US3834947A - Two-stage process of surface-hardening workpieces of hardenable ferrous alloys - Google Patents

Two-stage process of surface-hardening workpieces of hardenable ferrous alloys Download PDF

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Publication number
US3834947A
US3834947A US00182420A US18242071A US3834947A US 3834947 A US3834947 A US 3834947A US 00182420 A US00182420 A US 00182420A US 18242071 A US18242071 A US 18242071A US 3834947 A US3834947 A US 3834947A
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United States
Prior art keywords
workpiece
plasma
frequency
energy
austenite
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Expired - Lifetime
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US00182420A
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English (en)
Inventor
R Bloech
K Swoboda
A Kulmburg
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Gebrueder Boehler and Co AG
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Gebrueder Boehler and Co AG
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Priority claimed from AT849970A external-priority patent/AT315221B/de
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H1/00—Generating plasma; Handling plasma
    • H05H1/24—Generating plasma
    • H05H1/26—Plasma torches
    • H05H1/30—Plasma torches using applied electromagnetic fields, e.g. high frequency or microwave energy
    • 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
    • C21D1/06—Surface hardening
    • C21D1/09—Surface hardening by direct application of electrical or wave energy; by particle radiation

Definitions

  • the present invention relates to a process of surfacehardening workpieces of hardenable alloys of iron and steel, particularly a process which enables on the surface of the workpiece a formation of areas of metastable austenite, which have highly constant properties even after a very long treatment.
  • metastable austenite is the most important result of a two-stage surface-hardening process.
  • that process only small elemental areas of the surface of the workpiece are austenitized in succession in very short periods in the first stage so that the material around each elemental area remains initially cold. Heat flows thereafter from the austenitized area into the interior of the workpiece most rapidly so that the austenite is cooled rapidly and is substantially preserved rather than being transformed into martensite.
  • the austenite thus produced is comparable in its toughness properties to conventional austenite but distinguishes from the latter in that it is harder than the martensite which can be produced by the usual quench hardening process at a given carbon content.
  • This high austenite hardness is due to the fact that in the hardness test the penetrating indenter produces a plastically deformed region, which during its formation is transformed at least in part into an extremely hard martensite.
  • This metastable austenite differs basically from the conventional austenites, which are stable when stressed at room temperature and for this reason exhibit a low hardness in the hardness test.
  • This transformation of the metastable austenite to a higher or lower degree in the second stage takes place not only during the hardness test but when the material is subjected to any stress at room temperature.
  • the twostage surface-hardening process can be carried out in one operation, in which adjoining small elemental areas are austenitized in succession to produce a hardened strip or a hardened portion, e.g., a hardened cutting edge of a tool.
  • a hardened strip or a hardened portion e.g., a hardened cutting edge of a tool.
  • the way in which that operation is performed is decisive for the success of the process and for the quality of the workpiece surface which has been treated.
  • the results of such surface treatments can be recognized as white areas which can be etched only with difliculty and which cannot be resolved microscopically.
  • Intense etching treatments may be used to find out whether these white areas consist of martensite or of metastable austenite and result in the formation of martensite needles when austenite is present adjacent to the surface of the polished section.
  • martensite needles cannot be formed if the white areas are martensitic before being etched.
  • White areas can also be distinguished or identified by an X-ray examination to determine the proportion of austenite.
  • Areas of metastable austenite can be produced on workpieces of alloys of iron or steel if sufficiently high carbon contents can be dissolved within very short time in the austenitizing operation. If carbides are present which cannot be dissolved or can be dissolved only with difiiculty or if segregated graphite is present, the matrix must have a sufiiciently high carbon content and in that case the carbides or graphite are contained in an undissolved state in the white area.
  • the minimum carbon content which is required is about 0.6% with plain carbon steels and may be even lower with alloy steels.
  • Friction discs, plasma torches and electron beams have been used so far as sources of energy in carrying out the two-stage surface-hardening process.
  • An important requirement to be met by such source of energy resides in that it must enable such a concentration of energy that the required austenitization can be enforced within extremely short times, which amount to less than 10- second, although this figure is suggested by considerations which are merely qualitative.
