TWI362424B - Carbon steel sheet hiving high carburizing quenching property and manufacturing method thereof - Google Patents

Description

[Technical Field] The present invention relates to a carbon steel sheet excellent in carburizing and quenching property and a method for producing the same. The present application is filed in Japan on March 27, 2009. The special request of 2009-079959 is based on the priority, and its content is used for this.

BACKGROUND OF THE INVENTION In the past, automobile parts and industrial machine parts such as chain parts, gear parts, and clutch parts have been hardened by heat treatment such as quenching after forming.

However, in recent years, not only the shape of the parts has been complicated, but also the wear resistance and fatigue characteristics of the parts themselves have been required. Therefore, it is required that the column material not only has the workability to withstand complicated processing when processing the parts, but also satisfies the hardenability for surface hardening. The hardenability and processability of the billet are opposite characteristics from the viewpoint of material design. The softening of the general description is effective for the improvement of the processing, but the elements added to improve the hardenability increase the hardness of the steel core, and most of the workability is sacrificed. On the other hand, if the hardenability of the part after processing is poor, it will lead to an abnormal layer in the structure of the so-called wave iron, rough iron or spit iron. In order to manufacture a steel sheet having excellent workability and hardenability at low cost, it is effective to contain B in the steel sheet. However, because of the reactivity of B, | 3 1362424 changes in oxidation, deboronation, nitriding, etc. on the surface of the steel sheet, and it is difficult to ensure the hardenability of the surface portion. Further, in the B-added steel sheet, when carburizing with a carbon potential (Cp) which is generally used is about 0.8, the hardenability is increased by the carburization C, and the quenching abnormal layer is hard to be formed in the surface layer portion after quenching. So there is no big problem. However, since the weakly carburized region (e.g., CpS0.6) B having a low carbon potential deteriorates the hardenability due to the above reaction, the further hardenability due to C cannot be ensured, and thus the use is not extensive. The carbon potential referred to herein is a numerical value indicating the carburizing ability of the gas environment when the steel is carburized. The carbon potential is equivalent to the carbon concentration on the steel surface when the gas environment at the carburizing temperature is balanced. Therefore, B-added steel sheets are required to establish a series of materials from blanks to parts processing, such as manufacturing conditions that can fully exhibit the effect of adding B, workability for strict processing such as tooth formation, and surface hardening treatment such as carburization. Jiahua. Regarding the manufacturing conditions of the steel sheet containing B, although it is disclosed in Patent Document 1 that annealing is performed in a hydrogen atmosphere or an Ar gas atmosphere in which the nitrogen content is suppressed to 1 vol% or less, no relevant process is described. step. Further, there has not been revealed a technique which has considered the carburization treatment under low carbon potential (as an object in the present invention). [Prior Art Document] [Patent Document 1] Japanese Laid-Open Patent Publication No. Hei No. 5-331534. SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION In order to solve the aforementioned problems, the present invention solves the aforementioned problems to harden the nucleus even under carburization conditions with low carbon potential. It is also a problem that the provision of the 8 added steel sheets and the optimization of the manufacturing method thereof are provided. Means for Solving the Problems In order to solve the above problems, the present invention employs the following means. (1) A first aspect of the present invention is a carbon steel sheet comprising the following

Points: C: 0_20 quality. /〇 or more, 〇45 mass% or less; 〇〇: 〇〇5 mass% or more, 0_8 mass% or less; Mn: 〇85 mass% or more, 2 mass% or less; P: 0.001 mass% or more, 〇〇4 mass% Hereinafter, s : 〇〇〇〇 1% by mass or more, 0.006 mass% or less; 丨 丨: 〇〇 1% by mass or more, 〇 1% by mass or less; Τι : 0.005 mass % or more, 〇 3 mass % or less; b : 〇 _ 〇 005 mass% or more, 0.01 mass. /. In the following, and Ν: 〇〇〇1% by mass or more, 〇〇1% by mass or less; the remaining part is Fe and unavoidable impurities, and the κ value obtained by 3C+Mn+0.5Si is 2. 〇 or more; surface hardness Rockwell at b scale

