EP1489194B1 - Method of manufacture semifabricates of CuZnPbSn alloy for hot deformation - Google Patents

Abstract

The production of a semi-product of a CuZnPbSn alloy includes a spinning operation which does not include nor is it followed by a thermal treatment stage. Independent claims are also included for the following: (a) a finished product obtained fron the semi-product; and (b) the production of the finished product by deformation or machining, which does not include a thermal treatment stage.

Description

FIELD OF THE INVENTION

The present invention relates to the field of hot-stamping copper base alloys, intended for the manufacture of parts used essentially in drinking water distribution pipes (valves, valves, fittings).

STATE OF THE ART

• a) Alliage de matriçage traditionnel : CW617N,
• b) Alliages résistants à la dézincification, dont le plus couramment utilisé est le laiton à l'arsenic : CW602N,
• c) Une famille d'alliages de laiton à l'étain brevetée pour leur très bonne plasticité à chaud (brevet Européen n° EP 1 029 935 A1 publié le 23.08.2000).

At present, the most used alloys in this field, are according to the European nomenclature:

• a) Traditional stamping alloy: CW617N,
• (b) Dezincification resistant alloys, the most commonly used is arsenic brass: CW602N,
• c) A family of brass alloys tin patented for their very good hot plasticity (European Patent No. EP 1 029 935 A1 published 23.08.2000).

Furthermore, it is already known that the addition of tin in brass can improve corrosion resistance as mentioned in the book Metals Handbook, 9 ^th Ed., Volumel3, Corrosion (1987), and may be γ-gene character of tin in traditional α-β 'brass, as mentioned in HO HOFMANN, "Metallurgy of Copper", McGraw-Hill Book Company, Inc. (1924). EP 0947592 A1 discloses a family of brass tin alloys and its method of manufacture which comprises a spinning step at temperatures between 480 and 650 ° C.

PROBLEMS POSED

• a) résistance à la dézincification extrêmement faible,
• b) usinabilité moyenne.

Among these alloys, the traditional CW617N matrixing alloy has the following drawbacks:

• a) extremely low dezincification resistance,
• b) average machinability.

• a) mauvaise usinabilité (fragmentation des copeaux),
• b) gamme de fabrication lourde : nécessitant la réalisation d'un traitement thermique avant la livraison des barres et d'un autre après matriçage (robinets, valves, raccords),
• c) taux de relargage du plomb dans l'eau élevé.

As for arsenic brass alloys resistant to dezincification, they have the following drawbacks:

• a) poor machinability (chip fragmentation),
• b) heavy manufacturing range: requiring the completion of a heat treatment before delivery of the bars and another after stamping (valves, valves, fittings),
• c) high lead release rate in water.

• a) contrainte d'écoulement très élevée pour la plage de température préconisée pour matriçage, par rapport à CW617N (un ordre de grandeur de différence),
• b) susceptibilité importante au niveau de la température de matriçage; autrement dit, pour assurer la bonne malléabilité à chaud, la température de matriçage doit être très stable (± 20°C) ce qui nécessite le remplacement des modes de chauffage traditionnels, par des matrices chauffantes incorporées dans les presses.

Suite aux points a) et b) précités, l'utilisation des laitons à l'étain, objet du brevet susmentionné, nécessite la modification structurelle des presses de matriçage existantes.Finally, with regard to patented brass alloys tin for their very good hot plasticity, they have the following drawbacks:

• a) very high flow stress for the recommended temperature range for stamping, compared to CW617N (an order of magnitude difference),
• (b) significant susceptibility to stamping temperature; in other words, to ensure good heat malleability, the stamping temperature must be very stable (± 20 ° C) which requires the replacement of traditional heating modes, by heating matrices incorporated in the presses.

Following points a) and b) above, the use of tin bristles, subject of the aforementioned patent, requires the structural modification of existing stamping presses.

