WO2013012161A1 - 수소지연파괴 저항성이 우수한 선재와 그 제조방법 및 이를 이용한 고강도 볼트와 그 제조방법 - Google Patents

수소지연파괴 저항성이 우수한 선재와 그 제조방법 및 이를 이용한 고강도 볼트와 그 제조방법 Download PDF

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Publication number
WO2013012161A1
WO2013012161A1 PCT/KR2012/003757 KR2012003757W WO2013012161A1 WO 2013012161 A1 WO2013012161 A1 WO 2013012161A1 KR 2012003757 W KR2012003757 W KR 2012003757W WO 2013012161 A1 WO2013012161 A1 WO 2013012161A1
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WO
WIPO (PCT)
Prior art keywords
fracture resistance
wire rod
delayed fracture
hydrogen
bolt
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PCT/KR2012/003757
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English (en)
French (fr)
Korean (ko)
Inventor
이유환
김동현
류근수
Original Assignee
주식회사 포스코
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Application filed by 주식회사 포스코 filed Critical 주식회사 포스코
Priority to CN201280035144.XA priority Critical patent/CN103649354B/zh
Priority to US14/232,805 priority patent/US20140150934A1/en
Priority to JP2014520107A priority patent/JP5826383B2/ja
Priority to EP12814354.2A priority patent/EP2733229B9/en
Publication of WO2013012161A1 publication Critical patent/WO2013012161A1/ko

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0093—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
    • 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
    • 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
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • 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
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium

Definitions

  • the present invention relates to a wire rod used for bolts for automobile engines, and more particularly, a wire rod and a method of manufacturing the same, and a high strength bolt using the wire rod and a method of manufacturing the same, which have improved delayed fracture resistance by hydrogen. It is about.
  • High-strength bolts used up to now are made of alloy steels such as SCM435 and SCM440, and manufactured and used at 1200 MPa level through quenching and tempering.
  • alloy steels such as SCM435 and SCM440
  • the manufacturing process of the bolt after the low-temperature annealing is carried out for the purpose of sizing (sizing), it has a single phase structure of the final tempered Martensite through a process of spheroidizing heat treatment, bolt forming, quenching, soaking. Therefore, the strength of the bolt is determined by the composition, quenching, and heat treatment process. However, in the wire state, which is a raw material, the strength should be as low as possible to facilitate bolt forming.
  • alloying elements especially carbon
  • carbon is known to be the most effective method for strengthening steel with single phase structure of tempered martensite, but adding carbon not only increases wire strength but also rapidly increases the ductile-brittle transition temperature and increases hydrogen delay. Greatly reduce the resistance to fracture.
  • work hardening increases, which is disadvantageous for bolt molding and requires a separate softening heat treatment.
  • the bolt manufactured as described above is characterized in that the carbide precipitated phase is distributed in the grain boundary or the mouth as a tempered martensite structure, and the base material is a precipitate distributed in the ras martensite.
  • the main inhibitory factor in achieving the high strength of the base metal is a decrease in delayed fracture resistance due to the intrusion of hydrogen, and the intruded hydrogen deteriorates the strength of the grain boundary.
  • diffused hydrogen is added by adding a specific element while suppressing P and S that embrittle the austenite grain boundary as much as possible.
  • Conventional techniques for improving hydrogen delay resistance include: 1) corrosion inhibition of steel, 2) minimization of hydrogen intrusion, 3) suppression of diffusible hydrogen contributing to delayed destruction, and 4) high critical diffusion hydrogen concentrations.
  • Use of steel 5) minimization of tensile stress, 6) relaxation of stress concentration, and 7) miniaturization of austenite grain boundaries. As a means to achieve this, it is mainly used to pursue high alloying or to give surface coating or plating to prevent external hydrogen intrusion.
  • the inventions devised at home and abroad have a problem in that manufacturing cost is very high and the process is complicated, and rolling and cooling conditions are very precisely required when producing steel materials.
  • Ti, Nb, and V which are grain refinement elements
  • a technique of adding corrosion resistant elements such as Mo, Ni, Cu, Co, and carbide elements
  • the production cost is very high.
  • the hydrogen embrittlement was improved by using the ferrite structure precipitated at the grain boundary, but this is also not a chemical bond, there is a disadvantage that the product manufacturing cost is also increased by the addition of a significant amount of Mo.
  • the technique of securing final 1200 ⁇ 1500MPa using ferrite and pearlite abnormal microstructures is a method that can secure tensile strength without final heat treatment, but basically adds a large amount of Mo to destroy hydrogen delay In order to improve the resistance, there is no problem in that the manufacturing cost is high.
  • One aspect of the present invention is to provide an ultra-high strength through heat treatment, and at the same time to provide a wire rod and a method of manufacturing the same having excellent resistance to hydrogen delayed fracture.
  • the present invention is by weight, C: 0.3-0.7%, Si: 0.05-2.0%, Mn: 0.7-1.5%, La: 30-70ppm, Ni: 0.01-0.1%, the remainder containing Fe and inevitable impurities Provides high strength wire rod with excellent hydrogen delay fracture resistance.
  • the present invention comprises the steps of heating the steel satisfying the composition to Ae3 + 150 ⁇ Ae 3 + 250 °C;
  • It provides a high-strength wire rod excellent in hydrogen delayed fracture resistance comprising the step of cooling the rolled wire to 600 °C or less at 0.5 ⁇ 3 °C / s.
  • the present invention by weight, C: 0.3-0.7%, Si: 0.05-2.0%, Mn: 0.7-1.5%, La: 30-70ppm, Ni: 0.01-0.1%, the rest is Fe and inevitable impurities It provides a bolt that is excellent in hydrogen delayed fracture resistance having a tensile strength of 1200MPa or more.
  • the present invention comprises the steps of bolt forming the wire rod
  • Wire rod of the present invention is a high-strength wire used for fastening automobile parts or automobile parts, even if the addition of a very small amount of lanthanum and nickel, even if martensite microstructure after the final heat treatment excellent strength (1200 ⁇ 2000 MPa class) and hydrogen delayed fracture There is an advantage that can be produced at a low manufacturing cost wire that can have a resistance.
  • 1 is a schematic diagram showing the microstructure of the wire rod of the present invention.
  • Figure 2 is a schematic diagram showing a hydrogen trap of Mo precipitate when Mo is added in the prior art.
  • Figure 3 is a schematic diagram showing the hydrogen trap of the precipitate contained in the present invention wire.
  • Figure 4 shows the crystal structure of the precipitate of FIG.
  • the wire rod of the present invention will be described in detail.
  • the composition range of the wire rod of the present invention will be described (hereinafter, by weight).
  • C content of carbon
