CA1210672A - Method for at least partial isothermal bainitizing of workpieces made of ferrous materials - Google Patents
Method for at least partial isothermal bainitizing of workpieces made of ferrous materialsInfo
- Publication number
- CA1210672A CA1210672A CA000416913A CA416913A CA1210672A CA 1210672 A CA1210672 A CA 1210672A CA 000416913 A CA000416913 A CA 000416913A CA 416913 A CA416913 A CA 416913A CA 1210672 A CA1210672 A CA 1210672A
- Authority
- CA
- Canada
- Prior art keywords
- temperature
- bath
- intermediate cooling
- workpieces
- 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.)
- Expired
Links
Classifications
-
- 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
- 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
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Mechanical Engineering (AREA)
- Physics & Mathematics (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Heat Treatment Of Articles (AREA)
- Heat Treatments In General, Especially Conveying And Cooling (AREA)
- Heat Treatment Of Strip Materials And Filament Materials (AREA)
- Heat Treatment Of Steel (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A method is suggested for at least partial isothermal bainitizing, the said method being particularly suitable for thick-walled workpieces made of ferrous materials. After austenitizing, the workpieces are cooled in an intermediate cooling bath and are then adjusted to the bainitizing tempera-ture, where they are left until the desired transition takes place.
A method is suggested for at least partial isothermal bainitizing, the said method being particularly suitable for thick-walled workpieces made of ferrous materials. After austenitizing, the workpieces are cooled in an intermediate cooling bath and are then adjusted to the bainitizing tempera-ture, where they are left until the desired transition takes place.
Description
6~Z
The present invention relates to a method for at least partial isothermal bainitizing of workpieces made of ferrous materials, and to the use thereof for workpieces which, because o-f their inadequate cooling velocity, would have fully pearlitic cross-sections.
~ Iitherto-known bainite heat-treatment methods depend upon a critical cooliny velocity arising from the temperature-gradient between the austenitizing and cooling bath and the diameter of the workpiece.
French Patent 76 21 520 discloses a method whereby the workpieces are carried past the pearlite peak by rapid cooling to a selected intermediate-stage temperature and thereafter past the intermediate-stage rang~ quasi isother-mally~ i.e. the transition must be complete before the martensite starting line is reached. The continuous cooling pattern gives a mi~ed structure of upper and lower bainite stage.
It is the purpose of the invention to propose a bainite heat-treatment method whereby, in the case of thick-walled workpieces, the cooling velocity is increased to such an extent that the pearlite transition can be at least partly avoided. Furthermore, specific properties of the wor~pieces in the upper and lower bainite stage can be adjusted separately by isothermal treatment methods.
According to the present invention, this purpose is achieved in that there is provided a method for at least partial isothermal bainitizing of workpieces made of ferrous materials, characterized in that, after austenitizing, the workpieces are quenched in an intermediate cooling bath and are held7 for a predetermined length of time, supercooled, in the austenitic condition, the transition to bainite occurring when the temperature is raised to, and held at, -- 1 -- ..
the transition temperature, so that supercooling of the austenite is assured, even in the interior of the workpiece, by the cooling accelerated by the low0r intermediate cooling-bath temperature.
Additional advantayeous features will be evident frorn the description hereinafter.
The invention will be better understood by an examination of the following description, together with the accompanying drawings, in which Figs- 1, 2 and 3 illustrate cooling curves obtained with workpieces having differing wall thicknesses as discussed below.
If a thin-walled workpiece is immersed in a bainitizi~g bath, the outer layer is rapidly cooled to the temperature of the bath. Because of ~he short distance the heat must travel to the surface, and because of the ~avour-able ratio between the cooling surface and the total mass of the workpiece, the core will also rapidly reach the bainitizing temperature (Fig. 1).
Both of the cooiing curves shown in Fig. 1 remain in the austenitizing range until the temperature of the bath is reached. After the transition, therefore, bainite is obtained over the entire cross-section~ In the said figure, cooling curve 1 represents the cooling of the core, while cooling curve 2 represents that of the outer layerO
Conditions ar~ different in the case of workpieces in which, because of the wall-thickness ratios, cooling passes through the pearlite pea~- In this case, because of the larger volume of heat, the outer layer and the core cool so slcwly that a pearlite structure is obtained instead of bainite ~Fig. 2).
Because of the small amount of heat dissipated, :;~2~67~
the core will cool considerably more slowly than in thin-walled pieces, and the cooling curve therefore passes through the pearlite range.
It is now proposed to immerse thick-walled work-pieces into an intermediate cooling bath be~ore they are adjusted to the hainitizing temperature, the temperature of the said bath being below the temperature at which the desired bainite structure forms (Fig. 3). The workpiece is therefore, as it were, supercooled.
The temperature of the intermediate cooling bath is adapted to the critical wall-thickness of the workpiece.
The workpiece is cooled so rapidly in this bath that it passes through the pearlite peak and is thereafter trans~erred for transition of the structure at the bainiti-zing temperature.
