CA1296603C - Process for rapid quenching in a fluidized bed - Google Patents
Process for rapid quenching in a fluidized bedInfo
- Publication number
- CA1296603C CA1296603C CA000542520A CA542520A CA1296603C CA 1296603 C CA1296603 C CA 1296603C CA 000542520 A CA000542520 A CA 000542520A CA 542520 A CA542520 A CA 542520A CA 1296603 C CA1296603 C CA 1296603C
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- Canada
- Prior art keywords
- bed
- temperature
- article
- conductivity gas
- high conductivity
- Prior art date
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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
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
- C21D9/54—Furnaces for treating strips or wire
- C21D9/56—Continuous furnaces for strip or wire
- C21D9/573—Continuous furnaces for strip or wire with cooling
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
-
- 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
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/34—Methods of heating
- C21D1/53—Heating in fluidised beds
-
- 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
- C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Heat Treatment Of Articles (AREA)
- Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
- Crucibles And Fluidized-Bed Furnaces (AREA)
Abstract
PROCESS FOR RAPID QUENCHING IN A FLUIDIZED BED
Abstract A process enabling rapid quenching of articles in a fluidized bed wherein a bed of defined particle type and size is fluidized at a defined flowrate with a high conductivity gas.
Abstract A process enabling rapid quenching of articles in a fluidized bed wherein a bed of defined particle type and size is fluidized at a defined flowrate with a high conductivity gas.
Description
Technical Field This invention relates generally to the quenching of articles in a fluidized bed and is particularly advantageous ~or the quenching of metal p~rts in a fluidized bed.
Backqround Art Quenching is used extensively in the hea~
treating of objects in order to rapidly change the temperature of the object. Generally quenching is employed to rapidly reduce the object temperature although quenching may also be used ~o rapidly raise the object temperature. Often the objects to be quenched are metal parts.
Quenching is conventionally carried out in a number of ways. In spray quenchiny, a liquid is sprayed onto the object to be quenched. In gas quenching, the object is placed in a flowing s~ream of a gas or vapor such as air, nitrogen, argon, helium, hydrogen, steam or combustion products. In fog quenching, a gas or vapor stream with entrained liquid droplets is directed on~o the surface of the object ~o be quenched~ In immersion quenching, the object is immersed in a liquid bath such as water, brine, oil, molten salt, polymer solution, or a liquid cryogen.
Although these conventional guenching method~ have been employed satisfactorily, ~hey exhibit a numb~r of disadvantages. For example, liquids such as oil ~uenchants often leave a layer on ~he objects which must be cleaned off. Some ;-~ D-14887 IL;~ 3 quenchants, such as molten salts, have disposal problems. Other quenchants, ~uch as polymers and oils, degrade with age and must be replaced. Anther disadvantage of some quenchants i~ the fact that quenching temperatures are o~ten at their boiling temperature thus causing varying heat transfer rates along the surface of the article.
Fluidized beds are known for use in the quenching of objects and ~erve ~o overcome these problems, There i8 little or no cleaning of the object required after a fluidizsd bed quench. Also : the particles used in the fluidized bed are inert and do not degrade. However, fluidized beds have not been used extensively to quench objects such as metal parts because the quench rate has been too low ~o satisfactorily quench metal parts made of anything other than deep hardening alloys, without forming undesirable softer phases within the metal part.
It is therefore an object of this invention to provide an improved heat treating process wherein metal articles may be quenched in a fluidized b~d while avoiding the ~ormation of undesirable softer ~ phases within the metal article.
: 25 It is also an object of ~his invention to :; provide an improved heat treating process wherein an article rnay be effectively quenched by use of a fluidized bed.
Sun~narY Of The Invention The above and other objects, which will become apparent to one skilled in the art upon a .
~36~()3 reading of this disclosurP, are attained by the process of this invention, one aspect of which is:
A process for heat treating steel alloy articles comprising:
(a) providing a steel alloy ar~icle at an austenitizing temperature;
(b) fluidizing a bed comprised of fine ~olid particles with high conductivity gas at a flowrate at least 1.5 times the minimum fluidization ~: 10 flowrate;
(c) immersing the article in said : fluidized bed at a bed temperature below the Ms temperature of the alloy; and (d) quenching the article in the bed for a period of time and at a quench rate sufficient : to achieve the ~s tempera~ure of the alloy substantially without forming undesirable softer phases within the article while fluidizing the bed with high conductivi~y gas for at least a portion of the quench period and while maintaining the bed at a temperature below the Ms temperature of the alloy ~or the entire quench:period.
As used herein, the term "quenching" mean~
a rapid change in enthalpy of an object by heat :: 25 transfer across the boundary of the object, wherein : the rate of enthalpy chan~e exceeds that rate when : the object i5 placed in and is surrounded by still atmosphere.
As used herei~, the term "~uench rate"
means the amoun~ of heat transfer per uni~time across an object~boundary when the object is:being uenched.
~;
.~.. . . ., . ,, .:
_ 4 _ As used herein, ~he term "bed" means a defined volume of solid particles.
As used herein, the term "fine solid particles" means porous or non-porous particles having a density within the range of from 0.3 to 20 grams per cubic centimeter and a mean particle diameter within the range of from 30 to lOaO microns.
As used herein, ~he term "fluidized bed"
means a bed through which is passed fluid, such as gas and/or vapor, wherein the ~luid drag force of the fluid component causes movement of the solid component from its repose position in a manner that enhances mixing of both components in the bed. The term, 1uidized, is derived from the fluid-like characteristics, such as a zero angle of repose, mobility, and a pressure head equal to the bulk density of the bed, which the bed assumes.
As used herein the term "immersing" means that substantially all of the article to be txeated, or if only a portion of the article is to be treated, substantially all of that portion of the article to be treated, is made to be surrounded by the fluidized particles during the ~uench.
As used herein the term "minim~n fluidization flowrate" means the least volumetric flowrate of the fluid component through a bed which is ~ecessary or the bed ~o at~ain 1uidiæed bed characteristics under atmospheric pressure.
As used herein, the term "slumped bed"
means a bed through which no fluid is passing or through which fluid is passing a~ less ~han ~he minimum fluidization ~lowrate.
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: D-14887 : . ' ~3 ~
As used herein, the term "high conductivity gas" means a gas, gas mixture, vapor, vapor mixture or gas vapor mixture having a thermal c~nductiviky greater ~han or equal to the thermal conductivity o a mixture of 80 percent nitrogen and 20 percent helium at the same temperature and pressure co~ditions.
As used herein, the term "steel alloy article" means a shaped articlP comprised, at least in part, of a stePl or ferrous alloy.
As used herein the term "aus~enitizing temperature" means a tempera~ure at which the steel alloy of a steel alloy article îs austenite, As used herein, the term "Ms temperature"
means that temperature at which the austenite phase of a steel alloy begins to change to martensite.
As used herein the term "Mf temperature"
means that temperature at which substantially all of a steel alloy is converted to martensite.
As used herein, the term "softer phases"
means pearlite, ferrite, bainite and thé like, As used herein, the term "nose temperature"
means that temperature at which the time required for austenite to start ~ransforming into sof~er 2S phases is at a minimum.
Brief DescriPtion of the Drawinq The sole Figure is a schematic diagram o a steel alloy quench curve superimposed o~ a schematic steel alloy time, temperature, transformation (TTT) ~iagram.
Detailed Description The process of this invention is particularly useful for ~he heat treating of ~teel alloy articles and will be described in detail with reference to this type of heat treating.
