KR20220084557A - High-strength wire rod with excellent heat treatment property and resistance of hydrogen delayed fracture, heat treatment parts using the same, and methods for manufacturing thereof - Google Patents

Abstract

Disclosed herein are a high-strength cold-rolling wire rod, a heat-treated component, and a manufacturing method thereof having excellent heat treatment properties and hydrogen delayed fracture properties that can be applied to bolts and the like.
According to an embodiment of the disclosed high-strength cold-rolling wire rod having excellent heat treatment characteristics and hydrogen delayed fracture characteristics, in weight%, C: 0.3 to 0.6%, Si: 0.05 to 0.3%, Mn: 0.2 to 1.0%, Cr: 0.5 to 2.0%, Mo: 0.5 to 2.0%, Al: 0.02 to 0.05%, N: 0.01 to 0.03% including the remaining Fe and other impurities, and the microstructure is 80% or more of bainite by area fraction, 1 to 15 perlite % and 0.1 to 2% of martensite, and 2×10 ¹⁹ pieces/m ³ or more of aluminum nitride having a diameter of 5 to 50 nm.

Description

HIGH-STRENGTH WIRE ROD WITH EXCELLENT HEAT TREATMENT PROPERTY AND RESISTANCE OF HYDROGEN DELAYED FRACTURE, HEAT TREATMENT PARTS USING THE SAME, AND METHODS FOR MANUFACTURING THEREOF}

The present invention relates to a high-strength cold-rolling wire rod having excellent heat treatment characteristics and hydrogen delayed fracture characteristics, a heat treatment component, and a manufacturing method thereof. It relates to a wire rod for rolling, a heat treatment component, and a manufacturing method thereof.

In general, the wire rod for cold rolling is divided into a wire rod for a process omission type in which heat treatment and processing processes are omitted, and a wire rod for high-strength cold rolling that can achieve weight reduction of parts.

High-strength cold-rolling wire rods are manufactured into heat-treated parts, such as mechanical structures and automobile parts, through spheroidizing heat treatment, cold rolling, and quenching and tempering processes.

However, the metal structure of a general wire rod is mainly made of pearlite, and there is an inconvenience of having to heat-treat for a long time in order to dissolve cementite during austenitization heat treatment.

In addition, when austenitizing heat treatment is performed, a tempered martensite microstructure is formed, and it is difficult to use such a tempered martensite microstructure because it is very sensitive to hydrogen delayed fracture at high strength of 1300 MPa or more.

Therefore, it is necessary to develop a high-strength cold-rolling wire having excellent hydrogen-delayed fracture characteristics at high strength of 1300 MPa or more.

In order to solve the above-mentioned problems, the present invention is to provide a high-strength cold-rolling wire rod, heat-treated parts, and a manufacturing method thereof having excellent heat treatment characteristics and hydrogen delayed fracture characteristics.

As a means for achieving the above object, the present specification is, in weight %, C: 0.3 to 0.6%, Si: 0.05 to 0.3%, Mn: 0.2 to 1.0%, Cr: 0.5 to 2.0%, Mo: 0.5 to 2.0% , Al: 0.02 to 0.05%, N: 0.01 to 0.03% Contains remaining Fe and other impurities, and the microstructure contains 80% or more of bainite, 1 to 15% of pearlite, and 0.1 to 2% of martensite by area fraction Disclosed is a high-strength cold-rolling wire rod having excellent heat treatment characteristics and hydrogen-delayed fracture characteristics including aluminum nitride having a diameter of 5 to 50 nm and at least 2×10 ¹⁹ pieces/m ³ .

In addition, the prior austenite average grain diameter may be made of 10㎛ or less.

In addition, martensite may be included in the former austenite grain boundary 60% or more.

