Graphite steel wire rod for TV pam nut parts, graphite steel, its manufacturing method and cutting method

Abstract

The present invention aims to provide a component design and cutting conditions for graphite steel for manufacturing industrial parts, and to provide a steel wire rod, a manufacturing method of graphite steel, and a graphitization heat treatment for manufacturing graphite steel. [Solution] A method for producing a graphite steel wire rod for TV pum nut parts includes the steps of producing a billet containing, by weight, 0.60-0.79% carbon (C), 2.0-2.5% silicon (Si), 0.7-1.3% manganese (Mn), 0.2-0.5% sulfur (S), 0.01-0.05% aluminum (Al), 0.005-0.020% titanium (Ti), 0.003-0.015% nitrogen (N), 0.0001-0.015% phosphorus (P), and the remainder being iron (Fe) and unavoidable impurities; The method includes the steps of heating a billet, hot rolling the heated billet to produce a wire rod, and cooling the wire rod, wherein the heating step includes heat treatment at a temperature of 1050±100° C. for 60 minutes or more, the hot rolling step includes hot rolling at a temperature of 900 to 1150° C., and the cooling step includes cooling to 500° C. at a cooling rate of 0.1 to 10.0° C. / s, and further includes an air-cooling step after the cooling step.

Description

[Technical Field]

[0001] The present invention relates to graphite steel wire rods, graphite steel, and manufacturing and cutting methods thereof for TV pumnut parts, and more particularly to a cutting method for manufacturing industrial parts, and to graphite steel wire rods, graphite steel, and manufacturing methods thereof. [Background technology]

[0002] The PEM nut, also known as a self-clinching nut, is used to connect materials such as thin plates and sheet metal. It has a rounded shape, an embossed gear, and a guide groove on one end. It is a nut that can be used to clinch a high-strength internal thread into thin plates. Generally, free-cutting steels containing machinability-imparting elements such as Pb, Bi, and S are used as materials for machine parts and other applications that require machinability. To improve the machinability of steel, low-melting-point machinability-imparting elements such as Pb and Bi are added to the steel to utilize the liquid metal bromide phenomenon, or large amounts of MnS are formed in the steel. These free-cutting steels have excellent machinability, including surface roughness, chip treatment, and tool life during cutting.

[0003] However, Pb-added free-cutting steel, which has the best machinability, emits harmful substances such as toxic fumes during cutting, which are extremely harmful to the human body and are also disadvantageous for recycling steel. Therefore, the addition of S, Bi, Te, Sn, etc. has been proposed as an alternative, but these have been known to be problematic in that they are prone to cracking during steel manufacturing, making production very difficult, or they can cause cracking during hot rolling.

[0004] Graphite free-cutting steel was developed to solve the above problems. Graphite free-cutting steel is a steel containing fine graphite grains within a ferrite matrix or a ferrite and pearlite matrix. The fine graphite grains inside act as crack sources and chip breakers during cutting, resulting in good machinability.

[0005] However, despite these advantages of graphite free-cutting steel, it has not yet been commercialized. This is because, although graphite is a stable phase, when carbon is added to steel, it precipitates as cementite, a metastable phase, making it difficult to precipitate graphite without a separate, long-term heat treatment. This long-term heat treatment process causes decarburization, which adversely affects the performance of the final product.

[0006] Furthermore, even if graphite grains are precipitated through graphitization heat treatment, if they are unevenly distributed in irregular shapes, the distribution of physical properties during cutting will be uneven, resulting in poor chip processing and surface roughness, shortened tool life, and making it difficult to obtain the advantages of graphite free-cutting steel. Therefore, it is necessary to provide a graphite free-cutting steel wire that can significantly reduce the heat treatment time while uniformly distributing fine graphite steel within the matrix during heat treatment, and a cutting method (i.e., CNC combined lathe, CAM automatic lathe) with excellent machinability. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Korean Patent Publication No. 10-2015-0057400 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention aims to provide a composition design and cutting conditions for graphite steel for manufacturing industrial parts, and to provide a steel wire rod for manufacturing graphite steel, a method for manufacturing graphite steel, and graphitization heat treatment.