OBJECT OF THE INVENTION

1. 1) Procédé d'élaboration simple et économique,
2. 2) Très bonne résistance à la dézincification,
3. 3) Très bonne usinabilité (fragmentation des copeaux),
4. 4) Très bonne forgeabilité (faible résistance à la déformation et bonne malléabilité à chaud),
5. 5) Pas d'effet néfaste sur le taux de relargage du plomb dans l'eau potable.
   Cette dernière condition est motivée par les nouvelles réglementations concernant la qualité de l'eau potable.

The alloys according to the invention are intended for use in the manufacture of parts used essentially in drinking water distribution pipes (valves, valves, fittings), and are intended to simultaneously satisfy the following conditions:

1. 1) Simple and economical production process,
2. 2) Very good resistance to dezincification,
3. 3) Very good machinability (chip fragmentation),
4. 4) Very good forgeability (low resistance to deformation and good heat malleability),
5. 5) No adverse effect on the release rate of lead in drinking water.
   This last condition is motivated by the new regulations concerning the quality of drinking water.

DESCRIPTION OF THE INVENTION

An object of the invention is formed by the method of manufacturing a semi-finished product according to claim 1, which process typically comprises a spinning step, said spinning step not being followed by a heat treatment step. In this respect, the method according to the invention is therefore particularly economical.

• Excellente résistance à la dézincification
• Très bonne usinabilité (fragmentation de copeaux)
• Excellente forgeabilité à chaud
• Pas d'effet néfaste sur le taux de relargage du plomb dans l'eau potable
• Gamme de fabrication simple et économique (pas de nécessité de procéder à un traitement thermique ni chez le fabricant de laiton, ni chez les matriceurs après le matriçage des pièces)
• Recyclage simple.

The Applicant has observed that the tin-brass alloys according to the invention have, compared with prior art alloys used for the same applications, the optimum combination of the required characteristics.
Indeed, these alloys according to the invention are characterized by the simultaneous presence of the properties below:

• Excellent resistance to dezincification
• Very good machinability (chip fragmentation)
• Excellent hot forgeability
• No detrimental effect on the release rate of lead in drinking water
• Simple and economical manufacturing range (no need for heat treatment at the brass manufacturer or the die stampers after coin stamping)
• Simple recycling.

• une baisse du potentiel de corrosion de "γ" ce qui se traduirait par une susceptibilité à la corrosion accrue de cette phase. En présence d'un milieu corrosif, la phase "γ" s'attaquerait donc préférentiellement (démarrage de la corrosion) en protégeant le reste de la matrice. Autrement dit, la phase "γ" jouerait le rôle d'anode sacrificiel et protègerait le reste de l'alliage,
• une cinétique lente de corrosion (progression du front de dézincification). Ainsi, à cause de cette baisse de cinétique (et malgré la susceptibilité très élevée à la corrosion de la phase "γ") l'intensité globale de dézincification des alliages contenant de l'étain selon l'invention, se trouverait significativement baissée.
  Cependant, pour obtenir les propriétés recherchées selon l'invention, la phase "γ" doit d'une part être présente en faible quantité relative comme illustré sur la figure 1, et doit d'autre part présenter une morphologie fine et discontinue, comme cela apparaît sur la figure 2. En effet, la figure 2 montre que la phase "γ" est présente au joint de grain entre les phases α et β' sur une faible épaisseur et qu'elle est discontinue puisqu'elle est absente dans les deux autres jonctions de phases α et β' (à droite et à gauche) présentes sur la figure 2.
  Par ailleurs, dans le cadre de ses recherches, la demanderesse a pu démontrer le rôle néfaste de l'arsenic dans les laitons au plomb en ce qui concerne le relargage du plomb. En effet, s'il est connu que l'arsenic présent dans les laitons au plomb, se met au niveau des joints de grains, par contre la demanderesse a trouvé, comme illustré schématiquement sur la figure 4, que l'arsenic avait tendance à migrer à la surface et que, dans un milieu aqueux, l'arsenic étant plus noble que le plomb (E_As = 0.248V, E_Pb = - 0.126V), cela conduisait à la formation des piles électrochimiques entre l'arsenic et les particules de plomb, de sorte qu'ainsi, la dissolution du plomb dans l'eau potable (taux du relargage) se trouverait accélérée.

