KR101758520B1 - High strength structural steel sheet having excellent heat treatment resistance and method of manufacturing the same - Google Patents
High strength structural steel sheet having excellent heat treatment resistance and method of manufacturing the same Download PDFInfo
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- 238000010438 heat treatment Methods 0.000 title claims description 43
- 229910000746 Structural steel Inorganic materials 0.000 title claims description 13
- 238000004519 manufacturing process Methods 0.000 title description 12
- 229910001568 polygonal ferrite Inorganic materials 0.000 claims abstract description 15
- 239000012535 impurity Substances 0.000 claims abstract description 7
- 229910000859 α-Fe Inorganic materials 0.000 claims abstract description 7
- 229910052758 niobium Inorganic materials 0.000 claims abstract description 6
- 229910052750 molybdenum Inorganic materials 0.000 claims abstract description 5
- 229910000831 Steel Inorganic materials 0.000 claims description 75
- 239000010959 steel Substances 0.000 claims description 75
- 238000001816 cooling Methods 0.000 claims description 31
- 238000005096 rolling process Methods 0.000 claims description 24
- 238000000034 method Methods 0.000 claims description 9
- 238000001953 recrystallisation Methods 0.000 claims description 8
- 238000003303 reheating Methods 0.000 claims description 5
- 229910052759 nickel Inorganic materials 0.000 abstract description 5
- 229910001220 stainless steel Inorganic materials 0.000 abstract 1
- 230000000052 comparative effect Effects 0.000 description 39
- 239000002244 precipitate Substances 0.000 description 17
- 239000000463 material Substances 0.000 description 14
- 230000000694 effects Effects 0.000 description 11
- 239000013078 crystal Substances 0.000 description 10
- 229910045601 alloy Inorganic materials 0.000 description 9
- 239000000956 alloy Substances 0.000 description 9
- 230000006866 deterioration Effects 0.000 description 8
- 239000000203 mixture Substances 0.000 description 8
- 230000015572 biosynthetic process Effects 0.000 description 7
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 5
- 229910052748 manganese Inorganic materials 0.000 description 4
- 230000009466 transformation Effects 0.000 description 4
- 229910001566 austenite Inorganic materials 0.000 description 3
- 238000005728 strengthening Methods 0.000 description 3
- 238000005452 bending Methods 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 238000009863 impact test Methods 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910017263 Mo—C Inorganic materials 0.000 description 1
- 229910001563 bainite Inorganic materials 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 239000010960 cold rolled steel Substances 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- HEMHJVSKTPXQMS-UHFFFAOYSA-M sodium hydroxide Substances [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 238000009864 tensile test Methods 0.000 description 1
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- 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
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
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- 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
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- 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
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- 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
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- 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
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
-
- 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
- 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
- C21D2211/004—Dispersions; Precipitations
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- 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
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- 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
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- 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
Abstract
본 발명은 중량%로, C : 0.03 ~ 0.07%, Si : 0.05 ~ 0.2%, Mn : 1.6 ~ 2.3%, P : 0.008% 이하, S : 0.002% 이하, Al : 0.025% 이하, Cu : 0.1 ~ 0.4%, Ni : 1.4 ~ 2.3%, Mo : 0.08 ~ 0.2%, Nb : 0.01 ~ 0.025%, Ti : 0.008 ~ 0.02%, N: 0.001~0.008%, 나머지 Fe 및 불가피한 불순물을 포함하고, 표면 10mm이내에서의 미세조직은 부피분율로 80%이상의 침상 페라이트 및 20% 이하의 폴리고날 페라이트를 포함하는 열간 저항성이 우수한 고강도 구조용 강판에 관한 것이다.The present invention relates to a ferritic stainless steel comprising, by weight%, 0.03 to 0.07% of C, 0.05 to 0.2% of Si, 1.6 to 2.3% of Mn, 0.008% or less of P, 0.002% or less of S, 0.4 to 0.4%, Ni: 1.4 to 2.3%, Mo: 0.08 to 0.2%, Nb: 0.01 to 0.025%, Ti: 0.008 to 0.02%, N: 0.001 to 0.008%, remaining Fe and unavoidable impurities, In which the microstructure has a volume fraction of not less than 80% of needle-like ferrite and not more than 20% of polygonal ferrite.
Description
본 발명은 열간 저항성이 우수한 고강도 구조용 강판 및 그 제조방법에 관한 것이다.
The present invention relates to a high strength structural steel sheet excellent in thermal resistance and a method of manufacturing the same.
선박, 해양 및 건축 구조물의 외관은 평면과 곡면이 동시에 존재하는 구조를 가지고 있다.The appearance of ships, marine and building structures has a structure in which planes and curved surfaces exist at the same time.
평면에 대한 가공은 판재 성형 시 결정되기 때문에 선박, 해양구조물의 건조 시 별도의 공정을 거치지 않고 외관을 성형하지만, 곡면 성형 시에는 판재를 가공하는 과정을 거치게 되는데 이를 수행하기 위해 강판의 표면을 가열하는 작업인 선상가열을 행하게 된다.Since the planar surface is determined during the plate material forming process, the outer surface is formed without a separate process during the drying of the ship or the offshore structure. However, during the curved surface forming process, the plate material is processed. Line heating which is a work to be performed.
선상가열에 의한 굽힘가공은 가열부의 열팽창 후 냉각에 의해 수축할 때 주위의 비가열 영역으로부터의 구속에 의해 변형되는 성질을 이용한다. The bending process by the line heating utilizes the property that when it contracts due to cooling after the thermal expansion of the heating portion, it is deformed by the constraint from the surrounding non-heated region.
이러한 선상가열을 적용하기 위해서 강판의 표면은 600~900℃ 정도의 온도로 가열하거나 가열 후 수냉을 실시하여 하므로, 선상가열 후 강판의 물성이 열위해질 수 있다. 강재의 오스테나이트 개시 변태온도까지의 가열은 전위의 풀림 등에 의해, 변태온도 이상 또는 재결정온도 이상 가열되는 경우 결정립의 성장에 의해 주로 재질의 열화를 가져오게 된다. In order to apply such line heating, the surface of the steel sheet is heated to a temperature of about 600 to 900 ° C or water-cooled after heating, so that the physical properties of the steel sheet may be lowered after the surface heating. Heating to the austenite starting transformation temperature of the steel mainly causes deterioration of the material mainly due to the growth of crystal grains when heated above the transformation temperature or the recrystallization temperature due to loosening of dislocations or the like.
