US3228807A - Surface treatment of mild steel - Google Patents

Surface treatment of mild steel Download PDF

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Publication number
US3228807A
US3228807A US380026A US38002664A US3228807A US 3228807 A US3228807 A US 3228807A US 380026 A US380026 A US 380026A US 38002664 A US38002664 A US 38002664A US 3228807 A US3228807 A US 3228807A
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United States
Prior art keywords
steel
surface layer
nitrogen
mild steel
carbon
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US380026A
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Mitchell Eric
Dawes Cyril
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ZF International UK Ltd
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Lucas Industries Ltd
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Priority to US380026A priority Critical patent/US3228807A/en
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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
    • C23C8/06—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 gases
    • C23C8/08—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 gases only one element being applied
    • C23C8/24—Nitriding
    • C23C8/26—Nitriding of ferrous surfaces
    • 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
    • C23C8/06—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 gases
    • C23C8/28—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 gases more than one element being applied in one step
    • C23C8/30—Carbo-nitriding
    • C23C8/32—Carbo-nitriding of ferrous surfaces

Definitions

  • the present invention is concerned with the surface treatment of mild steel having low carbon content below 0.2%.
  • the surface of such steel can be strengthened considerably by heating the steel in an atmosphere of ammonia at a temperature above 450 C. but below 590 C. for a period sufficiently long to form in the steel an upper surface layer consisting of nitrogen combined with iron to form iron nitride, and a lower surface layer comprising nitrogen in solid solution, and then quenching the steel to cool it rapidly.
  • any heating time in excess of 30 minutes produces a useful result, the optimum effect occurring after about 3 hours.
  • the lower temperature is the temperature at which sufiicient nascent nitrogen will be present in the ammonia to form the lower surface layer, which in a typical case contains about 7% by weight of nitrogen at 570 C.
  • the upper temperature is chosen to be below the transition temperature of the steel. For steel having a carbon content below 0.2%, the transition temperature is normally in the region of 900 C. but, this temperature is lowered by the nitrogen to the value of 590 C. If the heating is carried out above 600 C. (allowing a 10 margin for safety), a transition occurs and on quenching the lower layer is converted to martensite.
  • the upper surface layers are subsantially the same Whether heating is carried out below 590 C. or above 600 C., and in each case improve seizure resistances, but the lower surface layers diifer.
  • the lower surface layer is very thick and may for example be 60 times thicker than the upper surface layer.
  • the lower surface layer is also very hard, but nevertheless it is possible to work a component after the surface treatment. Where heating is carried out above 600 C., the lower surface layer is thinner and may be only about ten times as thick as the upper surface layer. However, the lower surface layer is so hard that a component cannot be worked after treatment.
  • the atmosphere in which heating takes place may consist of ammonia, or ammonia together with a hydrocarbon or other carbon-containing gas.
  • a carboncontaining gas employed, the upper surface layer will consist of compounds of iron, nitrogen and carbon.
  • the amount of carbon-containing gas used depends on the particular upper surface layer required, but a figure of 20% by volume of carbon-containing gas is typical.
  • the component was placed in a furnace at a temperature of 570 C. in an atmosphere of ammonia together with about 20% by volume of a carbon-containing gas.
  • the com ponent was left in the furnace for 2 hours, and then quenched by immersing it in oil.
  • the component was found to have an upper surface layer 0.0005 inch thick containing compounds of iron, carbon and nitrogen, and a lower layer 0.03 inch thick containing nitrogen in solid solution.
  • the present invention should not be confused with the well known nitriding process for steel.
  • alloyed steel is used, that is to say the steel which is used has special components added to it to enable the nitriding to be carried out. Because of this, such steels are very expensive.
  • the present invention applies only to mild steels, i.e., steels having a carbon content below 0.2% and the usual impurities, but no other elements. Such steels are considerably cheaper than alloyed steels and so the present process is a great step forward. It is true that the actual process is similar to known nitriding processes, but nevertheless it has never been proposed to apply such processes to mild steels, in spite of the fact that great economic benefits are obtained, and nitriding has been known for about 40 years.
  • a method of treating the surface of mild steel which contains less than 0.2% carbon together with conventional impurities usually found in mild steel comprising heating the steel for at least 30 minutes in an atmosphere which consists predominantly of ammonia but includes in addition a carbon containing gas, at a temperature above 450 C. but below 590 C., said heating forming in the steel a relatively thin upper surface layer in which nitrogen is combined with iron and a considerably thicker lower surface layer in which nitrogen is in solid solution, and then quenching the steel.
  • a method of manufacturing a steel component having a hardened surface comprising the steps of forming the component in an unfinished condition from mild steel containing less than 0.2% carbon together with impurities usually found in mild steel, heating the component for at least 30 minutes in an atmosphere which consists predominantly of ammonia but includes in addition a carbon containing gas, at a temperature above 450 C. but below 590 C., said heating forming on the component a relatively thin upper surface layer in which nitrogen is combined with iron and a considerably thicker lower surface layer in which nitrogen is in solid solution, quenching the component and finally working the component to the desired shape.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)