The process of this invention can be employed to quench effectively an article comprised of any steel alloy. The process is particularly advantageous to quench chromium-molybdenum steels such as AISI types 4130 and 4140, nickel-chromium-molybdenum steels such as AISI 4340, 8620,8630 and 9860, nickel-molybdenum steels such as AISI 4640, chromium steels such as AISI 5140, series 1100 steels such as AISI 1144 and 1141, and heat treatable ductile and malleable irons.
The steel alloy article is brought to or is at an austenitizing temperature. The minimum austenitizing temperature for most steel alloys is in the range of from 1500F to 1700F. At an austenitizing temperature the structure of the ~teel alloy is substantially all austenite. The term, austenite, as well as the terms martensite, pearlite, ferrite and bainit~, are terms which are well known to those skilled in the art and d~finitions for these ~lloy structure terms can be found in many textbooks which relate to heat treating or met~llurgy such as Heat Treater's Guide, Standard Practices ~nd Procedures For Steel, Unterwei er et al. ed., ASM, Metals Park, Ohio (1982), Atlas of Isothermal Transformation and Cooling Transformation Diagrams, ASM, Me~als Park, !
~', - ~2~ 3 Ohio (1977) and Metals Handbook, Vol. 4 Heat Treating, ASM, Metals Park, Ohio (1~81).
The bed useful in the process of this invention is comprised of fine solid particles. As examples of the types of bed particles which can be employed with this invention one can name metal oxide powders such as aluminum oxide, chromium oxide, iron oxide and titanium oxide, refractory powders such as silicon dioxide, mullite, magnesite, zirconium oxide and fosterite, and pure elements in the solid state such as iron, copper, nickel and carbon.
The bed particles useful in the process of this invention have a mean particle diameter within the range of from 30 to 1000 microns. Smaller particles are difficult to 1uidize and give inadequate heat transfer while larger particles do .:~ not contact heat transfer surfaces with adequate frequency resulting in poor heat transfer and also ~; 20 require a large amount of gas to fluidize the bed.
The bed is fluidi~ed by the passage through the bed of a high conductivity gas. The use of a high conduc~ivity gas is important for the achievernent of the advantageous results of the process of this invention because the high conductivity, especially at the austenitizing temperatures, is necessary to achieve quench rates which will enable the attainment of the Ms temperature without orming softer phases within the : 30 steel alloy. Examples of high conductivity gases include helium, hydrogen and diassociated ammonia.
In addition, a mix~ure of a pur~ high conductivi~y ~' ~
gas such as hydrogen or helium with a low conductivity gas may be employed so long as the mixture is consistent with the reguirements for a high conductivity gas defined herein.
The bed is fluidized with the high conductivity gas at a gas flowrate which is at least 1.5 times the minimum fluidization flowrate for the specific bed particle type and size employed.
Preferably the high conductivity gas flowrate is 10 within the range of from 2 to 7 times the minimum fluidiæation flowrate. Below the minimum defined flowrate the particle circulation is sluggish resulting in poor heat transfer. At a flowrate above about 15 times the minimum fluidization 15 flowrate, smaller particles may begin to be conveyed out of the ~ed.
When the bed is fluidized with the high conductivity gas at the requisite gas flowrate the aus~enite steel alloy article is immersed in the 20 fluidized bed for quenching.
The steel alloy article is kepk in the bed for a period of time sufficient to reduce th0 temperature of the article to or below the Ms temperature. This temperature reduction is done at 25 a rapid rate, i.e., the article is quenched.
Initially the quenching is always carried out with the bed fluidized with high conductivity gas. Th~
quenching of the article ~o the Ms temperature can be carried out entirely with the bed ~luidized with 30 high conductivity gas or it can be carri~d ou~ in part with the bed in a slumpe~ condition and/or fluidized with:a low conductivity gas. For purposes ~ D-I48~7 : ~ :
,. ~ ` ~, ~Z~fi~Qu~
_ 9 ~
of this disclosure any gas which is not a high conductivity gas is a low conductivity gas.
However, it is very important that during the quenching step the quench rate of the article be sufficient to enable a reduction in temperature of the article sufficient to reach the Ms ~emperature with~ut the formation of softer phases within the alloy. In order to successfully carry out the quench, a practitioner may need to vary the fluidizing gas flowrate during the quench period while remaining with the defined limits.
The quench rate is generally measured by a procedure variously known in the art as the ~agne~ic Test, General Motors Quenchometer Test, or ~ickel Ball Test. The procedure comprises heating a 7/8-inch (22 mm) nickel sphere, weighing approximately 1.8 ounces (50 g) to a given high emperature and then quenching the sphere in the quenchant to be evaluated down to a given low temperature. The time it takes for the sphere temperature to go from the high to the low temperaturq is a measure of th~ quench rate. In the ~` process of this invention for the heat treating of steel alloy articles, the initial quench rate as measured by the Nickel Ball Test between the temperatures of 1600F and 684F is less than 24 seconds.
In order to ~ore clearly illustrate the process of this invention, reference is made to the Figure which is a schematic diagram of a steel alloy quench curve ~upeximposed on a schema~ic steel alloy time-temperature-transformation diagram. In the Figure, line 1 indicates the Ms temperature and line 2 indicates the Mf temperature. Line 3 indicates the threshold where a steel alloy will begin to ~orm softer phases and line 4 indicates where transormation into softer phases is completed. As can be seen the threshold line 3, which indicates where softer phases will be formed in the steel alloy if the Ms temperature is not first attained, exhibits a distinct leftward bulge or nose 6. The elapsed time for reaching the nose after the start of quenching will vary with the type of alloy and can be obtained from the Atlas which is referenced herein.
Curve 7 illustrates a generalized quenching curve for an article quenched by the process of this invention wherein the en~ire guenching period, when the temperature of the article goes from the austenitizing temperature to the MS temperature, is carried out while.the bed is fluidized with a high conductivity gas. The quench rate is the absolute value of the slope of quenching curve 7, and as can be seen, the guench rate is sufficient to enable intersection of the MS temperature at line 1 without crossing threshold line 3.
The bed is operated at a temperature which is less than the Ms temperature, and preferably will be operated at a temperature which is less than the Mf temperature, o the alloy.
As is known to those skilled in the art, a fast quench may not always be desirable because of the possibility of stress creation within the alloy. Therefore, if possible without crossing the softer phase threshold, one can reduce the quenching rate by changing the mode of operation o the bed.
After an initial period wherein the bed is 1uidized with a high conductivity qas, the process may be carried out with the bed fluidized with a low conductivity ~as, or with the bed in a slumped condition. One can alternate between these two modes of operation and one can, at any time, refluidize the bed with high conductivity gas. A
convenient time to change from fluidization with a high conductivity gas to another bed operating mode is when the article ~emperature has dropped below the nose temperature. As mentioned previously the quenching continues for a period of time and at a quench rate sufficient to achieve the Ms temperature of the alloy substantially without forming undesirable softer phases within the part.
Once the ~s temperature is attained one can, if desired, remove the article from the bed.
However, it is preferable that the article be kept in the bed and further quenched to the Mf temperature. This further quenching, which is also shown schematically in the Figure can be carried out with the bed fluidized with high conductiYity gas, but preferably is carried out with the bed slumped or fluidized with a low conductivity gas. One can carry out this further quenching with the bed in either of these three modes of operation and can switch between them, consistent with having a guench rate sufficient to achieve the M~ temperature without crossing sof~er phase threshold curve 4.
