JPS6389615A - Method for quenching in fluidized bed - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Minute Hand of the Invention The present invention relates to the quenching of articles in fluidized beds and is particularly useful for quenching metal parts in fluidized beds.

Quenching techniques are widely used to heat treat articles in order to rapidly change the temperature of the article. Generally, quenching techniques are used to rapidly reduce the article temperature (in this case referred to as quenching, quenching, etc.), although quenching techniques can also be used to rapidly increase the article temperature.

The articles to be quenched are often metal parts.

Quenching has traditionally been performed in a number of ways.

In subbreakquenching, a liquid is sprayed onto the article to be treated. In gas quenching, the article is
Placed in a flowing stream of gas or vapor such as air, nitrogen, argon, helium, hydrogen, steam or combustion products. In fog quenching, a stream of gas or vapor entraining droplets is directed onto the surface of the article to be quenched. In immersion quenching, the article is immersed in a liquid bath such as water, brine, oil, molten salt, polymer solution, or liquid cryogen.

Although these conventional quenching methods have been used satisfactorily, they exhibit a number of drawbacks.

For example, liquids such as oil quenching agents often leave layers on articles that must be removed and cleaned. Some quenching agents, such as molten salts, have disposal problems.

Other quenching agents such as polymers and oils degrade over time and must be replaced. Another disadvantage of some quenching agents is the fact that the quenching temperature is often at their boiling temperature, thus causing the rate of heat transfer to vary along the surface of the article.

Fluidized beds are known to be used in quenching articles and serve to overcome these problems. After fluidized bed quenching, little to no heat is required to purify the article. Also, the particles used in fluidized beds are inert and do not degrade. However, to date, fluidized beds have not been widely used to quench articles such as metal parts. The reason is that a low quenching rate is required to satisfactorily quench metal parts made of metal alloys other than cryogenic alloys without forming undesirable soft phases in the metal parts. It was too much.

OBJECTS OF THE INVENTION It is an object of the present invention to provide an improved heat treatment method that allows metal articles to be quenched in a fluidized bed while avoiding the formation of undesired soft phases in the metal articles.

It is another object of the present invention to provide an improved method of heat treatment in which articles can be effectively quenched through the use of a fluidized bed.

SUMMARY OF THE INVENTION The present invention, in broad concepts, comprises the steps of (&) providing an article at an initial temperature;
fluidizing a bed of fine solid particles using a highly conductive gas at a flow rate of at least 15 times the minimum fluidization flow rate; (e) immersing an article in said bed;
(1) If the desired temperature is higher than the initial temperature, while maintaining the bed at or above the desired temperature, quenching the article in the bed for a period sufficient to achieve the desired temperature while fluidizing the bed using a highly conductive gas for at least a portion of the quenching period. Provides a method for quenching the temperature.

In certain aspects thereof, the present invention comprises the steps of: (1) providing a steel alloy article at an austenitizing temperature; (e) immersing said article in said fluidized bed at a bed temperature below the Ms temperature of said alloy; and (d) at least part of a quenching period. While fluidizing the bed with a highly conductive gas during the entire quenching period and maintaining the bed at a temperature below the Ms humidity temperature of the alloy for the entire quenching period, the quenching process is performed without substantially forming undesired soft phases within the article. A method for heat treating a steel alloy article is provided that includes quenching the article in a bed for a period of time and at a quenching rate sufficient to achieve M wet temperature of the alloy.

Definition of Terms "Quenching" as used herein means:
A rapid change in the enthalpy of an article due to heat transfer across the article interface, where the rate of enthalpy change is taken to be greater than that when the article is placed in and surrounded by a quiescent atmosphere. .

"Quenching rate" is the rate at which an article is quenched in °C.
means the amount of heat transferred per unit time across the article interface.

The term "bed" means a defined volume or bulk formed by solid particles.

The term "thin fixed particles" refers to l111.3-209
Porous or non-porous particles having a density within the range of 7 cm'' and an average particle size within the range of 50 to 1000 microns.

The term "fluidized bed" means a bed through which a fluid, such as a gas and/or steam, is passed, in which the fluid motive force of the fluid component causes the movement of the solid component from its rest position into both components in the bed. inducing in a manner that enhances the mixing of The term "fluidization" derives from the fluid-like properties that the bed assumes, such as zero-body angle of repose, mobility, and a pressure head equal to the bulk density of the bed.

The term "immersion" refers to a process in which substantially all of the article to be treated, or if only a portion of the article is to be treated, substantially all of that portion is surrounded by fluidized particles during quenching. It means to do something.