  • the content is more than 0.7%, although often used in the form of a high-carbon wire rod using a conventional cold drawing, when the heat treatment proposed in the present invention is performed, carbides in the form of films at the austenite grain boundaries are frequently precipitated. This is undesirable because it lowers the hydrogen delayed fracture resistance.
  • C is preferably added at least 0.3% to secure sufficient strength.
  • the content of silicon (Si) is preferably made 0.05 to 2.0%. When the content exceeds 2.0%, the work hardening phenomenon occurs rapidly during the cold forging process for making bolts, which causes a lot of problems in workability, and less than 0.05% does not secure sufficient strength and adversely affects spheroidization of cementite. .
  • the content of manganese (Mn) is preferably set to 0.7 to 1.5%.
  • Mn is an element which forms a solid solution to form a solid solution to strengthen the solid solution and is very useful for high-tensile bolt characteristics.
  • tissue heterogeneity due to manganese segregation has a more detrimental effect on the bolt characteristics than the solid solution strengthening effect. That is, macro segregation and micro segregation are easy to occur depending on the segregation mechanism during steel solidification.
  • Manganese segregation promotes segregation due to the relatively low diffusion coefficient compared to other elements, and the improvement of hardenability is due to For example, it is the main cause of generating core martensite. That is, there is a problem in that the ideal of the tissue is intensified by increasing local quenchability due to manganese segregation and forming segregation zones during casting.
  • Ni is an important element as well as lanthanum as an element forming a compound in the mouth. Therefore, if it is added less than 0.01%, it is difficult to expect the effect of improving the hydrogen delayed fracture resistance due to the incomplete production of effective compounds, especially precipitates, and when exceeding 0.1%, the amount of retained austenite increases and impact toughness decreases. There is a concern that the production cost increases due to excessive addition.
  • the content of lanthanum (La) is preferably set to 0.003 to 0.007% (30 to 70 ppm).
  • La, together with Ni, is an element that forms a compound in the grains and is a very important element for reducing phosphorus and sulfur segregated at grain boundaries. If the La content is less than 30 ppm, effective compound formation is not achieved, and the removal of phosphorus and sulfur at grain boundaries is not easy. Therefore, although it is possible to secure tensile strength, there is a disadvantage in that excellent hydrogen delaying resistance cannot be expected in parallel. On the other hand, when it exceeds 70ppm, there is a problem that the manufacturing cost increases, and it is preferable to set the upper limit to 70ppm because it is difficult to expect improved hydrogen delayed resistance improvement due to excess addition.
  • the remainder contains Fe and unavoidable impurities.
  • the addition of effective ingredients other than the above composition is not excluded.
  • the wire rod of the present invention preferably includes La-based, Ni-based, or LaNi-based precipitates in the microstructure.
  • the type of the precipitate is not particularly limited, examples of the precipitate include LaNi 5 , LaPO 4 , La 2 O 2 S, and the like.
  • the precipitate is formed in the crystal grains or grain boundaries of the microstructure, traps the hydrogen invasion (trap) to prevent degradation of the strength of the intrusion of the grain boundary serves to improve the hydrogen delayed fracture resistance.
  • Figure 1 schematically shows that the precipitate is distributed by observing the microstructure of the wire rod of the present invention.
  • the precipitates of LaNi 5 , LaPO 4 , and La 2 O 2 S are distributed in the grains or in the grain boundaries, and it is also known that hydrogen is trapped and the LaNi 5 H 6 compound is present. have.
  • FIG. 2 schematically shows the effect of a hydrogen trap using Mo precipitates in the prior art. Mo precipitates were trapped at the interface between infiltrating hydrogen roll precipitates and crystal grains to improve hydrogen delayed fracture resistance.
  • FIG. 3 which schematically shows the effect of the hydrogen trap by the precipitate of the present invention, the precipitate of the present invention is not bound to the precipitate surface by hydrogen, but is a compound containing hydrogen (eg, LaNi 5 H 6). By forming), hydrogen in the steel is completely confined to improve resistance to hydrogen delayed fracture. Therefore, in the case of FIG.
  • FIG. 2 shows the crystal structure of LaNi 5 H 6 of FIG. 3, it can be seen that has a structure capable of storing a considerable amount of hydrogen therein.
  • the aspect ratio of the precipitate is preferably 1.2 to 2.0. If the aspect ratio of the precipitate is less than 1.2, it is almost impossible to secure due to the crystal structure, and if it exceeds 2.0, there is a problem that the precipitate is easily broken. If the precipitate is broken inside the material, there is a lack of continuity with the matrix and micro-voids are generated and present as defects, which may lead to wire breakage, and the expected hydrogen delaying resistance cannot be secured.
  • the size of the precipitate is preferably 100 ⁇ 400nm in equivalent circle diameter. If the diameter is less than 100 nm, the size of the precipitate is too small, so that the amount of hydrogen trapped in the precipitate is small, it is difficult to secure an effective hydrogen trap effect, if the size is too large (400 nm), it is distributed per unit area Since the surface area of the ferroelectric precipitate decreases because the number of precipitates decreases, the upper limit is preferably 400 nm because the effect of the hydrogen trap decreases.