D-14~87 ~L2~ 3 Specialized heat treating techniques, such as, martempering and modified martempering, can be carried out with the process of this invention.
To practice martempering with the process of this invention, one guenches the steel ~lloy article with the bed fluidized with high conductivity gas until the article temperature has dropped below the nose temperature but is still above the Ms ~emperature. The bed is then slumped until the article temperature equilihrates, i.e., when the temperature at the center of the article is substantially equal to the temperature at the article surface. Thereafter the bed is refluidized with low conductivity gas and the article is quenched in the bed to the Mf temperature.
In another way to practice martempering with ~he process of this invention, one quenches the steel alloy article with the bed fluidized with high conductivity gas until the article temperature has dropped below the nose temperature but ~s still above the Ms temperature. Thereafter the bed is 1uidized with low conductivity gas and the article quenched in the bed to the Mf temperature.
To practice modified martempering with the process of this invention one quenches the steel alloy article with the bed fluidized with high conductivity gas until the article temperature has dropped below the Ms temperature but is still above the Mf temperature. Thsreafter the bed is fluidized with low conductivity gas and ~he article guenched in the bed to the Mf temperature.
~ D-14887 : : :
~66~3 , ....
The process of this invention is further illustrated by reference to the following examples which are presented for illustrative purposes and are not intended to be limiting.
ExamPle 1 Steel alloy parts of 4140 steel were heated to an austenitizing temperature of 1625F. The Ms temperature of this steel alloy is 650F. A bed comprised of ~20 mesh aluminum oxide was fluidized ~ 10 with helium at a flowrate of 150 standard cubic feet -~ per hour (scfh) per square foot of bed which is about twice the minimum fluidization flowrate for these bed particles. The nose temperature for this alloy occurs at about 3 seconds after the start of quenching.
The parts were immersed in the fluidized bed and quenched until th~e part temperature reached 500F. Thereafter the hel~ium~flow was shut off and the bed was;slumped~or 15 minutes. The bed was the refluidized with nitrogen, a low conducti~ity gas, until the part temperature reached the Mf temperature and then reached the bed temperature of 17SF. The parts were removed from the bed and tested for hardness. The test showed a hardness of 52 ~c (Rockwell Hardnes~ Number on the c ~cale~ at both 1/16 inch and 7/16 inch below the part surface indicating the ~ormation of essentially a complete martensite structure without the formation of softer phases.
36Çi~3 Example 2 The procedure of Example 1 was repea~ed except that the steel alloy parts were comprised of 4340 steel which has an Ms temperature of 550~F.
The parts had a hardness value of 52 Rc at both 1/16 inch and 7/16 inch below the surface indicating the essentially complete formation of martensite without the formation of softer phases.
Example_3 `Steel alloy parts of 8620 steel, having a 5/8-inch diameter and a 6-inch length, were carburized to 1.0 percent carbon a~ the surface at a temperature of 1550F. A bed comprised of 220 mesh aluminum oxide was fluidized with helium at a flowrate of 225 scfh which is about three times the minimum fluidization flowrate. The parts were immersed in the fluidized bed and quenched for a time p riod until the part temperature was below the s temperature and was essentially egual to the bed temperature. This ~ime period was about 60 ~: seconds. The parts were removed from the bed and tempered for 1.5 hours at 400F. A me~allurgical sample was prepared by cutting a 1/2-inch section from the end of one of the parts. The surface hardness of the sample was 90 as measured on the 15N
scale, and the core, or center, harness was 45 as measured on the Rockwell C scale. The mini~urn acceptable hardness values for these parts are 80 and 30 for the surface and core, respectively.
For comparative purposes, the procedure of Example 3 was repeated with the exception that ths luidizing qaS used was nitrogen. The surface :~:
:
:
harness of the nitrogen fluid bed quenched sample was 89, but the core hardness was only 22, thus demonstrating the marked improvement in part hardness attainable by use of the process of ~his invention.
One may employ the rapid quenching process of this invention to carry out austempering of a alloy wherein the alloy structure is transformed into bainitic. This procedure may be especially useful in the heat treating of cast iron.
This further aspect of the process of this invention can be defined as follows:
; A process for the austempering of steel alloy articles to form a bainitic structure within the alloy comprising:
(a) providing a steel alloy article at an austenitizing temperature;
: (b) fluidizing a bed comprised of fine solid partic'es with high conductivity gas at a :; 20 f lowrate at least 1.5 times the minimum fluidization :~ flowrate, at a temperature within the range of from the Mf temperature to 50F greater than ~he Ms temperature of the alloy;
(c) immersing the article in said ~luidized bed and quenching the article in the fluidized bed for a period of time un~il the article temperature has been reduced to that of the fluidi~ed bed at the bed temperature while fluidiziny the bed with high conductivity gas for at leas~ a portion of the quench period; and thereafter ~d) stopping the flow of high cond~ctivity ga~ and maintaining the article in ~he 36~3 bed at the bed temperature for a time suffici~nt to avoid the substantial formation of martensite within the steel alloy.
Step (d) of the austempering treatment can be carried out with the bed slumped or fluidized with a low conductivity gas and one can alternate between these two modes of bed opera~ion.
The rapid quenching process of this invention also san be employed to quench effectively articles comprised of aluminum. Heretofore aluminum and aluminum alloys have been quenched with water or polymer quenchants and these quenchants have enabled ~uenching rates sufficient to achieve desired metallurgical properties such as high strength after aging and resistance to stress-corrosion cracking.
However, especially for relatively thin articles, the conventional quenchants may give rise to a significant amount of distortion which leads ~o substantial costs associated with straightening operations. The process of this invention can quench aluminum and aluminum alloys at suficiently high guench rates reguired or the formation of a uniform di~tribution of small precipitates within the part. This uniform distribution is necessary for the part to have high ~trength. However with the process of this invention one can adjust and control the quench rate by operating the bed in a ~lumped condition or by fluidizing the bed with a low conductivity gas so that one can quench an aluminum article at a quench rate which substantially avoids distortion within the article.
The process of this~invention as applied to the ~2~ 3 guenching of aluminum or aluminum alloys can be defined as follows:
A process for heat treating articles comprised of aluminum and/or aluminum alloy comprising:
(a) providing an article comprised of aluminum and/or al~ninum alloy a~ an elevated temperature sufficient to allow hardening of the article by ~u nehing;
(b) fluidizing a bed comprised of fine solid particlPs with high conductivity gas at a flowrate at least 1.5 times the minimum fluidiza~ion flowrate;
(c) immersing the article in said : 15 f luidized bed; :and : (di quenching the article in the bed at a quench rate such ~hat a 7~8 i~ch diameter : : nickel ball will be cooled from 750 to 550F in less than 28 seconds, for a time period sufficient to : 20 increase the hardness of the article while fluidizing the bed with high conductivity gas for at : least a part of the guench period.
Generally the elevated temperature of step (a) is at least 750F and usually exceeds B00F.
: 25 Step (d) can be carried out entirely with the bed fluidized with high conductivity gas, but g0nerally and pre~erably, i8 carried out in part with the bed f luidized with low conductivity gas or opera~ed in the slumped rnode. Step (d) may be conveniently continued until the article has reached ambient or near ambient temperature.