The properties of the alloys according to the invention are due in particular to the choice of the composition and especially to the well-targeted range of the tin content.
As part of its work, the Applicant has put forward the following hypothesis to explain the beneficial effect of tin.
The mechanism involved would be the following: strongly "γ-gene", the tin once added to the brass would cause the formation of the new phase "γ" within the duplex microstructure α-β '. This formation would be to the detriment of the β 'phase as shown in FIG. 1. Because of the high solubility of tin in the "γ" phase, the formation of tin would be accompanied by a phenomenon, kinetics very fast, pumping the tin matrix (phases α and β '), as shown in Figure 2.
The presence of tin within the "γ" phase would thus lead to:

• a decrease in the corrosion potential of "γ" which would result in an increased susceptibility to corrosion of this phase. In the presence of a corrosive medium, the "γ" phase would therefore preferentially attack (start of corrosion) by protecting the rest of the matrix. In other words, the "γ" phase would act as a sacrificial anode and protect the rest of the alloy,
• slow kinetics of corrosion (progression of the dezincification front). Thus, because of this drop in kinetics (and despite the very high susceptibility to corrosion of the "γ" phase), the overall dezincification intensity of tin-containing alloys according to the invention would be significantly reduced.
  However, to obtain the desired properties according to the invention, the "γ" phase must firstly be present in relatively small amounts as shown in FIG. 1, and must also have a fine and discontinuous morphology, as can be seen in FIG. appears on the Indeed, FIG. 2 shows that the phase "γ" is present at the grain boundary between the phases α and β 'on a small thickness and that it is discontinuous since it is absent in the other two junctions of phases α and β '(right and left) present in FIG.
  In addition, as part of its research, the Applicant has been able to demonstrate the harmful role of arsenic in leaded brasses with regard to the release of lead. Indeed, although it is known that the arsenic present in leaded brasses is at the level of the grain boundaries, the applicant has found, as illustrated schematically in FIG. 4, that arsenic has a tendency to to migrate to the surface and that, in an aqueous medium, arsenic being nobler than lead (E _As = 0.248V, E _Pb = - 0.126V), this led to the formation of electrochemical cells between arsenic and lead particles, so that the dissolution of lead in drinking water (release rate) would be accelerated.

DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram which gives the evolution of the weight percentages of the α, β 'and γ phases as a function of the weight concentration of tin, the CuZnPbSn alloys according to the invention being those for which Sn is between 1.3 and 1.7% by weight.

This diagram was obtained from the following 6 alloys with increasing Sn content: Sn% weight Pb% weight Fe% weight Zn% weight Cu% weight 0 2.16 0.19 38.6 Rest 0.59 2.06 0.20 39.9 Rest 1.13 2.12 0.19 39.1 Rest 1.71 2.19 0.17 38.5 Rest 2.19 2.08 0.20 38.1 Rest 2.73 2.02 0.18 37.5 Rest

FIG. 2 is a diagram giving the tin weight concentration of the α, β 'and γ phases of CuZnPbSn alloys according to the invention, concentration obtained on a micrographic section of a half-product obtained according to alloy No. 2 by analysis. punctual with a scanning microscope. On the ordinate is the weight content of Sn, and on the abscissa is the distance in μm between the different analysis points, distance taken along a straight line from an origin point taken in a phase α, which line successively cuts from left to right, phases α / β '/ α / γ / β' / α. This diagram shows a pumping phenomenon of tin phases α, β 'by the γ phase.

FIG. 3 is a photograph intended to highlight the hot malleability of the alloys according to the invention (alloys 2 and 4) by crushing tests of 55% (upper pions) and 80% (lower pions), carried out at 700, 750 and 825 ° C.

FIG. 4 is a diagram showing a section of a coin stamped according to the invention in contact with water, explanation of the mechanism of accelerating action of arsenic on the release rate of lead in drinking water

FIG. 5 is a diagram which shows the elements of the photograph of FIG.