In addition, as another means for achieving the above-mentioned object, the present specification is by weight %, C: 0.3 to 0.6%, Si: 0.05 to 0.3%, Mn: 0.2 to 1.0%, Cr: 0.5 to 2.0%, Mo: 0.5 to 2.0%, Al: 0.02 to 0.05%, N: 0.01 to 0.03% The billet containing the remaining Fe and other impurities is heated at 1000 to 1200° C., hot rolled to a finish hot rolling temperature of 750 to 950° C., and 0.2 to Including cooling at a cooling rate of 1.0 ° C. / s, the microstructure of the cooled wire rod comprises 80% or more of bainite, 1 to 15% of pearlite, and 0.1 to 2% of martensite as an area fraction, Disclosed is a method for manufacturing a high-strength cold-rolling wire rod having excellent heat treatment characteristics and hydrogen delayed fracture characteristics including 2×10 ¹⁹ pieces/m ³ or more of aluminum nitride having a diameter of 5 to 50 nm.

In addition, as another means for achieving the above-mentioned object, the present specification is by weight %, C: 0.3 to 0.6%, Si: 0.05 to 0.3%, Mn: 0.2 to 1.0%, Cr: 0.5 to 2.0%, Mo: 0.5 to 2.0%, Al: 0.02 to 0.05%, N: 0.01 to 0.03% Contains the remaining Fe and other impurities, and the microstructure is an area fraction, and contains 90% or more of tempered martensite, aluminum having a diameter of 5 to 50 nm Disclosed is a heat treatment component having excellent heat treatment characteristics and hydrogen delayed fracture characteristics including 2×10 ¹⁹ pieces/m ³ or more of nitride.

In addition, the prior austenite average grain diameter may be made of 5㎛ or less.

In addition, the heat-treated parts having excellent hydrogen-delayed fracture characteristics may have a tensile strength of 1400 MPa or more and an impact toughness of 60 J or more.

In addition, as another means for achieving the above object, the present specification is by weight %, C: 0.3 to 0.6%, Si: 0.05 to 0.3%, Mn: 0.2 to 1.0%, Cr: 0.5 to 2.0%, Mo: 0.5 to 2.0%, Al: 0.02 to 0.05%, N: 0.01 to 0.03% including the remaining Fe and other impurities, and the microstructure is 80% or more of bainite by area fraction, 1 to 15% of pearlite and 0.1 to 2 of martensite %, wherein the martensite is prepared as a steel wire by performing spheroidizing heat treatment and wire drawing at least once on a wire rod containing 60% or more in the old austenite grain boundary, and cold forging the prepared steel wire into a part, and the prepared part Heating at 800 to 900 ° C. for 1,000 to 2,000 seconds, quenching the heated part at 50 to 150 ° C., and tempering the quenched part at 500 to 600 ° C. for 3,000 to 10,000 seconds. Disclosed is a method for manufacturing an excellent heat treatment component.

According to the embodiment of the present invention, since the microstructure contains 80% or more of bainite, 1 to 15% of pearlite, and 0.1 to 2% of martensite by area fraction, the austenitizing heat treatment can be performed quickly, thereby Energy used in the heat treatment process can be reduced.

According to an embodiment of the present invention, since the structure of the wire rod is refined and fine carbides are distributed therein, the resistance to delayed hydrogen fracture can be improved.

1 is a graph showing the tensile strength of each invention example and comparative example.
2 is a graph showing the impact toughness of each invention example and comparative example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes preferred embodiments of the present invention. However, the embodiment of the present invention may be modified in various other forms, and the technical idea of the present invention is not limited to the embodiment described below. In addition, the embodiments of the present invention are provided in order to more completely explain the present invention to those of ordinary skill in the art.

The terms used in this application are only used to describe specific examples. Therefore, for example, a singular expression includes a plural expression unless the context clearly requires it to be singular. In addition, as used in this application, terms such as "comprises" or "includes" are used to clearly indicate that the features, steps, functions, components, or combinations thereof described in the specification exist, and other features It should be noted that the use is not intended to preliminarily exclude the existence of elements, steps, functions, components, or combinations thereof.

On the other hand, unless otherwise defined, all terms used herein should be regarded as having the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs. Accordingly, unless explicitly defined herein, specific terms should not be construed in an unduly idealistic or formal sense. For example, a singular expression herein includes a plural expression unless the context clearly dictates otherwise.

In addition, in this specification, "about", "substantially", etc. are used in or close to the numerical value when manufacturing and material tolerances inherent in the stated meaning are presented, and are used in a precise sense to help the understanding of the present invention. or absolute figures are used to prevent unreasonable use by unconscionable infringers of the mentioned disclosure.