[0009] However, the problems to be solved by the present application are not limited to those mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below. [Means for solving the problem]

[0010] The graphite steel wire rod of the present invention contains, by weight, carbon (C): 0.60 to 0.79%, silicon (Si): 2.0 to 2.5%, manganese (Mn): 0.7 to 1.3%, sulfur (S): 0.2 to 0.5%, aluminum (Al): 0.01 to 0.05%, titanium (Ti): 0.005 to 0.02%, nitrogen (N): 0.003 to 0.015%, phosphorus (P): 0.0001 to 0.015%, and the remainder consisting of iron (Fe) and unavoidable impurities.

[0011] A method for producing a graphite steel wire rod of the present invention includes the steps of producing a billet containing, by weight, 0.60 to 0.79% carbon (C), 2.0 to 2.5% silicon (Si), 0.7 to 1.3% manganese (Mn), 0.2 to 0.5% sulfur (S), 0.01 to 0.05% aluminum (Al), 0.005 to 0.02% titanium (Ti), 0.003 to 0.015% nitrogen (N), 0.0001 to 0.015% phosphorus (P), and the balance being iron (Fe) and unavoidable impurities; heating the billet; hot-rolling the heated billet to produce a wire rod; and cooling the wire rod.

[0012] The graphite steel of the present invention contains, by weight, 0.60 to 0.79% carbon (C), 2.0 to 2.5% silicon (Si), 0.7 to 1.3% manganese (Mn), 0.2 to 0.5% sulfur (S), 0.01 to 0.05% aluminum (Al), 0.005 to 0.02% titanium (Ti), 0.003 to 0.015% nitrogen (N), and 0.0001 to 0.015% phosphorus (P), with the remainder being iron (Fe) and unavoidable impurities. The graphite steel has a fine structure with graphite grains distributed in a ferrite matrix, a graphitization rate of 90% or more, and a pearlite fraction of less than 10%.

[0013] A method for producing graphite steel of the present invention includes the steps of producing a wire rod containing, by weight, 0.60 to 0.79% carbon (C), 2.0 to 2.5% silicon (Si), 0.7 to 1.3% manganese (Mn), 0.20 to 0.5% sulfur (S), 0.01 to 0.05% aluminum (Al), 0.005 to 0.02% titanium (Ti), 0.003 to 0.015% nitrogen (N), 0.0001 to 0.015% phosphorus (P), and the balance being iron (Fe) and unavoidable impurities, and performing a graphitization heat treatment on the produced wire rod.

[0014] The cutting method of the present invention is characterized in that the graphite steel is cut using one selected from a CNC combined lathe and a CAM automatic lathe. [Effects of the Invention]

[0015] The graphite free-cutting steel of the present invention has excellent cutting performance and can be used as a material for small parts such as TV pum nuts. DETAILED DESCRIPTION OF THE INVENTION

[0016] The graphite steel wire rod of the present invention contains, by weight, carbon (C): 0.60 to 0.79%, silicon (Si): 2.0 to 2.5%, manganese (Mn): 0.7 to 1.3%, sulfur (S): 0.2 to 0.5%, aluminum (Al): 0.01 to 0.05%, titanium (Ti): 0.005 to 0.02%, nitrogen (N): 0.003 to 0.015%, phosphorus (P): 0.0001 to 0.015%, and the remainder consisting of iron (Fe) and unavoidable impurities.

[0017] Preferred embodiments of the present invention will be described below. However, the embodiments of the present invention may be modified into various other forms, and the technical concept of the present invention is not limited to the embodiments described below. Furthermore, the embodiments of the present invention are provided to more completely explain the present invention to those having average knowledge in the art.

[0018] The terms used in this application are only used to describe specific examples. For example, singular expressions include plural expressions unless the context clearly requires a singular expression.

[0019] Hereinafter, unless otherwise specified, the unit is % by weight. Furthermore, when a part is described as "comprising" a certain component, this does not mean that other components are excluded, but that other components may also be included, unless otherwise specified.

[0020] Meanwhile, unless otherwise defined, all terms used herein should be considered to have the same meaning as that commonly understood by a person of ordinary skill in the art to which the present invention pertains. Therefore, unless clearly defined herein, specific terms should not be construed as having an overly ideal or formal meaning. For example, in this specification, the singular expression includes the plural expression unless there is a clear exception in the context.

