WO2018117507A1 - 저온인성이 우수한 저항복비 강판 및 그 제조방법 - Google Patents

저온인성이 우수한 저항복비 강판 및 그 제조방법 Download PDF

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WO2018117507A1
WO2018117507A1 PCT/KR2017/014411 KR2017014411W WO2018117507A1 WO 2018117507 A1 WO2018117507 A1 WO 2018117507A1 KR 2017014411 W KR2017014411 W KR 2017014411W WO 2018117507 A1 WO2018117507 A1 WO 2018117507A1
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steel sheet
low
less
temperature
toughness
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PCT/KR2017/014411
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English (en)
French (fr)
Korean (ko)
Inventor
김우겸
엄경근
방기현
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주식회사 포스코
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Priority to JP2019532672A priority Critical patent/JP6847225B2/ja
Priority to CN201780079094.8A priority patent/CN110100027B/zh
Priority to EP17882705.1A priority patent/EP3561107A4/en
Publication of WO2018117507A1 publication Critical patent/WO2018117507A1/ko

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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
    • C22C38/04—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
    • C21D1/26—Methods of annealing
    • C21D1/28—Normalising
    • 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
    • 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
    • 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
    • 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
    • C22C38/06—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
    • 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 steel sheet having excellent low temperature toughness and a method of manufacturing the same.
  • Steels with resistance yield ratio not only have excellent formability by increasing the difference between yield strength and tensile strength, but also delay the plastic deformation time until fracture can occur and absorb energy in this process to prevent collapse by external force. can do. In addition, even if there is a deformation, it is possible to repair before collapse, thereby preventing damage to property and life due to damage to the structure.
  • the technology of two phase organization of steel was developed. Specifically, the first phase is soft ferrite, and the remaining second phase is martensite, pearlite, or bainite, thereby implementing a resistance ratio.
  • the impact toughness due to the hard two phase and the carbon content is increased for the second phase, so that the toughness of the weld is degraded, thereby causing brittle fracture of the structure at low temperature.
  • Patent Literature 1 has been developed as a technique for securing both resistance ratio and low temperature impact toughness.
  • the microstructure includes 2-10 vol% of MA (martensite / austenite mixed structure) and 90 vol% or more of cyclic ferrite, thereby ensuring resistance ratio and excellent low temperature toughness.
  • Patent Document 1 it is possible to implement a yield ratio of about 0.8 but there is an insufficient problem to secure the seismic characteristics can not implement a sufficient resistance yield ratio. Therefore, there is a demand for development of a resistive yield ratio steel sheet excellent in low temperature toughness and a method of manufacturing the same which can ensure a lower yield ratio.
  • Patent Document 1 Korean Unexamined Patent Publication No. 2013-0076577
  • One aspect of the present invention is to provide a low-temperature toughness ratio steel sheet and a method of manufacturing the same.
  • One aspect of the present invention is by weight, C: 0.05 ⁇ 0.1%, Si: 0.3 ⁇ 0.7%, Mn: 1.0 ⁇ 2.0%, Al: 0.005 ⁇ 0.04%, Nb: 0.04 ⁇ 0.07%, Ti: 0.001 ⁇ 0.02 %, Cu: 0.05-0.4%, Ni: 0.1-0.6%, Mo: 0.01-0.08%, N: 0.001-0.008%, P: 0.015% or less, S: 0.003% or less, including remaining Fe and unavoidable impurities ,
  • the microstructure includes 80-92% ferrite and 8-20% MA (martensite / austenite mixed structure) as an area fraction, and the MA has excellent low-temperature toughness with an average size of 3 ⁇ m or less as measured by its equivalent diameter. It is related to bimetallic steel plate.
  • another aspect of the present invention is by weight%, C: 0.05 ⁇ 0.1%, Si: 0.3 ⁇ 0.7%, Mn: 1.0 ⁇ 2.0%, Al: 0.005 ⁇ 0.04%, Nb: 0.04 ⁇ 0.07%, Ti: 0.001 to 0.02%, Cu: 0.05 to 0.4%, Ni: 0.1 to 0.6%, Mo: 0.01 to 0.08%, N: 0.001 to 0.008%, P: 0.015% or less, S: 0.003% or less, remaining Fe and unavoidable impurities Heating the slab including 1050 to 1200 ° C;
  • T is a value measured in mm of the thickness of the hot rolled steel sheet.
  • the present invention it is possible to secure a resistance ratio and excellent low temperature toughness, and in particular, a low resistance ratio of 0.65 or less can be secured, thereby ensuring excellent seismic characteristics as well as formability. Accordingly, it can be applied to industrial fields such as construction, construction, and civil engineering requiring seismic characteristics, and also applicable to shipbuilding and marine structural steels.
  • Figure 2 is a photograph of the microstructure after the normalizing heat treatment of the test number 1 of the invention example.
  • Figure 3 is a photograph of the microstructure after the normalizing heat treatment of the test No. 9 of the comparative example.
  • Figure 4 is a photograph of the microstructure after the normalizing heat treatment of the test No. 10 of the comparative example.
  • the present inventors are able to secure a yield ratio of about 0.8 in the prior art, but the moldability can be secured to some extent, but it is not enough to realize a sufficient resistance ratio, and it is insufficient to secure seismic characteristics, and solved this problem. In order to study deeply.
  • the base material lacks the hardness difference from the MA as the ecuous ferrite, and the MA phase is grain boundary. It has been found that the formation of the structure at the core and the size of the MA are not sufficient to realize sufficient resistance ratio.
  • the microstructure of the base material as ferrite and uniformly distributing the fine MA phase in the ferrite grain boundary and the inside of the grain, a resistivity ratio of 0.65 or less can be ensured, and in order to secure such a structure, the structure before the normalizing heat treatment includes bainite. It was confirmed that control was required and the present invention was completed.
  • the resistive steel sheet having excellent low temperature toughness is wt%, C: 0.05 to 0.1%, Si: 0.3 to 0.7%, Mn: 1.0 to 2.0%, Al: 0.005 to 0.04%, and Nb: 0.04 ⁇ 0.07%, Ti: 0.001-0.02%, Cu: 0.05-0.4%, Ni: 0.1-0.6%, Mo: 0.01-0.08%, N: 0.001-0.008%, P: 0.015% or less, S: 0.003% or less , Remaining Fe and unavoidable impurities,
  • the microstructure includes 80-92% ferrite and 8-20% MA (martensite / austenite mixed structure) in an area fraction, and the MA has an average size of 3 ⁇ m or less measured in a circular equivalent diameter.
  • alloy composition of the present invention will be described in detail.
  • the unit of each element content below is weight% unless there is particular notice.
  • C is an element that causes solid solution strengthening and exists as carbonitride by Nb to secure tensile strength.
  • C content When the C content is less than 0.05%, the above effects are insufficient. On the other hand, if the C content is more than 0.1%, the MA is coarse and pearlite is formed, which may degrade the impact characteristics at low temperatures, and it is difficult to secure enough bainite. Therefore, it is preferable that C content is 0.05 to 0.1%.
  • the lower limit of the C content may be 0.055%, and the lower limit may be 0.06%.
  • the more preferable upper limit of C content may be 0.095%, and a more preferable upper limit may be 0.09%.
  • Si serves to deoxidize molten steel by assisting Al and is added to secure yield strength and tensile strength. Moreover, it is an element for controlling the fraction of MA desired by this invention.
  • Si content When the Si content is less than 0.3%, the above effects are insufficient. On the other hand, when the Si content is more than 0.7%, the impact characteristics may be degraded by coarsening of the MA, and the welding characteristics may be degraded. Therefore, it is preferable that Si content is 0.3 to 0.7%.
  • the lower limit of Si content may be 0.35%, and the lower limit may be 0.4%.
  • the more preferable upper limit of Si content may be 0.65%, and a more preferable upper limit may be 0.6%.
  • Mn contributes greatly to the strength increasing effect by solid solution strengthening and is an element that helps to form bainite.
  • Mn content is less than 1.0%, the above effects are insufficient. On the other hand, if excessively added, the toughness may be reduced due to formation of MnS inclusions and formation of the center portion, so the upper limit is 2.0%. Therefore, it is preferable that Mn content is 1.0 to 2.0%.
  • the lower limit of the Mn content may be 1.1%, and the lower limit may be 1.2%.
  • the more preferable upper limit of Si content may be 1.95%, and a more preferable upper limit may be 1.9%.
  • Al needs to be added 0.005% or more as a major deoxidizer of steel. However, when added in excess of 0.04%, the effect is saturated and may cause low temperature toughness by increasing the fraction and size of Al 2 O 3 inclusions.
  • Nb is an element that suppresses recrystallization during rolling or cooling by precipitation of solid solution or carbonitride, thereby making the structure fine and increasing the strength. Moreover, it is an element for controlling the fraction of MA desired by this invention.
  • Ti combines with oxygen or nitrogen to form precipitates, thereby inhibiting coarsening of tissues, contributing to miniaturization and improving toughness.
  • Cu is a component that does not significantly reduce the impact characteristics, and thus improves strength by solid solution and precipitation. In order to sufficiently improve the strength, it should be contained at 0.05% or more, but if the Cu content is more than 0.4%, surface cracks of the steel sheet due to Cu thermal shock may occur.
  • Ni is an element that can improve strength and toughness at the same time as the increase in content is not great, and is an element that helps to form bainite by decreasing the Ar3 temperature.
  • the Ni content is less than 0.1%, the above effects are insufficient. On the other hand, when the Ni content is more than 0.6%, the manufacturing cost may increase and the weldability may deteriorate.
  • Mo is an austenite stabilizing element that affects the amount of MA and plays a large role in improving the strength. It is also an element that prevents the drop in strength during heat treatment and helps to form bainite.
  • Mo is an expensive alloying element, there is a problem in that manufacturing cost increases when a large amount is added. Therefore, in the present invention, it is intended to secure MA by adding a large amount of Si, Nb and the like, and in the alloy composition of the present invention, Mo may be sufficiently secured by adding 0.01% or more. On the other hand, when the Mo content is more than 0.08%, there is a problem that the manufacturing cost increases and the base material toughness and post-weld toughness may be reduced.
  • N is an element that forms a precipitate with Ti, Nb, Al and the like to make the austenite structure fine when the slab is heated to help improve strength and toughness.
  • the N content is less than 0.001%, the above effects are insufficient.
  • the N content is more than 0.008%, it causes surface cracking at high temperatures, forms precipitates, and the remaining N remains in an atomic state, thereby reducing toughness.
  • P may cause grain boundary segregation as impurities and cause the steel to be withdrawn. Therefore, it is important to control the upper limit, and it is preferable to control it to 0.015% or less.
  • the lower limit of the P content is not particularly limited, but 0% may be excluded.
  • S as an impurity, mainly combines with Mn to form MnS inclusions, which are factors that inhibit low-temperature toughness. Therefore, it is important to control the upper limit, and in order to secure low temperature toughness, it is preferable to control S to 0.003% or less.
  • the lower limit of the S content is not particularly limited, but 0% may be excluded.
  • the remaining component of the present invention is iron (Fe).
  • impurities which are not intended from the raw material or the surrounding environment may be inevitably mixed, and thus cannot be excluded. Since these impurities are known to those skilled in the art, all of them are not specifically mentioned in the present specification.
  • the microstructure of the resistive steel sheet having excellent low temperature toughness includes 80 to 92% ferrite and 8 to 20% MA (martensite / austenite mixed structure) as an area fraction, and the MA is The average size measured by the circular equivalent diameter is 3 micrometers or less.
  • the fraction of microstructure means an area fraction unless otherwise specified.
  • Ferrite is to ensure basic toughness and strength, preferably 80% or more.
  • the upper limit is preferably 92%.
  • the ferrite does not contain the ecuous ferrite. This is because the Eccentric Ferrari cannot have sufficient resistance ratio because of its small hardness difference from MA.
  • the MA is less than 8%, it is difficult to secure a resistance ratio of 0.65 or less. If the MA is more than 20%, the impact toughness may be reduced, and the elongation may be reduced. In addition, when the average size measured by the equivalent circular diameter of the MA exceeds 3 ⁇ m, it is difficult to ensure the uniform distribution and resistance ratio of the MA is formed in the grain boundary grains.
  • the 100 ⁇ m straight line is drawn on the steel sheet of the present invention, as well as the MA fraction and size, it is preferable that 5 to 13 MAs are disposed on the straight line. That is, a plurality of straight lines are drawn up and down or left and right on a microstructure photograph having a size of 100 ⁇ m ⁇ 100 ⁇ m, and at this time, 5 to 13 MAs may be present on each line. This is because MA, which mainly causes breakage, is present in the grain boundary, and when the above conditions are satisfied, the MA is evenly distributed in the grain boundary and inside the grain, which is advantageous in securing a resistance ratio.
  • the ratio of the MA present in the ferrite grains and the MA present in the grain boundary may be 1: 3 to 1:10.
  • the ratio refers to the ratio of the number of MA, and by satisfying the ratio can be uniformly distributed so that the MA present in the ferrite grains becomes 0.5 to 5 area%.
  • the ferrite may have an average size of about 20 ⁇ m or less as measured by a circular equivalent diameter. This is because when the average size of the ferrite is greater than 20 ⁇ m, it may be difficult to secure sufficient toughness and strength.
  • the steel sheet according to the present invention is normalized (Normalizing) heat treatment and the microstructure of the steel sheet before the normalizing heat treatment may be 50 ⁇ 90 area% of bainite. Since the microstructure of the steel sheet before the heat treatment is bainite with carbides present therein, it is possible to distribute MA evenly in the grain boundary and the grain boundary after the heat treatment. Therefore, the microstructure of the steel sheet before the heat treatment is preferably 50 to 90 area%. Do.
  • the steel sheet according to the present invention has a yield ratio of 0.5 to 0.65, the low temperature impact characteristics at -40 °C may be 100J or more.
  • the yield ratio is 0.65 or less, which makes the difference between yield strength and tensile strength not only excellent in formability but also delays plastic deformation until breakage occurs and absorbs energy in this process to prevent collapse by external forces. Can be. Therefore, it can be preferably applied not only to the field of shipbuilding and marine structural steel but also to the industrial field requiring molding and seismic characteristics.
  • the yield strength of the steel sheet is 350 ⁇ 400MPa, tensile strength may be 600MPa or more.
  • t is a value measured in mm units of the hot rolled steel sheet.
  • the slab having the alloy composition described above is heated to 1050 ⁇ 1200 °C.
  • the heating temperature is more than 1200 °C austenite grains may be coarsened to lower the toughness, if less than 1050 °C Ti, Nb, etc. are not sufficiently dissolved, the strength may be reduced.
  • the heated slab is hot rolled to a finish rolling end temperature of 760 to 850 ° C. to obtain a hot rolled steel sheet.
  • the rolling temperature of the heat-treated steel is about 850 ⁇ 1000 °C general rolling is applied.
  • Re-crystallization rolling during hot rolling is necessary to refine the austenite grain size, and it is advantageous in terms of physical properties as the reduction ratio per pass increases.
  • Unrecrystallized rolling must be completed at a temperature of at least Ar3 of the steel and is at least about 760 ° C. More specifically, the finish rolling end temperature may be defined at 760 to 850 ° C. If the finish rolling finish temperature is higher than 850 °C, it is difficult to suppress the ferrite-pearlite transformation, and if it is less than 760 °C may cause non-uniformity of the microstructure in the thickness direction and to achieve a reduction in the amount of reduction by the load load of the rolling roll May not form tissue.
  • bainite structure is realized through cooling.
  • the initial structure of bainite is for uniform MA distribution after heat treatment.
  • MAs are mainly formed at grain boundaries, while in bainite structures, MAs are formed at both grain boundaries and inside grains.
  • the hot rolled steel sheet is cooled to 450 ° C. or less at a cooling rate of 5 ° C./s or more.
  • Bainite should be implemented to form fine and uniform MA. Cooling finish temperature and cooling rate are important factors for bainite formation. If the cooling finish temperature is higher than 450 °C, the grain size may become coarse and coarse carbide may cause coarse MA to be formed after heat treatment, which may lead to deterioration of toughness and secure more than 50 area% of bainite. Difficult to do
  • the cooling rate is less than 5 °C / s, the fine structure of the needle-like ferrite or ferrite + pearlite is formed in a large amount may cause a decrease in strength. There is a problem that the yield can be reduced, and it is difficult to secure 50 area% or more of bainite.
  • the microstructure of the cooled hot-rolled steel sheet may be 50 ⁇ 90 area% bainite. Since the microstructure of the steel sheet before the heat treatment is bainite with carbides present therein, it is possible to distribute MA evenly in the grain boundary and the grain boundary after the heat treatment. Therefore, the microstructure of the steel sheet before the heat treatment is preferably 50 to 90 area%. Do.
  • T is a value measured in mm units of the hot rolled steel sheet.
  • the normalizing temperature is less than 850 ° C or the holding time is less than (1.3t + 10) minutes, the reusability of cementite and pearlite in pearlite and bainite is difficult to re-use, resulting in a decrease in the amount of C employed, resulting in less strength and ultimately remaining The hardened phase remains coarse.
  • Table 3 below describes the bainite fraction and mechanical properties of the steel sheet before the normalizing heat treatment.
  • Table 4 below describes the MA fraction of the steel sheet after the normalizing heat treatment, the average MA size, the number of MAs over 100 ⁇ m, and the mechanical properties thereof.
  • MA it was ferrite, and the average grain size of the ferrite was 20 ⁇ m or less and was not separately described.
  • the average MA size is the average size measured by the equivalent diameter, and the number of MAs on a 100 ⁇ m line is the number of MAs on each line by drawing 10 straight lines up and down or left and right on a 100 ⁇ m X 100 ⁇ m microstructure photograph. After measuring the average number was described.
  • the unit of each element content in Table 1 is weight%.
  • Invention steels A to D are steel sheets satisfying the component range defined by the present invention, and comparative steels E to G are steel sheets which do not satisfy the component range defined by the present invention.
  • Comparative steel E is less than C content
  • comparative steel F is less than Si
  • comparative steel G is less than Mn content.
  • the MA fraction is higher than the comparative example.
  • Table 3 by securing a high bainite fraction before the normalizing heat treatment, the grains of the initial bainite structure, carbides in the grains are transformed into fine MA. It can also be seen that the yield ratio is determined by the formation of such fine MAs.

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  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
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  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)
PCT/KR2017/014411 2016-12-21 2017-12-08 저온인성이 우수한 저항복비 강판 및 그 제조방법 WO2018117507A1 (ko)

Priority Applications (3)

Application Number Priority Date Filing Date Title
JP2019532672A JP6847225B2 (ja) 2016-12-21 2017-12-08 低温靭性に優れた低降伏比鋼板及びその製造方法
CN201780079094.8A CN110100027B (zh) 2016-12-21 2017-12-08 具有优异的低温韧性的低屈服比的钢板及其制造方法
EP17882705.1A EP3561107A4 (en) 2016-12-21 2017-12-08 LOW ELASTICITY STEEL SHEET HAVING EXCELLENT LOW TEMPERATURE TENACITY AND MANUFACTURING METHOD THEREOF

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KR1020160176126A KR101917451B1 (ko) 2016-12-21 2016-12-21 저온인성이 우수한 저항복비 강판 및 그 제조방법
KR10-2016-0176126 2016-12-21

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JP7445686B2 (ja) * 2020-01-22 2024-03-07 ポスコ カンパニー リミテッド 黒鉛化熱処理用線材と黒鉛鋼及びその製造方法
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CN113061811A (zh) * 2021-03-17 2021-07-02 攀钢集团江油长城特殊钢有限公司 一种lng船用结构钢及其制备方法

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