KR101492800B1 - Spheroidizing-annealing heat method of carbon steel and blade-metal products - Google Patents

Abstract

The present invention relates to a spheroidizing-annealing heat treatment method of carbon steel, and to a carbon steel product spheroidizing-annealing heat treated thereby. More specifically, the present invention is to manufacture a carbon steel product having a specification of material properties to be acquired while spheroidizing-annealing treatment or simplified spheroidizing-annealing treatment is carried out in a shorter period of time than that of the existing spheroidizing-annealing process. The spheroidizing-annealing heat treatment method of carbon steel according to the present invention comprises a first step of heat-treating the carbon steel gone through a carbon restoration spheroidizing-annealing process at the temperature below 850-900°C for 2.5-3.5 hours, and then firstly heat-processing the carbon steel by quenching the carbon steel with nitrogen gas and the like.

Description

BACKGROUND OF THE INVENTION Field of the Invention [0001] The present invention relates to a method of annealing a carbon steel by spheroidizing annealing,

The present invention relates to a method for annealing a carbon steel by spheroidizing annealing, and more particularly, to a carbon steel product that is heat treated by spheroidizing annealing, which has excellent hardness and is excellent in economy by simplifying a heat treatment process while being performed under different heat treatment conditions Lt; / RTI >

The spheroidizing annealing is a process in which the carbide in the carbon steel or the special steel is changed into a ball shape. When the spheroidizing process is performed by an annealing operation, the toughness of the steel increases, and the workability is improved and the performance as a tool can be improved.

Generally, there are two types of furnaces used in the spheroidizing annealing process. They are divided into a batch annealing furnace and a continuous annealing line annealing furnace depending on the furnace type. Here, the Vetch type annealing furnace is also called a bell type because its shape is in the form of an overturned bell. The continuous annealing furnace is mainly used for low grade steel because of its large installation area and difficulty in controlling the internal atmosphere of the furnace because the steel sheet passes through the inside of the tunnelled furnace and is annealed.

In the conventional Vetch type annealing furnace, a hot-rolled coil is stacked on an upper portion of a coil support, the outer side of the coil is covered with an inner cover, the outer side of the inner cover is covered with an outer cover, Shape. A heat transfer plate is laid between each coil and the coil, and a gas discharge port is formed in the bottom of the inner cover for introducing and discharging the thermocouple and atmosphere gas. The gas burner, which is the heating source, is installed between the inner cover and the outer cover so that the heat source is indirect heating type that does not directly heat the coil. In this way, when a conventional coil-type annealing furnace is manufactured by using an indirect heating type, the temperature of a portion of the coil directly contacting with the coil is high and the temperature of the portion away from the heating source is low. To prevent deformation and to prevent oxidation of the coil by the heat source. The process for annealing the spheroidizing annealing using the above-described Vetch type annealing furnace is as follows. First, the coil is stacked on the upper part of the support plate, and the inner cover is covered with the nitrogen gas. Then, the inner cover is purged and is pursued. In this state, the gas burner is operated to heat between the outer cover and the inner cover, and the heated heat source is conducted to the stacked coils to reach the target spheroidizing annealing temperature and soaking at an appropriate time at this temperature Then, the annealing process is gradually cooled to take out the annealed coil. Here, the atmospheric gas in the spheroidizing annealing process is usually used in a reducing state by mixing nitrogen gas and hydrogen gas. The oxidizing atmosphere and various foreign substances present in the processing space in the inner cover are removed by purging, which is a pre- By controlling the heat treatment atmosphere in this manner, it is possible to prevent the formation of oxides on the surface of the steel sheet after the annealing treatment and to prevent decarburization. By such an atmosphere heat treatment, the surface of the steel sheet after annealing is beautiful and clean.

The spheroidizing annealing process can change the physical properties of the carbon steel or the special steel product. The conventional spheroidizing annealing process has a problem of performing spheroidizing annealing through a complicated multi-step process as shown in FIG. 2A and a long process time , The economy was inferior.

1. Korean Published Patent Application No. 10-2005-0006920 (January 17, 2005) 2. Korean Patent Application No. 10-2003-0095594 (December 24, 2003)

In the conventional spheroidizing annealing process, a complicated multi-stage process has to be carried out, resulting in an increase in production cost. Thus, after a long period of research, the present inventors have found that, while simplifying the spheroidizing annealing process, The present invention has been completed.