[0021] Furthermore, in this specification, the terms "about," "substantially," and the like are used in the sense of a numerical value or a value close to the numerical value when tolerances for manufacturing and materials inherent in the meanings mentioned are presented, and are used to prevent unscrupulous infringers from unfairly utilizing the disclosure content in which precise or absolute numerical values ​​are mentioned to aid in the understanding of the present invention.

[0022] Hereinafter, the graphite steel wire rod for TV pumnut parts, graphite steel having excellent cutting performance, and its manufacturing method and cutting method according to the present invention will be described in detail.

[0023] <Graphite steel wire rod>

[0024] The graphite steel wire rod of the present invention contains, by weight, carbon (C): 0.60 to 0.79%, silicon (Si): 2.0 to 2.5%, manganese (Mn): 0.7 to 1.3%, sulfur (S): 0.2 to 0.5%, aluminum (Al): 0.01 to 0.05%, titanium (Ti): 0.005 to 0.02%, nitrogen (N): 0.003 to 0.015%, phosphorus (P): 0.0001 to 0.015%, and the remainder consisting of iron (Fe) and unavoidable impurities.

[0025] Carbon (C): 0.60~0.79% by weight

[0026] Carbon is an essential element for forming graphite grains. If the carbon content is less than 0.60 wt%, the machinability improvement effect is insufficient and the graphite grains are unevenly distributed even after graphitization is completed. On the other hand, if the carbon content exceeds 0.79 wt%, the graphite grains are generated coarsely, increasing the aspect ratio and possibly deteriorating machinability, particularly surface roughness. Therefore, the upper limit of the carbon content is preferably 0.79 wt%.

[0027] Silicon (Si): 2.0 to 2.5% by weight

[0028] Silicon is an essential component as a deoxidizer during the production of molten steel. It also promotes graphitization by destabilizing cementite in steel, allowing carbon to precipitate as graphite. To achieve these effects, a silicon content of 2.0 wt% is preferred. However, excessive silicon content may saturate the effect, increase hardness due to solid solution strengthening, accelerate tool wear during cutting, and increase nonmetallic inclusions, potentially causing brittleness and excessive decarburization during hot rolling. Therefore, the upper limit of the silicon content is preferably 2.5 wt%.

[0029] Manganese (Mn): 0.7 to 1.3 wt%

[0030] Manganese improves the strength and impact properties of steel and contributes to improved machinability by combining with sulfur in the steel to form MnS inclusions. To achieve this effect, a manganese content of 0.7 wt% or more is preferred. However, excessive manganese content can inhibit graphitization, delaying the completion time of graphitization and increasing strength and hardness, thereby reducing machinability. Therefore, the upper limit of the manganese content is preferably 1.3 wt%.

[0031] Sulfur (S): 0.2~0.5% by weight

[0032] Sulfur combines with manganese to induce the formation of MnS inclusions, thereby improving machinability. However, excessive sulfur not only inhibits the graphitization of carbon in steel, but also segregates at grain boundaries, reducing toughness. It can also form low-melting-point sulfides, which can impair hot rolling properties. Furthermore, MnS elongated during rolling can cause mechanical anisotropy. Therefore, in the present invention, it is preferable to appropriately control the sulfur content so that it does not impair physical properties and improves machinability. Specifically, if the sulfur content is less than 0.2 wt%, insufficient inclusions such as MnS are formed, resulting in poor machinability. Therefore, the sulfur content must be controlled to a level above 0.2 wt%. However, if the sulfur content exceeds 0.5 wt%, quality defects such as surface defects may occur, so the sulfur content should be controlled below that level.

[0033] Aluminum (Al): 0.01 to 0.05% by weight

[0034] Aluminum is the element that promotes graphitization second only to silicon. This is because aluminum destabilizes cementite when present as solute aluminum, and therefore must exist as solute aluminum. To achieve this effect in the present invention, a content of 0.01 wt% or more is preferred. However, excessive aluminum content not only saturates the effect, but can also cause nozzle clogging during continuous casting. Furthermore, AlN is formed at austenite grain boundaries, resulting in the uneven distribution of graphite at the grain boundaries. Therefore, the upper limit of the aluminum content is preferably 0.05 wt%.

