US3224910A

US3224910A - Quenching process

Info

Publication number: US3224910A
Application number: US259176A
Authority: US
Inventors: Mcewen Malcolm
Original assignee: Monsanto Co
Current assignee: Monsanto Co
Priority date: 1963-02-18
Filing date: 1963-02-18
Publication date: 1965-12-21
Anticipated expiration: 1982-12-21

Description

HARDNESS,ROCKWELL C Dec. 21, 1965 M. McEWEN 3,224,910

QUENCHING PROCESS Filed Feb. 18, 1963 6 Sheets-Sheet 1 60 SSECONDS IGSECONDS 32SECONDS w 25 r- IO 2 Z 2 Lu uJ u 9 u 0 2 4 6 8 O 2 4 6 8 O 2 4 6 8 DISTANCE FROM SURFACE 1% INCH U 645ECOND5 4MINUTE5 u.] 20 a: a:

11: IO Z Z I O S O 2 4 6 8 O 2 4 6 8 DISTANCE FROM SURFACE a I NCH FIGURE 1. HARDNESS TRAVERSES ON l-INCH-DIAMETER HARDENABILITY BARS OF AISI I046 STEEL QUENCHED FOR THE INDICATED TIMES IN WATER FOLLOWED BY CHLORINATED BIPHENYL INVENTOR.

M ALCOLM MC. EWEN ATTORNEY Dec. 21, 1965 M. McEwEN 3,224,910

QUENCHING PROCESS Filed Feb. 18, 1963 6 Sheets-Sheet 2 u 60 SSECONDS I6SECONDS BZSECONDS I m 5 u 0 w In Q n a: u] w Q s z E m w O O 4 8 I2 I6 0 4 8 I2 [6 O 4 8 I2. I6

DISTANCE FROM SURFACE INCH U 64SECONDS 4M|NUTES .I g] 50 I 2 50 If) 3 20 c: cc Z if I'll IO Z 5 LU I U u o 4 8 l2 I6 0 4 8 I2 I6 DISTANC E FROM SURFACEINCH FIGURE 2. HARDNESS TRAVERSES ON Z'INCH-DIAMETER HARDENABILITY BARS OF AISI I046 STEEL QUENCHED FOR THE INDICATED TIMES IN WATER FOLLOWED BY CHLORINATED BIPHENYL INVENTOR MALCOLM Mc EWEN ATTORNEY Dec. 21, 1965 M. MCEWEN 3,224,910

QUENCHING PROCESS Filed Feb. 18, 1963 6 Sheets-Sheet 5 SSECON DS I6SECON DS BZSECONDS HARDNESS, ROCKWELL C .b. 0! o O 20 0C LIJ IO Z LL] O 2 4 6 8 O 2 4- 6 8 O 2 4 6 8 DISTANCE FROM SURFACE INCH 7O 64SECONDS 3M|NUTES 60 .J L|J 3 5O 5 O 40 U) (n 30 0 2O 5 I IO O 2 4 6 8 O 2 4 6 8 DISTANCE FROM SURFACE% INCH FIGURE 3, HARDNESS TRAVERSES ON I-INCH-DIAMETER HARDENABILITY BARS OF AISI 52|OO STEEL QUENCHED FOR THE INDICATED TIMES IN WATER FOLLOWED BY CHLORINATED BIPHENYL INVENTOR.

MALCOLM MC EWEN BY [WWW ATTORNEY HARDNESIS ROCKWELL C Dec. 21, 1965 Filed Feb. 18, 1963 FIGURE 4 HARDNESS M. MCEWEN 3,224,910

QUENCHING PROCESS 6 Sheets-Sheet 4 HARDNESS, ROCKWELL C SSECONDS IGSECONDS 3ZSECOND5 II 0: I]: LLI LLI I41 I- l- I- Z Z Z LLI LLI LLI 9 8 I2 I6 0 4 8 I2 I6 0 4 8 I2 I6 DISTANCE FROM SURFACEINCH 7O fi l-SECONDS 5MINUTES 20 [I 0: I41 LLI l- IO Z Z LLI LIJ 0 9 a 0 4 8 I2 I6 0 4 8 I2 I6 DISTANCE FROM SURFACEi INCH TRAVERSES ON Z'INCH-DIAMETER 52IOO STEEL IN WATER HARDENABILITY BARS OF AISI QUENCHED FOR THE INDICATED TIMES FOLLOWED BY CHLORINATED BIPHENYL INVENTOR.

