Alloy for a fibre-forming plate

Abstract

A metal alloy is for use at very high temperature, in particular the metal alloy can be used in a process for the manufacture of mineral wool by fiberizing a molten mineral composition. The metal alloy contains the following elements, the proportions being shown as percentage by weight of the alloy: TABLE-US-00001 Cr 20 to 35% Fe 10 to 25% W 2 to 10% Nb 0.5 to 2.5% Ti 0 to 1% C 0.2 to 1.2% Co less than 5% Si less than 0.9% Mn less than 0.9%
the remainder consisting of nickel and unavoidable impurities.

Claims

1. An alloy, consisting of, as percentage by weight of the alloy: TABLE-US-00008 Cr 20 to 35%; Fe 10 to 25%; W 2 to 10%; Nb 0.5 to 2.5%; Ti 0 to 1%; C 0.2 to 1.2%; Co less than 5%; Si less than 0.9%; Mn less than 0.9%; nickel; and unavoidable impurities.

2. The alloy of claim 1, comprising less than 0.5% by weight of Ti.

3. The alloy of claim 1, comprising no titanium other than in the form of unavoidable impurities.

4. The alloy of claim 1, comprising between 0.7% and 1% by weight of carbon.

5. The alloy of claim 1, having a (Nb+Ti)/C ratio is from 1 to 2.

6. The alloy of claim 1, comprising between 22 and 30% by weight of the chromium.

7. The alloy of claim 1, comprising between 15 and 20% by weight of the iron.

8. The alloy of claim 1, comprising from 0.5 to 2.0% by weight of niobium.

9. The alloy of claim 1, comprising from 3 to 9% by weight of tungsten.

10. The alloy of claim 1, wherein the alloy comprises less than 3% by weight of cobalt.

11. An article suitable for manufacturing mineral wool comprising the alloy of claim 1.

12. The article for the manufacture of mineral wool of claim 11, wherein the alloy is manufactured by founding.

13. The fiberizing spinner of claim 11, wherein the alloy is manufactured by founding.

14. A fiberizing spinner suitable for manufacturing mineral wool made of the alloy of claim 1.

15. A process for manufacturing mineral wool by internal centrifugation, comprising: pouring a flow of a molten mineral material comprising the alloy of claim 1 into a fiberizing spinner including a pierced peripheral band, pierced with a multitude of orifices through which filaments of the molten mineral material escape; and subsequently drawing the filaments to give wool under the action of a gas, wherein a temperature of the mineral material in the spinner is at least 1000° C.

16. The alloy of claim 1, wherein the (Nb+Ti)/C ratio is from 1.5 to 2.

17. The alloy of claim 1, comprising between 23 and 28% by weight of the chromium.

18. The alloy of claim 1, comprising from 0.7 to 1.7% by weight of the niobium.

19. The alloy of claim 1, comprising from 3 to 6% by weight of the tungsten.

20. The alloy of claim 1, comprising less than 1% by weight of the cobalt.

Description

(1) In a specific embodiment, the alloy according to the invention comprises:

(2) TABLE-US-00003 Cr 22 to 30%, preferably 23 to 28% Fe 12 to 23%, preferably 15 to 20% W 3 to 9%, preferably 3 to 6% Nb 0.5 to 2.5%, preferably 0.7 to 1.7%, C 0.7 to 1% Co less than 5% Si less than 0.9% Mn less than 0.9%
and does not comprise titanium other than in the form of unavoidable impurities, the remainder consisting of nickel and unavoidable impurities.

(3) The alloys which can be used according to the invention, which contain highly reactive elements, can be formed by founding, in particular by inductive melting under an at least partially inert atmosphere and sand mold casting.

(4) The casting can optionally be followed by a heat treatment.

(5) Another subject matter of the invention is a process for the manufacture of an article by founding starting from the alloys described above as subject matter of the invention.

(6) The process generally comprises a stage of appropriate heat treatment which makes it possible to obtain secondary carbides and makes possible their homogeneous distribution in the metal matrix, as described in FR 2675818 The heat treatment is preferably carried out at a temperature of less than 1000° C., indeed even of less than 950° C., for example from 800° C. to 900° C., for a period of time of at least 5 hours, indeed even at least 8 hours, for example from 10 to 20 hours.

(7) The process can comprise at least one cooling stage, after the casting and/or after or in the course of a heat treatment, for example by cooling in the air, in particular with a return to ambient temperature.

(8) The alloys which are subject matter of the invention can be used to manufacture all kinds of parts which are mechanically stressed at high temperature and/or caused to operate in an oxidizing or corrosive environment. Other subject matters of the invention are such articles manufactured from an alloy according to the invention, in particular by founding.

