EP0281249A1 - Procédé de traitement thermique de produits ferreux - Google Patents

Procédé de traitement thermique de produits ferreux Download PDF

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Publication number
EP0281249A1
EP0281249A1 EP88300891A EP88300891A EP0281249A1 EP 0281249 A1 EP0281249 A1 EP 0281249A1 EP 88300891 A EP88300891 A EP 88300891A EP 88300891 A EP88300891 A EP 88300891A EP 0281249 A1 EP0281249 A1 EP 0281249A1
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EP
European Patent Office
Prior art keywords
castings
furnace
temperature
austempering
cooling
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Application number
EP88300891A
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German (de)
English (en)
Inventor
William H. Moore
Ari Lehtonen
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Individual
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Individual
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Publication date
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Publication of EP0281249A1 publication Critical patent/EP0281249A1/fr
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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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
    • C21D1/20—Isothermal quenching, e.g. bainitic hardening
    • 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
    • C21D5/00—Heat treatments of cast-iron
    • 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor

Definitions

  • This invention relates to methods of heat treating cast iron or steel. More particularly, it relates to an improved method of treatment to produce a bainite structure and improved mechanical and physical characteristics.
  • cast iron or steel may be cooled from an elevated temperature where it is austenitic in structure, at such a rate that normal formation of pearlite is suppressed and austenite and martensite occur instead.
  • the austenite and martensite are stable at lower temperatures, such as room temperature.
  • a structure of bainite is formed instead. This bainite may contain varying quantities of pearlite, austenite or martensite, depending on the exact cooling conditions that prevail and the exact composition of the cast iron or steel.
  • austempering This process of producing bainite by heat treatment is known as austempering.
  • Conventional procedures involve heating the cast iron or steel to a temperature in excess of 1300 degrees F so that it becomes austenitic in structure. This temperature is known as the austenitizing temperature.
  • this austenizing temperature is held to a maximum value of 1900 degrees F and the period of time is usually 1 hour plus 30 minutes for every one inch of casting section. This time period is also somewhat dependent on the total mass of casting shapes in the furnace load and on the heat input into the furnace.
  • the cast iron or steel is then cooled rapidly to the holding temperature called the austempering temperature usually between 400 degrees F and 800 degrees F. After holding at this temperature for 1 to 4 hours, depending on mass section and composition, the cast iron or steel is then cooled to room temperature.
  • Austempering is usually conducted in a bath of hot salt or hot oil or any liquid medium that can be maintained at the austempering temperature. Shapes in cast iron or steel are transferred from a furnace at austenizing temperature and are quenched in the austempering bath. Such treatment involves two furnace systems as well as the handling of hot shapes, such as forgings or castings, in cast iron or steel. Further, after cooling to room temperature, the castings or forgings have to be washed or cleaned to remove all residual salts or traces of the quenching medium used. Because salt baths are quite expensive there is usually a limit to the size of the castings or shapes that can be austempered in the conventional manner.
  • Our invention is based on the discovery that fine jets or water or a gaseous medium like liquid nitrogen or carbon dioxide gas can be applied directly to castings or forgings while in position in the furnace so that the castings or forgings may be cooled and the furnace itself may be cooled down to the austempering temperature. This avoids the necessity of transferring the castings or forgings to a second furnace for austempering.
  • one object of our invention is to reduce the cost of the austempering process.
  • a further object is to provide a means of using only one furnace for the complete austempering process.
  • a further object is to economically allow the austempering of large castings or forgings.
  • the furnace is raised above the castings or is tilted back in order to expose the castings. This makes it easier to cool the furnace and to cool the castings. As soon as both the furnace and the castings have reached the required austempering temperature, the furnace is lowered or tilted back over the castings and the temperature of the furnace is then maintained for the desired length of time at the austempering temperature.