The hardness is 77 or less; the average content of N in the region from the surface layer to the depth of 1 〇〇 μm is 1 〇〇 PPm at 7. The carbon steel sheet is carburized in a carburizing gas atmosphere having a carbon potential of 0.6 or less. (2) The carbon steel sheet of the above (I) 5 may further contain one or more of the following types of knives. Nb · 〇. 〇 1% by mass or more, 〇 5 mass. Hereinafter, v 0.01 Berry% or more, 0.5% by mass or less; Ding & 〇 〇 〇 质量 mass% or more, 〇% or less ’ W. Any mass% or more, 〇 5 mass% or less; 〇丨% or more 0.0 0.03 mass% or less; 讥: 〇 〇〇 3 mass% or more.质 The quality is less than the following % and As: 〇 〇〇 3 mass% or more, 〇 〇 3 mass. ,. In the second aspect of the invention, the method for producing a carbon steel sheet according to the above (1) or (2), comprising: heating step of heating the steel slab at 1200 t or less; at 8 〇〇 ° C or higher And 94 (the hot rolling step of hot rolling the steel slab at a finishing temperature of TC or lower to obtain a steel sheet; and the first cooling step of cooling the steel sheet and the steel sheet to 650 ° C or lower at a cooling rate of 20 ° or more; Then, in the first cooling step, the second cooling step of cooling the steel sheet is performed at a cooling rate of 2 ° C/sec or less; the winding step of winding the steel sheet at 650 ° C or lower and 400 ° C or higher; pickling the aforementioned a pickling step of the steel sheet; and a dew point of -20 ° C or less at a hydrogen content of 95% or more to 4 ° C, and a dew point of 440 ° C or less in a gas atmosphere of _40 ° C or less at 660 ° The first annealing step of annealing the steel sheet at a temperature of C or higher for 10 hours or more. (4) In the method for producing a carbon steel sheet according to the above (3), the first annealing step may be such that the gas atmosphere is 95% or more of hydrogen. Annealing at an annealing temperature in the range of Acl ~ Acl + 5 ° ° C 'and annealing (5) The method for producing a carbon steel sheet according to the above (4), which may further include: after the pickling step, 5 In the method for producing a carbon steel sheet according to the above (5), the method of manufacturing the carbon steel sheet according to the above (5) may further include the first annealing step. Thereafter, the second cold rolling step of cold rolling the steel sheet at a rolling ratio of 60% or less; and after the second cold rolling step, the dew point of hydrogen at 95% or more to 400 ° C is _2〇C Hereinafter, the dew point of 400 C or more is in a gas atmosphere of -40 ° C or lower, and the second annealing step of the steel sheet is annealed at a temperature of 660 ° C or higher. 6 1362424 (7) The carbon steel sheet described in the above (6) In the manufacturing method, the second annealing step may be performed such that the gas atmosphere is 95% or more of hydrogen and the annealing temperature is in the range of Acl to Acl + 50 ° C, and after annealing to 8.5 c. The cooling rate is set to 5 ° C / hr or less. (8) In the method for producing a carbon steel sheet according to the above (7), The third cold rolling step of cold rolling the steel sheet at a rolling ratio of 5% or more and 60% or less after the second annealing step; and 95% or more of hydrogen after the third cold rolling step And in the gas environment where the dew point of the soil is below _2 〇 ° C and the dew point above 400 ° C is below -40 ° C, the steel sheet is annealed at a temperature of 660 ° C or higher. (9) In the method for producing a carbon steel sheet according to the above (8), the third annealing step may be such that the gas atmosphere is 953⁄4 or more and the annealing temperature is in the range of Acl to Acl + 50 〇C. Annealing was performed, and the cooling rate up to AcUOC after annealing was set to 5. 〇 / hour or less. (10) The method for producing a carbon steel sheet according to the above (6), further comprising: after the second annealing step, cold rolling the third steel sheet at a rolling ratio of 5% β and 60% or less a rolling step; and after the third cold rolling step, the dew point of the earth is 95% or more and 4 〇〇 °c, and the dew point of the soil is _2〇C or less, and the dew point of 4〇0°C or more is -4〇t In the following gas environment, the third annealing step of annealing the steel sheet at a temperature of 660 or higher. (11) In the method for producing a carbon steel sheet according to the above (10), the third annealing step may be performed by annealing the gas atmosphere to a hydrogen content of 95% or more and at an annealing temperature of from Ad to Acl + 5 〇 °C. The cooling rate up to the end after annealing was set to 5 ° C / hour or less. In the method for producing a carbon steel sheet according to the above (4), the second steel sheet may be further subjected to cold rolling of the steel sheet at a rolling ratio of 5% or more and 60% or less after the first annealing step. a cold rolling step; and after the second cold rolling step, the dew point of hydrogen at 95% or more to 400 ° C is -20 ° C or lower, and the dew point of 4 〇〇 t or more is -40 ° C or lower. In the gas atmosphere, the steel sheet is subjected to a second annealing step of annealing at a temperature of 66 ° C or higher. (13) In the method for producing a carbon steel sheet according to the above (12), the second annealing step may be performed by annealing the gas atmosphere to a hydrogen content of 95% or more and annealing at a temperature of Acl to Acl + 50t: The cooling rate up to 8-30 ° C after annealing is set to 5 ° C / hour or less. (14) In the method for producing a carbon steel sheet according to the above (13), the method further includes: after the second annealing step, cold rolling the third cold rolling of the steel sheet at a rolling ratio of 5% or more and 60% or less. Step; and 'after the third cold rolling step, the hydrogen is 95% or more and up to 40 (the dew point of TC is -2 〇 ° C or less, 400. (: the above dew point is -4 〇 ° C or less gas) (3) The third annealing step of annealing the steel sheet at a temperature of 660 ° C or higher in the environment. (15) In the method for producing a carbon steel sheet according to the above (14), the third annealing step may also cause the gas atmosphere to be hydrogen. 95% or more and annealing at an annealing temperature in the range of Acl to Acl + 5 CTC, and setting the cooling rate after annealing to 八 (: 1-30 ° 设定 is set to 5 ° C / hr or less. (16) 12) The method for producing a carbon steel sheet according to the present invention, further comprising: a third cold rolling step of cold rolling the steel sheet at a rolling ratio of 5% or more and 60°/〇 or less after the second annealing step; After the third cold rolling step, the dew point of hydrogen 95% or more and 400T: is -2 〇 ° C or less, 8 1362424 The dew point of 400 ° C or higher is -40. (: The third annealing step of annealing the steel sheet at a temperature of 660 ° C or higher in the following gas atmosphere. (17) Production of the carbon steel sheet according to the above (16) In the method, the third annealing step may also make the gas atmosphere be 95% or more of hydrogen and anneal at an annealing temperature in the range of Acl to Acl + 50 ° C, and set the cooling rate after annealing to Acl -30 ° C. (18) The method for producing a carbon steel sheet according to the above (3), further comprising: cold rolling at a rolling ratio of 5% or more and 60% or less after the pickling step (19) The method for producing a carbon steel sheet according to the above (18), further comprising: rolling at 5°/. or more and 60% or less after the first annealing step a second cold rolling step of cold rolling the steel sheet; and after the second cold rolling step, the hydrogen is 95% or more and up to 4 〇〇. The dew point is -20° C. or less, 40 〇r The above dew point is in the gas environment below -4 〇t, and the second steel plate is annealed at a temperature above 660. (20) In the method for producing a carbon steel sheet according to the above (19), the second annealing step may be such that the gas atmosphere is 95% or more of hydrogen and the annealing temperature is in the range of Ac 1 to Acl + 50 ° C. The annealing method is performed, and the cooling rate of the carbon steel sheet according to the above (20) may be further included in the method of manufacturing the carbon steel sheet according to the above (20). After the annealing step, the third cold rolling step of cold rolling the steel sheet at a rolling ratio of 5% or more and 6% or less; and after the third cold rolling step, the hydrogen is 95% or more and up to 4 〇〇. °C is the dew point of the soil below -20 °C, and the dew point above 400 °C is -40. In the following gas atmosphere, the steel sheet is subjected to a third annealing step of annealing at a temperature of 660 ° C or higher and 9 1362424. (22) In the method for producing a carbon steel sheet according to the above (21), the third annealing step may be such that the gas atmosphere reaches 95% or more of hydrogen and the annealing temperature is in the range of Acl to Acl + 50 ° C. The cooling rate after annealing to Acl-30 ° C was set to 5. 〇 / hour or less. (23) The method for producing a carbon steel sheet according to the above (19), further comprising: cold rolling the third cold rolling of the steel sheet at a rolling ratio of 5% or more and 60% or less after the second annealing step And; after the third cold rolling step, the hydrogen is 95% or more and up to 4 Torr. (The dew point is _2 〇 ° C or less, and the dew point of 400 ° C or higher is -40 ° C or less in a gas atmosphere of '66 〇. (: The third annealing step of annealing the steel sheet at the above temperature (24) In the method for producing a carbon steel sheet according to the above (23), the third annealing step may be performed by annealing the gas atmosphere to a hydrogen content of 95% or more and annealing at a temperature of from Acl to Acl + 50 °C. In the method for producing a carbon steel sheet according to the above (3), the cooling rate of the carbon steel sheet according to the above (3) may be further included in the first annealing. After the step, the second cold rolling step of cold rolling the steel sheet at a rolling ratio of 5% or more and 6 〇. / 〇 or less; and 95% or more to 400 ° C after the second cold rolling step The dew point is -20° C. or lower, and the second annealing step of annealing the steel sheet at a temperature of 660° C. or higher in a gas atmosphere having a dew point of −40° C. or higher at 400° C. or higher (26) In the method for producing a carbon steel sheet according to (25), in the second annealing step, the gas atmosphere may have a hydrogen content of 95% or more and an annealing temperature. Annealing is carried out in the range of Acl to Acl + 50 ° C, and the cooling rate after annealing to Acl -30 ° C is 10 1362424 is set to 5 〇 c / hr or less. (27) The carbon described in the above (26) In the method for producing a steel sheet, the third cold rolling step of cold rolling the steel sheet at a rolling ratio of 5% or more and 60°/min or less after the second annealing step may be further included; After the third cold rolling step, the dew point of hydrogen is 95% or more and up to 4 〇〇. The dew point is _2 〇 ° c or less, and the dew point of 400 ° C or more is _4 〇. In the gas environment below 〇, in 66 In the method for producing a carbon steel sheet according to the above (27), the third annealing step may be such that the gas atmosphere is 95% or more of hydrogen. Annealing is performed at an annealing temperature in the range of Ad to Acl + 50 ° C, and the cooling rate until annealing to Acl-3 {TC is set to 5 〇 c / hr or less. (29) The carbon described in the above (25) In the method for producing a steel sheet, the method further includes: after the second annealing step, cold rolling at a rolling ratio of 5% or more and 60% or less The third cold rolling step of the steel sheet; and after the third cold rolling step, the hydrogen is 95% or more and up to 4 〇〇. The dew point is _2 〇 ° C or less, and the dew point is 400 ° C or more. The third annealing step of annealing the steel sheet at a temperature of 660 ° C or higher in a gas atmosphere of -40 ° C or lower. (30) The third annealing in the method for producing a carbon steel sheet according to the above (29) The step may also be such that the gas atmosphere is more than 95% hydrogen and the annealing temperature is in the range of Ac 1 ～Acl+50° C., and the cooling rate after annealing to Acl -30° C. is set at 5° C./ Less than an hour. (31) A third aspect of the invention is a carbon steel sheet comprising the following components: C: 0.20 mass 〇 / ❶ or more, 〇 45 mass % or less; Si: 〇 · 〇 5 mass % or more '0.8 mass. /〇 below; Μη : 0.85 mass% or more '2.0 mass. /〇11 1162424

