Alloy for fiber-forming plate

Abstract

An alloy contains the following elements, the proportions being indicated as percentage by weight of the alloy (limit values included): Cr 20 to 35%, Fe 0 to 6%, W 3 to 8%, Nb 0.5 to 3%, Ti 0 to 1%, C 0.4 to 1%, Co 0 to 3%, Si 0.1 to 1.5%, Mn 0.1 to 1%, the remainder consisting of nickel and unavoidable impurities.

Claims

1. An alloy that contains the following elements, the proportions being indicated as percentage by weight of the alloy (limit values included): TABLE-US-00009 Cr   20 to 35% Fe    3 to 6% W    3 to 8% Nb   0.5 to 3% Ti    0 to 1% C   0.4 to 1% Co    0 to 3% Si 0.1 to 1.5% Mn   0.1 to 1% the remainder consisting of nickel and unavoidable impurities.

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

3. The alloy as claimed in claim 2, containing less than 0.4% by weight of Ti.

4. The alloy as claimed in claim 1, containing between 0.6% and 0.9% by weight of carbon.

5. The alloy as claimed in claim 4, containing between 0.6% and 0.7% by weight of carbon.

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

7. The alloy as claimed in claim 6, wherein the (Nb+Ti)/C ratio is from 1.5 to 2.

8. The alloy as claimed in claim 1, containing between 22 and 32% by weight of chromium.

9. The alloy as claimed in claim 8, containing between 28 and 30% by weight of chromium.

10. The alloy as claimed in claim 1, containing between 3 and 4% by weight of iron.

11. The alloy as claimed in claim 1, containing between 4 and 6% by weight of iron.

12. The alloy as claimed in claim 1, containing from 0.6 to 2.0% by weight of niobium.

13. The alloy as claimed in claim 1, containing between 4 and 7% by weight of tungsten.

14. The alloy as claimed in claim 1, containing less than 2% by weight of cobalt.

15. The alloy as claimed in claim 1, containing between 55% and 65% by weight of nickel.

16. The alloy as claimed in claim 1, containing less than 1.1% by weight of silicon.

17. An article for the conversion of glass, made of an alloy as claimed in claim 1.

18. An article for the manufacture of mineral wool, made of an alloy as claimed in claim 1.

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

20. A process for manufacturing mineral wool by internal centrifugation, comprising pouring a flow of molten mineral material into a fiberizing spinner as claimed in claim 19, a peripheral band of which is pierced with a multitude of orifices through which filaments of molten mineral material escape and 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.

Description

EXAMPLES

(1) A molten charge of a composition I1 (according to the invention) and C1 (according to FR 2675818) which are indicated 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. Table 1 indicates the proportions as percentage by weight of each element in the alloy, the remainder to 100% consisting of nickel and unavoidable impurities.

(2) TABLE-US-00005 TABLE 1 I1 C1 Cr 27.1 27.5 Fe 5.45 7 W 5.83 7.2 Nb 0.86 — Ti 0.14 — C 0.62 0.67 Co 0.78 0.80 Si 0.79 0.75 Mn 0.70 0.75 * optionally present in the form of unavoidable impurity

(3) 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.

(4) In this way, 200×110×25 mm ingots were manufactured.

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

(6) The resistance to creep was measured by a creep-traction test on test specimens 30.0 mm long, 8.0 mm wide and 2.0 mm thick. The tests were carried out at 1000° C. (normal operating temperature of a spinner), under loads of 45 MPa (corresponding to a normal stressing of the spinner), 63 MPa (corresponding to an extreme stressing of the spinner) and 100 MPa. Table 2 indicates the creep rate (in the secondary mode) in μm/h.

(7) 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 other hand, 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 Kp, expressed in g.Math.cm.sup.−2.Math.s.sup.−1/2, were calculated from monitoring the increase in 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. Table 2 indicates these constants in g.Math.cm.sup.−2.Math.s.sup.−1/2.

(8) 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, which underwent a heat treatment 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 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 comparatively the rate of corrosion of the alloys.

(9) TABLE-US-00006 TABLE 2 I1 C1 Creep 1000° C. 45 MPa 0.38 0.72 μm/h 63 MPa 1.03 2.48 100 MPa 32.51 54.47 Solidus T.sub.Solidus (° C.) 1292 1288 Oxidation Kinetic constant 8.7 × 10.sup.−12 5.5 × 10.sup.−12 Kp (g .Math. cm.sup.−2 .Math. s.sup.−1/2) Corrosion Polarization resistance 770 ± 15% 870 ± 15% Rp (Ohm/cm.sup.2)

(10) Comparing the data reported in table 2, there is observed, for the alloy I1 according to the invention, a significantly improved resistance to creep compared to the alloy C1 and substantially equivalent resistance to corrosion and to oxidation to that of the alloy C1. Moreover, the stability of the NbC carbides during the chromium migration process makes it possible to retain the mechanical properties required for the good resistance of the material and will be fully appreciated when analyzing the results of the application of this alloy to fiberizing spinners.

(11) Fiberizing spinners, respectively of diameter 400 mm and 600 mm, are subsequently formed with the alloy according to the prior art C1 and with the alloy I1 according to the invention.

(12) The spinners are prepared by the inductive melting technique under an inert argon atmosphere: a molten charge of the chosen composition (i.e. I1 or C1, see table 1 above) is prepared, which molten charge is subsequently formed by simple casting in a sand mold.

(13) The casting is followed by a heat treatment of 12 hours at 865° C. for precipitation of the secondary carbides. This treatment is followed by quenching with blown air.

(14) In this way, series of fiberizing spinners of diameter 400 mm and 600 mm are manufactured in the two alloys.

(15) The capacity of the spinners thus formed was evaluated in the application of glass wool fiberizing. More specifically, the spinners were placed in an industrial line for fiberizing a glass of the composition (in percentage by weight):

(16) TABLE-US-00007 SiO.sub.2 Al.sub.2O.sub.3 (B.sub.2O.sub.3) CaO MgO Na.sub.2O K.sub.2O Others 65.3 2.1 4.5 8.1 2.4 16.4 0.7 0.5

(17) This is a glass with a liquidus temperature of 900° C.

(18) The spinners are used until their stoppage is dictated following the ruin of the spinner, observed by visible deterioration on said spinner or by a quality of fiber produced becoming insufficient.

(19) The lifetimes of the spinners are reported in table 1. The results are indicated as tons of fiberized material before the spinner is ruined. The results reported in table 3 are a mean taken across at least three spinners from each category.

(20) TABLE-US-00008 TABLE 3 Composition spinner Diameter Alloy C1 Alloy I1 spinner (comparative) (inventive) 400 mm 170 tons 225 tons 600 mm 303 tons 381 tons

(21) It can be seen in table 3 that the spinners made with the alloys according to the invention always have the longest lifetimes for comparable conditions of use.