Calcium-containing graphite steel with excellent cutting performance and method for manufacturing the same

Abstract

The present invention provides a calcium-containing graphite steel having excellent cutting performance, which contains calcium (Ca) and can form Ca-Al oxides that act as nuclei for graphitization to promote graphitization, and can generate Ca sulfides to improve machinability, and a method for producing the same. [Solution] The steel sheet contains, by weight, 0.60-0.90% 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), 0.0001-0.050% calcium (Ca), with the remainder being iron (Fe) and unavoidable impurities. The steel sheet has a fine structure, graphite grains distributed in a ferrite matrix, a graphitization rate of 95% or more, and contains a total of 5% by weight or less of MnS inclusions and pearlite.

Description

Technical Field

[0001] The present invention relates to a graphite steel having excellent cutting performance and a method for manufacturing the same. More specifically, by containing calcium (Ca), it can form a Ca-Al-based oxide that acts as a nucleus for graphitization to promote graphitization, and can generate a Ca-based sulfide to improve cutting performance. The present invention relates to a calcium-containing graphite steel having excellent cutting performance and a method for manufacturing the same.

Background Art

[0002] Generally, as a material for mechanical parts etc. where cutting performance is required, free-cutting steel added with cutting performance-imparting elements such as Pb and Bi is used. In order to improve the cutting performance of steel, low melting point cutting performance-imparting elements such as Pb and Bi are added to the steel to utilize the liquid metal embrittlement phenomenon, or a large amount of MnS is formed in the steel. Such free-cutting steel has excellent cutting performance of steel such as surface roughness, chip disposability, and tool life during cutting.

[0003] However, in the case of Pb-added free-cutting steel generally known to have excellent cutting performance, harmful substances such as toxic fumes are emitted during cutting work, which is very harmful to the human body and is also very disadvantageous for the recycling of steel materials. Therefore, in order to replace this, the addition of S, Bi, Te, Sn, etc. has been proposed, but there are problems such as cracks being likely to occur during steel material production and production being very difficult, and it has been known to be very problematic in terms of causing cracks during hot rolling.

[0004] The free-cutting steel developed to solve the above problems is graphite steel. Graphite steel is a steel containing fine graphite grains inside a ferrite base or a ferrite and pearlite base, and the internal fine graphite grains act as a crack supply source during cutting and have the property of good cutting performance by serving as a chip breaker.

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

[0006] Furthermore, even if graphite particles are precipitated through graphitization heat treatment, if they are unevenly distributed in an irregular shape, the uneven distribution of physical properties during cutting results in very poor chip processing and surface roughness, shortening tool life and making it difficult to obtain the advantages of graphite steel. Therefore, there is a need to provide a method for manufacturing graphite free-cutting steel that utilizes graphite particles while also making use of MnS inclusions to achieve excellent cutting performance. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Korean Published Patent No. 10-2015-0057400 [Overview of the project] [Problems that the invention aims to solve]

[0008] The present invention aims to provide calcium-containing graphite steel with excellent cutting performance and a method for producing the same.

[0009] However, the problems that this application seeks to solve are not limited to those mentioned above, and other problems not mentioned should be clearly understood by an ordinary engineer from the description below. [Means for solving the problem]

[0010] The graphite steel of the present invention, which achieves the aforementioned objectives, qualityIn terms of amount, it contains carbon (C): 0.60-0.90%, silicon (Si): 2.0-2.5%, manganese (Mn): 0.7-1.3%, sulfur (S): 0.2-0.5%, aluminum (Al): 0.01-0.05%, titanium (Ti): 0.005-0.020%, nitrogen (N): 0.003-0.015%, calcium (Ca): 0.0001-0.050%, with the remainder being iron (Fe) and unavoidable impurities. It has a microstructure with graphite particles distributed in a ferrite matrix, and a graphitization rate of 95% or more. quality It may contain MnS inclusions and pearlite in amounts of % or less.

