanate bath
US4427461A (en) 1981-11-16 1984-01-24 The Garrett Corporation Nitridation and brazing of assemblies with titanium-containing iron based alloys
US20070193659A1 (en) * 2006-02-23 2007-08-23 Iljin Light Metal Co., Ltd. Method for nitriding metal in salt bath and metal manufactured using the same
US20100055496A1 (en) * 2006-02-23 2010-03-04 Iljin Light Metal Co., Ltd. Steel having high strength

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2454020A (en) * 1946-09-16 1948-11-16 Armco Steel Corp Ferrochrome process and product
US3136084A (en) * 1962-03-09 1964-06-09 Smith And Wesson Inc Gas cutting prevention in revolver firearms
US3475291A (en) * 1964-05-28 1969-10-28 Jacques Jean Caubet Method of electrolytically sulfiding ferrous parts in a thiocyanate bath
US4427461A (en) 1981-11-16 1984-01-24 The Garrett Corporation Nitridation and brazing of assemblies with titanium-containing iron based alloys
US20070193659A1 (en) * 2006-02-23 2007-08-23 Iljin Light Metal Co., Ltd. Method for nitriding metal in salt bath and metal manufactured using the same
US20100055496A1 (en) * 2006-02-23 2010-03-04 Iljin Light Metal Co., Ltd. Steel having high strength

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