또한 강판 표면의 가열, 냉각의 열사이클로 인해 취화되어 인성의 저하를 초래될 수 있다.
Further, the steel sheet may be brittle due to heat cycles of heating and cooling the surface of the steel sheet, resulting in deterioration of toughness.
따라서, 선상가열 후에도 항복강도, 인장강도 및 충격인성이 우수한 열간 저항성이 우수한 고강도 구조용 강판 및 그 제조방법에 대한 개발이 요구되고 있는 실정이다.
Therefore, there is a demand for development of a steel sheet for high strength structural steel excellent in the yield strength, tensile strength and impact toughness, excellent in the hot resistance even after the heating on the ship, and a manufacturing method thereof.
본 발명은 선상가열 후에도 항복강도, 인장강도 및 충격인성이 우수한 열간 저항성이 우수한 고강도 구조용 강판 및 그 제조방법을 제공하기 위함이다.
The present invention is to provide a high strength structural steel sheet excellent in yield strength, tensile strength and impact toughness and excellent in thermal resistance even after heating on a ship, and a method for producing the same.
한편, 본 발명의 과제는 상술한 내용에 한정하지 않는다. 본 발명의 과제는 본 명세서의 내용 전반으로부터 이해될 수 있을 것이며, 본 발명이 속하는 기술분야에서 통상의 지식을 가지는 자라면 본 발명의 부가적인 과제를 이해하는데 아무런 어려움이 없을 것이다.
On the other hand, the object of the present invention is not limited to the above description. It will be understood by those of ordinary skill in the art that there is no difficulty in understanding the additional problems of the present invention.
본 발명의 일 측면은 중량%로, C : 0.03 ~ 0.07%, Si : 0.05 ~ 0.2%, Mn : 1.6 ~ 2.3%, P : 0.008% 이하, S : 0.002% 이하, Al : 0.025% 이하, Cu : 0.1 ~ 0.4%, Ni : 1.4 ~ 2.3%, Mo : 0.08 ~ 0.2%, Nb : 0.01 ~ 0.025%, Ti : 0.008 ~ 0.02%, N: 0.001~0.008%, 나머지 Fe 및 불가피한 불순물을 포함하고, An aspect of the present invention is a steel sheet comprising, by weight%, 0.03 to 0.07% of C, 0.05 to 0.2% of Si, 1.6 to 2.3% of Mn, 0.008% or less of P, 0.002% or less of S, : 0.1 to 0.4% of Ni, 1.4 to 2.3% of Ni, 0.08 to 0.2% of Mo, 0.01 to 0.025% of Nb, 0.008 to 0.02% of Ti, 0.001 to 0.008% of N and Fe and unavoidable impurities,
표면 10mm이내에서의 미세조직은 부피분율로 80%이상의 침상 페라이트 및 20% 이하의 폴리고날 페라이트를 포함하는 열간 저항성이 우수한 고강도 구조용 강판을 제공하기 위함이다.
And a microstructure within 10 mm of the surface has a volume fraction of not less than 80% of needle-like ferrite and not more than 20% of polygonal ferrite.
본 발명의 다른 일 측면은 중량%로, C : 0.03 ~ 0.07%, Si : 0.05 ~ 0.2%, Mn : 1.6 ~ 2.3%, P : 0.008% 이하, S : 0.002% 이하, Al : 0.025% 이하, Cu : 0.1 ~ 0.4%, Ni : 1.4 ~ 2.3%, Mo : 0.08 ~ 0.2%, Nb : 0.01 ~ 0.025%, Ti : 0.008 ~ 0.02%, N: 0.001~0.008%, 나머지 Fe 및 불가피한 불순물을 포함하는 슬라브를 재가열하는 단계; Another aspect of the present invention is a steel sheet comprising, by weight, 0.03 to 0.07% of C, 0.05 to 0.2% of Si, 1.6 to 2.3% of Mn, 0.008% or less of P, 0.002% or less of S, Wherein the alloy contains 0.1 to 0.4% of Cu, 1.4 to 2.3% of Ni, 0.08 to 0.2% of Mo, 0.01 to 0.025% of Nb, 0.008 to 0.02% of Ti, 0.001 to 0.008% of N and Fe and unavoidable impurities Reheating the slab;
상기 재가열된 슬라브를 750~850℃에서 미재결정역 압연하는 단계; 및 Re-rolling the reheated slab at 750 to 850 ° C; And
미재결정역 압연 후 10℃/초 이상의 냉각속도로 380~440℃의 냉각종료온도까지 냉각단계;를 포함하는 열간 저항성이 우수한 고강도 구조용 강판의 제조방법을 제공하기 위함이다.
And cooling the steel sheet to a cooling end temperature of 380 to 440 캜 at a cooling rate of 10 캜 / second or more after the non-recrystallization reverse rolling.
덧붙여, 상기한 과제의 해결수단은, 본 발명의 특징을 모두 열거한 것은 아니다. 본 발명의 다양한 특징과 그에 따른 장점과 효과는 아래의 구체적인 실시형태를 참조하여 보다 상세하게 이해될 수 있을 것이다.
In addition, the solution of the above-mentioned problems does not list all the features of the present invention. The various features of the present invention and the advantages and effects thereof will be more fully understood by reference to the following specific embodiments.
본 발명에 따르면 선상가열 전에는 물론, 열간 저항성이 우수하여 선상가열 후에도 항복강도, 인장강도 및 저온 충격인성이 우수한 고강도 구조용 강판 및 그 제조방법을 제공할 수 있다.
According to the present invention, it is possible to provide a steel sheet for high-strength structural steel excellent in yield strength, tensile strength and low-temperature impact toughness even after the wire heating, and a method for producing the steel sheet.
도 1은 선상가열에 의한 곡면 성형의 일례를 나타낸 모식도이다.
도 2는 발명예 1의 강판의 표면으로부터 10mm깊이의 단면 조직 사진이다.1 is a schematic view showing an example of curved surface forming by linear heating.
2 is a cross-sectional photograph of a 10 mm depth from the surface of the steel sheet of Inventive Example 1. Fig.
이하, 본 발명의 바람직한 실시 형태들을 설명한다. 그러나, 본 발명의 실시형태는 여러 가지 다른 형태로 변형될 수 있으며, 본 발명의 범위가 이하 설명하는 실시 형태로 한정되는 것은 아니다. 또한, 본 발명의 실시형태는 당해 기술분야에서 평균적인 지식을 가진 자에게 본 발명을 더욱 완전하게 설명하기 위해서 제공되는 것이다.