DETAILED DESCRIPTION OF THE INVENTION

According to the invention, the tin content of the CuZnPbSn alloy can be between 1.4 and 1.6%. The lead content can be between 1.9 and 2.1%.

With regard to the secondary or trace elements, the iron content may be less than or equal to 0.2%.
Similarly, the arsenic content can be between 5 and 500 ppm.
The aluminum content can be between 5 and 500 ppm.
The antimony content can be between 5 and 100ppm.

The silicon content may be between 5 and 500 ppm.

Another subject of the invention comprises the semi-products obtained from the CuZnPbSn alloy according to the invention, in which the microstructure of the alloy is composed of three intermetallic phases: α, β 'and γ.
By image analysis of the microstructure, it has been observed that the surface percentage of the γ phase of these half-products can be between 5 and 9%, and that the surface percentage of the β 'phase can be between and 40%.

As illustrated in Table 3 of Example 1, said CuZnPbSn alloy may have a composition chosen so that, according to ISO 6509, said semi-product obtained from this alloy has a mean dezincification depth of less than 200 μm, and even typically less than 150 μm, so that said alloy CuZnPbSn, which is not arsenic, is much higher than the CW617N alloy and even approaches the performance of the arsenic alloy CW602N .

As illustrated in Table 5 of Example 2, said CuZnPbSn alloy may have a composition chosen so that the semi-product obtained from this alloy has, for a drilling operation performed under the usual machining conditions. according to standard NF E66-520-7 of the 2000 edition, an average chip size typically two times smaller than that obtained with the CW602N alloy which is a brass with arsenic.

As illustrated in Table 7 of Example 4 and in FIGS. 3 and 5, said CuZnPbSn alloy may have a composition chosen so that the hot-pressing test according to the ASTM E209-00 standard of the 2000 edition. , and made in the range of 600 ° C to 750 ° C, causes no cracking of said half-product obtained from this alloy.
Thus, the semi-finished products according to the invention have a large latitude of hot deformation, as regards both the temperature range and the crushing rate, without the appearance of cracks or cracks in the metal. These semi-finished products a great ability to deform without cracking or cracks, which is extremely advantageous in practice.

As illustrated in Table 6 of Example 3, said CuZnPbSn alloy of said half-product may have a composition chosen so that the release rate of lead in drinking water is below the regulatory threshold according to European Directive 98 / 83 / EC on the quality of water intended for human consumption.
It is important to note also the very low rate of Zn release compared to that of alloys Nos. 5 and 6.

As illustrated in Table 8 of Example 4, said CuZnPbSn alloy may have a composition chosen so that said half-product has a high heat malleability, and so that its crush resistance is lower. to that obtained with the CW602N alloy, and preferably two times less than that of said CW602N alloy.
It goes without saying that the power installed on the machines or devices for manufacturing the finished products, in particular when such manufacture comprises deformation of the half-product by crushing, will be less in the case of the semi-finished products according to the invention than in the case of the semi-finished products of the state of the art formed from alloys Nos. 5 and 6.

Another object of the invention is formed by the finished product obtained from the semi-finished product according to the invention, the half-product being typically chosen from: a tap, a valve, a coupling.

Another object of the invention is formed by the process for manufacturing the finished product according to the invention, in which process said finished product is typically formed by deformation or machining of said semi-finished product, said process not comprising a treatment step thermal, which is very advantageous and economical in practice compared to comparable processes of the state of the art.

Another object of the invention is formed by the use of a CuZnPbSn alloy according to the invention, or a semi-finished product according to the invention or obtained according to the invention, for the manufacture of finished products or used components. for sanitary water distribution such as valves, valves and fittings.

