Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • 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
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • 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
  • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • 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
  • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
  • C21D8/0226—Hot rolling
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • 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
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/50—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for welded joints
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • 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
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/002—Bainite

Definitions

• UOE steel pipes have been mainly used for linepipes to date from the viewpoint of transport efficiency, because steel pipes having a large diameter and a large thickness can be manufactured using a UOE steel pipe.
• high strength electric resistance welded steel pipes which are manufactured from hot-rolled steel sheets in a coil shape (hot-rolled steel strips) that are less expensive and have high productivity as a material, are being increasingly used for linepipes instead of UOE steel pipes nowadays.
• Electric resistance welded steel pipes have an advantage in that they are superior to UOE steel pipes in terms of deviation of a wall thickness and roundness in addition to cost advantage.
• the pipe production method for electric resistance welded steel pipes involves cold roll forming, the method is characteristic of much more plastic strain being given to steel pipes than to a UOE steel pipe when pipe production is performed.
• HIC is a phenomenon in which hydrogen ions having been generated by a corrosion reaction become hydrogen atoms on the surface of a steel, and the hydrogen atoms enter into the steel, accumulate around inclusions such as MnS, carbides having a large grain diameter such as NbC, and a second hard phase so as to increase internal pressure and cause the steel material to eventually crack.
• inclusions such as MnS, carbides having a large grain diameter such as NbC, and a second hard phase so as to increase internal pressure and cause the steel material to eventually crack.
• a steel material is given plastic strain, many dislocations are formed around the inclusions, carbides, and the second hard phase mentioned above, and hydrogen atoms are more likely to accumulate, which results in HIC being more likely to occur.
• Patent Literature 1 discloses a method for improving HIC resistance in which inclusions, which become the origins of HIC, are rendered harmless by controlling the total contents of chemical elements which combine respectively with S, O (oxygen), and N to form inclusions to be 0.01% or less or by controlling the maximum diameter of inclusions to be 5 ⁇ m or less, and in which the hardness of a center segregation part is controlled to be Hv 330 or less.
• Patent Literature 2 discloses a method for decreasing the area ratio of HIC by decreasing the size of TiN grains, which become the origin of HIC. Specifically, the size of Al-Ca-based sulfides in molten steel is decreased by controlling a weight ratio CaO/Al 2 O 3 to be 1.2 to 1.5 by adjusting the added contents of Al and Ca, and the grain diameter of Al-Ti-Ca-based complex inclusions which are formed using the sulfides as nuclei is controlled to be 30 ⁇ m or less.
• the present invention has been completed on the idea that, in the case of a hot-rolled steel sheet for a high strength linepipe having a TS of 540 MPa or more where there is an increase in sensitivity for HIC, a crack length ratio CLR is controlled to be small even in the presence of some amount of inclusions which become the origins of the occurrence of HIC, by improving propagation resistance of HIC as a result of decreasing the grain diameter of a microstructure in a center segregation part through an improvement in the hardenability of the center segregation part by controlling the chemical composition of steel. That is to say, the subject matter of the present invention is as follows.
• Si 0.05% or more and 0.25% or less
• Si be added so that the ratio Mn/Si is 4.0 or more and 12 or less.
• S is, like P, a chemical element which is inevitably contained in steel, and since S forms MnS in steel, it is preferable that the S content be as small as possible, but a S content of 0.0010% or less is acceptable.
• the S content is preferably 0.0006% or less.
• Nb is a chemical element which contributes to an increase in the strength of steel as a result of precipitating in the form of fine Nb carbonitrides in a coiling process when hot rolled steel sheets are manufactured. Also, Nb is a chemical element which contributes to an improvement in the toughness of a weld zone as a result of suppressing the growth of austenite grains when electric resistance welding is performed. Such effects are realized in the case where the Nb content is 0.020% or more. On the other hand, in the case where the Nb content is more than 0.060%, Nb carbonitrides having a large grain diameter, which become the origins of HIC, are more likely to be formed. Therefore, the Nb content is set to be 0.020% or more and 0.060% or less, or preferably 0.030% or more and 0.050% or less.
• one or more selected from among Cu, Ni, Cr, Mo, and V may be further added in the amounts described below.
• the cooling stop temperature is set to be 380°C or higher and 600°C or lower. In the case where the cooling stop temperature is higher than 600°C, since there is coarsening of precipitation strengthening grains such as Nb carbonitrides, there is a decrease in strength. Moreover, since there is an enhancement of increase in the concentration of carbon in a center segregation part, a fine martensite microstructure, an upper bainite microstructure, and a pearlite microstructure tend to be formed.
• Example 2 Steel Grade Thickness (mm) Slab Heating Temperature (°C) Cumulative Rolling Reduction Ratio in Finish Rolling (%) Finish Rolling Delivery Temperature (°C) Average Cooling Rate of Central Part in Thickness Direction (°C/s) Cooling Stop Temperature(°C) Note 1 A 16 1200 25 840 25 450 Example 2 A 20 1200 45 840 15 500 Example 3 A 10 1200 55 810 50 520 Example 4 A 8 1150 65 810 70 420 Example 5 B 12 1200 55 810 10 520 Example 6 C 12 1200 65 810 25 560 Example 7 D 25 1200 40 820 60 420 Example 8 D 25 1200 40 820 55 480 Example 9 D 25 1200 55 810 30 530 Example 10 A 16 1350 55 810 10 510 Comparative Example 11 A 20 1200 10 830 15 500 Comparative Example 12 A 10 1250 40 820 120 520 Comparative Example 13 A 8 1150 50 830 20 650 Comparative Example 14 E 19 1150 55 810 10 510 Comparative Example 15 F 19 1200
• a V-notched test piece was collected from the central part in the thickness direction of the obtained hot-rolled steel sheet so that the longitudinal direction was at a right angle to the rolling direction (C direction), and absorbed energy and a percent brittle fracture were determined by performing Charpy impact tests at temperatures in the range of -140°C to 0°C in accordance with JIS Z 2242 in order to determine a temperature (fracture transition temperature) at which the percent brittle fracture was 50%.
• three test pieces were used for one temperature in order to obtain the respective arithmetic averages of the determined absorbed energy and percent brittle fracture.
• the examples of the present inventions are all steel sheets having a high strength of 540 MPa or more and excellent HIC resistance.
• the comparative examples, which were out of the range according to the present invention did not achieve the desired properties as a hot rolled steel sheet for high strength electric resistance welded steel pipes excellent in terms of HIC resistance, because the desired strength or toughness was not achieved, or because there was a deterioration in HIC resistance.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Heat Treatment Of Steel (AREA)

Applications Claiming Priority (2)

Publications (3)

Family

ID=51227340

Family Applications (1)

Country Status (6)

Families Citing this family (10)

Family Cites Families (19)

• 2014
  • 2014-01-23 US US14/763,476 patent/US20150368737A1/en not_active Abandoned
  • 2014-01-23 KR KR1020157017735A patent/KR20150088320A/ko not_active Ceased
  • 2014-01-23 EP EP14742727.2A patent/EP2927338B1/fr active Active
  • 2014-01-23 WO PCT/JP2014/000319 patent/WO2014115548A1/fr not_active Ceased
  • 2014-01-23 JP JP2014558502A patent/JP5884201B2/ja not_active Expired - Fee Related
  • 2014-01-23 CN CN201480004904.XA patent/CN104937124A/zh active Pending

Also Published As

Similar Documents

Legal Events