[0035] Titanium (Ti): 0.005 to 0.020% by weight

[0036] Like aluminum, titanium combines with nitrogen to form nitrides such as TiN and AlN, which act as nuclei for graphite formation during isothermal heat treatment. However, because AlN has a low formation temperature, it precipitates unevenly at grain boundaries after austenite formation. In contrast, TiN, which has a higher formation temperature than AlN, crystallizes before austenite formation is complete and is uniformly distributed at the grain boundaries and within the austenite grains. Therefore, the graphite grains formed using TiN as nucleation sites are fine and uniformly distributed. To achieve this effect, a titanium content of 0.005 wt% or more is preferred. However, if the content exceeds 0.020%, coarse carbonitrides may form, consuming carbon necessary for graphite formation and inhibiting graphitization. Therefore, the upper limit of the titanium content is preferably 0.020 wt%.

[0037] Nitrogen (N): 0.003 to 0.015% by weight

[0038] Nitrogen combines with titanium and aluminum to form TiN, AlN, and other nitrides. Nitrogen, especially AlN, is primarily formed at austenite grain boundaries. During graphitization heat treatment, graphite forms around these nitrides, which can lead to uneven distribution of graphite. Therefore, an appropriate amount of nitrogen must be added. If excessive nitrogen is added, it cannot combine with nitride-forming elements and remains in the steel as solute nitrogen. This adversely affects the strength, stabilizes cementite, and retards graphitization. Therefore, in the present invention, the nitrogen content is limited to 0.003 wt.% as the lower limit and 0.015 wt.% as the upper limit, so that nitrogen is consumed to form nitrides that act as graphite nucleation sites and does not remain as solute nitrogen.

[0039] Phosphorus (P): 0.0001 to 0.015% by weight

[0040] A small amount of phosphorus weakens the grain boundaries of steel, which is beneficial for machinability. However, excessive phosphorus content increases the hardness of ferrite through solid solution strengthening, reducing the toughness and delayed fracture resistance of steel and promoting the occurrence of surface defects. Therefore, it is preferable to control its content as low as possible within the range of 0.0001 to 0.015% by weight. It is particularly important to control the upper limit, which in the present invention is controlled at 0.015% by weight.

[0041] Other ingredients

[0042] The remaining component of the present invention is iron (Fe). However, since unintended impurities can be unavoidably mixed in from raw materials or the surrounding environment during normal manufacturing processes, it is not possible to eliminate these. However, in the present invention, it is preferable that boron (B) and oxygen (O) are substantially absent. These impurities are known to anyone skilled in normal manufacturing processes, and therefore, the entire contents thereof will not be specifically mentioned in this specification.

[0043] <Microstructure>

[0044] Furthermore, according to the present invention, the graphite steel wire rod may have an area fraction of pearlite of 90% or more and an area fraction of ferrite of less than 10%, but preferably has an area fraction of pearlite of 95% or more and an area fraction of ferrite of less than 5%. In the present invention, graphite grains are generated by the decomposition of pearlite, so if the area fraction of pearlite is low, the graphite grain fraction is also low, resulting in a non-uniform distribution, which is undesirable. A higher area fraction of pearlite is advantageous for ensuring uniform and fine graphite grains, so there is no particular upper limit.

[0045] The graphite steel wire manufacturing method, graphite steel, graphite steel manufacturing method, and cutting method described below may all be applied to the graphite steel wire described above, and although detailed descriptions of overlapping parts are omitted, they may be equally applicable even if the descriptions are omitted.

[0046] <Graphite Steel Wire Rod Manufacturing Method>

[0047] A method for producing a graphite steel wire rod of the present invention includes the steps of producing a billet containing, by weight, 0.60 to 0.79% carbon (C), 2.0 to 2.5% silicon (Si), 0.7 to 1.3% manganese (Mn), 0.2 to 0.5% sulfur (S), 0.01 to 0.05% aluminum (Al), 0.005 to 0.02% titanium (Ti), 0.003 to 0.015% nitrogen (N), 0.0001 to 0.015% phosphorus (P), and the balance being iron (Fe) and unavoidable impurities; heating the billet; hot-rolling the heated billet to produce a wire rod; and cooling the wire rod.

[0048] heating process

[0049] In addition, the heating step of the present invention may include maintaining the temperature in the range of 1050±100° C. for 60 minutes or more.