MALCOLM MC EWEN BY 6. mam/1W ATTORNEY Dec. 21, 1965 M. McEWEN 3,224,910

QUENCHING PROCESS Filed Feb. 18, 1963 6 Sheets-Sheet 5 AISI |O46-- (n m I .025-

I I.- E 3 .020-

E u .015- U z I 0 Z .0|0- AISI 52|00\ 9 I. CC 0 I,- Q .005- o o l l l l I n TIME IN WATER,SECOND5 FIGURE 5. DISTORTION OF AISI I046 AND AISI 52IOO STEEL QUENCHED IN WATER FOLLOWED BY CHLORINATED BIPHENYL INVENTOR.

MALCOLM MC EWEN ATTORNEY HARDNESS, ROCKWELL C Dec. 21, 1965 M. MCEWEN 3,224,910

QUENCHING PROCESS Filed Feb. 18, 1963 6 Sheets-Sheet 6 7O 4SECONDS SSECONDS IZSECONDS 2o 5 5 IO E 5 LL! 0 a g o 4 8 l2 l6 0 4 8 I2 I6 DISTANCE FROM suRFAcE% INCH IGSECONDS ISOSECONDS .J LT} 3 K g 0 n uJ Z D: Q m I'- I Z LIJ L. o 4 8 I2 l6 0 4 8 I2 [6 DISTANCE FROM SURFACE-L INCH FIGURE 6. HARDNESS TRAVERSES ON 2" INCH- DIAMETER HARDENABILITY BARS OF AISI I046 STEEL QUENCHED FOR THE INDICATED TIMES IN 9 PER CENT BRINE FOLLOWED BY CHLORINATED BIFHENYL INVENTOR.

MALCOLM MC. EWEN BY a ATTOR N EY United States Patent G 3,224,910 QUENCHING PROCESS Malcolm McEwen, Glendale, Mo., assignor to Monsanto Company, a corporation of Delaware Filed Feb. 18, 1963, Ser. No. 259,176 11 Claims. (Cl. 148143) This invention relates to an improved quenching process for metals, particularly steel, and more particularly to an improved quenching process using a novel twophase quenching composition.

The mechanical properties of the metals used for the manufacture of shaped articles, such as iron, copper, nickel, aluminum, magnesium, zinc, gold, silver, lead and tin and their alloys, can be modified by various known methods of heat treatment wherein the metal is heated to some definite temperature and then cooled. In many of such heat treating operations, the hot metal is cooled more or less rapidly and such rapid cooling operations are generally known as quenching. Generally, quenching is accomplished by immersing the hot metal in a bath of a liquid such as water or oil. A common quenching operation is the quenching of steel in water or other aqueous liquids or in oil.

Since steel is by far the metal most commonly quenched, the following discussion of the present invention will be primarily with respect to steel although it is to be realized that such a procedure is in no manner a limitation of the scope of said invention.

The heating of steel to high temperatures results in the transformation of the steel to austenite, a solid solution of carbon in face centered cubic iron. Upon subsequent rapid cooling (quenching), austenite transforms to martensite, a hard, brittle form of steel which, when properly tempered, possesses the combination of strength and toughness usually associated With steel. Cooling at slower rates than that required to form martensite results in the transformation, at temperatures above those associated with martensite formation, of austenite to less desirable structures such as mixtures of pearlite and bainite.

The hardness of a steel, in the martensitic condition, depends, for the most part, on the carbon content of the steel. Alloying elements are added to heat treatable steels for the purpose of decreasing the cooling rate needed to insure that fully martensitic structures will be obtained. In a part being quenched, the cooling rate decreases with increasing distance below the surface being quenched. Therefore, alloying elements control the size of a part that can be quenched to a fully martensitic structure, or, in other words, the hardenability of the steel. High alloy steels have high hardenability and a part of a given size will harden throughout with a relatively low cooling rate, but high alloy steels are expensive. On the other hand, cheaper, low alloy or plain carbon steels require a higher cooling rate to obtain thorough hardening in a given part due to their having low hardenabilities. But with the more severe quenching (higher cooling rate), distortion and quench cracking may be encountered.