The high-strength cold-rolling wire rod having excellent heat treatment characteristics and hydrogen-delayed fracture characteristics according to the present invention is, by weight, C: 0.3 to 0.6%, Si: 0.05 to 0.3%, Mn: 0.2 to 1.0%, Cr: 0.5 to 2.0% , Mo: 0.5 to 2.0%, Al: 0.02 to 0.05%, N: 0.01 to 0.03%, including the remainder of Fe and other impurities.

Hereinafter, the reason for limiting the alloy composition will be described in detail. All of the following component compositions refer to % by weight unless otherwise specified.

Carbon (C): 0.3 to 0.6 wt%

C is an element added to secure product strength. When the C content is less than 0.3%, it is difficult to secure the target strength, and it is not easy to secure sufficient hardenability after the final Q/T (Quenching/Tempering) heat treatment. Conversely, when the content of C exceeds 0.6%, there is a problem in that the fatigue life is reduced due to excessive generation of carbides. Accordingly, the upper limit of the C content in the present invention is limited to 0.6%.

Silicon (Si): 0.05 to 0.3 wt%

Si is not only used for deoxidation of steel, but also is an element advantageous for securing strength through solid solution strengthening. In the present invention, Si is added in an amount of 0.05% or more in order to deoxidize and secure strength. However, when the content is excessive, there is a problem in that the cold pressing composition is lowered, making it difficult to process parts having a complex shape such as bolts. Accordingly, the upper limit of the Si content in the present invention is limited to 0.3%.

Manganese (Mn): 0.2 to 1.0 wt%

Mn is advantageous in securing strength by improving hardenability of parts, and is an element that increases rollability and reduces brittleness. In order to secure sufficient strength, 0.2% or more is added. However, when the content is excessive, it is easy to generate a hard structure during cooling after hot rolling, and there is a problem in that a large amount of MnS inclusions are generated and fatigue properties are deteriorated. Accordingly, the upper limit of the Mn content in the present invention is limited to 1.0%.

Chromium (Cr): 0.5 to 2.0 wt%

Cr, together with Mn, is effective in improving hardenability and is an element that improves the corrosion resistance of steel. When the Cr content is less than 0.5%, sufficient corrosion resistance cannot be ensured. On the other hand, when the content is excessive, impact toughness is lowered, and there is a problem in that coarse carbides are formed that are inferior to hydrogen delayed fracture resistance. Accordingly, the upper limit of the Cr content in the present invention is limited to 2.0%.

Molybdenum (Mo): 0.5 to 2.0 wt%

Mo is an element that improves hardenability through precipitation and solid solution strengthening by precipitation of fine carbides. The improvement of hardenability due to Mo is more effective than Mn and Cr. When the Mo content is less than 0.5%, it is difficult to secure strength because fine carbides are not sufficiently precipitated during Q/T heat treatment. On the other hand, if the content is excessive, the hardenability is excessively increased, and the shape of the part is distorted after quenching, so that an additional process is required to correct this, or there is a problem that microcracks are defective inside the part. Accordingly, the upper limit of the Mo content in the present invention is limited to 2.0%.

Aluminum (Al): 0.02 to 0.05%

Al is an element frequently used as a deoxidizer in the steelmaking process. Al reacts with N to form aluminum nitride (AlN), which is a nitrogen compound, and refines austenite grains. When the content of Al is less than 0.02%, the number of nitrogen compounds is not sufficient, so that grain refinement is not easy. On the other hand, when the content is excessive, there is a problem in that the generation of non-metallic inclusions such as alumina is excessively generated, and the occurrence of defects in the steel material is deepened. Accordingly, the upper limit of the Al content in the present invention is limited to 0.05%.

Nitrogen (N): 0.01 to 0.03%

N is an element used instead of an expensive alloying element for grain refinement. N reacts with Al to form aluminum nitride (AlN), a nitrogen compound, and refines austenite grains. When the content of N is less than 0.01%, the number of nitrogen compounds is not sufficient, so that grain refinement is not easy. On the other hand, if the content is excessive, movement and proliferation of dislocations occur inside the material due to forging heat generated during cold forging, and free nitrogen is fixed to dislocations to increase deformation strength, thereby reducing the life of the mold. Accordingly, the upper limit of the N content in the present invention is limited to 0.03%.

