Ni—Al base material having optimized oxidation resistant at high temperatures and furnace transfer rolls made therefrom

Abstract

A high temperature oxidation resistant nickel-aluminide alloy composition and furnace rolls formed therefrom. The inventive nickel-aluminide alloy composition comprises 0.08-0.1 wt. % Zr, 2.5-3.0 wt. % Mo, 7.5-8.5 wt. % Al, 7.5-8.5 wt. % Cr, about 0.01 wt. % B and the balance being substantially nickel.

Claims

1. A nickel-aluminide ahoy comprising: 0.15 wt % or less Zr{circumflex over ( )} 2.5 to 3.0 wt. % Mo; 7.5 to 8.5 wt. % Cr; and 7.5 to 8.5 wt. % Al; and the balance being Ni.

2. The nickel-aluminide alloy of claim 1, wherein said Zr ranges from about 0.08 to 0.1 wt %.

3. The nickel-aluminide alloy of claim 1, wherein said ahoy comprises about 2.8 wt % Mo.

4. The nickel-aluminide alloy of claim 1, wherein said alloy further comprises about 0.015 wt. % B or less.

5. The nickel-aluminide alloy of claim 4, wherein said alloy further comprises about 0.01 wt. % B.

6. The nickel-aluminide alloy of claim 1, wherein said alloy further comprises in wt. %: C—0.05 max; Si—0.1 max; Fe—0.3 max; S—0.005 max; Mn—0.1 max; P—0.01 max; and Cu—0.3 max.

7. The nickel-aluminide alloy of claim 6, wherein said alloy contains no more than trace amounts of the other elements from group IVB, VB and VIB of the periodic table.

8. A furnace roll comprising: a Cast roll of a nickel-aluminide alloy comprising: 0.15 wt % or less Zr 2.5 to 3.0 wt. % Mo; 7.5 to 8.5 wt. % Cr; and 7.5 to 8.5 wt. % Al; and the balance being Ni.

9. The furnace roll of claim 8, wherein said Zr ranges from about 0.08-0.1 wt %.

10. The furnace roll of claim 8, wherein said alloy further comprises about 2.8 wt % Mo.

11. The furnace roll of claim 8, wherein said alloy further comprises from about 0.015 wt. % B or less.

12. The furnace roll of claim 11, wherein said alloy further comprises about 0.01 wt. % B.

13. The furnace roll of claim 8, wherein said alloy further comprises in wt. %: C—0.05 max; Si—0.1 max; Fe—0.3 max; S—0.005 max; Mn—0.1 max; P—0.01 max; and Cu—0.3 max.

14. The furnace roll of claim 13, wherein said alloy contains no more than trace amounts of the other elements from group IVB, VB and VIB of the periodic table.

15. The furnace roll of claim 8, further comprising a protective Al.sub.2O.sub.3 layer after oxidation.

16. The furnace roll of claim 8, wherein after oxidation, NiO nodules are not present.

17. A nickel-aluminide ahoy comprising: 0.15 wt % or less Zr 2.5 to 3.0 wt. % Mo; 7.5 to 8.5 wt % Cr; and 7.5 to 8.5 wt % Al; and the balance being Ni, wherein the alloy contains no more than trace amounts of the other elements from group IVB, VB and VIB of the periodic table.

18. A furnace roll for comprising: a cast roll of a nickel-aluminide alloy comprising: 0.15 wt. % or less Zr 2.5 to 3.0 wt. % Mo; 7.5 to 8.5 wt. % Cr; and 7.5 to 8.5 wt. % Al; and the balance being Ni, wherein the alloy contains no more than trace amounts of the other elements from group IVB, VB and VIB of the periodic table.

19. The furnace roll of claim 8, further comprising: a continuous protective layer of Al.sub.2O.sub.30n a surface of the nickel-aluminide alloy after oxidation of the furnace roll.