A quenching operation may be conveniently described as consisting of three stages:

(1) In the first stage, or vapor blanket stage, the temperature of the metal is so high that the quenching media is vaporized at the surface of the metal and a thin stable vapor film surrounds the part. The vapor envelope acts as an insulator, and cooling takes place principally by radiation through the vapor film. Cooling speed is relatively slow through this stage.

(2) The second stage, or vapor boiling stage, begins when the metal has cooled to such a temperature that the vapor film is no longer stable. The quenching media then tends to wet the surface of the metal, and violent 3,224,910 Patented Dec. 21, 1965 boiling ensues. Heat is removed from the metal at a very rapid rate as latent heat of vaporization. Cooling is most rapid in this stage.

(3) The third stage, or contact stage, begins when the surface temperature of the metal is reduced to the boiling point or range of the quenching liquid. Below this, boiling ceases and slow cooling takes place by conduction or convection. The rate of cooling is slowest in the third stage.

Water, water solutions, molten salts, oil, and oil emulsions are some of the materials which have been used as quenching media. Although water and water solutions of inorganic salts are the oldest and cheapest quenching media and impart maximum hardenability because they have the highest initial quenching speeds, they have the disadvantage that the high quenching speeds persist to low temperatures, resulting in warping, distortion, brittleness, uneven hardness and cracking. The low boiling point of water is responsible for these characteristics.

When quenching oils are used, the duration of the vapor blanket stage is longer; the rate of cooling in the boiling stage is slower; and the duration of the boiling stage is shorter. Because of these characteristics, quenching with oils is far less drastic than quenching with water, since the transition from the second stage (boiling) to the third stage (contact) is more gradual and distortion is minimized. As a result, oil emulsions or various oils such as fish and marine oil, animal oils, mineral oils, and their mixtures, have largely supplanted aqueous quenching compositions. Although quenching oils and oil emulsions in part minimize the internal stresses formed during hardening, and although quench cracking tendencies are reduced, metals quenched in such media may not fully harden as they would when quenched in aqueous media since the quenching speed of such quenchants is substantially slower, thus permitting the formation of mixtures of the softer, higher temperature transformation products. In addition, oil and oil emulsions tend to oxidize, form sludge, thicken, break down, and decompose at elevated temperatures, which greatly decrease the life of the quenchants, make them troublesome to use, and produce results which are not uniform. The flammable nature of oils also presents a serious fire hazard in quenching operations and, accordingly, the art has long sought for substitutes for oil but without much success.

Thus, an optimum quenching composition would be one that in the early stages of quenching had the cooling characteristics of a severe quenchant, but in the lower temperature range where the martensitic transformation takes place, would provide the slower cooling rate of a low severity quenchant. The high initial quenching rate would allow the use of low hardenability steels while the slow cooling rate during transformation would reduce the thermal gradients which cause distortion. and quench cracking. In addition, the optimum quenching media would be stable in service and would be fire resistant.

In order to try and obtain results approaching the results to be expected when quenching with an optimum quenching composition, it has previously been proposed to quench metals in both water and oil, in that order, so as to take advantage of the high quenching rate of water for the initial stages followed by the slower quenching rate of oil to develop the desirable properties only obtainable with oil. However, in order to quench with a two-phase composition composed of water and oil, it is necessary to maintain each phase in a separate quench tank since if a single quench tank were used the oil would float on top of the water and no advantages would result. On the other hand, the use of two separate quench tanks has many practical disadvantages which have discouraged such a practice.

It is, therefore, an object of this invention to provide a new and improved two-phase quenching composition which is effective in hardening steel and other metal articles to the extent normally associated with aqueous quenching without sacrificing the freedom from warping and cracking and other defects which distinguishes oil from water as a quenching media. It is an object of this invention to provide an improved quenching process employing a novel two-phase quenching composition.

