WO1992012267A1

WO1992012267A1 - Composition, bath and method for quenching metals

Info

Publication number: WO1992012267A1
Application number: PCT/FR1991/001059
Authority: WO
Inventors: Serge Gosset; Jean-Michel Ludot; Michel Deck
Original assignee: Roquette Freres; Castrol France S.A.
Priority date: 1990-12-27
Filing date: 1991-12-23
Publication date: 1992-07-23
Also published as: ATE137271T1; KR930703471A; KR0167364B1; FR2671103A1; FR2671103B1; JPH06504813A; EP0564549A1; EP0564549B1; DE69119094D1

Abstract

A concentrated aqueous composition is provided for baths for quenching metals and/or alloys thereof, and contains at least one starchy compound. The quenching bath obtained therewith and a quenching method using said bath are also described.

Description

COMPOSITION, BATH AND METHOD OF HARDENING METALS

The subject of the present invention is a concentrated aqueous composition for quenching metals and their alloys. It also relates to the quenching baths obtained from this composition as well as the process for quenching metals using said composition.

It is known that the optimal mechanical characteristics of metals or alloys are only obtained after heating at high temperature, which allows the appearance of crystalline phases or configurations which only exist at high temperature or which cannot form. only from the stable phase at high temperature.

In the case of steel, for example, heating, followed by maintenance at high temperature (between 780 and 900 ° C for structural steel) ensures the dissolution of carbon and the uniformity of its distribution in iron (austenitic structure).

Heating is followed by quenching proper, that is to say more or less rapid cooling, depending on the metal and the type of part; this makes it possible to keep the molecular distribution of the hot stable state cold, by freezing the crystalline phases or configurations obtained.

^* The speed and the metal cooling conditions during hardening, détermi¬ have a decisive effect on the mechanical properties.

On the one hand, it is necessary to cool the metal or the alloy sufficiently quickly enough, previously brought to the temperature range where the desired structure is formed, in order to freeze it and to avoid incomplete transformations.

On the other hand, for reasons of dimensions or regularity of shape of the parts, or even for certain alloy compositions, cooling is not desired to be too rapid.

In fact, if this is the case, we are witnessing the formation of internal stresses, distortions and possibly cracks called tapures.

It follows that quenching is a meticulous operation which requires a lot of precautions. It is in particular advisable to use suitable quenching baths capable of varying the cooling rate within the desired limits in order to obtain the desired characteristics and, in particular, of slowing down the quenching so as to avoid curling and the like. disadvantages inherent in too rapid quenching.

Known quenching media are very varied: for example, aqueous, oily, saline media, molten metals, air, gases, pulsed or not.

Oily media or quenching oils generally offer satisfactory results with regard to the characteristics of the quenched parts. However, it is obvious that in industrial practice, the use of quenching oils has a certain number of drawbacks, such as environmental pollution, the release of unpleasant odors, the risks of ignition. In addition to these faults relating to health and safety conditions, there are manufacturing easements such as the need to preheat the oil tanks and degrease the hardened parts.

These various drawbacks have led those skilled in the art to envisage the development of aqueous quenching media which would ensure that the quenched parts have characteristics substantially identical to those obtained thanks to oil quenching, while avoiding the faults previously cited.

The use of polyalkylene glycols has been recommended for the constitution of aqueous quenching media, for example according to patent FR 1,384,244.

The US patent 4,087,290 recommends meanwhile the use of a water-soluble salt of polyacrylic acid in water allowing slow cooling, due to the formation of a stable and uniform film on the surface of the quenched parts.

In patent WO 83/00825, the retarding agent is a water-soluble salt of a copolymer of long chain olefin and maleic, citraconic or itaconic anhydride.

The very recent articles published in "Advanced Materials & Processes" 3/90, pages 19 to 28 and 51 to 53, and entitled respectively "Polymer Quenchants: a European overview" and "Polymer quenchants: the Basics" review the different polymers currently used for quenching, as well as their properties.

