# US 2017/0283918 A1 · High-strength seamless steel pipe for oil country tubular goods and method of producing the same > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2017/0283918 A1 - Document ID: US20170283918A1 - Status: Published application - Kind: A1 - Application number: 15/509,350 - Filed: 2015-08-20 - Published: 2017-10-05 - Earliest claimed: 2014-09-08 - Assignees: Jfe Steel Corporation - Applicants: Jfe Steel Corporation - Inventors: Masao Yuga; Yasuhide Ishiguro; Mitsuhiro Okatsu; Kazuki Fujimura - Web page: https://patentgrep.com/patent/US20170283918A1 ## CPC - C22C 38/12: containing tungsten, tantalum, molybdenum, vanadium, or niobium - C21D 8/10: during manufacturing of tubular bodies - C21D 9/085: {Cooling or quenching} - C22C 38/001: {containing N} - C22C 38/02: containing silicon - C22C 38/04: containing manganese - C22C 38/06: containing aluminium - C22C 38/18: containing chromium - C22C 38/22: with molybdenum or tungsten - C22C 38/24: with vanadium - C22C 38/26: with niobium or tantalum - C22C 38/32: with boron - F16L 9/02: of metal (F16L9/16 - F16L9/22 take precedence) - C21D 2211/008: Martensite - C22C: ALLOYS (treatment of alloys C21D, C22F) - C21D: MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass C23F17/00; unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid materials C30B) - F16L: PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL ## Abstract Provided is a high-strength seamless steel pipe having the composition which contains, by mass %, 0.20 to 0.50% C, 0.05 to 0.40% Si, 0.3 to 0.9% Mn, 0.015% or less P, 0.005% or less S, 0.005 to 0.1% Al, 0.008% or less N, more than 0.6% and 1.7% or less Cr, more than 1.0% and 3.0% or less Mo, 0.01 to 0.30% V, 0.001% or more and less than 0.01% Nb, 0.0003 to 0.0030% B, and 0.0030% or less O (oxygen). The high-strength seamless steel pipe has the microstructure where a volume fraction of a tempered martensitic phase is 95% or more, and prior austenitic grains have a grain size number of 8.5 or more, and a segregation degree index Ps which is defined by a formula Ps=8.1 (XSi+XMn+XMo)+1.2XP is set to less than 65. ## Claims ### Claim 1 A high-strength seamless steel pipe for an oil country tubular goods having the composition which contains, by mass %, 0.20 to 0.50% C, 0.05 to 0.40% Si, 0.3 to 0.9% Mn, 0.015% or less P, 0.005% or less S, 0.005 to 0.1% Al, 0.008% or less N, more than 0.6% and 1.7% or less Cr, more than 1.0% and 3.0% or less Mo, 0.01 to 0.30% V, 0.001% or more and less than 0.01% Nb, 0.0003 to 0.0030% B, 0.0030% or less O (oxygen), and Fe and unavoidable impurities as a balance, wherein the steel pipe has the microstructure where a volume fraction of a tempered martensitic phase is 95% or more, and prior austenitic grains have a grain size number of 8.5 or more, and a segregation degree index Ps which is defined by a following formula (1) using XM which is a ratio between a segregated portion content obtained by performing an area analysis of respective elements by an electron probe micro analyzer (EPMA) in a region having the center thereof positioned at ¼ t (t: wall thickness) from an inner surface of the steel pipe and an average content is set to less than 65, and a yield strength YS is 862 MPa or more, wherein Ps=8.1 (XSi+XMn+XMo)+1.2XP (1) where XM: (segregated portion content (mass %) of element M)/(average content (mass %) of element M). ### Claim 2 (depends on 1) The high-strength seamless steel pipe for an oil country tubular goods according to claim 1, wherein the composition further contains, by mass %, 0.005% to 0.030% Ti such that Ti/N which is a ratio between the content of Ti and the content of N is set to a value which falls within a range of 2.0 to 5.0. ### Claim 3 (depends on 1) The high-strength seamless steel pipe for an oil country tubular goods according to claim 1, wherein the composition further contains one kind or two kinds or more of elements selected from a group consisting of, by mass %, 1.0% or less Cu, 1.0% or less Ni, and 3.0% or less W. ### Claim 4 (depends on 2) The high-strength seamless steel pipe for an oil country tubular goods according to claim 2, wherein the composition further contains one kind or two kinds or more of elements selected from a group consisting of, by mass %, 1.0% or less Cu, 1.0% or less Ni, and 3.0% or less W. ### Claim 5 (depends on 1) The high-strength seamless steel pipe for an oil country tubular goods according to any one of claim 1, wherein the composition further contains 0.0005 to 0.005% Ca by mass %. ### Claim 6 (depends on 2) The high-strength seamless steel pipe for an oil country tubular goods according to any one of claim 2, wherein the composition further contains 0.0005 to 0.005% Ca by mass %. ### Claim 7 (depends on 3) The high-strength seamless steel pipe for an oil country tubular goods according to any one of claim 3, wherein the composition further contains 0.0005 to 0.005% Ca by mass %. ### Claim 8 (depends on 4) The high-strength seamless steel pipe for an oil country tubular goods according to any one of claim 4, wherein the composition further contains 0.0005 to 0.005% Ca by mass %. ### Claim 9 (depends on 1) A method of manufacturing a high-strength seamless steel pipe for an oil country tubular goods which is a method of manufacturing a seamless steel pipe having a predetermined shape by applying heating and hot working to a steel pipe material, and which is a method of manufacturing the high-strength seamless steel pipe for an oil well according to claim 1, wherein a heating temperature in the heating is set to a temperature which falls within a range of 1050 to 1350° C., cooling after the above-mentioned hot working is performed such that the cooling is performed until a surface temperature becomes a temperature equal to or below 200° C. at a cooling rate equal to or higher than air cooling and, after the cooling, quenching treatment in which the steel pipe is reheated at a temperature which falls within a range of Ac3 transformation temperature or above to 1000° C. or below and the steel pipe is rapidly cooled to a temperature such that a surface temperature becomes 200° C. or below is performed one time or more, and after the quenching treatment, tempering treatment which heats the steel pipe to a temperature which falls within a range of 600 to 740° C. is performed. ### Claim 10 (depends on 2) A method of manufacturing a high-strength seamless steel pipe for an oil country tubular goods which is a method of manufacturing a seamless steel pipe having a predetermined shape by applying heating and hot working to a steel pipe material, and which is a method of manufacturing the high-strength seamless steel pipe for an oil well according to claim 2, wherein a heating temperature in the heating is set to a temperature which falls within a range of 1050 to 1350° C., cooling after the above-mentioned hot working is performed such that the cooling is performed until a surface temperature becomes a temperature equal to or below 200° C. at a cooling rate equal to or higher than air cooling and, after the cooling, quenching treatment in which the steel pipe is reheated at a temperature which falls within a range of Ac3 transformation temperature or above to 1000° C. or below and the steel pipe is rapidly cooled to a temperature such that a surface temperature becomes 200° C. or below is performed one time or more, and after the quenching treatment, tempering treatment which heats the steel pipe to a temperature which falls within a range of 600 to 740° C. is performed. ### Claim 11 (depends on 3) A method of manufacturing a high-strength seamless steel pipe for an oil country tubular goods which is a method of manufacturing a seamless steel pipe having a predetermined shape by applying heating and hot working to a steel pipe material, and which is a method of manufacturing the high-strength seamless steel pipe for an oil well according to claim 3, wherein a heating temperature in the heating is set to a temperature which falls within a range of 1050 to 1350° C., cooling after the above-mentioned hot working is performed such that the cooling is performed until a surface temperature becomes a temperature equal to or below 200° C. at a cooling rate equal to or higher than air cooling and, after the cooling, quenching treatment in which the steel pipe is reheated at a temperature which falls within a range of Ac3 transformation temperature or above to 1000° C. or below and the steel pipe is rapidly cooled to a temperature such that a surface temperature becomes 200° C. or below is performed one time or more, and after the quenching treatment, tempering treatment which heats the steel pipe to a temperature which falls within a range of 600 to 740° C. is performed. ### Claim 12 (depends on 4) A method of manufacturing a high-strength seamless steel pipe for an oil country tubular goods which is a method of manufacturing a seamless steel pipe having a predetermined shape by applying heating and hot working to a steel pipe material, and which is a method of manufacturing the high-strength seamless steel pipe for an oil well according to claim 4, wherein a heating temperature in the heating is set to a temperature which falls within a range of 1050 to 1350° C., cooling after the above-mentioned hot working is performed such that the cooling is performed until a surface temperature becomes a temperature equal to or below 200° C. at a cooling rate equal to or higher than air cooling and, after the cooling, quenching treatment in which the steel pipe is reheated at a temperature which falls within a range of Ac3 transformation temperature or above to 1000° C. or below and the steel pipe is rapidly cooled to a temperature such that a surface temperature becomes 200° C. or below is performed one time or more, and after the quenching treatment, tempering treatment which