The remaining component of the present invention is iron (Fe). However, since unintended impurities from raw materials or the surrounding environment may inevitably be mixed in the normal manufacturing process, this cannot be excluded. Since the impurities are known to any person skilled in the art of a conventional manufacturing process, all details thereof are not specifically mentioned in the present specification.

In addition, since coarse carbonitride strongly traps hydrogen and can cause hydrogen embrittlement, it is necessary to control so that it is not generated as much as possible. For reference, vanadium (V), which is added a lot in high-strength CHQ (Cold Heading Quality) steels having a tensile strength of 1400 MPa or more, can form coarse carbides that are inferior to hydrogen delayed fracture resistance. Even if a large-sized part with a body diameter of 16 to 30 mm is manufactured by configuring the composition, resistance to delayed hydrogen fracture can be secured by configuring so that undissolved coarse carbides do not remain after Q/T heat treatment.

The microstructure of the wire rod for cold rolling according to an embodiment of the present invention includes 80% or more of bainite, 1 to 15% of pearlite, and 0.1 to 2% of martensite, as an area fraction, and when the microstructure is made in this way, austen It is possible to reduce the heat treatment time for dissolving cementite during the nitriding heat treatment.

In addition, the microstructure may include 2×10 ¹⁹ pieces/m ³ or more of aluminum nitride having a diameter of 5 to 50 nm, and the prior austenite average grain diameter may be 10 μm or less. When aluminum nitride having a diameter of 5 to 50 nm is included in 2×10 ¹⁹ pieces/m ³ , austenite grains can be refined and resistance to delayed hydrogen fracture can be improved. Here, the old austenite grain boundary of the wire rod means the grain boundary of the austenite structure of the wire rod after winding and before cooling.

In addition, martensite may be included in the former austenite grain boundary 60% or more. When martensite is included in the prior austenite grain boundary by 60% or more, the tensile strength of 1400Mpa and the impact toughness of 60J or more can be secured.

The present inventors found that, when the relationship between C, Cr, and Mo contents satisfies a specific condition, the strength and resistance to hydrogen delayed fracture of the wire rod for cold rolling could be further improved, and the following component relation was derived. The wire rod for cold rolling according to an embodiment of the present invention may satisfy the above-described alloy composition and, at the same time, satisfy the following formula (1).

(1) 7.2C+Cr+2.7Mo ≥ 6.65

In the above formula (1), C, Cr, and Mo mean the weight% of each element. In addition, if there is an alloy component that is not included among C, Cr, and Mo, 0 is substituted for the numerical value of the corresponding alloy component.

In order to further improve the hydrogen-delayed fracture resistance, it is necessary to secure a fine carbide capable of trapping diffusible hydrogen. Microcarbides capable of trapping hydrogen include CrC and MoC carbides containing Cr and Mo as main components, respectively. Only by securing a certain level of the number of such fine carbides, it is possible to secure a strength of 1400 MPa or more at a tempering temperature of 500 to 600° C. and maximize the hydrogen trap effect. In consideration of this, if the alloy composition is controlled to satisfy Equation (1), the strength and resistance to hydrogen delayed fracture of heat-treated parts can be improved at a high tempering temperature (500 to 600° C.).

Hereinafter, a method for manufacturing a high-strength cold-rolling wire rod having excellent hydrogen delayed fracture characteristics according to the present invention will be described.

The method for manufacturing a high-strength cold-rolling wire rod having excellent heat treatment characteristics and hydrogen-delayed fracture characteristics according to an embodiment of the present invention includes the steps of heating a billet satisfying the above-described component system, preparing the heated billet as a wire rod, and cooling the wire rod may include the step of

In the step of heating the billet, the billet satisfies the above-described component system, and heating may be performed at 1000 to 1200°C. In addition, the billet may satisfy the above-mentioned formula (1).

In the step of preparing the heated billet as a wire rod, the heated billet may be finish hot rolled and wound at 750 to 950° C. to prepare a wire rod.