Finally, in Polish Patent No. 120,857, aqueous quenching baths based on native starch are exemplified. However, these present unacceptable problems of instability over time, inherent in the very nature of the starch and the way it is dissolved.

Indeed, the glue obtained according to this patent has a very high viscosity which makes this product unsuitable for distribution and storage under industrial conditions. In addition, this already high viscosity increases over time. Finally, the dilution of such an adhesive for obtaining a quench bath is extremely difficult and leads to a phenomenon of syneresis.

Baths based on native starch as exemplified in Polish patent n ^β 120,857 cannot therefore be used industrially; they do not make it possible to achieve the desired efficiency in terms of quenching and in any case only offer limited properties, which cannot be varied or modified according to the conditions chosen for quenching, the nature of the parts to be treated and / or the performances sought for the latter.

Furthermore, we observe that in most aqueous quenching media, the third stage of cooling, by natural convection, may be too rapid. In addition, the transition between the nucleated boiling regime and the convection regime is generally located at a temperature level significantly lower than in oil quench baths. An efficient aqueous quenching bath should make it possible to obtain a fairly slow cooling rate at around 300 ° C.

However, the Applicant companies have, after long and difficult research, shown that it is possible to obtain aqueous quenching baths of metals or their alloys which give excellent performance, which meet the different requirements. of the technique, without however having the aforementioned drawbacks. The Applicant companies have in fact shown that, surprisingly and unexpectedly, aqueous quenching baths meeting all the requirements of the technique and based on a starchy compound can be obtained as soon as the nature is selected of the starchy compound and / or the conditions for its dissolution so that no essential variation occurs for a period of time compatible with industrial exploitation.

The concentrated compositions for quenching bath according to the invention are therefore characterized in that they comprise at least one starchy compound and that they are stable over time.

This condition of stability is extremely dif¬ ficult to achieve because the starchy compounds in solution are subject to more less marked phenomena of retro¬ gradation and / or synérese leading to changes in viscosity which can be very significant, and in the most irreversible cases, this resulting in the formation of gels or in a demixing. And it is to the credit of the Applicant companies for having known how to find and develop concentrated aqueous bath compositions quenching of metals and / or their alloys which are per¬ forming and stable, said compositions being based on starchy compounds.

By the term starchy compound, within the meaning of the present invention, is meant any type of starch, whatever its origin, native or modified, as well as their mixtures.

When a native starch is used for the constitution of the aqueous compositions for the quench bath in accordance with the invention, a natural or hybrid starch is used, originating in particular from maize, corn with a high amylopectin content. (waxy starch), corn with a high amylose content, wheat, peas, rice, potato, cassava, and it is dissolved in water under conditions such as its viscosity, once developed , no longer changes significantly over time. For this, special conditions are chosen for cooking, or for dissolving said native starch.

In order to achieve this result with compositions based on a native starchy compound, this can be done in several ways.

It is thus possible to cook the native starch in an appliance of the jet cooker type, under high pressure, in particular in the vapor phase, and optionally in the presence of adjuvants. It is also possible to cook the native starch on devices of the drum-dryer type, possibly in the presence of adjuvants. Among the adjuvants known to give good stability to a "glue" of native starch, there may be mentioned, for example, alkaline agents and ethoxylated alcohols as described in particular in US Patent No. 4,021,260.

Preferably, when use is made, for the composition of the concentrated aqueous compositions according to the invention, of a native starchy compound, a waxy starch is used, that is to say comprising a higher amylopectin content. to that found in the corresponding natural starch. When a modified starch is used, a natural or hybrid starch, from any source, having undergone a chemical modification treatment, and / or a physical modification treatment, is used.

By chemical modification treatment is meant in particular the operations or reactions of oxidation, dextrinification, fluidification (acid or enzymatic), esterification, etherification and / or crosslinking.

The term “physical modification treatment” means in particular the gelatinization operations on a drum, the extrusion cooking treatments, the treatments by microwaves and the ultrasound treatments.

In the context of the invention, starchy compounds can be used resulting both from one or more modifications by physical means and from one or more modifications by chemical means, the modifications being able to be carried out simultaneously.

