WO2022131752A1 - 지연파괴 저항성이 향상된 선재, 부품 및 그 제조방법 - Google Patents
지연파괴 저항성이 향상된 선재, 부품 및 그 제조방법 Download PDFInfo
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- WO2022131752A1 WO2022131752A1 PCT/KR2021/018977 KR2021018977W WO2022131752A1 WO 2022131752 A1 WO2022131752 A1 WO 2022131752A1 KR 2021018977 W KR2021018977 W KR 2021018977W WO 2022131752 A1 WO2022131752 A1 WO 2022131752A1
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- wire rod
- delayed fracture
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- 230000003111 delayed effect Effects 0.000 title claims abstract description 69
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 17
- 238000000034 method Methods 0.000 title claims abstract description 15
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 12
- 239000012535 impurity Substances 0.000 claims abstract description 11
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 11
- 229910000831 Steel Inorganic materials 0.000 claims description 25
- 239000010959 steel Substances 0.000 claims description 25
- 229910001566 austenite Inorganic materials 0.000 claims description 22
- 238000010438 heat treatment Methods 0.000 claims description 21
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 claims description 19
- 230000000717 retained effect Effects 0.000 claims description 11
- 229910052710 silicon Inorganic materials 0.000 claims description 11
- 229910052717 sulfur Inorganic materials 0.000 claims description 10
- 229910052796 boron Inorganic materials 0.000 claims description 9
- 229910000734 martensite Inorganic materials 0.000 claims description 9
- 239000000463 material Substances 0.000 claims description 9
- 238000005096 rolling process Methods 0.000 claims description 9
- 238000010791 quenching Methods 0.000 claims description 8
- 230000000171 quenching effect Effects 0.000 claims description 8
- 238000005496 tempering Methods 0.000 claims description 8
- 229910052719 titanium Inorganic materials 0.000 claims description 8
- 238000004804 winding Methods 0.000 claims description 8
- 229910052799 carbon Inorganic materials 0.000 claims description 5
- 230000000052 comparative effect Effects 0.000 description 33
- 239000011572 manganese Substances 0.000 description 31
- 239000010936 titanium Substances 0.000 description 30
- 238000005728 strengthening Methods 0.000 description 17
- 230000000694 effects Effects 0.000 description 13
- 239000006104 solid solution Substances 0.000 description 13
- 239000000047 product Substances 0.000 description 12
- 229910052757 nitrogen Inorganic materials 0.000 description 8
- 229910045601 alloy Inorganic materials 0.000 description 7
- 239000000956 alloy Substances 0.000 description 7
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 7
- 239000000203 mixture Substances 0.000 description 7
- 239000013078 crystal Substances 0.000 description 6
- 238000007670 refining Methods 0.000 description 6
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 4
- 229910052739 hydrogen Inorganic materials 0.000 description 4
- 239000001257 hydrogen Substances 0.000 description 4
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- KZEVSDGEBAJOTK-UHFFFAOYSA-N 1-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)-2-[5-[2-[[3-(trifluoromethoxy)phenyl]methylamino]pyrimidin-5-yl]-1,3,4-oxadiazol-2-yl]ethanone Chemical compound N1N=NC=2CN(CCC=21)C(CC=1OC(=NN=1)C=1C=NC(=NC=1)NCC1=CC(=CC=C1)OC(F)(F)F)=O KZEVSDGEBAJOTK-UHFFFAOYSA-N 0.000 description 2
- YJLUBHOZZTYQIP-UHFFFAOYSA-N 2-[5-[2-(2,3-dihydro-1H-inden-2-ylamino)pyrimidin-5-yl]-1,3,4-oxadiazol-2-yl]-1-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)ethanone Chemical compound C1C(CC2=CC=CC=C12)NC1=NC=C(C=N1)C1=NN=C(O1)CC(=O)N1CC2=C(CC1)NN=N2 YJLUBHOZZTYQIP-UHFFFAOYSA-N 0.000 description 2
- APLNAFMUEHKRLM-UHFFFAOYSA-N 2-[5-[2-(2,3-dihydro-1H-inden-2-ylamino)pyrimidin-5-yl]-1,3,4-oxadiazol-2-yl]-1-(3,4,6,7-tetrahydroimidazo[4,5-c]pyridin-5-yl)ethanone Chemical compound C1C(CC2=CC=CC=C12)NC1=NC=C(C=N1)C1=NN=C(O1)CC(=O)N1CC2=C(CC1)N=CN2 APLNAFMUEHKRLM-UHFFFAOYSA-N 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 2
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 2
- 238000005275 alloying Methods 0.000 description 2
- 150000002431 hydrogen Chemical class 0.000 description 2
- 239000011159 matrix material Substances 0.000 description 2
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- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 1
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
- 229910001182 Mo alloy Inorganic materials 0.000 description 1
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- 238000009825 accumulation Methods 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 238000005261 decarburization Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
