WO2017086745A1 - High-strength cold rolled steel sheet having excellent shear processability, and manufacturing method therefor - Google Patents

High-strength cold rolled steel sheet having excellent shear processability, and manufacturing method therefor Download PDF

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WO2017086745A1
WO2017086745A1 PCT/KR2016/013362 KR2016013362W WO2017086745A1 WO 2017086745 A1 WO2017086745 A1 WO 2017086745A1 KR 2016013362 W KR2016013362 W KR 2016013362W WO 2017086745 A1 WO2017086745 A1 WO 2017086745A1
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steel sheet
rolled steel
cold rolled
high strength
relation
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PCT/KR2016/013362
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French (fr)
Korean (ko)
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김성일
서석종
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주식회사 포스코
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Priority to JP2018525787A priority Critical patent/JP6684905B2/en
Priority to US15/772,644 priority patent/US20190136339A1/en
Priority to CN201680067955.6A priority patent/CN108350550B/en
Publication of WO2017086745A1 publication Critical patent/WO2017086745A1/en

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    • C—CHEMISTRY; METALLURGY
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    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/02—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling heavy work, e.g. ingots, slabs, blooms, or billets, in which the cross-sectional form is unimportant ; Rolling combined with forging or pressing
    • B21B1/026—Rolling
    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • B21B—ROLLING OF METAL
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    • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
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    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
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    • C21D8/0426—Hot rolling

Definitions

  • the present invention relates to a high strength cold rolled steel sheet excellent in shear workability and a method of manufacturing the same.
  • the crack generation by the shearing process is not only small, but the crack propagation due to the frictional heat must be suppressed, and high strength and high hardness are required.
  • Patent Document 1 As the conventional high strength cold rolled steel sheet for friction plates or hardness guarantee, as described in Patent Document 1, a technique for performing annealing heat treatment after cold rolling using a recovery annealing method for a medium containing carbon steel or various alloying elements. In addition, a method using a spheroidizing heat treatment process is commonly used for high carbon steel, and Patent Document 2 proposes a technique using two cold rolling methods of cold rolling, annealing, and cold rolling.
  • a high strength steel sheet using the recovery annealing method has a problem that it is difficult to manufacture a steel having a high strength, the technique of spheroidizing heat treatment using high carbon steel and the two cold rolling technology has a problem that the manufacturing cost is high.
  • alloy components such as C, Si, Mn, Mo, Cr, which are mainly used to manufacture cold rolled high strength steel sheet, are effective to improve the strength of the steel sheet by solid solution strengthening effect. It causes unevenness of stone and microstructure. In particular, the hardenability of the steel is increased during cooling, which significantly delays the ferrite phase transformation, generates low-temperature phases (martensite and austenite phases), uneven grain boundaries, and increases cracking during shearing. It propagates easily and causes defects.
  • Patent Document 1 Application No. KR 1998-0059809
  • Patent Document 2 Application No. DE 2005-10031462
  • An object of the present invention is to provide a high strength cold rolled steel sheet having excellent shearing property capable of suppressing cracking caused by shearing and cracking by frictional heat, and a method of manufacturing the same.
  • One aspect of the present invention is by weight, C: 0.05 ⁇ 0.10%, Si: 0.01 ⁇ 0.5%, Mn: 1.2 ⁇ 2.0%, Al: 0.01 ⁇ 0.1%, Cr: 0.005 ⁇ 0.3%, B: 0.0003 ⁇ 0.0010 %, Mo: 0.005-0.2%, P: 0.001-0.05%, S: 0.001-0.01%, N: 0.001-0.01%, Nb: 0.005-0.08%, Ti: 0.005-0.13%, V: 0.005-0.2%
  • the present invention relates to a high strength cold rolled steel sheet including shear Fe and unavoidable impurities, satisfying the following relations (1) and (2), and having excellent shearing property including at least one of carbide, nitride, and carbonitride.
  • Another aspect of the invention is by weight, C: 0.05-0.10%, Si: 0.01-0.5%, Mn: 1.2-2.0%, Al: 0.01-0.1%, Cr: 0.005-0.3%, B: 0.0003- 0.0010%, Mo: 0.005 to 0.2%, P: 0.001 to 0.05%, S: 0.001 to 0.01%, N: 0.001 to 0.01%, Nb: 0.005 to 0.08%, Ti: 0.005 to 0.13%, V: 0.005 to 0.2 Heating the steel slab containing%, remaining Fe and inevitable impurities, and satisfying the following relations (1) and (2) to 1200 to 1350 ° C; Hot rolling the heated steel slab at a temperature in the range of 850 ° C to 1150 ° C; Cooling and winding to a temperature in the range of 550 to 750 ° C. after the hot rolling; And it relates to a method for producing a high strength cold rolled steel sheet having excellent shear workability comprising the step of cold rolling at 60 ⁇ 70% cold reduction
  • each element symbol represents the weight% of the alloy element.
  • a high strength cold rolled steel sheet having excellent shearing property and a method of manufacturing the same, which can secure high strength and high hardness, and can suppress cracking caused by shearing and cracking caused by frictional heat.
  • 1 is a graph showing the values of relation (1) and relation (2) of the embodiments.
  • the high strength cold rolled steel sheet having excellent shearability according to the present invention is a weight%, C: 0.05 ⁇ 0.10%, Si: 0.01 ⁇ 0.5%, Mn: 1.2 ⁇ 2.0%, Al: 0.01 ⁇ 0.1%, Cr: 0.005 ⁇ 0.3% , B: 0.0003 to 0.0010%, Mo: 0.005 to 0.2%, P: 0.001 to 0.05%, S: 0.001 to 0.01%, N: 0.001 to 0.01%, Nb: 0.005 to 0.08%, Ti: 0.005 to 0.13%, V: 0.005-0.2%, remaining Fe and inevitable impurities, satisfying the following relations (1) and (2), and include at least one of carbide, nitride and carbonitride.
  • the C is the most economical and effective element to strengthen the steel, and as the amount added increases the precipitation strengthening effect or the fraction of bainite phase, the tensile strength is increased. If the content is less than 0.05%, the reaction for forming precipitates with Ti, Nb, V and the like is small, and the precipitation strengthening effect is low. On the other hand, when the carbon content exceeds 0.10% by weight, coarse carbides are likely to occur at grain boundaries, and fine shear occurs at coarse carbide interfaces during shearing, resulting in inferior shearing properties. Therefore, the content of C is preferably contained in 0.05 to 0.10% by weight.
  • the Si deoxidizes molten steel and has a solid solution strengthening effect, and is advantageous in improving moldability by delaying coarse carbide formation.
  • the content is less than 0.01%, the effect of delaying the formation of carbides is small, so that it is difficult to improve the formability.
  • the content exceeds 0.5%, the red scale due to Si is formed on the surface of the steel sheet during hot rolling. In addition, there is a problem that the ductility and weldability is also reduced. Therefore, the content of Si is preferably contained in 0.01 ⁇ 0.5%.
  • Mn is an effective element to solidify the steel and increases the hardenability of the steel to facilitate the formation of the bainite phase in the weld heat affected zone after welding.
  • the content is less than 1.2%, the above effect by addition cannot be sufficiently obtained.
  • the content exceeds 2.0%, the hardenability is greatly increased, the ferrite phase transformation is delayed, and the precipitation strengthening effect is also reduced, and the segregation part is greatly developed at the center of thickness during slab casting in the casting process, and when cooled after hot rolling In the non-uniform microstructure in the thickness direction, the occurrence of cracks during shearing is greatly increased. Therefore, the content of Mn is preferably included in 1.2 to 2.0%.
  • the Mo strengthens the steel and increases the hardenability of the steel, thereby increasing the strength of the steel.
  • the content is less than 0.005%, the above effect may not be obtained, and if the content exceeds 0.2%, ferrite phase transformation is delayed due to excessive increase in quenchability, and the precipitation strengthening effect is also reduced. It is also economically disadvantageous and also detrimental to weldability. Therefore, the content of Mo is preferably limited to 0.01 ⁇ 0.2%.
  • the Cr increases the strength of the steel by solidifying the steel and increasing the hardenability of the steel. However, if the content is less than 0.005%, the above effect may not be obtained. If the content exceeds 0.3%, the ferrite transformation is excessively delayed, the elongation is inferior to martensite phase formation, and the precipitation strengthening effect is also reduced. In addition, segregation at the center of thickness is greatly developed similarly to Mn, and inferior shear processing property by uneven thickness direction microstructure. Therefore, the content of Cr is preferably limited to 0.005 to 0.3%.
  • B is an element that improves the hardenability even when a small amount is added to the steel.
  • B may be segregated at the austenite grain boundary at high temperature to stabilize the grain boundary and improve impact resistance, but if it is less than 0.0003%, It is not enough to get the effect.
  • the content is added more than 0.0010%, the recrystallization during hot rolling delayed to increase the elongated grains and the ferrite phase transformation during cooling causes the microstructure to be uneven.
  • the precipitation strengthening effect is also reduced to obtain the desired strength, and the non-uniformity of the initial hot rolled plate microstructure is a disadvantage in the present invention because it causes local stress concentration during cold rolling. Therefore, the content of B is preferably limited to 0.0003 ⁇ 0.0010%.
  • P has a solid solution strengthening effect and a ferrite transformation promoting effect.
  • it is economically disadvantageous to manufacture the content to less than 0.001%, and it is economically disadvantageous and insufficient to obtain strength. If the content exceeds 0.05%, brittleness due to intergranular segregation occurs and fine cracking occurs during shearing. It is easy to do and deteriorates ductility and impact resistance significantly. Therefore, the P is preferably limited to 0.001 to 0.05%.
  • S is an impurity present in steel, and if its content exceeds 0.01%, it combines with Mn to form a non-metallic inclusion. Therefore, when the steel is cut, fine cracks are likely to occur and the elongation flange and impact resistance are greatly reduced. In addition, in order to manufacture less than 0.001%, the steelmaking industry takes a lot of time and productivity is reduced. Therefore, it is preferable to limit the content to 0.001 to 0.01%.
  • Al is a component mainly added for deoxidation. If the content is less than 0.01%, the addition effect is insufficient. On the other hand, if the content exceeds 0.1%, AlN is formed by combining with nitrogen, which is likely to cause corner cracks in the slab during casting, and defects due to inclusions are easily generated at edges of the hot rolled sheet. In addition, there may be a problem that the surface quality is lowered due to the occurrence of surface defects during cold rolling after hot rolling. Therefore, it is preferable to limit the content to 0.01 to 0.1%.
  • N is a representative solid solution strengthening element together with C to form coarse precipitates together with Ti, Al and the like.
  • the solid solution strengthening effect of N is better than carbon, but the problem of toughness is greatly reduced as the amount of N in the steel increases.
  • it is preferable to limit the content to 0.001 to 0.01%.
  • Ti is a representative precipitation enhancing element and forms coarse TiN in steel with strong affinity with N.
  • TiN has an effect of suppressing grain growth during heating for hot rolling.
  • Ti remaining after reacting with nitrogen is dissolved in carbon to bond with carbon to form TiC precipitates, which is a useful component for improving the strength of steel. Therefore, if the Ti content is less than 0.005%, the above effect cannot be obtained. If the Ti content exceeds 0.13%, there is a problem of inferior shear workability during shear processing due to the generation of coarse TiN. Therefore, in the present invention, it is preferable to limit the content to 0.005 to 0.13%.
  • Nb is a representative precipitation enhancing element, and is precipitated during hot rolling, and is effective in improving the strength and impact toughness of the steel by refining grains by delaying recrystallization.
  • the Nb content is less than 0.005%, the above effect cannot be sufficiently obtained.
  • the Nb content exceeds 0.08%, the shearability is inferior due to the formation of stretched grains and coarse composite precipitates due to excessive recrystallization during hot rolling. There is a problem to let. Therefore, in the present invention, it is preferable to limit the content to 0.005 ⁇ 0.08%.
  • V is a representative precipitation strengthening element together with Nb and Ti, and is effective in improving the strength of steel by forming a precipitate after winding. Therefore, if the content of V is less than 0.005%, the above effects cannot be sufficiently obtained. If the content of V is more than 0.2%, the shear workability is inferior due to the formation of coarse complex precipitates, and it is economically disadvantageous. Therefore, in the present invention, it is preferable to limit the content to 0.005 to 0.2%.
  • 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 alloy composition must satisfy the following relations (1) and (2) to uniformly form the microstructure of the steel after hot rolling to suppress cracking during shearing after cold rolling.
  • each element symbol represents the weight% of the alloy element.
  • the relation (1) is related to the hardenability and segregation of the steel, taking into account the effect of strengthening the solid solution of the steel and the nonuniformity of the microstructure.
  • the relation (1) is less than 2.0, there is a problem that a sufficient high strength is not obtained because the solid solution strengthening effect of the steel is insufficient. On the other hand, if the relation (1) exceeds 2.5, there is a problem that the microstructure in the thickness direction of the steel is formed non-uniformly, delaying the ferrite phase transformation to reduce the precipitation strengthening effect of the steel.
  • relation (1) may be 2.0-2.5.
  • the relation (2) restricts the components related to the formation of precipitates in the steel, and since the formation of the precipitates is correlated with the contents of Ti, Nb, V, C, and N in the composition, the addition amount of Ti, Nb, and V alloy elements is defined as C, It is intended to set according to the content of N.
  • the relation (2) is less than 0.2, the precipitation strengthening effect is significantly reduced, and thus the desired strength and hardness value cannot be obtained. If the ratio exceeds 0.5, the yield strength is greatly increased due to the formation of a large amount of fine precipitates. There is a problem that the precipitate is formed non-uniformly in the direction of the plate thickness, so that the occurrence of cracks during shearing after cold rolling is severe.
  • relation (2) may be 0.2-0.5.
  • the cold rolled steel sheet according to the present invention is obtained by cold rolling a hot rolled sheet having a microstructure of ferrite and fine perlite, and thus has a microstructure (Full Hard microstructure) that is severely deformed in the rolling direction. At this time, each phase cannot be specified in the microstructure of the cold rolled steel sheet.
  • the hot rolled steel sheet before cold rolling has an area fraction of more than 90%, a fine pearlite phase of less than 5%, and other bainite phases. Can be included.
  • the high strength cold rolled steel sheet having excellent shearability according to the present invention includes at least one of carbide, nitride and carbonitride.
  • carbide nitride and carbonitride.
  • the average size of the carbide, nitride and carbonitride is preferably 10 ⁇ 50nm.
  • the yield strength of the hot rolled sheet is excessively increased, so that local work hardening deviation occurs easily during cold rolling, and cracks occur during shearing and heat treatment of the cold rolled sheet.
  • the cold rolled steel sheet may have a tensile strength of 1200 MPa or more and a hardness value (Micro-Vickers) of 340 Hv or more. By satisfying the tensile strength and the hardness value, it can be preferably applied to the friction plate of the automobile automatic transmission.
  • the crack generated during the shearing of the cold rolled steel sheet preferably has a maximum crack length of 1 mm or less.
  • the maximum crack length is a result of measuring the maximum crack length in the cross section after punching under a condition of Clearance 6% using a circular mold having a diameter of 10 mm, followed by heat treatment at 200 ° C. for 1 hour.
  • the crack generation amount is increased and the crack can be easily propagated during shearing, and if the temperature rises by frictional heat, the crack can be more easily propagated.
  • a method of manufacturing a high strength cold rolled steel sheet having excellent shearing property includes heating a steel slab satisfying the above-described alloy composition to 1200 to 1350 ° C .; Hot rolling the heated steel slab at a temperature in the range of 850 ° C to 1150 ° C; Cooling and winding to a temperature in the range of 550 to 750 ° C. after the hot rolling; And pickling after the winding to cold roll at a cold reduction rate of 60 to 70%.
  • the steel slab that satisfies the alloy composition described above is heated to 1200 to 1350 ° C.
  • the reheating temperature is preferably limited to 1200 to 1350 ° C.
  • the steel slab may be produced in a process in which the continuous casting process and the hot rolling process are directly connected.
  • the continuous casting process and the hot rolling process as described above can be preferably applied to the process directly connected.
  • the heated steel slabs are hot rolled at a temperature in the range of 850-1150 ° C.
  • Initiating hot rolling at a temperature higher than 1150 ° C. increases the temperature of the hot rolled steel sheet, resulting in coarse grain size and inferior surface quality of the hot rolled steel sheet.
  • the hot rolling is terminated at a temperature lower than 850 ° C., the development and high yield ratio of the stretched grains may be attained due to excessive recrystallization delay, resulting in inferior cold rolling and poor shearing properties.
  • the bainite phase and martensite phase in the steel are formed, and the material of the steel may become thermally damaged. If it is wound up to more than 750 °C, coarse ferrite grains are formed and coarse carbide and nitride are formed. It can become easy and the material of steel may be inferior.
  • the average cooling rate is less than 10 °C / sec during cooling coarse ferrite grains are formed may be a non-uniform microstructure, if the average cooling rate is more than 70 °C / sec, bainite phase is easily formed and the thickness direction of the plate
  • the microstructure into the furnace may also be non-uniform, leading to inferior shearing workability of the steel.
  • the cold reduction ratio is less than 60%, it is difficult to obtain sufficient work hardening effect and thus it is difficult to secure the strength and hardness of the steel.
  • the cold reduction rate exceeds 70%, the edge quality of the steel is deteriorated, and the shear workability may be inferior.
  • the cold rolled steel sheet manufactured by the above-described manufacturing method can secure high strength and high hardness, as well as suppress cracking caused by shearing and cracking caused by frictional heat.
  • the cold rolled steel sheet produced by the above production method includes at least one of carbide, nitride and carbonitride, the average size of the carbide, nitride and carbonitride may be 10 ⁇ 50nm.
  • the tensile strength is 1200MPa or more and the hardness value may be more than 340Hv, cracks generated during shearing may have a maximum crack length of 1mm or less.
  • the steel slab having the component composition shown in Table 1 below was heated to 1250 ° C, and a cold rolled steel sheet was manufactured by applying the production conditions shown in Table 2 below. At this time, the cooling rate after the hot rolling was set to 20 ⁇ 30 °C / sec.
  • Table 3 shows the mechanical properties and microstructure observation results of the invention and comparative examples.
  • TS, Hv, and the maximum crack length mean the tensile strength and micro-ickers hardness value of the cold rolled sheet, respectively, and the maximum crack length was punched under the condition of Clearance 6% using a circular mold having a diameter of 10 mm, and then 200 ° C. This is the result of measuring the maximum crack length in cross section after heat treatment for 1 hour at. The length of the cracks was measured from the results of observation of optical magnification 100 times.
  • the size of carbides, nitrides and carbonitrides formed in steel were analyzed for hot rolled plates before cold rolling.
  • Carbide, nitride and carbonitride with an average size of 10 ⁇ 50nm formed in steel are not changed in size and fraction by cold rolling, and it is difficult to accurately observe the size and fraction in the microstructure that is severely deformed after cold rolling.
  • the hot rolled plate was analyzed.
  • the average size of carbides, nitrides and carbonitrides was determined from the results measured using a transmission electron microscope.
  • the measurement of carbides and nitrides with an average size of 100 nm or more was used for the measurement of 50,000 magnification, and the results of 100,000 magnifications were used for precipitates with an average size of less than 100 nm.
  • the tensile test was taken as the test piece collected based on JIS5 standard based on 0 degree direction with respect to the rolling direction of a rolled sheet material.
  • Comparative Examples 1 and 2 did not satisfy both the relational formula (1) and the relational formula (2), and Comparative Example 1 did not satisfy the C content. Both comparative examples did not achieve sufficient solid solution effect, and exceeded the upper limit of relation (2) due to relatively low C content and relatively excessive Ti, Nb, and V. Therefore, the size of carbon, nitride and precipitates formed in the steel was fine, but the strength of the steel was not sufficiently secured.
  • Comparative Example 2 as a result of giving the cold reduction ratio exceeding the range controlled in the present invention, it can be confirmed that the cracks in the shearing surface after the punching process occurs slightly worse, the quality of the shearing surface is inferior.
  • Comparative Examples 3 and 5 did not satisfy the relational expression (1).
  • Comparative Example 3 segregation was increased at the center of the steel beyond the scope of the relational expression (1).
  • Comparative Example 5 had a low Mn, Cr, B content and the like, segregation was less, so the quality of the shearing surface was very good, but sufficient solid-solution strengthening effect was not obtained, so that the target strength and hardness could not be obtained.
  • Comparative Examples 4 and 6 did not satisfy the relation (2).
  • Comparative Example 4 surplus C remained to form coarse precipitates and carbides, and the precipitation strengthening effect was insufficient to obtain the target strength and hardness values. It was.
  • Comparative Example 6 a large amount of fine precipitates were formed in excess of the scope of the formula (2) and high strength was obtained, but cracks were severe in the shear processing part.
  • Comparative Examples 7, 8, 9 and 10 are steels manufactured for the purpose of tensile strength of 1350 MPa or more and hardness value of 355 Hv or more after cold rolling. Comparative Example 7 does not satisfy the relational formula 1, but has high cold rolling properties. Secured. However, due to the high cold rolling rate, cracking was more severe in the shearing part.

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Abstract

One aspect of the present invention relates to a high-strength cold rolled steel sheet having excellent shear processability, comprising, by wt%, 0.05-0.10% of C, 0.01-0.5% of Si, 1.2-2.0% of Mn, 0.01-0.1% of Al, 0.005-0.3% of Cr, 0.0003-0.0010% of B, 0.005-0.2% of Mo, 0.001-0.05% of P, 0.001-0.01% of S, 0.001-0.01% of N, 0.005-0.08% of Nb, 0.005-0.13% of Ti, 0.005-0.2% of V, and the balance of Fe and inevitable impurities, satisfying the following relations (1) and (2), and containing one or more of a carbide, a nitride and a carbonitride. Relation (1): 2.0 ≤ [Mn]+2.5[Mo]+1.5[Cr]+300[B] ≤ 2.5 Relation (2): 0.2 ≤ ([Nb]/93+[Ti]/48+[V]/51)/([C]/12+[N]/14) ≤ 0.5 (In relations (1) and (2), each element symbol represents the wt% of the corresponding alloying element.)

Description

전단가공성이 우수한 고강도 냉연강판 및 그 제조방법High strength cold rolled steel with excellent shearing process and manufacturing method
본 발명은 전단가공성이 우수한 고강도 냉연강판 및 그 제조방법에 관한 것이다.The present invention relates to a high strength cold rolled steel sheet excellent in shear workability and a method of manufacturing the same.
자동차 자동변속기의 마찰판 용도 등에 사용하기 위해서는 전단 가공에 의한 균열발생이 적을 뿐만 아니라, 마찰열에 의한 균열 전파가 억제되어야 하며, 고강도 및 고경도가 요구된다.In order to use the friction plate of the automobile automatic transmission, the crack generation by the shearing process is not only small, but the crack propagation due to the frictional heat must be suppressed, and high strength and high hardness are required.
종래의 마찰판용 또는 경도보증용 고강도 냉연강판은 특허문헌 1에 제시된 바와 같이, 중탄소강 또는 다양한 합금원소를 포함한 강에 대해 회복소둔법을 이용하여 냉간압연 후 소둔열처리를 하는 기술이 적용되었다. 또한, 고탄소강에 대하여 구상화 열처리 공정을 이용하는 방법이 보편적으로 사용되고 있으며, 특허문헌 2에서는 냉간압연-소둔-냉간압연의 2회 냉간압연법을 이용하는 기술이 제안되었다.As the conventional high strength cold rolled steel sheet for friction plates or hardness guarantee, as described in Patent Document 1, a technique for performing annealing heat treatment after cold rolling using a recovery annealing method for a medium containing carbon steel or various alloying elements. In addition, a method using a spheroidizing heat treatment process is commonly used for high carbon steel, and Patent Document 2 proposes a technique using two cold rolling methods of cold rolling, annealing, and cold rolling.
그러나, 회복소둔법을 이용한 고강도강판은 높은 강도를 갖는 강을 제조하기 어려운 문제점이 있으며, 고탄소강을 이용하여 구상화 열처리하는 기술과 2회 냉간압연는 기술은 제조비용이 많이 소요되는 문제점이 있다. However, a high strength steel sheet using the recovery annealing method has a problem that it is difficult to manufacture a steel having a high strength, the technique of spheroidizing heat treatment using high carbon steel and the two cold rolling technology has a problem that the manufacturing cost is high.
또한, 냉간압연된 고강도강판을 제조하기 위해 주로 활용하는 C, Si, Mn, Mo, Cr 등의 합금성분은 고용강화효과에 의해 강판의 강도를 향상시키는데 효과적이지만 필요 이상으로 첨가되면 합금성분의 편석과 미세조직의 불균일을 초래한다. 특히, 냉각시 강의 경화능이 증가되어 페라이트 상변태가 크게 지연되며 저온상(마르텐사이트와 오스테나이트상)이 발생하고 결정립계가 불균일해져 전단가공시 균열 발생이 증가하게 되고, 사용 중 마찰열이 발생하면 균열이 쉽게 전파되어 결함이 발생하게 된다. In addition, alloy components such as C, Si, Mn, Mo, Cr, which are mainly used to manufacture cold rolled high strength steel sheet, are effective to improve the strength of the steel sheet by solid solution strengthening effect. It causes unevenness of stone and microstructure. In particular, the hardenability of the steel is increased during cooling, which significantly delays the ferrite phase transformation, generates low-temperature phases (martensite and austenite phases), uneven grain boundaries, and increases cracking during shearing. It propagates easily and causes defects.
또한, 추가적인 강도향상을 위해 활용되는 Ti, Nb, V 등의 합금성분이 부적절하게 첨가되면, 결정립계에서 조대한 탄화물, 질화물 및 석출물이 형성되어 전단가공시 균열 발생량이 증가하고 전단가공시 쉽게 균열이 전파하게 되는 문제가 있다. 더욱이, 전단가공된 부위는 사용 중 마찰열이 발생할 경우 균열의 전파가 더욱 용이하게 발생하는 문제가 있다.In addition, when improperly added alloying elements such as Ti, Nb, and V, which are used for additional strength, coarse carbides, nitrides, and precipitates are formed at grain boundaries, resulting in increased cracking during shearing and easy cracking during shearing. There is a problem of propagation. In addition, the sheared portion has a problem that the propagation of cracks more easily occurs when frictional heat occurs during use.
(선행기술문헌)(Prior art document)
(특허문헌 1) 출원번호 KR 1998-0059809(Patent Document 1) Application No. KR 1998-0059809
(특허문헌 2) 출원번호 DE 2005-10031462(Patent Document 2) Application No. DE 2005-10031462
본 발명은 전단가공에 의한 균열 및 마찰열에 의한 균열을 억제할 수 있는 전단가공성이 우수한 고강도 냉연강판 및 그 제조방법을 제공하고자 한다.An object of the present invention is to provide a high strength cold rolled steel sheet having excellent shearing property capable of suppressing cracking caused by shearing and cracking by frictional heat, and a method of manufacturing 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.In addition, the subject of this invention is not limited to the content mentioned above. The problem of the present invention will be understood from the general contents of the present specification, those skilled in the art will have no difficulty understanding the additional problem of the present invention.
본 발명의 일 측면은 중량%로, C: 0.05~0.10%, Si: 0.01~0.5%, Mn: 1.2~2.0%, Al: 0.01~0.1%, Cr: 0.005~0.3%, B: 0.0003~0.0010%, Mo: 0.005~0.2%, P: 0.001~0.05%, S: 0.001~0.01%, N: 0.001~0.01%, Nb: 0.005~0.08%, Ti: 0.005~0.13%, V: 0.005~0.2%, 나머지 Fe 및 불가피한 불순물을 포함하며, 하기 관계식 (1) 및 관계식 (2)를 만족하고, 탄화물, 질화물 및 탄질화물 중 1이상을 포함하는 전단가공성이 우수한 고강도 냉연강판에 관한 것이다.One aspect of the present invention is by weight, C: 0.05 ~ 0.10%, Si: 0.01 ~ 0.5%, Mn: 1.2 ~ 2.0%, Al: 0.01 ~ 0.1%, Cr: 0.005 ~ 0.3%, B: 0.0003 ~ 0.0010 %, Mo: 0.005-0.2%, P: 0.001-0.05%, S: 0.001-0.01%, N: 0.001-0.01%, Nb: 0.005-0.08%, Ti: 0.005-0.13%, V: 0.005-0.2% The present invention relates to a high strength cold rolled steel sheet including shear Fe and unavoidable impurities, satisfying the following relations (1) and (2), and having excellent shearing property including at least one of carbide, nitride, and carbonitride.
본 발명의 다른 일 측면은 중량%로, C: 0.05~0.10%, Si: 0.01~0.5%, Mn: 1.2~2.0%, Al: 0.01~0.1%, Cr: 0.005~0.3%, B: 0.0003~0.0010%, Mo: 0.005~0.2%, P: 0.001~0.05%, S: 0.001~0.01%, N: 0.001~0.01%, Nb: 0.005~0.08%, Ti: 0.005~0.13%, V: 0.005~0.2%, 나머지 Fe 및 불가피한 불순물을 포함하며, 하기 관계식 (1) 및 관계식 (2)를 만족하는 강 슬라브를 1200~1350℃로 가열하는 단계; 상기 가열된 강 슬라브를 850~1150℃의 범위의 온도에서 열간압연하는 단계; 상기 열간압연 후 550~750℃의 범위의 온도까지 냉각하고 권취하는 단계; 및 상기 권취 후 산세하여 냉간압하율 60~70%으로 냉간압연하는 단계를 포함하는 전단가공성이 우수한 고강도 냉연강판의 제조방법에 관한 것이다.Another aspect of the invention is by weight, C: 0.05-0.10%, Si: 0.01-0.5%, Mn: 1.2-2.0%, Al: 0.01-0.1%, Cr: 0.005-0.3%, B: 0.0003- 0.0010%, Mo: 0.005 to 0.2%, P: 0.001 to 0.05%, S: 0.001 to 0.01%, N: 0.001 to 0.01%, Nb: 0.005 to 0.08%, Ti: 0.005 to 0.13%, V: 0.005 to 0.2 Heating the steel slab containing%, remaining Fe and inevitable impurities, and satisfying the following relations (1) and (2) to 1200 to 1350 ° C; Hot rolling the heated steel slab at a temperature in the range of 850 ° C to 1150 ° C; Cooling and winding to a temperature in the range of 550 to 750 ° C. after the hot rolling; And it relates to a method for producing a high strength cold rolled steel sheet having excellent shear workability comprising the step of cold rolling at 60 ~ 70% cold reduction rate after pickling.
관계식(1): 2.0 ≤ [Mn]+2.5[Mo]+1.5[Cr]+300[B] ≤ 2.5 Relation (1): 2.0 ≤ [Mn] + 2.5 [Mo] + 1.5 [Cr] + 300 [B] ≤ 2.5
관계식(2): 0.2 ≤ ([Nb]/93+[Ti]/48+[V]/51)/([C]/12+[N]/14) ≤ 0.5Relation (2): 0.2 ≤ ([Nb] / 93 + [Ti] / 48 + [V] / 51) / ([C] / 12 + [N] / 14) ≤ 0.5
(단, 상기 관계식(1) 및 (2)에서 각 원소기호는 해당 합금원소의 중량%를 나타냄.)(In the relations (1) and (2), each element symbol represents the weight% of the alloy element.)
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 said subject does not enumerate all the features of this invention. Various features of the present invention and the advantages and effects thereof may be understood in more detail with reference to the following specific embodiments.
본 발명에 따르면 고강도 및 고경도를 확보할 수 있음은 물론, 전단가공에 의한 균열 및 마찰열에 의한 균열을 억제할 수 있는 전단가공성이 우수한 고강도 냉연강판 및 그 제조방법을 제공할 수 있는 효과가 있다.According to the present invention, it is possible to provide a high strength cold rolled steel sheet having excellent shearing property and a method of manufacturing the same, which can secure high strength and high hardness, and can suppress cracking caused by shearing and cracking caused by frictional heat. .
도 1은 실시예들의 관계식(1) 및 관계식(2)의 값을 나타낸 그래프이다.1 is a graph showing the values of relation (1) and relation (2) of the embodiments.
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, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below. In addition, the embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.
이하, 본 발명에 따른 전단가공성이 우수한 고강도 냉연강판에 대하여 상세히 설명한다. 이하, 합금조성의 단위는 중량%임을 유의할 필요가 있다.Hereinafter, a high strength cold rolled steel sheet excellent in shearing process according to the present invention will be described in detail. It should be noted that the unit of the alloy composition is below% by weight.
본 발명에 따른 전단가공성이 우수한 고강도 냉연강판은 중량%로, C: 0.05~0.10%, Si: 0.01~0.5%, Mn: 1.2~2.0%, Al: 0.01~0.1%, Cr: 0.005~0.3%, B: 0.0003~0.0010%, Mo: 0.005~0.2%, P: 0.001~0.05%, S: 0.001~0.01%, N: 0.001~0.01%, Nb: 0.005~0.08%, Ti: 0.005~0.13%, V: 0.005~0.2%, 나머지 Fe 및 불가피한 불순물을 포함하며, 하기 관계식 (1) 및 관계식 (2)를 만족하고, 탄화물, 질화물 및 탄질화물 중 1이상을 포함한다.The high strength cold rolled steel sheet having excellent shearability according to the present invention is a weight%, C: 0.05 ~ 0.10%, Si: 0.01 ~ 0.5%, Mn: 1.2 ~ 2.0%, Al: 0.01 ~ 0.1%, Cr: 0.005 ~ 0.3% , B: 0.0003 to 0.0010%, Mo: 0.005 to 0.2%, P: 0.001 to 0.05%, S: 0.001 to 0.01%, N: 0.001 to 0.01%, Nb: 0.005 to 0.08%, Ti: 0.005 to 0.13%, V: 0.005-0.2%, remaining Fe and inevitable impurities, satisfying the following relations (1) and (2), and include at least one of carbide, nitride and carbonitride.
C: 0.05~0.10% C: 0.05 to 0.10%
상기 C는 강을 강화시키는데 가장 경제적이며 효과적인 원소이고 첨가량이 증가하면 석출강화효과 또는 베이나이트상 분율이 증가하여 인장강도가 증가하게 된다. 그 함량이 0.05% 미만이면 Ti, Nb 및 V 등과 석출물을 형성하는 반응이 적어 석출강화 효과가 낮다. 반면에, 상기 탄소의 함량이 0.10 중량%를 초과하는 경우에는 결정립계에서 조대한 탄화물이 발생하기 쉬우며, 전단가공시 미세 균열이 조대한 탄화물 계면에서 발생하여 전단가공성이 열위해진다. 따라서, 상기 C의 함량은 0.05~0.10중량%로 포함되는 것이 바람직하다. The C is the most economical and effective element to strengthen the steel, and as the amount added increases the precipitation strengthening effect or the fraction of bainite phase, the tensile strength is increased. If the content is less than 0.05%, the reaction for forming precipitates with Ti, Nb, V and the like is small, and the precipitation strengthening effect is low. On the other hand, when the carbon content exceeds 0.10% by weight, coarse carbides are likely to occur at grain boundaries, and fine shear occurs at coarse carbide interfaces during shearing, resulting in inferior shearing properties. Therefore, the content of C is preferably contained in 0.05 to 0.10% by weight.
Si: 0.01~0.5 %Si: 0.01 ~ 0.5%
상기 Si는 용강을 탈산시키고 고용강화 효과가 있으며, 조대한 탄화물 형성을 지연시켜서 성형성을 향상시키는데 유리하다. 그러나 그 함량이 0.01%미만이면 탄화물 형성을 지연시키는 효과가 적어 성형성을 향상시키기 어려우며, 0.5%를 초과하면 열간압연시 강판표면에 Si에 의한 붉은색 스케일이 형성되어 강판표면 품질이 매우 나빠질 뿐만 아니라 연성과 용접성도 저하되는 문제점이 있다. 따라서, 상기 Si의 함량은 0.01~0.5%로 포함되는 것이 바람직하다.The Si deoxidizes molten steel and has a solid solution strengthening effect, and is advantageous in improving moldability by delaying coarse carbide formation. However, if the content is less than 0.01%, the effect of delaying the formation of carbides is small, so that it is difficult to improve the formability. If the content exceeds 0.5%, the red scale due to Si is formed on the surface of the steel sheet during hot rolling. In addition, there is a problem that the ductility and weldability is also reduced. Therefore, the content of Si is preferably contained in 0.01 ~ 0.5%.
Mn: 1.2~2.0%Mn: 1.2 ~ 2.0%
상기 Mn은 Si과 마찬가지로 강을 고용 강화시키는데 효과적인 원소이며 강의 경화능을 증가시켜 용접후 용접열영향부에서 베이나이트상의 형성을 용이하게 한다. 하지만, 그 함량이 1.2% 미만이면 첨가에 따른 상기 효과를 충분히 얻을 수 없다. 반면에, 그 함량이 2.0%를 초과하면 경화능이 크게 증가하여 페라이트 상변태가 지연되어 석출강화 효과도 감소하게 되며, 연주공정에서 슬라브 주조시 두께중심부에서 편석부가 크게 발달되고, 열간압연 후 냉각시에 두께방향으로의 미세조직을 불균일하게 형성하여 전단가공시 균열의 발생이 크게 증가하게 된다. 따라서, 상기 Mn의 함량은 1.2~2.0%로 포함하는 것이 바람직하다.Mn, like Si, is an effective element to solidify the steel and increases the hardenability of the steel to facilitate the formation of the bainite phase in the weld heat affected zone after welding. However, if the content is less than 1.2%, the above effect by addition cannot be sufficiently obtained. On the other hand, if the content exceeds 2.0%, the hardenability is greatly increased, the ferrite phase transformation is delayed, and the precipitation strengthening effect is also reduced, and the segregation part is greatly developed at the center of thickness during slab casting in the casting process, and when cooled after hot rolling In the non-uniform microstructure in the thickness direction, the occurrence of cracks during shearing is greatly increased. Therefore, the content of Mn is preferably included in 1.2 to 2.0%.
Mo: 0.005~0.2%Mo: 0.005-0.2%
상기 Mo는 강을 고용강화시키며 강의 경화능을 증가시켜 강의 강도를 높이게 된다. 하지만, 0.005% 미만이면 첨가에 따른 상기 효과를 얻을 수 없고, 0.2%를 초과하면 과도한 소입성 증가로 페라이트 상변태가 지연되고 석출강화효과도 감소하게 된다. 또한, 경제적으로도 불리하며 용접성에도 해롭다. 따라서, 상기 Mo의 함량은 0.01~0.2%로 제한하는 것이 바람직하다.The Mo strengthens the steel and increases the hardenability of the steel, thereby increasing the strength of the steel. However, if the content is less than 0.005%, the above effect may not be obtained, and if the content exceeds 0.2%, ferrite phase transformation is delayed due to excessive increase in quenchability, and the precipitation strengthening effect is also reduced. It is also economically disadvantageous and also detrimental to weldability. Therefore, the content of Mo is preferably limited to 0.01 ~ 0.2%.
Cr: 0.005~0.3%Cr: 0.005-0.3%
상기 Cr은 강을 고용강화시키며 강의 경화능을 증가시켜 강의 강도를 높이게 된다. 하지만, 0.005% 미만이면 첨가에 따른 상기 효과를 얻을 수 없고, 0.3%를 초과하면 페라이트 변태를 과도하게 지연하여 마르텐사이트상 형성으로 연신율이 열위하게되며, 석출강화 효과도 감소하게 된다. 또한, Mn과 유사하게 두께중심부에서의 편석부가 크게 발달되며, 두께방향 미세조직을 불균일하게 하여 전단가공성을 열위하게 한다. 따라서, 상기 Cr의 함량은 0.005~0.3%로 제한하는 것이 바람직하다.The Cr increases the strength of the steel by solidifying the steel and increasing the hardenability of the steel. However, if the content is less than 0.005%, the above effect may not be obtained. If the content exceeds 0.3%, the ferrite transformation is excessively delayed, the elongation is inferior to martensite phase formation, and the precipitation strengthening effect is also reduced. In addition, segregation at the center of thickness is greatly developed similarly to Mn, and inferior shear processing property by uneven thickness direction microstructure. Therefore, the content of Cr is preferably limited to 0.005 to 0.3%.
B: 0.0003~0.0010% B: 0.0003-0.0010%
B는 강 중에 소량을 첨가해도 경화능을 향상시키는 원소로서, 그 함량이 0.0003% 이상 첨가되는 경우, 고온에서 오스테나이트 입계에 편석되어 결정립계를 안정화 시키고 내충격성을 개선할 수 있으나, 0.0003% 미만이면 그 효과를 얻기에 충분하지 않다. 반면에, 그 함량이 0.0010% 초과로 첨가되는 경우, 열간압연 중 재결정을 지연시켜 연신된 결정립이 증가하며 냉각 중 페라이트 상변태를 지연시켜 미세조직이 불균일하게 된다. 또한, 석출강화 효과도 감소하여 원하는 강도를 얻기 어렵고, 초기 열연판 미세조직의 불균일성은 냉간압연시 국부적인 응력집중의 원인이 되므로 본 발명에 있어서 불리하다. 따라서, 상기 B의 함량은 0.0003~0.0010% 로 제한하는 것이 바람직하다. B is an element that improves the hardenability even when a small amount is added to the steel. When the content is added to 0.0003% or more, B may be segregated at the austenite grain boundary at high temperature to stabilize the grain boundary and improve impact resistance, but if it is less than 0.0003%, It is not enough to get the effect. On the other hand, when the content is added more than 0.0010%, the recrystallization during hot rolling delayed to increase the elongated grains and the ferrite phase transformation during cooling causes the microstructure to be uneven. In addition, the precipitation strengthening effect is also reduced to obtain the desired strength, and the non-uniformity of the initial hot rolled plate microstructure is a disadvantage in the present invention because it causes local stress concentration during cold rolling. Therefore, the content of B is preferably limited to 0.0003 ~ 0.0010%.
P: 0.001~0.05%P: 0.001-0.05%
상기 P는 Si과 마찬가지로 고용강화 및 페라이트 변태 촉진효과를 동시에 가지고 있다. 하지만 그 함량을 0.001% 미만으로 제조하기 위해서는 제조비용이 많이 소요되어 경제적으로 불리하며 강도를 얻기에도 불충분 하고 그 함량이 0.05%를 초과하면 입계편석에 의한 취성이 발생하며 전단가공시 미세한 균열이 발생하기 쉽고 연성과 내충격특성을 크게 악화시킨다. 따라서 상기 P는 0.001~0.05%로 제한하는 것이 바람직하다.Like Si, P has a solid solution strengthening effect and a ferrite transformation promoting effect. However, it is economically disadvantageous to manufacture the content to less than 0.001%, and it is economically disadvantageous and insufficient to obtain strength. If the content exceeds 0.05%, brittleness due to intergranular segregation occurs and fine cracking occurs during shearing. It is easy to do and deteriorates ductility and impact resistance significantly. Therefore, the P is preferably limited to 0.001 to 0.05%.
S: 0.001~0.01%S: 0.001-0.01%
상기 S는 강 중에 존재하는 불순물로써, 그 함량이 0.01%를 초과하면 Mn 등과 결합하여 비금속개재물을 형성하며 이에 따라 강의 절단가공시 미세한 균열이 발생하기 쉽고 신장플렌지성과 내충격성을 크게 떨어뜨리는 문제점이 있으며, 또한 0.001%미만으로 제조하기 위해서는 제강조업시 시간이 많이 소요되어 생산성이 떨어지게 된다. 따라서, 그 함량을 0.001~0.01%로 제한하는 것이 바람직하다.S is an impurity present in steel, and if its content exceeds 0.01%, it combines with Mn to form a non-metallic inclusion. Therefore, when the steel is cut, fine cracks are likely to occur and the elongation flange and impact resistance are greatly reduced. In addition, in order to manufacture less than 0.001%, the steelmaking industry takes a lot of time and productivity is reduced. Therefore, it is preferable to limit the content to 0.001 to 0.01%.
Al: 0.01~0.1%Al: 0.01 ~ 0.1%
상기 Al은 주로 탈산을 위하여 첨가하는 성분이다. 그 함량이 0.01% 미만이면 그 첨가 효과가 부족하다. 반면에, 그 함량이 0.1%를 초과하면 질소와 결합하여 AlN이 형성되어 연주주조시 슬라브에 코너크랙이 발생하기 쉬우며 열연판의 엣지(Edge)부에 개재물 형성에 의한 결함이 발생하기 쉽다. 또한, 열간압연 후 냉간압연시 표면 결함 발생으로 표면품질이 떨어지는 문제점이 발생할 수 있다. 따라서, 그 함량을 0.01~0.1%로 제한하는 것이 바람직하다.Al is a component mainly added for deoxidation. If the content is less than 0.01%, the addition effect is insufficient. On the other hand, if the content exceeds 0.1%, AlN is formed by combining with nitrogen, which is likely to cause corner cracks in the slab during casting, and defects due to inclusions are easily generated at edges of the hot rolled sheet. In addition, there may be a problem that the surface quality is lowered due to the occurrence of surface defects during cold rolling after hot rolling. Therefore, it is preferable to limit the content to 0.01 to 0.1%.
N: 0.001~0.01%N: 0.001-0.01%
상기 N은 C와 함께 대표적인 고용강화 원소이며 Ti, Al 등과 함께 조대한 석출물을 형성한다. 일반적으로, N의 고용강화 효과는 탄소보다 우수하지만, 강 중에 N의 양이 증가될수록 인성이 크게 떨어지는 문제점이 있다. 또한 0.001% 미만으로 제조하기 위해서는 제강조업시 시간이 많이 소요되어 생산성이 떨어지게 된다. 따라서, 본 발명에서는 그 함량을 0.001~0.01%로 제한하는 것이 바람직하다.N is a representative solid solution strengthening element together with C to form coarse precipitates together with Ti, Al and the like. In general, the solid solution strengthening effect of N is better than carbon, but the problem of toughness is greatly reduced as the amount of N in the steel increases. In addition, in order to manufacture less than 0.001% takes a lot of time in the steelmaking industry productivity is reduced. Therefore, in the present invention, it is preferable to limit the content to 0.001 to 0.01%.
Ti: 0.005~0.13%Ti: 0.005-0.13%
상기 Ti은 Nb, V와 함께 대표적인 석출강화 원소이며 N와의 강한 친화력으로 강중 조대한 TiN을 형성한다. TiN은 열간압연을 위한 가열과정에서 결정립이 성장하는 것을 억제하는 효과가 있다. 또한 질소와 반응하고 남은 Ti이 강 중에 고용되어 탄소와 결합함으로써 TiC 석출물이 형성되어 강의 강도를 향상시키는데 유용한 성분이다. 따라서, Ti의 함량이 0.005%미만이면 상기 효과를 얻을 수 없고, Ti함량이 0.13%를 초과하면 조대한 TiN의 발생으로 전단가공시 전단가공성을 열위하게 하는 문제점이 있다. 따라서, 본 발명에서는 그 함량을 0.005~0.13%로 제한하는 것이 바람직하다.Ti, together with Nb and V, is a representative precipitation enhancing element and forms coarse TiN in steel with strong affinity with N. TiN has an effect of suppressing grain growth during heating for hot rolling. In addition, Ti remaining after reacting with nitrogen is dissolved in carbon to bond with carbon to form TiC precipitates, which is a useful component for improving the strength of steel. Therefore, if the Ti content is less than 0.005%, the above effect cannot be obtained. If the Ti content exceeds 0.13%, there is a problem of inferior shear workability during shear processing due to the generation of coarse TiN. Therefore, in the present invention, it is preferable to limit the content to 0.005 to 0.13%.
Nb: 0.005~0.08%Nb: 0.005-0.08%
상기 Nb는 Ti, V와 함께 대표적인 석출강화 원소이며 열간압연 중 석출하여 재결정 지연에 의한 결정립 미세화 효과로 강의 강도와 충격인성 향상에 효과적이다. 그러나, Nb의 함량이 0.005%미만이면 상기 효과를 충분히 얻을 수 없고, Nb함량이 0.08%를 초과하면 열간압연 중 지나친 재결정 지연에 의한 연신된 결정립 형성 및 조대한 복합석출물의 형성으로 전단가공성을 열위하게 하는 문제점이 있다. 따라서, 본 발명에서는 그 함량을 0.005~0.08%로 제한하는 것이 바람직하다.Nb, together with Ti and V, is a representative precipitation enhancing element, and is precipitated during hot rolling, and is effective in improving the strength and impact toughness of the steel by refining grains by delaying recrystallization. However, if the Nb content is less than 0.005%, the above effect cannot be sufficiently obtained. If the Nb content exceeds 0.08%, the shearability is inferior due to the formation of stretched grains and coarse composite precipitates due to excessive recrystallization during hot rolling. There is a problem to let. Therefore, in the present invention, it is preferable to limit the content to 0.005 ~ 0.08%.
V: 0.005~0.2%V: 0.005-0.2%
상기 V는 Nb, Ti와 함께 대표적인 석출강화 원소이며 권취이후 석출물을 형성하여 강의 강도 향상에 효과적이다. 따라서, V의 함량이 0.005%미만이면 상기 효과를 충분히 얻을 수 없고, 0.2%를 초과하면 조대한 복합석출물의 형성으로 전단가공성이 열위하게 되며, 경제적으로도 불리하다. 따라서, 본 발명에서는 그 함량을 0.005~0.2%로 제한하는 것이 바람직하다.V is a representative precipitation strengthening element together with Nb and Ti, and is effective in improving the strength of steel by forming a precipitate after winding. Therefore, if the content of V is less than 0.005%, the above effects cannot be sufficiently obtained. If the content of V is more than 0.2%, the shear workability is inferior due to the formation of coarse complex precipitates, and it is economically disadvantageous. Therefore, in the present invention, it is preferable to limit the content to 0.005 to 0.2%.
본 발명의 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 remaining component of the present invention is iron (Fe). However, in the conventional manufacturing process, 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.
본 발명에서는 상기 합금조성이 하기 관계식(1) 및 관계식(2)를 만족해야 열간압연 후 강의 미세조직이 균일하게 형성되어 냉간압연 후 전단가공시 균열발생을 억제할 수 있다. In the present invention, the alloy composition must satisfy the following relations (1) and (2) to uniformly form the microstructure of the steel after hot rolling to suppress cracking during shearing after cold rolling.
관계식(1): 2.0 ≤ [Mn]+2.5[Mo]+1.5[Cr]+300[B] ≤ 2.5 Relation (1): 2.0 ≤ [Mn] + 2.5 [Mo] + 1.5 [Cr] + 300 [B] ≤ 2.5
관계식(2): 0.2 ≤ ([Nb]/93+[Ti]/48+[V]/51)/([C]/12+[N]/14) ≤ 0.5Relation (2): 0.2 ≤ ([Nb] / 93 + [Ti] / 48 + [V] / 51) / ([C] / 12 + [N] / 14) ≤ 0.5
(단, 상기 관계식(1) 및 (2)에서 각 원소기호는 해당 합금원소의 중량%를 나타냄.)(In the relations (1) and (2), each element symbol represents the weight% of the alloy element.)
관계식(1)은 강의 소입성 및 편석과 관련된 것으로서, 강의 고용강화 효과 및 미세조직의 불균일성을 고려한 것이다.The relation (1) is related to the hardenability and segregation of the steel, taking into account the effect of strengthening the solid solution of the steel and the nonuniformity of the microstructure.
관계식(1)이 2.0 미만인 경우, 강의 고용강화 효과가 불충분하여 충분한 고강도를 얻을 수 없는 문제점이 있다. 반면에, 관계식(1)이 2.5를 초과하는 경우, 강의 두께방향으로의 미세조직이 불균일하게 형성되고, 페라이트 상변태를 지연시켜 강의 석출강화 효과를 감소시키는 문제가 있다. If the relation (1) is less than 2.0, there is a problem that a sufficient high strength is not obtained because the solid solution strengthening effect of the steel is insufficient. On the other hand, if the relation (1) exceeds 2.5, there is a problem that the microstructure in the thickness direction of the steel is formed non-uniformly, delaying the ferrite phase transformation to reduce the precipitation strengthening effect of the steel.
따라서, 관계식 (1) 이 2.0~2.5이 되도록 제어하는 것이 바람직하다.Therefore, it is preferable to control so that relation (1) may be 2.0-2.5.
관계식(2)는 강의 석출물 형성과 관련된 성분을 제한한 것으로 석출물의 형성이 상기 조성의 Ti, Nb, V 및 C, N의 함량과 상관이 있으므로, Ti, Nb, V 합금원소의 첨가량을 C, N의 함량에 부합하게 설정하고자 함이다. The relation (2) restricts the components related to the formation of precipitates in the steel, and since the formation of the precipitates is correlated with the contents of Ti, Nb, V, C, and N in the composition, the addition amount of Ti, Nb, and V alloy elements is defined as C, It is intended to set according to the content of N.
관계식(2)가 0.2 미만인 경우, 석출강화효과가 현저히 감소하여 원하는 강도와 경도값을 얻을 수 없으며, 0.5를 초과하는 경우, 다량의 미세한 석출물의 형성으로 항복강도가 크게 증가하여 냉간압연성이 열위해지며, 판두께 방향으로 석출물이 불균일하게 형성되어 냉간압연 후 전단가공시 균열의 발생이 심해지는 문제가 있다. If the relation (2) is less than 0.2, the precipitation strengthening effect is significantly reduced, and thus the desired strength and hardness value cannot be obtained. If the ratio exceeds 0.5, the yield strength is greatly increased due to the formation of a large amount of fine precipitates. There is a problem that the precipitate is formed non-uniformly in the direction of the plate thickness, so that the occurrence of cracks during shearing after cold rolling is severe.
따라서, 관계식 (2)가 0.2~0.5가 되도록 제어하는 것이 바람직하다.Therefore, it is preferable to control so that relation (2) may be 0.2-0.5.
상기 합금조성을 만족하도록 제어함으로써, 고강도 및 고경도를 확보할 수 있음은 물론, 전단가공에 의한 균열 및 마찰열에 의한 균열을 억제할 수 있는 전단가공성이 우수한 고강도 냉연강판을 얻을 수 있다.By controlling to satisfy the alloy composition, high strength and high hardness can be secured, and a high strength cold rolled steel sheet excellent in shearing property capable of suppressing cracking by shearing and cracking by frictional heat can be obtained.
본 발명에 따른 냉연강판은 페라이트와 미세한 펄라이트의 미세조직을 갖는 열간압연판을 냉간압연하여 얻으므로 압연방향으로 심하게 변형된 미세조직(Full Hard의 미세조직)을 갖는다. 이 때 냉간압연된 강판의 미세조직에서 각각의 상을 특정할 수는 없으나, 냉간압연 전인 열간압연된 강판은 페라이트 상의 면적분율이 90%이상이며 미세한 펄라이트 상이 5%미만이고 그 외에 베이나이트 상이 불가피하게 포함될 수 있다. The cold rolled steel sheet according to the present invention is obtained by cold rolling a hot rolled sheet having a microstructure of ferrite and fine perlite, and thus has a microstructure (Full Hard microstructure) that is severely deformed in the rolling direction. At this time, each phase cannot be specified in the microstructure of the cold rolled steel sheet. However, the hot rolled steel sheet before cold rolling has an area fraction of more than 90%, a fine pearlite phase of less than 5%, and other bainite phases. Can be included.
본 발명에 따른 전단가공성이 우수한 고강도 냉연강판은 탄화물, 질화물 및 탄질화물 중 1이상을 포함한다. 예를 들어, TiN, TiC, NbC, NbN, (Ti,Nb)(C,N), (Ti,Mo,Nb)(C,N) 및 (Fe,Mn)3C, (Fe,Mn,Mo)C 중 1이상을 포함할 수 있다. The high strength cold rolled steel sheet having excellent shearability according to the present invention includes at least one of carbide, nitride and carbonitride. For example, TiN, TiC, NbC, NbN, (Ti, Nb) (C, N), (Ti, Mo, Nb) (C, N) and (Fe, Mn) 3 C, (Fe, Mn, Mo May contain one or more of C).
이때, 상기 탄화물, 질화물 및 탄질화물의 평균 크기는 10~50nm인 것이 바람직하다.At this time, the average size of the carbide, nitride and carbonitride is preferably 10 ~ 50nm.
그 평균 크기가 10nm 미만인 경우에는, 열간압연판의 항복강도가 지나치게 상승하여 냉간압연시 국부적인 가공경화 편차가 발생하기 쉽고 냉간압연판의 전단가공 및 열처리시 균열이 발생하기 쉬운 문제점이 있다.When the average size is less than 10 nm, the yield strength of the hot rolled sheet is excessively increased, so that local work hardening deviation occurs easily during cold rolling, and cracks occur during shearing and heat treatment of the cold rolled sheet.
반면에, 그 평균 크기가 50nm 초과인 경우에는, 목표로 한 인장강도와 경도값을 얻기 어려운 문제점이 있다.On the other hand, when the average size is more than 50 nm, there is a problem that it is difficult to obtain a target tensile strength and hardness value.
한편, 상기 냉연강판은 인장강도가 1200MPa이상이고 경도값(Micro-Vickers)이 340Hv이상일 수 있다. 이러한 인장강도 및 경도값을 만족함으로써, 자동차 자동변속기의 마찰판 용도 등에 바람직하게 적용될 수 있다.Meanwhile, the cold rolled steel sheet may have a tensile strength of 1200 MPa or more and a hardness value (Micro-Vickers) of 340 Hv or more. By satisfying the tensile strength and the hardness value, it can be preferably applied to the friction plate of the automobile automatic transmission.
또한, 상기 냉연강판을 전단가공시 발생하는 균열은 최대 균열의 길이가 1mm이하인 것이 바람직하다.In addition, the crack generated during the shearing of the cold rolled steel sheet preferably has a maximum crack length of 1 mm or less.
상기 최대 균열의 길이는 직경 10mm의 원형 금형을 이용하여 Clearance 6% 조건으로 펀칭한 후, 200℃에서 1시간 열처리한 후 단면에서 발생한 최대균열의 길이를 측정한 결과이다.The maximum crack length is a result of measuring the maximum crack length in the cross section after punching under a condition of Clearance 6% using a circular mold having a diameter of 10 mm, followed by heat treatment at 200 ° C. for 1 hour.
최대 균열의 길이가 1mm를 초과하는 경우, 균열 발생량이 증가하고 전단가공시 균열이 쉽게 전파될 수 있으며, 마찰열에 의해 온도가 상승하는 경우 균열이 더욱 쉽게 전파될 수 있는 문제점이 있기 때문이다.If the maximum crack length exceeds 1mm, the crack generation amount is increased and the crack can be easily propagated during shearing, and if the temperature rises by frictional heat, the crack can be more easily propagated.
이하, 본 발명의 다른 일 측면인 전단가공성이 우수한 고강도 냉연강판의 제조방법에 대하여 상세히 설명한다.Hereinafter, another aspect of the present invention will be described in detail a method for producing a high strength cold rolled steel sheet excellent in shear workability.
본 발명의 다른 일 측면에 따른 전단가공성이 우수한 고강도 냉연강판의 제조방법은 상술한 합금조성을 만족하는 강 슬라브를 1200~1350℃로 가열하는 단계; 상기 가열된 강 슬라브를 850~1150℃의 범위의 온도에서 열간압연하는 단계; 상기 열간압연 후 550~750℃의 범위의 온도까지 냉각하고 권취하는 단계; 및 상기 권취 후 산세하여 냉간압하율 60~70%으로 냉간압연하는 단계를 포함한다.According to another aspect of the present invention, a method of manufacturing a high strength cold rolled steel sheet having excellent shearing property includes heating a steel slab satisfying the above-described alloy composition to 1200 to 1350 ° C .; Hot rolling the heated steel slab at a temperature in the range of 850 ° C to 1150 ° C; Cooling and winding to a temperature in the range of 550 to 750 ° C. after the hot rolling; And pickling after the winding to cold roll at a cold reduction rate of 60 to 70%.
가열단계Heating stage
상술한 합금조성을 만족하는 강 슬라브를 1200~1350℃로 가열한다. The steel slab that satisfies the alloy composition described above is heated to 1200 to 1350 ° C.
가열온도가 1200℃ 미만이면 석출물이 충분히 재고용되지 않아 열간압연 이후의 공정에서 석출물의 형성 감소하게 되며, 조대한 TiN이 잔존하게 된다. 반면에 가열온도가 1350℃를 초과하면 오스테나이트 결정립의 이상 입성장(Abnormal Grain Growth)에 의하여 강도가 저하되므로, 상기 재가열온도는 1200~1350℃로 제한하는 것이 바람직하다.If the heating temperature is less than 1200 ° C., the precipitates are not sufficiently reused, thereby reducing the formation of precipitates in the process after hot rolling, and coarse TiN remains. On the other hand, when the heating temperature exceeds 1350 ° C., the strength decreases due to the abnormal grain growth of the austenite grains. Therefore, the reheating temperature is preferably limited to 1200 to 1350 ° C.
이때, 상기 강슬라브는 연속주조 공정과 열연공정이 직결화된 공정에서 생산된 것일 수 있다.In this case, the steel slab may be produced in a process in which the continuous casting process and the hot rolling process are directly connected.
TiN, TiC, NbC, NbN, (Ti,Nb)(C,N), (Ti,Mo,Nb)(C,N)의 석출물의 재고용을 위해 강 슬라브의 온도를 1200~1350℃로 하는 것이 중요하므로, 상기와 같은 연속 주조 공정과 열연공정이 직결화된 공정에도 바람직하게 적용될 수 있는 것이다.It is important to set the temperature of the steel slab to 1200 ~ 1350 ° C for reconstruction of the precipitates of TiN, TiC, NbC, NbN, (Ti, Nb) (C, N), (Ti, Mo, Nb) (C, N). Therefore, the continuous casting process and the hot rolling process as described above can be preferably applied to the process directly connected.
열간압연단계Hot rolling stage
상기 가열된 강 슬라브를 850~1150℃의 범위의 온도에서 열간압연한다.The heated steel slabs are hot rolled at a temperature in the range of 850-1150 ° C.
1150℃보다 높은 온도에서 열간압연을 개시하면 열연강판의 온도가 높아져 결정립 크기가 조대해지고 열연강판의 표면품질이 열위해질 수 있다. 또한, 열간압연을 850℃보다 낮은 온도에서 종료하면 지나친 재결정 지연에 의해 연신된 결정립의 발달 및 고항복비가 얻어져 냉간압연성이 열위해지고 전단가공성도 나빠질 수 있다.Initiating hot rolling at a temperature higher than 1150 ° C. increases the temperature of the hot rolled steel sheet, resulting in coarse grain size and inferior surface quality of the hot rolled steel sheet. In addition, when the hot rolling is terminated at a temperature lower than 850 ° C., the development and high yield ratio of the stretched grains may be attained due to excessive recrystallization delay, resulting in inferior cold rolling and poor shearing properties.
냉각 및 권취단계Cooling and winding stage
상기 열간압연 후 550~750℃의 범위의 온도까지 냉각하고 권취한다.After the hot rolling is cooled to a temperature in the range of 550 ~ 750 ℃ and wound.
550℃ 이하로 냉각하여 권취되면 강중 베이나이트상과 마르텐사이트상이 형성되어 강의 재질이 열위해 질 수 있으며, 750℃이상으로 냉각되어 권취되면 조대한 페라이트 결정립이 형성되며 조대한 탄화물과 질화물이 형성되기 쉬워져 강의 재질이 열위해질 수 있다.If it is wound up to 550 ℃ or lower, the bainite phase and martensite phase in the steel are formed, and the material of the steel may become thermally damaged. If it is wound up to more than 750 ℃, coarse ferrite grains are formed and coarse carbide and nitride are formed. It can become easy and the material of steel may be inferior.
이때, 평균 냉각속도 10~70℃/sec로 냉각할 수 있다.At this time, it can be cooled at an average cooling rate of 10 ~ 70 ℃ / sec.
냉각시 평균 냉각속도가 10℃/sec 미만이면 조대한 페라이트 결정립이 형성되어 미세조직이 불균일해질 수 있으며, 평균 냉각속도가 70℃/sec 초과인 경우, 베이나이트 상이 형성되기 쉬워지고 판의 두께방향으로의 미세조직도 불균일하게 되어 강의 전단가공성이 열위해질 수 있다.If the average cooling rate is less than 10 ℃ / sec during cooling coarse ferrite grains are formed may be a non-uniform microstructure, if the average cooling rate is more than 70 ℃ / sec, bainite phase is easily formed and the thickness direction of the plate The microstructure into the furnace may also be non-uniform, leading to inferior shearing workability of the steel.
냉간압연단계Cold rolling stage
상기 권취 후 산세하여 냉간압하율 60~70%으로 냉간압연한다.After the winding, it is pickled and cold rolled at a cold reduction ratio of 60 to 70%.
냉간압하율이 60%미만이면 충분한 가공경화 효과를 얻지 못하여 강의 강도와 경도를 확보하기 곤란하다. 반면에, 냉간압하율이 70%를 초과하면 강의 Edge부 품질이 나빠지며, 전단가공성이 열위할 수 있다.If the cold reduction ratio is less than 60%, it is difficult to obtain sufficient work hardening effect and thus it is difficult to secure the strength and hardness of the steel. On the other hand, if the cold reduction rate exceeds 70%, the edge quality of the steel is deteriorated, and the shear workability may be inferior.
상기의 제조방법으로 제조된 냉연강판은 고강도 및 고경도를 확보할 수 있음은 물론, 전단가공에 의한 균열 및 마찰열에 의한 균열을 억제할 수 있다.The cold rolled steel sheet manufactured by the above-described manufacturing method can secure high strength and high hardness, as well as suppress cracking caused by shearing and cracking caused by frictional heat.
한편, 상기의 제조방법으로 제조한 냉연강판은 탄화물, 질화물 및 탄질화물 중 1이상을 포함하며, 탄화물, 질화물 및 탄질화물의 평균 크기는 10~50nm일 수 있다. 또한, 인장강도가 1200MPa이상이고 경도값이 340Hv이상일 수 있으며, 전단가공시 발생하는 균열은 최대 균열의 길이가 1mm이하일 수 있다.On the other hand, the cold rolled steel sheet produced by the above production method includes at least one of carbide, nitride and carbonitride, the average size of the carbide, nitride and carbonitride may be 10 ~ 50nm. In addition, the tensile strength is 1200MPa or more and the hardness value may be more than 340Hv, cracks generated during shearing may have a maximum crack length of 1mm or less.
이하, 실시예를 통하여 본 발명을 보다 구체적으로 설명하고자 한다. 다만, 하기의 실시예는 본 발명을 예시하여 보다 상세하게 설명하기 위한 것일 뿐, 본 발명의 권리범위를 한정하기 위한 것이 아니라는 점에 유의할 필요가 있다. 본 발명의 권리범위는 특허청구범위에 기재된 사항과 이로부터 합리적으로 유추되는 사항에 의해 결정되는 것이기 때문이다.Hereinafter, the present invention will be described in more detail with reference to Examples. However, it is necessary to note that the following examples are only for illustrating the present invention in more detail, and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the claims and the matters reasonably inferred therefrom.
하기 표 1에 나타낸 성분조성을 갖는 강 슬라브를 1250℃로 가열하고, 하기 표 2에 나타낸 제조조건을 적용하여 냉연강판을 제조하였다. 이때, 열간압연 후 냉각속도는 20~30℃/sec 로 하였다.The steel slab having the component composition shown in Table 1 below was heated to 1250 ° C, and a cold rolled steel sheet was manufactured by applying the production conditions shown in Table 2 below. At this time, the cooling rate after the hot rolling was set to 20 ~ 30 ℃ / sec.
또한, 하기 표 2에는 비교예 및 발명예에 대하여 관계식(1) 및 관계식(2)의 값을 계산하여 나타내었으며, FDT와 CT는 각각 열간압연시 마무리압연 종료온도 및 권취온도를 의미한다.In addition, in Table 2 below, the values of the relational formula (1) and the relational formula (2) were calculated for the comparative example and the inventive example, and FDT and CT mean finish rolling end temperature and winding temperature during hot rolling, respectively.
또한, 하기 표 3에는 발명예와 비교예의 기계적 성질과 미세조직 관찰결과를 나타내었다. 하기 표 3에서 TS, Hv, 최대균열 길이는 각각 냉간압연판의 인장강도, Micro-Vickers 경도값을 의미하며 최대 균열길이는 직경 10mm의 원형 금형을 이용하여 Clearance 6% 조건으로 펀칭한 후 200℃에서 1시간 열처리한 후 단면에서 발생한 최대균열의 길이를 측정한 결과이다. 균열의 길이는 광학현미경 100배율 관찰결과로부터 측정하였다. In addition, Table 3 shows the mechanical properties and microstructure observation results of the invention and comparative examples. In Table 3 below, TS, Hv, and the maximum crack length mean the tensile strength and micro-ickers hardness value of the cold rolled sheet, respectively, and the maximum crack length was punched under the condition of Clearance 6% using a circular mold having a diameter of 10 mm, and then 200 ° C. This is the result of measuring the maximum crack length in cross section after heat treatment for 1 hour at. The length of the cracks was measured from the results of observation of optical magnification 100 times.
강 중 형성된 탄화물, 질화물 및 탄질화물의 크기는 냉간압연 전인 열간압연판에 대하여 분석하였다. 강 중 형성된 평균 크기 10~50nm의 탄화물, 질화물 및 탄질화물은 냉간압연에 의해 그 크기와 분율이 변화하지는 않으며, 냉간압연 이후 심하게 변형된 미세조직에서는 그 크기와 분율을 정확하게 관찰하기 어려운 문제가 있으므로 열간압연판에 대하여 분석하였다. 탄화물, 질화물 및 탄질화물의 평균크기는 투과전자현미경을 이용하여 측정한 결과로부터 결정하였다. 평균크기 100nm이상의 탄화물과 질화물의 측정은 50,000배율 측정결과를 이용하였으며 평균크기 100nm이하의 석출물은 100,000배율 측정결과를 이용하였다. 인장시험은 압연판재의 압연방향에 대하여 0°방향을 기준으로 JIS5호 규격에 의거하여 채취된 시험편으로 하였다. The size of carbides, nitrides and carbonitrides formed in steel were analyzed for hot rolled plates before cold rolling. Carbide, nitride and carbonitride with an average size of 10 ~ 50nm formed in steel are not changed in size and fraction by cold rolling, and it is difficult to accurately observe the size and fraction in the microstructure that is severely deformed after cold rolling. The hot rolled plate was analyzed. The average size of carbides, nitrides and carbonitrides was determined from the results measured using a transmission electron microscope. The measurement of carbides and nitrides with an average size of 100 nm or more was used for the measurement of 50,000 magnification, and the results of 100,000 magnifications were used for precipitates with an average size of less than 100 nm. The tensile test was taken as the test piece collected based on JIS5 standard based on 0 degree direction with respect to the rolling direction of a rolled sheet material.
구분division CC SiSi MnMn CrCr AlAl PP SS NN MoMo TiTi NbNb VV BB
비교예1Comparative Example 1 0.040.04 0.20.2 1.61.6 0.010.01 0.030.03 0.010.01 0.0040.004 0.0040.004 0.0050.005 0.10.1 0.040.04 0.0050.005 0.00030.0003
비교예2Comparative Example 2 0.050.05 0.10.1 1.41.4 0.10.1 0.030.03 0.0080.008 0.0030.003 0.0040.004 0.0070.007 0.060.06 0.030.03 0.10.1 0.00030.0003
비교예3Comparative Example 3 0.060.06 0.10.1 1.91.9 0.20.2 0.0350.035 0.010.01 0.0030.003 0.0050.005 0.050.05 0.080.08 0.030.03 0.0050.005 0.0010.001
비교예4Comparative Example 4 0.070.07 0.20.2 1.81.8 0.010.01 0.050.05 0.010.01 0.0050.005 0.0040.004 0.10.1 0.0350.035 0.030.03 0.0050.005 0.00030.0003
비교예5Comparative Example 5 0.080.08 0.30.3 1.41.4 0.010.01 0.0250.025 0.0090.009 0.0030.003 0.0040.004 0.10.1 0.080.08 0.0050.005 0.050.05 0.00030.0003
비교예6Comparative Example 6 0.070.07 0.20.2 1.71.7 0.10.1 0.030.03 0.010.01 0.0030.003 0.0030.003 0.050.05 0.120.12 0.0550.055 0.0060.006 0.00030.0003
비교예7Comparative Example 7 0.0850.085 0.10.1 1.81.8 0.010.01 0.050.05 0.010.01 0.0040.004 0.0040.004 0.0090.009 0.090.09 0.040.04 0.0050.005 0.00030.0003
비교예8Comparative Example 8 0.090.09 0.050.05 1.91.9 0.10.1 0.0250.025 0.0070.007 0.0030.003 0.0040.004 0.0070.007 0.110.11 0.0350.035 0.050.05 0.00030.0003
비교예9Comparative Example 9 0.120.12 0.20.2 22 0.010.01 0.50.5 0.010.01 0.0030.003 0.0040.004 0.0060.006 0.120.12 0.030.03 0.10.1 0.00030.0003
비교예10Comparative Example 10 0.080.08 0.50.5 2.22.2 0.010.01 0.10.1 0.010.01 0.0030.003 0.0040.004 0.050.05 0.150.15 0.030.03 0.020.02 0.00120.0012
발명예1Inventive Example 1 0.0550.055 0.10.1 1.71.7 0.010.01 0.030.03 0.010.01 0.0030.003 0.0050.005 0.10.1 0.060.06 0.020.02 0.0050.005 0.00030.0003
발명예2Inventive Example 2 0.060.06 0.150.15 1.81.8 0.010.01 0.0280.028 0.0060.006 0.0040.004 0.0040.004 0.050.05 0.110.11 0.020.02 0.0050.005 0.00030.0003
발명예3Inventive Example 3 0.070.07 0.10.1 1.91.9 0.010.01 0.030.03 0.0080.008 0.0030.003 0.0040.004 0.150.15 0.050.05 0.060.06 0.0050.005 0.00030.0003
발명예4Inventive Example 4 0.070.07 0.20.2 1.91.9 0.010.01 0.0350.035 0.010.01 0.0020.002 0.0030.003 0.150.15 0.0550.055 0.0450.045 0.0050.005 0.00030.0003
발명예5Inventive Example 5 0.070.07 0.10.1 1.71.7 0.10.1 0.030.03 0.0090.009 0.0030.003 0.0040.004 0.050.05 0.080.08 0.030.03 0.050.05 0.00030.0003
발명예6Inventive Example 6 0.070.07 0.40.4 1.91.9 0.010.01 0.0370.037 0.010.01 0.0030.003 0.0040.004 0.140.14 0.120.12 0.030.03 0.0050.005 0.00030.0003
발명예7Inventive Example 7 0.070.07 0.150.15 1.951.95 0.150.15 0.030.03 0.010.01 0.0040.004 0.0030.003 0.050.05 0.10.1 0.020.02 0.0050.005 0.00030.0003
발명예8Inventive Example 8 0.0750.075 0.20.2 1.81.8 0.010.01 0.030.03 0.0070.007 0.0030.003 0.0040.004 0.10.1 0.090.09 0.020.02 0.060.06 0.00030.0003
시편Psalter 관계식(1)Relational formula (1) 관계식(2)Relational formula (2) FDT(℃)FDT (℃) CT(℃)CT (℃) 냉간압하율(%)Cold rolling reduction (%)
비교예1Comparative Example 1 1.72 1.72 0.72 0.72 887887 605605 6666
비교예2Comparative Example 2 1.66 1.66 0.80 0.80 889889 614614 7373
비교예3Comparative Example 3 2.63 2.63 0.39 0.39 908908 613613 6262
비교예4Comparative Example 4 2.16 2.16 0.19 0.19 892892 615615 6565
비교예5Comparative Example 5 1.76 1.76 0.39 0.39 894894 604604 6363
비교예6Comparative Example 6 2.07 2.07 0.53 0.53 895895 612612 6262
비교예7Comparative Example 7 1.93 1.93 0.33 0.33 901901 614614 7272
비교예8Comparative Example 8 2.16 2.16 0.47 0.47 898898 608608 5656
비교예9Comparative Example 9 2.12 2.12 0.47 0.47 905905 599599 7474
비교예10Comparative Example 10 2.70 2.70 0.55 0.55 911911 617617 6565
발명예1Inventive Example 1 2.06 2.06 0.32 0.32 899899 612612 6767
발명예2Inventive Example 2 2.03 2.03 0.49 0.49 905905 610610 6666
발명예3Inventive Example 3 2.38 2.38 0.29 0.29 909909 623623 6262
발명예4Inventive Example 4 2.38 2.38 0.29 0.29 912912 601601 6565
발명예5Inventive Example 5 2.07 2.07 0.49 0.49 915915 625625 6565
발명예6Inventive Example 6 2.36 2.36 0.48 0.48 915915 624624 6464
발명예7Inventive Example 7 2.39 2.39 0.40 0.40 918918 626626 6868
발명예8Inventive Example 8 2.16 2.16 0.50 0.50 913913 627627 6363
구분division 인장강도(MPa)Tensile Strength (MPa) 경도(Hv)Hardness (Hv) 목표TS(MPa)Goal TS (MPa) 목표경도(Hv)Target hardness (Hv) 탄화물, 질화물 및 탄질화물의 평균 크기 (nm)Average size of carbides, nitrides and carbonitrides (nm) 전단가공부최대균열 길이(mm)Shear processing part Maximum crack length (mm) 전단가공부단면품질Shear Processing Section Quality
비교예1Comparative Example 1 12371237 334334 ≥1200≥1200 ≥340≥340 44 0.060.06 ◎◎
비교예2Comparative Example 2 12601260 341341 77 44 △△
비교예3Comparative Example 3 12381238 334334 1212 22 △△
비교예4Comparative Example 4 10981098 297297 3535 0.030.03 ◎◎
비교예5Comparative Example 5 12361236 334334 1313 0.080.08 ◎◎
비교예6Comparative Example 6 13151315 356356 88 66 XX
비교예7Comparative Example 7 13721372 362362 ≥1350≥1350 ≥355≥355 1515 33 △△
비교예8Comparative Example 8 12911291 349349 1313 0.050.05 ○○
비교예9Comparative Example 9 14341434 384384 2222 88 XX
비교예10Comparative Example 10 14601460 390390 88 1010 XX
발명예1Inventive Example 1 12711271 344344 ≥1200≥1200 ≥340≥340 1515 0.060.06 ◎◎
발명예2Inventive Example 2 13301330 353353 1616 0.20.2 ○○
발명예3Inventive Example 3 12631263 342342 1818 0.40.4 ○○
발명예4Inventive Example 4 12811281 346346 1919 0.050.05 ◎◎
발명예5Inventive Example 5 12871287 348348 1818 0.040.04 ◎◎
발명예6Inventive Example 6 13841384 368368 ≥1350≥1350 ≥355≥355 2121 0.80.8 ○○
발명예7Inventive Example 7 13741374 370370 2222 0.60.6 ○○
발명예8Inventive Example 8 13591359 367367 1515 0.30.3 ○○
비교예 1과 2는 관계식(1)과 관계식(2)를 모두 만족하지 못하였으며, 비교예 1은 C의 함량도 발명의 범위를 만족하지 못하였다. 두 비교예 모두 충분한 고용강화 효과를 얻지 못하였으며, 비교적 낮은 C함량 및 상대적으로 과도한 Ti, Nb, V에 의해 관계식(2)의 상한을 초과하였다. 따라서, 강중 형성된 탄,질화물 및 석출물의 크기가 미세하였으나 강의 강도를 충분히 확보하지는 못하였다. 또한, 비교예 2는 냉간압하율이 본 발명에서 제어한 범위를 초과하여 부여한 결과, 펀칭가공 후 전단가공면에서의 균열이 다소 심하게 발생하여 전단가공면의 품질이 열위함을 확인할 수 있다.Comparative Examples 1 and 2 did not satisfy both the relational formula (1) and the relational formula (2), and Comparative Example 1 did not satisfy the C content. Both comparative examples did not achieve sufficient solid solution effect, and exceeded the upper limit of relation (2) due to relatively low C content and relatively excessive Ti, Nb, and V. Therefore, the size of carbon, nitride and precipitates formed in the steel was fine, but the strength of the steel was not sufficiently secured. In addition, Comparative Example 2, as a result of giving the cold reduction ratio exceeding the range controlled in the present invention, it can be confirmed that the cracks in the shearing surface after the punching process occurs slightly worse, the quality of the shearing surface is inferior.
비교예 3과 5는 관계식(1)을 만족하지 못한 경우로 비교예 3은 관계식 (1)의 발명범위를 초과하여 강의 중심부에서의 편석발생이 증가하여 전단가공부에서의 품질이 열위하였다. 또한, 비교예 5는 Mn, Cr, B함량 등이 적어 편석발생이 적어 전단가공면의 품질은 매우 양호하였으나 충분한 고용강화 효과를 얻지 못하여 목표로 한 강도와 경도값을 얻지 못하였다. Comparative Examples 3 and 5 did not satisfy the relational expression (1). In Comparative Example 3, segregation was increased at the center of the steel beyond the scope of the relational expression (1). In addition, Comparative Example 5 had a low Mn, Cr, B content and the like, segregation was less, so the quality of the shearing surface was very good, but sufficient solid-solution strengthening effect was not obtained, so that the target strength and hardness could not be obtained.
비교예 4와 6은 관계식(2)를 만족하지 못한 경우로, 비교예 4는 잉여 C이 잔류하여 조대한 석출물 및 탄화물을 형성하였으며 석출강화 효과가 부족하여 목표로 한 강도와 경도값을 얻지 못하였다. Comparative Examples 4 and 6 did not satisfy the relation (2). In Comparative Example 4, surplus C remained to form coarse precipitates and carbides, and the precipitation strengthening effect was insufficient to obtain the target strength and hardness values. It was.
비교예 6은 관계식(2)의 발명범위를 초과하여 미세한 석출물이 다량 형성되었으며 높은 강도를 얻을 수 있었으나, 전단가공부에서의 균열 발생이 심하였다. In Comparative Example 6, a large amount of fine precipitates were formed in excess of the scope of the formula (2) and high strength was obtained, but cracks were severe in the shear processing part.
비교예 7, 8, 9, 10은 냉간압연 후 인장강도 1350MPa이상, 경도값 355Hv이상을 목표로 제조한 강으로 비교예 7은 관계식 1을 만족하지 못하였으나 높은 냉간압하율로 목표로 한 물성을 확보하였다. 하지만, 높은 냉간압하율에 의해 전단가공부에서의 균열발생이 다소 심하였다.Comparative Examples 7, 8, 9 and 10 are steels manufactured for the purpose of tensile strength of 1350 MPa or more and hardness value of 355 Hv or more after cold rolling. Comparative Example 7 does not satisfy the relational formula 1, but has high cold rolling properties. Secured. However, due to the high cold rolling rate, cracking was more severe in the shearing part.
비교예 8과 9는 모두 관계식(1)과 (2)를 만족하였으나 냉간압하율이 부적합하여 목표 물성을 얻지 못하였거나 전단가공부의 품질이 열위하였다. 비교예 10은 관계식(1)과 (2)를 모두 만족하지 않은 경우로, 전단가공부의 품질이 열위하였다.In Comparative Examples 8 and 9, the relations (1) and (2) were satisfied, but the cold reduction ratio was not suitable, so that the target properties were not obtained or the quality of the shear processing part was inferior. In Comparative Example 10, the relations (1) and (2) were not satisfied, and the quality of the shear processing portion was inferior.
반면에, 발명예들은 모두 본 발명에서 제안한 성분범위와 제조조건 및 관계식(1), (2)를 모두 만족하여 목표로 한 재질을 확보할 수 있으며, 전단가공부의 품질도 우수함을 확인할 수 있다. On the other hand, all of the invention examples can ensure the target material by satisfying both the component range and manufacturing conditions proposed in the present invention and relations (1), (2), it can be confirmed that the quality of the shear processing part is also excellent.
발명예와 비교예의 관계식(1), 관계식(2)와 전단가공부 최대균열의 길이의 관계를 도1에 나타내었다. 도1에서 빗금친 영역이 본 발명의 범위에 해당한다.The relationship between the relational expression (1), the relational expression (2) of the invention example and the comparative example, and the length of the maximum crack of the shear processing part is shown in FIG. The hatched areas in FIG. 1 correspond to the scope of the invention.
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.Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and changes can be made without departing from the technical spirit of the present invention described in the claims. It will be obvious to those of ordinary skill in the field.

Claims (10)

  1. 중량%로, C: 0.05~0.10%, Si: 0.01~0.5%, Mn: 1.2~2.0%, Al: 0.01~0.1%, Cr: 0.005~0.3%, B: 0.0003~0.0010%, Mo: 0.005~0.2%, P: 0.001~0.05%, S: 0.001~0.01%, N: 0.001~0.01%, Nb: 0.005~0.08%, Ti: 0.005~0.13%, V: 0.005~0.2%, 나머지 Fe 및 불가피한 불순물을 포함하며, By weight%, C: 0.05-0.10%, Si: 0.01-0.5%, Mn: 1.2-2.0%, Al: 0.01-0.1%, Cr: 0.005-0.3%, B: 0.0003-0.0010%, Mo: 0.005- 0.2%, P: 0.001-0.05%, S: 0.001-0.01%, N: 0.001-0.01%, Nb: 0.005-0.08%, Ti: 0.005-0.13%, V: 0.005-0.2%, remaining Fe and unavoidable impurities Including;
    하기 관계식(1) 및 관계식(2)를 만족하고,Satisfies the following relation (1) and relation (2),
    탄화물, 질화물 및 탄질화물 중 1이상을 포함하는 전단가공성이 우수한 고강도 냉연강판.High strength cold rolled steel sheet with excellent shearing properties including at least one of carbide, nitride and carbonitride.
    관계식(1): 2.0 ≤ [Mn]+2.5[Mo]+1.5[Cr]+300[B] ≤ 2.5 Relation (1): 2.0 ≤ [Mn] + 2.5 [Mo] + 1.5 [Cr] + 300 [B] ≤ 2.5
    관계식(2): 0.2 ≤ ([Nb]/93+[Ti]/48+[V]/51)/([C]/12+[N]/14) ≤ 0.5Relation (2): 0.2 ≤ ([Nb] / 93 + [Ti] / 48 + [V] / 51) / ([C] / 12 + [N] / 14) ≤ 0.5
    (단, 상기 관계식(1) 및 (2)에서 각 원소기호는 해당 합금원소의 중량%를 나타냄.)(In the relations (1) and (2), each element symbol represents the weight% of the alloy element.)
  2. 제 1항에 있어서,The method of claim 1,
    상기 탄화물, 질화물 및 탄질화물의 평균 크기는 10~50nm인 것을 특징으로 하는 전단가공성이 우수한 고강도 냉연강판.The high strength cold rolled steel sheet having excellent shearability, characterized in that the average size of the carbide, nitride and carbonitride is 10 ~ 50nm.
  3. 제 1항에 있어서, The method of claim 1,
    상기 냉연강판은 인장강도가 1200MPa이상이고 경도값이 340Hv이상인 것을 특징으로 하는 전단가공성이 우수한 고강도 냉연강판.The cold rolled steel sheet is a high strength cold rolled steel sheet having excellent shear workability, characterized in that the tensile strength is 1200MPa or more and the hardness value is 340Hv or more.
  4. 제 1항에 있어서,The method of claim 1,
    전단가공시 발생하는 균열은 최대 균열의 길이가 1mm이하인 것을 특징으로 하는 전단가공성이 우수한 고강도 냉연강판.High strength cold rolled steel sheet having excellent shearability, characterized in that cracks generated during shearing have a maximum crack length of 1 mm or less.
  5. 제 1항에 있어서,The method of claim 1,
    상기 냉연강판의 냉간압연 전 미세조직은 페라이트 상의 면적분율이 90%이상이며 미세한 펄라이트 상이 5%미만이고 그 외에 베이나이트 상이 불가피하게 포함하는 것을 특징으로 하는 전단가공성이 우수한 고강도 냉연강판.The microstructure before cold rolling of the cold rolled steel sheet has an area fraction of more than 90%, a fine pearlite phase of less than 5%, and a high strength cold rolled steel sheet having excellent shear workability, which inevitably includes a bainite phase.
  6. 중량%로, C: 0.05~0.10%, Si: 0.01~0.5%, Mn: 1.2~2.0%, Al: 0.01~0.1%, Cr: 0.005~0.3%, B: 0.0003~0.0010%, Mo: 0.005~0.2%, P: 0.001~0.05%, S: 0.001~0.01%, N: 0.001~0.01%, Nb: 0.005~0.08%, Ti: 0.005~0.13%, V: 0.005~0.2%, 나머지 Fe 및 불가피한 불순물을 포함하며, 하기 관계식(1) 및 관계식(2)를 만족하는 강 슬라브를 1200~1350℃로 가열하는 단계;By weight%, C: 0.05-0.10%, Si: 0.01-0.5%, Mn: 1.2-2.0%, Al: 0.01-0.1%, Cr: 0.005-0.3%, B: 0.0003-0.0010%, Mo: 0.005- 0.2%, P: 0.001-0.05%, S: 0.001-0.01%, N: 0.001-0.01%, Nb: 0.005-0.08%, Ti: 0.005-0.13%, V: 0.005-0.2%, remaining Fe and unavoidable impurities It comprises, and heating the steel slab satisfying the following relation (1) and relation (2) to 1200 ~ 1350 ℃;
    상기 가열된 강 슬라브를 850~1150℃의 범위의 온도에서 열간압연하는 단계;Hot rolling the heated steel slab at a temperature in the range of 850 ° C to 1150 ° C;
    상기 열간압연 후 550~750℃의 범위의 온도까지 냉각하고 권취하는 단계; 및Cooling and winding to a temperature in the range of 550 to 750 ° C. after the hot rolling; And
    상기 권취 후 산세하여 냉간압하율 60~70%으로 냉간압연하는 단계를 포함하는 전단가공성이 우수한 고강도 냉연강판의 제조방법.The method of producing a high strength cold rolled steel sheet having excellent shearability, comprising the step of pickling after the winding and cold rolling at a cold reduction ratio of 60 to 70%.
    관계식(1): 2.0 ≤ [Mn]+2.5[Mo]+1.5[Cr]+300[B] ≤ 2.5 Relation (1): 2.0 ≤ [Mn] + 2.5 [Mo] + 1.5 [Cr] + 300 [B] ≤ 2.5
    관계식(2): 0.2 ≤ ([Nb]/93+[Ti]/48+[V]/51)/([C]/12+[N]/14) ≤ 0.5Relation (2): 0.2 ≤ ([Nb] / 93 + [Ti] / 48 + [V] / 51) / ([C] / 12 + [N] / 14) ≤ 0.5
    (단, 상기 관계식(1) 및 (2)에서 각 원소기호는 해당 합금원소의 중량%를 나타냄.)(In the relations (1) and (2), each element symbol represents the weight% of the alloy element.)
  7. 제 6항에 있어서,The method of claim 6,
    상기 강 슬라브는 연속 주조 공정에 의해 생산된 것을 특징으로 하는 전단가공성이 우수한 고강도 냉연강판의 제조방법.The steel slab is produced by a continuous casting process characterized in that the high strength cold rolled steel sheet having excellent shear workability.
  8. 제 6항에 있어서,The method of claim 6,
    상기 냉각은 평균 냉각속도 10~70℃/sec로 행하는 것을 특징으로 하는 전단가공성이 우수한 고강도 냉연강판의 제조방법.The cooling method of producing a high strength cold rolled steel sheet having excellent shear workability, characterized in that performed at an average cooling rate 10 ~ 70 ℃ / sec.
  9. 제 6항에 있어서,The method of claim 6,
    상기 냉연강판은 탄화물, 질화물 및 탄질화물 중 1이상을 포함하며, 탄화물, 질화물 및 탄질화물의 평균 크기는 10~50nm인 것을 특징으로 하는 전단가공성이 우수한 고강도 냉연강판의 제조방법.The cold rolled steel sheet includes at least one of carbide, nitride, and carbonitride, and an average size of carbide, nitride, and carbonitride is 10 to 50nm, the method of manufacturing high strength cold rolled steel sheet having excellent shear workability.
  10. 제 6항에 있어서,The method of claim 6,
    상기 냉연강판은 인장강도가 1200MPa이상이고 경도값이 340Hv이상인 것을 특징으로 하는 전단가공성이 우수한 고강도 냉연강판의 제조방법.The cold rolled steel sheet is a method of producing a high strength cold rolled steel sheet having excellent shear workability, characterized in that the tensile strength is 1200MPa or more and the hardness value is 340Hv or more.
PCT/KR2016/013362 2015-11-20 2016-11-18 High-strength cold rolled steel sheet having excellent shear processability, and manufacturing method therefor WO2017086745A1 (en)

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