The aqueous concentrated compositions in accordance with the invention are obtained by using said starchy compounds in the presence of water. In the context of the present invention, this implementation must be carried out under conditions suitable for leading to the obtaining of colloidal solutions.

While it is true that some of the physically modified starches have solubility in water at room temperature, it is different from most of the starchy compounds according to the invention.

Any means known per se is therefore used which is capable of allowing said starchy products to dissolve in an aqueous medium.

According to a preferred embodiment of the invention, recourse can be had to this effect in bursting in an alkaline medium.

In this case, the action for example of the sodium hydroxide can be carried out with simple stirring making it possible to maintain a suitable homogeneity of the medium. Low material dry, any conventional mixer can be used. At high dry matter, it will be necessary to use a device of the kneader type or high speed delitor, which are devices with high shear rate.

It is considered on this occasion that the colloidal solution obtained results from the combined action of mechanical and chemical means.

According to a particularly advantageous embodiment, the starchy compounds are dissolved in water by the concomitant action of temperature and pressure. This type of operation is generally carried out on installations commonly known as JET COOKER.

In this case, the solution undergoes during cooking very high shear rates due to both a high temperature and a pressure level characteristic of cooking in the vapor phase.

The colloidal solutions obtained by direct action of the steam will preferably be produced continuously, insofar as such a technique allows the use of steam at high pressure and thereby gelatinization of the starch at high temperature.

According to another mode of preparation of the starchy compositions in accordance with the invention, it can be envisaged, for simple technical and economic reasons, to carry out the chemical modification of the starches simultaneously with the above-mentioned solubilization operations. When the chemical modification is carried out simultaneously with the cooking operation, the necessary reagents must be added to the starch suspension.

Thus, the cooking of a starch in the presence for example of an oxidizing agent will allow, by the choice of the quantity of oxidizing agent used and the thermal conditions of the operation, the production of a col¬ starch mixture meeting the requirements of the intended application. Indeed, the controlled oxidation of starchy material promotes the production of colloidal solution whose viscosity is stable over time, in particular with respect to shearing phenomena, and reduces the phenomena of syneresis.

It is also possible to introduce adjuvants, such as those described above, at the time of cooking the starchy compound previously or simultaneously modified.

It being understood that the compositions and the baths in accordance with the invention must, in order to meet all the requirements of the technique, have a suitable viscosity and great stability, it will preferably be used, as has been said previously, to waxy starches insofar as the starchy compound retained will be one of the native starches previously described.

According to another embodiment of the invention, it is possible to obtain a suitable viscosity as well as great stability, by using modified starches of the type of those previously described. The viscosity and the stability will be those corresponding to the starchy compound chosen according to the nature of the quenching operation: surface or mass quenching.

In particular, it is possible to use esterified starches such as acetylated starches, and etherified starches such as carboxymethylated, hydroxyalkylated and cationic starches, or mixtures thereof. Particular preference is given to cationic starches.

These can be obtained by reaction in the milk phase of a native starch with one of the reagents of the type described in patent EP 0 139 597. It can also be a question of cationic starches obtained by the dry route such as those described. in patent FR 2,434,821. It can also be cationization in the adhesive phase, or even in the solvent phase. According to a preferred embodiment of the invention, it will be retained as a starchy compound. cationic waxy starches. Due to their original polymer structure, cationic waxy starches give particularly advantageous viscosity and stability characteristics to quench baths. Such baths provide unmatched performance to date.

The aminotertiary reagents or quaternary ammonium commonly used for the cationization of starches have a halide as counter-anion. This halide is most often chloride.

Thus, starches modified by cationization generally have a residual chloride level.

However, the chloride ions are known for their marked corrosive character, which can prove to be troublesome in the application of these starches to the quenching of metals. To overcome this drawback, it is therefore preferable to use starches whose chloride level has been lowered. Such starches can be obtained according to the process described in French patent application 90 08767. A very particular preference will go to cationic waxy starches with reduced chloride content.