Lower; P: 0.001% by mass or more, 0. 04 mass. /〇:; S: 0.0001% by mass or more, 0.006 mass% or less; A1: 0.01% by mass or more, 0.1% by mass or less; Ti: 0.005% by mass or more, 0.3% by mass or less; B: 0.0005% by mass or more, 0.01% by mass And N: 0.001% by mass or more and 0.01% by mass or less; and further containing one or more of the following components: Cr: 0.01% by mass or more, 2.0% by mass or less; Ni: 0.01% by mass or more, 1.0 5% by mass or less; Cu: 0.005 mass% or more, 0.5 mass% or less; and Mo: 0.01 mass% or more and 1.0 mass% or less; the balance of Fe and unavoidable impurities; 3C+Mn+0.5Si+Cr+ The K' value obtained by Ni+Mo+Cu is 2.0 or more; the surface hardness is 77 or less in the B-scale Rockwell hardness; and the average content of N is less than 100 ppm in the region from the surface depth ΙΟΟμιη. The carbon steel sheet is carburized in a carburizing gas atmosphere having a carbon potential of 0.6 or less.

(32) The carbon steel according to the above (31) may further contain one or more of the following components: Nb: 0.01% by mass or more, 0.5% by mass or less; and V: 0.01% by mass or more and 0.5% by mass or less; Ta: 0_01% by mass or more, 0.5% by mass or less; W: 0.01% by mass or more, 0.5% by mass or less; Sn: 0.003% by mass or more, 0.03% by mass or less; Sb: 0.003% by mass or more, 0.03% by mass or less; As: 0.0003 mass% or more and 0.03 mass% or less. (33) A method for producing a carbon steel sheet according to the above (31) or (32), comprising: a heating step of heating the steel slab at 1200 ° C or lower; and a finishing temperature of 800 ° C or higher and 940 ° C or lower; a hot rolling step of rolling the steel slab to obtain a steel sheet; a first cooling step of cooling the steel sheet to a temperature of 650 ° C or lower at a cooling rate of 20 ° C /sec or more; and then the first cooling step at 20 ° C a second cooling step of cooling the steel sheet at a cooling rate of sec or less; a winding step of winding the steel sheet at a temperature of 400 C or more at 12; a pickling step of pickling the steel sheet; and a hydrogen removal of 95% or more

The wire is below Russia, and the dew point above is the first annealing step of annealing (7) hours or more at a temperature of 66 GC or higher. Advantageous Effects of Invention In the structures of the above (1) and (31), the value of κ or κ is specified.