According to an aspect of the present invention, there is provided a method of annealing a carbon steel for spheroidizing annealing, comprising: subjecting a carbon steel subjected to a carbon annealing process to a heat treatment at 850 to 900 ° C for 2.5 to 3.5 hours and then quenching under nitrogen gas; Step one; A second step of subjecting the quenched carbon steel to a second heat treatment at 710 to 750 ° C for 7.5 to 8.5 hours; A third heat treatment after performing the second heat treatment, a heat treatment at 630 to 660 ° C for 7.5 to 8.5 hours, followed by cooling to 380 to 420 ° C, followed by quenching with nitrogen gas, and a third heat treatment; 4) performing the tempering of the third heat treated carbon steel at 680 to 720 캜 for 4.5 to 5.5 hours; And 5) cooling the tempered carbon steel to 280 to 320 ° C, followed by quenching with nitrogen gas.

In addition, the present invention relates to a blade carbon steel product, which is characterized in that spheroidizing annealing is performed by the above-described method.

The present invention is characterized in that the spheroidizing annealing method is a carbon steel product having excellent properties with a desired physical property specification, in particular, a surface hardness HR 88 to 92, which is not complicated in heat treatment change conditions, In the present invention.

1 is a schematic view of a carbon-carbon slowing process for carbon steel according to the conventional spheroidizing annealing process.
FIG. 2A is a schematic view of a vacuum degassing process according to a conventional spheroidizing annealing process, and FIG. 2B is a schematic diagram of a tempering process during a conventional spheroidizing annealing process.
Fig. 3 is a schematic view of the carbon-carbon slowing process of carbon steel according to the spheroidizing annealing treatment of the present invention.
FIG. 4A is a schematic view of a vacuum degassing process according to the present invention, and FIG. 4B is a schematic view of a tempering process during the spheroidizing annealing process of the present invention.
5 is a photograph showing a vacuum annealing furnace.
6A to 6C are photographs of each of the blades of Preparation Examples 1 to 3, respectively.
7A to 7C each show a photograph of the blades of Preparation Example 1 to Preparation Example 3 after grinder polishing is carried out to check the surface components of the blade.
8A to 8C are SEM photographs of the surface of each of the blinders of Examples 1 to 3 as photos showing the decarburization carried out in Experimental Example 1. FIG.

Hereinafter, the present invention will be described in detail.

The present invention relates to a method of heat-treating a carbon steel by spheroidizing annealing, comprising the steps of: 1) subjecting a carbon steel subjected to a cubic annealing process to a first heat treatment and then quenching it under a nitrogen gas; A second step of subjecting the quenched carbon steel to a second heat treatment; A third heat treatment after the second heat treatment, a third heat treatment, followed by cooling to 380 to 420 ° C, followed by quenching with nitrogen gas; A fourth step of tempering the third annealed carbon steel; And a fifth step of cooling the tempered carbon steel product to 280 to 320 DEG C and then quenching it with nitrogen gas. BACKGROUND OF THE INVENTION

In the first step, carbon steel subjected to the cubic carbon annealing process is subjected to the first heat treatment. In the conventional method, the carbon-carbon annealing process is heat-treated at about 880 캜 for about 4 hours as shown in Fig. 1, After cooled, it was evacuated and subjected to a cobalt annealing treatment.

However, in the present invention, as shown in an example of FIG. 3, after annealing at 850 to 900 ° C for 5 to 6 hours, cooling slowly to 410 to 450 ° C, followed by quenching to carbon steel annealing Respectively. In other words, during the annealing process of the carbon steel, the carbon steel was removed at a temperature lower than the conventional temperature by 150 to 190 ° C to change the treatment process. At this time, manganese content in the surface of the carbon steel may increase if the carbon steel off-gas temperature exceeds 450 ° C, and it may become carbon steel that does not meet the vacuum sintering treatment condition of the later process of the present invention. The cooling temperature is preferably slow cooling to 410 to 450 ° C for about 24 hours, preferably 18 to 22 ° C / hr, more preferably 19 to 20 ° C / hr, When the cooling rate is out of the above range, the content of carbon or the like in the surface of the carbon steel may be too low or high, and the cooling may be performed slowly at the cooling rate.

The carbon steel before the carbonitriding treatment contains 0.8000 to 0.9000 wt% of carbon (C), 0.2000 to 0.5000 wt% of silicon (Si), 0.5500 to 0.7500 wt% of manganese (Mn), 0.0080 to 0.010 wt% of phosphorus (P) 0.001 to 0.070 wt% of chromium (Cr), 0.0020 wt% or less of molybdenum (Mo), 0.0150 wt% or less of nickel (Ni), 0.0100 wt% or less of copper (Cu) , 0.0010 wt% or less of tin (Sn), 0.5000 to 3.0000 wt% of aluminum (Al), 0.0020 wt% or less of cobalt (Co), and 0.0010 to 0.0040 wt% of titanium.