The aqueous concentrated compositions in accordance with the invention have a starch content expressed in dry matter of between 1 and 50%, preferably between 2 and 45% and more preferably still between 5 and 30%.

In addition to the starchy compound (s), the aqueous compositions according to the invention preferably contain the additives conventionally used in aqueous quenching baths such as in particular anticorrosion agents, preservatives and defoamers.

The quenching baths according to the invention contain 0.1% to 30% of starchy compound, preferably from 1% to 15%, more preferably still from 2 to 10%.

They can be obtained by simple dilution of the aqueous composition according to the invention. They can be used in a range of temperatures from about 10 "C. to about 80 ° C. Higher temperatures, possible, have the drawback of excessive evaporation.

In addition to the positive effects brought by the chemical and / or physical modifications of the starchy compound on the stability of the solutions, it can be seen that they have a considerable influence on the cooling power of the colloidal solutions during the quenching operation.

In addition, the general appearance of the cooling curves obtained is characteristic of each of the physical or chemical modifications carried out and thus allows the adaptation of the treatments to the desired end goal, that is to say the choice of a curve. suitable cooling.

Finally, these concentrated aqueous compositions based on colloidal solutions of starchy compound (s) and the quenching baths containing these compositions have the advantage of almost total biodegradability, which makes it possible to solve the problems posed by the most of the prior art baths vis-à-vis the environment.

They also have other advantages such as the absence of an unpleasant odor, the risk of flammability and toxicity.

The advantage of the invention will be better understood with the aid of the comparative tests and of the following examples.

The process for quenching metals and their alloys using the aqueous composition according to the invention is described and illustrated below.

In order to determine the properties of the quench baths according to the invention and to compare them with those of the baths of the prior art, drasticity curves were produced according to the procedures of the two tests described below.

In the first test (I), we use a drastometer made up of a silver cylinder, of equal diameter at 8 mm and length equal to 24 mm. This silver sensor is brought to a temperature of 800 ^β C and then suddenly immersed in a quench bath of about 20 1 stirred by recir¬ culation using a pump whose flow can be adjusted. In this case, it was set for tests at 1000 l / h. The discharge of this pump is connected to a vertical tube located in the center of the quench tank. The silver sensor is immersed in the central tube, always full and permanently agitated thanks to the regular flow of the pump. The bath temperature is kept constant at 30 ^β C using thermostatic regulation.

From the moment the silver sensor is immersed in the quenching bath, the temperature (in ^β C) of said sensor is recorded as a function of time (in seconds) and the curve θ ≈ f (t) is plotted.

We also draw the curve dθ / dt ≈ f (θ) which shows the evolution of the cooling rate dθ / dt (in ^β C per second) as a function of the temperature θ.

In the second test (II), a drasticimeter is used, consisting of a INCONEL 600 cylinder 12.5 mm in diameter and 60 mm in length, fitted at its center with a thermocouple. This INCONEL sensor is heated to 850 ^β C and then quenched in 2 liters of unstirred quench bath, maintained unless maintained at a temperature of 30 ^β C.

Two curves are drawn simultaneously, the first ¬ = f (t) representing the change in temperature (in ° C) as a function of time (in seconds); the second dθ / dt = f (θ) representing the change in the cooling rate as a function of the temperature.

From these two curves are extracted the following data:

- time elapsed to cool the test piece

- from 850 ^β C to 600 ^β C

- from 850 ^β C to 400 ^β C

- from 850 ° C to 200 ° C

- maximum cooling rate, in ° C / sec, - temperature corresponding to the maximum speed,

- cooling rate at 300 ^β C, in ^β C / sec.

EXAMPLE 1

First, according to test (I), a drasticity curve characteristic of the quenching fluids of the prior art is produced using a quenching bath consisting of an aqueous solution of polyalkylene glycol of the brand ILOQUENCH 500 AQUA. , marketed by the company CASTROL, and diluted with a dilution factor of 10%, the polymer concentration being therefore equal to 4.4%.