[0050] Before hot rolling, the billet is maintained at a temperature in the range of 1050±100°C for at least 60 minutes. If the billet heating temperature is less than 950°C, the load increases during rolling, which can reduce rolling productivity, so a low heating temperature has disadvantages. If the heating temperature exceeds 1150°C, not only does it increase costs, but it also accelerates decarburization, resulting in a thick decarburized layer that remains in the final product, which is undesirable. The reason for setting the heating maintenance time at 60 minutes or more is that if it is less than 60 minutes, it is difficult to ensure uniform temperature distribution inside and outside the billet for wire rolling.

[0051] Rolling process

[0052] In addition, the step of hot rolling the wire rod according to the present invention may include hot rolling at a temperature range of 900 to 1150°C.

[0053] The reason why the rolling temperature of the wire rod is set in the range of 900 to 1150°C is that if the temperature is less than 900°C, surface scratches are likely to occur during hot rolling, the rolling load increases, and rolling becomes difficult, whereas if the temperature exceeds 1150°C, the AGS (Austenite Grain Size) becomes coarse, which may lengthen the graphitization heat treatment time after wire rod rolling.

[0054] cooling process

[0055] In addition, the cooling step of the present invention may include cooling to 500°C at a cooling rate of 0.1 to 10.0°C / s, and specifically, cooling to 500°C at a cooling rate of 0.1 to 10.0°C / s in a temperature range of 750 to 900°C.

[0056] In addition, the present invention may include an air-cooling step after the cooling step.

[0057] A cooling rate of more than 10.0°C / s is undesirable because a hard phase such as martensite is generated, which may cause wire breakage during cold drawing, the process following wire rolling. A cooling rate of less than 0.1°C / s is undesirable because an excessive amount of saltpeter phase is generated, which may reduce the fraction of pearlite or coarsen the crystal grains, resulting in non-uniform distribution of graphite grains generated after graphitization heat treatment.

[0058] <Graphite steel>

[0059] The graphite steel of the present invention includes, by weight, 0.60 to 0.79% carbon (C), 2.0 to 2.5% silicon (Si), 0.7 to 1.3% manganese (Mn), 0.2 to 0.5% sulfur (S), 0.01 to 0.05% aluminum (Al), 0.005 to 0.02% titanium (Ti), 0.003 to 0.015% nitrogen (N), 0.0001 to 0.015% phosphorus (P), with the remainder being iron (Fe) and unavoidable impurities, and includes one having a fine structure in which graphite grains are distributed in a ferrite matrix, a pearlite fraction of less than 10%, and a graphitization rate of 90% or more.

[0060] The graphitization rate of the graphite steel of the present invention may be preferably 95% or more, and more preferably 99%.

[0061] Meanwhile, the graphitization ratio means the ratio of the carbon content present in the graphite state to the carbon content added to the steel, and is defined by the following relational expression 1.

[0062] [Relationship 1] Graphitization rate (%) = (1 - carbon content in undecomposed pearlite / carbon content in steel) x 100

[0063] (Here, if there is no undecomposed pearlite, the graphitization rate will be 100%)

[0064] The graphitization rate of 90% or more means that most of the added carbon has been consumed to produce graphite, and that there is no undecomposed pearlite, i.e., a fine structure in which graphite grains are distributed in a ferrite matrix. In this case, the amount of dissolved carbon in ferrite and dissolved carbon in fine carbides is not taken into consideration because it is very small.

[0065] <Graphite steel manufacturing method>

[0066] A method for producing graphite steel of the present invention includes the steps of producing a wire rod containing, by weight, 0.60 to 0.79% carbon (C), 2.0 to 2.5% silicon (Si), 0.7 to 1.3% manganese (Mn), 0.2 to 0.5% sulfur (S), 0.01 to 0.05% aluminum (Al), 0.005 to 0.02% titanium (Ti), 0.003 to 0.015% nitrogen (N), 0.0001 to 0.015% phosphorus (P), and the balance being iron (Fe) and unavoidable impurities, and performing a graphitization heat treatment on the produced wire rod.

[0067] Also, according to the present invention, the graphitization heat treatment may include heat treatment at a temperature range of 700 to 800° C. for 5 hours or more, preferably 5 to 20 hours.