2, 〇 , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , According to the structures described in the above (2) and (32), the effect of improving the virginity and the bouncing property of the precipitate and the effect of suppressing the compositional fluctuation of the surface layer portion of the steel sheet can be obtained. By the method of the above (3) and (33), it is possible to stably produce a carbon steel sheet excellent in workability and carburization property after processing.

According to the method described in the above (4) to (30), the workability and softening of the carbon steel sheet can be further improved. As described above, according to the present invention, it is possible to produce an excellent carburizing and quenching property which not only prevents the occurrence of an abnormal layer which is caused by the poor hardenability of the B-added steel during carburization, but also has excellent workability for parts and the like. . BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram showing the relationship between the value of K or κ generated by an abnormal layer during carburizing and quenching, and the average amount of N in the surface layer. [Fig. 2] Schematic diagram of the crack in the tooth profile and the hardness of the blank during the tooth profile processing 13 1362424. [30th] A flow chart for explaining the manufacturing method. [Embodiment] In order to carry out the invention, in July, the composition of the B-added steel sheet and the manufacturing conditions in the manufacturing step were changed, and the surface layer hardness change and the structure investigation during the quenching of the material were determined. The relationship between the structure of the surface layer of the quenched material and the forming of the knife. As a result, it is known that in the surface layer, a structure which is not softened by the granulated iron, such as a ferritic iron, a rough smear, or a smear iron, which is not a granulated iron, is particularly likely to be formed from the surface to a pole of about 100 μm. Surface layer. Fig. 1 shows the generation of an anomalous layer of a material in which the carbon potential of 〇.22% C system is subjected to carburizing and quenching in 〇.3. It was judged that the abnormal layer was a nitrogen (N) content (surface average) from the surface of the steel sheet to the thickness of the steel sheet, and the K value (or K value) obtained by the steel sheet component was significantly related. Here, the average amount of surface layer N is a value obtained by analyzing the surface portion of the steel sheet before carburizing and quenching from the surface in the thickness direction by 平μηι' to analyze the content of nitrogen (Ν) in the chips of the steel sheet collected. In order to find the influence of the steel sheet component, 'the Κ value expressed by the formula (1) and the Κ' value expressed by the formula (2) are introduced. Κ value = 3C + Mn + 0.5Si . . . (1) However, C, Μη, Si represent the content (% by mass) of each element. K' value = 3C + Mn + 〇. 5Si + Cr + Ni + Mo + Cu . . . (2) However, 'C, Μη, Si, Cr 'Ni ' Mo, Cu represents the content (% by mass) of each element. Furthermore, it is treated as zero when the above components are not contained. 14 1362424 As seen in Figure 1, if the K value (including Cr, Ni, Mo, Cu, Κ' value) is above 2.0, and the average surface enthalpy is below 100 ppm, no abnormal layer will be seen and the seepage will be judged. Excellent in carbon hardenability. The reason for obtaining a good range as described above is considered to be that the higher the average N amount of the surface layer, the higher the precipitation amount of nitrogen (ν) in the form of nitride in the production step, and the growth of the Worstian iron crystal grains during carburizing and quenching is delayed. And the hardenability deteriorates. Especially think that @N caused

B is nitrided to form BN', so B in the steel disappears, and the hardenability of the steel sheet is hindered. In addition, from the viewpoint of the hardenability of the steel sheet, it is necessary to have a certain amount of alloying elements in the steel sheet, and the amount of the alloying elements is adjusted by the K value (K' value) shown here, and the hardenability is clearly understood. The higher the value, the higher the hardness, the more favorable the quenching property is. However, if the hardness is too high, the hardness of the steel sheet is increased, and the processing is deteriorated. The quenching or the like may occur during quenching depending on the shape of the part. The upper limit of the K value (K for Cr, Ni, Mo, and Cu) is not 2

It is limited to ‘only if it’s more than 3, it’s too high, and it’s also possible to consider the possibility of defects such as smashing and cracking. From the viewpoint of workability, in the present invention, the surface of the steel sheet is hard and the Rockwell hardness (deletion) is 77 or less. In this case, the steel parts are used for the parts of the wheel of the special-purpose steel parts. Therefore, it is necessary to have a processing image which can withstand it: Tooth In the present invention, the processing of the simulated tooth profile processing is carried out. Evaluation, to investigate the shear deformation at the root of the tooth shape, = sex = raw; steel is the use of G.22% C system of the composition of the steel two changes & cracked toothed ▼ annealing conditions to make the thickness of 3_ The shape of the steel sheet as the test material 15 1362424 is a rack-like change using a modulus of 1.5 mm as defined in JIS-B1703, and a steel sheet having a thickness of 3 mm is subjected to 2 mm pressing to evaluate the presence or absence of cracks in the tooth-forming portion. . The results are shown in Fig. 2. For the strict processing like the formation of the teeth, the occurrence of the crack indicates a good correspondence with the surface hardness, and it is effective to judge that the softness of the desired surface hardness is HRB77 or less as a material for forming the tooth. On the other hand, in the present invention, the lower limit of the κ value (K, value) is defined from the viewpoint of ensuring the hardenability as described above. The higher the K, the harder it is. Although it is advantageous for the hardness at the time of quenching, problems such as cracks occur during processing due to poor workability. Therefore, it is necessary to carry out the production method specified in the present invention while controlling the gas atmosphere at the time of softening and annealing the steel sheet. Hereinafter, the steel sheet component and the manufacturing conditions will be described. c : is the basic element necessary to obtain the strength of the steel sheet. At a carbon content of less than 0.20%, the strength required for the product cannot be obtained, and the hardenability of the center portion of the part is also lowered, and the desired characteristics cannot be obtained. However, if a large amount of C is contained in an amount of more than 0.45%, it is difficult to ensure toughness and formability after heat treatment, so the C content is set to 0.20 to 0.45 mass% (hereinafter, the content is expressed by mass% unless otherwise specified) range. A better range is from 0.20 to 0.40%.