The two curves θ = f (t) and dθ / dt = f (θ) obtained are represented in Figure la respectively by C _la and C _2a .

Examination of these curves shows that the cooling rate in the lower part of the curve is too high, which favors deformations and pure values.

A drasticity curve is also produced according to this same test (I) with mineral oil type 100 neutral, sold under the brand ILOQUENCH 43 by the company CASTROL. The curves θ = f (t) and dθ / dt = f (θ) obtained are represented in figure lb by the curves C ^ _j -, and ^c 2b-

EXAMPLE 2

The preparation of a starchy colloidal solution is carried out as follows:

A corn starch milk is prepared by dispersing in water native waxy corn starch, consisting for at least 95% of amylopectin, in an amount of 429 g of commercial starch for one liter of water.

To this starch milk is added 9.13 g of causal soda at 48 ° balm, this amount corresponding to 1% of dry soda relative to the commercial waxy corn starch. The whole is pumped using a volume pump- stick through a jet-cooker for continuous preparation.

The characteristics of the cooker are as follows:

- coil with a capacity of 4.6 1,

- steam at a pressure of 10 bars feeding a nozzle,

- flow 45 1 / h to 150 1 / h according to setting.

The working conditions used for this preparation are:

- contact time: 3 minutes

- cooking temperature: 150 ^β C,

- pressure in the coil maintained by a back-pressure valve: 5 bars.

On leaving the coil, the adhesive obtained is cooled by expansion in an atmospheric flash. In this way, a colloidal solution with 20.5% refractometric dry matter (MS) is obtained. Its viscosity is 16,000 cps at room temperature. The pH is 10.4.

This colloidal solution is diluted to 3.8% DM to be subjected to the test (I).

FIG. 2 (curves C3 and C4) clearly illustrates the advantages provided by the process which is the subject of said invention.

The transition zone between heat build up and nucleated boiling is higher in this case and reaches the value obtained with oil quench baths. In addition and above all, the transition zone between nucleated boiling and convection is very markedly increased, while the cooling rate in the low temperature range is greatly reduced.

EXAMPLE 3

In this example, the waxy corn starch is modified by carrying out a carboxymethylation reaction "in situ" by adding sodium monochloroacetate to the starch milk before it passes over the cooker. The characteristics of the cooker for obtaining a colloidal solution are identical to those expressed in Example 2 (cooking on "jet-cooker").

Waxy corn starch milk is prepared in water at the rate of 429 g per liter of water. Sufficient amounts of caustic soda and sodium monochloroacetate are added to this starch milk as defined in table n ^β I.

The setting characteristics of the installation are as follows:

- contact time: 3 minutes,

- cooking temperature: 150 ° C,

- pressure in the coil: 5 bars.

The characteristics of the colloidal solutions obtained are recorded in Table No. I. These solutions are diluted to 3.8% DM in order to test them on the drasticimeter, according to the test (I) described above.

Figures 3a and 3b relate to this exemplary embodiment of the invention and show the advantage of such solutions obtained by carboxymethylation of the ami¬ donated waxy corn.

Curves C5-C6 and C7-C8 correspond successively to colloidal carboxymethylated solutions with 2% and 4% of sodium monochloroacetate counted by weight relative to commercial corn starch.

CHARACTERISTICS OF THE SOLUTIONS AT THE END OF THE COOKER

TABLE I

MONO- MS REFRACTO- VISCOSITY pH RATE

METRIC CHLORACETATE SODA AT 20 ° C IN AT 20 ° C IN% cps

1 2 20.2 14,300 11

1.5 4 20 20 600 10.8

The carboxymethylation makes it possible to raise the abovementioned transition zones and accentuates the slowing down of the cooling in the zone of low temperatures. EXAMPLE 4

In this example, the colloidal solution is obtained according to the process described in Example 2 from a cationic commercial starch (brand HI-CAT 160, marketed by the company ROQUETTE FRERES).

A cationic potato starch milk is first prepared at the rate of 467 g of HI-CAT 160 brand starch per liter of water.