[0011] The present invention's method for producing graphite steel is: quality The process may include the steps of: producing a billet containing, in terms of amount, carbon (C): 0.60-0.90%, silicon (Si): 2.0-2.5%, manganese (Mn): 0.7-1.3%, sulfur (S): 0.2-0.5%, aluminum (Al): 0.01-0.05%, titanium (Ti): 0.005-0.020%, nitrogen (N): 0.003-0.015%, calcium (Ca): 0.0001-0.050%, with the remainder being iron (Fe) and unavoidable impurities; producing a wire rod by hot rolling the billet; and graphitizing the produced wire rod. [Effects of the Invention]

[0012] According to the present invention, graphite steel can promote graphitization by forming Ca-Al oxides that act as nuclei for graphitization due to the presence of calcium (Ca), and can improve machinability by generating Ca-based sulfides, thereby providing graphite steel with excellent cutting performance that can replace conventional free-cutting steel materials, and a method for producing the same.

[0013] The graphite steel according to the present invention has excellent cutting performance, can replace conventional free-cutting steel materials, and can provide an environmentally friendly graphite free-cutting steel that replaces harmful elements such as Pb and Bi. [Modes for carrying out the invention]

[0014] The graphite steel of the present invention is quality In terms of amount, it contains carbon (C): 0.60-0.90%, silicon (Si): 2.0-2.5%, manganese (Mn): 0.7-1.3%, sulfur (S): 0.2-0.5%, aluminum (Al): 0.01-0.05%, titanium (Ti): 0.005-0.02%, nitrogen (N): 0.003-0.0150%, calcium (Ca): 0.0001-0.050%, with the remainder being iron (Fe) and unavoidable impurities. It has a microstructure with graphite particles distributed in a ferrite matrix, and a graphitization rate of 95% or more. quality Contains MnS inclusions and perlite in amounts of % or less.

[0015] Preferred embodiments of the present invention are described below. However, embodiments of the present invention can be modified into a variety of other forms, and the technical concept of the present invention is not limited to the embodiments described below. Furthermore, embodiments of the present invention are provided to give a more complete explanation of the present invention to a person with average skill in the art.

[0016] The terminology used in this application is for illustrative purposes only. For example, a singular expression may include plural expressions unless it is clearly required to be singular in the context.

[0017] Unless otherwise specified below, the units are: quality The quantity is expressed as a percentage. Furthermore, when a part is described as "containing" a certain component, this does not mean that other components are excluded, unless otherwise stated, but rather that other components may be included.

[0018] On the other hand, unless otherwise defined, all terms used herein should be considered to have the same meaning as that generally understood by a person of ordinary skill in the art to which this invention pertains. Therefore, unless explicitly defined herein, no particular term should be interpreted in an overly idealistic or formal sense. For example, in this specification, singular expressions include plural expressions unless there is an obvious exception in the context.

[0019] In addition, terms such as "about" and "substantially" in this specification are used in a sense that is the same as or close to the numerical value when manufacturing and material tolerances inherent to the recited meaning are presented, and are used to prevent unscrupulous infringers from misusing disclosure content where exact or absolute numerical values are recited to assist in understanding the present invention.

[0020] Hereinafter, the graphite steel with excellent cutting performance corresponding to the present invention and its manufacturing method will be described in detail.

[0021] <Graphite steel>

[0022] The graphite steel of the present invention quality in mass %, contains carbon (C): 0.60 to 0.90%, 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 0.020%, nitrogen (N): 0.003 to 0.015%, calcium (Ca): 0.0001 to 0.050%, and the balance can consist of iron (Fe) and unavoidable impurities.

[0023] <Component range>

[0024] Carbon (C): 0.60 to 0.90 quality mass %

[0025] Carbon is an essential element for forming graphite grains. When the content of the carbon is less than 0.60 quality mass %, the effect of improving machinability is insufficient, and the distribution of graphite grains is uneven even at the completion of graphitization. On the other hand, when the content exceeds 0.90 quality mass % and is excessive, the graphite grains are generated coarsely, the aspect ratio becomes large, and there is a risk that the machinability, particularly the surface roughness, will decrease. Therefore, it is preferable that the upper limit of the carbon content is 0.90 quality mass %.

