Sulphide stress cracking resistant steel, tubular product made from said steel, process for manufacturing a tubular product and use thereof

Abstract

The present invention relates to low alloy steels with a high yield strength that present an improved sulphide stress cracking behaviour. The present invention also relates to tubular products, such as tubes or pipes, made from said steel, as well as a process for manufacturing such tubular products. In addition, the present invention concerns use of such tubular products for well drilling and/or for production, extraction and/or transportation of oil and gas.

1 . A steel having a chemical composition consisting of, in weight %, relative to the total weight of said chemical composition:
 0.32≤C<0.46;   0.10≤Si≤0.45;   0.10≤Mn≤0.50;   0.30≤Cr≤1.25;   1.10≤Mo≤2.10;   0.10≤V≤0.30;   0.01≤Nb≤0.10;   Fe, and   one or more residual elements comprising Cu; and   wherein the chemical composition satisfies formula between C, Si, Mn, Cr, Mo, V, Nb and Cu, the contents of which are expressed in weight %:
   β+1.5*α−165≥0
 
   in which,   α=−90+274*C−25*Si−64*Mn+22*Cr+17*Mo+268*V−225*Nb+184*Cu, and   β=54+162*C−86*Si−49*Mn−31*Cr+22*Mo+20*V−172*Nb−364*Cu.   
     
     
         2 . The steel according to  claim 1 , having a yield strength greater than or equal to 862 MPa (125 ksi) in standards ASTM A370-17 and ASTM E8/E8M-13a. 
     
     
         3 . The steel according to either  claim 1 , wherein the chemical composition contains in weight %, relative to the total weight of said chemical composition: 0.34≤C≤0.44. 
     
     
         4 . The steel according to  claim 1 , wherein the chemical composition contains in weight %, relative to the total weight of said chemical composition: 0.20≤Mn≤0.40. 
     
     
         5 . The steel according to  claim 1 , wherein the chemical composition contains in weight %, relative to the total weight of said chemical composition: 0.30≤Cr≤1.20. 
     
     
         6 . The steel according to  claim 1 , wherein the chemical composition contains in weight %, relative to the total weight of said chemical composition: 1.10<Mo≤1.60. 
     
     
         7 . The steel according to  claim 1 , wherein the chemical composition contains in weight %, relative to the total weight of said chemical composition: 0.11≤V≤0.25. 
     
     
         8 . The steel according to  claim 1 , wherein the chemical composition contains in weight %, relative to the total weight of said chemical composition: 0.01≤Nb≤0.05. 
     
     
         9 . The steel according to  claim 1 , wherein the sum of residual element contents is lower than 0.4% by weight of the total weight of the chemical composition. 
     
     
         10 . The steel according to  claim 1 , having a microstructure made of at least 90% of tempered martensite. 
     
     
         11 . A tubular product, made from the steel according to  claim 1 . 
     
     
         12 . A process for manufacturing the tubular product of  claim 11 , the process comprising:
 (a) providing a steel having the chemical composition,   (b) heating up the steel provided at (a) to a temperature ranging from 1100 to 1300° C.,   (c) hot forming the steel heated at (b) through hot forming processes, at a temperature ranging from 900 to 1300° C. to obtain a tubular product,   (d) cooling down the tubular product obtained at (c) to room temperature, before carrying out the following sequences (e) and (f) at least once:   (e) heating up the cooled tubular product to an austenitization temperature (AT) ranging from Ac3 to 1000° C. before keeping said tubular product at the temperature AT during a time comprised between 2 and 60 minutes to obtain an austenitized tubular product, and then cooling said austenitized tubular product down to ambient temperature to obtain a quenched tubular product,   and either repeating sequence (e) one more time or carrying out the following sequence (f):   (f) heating up the quenched tubular product to a tempering temperature (TT) ranging from 500° C. to Ac1 before keeping said tubular product at the temperature TT during a tempering time (Tt) comprised between 5 and 120 minutes, and then cooling said tubular product down to ambient temperature to obtain a quenched and tempered tubular product;   it being understood that:   Ac1=723−10.7*Mn−16.9*Ni+29.1*Si+16.9*Cr+6.38*W+290*As; and   Ac3=910−203*√C−15.2*Ni+44.7*Si+104*V+13.1*W+31.5*Mo−30*Mn;   Ac1 and Ac3 being expressed in ° C.   
     
     
         13 . The process according to  claim 12 , wherein the sequence (e) is performed at least two times. 
     
     
         14 . The process according to  claim 12 , wherein the sequences (e) and (f) are performed at least two times. 
     
     
         15 . The process according to  claim 12 , wherein the tempering temperature (TT) ranges from 600° C. to Ac1. 
     
     
         16 . The process according to  claim 12 , wherein the tempering time (Tt) is comprised between 10 and 60 minutes. 
     
     
         17 . A method, comprising:
 well drilling, producing, extracting and/or transporting oil and gas with the tubular product according to  claim 11 .