"Minimum fluidization flow rate" means the minimum volumetric flow rate of a fluid component through a bed that is necessary for the bed to achieve fluidized bed characteristics at atmospheric pressure.

"Settled bed" means a bed that has no fluid passed through it or only has fluid passed through it at less than a minimum fluidized flow rate.

The term "highly conductive gas" is also referred to as a high conductivity gas, and refers to a single gas or gas mixture that has a thermal conductivity greater than or equal to the thermal conductivity of a mixture of 80% nitrogen and 20% helium under the same temperature and pressure conditions. , steam, steam mixture or gas-steam mixture.

The term "steel alloy article" means a shaped article consisting at least in part of steel or iron-based alloy.

The term "austenitizing temperature" means the temperature at which the steel alloy of a steel alloy article is austenitic.

"Ms1 temperature" means the temperature at which the austenite phase of the steel alloy begins to change to martensite.

"rMf temperature" means the temperature at which substantially all of the steel alloy is converted to martensite.

"Soft phase" means pearlite, ferrite, bainite, etc.

By "nose m degrees" is meant the temperature at which the time required for austenite to begin transformation into a soft phase is minimal.

DETAILED DESCRIPTION OF THE INVENTION The method of the present invention is particularly useful for heat treating steel alloy articles and will therefore be detailed with reference to this type of heat treatment. Therefore, herein, quenching generally refers to quenching (quenching).

The method of the present invention can be used to effectively quench articles made of any steel alloy. The method is applicable to the production of molybdenum steels such as Al5I types 4130 and 4140, Al5I454o, 8620, 8630 and 9860.
Nickel-chromium-molybdenum steels such as Al5I4
640-like nickel-solipden fi, Al5I5
Rom steel like 140, Al511144 and 114
It is particularly useful for quenching Series 1100 steels such as No. 1 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 1500-1700? within the range of

At the austenitizing temperature, the structure of the steel alloy is substantially all austenitic. The term austenite, like the terms martensite, nozorite, ferrite, and bainite, is well known to those in the field, and the definitions of these structures are related to heat treatment or metallographic structures such as: Found in the text:
“Heat Treaters Guide, Standard Practice and Procedures for Steel J ASMSM@tals Park (1982)
, “Atlas Opisothermal Transformation and Cooling Transformation Diagrams JASM.

M@tals Park (1977) and Metals
Handbook 1Vo14 Heat Treating,
ASM, Metals Park (1981).

Beds useful in the process of this invention consist of fine solid particles.

Examples of the types of bed particles that may be used in the present invention include:
Metal oxide powders such as aluminum oxide, chromium oxide, iron oxide, titanium oxide, refractory powders such as silicon dioxide, mullite, magnesite, zirconium oxide and forsterite, and solids such as iron, copper, nickel and carbon. Pure elements can be mentioned.

Bed particles useful in this method have an average particle diameter within the range of 30 to 1000 microns. Particles smaller than this are difficult to fluidize and provide insufficient heat transfer, while particles larger than this do not contact the heat transfer surface frequently enough and result in poor heat transfer and fluidize the bed. It requires a large amount of gas.

The bed is fluidized by flowing a highly conductive gas through the bed. The use of high conductivity gases is important to achieving the beneficial results of the method. This is because high conductivity is required, especially at the austenitizing temperature, to achieve quenching rates that allow Ms wet temperatures to be achieved without forming soft phases within the steel alloy. Examples of highly conductive gases include helium, hydrogen and dissociated ammonia. In addition, mixtures of high conductivity pure gases such as hydrogen and helium with low conductivity gases,
It may be used as long as it meets the high conductivity gas requirements defined above.

The bed is fluidized with a high conductivity gas at a gas flow rate that is at least 15 times the minimum fluidization flow rate depending on the dust type and size of the particular bed particles used.

Preferably, the high conductivity gas flow rate is between 2 and 2 of the minimum fluidization flow rate.
It is within the range of 7 times. If the flow rate is less than the minimum flow rate,
The circulation of particles becomes slow, resulting in poor heat transfer. At flow rates greater than about 15 times the minimum fluidization flow rate, small particles can begin to be carried out of the bed.

When the bed is fluidized with a highly conductive gas at a predetermined gas flow rate, an austenitic steel alloy article is immersed into the fluidized bed for quenching.