Hereinafter, preferred embodiments of the present invention will be described. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. Further, the embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art.
본 발명자들은 선박, 해양 및 건축 구조물의 외관이 곡면을 갖도록 고강도 구조용 강판을 선상가열하여 곡가공하는 경우, 선상가열 후 강판의 물성이 열위해질 수 있음을 발견하였다. The inventors of the present invention have found that when the steel plate for high-strength structural members is curved so as to have a curved surface in the appearance of ships, marine structures and building structures, the properties of the steel sheet after the linear heating can be degraded.
이러한 선상가열은 강판의 표면을 600~900℃까지 가열하기 때문에 기지조직 및 결정립계의 연화, 결정립 성장, 카바이드(Fe3C)의 조대화 등에 의해 강도 및 인성이 동시에 저하되는 현상이 발생하게 된다. This linearly arranged heating is a phenomenon that the strength and toughness decrease at the same time by a coarsening of the base tissues and softening of the grain boundary, crystal grain growth, carbide (Fe 3 C) due to heat the surface of the steel sheet to 600 ~ 900 ℃.
또한, 오스테나이트 개시 변태온도까지의 가열은 전위의 풀림 등에 의해 재질의 열화가 발생되며, 변태온도 이상 또는 재결정온도 이상 가열되는 경우 결정립의 성장에 의해 주로 재질의 열화를 가져오게 된다.
Further, the heating up to the austenite starting transformation temperature causes deterioration of the material due to loosening of the dislocations or the like. When heated above the transformation temperature or above the recrystallization temperature, the growth of the crystal grains leads mainly to deterioration of the material.
본 발명자들은 상기 문제점들을 해결하기 위해서 고Mn, Ni의 첨가로 Ar3온도를 낮추어 저온 압연 및 강냉에 의해 표면 10mm이내에서의 미세조직이 부피분율로 80% 이상의 침상 페라이트 및 20% 이하의 폴리고날 페라이트를 포함하도록 함으로써, 선상가열 이후의 결정립 성장을 방지할 수 있으며, NbC, Mo2C의 석출물들의 결정립계 pinning 효과를 이용하여 결정립의 성장 및 조대한 카바이드의 형성을 방지할 수 있어, 선상가열 전에는 물론, 선상가열 후에도 항복강도, 인장강도 및 저온 충격인성이 우수한 고강도 구조용 강판 및 그 제조방법을 제공할 수 있음을 깨닫고 본 발명을 완성하게 되었다.
In order to solve the above problems, the inventors of the present invention have found that by reducing the Ar3 temperature by the addition of high Mn and Ni, the microstructure within 10 mm of the surface by low-temperature rolling and cold- It is possible to prevent crystal grain growth after the linear heating and to prevent crystal grain growth and coarse carbide from being formed by utilizing the grain boundary pinning effect of precipitates of NbC and Mo 2 C, Strength steel sheet excellent in yield strength, tensile strength and low-temperature impact toughness even after heating on a line, and a method for producing the same.
이하, 본 발명의 일 측면에 따른 열간 저항성이 우수한 고강도 구조용 강판에 대하여 설명한다.
Hereinafter, a high strength structural steel sheet having excellent thermal resistance according to one aspect of the present invention will be described.
본 발명의 일 측면에 따른 열간 저항성이 우수한 고강도 구조용 강판은 중량%로, C : 0.03 ~ 0.07%, Si : 0.05 ~ 0.2%, Mn : 1.6 ~ 2.3%, P : 0.008% 이하, S : 0.002% 이하, Al : 0.025% 이하, Cu : 0.1 ~ 0.4%, Ni : 1.4 ~ 2.3%, Mo : 0.08 ~ 0.2%, Nb : 0.01 ~ 0.025%, Ti : 0.008 ~ 0.02%, N : 0.001~0.008%, 나머지 Fe 및 불가피한 불순물을 포함하고, 표면 10mm이내에서의 미세조직은 90%이상의 침상 페라이트를 포함한다.
According to one aspect of the present invention, there is provided a high strength structural steel sheet excellent in thermal resistance, comprising 0.03 to 0.07% of C, 0.05 to 0.2% of Si, 1.6 to 2.3% of Mn, 0.008% or less of P, , Nb: 0.01 to 0.025%, Ti: 0.008 to 0.02%, N: 0.001 to 0.008%, N: 0.02 to 0.25% The remaining Fe and inevitable impurities, and the microstructure within 10 mm of the surface contains 90% or more of needle-like ferrite.
C : 0.03 ~ 0.07중량%(이하, 각 원소 함량의 단위는 중량%이다.)C: 0.03 to 0.07% by weight (hereinafter, the unit of each element content is% by weight)
C은 강도를 확보하기 위한 매우 중요한 원소이다. C is a very important element for securing strength.
충분한 강도 확보를 위하여 0.03% 이상 첨가하는 것이 바람직하다. 반면에 과다 첨가하는 경우, 선상가열 이후의 냉각 중 조대한 탄화물을 형성하여 충격인성을 저하시킬 우려가 있으므로 그 상한은 0.07%인 것이 바람직하다.
It is preferable to add 0.03% or more for ensuring sufficient strength. On the other hand, in the case of excessive addition, since there is a possibility of forming a coarse carbide during cooling after the linear heating to lower the impact toughness, the upper limit is preferably 0.07%.
Si : 0.05 ~ 0.2%Si: 0.05 to 0.2%
Si는 탈산제로 유용한 원소이지만 그 함량이 과다한 경우 인성의 저하의 원인이 될 수 있다. 탈산을 위해서는 Si 함량이 0.05% 이상인 것이 바람직하며, Si 함량이 0.2%를 초과하는 경우에는 인성이 저하될 수 있다. 따라서, Si 함량은 0.05~0.2%인 것이 바람직하다.
Although Si is a useful element as a deoxidizer, if it is excessive, it may cause deterioration of toughness. For deoxidation, the Si content is preferably 0.05% or more, and if the Si content exceeds 0.2%, the toughness may be lowered. Therefore, the Si content is preferably 0.05 to 0.2%.
