US3826694A - Thermal treatment of steel - Google Patents

Thermal treatment of steel Download PDF

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Publication number
US3826694A
US3826694A US00254454A US25445472A US3826694A US 3826694 A US3826694 A US 3826694A US 00254454 A US00254454 A US 00254454A US 25445472 A US25445472 A US 25445472A US 3826694 A US3826694 A US 3826694A
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Prior art keywords
temperature
steel
pearlite
carbide
carbides
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Expired - Lifetime
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US00254454A
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English (en)
Inventor
J Woodilla
G Hunt
W Green
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Timken US LLC
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Torrington Co
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Publication date
Application filed by Torrington Co filed Critical Torrington Co
Priority to US00254454A priority Critical patent/US3826694A/en
Priority to CA168,665A priority patent/CA994656A/en
Priority to AU54589/73A priority patent/AU477404B2/en
Priority to GB5210375A priority patent/GB1439072A/en
Priority to GB2306473A priority patent/GB1439071A/en
Priority to BR3565/73A priority patent/BR7303565D0/pt
Priority to DE19732324750 priority patent/DE2324750B2/de
Priority to JP5480473A priority patent/JPS568889B2/ja
Priority to US468497A priority patent/US3895972A/en
Priority to US468495A priority patent/US3922181A/en
Application granted granted Critical
Publication of US3826694A publication Critical patent/US3826694A/en
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    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
    • 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
    • C21D1/78—Combined heat-treatments not provided for above