[0068] If the wire is heat-treated at a temperature in the range of 700 to 800°C for 5 hours or more, a graphitization rate of 90% or more can be achieved. If the temperature is lower than 700°C, the graphitization heat treatment time will be longer, exceeding 20 hours, and if the temperature is higher than 800°C, the graphitization time will be longer, which is not preferable.

[0069] <Cutting method>

[0070] The cutting method of the present invention is characterized in that the graphite steel according to the present invention is cut using one selected from a CNC combined lathe and a CAM automatic lathe.

[0071] Furthermore, according to the present invention, the CNC combined lathe may have a cutting speed of 1500 RPM or more and a feed speed of 0.03 mm / rev or more, and the CAM automatic lathe may also have a cutting speed of 1500 RPM or more and a feed speed of 0.03 mm / rev or more.

[0072] The graphite free-cutting steel wire rod thus produced is then cut by a cutting company to produce small industrial parts, such as TV pan nuts. Market entry is impossible without the same cutting performance as general free-cutting steel. To overcome this, the present invention proposes a manufacturing method using a CNC multi-task lathe and / or a CAM-based automatic lathe at a cutting speed of 1500 RPM or more and a feed rate of 0.03 mm / rev or more. Cutting performance deteriorates when the CNC multi-task lathe and / or CAM-based automatic lathe is set to a cutting speed less than 1500 RPM and / or a feed rate less than 0.03 mm / rev. The faster the cutting speed and feed rate, the better the cutting performance, achieving a level comparable to that of general free-cutting steel.

[0073] The present invention will be described in more detail below with reference to examples.

[0074] The following examples are presented to fully convey the concept of the present invention to those skilled in the art, and the present invention is not limited to the examples presented herein and may be embodied in other forms.

[0075] <Example>

[0076] A billet having the composition shown in Table 1 below was maintained at a heating temperature of 1050° C. for 90 minutes and subjected to high speed wire rolling to produce wires of Examples 1 to 11 and Comparative Examples 1 to 7 having a diameter of 19 mm.

[0077] [Table 1]

[0078] In addition, in the production of the wire, the wire was cooled after rolling, and then the pearlite area fraction in the microstructure was measured. The cooling start temperature, cooling rate, and pearlite area fraction are shown in Table 2 below.

[0079] The prepared wire rod was subjected to a graphitization heat treatment, during which the graphitization heat treatment duration and graphitization rate were measured and shown in Table 2. The graphitization heat treatment was carried out at a constant temperature of -50°C.

[0080] [Table 2]

[0081] In Table 2, the (100%-graphitization rate) structure is composed of MnS inclusions, pearlite, and some commonly present inclusions, and the graphitized structure is composed of ferrite and graphite grains.

[0082] It can be seen that the pearlite fraction and graphitized fraction are achieved under the manufacturing conditions of wire rod and graphitized material as shown in Table 2 above.

[0083] In addition, examples and comparative examples according to cutting conditions for manufacturing TV pumnut parts are shown in Tables 3 and 4 below. Table 3 shows the CNC lathe cutting conditions, and Table 4 shows the lathe cutting conditions.

[0084] [Table 3]

[0085] [Table 4]

[0086] In Tables 3 and 4, the machinability is a numerical value based on the cutting performance of general free-cutting steel (100% means the same level).

[0087] The Examples and Comparative Examples will be evaluated below with reference to Tables 1 to 4.

[0088] It can be confirmed that Examples 1 to 11 satisfy the alloy composition range of the present invention and the cooling rate of 0.1 to 10°C / s, and therefore the graphite steel wire rod has a pearlite area fraction of 95.1% or more and a graphitization rate of 97.5% or more. On the other hand, it can be confirmed that Comparative Examples 1 to 7, which have a cooling rate outside the range of 0.1 to 10°C / s, have a pearlite area fraction of only 93.0 to 94.2% and a graphitization rate of only 75 to 86%.

[0089] Furthermore, Examples 1 to 11, which satisfied the conditions of a CNC combined lathe and a CAM automatic lathe cutting speed of 1500 RPM or more and a feed rate of 0.03 mm / rev or more, were evaluated as having cutting performance equivalent to that of general free-cutting steel (100% of that of general free-cutting steel) through material cutting processing, while Comparative Examples 1 to 7, which did not satisfy the above cutting speed and feed rate conditions, were found to have cutting performance that was only 80 to 95% of that of general free-cutting steel.