Description

United States Patent 3,228,807 SURFACE TREATMENT OF MILD STEEL Eric Mitchell, Warwick, and Cyril Dawes, Wednesbury, England, assignors to Joseph Lucas (Industries) Limited, Birmingham, England No Drawing. Filed July 2, 1964, Ser. No. 380,026 2 Ciaims. (Cl. 148-121) This invention is a continuation-in-part of our application No. 214,819 filed August 6, 1962, now abandoned and entitled Surface Treatment of Unalloyed Steel.
The present invention is concerned with the surface treatment of mild steel having low carbon content below 0.2%. We have found that the surface of such steel can be strengthened considerably by heating the steel in an atmosphere of ammonia at a temperature above 450 C. but below 590 C. for a period sufficiently long to form in the steel an upper surface layer consisting of nitrogen combined with iron to form iron nitride, and a lower surface layer comprising nitrogen in solid solution, and then quenching the steel to cool it rapidly. We find that any heating time in excess of 30 minutes produces a useful result, the optimum effect occurring after about 3 hours.
The lower temperature is the temperature at which sufiicient nascent nitrogen will be present in the ammonia to form the lower surface layer, which in a typical case contains about 7% by weight of nitrogen at 570 C. The upper temperature is chosen to be below the transition temperature of the steel. For steel having a carbon content below 0.2%, the transition temperature is normally in the region of 900 C. but, this temperature is lowered by the nitrogen to the value of 590 C. If the heating is carried out above 600 C. (allowing a 10 margin for safety), a transition occurs and on quenching the lower layer is converted to martensite. This procedure forms the subject matter of a further application filed with this application as a continuationin-part of application No. 214,818. The upper surface layers are subsantially the same Whether heating is carried out below 590 C. or above 600 C., and in each case improve seizure resistances, but the lower surface layers diifer. In the present application, the lower surface layer is very thick and may for example be 60 times thicker than the upper surface layer. The lower surface layer is also very hard, but nevertheless it is possible to work a component after the surface treatment. Where heating is carried out above 600 C., the lower surface layer is thinner and may be only about ten times as thick as the upper surface layer. However, the lower surface layer is so hard that a component cannot be worked after treatment.
The atmosphere in which heating takes place may consist of ammonia, or ammonia together with a hydrocarbon or other carbon-containing gas. Where a carboncontaining gas is employed, the upper surface layer will consist of compounds of iron, nitrogen and carbon. The amount of carbon-containing gas used depends on the particular upper surface layer required, but a figure of 20% by volume of carbon-containing gas is typical.
In one particular example it was required to treat the surface of a mild steel component containing up to 0.2%
carbon together with impurities which typically may include manganese, silicon, sulfur and phosphorus. The component was placed in a furnace at a temperature of 570 C. in an atmosphere of ammonia together with about 20% by volume of a carbon-containing gas. The com ponent was left in the furnace for 2 hours, and then quenched by immersing it in oil. The component was found to have an upper surface layer 0.0005 inch thick containing compounds of iron, carbon and nitrogen, and a lower layer 0.03 inch thick containing nitrogen in solid solution.
The present invention should not be confused with the well known nitriding process for steel. In all known nitriding processes, alloyed steel is used, that is to say the steel which is used has special components added to it to enable the nitriding to be carried out. Because of this, such steels are very expensive. The present invention applies only to mild steels, i.e., steels having a carbon content below 0.2% and the usual impurities, but no other elements. Such steels are considerably cheaper than alloyed steels and so the present process is a great step forward. It is true that the actual process is similar to known nitriding processes, but nevertheless it has never been proposed to apply such processes to mild steels, in spite of the fact that great economic benefits are obtained, and nitriding has been known for about 40 years.
Havin thus described our invention what we claim as new and desire to secure by Letters Patent is:
1. A method of treating the surface of mild steel which contains less than 0.2% carbon together with conventional impurities usually found in mild steel, comprising heating the steel for at least 30 minutes in an atmosphere which consists predominantly of ammonia but includes in addition a carbon containing gas, at a temperature above 450 C. but below 590 C., said heating forming in the steel a relatively thin upper surface layer in which nitrogen is combined with iron and a considerably thicker lower surface layer in which nitrogen is in solid solution, and then quenching the steel.
2. A method of manufacturing a steel component having a hardened surface, comprising the steps of forming the component in an unfinished condition from mild steel containing less than 0.2% carbon together with impurities usually found in mild steel, heating the component for at least 30 minutes in an atmosphere which consists predominantly of ammonia but includes in addition a carbon containing gas, at a temperature above 450 C. but below 590 C., said heating forming on the component a relatively thin upper surface layer in which nitrogen is combined with iron and a considerably thicker lower surface layer in which nitrogen is in solid solution, quenching the component and finally working the component to the desired shape.
References Cited by the Examiner UNITED STATES PATENTS DAVID L. RECK, Primary Examiner.