Si: It is used as a deoxidizer for steel, and is also effective from the viewpoint of hardenability, and must contain 0.05% or more of Si. However, since the surface properties deteriorate due to the increase in the Si content and the oxidation scale during hot rolling, the upper limit is 0.80% » the better range is 〇〇5 16 Ο.5〇0/ 0 〇Μη: Used as a deoxidizer, it is also known from the viewpoint of hardenability. In the case of the present invention, it is necessary to add 〇·85% or more from the viewpoint of ensuring bonfire under the carburization performed with a low Cp. However, since it is too high, the quenching and the tempering of the tissue change may cause an impact. Special _ inferior two and the reason for the difference, will be the upper limit; ^ in the knowledge. The better range is 〇9〇~1.8〇〇/0 〇

p: In the steel of the present invention, it is harmful from the viewpoint of toughness and workability. The lower the P content, the better, and the upper limit is set to 4%. In addition, although it is desirable that the lower limit is as low as possible, since it is lower than 〇 〇〇 1%, the industrial cost is greatly increased, so the lower limit is set at 〇 〇〇 1%. A better range is from 0.003 to 0.025%.

S: S promotes the formation of non-metallic inclusions in steel and deteriorates the formability and toughness after heat treatment. Therefore, it is desirable that the upper limit of 8 is as low as 0.006%. Although it is desirable that the lower limit is as low as possible, since it is less than 0.0001%, the cost is industrially increased, so the lower limit is specified to be 0.000001%. A better range is from 0.0001 to 0.003%. Α1: As a deoxidizer for steel, it must be used for Α1 of 1% or more. However, even if it is added more than 〇.... /. The gossip will also have a saturated effect and will be prone to surface defects. In addition, Α1 is also effective for fixing Ν, which promotes nitrogen absorption during steel sheet manufacture. However, if the content exceeds 〇10%, the Α1 nitride stabilizes and hinders the grain growth during the carburizing heat treatment, which causes deterioration of the hardenability. Therefore, the content of Α1 is specified in the range of 〇.〇1~〇·ι〇〇/0. The better red circumference is in 〇.〇1~〇 06%. 17 Τι : It is effective for the deoxidizer of steel and the fixation of N. From the relationship with the amount of N, it is necessary to add 〇·嶋 or more. However, even if Ti is added more than 0.30%, the effect is saturated, and the cost is increased. Further, since the amount of precipitates is increased as recorded in the production step, grain growth at the time of carburization is inhibited, which causes deterioration of hardenability. Therefore, the specification of Ti is specified to be 0.01 to 0.30%. The better range is 〇 〇1~〇 1〇%. B: It is an effective element for improving the hardenability of steel, and its effect can be seen from a very small amount. In order to obtain an effect of improving hardenability, it is necessary to add 〇 5% or more. However, if a large amount of B exceeding 0_01% is contained, the workability is deteriorated, and cracks are generated when the product is cast. In addition, the formation of (iv) compounds in steel can cause adverse effects such as (four) reduction. Therefore, the 'B content is specified at 5% to 0.01% after reading. A better range is 0.0005~0 005%. N: combines with B to form a nitride, which deteriorates the hardenability improving effect of B. Therefore, the lower the N content, the better, but lowering to less than 〇〇〇1% will result in an increase in cost. In addition, when the content exceeds 1% of the average composition of steel, it is necessary to fix n elements such as lAl or Τι, and precipitates such as A1N or TiN may inhibit grain growth during carburization and lower the hardenability. Not only does it cause an abnormal layer, but also mechanical properties such as toughness are deteriorated. Therefore, the upper limit of the N content is specified to be 0.01%. A better range is 0.001~〇 〇〇6%. In addition, in the production step, it is easy to know that the steel enters from the hot environment during heating or annealing, so that the concentration in the surface layer is likely to increase. To suppress the influence, it is necessary to prevent deterioration of the surface portion of the part. When the nitrogen intrusion from the gas atmosphere during heating or annealing exceeds 1 〇〇 ppm, the amount of precipitation of nitride at the time of coiling or annealing increases, and the grain growth after the addition of 18 1362424 before quenching is delayed. And the hardenability is deteriorated. Therefore, it is important that the content (the surface layer to the thickness direction of 100 μm) _ content (surface layer) is less than 1 〇〇 ppm. The ν content in the surface layer is more than 70 ppm.

Cr. The steel, 4 fire point of view is an effective element that can be added, the effect is more than 0.01%, but even if added more than 2%, the effect will be saturated, and the cost will increase. Therefore, the content thereof is specified to be 0.01 to ^2.0%. The better range is 〇 〇 5~〇 5〇%. Νί : It is an effective element from the viewpoint of the hardenability of steel and the improvement of the edge resistance. It is effective to add 0.01% or more, but if it is added more than 1%, it will only increase the cost. The effect is not changed. Therefore, the content is specified in _ 〇 _ 〇 2 to 1.0%. The better range is 〇 〇 5~〇 5〇%. • Cu. It is an effective element from the viewpoint of hardenability and toughness of steel. It is effective to add 0.01% or more. However, if it is added more than 〇5%, it will only increase the cost, but the effect will not change. Therefore, the content is specified at 0.005 to 0.5%. A better range is 0.02~〇 35〇/〇.

Mo: is an effective element for improving the hardenability of steel, and is an effective element for improving the softening resistance caused by tempering. In order to obtain this effect, it is necessary to add 0.01% or more. However, even if the content exceeds 〇%, the effect is saturated and the cost is increased, so it is specified as 〇%. Better range • At 0.01 to 0.40%.

Nb: carbonitride is formed, and the stability and initial improvement of the precipitate are more than 1% of 〇〇, but the addition of more than 5% will incur an increase in cost and cause quenching due to carbide formation. The sex is reduced, so 19 1362424 defines its range as 0.01 to 0.5%. A better range is 0.01~〇 20〇/〇. V: Carbonitrides are formed in the same manner as Nb. 〇·〇ι〇/0 or more has an effect on the stability of the precipitate and the improvement of toughness. However, even if it is added more than 〇, 5% will only incur an increase in cost. It does not change much, and it causes a decrease in hardenability due to the formation of charcoal. Therefore, the range is specified to be 0.01 to 0.5%. A better range is 0.01 to 0.20%.