It is a further object of this invention to provide a new and impr-oved two-phase quenching composition which provides the advantages of oil in terms of the quality of quenched articles but which, unlike oil, is extremely fire resistant and is, therefore, more desirable than oil. More particularly, it is an object of this invention to provide a two-phase quenching composition in which one phase is an aqueous phase but said aqueous phase is the upper phase.

It is also an object of this invention to provide a new and useful quenching composition for use in heat treating metals which has no fire hazards, offensive odor, fumes or foaming problems and which is substantially uniform in quenching effect over long periods of usage, stable, long lived, low in cost, and can be used at various temperatures to provide different advantageous quenching rates.

It has now been found that a two-phase quenching composition which overcomes the practical disadvantages of a Water and oil system but yet retains the desirable aspects of such a system, is obtained by the use of an aqueous upper phase, and a lower phase of chlorinated biphenyl. Such a composition offers the advantage of an initial high speed aqueous quench followed by a slower quench, at a rate typical of oil, wherein one quench tank can be used due to the fact that chlorinated biphenyl is heavier than water and water based media and thus is the lower phase. Other advantages of the novel twophase quenching composition of this invention, as will be more evident hereinafter, include the great fire resistance of the system, good oxidative and thermal stability, hydrolytic stability of the lower phase resulting in uniform quenching rates over longer periods of time and low cost. A further advantage is that the two-phase composition of this invention allow the use of low cost metals, instead of high cost alloys, since the same depth of hardening can be obtained with an oil quench yet the undesirable results associated with an aqueous quench such as distortion and cracking are avoided. Also the two-phase quenchant of this invention can be used for case hardening and carburizing processes.

The quenching process of this invention, which involves utilizing the quenching composition of this invention, consists in immersing a heated metal article in the upper aqueous phase for a short time and then immersing the article in the lower chlorinated biphenyl phase. The duration of the time an article is maintained in the tures even to the extent of incorporating a quenching and a tempering process in one operation.

When reference is made herein to immersing an article in a quenching composition, it is to be understood that the various means for effecting contact customarily used in the art can be employed. Thus, for example, the water phase could be sprayed or each phase could be flowed upon the article to be quenched.

Chlorinated biphenyl containing from about 20% to about 60% by weight of combined chlorine is generally useful in this invention, however, chlorinated biphenyl containing from about 40% to by weight of combined chlorine is preferred as providing quenching media having viscosity characteristics most suitable for use at usual quenching temperatures. Chlorinated biphenyl is commercially available as products containing about 21%, 32%, 42%, 48%, 54% or of combined chlorine corresponding approximately to mono-, di-, tri-, tetra-, pentaand hexachlorobiphenyl, respectively. The expressions chlorinated biphenyl containing about 40% to about 50% of combined chlorine and chlorinated biphenyl containing about 20% to about 60% of combined chlorine are used herein as not only including these chlorinated products, but also as blends of one or more of the chlorinated biphenyls whereby the total chlorine content is broadly within the range of 20% to 60%, preferably within the range of 40% to 50% by weight. For example, chlorinated biphenyl containing a total of 45% by Weight of combined chlorine can be effectively prepared, for the purpose of this invention, by blending together 50 parts by weight of chlorinated biphenyl containing 42% by weight of combined chlorine and 50 parts by weight of chlorinated biphenyl containing 48% by weight of combined chlorine. In a similar manner, to further illustrate, chlorinated biphenyl containing a total of 58% by Weight of combined chlorine, for purposes of this invention, may be effectively prepared by blending together 25 parts by Weight of chlorinated biphenyl containing 52% by weight of combined chlorine and parts by weight of chlorinated biphenyl containing 60% by weight of combined chlorine. Therefore, for purposes of this invention, chlorinated biphenyl containing generally about 20% to about 60%, or preferably about 40% to about 50%, by weight of combined chlorine may be obtained either by direct chlorination of the biphenyl to obtain the desired combined chlorine content, or a satisfactory material may be obtained by blending together two or more chlorinated biphenyls to obtain a resulting blend of chlorinated biphenyl containing an effective quantity of combined chlorine within the ranges designated above.

The general physical properties of chlorinated biphenyl having varying amounts of combined chlorine are given below.