  • a steel material satisfying the above composition is heated to a temperature of Ae3 + 150 ° C to Ae3 + 250 ° C.
  • the heating to the above temperature is for maintaining the austenite single phase, the range in which the austenite crystal grains are not coarsened, and the temperature at which the segregation, carbides and inclusions remaining can be effectively dissolved.
  • the temperature exceeds Ae3 + 250 ° C.
  • the austenitic grains become very coarse, so that the tendency of coarsening of the final microstructure formed after cooling is not high, and thus a high strength high toughness wire cannot be obtained.
  • the heating temperature is less than Ae3 + 150 ° C, the effect of heating cannot be obtained, and therefore, the heating temperature is preferably Ae3 + 150 ° C to Ae3 + 250 ° C.
  • the said heating for 30 minutes-1 hour 30 minutes. If the heating time is less than 30 minutes, there is a problem that the overall temperature cannot be made uniform, and if it exceeds 1 hour 30 minutes, not only the possibility of coarsening of austenite grains increases, but also the productivity decreases significantly.
  • the heated steel is cooled and hot rolled.
  • the cooling is cooled at a cooling rate of 5 ⁇ 15 °C / s, and rolled at Ae 3 + 50 °C ⁇ Ae 3 + 150 °C to produce a wire rod.
  • the cooling is controlled for the purpose of minimizing the transformation of the microstructure, when the cooling rate before the hot rolling is less than 5 °C / s because productivity is reduced, and additional equipment is required to maintain the slow cooling, heating time for a long time This is because the strength and toughness of the wire rod decrease after hot rolling as in the case of holding.
  • the cooling rate exceeds 15 °C / s because the driving force of the transformation of the steel before rolling increases the possibility of the appearance of a new microstructure during rolling increases, there is a problem that must be reset the rolling temperature low.
  • the rolling temperature is a temperature at which the appearance of the microstructure due to deformation during rolling is suppressed, recrystallization does not occur, and only sizing rolling is possible.
  • the rolling temperature is less than Ae3 + 50 ° C.
  • the microstructure of the present invention cannot be secured by approaching the dynamic recrystallization temperature, and a general soft ferrite is very likely to be secured.
  • the upper limit is set as described above.
  • the wire rod manufactured by rolling is cooled to 600 ° C. or less at 0.5 to 3 ° C./s.
  • the cooling rate refers to the cooling rate that can be effectively produced while the diffusion of carbon is prevented by the addition of manganese, and the generation of incomplete pearlite and having a sufficient area fraction. If the cooling rate is less than 0.5 °C / s, the cooling rate is too slow, there is a side that the productivity is difficult to difficult to operate, if it exceeds 3 °C / s, due to the improvement of the curing ability due to the overlap effect of the added elements Ferrite / pearlite transformation is delayed and low temperature tissue such as martensite / bainite occurs.
  • the bolt manufactured using the wire rod of the present invention can secure ultra high strength, and can secure excellent hydrogen delayed fracture resistance by the precipitate.
  • the bolt of the present invention ensures ultra high strength of 1200MPa or more and has excellent hydrogen delayed fracture resistance.
  • the manufacturing method for securing the tensile strength of 1200 MPa or more is preferably based on the following method.
  • the heat treatment is for homogenization of the tissue through austenizing. If it is less than 850 degreeC, it will be hard to fully homogenize, and if it exceeds 950 degreeC, it will be hard to obtain the effect of temperature rise any more, and since ductility may fall by coarsening of a grain, it is preferable to set the upper limit to 950 degreeC.
  • the homogenized tissue through the quench forms a low temperature transformation tissue such as martensite tissue, thereby improving the strength of the bolt.
  • the tempering is to remove the residual stress caused by the quenching, to improve the adjustment and brittleness of the strength.
  • the temperature is less than 300 ° C, not only is it difficult to remove sufficient residual stress, but also brittle occurs due to a phenomenon called temper brittleness, and therefore, the temperature is preferably 300 ° C or higher. It is preferable to carry out at 300-500 degreeC, since it is difficult to ensure the intensity
  • the method of manufacturing the bolt is to secure the required strength by applying a conventional heat treatment, which is to be applied by controlling the temperature and time to ensure the strength required by those of ordinary skill in the present invention, In the present invention, this is not particularly limited.
  • the tensile strength and hydrogen delayed fracture resistance of the bolts thus prepared were measured, and the results are shown in Table 3.
  • the hydrogen delayed fracture resistance was measured in the state in which each bolt was immersed in the test solution using a test solution consisting of H 2 O: 2000cc, CH 3 COOH: 80ml, NaCl: 100g having an acidity (pH) of about 2
  • a tensile strength of about 0.9 times the tensile strength was added and the time taken for the specimen to break was measured. It is evaluated that the resistance to hydrogen delayed destruction is excellent when maintained for more than 100 hours through the test.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
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  • Crystallography & Structural Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Heat Treatment Of Steel (AREA)
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PCT/KR2012/003757 2011-07-15 2012-05-14 수소지연파괴 저항성이 우수한 선재와 그 제조방법 및 이를 이용한 고강도 볼트와 그 제조방법 WO2013012161A1 (ko)