Mn : 1.6 ~ 2.3%Mn: 1.6 to 2.3%
Mn은 고용강화 원소로서 강도를 향상시키고 결정립 미세화 및 모재 인성을 개선하는 효과를 가진다. 또한, Ar3온도를 낮추어 저온 압연 및 강냉에 의해 폴리고날 페라이트의 형성을 최소화할 수 있다.Mn has an effect of improving strength as a solid solution strengthening element and improving grain refinement and base material toughness. In addition, formation of polygonal ferrite can be minimized by low temperature rolling and cold cooling by lowering the Ar3 temperature.
상기 효과를 충분히 나타내기 위하여 1.6% 이상 첨가하는 것이 바람직하다. 반면에 과다 첨가하는 경우, 중심부에 MnS의 비금속 개재물을 형성하고, 상기 MnS 개재물은 압연 후 연신되어 저온인성을 크게 저하시킬 수 있다. 따라서, 그 상한은 2.3%인 것이 바람직하다.
In order to sufficiently exhibit the above effect, it is preferable to add 1.6% or more. On the other hand, in the case of excessive addition, a nonmetallic inclusion of MnS is formed in the center portion, and the MnS inclusions are stretched after rolling to greatly lower the low temperature toughness. Therefore, the upper limit is preferably 2.3%.
P : 0.008% 이하P: not more than 0.008%
P는 강도 향상과 내식성에 유리한 원소이지만, 충격인성을 크게 저해하는 원소이므로 가능한 낮게 유지하는 것이 유리하므로 그 상한을 0.008%로 하는 것이 바람직하다.
P is an element favorable for strength improvement and corrosion resistance, but it is an element which greatly hinders impact toughness, so it is advantageous to keep it as low as possible, and therefore the upper limit is preferably 0.008%.
S : 0.002% 이하S: not more than 0.002%
S는 MnS 등을 형성하여 충격인성을 크게 저해하므로 가능한 낮게 하는 것이 유리하므로 그 상한을 0.002%로 하는 것이 바람직하다.
Since S forms MnS or the like to greatly inhibit the impact toughness, it is advantageous to make it as low as possible, so that the upper limit is preferably 0.002%.
Al : 0.025% 이하Al: 0.025% or less
Al는 효과적으로 탈산을 할 수 있는 원소로서 0.005~0.025% 로 제어하는 것이 바람직하다. 그 하한을 특별히 제어할 필요는 없으나, 탈산을 위해 0.005% 이상 포함될 수 있다.
Al is preferably controlled to 0.005 to 0.025% as an element capable of effectively performing deoxidation. It is not necessary to specifically control the lower limit, but 0.005% or more may be included for deoxidation.
Cu : 0.1 ~ 0.4%Cu: 0.1 to 0.4%
Cu는 고용강화 및 석출강화 원소로서 모재의 인성 저하를 최소화하면서 강도를 향상시킬 수 있는 원소이다. 충분한 강도 향상의 효과를 달성하기 위해서는 0.1% 이상 함유되는 것이 바람직하다. 반면에 과도한 첨가는 열간취성에 의한 강재 표면의 결함을 야기할 수 있으므로 그 상한은 0.4% 이하로 하는 것이 바람직하다.
Cu is an element capable of improving the strength while minimizing the decrease in toughness of the base material as a solid solution strengthening and precipitation strengthening element. In order to achieve an effect of sufficient strength improvement, it is preferable that the content is 0.1% or more. On the other hand, excessive addition may cause defects on the surface of the steel due to hot brittleness, so the upper limit is preferably 0.4% or less.
Ni : 1.4 ~ 2.3%Ni: 1.4 to 2.3%
Ni은 모재의 강도와 인성을 동시에 향상시킬 수 있는 원소이다. 또한, Ar3온도를 낮추어 저온 압연 및 강냉에 의해 폴리고날 페라이트의 형성을 최소화할 수 있다. Ni is an element capable of simultaneously improving the strength and toughness of a base material. In addition, formation of polygonal ferrite can be minimized by low temperature rolling and cold cooling by lowering the Ar3 temperature.
Ni 함량이 1.4% 미만인 경우에는 상술한 효과가 불충분하고, Ni 함량이 2.3% 초과인 경우에는 경화능이 상승되고, 베이나이트 형성으로 충격인성이 저하될 수 있다. 따라서, Ni 함량은 1.4~2.3%인 것이 바람직하다.
When the Ni content is less than 1.4%, the above-mentioned effect is insufficient. When the Ni content exceeds 2.3%, the curability is increased and the impact toughness may be lowered due to the formation of bainite. Therefore, the Ni content is preferably 1.4 to 2.3%.
Mo : 0.08 ~ 0.2%Mo: 0.08 to 0.2%
Mo는 소량의 첨가로 강도를 효과적으로 상승시키는 원소로서 선상가열 후 미세한 Mo-C 계열의 석출물을 형성하여 강도의 열화를 방지하기 때문에 0.08% 이상 첨가하는 것이 바람직하다. 하지만 과도한 Mo 첨가로 인해 석출물의 조대화가 발생할 수 있으므로 그 상한은 0.2% 이하인 것이 바람직하다.
Mo is an element which effectively increases the strength by the addition of a small amount, and it is preferable that Mo is added in an amount of 0.08% or more to form a fine Mo-C type precipitate after the linear heating to prevent deterioration of strength. However, coarsening of the precipitate may occur due to excessive addition of Mo, so the upper limit is preferably 0.2% or less.
Nb : 0.01 ~ 0.025%Nb: 0.01 to 0.025%
선상가열 전 강판에 고용되어 있던 Nb는 선상가열시 NbC, NbCN 등의 형태로 석출되어 모재의 강도를 향상시킨다. 이는 선상가열 후 강도 유지에 중요하며, Nb의 첨가효과를 유효하게 발휘하기 위해서 0.01% 이상이 첨가되어야 한다. 하지만 과도한 Nb 첨가로 인해 석출물의 조대화가 발생할 수 있으므로 그 상한은 0.025% 이하인 것이 바람직하다.
The Nb dissolved in the steel sheet before the linear heating is precipitated in the form of NbC, NbCN or the like during the linear heating, thereby improving the strength of the base material. It is important to maintain the strength after heating on the line, and 0.01% or more should be added in order to effectively exhibit the addition effect of Nb. However, since excessive Nb addition may cause coarsening of the precipitate, the upper limit is preferably 0.025% or less.
Ti : 0.008 ~ 0.02%Ti: 0.008 to 0.02%
Ti는 N과 질화물을 형성하여 고온에서 결정립이 성장하는 것을 방지한다. 이러한 효과를 충분히 확보하기 위해서는 0.008% 이상 포함되는 것이 바람직하다. 반면에, 과도한 Ti첨가는 Ti 석출물의 조대화에 따라 충격인성이 저하되는 문제점이 있으므로 그 상한은 0.02%인 것이 바람직하다.