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The rapid quenching process of this invention also can be employed to rapidly lower or to rapidly raise the temperature of an article comprised of any effectively hea~ treatable material such as metal, glass, ceramic or plastic. The rapid quenching process of this invention as applied to the rapid temperature decrease sr increase of an article can be defined as follows:
A process for quenching articles to a desired temperature comprising:
(a) providing an article at an initial temperature;
(b) fluidizing a bed comprised of fine solid particles with high conductivity yas at a flowrate at least 1.5 times the minimum fluidization flowrate;
~c) immersing the article in said fluidized bed; and (d) quenching the article in the bed for a period of time sufficient ~o achieve the desired temperature while (i) maintaining the bed at or below the desired temperature if the desired temperature is less than the initial temperature, or Sii) maintaining the bed at or above the desired temperature if the desired temperature is greater than the initial temperature, while fluidizing the bed with high conductivity gas for at least a portion of the quench period.
Step (d) can be carried out entirely with the bed fluidized with high conductivity gas sr step (d) can be carried out in part with the bed ~:
fi~3 fluidized with low conductivity gas or opsrated in the slumped mode.
Now by the use of the process of this invention one can rapidly change the temperature of articles by u~e of a fluidized bed thus enabling greater con~rol over the temperature change process than is otherwise possible with conventional quenchants~ Furthermore the quenching process of this invention is much more convenient and generally is cleaner than conventional quenching processes.
The rapid quenching process of this invention is particularly applicable to and advantageous for the heat treating of metal parts to attain a desired ~5 internal metal structure.
Backqround Art Quenching is used extensively in the hea~
treating of objects in order to rapidly change the temperature of the object. Generally quenching is employed to rapidly reduce the object temperature although quenching may also be used ~o rapidly raise the object temperature. Often the objects to be quenched are metal parts.
Quenching is conventionally carried out in a number of ways. In spray quenchiny, a liquid is sprayed onto the object to be quenched. In gas quenching, the object is placed in a flowing s~ream of a gas or vapor such as air, nitrogen, argon, helium, hydrogen, steam or combustion products. In fog quenching, a gas or vapor stream with entrained liquid droplets is directed on~o the surface of the object ~o be quenched~ In immersion quenching, the object is immersed in a liquid bath such as water, brine, oil, molten salt, polymer solution, or a liquid cryogen.
Although these conventional guenching method~ have been employed satisfactorily, ~hey exhibit a numb~r of disadvantages. For example, liquids such as oil ~uenchants often leave a layer on ~he objects which must be cleaned off. Some ;-~ D-14887 IL;~ 3 quenchants, such as molten salts, have disposal problems. Other quenchants, ~uch as polymers and oils, degrade with age and must be replaced. Anther disadvantage of some quenchants i~ the fact that quenching temperatures are o~ten at their boiling temperature thus causing varying heat transfer rates along the surface of the article.
Fluidized beds are known for use in the quenching of objects and ~erve ~o overcome these problems, There i8 little or no cleaning of the object required after a fluidizsd bed quench. Also : the particles used in the fluidized bed are inert and do not degrade. However, fluidized beds have not been used extensively to quench objects such as metal parts because the quench rate has been too low ~o satisfactorily quench metal parts made of anything other than deep hardening alloys, without forming undesirable softer phases within the metal part.
It is therefore an object of this invention to provide an improved heat treating process wherein metal articles may be quenched in a fluidized b~d while avoiding the ~ormation of undesirable softer ~ phases within the metal article.
: 25 It is also an object of ~his invention to :; provide an improved heat treating process wherein an article rnay be effectively quenched by use of a fluidized bed.
Sun~narY Of The Invention The above and other objects, which will become apparent to one skilled in the art upon a .
~36~()3 reading of this disclosurP, are attained by the process of this invention, one aspect of which is:
A process for heat treating steel alloy articles comprising:
(a) providing a steel alloy ar~icle at an austenitizing temperature;
(b) fluidizing a bed comprised of fine ~olid particles with high conductivity gas at a flowrate at least 1.5 times the minimum fluidization ~: 10 flowrate;
(c) immersing the article in said : fluidized bed at a bed temperature below the Ms temperature of the alloy; and (d) quenching the article in the bed for a period of time and at a quench rate sufficient : to achieve the ~s tempera~ure of the alloy substantially without forming undesirable softer phases within the article while fluidizing the bed with high conductivi~y gas for at least a portion of the quench period and while maintaining the bed at a temperature below the Ms temperature of the alloy ~or the entire quench:period.
As used herein, the term "quenching" mean~
a rapid change in enthalpy of an object by heat :: 25 transfer across the boundary of the object, wherein : the rate of enthalpy chan~e exceeds that rate when : the object i5 placed in and is surrounded by still atmosphere.
As used herei~, the term "~uench rate"
means the amoun~ of heat transfer per uni~time across an object~boundary when the object is:being uenched.
~;
.~.. . . ., . ,, .:
_ 4 _ As used herein, ~he term "bed" means a defined volume of solid particles.
As used herein, the term "fine solid particles" means porous or non-porous particles having a density within the range of from 0.3 to 20 grams per cubic centimeter and a mean particle diameter within the range of from 30 to lOaO microns.
As used herein, ~he term "fluidized bed"
means a bed through which is passed fluid, such as gas and/or vapor, wherein the ~luid drag force of the fluid component causes movement of the solid component from its repose position in a manner that enhances mixing of both components in the bed. The term, 1uidized, is derived from the fluid-like characteristics, such as a zero angle of repose, mobility, and a pressure head equal to the bulk density of the bed, which the bed assumes.
As used herein the term "immersing" means that substantially all of the article to be txeated, or if only a portion of the article is to be treated, substantially all of that portion of the article to be treated, is made to be surrounded by the fluidized particles during the ~uench.
As used herein the term "minim~n fluidization flowrate" means the least volumetric flowrate of the fluid component through a bed which is ~ecessary or the bed ~o at~ain 1uidiæed bed characteristics under atmospheric pressure.
As used herein, the term "slumped bed"
means a bed through which no fluid is passing or through which fluid is passing a~ less ~han ~he minimum fluidization ~lowrate.
, :
: D-14887 : . ' ~3 ~
As used herein, the term "high conductivity gas" means a gas, gas mixture, vapor, vapor mixture or gas vapor mixture having a thermal c~nductiviky greater ~han or equal to the thermal conductivity o a mixture of 80 percent nitrogen and 20 percent helium at the same temperature and pressure co~ditions.
As used herein, the term "steel alloy article" means a shaped articlP comprised, at least in part, of a stePl or ferrous alloy.
As used herein the term "aus~enitizing temperature" means a tempera~ure at which the steel alloy of a steel alloy article îs austenite, As used herein, the term "Ms temperature"
means that temperature at which the austenite phase of a steel alloy begins to change to martensite.
As used herein the term "Mf temperature"
means that temperature at which substantially all of a steel alloy is converted to martensite.
As used herein, the term "softer phases"
means pearlite, ferrite, bainite and thé like, As used herein, the term "nose temperature"
means that temperature at which the time required for austenite to start ~ransforming into sof~er 2S phases is at a minimum.
Brief DescriPtion of the Drawinq The sole Figure is a schematic diagram o a steel alloy quench curve superimposed o~ a schematic steel alloy time, temperature, transformation (TTT) ~iagram.
Detailed Description The process of this invention is particularly useful for ~he heat treating of ~teel alloy articles and will be described in detail with reference to this type of heat treating.