Claims (1)

1. A METHOD OF TREATING THE SURFACE OF MILD STEEL WHICH CONTAINS LESS THAN 0.2% CARBON TOGETHER WITH CONVENTIONAL IMPURITIES USUALLY FOUND IN MILD STEEL, COMPRISING HEATING THE STEEL FOR AT LEAST 30 MINUTES IN AN ATMOSPHERE WHICH CONSISTS PREDOMINANTLY OF AMMONIA BUT INCLUDES IN ADDITION A CARBON CONTAINING GAS, AT A TEMPERATURE ABOVE 450*C. BUT BELOW 590*C., SAID HEATING FORMING IN THE STEEL A RELATIVELY THIN UPPER SURFACE LAYER IN WHICH NITROGEN IS COMBINED WITH IRON AND A CONSIDERABLY THICKER LOWER SURFACE LAYER IN WHICH NITROGEN IS IN SOLID SOLUTION, AND THEN QUENCHING THE STEEL.
US380026A 1964-07-02 1964-07-02 Surface treatment of mild steel Expired - Lifetime US3228807A (en)

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3357869A (en) * 1965-01-29 1967-12-12 Mo Automobilny Zd I A Likhache Method of heat-treating steel machine parts
US4003764A (en) * 1973-05-17 1977-01-18 Firma J. Aichelin Preparation of an ε-carbon nitride surface layer on ferrous metal parts
US4039354A (en) * 1974-08-23 1977-08-02 Borg-Warner Corporation Method of making Belleville springs

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3137596A (en) * 1962-10-03 1964-06-16 Paul M Unterweiser Method for hardening a nitrided steel
US3139359A (en) * 1961-06-12 1964-06-30 Jones & Laughlin Steel Corp Method of producing high strength thin steel

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3139359A (en) * 1961-06-12 1964-06-30 Jones & Laughlin Steel Corp Method of producing high strength thin steel
US3137596A (en) * 1962-10-03 1964-06-16 Paul M Unterweiser Method for hardening a nitrided steel

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3357869A (en) * 1965-01-29 1967-12-12 Mo Automobilny Zd I A Likhache Method of heat-treating steel machine parts
US4003764A (en) * 1973-05-17 1977-01-18 Firma J. Aichelin Preparation of an ε-carbon nitride surface layer on ferrous metal parts
US4039354A (en) * 1974-08-23 1977-08-02 Borg-Warner Corporation Method of making Belleville springs

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