Martensitic-ferritic stainless steel, manufactured product and process using the s

Abstract

The present invention relates to a martensitic-ferritic stainless steel with high corrosion resistance that comprises the following chemical composition: C: from 5 0.005 to 0.030%; Si: from 0.10 to 0.40%; Mn from 0.20 to 0.80%; P: 0.020% max; S: 0.005% max; Cr: from 13 to 15%; Ni: from 4.0 to 6.0%; Mo: from 2.0 to 4.5%; V: from 0.01 to 0.10%; Nb: from 0.01 to 0.50%; N: from 0.001 to 0.070%; Al: from 0.001 to 0.060%; Ti: from 0.001 to 0.050%; Cu: from 0.01 to 1.50%; O: 0.005% max (all in weight percent), wherein the balance is performed by Fe and unavoidable impurities 10 from the industrial possessing in acceptable levels. Additionally, the martensitic-ferritic stainless steel of the present invention has the localized corrosion parameter (LCP), between 3.2 and 6.2, as defined by equation below; LCP=0.500−% Cr+1.287·% Mo+1.308·% N−5.984 The present invention also relates to a manufactured product comprising the martensitic-ferritic stainless steel of the invention; to a process for 15 production of forged or rolled parts or bars; and to a process for production of seamless tube from this martensitic-ferritic stainless steel of the present invention, wherein the processes of the invention have a heating temperature in determined step following the equation below: T Proc −16.9*% Cr−49.9*% Mo>535

1 - 17 . (canceled) 
     
     
         18 . MARTENSITIC-FERRITIC STAINLESS STEEL, wherein it comprises a martensitic-ferritic microstructure, and a chemical composition in the range of C: from 0.005 to 0.030%; Si: from 0.10 to 0.40%; Mn from 0.20 to 0.80%; P: 0.020% max; S: 0.005% max; Cr: from 13 to 15%; Ni: from 4.0 to 6.0%; Mo: from 2.0 to 4.5%; V: from 0.01 to 0.10%; Nb: from 0.01 to 0.50%; N: from 0.001 to 0.070%; Al: from 0.001 to 0.060%; Ti: from 0.001 to 0.050%; Cu: from 0.01 to 1.50%; O: 0.005% max (in weight percent), wherein the balance is performed by Fe and unavoidable impurities from the industrial possessing in acceptable levels and having the localized corrosion parameter (LCP) between 3.2 and 6.2, defined by the equation bellow:
   LCP=0500·% Cr+1287·% Mo+1.308·% M−5.984.
   
     
     
         19 . MARTENSITIC-FERRITIC STAINLESS STEEL, according to the  claim 18 , wherein it comprises a C content from 0.005 to 0.015%. 
     
     
         20 . MARTENSITIC-FERRITIC STAINLESS STEEL, according to  claim 18 , wherein it comprises a Cr content from 13.5 to 14.5%. 
     
     
         21 . MARTENSITIC-FERRITIC STAINLESS STEEL, according to  claim 18 , wherein it comprises a Ni content from 4.5 to 5.5%. 
     
     
         22 . MARTENSITIC-FERRITIC STAINLESS STEEL, according to  claim 18 , wherein it comprises a Mo content from 3.0 to 4.0%. 
     
     
         23 . MARTENSITIC-FERRITIC STAINLESS STEEL, according to  claim 18 , wherein it comprises a Nb content from 0.03 to 0.20% and N content from 0.006 to 0.020%. 
     
     
         24 . MARTENSITIC-FERRITIC STAINLESS STEEL, according to  claim 18 , wherein it comprises a Nb content from 0.20 to 0.50% and N content from 0.020 to 0.050%. 
     
     
         25 . MARTENSITIC-FERRITIC STAINLESS STEEL, according to  claim 18 , wherein it comprises a Cu content from 0.8 to 1.2%. 
     