20. The furnace roll of claim 8, wherein NiO nodules do not form on a surface of the nickel-aluminide alloy during oxidation of the furnace roll.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1a-1i are cross sectional SEM images of samples having varied Zr content (M-0=0 wt. % Zr, M-2=0.3 wt. % Zr, and the prior art alloy IC-221M=1.8 wt. % Zr), oxidized at 900° C. for 1500, 3000 and 18000 hrs inside a hardening furnace.

DETAILED DESCRIPTION OF THE INVENTION

(2) The inventive Ni—Al compositions provide the superior strength and creep properties of the Ni aluminide family and solve the oxidation problems that the prior composition/rolls experienced in high temperature service. The new Ni aluminide alloy composition comprises 0.08-0.1 wt. % Zr, 2.5-3.0 wt. % Mo, 7.5-8.5 wt. % Al, 7.5-8.5 wt. % Cr, about 0.01 wt. % B and the balance being substantially nickel. This new composition will extend the life of the Ni-aluminide transfer rolls use in the plate mill austenitizing furnaces and will sustain the use of Ni-aluminide rolls for superior temperature strength, wear, oxidation resistance and better plate surface quality control.

(3) Thus, the new alloy composition will reduce the number of plates rejected due to surface marks. Further, in terms of energy costs, there are five major benefits of using Ni-aluminide rolls in comparison with HP-type of rolls: (1) energy savings due to the elimination of shutdowns and restarts for roll repair and maintenance, (2) energy savings due to straight through processing, (3) cost savings due to the elimination of roll maintenance labor, (4) fewer plates downgraded or rejected as the result of elimination of HP-type roll bulging and the oxide protrusions in the prior art Ni—Al rolls, (5) cost savings due to the reduction in roll inventory because of longer roll life.

(4) The present inventors conducted an extensive investigation to understand the oxidation behavior of the prior art Ni—Al alloy through the microstructural changes and oxidation behavior of the Ni-aluminide rolls. The mechanisms and kinetics of oxidation of the rolls subjected to the prolonged exposure to the hardening temperature was established through the analysis of rolls in service and oxidation laboratory simulations. The results of the study showed that the presence of Zr in the alloy was detrimental to the oxidation properties at operation temperatures due to preferential oxidation of Zr which in turn creates a non-uniform oxidation of the surface.

(5) The study also showed that nickel-oxide nodules are formed as protrusions on the roll surface in a manner that follows the micro-segregation patterns in the as-cast microstructure. It was seen that internal oxidation that extended from the roll surface into the matrix was highly concentrated in the vicinity of the zirconium inclusions or the eutectic zones. Further, NiO nodules were responsible for the formation of the hard protrusions on the rolls and hence to the rolls surface deterioration due to their growth, coalescence and/or spallation.

(6) Despite the oxidation problems exhibited by the prior art alloy, Ni-aluminide alloys, in general, provide excellent strength and creep properties at high temperature with a roll life 3 times longer than HP alloy roll. Therefore, the present inventors set about redesigning the Ni-aluminide roll chemistry to develop an alloy that prevents formation of detrimental oxide nodules.

(7) The first phase of the study investigated Ni aluminide alloys with variable Zr (0-1 wt. %) and Mo(0-3 wt. %). Samples were produced for oxidation simulations in laboratory and industrial environments. The oxidation behavior of the samples in the laboratory conditions were examined after 72, 900, 1500, 3000 and 5000 hrs at 900° C. to down-select the most promising alloys. Afterwards, long-term oxidation experiments were performed with selected alloys inside an actual furnace environment for up to 18,000 hours and a correlation with the laboratory results was established.

(8) FIGS. 1a-1i are cross sectional SEM images of samples having varied Zr content (M-0=0 wt. % Zr, M-2=0.3 wt. % Zr, and the prior art alloy IC-221M=1.8 wt. % Zr), oxidized at 900° C. for 1500, 3000 and 18000 hrs inside a hardening furnace. FIGS. 1a-1c are the results of the three samples, IC-221M, M-2, and M-0, respectively, oxidized at 900° C. for 1500 hours. As can be seen from FIG. 1a, even at this sort of service time, the prior art alloy (with 1.8 wt. % Zr) has developed significant NiO nodules on the surface thereof. Further, it can be seen from FIG. 1b that the alloy with 0.3 wt % Zr starts to form small NiO nodules as well. Significantly, the alloy with no Zr does not form any NiO nodules, but instead forms a protective Al.sub.2O.sub.3 surface, see FIG. 1c.