The process of this invention can be employed to quench effectively an article comprised of any steel alloy. The process is particularly advantageous to quench chromium-molybdenum steels such as AISI types 4130 and 4140, nickel-chromium-molybdenum steels such as AISI 4340, 8620,8630 and 9860, nickel-molybdenum steels such as AISI 4640, chromium steels such as AISI 5140, series 1100 steels such as AISI 1144 and 1141, and heat treatable ductile and malleable irons.
The steel alloy article is brought to or is at an austenitizing temperature. The minimum austenitizing temperature for most steel alloys is in the range of from 1500F to 1700F. At an austenitizing temperature the structure of the ~teel alloy is substantially all austenite. The term, austenite, as well as the terms martensite, pearlite, ferrite and bainit~, are terms which are well known to those skilled in the art and d~finitions for these ~lloy structure terms can be found in many textbooks which relate to heat treating or met~llurgy such as Heat Treater's Guide, Standard Practices ~nd Procedures For Steel, Unterwei er et al. ed., ASM, Metals Park, Ohio (1982), Atlas of Isothermal Transformation and Cooling Transformation Diagrams, ASM, Me~als Park, !
~', - ~2~ 3 Ohio (1977) and Metals Handbook, Vol. 4 Heat Treating, ASM, Metals Park, Ohio (1~81).
The bed useful in the process of this invention is comprised of fine solid particles. As examples of the types of bed particles which can be employed with this invention one can name metal oxide powders such as aluminum oxide, chromium oxide, iron oxide and titanium oxide, refractory powders such as silicon dioxide, mullite, magnesite, zirconium oxide and fosterite, and pure elements in the solid state such as iron, copper, nickel and carbon.
The bed particles useful in the process of this invention have a mean particle diameter within the range of from 30 to 1000 microns. Smaller particles are difficult to 1uidize and give inadequate heat transfer while larger particles do .:~ not contact heat transfer surfaces with adequate frequency resulting in poor heat transfer and also ~; 20 require a large amount of gas to fluidize the bed.
The bed is fluidi~ed by the passage through the bed of a high conductivity gas. The use of a high conduc~ivity gas is important for the achievernent of the advantageous results of the process of this invention because the high conductivity, especially at the austenitizing temperatures, is necessary to achieve quench rates which will enable the attainment of the Ms temperature without orming softer phases within the : 30 steel alloy. Examples of high conductivity gases include helium, hydrogen and diassociated ammonia.
In addition, a mix~ure of a pur~ high conductivi~y ~' ~
gas such as hydrogen or helium with a low conductivity gas may be employed so long as the mixture is consistent with the reguirements for a high conductivity gas defined herein.
The bed is fluidized with the high conductivity gas at a gas flowrate which is at least 1.5 times the minimum fluidization flowrate for the specific bed particle type and size employed.
Preferably the high conductivity gas flowrate is 10 within the range of from 2 to 7 times the minimum fluidiæation flowrate. Below the minimum defined flowrate the particle circulation is sluggish resulting in poor heat transfer. At a flowrate above about 15 times the minimum fluidization 15 flowrate, smaller particles may begin to be conveyed out of the ~ed.
When the bed is fluidized with the high conductivity gas at the requisite gas flowrate the aus~enite steel alloy article is immersed in the 20 fluidized bed for quenching.
The steel alloy article is kepk in the bed for a period of time sufficient to reduce th0 temperature of the article to or below the Ms temperature. This temperature reduction is done at 25 a rapid rate, i.e., the article is quenched.
Initially the quenching is always carried out with the bed fluidized with high conductivity gas. Th~
quenching of the article ~o the Ms temperature can be carried out entirely with the bed ~luidized with 30 high conductivity gas or it can be carri~d ou~ in part with the bed in a slumpe~ condition and/or fluidized with:a low conductivity gas. For purposes ~ D-I48~7 : ~ :
,. ~ ` ~, ~Z~fi~Qu~
_ 9 ~
of this disclosure any gas which is not a high conductivity gas is a low conductivity gas.
However, it is very important that during the quenching step the quench rate of the article be sufficient to enable a reduction in temperature of the article sufficient to reach the Ms ~emperature with~ut the formation of softer phases within the alloy. In order to successfully carry out the quench, a practitioner may need to vary the fluidizing gas flowrate during the quench period while remaining with the defined limits.
The quench rate is generally measured by a procedure variously known in the art as the ~agne~ic Test, General Motors Quenchometer Test, or ~ickel Ball Test. The procedure comprises heating a 7/8-inch (22 mm) nickel sphere, weighing approximately 1.8 ounces (50 g) to a given high emperature and then quenching the sphere in the quenchant to be evaluated down to a given low temperature. The time it takes for the sphere temperature to go from the high to the low temperaturq is a measure of th~ quench rate. In the ~` process of this invention for the heat treating of steel alloy articles, the initial quench rate as measured by the Nickel Ball Test between the temperatures of 1600F and 684F is less than 24 seconds.
In order to ~ore clearly illustrate the process of this invention, reference is made to the Figure which is a schematic diagram of a steel alloy quench curve ~upeximposed on a schema~ic steel alloy time-temperature-transformation diagram. In the Figure, line 1 indicates the Ms temperature and line 2 indicates the Mf temperature. Line 3 indicates the threshold where a steel alloy will begin to ~orm softer phases and line 4 indicates where transormation into softer phases is completed. As can be seen the threshold line 3, which indicates where softer phases will be formed in the steel alloy if the Ms temperature is not first attained, exhibits a distinct leftward bulge or nose 6. The elapsed time for reaching the nose after the start of quenching will vary with the type of alloy and can be obtained from the Atlas which is referenced herein.
Curve 7 illustrates a generalized quenching curve for an article quenched by the process of this invention wherein the en~ire guenching period, when the temperature of the article goes from the austenitizing temperature to the MS temperature, is carried out while.the bed is fluidized with a high conductivity gas. The quench rate is the absolute value of the slope of quenching curve 7, and as can be seen, the guench rate is sufficient to enable intersection of the MS temperature at line 1 without crossing threshold line 3.
The bed is operated at a temperature which is less than the Ms temperature, and preferably will be operated at a temperature which is less than the Mf temperature, o the alloy.
As is known to those skilled in the art, a fast quench may not always be desirable because of the possibility of stress creation within the alloy. Therefore, if possible without crossing the softer phase threshold, one can reduce the quenching rate by changing the mode of operation o the bed.
After an initial period wherein the bed is 1uidized with a high conductivity qas, the process may be carried out with the bed fluidized with a low conductivity ~as, or with the bed in a slumped condition. One can alternate between these two modes of operation and one can, at any time, refluidize the bed with high conductivity gas. A
convenient time to change from fluidization with a high conductivity gas to another bed operating mode is when the article ~emperature has dropped below the nose temperature. As mentioned previously the quenching continues for a period of time and at a quench rate sufficient to achieve the Ms temperature of the alloy substantially without forming undesirable softer phases within the part.
Once the ~s temperature is attained one can, if desired, remove the article from the bed.
However, it is preferable that the article be kept in the bed and further quenched to the Mf temperature. This further quenching, which is also shown schematically in the Figure can be carried out with the bed fluidized with high conductiYity gas, but preferably is carried out with the bed slumped or fluidized with a low conductivity gas. One can carry out this further quenching with the bed in either of these three modes of operation and can switch between them, consistent with having a guench rate sufficient to achieve the M~ temperature without crossing sof~er phase threshold curve 4.
D-14~87 ~L2~ 3 Specialized heat treating techniques, such as, martempering and modified martempering, can be carried out with the process of this invention.