The surface of the carbon steel product preferably has a surface of 0.90 to 1.04% by weight of carbon (C), 0.020 to 0.100% by weight of silicon (Si) Preferably from 0.920 to 1.010% by weight of carbon, from 0.200 to 0.800% by weight of silicon, from 0.400 to 0.700% by weight of manganese (Mn), from 0.030 to 0.050% by weight of phosphorus (P) Carbon steel containing 0.500 to 0.600 wt% of manganese, 0.040 to 0.045 wt% of phosphorus and 0.010 to 0.050 wt% of sulfur.

The first heat treatment, the second heat treatment and the third heat treatment in the first to third steps are performed in the vacuum sintering process shown in FIG. 4A and the spheroidizing annealing process in the vacuum sintering annealing furnace in FIG.

In the present invention, the first heat treatment in the first step is performed at a temperature of 850 to 900 ° C for 2.5 to 3.5 hours, preferably at a temperature of 860 to 890 ° C for 2.5 to 3.5 hours, more preferably, If the first heat treatment temperature is less than 850 ° C, the formation of spheroidized structure of carbon steel may be unstable, and even if the first heat treatment temperature exceeds 900 ° C, there is no improvement in physical properties. , It is preferable to perform the first heat treatment within the temperature range because it is uneconomical. And, the first heat treatment time is an appropriate time relatively determined to perform at the temperature.

The second heat treatment in the second step is carried out at 710 to 750 ° C for 7.5 to 8.5 hours, preferably at 715 to 745 ° C for 7.5 to 8.5 hours, more preferably at 725 to 740 ° C If the second heat treatment temperature is less than 710 DEG C, the formation of spheroidized structure of the carbon steel may be unstable, and even if the second heat treatment temperature exceeds 750 DEG C, there is no improvement in physical properties, It is preferable to perform the second heat treatment within the temperature range. And, the second heat treatment time is an appropriate time relatively determined to perform at the temperature.

It is preferable that the third heat treatment in the third step is performed at 630 to 660 ° C for 7.5 to 8.5 hours, preferably at 635 to 655 ° C for 7.5 to 8.5 hours, more preferably at 645 to 655 ° C If the third heat treatment temperature is less than 630 DEG C, the formation of spheroidized structure of carbon steel may be unstable. If the third heat treatment temperature exceeds 660 DEG C, there is no improvement in physical properties, It is preferable to perform the third heat treatment within the above-mentioned temperature range. And, the third heat treatment time is an appropriate time relatively determined to perform at the temperature.

After the third heat treatment, the substrate is quenched to 380 to 420 ° C, preferably 390 to 410 ° C, and quenched to about room temperature (15 to 35 ° C) with nitrogen gas. The furnace is slowly cooled to a temperature of 380 to 420 ° C at a cooling rate of 40 to 50 ° C / hr, preferably at a cooling rate of 42 to 47 ° C / hr, more preferably at a cooling rate of 44 to 45 ° C / After cooling, quenching is carried out. At this time, if the cooling rate is less than 42 ° C / hr, the cooling rate is too slow, and the whole process time of spheroidizing annealing becomes too long. If the cooling rate exceeds 50 ° C / hr, the cooling rate becomes too fast, It is advisable to carry out the furnace cooling at the cooling rate.

The 4-step tempering is a step of stabilizing the structure of the carbon steel by suitably lowering the hardness of the carbon steel. As shown in FIG. 4B, it is preferably performed by heat treatment at 680 to 720 ° C for 4.5 to 5.5 hours, preferably 690 To < RTI ID = 0.0 > 710 C < / RTI > for 4.5 to 5.5 hours. At this time, if the tempering heat treatment temperature is less than 680 ° C, the carbon steel may not have sufficient structural stability and the hardness may be too high. If the tempering temperature exceeds 720 ° C, the hardness of the carbon steel may be too low. It is appropriate.

