EP0100280A1 - Quenching bath, and process for quenching metals - Google Patents

Abstract

Bath for the quenching of ferrous and nonferrous metals and their alloys, comprising a hydrogenated starch hydrolysate having, expressed with respect to the dry matter, a percentage of products of degree of polymerization 1 and 2 comprised between 1 and 90, the complement to 100 being constituted by products of degree of polymerization equal to or higher than 3.

Description

The present invention relates to an aqueous bath for quenching ferrous and non-ferrous metals and their alloys. It also relates to the method of quenching metals using said bath as well as the application to quenching metals of the constituents of the bath.

The search for high mechanical characteristics for certain metals or alloys leads to the freezing of crystallographic phases or configurations which exist only at high temperature or else to obtaining crystallographic phases or configurations which can only form from the stable phase. at high temperature.

For this it is necessary to carry out a quenching in baths allowing this freezing (or this transformation), that is to say capable of cooling sufficiently. quickly the metal or alloy previously brought into the temperature range where the desired structures are formed, so that these structures are essentially preserved or transformed and to avoid diffusion phenomena due to progressive cooling.

The transformation law can be expressed as follows: for there to be quenching, it is essential that before the above-mentioned cooling the critical point corresponding to the end of the transformation due to heating is exceeded and that the temperature of the metal either such that it is completely in the stable state when hot.

In the case of steel, it is the uniformity of distribution of the carbon obtained when hot which must be fixed by quenching. In its final tempered state, the metal is then characterized by a martensitic (or bainitic) structure.

To keep a metal in the state of maximum homogeneity, the cooling must be fast enough. A limit is imposed by the brittleness conferred on the hardened surface, brittleness which increases at the same time as the hardness increases because too rapid cooling produces molecular tensions which bring about unwanted curls and deformations.

It may also be necessary to seek, in the case of steels, an elastic limit as high as possible, combined with sufficient resilience. In the case of light alloys, the temperature zone corresponding to the desired structure, that is to say at the point! equilibrium where the solubility of the various constituent elements is maximum, is sometimes between limits very little apart from each other. After bringing the alloy to the temperature necessary to obtain the desired state, the actual quenching is carried out, that is to say a more or less rapid cooling depending on the alloy and the kind of room ; the molecular distribution of the hot stable state is thus kept cold, which makes it possible to advantageously modify the mechanical characteristics of the alloy. It follows that, depending on the nature and composition of the metals or alloys to be treated, the quenching methods and the most suitable media for this operation are different. The liquids used for quenching are therefore very varied: cold water, water containing sodium chloride or soda, lime water, acid water, hot water, petroleum, oils, tallow, and more recently water and polyvinyl alcohol , water and polyalkylene glycols.

It follows from the above 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 to obtain the desired characteristics.

It was therefore advantageous to be able to have new quenching baths, especially since some of the products currently used and mentioned above are not without drawbacks; in this regard, we can cite the corrosive action of salts and the high cost of petroleum products.

Now, it is to the credit of the Applicant Company to have found that the application to quenching of ferrous and non-ferrous metals and their alloys, of a hydrogenated starch hydrolyzate having, the percentages being expressed on the dry matter , a percentage of products of degree of polymerization (DP) 1 and 2 of between 1 and 90%, the complement to 100% being constituted by products of degree of polymerization equal to or greater than 3, leads to particularly advantageous results and allows among other things to modify the cooling rate.

It follows that the quench bath according to the invention is characterized by a content of 0.2 to 80% by weight of the above hydrolyzate.

Furthermore, the quenching method according to the invention is characterized in that said metals are immersed, the temperature of which is brought beforehand inside the range corresponding to the desired structures, in an aqueous bath comprising of 0.2 to 80% by weight of the above hydrogenated starch hydrolyzate.

It is recalled that the starch can be hydrolyzed, by the acid route, by the enzymatic route or by the mixed acid-enzymatic route, to different degrees, the degree of hydrolysis being generally characterized by the Dextrose-Equivalent (DE) defined as being the reducing power of the hydrolyzate, expressed in D-glucose and related to the dry matter.