(9) As the oxidation time is increased to 3000 and finally 18,000 hours it can be seen that NiO nodules of the sample having 1.8 wt. % Zr and the sample having 0.3 wt. % Zr grow significantly. This can be seen in FIGS. 1d, 1g (1.8 wt. % Zr) and 1e, 1h (0.3 wt. % Zr). In contradistinction thereto, the alloy with no Zr does not form any NiO nodules even at oxidation times of 3000 and 18,000 hours.

(10) The results of the long term oxidation experiments showed that NiO dominates the oxidation products in samples with more than about 0.15 wt. % Zr. Internal oxidation was highly concentrated in the vicinity of the Zr inclusions and the eutectic zones. A protective continuous Al.sub.2O.sub.3 layer does not form, rather, the surface oxide consist of a discontinuous mixture of NiAl.sub.2O.sub.4, NiO and Al.sub.2O.sub.3. The protective Al.sub.2O.sub.3 layer was found to be formed on the surface of the alloys with about 0.15% Zr or less. Mo was added in order to improve the high temperature strength and did not affect the oxidation behavior of the alloys.

(11) The conclusions of the investigation show that the most suitable composition in order to avoid oxidation deterioration of transfer rolls are Ni aluminides that contain: zirconium ranging from 0 to 0.15 wt. %, preferably about 0.08-0.1 wt % Zr; molybdenum ranging from 2.5 to 3.0 wt. %, preferably about 2.8 wt % Mo; aluminum ranging from about 7.5 to 8.5 wt. %; chromium ranging from about 7.5 to 8.5 wt. %; boron maximum of 0.015 wt. %, but preferably about 0.01 wt. %, C, Si, Fe, S, Mn, P and Cu should be kept as low as possible, with aimed maximum concentrations indicated in the Table I; and other elements from the group IVB, VB and VIB of the periodic table should be kept as low as possible.

(12) TABLE-US-00001 TABLE 1 Weight percent (wt. %) Atomic percent (at. %) Element Aim composition Range Aim composition Range Ni balance balance balance balance Al 8 7.5-8.5 15.9 14.9-16.8 Cr 7.7 7.5-8.5 7.9 7.8-8.7 Zr 0.1 0.05-0.15 0.05 0.03-0.09 Mo 2.8 2.5-3.0 1.6 1.4-1.7 B 0.01 0.015 max  0.050 0.05-0.07 C 0.05 max  Si 0.1 max Fe 0.3 max S 0.005 max  Mn 0.1 max P 0.01 max  Cu 0.3 max

(13) Ni-aluminide rolls with inventive alloy composition were centrifugal cast for production trial. Additional rolls with different chemical composition, including the prior art IC-221M chemistry, were also produced for the benchmarking of the new alloy. The tensile properties of the rolls were determined at varying temperatures up to 1000° C. in round 35 mm gauge section specimens. Table 2 lists the tensile properties of the inventive and prior art alloys.

(14) TABLE-US-00002 TABLE 2 Tensile Strength (ksi) Production Production Production Temp. Temp. Experiment Experiment Experiment Experiment Roll 131 Roll 156 Roll 157 ° C. ° F. roll 2.1% Zr roll 1.2% Zr roll 0% Zr roll 0.1% Zr 0.1% Zr 0.1% Zr 0.1% Zr 25 70 100 100 132 122.8 105.3 107 98 700 1292 110 104 77.5 84.15 86.3 72.05 85.35 925 1697 80 77 29.3 42.55 31.1 30.25 26.25 982 1800 47 40 16.1 32.7 30.25 14 14 1038 1900 15.125

(15) It is to be understood that the disclosure set forth herein is presented in the form of detailed embodiments described for the purpose of making a full and complete disclosure of the present invention, and that such details are not to be interpreted as limiting the true scope of this invention as set forth and defined in the appended claims.