To practice martempering with the process of this invention, one guenches the steel ~lloy article with the bed fluidized with high conductivity gas until the article temperature has dropped below the nose temperature but is still above the Ms ~emperature. The bed is then slumped until the article temperature equilihrates, i.e., when the temperature at the center of the article is substantially equal to the temperature at the article surface. Thereafter the bed is refluidized with low conductivity gas and the article is quenched in the bed to the Mf temperature.
In another way to practice martempering with ~he process of this invention, one quenches the steel alloy article with the bed fluidized with high conductivity gas until the article temperature has dropped below the nose temperature but ~s still above the Ms temperature. Thereafter the bed is 1uidized with low conductivity gas and the article quenched in the bed to the Mf temperature.
To practice modified martempering with the process of this invention one quenches the steel alloy article with the bed fluidized with high conductivity gas until the article temperature has dropped below the Ms temperature but is still above the Mf temperature. Thsreafter the bed is fluidized with low conductivity gas and ~he article guenched in the bed to the Mf temperature.
~ D-14887 : : :
~66~3 , ....
The process of this invention is further illustrated by reference to the following examples which are presented for illustrative purposes and are not intended to be limiting.
ExamPle 1 Steel alloy parts of 4140 steel were heated to an austenitizing temperature of 1625F. The Ms temperature of this steel alloy is 650F. A bed comprised of ~20 mesh aluminum oxide was fluidized ~ 10 with helium at a flowrate of 150 standard cubic feet -~ per hour (scfh) per square foot of bed which is about twice the minimum fluidization flowrate for these bed particles. The nose temperature for this alloy occurs at about 3 seconds after the start of quenching.
The parts were immersed in the fluidized bed and quenched until th~e part temperature reached 500F. Thereafter the hel~ium~flow was shut off and the bed was;slumped~or 15 minutes. The bed was the refluidized with nitrogen, a low conducti~ity gas, until the part temperature reached the Mf temperature and then reached the bed temperature of 17SF. The parts were removed from the bed and tested for hardness. The test showed a hardness of 52 ~c (Rockwell Hardnes~ Number on the c ~cale~ at both 1/16 inch and 7/16 inch below the part surface indicating the ~ormation of essentially a complete martensite structure without the formation of softer phases.
36Çi~3 Example 2 The procedure of Example 1 was repea~ed except that the steel alloy parts were comprised of 4340 steel which has an Ms temperature of 550~F.
The parts had a hardness value of 52 Rc at both 1/16 inch and 7/16 inch below the surface indicating the essentially complete formation of martensite without the formation of softer phases.
Example_3 `Steel alloy parts of 8620 steel, having a 5/8-inch diameter and a 6-inch length, were carburized to 1.0 percent carbon a~ the surface at a temperature of 1550F. A bed comprised of 220 mesh aluminum oxide was fluidized with helium at a flowrate of 225 scfh which is about three times the minimum fluidization flowrate. The parts were immersed in the fluidized bed and quenched for a time p riod until the part temperature was below the s temperature and was essentially egual to the bed temperature. This ~ime period was about 60 ~: seconds. The parts were removed from the bed and tempered for 1.5 hours at 400F. A me~allurgical sample was prepared by cutting a 1/2-inch section from the end of one of the parts. The surface hardness of the sample was 90 as measured on the 15N
scale, and the core, or center, harness was 45 as measured on the Rockwell C scale. The mini~urn acceptable hardness values for these parts are 80 and 30 for the surface and core, respectively.
For comparative purposes, the procedure of Example 3 was repeated with the exception that ths luidizing qaS used was nitrogen. The surface :~:
:
:
harness of the nitrogen fluid bed quenched sample was 89, but the core hardness was only 22, thus demonstrating the marked improvement in part hardness attainable by use of the process of ~his invention.
One may employ the rapid quenching process of this invention to carry out austempering of a alloy wherein the alloy structure is transformed into bainitic. This procedure may be especially useful in the heat treating of cast iron.
This further aspect of the process of this invention can be defined as follows:
; A process for the austempering of steel alloy articles to form a bainitic structure within the alloy comprising:
(a) providing a steel alloy article at an austenitizing temperature;
: (b) fluidizing a bed comprised of fine solid partic'es with high conductivity gas at a :; 20 f lowrate at least 1.5 times the minimum fluidization :~ flowrate, at a temperature within the range of from the Mf temperature to 50F greater than ~he Ms temperature of the alloy;
(c) immersing the article in said ~luidized bed and quenching the article in the fluidized bed for a period of time un~il the article temperature has been reduced to that of the fluidi~ed bed at the bed temperature while fluidiziny the bed with high conductivity gas for at leas~ a portion of the quench period; and thereafter ~d) stopping the flow of high cond~ctivity ga~ and maintaining the article in ~he 36~3 bed at the bed temperature for a time suffici~nt to avoid the substantial formation of martensite within the steel alloy.
Step (d) of the austempering treatment can be carried out with the bed slumped or fluidized with a low conductivity gas and one can alternate between these two modes of bed opera~ion.
The rapid quenching process of this invention also san be employed to quench effectively articles comprised of aluminum. Heretofore aluminum and aluminum alloys have been quenched with water or polymer quenchants and these quenchants have enabled ~uenching rates sufficient to achieve desired metallurgical properties such as high strength after aging and resistance to stress-corrosion cracking.
However, especially for relatively thin articles, the conventional quenchants may give rise to a significant amount of distortion which leads ~o substantial costs associated with straightening operations. The process of this invention can quench aluminum and aluminum alloys at suficiently high guench rates reguired or the formation of a uniform di~tribution of small precipitates within the part. This uniform distribution is necessary for the part to have high ~trength. However with the process of this invention one can adjust and control the quench rate by operating the bed in a ~lumped condition or by fluidizing the bed with a low conductivity gas so that one can quench an aluminum article at a quench rate which substantially avoids distortion within the article.
The process of this~invention as applied to the ~2~ 3 guenching of aluminum or aluminum alloys can be defined as follows:
A process for heat treating articles comprised of aluminum and/or aluminum alloy comprising:
(a) providing an article comprised of aluminum and/or al~ninum alloy a~ an elevated temperature sufficient to allow hardening of the article by ~u nehing;
(b) fluidizing a bed comprised of fine solid particlPs with high conductivity gas at a flowrate at least 1.5 times the minimum fluidiza~ion flowrate;
(c) immersing the article in said : 15 f luidized bed; :and : (di quenching the article in the bed at a quench rate such ~hat a 7~8 i~ch diameter : : nickel ball will be cooled from 750 to 550F in less than 28 seconds, for a time period sufficient to : 20 increase the hardness of the article while fluidizing the bed with high conductivity gas for at : least a part of the guench period.
Generally the elevated temperature of step (a) is at least 750F and usually exceeds B00F.
: 25 Step (d) can be carried out entirely with the bed fluidized with high conductivity gas, but g0nerally and pre~erably, i8 carried out in part with the bed f luidized with low conductivity gas or opera~ed in the slumped rnode. Step (d) may be conveniently continued until the article has reached ambient or near ambient temperature.