Priority Applications (4)

Application Number Priority Date Filing Date Title
CN201280035144.XA CN103649354B (zh) 2011-07-15 2012-05-14 具有优异耐氢致延迟断裂性的线材、制造所述线材的方法、使用所述线材的高强度螺栓和制造螺栓的方法
US14/232,805 US20140150934A1 (en) 2011-07-15 2012-05-14 Wire rod having superior hydrogen delayed fracture resistance, method for manufacturing same, high strength bolt using same and method for manufacturing bolt
JP2014520107A JP5826383B2 (ja) 2011-07-15 2012-05-14 水素遅れ破壊抵抗性に優れた線材及びその製造方法、並びにこれを用いた高強度ボルト及びその製造方法
EP12814354.2A EP2733229B9 (en) 2011-07-15 2012-05-14 Wire rod having superior hydrogen delayed fracture resistance, method for manufacturing same, high strength bolt using same and method for manufacturing bolt

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
KR1020110070206A KR101325317B1 (ko) 2011-07-15 2011-07-15 수소지연파괴 저항성이 우수한 선재와 그 제조방법 및 이를 이용한 고강도 볼트와 그 제조방법
KR10-2011-0070206 2011-07-15

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WO2013012161A1 true WO2013012161A1 (ko) 2013-01-24

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US (1) US20140150934A1 (zh)
EP (1) EP2733229B9 (zh)
JP (1) JP5826383B2 (zh)
KR (1) KR101325317B1 (zh)
CN (1) CN103649354B (zh)
WO (1) WO2013012161A1 (zh)

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CN103820726A (zh) * 2014-03-17 2014-05-28 河南赛诺米特种设备有限公司 一种疲劳强度较高螺栓的制造方法
JP6601284B2 (ja) * 2016-03-11 2019-11-06 日本製鉄株式会社 高強度ボルト
US11572612B2 (en) 2017-12-11 2023-02-07 Korea Institute Of Materials Science High-entropy alloy, and method for producing the same
WO2021193057A1 (ja) 2020-03-27 2021-09-30 Ｍｏｔｐ合同会社 鋼材及びその製造方法

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EP2733229A1 (en) 2014-05-21
US20140150934A1 (en) 2014-06-05
KR20130009248A (ko) 2013-01-23
EP2733229B1 (en) 2016-04-06
JP5826383B2 (ja) 2015-12-02
JP2014525987A (ja) 2014-10-02
EP2733229B9 (en) 2016-07-13
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