  • the whole process of austempering may in this manner be conducted without the necessity of moving the castings or of having a second furnace.
  • Figure 1 is a diagrammatic illustration of the preferred method of the invention.
  • Position (a) shows a furnace containing a casting on the furnace bottom plate and with the furnace in the austenitizing mode.
  • Position (b) shows the furnace tilted back for cooling and the quenching mode.
  • Position (c) shows the furnace back in position over the casting and the casting in the austempering mode.
  • Figure 2 shows a typical temperature time cooling curve when a given casting, in this case a 3 ⁇ diameter bar, is quenched in a salt bath and is subsequently held in this bath to produce bainite. Shown also is a curve indicating the cooling rate obtained when water is applied to the casting in a furnace and the casting as well as the furnace are cooled by air circulation to the austempering temperature. We have found that manipulation of the amount of water used as well as the amount of air circulated will allow the cooling rate in the casting to be varied over a relatively wide range of cooling rates.
  • the curve A represents the cooling rate obtained in a salt bath where the line CC is the austenitizing temperature and line DD is the austempering temperature.
  • the austempering temperature is reached in a 10 minute time period. F and at this time the furnace was tilted back to cover the castings after cutting off air and water circulation.
  • the furnace was maintained at a temperature of 620 degrees F for a period of 2 hours and the casting load was then removed from the furnace.
  • the temperatures, velocities and amounts of the fluids applied to the mass of the castings will determine the rate of cooling in a manner known to or easily determinable by those skilled in the art. That rate must suffice to cool the castings within a ten to twenty minute period in order to avoid the formation of pearlite and thereby to obtain the desired bainitic structure. While the rate of cooling required to suppress pearlite will vary according to the composition of the ferrous metal involved and may be exactly determined by means of a time-temperature-transformation diagram for the particular metal involved, the time required for cooling normally will be less than 20 minutes.
  • Curve B represents the cooling rate when air was circulated in the furnace while water was applied to the casting. In this case the austempering temperature was reached in a 12 minute time period.
  • Figure 3 shows the bainite structure resulting from a nodular iron bar cooled by water treatment at the rate indicated in Figure 2.
  • a load of castings consisting of twelve bars ranging in diameter from 2 ⁇ to 4 ⁇ and about 24 ⁇ in length were placed in a furnace 3′ ⁇ 4′ and 4′ high.
  • the furnace was lined with fibre refractory and was pivoted at its back end so it could be tilted back from the castings placed on a fixed floor.
  • the furnace had as a heat source a series of propane-air burners.
  • the furnace load was headed to 1650 degrees F and was held at this temperature for 2 hours when the propane was shut off and the furnace was tilted back to expose the casting load.
  • the air was circulated from the burners while the furnace was tilted back and an additional fan was used to blow air on the furnace to cool it down to 620 degrees F.
  • a fan was used to blow air directly on the casting and water was introduced by pressure jet so as to impinge directly on the casting load.
  • a thermocouple placed strategically in the casting load was used to indicate when this load had reached an approximate temperature of 600 degrees
EP88300891A 1987-03-06 1988-02-03 Procédé de traitement thermique de produits ferreux Withdrawn EP0281249A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US2272087A 1987-03-06 1987-03-06
US22720 1987-03-06

Publications (1)

Publication Number Publication Date
EP0281249A1 true EP0281249A1 (fr) 1988-09-07

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ID=21811087

Family Applications (1)

Application Number Title Priority Date Filing Date
EP88300891A Withdrawn EP0281249A1 (fr) 1987-03-06 1988-02-03 Procédé de traitement thermique de produits ferreux

Country Status (5)

Country Link
EP (1) EP0281249A1 (fr)
JP (1) JPS63317620A (fr)
CN (1) CN88101145A (fr)
DK (1) DK68788A (fr)
FI (1) FI880858A (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2697535A1 (fr) * 1992-11-02 1994-05-06 Schissler Jean Marie Procédé amélioré de traitement thermique d'alliages ferreux ou non-ferreux, et son application à l'élaboration de fonte bainitique.
AU707536B2 (en) * 1996-02-16 1999-07-15 Australian Wool Research & Promotion Organisation Improvements in shearing combs and cutters