Ta. Carbonitrides are formed in the same manner as Nb and V, and it is effective in improving the stability and toughness of precipitates in (4) (9) or more, but even if the addition exceeds 5%, the cost is increased, but the effect is not changed. Moreover, it causes a decrease in hardenability due to carbide formation. Therefore, the range is specified to be 0.01 to 0.5%. The better range is 〇.〇1~〇 3〇%. W. Forming carbonitrides in the same manner as Nb, V, and Ta, and it is effective in improving the stability and toughness of precipitates in 〇〇1% or more, but even if it is added more than 0.5%, it will only cause an increase in cost, but the effect is not Too much change, and, as a result, a decrease in hardenability due to carbide formation. Therefore, the range is specified to be 0.01 to 0.5 〇 / 。. The better range is 〇〇1~〇2〇%. Further, in addition to the above, in order to suppress variations in the composition of the surface layer portion of the steel sheet, in the present invention, it is also possible to add sn, sb, As & i or two or more kinds in the required amount.

Sn, Sb, and As: respectively, 〇〇3〇〇〇_〇3〇/〇Sn, Sb, and As are elements having a high segregation tendency toward the interface and the surface, and have a manufacturing step that suppresses inhalation and decarburization. The role of the surface reaction. By the addition, even in the state in which the steel material is subjected to the hot rolling step or in the high-temperature gas atmosphere during the annealing, the reaction of elements which are easily changed by components such as nitrogen and carbon is suppressed, and significant component variation can be prevented. effect. 20 1362424 Thus, it can be added as needed. When the amount of addition is less than 0.003%, the effect is small, and even if it is added in a large amount of more than 0.03%, not only the effect is saturated, but also the reduction of toughness and the long time of carburization time are caused, resulting in cost. increase. Therefore, it is desirable to add 0.003 to 0.03%. In the steel sheet according to the present invention, although the content of oxygen (0) is not specified, the oxide aggregation is coarsened, and the ductility is lowered. Therefore, the oxygen content is preferably 0.025% or less. Although oxygen is less preferred, it is technically difficult to be less than 0001.0001%, so it is preferably 0.0001% or more. In addition, the carbon steel sheet of the present invention may contain impurities which are inevitably mixed in the production step or the like in addition to the above-mentioned elements, but it is preferred that impurities are not mixed as much as possible. Next, the manufacturing conditions will be described with reference to the flowchart of Fig. 3. Hot rolling is considered to be a continuous optimization of the steel component and the subsequent annealing step, and is very important in the present invention. It is important to suppress the compositional variation of the surface layer of the steel sheet as much as possible, that is, N intrusion and decarburization of the surface portion. . Therefore, heating is not applicable to the high temperature heating of 1200 °C which is usually used, and it is below 1200 °C (S1). Further, at this time, since the longer the soaking time is, the more nitrogen is intruded into the surface layer portion, which affects the quenching property of the product. Therefore, it is important not to make the heating time long. Specifically, it is desirable to keep the time in ^(9)^ no more than 60 minutes, at 11〇〇. 〇 Do not heat for more than 9 minutes. Next, hot rolling is performed at a finishing temperature of 800 ° C or more and 940 ° C or less (S2). If the finish rolling temperature is lower than 800 ° C, defects caused by sintering are generated in a large amount, and if it is higher than 940 ° C, the frequency of occurrence of defects due to oxidized scale is increased, and the yield of the product is lowered, and Increase costs. 21 丄 362424 After the finish rolling of hot rolling, cool down to 65 用 with a cooling rate of C / sec or more. (The following (S3, first cooling). If cooling is performed from the end of rolling to 650 °C by cooling with a gentle cooling ratio of 20 ° C / sec, a so-called wave-like iron band structure accompanying segregation occurs. The difference 'causes the deterioration of the workability. Therefore, the cooling rate of 20 ° C / sec or more from the end of the rolling to 650 ° C or less is controlled, and then the uniform wave-induced iron metamorphosis and the wave are obtained. The iron + variable iron structure and the entire ferrous structure are subjected to slow cooling (S4, second cooling) of 20 〇 / sec or less. This can suppress the occurrence of unevenness in the structure of the coil. Taking the temperature to obtain the uniformity of the structure as described above, the structure variation (S5) in the coil can be reduced by winding at a temperature of 650 ° C or lower and 400 ° C or higher. The hot rolling is performed by the above steps. The steel sheet is subjected to pickling (S6). After pickling, annealing and cold rolling are performed according to the product thickness and the required softening level, and the following matters are important as the manufacturing conditions at this time. The carbon content of the steel plate is high, so it is clear The continuous annealing process used for the mild steel sheet cannot obtain its characteristics. Basically, the batch annealing or box annealing of the s stomach is applied to maintain the coil-invariant annealing process (S7, first annealing). From the viewpoint of preventing an increase in the nitrogen concentration in the surface layer portion, the atmosphere of the annealing gas is mainly composed of hydrogen, and the hydrogen concentration thereof is 95% or more. Further, in the case of annealing with a hydrogen atmosphere, it is temporarily from the viewpoint of safety. At room temperature, it will be replaced by nitrogen, and after nitrogen formation, it will be replaced by hydrogen. At this time, it is desirable to replace it with hydrogen and then raise the temperature to prevent gasification. However, it is necessary to replace the hydrogen into a hydrogen atmosphere. 22 1362424 The temperature is low and the hydrogen concentration is 95% or more. In addition, when the temperature rises, especially until ij 400 C, the temperature is -20 C or less, and the temperature is maintained at 400 C or more (the retention time is related to the material). In order to soften the steel sheet according to the present invention, it is desirable to maintain the temperature at 660 ° C or higher for 10 hours or more. The dew point is _4 〇〇 c or less, which is important from the viewpoint of preventing compositional changes in the surface layer portion. When the point is high, deboration, decarburization, etc. occur, and in the case of carburizing at a low carbon potential, an abnormal layer of poor bonfire is generated. By performing this series of steps (hot rolling + heat treatment), excellent workability can be obtained. In addition, in the carburizing treatment after the processing, the carburizing and quenching property is also excellent in the steel sheet of the present invention. From the viewpoint of softening, high-temperature annealing at a temperature higher than Acl is also effective. ac1+50° above the Acl point. Annealing is performed in the temperature range below C, and the cooling rate after annealing is preferably 5 liters or less until Acl -30 ° C or lower. (The cooling rate is less than or equal to the hour. Therefore, the Worthite iron phase formed above Acl is used. The removal of carbides is likely to cause coarsening of the iron phase of the fertilizer produced by cooling at 5 ° C / hour or less, and softening is promoted. Annealing in a high temperature region of 50 C or more higher than Acl will cause some of the Wolla iron to be hardened and hardened when the Worthite iron phase is too high in the composition of the steel of the present invention. Therefore, the temperature of the high temperature annealing in the present invention is preferably Acl + 5 〇 C or less. In addition, since the steel of the present invention is cooled to a temperature below ACl-3 (TC, the effect is saturated, and the cost due to the annealing time is increased, the end temperature of the slow cooling is up to the above-mentioned Acl- 3〇°c is preferred. The Acl here indicates the temperature of the Worthfield iron phase in the lift-up process. The present invention collects samples from hot-rolled steel sheets and uses a phase change test 23 1362424 (Formaster