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- 238000013100 final test Methods 0.000 description 1
- 238000005098 hot rolling Methods 0.000 description 1
- 230000002706 hydrostatic effect Effects 0.000 description 1
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- 229910052742 iron Inorganic materials 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
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- 239000010703 silicon Substances 0.000 description 1
- 238000004088 simulation Methods 0.000 description 1
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- 239000002344 surface layer Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 239000013585 weight reducing agent Substances 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
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
- C21D1/32—Soft annealing, e.g. spheroidising
-
- 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
- C21D9/0093—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for screws; for bolts
-
- 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
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
-
- 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
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/001—Austenite
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
Definitions
- the present invention relates to a wire rod, parts, and a method for manufacturing the same having improved delayed fracture resistance, and more particularly, to a wire rod, a part, and a method for manufacturing the same, which can be used in automobiles and bolts for fastening structures exposed to various stress and corrosive environments. it's about
- Wire rods used as materials such as bolts for fastening automobiles and structures are required to increase in strength according to the weight reduction of automobiles and miniaturization of structures.
- cold working, grain refinement, martensite strengthening and precipitation strengthening which are metal strengthening mechanisms, are used.
- dislocations, grain boundaries, martensite lath boundaries, and fine precipitate boundaries used as such strengthening mechanisms act as hydrogen traps in the steel and also act as a cause of inferior delayed fracture. For this reason, there is a problem in that delayed failure is inferior in high-strength bolts with a tensile strength of 1 GPa or more.
- One aspect of the present invention is to provide a wire rod for high-strength bolts, a bolt, and a manufacturing method thereof, having improved delayed fracture resistance by optimizing the solid solution strengthening effect of Mn-B steel and improving formability through control of alloying elements.
- the wire rod with improved delayed fracture resistance is, by weight, C: 0.15 to 0.30%, Si: 0.15 to 0.25%, Mn: 0.95 to 1.35%, P: 0.030% or less, S: 0.030%
- the remainder includes Fe and unavoidable impurities, and the following relational expression 1 is satisfied.
- the size of the TiN inclusions may be 15 ⁇ m or less.
- the method of manufacturing a wire rod having improved delayed fracture resistance is, by weight, C: 0.15 to 0.30%, Si: 0.15 to 0.25%, Mn: 0.95 to 1.35%, P: 0.030% or less, S : 0.030% or less, Ti: 0.015 to 0.030%, B: 0.0010 to 0.0040%, N: 0.0010 to 0.0080%, the remainder including Fe and unavoidable impurities, and finishing the steel material satisfying the following relation 1 at 880 to 980 ° C. rolling; and
- the steel material may satisfy the following relational expression (2).
- a method for manufacturing a component having improved delayed fracture resistance comprising: drawing a wire rod manufactured according to the present invention; spheroidizing heat treatment of the wire rod at 745 to 770°C; Heating the spheroidizing heat-treated wire rod in a temperature range of 870 to 940 °C; Quenching the spheroidizing heat-treated wire rod in a temperature range of 50 to 80 °C; and tempering the quenched part in a temperature range of 400 to 600°C.
- the component with improved delayed fracture resistance is, by weight, C: 0.15 to 0.30%, Si: 0.15 to 0.25%, Mn: 0.95 to 1.35%, P: 0.030% or less, S: 0.030%
- the remainder includes Fe and unavoidable impurities, and the following relational expression 1 is satisfied.
- the component satisfies the following relational expression (2).
- the part includes, by volume fraction, 0.3 to 2% of retained austenite and a residual tempered martensitic structure.
- the parts for high-strength bolts with improved delayed fracture resistance improve the formability during bolt thread processing of Mn-B steel, thereby suppressing delayed fracture in 1Gpa-class high-strength bolts without generating cracks in the bolt thread part.