(9) Mention may in particular be made, among such applications, of the manufacture of articles which can be used for the melting or the hot conversion of glass, for example fiberizing spinners for the manufacture of mineral wool.

(10) Thus, another subject matter of the invention is a process for the manufacture of mineral wool by internal centrifugation, in which a flow of molten mineral material is poured into a fiberizing spinner, the peripheral band of which is pierced with a multitude of orifices through which filaments of molten mineral material escape, which filaments are subsequently drawn to give wool under the action of a gas, the temperature of the mineral material in the spinner being at least 900° C., indeed even at least 950° C. or at least 1000° C., indeed even at least 1040° C., and the fiberizing spinner being formed of an alloy as defined above.

(11) The alloys according to the invention thus make it possible to fiberize a molten mineral material having a liquidus temperature (T.sub.liq) of 800° C. or more, for example of 850° C., indeed even 900° C., to 1030° C., indeed even 1000° C. or even 950° C.

(12) Generally, the fiberizing of these mineral materials can be carried out in a range of temperatures (for the molten material arriving in the spinner) of between T.sub.liq and T.sub.log3, where T.sub.log3 is the temperature at which the molten composition exhibits a viscosity of 100 Pa.Math.s, typically of the order of less than 1200° C., indeed even of less than 1150° C., preferably between 1020 and 1100° C., indeed even between 1050 and 1080° C. The difference between T.sub.log3 and T.sub.liq is generally greater than 50° C.

(13) The composition of the mineral material to be fiberized is not particularly limited as long as it can be fiberized by an internal centrifugation process. It can vary as a function of the properties desired for the mineral fibers produced, for example biosolubility, fire resistance or thermal insulation properties. The material to be fiberized is preferably a glass composition of soda-lime-silica-borate type. It can in particular exhibit a composition which includes the constituents below, in the proportions by weight defined by the following limits:

(14) TABLE-US-00004 SiO.sub.2 35 to 80%, Al.sub.2O.sub.3 0 to 30%, CaO + MgO 2 to 35%, Na.sub.2O + K.sub.2O 0 to 20%,
it being understood that, in general,
SiO.sub.2+Al.sub.2O.sub.3 is within the range extending from 50 to 80% by weight and that Na.sub.2O+K.sub.2O+B.sub.2O.sub.3 is within the range extending from 5 to 30% by weight.

(15) The material to be fiberized can in particular exhibit one the following composition:

(16) TABLE-US-00005 SiO.sub.2 50 to 75%, Al.sub.2O.sub.3 0 to 8%, CaO + MgO 2 to 20%, Fe.sub.2O.sub.3 0 to 3%, Na.sub.2O + K.sub.2O 12 to 20%, B.sub.2O.sub.3 2 to 10%.

(17) The material to be fiberized can be prepared from pure constituents but it is generally obtained by melting in a mixture of natural starting materials introducing different impurities.

(18) Although the invention has been described mainly in the context of the manufacture of mineral wool, it can be applied to the glass industry in general for producing furnace, bushing or feeder components or fittings, in particular for the production of yarns of textile glass, of packaging glass, and the like.

(19) Outside the glass industry, the invention can be applied to the manufacture of a very wide variety of articles, when the latter have to exhibit a high mechanical strength in an oxidizing and/or corrosive environment, in particular at high temperature.

(20) The examples which follow, which are in no way restrictive of the compositions according to the invention or of the conditions for employing the fiberizing spinners according to the invention, illustrate the advantages of the present invention.

EXAMPLE

(21) A molten charge of the compositions I1, I2 (according to the invention) and C1 (according to FR 2675818) which are shown in table 1 is prepared by the inductive melting technique under an inert atmosphere (in particular argon), which molten charge is subsequently formed by simple casting in a sand mold. The proportions as for the percentage by weight of each element in the alloy are shown in table 1, the remainder to 100% consisting of nickel and unavoidable impurities.

(22) TABLE-US-00006 TABLE 1 I1 I2 C1 Cr 25 25 28.5-29.5 Fe 17 17 4-9 W 5 5 7.2-7.6 Nb 1.5 1 * Ti * 0.5 * C 0.9 0.9 0.69-0.73 Co 3 3 * * possibly present in the form of unavoidable impurity

(23) The casting is followed by a heat treatment for precipitation of the secondary carbides at 865° C. for 12 hours, finishing with a cooling in air down to ambient temperature.

(24) In this way, 150*100*25 mm ingots were manufactured.

(25) The properties of resistance to creep, to oxidation and to corrosion of the alloys I1, I2 and C1 were subsequently evaluated.

