Classifications

• • 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
  • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of 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
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • 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
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/02—Hardening articles or materials formed by forging or rolling, with no further heating beyond that required for the formation
• • 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
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/18—Hardening; Quenching with or without subsequent tempering
• • 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
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/001—Heat treatment of ferrous alloys containing Ni
• • 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
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/005—Heat treatment of ferrous alloys containing Mn
• • 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 by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous 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 by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0221—Modifying the physical properties 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
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
• • 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 by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
  • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following 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
  • C21D9/46—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
  • C22C33/00—Making ferrous alloys
  • C22C33/04—Making ferrous alloys by melting
• • 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
  • C22C38/18—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
  • C22C38/48—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
• • 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
  • C21D2211/005—Ferrite

Definitions

• the present invention relates to a high-strength ultra-thick steel material having excellent core cryogenic deformation aging impact toughness and a manufacturing method thereof.
• the steel material when manufacturing a ship, the steel material is not used as it is in the original plate shape, but is processed into the shape of the hull through partial deformation. When this deformation is applied to the steel material, the impact toughness due to the deformation decreases. In addition, as time passes after deformation, elements such as carbon and nitrogen enter into the potential generated by the deformation, and the impact toughness deteriorates further due to the increase in strength.
• the test item of the base metal includes a strain aging impact test that measures the impact toughness after 5% deformation and heat treatment at 250°C for 1 hour.
• One aspect of the present invention is to provide a high-strength ultra-thick steel material having excellent core cryogenic deformation aging impact toughness and a method of manufacturing the same.
• An embodiment of the present invention is by weight %, C: 0.02 ⁇ 0.06%, Mn: 1.8 ⁇ 2.2%, Ni: 0.7 ⁇ 1.1%, Mo: 0.2 ⁇ 0.5%, Nb: 0.005 ⁇ 0.03%, Ti: 0.005 ⁇ 0.018%, P: 80 ppm or less, S: 20 ppm or less, the balance contains Fe and other inevitable impurities, and has a high boundary angle of 15 degrees or more measured by EBSD in the region of 3/8t to 5/8t in the thickness (t) direction.
• a high-strength, ultra-thick steel material having an average grain size of 15 ⁇ m or less and excellent in cryogenic strain aging impact toughness at the center.
• Another embodiment of the present invention is by weight %, C: 0.02 to 0.06%, Mn: 1.8 to 2.2%, Ni: 0.7 to 1.1%, Mo: 0.2 to 0.5%, Nb: 0.005 to 0.03%, Ti: 0.005 Reheating the steel slab containing ⁇ 0.018%, P: 80ppm or less, S: 20ppm or less, the balance Fe and other inevitable impurities to a temperature of 1000 ⁇ 1080 °C; Rough rolling the reheated steel slab at a temperature of 850 to 1050°C to obtain a bar; Finishing rolling the bar at a temperature of 700 to 800° C. at a total reduction ratio of more than 60% to obtain a hot-rolled steel material; And cooling the hot-rolled steel to a temperature of 500°C or less at a cooling rate of 3°C/s or more.
• a high-strength ultra-thick steel material having excellent core cryogenic strain aging impact toughness and a manufacturing method thereof, having a yield strength of 500 MPa or more, and a transition temperature of -60° C. or less during a strain aging impact test at a center of thickness I can.
• the unit of the alloy composition described below means% by weight unless otherwise specified.
• C is the most important element in securing basic strength in the present invention, so it needs to be contained in the steel within an appropriate range. However, if the content of C exceeds 0.06%, a large amount of C adheres to the electric potential during the strain aging impact test to increase the strength, so that the strain aging impact toughness decreases, and when it is less than 0.02%, the strength decreases.
• the content of C is preferably in the range of 0.02 to 0.06%.
• the lower limit of C is more preferably 0.024%, even more preferably 0.028%, and most preferably 0.3%.
• the upper limit of C is more preferably 0.058%, even more preferably 0.054%, and most preferably 0.05%.