- the inventors of the present invention have found that by controlling the content of Si and Mn, it is possible to optimize the solid solution strengthening effect and improve the formability while securing the strength, and it is possible to suppress the occurrence of cracks due to the molding defect of the screw portion and improve the delayed fracture resistance. found out that
- the wire rod with improved delayed fracture resistance is, by weight, C: 0.15 to 0.30%, Si: 0.15 to 0.25%, Mn: 0.95 to 1.35%, P: 0.030% or less, S: 0.030%
- the remainder contains Fe and unavoidable impurities.
- the unit is % by weight.
- the content of carbon (C) is 0.15 to 0.30%.
- C is an element added to secure product strength.
- the carbon content is less than 0.15%, it is difficult to secure the target strength in the present invention, and when it exceeds 0.30%, mechanical stability formed by hydrostatic pressure at the lath martensite boundary during quenching (mechanical stability) Stabilization) may prevent the formation of excellent retained austenite, resulting in poor resistance to delayed fracture. Therefore, in the present invention, the content of C is limited to 0.15 to 0.30%.
- the content of silicon (Si) is 0.15 to 0.25%.
- Si is not only useful for deoxidation of steel, but is also an effective element for securing strength through solid solution strengthening.
- the content of Si is less than 0.15%, it is not sufficient to secure strength through deoxidation and solid solution strengthening of steel, and when it exceeds 0.25%, formability and impact properties by solid solution strengthening may be inferior. Therefore, in the present invention, the content of Si is limited to 0.15 to 0.25%.
- the content of manganese (Mn) is 0.95 to 1.35%.
- Mn is an element that improves hardenability, and is a very useful element that forms a substitutional solid solution in the matrix structure to produce a solid solution strengthening effect.
- the content of Mn is less than 0.95%, it is difficult to secure the strength targeted in the present invention because the above-described solid solution strengthening effect and hardenability are not sufficient, and when it exceeds 1.35%, the formability may be inferior due to the solid solution strengthening effect. . Therefore, in the present invention, the content of Mn is limited to 0.95 to 1.35%.
- the content of phosphorus (P) is 0.030% or less. (excluding 0%)
- P is an element that segregates at grain boundaries to reduce toughness and reduce resistance to delayed fracture. Therefore, in the present invention, the upper limit of P is limited to 0.030%.
- the content of sulfur (S) is 0.030% or less. (excluding 0%)
- S is segregated at grain boundaries to reduce toughness, and is an element that inhibits hot rolling by forming a low melting point emulsion. Therefore, in the present invention, the upper limit of S is limited to 0.030%.
- the content of titanium (Ti) is 0.015 to 0.030%.
- Ti is an element that combines with N flowing into the steel to form titanium carbonitride (TiN).
- TiN can suppress the occurrence of cracks due to poor forming during part molding by refining the crystal grains and improve the delayed fracture resistance. Further, since Ti forms TiN, it is also possible to prevent free-N (free N) from bonding with B, thereby suppressing the formation of BN which deteriorates formability.
- the content of Ti is less than 0.015%, sufficient TiN is not formed as described above, and since free N forms BN, it is difficult to utilize the hardenability effect of B, and when it exceeds 0.03%, coarse carbonitride is formed formed, and the delayed fracture resistance may be inferior. Therefore, in the present invention, the content of Ti is limited to 0.015 to 0.03%.
- the content of boron (B) is 0.0010 to 0.0040%.
- B is an element which improves hardenability.
- the content of B is less than 0.0010%, it is difficult to expect the effect of improving the hardenability described above, and when it exceeds 0.0040%, Fe 23 (CB) 6 carbides are formed at the grain boundaries to cause brittleness of the austenite grain boundaries, and BN By forming, the moldability is inferior, and the delayed fracture resistance is inferior. Therefore, in the present invention, the B content is limited to 0.0010 to 0.0040%.
- the content of nitrogen (N) is 0.0010 to 0.0080%.
- N is an element that forms carbonitrides.
- the content of N is less than 0.0010%, TiN precipitates for refining crystal grains cannot be sufficiently formed, and when it exceeds 0.0080%, the amount of dissolved nitrogen increases and the toughness and ductility of the steel may be deteriorated, ) can combine with B to form BN, which makes formability inferior. Therefore, in the present invention, the content of N is limited to 0.0010 to 0.0080%.