Percent chlorine Property Density:

' Specific gravity, 25l25 C. (77/77 F.) 1.18 1. 26 1. 38 1. 45 1. 54 1.62 Pounds per gallon, 25 C. (77 F. 9. 10. 55 11. 50 12.04 12.82 13. 50 Initial boiling point at 760 mm. Hg, F 527 55 617 644 689 725 Flash point: Cleveland Open Cup, F 286-302 305-310 348-355 379-384 None None Fire point: Cleveland Open Cup, F 349 395 None None None None Visc0sity-Sayb0lt Universal sec. (ASTM- None indicates-N 0 fire point up to boiling temperature.

aqueous phase is dependent upon the section size of said article, its composition, and the depth of hardening desired as described more fully hereinafter. Further control of the quenching operation can also be obtained by controlling both the aqueous and organic phase tempera- From the above it is seen that chlorinated biphenyl is considerably heavier than Water, heavier than up to over a 20% brine solution, that it has a very high boiling point, that it is almost completely fire resistant and that the viscosities of chlorinated biphenyl offer wide latitude for various applications and operating temperatures.

In order to demonstrate the operation of the method of this invention and the uniqueness of the two-phase quenchant of this invention, two steels having considerably different properties, a low hardenability steel, AISI 1046, and a high hardenability steel, AISI 52100, were heat treated by austenitizing followed by quenching according to the process of this invention in the novel quenchant of this invention.

The samples of each steel which were heat treated consisted of one-inch and two-inch diameter hardenability bars and C-shaped, Navy-type distortion specimens. Austenitizing of the test samples was done in a controlledatmosphere furnace with a continuous flow of endothermic gas (carbon monoxide/carbon dioxide) to prevent oxidation and decarburization. A temperature of 1550" F. was used for both steels, and exhaust gas dew point of 55 F. and 35 F. were used for the AISI 1046 and AISI 52100 steels, respectively. The one-inch hardenability bars and the distortion specimens were heated in the furnace for one hour, whereas the two-inch hardenability bars were heated for two hours.

The quenching procedure consisted in immersing the heated test samples in the water layer for various lengths of time and then passing the samples into the chlorinated biphenyl layer. For convenience, chlorinated biphenyl containing 42% by weight combined chlorine was used. The quenched hardenability bars were sectioned transversely at mid-length (length equaled four times the diameter) with an abrasive cut-off wheel and a transverse slice approximately five-eights inch thick was removed. Approximately 0.0300.040- inch was then ground from the surfaces to be studied so as to remove any burning (tempering) resulting from the cut-off step. Each specimen was checked for burning by etching for 15 seconds in 5% nitric acid followed by 15 seconds in hydrochloric acid. No burning was found in any of the samples.

Hardness traverses were made on the transverse sections with Rockwell C hardness readings taken at onesixteenth inch intervals across at least two diameters. The results of the hardenability tests on one-inch AISI 1046 bars (average values) are plotted in FIGURE 1 and by inspection thereof it is evident that hardening essentially equal to that attained in what amounts to a straight water quench (4 minutes) was obtained with the specimens quenched in water for sixteen seconds followed by chlorinated biphenyl. Similar results were obtained with the two-inch bars as shown in FIGURE 2. The results of the hardenability tests on one-inch and two-inch AISI 52100 bars (average values) are plotted in FIGURES 3 and 4 from which it is evident that with the one-inch samples of this steel full hardening was obtained for all combinations of water-chlorinated biphenyl quenching and that with the two-inch samples quenching in Water for thirty-two seconds followed by chlorinated biphenyl gave hardening about equivalent to a straight Water quench (3 and 5 minutes, respectively).

For the distortion tests an optical comparator was used to measure the gap width before and after heat treatment. The difference in these two values is a measure of the distortion. The results of the distortion tests (average values) are plotted in FIGURE 5 from which it is evident that distortion is considerably reduced by use of timed water-chlorinated biphenyl quenching, yet no cracking was observed to have occunred in the timed Water-chlorinated biphenyl quench.