heats the steel pipe to a temperature which falls within a range of 600 to 740° C. is performed. ### Claim 13 (depends on 5) A method of manufacturing a high-strength seamless steel pipe for an oil country tubular goods which is a method of manufacturing a seamless steel pipe having a predetermined shape by applying heating and hot working to a steel pipe material, and which is a method of manufacturing the high-strength seamless steel pipe for an oil well according to claim 5, wherein a heating temperature in the heating is set to a temperature which falls within a range of 1050 to 1350° C., cooling after the above-mentioned hot working is performed such that the cooling is performed until a surface temperature becomes a temperature equal to or below 200° C. at a cooling rate equal to or higher than air cooling and, after the cooling, quenching treatment in which the steel pipe is reheated at a temperature which falls within a range of Ac3 transformation temperature or above to 1000° C. or below and the steel pipe is rapidly cooled to a temperature such that a surface temperature becomes 200° C. or below is performed one time or more, and after the quenching treatment, tempering treatment which heats the steel pipe to a temperature which falls within a range of 600 to 740° C. is performed. ### Claim 14 (depends on 6) A method of manufacturing a high-strength seamless steel pipe for an oil country tubular goods which is a method of manufacturing a seamless steel pipe having a predetermined shape by applying heating and hot working to a steel pipe material, and which is a method of manufacturing the high-strength seamless steel pipe for an oil well according to claim 6, wherein a heating temperature in the heating is set to a temperature which falls within a range of 1050 to 1350° C., cooling after the above-mentioned hot working is performed such that the cooling is performed until a surface temperature becomes a temperature equal to or below 200° C. at a cooling rate equal to or higher than air cooling and, after the cooling, quenching treatment in which the steel pipe is reheated at a temperature which falls within a range of Ac3 transformation temperature or above to 1000° C. or below and the steel pipe is rapidly cooled to a temperature such that a surface temperature becomes 200° C. or below is performed one time or more, and after the quenching treatment, tempering treatment which heats the steel pipe to a temperature which falls within a range of 600 to 740° C. is performed. ### Claim 15 (depends on 7) A method of manufacturing a high-strength seamless steel pipe for an oil well-country tubular goods which is a method of manufacturing a seamless steel pipe having a predetermined shape by applying heating and hot working to a steel pipe material, and which is a method of manufacturing the high-strength seamless steel pipe for an oil well according to claim 7, wherein a heating temperature in the heating is set to a temperature which falls within a range of 1050 to 1350° C., cooling after the above-mentioned hot working is performed such that the cooling is performed until a surface temperature becomes a temperature equal to or below 200° C. at a cooling rate equal to or higher than air cooling and, after the cooling, quenching treatment in which the steel pipe is reheated at a temperature which falls within a range of Ac3 transformation temperature or above to 1000° C. or below and the steel pipe is rapidly cooled to a temperature such that a surface temperature becomes 200° C. or below is performed one time or more, and after the quenching treatment, tempering treatment which heats the steel pipe to a temperature which falls within a range of 600 to 740° C. is performed. ### Claim 16 (depends on 8) A method of manufacturing a high-strength seamless steel pipe for an oil country tubular goods which is a method of manufacturing a seamless steel pipe having a predetermined shape by applying heating and hot working to a steel pipe material, and which is a method of manufacturing the high-strength seamless steel pipe for an oil well according to claim 8, wherein a heating temperature in the heating is set to a temperature which falls within a range of 1050 to 1350° C., cooling after the above-mentioned hot working is performed such that the cooling is performed until a surface temperature becomes a temperature equal to or below 200° C. at a cooling rate equal to or higher than air cooling and, after the cooling, quenching treatment in which the steel pipe is reheated at a temperature which falls within a range of Ac3 transformation temperature or above to 1000° C. or below and the steel pipe is rapidly cooled to a temperature such that a surface temperature becomes 200° C. or below is performed one time or more, and after the quenching treatment, tempering treatment which heats the steel pipe to a temperature which falls within a range of 600 to 740° C. is performed.