- the balance other than the alloy composition is iron (Fe).
- the wire rod with improved delayed fracture resistance of the present invention may contain other impurities that may be included in the industrial production process of ordinary steel. These impurities are not particularly limited in the present invention, because the content can be known by anyone having ordinary knowledge in the technical field to which the present invention pertains.
- the wire rod having improved delayed fracture resistance according to an embodiment of the present invention satisfies the following relational expression (1).
- each of [Si] and [Mn] means the content (wt%) of the corresponding element.
- Relation 1 thus derived is an equation for optimizing the employment strengthening effect. If the 5.5 ⁇ [Si]+[Mn] value of Relation 1 is less than 2.0, the strength targeted in the present invention cannot be secured, and when the 5.5 ⁇ [Si]+[Mn] value exceeds 2.4, excessive employment When forming high-strength parts due to the reinforcing effect, cracks may occur due to poor forming, which may lead to delayed failure. Therefore, in the present invention, in order to improve the delayed fracture resistance, the value of 5.5 ⁇ [Si]+[Mn] is limited to 2.0 to 2.4.
- the wire rod having improved delayed fracture resistance according to an embodiment of the present invention satisfies the following relational expression (2).
- each of [Ti] and [N] means the content (wt%) of the corresponding element.
- the [Ti]/3.42[N] value of Relation 2 is 1.0 or less, the formability may be inferior due to BN formed by free-N that is not combined with Ti, and the [Ti]/3.42[N] value is When it is 2.0 or more, TiN is coarsened by excess Ti (excess Ti), and the effect of refining grains cannot be exhibited. Therefore, in the present invention, the [Ti]/3.42[N] value is limited to more than 1.0 and less than 2.0.
- the size of the TiN inclusions for refining the crystal grains may be 15 ⁇ m or less. As described above, when the maximum size of the TiN inclusions exceeds 15 ⁇ m, it is difficult to secure delayed fracture resistance due to grain refinement.
- the part with improved delayed fracture resistance manufactured by the wire rod according to the present invention contains 0.3 to 2% of retained austenite and a residual tempered martensite structure by volume fraction.
- the retained austenite structure fraction is less than 0.3%, it is difficult to expect the role of an obstacle to delay hydrogen diffusion, which makes the delayed fracture resistance inferior. Since it is formed thick, it is difficult to delay hydrogen diffusion, and thus, the effect of improving the delayed fracture resistance may be reduced.
- the wire rod and component having improved delayed fracture resistance according to the present invention can be manufactured by various methods, and the manufacturing method is not particularly limited. However, as an embodiment, it may be manufactured by the following method.
- the wire rod with improved delayed fracture resistance according to the present invention is, by weight, C: 0.15 to 0.30%, Si: 0.15 to 0.25%, Mn: 0.95 to 1.35%, P: 0.030% or less, S: 0.030% or less, Ti: 0.015 to 0.030%, B: 0.0010 to 0.0040%, N: 0.0010 to 0.0080%, the rest of the steel including Fe and unavoidable impurities, finishing rolling at 880 to 980 °C; and winding at 830 to 930 °C.
- a steel material satisfying the above-described alloy composition is prepared, and the finish wire is rolled at 880 to 980°C. Thereafter, the rolled wire rod is wound in a coil shape at 830 to 930°C.
- a surface ferrite decarburized layer may be formed by phase transformation, and a ferrite decarburized layer on the surface even during heat treatment of bolts formed, which may result in inferior resistance to delayed fracture.
- the prior austenite grain size of the bolt product may become fine, and the retained austenite fraction may be increased to deteriorate the delayed fracture resistance.
- the decarburization is accelerated by diffusion and a ferrite decarburized layer may be formed on the surface, and the old austenite grain size becomes coarse, delay fracture resistance may be inferior.
- the wound wire rod can be made into final bolt parts by wire drawing-spheroidizing heat treatment-encapsulation treatment-bolt forming-austenitenizing-quenching-tempering according to the purpose.
- it may be manufactured by the following method.
- a method of manufacturing a part for bolts according to an embodiment of the present invention includes: drawing a wire rod manufactured according to the present invention; spheroidizing heat treatment of the wire rod at 745 to 770°C; heating the spheroidizing heat-treated wire rod at 870 to 940°C; Quenching the spheroidizing heat-treated wire rod at 50 to 80°C; and tempering at 400 to 600°C.