Definitions

  • the process includes high temperature solid solution of the carbide phase present in the material, controlled cooling through a selected area of the time-temperature-transformation for the material to form pearlite, (a ferrite and carbide lamellar structure) and cementite reheating to austenitize the material, and finally, quenching to produce a structure with an ultrafine grain and a natural dispersion of very small excess carbides that results in an improvement of fatigue life and an increase in compressive yield strength.
  • the present invention relates to a method of treating steel to improve mechanical properties. More particularly the invention is a heat treatment for hypereutectoid steel which develops a structure with an ultra-fine grain and a natural dispersion of predominantly very small excess carbides.
  • FIG. 1a and b are photomicrographs showing pearlite and spheroidized carbides, respectively, in AISI 52100 steel;
  • FIG. 2 is the iron-carbon equilibrium diagram
  • FIG. 3 is the time-temperature-transformation curve for alloy AISI 52100 steel
  • FIG. 4 is another photomicrograph showing conventionally hardened AISI 52100 steel
  • FIG. 5 is a photomicrograph showing the' same steel heat treated according to our invention.
  • FIG. 6 is a photomicrograph showing two microcracks in AISI 52100 steel.
  • FIG. 7 is a time-temperature profile comparing our method with other heat treating cycles.
  • Carbides in low alloy compositions of steel can form platelets or spheroids as shown in FIGS. 1a and b, respectively.
  • One of these structures is the usual starting condition for the heat treatments to be described.
  • the well-known iron-carbon equilibrium diagram, FIG. 2 shows that when a hypereutectoidl composition is heated and allowed to reach equilibrium at an elevated temperature, it will undergo transformations in phase from pearlite and cementite to austenite and cementite, then to anstenite, a solid solution of carbon in gamma iron. Cooling slowly enough to establish equilibrium at any particular temperature will restore the phase normal to that temperature.
  • time-temperature-transformation curves (commonly called S curves) shown in FIG. 3 vary with different composition. Those illustrated are typical for a steel designated as AISI 52100, a low alloy steel having the composition shown in TABLE 1. They show that transformation at 700 F. begins and is completed sooner if the metal is conventionally austenitized at 1550 F. (the broken curves in FIG. 3) than at 1950 F. (the solid pair of curves).
  • AISI 52100 a low alloy steel having the composition shown in TABLE 1. They show that transformation at 700 F. begins and is completed sooner if the metal is conventionally austenitized at 1550 F. (the broken curves in FIG. 3) than at 1950 F. (the solid pair of curves).
  • Path X in FIGS 3 and 7, and taught by Pat. No. 3,337,376, the carbon is retained in the structure and does not form a carbide. Instead a needle-like structure, called martensite, is formed.
  • the pearlite transformation range For a better understanding of the pearlite transformation range, it is helpful to refer to the iron-carbon equilibrium diagram, FIG. 2, where it can be seen that pearlite is not stable above 1333 F. (the A line), and therefore, will not form above this temperature. Further, the S curve shows that the time for pearlite transformation becomes unattractively long as the upper temperature limit is approached.
  • the lower temperature limit of the pearlite forming range is more difiicult to define since pearlite and bainite coexist over a range of temperatures. This range of coexistence is dependent on the amount of carbon in solution, the temperature range rising as the carbon in solution increases.
  • theamount of carbon in solution is directly dependent on the completeness of the high temperature solid solution process.
  • the carbon content varies throughout the case and this gradient of composition correspondingly varies the range of coexistence of pearlite and bainite as one proceeds into the core region of the workpiece.
  • the pearlite lamellae that coexist with the bainite are very closely spaced, whereas the bainite, known as upper bainite when formed in this temperature range, is coarse.
  • the fine pearlite produces very small excess carbide particles, while the coarse bainite transforms during this heat treatment to large coarse particles (however, still smaller than the conventional spheroidized particles).
  • the presence of upper bainite in the microstructure prior to the final heat treatment is undesirable.
  • the lower temperature limit of the pearlite forming range can be defined as that temperature immediately below which upper bainite will form. This observation for upper bainite can be made only with an electron microscope. Since the spacing between the carbide lamellae decreases as the transformation temperature decreases, the optimum temperature for producing pearlite is near the low temperature limit. In this way, the thin carbide lamellae in the pearlite ultimately produce the finest excess carbide particles.
  • the remaining steps in the process are an austenitizing treatment and subsequent quench which produce a microstructure as depicted in FIG. 5, a natural dispersal of very small excess carbides in an ultrafine grained matrix.
  • This austenitizing treatment may be performed directly after producing the pearlite, that is, reheating from the pearlite forming temperature; or, if the part is cooled to room temperature after producing pearlite, any time thereafter.
  • the heating rate for the final ausenitizing treatment is important, since there is a critical temperature range through which the parts must be heated rapidly. Failure to pass through this temperature range with rapidity will cause the pearlite lamellae to break up into excess carbides which will then grow in size, since the carbide phase is stable in this temperaure range.
  • the critical temperature range of any hypereutectoid steel lies between the A and A boundaries of its equilibrium diagram. For a one percent carbon alloy such as AISI 52100 these boundaries are approximately 1333 F. and 1440 F., respectively. The upper limit will be higher if the part has a carburized case with more than one percent carbon content.
  • the critical temperature range has been shaded in FIG. 2 and our hardening heat treating cycle is depicted by path Z'in FIG. 7.
  • This rapid temperature transition may be accomplished in several ways.
  • One isby the use of a two-step heat treatment with a salt or lead bath, where the first bath is a preheat to just below the A and the second is the final desired temperature.
  • Other acceptable methods include induction heating and resistance heating.
  • FIGS. 4 and 5 are photomicrographs illustrating the microstructures produced by conventional, heat treating andby the new method of heat treating, respectively.
  • the material in both cases is AISI 52100.
  • Rolling contact fatigue life testing has shown a 250% o 300% improvement in B life when material with the new microstructure, FIG. 5, is used.
  • the compressive yield strength was increased about 30 to 35 percent.
  • One of the primary features of this process which contributes to the extended fatigue life is the ultra-fine grain size.
  • a substantial increase in the number of grains within a given volume of metal is believed to be a primary strengthening mechanism and an important contributor to the improved fatigue life of a material.
  • grain boundaries are preferred sites for the nucleation of phase transformations, and with ultra-fine grained material, an enormous increase in the number of preferred sites results.
  • An undesirable transformation may occur during the quench from the final austenitizing temperature. This is the formation of an aggregate of ferrite plus carbide known as slow quench product which precipitates at the boundaries of the ultra-fine grained material, thereby weakening this important strengthening agent.
  • alloying elements such as manganese and silicon, which increase the hardenability of steel, suppress the formation of the undesirable slow quench products.”
  • the ultra-fine grain size reduces the effectiveness of these alloying elements.
  • Modified AISI 52100 (ASTM A485, grade No. 2) containing 1.40% to 1.70% manganese and 0.50% to 0.80% silicon, which is normally used when greater hardenability is required, has shown slow quench product formation at the center of a cross section of only A of an inch when observed with an electron microscope.
  • Another modification to our process provides for the insertion of an additional step involving cold work and plastic deformation after the formation of pearlite.
  • this may involve drawing a wire through a series of dies to produce a wire of smaller cross section.
  • This wire would have been given the high temperature carbide solution heat treatment and the quench to the pearlite-forming temperature.
  • the rapid austenitizing heat treatment is then performed, by which the ultra-fine grained material with refined carbides is produced.
  • other means of mechanical deformation which may be introduced include swaging, cold-rolling, and shaping and forming operations which must be performed before the final rapid austenitizing heat treatment, while the part is still in the unhardened condition.
  • compositions of steel have been successfully heat treated according to our process, the method is not limited to these alone. Many hypereutectoid steels having less than 10% total alloy content will respond to this method.
  • a method for producing hardened hypereutectoid steels of less than about 10% total alloy resulting in a structure with an ultra-fine grain size free from microcracks, and very small well dispersed excess carbides comprising the steps of:

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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)
  • Manufacturing & Machinery (AREA)
  • Heat Treatment Of Steel (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)
US00254454A 1972-05-18 1972-05-18 Thermal treatment of steel Expired - Lifetime US3826694A (en)

Priority Applications (10)

Application Number Priority Date Filing Date Title
US00254454A US3826694A (en) 1972-05-18 1972-05-18 Thermal treatment of steel
CA168,665A CA994656A (en) 1972-05-18 1973-04-11 Thermal treatment of steel
AU54589/73A AU477404B2 (en) 1972-05-18 1973-04-17 Process for hardening hypereutectoid steels and hypereutectoid carburised cases
GB2306473A GB1439071A (en) 1972-05-18 1973-05-15 Thermal treatment of steel
GB5210375A GB1439072A (en) 1972-05-18 1973-05-15 Thermal treatment of steel
BR3565/73A BR7303565D0 (pt) 1972-05-18 1973-05-16 Processo para produzir acos hipereutectoides temperados,lga e processo para produzir um estojo
DE19732324750 DE2324750B2 (de) 1972-05-18 1973-05-16 Waermebehandlungsverfahren fuer stahl
JP5480473A JPS568889B2 (pt) 1972-05-18 1973-05-18
US468497A US3895972A (en) 1972-05-18 1974-05-09 Thermal treatment of steel
US468495A US3922181A (en) 1972-05-18 1974-05-09 Thermal treatment of steel

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US00254454A US3826694A (en) 1972-05-18 1972-05-18 Thermal treatment of steel

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US3826694A true US3826694A (en) 1974-07-30

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US (1) US3826694A (pt)
JP (1) JPS568889B2 (pt)
BR (1) BR7303565D0 (pt)
CA (1) CA994656A (pt)
DE (1) DE2324750B2 (pt)
GB (2) GB1439072A (pt)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4021272A (en) * 1974-04-19 1977-05-03 Hitachi Metals, Ltd. Method of isothermal annealing of band steels for tools and razor blades
US10894992B2 (en) 2018-01-25 2021-01-19 Toyota Jidosha Kabushiki Kaisha Method for producing steel member

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS57137790U (pt) * 1981-02-23 1982-08-28
NO854396L (no) * 1985-11-05 1987-05-06 Kverneland As Fremgangsmaate ved herding av staal.
JP3646467B2 (ja) * 1996-07-31 2005-05-11 日本精工株式会社 転がり軸受
FR2761699B1 (fr) * 1997-04-04 1999-05-14 Ascometal Sa Acier et procede pour la fabrication d'une piece pour roulement
DE19849679C1 (de) 1998-10-28 2000-01-05 Skf Gmbh Verfahren zur Wärmebehandlung von Werkstücken aus Stahl

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4021272A (en) * 1974-04-19 1977-05-03 Hitachi Metals, Ltd. Method of isothermal annealing of band steels for tools and razor blades
US10894992B2 (en) 2018-01-25 2021-01-19 Toyota Jidosha Kabushiki Kaisha Method for producing steel member

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Publication number Publication date
CA994656A (en) 1976-08-10
GB1439071A (en) 1976-06-09
GB1439072A (en) 1976-06-09
DE2324750B2 (de) 1976-05-20
BR7303565D0 (pt) 1974-06-27
DE2324750A1 (de) 1973-11-29
JPS4966524A (pt) 1974-06-27
JPS568889B2 (pt) 1981-02-26
AU5458973A (en) 1974-10-17

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