This method makes it possible to control the cooling velocity in such a manner that even greater wall-thicknesses do not pass through a pearlite transition, at least in the edge areas.
After the transition, therefore, the desired bainitic structure, with its known ad~antageous mechanical properties, is obtained at least partly o~er the cross-section of the workpiece.
The present invention relates to a method for at least partial isothermal bainitizing of workpieces made of ferrous materials, and to the use thereof for workpieces which, because o-f their inadequate cooling velocity, would have fully pearlitic cross-sections.
~ Iitherto-known bainite heat-treatment methods depend upon a critical cooliny velocity arising from the temperature-gradient between the austenitizing and cooling bath and the diameter of the workpiece.
French Patent 76 21 520 discloses a method whereby the workpieces are carried past the pearlite peak by rapid cooling to a selected intermediate-stage temperature and thereafter past the intermediate-stage rang~ quasi isother-mally~ i.e. the transition must be complete before the martensite starting line is reached. The continuous cooling pattern gives a mi~ed structure of upper and lower bainite stage.
It is the purpose of the invention to propose a bainite heat-treatment method whereby, in the case of thick-walled workpieces, the cooling velocity is increased to such an extent that the pearlite transition can be at least partly avoided. Furthermore, specific properties of the wor~pieces in the upper and lower bainite stage can be adjusted separately by isothermal treatment methods.
According to the present invention, this purpose is achieved in that there is provided a method for at least partial isothermal bainitizing of workpieces made of ferrous materials, characterized in that, after austenitizing, the workpieces are quenched in an intermediate cooling bath and are held7 for a predetermined length of time, supercooled, in the austenitic condition, the transition to bainite occurring when the temperature is raised to, and held at, -- 1 -- ..
the transition temperature, so that supercooling of the austenite is assured, even in the interior of the workpiece, by the cooling accelerated by the low0r intermediate cooling-bath temperature.
Additional advantayeous features will be evident frorn the description hereinafter.
The invention will be better understood by an examination of the following description, together with the accompanying drawings, in which Figs- 1, 2 and 3 illustrate cooling curves obtained with workpieces having differing wall thicknesses as discussed below.
If a thin-walled workpiece is immersed in a bainitizi~g bath, the outer layer is rapidly cooled to the temperature of the bath. Because of ~he short distance the heat must travel to the surface, and because of the ~avour-able ratio between the cooling surface and the total mass of the workpiece, the core will also rapidly reach the bainitizing temperature (Fig. 1).
Both of the cooiing curves shown in Fig. 1 remain in the austenitizing range until the temperature of the bath is reached. After the transition, therefore, bainite is obtained over the entire cross-section~ In the said figure, cooling curve 1 represents the cooling of the core, while cooling curve 2 represents that of the outer layerO
Conditions ar~ different in the case of workpieces in which, because of the wall-thickness ratios, cooling passes through the pearlite pea~- In this case, because of the larger volume of heat, the outer layer and the core cool so slcwly that a pearlite structure is obtained instead of bainite ~Fig. 2).
Because of the small amount of heat dissipated, :;~2~67~
the core will cool considerably more slowly than in thin-walled pieces, and the cooling curve therefore passes through the pearlite range.
It is now proposed to immerse thick-walled work-pieces into an intermediate cooling bath be~ore they are adjusted to the hainitizing temperature, the temperature of the said bath being below the temperature at which the desired bainite structure forms (Fig. 3). The workpiece is therefore, as it were, supercooled.
The temperature of the intermediate cooling bath is adapted to the critical wall-thickness of the workpiece.
The workpiece is cooled so rapidly in this bath that it passes through the pearlite peak and is thereafter trans~erred for transition of the structure at the bainiti-zing temperature.
This method makes it possible to control the cooling velocity in such a manner that even greater wall-thicknesses do not pass through a pearlite transition, at least in the edge areas.
After the transition, therefore, the desired bainitic structure, with its known ad~antageous mechanical properties, is obtained at least partly o~er the cross-section of the workpiece.
Claims (9)
1. A method for at least partial isothermal bainitizing of workpieces made of ferrous materials, characterized in that, after austenitizing, the workpieces are quenched in an intermediate cooling bath and are held, for a predetermined length of time, supercooled, in the austenitic condition, the transition to bainite occurring when the temperature is raised to, and held at, the transition temperature, so that supercooling of the austenite is assured, even in the interior of the workpiece, by the cooling accelerated by the lower intermediate cooling-bath temperature.
2. A method according to claim 1, characterized in that the workpiece is held in the intermediate cooling bath until temperature equalization is attained.
3. A method according to claim 1, characterized in that in the case of thick-walled workpieces, having a corresponding thermal capacity, the temperature of the intermediate cooling bath is below the martensite starting line in the time-temperature transformation (TTT) diagram, with no martensite occurring during the predetermined holding period.
4. A method according to claim 1, characterized in that the bainitizing temperature is equal to, or higher than, that of the intermediate cooling bath.
5. A method according to claim 1 or 2, characterized in that vaporizing cooling media, e.g. oil, low-melting metals, are used for intermediate cooling.