A quantity of sodium hydroxide equivalent to 2% of sodium hydroxide is added to this preparation relative to the commercial starch.

The setting characteristics of the installation are as follows:

- contact time: 3 minutes,

- cooking temperature: 160 ^β C,

- pressure in the coil: 7 bars.

The refractometric dry matter of the solution obtained is equal to 18%. The viscosity is 8900 cps at room temperature. The pH is equal to 11.

This colloidal solution is diluted to 3.8% DM to be tested on the drasticimeter described previously, according to test (I).

Curves C9 and C10 shown in FIG. 4 show that the cationic starch prepared according to the method described in this example meets the requirements of the technique. The boiling range is in fact shifted towards high temperatures, and the cooling rate in the low temperature range is reduced.

EXAMPLE 5

In this example, the use of a cationic commercial starch is envisaged in order to prepare a colloidal solution according to the method described in example 2 by "jet cooker" cooking.

A waxy cationic corn starch milk is prepared, sold under the brand HI-CAT 260 by the Company ROQUETTE FRERES, at a rate of 429 g of commercial starch for one liter of water.

A quantity of sodium hydroxide equivalent to 2% of dry sodium hydroxide relative to the commercial starch is added to this preparation.

The setting characteristics of the installation are as follows:

- contact time: 3 minutes,

- cooking temperature: 160 ^β C,

- pressure in the coil: 7 bars.

A colloidal solution is obtained whose refractometric DM is equal to 18.7%. Its viscosity is 5600 cps at room temperature. The pH is 10.9.

This colloidal solution is diluted to 3.8% DM to be tested on the drasticimeter, according to the test

(I).

The Cil-Cl2 curves shown in Figure 5 represent the change in temperature during the cooling of the sensor immersed in this solution according to the invention. There is in particular an improvement in the shape of the curve in low temperature zones which makes this solution very perfor¬ mant vis-à-vis the solutions of the prior art.

EXAMPLE 6

In this example, a cationic starch with the same characteristics as HI-CAT 260 mentioned in example 5 is used, but on which the chloride content has been greatly reduced using the ion permutation process as described in the application. French Patent No. 9008767.

This ion permutation process makes it possible to obtain cationic starches which are particularly suitable for quenching processes in the aqueous phase, for which a too high chloride content may have drawbacks due to the corrosive action of these anions. A colloidal solution of this cationic starch of HI-CAT 260 type, previously permuted, is therefore prepared, with a chloride content of approximately 100 ppm on dry matter, by cooking on a "jet-cooker".

Thus, 437 g of this cationic starch are dispersed in a liter of water, and the cooking is carried out under the following conditions:

- contact time: 6 minutes

- cooking temperature: 160 ^β C

- pressure in the coil: 5 bars.

A colloidal solution is obtained, the fracture MS of which is 23.4% and whose viscosity at 20 ^β C is 3100 centipoise.

This concentrated composition has a viscosity which is perfectly stable over time, no change being observed after three months of storage at 20 ° C.

This concentrated composition, adjuvanted by conventional additives and in particular by an anti-corrosion agent, is diluted in distilled water according to three different dilution factors: 10, 15 and 20%, corresponding respectively to dry matter rates 2.34%, 3.51% and 4.68%. The quenching baths obtained are then subjected to the second drasticity test (II), using the INCONEL sensor.

Figure 6 shows the curves obtained. Curves C13 and C14, curves C15 and C16, and curves Cl7 and Cl8 respectively represent the curves recorded with the dilutions of 10, 15% and 20%.

The first three lines of Table II group together the results obtained during these tests.