The steel alloy article is held in the bed for a sufficient period of time to reduce the temperature of the article at or below the Ms wet temperature. This temperature reduction occurs rapidly. That is, the article is rapidly cooled. Initially, quenching is always carried out while fluidizing the bed with a highly conductive gas. Quenching of articles at Ms wet temperature may be carried out with the bed fluidized with a high conductivity gas for the entire period or with the bed quiescent and/or fluidized with a low conductivity gas for a portion of the period. You can also do that. For purposes of this invention, any gas that is not a high conductivity gas is a low conductivity gas. However, it is critical that the cooling rate of the article during the quenching step is sufficient to prevent the formation of soft phases in the alloy (Ms wet temperature). For successful implementation, under some circumstances it may be necessary to vary the fluidization gas flow rate while adhering to defined limits during the quenching period.

Quenching rate is generally measured by a method known variously in the art as the Magnetic Test 1 General Motors Quenchiometer Test or the Nickel Ball Test. This method involves heating a 1 inch (22-) nickel ball weighing approximately 18 ounces (50 g) to a predetermined high temperature and quenching the ball to a predetermined low temperature in a quenching agent to be subsequently evaluated. consists of things. The time required for the temperature of the ball to drop from high to low is a measure of the quenching rate. In the inventive method for heat treatment of steel alloy articles, the initial quenching rate as measured by the nickel ball test between temperatures of 1 (500? and 6847) is less than 24 seconds.

To more clearly illustrate the method, reference is made to the drawing in which a quenching curve is superimposed on a schematic steel alloy time-temperature-transformation diagram. In the drawings, line 1 represents the Ms humidity temperature and line 2 represents the Mf humidity temperature.

Line 3 indicates the transformation initiation line where the steel alloy begins to form a soft phase transformation and line 4 indicates where the transformation to the soft phase is complete. As can be seen from the drawing, line 3 indicates where the soft phase will form in the steel alloy if the Ms humidity temperature is not first achieved.
6 is shown. The elapsed time from initiation of quenching to reaching the nose varies with alloy type and can be obtained from the TTT diagrams referenced herein.

Curve 7 shows that Ms
Figure 2 illustrates a generalized quenching curve for an article quenched by the present method when the entire quenching period is carried out with flowing highly conductive gas through the bed as the temperature decreases. Quenching speed is quenching curve 7
is the absolute value of the slope of . As can be seen from the figure, the quenching rate is sufficient to allow crossing the Ms wet temperature line 1 without intersecting the transformation onset line 5. The O bed is flowed at a temperature lower than the Ml temperature. It is then preferably flowed at a temperature lower than the Mf humidity temperature of the alloy.

As is known to those skilled in the art, 1 rapid cooling is not necessarily desired as it can induce stresses in the alloy. Therefore, the quenching rate can be reduced by changing the bed operating regime if possible without intersecting the soft phase transformation initiation line. After an initial period of fluidizing the bed with a high conductivity gas, purges can be performed with the bed fluidized to a low conductivity gas or with the bed quiescent. It is possible to alternate between these two modes of operation and to refluidize the powder with a highly conductive gas at any point. A convenient point to change from fluidization using highly conductive gas to another mode of bed operation is when the article temperature falls below nose temperature. As previously mentioned,
Quenching is continued for a predetermined period of time at a quenching rate sufficient to achieve the Ms wet temperature of the alloy without substantially forming undesired soft phases in the article.

Once the Ms humidity temperature is reached, the article may be removed from the floor if desired. However, if the item is kept in the floor and M
It is preferable to further quenotate at a humid temperature. This additional quenching is shown schematically in the drawing.
It may be carried out using a high conductivity gas to fluidize the bed, but preferably it may be carried out with the bed quiescent or with a low conductivity gas fluidizing the bed. Additional quenching can be carried out in any of these three operating modes and without intersecting the soft phase transformation initiation line 4 (Mf
It is possible to switch between them as long as the quenching rate is sufficient to achieve the humidity temperature.

Special heat treatment techniques such as martempering and modified marten/curling can be performed using the present method.

To perform martempering using this method,
While the steel alloy article temperature drops below the nose temperature but is still above the Ms temperature, the article is quenched while fluidizing the bed using a highly conductive gas. The bed is then allowed to settle until the article temperature equilibrates, ie, the temperature at the center of the article is substantially equal to the temperature at the surface of the article. The bed is then refluidized using a low conductivity gas and the article is quenched in the bed at Mf humid temperature.