The more the starch is hydrolyzed and the higher the DE, the final stage of hydrolysis corresponding in theoretically done to a hydrolyzate that would only contain dextrose. Depending on the mode of hydrolysis used (type of enzymes for example) and according to the degree of hydrolysis, it is possible to obtain starch hydrolysates of different EDs and having a very varied distribution of products of different degrees of polymerization: glucose ( DP 1), maltose and isomaltose (DP 2), maltotriose (DP 3), oligosaccharides and polysaccharides.

The starch hydrolysates of varied composition thus obtained can then be hydrogenated, in a manner known per se, generally under hydrogen pressures and at high temperatures and in the presence of catalysts such as, for example, Raney nickel. The various sugars constituting the starch hydrolyzate are thus transformed into corresponding polyols.

The hydrogenated starch hydrolyzate used for the constitution of the aqueous quenching baths according to the invention has a percentage of reducing sugars of less than 5% (percentage expressed on the dry matter of the hydrolyzate), preferably less than 2% and more preferably still less than 0.5%.

Preferably, the hydrogenated starch hydrolyzate applied in accordance with the invention has a percentage of products of DP 1 and DP 2 of between 2 and 75%, and more preferably still of between 2 and 65%, the complement to 100 being consisting of products with a PD greater than or equal to 3.

The preferred hydrogenated starch hydrolysates are obtained by hydrogenation of starch hydrolysates having a DE of between 15 and 70.

In the following text, the hydrogenated starch hydrolyzate will be designated by the abbreviation HAH.

(t) ) ou en fonction de la température (soit (8) ).The advantageous properties conferred on aqueous quenching baths by the application in accordance with the invention of the above HAH have in particular been able to be demonstrated by the study of the evolution of the temperature of the quenched sample as a function of time (i.e. θ = f (t)) as well as by studying the evolution of the cooling rate of the quenched sample as a function of time (i.e.

(t)) or as a function of temperature (i.e. (8)).

It was thus possible to show very particularly that the quenching bath in accordance with the invention had performances significantly superior to those of aqueous quenching baths of the prior art comprising polyhydric alcohols selected from the group consisting of sorbitol, mannitol, maltitol and lactitol; these baths had previously been considered satisfactory.

The properties of the quench bath according to the invention vary according to the chosen concentration of HAH.

Thus one can obtain an accelerated quenching effect or a quenching retarding effect with respect to water alone depending on the concentration used.

Baths with an accelerating effect contain from 0.2 to 40% and preferably from 0.5 to 35% by weight of HAH.

Baths which delay the cooling rate compared to water contain 40 to 80%, preferably 40 to 75% HAH.

It is in the acceleration of the cooling rate with respect to water that the application of the above-mentioned hydrogenated starch hydrolyzate according to the invention proves to be most advantageous. The accelerating effect obtained is indeed as good, or even better, than that obtained with the mineral salts used until then.

A decisive advantage further lies in the fact that the accelerating effect imparted to the bath by the application according to the invention of the above HAH, is felt roughly constant in a relatively large concentration zone of approximately 3 to 25% by weight, hence excellent operational safety despite the phenomena of evaporation or exhaustion of the baths. This is indeed not always the case for the prior art quenching baths containing mineral salts, for which the variations in the concentration have much more significant effects.

The quenching bath according to the invention, comprising from 0.2 to 80 3b of HAH, can be used at temperatures varying in particular from 4 to 60 ° C, preferably from 4 to 50 ° C and, more preferably still , from 10 to 45 ° C.

The HAH applied in accordance with the invention to the constitution of the quench bath according to the invention, not only modifies, as indicated above, the cooling rate of the quenched metals, but also has other other advantages. First of all, it does not exhibit aggressiveness with respect to metals and their alloys and can, on the contrary, even have a protective effect on surfaces. It avoids in particular the granular corrosion of aluminum alloys, corrosion which is formed in particular in quenching baths containing compounds of mineral origin such as sodium or potassium derivatives whose aggressiveness both with respect to ferrous alloys and light alloys is important.

More particularly and always in the case of aluminum and its alloys, the hardness imparted to the parts treated in accordance with the invention is greater than that of the parts treated conventionally, for example by water quenching.

Another advantage lies in the non-toxicity of the hydrogenated starch hydrolysates used in accordance with the invention, in their perfect biodegradability as well as in their non-flammability.

According to a particular aspect of the present invention and in particular to act on the cooling rate, it is possible to add to the hydrogenated starch hydrolyzate one or more oxyanion salts chosen in particular from the group of boron, tin , germanium, tellurium or arsenic, these salts being capable of forming water-soluble complexes with the hydrogenated starch hydrolyzate.