test) machine to measure 0.3 C. The expansion curve at the temperature of /s is 'to pay for the A1 metamorphic point. In addition, there is a simple method for obtaining Acl from the component in the literature, etc.' as an example, showing the Physical Metallurgy of Steel by William C. Leslie, Acl ( °C) = 723-10.7x%Mn-16.9x%Ni+29.1x%Si+16.9 x%Cr+ 29〇x%As+6.38x%W, and these empirical formulas can also be used. The product thickness is completed with high precision, and is combined with annealing to effectively perform softening. Therefore, among the foregoing series of steps, after hot rolling and coiling (S5), pickling (S6) After that, cold rolling (S6-2, first cold rolling) may be performed. In particular, the rolling rate is 5%. The upper cold rolling promotes the spheroidization of the carbides. The particle size at the end of recrystallization and recrystallization without nucleation is relatively large, and coarsening due to grain growth is likely to occur, and softening is promoted. The upper limit is not particularly limited. However, the rolling rate is over 60%, although the uniformity of the metal structure of the steel sheet due to cold rolling is further improved, but the higher the cold rolling rate, the finer the recrystallized grains during annealing, in order to soften Since the annealing time must be long, the cold rolling ratio can be determined from the viewpoint of cost and product homogenization. In the manufacturing method of the present invention, after the above annealing, the steel sheet is again subjected to cold rolling at a rolling reduction ratio of 5% or more (S7). -2, second lyophilization), followed by annealing in a gas atmosphere containing chlorine or more (S7-3, second annealing). After the above annealing (S7 1 'annealing), by undergoing cold rolling (S7_2 In the step of fire (S7-3 'second cold rolling), it is desirable to obtain uniformity of the structure or grain enlargement of the granules, and it is possible to improve the addition of X and the softening of the step. 24 1362424 In the manufacturing method of the present invention, further on After the annealing (S7-3' second annealing), the steel sheet is subjected to cold rolling (S7-4 '3rd cold milk) having a reduction ratio of 5% or more. Next, annealing is performed in a gas atmosphere containing 95% of hydrogen ( S7-5 '3rd Annealing> The annealing conditions in this case may be as described above. Further, in the manufacturing method t of the present invention, the above annealing step and cold rolling may be combined more than 3 times from the viewpoint of softening. To implement, this situation must also be implemented within the above manufacturing conditions. The carbon steel sheet according to an embodiment of the present invention may be, in other words, C: 0.20 to 0.45% 'Si: 0.05 to 0.8%, Μη: 0.85 to 2.0%, in terms of mass%. P : 0.001 ~ 0.04%, S : 0 0001 ~ 0.006%, Α 1 : 0.01 ~ 0.1%, Ή : 0.005~0.3%, Β : 0 0005 〜0.01%, N : 〇_〇〇1~0.01%, the remainder It consists of Fe and impurities that are not avoided. The value represented by 3C+Mn+〇.5Si+Cr+Ni+M〇+Cu is 2.0 or more, and the surface hardness of the steel plate has a B-scale Rockwell hardness (HRB) of 77 or less. 'The nitrogen (N) content from the surface depth to the ΙΟΟμηι is equal to 100 ppm or less.' Carbon steel sheet excellent in carburizing and quenching properties used in the weakly permeable carbon gas environment with a carbon potential (Cp) of 0.6 or less. However, C, Mn, Si'Cr N, Mo, and Cu represent the content (% by mass) of each element, and it is sometimes not treated with zero. The above carbon steel sheet further contains, by mass%, Cr: 0 01 to 2.0 〇 / ° Ν ι · 0.01 〜 1.0 〇 / 〇, Cu: 0.005 to 0.5 〇 / 〇, Mo: 0 · 01 〜 l.o0 /. The bran value of one or two or more types and 3C+Mn+〇 5Si+Cr+Ni+M〇+Cu axe may be 2.0 or more. The above carbon steel sheet further contains, by mass%, Nb: 〇01 to 25 1362424 0.5%, V: 0_01 ～0·5 ο/〇, Ta: 0.01 〇·5%, W: 0.01 ～0.5% of one type or Two or more types are also available. The above-mentioned carbon steel sheet may further contain one or two or more kinds of Sn: 0.003 to 0.03%, Sb: 0.003 to 0.03%, and As: 0.003 to 0.03% by mass. When the slab having the above components is subjected to hot rolling, it may be heated at 1200 ° C or lower, the final rolling temperature of hot rolling is 800 ° C or higher and 940 ° C or lower, and after the end rolling, the cooling rate is 20 ° C / sec or more. The mixture was cooled to 650 ° C, and then cooled at a cooling rate of 20 ° C / sec or less '400 at a coiling temperature of 650 ° C or lower. (: The above coiling, after pickling, the hydrogen is 95 ° /. or more, and until 4 〇〇. The dew point is -2 ° ° C below ' 4 〇〇. (: The above dew point is - In a gas atmosphere of 4 ° C or less, the steel sheet is annealed at a temperature of 66 ° C or higher for 10 hours or more to produce a carbon steel sheet excellent in carburization and smoldering properties. After the pickling, the rolling rate may be 5% or more and 60% or less. After the cold rolling, the annealing is performed. After the annealing, the rolling rate of 5% or more and 60°/min or less may be performed after the cooling is performed, and then the dew point is _2 直到 until the gas is 95% or more. 〇In the following, a gas atmosphere with a dew point of 4°°C or higher and a dew point of −40°C or lower is re-annealed at a temperature of 660°C or higher. After the second annealing, a rolling of 5% or more and 60% or less may be performed. The rate of cold rolling is 95% or more of hydrogen' and the dew point up to 400 °C is _2〇<>c or less, and the dew point of 4〇〇°C or more is _40°C or less. It is annealed at a temperature of 660. In the annealing of the hot-rolled or cold-rolled sheet, it is also possible to have a hydrogen content of 95% in the gas 26 1362424 environment. The annealing temperature is annealed in the range of Acl~Acl+5〇t:, and the cooling rate after annealing is slowed down to a cooling rate of 5 t/hour or less until Acl-3〇°c. The present invention will be described based on the examples. Steels having the compositions shown in Tables 1 to 6 were vacuum casted into 50 kg steel blocks, and the steel sheets obtained by hot rolling were prepared under the conditions described in Tables 7 to 12. It is heated in an air atmosphere, and the thickness of the hot-rolled sheet is 3 mm when cold rolling is not performed, and when cold rolling is performed, the thickness of the hot-rolled sheet is set to set the hot-rolled sheet thickness. The hot-rolled sheet is pickled with hydrochloric acid. Thereafter, annealing or cold rolling was performed to prepare a steel plate for evaluation having a thickness of 3 mm. Detailed production conditions and evaluation results are shown in Tables 7 to 12. Thereafter, annealing was performed under the conditions described in Tables 7 to 12, or in the cold. Annealing is performed after rolling, and further, cold rolling and annealing (second annealing) are performed after the second annealing, and then the matter is repeated again (third annealing) as shown in Table 7 to Table 12 Each processing condition is implemented. The annealed gas environment is at normal temperature. When the furnace was replaced with nitrogen, it was introduced until the hydrogen of the nitrogen gas was introduced, and then the temperature was raised. Further, the dew point was measured by using a dew point meter prepared by a thin film alumina moisture sensor. HRB) The surface hardness of the obtained steel sheet was measured. In addition, the average surface enthalpy of the steel sheet was analyzed for the swarf of the steel sheet collected from the surface to the thickness direction of the surface of the steel sheet before the carburization and quenching. The content of the nitrogen (Ν). After that, the sample subjected to the tooth profile processing was carburized and quenched to investigate the presence or absence of the surface anomaly layer. Further, the carburization treatment was carried out by gas carburization, and the carbon potential was utilized by 27 1362424 using infrared rays. The CO 2 amount control method obtained by the gas analyzer was measured. The numerical portion of the No. block of Tables 7 to 12 corresponds to the No. of Tables 1 to 6, and it is known which materials are used to which the components are used. As shown in Tables 7 to 12, the conditions of the conditions of the invention (underlined) and the comparative steel may occur in the hardness of the product, the crack during the tooth forming, or the normal layer of the surface portion at the time of carburizing and quenching, and the present invention The effect has been clarified.