• Mn is a useful element that improves strength through solid solution strengthening and hardenability improvement, it is necessary to add 1.8% or more of Mn in order to satisfy the yield strength of 500 MPa or more to be obtained in the present invention.
• the content of Mn is 1.8 to 2.2. It is preferred to have a range of %.
• the lower limit of Mn is more preferably 1.83%, even more preferably 1.86%, and most preferably 1.9%.
• the upper limit of Mn is more preferably 2.17%, even more preferably 2.14%, and most preferably 2.1%.
• Ni is an important element in improving the strength by improving the impact toughness and hardenability by facilitating the cross slip of dislocations at low temperatures. It is preferable that it is added in% or more. However, when it exceeds 1.1%, there is a problem that the hardenability is excessively increased and a large amount of low-temperature transformation phase is generated, thereby lowering the toughness, and increasing the manufacturing cost. Therefore, it is preferable that the content of Ni has a range of 0.7 to 1.1%. It is preferable that the content of Mn has a range of 1.8 to 2.2%.
• the lower limit of Ni is more preferably 0.73%, even more preferably 0.76%, and most preferably 0.8%.
• the upper limit of Ni is more preferably 1.07%, even more preferably 1.03%, and most preferably 1%.
• Mo is an important element for improving the strength by improving the hardenability, and as an alloying element that has little decrease in toughness compared to the improvement in strength, it is preferable to add 0.2% or more in order to secure a high-strength steel having a yield strength of 500 MPa or more.
• the content of Mo has a range of 0.2 to 0.5%.
• the lower limit of Mo is more preferably 0.23%, even more preferably 0.26%, and most preferably 0.3%.
• the upper limit of Mo is more preferably 0.48%, even more preferably 0.44%, and most preferably 0.4%.
• Nb precipitates in the form of NbC or NbCN to improve the strength of the base metal.
• solid solution Nb precipitates very finely in the form of NbC during rolling, thereby suppressing recrystallization of austenite, thereby minimizing the structure.
• the content of Nb has a range of 0.005 to 0.03%.
• the lower limit of Nb is more preferably 0.008%, even more preferably 0.011%, and most preferably 0.015%.
• the upper limit of Nb is more preferably 0.028%, even more preferably 0.026%, and most preferably 0.025%.
• Ti precipitates as TiN during reheating, suppressing the growth of crystal grains in the base metal and the heat-affected zone of welding, greatly improving the low-temperature toughness, and 0.005% or more should be added for effective TiN precipitation.
• the content of Ti is preferably in the range of 0.005 to 0.018%.
• the lower limit of Ti is more preferably 0.006%, even more preferably 0.008%, and most preferably 0.01%.
• the upper limit of Ti is more preferably 0.017%, even more preferably 0.016%, and most preferably 0.015%.
• P is an element that induces brittleness by inducing brittleness at grain boundaries or by forming coarse inclusions.
• the content of P is preferably limited to 80 ppm or less.
• S is an element that induces brittleness by inducing brittleness at grain boundaries or by forming coarse inclusions.
• the content of S is preferably limited to 20 ppm or less.
• the remaining component of the steel material of the present invention is iron (Fe).
• Fe iron
• the steel material of the present invention has an average grain size of 15 ⁇ m or less with a high boundary angle of 15 degrees or more as measured by EBSD in a region of 3/8t to 5/8t in the thickness (t) direction.
• the average grain size of grains having a high boundary angle of 15 degrees or more measured by EBSD in the region of 3/8t to 5/8t in the thickness (t) direction exceeds 15 ⁇ m, the effective grain size increases due to the grain size coarsening. Accordingly, there may be a problem in that the impact transition temperature is increased and the deformation aging impact toughness is deteriorated.
• the microstructure of the steel material of the present invention may be a mixed structure including ashular ferrite, granular bainite, and upper bainite.
• the steel material of the present invention may have a thickness of 5 to 90mm.
• the steel material of the present invention provided as described above may have a yield strength of 500 MPa or more.
• heat treatment is performed at 250° C. for 1 hour, and the transition temperature may be -60° C. or less during the deformation aging impact test.
• the steel slab is reheated to a temperature of 1000 ⁇ 1080°C.