In the step of cooling the wire rod, the wire rod may be cooled at a cooling rate of 0.2 to 1.0° C./s so that the average austenite grain size after winding is 10 μm or less. The cooling method is not particularly limited, but may be performed by air cooling.

The microstructure of the cooled wire rod may include, as an area fraction, bainite: 80% or more, pearlite: 1 to 15%, and martensite: 0.1 to 2%, and the area ratio of martensite formed at the prior austenite grain boundary is It may be more than 60%. Here, the old austenite grain boundary means the grain boundary of the austenite structure of the wire rod after winding and before cooling. In addition, the microstructure of the cooled wire rod may contain 2×10 ¹⁹ pieces/m ³ or more of aluminum nitride having a diameter of 5 to 50 nm.

Hereinafter, a method for manufacturing a high-strength heat treatment component having excellent heat treatment characteristics and hydrogen delayed fracture characteristics using the above-described cold-rolling wire rod will be described.

According to the method for manufacturing a high-strength heat treatment component having excellent hydrogen delayed fracture characteristics according to an example of the present invention, the step of lowering the strength by spheroidizing the cooled wire rod following the manufacturing method of the cold-rolling wire rod to lower the strength, cold forging the wire rod, It may include a step of preparing the part, heating the part, quenching the heated part, and tempering the quenched part, and after spheroidizing heat treatment, wire drawing may be performed one or more times. Each step is described in detail below.

According to the manufacturing method of the wire rod as described above, the cooled wire rod may be subjected to spheroidizing heat treatment and wire drawing at least once to prepare a steel wire. The spheroidizing heat treatment is appropriately performed to impart a processing amount to the steel material prior to wire drawing, and the wire drawing may be appropriately performed in consideration of the wire drawing limit. According to the present invention, it is possible to prepare a steel wire having a narrow diameter capable of manufacturing complex-shaped parts by spheroidizing heat treatment and wire drawing of the wire rod.

The steel wire may be cold forged and provided as a part. Examples of the part include screws and bolts, and in the case of the bolt, the diameter of the body portion may be 12 to 30 mm.

The part may then be heated to a high temperature. The heating of the component is a step of re-dissolving the carbide precipitated during wire rolling, and may be heated so that the composition of the alloy component is homogeneous and the average austenite grain size is 5 μm or less. According to one embodiment, the part may be heated between 800 and 900° C., and the heating time may be between 1000 and 2000 seconds.

In the step of quenching the heated part, the heated part may be quenched to 50 to 150°C. The quenching method is not particularly limited, but may be performed by immersing the heated part in oil at 50 to 150°C.

The step of tempering the quenched part is a step for controlling the final microstructure of the heat-treated part to be tempered martensite. According to one example, the tempering step may be performed by tempering at 500 to 600 ℃. At this time, the tempering time may be 3000 to 10000 seconds.

The heat-treated parts having excellent heat treatment characteristics and hydrogen-delayed fracture characteristics according to the present invention manufactured by the above-described manufacturing method are, in weight %, C: 0.3 to 0.6%, Si: 0.05 to 0.3%, Mn: 0.2 to 1.0%, Cr: 0.5 to 2.0%, Mo: 0.5 to 2.0%, Al: 0.02 to 0.05%, N: 0.01 to 0.03% Containing the remaining Fe and other impurities, the microstructure includes 90% or more of tempered martensite as an area fraction, , 2×10 ¹⁹ pieces/m ³ or more of aluminum nitride having a diameter of 5 to 50 nm.

In addition, the prior austenite average grain diameter may be made of 5㎛ or less. Here, the prior austenite average grain diameter means the average grain diameter of the austenite structure before quenching after being heated in the step of heating the part.

In addition, the tensile strength may be 1400 MPa or more, the impact toughness may be 60 J or more, and when the heat treatment part is a bolt, the final part having a body diameter of 12 to 30 mm may have a tensile strength of 1400 MPa or more, and an impact toughness of 60 J or more.

According to an example of the present invention, the heat treatment component satisfying the above-described alloy composition may satisfy the following formula (1). The reason for limitation to Equation (1) is the same as described above, so it is omitted.