Ti forms N and a nitride to prevent the crystal grains from growing at a high temperature. In order to sufficiently secure such effect, it is preferable that the content is 0.008% or more. On the other hand, the excessive Ti addition causes a problem that impact toughness is lowered due to coarsening of the Ti precipitates, so that the upper limit is preferably 0.02%.
N: 0.001~0.008%N: 0.001 to 0.008%
N은 Ti, Nb, Al등과 함께 석출물을 형성하여 재가열시 오스테나이트 조직을 미세하기 만들어 강도와 인성을 향상시키는 원소이다. N is an element which forms a precipitate together with Ti, Nb and Al to improve the strength and toughness by making the austenite structure finer during reheating.
N 함량이 0.001% 미만인 경우에는 상술한 효과를 충분히 얻을 수 없다. 반면에, N 함량이 0.008% 초과인 경우에는 고온에서 표면 크랙을 유발할 수 있고, 잔류하는 N은 원자상태로 존재하여 인성을 감소시킬 수 있다. 따라서, N 함량은 0.001~0.008%인 것이 바람직하다.
When the N content is less than 0.001%, the above-mentioned effect can not be sufficiently obtained. On the other hand, when the N content exceeds 0.008%, surface cracking may occur at a high temperature, and the residual N may exist in an atomic state to reduce toughness. Therefore, the N content is preferably 0.001 to 0.008%.
본 발명의 강판의 나머지 성분은 철(Fe)이다. 다만, 통상의 제조과정에서는 원료 또는 주위 환경으로부터 의도되지 않는 불순물들이 불가피하게 혼입될 수 있으므로, 이를 배제할 수는 없다. 이들 불순물들은 통상의 제조과정의 기술자라면 누구라도 알 수 있는 것이기 때문에 그 모든 내용을 특별히 본 명세서에서 언급하지는 않는다.
The remainder of the steel sheet of the present invention is iron (Fe). However, in the ordinary manufacturing process, impurities which are not intended from the raw material or the surrounding environment may be inevitably incorporated, so that it can not be excluded. These impurities are not specifically mentioned in this specification, as they are known to any person skilled in the art of manufacturing.
이하, 본 발명의 일 측면에 따른 열간 저항성이 우수한 고강도 구조용 강판의 미세조직에 대하여 설명한다.
Hereinafter, the microstructure of a high strength structural steel sheet having excellent thermal resistance according to one aspect of the present invention will be described.
본 발명의 일 측면에 따른 열간 저항성이 우수한 고강도 구조용 강판의 표면 10mm이내에서의 미세조직은 부피분율로 80%이상의 침상 페라이트 및 20% 이하의 폴리고날 페라이트를 포함한다. According to one aspect of the present invention, a microstructure within 10 mm of the surface of a high-strength structural steel sheet having excellent thermal resistance includes an acicular ferrite of 80% or more and a polygonal ferrite of 20% or less in volume fraction.
폴리고날 페라이트는 가열에 의한 결정립 성장이 쉽게 이루어지기 때문에, 폴리고날 페라이트가 10mm이내에서의 미세조직에 20부피%를 초과하여 존재하는 경우에는 선상가열시 결정립 성장, 조대한 카바이드 형성 및 기지조직의 열화의 원인이 될 수 있다.
Since the polygonal ferrite is easily grown by heating, when the polygonal ferrite is present in a microstructure in an amount of more than 20% by volume in the microstructure within 10 mm, the grain growth, coarse carbide formation, Which may cause deterioration.
또한, 상기 강판의 두께는 40mm이하인 것이 바람직하다. 강판의 두께가 40mm를 초과하는 경우, 선상가열에 의한 곡가공을 적용하기 어렵기 때문이다. 이때, 강판의 최소 두께는 12mm일 수 있다.
The thickness of the steel sheet is preferably 40 mm or less. When the thickness of the steel sheet exceeds 40 mm, it is difficult to apply the curving process by the line heating. At this time, the minimum thickness of the steel sheet may be 12 mm.
상기와 같이 합금조성 및 미세조직을 제어함으로써, 상기 강판은 항복강도가 500MPa이상이며, 인장강도가 600MPa 이상이고, -40℃에서 충격인성이 100J 이상이다. 이에 따라, 선박, 해양 및 건축 구조물 등에 바람직하게 이용될 수 있다.
By controlling the alloy composition and microstructure as described above, the steel sheet has a yield strength of 500 MPa or more, a tensile strength of 600 MPa or more, and an impact toughness of 100 J or more at -40 캜. Accordingly, it can be suitably used for ships, marine and building structures, and the like.
상술한 바와 같은 합금조성 및 미세조직을 갖는 열간 저항성이 우수한 고강도 구조용 강판을 선상가열시, Mo2C 석출물 및 NbC 석출물 중 하나 이상이 석출되게 된다.
At least one of the Mo 2 C precipitates and the NbC precipitates is precipitated when the steel sheet for high-strength structural steel excellent in the hot resistance and having the alloy composition and microstructure as described above is heated on the line.
선상가열에 의한 곡가공의 일 례인 도 1을 참조하여 설명하면, 선상가열에 의한 곡가공(굽힘가공)은 가열부의 열팽창 후 냉각에 의해 수축할 때 주위의 비가열 영역으로부터의 구속에 의해 변형되는 성질을 이용한다.
1, curving (bending) by linear heating is deformed by constraint from the surrounding non-heated region when it contracts by cooling after thermal expansion of the heating portion Property.
또한, 선상가열은 일반적으로 강판의 표면을 600~900℃까지 가열하게 되는데, 비교적 낮은 온도인 600~800℃에서는 강판에 고용되어 있던 Mo가 선상가열 후 냉각시 Mo2C로 석출되고, 비교적 높은 온도인 800℃ 이상에서는 강판에 고용되어 있던 Nb가 선상가열 후 냉각시 NbC로 석출된다.
On the other hand, in the case of linear heating, the surface of a steel sheet is generally heated to 600 to 900 ° C. Mo at a relatively low temperature of 600 to 800 ° C is precipitated as Mo 2 C upon cooling after the linear heating, At a temperature of 800 ° C or higher, Nb dissolved in the steel sheet is precipitated as NbC upon cooling after the linear heating.