In yet another method of performing martempering using the present method, the steel alloy article is heated at a temperature of
The bed is then fluidized using a low conductivity gas and quenched while the bed is fluidized using a high conductivity gas until the temperature drops below the The article is quenched in the bed at Mf humidity temperature.

To perform modified martempering using this method, Mf
The steel alloy article is quenched while the humidity temperature is still high while fluidizing the bed using a highly conductive gas. The bed is then fluidized using a low conductivity gas and the article is quenched in the bed at Mf humidity temperature.

The method of the invention will be explained in more detail on the basis of the following examples, which are presented for illustrative purposes.

Example 1 A steel alloy part made of 4140 steel was heated to an austenitizing temperature of 16257. The Mm temperature of this steel alloy is 650
? It is. A bed consisting of 220 mesh aluminum oxide grains was heated using helium at 150 mesh per ft” of bed.
The alloy was fluidized at a flow rate of f t”/hr (standard conditions), which is approximately twice the bed minimum fluidization flow rate. Ru.

The part is immersed in a fluidized bed and the part temperature is 50°C.
It was quenched when it reached 07. Thereafter, the helium flow was shut off and the bed was allowed to settle for 15 minutes. Using nitrogen (low conductivity gas) on the bed, the part temperature reaches Mf humidity temperature and then 175? The mixture was refluidized until a bed temperature of . The parts were removed from the floor and subjected to hardness testing. The test was carried out at 52R on both the inch and 1 inch parts below the surface of the part.
c (Rockwell hardness number on the C scale), which indicates that a substantially complete rutinsite structure was formed without the formation of a soft phase.

Example 2 The procedure of Example 1 was repeated for steel alloy parts of 55°? was repeated except that it was made of 4 540 il with an M3 temperature of . The parts are 52Rc at the bottom inch and 1 inch area.
Example 3: 862%, having dimensions of 862% inch diameter x 6 inch length, indicating substantially complete martensite formation without the formation of a soft phase.
o! EXAMPLE 1 Steel alloy parts manufactured by No. 1 were carburized to 10% carbon on the surface at temperatures below 1550°C. A bed of 220 mesh aluminum oxide grains was heated to 225 f using helium.
The part was immersed in the fluidized bed and the part temperature was below the M-temperature and substantially equal to the bed temperature. This period was approximately 60 seconds.The part was removed from the floor and quenched for a period of 4007 seconds.
It was tempered for 15 hours. Metallographic specimens were prepared by cutting inch pieces from one end of the part. The surface hardness of the test piece is 9 as measured on a 15N scale.
0, N, and the hardness of the core or center is Rockwell C
It was 45 when measured on a scale.

The minimum acceptable hardness values for these parts were 80 and 30 for the surface and core, respectively.

For comparative purposes, the process of Example 3 was repeated except that nitrogen was used as the flow gas. The surface hardness of this nitrogen fluidized bed sample was 89, but the core hardness was only 22. This fact demonstrates the significant improvement in part hardness that can be achieved by using the method of the invention.

The quenching method of the present invention can be used to perform austenoring of an alloy that transforms the alloy structure to bainitic. This method is particularly useful for heat treating cast iron. This additional aspect of the method of the invention can be formulated as follows: A method for austempering a steel alloy article to form a bainitic structure in the steel alloy, comprising:
(&) providing a steel alloy article at an austenitizing temperature; (c) immersing an article in said fluidized bed until the article temperature decreases to the temperature of the fluidized bed at said bed temperature; quenching the article in the fluidized bed for a period of time and simultaneously fluidizing the bed with a highly conductive gas for at least a portion of the quenching period; (d) stopping the flow of the highly conductive gas and discharging the article; maintaining the bed at bed temperature for a period sufficient to avoid substantial formation of martensite in the steel alloy.

Step (d) of the austempering process can be carried out with the bed settled or with the bed fluidized with a low conductivity gas and can be alternated between these two modes of bed operation.