: :
' - 18 ~
The rapid quenching process of this invention also can be employed to rapidly lower or to rapidly raise the temperature of an article comprised of any effectively hea~ treatable material such as metal, glass, ceramic or plastic. The rapid quenching process of this invention as applied to the rapid temperature decrease sr increase of an article can be defined as follows:
A process for quenching articles to a desired temperature comprising:
(a) providing an article at an initial temperature;
(b) fluidizing a bed comprised of fine solid particles with high conductivity yas at a flowrate at least 1.5 times the minimum fluidization flowrate;
~c) immersing the article in said fluidized bed; and (d) quenching the article in the bed for a period of time sufficient ~o achieve the desired temperature while (i) maintaining the bed at or below the desired temperature if the desired temperature is less than the initial temperature, or Sii) maintaining the bed at or above the desired temperature if the desired temperature is greater than the initial temperature, while fluidizing the bed with high conductivity gas for at least a portion of the quench period.
Step (d) can be carried out entirely with the bed fluidized with high conductivity gas sr step (d) can be carried out in part with the bed ~:
fi~3 fluidized with low conductivity gas or opsrated in the slumped mode.
Now by the use of the process of this invention one can rapidly change the temperature of articles by u~e of a fluidized bed thus enabling greater con~rol over the temperature change process than is otherwise possible with conventional quenchants~ Furthermore the quenching process of this invention is much more convenient and generally is cleaner than conventional quenching processes.
The rapid quenching process of this invention is particularly applicable to and advantageous for the heat treating of metal parts to attain a desired ~5 internal metal structure.
Claims (38)
1. A process for heat treating steel alloy articles comprising:
(a) providing a steel alloy article at an austenitizing temperature;
(b) fluidizing a bed comprised of fine solid particles with high conductivity gas at a flowrate at least 1.5 times the minimum fluidization flowrate;
(c) immersing the article in said fluidized bed at a bed temperature below the Ms temperature of the alloy; and (d) quenching the article in the bed for a period of time and at a quench rate sufficient to achieve the Ms temperature of the alloy substantially without forming undesirable softer phases within the article while fluidizing the bed with high conductivity gas for at least a portion of the quench period and while maintaining the bed at a temperature below the Ms temperature of the alloy for the entire quench period.
(a) providing a steel alloy article at an austenitizing temperature;
(b) fluidizing a bed comprised of fine solid particles with high conductivity gas at a flowrate at least 1.5 times the minimum fluidization flowrate;
(c) immersing the article in said fluidized bed at a bed temperature below the Ms temperature of the alloy; and (d) quenching the article in the bed for a period of time and at a quench rate sufficient to achieve the Ms temperature of the alloy substantially without forming undesirable softer phases within the article while fluidizing the bed with high conductivity gas for at least a portion of the quench period and while maintaining the bed at a temperature below the Ms temperature of the alloy for the entire quench period.
2. The process of claim 1 wherein the bed is fluidized with high conductivity gas during the entire period of step (d).
3. The process of claim 1 wherein the bed is fluidized with high conductivity gas during only a portion of the period of step (d).
4. The process of claim 3 wherein that portion of step (d) wherein the bed is fluidized with high conductivity gas is the initial portion of the period.
5. The process of claim 3 wherein during at least some of the period of step (d) when the bed is not fluidized with high conductivity gas, the bed is fluidized with low conductivity gas.
6. The process of claim 3 wherein during at least some of the period of step (d) when the bed is not fluidized with high conductivity gas, the bed is operated in a slumped condition.
7. The process of claim 1 wherein the high conductivity gas is helium.
8. The process of claim 1 wherein the high conductivity gas is hydrogen.
9. The process of claim 1 wherein after step (d) the article is kept in the bed for a further period of time and further quenched to the Mf temperature.
10. The process of claim 9 wherein during at least some of the further period, the bed is fluidized with high conductivity gas.
11. The process of claim 9 wherein during at least some of the further period, the bed is fluidized with low conductivity gas.
12. The process of claim 9 wherein during at least some of the further period, the bed is operated in a slumped condition.
13. The process of claim 1 wherein the bed temperature is maintained below the Mf temperature.
14. The process of claim 1 wherein the initial quench rate at the start of step (d) is such that a 7/8 inch diameter nickel ball would be cooled from 1600 to 680°F in less than 24 seconds.
15. The process of claim 9 for martempering steel alloy articles wherein, when the article temperature has dropped below the nose temperature but is still above the Ms temperature, the bed is fluidized with low conductivity gas and the article is quenched in the bed to the Mf temperature.
16. The process of claim 9 for martempering steel alloy articles wherein, when the article temperature has dropped below the nose temperature but is still above the Ms temperature, the bed is slumped for a period of time sufficient for the article temperature to equilibrate and thereafter the bed is refluidized with low conductivity gas and the article is quenched in the bed to the Mf temperature.
17. The process of claim 9 for modified martempering steal alloy articles wherein, when the article temperature has dropped below the Ms temperature. but is still above the Mf temperature, the bed is fluidized with low conductivity gas and the article is quenched in the bed to the Mf temperature.
18. The process of claim 9 for modified martempering steel alloy articles wherein, when the article temperature has dropped below the Ms temperature but is still above the Mf temperature, the bed is slumped for a period of time sufficient for the article temperature to equilibrate and thereafter the bed is refluidized with low conductivity gas and the article is quenched in the bed to the Mf temperature.
19. A process for the austempering of steel alloy articles to form a bainitic structure within the the alloy comprising:
(a) providing a steel alloy article at an austenitizing temperature;
(b) fluidizing a bed comprised of fine solid particles with high conductivity gas at a flowrate at least 1.5 times the minimum fluidization flowrate, at a temperature within the range of from the Mf temperature to 50°F greater than the Ms temperature of the alloy;
(c) immersing the article in said fluidized bed and quenching the article in the fluidized bed for a period of time until the article temperature has been reduced to that of the fluidized bed while fluidizing the bed with high conductivity gas for at least a portion of the quench period; and thereafter (d) stopping the flow of high conductivity gas and maintaining the article in the bed at the bed temperature for a time sufficient to avoid the substantial formation of martensite within the steel alloy.
(a) providing a steel alloy article at an austenitizing temperature;
(b) fluidizing a bed comprised of fine solid particles with high conductivity gas at a flowrate at least 1.5 times the minimum fluidization flowrate, at a temperature within the range of from the Mf temperature to 50°F greater than the Ms temperature of the alloy;
(c) immersing the article in said fluidized bed and quenching the article in the fluidized bed for a period of time until the article temperature has been reduced to that of the fluidized bed while fluidizing the bed with high conductivity gas for at least a portion of the quench period; and thereafter (d) stopping the flow of high conductivity gas and maintaining the article in the bed at the bed temperature for a time sufficient to avoid the substantial formation of martensite within the steel alloy.
20. The process of claim 19 wherein at least a portion of step (d) is carried out with the bed in a slumped condition.
21. The process of claim 19 wherein at least a portion of step (d) is carried out with the bed fluidized with a low conductivity gas.
22. A process for heat treating articles comprised of aluminum and/or aluminum alloy comprising:
(a) providing an article comprised of aluminum and/or aluminum alloy at an elevated temperature sufficient to allow hardening of the article by quenching;
(b) fluidizing a bed comprised of fine solid particles with high conductivity gas at a flowrate at least 1.5 times the minimum fluidization flowrate;
(c) immersing the article in said fluidized bed; and (d) quenching the article in the bed at a quench rate such that a 7/8 inch diameter nickel ball will be cooled from 750 to 550°F in less than 28 seconds, for a time period sufficient to increase the hardness of the article while fluidizing the bed with high conductivity gas for at least a part of the quench period.