[0026] Silicon (Si): 2.0 to 2.5 quality mass %

[0027] Silicon is an essential component as a deoxidizing agent in the production of molten steel, and it is a graphitization-promoting element that destabilizes cementite in steel, causing carbon to precipitate as graphite. Therefore, its inclusion is essential and preferable. In order to exhibit such effects in the present invention, 2.0 quality It is preferable that the amount be in percent.

[0028] On the other hand, if the content is excessive, not only will the effect saturate, but the hardness will increase due to the solid solution strengthening effect, accelerating tool wear during cutting, inducing brittleness due to an increase in nonmetallic inclusions, and potentially inducing excessive decarburization during hot rolling. Therefore, the upper limit of the silicon content is 2.5 quality It is preferable that the amount be in percent.

[0029] Manganese (Mn): 0.7~1.3 quality amount%

[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. In order to exhibit these effects in the present invention, 0.7 quality It is preferable that it contains % or more of the above.

[0031] On the other hand, if the content is excessive, it may inhibit graphitization, delaying the completion time of graphitization, and potentially increasing strength and hardness while reducing machinability. Therefore, the upper limit of the manganese content is 1.3 quality It is preferable that the amount be in percent.

[0032] Sulfur (S): 0.2~0.5 quality amount%

[0033] Sulfur can combine with manganese to form MnS inclusions, and the formation of MnS can improve machinability. However, if sulfur is present in excess, it can inhibit the graphitization of carbon in the steel, segregate at grain boundaries to reduce toughness, form low-melting-point sulfides to inhibit hot rolling, and cause mechanical anisotropy due to the stretched MnS produced by rolling. Therefore, in this invention, the sulfur (S) content can be adjusted within a range that does not cause mechanical anisotropy and contributes to improving machinability to induce the formation of MnS inclusions.

[0034] Therefore, the sulfur content is 0.2 quality If the amount is controlled to less than %, it is not possible to create a fraction sufficient to improve the cutting performance of MnS inclusions. Also, 0.5 quality If the amount exceeds a certain percentage, the anisotropy of the material increases, which can lead to breakage during machining and pose a safety hazard during processing.

[0035] Aluminum (Al): 0.01~0.05 quality amount%

[0036] Aluminum is the element that promotes graphitization second only to silicon. This is because when aluminum exists as solid solution Al, it destabilizes cementite, and therefore it must exist as solid solution Al. In order to exhibit this effect in the present invention, 0.01 quality It is preferable that it contains % or more of the above.

[0037] On the other hand, if the content is excessive, not only will the effect be saturated, but it may also induce nozzle clogging during continuous casting, leading to the formation of AlN at the austenite grain boundaries, which in turn cause graphite to be unevenly distributed at the grain boundaries. Therefore, the upper limit of the aluminum content is 0.05 quality It is preferable that the amount be in percent.

[0038] Titanium (Ti): 0.005~0.020 quality amount%

[0039] Titanium, like aluminum, combines with nitrogen to form nitrides such as TiN and AlN, and these nitrides act as nuclei for graphite formation during constant-temperature heat treatment.

[0040] However, while AlN precipitates unevenly at grain boundaries after austenite formation due to its low formation temperature, TiN crystallizes before austenite formation is complete because its formation temperature is higher than AlN's, resulting in a uniform distribution at austenite grain boundaries and within grains. Consequently, graphite grains formed with TiN as nucleation sites are also fine and uniformly distributed.

[0041] To demonstrate this effect, 0.005 quality It is preferable that the content be % or more, but if the content exceeds 0.02%, it can become coarse carbonitrides and consume the carbon necessary for graphite formation, thereby inhibiting graphitization. Therefore, the upper limit of the titanium content is 0.020%. quality It is preferable that the amount be in percent.

[0042] Nitrogen (N): 0.003~0.015 quality amount%

[0043] Nitrogen combines with titanium and aluminum to form TiN, AlN, and other nitrides, particularly AlN, which are mainly formed at austenite grain boundaries. During graphitization heat treatment, graphite is formed using these nitrides as nuclei, which can induce a non-uniform distribution of graphite, so the appropriate amount of nitrogen added is necessary.

[0044] When the amount of nitrogen added is excessive and it cannot bond with the elements that form nitrides, it ends up existing in the steel as dissolved nitrogen. This has the detrimental effect of increasing strength, stabilizing cementite, and delaying graphitization.