(1) 7.2C+Cr+2.7Mo ≥ 6.65

In formula (1), C, Cr, and Mo mean the weight % of each element.

Hereinafter, the present invention will be described in more detail through examples. However, the following examples are only provided to illustrate the present invention in more detail, and the technical spirit of the present invention is not limited to the following examples.

{Example}

The billet having the composition shown in Table 1 was heated to 1000 to 1200 °C, and then wound up at 730 to 900 °C after finish rolling at 750 to 950 °C. After winding, the cooling rate was 0.2 to 1°C/s. After cooling was completed, the microstructure of each wire rod contained 80% or more of bainite, 1 to 15% of pearlite, 0.1 to 2% of martensite as an area fraction, and the ratio of martensite formed at the grain boundaries of prior austenite was 60% or more. lost. In addition, more than 2×10 ¹⁹ pieces/m ³ of aluminum nitride having a size of 5 to 50 nm appeared.

On the other hand, in Table 1, 'Equation (1)' is obtained by substituting the contents (wt%) of each C, Cr, Mo into '7.2C+Cr+2.7Mo', which is the component relational expression of Formula (1) disclosed in this specification. was derived The number of AlN means the number of aluminum nitrides having a size of 5 to 50 nm.

division Alloy composition (wt%) Formula (1) Grain boundary martensite ratio (%) AlN number
(/m ³ ) C Si Mn Cr Mo Al N Invention Example 1 0.32 0.11 0.71 1.23 1.19 0.04 0.015 6.747 63 4.3x10 ¹⁹ Invention example 2 0.41 0.11 0.62 1.01 1.12 0.03 0.016 6.986 62 3.4x10 ¹⁹ Invention example 3 0.56 0.12 0.82 0.81 0.92 0.03 0.016 7.326 64 3.6x10 ¹⁹ Invention Example 4 0.42 0.10 0.72 1.52 0.95 0.03 0.017 7.109 63 5.0x10 ¹⁹ Invention Example 5 0.40 0.11 0.56 0.57 1.45 0.03 0.014 7.365 70 3.1x10 ¹⁹ Comparative Example 1 0.32 0.13 0.69 1.25 0.85 0.03 0.016 5.849 65 3.6x10 ¹⁹ Comparative Example 2 0.40 0.11 0.65 0.94 1.19 0.04 0.015 7.033 54 3.7x10 ¹⁹ Comparative Example 3 0.54 0.11 0.75 0.83 0.94 0.03 0.009 7.256 68 1.9x10 ¹⁹ Comparative Example 4 0.43 0.13 0.66 2.12 1.05 0.03 0.016 8.051 72 3.4x10 ¹⁹ Comparative Example 5 0.41 0.10 0.76 0.77 2.21 0.04 0.015 9.689 74 3.7x10 ¹⁹

In the case of the invention example in [Table 1] above, the value of formula (1) is 6.65 or more, the ratio of grain boundary martensite is 60% or more, and the aluminum nitride of 5 to 50 nm size is 2×10 ¹⁹ pieces/m ³ or more to be.

In contrast, in Comparative Example, the value of formula (1) is less than 6.65, the ratio of intergranular martensite is less than 60%, or the aluminum nitride of 5 to 50 nm size is less than 2×10 ¹⁹ pieces/m ³ , or the alloy composition is C : 0.3 to 0.6%, Si: 0.05 to 0.3%, Mn: 0.2 to 1.0%, Cr: 0.5 to 2.0%, Mo: 0.5 to 2.0%, Al: 0.02 to 0.05%, N: outside the range of 0.01 to 0.03% have.

In addition, after processing the hot-rolled wire rod having the composition shown in Table 1 into a round specimen with a diameter of 25 mm, heated at 860° C. for 1,500 seconds, then immersed in 100° C. oil and quenched, and then maintained at 500 to 600° C. for 5,000 seconds. Tempering was performed, and after processing the specimen in accordance with ASTM E8 and ASTM E23 standards, tensile and impact tests were performed. The tensile and impact test results are shown in FIGS. 1 and 2 . Inventive Examples all showed 1,400 MPa or more and an impact toughness of 60J or more in the tempering temperature range of 500 to 600° C., whereas Comparative Examples showed a decrease in tensile properties and impact toughness.