- the spheroidizing heat treatment may be performed at 745 to 770 °C.
- the heat treatment temperature is less than 745 ° C. or exceeds 770 ° C., as the spheroidization rate is lowered, the hardness of the spheroidization heat treatment material increases and the formability is deteriorated during thread processing after bolt forming, which may cause thread cracks.
- the austenitization heat treatment may be performed at 870 to 940°C.
- the heat treatment temperature is less than 870° C.
- the reverse austenite transformation does not occur sufficiently, so that the martensite structure is non-uniformly formed after quenching, and the toughness may be inferior.
- the heat treatment temperature exceeds 940 ° C., the grain size of prior austenite becomes coarse and delayed fracture resistance may be inferior.
- the quenching may be carried out in a temperature range of 50 to 80 °C. If the temperature of the quenching refrigerant is less than 50°C, minute quenching cracks may occur in the screw thread of the bolt due to thermal deformation, which may cause delayed destruction. In addition to the mechanically stable retained austenite, retained austenite is formed at the grain boundary of the old austenite, and rather acts as an accumulation part of hydrogen to cause delayed fracture.
- tempering may be performed in a temperature range of 400 to 600° C., and strength and toughness may be imparted according to the use and purpose of the final product. If the tempering temperature is less than 400 °C, brittleness may be caused by tempering, and if it exceeds 600 °C, it is difficult to implement the strength intended in the present invention.
- the part with improved delayed fracture resistance manufactured according to the present invention includes, by volume fraction, 0.3 to 2% of retained austenite and a residual tempered martensitic structure.
- the wire rods of Inventive Examples 1 to 9 and Comparative Examples 1 to 7 satisfying the alloy compositions of Table 1 below were manufactured under the manufacturing conditions according to the present invention to obtain final test bolts. Specifically, a steel piece satisfying the alloy composition of Table 1 was finish wire rolled at 880 to 980 ° C., wound in a coil shape at 830 to 930 ° C., and then the wound wire rod was subjected to spheroidization heat treatment at a maximum temperature of 745 to 770 ° C. Then, the spheroidizing heat-treated wire rod is formed with a bolt, austenitized at 870 to 940° C., and then quenched in a refrigerant at 50 to 80° C., and then at 400 to 600° C. to secure a tensile strength of 1050 ⁇ 16 MPa. Tempering at temperature gave the final bolted product.
- Maximum TiN Precipitation Size cuts the bolt product in the L section (longitudinal direction), observes an area of 160 mm 2 in 30 fields, and defines the size of the inclusions measured through extreme value analysis as the maximum inclusion size, and the values are shown in the table below 2 is shown.
- Delayed fracture resistance was performed by a delayed fracture simulation method in which the bolt product was fastened to the structure with a clamping force of yield strength, immersed in 5% hydrochloric acid + 95% distilled water solution for 10 minutes, and observed for cracks in the screw thread, which is the stress concentration part.
- a case in which no cracks occurred was indicated by X, and a case in which cracks occurred was indicated by ⁇ .
- Comparative Example 1 had a [Ti]/3.42[N] value of 2.506, exceeding 2.0, which is the upper limit suggested by the present invention, and coarse TiN was formed, which resulted in delayed fracture cracks.
- Comparative Example 3 the Si content is 0.26%, which exceeds the upper limit of 0.25% proposed by the present invention, and the 5.5 ⁇ [Si]+[Mn] value is 2.58, which exceeds the upper limit of 2.4, which is the upper limit proposed by the present invention. Due to the reinforcing effect, after spheroidizing heat treatment, the formability of the bolt thread part deteriorated, and delayed fracture cracks occurred. 1 is a photograph of observing the screw portion of Comparative Example 3 before the delayed fracture resistance evaluation. Referring to FIG. 1 , it can be confirmed that Comparative Example 3 did not satisfy the conditions suggested by the present invention, so that delayed fracture cracks occurred, and delayed fracture resistance was not secured.
- Comparative Example 5 the C content was 0.33%, exceeding the upper limit of 0.30% proposed in the present invention, and formation of a retained austenite structure with excellent mechanical stability was suppressed, resulting in delayed fracture cracks.
