Aluminum containing iron-base alloys useful as electrical resistance heating elements

• US 5,595,706 A
• Filed: 12/29/1994
• Issued: 01/21/1997
• Est. Priority Date: 12/29/1994
• Status: Expired due to Fees

• Current Assignee: Philip Morris USA Incorporated (Altria Group, Inc.)
• Original Assignee: Philip Morris USA Incorporated (Altria Group, Inc.)
• Inventors: Hajaligol, Mohammad R., Sikka, Vinod K., Deevi, Seetharama C., Lilly, A. Clifton Jr., Fleischhauer, Grier S.
• Primary Examiner(s): Yee, Deborah
• Application Number:
  US08/365,952
• Time in Patent Office: 754 Days
• Field of Search: 420/81
• US Class Current: 420/81
• CPC Class Codes: B22F 2201/05 Water or water vapour
• CPC Class Codes: B22F 2998/10 Processes characterised by the sequence of their steps
• CPC Class Codes: B22F 2999/00 Aspects linked to processes or compositions used in powder metallurgy
• CPC Class Codes: B22F 3/10 Sintering only
• CPC Class Codes: B22F 3/1208 Containers or coating used therefor
• CPC Class Codes: B22F 3/15 Hot isostatic pressing
• CPC Class Codes: B22F 3/18 by using pressure rollers
• CPC Class Codes: B22F 3/20 by extruding
• CPC Class Codes: B22F 3/23 involving a self-propagating high-temperature synthesis or reaction sintering step making cermets by reaction sintering C22C1/051
• CPC Class Codes: B22F 9/082 atomising using a fluid using centrifugal force B22F9/10
• CPC Class Codes: C22C 1/047 comprising intermetallic compounds C22C1/0441 takes precedence
• CPC Class Codes: C22C 33/0278 with at least one alloying element having a minimum content above 5%
• CPC Class Codes: C22C 38/06 containing aluminium

Abstract

The invention relates generally to aluminum containing iron-base alloys useful as electrical resistance heating elements. The aluminum containing iron-base alloys have a disordered body centered cubic structure and improved room temperature ductility, electrical resistivity, cyclic fatigue resistance, high temperature oxidation resistance, low and high temperature strength, and/or resistance to high temperature sagging. The alloy has an entirely ferritic microstructure which is free of austenite and includes, in weight %, 4 to 9.5% Al, 0.2-2.0% Ti, 0.5-2% Mo, 0.1 to 0.8% Zr, 0.01-0.5% C, balance Fe.

Claims

1. An iron-based alloy useful as an electrical resistance heating element and having a disordered body centered cubic structure, the alloy having improved room temperature ductility, resistance to cyclic oxidation, thermal fatigue resistance, electrical resistivity and high temperature sag resistance, and comprising, in weight %, 4 to 9.5% Al, 0.5-2.0% Ti, 0.5-2% Mo, 0.1 to 0.8% Zr, 0.01-0.5% C, balance Fe.

2. The iron-based alloy of claim 1, wherein the alloy is Ni-free.

3. The iron-based alloy of claim 1, wherein the alloy has a microstructure which is austenite-free.

4. The iron-based alloy of claim 1, wherein the alloy has an entirely ferritic microstructure.

5. The iron-based alloy of claim 1, wherein the alloy is free of ceramic particles.

6. The iron-based alloy of claim 1, wherein the alloy includes ≦

2% Si, ≦

30% Ni, ≦

0.5% Y, ≦

0.1% B, ≦

1% Nb and ≦

1% Ta.

7. The iron-based alloy of claim 1, wherein the alloy consists essentially of 8.0-9.0% Al, 0.75-1.5% Ti, 0.75-1.5% Mo, 0.15-0.75% Zr, 0.05-0.35% C, balance Fe.

8. The iron-based alloy of claim 1, wherein the alloy consists essentially of 8.0-9.0% Al, 0.75-1.25% Ti, 0.75-1.25% Mo, 0.2 to 0.6% Zr, 0.03-0.09% C, 0.01-0.1% Y, balance Fe.

9. The iron-based alloy of claim 1, wherein the alloy consists essentially of 8.0-9.0% Al, 0.75-1.25% Ti, 0.75-1.25% Mo, 0.1-0.3% Zr, 0.01-0.1% C, 0.25-0.75% Nb, 0.25-0.75% Ta and 0.01-0.1% Y, balance Fe.

10. The iron-based alloy of claim 1, wherein the alloy consists essentially of 8.0-9.0% Al, 0.75-1.25% Ti, 0.75-1.25% Mo, 0.5-0.75% Zr, 0.05-0.15% C and 0.01-0.2% Si, balance Fe.

11. The iron-based alloy of claim 1, wherein the alloy consists essentially of 8.0-9.0% Al, 0.05-0.15% Si, 0.75-1.25% Ti, 0.75-1.25% Mo, 0.1-0.3% Zr and 0.2-0.4% C, balance Fe.

12. The iron-based alloy of claim 1, wherein the alloy comprises an electrical resistance heating element having a room temperature resistivity of 80-400 μ

Ω

·

cm.

13. The iron-based alloy of claim 1, wherein the alloy exhibits room temperature ductility of at least 3%.

14. The iron-based alloy of claim 1, wherein the alloy heats to 900°

C. in less than 1 second when a voltage up to 10 volts and up to 6 amps is passed through the alloy.

15. The iron-based alloy of claim 1, wherein the alloy exhibits a weight gain of less than 4% when heated in air to 1000°

C. for three hours.

16. The iron-based alloy of claim 1, wherein the alloy has a resistance of 0.05 to 7 ohms throughout a heating cycle between ambient and 900°

C.

17. The iron-based alloy of claim 1, wherein the alloy has a resistivity of 80 to 200 Ω

·

cm throughout a heating cycle between ambient and 900°

C.

18. The iron-based alloy of claim 1, wherein the alloy exhibits a room temperature reduction in area of at least 14%.

19. The iron-based alloy of claim 1, wherein the alloy exhibits a room temperature elongation of at least 15%.

20. The iron-based alloy of claim 1, wherein the alloy exhibits a room temperature yield strength of at least 50 ksi.

21. The iron-based alloy of claim 1, wherein the alloy exhibits a room temperature tensile strength of at least 80 ksi.

22. The iron-based alloy of claim 1, wherein the alloy exhibits a high temperature reduction in area at 800°

C. of at least 30%.

23. The iron-based alloy of claim 1, wherein the alloy exhibits a high temperature elongation at 800°

C. of at least 30%.

24. The iron-based alloy of claim 1, wherein the alloy exhibits a high temperature yield strength at 800°

C. of at least 7 ksi.

25. The iron-based alloy of claim 1, wherein the alloy exhibits a high temperature tensile strength at 800°

C. of at least 10 ksi.

26. The iron-based alloy of claim 1, wherein the alloy exhibits thermal fatigue resistance of over 10,000 cycles without breaking when heated from room temperature to 1000°

C. for 0.5 to 5 seconds in each of the cycles.

27. The iron-based alloy of claim 1, wherein the alloy is Cr-free.

28. The iron-based alloy of claim 1, wherein the alloy is Mn-free and/or Si-free.