The preferred oxyanion consists of boron, and the salts preferably used are borates.

These oxyanion salts, when used, can be added in a fairly wide range of concentrations, limited in practice by their limit of solubility in water. Preferably, however, the HAH (MS) / salt ratio is chosen between 100/1 and 1/2, and more preferably between 30/1 and 1/1.

Preferably, these salts are dissolved in the hydrogenated starch hydrolyzate syrup and allowed to react with the latter before the formation of the baths.

The quench bath according to the invention can also contain various adjuvants such as antioxidants, anti-corrosion agents, bactericidal agents, and the like. One can also consider adding products already known to it for their properties of modifying the rate of cooling of metals, in order to optimize, if necessary, its performance.

The invention can in any case be better understood with the aid of the examples which follow.

EXAMPLE 1

In order to study the performance of the quenching bath according to the invention and to compare them with those of certain baths currently used, drasticity measurements were carried out according to the procedure described below.

A CETIM drasticimeter (Technical Center of In of Mechanical Industries SENLIS-FRANCE) constituted by a silver cylinder of revolution, of diameter equal to 8 mm and length equal to 24 mm, is brought to a temperature of 800 ° C and is then suddenly immersed in a quenching bath of 200 cm ³ not agitated. At the moment when the drasticimeter or sensor is immersed in the bath, we begin to record the temperature 8 (in ° C) as a function of time t (in seconds) and we draw the curve 8 = f (t).

(8) ; cette courbe représente l'évolution de la vitesse de refroidissement

(en °C par seconde) en fonction de la température θ.We also draw the curve

(8); this curve represents the evolution of the cooling rate

(in ° C per second) as a function of temperature θ.

First, a control curve is produced with a bath consisting solely of distilled water, at a temperature of 30 ° C.

(8) obtenues sont montrées sur la figure 1 respectivement en C₁ et C₂.The two curves 8 = f (t) and

(8) obtained are shown in FIG. 1 respectively in C ₁ and C ₂ .

Examination of these curves shows that cooling with distilled water leads to large irregularities.

It is also emphasized that the transition points between the zones of heating, boiling and convection can be completely different from one measurement to another, which illustrates the instability and the lack of repeatability of cooling. with distilled water, possible causes, obviously, of considerable heterogeneity in terms of the hardness of the parts.

The same drasticity measurements were carried out, under the same conditions as previously, the quenching fluid now consisting of a 5% solution of dry matter of a hydrogenated starch hydrolyzate (HAH 1) in the distilled water.

This HAH 1 hydrolyzate was prepared from a starch hydrolyzate whose DE before hydrogenation was equal to 55 and which itself had previously been prepared by enzymatic double hydrolysis, with α-amylase then with β-amylase.

The percentage of reducing sugars in the hydrolyzate HAH 1 is less than 0.20 and its composition (in% on dry matter) as follows:

(8) enregistrées avec le bain de trempe à base de l'hydrolysat HAH 1 sont montrées sur la figure 1 en C₃ et C₄ respectivement.Curves 8 = f (t) and

(8) recorded with the quench bath based on the hydrolyzate HAH 1 are shown in Figure 1 in C ₃ and C ₄ respectively.

The comparison of curves C ₁ and C ₂ with curves C ₃ and C ₄ shows that the presence of HAH leads to a very marked acceleration of the cooling rate during quenching.

EXAMPLE 2

This example is a comparative example of the performances obtained with the hydrolyzate HAH 1 and two other hydrogenated hydrolysates HAH 2 and HAH 3, prepared by hydrogenation of starch hydrolysates of different composition having before hydrogenation EDs of 33 and 30 respectively.

The composition of the HAH 2 and HAH 3 hydrolysates was as follows:

The percentage of reducing sugars (on m.s. = dry matter) of the hydrolysates HAH 2 and HAH 3 was less than 0.20.

The conditions of the tests were identical to those of Example 1, the quench baths tested containing respectively 5% of each of HAH 1, 2 and 3 and their temperature being 30 ° C.

The results obtained are expressed by the curves C ₁ , ^C ₂ (HAH 1), C ₅ , C ₆ (HAH 2) and C ₇ , C _a (HAH 3) shown in FIG. 2.