After tempering in step 5, furnace cooling is performed from 280 to 320 ° C, preferably from 290 to 310 ° C. It is desirable to carry out the furnace cooling to the above temperature from the standpoint of maintaining the stable structure of carbon steel through appropriate tempering and economical efficiency Do. At this time, the furnace cooling is preferably carried out at a cooling rate of 70 to 85 ° C / hr, preferably at a cooling rate of 75 to 82 ° C / hr, more preferably 78 to 80 ° C / If the speed is less than 70 ° C / hr, the cooling rate is too slow, resulting in an excessively long process time, resulting in poor economical efficiency. If the cooling rate exceeds 85 ° C / hr, It is preferable to cool the furnace to about 280 to 320 ° C at the cooling rate.

Carbon steel products subjected to vacuum spheroidization annealing and tempering through the first, second and third heat treatments in steps 1 to 5 have high carbon steels which have undergone a double carbon reduction process. That is, the surface of the carbon steel up to Step 5 is composed of 0.600 to 0.750 wt% of carbon (C), 0.500 to 1.500 wt% of silicon (Si), 0.650 to 0.850 wt% of manganese (Mn), 0.010 to 0.150 wt % And sulfur (S) 0.010 to 0.200% by weight, that is, high carbon steel.

As described above, when the rockwell hardness of the carbon steel product subjected to spheroidization annealing according to the present invention is measured, it has a surface hardness of about HRB 88-92, preferably HRB 88-90. The carbon steel product of the present invention has various uses as various carbon steel parts and carbon steel products, and is particularly suitable for use as a blade carbon steel product. Specifically, for example, a blade for shearing clippers having excellent hardness can be produced with high economic efficiency.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited by the following examples.

[Example]

Preparation examples 1 to 3

A blade as shown in Fig. 6 was prepared, and A of Fig. 6 was defined as Preparation Example 1. Fig. Further, each of the blades B to C of Fig. 6 is defined as Preparation Example 2 and Preparation Example 3, respectively.

Each of the blades of Preparative Examples 1 to 3 was measured for Rockwell hardness, and the surface hardness thereof is shown in Table 1 below.

division Rockwell hardness Preparation Example 1 HRB 48.53 Preparation Example 2 HRB 44.44 Preparation Example 3 HRB 66.61

The components of each of the blades of Preparation Examples 1 to 3 were measured and are shown in Table 2 below.

Category (% by weight) Preparation Example 1 Preparation Example 2 Preparation Example 3 Carbon (C) 0.83860 0.84372 0.87813 Silicon (Si) 0.48385 0.24283 0.20448 Manganese (Mn) 0.71944 0.64955 0.59405 In (P) 0.00825 0.00915 0.00961 Sulfur (S) 0.01607 0.01105 0.01508 Chromium (Cr) 0.03082 0.00618 0.01720 Molybdenum (Mo) 0.00155 0 0 Nickel (Ni) 0.01371 0.00130 0.00536 Copper (Cu) 0.02526 0.01501 0.02385 Tin (Sn) 0.00094 0 0.00037 Vanadium (V) 0 0 0 Aluminum (Al) 0.62975 2.9546 1.8933 Cobalt (Co) 0.00191 0.00014 0.00119 Titanium (Ti) 0.00374 0.00166 0.00158 Tungsten (W) 0 0 0

Example 1

(1) Better carbon deceleration process

The blades of Preparation Example 1 were heat-treated at 880 캜 for 5.5 hours, then slowly cooled to 430 캜 for 23 hours and 30 minutes, and then the blades were poured out and then quenched in the air.

A grinder polishing was carried out as shown in Fig. 7A to examine the surface components of the blades subjected to the carbon nano-blooming process, and the surface components thereof are shown in Table 3 below.

(2) Vacuum spheroidization annealing process

The blades subjected to the carbon reduction annealing step were put in a vacuum forming furnace shown in Fig. 5, followed by a first heat treatment at 880 캜 for 3 hours, followed by quenching under a nitrogen gas.

Subsequently, the resultant was subjected to a second heat treatment at 730 ° C for 8 hours, followed by a third heat treatment at 650 ° C for 8 hours, followed by cooling to 400 ° C slowly for 5 hours and 30 minutes, followed by cooling with nitrogen .

(3) Tempering process

Next, the third heat-treated and nitrogen-cooled blades were heat-treated at 700 ° C for 5 hours, cooled slowly to 300 ° C for 8 hours, and then cooled with nitrogen to prepare a blade product for final shearing.

Table 4 shows the surface components of the manufactured blade products.

Examples 2 to 3

The same procedure as in Example 1 was followed to perform a spheroidizing annealing heat treatment (a carbon burning step, a vacuum spheroidizing annealing step and a tempering step), but the blades of Preparation Example 2 and Preparation Example 3 were used instead of the blades of Preparation Example 1, 2 and 3, respectively.