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111041164B (zh) * 2019-12-25 2022-01-25 浙江金固股份有限公司 辊型模具的热处理修复方法

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE848203C (de) * 1949-10-04 1952-09-01 Walter Sellerbeck Ofen fuer zu erwaermende und regelbar beschleunigt abzukuehlende Werkstuecke
DE863070C (de) * 1951-04-22 1953-01-15 Ofu Ofenbau Union G M B H Verfahren und Vorrichtung zum Abschrecken von Stahlgegenstaenden mittels gasfoermiger Medien
DE1228643B (de) * 1965-05-19 1966-11-17 Ofag Ofenbau Ges M B H Verfahren und Ofenanlage zur Waermebehandlung von zylindrischen Koerpern aus Gusseisenwerkstoffen nach bestimmten Zeittemperaturkurven
DE1433715A1 (de) * 1964-01-17 1968-12-12 Breitenbach Gmbh Ed Verfahren zur Waermebehandlung von schweren Werkstuecken aus Schmiede- oder Gussstahl
FR2379607A1 (fr) * 1977-02-03 1978-09-01 Vide & Traitement Sa Procede pour le traitement thermique de metaux
EP0087634A1 (fr) * 1982-03-01 1983-09-07 Pont-A-Mousson S.A. Tube centrifugé en fonte à graphite sphéroidal et son procédé de fabrication
DD219268A1 (de) * 1983-11-18 1985-02-27 Beimler Lokomotivbau Einrichtung zum spruehabschrecken im muffelofen

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE848203C (de) * 1949-10-04 1952-09-01 Walter Sellerbeck Ofen fuer zu erwaermende und regelbar beschleunigt abzukuehlende Werkstuecke
DE863070C (de) * 1951-04-22 1953-01-15 Ofu Ofenbau Union G M B H Verfahren und Vorrichtung zum Abschrecken von Stahlgegenstaenden mittels gasfoermiger Medien
DE1433715A1 (de) * 1964-01-17 1968-12-12 Breitenbach Gmbh Ed Verfahren zur Waermebehandlung von schweren Werkstuecken aus Schmiede- oder Gussstahl
DE1228643B (de) * 1965-05-19 1966-11-17 Ofag Ofenbau Ges M B H Verfahren und Ofenanlage zur Waermebehandlung von zylindrischen Koerpern aus Gusseisenwerkstoffen nach bestimmten Zeittemperaturkurven
FR2379607A1 (fr) * 1977-02-03 1978-09-01 Vide & Traitement Sa Procede pour le traitement thermique de metaux
EP0087634A1 (fr) * 1982-03-01 1983-09-07 Pont-A-Mousson S.A. Tube centrifugé en fonte à graphite sphéroidal et son procédé de fabrication
DD219268A1 (de) * 1983-11-18 1985-02-27 Beimler Lokomotivbau Einrichtung zum spruehabschrecken im muffelofen

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
H[RTEREI-TECHNISCHE MITTEILUNGEN, vol. 41, no. 1, January-February 1986, pages 28-32, Munich; P. LISTEMANN "Gestuftes Abk}hlen zum H{rten und isothermes Umwandeln im Bainitbereich zur verzugsarmen W{rmebehandlung in Vakuumanlagen" *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2697535A1 (fr) * 1992-11-02 1994-05-06 Schissler Jean Marie Procédé amélioré de traitement thermique d'alliages ferreux ou non-ferreux, et son application à l'élaboration de fonte bainitique.
AU707536B2 (en) * 1996-02-16 1999-07-15 Australian Wool Research & Promotion Organisation Improvements in shearing combs and cutters

Also Published As

Publication number Publication date
FI880858A0 (fi) 1988-02-24
JPS63317620A (ja) 1988-12-26
DK68788D0 (da) 1988-02-10
CN88101145A (zh) 1988-09-14
FI880858A (fi) 1988-09-07
DK68788A (da) 1988-09-07

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