• the heating temperature is preferably 1000° C. or higher, in order to solidify the carbonitride of Ti and/or Nb formed during casting. Further, heating to 1030°C or higher is more preferable in order to sufficiently dissolve the carbonitride of Ti and/or Nb.
• the central austenite may become coarse, so the reheating temperature is preferably 1080°C or less, and more preferably 1070°C or less.
• the reheated steel slab is roughly rolled at a temperature of 850 to 1050°C to obtain a bar.
• the slab reheated as described above is roughly rolled to adjust its shape.
• the total reduction rate during rough rolling is preferably 40% or more.
• the bar is finished rolling at a temperature of 700 to 800° C. with a total reduction ratio of more than 60% to obtain a hot-rolled steel.
• the austenite structure of the bar is pencaked, and fine rolling is performed to introduce dislocations.
• the finishing rolling is preferably carried out at a temperature of 700 ⁇ 800 °C so that the deformation applied to the center as much as possible can be maintained.
• the finishing rolling temperature is less than 700°C, ferrite precipitates during deformation, resulting in a decrease in both strength and toughness, and when it exceeds 800°C, there is a disadvantage in that the particle size increases and impact toughness deteriorates and sufficient strength is not secured. .
• the lower limit of the finishing rolling temperature is more preferably 720°C, and even more preferably 740°C.
• the upper limit of the finishing rolling temperature is more preferably 780°C, and even more preferably 760°C.
• the total reduction ratio during the finishing rolling is more preferably 61% or more, and even more preferably 62%.
• the hot-rolled steel is cooled to a temperature of 500°C or less at a cooling rate of 3°C/s or more.
• the cooling rate is lower than 3°C/s or the cooling stop temperature is higher than 500°C, the present invention may not properly form fine grains, and the yield strength may be 500 MPa or less.
• the central deformation aging impact test was performed by taking a specimen from the central portion of the steel material, performing heat treatment at 250°C for 1 hour after 5% deformation, and then performing an impact test to measure the transition temperature. .
• Comparative Example 3 by having a value higher than the upper limit of C suggested in the present invention, a large amount of coarse bainite phase was generated due to high hardenability, showing very high yield strength, and also 3/8t to 5/8t part of crystal grains. Even though the average particle size is 15 ⁇ m or less, it can be seen that the strain aging impact transition temperature exceeds -60°C as a large amount of C adheres to the dislocation during the strain aging impact test.
• Comparative Example 4 by having a value higher than the upper limit of Mn suggested in the present invention, a large amount of coarse bainite phase is generated due to high hardenability, showing very high yield strength, but the average of 3/8t to 5/8t part grains It can be seen that the particle size exceeds 15 ⁇ m, and the strain aging impact transition temperature exceeds -60°C.
• Comparative Example 5 by having a value lower than the lower limit of C and Mn suggested in the present invention, a large amount of soft phase such as polygonal ferrite was generated in the center, and thus, it can be seen that the yield strength is lower than 500Mpa. have.
• Comparative Example 6 had a value lower than the upper limit of Ni suggested in the present invention, and thus the deformation aging impact due to the decrease in toughness due to the low Ni content, even though the average particle size of the 3/8t to 5/8t part grains was 15 ⁇ m or less. It can be seen that the transition temperature exceeds -60°C.
• Comparative Example 7 by having a value higher than the upper limit of Mo suggested in the present invention, a large amount of coarse bainite phases were generated due to high hardenability, showing very high yield strength, but the average particle size of 3/8t to 5/8t parts It can be seen that it exceeds 15 ⁇ m, and the strain aging impact transition temperature exceeds -60°C.
• Comparative Example 8 by having a value higher than the upper limit of Ti and Nb suggested in the present invention, the strength was increased due to excessive hardenability and formation of precipitates, and the strain aging impact transition temperature was due to the effect of the decrease in toughness due to precipitation strengthening. It can be seen that it exceeds -60°C.

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• 2019
  • 2019-10-01 KR KR1020190121723A patent/KR102237486B1/ko active IP Right Grant
• 2020
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