Comparative Example 1

In the same manner as in Example 1, the blades of Preparation Example 1 were subjected to spheroidizing annealing heat treatment through the same steps as in Figs. 1, 2A and 2B. In the double-carbon slowing process, the blades of Preparation Example 1 were heat-treated at 880 캜 for 5.5 hours, the blades were removed at 600 캜, and then quenched in the air.

Category (% by weight) Example 1 Example 2 Example 3 Comparative Example 1 Carbon (C) 1,000 0.925 1,000 0.912 Silicon (Si) 0.499 0.625 0.523 3.949 Manganese (Mn) 0.506 0.582 0.506 0.798 In (P) 0.047 0.042 0.040 0.051 Sulfur (S) 0.014 0.029 0.048 0.224 * Content specification (spec.)
Carbon 0.90 to 1.04 weight% / silicon 0.200 to 0.100 weight% / manganese 0.400 to 0.700 weight% / phosphorus 0.030 to 0.050 weight% / sulfur 0.010 to 0.100 weight%

Category (% by weight) Example 1 Example 2 Example 3 Comparative Example 1 Carbon (C) 0.603 0.616 0.656 0.623 Silicon (Si) 0.652 0.630 0.608 1.712 Manganese (Mn) 0.754 0.724 0.768 0.902 In (P) 0.083 0.077 0.088 0.165 Sulfur (S) 0.016 0.013 0.180 0.022 * Content specification (spec.)
Carbon 0.600 ~ 0.750 wt% / silicon 0.500 ~ 1.500 wt% / manganese 0.650 ~ 0.850 wt% / phosphorus 0.010 ~ 0.150 wt% / sulfur 0.010 ~ 0.200 wt%

As shown in Table 3 and Table 4, changes in component in the blades can be confirmed by performing the vacuum sophisticated annealing and tempering processes, and it was confirmed that the blend satisfies the component specifications of the blade to be manufactured in the final product. However, in the case of Comparative Example 1 in which the carbon nano-particles were sintered under the other conditions suggested by the present invention, the other components satisfied the specifications, but the content of silicon, manganese and phosphorus exceeded the specification range.

Experimental Example 1

Each of the blades produced by performing the spheroidizing annealing treatment in Examples 1 to 3 was cut and the surface of the blades was measured by SEM (Scanning Electron Microscope) to determine whether decarburization occurred on the surface. The measurement photographs thereof were shown in A to C Respectively. 8, it was confirmed that decarburization did not occur.

Comparative Example 2

In the same manner as in Example 1, the same double carbon-sintering step was carried out using the blades of Preparation Example 1. In addition, the vacuum sphere annealing process and the tempering process were performed in the same manner, but the first heat treatment was performed at 800 ° C. for 3 hours instead of 880 ° C. in the vacuum sphere annealing process.

Comparative Example 3

In the same manner as in Example 1, the same double carbon-sintering step was carried out using the blades of Preparation Example 1. In addition, the vacuum sphere annealing process and the tempering process were performed in the same manner, but the second heat treatment was performed at 680 캜 for 8 hours instead of 730 캜 in the vacuum sphere annealing process.

Comparative Example 4

In the same manner as in Example 1, the same double carbon-sintering step was carried out using the blades of Preparation Example 1. Also, the vacuum sphere annealing process and the tempering process were performed in the same manner, but the third annealing process was performed at 600 캜 for 8 hours instead of 650 캜 in the vacuum sphere annealing process.

Comparative Example 5

In the same manner as in Example 1, the same double carbon-sintering step was carried out using the blades of Preparation Example 1. After the third heat treatment in the vacuum sphere-annealing step, the substrate was rapidly cooled at a cooling rate of 60 / / hr in a furnace cooling to 400 캜 in the vacuum sphere annealing process and the tempering process in the same manner.