The quenching method of the present invention can also be used to effectively quench aluminum articles. Traditionally, aluminum and aluminum alloys have been quenched using water or polymeric quenching agents, and these quenching agents achieve desired metallurgical properties such as high strength after aging and resistance to stress corrosion cracking. This enabled a sufficient quenching rate to be achieved. However, especially for relatively thin-walled articles, conventional quenching agents
The method of the present invention tends to induce a considerable amount of distortion, which results in a considerable increase in costs associated with straightening operations. Aluminum and aluminum alloys can be quenched at high quenching rates. This -like distribution is necessary for the component to have high strength. Moreover, using the method of the invention, the quenching rate can be adjusted and controlled by operating the bed in a quiescent state or by fluidizing the bed using low conductivity gases. , an aluminum article can be quenched at a quenching rate that substantially avoids distortion in the material. The method of the invention as applied to aluminum or aluminum alloys can be defined as follows: (-) Aluminum and/or aluminum alloys at an elevated temperature sufficient to enable hardening of the article by quenching. (b) fluidizing a bed of fine solid particles using a highly conductive gas at a flow rate of at least 15 times the minimum fluidization flow rate; and (c) providing an article comprising: immersing in the fluidized bed; (d)
) 750T to 550 inch diameter nickel balls are released in the bed while fluidizing the bed using a highly conductive gas for at least part of the quenching period. quenching for a period sufficient to increase the hardness of the article at a quenching rate such that the article is cooled in less than 28 seconds.

Generally, the temperature and humidity of the stage (&) is at least 7507 and usually 800? exceed. Stage N(d) can be carried out with the bed fluidized with a high conductivity gas for the entire period at °C, but generally and preferably with the bed fluidized with a low conductivity gas for a portion of the period, or the bed is operated in a subdued mode. The stage to be carried out (
d) is conveniently continued until the article reaches ambient or near ambient temperature.

The quenching method of the present invention is applicable to metal, glass 1-cell
It may also be used to rapidly cool down or rapidly raise the temperature of articles made of any effectively heat treatable material such as wood or plastic. The present quenching method as applied to rapid temperature increases and decreases of an article can be defined as: (c) providing an article at an initial temperature;
b) fluidizing a bed of fine solid particles using a highly conductive gas at a flow rate of at least 15 times the minimum fluidization flow rate; (1) immersing an article in said bed; 1)
(1) If the desired temperature is higher than the initial temperature, the bed is maintained at or above the desired temperature while simultaneously quenching the bed. quenching the article in the bed for a period sufficient to achieve the desired temperature while fluidizing the bed using a highly conductive gas for at least a portion of the quenching period. A method for quenching.

Stage N(d) may be carried out with the bed fluidized using a high conductivity gas for the entire period, or stage (d) may be carried out with the bed fluidized for a portion of the time using a low conductivity gas or in a subdued manner. It can be implemented by manipulating.

ADVANTAGES OF THE INVENTION The use of the method of the invention allows rapid changes in the temperature of an article through the use of a fluidized bed, thereby providing greater control over the temperature change process than was possible using conventional quenching agents. Make it seem possible. Additionally, the quenching process of the present invention is much easier to operate and cleaner than conventional processes. The method of the invention can be particularly advantageously applied to heat treating metal parts to achieve a desired internal metallographic structure.

The drawing is a diagram showing both a time-temperature-transformation (TTT) diagram and a steel alloy quenching curve.

Shizej

Claims (1)