  • Plasma torches according to the invention utilize the energy which is released by the recombination of the charge carriers of the plasma on electrically conducting surfaces.
  • a hot plasma which is produced by the dissociation of the process gas by means of an electric arc
  • the areas in which these charge carriers are present are surrounded by a hot stream of gas, which is not dissociated and which supplies undesirably large heat quantities to the workpiece so that the previously formed austenite layers are destroyed by tempering actions and additional layers cannot be formed because the temperature of the workpiece is too high.
  • This remark will be particularly applicable if the treatment is carried out for a relatively long time. For this reason, it has already been proposed to use the cold flame of a high-frequency plasma torch in a surface-hardening process.
  • That flame constitutes a cold plasma, in which paper cannot be ignited.
  • the desired charge recombination can also be effected with a cold plasma on electrically conducting surfaces, such as metallic surfaces, so that an extremely rapid heating can be ensured Without disturbing secondary effects produced by hot gases.
  • a cold plasma has the advantages that it can be used in a normal atmosphere, the plant required has reasonable costs, and the process is independent of the configuration and the dimensional tolerances of the workpieces to be treated.
  • An essential requirement for a commercial two-stage surface-hardening process using a cold plasma resides in that energy must be supplied to the workpiece at a uniform rate during the treatment. This requirement can be met if, in accordance with the invention, the workpiece to be treated is included in an electric circuit which is operated at a constant, high frequency and which is conductively closed by the cold plasma flame.
  • the invention provides a two-stage process of surface-hardening workpieces of hardenable alloys of iron and steel, and the invention resides in that a cold plasma is used to supply energy at a uniform rate into the workpiece during the treatment to produce elemental surface areas which consist of metastable austenite and have constant cross-sectional shapes and constant properties and said plasma conductively closes a circuit operated at a constant high frequency.
  • FIG. 1 shows an arrangementfor carrying out the process according to the invention
  • FIG. 2 shows a plasma torch for use in the process.
  • the arrangement shown in FIG. 1 comprises a frequency-stabilized high-frequency generator, the output power of which can be infinitely controlled.
  • the arrangement also comprises a torch 2 for producing a cold plasma 3, which is used to treat a workpiece 5, which is grounded at 4 just as the high-frequency generator.
  • the arrangement also comprises a matching unit 6 of conventional design, which is connected between the high-frequency generator and the torch and serves to control the optimum rate at which energy is supplied to the workpiece. That rate can be checked by means of a power meter 7 for measuring the power which is supplied to the workpiece and a power meter 8 for measuring the reflected power.
  • the high-frequency circuit should be operated at a frequency of at least 10 megacycles per second. It is pres ently believed that the upper frequency limit is 100 megacycles per second.
  • the frequency which is selected must comply with the regulations imposed by the telecommunications authorities. A frequency of 13.56 megacycles is preferred at the present time.
  • the maximum power of the high-frequency generators should lie between at least 1 and 5 kilowatts and should be infinitely variable so that the useful power supplied to the workpiece can be varied as required.
  • the matching unit is required to ensure that the useful power supplied to the workpiece is as high as possible and the reflected power or power loss is minimized. A measurement of these powers is also required to enable a very simple recording of the energy which has been supplied to the workpiece during the treatment so that complicated and time consuming subsequent checks are not required.
  • Plasma torches for producing cold plasma are known. They essentially comprise a tube in which the plasma is formed either by a high-frequency electric field established by means of an electrode axially extending in the tube, or by a high-frequency magnetic field established by a high-frequency coil which surrounds the tube. An ignition in the torch results in a liberation of electrons from the process gas. In the high-frequency field, these electrons are subjected to such a high acceleration that they can dissociate and ionize the molecules of the process gas to form a plasma.
  • the plasma torch shown in FIG. 2 comprises a rodshaped electrode 9, which by a cable 10 can be connected to the source of high-frequency power.
  • the torch also comprises a tube 11, which surrounds the electrode and can receive process gas through a short connecting pipe 12.
  • the torch comprises an electrode holder 13 for holding the electrode in an axial position in the tube, and a nozzle 14 for shaping the plasma flame 15.