상기 Mo2C 석출물 또는 NbC 석출물은 결정립계에 석출되어 결정립의 성장을 억제(pinning 효과)하고 조대한 카바이드의 형성을 방지할 수 있는 효과가 있다. 또한, C가 석출물로 많이 소모됨에 따라서, 카바이드의 생성 및 조대화를 방지할 수 있다. 이때, 상기 Mo2C 석출물 및 NbC 석출물의 크기는 2~20nm인 것이 바람직하다.
The Mo 2 C precipitates or NbC precipitates are precipitated in grain boundaries to inhibit the growth of crystal grains (pinning effect) and prevent the formation of coarse carbides. Further, as C is consumed as a precipitate, generation and coarsening of carbide can be prevented. At this time, the size of the Mo 2 C precipitates and the NbC precipitates is preferably 2 to 20 nm.
따라서, 본 발명에 따른 강판은 600~900℃로 선상가열하고 곡가공을 하여도 항복강도가 500MPa이상이며, 인장강도가 600MPa 이상이고, -40℃에서 충격인성이 100J 이상을 확보할 수 있는 것이다.
Therefore, even if the steel sheet according to the present invention is linearly heated to 600 to 900 ° C. and subjected to curving, the steel sheet has a yield strength of 500 MPa or more, a tensile strength of 600 MPa or more, and an impact tensile strength of 100 J or more at -40 ° C. .
이하, 본 발명의 다른 일 측면인 열간 저항성이 우수한 고강도 구조용 강판의 제조방법에 대하여 설명한다.
Hereinafter, a method of manufacturing a high strength structural steel sheet having excellent thermal resistance, which is another aspect of the present invention, will be described.
본 발명의 또 다른 일 측면인 열간 저항성이 우수한 고강도 구조용 강판의 제조방법은 상술한 합금조성을 갖는 슬라브를 재가열하는 단계; 상기 재가열된 슬라브를 750~850℃에서 미재결정역 압연하는 단계; 및 미재결정역 압연 후 10℃/초 이상의 냉각속도로 380~440℃의 냉각종료온도까지 냉각단계;를 포함한다.
According to another aspect of the present invention, there is provided a method of manufacturing a high strength structural steel sheet excellent in thermal resistance, comprising: reheating a slab having the above-described alloy composition; Re-rolling the reheated slab at 750 to 850 ° C; And cooling to a cooling end temperature of 380 to 440 占 폚 at a cooling rate of 10 占 폚 / sec or more after the non-recrystallized reverse rolling.
재가열 단계Reheat step
상술한 합금조성을 갖는 슬라브를 재가열한다. 상기 슬라브의 재가열온도는 특별히 한정되는 것은 아니지만, 1100~1200℃로 하는 것이 바람직하다.
The slab having the above-described alloy composition is reheated. The reheating temperature of the slab is not particularly limited, but is preferably 1100 to 1200 ° C.
미재결정역Non recrystallization station 압연 단계 Rolling step
상기 재가열된 슬라브를 750~850℃에서 미재결정역 압연한다. 결정립을 미세화하기 위함이다. The reheated slab is subjected to non-recrystallization back-rolling at 750 to 850 ° C. This is for finer grain.
결정립을 미세화하기 위해서는 미재결정 압연이 Ar3온도 직상의 최대한 낮은 온도에서 수행해야 되는데, 본 발명에서는 충분히 낮은 Ar3온도를 갖기 위해 Mn, Ni의 함량을 높게함으로써 충분히 낮은 Ar3온도를 갖도록 하였으므로 750℃ 이상에서 미재결정역 압연을 행하는 것이 바람직하다. 또한, 미재결정 압연 온도가 850℃ 초과인 경우에는 결정립 미세화가 이루어지기 어려워 인성이 열위해진다. 따라서, 미재결정 압연 온도의 상한은 850℃가 바람직하며, 보다 바람직한 상한은 800℃이다.
In order to make the crystal grains finer, the non-recrystallization rolling should be performed at a temperature as low as the Ar3 temperature. In the present invention, since the Ar3 temperature is sufficiently low by increasing the content of Mn and Ni in order to have a sufficiently low Ar3 temperature, It is preferable to carry out the non-recrystallization reverse rolling. When the non-recrystallized rolling temperature is higher than 850 DEG C, grain refinement is difficult to occur and the toughness is weakened. Therefore, the upper limit of the non-recrystallized rolling temperature is preferably 850 占 폚, and the more preferable upper limit is 800 占 폚.
냉각단계Cooling step
미재결정역 압연 후 10℃/초 이상의 냉각속도로 380~440℃의 냉각종료온도까지 냉각한다. After the non-recrystallized reverse rolling, the steel sheet is cooled to a cooling end temperature of 380 to 440 캜 at a cooling rate of 10 캜 / second or more.
상기와 같이 냉각단계를 제어함으로써, 강판 표면으로부터 10mm이내에서의 미세조직이 부피분율로 80% 이상의 침상 페라이트 및 20% 이하의 폴리고날 페라이트를 포함하도록 할 수 있다. By controlling the cooling step as described above, the microstructure within 10 mm from the surface of the steel sheet can contain at least 80% of needle-shaped ferrite and at most 20% of polygonal ferrite in a volume fraction.
냉각속도가 10℃/초 미만이거나, 냉각종료온도가 440℃를 초과하는 경우에는 충분한 냉각이 이루어지지 않아 폴리고날 페라이트가 다량 형성되고 선상가열시 결정립 성장과 기지의 열화가 발생하게 된다.
When the cooling rate is less than 10 DEG C / sec or the cooling termination temperature is more than 440 DEG C, sufficient cooling is not performed and a large amount of polygonal ferrite is formed, and grain growth and deterioration of the matrix are caused during the heating on the line.
한편, 상기 냉각된 강판을 600~900℃에서 선상가열하여 곡가공 하는 단계를 추가로 행할 수 있다. On the other hand, a step of heating the cold-rolled steel sheet at a temperature of 600 to 900 DEG C to perform curving can be further performed.
상기와 같은 선상가열에 의해, 강판의 곡가공이 가능하게 되며, 선상가열 후 냉각시 Mo2C 석출물 및 NbC 석출물이 석출됨으로써, 결정립의 성장을 억제(pinning 효과)하고 조대한 카바이드의 형성을 방지할 수 있다.
By the above-mentioned linear heating, it is possible to bend the steel sheet, and the Mo 2 C precipitates and the NbC precipitates are precipitated upon cooling after the linear heating, thereby preventing the growth of the crystal grains (pinning effect) and preventing formation of coarse carbide can do.