- the rolling temperature was 870°C, which did not reach the lower limit of 880°C suggested by the present invention, and the winding temperature was also 820°C, which did not reach the lower limit of 830°C, the lower limit suggested by the present invention, so that the prior austenite grain size in the wire rod becomes finer, and as the prior austenite grain size of the bolt product also becomes finer, the retained austenite fraction increases, and delayed fracture cracks occur.
- the austenitizing heat treatment temperature was 950 ° C., which exceeded the upper limit of 940 ° C. proposed by the present invention, and as the old austenite grain size of the bolt product became coarse, delayed fracture cracks occurred.
- the austenitization heat treatment temperature was 860° C., which did not reach the lower limit of 870° C. suggested by the present invention, and the bolt product was subjected to QT heat treatment in a state in which it was not sufficiently austenitized to form undissolved pearlite, As a result, delayed fracture cracks occurred.
- Comparative Example 6-5 has a spheroidization temperature of 740 ° C., which does not reach the lower limit of 745 ° C. proposed by the present invention, and Comparative Example 6-6 has a spheroidization temperature of 775 ° C., exceeding the upper limit of 770 ° C. Delayed fracture cracks occurred due to poor formability due to low spheroidization rate and insufficient heat treatment.
Abstract
Description
구분 | 합금 조성(중량%) | |||||||
C | Si | Mn | P | S | Ti | B | N | |
발명예1 | 0.29 | 0.21 | 0.99 | 0.011 | 0.005 | 0.018 | 0.0023 | 0.0041 |
발명예2 | 0.16 | 0.20 | 1.30 | 0.012 | 0.005 | 0.019 | 0.0020 | 0.0049 |
발명예3 | 0.24 | 0.19 | 0.96 | 0.008 | 0.005 | 0.027 | 0.0024 | 0.0040 |
발명예4 | 0.21 | 0.20 | 1.11 | 0.010 | 0.005 | 0.018 | 0.0023 | 0.0051 |
발명예5 | 0.23 | 0.16 | 1.20 | 0.009 | 0.005 | 0.028 | 0.0020 | 0.0048 |
발명예6 | 0.22 | 0.23 | 0.99 | 0.010 | 0.005 | 0.025 | 0.0019 | 0.0055 |
비교예1 | 0.23 | 0.19 | 0.98 | 0.008 | 0.005 | 0.018 | 0.0023 | 0.0021 |
비교예2 | 0.24 | 0.21 | 1.02 | 0.010 | 0.005 | 0.042 | 0.0021 | 0.0040 |
비교예3 | 0.20 | 0.26 | 1.15 | 0.009 | 0.005 | 0.019 | 0.0020 | 0.0050 |
비교예4 | 0.23 | 0.21 | 1.45 | 0.011 | 0.005 | 0.022 | 0.0021 | 0.0050 |
비교예5 | 0.33 | 0.20 | 1.10 | 0.010 | 0.005 | 0.018 | 0.0022 | 0.0050 |
구분 | 관계식1 5.5Х[Si]+[Mn] |
관계식2 [Ti]/3.42[N] |
TiN 최대 크기 (㎛) |
지연파괴 크랙 유무 |
