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: 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, comprising the following elements, the proportions being shown as percentage by weight of the alloy: TABLE-US-00007 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.

2. The alloy as claimed in claim 1, wherein the alloy comprises less than 0.5% by weight of Ti.

3. The alloy as claimed in claim 1, wherein the alloy does not comprise titanium other than in the form of unavoidable impurities.

4. The alloy as claimed in claim 1, wherein the alloy comprises between 0.7% and 1% by weight of carbon.

5. The alloy as claimed in claim 1, wherein the (Nb+Ti)/C ratio is from 1 to 2.

6. The alloy as claimed in claim 1, wherein the alloy comprises between 22 and 30% by weight of chromium.

7. The alloy as claimed in claim 1, wherein the alloy comprises between 15 and 20% by weight of iron.

8. The alloy as claimed in claim 1, wherein the alloy comprises from 0.5 to 2.0% by weight of niobium.

9. The alloy as claimed in claim 1, wherein the alloy comprises from 3 to 9% by weight of tungsten.

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

11. An article for the manufacture of mineral wool comprising the alloy as claimed in claim 1.

12. A fiberizing spinner for the manufacture of mineral wool made of the alloy as claimed in claim 1.

13. A process for the manufacture of mineral wool by internal centrifugation, comprising: pouring a flow of molten mineral material into the fiberizing spinner as claimed in claim 12, 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 1000 C.

14. The alloy as claimed in claim 1, wherein the (Nb+Ti)/C ratio is from 1.5 to 2.

15. The alloy as claimed in claim 1, wherein the alloy comprises between 23 and 28% by weight of chromium.

16. The alloy as claimed in claim 1, wherein the alloy comprises from 0.7 to 1.7% by weight of niobium.

17. The alloy as claimed in claim 1, wherein the alloy comprises from 3 to 6% by weight of tungsten.

18. The alloy as claimed in claim 1, wherein the alloy comprises less than 1% by weight of cobalt.

19. The article for the manufacture of mineral wool as claimed in claim 11, wherein the alloy is manufactured by founding.

20. The fiberizing spinner as claimed in claim 11, wherein the alloy is manufactured by founding.

Description

EXAMPLE

[0038] 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.

TABLE-US-00005 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

[0039] 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.

[0040] In this way, 150*100*25 mm ingots were manufactured.

[0041] The properties of resistance to creep, to oxidation and to corrosion of the alloys I1, I2 and C1 were subsequently evaluated.

[0042] 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.

[0043] 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.cm.sup.2.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.

TABLE-US-00006 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.

[0044] 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.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.

[0045] 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.