Low alloy steel with a high yield strength and high sulphide stress cracking resistance
A steel contains, by weight: C: 0.2% to 0.5%, Si: 0.1% to 0.5%, Mn: 0.1% to 1%, P: 0.03% or less, S: 0.005% or less, Cr: 0.3% to 1.5%, Mo: 0.3% to 1%, Al: 0.01% to 0.1%, V: 0.1% to 0.5%, Nb: 0.01% to 0.05%, Ti: 0 to 0.01%, W: 0.3% to 1%, N: 0.01% or less, the remainder of the chemical composition of the steel being constituted by Fe and impurities or residuals resulting from or necessary to steel production and casting processes. The steel can be used to produce seamless tubes with a yield strength after heat treatment of 861 MPa or more.
1. A low alloy steel comprising the following components, by weight:
C: 0.2% to 0.5%
Si: more than 0.1% to 0.5%
Mn: more than 0.1% to 1%
P: 0.03% or less
S: 0.005% or less
Cr: 0.3% to 1.5%
Mo: 0.3% to 1%
Al: 0.01% to 0.1%
V: 0.1% to 0.5%
Nb: 0.01% to 0.05%
W: 0.43% to 0.46%
N: 0.01% or less,
the remainder of the chemical composition of said steel comprising Fe and impurities or residuals resulting from or necessary to steel production and casting processes, wherein W is present in the steel in a Mo tolerance increasing effective amount.
2. A steel according to claim 1 , wherein its C content is in the range of from 0.3% to 0.4%.
3. A steel according to claim 1 , wherein its Mn content is in the range of from 0.3% to 0.6%.
4. A steel according to claim 1 , wherein its Cr content is in the range of from 0.4% to 0.6%.
5. A steel according to claim 1 , wherein its Mo content is in the range of from 0.4% to 0.6%.
6. A steel according to claim 5 , wherein its Cr content is in the range of from 0.4% to 0.6%.
7. A steel according to claim 1 , wherein its S content is 0.003% or less.
8. A steel according to claim 1 , wherein its Al content is in the range of from 0.01% to 0.05%.
9. A steel according to claim 1 , wherein its V content is in the range of from 0.1% to 0.2%.
10. A steel according to claim 1 , wherein its Nb content is in the range of from 0.01% to 0.03%.
11. A steel product according to claim 1 , wherein said steel is heat treated so that its yield strength is 861 MPa (125 ksi) or more.
12. A steel product produced from the steel according to claim 1 , wherein said steel product has a yield strength of 861 MPa or more and wherein said steel product has SSC resistance such that rupture does not occur after 720 hours of treatment in accordance with method A of specification NACE TM0177.
13. A steel according to claim 1 , wherein an amount of W is present in the alloy which is effective in limiting microcarbide size increase in the alloy.
14. A steel product produced from the steel according to claim 13 , wherein said steel product has a yield strength of 861 MPa or more and wherein said steel product has SSC resistance such that rupture does not occur after 720 hours of treatment in accordance with method A of specification NACE TM0177.
15. A steel according to claim 1 , wherein if Ti is present in the steel as an impurity, Ti is present in an amount less than 0.005%.
16. A low alloy steel consisting essentially of the following components, by weight:
C: 0.2% to 0.5%
Si: more than 0.1% to 0.5%
Mn: more than 0.1% to 1%
P: 0.03% or less
S: 0.005% or less
Cr: 0.3% to 1.5%
Mo: 0.3% to 1%
Al: 0.01% to 0.1%
V: 0.1% to 0.5%
Nb: 0.01% to 0.05%
W: 0.43% to 0.46%
N: 0.01% or less,
the remainder of the chemical composition of said steel consisting essentially of Fe and impurities or residuals resulting from or necessary to steel production and casting processes, wherein W is present in the steel in a Mo tolerance increasing effective amount.
17. A steel according to claim 16 , wherein its Mo content is in the range of from 0.4% to 0.6%.
18. A steel according to claim 17 , wherein its Cr content is in the range of from 0.4% to 0.6%.
19. A steel product produced from the steel according to claim 16 , wherein said steel product has a yield strength of 861 MPa or more and wherein said steel product has SSC resistance such that rupture does not occur after 720 hours of treatment in accordance with method A of specification NACE TM0177.
20. A steel according to claim 16 , wherein an amount of W is present in the alloy which is effective in limiting microcarbide size increase in the alloy.
21. A steel product produced from the steel according to claim 20 , wherein said steel product has a yield strength of 861 MPa or more and wherein said steel product has SSC resistance such that rupture does not occur after 720 hours of treatment in accordance with method A of specification NACE TM0177.