[0045] Therefore, in order to ensure that it is consumed in forming nitrides that act as nucleation sites for graphite and does not remain as solid dissolved nitrogen, the present invention uses 0.003 quality With the quantity % as the lower limit, 0.015 quality It is preferable to limit the amount to a percentage upper limit.

[0046] Calcium (Ca): 0.0001~0.050 quality amount%

[0047] In the steel composition of the present invention, calcium forms Ca-Al oxides, which act as nuclei for graphitization, thereby promoting graphitization and generating Ca-Sulfides to improve machinability. Stress concentrates at the interface between the Ca-Sulfides and the matrix structure during cutting, creating voids that grow and propagate as cracks, resulting in the separation and cutting of chips within the steel.

[0048] This effect occurs when the calcium content is 0.0001 quality The effect is insufficient at amounts less than %. quality If the calcium content exceeds a certain percentage, a large amount of coarse oxide-based nonmetallic inclusions may be generated, potentially reducing the fatigue strength of machine parts. Therefore, the calcium content should be between 0.0001 and 0.050%. quality It is preferable that it be included in a quantity within a percentage range.

[0049] Other ingredients

[0050] The remaining component of this invention is iron (Fe). However, in the normal manufacturing process, unintended impurities may inevitably be introduced from the raw materials or the surrounding environment, and it is not possible to eliminate them. However, the graphite steel according to the present invention does not need to contain phosphorus (P) or oxygen (O). Since these impurities are known to any technician in the normal manufacturing process, not all of them are specifically mentioned in this specification.

[0051] <Microstructure>

[0052] The graphite steel according to the present invention has a fine structure in which graphite grains are distributed in a ferrite matrix, and the graphitization rate is 95% or higher, total 5 quality Contains MnS inclusions and pearlite in amounts of less than 1%.

[0053] The graphitization rate of the graphite steel of the present invention may preferably be 98% or more, more preferably 99% or more, and most preferably 99.5% or more.

[0054] On the other hand, the graphitization rate refers to the ratio of the carbon content present in the graphitized state to the carbon content added to the steel, and is defined by the following relational equation 1. Graphitization of 95% or more means that most of the added carbon has been consumed in generating graphite (the amount of solid-solution carbon in ferrite and carbon dissolved in fine carbides is extremely small and therefore not considered), and that there is no undecomposed pearlite, meaning that the ferrite matrix has a microstructure in which graphite particles are distributed.

[0055] [Relationship 1] Graphitization rate (%) = (1 - carbon content in undecomposed pearlite / carbon content in steel) × 100

[0056] (Here, if there is no undecomposed perlite, the graphitization rate will be 100%.)

[0057] The method for manufacturing graphite steel, described later, can be applied to all of the information described above for graphite steel. Although detailed explanations of overlapping parts have been omitted, the method can still be applied identically even without those explanations.

[0058] <Manufacturing method for graphite steel>

[0059] The present invention's method for producing graphite steel is: quality The process includes the steps of: producing a billet containing, in terms of amount, carbon (C): 0.60-0.90%, silicon (Si): 2.0-2.5%, manganese (Mn): 0.7-1.3%, sulfur (S): 0.2-0.5%, aluminum (Al): 0.01-0.05%, titanium (Ti): 0.005-0.02%, nitrogen (N): 0.003-0.0150%, calcium (Ca): 0.0001-0.05%, with the remainder being iron (Fe) and unavoidable impurities; producing a wire rod by hot rolling the billet; and graphitizing the produced wire rod.

[0060] Rolling process

[0061] Furthermore, according to the present invention, the hot rolling step may include hot rolling in a temperature range of 900 to 1150°C. Specifically, the hot rolling step may be a step in which rolling is performed after heat treatment for a predetermined time in a temperature range of 900 to 1150°C.

[0062] The reason for setting the wire rod rolling temperature in the range of 900 to 1150°C is that below 900°C, surface grooves are likely to form during hot rolling, increasing the rolling load and making rolling difficult, while above 1150°C, the Austenite Grain Size (AGS) may become coarser, potentially increasing the graphitization heat treatment time after wire rod rolling.