(a) providing an article comprised of aluminum and/or aluminum alloy at an elevated temperature sufficient to allow hardening of the article by quenching;
(b) fluidizing a bed comprised of fine solid particles with high conductivity gas at a flowrate at least 1.5 times the minimum fluidization flowrate;
(c) immersing the article in said fluidized bed; and (d) quenching the article in the bed at a quench rate such that a 7/8 inch diameter nickel ball will be cooled from 750 to 550°F in less than 28 seconds, for a time period sufficient to increase the hardness of the article while fluidizing the bed with high conductivity gas for at least a part of the quench period.
23. The process of claim 22 wherein said elevated temperature is at least 750°F.
24. The process of claim 22 wherein step (d) is carried out entirely with the bed fluidized with high conductivity gas.
25. The process of claim 22 wherein step (d) is carried out in part with the bed fluidized with low conductivity gas.
26. The process of claim 22 wherein step (d) is carried out in part with the bed in a slumped condition.
27. A process for quenching articles to a desired temperature comprising: :
(a) providing an article at an initial temperature;
(b) fluidizing a bed comprised of fine solid particles with high conductivity gas at a flowrate at least 1.5 times the minimum fluidization flowrate;
(c) immersing the article in said fluidized bed; and (d) quenching the article in the bed for a period of time sufficient to achieve the desired temperature while (i) maintaining the bed at or below the desired temperature if the desired temperature is less than the initial temperature, or (ii) maintaining the bed at or above the desired temperature if the desired temperature is greater than the initial temperature, while fluidizing the bed with high conductivity gas for at least a portion of the quench period.
(a) providing an article at an initial temperature;
(b) fluidizing a bed comprised of fine solid particles with high conductivity gas at a flowrate at least 1.5 times the minimum fluidization flowrate;
(c) immersing the article in said fluidized bed; and (d) quenching the article in the bed for a period of time sufficient to achieve the desired temperature while (i) maintaining the bed at or below the desired temperature if the desired temperature is less than the initial temperature, or (ii) maintaining the bed at or above the desired temperature if the desired temperature is greater than the initial temperature, while fluidizing the bed with high conductivity gas for at least a portion of the quench period.
28. The process of claim 27 wherein step (d) is carried out entirely with the bed fluidized with high conductivity gas.
29. The process of claim 27 wherein step (d) is carried out in part with the bed fluidized with low conductivity gas.
30. The process of claim 27 wherein step (d) is carried out in part with the bed in a slumped condition.
31. The process of Claim 1, Claim 19, Claim 22 or Claim 27 wherein said fine solid particles are selected from the group consisting of metal oxide powders, refractory powders, and pure elements in a solid state, or combinations thereof, and wherein said pure element in a solid state is selected from the group consisting of iron, copper, nickel and carbon.
32. The process of Claim 31 wherein said high conductivity gas comprises a gas selected from the group consisting of helium, hydrogen, dissociated ammonia, and mixtures thereof.
33. The process of Claim 31 wherein said high conductivity gas comprises a mixture of gases, wherein at least one of said gases exhibits high conductivity and at least one other of said gases exhibits a thermal conductivity greater than or equal to a mixture of 80 percent nitrogen and 20 percent helium at the same temperature and pressure.
34. The process of Claim 32 wherein said high conductivity gas flow rate is within the range of about 1.5 to 15 times the minimum fluidization flow rate.
35. The process of Claim 34 wherein said high conductivity gas flow rate is within the range of about 2 to 7 times the minimum fluidization flow rate.
36. The process of Claim 33 wherein said high conductivity gas flow rate is within the range of about 1.5 to 15 times the minimum fluidization flow rate
37. The process of Claim 36 wherein said high conductivity gas flow rate is within the range of about 2 to 7 times the minimum fluidization flow rate.
38. The process of Claim 1, Claim 19, Claim 22 or Claim 27 wherein said fine solid particles have a density within the range of from 0.3 to 20 grams per cubic centimeter and a mean particle size within the range of from 30 to 1000 microns.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US913,320 | 1978-06-07 | ||
| US91332086A | 1986-09-30 | 1986-09-30 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1296603C true CA1296603C (en) | 1992-03-03 |
Family
ID=25433163
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000542520A Expired - Lifetime CA1296603C (en) | 1986-09-30 | 1987-07-20 | Process for rapid quenching in a fluidized bed |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0262324A1 (en) |
| JP (1) | JPS6389615A (en) |
| KR (1) | KR880004112A (en) |
| CN (1) | CN87105737A (en) |
| BR (1) | BR8703860A (en) |
| CA (1) | CA1296603C (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5080729A (en) * | 1987-11-10 | 1992-01-14 | Union Carbide Industrial Gases Technology Corporation | Process for rapid quenching in a collapsed bed |
| CN1311088C (en) * | 2002-01-18 | 2007-04-18 | 王新辉 | Pneumatic steet shot heat treating method and fluidized bed unit |
| CN101333593B (en) * | 2008-07-25 | 2010-06-30 | 张家港市东航机械有限公司 | Low level sand returning machine in fluidized bed furnace for quenching steel wire of steel wire tire cord |
| CN101886159B (en) * | 2010-07-13 | 2011-11-16 | 贾会平 | Method and device for heating steel billet |
| WO2019239184A1 (en) | 2018-06-13 | 2019-12-19 | Arcelormittal | Vacuum deposition facility and method for coating a substrate |
| WO2019239186A1 (en) | 2018-06-13 | 2019-12-19 | Arcelormittal | Vacuum deposition facility and method for coating a substrate |
| WO2020012222A1 (en) * | 2018-07-11 | 2020-01-16 | Arcelormittal | Method to control the cooling of a metal product |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3053704A (en) * | 1953-11-27 | 1962-09-11 | Exxon Research Engineering Co | Heat treating metals |
| FR2447968A1 (en) * | 1979-01-30 | 1980-08-29 | Celes Sa | Surface hardening of high carbon steels - which are induction heated and then quenched in fluidised bed or stream of particles, which may be heated for isothermal quenching |
| JPS565917A (en) * | 1979-06-28 | 1981-01-22 | Komatsu Ltd | Fluidized bed hardening device |
| JPS6043410B2 (en) * | 1981-11-11 | 1985-09-27 | 東レエンジニアリング株式会社 | Metal heat treatment method using fluidized bed furnace |
| DE3230531A1 (en) * | 1982-08-17 | 1984-02-23 | Ruhrgas Ag, 4300 Essen | METHOD FOR INTERIM COMPENSATION OF WORKPIECES |
| US4717433A (en) * | 1983-03-07 | 1988-01-05 | Rockwell International Corporation | Method of cooling a heated workpiece utilizing a fluidized bed |
| JPS60121253A (en) * | 1983-12-05 | 1985-06-28 | Nissan Motor Co Ltd | Spheroidal graphite cast iron |
-
1987
- 1987-07-20 CA CA000542520A patent/CA1296603C/en not_active Expired - Lifetime
- 1987-07-24 EP EP87110765A patent/EP0262324A1/en not_active Withdrawn
- 1987-07-24 BR BR8703860A patent/BR8703860A/en unknown
- 1987-07-30 JP JP62189051A patent/JPS6389615A/en active Pending
- 1987-08-03 KR KR1019870008490A patent/KR880004112A/en not_active Application Discontinuation
- 1987-08-19 CN CN198787105737A patent/CN87105737A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| CN87105737A (en) | 1988-05-04 |
| BR8703860A (en) | 1988-05-03 |
| KR880004112A (en) | 1988-06-01 |
| JPS6389615A (en) | 1988-04-20 |
| EP0262324A1 (en) | 1988-04-06 |
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