(26) The resistance to creep was measured by a creep-traction test on cylindrical test specimens with a diameter of 3.0 mm, with a total length of 60.0 mm and with a length of 20.0 mm between marks. The tests were carried out at 1000° C. (normal operating temperature of a spinner) and 1050° C., under loads of 31 MPa (corresponding to a normal stressing of the spinner), 63 MPa (corresponding to an extreme stressing of the spinner) and 100 MPa. Table 2 shows the time (t), in hours, and the elongation (E), as percentage, before breaking.

(27) The resistance to oxidation depends, on the one hand, on the kinetics of oxidation of the alloy and, on the other hand, on the quality of adhesion of the oxide layer formed on the surface of the alloy. This is because poor adhesion of the oxide layer to the surface of the alloy accelerates oxidation of the latter: when the oxide layer comes off, a nonoxidized alloy surface is then exposed directly to the oxygen of the air, which brings about the formation of a new oxide layer, in its turn capable of coming off, thus propagating the oxidation. On the contrary, when the oxide layer remains adherent to the surface of the alloy, it forms a barrier layer which limits, indeed even halts, the progression of the oxidation. The oxidation rate constants, expressed in mg.Math.cm.sup.−2.Math.h.sup.−1/2, were calculated from the monitoring of increasing weight resulting from the oxidation of samples placed at 1000° C. for 50 h in a furnace equipped with a microbalance under a stream of air. To evaluate the quality of adhesion of the oxide layer, samples housed in individual crucibles were placed in a furnace at 1000° C. under a stream of air for 5, 10, 24, 36 and 50 hours respectively. The presence of powder at the bottom of the crucible indicates detachment of the oxide layer. Table 2 shows the amount of powder observed in the crucible for each of the samples (⊚: absence of powder; ∘: little powder; .Math.: much powder). The greater the amount of powder, the less adherent the oxide layer.

(28) TABLE-US-00007 TABLE 2 I1 I2 C1 Creep 1000° C. 31 MPa 1293.6/1.40  1310/1.50  567.8/5.55  t(h)/E(%) 63 MPa 32.9/6.7  33.0/37.5 9.05/17.8 100 MPa 1.57/22.8 0.93/48.8  0.5/40.9 1050° C. 63 MPa 5.78/10.7 4.23/37.sup.  1.87/33.2 Oxidation Kinetic constant 0.31 0.42 0.28 Adhesion 5 h ⊚ ⊚ ⊚ of the 10 h ⊚ ⊚ ◯ oxide 24 h ⊚ ⊚ ◯ layer 36 h ⊚ ◯ .Math. 50 h ⊚ ◯ .Math.

(29) The tests of resistance to corrosion are carried out using a three-electrode assembly, which electrodes are immersed in a rhodium/platinum crucible containing the molten glass. The rhodium/platinum crucible is used as counterelectrode. The comparison electrode is conventionally the air-fed stabilized zirconia electrode. The cylindrical samples of alloys to be evaluated, oxidized beforehand in air at 1000° C. for 2 h, are sealed with zirconia cement to an alumina sheath to form the working electrode. The sample constituting the working electrode is fitted to a rotating axis, in order to represent the frictional exertions of the glass on the surface of the alloy, and immersed in the molten glass at 1000° C. (composition as percentage by weight: SiO.sub.2 65.6; Al.sub.2O.sub.3 1.7; Na.sub.2O 16.4; K.sub.2O 0.7; CaO 7.4; MgO 3.1; B.sub.2O.sub.3 4.8). The resistance of the alloys to corrosion by the glass is evaluated by measuring and the polarization resistance (Rp). In order to measure the corrosion potential (E.sub.c), no current is applied between the working electrode and the counterelectrode, and the potential measured between the working electrode and the comparison electrode is that of the metal/glass pair at the given temperature. This thermodynamic information makes it possible to determine the corrosion reactions and the passivable nature of the metal studied. The measurement of the polarization resistance (Rp) is obtained by periodically varying the electric potential in the vicinity of the potential E.sub.c and by measuring the change in the current density which results. The slope of the current/potential curve recorded over this range is inversely proportional to Rp. The greater Rp (expressed in ohm.Math.cm.sup.2), the more resistant the material is to corrosion, the rate of degradation being inversely proportional to Rp. The determination of Rp thus makes it possible to evaluate, at least comparatively, the rate of corrosion of the alloys. The results are presented in FIG. 1.

(30) On comparing the data given in table 2 and in FIG. 1, there is observed, for the alloys I1 and I2 according to the invention, a resistance to creep and to oxidation which are significantly improved with respect to the alloy C1 and a resistance to corrosion which is substantially equivalent to that of the alloy C1. The alloy I1, which does not comprise titanium, furthermore shows a substantially better behavior than the alloy I2 with regard to the resistance to oxidation.