     
         26 . MARTENSITIC-FERRITIC STAINLESS STEEL, according to  claim 18 , wherein it comprises a Cr content from 13.5 to 14.5%; Mo content from 3.0 to 4.0%; Nb content from 0.03 to 0.20% and N content from 0.006 to 0.020%. 
     
     
         27 . MARTENSITIC-FERRITIC STAINLESS STEEL, according to  claim 18 , wherein it comprises a Cr content from 13.5 to 14.5%; Mo content from 3.0 to 4.0%; Nb content from 0.20 to 0.50% and N content from 0.020 to 0.050%. 
     
     
         28 . MARTENSITIC-FERRITIC STAINLESS STEEL, according to  claim 18 , wherein it comprises a volumetric fraction of niobium carbonitride between 0.01 and 0.50%. 
     
     
         29 . MARTENSITIC-FERRITIC STAINLESS STEEL, according to  claim 18 , wherein it comprises a LCP between 4.2 and 5.2. 
     
     
         30 . MARTENSITIC-FERRITIC STAINLESS STEEL, according to  claim 18 , wherein it comprises a Pitting Resistance Equivalent Number (PREN) over 24, wherein PREN is defined by PREN−% Cr+3.3% Mo+16% N. 
     
     
         31 . MANUFACTURED PRODUCT, for oil and gas application, wherein it comprises the martensitic-ferritic stainless steel, as defined in  claim 18 , having a final microstructure composed by δ ferrite, martensite, retained austenite and worthless amounts of deleterious phases such as Chi or Sigma; wherein the amount of δ ferrite ranges from 20 to 50%, the amount of martensite ranges from 50 to 80% and have no more than 15% of retained austenite. 
     
     
         32 . MANUFACTURED PRODUCT, according to  claim 31 , wherein of being seamless tube, fittings, accessories, forged or rolled parts or bars. 
     
     
         33 . MANUFACTURED PRODUCT, according to  claim 31 , wherein of being seamless tube for casing. 
     
     
         34 . MANUFACTURED PRODUCT, according to  claim 31 , wherein of being seamless tube for tubings. 
     
     
         35 . PROCESS FOR PRODUCTION OF FORGED OR ROLLED PARTS OR BARS OF MARTENSITIC-FERRITIC STAINLESS STEEL, wherein it comprises the following steps:
 a) production of martensitic-ferritic stainless steel, as defined in  claim 18 , by melting of the chemical elements;   b) casting of material melted in step a);   c) homogenization of the ingot of step b) by heat treatment;   d) hot conformation of the product of step c) by rolling or forging, wherein the processing temperature at the end of this step shall follow the following equation:
   T Proc −16.9*% Cr−49.9*% Mo>535;
 
   e) optionally, heat treat the product of step d).   
     
     
         36 . PROCESS, according to  claim 34 , wherein the melting the chemical elements is performed in air induction furnace, vacuum induction furnace or electric furnace. 
     
     
         37 . PROCESS, according to  claim 35 , wherein the casting is performed by conventional or continuous casting. 
     
     
         38 . PROCESS FOR PRODUCTION OF SEAMLESS TUBE OF MARTENSITIC-FERRITIC STAINLESS STEEL, wherein it comprises the following steps:
 a) rolling of the tube that comprises the martensitic-ferritic stainless steel, as defined in  claim 18 , followed by a heat treatment, wherein the heating temperature for the finishing steps shall follow the equation bellow:
   T Proc −16.9*% Cr−49.9*% Mo>535;
 
   b) heat treatment, divided in the following sub steps:   b1) optionally quenching, and, when present, shall follow the heating temperature equation of step a);   b2) single or double tempering, comprising temperatures between 550 and 680° C., directly after rolling or after a thermal cycle of quenching; and   c) air or water cooling after quenching or tempering.   
     
     
         39 . PROCESS, according to  claim 38 , wherein the rolling is performed in a mandrel continuous mill or in a Stiefel-type not reversible duo mill (plug mill). 
     
     
         40 . PROCESS, according to  claim 38 , wherein the tube rolling can be done using direct or cold charging for the finishing rolling.