EXAMPLES OF REALIZATION

Table 1 gives the chemical compositions of the alloys tested according to the invention (% by weight). <b> Table 1 </ b>: Chemical composition (weight%) of the alloys tested according to the invention. Cu Pb Sn Fe Zn Alloy 1 63.2 1.83 1.55 0.18 rest Alloy 2 61.2 2.04 1.57 0.17 Rest Alloy 3 60.2 2.01 1.42 0.19 Rest Alloy 4 59.1 1.82 1.51 0.18 Rest Alloy 5 59.5 1.95 0.22 0.21 Rest Traditional CW617N stamping alloy Alloy 6 * 61.2 2.20 0.06 0.01 Rest Dezincification resistant alloy CW602N * 6 alloy that contains 0.12% arsenic

The alloys of Table 1 were made according to a conventional range comprising the steps listed in Table 2 . <b> Table 2 </ b>: Operating conditions for the manufacture of the brans tested • Casting T = 1060 ± 20 ° C, ∅ billet = 110 mm • Reverse spin: T = 700 ± 20 ° C, Warm-up time = 2 h, ∅ bars = 26 mm • Spin ratio = 94%

Example 1

In this example, the influence of the composition of the alloy on dezincification has been studied.
The dezincification tests were carried out in the longitudinal direction (direction of spinning) according to ISO 6509. The average dezincification depths were measured using an image analysis system (average of twenty measurements).

Table 3 shows the results of the measurements: <b> Table 3 </ b>: Dezincification depth measurement results. Dezincification depth (μm) Average Standard deviation Alloy 1 750 27 Alloy 2 149 15 Alloy 3 135 13 Alloy 4 146 17 Alloy 5 1320 31 Alloy 6 80 10

1. 1) l'alliage de référence (alliage 6), c'est à dire le CW602N, montre la meilleure résistance à la dézincification.
   Cette résistance est, en effet, la conséquence d'une part, de la microstructure monophasée de cet alliage (100% alpha) et d'autre part, de la présence de l'arsenic dans l'alliage.
   Il est à noter cependant que l'alliage CW602N nécessite la réalisation de deux traitements thermiques (à ~500°C) l'un au cours de sa fabrication (chez le fabricant de l'alliage), et l'autre, après l'opération de matriçage.
2. 2) l'alliage traditionnel de matriçage (alliage 5), c'est à dire le CW617N, montre la plus faible résistance à la dézincification.
3. 3) l'addition de l'étain selon l'invention (alliages 2, 3 et 4) donne des résultats proches de ceux obtenus pour l'alliage indézincifiable CW602N. Autrement dit, l'addition de l'étain selon l'invention améliore significativement la résistance à la dézincification des laitons de matriçage (comparaison des alliages n° 2, 3 et 4 avec l'alliage n° 5).
4. 4) l'alliage n° 1 ayant une teneur trop élevée en cuivre (en dehors de la fourchette selon l'invention, c'est à dire, 59,5 à 61,5% pds) présente une profondeur de dézincification presque cinq fois supérieure à celles obtenues pour les alliages n°2, 3 et 4

The results in this table highlight the following points:

1. 1) the reference alloy (alloy 6), ie the CW602N, shows the best resistance to dezincification.
   This resistance is, in fact, the consequence of the one hand, the single-phase microstructure of this alloy (100% alpha) and secondly, the presence of arsenic in the alloy.
   It should be noted, however, that the CW602N alloy requires the completion of two heat treatments (at ~ 500 ° C) one during its manufacture (at the manufacturer of the alloy), and the other, after the stamping operation.
2. 2) The traditional die-casting alloy (alloy 5), ie the CW617N, shows the lowest resistance to dezincification.
3. 3) the addition of the tin according to the invention (alloys 2, 3 and 4) gives results close to those obtained for the indissincifiable alloy CW602N. In other words, the addition of tin according to the invention significantly improves the dezincification resistance of the stamping brasses (comparison of alloys No. 2, 3 and 4 with alloy No. 5).
4. 4) alloy No. 1 having a copper content too high (outside the range according to the invention, ie, 59.5 to 61.5% wt) has a dezincification depth almost five times greater than those obtained for alloys Nos. 2, 3 and 4

Example 2

In this example, the workability of the alloys according to the invention has been studied in comparison with the CW617N and the CW602N.