발명예1 | 2.15 | 1.284 | 13.2 | X |
발명예2 | 2.40 | 1.134 | 11.1 | X |
발명예3 | 2.01 | 1.974 | 14.5 | X |
발명예4 | 2.21 | 1.032 | 10.2 | X |
발명예5 | 2.08 | 1.706 | 13.9 | X |
발명예6 | 2.26 | 1.329 | 12.1 | X |
비교예1 | 2.03 | 2.506 | 15.9 | ○ |
비교예2 | 2.18 | 3.070 | 17.8 | ○ |
비교예3 | 2.58 | 1.111 | 10.3 | ○ |
비교예4 | 2.61 | 1.287 | 13.5 | ○ |
비교예5 | 2.20 | 1.053 | 11.5 | ○ |
구분 | 온도 (℃) | 지연파괴 크랙유무 |
|||
마무리압연 온도 |
권취 온도 |
구상화열처리 온도 |
오스테나이트화 온도 |
||
발명예 3 | 930 | 880 | 755 | 910 | X |
비교예 6-1 | 990 | 940 | 755 | 910 | ○ |
비교예 6-2 | 870 | 820 | 755 | 910 | ○ |
비교예 6-3 | 930 | 880 | 755 | 950 | ○ |
비교예 6-4 | 930 | 880 | 755 | 860 | ○ |
비교예 6-5 | 930 | 880 | 740 | 910 | ○ |
비교예 6-6 | 930 | 880 | 775 | 910 | ○ |
Claims (9)
- 중량%로, C: 0.15 내지 0.30%, Si: 0.15 내지 0.25%, Mn: 0.95 내지 1.35%, P: 0.030% 이하, S: 0.030% 이하, Ti: 0.015 내지 0.030%, B: 0.0010 내지 0.0040%, N: 0.0010 내지 0.0080%, 나머지는 Fe 및 불가피한 불순물을 포함하고,하기 관계식 1을 만족하며, 지연파괴 저항성이 향상된, 선재.[관계식 1] 2.0 ≤ 5.5Х[Si]+[Mn] ≤ 2.4(관계식 1에서, [Si] 및 [Mn] 각각은 해당 원소의 함량(중량%)을 의미한다)
- 제1항에 있어서,하기 관계식 2를 만족하는, 선재.[관계식 2] 1.0 < [Ti]/3.42[N] < 2.0(관계식 2에서, [Ti] 및 [N] 각각은 해당 원소의 함량(중량%)을 의미한다)
- 제1항에 있어서,TiN 개재물의 크기가 15㎛ 이하인, 선재.
- 중량%로, C: 0.15 내지 0.30%, Si: 0.15 내지 0.25%, Mn: 0.95 내지 1.35%, P: 0.030% 이하, S: 0.030% 이하, Ti: 0.015 내지 0.030%, B: 0.0010 내지 0.0040%, N: 0.0010 내지 0.0080%, 나머지는 Fe 및 불가피한 불순물을 포함하고, 하기 관계식 1을 만족하는 강재를 880 내지 980℃에서 마무리 압연하는 단계; 및830 내지 930℃에서 권취하는 단계;를 포함하며, 지연파괴 저항성이 향상된, 선재의 제조방법.[관계식 1] 2.0 ≤ 5.5Х[Si]+[Mn] ≤ 2.4(관계식 1에서, [Si] 및 [Mn] 각각은 해당 원소의 함량(중량%)을 의미한다)
- 제4항에 있어서,상기 강재는 하기 관계식 2를 만족하는, 선재의 제조방법.[관계식 2] 1.0 < [Ti]/3.42[N] < 2.0(관계식 2에서, [Ti] 및 [N] 각각은 해당 원소의 함량(중량%)을 의미한다)
- 제4항 내지 제5항에 따라 제조된 선재를 신선하는 단계;상기 신선재를 745 내지 770℃에서 구상화 열처리하는 단계;상기 구상화 열처리된 신선재를 870 내지 940℃의 온도 범위에서 가열하는 단계;상기 구상화 열처리된 신선재를 50 내지 80℃의 온도 범위에서 담금질하는 단계; 및상기 담금질된 부품을 400 내지 600℃의 온도범위에서 템퍼링하는 단계;를 포함하며, 지연파괴 저항성이 향상된, 부품의 제조방법.
- 중량%로, C: 0.15 내지 0.30%, Si: 0.15 내지 0.25%, Mn: 0.95 내지 1.35%, P: 0.030% 이하, S: 0.030% 이하, Ti: 0.015 내지 0.030%, B: 0.0010 내지 0.0040%, N: 0.0010 내지 0.0080%, 나머지는 Fe 및 불가피한 불순물을 포함하고, 하기 관계식 1을 만족하며, 지연파괴 저항성이 향상된, 부품.[관계식 1] 2.0 ≤ 5.5Х[Si]+[Mn] ≤ 2.4(관계식 1에서, [Si] 및 [Mn] 각각은 해당 원소의 함량(중량%)을 의미한다)
- 제7항에 있어서,하기 관계식 2를 만족하는, 부품.[관계식 2] 1.0 < [Ti]/3.42[N] < 2.0(관계식 2에서, [Ti] 및 [N] 각각은 해당 원소의 함량(중량%)을 의미한다)
- 제7항에 있어서,부피 분율로, 잔류 오스테나이트를 0.3 내지 2% 및 잔여 템퍼드 마르텐사이트 조직을 포함하는, 부품.
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