[0090] While exemplary embodiments of the present invention have been described above, the present invention is not limited thereto, and it should be understood that various changes and modifications can be made by those skilled in the art without departing from the concept and scope of the claims set forth below. [Industrial Applicability]

[0091] The graphite free-cutting steel of the present invention does not generate fumes and has excellent cutting performance, so it can be used as a material for small parts such as TV panel nuts, and is therefore recognized to have industrial applicability.

Claims

1. Graphite steel wire for TV pumnut parts, characterized by containing, by weight, 0.60 to 0.79% carbon (C), 2.0 to 2.5% silicon (Si), 0.7 to 1.3% manganese (Mn), 0.2 to 0.5% sulfur (S), 0.01 to 0.05% aluminum (Al), 0.005 to 0.020% titanium (Ti), 0.003 to 0.015% nitrogen (N), and 0.0001 to 0.015% phosphorus (P), with the remainder consisting of iron (Fe) and unavoidable impurities.

2. 2. The graphite steel wire for TV pum nut parts according to claim 1, wherein the area fraction of pearlite is 95% or more.

3. producing a billet containing, in weight percent, 0.60 to 0.79% carbon (C), 2.0 to 2.5% silicon (Si), 0.7 to 1.3% manganese (Mn), 0.2 to 0.5% sulfur (S), 0.01 to 0.05% aluminum (Al), 0.005 to 0.020% titanium (Ti), 0.003 to 0.015% nitrogen (N), 0.0001 to 0.015% phosphorus (P), with the balance being iron (Fe) and unavoidable impurities; heating the billet; hot rolling the heated billet into a wire rod; and a step of cooling the wire.

4. 4. The method of claim 3, wherein the heating step comprises maintaining the temperature in the range of 1050±100° C. for 60 minutes or more.

5. 4. The method of claim 3, wherein the hot-rolling step comprises hot-rolling the wire at a temperature in the range of 900 to 1150°C.

6. 4. The method of claim 3, wherein the cooling step comprises cooling the wire to 500° C. at a cooling rate of 0.1 to 10.0° C. / s.

7. 4. The method of claim 3, further comprising the step of air-cooling after the step of cooling.

8. The alloy contains, by weight, 0.60 to 0.79% carbon (C), 2.0 to 2.5% silicon (Si), 0.7 to 1.3% manganese (Mn), 0.2 to 0.5% sulfur (S), 0.01 to 0.05% aluminum (Al), 0.005 to 0.020% titanium (Ti), 0.003 to 0.015% nitrogen (N), and 0.0001 to 0.015% phosphorus (P), with the remainder consisting of iron (Fe) and unavoidable impurities; Graphite steel for TV pumnut parts, characterized in that it has a fine structure, graphite grains are distributed in a ferrite matrix, the graphitization rate is 90% or more, and the pearlite fraction is less than 10%.

9. 9. The graphite steel for TV pum nut parts according to claim 8, wherein the graphitization rate is 99% or more.

10. A step of manufacturing a wire containing, in weight percent, 0.60 to 0.79% carbon (C), 2.0 to 2.5% silicon (Si), 0.7 to 1.3% manganese (Mn), 0.2 to 0.5% sulfur (S), 0.01 to 0.05% aluminum (Al), 0.005 to 0.020% titanium (Ti), 0.003 to 0.015% nitrogen (N), and 0.0001 to 0.015% phosphorus (P), with the balance being iron (Fe) and unavoidable impurities; a graphitizing heat treatment of the wire rod;

11. 11. The method of claim 10, wherein the graphitization heat treatment comprises heat treating at a temperature of 700 to 800° C. for 5 hours or more.

12. A cutting method for cutting the graphite steel for TV pumnut parts according to claim 8 using one selected from a CNC compound lathe and a CAM automatic lathe.

13. 13. The cutting method according to claim 12, wherein the CNC combined lathe has a cutting speed of 1500 RPM or more and a transfer speed of 0.03 mm / rev or more.

14. 13. The cutting method according to claim 12, wherein the CAM automatic lathe has a cutting speed of 1500 RPM or more and a transfer speed of 0.03 mm / rev or more.

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