• Vitesse de coupe (Vc) = 280 m/min
• Avance par tour (f) = 0,56 mm/tour
• Foret :
  • ◆ Monobloc en carbure
  • ◆ Diamètre 10 mm
  • ◆ Profondeur de perçage (pp) = 25 mm
• Lubrification : à l'aide du LACTUCUT 2, lubrifiant commercialisé par TOTAL®.

The machinability tests were performed on an instrumented and automatic piercing bench. The operating conditions used are as follows:

• Cutting speed (Vc) = 280 m / min
• Feed per turn (f) = 0.56 mm / turn
• Forest:
  • ◆ Carbide monobloc
  • ◆ Diameter 10 mm
  • ◆ Drilling depth (pp) = 25 mm
• Lubrication: using LACTUCUT 2, a lubricant marketed by TOTAL®.

The parameters measured were the axial drilling force and the average chip size evaluated by a parameter called the "medium chip" (CM).

The CM was calculated as follows:
The chips resulting from the drilling are added on a series of 7 superimposed sieves marked with 1 to 7. Table 4 gives the opening of the square meshes (in mm) of each sieve as well as an arbitrary index which refers to it (index sieves). <b> Table 4 </ b>: Characteristics of sieves used No. sieve Opening of the stitches (mm) Sieve index 1 2.5 7 2 2 6 3 1.6 5 4 1.25 4 5 0.9 3 6 0.56 2 7 0 (Background - No aperture) 1

The screens are mounted on a vibratory support which is vibrated for five minutes for each sieving operation.

où : I_i = indice du tamis n° "i".
m_i = poids des copeaux du tamis n° "i".The contents of each sieve are then weighed. The "average chip" (CM) parameter is then calculated using the following equation [ Eq.2 ]: $$\mathrm{VS}.M.\left(\mathit{without\; unity}\right)=\frac{{\displaystyle \underset{i=1}{\overset{7}{\Sigma }}\left(I_i*m_i\right)}}{{\displaystyle \underset{i=1}{\overset{7}{\Sigma }}\left(m_i\right)}}$$

where: I _i = sieve number n "i".
m _i = weight of sieve chips No. "i".

The fragmentation of chips from drilling an alloy is better than the CM is small.

Table 5 summarizes the results obtained. Each parameter is calculated using the average of the results of five different measurements <b> Table 5 </ b>: Machining test results (drilling) Drilling force (N) CM Alloy 1 2739 ± 25 4.2 ± 0.2 Alloy 2 2940 ± 36 3.80 ± 0.2 Alloy 3 3082 ± 41 3.75 ± 0.1 Alloy 4 3193 ± 48 3.70 ± 0.2 Alloy 5 3232 ± 42 4.5 ± 0.2 Alloy 6 2642 ± 30 7.3 ± 0.2

The results in Table 5 show that compared to the alloy CW617N (No. 5), the alloys according to the invention (Nos. 2, 3 and 4) exhibit both a lower level of force and a much better fragmentation of the chips. .

As for the comparison with the alloy with arsenic, ie the CW602N (No. 6), it is noted that the alloys according to the invention have higher levels of force. However, this difference is largely counterbalanced by the excellent fragmentation of tin bran chips.

Example 3

In this example, the release of lead, copper and zinc in drinking water has been studied. The release tests were carried out over a period of three weeks using the leaching solution of "Old-BSI 7766" [DD 201 - 1991 of the British Standard Institution].

The tests were carried out on "buckets" machined in bars 26 mm in diameter. The effective area of each bucket is 1.90 dm ² and contains 0.4 l of the above leaching solution.

In order to overcome the phenomenon of superficial contamination of the buckets by the lead (formation of a thin film of this element at the machined surfaces), all buckets have undergone a surface treatment (ECOWAVE® treatment of the Company). KME).

Water samples were taken during the 3 ^rd week of testing with one sampling every 24 hours (stagnation).

For each element, it is the average of the 7 results obtained during the 3 ^rd week of testing, which was considered for comparison.