It is found, on examination of these curves, that the three hydrogenated starch hydrolysates allow a significant acceleration of the cooling rate.

We also note that the acceleration obtained with HAH 2 (DE before hydrogenation = 33) is more accentuated than that obtained with HAH 1 (DE before hydrogenation = 55).

The comparison of the curves obtained with the hydrolyzates HAH 2 and HAH 3 shows that the acceleration obtained with the hydrolyzate prepared from a DE of 30 (HAH 3) is less important than that obtained with that prepared from the DE 33 (HAH 2).

This observation highlights the importance of the presence and distribution of oligosaccharides and hydrogenated polysaccharides in the hydrolysates applied in accordance with the invention and makes it possible to vary the properties of the quench baths by varying the distribution of HAH in products of different degrees of polymerization, which is made possible by current advances in technology starch hydrolysis, in particular by enzymatic route.

EXAMPLE 3

This example was carried out to compare the performances recorded for the acceleration of the cooling rate, on the one hand, in the case of a quenching bath according to the invention and, on the other hand, in the case of two quenching baths according to the prior art.

The quench bath according to the invention consisted of a 5% solution of m.s. HAH 2 hydrolyzate in distilled water.

• - une solution aqueuse de sorbitol à 5 % de m.s.,
• - une solution aqueuse de sels sodiques à 5 % de m.s.

The two prior art quench baths consisted of:

• - an aqueous solution of sorbitol at 5% of ms,
• - an aqueous solution of sodium salts at 5% of ms

The temperature of the three baths was 30 ° C.

In FIG. 3, the drasticity curves obtained are shown, namely:

• - a une action beaucoup plus importante et beaucoup plus régulière sur la vitesse de refroidissement que ne peut l'avoir le sorbitol,
• - présente des performances très sensiblement équivalentes à celles des bains contenant des sels minéraux.

It can be seen that the HAH 2 hydrolyzate:

• - has a much greater and more regular action on the cooling rate than sorbitol can have,
• - has performances very roughly equivalent to those of baths containing mineral salts.

EXAMPLE 4

In this example, the performances obtained in the case of the hydrolyzate HAH 3 are compared with those obtained in the case of the same hydrolyzate in which borax had previously been dispersed in a proportion of 10% of borax decahydrate (percentage expressed as material as it is on the dry matter of the hydrolyzate).

As in the previous examples, the quench baths were at a concentration of 5% m. s. and at a temperature of 30 ° C.

In FIG. 4, the drasticity curves obtained are shown, namely:

It is found that the addition of borax slightly modifies the cooling rate obtained using the hydrolyzate alone.

EXAMPLE 5

In this example, the influence on the tempering rate of the concentration of the quenching baths according to the invention in hydrolyzate is studied.

This study is motivated by the fact that, under industrial operating conditions, this parameter varies easily as a result, for example, of evaporation.

We therefore established drasticity curves in the same way as above with quenching baths containing respectively 5%, 10% and 20% (in dry matter) of the hydrolyzate HAH 3.

In FIG. 5, the curves obtained are shown, namely:

We see that variations in the concentration between 5% and 20% of dry matter cause only a very small variation in the appearance of the curves.

This constitutes a decisive advantage of the quench baths according to the invention since their performance will be insensitive to evaporation and subsequent variations in concentration.

EXAMPLE 6

It is certain that the temperature of a quench bath can be maintained at around 30 ° C, but in reality the variations can range from a temperature of about 10 ° C, for a "fresh" quench bath, to 60 ° C approximately, for a very stressed quench bath if vigorous temperature control is not used.

Always proceeding in the same way and using the hydrolyzate HAH 3, the drasticity measurements were carried out at bath temperatures of 20 ° C, 40 ° C, 50 ° C and 60 ° C, the bath having a concentration 5% dry matter.

We show, in Figure 6, the results illustrated by the curves

It is observed that from about 40 ° C appears a zone of caulking. At 50 and 60 ° C, a delaying effect appears, more and more marked.

It is therefore preferable to regulate the temperature of the accelerator bath so that it does not rise too much above about 40 ° C.

EXAMPLE 7

The purpose of this example is to illustrate the advantages brought by the use of the baths according to the invention within the framework of their application to the quenching of parts in aluminum or in alloys of this metal.

The hydrogenated starch hydrolyzate used corresponds to that identified in Example 2 by HAH 3.

