Method of manufacturing hot rolled steel

Abstract

A hot rolled steel having a composition including the following elements, expressed in percentage by weight 15%≤Nickel≤25%, 6%≤Cobalt≤12%, 2%≤Molybdenum≤6%, 0.1%≤Titanium≤1%, 0.0001%≤Carbon≤0.03%, 0.002%≤Phosphorus≤0.02%, 0%≤Sulfur≤0.005%, 0%≤Nitrogen≤0.01%, and can contain one or more of the following optional elements 0%≤Aluminum≤0.1%, 0%≤Niobium≤0.1%, 0%≤Vanadium≤0.3%, 0%≤Copper≤0.5%, 0%≤Chromium≤0.5% the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of the steel sheet including in area fraction, 20% to 40% Tempered Martensite, at least 60% of Reverted Austenite and inter-metallic compounds of Molybdenum, Titanium and Nickel.

What is claimed is: 
     
         1 . A method of production of a hot rolled steel comprising the following successive steps:
 providing a semi-finished product having a composition comprising the following elements, expressed in percentage by weight:
 15%≤Nickel≤25% 
 6%≤Cobalt≤12% 
 2%≤Molybdenum≤6% 
 0.1%≤Titanium≤1% 
 0.0001%≤Carbon≤0.03% 
 0.002%≤Phosphorus≤0.02% 
 0%≤Sulfur≤0.005% 
 0%≤Nitrogen≤0.01% 
 and optionally one or more of the following elements: 
 0%≤Aluminum≤0.1% 
 0%≤Niobium≤0.1% 
 0%≤Vanadium≤0.3% 
 0%≤Copper≤0.5% 
 0%≤Chromium≤0.5% 
 0%≤Boron≤0.001% 
 0%≤Magnesium≤0.0010% 
   a remainder of the composition being composed of iron and unavoidable impurities caused by processing;   reheating the semi-finished product to a temperature between 1150° C. and 1300° C.;   rolling the semi-finished product in the austenitic range wherein the hot rolling finishing temperature is between 800° C. and 975° C. to obtain a hot rolled steel strip;   then cooling the hot rolled steel strip to a temperature range between 10° C. and Ms;   thereafter reheating the hot rolled steel strip to an annealing temperature between Ae3 and Ae3+350° C., holding the hot rolled steel strip at such temperature for more than 30 minutes and cooling the hot rolled steel strip at a rate between 1° C./s and 100° C./s to temperature range between 10° C. and Ms;   thereafter reheating the hot rolled steel strip to a tempering temperature range between 575° C. and 700° C. with a heating rate between 0.1° C./s and 100° C./s and holding the hot rolled steel strip in the tempering temperature range for a duration between 30 minutes and 72 hours; and   then cooling the hot rolled steel strip to room temperature to obtain a hot rolled steel.   
     
     
         2 . The method as recited in  claim 1  wherein the reheating temperature for semi-finished product is between 1150° C. and 1275° C. 
     
     
         3 . The method as recited in  claim 1  wherein the hot rolling finishing temperature is between 800° C. and 950° C. 
     
     
         4 . The method as recited in  claim 1  wherein the cooling temperature range for hot rolled strip after finishing hot rolling is between 15° C. and Ms-20° C. 
     
     
         5 . The method as recited in  claim 1  wherein the annealing temperature range is between Ae3+20° C. and Ae3+350° C. 
     
     
         6 . The method as recited in  claim 5  wherein the annealing temperature range is between Ae3+40° C. and Ae3+300° C. 
     
     
         7 . The method as recited in  claim 1  wherein the cooling rate after annealing is between 1° C./s and 80° C./s. 
     
     
         8 . The method as recited in  claim 7  wherein the cooling rate after annealing is between 1° C./s and 50° C./s. 
     
     
         9 . The method as recited in  claim 1  wherein the cooling temperature range after annealing is between 15° C. and Ms-20° C. 
     
     
         10 . The method as recited in  claim 1  wherein the tempering temperature range is between 575° C. and 675° C. 
     
     
         11 . The method as recited in  claim 10  wherein the tempering temperature range is between 590° C. and 660° C. 
     
     
         12 . The method as recited in  claim 1  wherein the heating rate for tempering is between 0.1° C./s and 50° C./s. 
     
     
         13 . The method as recited in  claim 12  wherein the heating rate for tempering is between 0.1° C./s and 30° C./s. 
     
     
         14 . A method for manufacturing structural or operational parts for oil and gas wells comprising using a hot rolled steel having a composition comprising the following elements, expressed in percentage by weight:
 15%≤Nickel≤25%   6%≤Cobalt≤12%   2%≤Molybdenum≤6%   0.1%≤Titanium≤1%   0.0001%≤Carbon≤0.03%   0.002%≤Phosphorus≤0.02%   0%≤Sulfur≤0.005%   0%≤Nitrogen≤0.01%   and optionally one or more of the following elements:   0%≤Aluminum≤0.1%   0%≤Niobium≤0.1%   0%≤Vanadium≤0.3%   0%≤Copper≤0.5%   0%≤Chromium≤0.5%   0%≤Boron≤ 0.001%   0%≤Magnesium≤0.0010%   a remainder of the composition being composed of iron and unavoidable impurities caused by processing;
 a microstructure of the steel comprising in area fraction, 20% to 40% Tempered Martensite, at least 60% of Reverted Austenite and inter-metallic compounds of Molybdenum, Titanium and Nickel. 
   
     
     
         15 . A method for manufacturing structural or operational parts for oil and gas wells comprising using the steel produced according to the method as recited in  claim 1 . 
     
     
         16 . A seamless tube, pipe or a part obtained according to the method as recited in  claim 15 . 
     
     
         17 . A seamless tube, pipe or a part obtained according to the method as recited in  claim 14 .