LOW STRAIN HIGH DUCTILITY ALLOY

Abstract

The present invention relates to alloys used to prepare a low strain steel pipes for use in chemical engineering applications. In particular, the invention relates to low carbon high strength steel alloys and pipes made from such alloys which have low strain but high ductility at elevated temperatures. Such pipes are typically used in chemical plants for transporting reactants and products, as the inlet manifolds in plants for producing hydrogen and methanol. They may be used in plant such as steam reformer furnaces which include inlet manifolds that need to possess good creep resistance (low strain) as well as having good thermo-mechanical fatigue resistance (high ductility).

Claims

1. A steel consisting of: from 20.0 to 40.0 atomic % nickel, from 20.0 to 40.0 atomic % chromium, from 1.0 to 3.0 atomic % silicon, from 0.2 to 1.0 atomic % carbon, from 0.01 to 1.0 atomic % nitrogen, from 0.30 to 0.90 atomic % niobium, from 0.5 to 3.0 atomic % manganese, and from 0.01 to 0.90 atomic % of one or more second carbide forming elements selected from: titanium, hafnium, zirconium, vanadium, tungsten, or molybdenum, wherein: (a) a total amount of niobium and the one or more second carbide forming elements is from 0.50 to 0.91 atomic %; (b) a total amount of carbon plus nitrogen is in the range of 0.2 to 1.2 atomic %; (c) an amount (nitrogen/carbon) is in the range 0.60 to 0.90, and (d) an amount [nitrogen/(the one or more second carbide forming elements plus niobium)] is in the range 0.2 to 1.1; with the balance of the composition being iron and incidental impurities.

2. A steel consisting of: from 20.0 to 40.0 atomic % nickel, from 20.0 to 40.0 atomic % chromium, from 1.0 to 3.0 atomic % silicon, from 0.2 to 1.0 atomic % carbon, from 0.01 to 1.0 atomic % nitrogen, from 0.50 to 0.91 atomic % niobium, and from 0.5 to 3.0 atomic % manganese, and wherein: (a) a total amount of carbon plus nitrogen is in the range of 0.2 to 1.2 atomic %; (b) an amount (nitrogen/carbon) is in the range 0.60 to 0.90, and (c) an amount (nitrogen/niobium) is in the range 0.2 to 1.1; with the balance of the composition being iron and incidental impurities.

3. A steel as claimed in claim 1, wherein titanium is present in the range of from 0.01 to 0.20 atomic %.

4. A steel as claimed in claim 1, wherein carbon is present in the range of from 0.4 to 0.7 atomic %.

5. A steel as claimed in claim 1, wherein nitrogen is present in an amount in the range of from 0.30 to 0.60 atomic %.

6. A steel as claimed in claim 1, wherein the amount (nitrogen/carbon) is in the range of from 0.70 to 0.80 atomic %.

7. A steel as claimed in claim 1, wherein nickel is present in the range of from 25.0 to 35.0 atomic %.

8. A steel as claimed in claim 7, wherein nickel is present in an amount from 30.0 to 33.0 atomic %.

9. A steel as claimed in claim 1, wherein chromium is present in the range of from 20.0 to 30.0 atomic %.

10. A steel as claimed in claim 8, wherein chromium is present in an amount from 22.5 to 27.5 atomic %.

11. A steel pipe made from an alloy according to claim 1.

12. A steel pipe as claimed in claim 11, wherein the time to rupture is at least 215 hrs when tested at 1050° C. with 30 MPa Stress.

13. A steel pipe as claimed in claim 11, wherein the time to rupture is at least 210 hrs when tested at 1000° C. with 40 MPa Stress.

14. A steel as claimed in claim 2, wherein carbon is present in the range of from 0.4 to 0.7 atomic %.

15. A steel as claimed in claim 2, wherein nitrogen is present in an amount in the range of from 0.30 to 0.60 atomic %.

16. A steel as claimed in claim 2, wherein the amount (nitrogen/carbon) is in the range of from 0.70 to 0.80 atomic %.

17. A steel as claimed in claim 2, wherein nickel is present in the range of from 25.0 to 35.0 atomic %.

18. A steel as claimed in claim 17, wherein nickel is present in an amount from 30.0 to 33.0 atomic %.

19. A steel as claimed in claim 2, wherein chromium is present in the range of from 20.0 to 30.0 atomic %.

20. A steel as claimed in claim 18, wherein chromium is present in an amount from 22.5 to 27.5 atomic %.

Description

[0087] FIGS. 1 to 3 show the properties of the steels H39WM, CR32W (a conventional steel alloy) and LC+ (a steel alloy according to the invention).

[0088] FIG. 1 shows the improvements in MSW thickness,

[0089] FIG. 2 shows the Larson-Miller curves of H39WM and LC+, and

[0090] FIG. 3 shows a constant stress creep test at 950 C of CR32W and LC+. The superior properties of the steels of the present invention are also evident in each case relative to the conventional steel from the following data for LC+.

[0091]

TABLE-US-00002 Room temperature tensile properties (Minimum values) N/mm.sup.2) UTS 450 0.2% PS 250 Elongation 15%

TABLE-US-00003 Coefficient of linear expansion mm/mm ° C. (1/K) 20-100° C. 14.5 × 10.sup.−6 20-750° C. 17.5 × 10.sup.−6  20-1000° C. 18.5 × 10.sup.−6

TABLE-US-00004 Density 7.94 Gm/cc (0.288 lb/in.sup.3)

TABLE-US-00005 Hot tensile properties N/mm.sup.2 (Typical value) 800° C. 900° C. Uts 238 145 0.2% PS 150 90 Elongation 40% 47%

TABLE-US-00006 Thermal conductivity (w/mK)  100° C. 13.4  800° C. 25.9 1000° C. 30.5

TABLE-US-00007 Temp Stress Creep test (° C.) (Mpa) life (hrs) 800 83.44 544 850 62.77 889 870 58.8 1,243 (sample including a weld) 950 35.9 1,414 950 41.52 416 983 27.58 1,427 1000 30.9 442 1050 20.82 414 1075 18.72 215 1100 16 117

[0092] Further steel alloys having the following compositions were produced.