Experimental Example 2

The surface hardness of each of the blades prepared in Examples and Comparative Examples was measured for Rockwell hardness, and the results are shown in Table 5 below. The measured values in Table 5 are measured at five arbitrary points of each blade, and the average values thereof are shown.

division Example 1 Example 2 Example 3 Comparative Example 1 Measures HRB 89.2 HRB 89.8 HRB 89.5 HRB 94.8 division Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Measures HRB 89.2 HRB 89.8 HRB 87.6 HRB 92.4 * Surface hardness spec: HRB 88 ~ 92

As a result of the hardness measurement in Table 5, it was confirmed that the hardness values of Examples 1 to 3 have a desired surface hardness specification of HRB 89 to 90 or so. However, in the case of Comparative Example 1, it was confirmed that the surface hardness exceeded HRB 92. And,

Comparative Example 2 performed at 800 占 폚 where the first heat treatment temperature was lower than 850 占 폚, Comparative Example 2 where the second heat treatment temperature was 710? Comparative Example 3 performed at 680? And the third heat treatment temperature of 630? In Comparative Example 4, the hardness was lower than HRB 88, which is considered to be the result that the internal structure of the blade was relatively unstably formed as compared with Example 1. As a result, the first heat treatment to the third heat treatment It was confirmed that it is possible to produce a carbon steel product having a desired surface hardness specification (HRB 88 to 92) in which the heat treatment temperature is to be performed within the range suggested by the present invention. After the third heat treatment, in Comparative Example 5 in which the furnace was cooled at a rate of 60? / Hr or more of 50? / Hr, the hardness exceeded HRB 92, which is considered to be rather higher as a result of cooling too fast .

Through the foregoing Examples and Experimental Examples, it was confirmed that a carbon steel product having excellent hardness, that is, a blade product can be provided through the spheroidizing annealing process. Further, the vacuum annealing process time is reduced through the annealing process simplified as compared with the conventional vacuum annealing process shown in FIGS. 2A and 2B, and the annealing annealing process having a high economical efficiency as a whole by reducing the time for performing the annealing process. Carbon steel products.

Claims (13)

A first step of performing a first heat treatment in which carbon steel having undergone the cubic carbon annealing treatment is heat-treated at 850 to 900 ° C for 2.5 to 3.5 hours and then quenched under a nitrogen gas;
A second step of subjecting the quenched carbon steel to a second heat treatment at 710 to 750 ° C for 7.5 to 8.5 hours;
A third heat treatment after performing the second heat treatment, a heat treatment at 630 to 660 ° C for 7.5 to 8.5 hours, followed by cooling to 380 to 420 ° C, followed by quenching with nitrogen gas, and a third heat treatment; And
4) performing the tempering of the third heat treated carbon steel at 680 to 720 캜 for 4.5 to 5.5 hours; And
Cooling the tempered carbon steel to 280 to 320 DEG C, and quenching it with nitrogen gas;
Wherein the annealing is performed at a temperature higher than the melting point of the carbon steel. The method of claim 1, wherein the furnace annealing in three stages is performed at a cooling rate of 40 to 50 ° C / hr. The method according to claim 1, wherein the furnace cooling in step 5 is performed at a cooling rate of 75 to 82 ° C / hr. The method of manufacturing a carbon steel according to claim 1,
Annealing at 850 to 900 캜 for 5 to 6 hours and then cooling to 410 to 450 캜 and then quench and quench the carbon steel. The method for annealing a spheroidizing annealing of carbon steel according to claim 4, wherein the cooling in the step of annealing the carbon nanotubes is performed at a temperature of 19 to 20 캜 / hr. The method according to claim 1, wherein the carbon steel subjected to the one-step carbon annealing step is a minimum strength steel, and the carbon steel product after the fifth step is high carbon steel. 2. The method of claim 1, wherein the surface of the carbon steel that has undergone the carbon annealing process comprises 0.90 to 1.04 wt% of carbon (C), 0.450 to 4.000 wt% of silicon (Si), 0.400 to 0.700 wt% of manganese P) 0.040 to 0.050 wt%, and sulfur (S) 0.010 to 0.250 wt%. The method of claim 1, wherein the surface of the carbon steel up to step 5 is 0.600 to 0.750 wt% carbon, 0.500 wt% to 1.500 wt% silicon, 0.650 wt% to 0.850 wt% manganese, 0.010 to 0.150 wt.% Of sulfur (S) and 0.010 to 0.200 wt.% Of sulfur (S). The method for annealing annealed spheroidal carbon steel according to claim 1, wherein the carbon steel after the quenching and quenching in step 5 is a blade carbon steel product. The method according to claim 9, wherein the blade carbon steel product has an HRB of 88 to 92 in Rockwell hardness measurement. A blade carbon steel product having undergone spheroidizing annealing by the method of claim 9. 12. The blade carbon steel product according to claim 11, wherein the blade carbon steel product is a shear blade. The blade carbon steel product according to claim 11, wherein the hardness of the Rockwell hardness is HRB 88-92.

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