[0063] Graphitization heat treatment process

[0064] Furthermore, according to the present invention, the step of graphitizing heat treatment may include heat treatment at a temperature range of 700 to 800°C for 5 hours or more, preferably 5 hours or more but less than 20 hours.

[0065] If the aforementioned wire is subjected to heat treatment at a temperature of 700-800°C for 5 hours or more, a graphitization rate of 95% or more can be achieved. However, below 700°C, the graphitization heat treatment time becomes longer, exceeding 20 hours, and above 800°C, not only does the graphitization time become longer, but austenite is generated by the reverse transformation of pearlite, and pearlite may be generated again during cooling, which is undesirable.

[0066] The present invention will be described in more detail below through examples.

[0067] The following embodiments are provided to fully convey the concept of the present invention to those with ordinary skill in the art to which the present invention pertains. The present invention is not limited to the embodiments presented herein and can be embodied in other forms.

[0068] <Examples>

[0069] A billet having the composition shown in Table 1 was heated at a temperature of 1050°C for 90 minutes and then rolled at high speed to produce a wire with a diameter of 19 mm. The graphitization heat treatment time and graphitization rate are shown in Table 2. The graphitization heat treatment was carried out at a constant temperature of "A1 temperature - 50°C".

[0070] In Tables 1 and 2 below, Examples 1 to 11 correspond to graphite steel wire rods that satisfy the alloy composition range and manufacturing conditions of the present invention, while Comparative Examples 1 to 7 correspond to wire rods that do not satisfy the alloy composition range and / or manufacturing conditions of the present invention.

[0071] [Table 1]

[0072] [Table 2]

[0073] In Table 2 above, the microstructure of (100% - graphitization rate) consists of MnS inclusions, pearlite, and some normally present inclusions, while the graphitized microstructure consists of ferrite + graphite grains.

[0074] In Table 2 above, the machinability is a value based on the cutting performance of general free-cutting steel (100% means equivalent performance).

[0075] Table 2 confirms that the graphitization fraction and machinability can be achieved under the manufacturing conditions of graphite free-cutting steel.

[0076] The examples and comparative examples are evaluated below with reference to Tables 1 and 2.

[0077] Examples 1 to 11 confirmed that by satisfying the alloy composition range and manufacturing conditions of the present invention, the graphitization rate was 98.5% or higher, and the cutting performance compared to lead-free cutting steel was 100%.

[0078] On the other hand, calcium is 0.05 quality Comparative Examples 1-7, which had an alloy composition exceeding a certain percentage and whose graphitization heat treatment was maintained for less than 5 hours, showed a graphitization rate of only 92% or less, and their machinability was also only 95% or less.

[0079] Specifically, the manganese content is 1.3 quality The amount exceeds %, and the sulfur content is 0.2 quality The amount is less than %, and the calcium content is 0.05 quality Comparative Examples 1 and 2, which exceeded the amount in percent, did not produce sufficient MnS inclusions, resulting in cutting performance of only 88% and 95% respectively compared to lead free-cutting steel, and the graphitization heat treatment was maintained for 3.5 hours or less, resulting in a graphitization rate of only 86% or less.

[0080] Also, the manganese content is 1.50 quality The amount is in percent, and the sulfur content is 0.56 quality The amount is in percent, and the calcium content is 0.08 quality In Comparative Example 3, the cutting performance of the graphite steel, which was measured by quantity, was only 89% of that of lead free-cutting steel, and even after the graphitization heat treatment was maintained for 3.0 hours, the graphitization rate was only 86%.

[0081] Also, the carbon content is 0.95 quality Amount %, manganese content 0.40 quality Amount, %, sulfur content 0.011 quality The amount is in percent, and the calcium content is 0.07 quality The cutting performance of the graphite steel in Comparative Example 4, which is expressed as a percentage, was only 92% of that of lead free-cutting steel, and even after the graphitization heat treatment was maintained for 4.5 hours, the graphitization rate was only 84%.