Even though direct comparisons are diflic-ult to make between the results of the hardenability tests and the distortion tests, due to the large differences in section size, it is noteworthy that the maximum hardening obtainable was obtained for the AISI 1046 steel in a 16 seconds in water-chlorinated biphenyl quench, yet upon reference to FIGURE 5 it is readily seen that the distortion resulting from such a sequence was considerably less than obtained in quenches employing longer times in water. In the case of the AISI 52100 steel, the test results also show that a reduction in distortion, without a corresponding loss in hardness, can be obtained by the use of a timed water-chlorinated biphenyl quench.

Since it is known that quenching in brine is more severe than quenching in water, i.e. the cooling rate of an article being quenched is faster in brine than in water, hardenability tests were run on two-inch diameter hardenability bars of AISI 1046 steel using a timed brinechlorinated biphenyl quench. The brine used was a nine percent sodium chloride solution. The heat treating procedure was the same as described above. The results of these tests are shown in FIGURE 6 from which it is evident that the maximum depth of hardening was obtained in a 12 seconds in brine-chlorinated biphenyl quench. Data from distortion tests indicated that less distortion was obtained in the 12 seconds in brine-chlorinated biphenyl quench than in quenches involving longer times in brine. Importantly, however, no quench cracks were observed. Similar results are obtained with other typical brine quenchants, such as those containing 612% sodium chloride.

From the results of the timed water-chlorinated biphenyl quench and brine-chlorinated biphenyl quench it is evident that the present invention, involving the use of a two-phase quenching composition composed of an upper aqueous layer and a lower chlorinated biphenyl layer provides the art with an improved means for quenching metals whereby great increases in hardenability are realized without attendant distortion, cracking and the like.

Chlorinated biphenyl, as described above, comprises the major proportion of the lower or organic phase of the two-phase quenching composition of this invention, and it is generally preferred because of fire prevention considerations that chlorinated biphenyl constitute at least 50% and even more desirably essentially :all of the lower phase of the quenching medium of this invention. However, it is contemplated that within the scope of this invention the two phase quenchamt will comprise an upper aqueous phase and a lower homogenous phase composed of blends of chlorinated biphenyl and oil, e.g. fish oils, marine oils, animal oils and mineral oils, or other material which blends still have a density appreciably greater than the aqueous phase at the operating temperature of the composition. An example of the physical properties of typical mineral oil-chlorinated biphenyl blends having a suitable density are given in the table below. The oil had the following properties:

API gravity 22-23 Viscosity210 C., SUS 160 Flash Point, F. 545

PHYSICAL PROPERTIES OF OIL-CHLORINATED BIPHENYL BLENDS Percent by wt.

Specific Pouu ds/ gravity gal. Chlorinated biphenyl. Oil

48% chlorine sulting blend are significantly reduced by such use of trichlorobenzene without also effecting a significant undesired decrease in the other properties of the organic phase.

It is also contemplated that either the aqueous phase or the organic phase or both phases of the two-phase quenchant of this invention can contain various functional additives such as quenching speed modifiers, viscosity modifiers, wetting agents, antioxidants, rust inhibitors, pour point depressants, and the like, such as organic sulfonates, fatty acids, amines, silica sols, high molecular weight ethylene or propylene oxide polymers,

soluble gums, such as carboxy methyl cellulose, methyl cellulose and hydroxy ethyl cellulose, terpene polymer resins, heat treated vegetable oils, residues from petroleum refining, partially oxidized petroleum hydrocarbons, alkylphenol-ethylene oxide condensates, alkylphenol polyethylene glycols, sodium alkyl sulfates, polyoxyethylene esters of tall oil, organic sulfonates, e.g. sodium sulfonate, barium and calcium sulfonate, metal naphthenates, reaction products of organic sulfonates and a phosphorus sulfide, reaction products of a phosphorus sulfide and an organic amine, mono-, diand triethanolamine, sodium, potassium or ammonium bonate, dimers of linoleic acid and other fatty acids, the reaction products of an alkenyl suocinic anhydride, aliphatic acid and polyalkylene polyamine, phosphites, and phenyl-alpha-naphthylamine.