  • the electrode is touched with a metal or carbon rod, which is secured in an insulator. As the rod is withdrawn, a high-frequency electric arc is formed, which initiates the formation of the plasma flame, which issues from the electrode and is maintained in the normal atmosphere.
  • the electrode may consist of thoriated tungsten.
  • Commercially available argon as used for welding has proved most satisfactory as a process gas in the two-stage surfacehardening process.
  • That tube may consist of electrically non-conducting material or of metal, e.g., copper, if the process gas flows at such a high velocity as to prevent a flash-over between the electrode and the metal tube.
  • An electrically non-conducting material must be selected for the electrode holder.
  • the torch tube may be subjected to excessively high stresses by the radiant heat from the workpiece. In that case the tube must be protected by suitable means. Such protection may be provided in that the tube is cooled or provided with a nozzle for shaping the plasma flame.
  • the nozzle must consist of electrically non-conducting material and must have an adequate resistance to the radiant heat. Every refractory ceramic composition may be used in practice for this purpose.
  • high-frequency generator of that plant was operated at a stabilized frequency of 13.56 megacycles per second and had a maximum power input of 1.25 kilowatts.
  • the workpiece consisted of a water-hardened plate havin dimensions of 100 x 60 x 14 millimeters and made from plain carbon steel containing 1.1% carbon. That plate was treated to form traces of metastable austenite in a width of 25 millimeters. These traces had in crosssection the shape of a segment of a circle with a depth of 0.3 millimeter. The microhardness of these traces was determined under a load of 100 grams and amounted to 950-1000 kilograms per square millimeter whereas the water-hardened surface had a microhardness of 800 kilograms per square millimeter. The traces were entirely uniform in cross-section throughout their length. The p'ate was moved past the torch at a distance of about 5 millimeters therefrom and at a feed rate of 160 millimeters per minute and the power supplied through the plasma flame to the plate amounted to 500 watts.
  • the workpiece consisted of a reinforcing bar having a cross-section of 8 x 2 millimeters and a length of 2000 millimeters and consisting of a heat-treated steel containing 06% carbon, 03% silicon, 0.6% Mn and 0.1% Cr.
  • the plate had a microhardness of 360 kilograms per square millimeter.
  • To harden an edge of the plate a portion of metastable austenite was produced. That portion had the shape of an isosceles triangle in cross-section. The legs of the triangle extending from the edge had a length of 0.5 millimeter.
  • a microhardness of 900950 kilograms per square millimeter was measured in the austenitic portion.
  • the treatment of that reinforcing bar was carried out at a feed rate of 810 millimeters per minute and with a useful power of 300 watts.
  • the workpieces consisted of various bandsaws for wood having cross-sections of 0.7 x 10 millimeters, 0.7 x 20 millimeters and 0.7 x 25 millimeters and a tooth depth of 2.02.6 millimeters.
  • these tooth tips were moved past the plasma torch at a distance of about 5 millimeters and at a feed rate of 810 millimeters per minute.
  • the useful power amounted to 150 watts.
  • the tooth tips of these saws had portions which were triangular in cross-section and consisted of metastable austenite.
  • the austenitic portions had a microhardness between 930 and 1000 kilograms per square millimeter.
  • the edge life of saws having tooth tips of metastable austenite was twice to four times the edge life of conventional saws.
  • a method of surface hardening hardenable steels which comprises the steps of passing a stream of ionizable gas through an alternating electromagnetic field produced by an electrode connected to the first output of a high frequency power source with a maximum power input between 1 and 5 kilowatts which is operable at a stabilized frequency between 10 and megacycles per second, by which means a cold electrically conducting plasma is produced, bringing successive adjoining elemental surface areas of a workpiece of hardenable ferrous alloy, which workpiece is electrically connected to the second output of said high frequency power source, into contact with said plasma thereby closing an electric circuit, controlling the rate at which energy is supplied to said surface areas by measuring the useful power applied to the workpiece and the power lost therefrom and adjusting both of these quantities to ensure the former is optimal and the latter minimal, whereby the surface areas of the workpiece are rapidly raised to a temperature between the upper transformation point and the melting point of said ferrous alloy by the recombination of opposite sign charge carriers of the plasma to form after rapid dissipation of heat by the
US00182420A 1970-09-21 1971-09-21 Two-stage process of surface-hardening workpieces of hardenable ferrous alloys Expired - Lifetime US3834947A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AT849970A AT315221B (de) 1970-09-21 1970-09-21 Verfahren zur zweistufigen Oberflächenhärtung von Werkstücken aus Eisen- und Stahllegierungen und Anordnung Durchführung des Verfahrens
AT1007371A AT322599B (de) 1970-09-21 1971-11-23 Verfahren zur zweistufigen oberflächenhärtung von werkstücken aus eisen- und stahllegierungen