[0082] Also, the carbon content is 0.55 quality Amount %, Silicon content is 2.6 quality Quantity %, manganese content 0.56 quality Amount, %, sulfur content 0.60 quality Amount, titanium content is 0.025 quality The amount is in percent, and the calcium content is 0.1 qualityThe cutting performance of the graphite steel in Comparative Example 5, which is expressed as a percentage, was only 91% compared to lead free-cutting steel, and even after the graphitization heat treatment was maintained for 2.5 hours, the graphitization rate was still only 91%.

[0083] Also, the silicon content is 2.75 quality Amount %, manganese content 0.65 quality Amount, %, sulfur content 0.15 quality Amount, titanium content is 0.03 quality The amount is in percent, and the calcium content is 0.085 quality The cutting performance of the graphite steel in Comparative Example 6, which is expressed as a percentage, was only 93% of that of lead free-cutting steel, and even after the graphitization heat treatment was maintained for 3.0 hours, the graphitization rate was only 92%.

[0084] Also, the silicon content is 2.8 quality Amount %, manganese content 0.60 quality Amount, %, sulfur content 0.10 quality Amount %, titanium content 0.002 quality The amount is in percent, and the calcium content is 0.07 quality Comparative Example 7, which was expressed as a percentage, had cutting performance of only 90% compared to lead free-cutting steel, and even after the graphitization heat treatment was maintained for 4.5 hours, the graphitization rate was still only 90%.

[0085] Although exemplary embodiments of the present invention have been described above, the present invention is not limited thereto, and a person with ordinary skill in the art should understand that various modifications and variations are possible without departing from the concepts and scope of the claims described below. [Industrial applicability]

[0086] According to the present invention, because it has excellent cutting performance, it can replace conventional free-cutting steel materials, and it can provide an environmentally friendly graphite free-cutting steel that replaces harmful elements such as Pb and Bi, thus demonstrating its industrial applicability.

Claims

1. A material comprising, by mass%, carbon (C): 0.60-0.90%, silicon (Si): 2.0-2.5%, manganese (Mn): 0.7-1.3%, sulfur (S): 0.2-0.5%, aluminum (Al): 0.01-0.05%, titanium (Ti): 0.005-0.020%, nitrogen (N): 0.003-0.015%, calcium (Ca): 0.0001-0.050%, with the remainder being iron (Fe) and unavoidable impurities. A calcium-containing graphite steel with excellent cutting performance, characterized by a fine structure in which graphite particles are distributed within a ferrite matrix, a graphitization rate of 95% or more, and a total content of MnS inclusions and pearlite of 5% by mass or less.

2. The aforementioned graphite steel is characterized in that the graphitization rate is 99% or more, and is a calcium-containing graphite steel with excellent cutting performance as described in claim 1.

3. The calcium-containing graphite steel with excellent cutting performance according to Claim 1, characterized in that the unavoidable impurity includes phosphorus (P).

4. A method for producing calcium-containing graphite steel with excellent cutting performance, A step in manufacturing a billet containing, by mass%, carbon (C): 0.60-0.90%, silicon (Si): 2.0-2.5%, manganese (Mn): 0.7-1.3%, sulfur (S): 0.2-0.5%, aluminum (Al): 0.01-0.05%, titanium (Ti): 0.005-0.020%, nitrogen (N): 0.003-0.015%, calcium (Ca): 0.0001-0.05%, with the remainder being iron (Fe) and unavoidable impurities. The steps include: hot rolling the billet to produce a wire rod, and The process includes a step of graphitizing the manufactured wire, The method for producing calcium-containing graphite steel with excellent cutting performance is characterized in that the graphite steel has a fine structure in which graphite particles are distributed in a ferrite matrix, has a graphitization rate of 95% or more, and contains a total of 5% by mass or less of MnS inclusions and pearlite.

5. The method for producing calcium-containing graphite steel with excellent cutting performance according to claim 4, characterized in that the hot rolling step is performed in a temperature range of 900 to 1150°C.

6. The method for producing calcium-containing graphite steel with excellent cutting performance according to claim 4, characterized in that the graphitization heat treatment step is performed at a temperature range of 700 to 800°C for 5 hours or more.

7. The method for producing calcium-containing graphite steel with excellent cutting performance according to claim 6, characterized in that the graphitization heat treatment is carried out for 5 to 20 hours.

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