While this invention has been described with respect to various specific examples :and embodiments, it is understood that the invention is not limited to such examples and embodiments and that it can be variously practiced within the scope of the following claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A two-phase quenching composition comprising (a) an upper aqueous phase and (b) a lower phase of chlorinated biphenyl containing from about 20% to about 60% by weight of combined chlorine.

2. A two-phase quenching composition comprising (a) an upper water phase and (b) a lower phase of chlorinated biphenyl containing from about 40% to about 50% by weight of combined chlorine.

3. A two-phase quenching composition comprising (a) an upper brine phase and (b) a lower phase of chlorinated biphenyl containing from about 40% to about 50% by weight of combined chlorine.

4. A two-phase quenching composition comprising (a) an upper aqueous phase and (b) a lower phase of chlorinated biphenyl containing from about 20% to about 60% by weight of combined chlorine and oil.

5. In a process for quenching heated metal in a twophase composition comprising (a) an upper aqueous phase and (b) a lower phase of chlorinated biphenyl containing from about 20% to about 60% by weight of combined chlorine, the steps comprising immersing said heated metal in the aqueous phase for a time sufficient to partially quench said heated metal and then immersing said heated metal in the chlorinated biphenyl phase for a time sufficient to further quench said heated metal.

6. In a process for quenching heated metal in a twophase composition comprising (a) an upper water phase and (b) a lower phase of chlorinated biphenyl containing from about 40% to about 50% by Weight of combined 8 chlorine, the steps comprising immersing said heated metal in the water phase for a time sufficient to partially quench said heated metal and then immersing said heated metal in the chlorinated biphenyl phase for a time suflicient to further quench said heated metal.

7. In a process for quenching heated metal in a twophase composition comprising (a) an upper brine phase and (b) a lower phase of chlorinated biphenyl containing from about 40% to about 50% by weight of combined chlorine, the steps comprising immersing said heated metal in the brine phase for a time sufficient to partially quench said heated metal and then immersing said heated metal in the chlorinated biphenyl phase for a time sufiicient to further quench said heated metal.

8. In a process for quenching heated metal in a twophase composition comprising (a) an upper aqueous phase and (b) a lower phase of chlorinated biphenyl and oil containing from about 20% to about 60% by weight of combined chlorine, the steps comprising immersing said heated metal in the aqueous phase for a time sufficient to partially quench said heated metal and then immersing said heated metal in the chlorinated biphenyloil phase for a time sufficient to further quench said heated metal.

9. In a process for quenching heated steel in a twophase composition comprising (a) an upper aqueous phase and (b) a lower phase of chlorinated biphenyl containing from about 20% to about 60% by weight of combined chlorine, the steps comprising immersing said heated steel in the aqueous phase for a time sufiicient to partially quench said heated steel and then immersing said heated steel in the chlorinated biphenyl phase for a time sufficient to further quench said heated steel.

10. In a process for quenching heated steel in a twophase composition comprising (a) an upper water phase and (b) a lower phase of chlorinated biphenyl containing from about 40% to about 50% by weight of combined chlorine, the steps comprising immersing said heated steel in the water phase for a time sufficient to partially quench said heated steel and then immersing said heated steel in the chlorinated biphenyl phase for a time sufficient to further quench said heated steel.

11. In a process for quenching heated steel in a twophase composition comprising (a) an upper aqueous phase and (b) a lower phase of chlorinated biphenyl and oil containing from about 20% to about 60% by weight of combined chlorine, the steps comprising immersing said heated steel in the aqueous phase for a time sufiicient to partially quench said heated steel and then immersing said heated steel in the chlorinated biphenyl-oil phase for a time sufficient to further quench said heated steel.

References Cited by the Examiner UNITED STATES PATENTS 1,882,809 10/1932 Grebe 252-67 2,304,451 12/1942 Gottlieb 148 18 2,334,652 11/1943 Schmitt 14830 3,022,205 2/1962 Chase et a1. 14820.6

OTHER REFERENCES Handbook of Chemistry and Physics: (27th Ed.) 1943, published by Chemical Rubber Publishing Co. 2310 Superior Ave. NE. Cleveland, Ohio. (Pages 6567 relied on.)

HYLAND BIZOT, Primary Examiner.

DAVID L. RECK, Examiner,