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US (1) US3834947A (de)
AT (1) AT322599B (de)
BE (2) BE772883A (de)
CA (1) CA946482A (de)
CH (1) CH575468A5 (de)
DD (1) DD94831A5 (de)
DE (2) DE2111183B2 (de)
ES (3) ES395042A1 (de)
FI (1) FI52108C (de)
FR (2) FR2107739A5 (de)
GB (2) GB1347555A (de)
IT (1) IT939438B (de)
NL (1) NL7112313A (de)
NO (1) NO134492C (de)
SE (1) SE381474B (de)
ZA (1) ZA715382B (de)

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3944443A (en) * 1974-05-01 1976-03-16 Francis Lee Jones Ultra high temperature chemical reactions with metals
US4157923A (en) * 1976-09-13 1979-06-12 Ford Motor Company Surface alloying and heat treating processes
US5360495A (en) * 1989-07-25 1994-11-01 Albert Schuler Process for hardening cutting edges with an oval shaped plasma beam
US20070227010A1 (en) * 2006-03-29 2007-10-04 Andrew Zhuk Multi-blade razors and blades for same
US20070227008A1 (en) * 2006-03-29 2007-10-04 Andrew Zhuk Razors
US20070227009A1 (en) * 2006-03-29 2007-10-04 Andrew Zhuk Razor blades and razors
US20070234577A1 (en) * 2006-04-10 2007-10-11 William Masek Cutting members for shaving razors
US20070234576A1 (en) * 2006-04-10 2007-10-11 William Masek Cutting members for shaving razors
US20100011590A1 (en) * 2008-07-16 2010-01-21 Depuydt Joseph Allan Razors and razor cartridges
US20140190958A1 (en) * 2011-08-08 2014-07-10 Siemens Aktiengesellschaft Method for coating an insulation component and insulation component

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
ATA410976A (de) * 1976-06-04 1981-06-15 Siemens Ag Oesterreich Foerderrolle fuer durchlaufofen
GB2160227B (en) * 1984-05-04 1988-09-07 John Durham Hawkes Heat treatment process
FR2653137B1 (fr) * 1989-10-17 1993-06-11 Siderurgie Fse Inst Rech Procede de traitement de surface de produits siderurgiques par action d'un plasma.

Cited By (21)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3944443A (en) * 1974-05-01 1976-03-16 Francis Lee Jones Ultra high temperature chemical reactions with metals
US4157923A (en) * 1976-09-13 1979-06-12 Ford Motor Company Surface alloying and heat treating processes
US5360495A (en) * 1989-07-25 1994-11-01 Albert Schuler Process for hardening cutting edges with an oval shaped plasma beam
US7882640B2 (en) 2006-03-29 2011-02-08 The Gillette Company Razor blades and razors
US20070227010A1 (en) * 2006-03-29 2007-10-04 Andrew Zhuk Multi-blade razors and blades for same
US20070227009A1 (en) * 2006-03-29 2007-10-04 Andrew Zhuk Razor blades and razors
US9027443B2 (en) 2006-03-29 2015-05-12 The Gillette Company Method of making a razor
US20070227008A1 (en) * 2006-03-29 2007-10-04 Andrew Zhuk Razors
US7448135B2 (en) 2006-03-29 2008-11-11 The Gillette Company Multi-blade razors
US20110120973A1 (en) * 2006-03-29 2011-05-26 Andrew Zhuk Razor blades and razors
US8011104B2 (en) 2006-04-10 2011-09-06 The Gillette Company Cutting members for shaving razors
US20070234576A1 (en) * 2006-04-10 2007-10-11 William Masek Cutting members for shaving razors
US8347512B2 (en) 2006-04-10 2013-01-08 The Gillette Company Cutting members for shaving razors
US8499462B2 (en) 2006-04-10 2013-08-06 The Gillette Company Cutting members for shaving razors
US8640344B2 (en) 2006-04-10 2014-02-04 The Gillette Company Cutting members for shaving razors
US8752300B2 (en) 2006-04-10 2014-06-17 The Gillette Company Cutting members for shaving razors
US20070234577A1 (en) * 2006-04-10 2007-10-11 William Masek Cutting members for shaving razors
US9446443B2 (en) 2006-04-10 2016-09-20 The Gillette Company Cutting members for shaving razors
US20100011590A1 (en) * 2008-07-16 2010-01-21 Depuydt Joseph Allan Razors and razor cartridges
US9248579B2 (en) 2008-07-16 2016-02-02 The Gillette Company Razors and razor cartridges
US20140190958A1 (en) * 2011-08-08 2014-07-10 Siemens Aktiengesellschaft Method for coating an insulation component and insulation component

Also Published As

Publication number Publication date
SE381474B (sv) 1975-12-08
DE2249642C3 (de) 1979-06-28
DE2111183A1 (de) 1972-03-23
DD94831A5 (de) 1973-01-05
AT322599B (de) 1975-05-26
NO134492C (de) 1976-10-20
FR2160857B2 (de) 1977-01-14
BE791565R (fr) 1973-03-16
DE2111183C3 (de) 1978-11-30
IT939438B (it) 1973-02-10
CA946482A (en) 1974-04-30
FI52108B (de) 1977-02-28
GB1365180A (en) 1974-08-29
FR2107739A5 (de) 1972-05-05
ES399732A1 (es) 1975-06-16
DE2249642A1 (de) 1973-05-30
NO134492B (de) 1976-07-12
BE772883A (fr) 1972-01-17
FR2160857A2 (de) 1973-07-06
NL7112313A (de) 1972-03-23
ZA715382B (en) 1972-04-26
FI52108C (fi) 1977-06-10
GB1347555A (en) 1974-02-27
ES408284A2 (es) 1975-11-16
CH575468A5 (de) 1976-05-14
ES395042A1 (es) 1973-12-01
DE2249642B2 (de) 1978-10-26
DE2111183B2 (de) 1978-03-23

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