이하, 실시예를 통하여 본 발명을 보다 구체적으로 설명하고자 한다.
Hereinafter, the present invention will be described more specifically by way of examples.
(( 실시예Example ))
하기 표 1과 같은 합금조성을 갖는 용강을 마련한 후 연속주조를 이용하여 강슬라브를 제조하였다. 발명강 A, B, C는 본 발명에서 규정한 성분범위를 만족하는 강판이며, 비교강 D, F, G, H는 본 발명의 성분범위를 초과하거나, 미달된 합금 성분이 포함되는 강판으로서 비교강 D는 탄소, 비교강 E는 Mo, 비교강 F는 Nb, 비교강 G는 Ni, Mn의 성분이 본 발명의 성분범위를 벗어난 경우이다.
Steel slabs were prepared using continuous casting after providing molten steel having the same alloy composition as shown in Table 1 below. Inventive steels A, B and C are steel plates satisfying the component ranges defined in the present invention, and the comparative steels D, F, G, and H are steel plates having an exceeded component range or an under- The steel D is carbon, the comparative steel E is Mo, the comparative steel F is Nb, and the comparative steel G is Ni and Mn are out of the range of the present invention.
상기 발명강 및 비교강을 하기 표 2의 제조조건으로 압연, 냉각하여 후강판을 제조하였다. 구체적으로 압연종료온도 780℃, 880℃, 냉각종료온도 400℃, 600℃로 수행하였다. 그리고 제조된 강판을 선상가열할 수 있는 사이즈로 절단하여 4개의 온도조건(600℃, 700℃, 800℃, 900℃)으로 곡가공을 위한 선상가열을 수행하였다.
The steel of the invention and the comparative steel were rolled and cooled under the manufacturing conditions shown in Table 2 to prepare a steel sheet. Concretely, the rolling finish temperature was 780 캜, 880 캜, and the cooling end temperature was 400 캜 and 600 캜. The prepared steel sheet was cut into a size capable of being heated in a line, and line heating for curving was performed under four temperature conditions (600 ° C, 700 ° C, 800 ° C and 900 ° C).
또한, 하기 표 3에는 상기 조건들로 제조된 모재의 기계적 물성 및 선상가열후의 기계적 물성을 나타내었다. In Table 3, the mechanical properties of the base material and the mechanical properties after the linear heating are shown.
모재의 인장강도는 강판의 전두께로부터 압연방향에 수직한 방향으로 JIS1B호 시편을 채취하여 상온에서 인장시험을 실시하여 인장강도를 측정하였다. 모재의 저온인성은 강판의 표면부 2mm직하 부위로부터 압연방향에 수직한 방향으로 시편을 채취하여 V-노치 시험편을 제작 후 -40℃에서 샤르피 충격 시험을 3회 실시하여 평균값을 표 3에 나타내었다. The tensile strength of the base material was measured by taking tensile test at room temperature by taking JIS1B specimen in the direction perpendicular to the rolling direction from the total thickness of the steel sheet. The low-temperature toughness of the base material was measured by taking a test specimen in a direction perpendicular to the rolling direction from a position immediately below the surface portion 2 mm from the surface of the steel sheet, preparing a V-notch test piece, and performing Charpy impact test three times at -40 ° C. The average value is shown in Table 3 .
또한, 강판 표면 10mm이내에서의 미세조직을 관찰하여 폴리고날 페라이트의 부피분율을 표 3에 기재하였다. 폴리고날 페라이트 외의 조직은 침상 페라이트였다.
Table 3 also shows the volume fraction of polygonal ferrite by observing the microstructure within 10 mm of the surface of the steel sheet. The structure other than polygonal ferrite was needle-shaped ferrite.
단, 상기 표 1에서 각 원소 함량의 단위는 중량%이다.
However, in Table 1, the unit of each element content is% by weight.
단, 상기 표 2에서 온도의 단위는 ℃이고, 냉각속도의 단위는 ℃/초이고, FM 시작온도는 미재결정역 압연 시작온도를 뜻하며, FM 종료온도는 미재결정역 압연 종료온도를 뜻한다.
In Table 2, the units of the temperature are in 占 폚, the unit of the cooling rate is in 占 폚 / second, the FM start temperature means the non-recrystallized reverse rolling start temperature, and the FM end temperature means the non-recrystallized reverse rolling end temperature.
단, 상기 표 3에서 항복강도 및 인장강도의 단위는 MPa이며, 충격인성의 단위는 J이다.
However, in Table 3, the unit of yield strength and tensile strength is MPa, and the unit of impact toughness is J.
상기 표 3에 모재의 기계적 물성 및 선상가열후 기계적 물성을 비교하여 보면, 본 발명에 따른 합금조성 및 제조조건을 모두 만족하는 발명예 1 내지 3의 경우, 항복강도, 인장강도 및 -40℃에서의 충격인성이 모두 목표한 물성에 만족하고 있다. When the mechanical properties of the base material and the mechanical properties after the linear heating were compared in Table 3, in Examples 1 to 3, which all satisfied the alloy composition and manufacturing conditions according to the present invention, the yield strength, tensile strength, And the impact toughness of all of them are satisfied with the desired properties.
구체적으로 선상가열 전후 모두 항복강도 500MPa 이상, 인장강도 600MPa이상, -40도 충격인성 100J이상의 특성을 보이고 있다.
Specifically, before and after heating, both the yield strength and the tensile strength are more than 500 MPa, the tensile strength is more than 600 MPa, and the impact strength is more than 100 J.
비교예 3은 C의 성분이 초과된 비교강 D를 이용한 경우로서, 강도는 목표 수준을 크게 상향하고 있으나 충격인성은 현저하게 감소하는 것을 알 수 있다. 이는 조대한 카바이드 형성으로 충격 테스트시 파괴의 원인이 되기 때문인 것으로 판단된다. In Comparative Example 3, the comparative steel D in which the component C was exceeded was used, and the strength was greatly increased to the target level, but the impact toughness was remarkably decreased. It is considered that this is due to the formation of coarse carbide which causes fracture in impact test.