Table 6 presents the results for lead, copper and zinc. <b> Table 6 </ b>: Results of release tests Average release rate (μg / dm ² ) Pb Cu Zn Alloy 1 0.73 5.17 100.75 Alloy 4 1.15 5.31 93.8 Alloy 5 1.07 5.35 221.66 Alloy 6 2.03 7.98 160.05

It is noted that the alloy according to the invention (No. 4) gives less release (Pb, Cu and Zn) than the CW602N alloy (alloy 6) and much less Zn release than the CW617N (alloy 5) .

Example 4

• Géométrie des échantillons : cylindres de 15mm de diamètre et de 15mm de hauteur,
• Lubrification à l'aide d'un bâton de graphite,
• Température : 600, 700, 750 et 825°C,
• Taux d'écrasement* (ε) : 55 et 80%,
  • * ε = [(H₀-h)/H₀] 100%
    où H₀ et h sont respectivement les hauteurs de l'échantillon avant et après le test d'écrasement
• Vitesse de déformation généralisée: ε⁰ = 34 s^-1

In this example, the hot forgeability (hot stamping ability) of the alloys according to the invention was studied.
In order to evaluate the forgeability, hot crushing tests were carried out using a traction machine. The operating conditions used are as follows:

• Geometry of the samples: cylinders 15mm in diameter and 15mm high,
• Lubrication using a graphite stick,
• Temperature: 600, 700, 750 and 825 ° C,
• Crush rate * (ε): 55 and 80%,
  • * ε = [(H ₀ -h) / H ₀ ] 100%
    where H ₀ and h are respectively the heights of the sample before and after the crush test
• Generalized deformation velocity: ε ⁰ = 34 s ^-1

1. 1) la résistance à la déformation.
   Celle-ci a été directement mesurée par la machine de traction. Elle reflète la puissance nécessaire au matriçage des échantillons.
2. 2) la malléabilité à chaud.
   Elle est évaluée à l'oeil à l'aide de l'aspect extérieur des pions comprimés (fissuration, peaux d'orange, ...).

Forgeability was evaluated using two parameters:

1. 1) resistance to deformation.
   This was directly measured by the traction machine. It reflects the power required to stamp the samples.
2. 2) hot malleability.
   It is evaluated by the eye using the appearance of compressed pawns (cracking, orange peel, ...).

Table 7 presents the results of visual examinations of hot-crushed samples. FIG. 3 shows the photograph of a part of the crushed pieces, FIG. 5 being a schematic representation of the crushed samples of FIG. <b> Table 7: </ b> Hot Swap Test Results (+: No Cracks, -: Cracked) T (° C) Crush Rate% No. Alloy 1 2 3 4 5 6 600 55 + + + + + - 80 - + + + - - 700 55 + + + + + - 80 - + + + + + 750 55 + + + + + + 80 - + + + - - 825 55 + + + + - + 80 - - - - - -

It is noted that unlike the alloys CW617N and CW602N, the alloys according to the invention (No. 2, 3 and 4) are molded very well between 600 and 750 ° C and this for the two crash rates tested.

As for the resistance to deformation (hot crushing force), Table 8 summarizes the results obtained (expressed in Kg) for a crush rate of 55%. <b> Table 8 </ b>: Results of crushing forces (kg) T (° C) No. alloy 1 2 3 4 5 6 700 1725 1000 735 700 720 1650 750 1025 650 540 500 550 995 825 460 530 420 400 390 425

Table 8 shows that the alloys according to the invention have crush stress levels lower than those of alloy No. 6 (CW602N), and close to those of alloy No. 5 (CW617N).

ADVANTAGES OF THE INVENTION

• a) procédé d'élaboration simple et économique,
• b) très bonne résistance à la dézincification,
• c) très bonne usinabilité (fragmentation des copeaux),
• d) très bonne forgeabilité (faible résistance à la déformation et bonne malléabilité à chaud),
• e) pas d'effet néfaste sur le taux de relargage du plomb dans l'eau potable.