Claims: 1) (a) providing a steel alloy article at an austenitizing temperature; (c) immersing said article in said fluidized bed at a bed temperature below the Ms temperature of said alloy; and (d) for at least a portion of a quenching period. While fluidizing the bed with a highly conductive gas and maintaining the bed at a temperature below the Ms temperature of the alloy for the entire quenching period, the alloy can be quenched without substantially forming undesired soft phases within the article. quenching the article in a bed for a period and at a quenching rate sufficient to achieve a Ms temperature. 2) A method according to claim 1, wherein the bed is fluidized with a highly conductive gas during the entire period of step (d). 3) A method according to claim 1, wherein the bed is fluidized with highly conductive gas only during a part of step (d). 4) A method according to claim 3, wherein the period portion of step (d) in which the bed is fluidized with a highly conductive gas is an initial portion of the period. 5) Stage (d) where the bed is not fluidized with highly conductive gas.
4. The method of claim 3, wherein the bed is fluidized with a low conductivity gas during at least part of the period of . 6) Stage (d) where the bed is not fluidized with highly conductive gas.
4. The method of claim 3, wherein the bed is operated in a quiescent state during at least part of the period. 7) Claim 1 in which the highly conductive gas is helium
The method described in section. 8) The method according to claim 1, wherein the highly conductive gas is hydrogen. 9) The method of claim 1, wherein after step (d), the article is held in the bed for an additional period of time and additionally quenched to the Mf temperature. 10) The method of claim 9, wherein during at least part of the additional period the bed is fluidized with a highly conductive gas. 11) The method of claim 9, wherein during at least part of the additional period the bed is fluidized with a low conductivity gas. 12) The method of claim 9, wherein the bed is operated in a quiescent state during at least part of the additional period. 13) The method of claim 1, wherein the bed temperature is maintained below the Mf temperature. 14) Initial quenching rate at the beginning of step (d) for 7/8 inch diameter nickel balls from 1600°F to 6
The method of claim 1, wherein the method is such that the temperature is cooled to 80°F in less than 24 seconds. 15) Steel alloys in which the bed is fluidized with a low conductivity gas and the article is quenched in the bed to the Mf temperature when the article temperature falls below the nose temperature, but while still above the Ms temperature. A method according to claim 9 for martempering articles. 16) When the article temperature falls below the nose temperature, but while still above the Ms temperature, the bed is allowed to settle for a period sufficient for the article temperature to equilibrate and the bed is refilled with a low conductivity gas. 10. The method of claim 9 for martempering of steel alloy articles, wherein the article is fluidized and the article is quenched in a bed to Mf temperature. 17) When the article temperature falls below the Ms temperature, however, Mf
Claim 9 for improved martempering of steel alloy materials in which the bed is fluidized with a low conductivity gas and the article is quenched in the bed to the Mf temperature while still above the Mf temperature. the method of. 18) When the article temperature drops below the Ms temperature, provided that M
While still above the f temperature, the bed is allowed to settle for a period sufficient for the article temperature to equilibrate and the bed is refluidized with a low conductivity gas and the article is quenched in the bed to the Mf temperature. 10. The method of claim 9 for improved martempering of steel alloy articles. 19) A method for austempering a steel alloy article to form a bainitic structure in the steel alloy, the method comprising: (1) providing a steel alloy article at an austenitizing temperature; and (b) fine solid particles. fluidizing the bed using a highly conductive gas at a flow rate of at least 1.5 times the minimum fluidization flow rate at a temperature within the range of the Mf temperature of the alloy to 50° F above the Ms temperature; (c) immersing the article in the fluidized bed and quenching the article in the fluidized bed for a period of time until the article temperature decreases to the temperature of the fluidized bed at the bed temperature, while at least a portion of the quenching period; fluidizing the bed with a highly conductive gas for a period of time; (d) stopping the flow of the highly conductive gas and placing the article in the bed at bed temperature to avoid substantial formation of martensite in the steel alloy; and maintaining for a sufficient period of time. 20) The method of claim 19, wherein at least a portion of step (d) is carried out with the bed in a quiescent state. 21) Claim 19, wherein at least a portion of step (d) is carried out while fluidizing the bed using a low conductivity gas.
The method described in section. 22) (a) providing an article of aluminum and/or an aluminum alloy at an elevated temperature sufficient to enable hardening of the article by quenching; and (b) rendering a bed of fine solid particles highly conductive. (c) immersing the article in said fluidized bed; and (d) at least part of the quenching period. A quenching rate such that a 7/8 inch diameter nickel ball cools the article from 750°F to 550°F in less than 28 seconds while fluidizing the bed using a highly conductive gas during the A method for heat treating an article made of aluminum and/or an aluminum alloy comprising the step of quenching for a period sufficient to increase the hardness of the article. 23) The method of claim 22, wherein the elevated temperature is at least 750°F. 24) A method according to claim 22, wherein step (d) is carried out during the entire period by fluidizing the bed with a highly conductive gas. 25) The method of claim 22, wherein step (d) is carried out by fluidizing the bed with a low conductivity gas for a portion of the time. 26) The method of claim 22, wherein step (d) is carried out with the bed quiescent for a portion of the period. 27) (a) providing the article at an initial temperature;
(b) fluidizing a bed of fine solid particles using a highly conductive gas at a flow rate of at least 1.5 times the minimum fluidization flow rate; and (c) immersing an article in said bed. and (d) (i) maintaining the bed at or below the desired temperature if the desired temperature is lower than the initial temperature, or (ii) maintaining the bed at or above the desired temperature if the desired temperature is higher than the initial temperature. quenching the article in the bed for a period sufficient to achieve the desired temperature while fluidizing the bed using a highly conductive gas for at least a portion of the quenching period. A method for quenching a containing article to a desired temperature. 28) A method according to claim 27, wherein step (d) is carried out during the entire period by fluidizing the bed with a highly conductive gas. 29) The method of claim 27, wherein step (d) is carried out by fluidizing the bed with a low conductivity gas for a portion of the time. 30) The method of claim 27, wherein step (d) is carried out with the bed quiescent for a portion of the period.