비교예 4는 Mo 성분이 미달되는 비교강 E를 이용한 경우이고, 비교예 5는 Nb 성분이 미달되는 비교강 F를 이용한 경우로서, 강도가 현저하게 감소하고 충격인성도 저하된 것을 확인할 수 있다. 이는 고용된 Mo, Nb 양이 작고 선상가열 이후 석출물을 형성할 충분한 Mo, Nb의 양이 부족하기 때문이다. 만약 Mo, Nb가 과도하게 첨가될 경우 조대한 석출물로 인해 오히려 인성의 저하가 발생할 수 있기 때문에 본 발명에서 제어하는 범위로 첨가하여야 한다.
In Comparative Example 4, the comparative steel E in which the Mo component was not used was used, and in Comparative Example 5, the comparative steel F in which the Nb component was inferior was used, and it was confirmed that the strength was remarkably decreased and the impact toughness was also lowered. This is because the amount of dissolved Mo and Nb is small and the amount of Mo and Nb sufficient to form a precipitate after the linear heating is insufficient. If Mo and Nb are added excessively, toughness may be deteriorated due to coarse precipitates.
또한, 비교예 6은 Mn, Ni의 성분이 미달되는 비교강 G를 이용한 경우로서, 충분히 낮은 Ar3온도의 확보가 되지 않아 낮은 온도에서의 압연시 폴리고날 페라이트가 다량 형성되어 강도와 인성의 저하를 초래하였다.
In Comparative Example 6, comparative steel G in which the Mn and Ni components were not used was used. As a result, a sufficiently low Ar3 temperature could not be secured and a large amount of polygonal ferrite was formed during rolling at a low temperature, Respectively.
비교예 1의 경우 본 발명의 합금조성은 만족하였으나, 압연온도가 850℃를 초과하여 충격 인성이 열위하였다. 비교예 3의 경우 본 발명의 합금조성은 만족하였으나, 냉각 조건이 본 발명의 범위를 벗어나서 폴리고날 페라이트 분율의 증대로 인하여 선상가열 후 결정립 성장에 의한 강도와 인성의 저하가 발생하였다.
In the case of Comparative Example 1, the alloy composition of the present invention was satisfied, but the impact toughness was lowered at a rolling temperature exceeding 850 ° C. In the case of Comparative Example 3, the alloy composition of the present invention was satisfied, but the cooling conditions were out of the range of the present invention, and the strength and toughness of the crystal grains were lowered due to the increase of the polygonal ferrite fraction after the linear heating.
이상에서 본 발명의 실시예에 대하여 상세하게 설명하였지만 본 발명의 권리범위는 이에 한정되는 것은 아니고, 청구범위에 기재된 본 발명의 기술적 사상을 벗어나지 않는 범위 내에서 다양한 수정 및 변형이 가능하다는 것은 당 기술분야의 통상의 지식을 가진 자에게는 자명할 것이다.
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It will be obvious to those of ordinary skill in the art.
Claims (6)
표면 10mm이내에서의 미세조직은 부피분율로 80%이상의 침상 페라이트 및 20% 이하의 폴리고날 페라이트를 포함하고,
항복강도가 500MPa이상이며, 인장강도가 600MPa 이상이고, -40℃에서 충격인성이 100J 이상인 열간 저항성이 우수한 고강도 구조용 강판.
The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 0.03 to 0.07% of C, 0.05 to 0.2% of Si, 1.6 to 2.3% of Mn, 0.008% or less of P, 0.002% or less of S, , Ni: 1.4 to 2.3%, Mo: 0.08 to 0.2%, Nb: 0.01 to 0.025%, Ti: 0.008 to 0.02%, N: 0.001 to 0.008%
The microstructure within 10 mm of the surface contains 80% or more of needle-shaped ferrite and 20% or less of polygonal ferrite in a volume fraction,
High strength structural steel sheet excellent in thermal resistance with a yield strength of 500 MPa or more, a tensile strength of 600 MPa or more, and impact tensile strength of 100 J or more at -40 ° C.
상기 강판의 두께는 40mm이하인 것을 특징으로 하는 열간 저항성이 우수한 고강도 구조용 강판.
The method according to claim 1,
Wherein the thickness of the steel sheet is 40 mm or less.
상기 강판은 600~900℃로 선상가열하고 곡가공한 후의 항복강도가 500MPa이상이며, 인장강도가 600MPa 이상이고, -40℃에서 충격인성이 100J 이상인 것을 특징으로 하는 열간 저항성이 우수한 고강도 구조용 강판.
The method according to claim 1,
Wherein the steel sheet has a yield strength of 500 MPa or more, a tensile strength of 600 MPa or more, and an impact tensile strength of 100 J or more at -40 캜 after being linearly heated to 600 to 900 캜 and subjected to curving.
상기 재가열된 슬라브를 750~850℃에서 미재결정역 압연하는 단계; 및
미재결정역 압연 후 10℃/초 이상의 냉각속도로 380~440℃의 냉각종료온도까지 냉각단계;를 포함하는 열간 저항성이 우수한 고강도 구조용 강판의 제조방법.
The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 0.03 to 0.07% of C, 0.05 to 0.2% of Si, 1.6 to 2.3% of Mn, 0.008% or less of P, 0.002% or less of S, Reheating a slab containing 1.4 to 2.3% of Ni, 0.08 to 0.2% of Mo, 0.01 to 0.025% of Nb, 0.008 to 0.02% of Ti, 0.001 to 0.008% of N, and the balance Fe and unavoidable impurities;
Re-rolling the reheated slab at 750 to 850 ° C; And
And cooling the steel sheet to a cooling end temperature of 380 to 440 占 폚 at a cooling rate of 10 占 폚 / sec or more after the non-recrystallization reverse rolling.
상기 냉각된 강판을 600~900℃에서 선상가열한 후 곡가공하는 단계를 추가로 포함하는 것을 특징으로 하는 열간 저항성이 우수한 고강도 구조용 강판의 제조방법.
6. The method of claim 5,
Further comprising a step of heating the cooled steel sheet at a temperature of 600 to 900 DEG C and then performing a curving process.
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| JP2018533626A JP6718510B2 (en) | 2015-12-23 | 2016-12-21 | High-strength structural steel sheet excellent in hot resistance and manufacturing method thereof |
| PCT/KR2016/014964 WO2017111443A1 (en) | 2015-12-23 | 2016-12-21 | High-strength structural steel sheet excellent in hot resistance and manufacturing method thereof |
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| KR20170075851A (en) | 2017-07-04 |
| EP3395988A1 (en) | 2018-10-31 |
| JP6718510B2 (en) | 2020-07-08 |
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| WO2017111443A8 (en) | 2017-10-26 |
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