6. A method according to claim 1 or 2, characterized in that non-vaporizing cooling media, e.g. air, salts, high-melting metals, are used for intermediate cooling.
7. A method according to claim 1, characterized in that the bainite transition is carried out in air.
8. A method according to claim 1, characterized in that the bainite transition is carried out in a bath, e.g. a bath of oil, salt or metal.
9. Use of the method according to one of claims 1 to 3, for workpieces which, with no intermediate cooling, form a pearlitic structure.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CH7726/81A CH648350A5 (en) | 1981-12-03 | 1981-12-03 | METHOD FOR isothermal austempering OF workpieces made of ferrous materials. |
| CH7726/81-5 | 1981-12-03 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1210672A true CA1210672A (en) | 1986-09-02 |
Family
ID=4329552
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000416913A Expired CA1210672A (en) | 1981-12-03 | 1982-12-02 | Method for at least partial isothermal bainitizing of workpieces made of ferrous materials |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0095470A1 (en) |
| BR (1) | BR8208004A (en) |
| CA (1) | CA1210672A (en) |
| CH (1) | CH648350A5 (en) |
| IT (1) | IT1153659B (en) |
| WO (1) | WO1983001959A1 (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2590508B1 (en) * | 1985-11-27 | 1988-06-24 | Pont A Mousson | PROCESS FOR OBTAINING CAST IRON MEMBERS WITH SPHEROIDAL GRAPHITE AND CAST IRON OBTAINED BY THIS PROCESS |
| IT1216347B (en) * | 1986-11-20 | 1990-02-22 | Necchi Spa | PROCEDURE FOR OBTAINING BAINITE SPHEROIDAL CAST IRON |
| FR2697535B1 (en) * | 1992-11-02 | 1995-01-13 | Schissler Jean Marie | Improved process for heat treatment of ferrous or non-ferrous alloys, and its application to the production of bainitic cast iron. |
| DE4313569C1 (en) * | 1993-04-26 | 1994-05-26 | Daimler Benz Ag | Heat treatment of spheroidal graphite cast iron - to improve mechanical properties. |
| SE510344C2 (en) * | 1997-08-01 | 1999-05-17 | Ovako Steel Ab | Way for complete bainite hardening of steel |
| DE102006059050A1 (en) * | 2006-12-14 | 2008-06-19 | Schaeffler Kg | Process for the heat treatment of rolling bearing components made of through hardened, bainitic bearing steel |
| CN104294014B (en) * | 2013-07-18 | 2016-12-28 | 首都航天机械公司 | The bainite isothermal heat treatment method of middle carbon silicomanganese chromium nickel series low-alloy steel |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB601588A (en) * | 1943-07-06 | 1948-05-10 | Charles Greiner Purnell | Improvements in and relating to heat treatment of hardenable steel |
| US2258566A (en) * | 1940-07-30 | 1941-10-07 | American Steel & Wire Co | Hardenable steel heat treatment |
| DE872956C (en) * | 1943-08-28 | 1953-04-09 | Deutsche Edelstahlwerke Ag | Intermediate quenching of unalloyed and alloyed steels |
| DE2054416C3 (en) * | 1970-11-05 | 1974-09-05 | Gesellschaft Zur Foerderung Der Eisenhuettentechnik Mbh, 4000 Duesseldorf | Process for the heat treatment of quenched and tempered steels |
| US3860457A (en) * | 1972-07-12 | 1975-01-14 | Kymin Oy Kymmene Ab | A ductile iron and method of making it |
| US3784416A (en) * | 1972-09-29 | 1974-01-08 | Canron Ltd | Manufacture of white cast iron |
| FR2358465A1 (en) * | 1976-07-13 | 1978-02-10 | Bochumer Eisen Heintzmann | Bainitic steel support sections with predetermined strength - esp. for supporting subterranean galleries |
| DE2853870A1 (en) * | 1978-12-13 | 1980-07-03 | Schmidt Gmbh Karl | BALL GRAPHITE CAST IRON WITH AUSTENITIC-BAINITIC MIXED TEXTURE |
-
1981
- 1981-12-03 CH CH7726/81A patent/CH648350A5/en not_active IP Right Cessation
-
1982
- 1982-11-23 IT IT24385/82A patent/IT1153659B/en active
- 1982-12-02 EP EP82903445A patent/EP0095470A1/en not_active Withdrawn
- 1982-12-02 CA CA000416913A patent/CA1210672A/en not_active Expired
- 1982-12-02 WO PCT/CH1982/000126 patent/WO1983001959A1/en not_active Application Discontinuation
- 1982-12-02 BR BR8208004A patent/BR8208004A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| IT8224385A1 (en) | 1984-05-23 |
| IT1153659B (en) | 1987-01-14 |
| IT8224385A0 (en) | 1982-11-23 |
| EP0095470A1 (en) | 1983-12-07 |
| CH648350A5 (en) | 1985-03-15 |
| BR8208004A (en) | 1983-10-18 |
| WO1983001959A1 (en) | 1983-06-09 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |