WO2022265289A1 - 신선 가공성이 우수한 선재 및 그 제조방법 - Google Patents
신선 가공성이 우수한 선재 및 그 제조방법 Download PDFInfo
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- WO2022265289A1 WO2022265289A1 PCT/KR2022/008084 KR2022008084W WO2022265289A1 WO 2022265289 A1 WO2022265289 A1 WO 2022265289A1 KR 2022008084 W KR2022008084 W KR 2022008084W WO 2022265289 A1 WO2022265289 A1 WO 2022265289A1
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- Prior art keywords
- wire rod
- less
- rolling
- wire
- billet
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- 238000004519 manufacturing process Methods 0.000 title claims abstract description 34
- 238000000034 method Methods 0.000 claims abstract description 24
- 238000010438 heat treatment Methods 0.000 claims description 72
- 238000005096 rolling process Methods 0.000 claims description 58
- 238000001816 cooling Methods 0.000 claims description 56
- 229910001567 cementite Inorganic materials 0.000 claims description 43
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 claims description 43
- 239000013078 crystal Substances 0.000 claims description 21
- 238000005491 wire drawing Methods 0.000 claims description 21
- 229910001566 austenite Inorganic materials 0.000 claims description 17
- 229910052799 carbon Inorganic materials 0.000 claims description 13
- 229910001562 pearlite Inorganic materials 0.000 claims description 13
- 229910052782 aluminium Inorganic materials 0.000 claims description 10
- 239000012535 impurity Substances 0.000 claims description 8
- 239000000203 mixture Substances 0.000 claims description 7
- 229910052757 nitrogen Inorganic materials 0.000 claims description 7
- 229910045601 alloy Inorganic materials 0.000 claims description 6
- 239000000956 alloy Substances 0.000 claims description 6
- 229910052804 chromium Inorganic materials 0.000 claims description 6
- 229910052748 manganese Inorganic materials 0.000 claims description 6
- 229910052710 silicon Inorganic materials 0.000 claims description 6
- 239000002245 particle Substances 0.000 claims description 5
- 238000004804 winding Methods 0.000 claims description 4
- 238000005098 hot rolling Methods 0.000 claims description 2
- 238000010276 construction Methods 0.000 abstract description 3
- 229910000831 Steel Inorganic materials 0.000 description 53
- 239000010959 steel Substances 0.000 description 53
- 230000000052 comparative effect Effects 0.000 description 41
- 239000000463 material Substances 0.000 description 19
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 17
- PMHQVHHXPFUNSP-UHFFFAOYSA-M copper(1+);methylsulfanylmethane;bromide Chemical compound Br[Cu].CSC PMHQVHHXPFUNSP-UHFFFAOYSA-M 0.000 description 14
- 238000005121 nitriding Methods 0.000 description 14
- 239000011572 manganese Substances 0.000 description 11
- 239000011651 chromium Substances 0.000 description 9
- 230000007547 defect Effects 0.000 description 9
- 230000000694 effects Effects 0.000 description 9
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 7
- 238000001887 electron backscatter diffraction Methods 0.000 description 7
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 7
- 229910000859 α-Fe Inorganic materials 0.000 description 7
- 229910000734 martensite Inorganic materials 0.000 description 6
- 239000006104 solid solution Substances 0.000 description 6
- 229910001563 bainite Inorganic materials 0.000 description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- 238000009792 diffusion process Methods 0.000 description 4
- 238000005242 forging Methods 0.000 description 4
- 238000010273 cold forging Methods 0.000 description 3
- 238000010791 quenching Methods 0.000 description 3
- 230000000171 quenching effect Effects 0.000 description 3
- 238000004904 shortening Methods 0.000 description 3
- 230000009466 transformation Effects 0.000 description 3
- FGRBYDKOBBBPOI-UHFFFAOYSA-N 10,10-dioxo-2-[4-(N-phenylanilino)phenyl]thioxanthen-9-one Chemical compound O=C1c2ccccc2S(=O)(=O)c2ccc(cc12)-c1ccc(cc1)N(c1ccccc1)c1ccccc1 FGRBYDKOBBBPOI-UHFFFAOYSA-N 0.000 description 2
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 2
- 238000005266 casting Methods 0.000 description 2
- 238000005520 cutting process Methods 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- -1 nitro nitride Chemical class 0.000 description 2
- 239000002244 precipitate Substances 0.000 description 2
- 238000003825 pressing Methods 0.000 description 2
- 239000000047 product Substances 0.000 description 2
- 238000005204 segregation Methods 0.000 description 2
- 238000004513 sizing Methods 0.000 description 2
- 238000005728 strengthening Methods 0.000 description 2
- 238000005496 tempering Methods 0.000 description 2
- TVEXGJYMHHTVKP-UHFFFAOYSA-N 6-oxabicyclo[3.2.1]oct-3-en-7-one Chemical compound C1C2C(=O)OC1C=CC2 TVEXGJYMHHTVKP-UHFFFAOYSA-N 0.000 description 1
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- PIGFYZPCRLYGLF-UHFFFAOYSA-N Aluminum nitride Chemical compound [Al]#N PIGFYZPCRLYGLF-UHFFFAOYSA-N 0.000 description 1
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- 229910001208 Crucible steel Inorganic materials 0.000 description 1
- 229910000604 Ferrochrome Inorganic materials 0.000 description 1
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 150000001721 carbon Chemical class 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 230000006355 external stress Effects 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 238000000265 homogenisation Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- 150000004767 nitrides Chemical group 0.000 description 1
- 235000019362 perlite Nutrition 0.000 description 1
- 239000010451 perlite Substances 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 238000007711 solidification Methods 0.000 description 1
- 230000008023 solidification Effects 0.000 description 1
Images
Classifications
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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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
-
- 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
- B21B1/16—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 wire rods, bars, merchant bars, rounds wire or material of like small cross-section
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
- B21C47/00—Winding-up, coiling or winding-off metal wire, metal band or other flexible metal material characterised by features relevant to metal processing only
- B21C47/02—Winding-up or coiling
-
- 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
- C21D8/0221—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
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
-
- 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
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
- C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires 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
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
-
- 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
- C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
- C21D9/525—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length for wire, for rods
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
Definitions
- the present invention relates to a wire rod for mechanical structure applicable to automobiles, construction parts, etc., and a manufacturing method thereof, and relates to a wire rod having excellent wire-drawing performance and a method for manufacturing the same.
- Steels for mechanical structures used in automobiles and construction parts, for example, parts such as bearings, are typically manufactured by drawing a rolled wire rod and cold-processing the wire rod into a complex shape.
- the spherical softening heat treatment as described above is intended to improve cold workability, spherical cementite in the microstructure and induces a homogeneous particle distribution. Through this, it is possible to prevent disconnection during wire drawing, improve the life of the processing die, and lower the hardness of the material to be processed.
- One aspect of the present invention is to provide a wire rod used for mechanical structural parts such as bearings and a manufacturing method thereof, specifically, a wire rod capable of omitting or shortening spherical soft nitriding heat treatment and securing excellent wire drawing characteristics and strength. And to provide a manufacturing method thereof.
- C 0.8 to 1.2%
- Si 0.01 to 0.6%
- Mn 0.1 to 0.6%
- Cr 0.8 to 2.0%
- Al 0.01 to 0.06%
- N 0.02% or less (excluding 0)
- the remainder including Fe and unavoidable impurities
- the microstructure includes proeutectoid cementite in the pearlite main structure,
- a wire rod having excellent drawing workability including a microstructure that satisfies the following relational expression 1.
- C 0.8 ⁇ 1.2%
- Si 0.01 ⁇ 0.6%
- Mn 0.1 ⁇ 0.6%
- Cr 0.8 ⁇ 2.0%
- Al 0.01 ⁇ 0.06%
- N 0.02%
- the rest is heating a steel piece containing Fe and unavoidable impurities, and performing steel piece rolling to prepare a billet;
- the wire rod rolling is performed so that the austenite grain size (AGS) before finish rolling is 5 to 20 ⁇ m, and the finish rolling is performed at a deformation amount of 0.3 or more in a temperature range of 730 ° C. to Acm.
- a method for manufacturing a wire rod is provided.
- the present invention it is possible to provide a wire rod for mechanical parts such as bearings having excellent strength and wire-drawing performance and a manufacturing method thereof, even though the spheroidal softening heat treatment can be omitted or shortened. Through this, cost reduction and carbon reduction effects in the manufacturing process can be obtained.
- Example 1 is a photograph of the microstructure of Inventive Example 1 in Examples of the present invention observed with a scanning electron microscope (Scanning Electron Microscope, SEM).
- Figure 2 is a photograph of the microstructure of Comparative Example 5 in Examples of the present invention observed with a scanning electron microscope (Scanning Electron Microscope, SEM).
- Example 3 is a photograph of the microstructure of Inventive Example 1 in Examples of the present invention observed by EBSD (Electron Backscatter Diffraction).
- the inventors of the present invention recognized that in the case of performing spheroidal softening heat treatment on wire rods used for mechanical structural parts such as bearings, it takes a lot of heat treatment cost and time, and acts as an environmental burden. Therefore, even if the spherical soft nitriding heat treatment is shortened or omitted, a method for securing excellent wire drawing performance during wire drawing for manufacturing parts was studied in depth. As a result, it has led to the present invention.
- the C is an element added to secure a certain level of strength.
- the C content is less than 0.8%, it is difficult to secure sufficient strength even after spheroidal nitriding heat treatment and quenching and tempering heat treatment that proceeds after the forging process due to the decrease in strength of the base material, and when it exceeds 1.2% (FeCr ) Precipitates of new phases such as 3 C may cause problems such as center segregation during solidification of cast steel such as bloom. Therefore, the C content is preferably 0.8 to 1.2%, more preferably 0.9 to 1.1%.
- Si is a typical substitutional element and is added to secure a certain level of strength. If Si is less than 0.01%, it is difficult to secure strength and sufficient hardenability of steel, and if it exceeds 0.6%, there is a disadvantage in that cold forging workability is deteriorated during forging after spheroidal soft nitriding heat treatment. Therefore, the Si content is preferably 0.01 to 0.6%.
- Mn is an element that forms a substitutional solid solution in the base structure to strengthen solid solution, and is an element capable of securing desired strength without deterioration of ductility, and is a representative austenite former. If the Mn is less than 0.1%, the strength by solid solution strengthening is not guaranteed, and it is difficult to expect the effect of improving toughness. In addition, when the Mn content exceeds 0.6%, since defects such as chevron cracks may occur due to MnS during forging after spherical soft nitriding heat treatment, the Mn content is 0.1 to 0.6% it is desirable
- Cr like Mn, is an element that increases hardenability of steel. If the Cr is less than 0.8%, it is difficult to secure sufficient hardenability to obtain martensite during quenching and tempering heat treatment after the forging process, and if it exceeds 2.0%, a large amount of low-temperature structure in the wire is generated due to the promotion of center segregation Chances are higher. Accordingly, the content of Cr is preferably 0.8 to 2.0%, more preferably 1.0 to 2.0%.
- the Al is an element that not only has a deoxidizing effect, but also helps to suppress the growth of austenite grains by precipitating Al-based carbonitrides and to secure a pro-eutectoid ferrite fraction close to the equilibrium phase.
- Al content is less than 0.01%, most of the Al is dissolved due to insufficient solid-solution aluminum, so that aluminum nitride (AlN) is not sufficiently produced to suppress austenite grain growth during heat treatment, so it is preferably 0.01% or more.
- AlN aluminum nitride
- the Al content is preferably 0.01 to 0.06%.
- the N has a solid solution strengthening effect, but when it exceeds 0.02%, the toughness and ductility of the material may be lowered due to solid solution nitrogen that is not bonded to nitride, so the N content is preferably managed to 0.02% or less. .
- the rest includes iron (Fe), and since unintended impurities from raw materials or the surrounding environment may inevitably be mixed in a normal manufacturing process, they cannot be excluded. Since these impurities are known to anyone skilled in the art during the manufacturing process, not all of them are specifically mentioned in the present specification.
- the microstructure of the wire rod which is one aspect of the present invention, includes pro-eutectoid cementite in the pearlite main structure.
- the pro-eutectoid cementite is formed in a network at the grain boundary along the old austenite grains, and complete pearlite is formed within the grains.
- supersaturated carbon in austenite precipitates as Fe 3 C during cooling
- proeutectoid cementite is formed at the old austenite grain boundary, and proeutectoid cementite takes on a network shape due to refinement of crystal grains, which are diffusion paths of elements.
- AlN is precipitated in the microstructure, and it is preferable that 20 or more AlNs having an average particle diameter of 30 nm or less are distributed per unit area ( ⁇ m 2 ).
- the average particle diameter of the AlN exceeds 30 nm, since the effect of suppressing crystal grain growth by pinning is significantly reduced, it is preferable to have a size of 30 nm or less, and if it is less than 20 per unit area ( ⁇ m 2 ), , Even if AlN is generated, the number of AlN to suppress grain growth is not sufficient, and thus grains may be coarsened.
- the number of AlN having a size of 30 nm or less per unit area ( ⁇ m 2 ) is more preferably 50 or more.
- the pearlite and pro-eutectoid cementite contain 10% or less of pro-eutectoid cementite in area fraction, preferably the remainder is pearlite, and incidentally contain one or more of pro-eutectoid ferrite, bainite and martensite of 5% or less can If the fraction of the pro-eutectoid cementite exceeds 10%, since toughness may rapidly deteriorate, it is preferable not to exceed 10%. On the other hand, one or more of pro-eutectoid ferrite, bainite, and martensite may partially occur in the wire rod manufacturing process, but if it exceeds 5%, breakage during drawing may easily occur, so it is preferable not to exceed 5%.
- the grain boundary characteristics play a role in determining the total heat treatment time as a major factor determining the diffusion rate.
- the cementite in the pearlite structure changes its shape from a plate to a spherical shape, and the strength of the material decreases according to the degree of spheroidization.
- metal atoms move in various diffusion paths through the defect space in the material, such as vacancy, which is an atomic unit defect, and dislocation or pipe, which is a kind of other line defects, and grain boundaries. spread through the Dislocations compared to atomic defects and grain boundaries are advantageous for rapid diffusion because their spaces are relatively wide.
- the wire rod of the present invention can obtain a wire rod having excellent drawing performance through a microstructure that satisfies the following relational expression 1, even if the spherical soft nitriding heat treatment is omitted or shortened.
- the block crystal grains mean crystal grains of a group having the same orientation of ferrite among cementite and ferrite constituting pearlite, and the average size means the average grain size of the crystal grains.
- the length of pro-eutectoid cementite means the total length of pro-eutectoid cementite measured in a unit area (1200 ⁇ m 2 ). As described above, since the proeutectoid cementite is formed along the old austenite grain boundary, the length of the proeutectoid cementite preferably means a length measured along the grain boundary.
- the wire rod of the present invention can be drawn by 15% or more without spherical soft nitriding heat treatment before the drawing process, has a tensile strength (TS) of 1200 MPa or more, and a cross-sectional area reduction rate of 20% or more.
- the wire rod of the present invention can be wire-drawn even if the spherical softening heat treatment is omitted.
- Commonly used materials may cause defects such as chevron cracks even with a freshness of about 10% due to the coarse grain size. However, defects such as cracks do not occur inside the wire rod of the present invention even when the amount of drawing exceeds 15% and is about 30%.
- wire rods are manufactured into steel wires, and two rounds of spheroidal nitriding heat treatment and a wire drawing process for sizing of the material are usually applied.
- Conventional spherical soft nitriding heat treatment is performed at a temperature of Ae1 to Ae1 + 100 ° C, and after heat treatment, carbides having an average cementite aspect ratio of 3 or less are generated in the entire surface to center region.
- the wire rod of the present invention imparts a greater amount of drawing than conventional materials through improved wire drawing processability through the production of fine-grained wire rods, and promotes the generation of spheroidized cementite during spheroidizing heat treatment, so that only one spheroidizing heat treatment after drawing Since the average aspect ratio is 3 or less and a low tensile strength of 740 MPa or less is obtained, it is possible to facilitate cold pressing or cold forging for manufacturing final products.
- a method for manufacturing a wire rod which is another aspect of the present invention, will be described in detail.
- a billet is prepared by heating and rolling a steel piece having the above-described alloy composition, for example, bloom, and heating, wire rod rolling, winding and cooling the billet It can be manufactured by Each step is described in detail below.
- a steel piece having the above-described alloy composition for example, a bloom is prepared, and heated to 1100 to 1300 ° C.
- the heating temperature of the slab is less than 1100° C., the temperature is low and is not sufficient to diffuse the elements in the slab, making it difficult to resolve the segregated layer generated during casting.
- the temperature exceeds 1300 ° C., scale is rapidly formed on the surface of the slab, resulting in surface defects during rolling or reduced productivity due to material loss.
- the heating time of the steel piece is preferably 2 to 10 hours, and if the heating time of the steel piece is less than 2 hours, it is difficult to reach the target temperature to the inside of the steel piece, and if it exceeds 10 hours, the depth of the surface decarburized layer becomes thicker even after rolling is finished. A decarburized layer may remain, so it is preferable not to exceed 10 hours.
- the heated steel piece is rolled into a steel piece to produce a billet.
- the billet produced after the steel strip rolling is generally cooled to room temperature through air cooling, but in the present invention, the billet at 500 ° C or higher is cooled at a cooling rate of 5 ° C / s or higher.
- water cooling is preferably performed, and as a specific example, it is preferable to prevent AlN precipitation and coarsening as much as possible by charging the AlN into a water cooling chamber.
- the billet is water-cooled below 500° C., AlN is precipitated and coarsened, and AlN is not sufficiently dissolved during billet heating for wire rod manufacturing, which is the next step, making it difficult to secure AlN of 30 nm or less.
- the prepared billet is heated to a temperature range of 950 to 1050 ° C. If the billet heating temperature is less than 950 ° C, the rollability is reduced, and if the billet heating temperature exceeds 1050 ° C, rapid cooling is required for rolling, so that not only is it difficult to control cooling, but also cracks occur, resulting in good Ensuring product quality can be difficult.
- the heating time is preferably 80 to 120 minutes. If the heating time is less than 80 minutes, it is difficult to reach the target temperature to the inside of the material, and an atmosphere in which reverse transformation is not partially completed may occur. If the time exceeds 120 minutes, the depth of the surface decarburized layer becomes thick, and the decarburized layer may remain after rolling is finished, which is not preferable.
- the heated billet is wire rod rolled to obtain a wire rod.
- the wire rod rolling is preferably a ball-shaped rolling in which the billet has a shape of a wire rod.
- the austenite grain size (AGS) is 5 to 20 ⁇ m before finish rolling in order to refine the crystal grains during final finish rolling.
- finish rolling is preferably performed at a deformation amount of 0.3 or more in a temperature range of 730° C. to Acm. It is more preferable that the said distortion amount is 0.5 or more.
- Acm means the temperature at which cementite is dissolved during heating in the hypereutectoid steel or cementite is precipitated during cooling.
- the AGS before the finish rolling is less than 5 ⁇ m, since it is implemented through rough rolling at a low temperature, there is a problem that the roll load increases and the equipment life is shortened. It is difficult to manufacture wire rods with fine grains.
- the finish rolling temperature is lower than 730 ° C., the rolling roll load increases and the life span of the equipment is shortened.
- the finish rolling temperature is higher than Acm, phase transformation does not occur, making it difficult to manufacture fine-grained wire rods.
- Carbon content affects the production of cementite (Fe 3 C) in the manufactured wire rod and spheroidized heat treatment material, which affects mechanical properties such as tensile strength, so it must contain appropriate carbon, and Al is the amount The smaller the amount, the smaller the amount of AlN precipitated, so that crystal grain growth cannot be suppressed, so an optimal amount is required.
- the rolling amount and finish rolling temperature must be lowered in order to refine grains as the AGS before finish rolling increases, it is preferable to manage the appropriate AGS and finish rolling temperature from the viewpoint of process cost.
- the relational expression 2 reflects this technical point of view, and when the value of the relational expression 2 exceeds 80, it is difficult to expect proper cementite formation and grain refinement effect.
- the cooling is preferably performed at an average cooling rate of 3° C./sec or more to a temperature range of 550 to 650° C., and then cooled at an average cooling rate of 1° C./sec or less after 550 to 650° C.
- the average cooling rate up to the temperature range of 550 to 650 ° C is less than 3 ° C / sec, it is difficult to maintain the fine grains obtained during rolling to the transformation point or less.
- the cooling rate below that is preferably 1 ° C / sec or less in terms of suppressing low-temperature structures such as bainite and martensite.
- heating at Ae1 to Ae1 + 100 ° C, holding for 5 to 15 hours, and then performing spheroidization heat treatment to cool at 20 ° C / hr or less to 660 ° C to prepare a spheroidized material can do.
- the heating temperature is less than Ae1
- Ae1 means the temperature at which austenite is formed during heating or at which austenite disappears during cooling.
- the holding time is less than 5 hours, there may be a disadvantage in that the aspect ratio of cementite increases because the spheroidization heat treatment does not sufficiently proceed, and if the holding time exceeds 15 hours, there may be a disadvantage in that the cost increases. If the cooling rate exceeds 20 °C / hr, there may be a disadvantage in that pearlite is formed again due to the fast cooling rate. After the spheroidization heat treatment, the wire rod has a low tensile strength of 740 MPa or less and an average cementite aspect ratio of 3 or less, so that cold pressing or cold forging processing for final product manufacturing can be facilitated.
- the austenite grain size (AGS) before finish rolling was collected by cutting the material through a cutting crop performed before finish hot rolling and immediately quenching in water, using the ASTM E112 method. to measure AGS. For the specimens collected, 5 random points of 1/4 from the diameter were measured and expressed as the average value.
- the average block grain size was measured using EBSD and ASTM E112 methods.
- a block is a region with the same crystal orientation of ferrite in pearlite, and the block size is defined as a size having a difference of more than 15 degrees in crystal orientation.
- Inventive Example 1 and Comparative Example 5 among the following Examples were observed and shown in FIGS. 3 and 4, respectively.
- the size of the block was quantified using the ASTM E112 method.
- the measured material was measured at 5 arbitrary points of 1/4 from the diameter of the sample collected after removing the uncooled part after rolling the wire, and then expressed as an average value.
- the length of pro-eutectoid cementite was taken by X3000 times using SEM at 1/4 random 5 points from the diameter of the sample taken after removing the uncooled portion after rolling the wire, and using Leica's Clemex vision software The total length was analyzed and the average of 5 points was obtained.
- the wire drawing processability evaluation was evaluated by drawing the manufactured 9mm wire rod at a cross-sectional reduction rate of 5 to 50%, and photographing the center of the L section of the drawn material at 5000 times, and chevron cracks such as pearlite interface, proeutectoid cementite interface, etc. ) was confirmed, and the presence or absence was indicated by O/X.
- the average aspect ratio of cementite was photographed with 3 fields of view at 1/4 to 1/2 points in the diameter direction of the wire rod with 3000 times SEM, and using an image measurement program, the long axis / The shortening was measured through statistical processing after automatic measurement.
- relational expression 2 is 2500*([C]-1) 2 +100000*([Al]-0.035) 2 +(AGS-12.5) 4 /130+(finish rolling temperature-760) 2/65 Calculated, where [C] and [Al] are the contents (wt%) of C and Al in the alloy composition, AGS is the average grain size of austenite in ⁇ m, and the unit of finish rolling temperature is °C
- pro-eutectoid C denotes pro-eutectoid cementite
- P denotes perlite
- B denotes bainite
- M denotes martensite.
- relational expression 1 means (average size of block crystal grains ( ⁇ m)) 2 / (length of pro-eutectoid cementite ( ⁇ m/1200 ⁇ m 2 )).
- FIG. 1 is a photograph of the wire rod microstructure of Inventive Example 1 observed with a scanning electron microscope (SEM). Referring to FIG. 1, Inventive Example 1 is composed of proeutectoid cementite and complete pearlite, and the arrow in FIG.
- proeutectoid cementite As shown in FIG. 1, it can be confirmed that the pro-eutectoid cementite is formed along the old austenite grain boundary.
- 3 is an EBSD photograph of Inventive Example 1, and it can be confirmed that the grain orientation difference is 2 degrees or more, and thus, the average block grain size of Inventive Example 1 is about 4.7 ⁇ m, which is very small compared to normal manufacturing conditions.
- Comparative Example 1 air cooling was performed after steel strip rolling, resulting in coarsening of AlN in the steel, and in case of Comparative Example 2, almost no AlN was produced due to the low Al content in the steel composition.
- the number of AlNs having a size of 30 nm or less per ⁇ m 2 was 20 or less, and the size of block grains was not controlled because grain growth could not be suppressed during wire cooling.
- Comparative Example 3 the carbon content is low and pro-eutectoid ferrite remains in the wire rod, so the wire drawing characteristics are superior to other comparative examples, but the strength is low due to the low carbon content, which is unsuitable for use due to the low strength of the material even after spheroidization heat treatment. difficult to use properly.
- Comparative Example 4 the AGS size before finish rolling is larger than that of the inventive examples due to the high billet heating temperature. Since grain refinement of coarse AGS can be achieved through a high critical strain amount, an insufficient amount of finish rolling strain eventually causes coarse grains to appear in the wire rod, resulting in poor drawing performance. In Comparative Example 5, fine crystal grains were not obtained due to the high finish rolling temperature, and the drawing characteristics were not excellent due to coarse crystal grains, similar to Comparative Example 4.
- 2 is a photograph of the wire rod microstructure of Comparative Example 5 observed by SEM, and it can be confirmed that the grain size is larger than that of FIG. 1, and the length of pro-eutectoid cementite produced along the old austenite grain boundary is short.
- FIG. 4 is an EBSD photograph of Comparative Example 5, and the grain orientation difference is classified as in FIG. 3. When compared with FIG. 3, it can be seen that the block grain size of Comparative Example 5 of FIG. 4 is coarse.
- Comparative Example 6 fine crystal grains were not obtained due to a small amount of finish rolling, and coarse crystal grains appeared on the wire rod, resulting in poor drawing characteristics.
- the wire rod of Comparative Example 7 fine crystal grains made by rolling were coarsened due to a low cooling rate at the beginning, so that fine wire rod crystal grains could not be obtained, resulting in poor drawing characteristics.
- Comparative Example 8 due to the fast cooling rate, martensite and bainite appeared, and it was confirmed that internal cracks occurred even with 5% wire drawing.
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Abstract
Description
강종 | C | Si | Mn | Cr | Al | N |
강종 1 | 1.05 | 0.29 | 0.30 | 1.69 | 0.023 | 0.006 |
강종 2 | 1.01 | 0.28 | 0.35 | 1.33 | 0.024 | 0.005 |
강종 3 | 0.96 | 0.25 | 0.35 | 1.36 | 0.023 | 0.004 |
강종 4 | 1.00 | 0.25 | 0.33 | 1.36 | 0.027 | 0.006 |
강종 5 | 0.95 | 0.24 | 0.33 | 1.39 | 0.029 | 0.005 |
강종 6 | 1.00 | 0.30 | 0.27 | 1.51 | 0.025 | 0.003 |
강종 7 | 0.97 | 0.23 | 0.33 | 1.41 | 0.003 | 0.006 |
강종 8 | 0.50 | 0.20 | 0.27 | 1.48 | 0.023 | 0.006 |
강종 9 | 0.97 | 0.20 | 0.32 | 1.34 | 0.030 | 0.003 |
강종 10 | 1.04 | 0.22 | 0.27 | 1.57 | 0.030 | 0.003 |
강종 11 | 0.98 | 0.23 | 0.27 | 1.65 | 0.026 | 0.003 |
강종 12 | 0.98 | 0.28 | 0.30 | 1.50 | 0.024 | 0.007 |
강종 13 | 1.03 | 0.25 | 0.27 | 1.60 | 0.021 | 0.007 |
강종 | 구분 | 강편 압연 후 냉각방법 | 빌렛 가열온도 (℃) |
빌렛 가열시간 (분) |
마무리 압연 전 AGS (㎛) |
마무리 압연 온도 (℃) |
마무리 압연 변형량 |
관계식 2 | 600℃까지 냉각속도 (℃/sec) |
600℃ 이후 냉각속도 (℃/sec) |
강종 1 | 발명예 1 | 수냉 | 960 | 83 | 10 | 779 | 0.6 | 28 | 3.2 | 0.6 |
강종 2 | 발명예 2 | 수냉 | 1030 | 92 | 12 | 769 | 1 | 14 | 4.7 | 1 |
강종 3 | 발명예 3 | 수냉 | 1050 | 105 | 8 | 761 | 0.5 | 22 | 4.9 | 1 |
강종 4 | 발명예 4 | 수냉 | 1003 | 110 | 7 | 773 | 1 | 16 | 3.6 | 0.8 |
강종 5 | 발명예 5 | 수냉 | 955 | 97 | 10 | 754 | 0.5 | 11 | 4.4 | 0.7 |
강종 6 | 비교예 1 | 공냉 | 959 | 99 | 12 | 769 | 1 | 11 | 3.5 | 0.6 |
강종 7 | 비교예 2 | 수냉 | 1049 | 83 | 8 | 746 | 0.8 | 111 | 4.3 | 0.8 |
강종 8 | 비교예 3 | 수냉 | 1014 | 105 | 7 | 739 | 0.6 | 654 | 3.8 | 0.9 |
강종 9 | 비교예 4 | 수냉 | 1237 | 85 | 24 | 747 | 0.9 | 142 | 3.5 | 0.7 |
강종 10 | 비교예 5 | 수냉 | 1050 | 99 | 12 | 876 | 0.5 | 214 | 4.9 | 1 |
강종 11 | 비교예 6 | 수냉 | 982 | 88 | 11 | 758 | 0.2 | 10 | 3 | 0.6 |
강종 12 | 비교예 7 | 수냉 | 977 | 94 | 12 | 760 | 0.5 | 13 | 1.2 | 0.5 |
강종 13 | 비교예 8 | 수냉 | 968 | 105 | 10 | 761 | 1 | 22 | 3.7 | 5 |
구분 | 미세조직 | ㎛2 당, 30㎚ 이하의 AlN 개수 | 블록 결정립 평균 크기 (㎛) |
초석 세멘타이트 길이 (㎛/1200㎛2) |
관계식 1 | 인장강도 (MPa) |
단면 감소율 (%) |
발명예 1 | 초석C + P | 67 | 4.7 | 212 | 0.10 | 1270 | 28 |
발명예 2 | 초석C + P | 90 | 3.2 | 206 | 0.05 | 1251 | 35 |
발명예 3 | 초석C + P | 68 | 6.4 | 225 | 0.18 | 1239 | 26 |
발명예 4 | 초석C + P | 69 | 3 | 241 | 0.04 | 1262 | 37 |
발명예 5 | 초석C + P | 71 | 7.2 | 156 | 0.33 | 1292 | 31 |
비교예 1 | 초석C + P | 13 | 10.2 | 63 | 1.65 | 1178 | 17 |
비교예 2 | 초석C + P | 16 | 9.7 | 67 | 1.40 | 1182 | 19 |
비교예 3 | 초석C + P | 76 | 4.3 | 230 | 0.08 | 850 | 31 |
비교예 4 | 초석C + P | 60 | 12.4 | 70 | 2.20 | 1157 | 17 |
비교예 5 | 초석C + P | 86 | 11.6 | 62 | 2.17 | 1162 | 19 |
비교예 6 | 초석C + P | 79 | 12.1 | 57 | 2.57 | 1171 | 16 |
비교예 7 | 초석C + P | 69 | 9 | 112 | 0.72 | 1192 | 19 |
비교예 8 | 초석C + P + B + M | 48 | 측정불가 | 192 | 측정불가 | 1491 | 12 |
구분 | 신선량(%)에 따른 소재 내부 크랙 발생 여부 | 적용 신선량과 구상화 열처리 후 미세조직 및 기계적 물성 | ||||||||
5 | 10 | 15 | 20 | 30 | 40 | 50 | 구상화 열처리 전 신선량(%) | 구상화 열처리 후 세멘타이트 평균 종횡비 | 구상화 열처리 후 인장강도 (MPa) | |
발명예 1 | ○ | ○ | ○ | ○ | ○ | ○ | X | 30 | 1.7 | 716 |
발명예 2 | ○ | ○ | ○ | ○ | ○ | ○ | ○ | 20 | 2.3 | 724 |
발명예 3 | ○ | ○ | ○ | ○ | ○ | ○ | ○ | 40 | 2.5 | 721 |
발명예 4 | ○ | ○ | ○ | ○ | ○ | X | X | 30 | 2.5 | 730 |
발명예 5 | ○ | ○ | ○ | ○ | ○ | ○ | X | 40 | 1.6 | 726 |
비교예 1 | ○ | X | X | X | X | X | X | 5 | 5.7 | 811 |
비교예 2 | ○ | ○ | X | X | X | X | X | 10 | 6.1 | 807 |
비교예 3 | ○ | ○ | ○ | ○ | ○ | ○ | X | 40 | 2.3 | 607 |
비교예 4 | ○ | X | X | X | X | X | X | 5 | 7.3 | 813 |
비교예 5 | ○ | X | X | X | X | X | X | 5 | 6.2 | 827 |
비교예 6 | ○ | X | X | X | X | X | X | 5 | 6.9 | 832 |
비교예 7 | ○ | ○ | X | X | X | X | X | 10 | 5.8 | 789 |
비교예 8 | X | X | X | X | X | X | X | 0 | 7.6 | 812 |
Claims (10)
- 중량%로, C: 0.8~1.2%, Si: 0.01~0.6%, Mn: 0.1~0.6%, Cr: 0.8~2.0%, Al: 0.01~0.06%, N: 0.02% 이하(0은 제외), 나머지는 Fe와 불가피한 불순물을 포함하고,미세조직은 펄라이트 주조직에 초석 세멘타이트를 포함하며,평균입경 30㎚ 이하의 AlN이 단위면적(㎛2) 당 20개 이상 포함하고,하기 관계식 1을 만족하는 미세조직을 포함하는 신선 가공성이 우수한 선재.[관계식 1](블록 결정립 평균 크기(㎛))2/(초석 세멘타이트 길이(㎛/1200㎛2))≤0.5
- 청구항 1에 있어서,상기 초석 세멘타이트는 구오스테나이트 결정립을 따라 결정립계에 형성되고, 망상형으로 형성된 신선 가공성이 우수한 선재.