In the above description, exemplary embodiments of the present invention have been described, but the present invention is not limited thereto, and those of ordinary skill in the art will not depart from the concept and scope of the following claims. It will be appreciated that various modifications and variations are possible.

Claims (8)

By weight%, C: 0.3 to 0.6%, Si: 0.05 to 0.3%, Mn: 0.2 to 1.0%, Cr: 0.5 to 2.0%, Mo: 0.5 to 2.0%, Al: 0.02 to 0.05%, N: 0.01 to 0.03% remaining Fe and other impurities;
The microstructure includes 80% or more of bainite, 1 to 15% of pearlite, and 0.1 to 2% of martensite as an area fraction,
High-strength cold-rolling wire rod with excellent heat treatment characteristics and hydrogen-delayed fracture characteristics containing aluminum nitride with a diameter of 5 to 50 nm and at least 2×10 ¹⁹ pieces/m ³ . The method of claim 1,
High-strength cold-rolling wire rod with excellent heat treatment characteristics and hydrogen-delayed fracture characteristics with a prior austenite average grain diameter of 10 µm or less. The method of claim 1,
The martensite is a high-strength cold-rolling wire rod having excellent heat treatment characteristics and hydrogen delayed fracture characteristics including 60% or more in the old austenite grain boundary. By weight%, C: 0.3 to 0.6%, Si: 0.05 to 0.3%, Mn: 0.2 to 1.0%, Cr: 0.5 to 2.0%, Mo: 0.5 to 2.0%, Al: 0.02 to 0.05%, N: 0.01 to heating the billet comprising 0.03% remaining Fe and other impurities at 1000 to 1200° C.;
Hot rolling at a finish hot rolling temperature of 750 to 950 ° C,
Including cooling at a cooling rate of 0.2 to 1.0 °C / s,
The microstructure of the cooled wire rod is an area fraction, and includes 80% or more of bainite, 1 to 15% of pearlite, and 0.1 to 2% of martensite,
A method of manufacturing a high-strength cold-rolling wire rod having excellent heat treatment characteristics and hydrogen-delayed fracture characteristics containing aluminum nitride having a diameter of 5 to 50 nm and at least 2×10 ¹⁹ pieces/m ³ . By weight%, C: 0.3 to 0.6%, Si: 0.05 to 0.3%, Mn: 0.2 to 1.0%, Cr: 0.5 to 2.0%, Mo: 0.5 to 2.0%, Al: 0.02 to 0.05%, N: 0.01 to 0.03% remaining Fe and other impurities;
The microstructure is an area fraction, and it contains 90% or more of tempered martensite, and 2×10 ¹⁹ pieces/m ³ or more of aluminum nitride with a diameter of 5 to 50 nm. 6. The method of claim 5,
A heat-treated part with excellent heat treatment characteristics and hydrogen-delayed fracture characteristics with a prior austenite average grain diameter of 5㎛ or less. 6. The method of claim 5,
A heat-treated part with a tensile strength of 1400 MPa or more, an impact toughness of 60 J or more, and excellent heat treatment characteristics and hydrogen delayed fracture characteristics. By weight%, C: 0.3 to 0.6%, Si: 0.05 to 0.3%, Mn: 0.2 to 1.0%, Cr: 0.5 to 2.0%, Mo: 0.5 to 2.0%, Al: 0.02 to 0.05%, N: 0.01 to Contains 0.03% remaining Fe and other impurities, and the microstructure includes 80% or more of bainite, 1 to 15% of pearlite, and 0.1 to 2% of martensite by area fraction, wherein the martensite is 60 at the prior austenite grain boundary % or more of the wire rod is prepared as a steel wire by performing spheroidization heat treatment and wire drawing at least once,
The prepared steel wire is cold forged to prepare parts,
Heating the prepared parts at 800 to 900 ° C for 1,000 to 2,000 seconds,
Quenching the heated part to 50 to 150 ℃,
A method of manufacturing a heat treatment component excellent in heat treatment characteristics and hydrogen delayed fracture characteristics, in which the quenched component is tempered at 500 to 600° C. for 3,000 to 10,000 seconds.

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