It is used at a concentration of 4.5% expressed as dry matter in water.

The parts treated by the so-called potting method are cast aluminum alloy parts of the AU 5 GT type.

The bath is at room temperature.

To ensure that the temperature of the pieces is uniform throughout their thickness at the time of quenching, they are kept before quenching at a temperature of 525 ° C. for a sufficient period of approximately three hours.

The duration of the immersion is 8 minutes.

The hardness changes, thanks to this quenching, from a non-uniform value of 70-78 HB (Hardness Brinnel, norm P: 10 D2) before quenching to a uniform value of 90-94 HB after quenching.

It will be recalled that the hardness generally required for quenched parts is at least 80 HB, a value which is just obtained by conventional quenching with water.

EXAMPLE 8

The purpose of this example is to illustrate the retarding effect exhibited by the baths according to the invention when their concentration is high.

We compare the drasticity curves (respectively cooling rate and temperature change) obtained with distilled water on the one hand and with quenching baths at 50% m.s. based on the hydrolyzate HAH 3 without, then with borax as described in Example 4 on the other hand.

The bath temperature was always 30 ° C.

• ^C ₂₅ et C₂₆ pour l'eau distillée
• ^C ₂₇ et C₂₈ pour HAH 3
• ^C ₂₉ et C₃₀ pour HAH 3 boraté.

The curves obtained are shown in FIG. 7, namely:

• ^C ₂₅ and C ₂₆ for distilled water
• ^C ₂₇ and C ₂₈ for HAH 3
• ^C ₂₉ and C ₃₀ for HAH 3 borate.

• - l'évolution de la température en fonction du temps met bien en évidence l'action retardatrice de l'hydrolysat HAH 3, notamment dans la zone de caléfaction,
• - l'action du borax est de diminuer notablement la vitesse de refroidissement dans la seconde partie de la courbe, soit essentiellement entre 550°C environ et 100°C.

Upon examination of these curves, it can be seen that:

• - the evolution of the temperature as a function of time clearly highlights the delaying action of the HAH 3 hydrolyzate, in particular in the heat-forming zone,
• - the action of borax is to significantly decrease the cooling rate in the second part of the curve, ie essentially between around 550 ° C and 100 ° C.

As goes without saying and as it already follows from the foregoing, the invention is in no way limited to the modes of application and embodiments which have been more particularly envisaged; on the contrary, it embraces all its variants.

Claims (8)

1. Application to the quenching of ferrous and non-ferrous metals and their alloys; a hydrogenated starch hydrolyzate having, expressed on the dry matter, a percentage of products of degree of polymerization 1 and 2 of between 1 and 90, the complement to 100 being constituted by products of degree of polymerization equal to or greater than 3. 2. Application according to claim 1, characterized in that the hydrogenated starch hydrolyzate used has a percentage of reducing sugars of less than 5%, preferably less than 2% and more preferably still%, less than 0, 5%. 3. Application according to one of claims 1 and 2, characterized in that the hydrogenated starch hydrolyzate used has a percentage of products of degree of polymerization 1 and 2 between 2 and 75, preferably between 2 and 65, the complement to 100 consisting of products with a degree of polymerization greater than or equal to 3. 4. Bath for quenching ferrous and non-ferrous metals and their alloys, characterized in that it comprises an aqueous solution of one of the hydrogenated starch hydrolysates applied in accordance with one of claims 1 to 3, la concentration of said aqueous hydrolyzate solution being from 0.2 to 80% by weight. 5. Bath according to claim 4, with an accelerating effect on the cooling rate, containing from 0.2 to 40%, preferably from 0.5 to 35% by weight of hydrogenated starch hydrolyzate. 6. Bath according to claim 4, delaying effect on the cooling rate, containing 40 to 80%, preferably 40 to 75% by weight of hydrogenated starch hydrolyzate. 7. Bath according to one of claims 4 to 6, characterized in that it contains, in addition to the hydrolyte hydrogenated starch sat, at least one oxyanion salt chosen from the group comprising boron, tin, germanium, tellurium and arsenic. 8. A method of quenching ferrous and non-ferrous metals and their alloys, characterized in that the metal is immersed beforehand brought to a temperature at which it has the desired structure in an aqueous bath according to one of claims 4 to 7 and whose temperature is from 10 to 60 ° C.

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