As already indicated, the invention makes it possible to solve many problems simultaneously insofar as it makes it possible simultaneously to satisfy the five conditions previously set, namely:

• a) simple and economical process of elaboration,
• b) very good resistance to dezincification,
• c) very good machinability (chip fragmentation),
• d) very good forgeability (low resistance to deformation and good heat malleability),
• e) no detrimental effect on the release rate of lead in drinking water.

Thus, the comparison of the alloys according to the invention (alloys Nos. 2 to 4) with the alloys of the state of the art (alloy No5 = CW617N, and No6 = CW602N) clearly showed the overall superiority of the former over the latter. .

Claims (19)

1. Process for manufacturing a semi-finished product made of CuZnPbSn alloy in which the said alloy composition by weight is:

   - copper: from 59.5% to 61.5%,

   - lead: from 1.8% to 2.2%,

   - tin: from 1.3% to 1.7%,

   - sum of other elements except Zn < 0.3%,

   - zinc: the remainder,

   characterised in that it comprises an extrusion step carried out at a temperature of 700°C ± 20°C, the said extrusion step not including or not being followed by a heat treatment step.
2. Process according to claim 1 in which the tin content is between 1.4% and 1.6%.
3. Process according to either of claims 1 and 2 in which the lead content is between 1.9% and 2.1%.
4. Process according to any one of claims 1 to 3, in which the iron content is less than or equal to 0.2%.
5. Process according to any one of claims 1 to 4, in which the arsenic content is between 5 and 500 ppm.
6. Process according to any one of claims 1 to 5, in which the aluminium content is between 5 and 500 ppm.
7. Process according to any one of claims 1 to 6, in which the antimony content is between 5 and 100 ppm.
8. Process according to any one of claims 1 to 7, in which the silicon content is between 5 and 500 ppm.
9. Process according to any one of claims 1 to 8, in which the said partly finished product has an alloy microstructure composed of three intermetallic phases, α, β' and γ.
10. Process according to claim 9, in which the percentage of the surface area of the γ phase is between 5% and 9%.
11. Process according to either of claims 9 and 10, in which the percentage of the surface area of the β' phase is between 25% and 40%.
12. Process according to any one of claims 9 to 11, in which the composition of the said CuZnPbSn alloy is chosen such that the average dezincification depth of the said partly finished product according to ISO standard 6509 is less than 200 µm.
13. Process according to any one of claims 9 to 12 in which the composition of the said CuZnPbSn alloy is chosen such that the average swarf size for a drilling operation carried out on the semi-finished product under normal machining conditions according to NF standard E66-520-7, 2000 edition, is typically half the size of that obtained with the CW602N alloy that is a brass with arsenic.
14. Process according to any one of claims 9 to 13, in which the composition of the said CuZnPbSn alloy is chosen such that the hot compression test carried out according to ASTM standard E209-00, 2000 edition within the 600°C and 750°C range, does not cause any cracking of the said partly finished product.
15. Process according to any one of claims 9 to 14, in which the composition of the said CuZnPbSn alloy is chosen such that the release ratio of lead into drinking water is less than the regulatory threshold according to European Directive 98/83/EC related to the water quality intended for human consumption.
16. Process according to any one of claims 9 to 15, in which the composition of the said CuZnPbSn alloy is chosen such that the hot workability of the said semi-finished product is high, and such that its compression strength is less than that obtained with the CW602N alloy, and preferably half as much as that obtained with the said CW602N alloy.
17. Finished product obtained from the partly finished product obtained using the process according to any one of claims 1 to 16, the said finished product typically being chosen from among a tap, a valve and a fitting.
18. Process for manufacturing the finished product according to claim 17 in which the said finished product is formed typically by deformation or machining of the said semi-finished product, the said process not including any heat treatment step.
19. Use of a partly finished product made of a CuZnPbSn alloy obtained using the process according to any one of claims 1 to 16 for manufacturing finished products or components used for distribution of domestic supply water such as taps, valves and fittings.

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