This table shows the immersion times (in seconds) to cool the test piece from 850 ° C to 600C °, from 850 ^β C to 400 ^β C and from 850 ° C to 200 ^β C, the cooling rate maximum smoothing in ^β C per second, the temperature corresponding to the maximum speed, as well as the cooling rate at 300 ^β C in ^β C per second. We can see from these curves and this table that:

- the retarding effect of the solutions increases proportionally with their concentration of cationic friendliness,

at a significantly lower concentration (4.68% in cationic starch against 8.8% for polyalkylene glycol), the cooling rate at 300 ° C. (field of quenching tapures) is significantly slower than for polyalkylene glycols and closer to that of a mineral oil,

- The maximum cooling rates can be located, depending on the concentration and bath temperature conditions selected, at temperatures higher than those of polyalkylè¬ glycols, which is favorable to avoid incomplete martensitic transformations. Table II also groups together the results obtained using the same concentrated composition based on cationic starch with low chloride content, for dilution factors of 7%, 10% and 15% corresponding to dry matter contents. 1.64%, 2.34% and 3.51% respectively, and at two different temperatures: 40 ° and 50 °.

FIG. 7 shows the curves Cl9 and C20 obtained at the temperature of 30 ° C, the curves C21 and C22 obtained at the temperature of 40 ^β C, and the curves C23 and C24 obtained at the temperature of 50 ° C, the dilution factor being 10%, which corresponds to a DM rate of 2.34%.

It can be seen that increasing the temperature of the quench bath makes it possible to lower the maximum cooling rates and their corresponding temperatures. This influence of temperature allows the realization, with a single concentration, of drasticities "on measure "suitable for hardening steels and favorable for reducing the deformation of delicate parts with tormented geometry.

Finally, a comparison was made between the mineral oil ILOQUENCH 43, marketed by the company CASTROL, the polyalkylene glycol marketed under the brand ILOQUENCH 500 AQUA also by the company CASTROL and diluted to 20%, ie a DM level of 8 , 8%, and the quenching bath obtained after dilution to 20% of the above composition, ie a DM content of 4.68%.

The quenching temperature was 30 ° C for aqueous quenching, and 40 ° C for the oil bath.

FIG. 8 presents the drasticity curves recorded, the curves C25 and C26 being obtained with the quenching bath in accordance with the invention, the curves C27 and C28 being obtained with the polyalkylene glycol, and the curves C29 and C30 being obtained with the bath oil quenching.

It can be seen that the quenching bath according to the invention has entirely satisfactory performance in comparison with the baths of the prior art.

TABLE II (Data obtained from test II)

o

Claims

1. Concentrated aqueous composition for quenching bath of metals and / or their alloys, comprising at least one starchy compound and stable over time.

2. Composition according to Claim 1, characterized in that the starchy compound is chosen from native starches and starches modified by chemical modification treatment and / or by physical modification treatment, as well as their mixtures.

3. Composition according to claim 2, caracté¬ ized in that the native starches are cooked in the vapor phase, preferably in the presence of additives capable of imparting good stability to the starch glue obtained.

4. Composition according to Claim 2, characterized in that the chemical modification treatment comprises the operations or reactions of oxidation, dextrinification, fluidification, esterification, etherification and / or crosslinking .

5. Composition according to claim 2, characterized by the fact that the physical modification treatment comprises the gelatinization operations on a drum, cooking-extrusion, microwave treatment and / or ultrasound treatment.

6. Composition according to any one of claims 2, 4 and 5, characterized in that the starchy compound is a cationic starch.

7. Composition according to Claim 6, characterized in that the cationic starch has a reduced content of chloride ions.

8. Composition according to any one of claims 1 to 7, characterized in that the starch is a waxy starch.

9. Composition according to any one of claims 1 to 8, characterized in that it has a content of starchy compound, expressed in dry matter, between 1 and 50%, preferably between 2 and 45% and even more preferably between 5 and 30%.

10. Composition according to any one of the claims 1 to 9, characterized in that it also contains additives such as anti-corrosion agents, preserving agents and / or anti-foaming agents.

11. Quenching bath for metals and / or their alloys, characterized in that it is obtained from a composition according to any one of claims

I to 10.

12. Quenching bath according to claim 11, ca¬ characterized in that it comprises from 0.1 to 30% of starchy compound, preferably from 1% to 15%, and more preferably still from 2 to 10%.

13. A method of quenching metals and / or their alloys, characterized in that it consists in using a quenching bath according to either of the claims

II and 12.