- 청구항 1에 있어서,상기 미세조직은 면적분율로 10% 이하의 초석 세멘타이트와 나머지는 펄라이트인 신선 가공성이 우수한 선재.
- 청구항 1에 있어서,상기 선재는 인장강도 1200MPa 이상, 단면감소율이 20% 이상인 신선 가공성이 우수한 선재.
- 청구항 1에 있어서,상기 선재는 신선공정 전 구상 연질화 열처리하지 않고, 신선 시 15% 이상 신선되는 신선 가공성이 우수한 선재.
- 청구항 1에 있어서,상기 선재는 신선 및 구상화 열처리 후 시멘타이트의 평균 종횡비가 3 이하인 신선 가공성이 우수한 선재.
- 중량%로, C: 0.8~1.2%, Si: 0.01~0.6%, Mn: 0.1~0.6%, Cr: 0.8~2.0%, Al: 0.01~0.06%, N: 0.02% 이하(0은 제외), 나머지는 Fe와 불가피한 불순물을 포함하는 강편을 가열하고, 강편압연을 행하여 빌렛을 제조하는 단계;상기 제조된 빌렛을 냉각하는 단계;상기 빌렛을 950~1050℃로 가열하는 단계;상기 가열된 빌렛을 선재압연하여 선재를 제조하는 단계; 및상기 선재를 권취하고, 550~650℃까지 3℃/sec 이상의 평균 냉각속도로 냉각하고, 550~650℃ 이하의 온도에서는 1℃/sec 이하의 평균 냉각속로 냉각하는 단계를 포함하고,상기 선재압연은 마무리 압연 전 오스테나이트 결정립 사이즈(austenite grain size, AGS)가 5~20㎛이 되도록 행하고, 마무리 압연은 730℃~Acm의 온도범위에서 변형량 0.3 이상으로 행하는 것을 포함하는 신선 가공성이 우수한 선재의 제조방법.
- 청구항 7에 있어서,상기 열간압연은 하기 식 (2)의 조건을 충족하도록 행하는 신선 가공성이 우수한 선재의 제조방법.[관계식 2]2500*([C]-1)2+100000*([Al]-0.035)2+(AGS-12.5)4/130+(마무리압연온도-760)2/65 ≤ 80(상기 관계식 (2)에서 [C] 및 [Al]은 합금조성 C와 Al의 함량(중량%)을 의미하고, AGS의 단위는 ㎛이고, 마무리압연온도의 단위는 ℃임.)
- 청구항 7에 있어서,상기 강편을 1100~1300℃의 온도범위에서 2~10 시간 가열하고, 상기 강편압연 후 500℃ 이상의 빌렛을 5℃/s 이상의 냉각속도로 냉각하는 신선 가공성이 우수한 선재의 제조방법.
- 청구항 7에 있어서,상기 빌렛 가열시간은 80~120분인 신선 가공성이 우수한 선재의 제조방법.
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JP2012041587A (ja) * | 2010-08-17 | 2012-03-01 | Nippon Steel Corp | 高強度かつ耐水素脆化特性に優れた機械部品用線材、鋼線、および機械部品とその製造方法 |
KR20160099671A (ko) * | 2014-01-10 | 2016-08-22 | 신닛테츠스미킨 카부시키카이샤 | 베어링 부품, 베어링 부품용 강재 및 그들의 제조 방법 |
KR20170054492A (ko) * | 2014-10-20 | 2017-05-17 | 신닛테츠스미킨 카부시키카이샤 | 신선 가공성 및 신선 가공 후의 코일 성형성이 우수한 베어링용 강선재 |
KR20210000023A (ko) * | 2019-06-24 | 2021-01-04 | 현대제철 주식회사 | 신선 가공성이 우수한 경강 선재 제조방법 및 이에 의해 제조된 경강 선재 |
CN110846557A (zh) * | 2019-12-05 | 2020-02-28 | 宝钢特钢韶关有限公司 | 高碳铬磨球钢及其制备方法 |
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KR20220169272A (ko) | 2022-12-27 |
JP2024521184A (ja) | 2024-05-28 |
EP4357477A1 (en) | 2024-04-24 |
CN117396626A (zh) | 2024-01-12 |
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