28 1362424

1 1 1 1 Preparation for Invention Steel 1 Invention Steel Invention Steel Invention Steel Invention Steel Acl /—NP V_^ Bu δ K Value (Κ, value) 2.04 2.02 2.04 (2.15) (2.11) > 〇S 0.02 0.15 0.15 Φ 0.0024 0.0035 0.0028 0.0033 0.0022 CQ 0.0035 0.0023 ON s ο ο 0.0017 0.0033 0.015 0.022 0.023 0.014 0.034 0.022 0.032 0.034 0.057 0.044 m 0.0022 0.0055 0.0032 0.0022 0.0041 0.023 0.035 0.018 0.025 0.013 1 VO CN Τ-Η 1.08 0.87 0.85 m 0.12 (N d 0.24 0.25 0.33 u 0.24 0.28 0.35 0.34 0.22 〇Z (N ΓΛ inch 29 1362424 [<N^] Remarks Invention Steel Invention Steel Invention Steel Invention Steel Invention Steel Acl (°C) s Bu On T—^ r- 719 K Value ( K, value) (2.41) (2.49) (2.25) 2.39 2.08 Composition (%) > 0.21 0.03 Ο 0.08 0.06 0.01 in 0.12 0.015 0.03 0.21 0.0029 0.0035 0.0036 0.0019 0.0032 PQ 0.0019 0.0036 0.0028 0.0028 0.0033 0.012 0.023 0.021 0.028 0.033 0 . 023 0.046 0.032 0.026 0.033 cn 0.0013 0.0025 0.0015 0.0054 0.005 (=U 0.009 0.015 0.022 0.018 0.027 c s 1.22 1.34 (N 1.44 0.88 00 0.05 0.45 0.22 0.22 0.42 (J 0.21 0.24 0.22 0.28 0.33 Ο Ό 00 00 Os Ο 1362424

Remarks Invention Steel Invention Steel Invention Steel Invention Steel Invention Steel Acl (°C) Os τ-^ oo Os r—" Divination κ Value (κ, Value) 2.08 2.10 2.01 2.69 2.82 Composition (%) eg 0.08 0.08 0.28 0.28 > m 0.03 0.015 0.023 〇0.0037 0.0022 0.0027 0.0031 0.0028 CQ 0.0023 0.0028 0.0042 0.0028 0.0038 Ρ 0.015 0.033 0.027 0.027 0.049 0.031 0.028 0.045 0.019 0.033 0.0023 0.0044 0.0033 0.0048 0.0021 CL, 0.027 0.017 0.025 0.033 0.031 1 1.25 0.96 1.82 1.55 0.28 0.23 0.23 0.42 U 0.23 0.29 0.31 0.22 0.34 Ο % CN m inch 31 1362424 [inch <]

Remarks Invention Steel Invention Steel Invention Steel Invention Steel Invention Steel Acl (°C) ΓΛ (N Bu 717 717 〇1^^ K Value (Κ, value) 2.31 (2.05) (2-57) (2.17) (2.45) Composition (%) 0.012 0.015 0.02 0.013 > 0.02 0.08 0.03 0.012 〇0.05 0.04 0.06 0.08 0.05 0.35 0.12 0.0025 0.0034 0.0036 0.0023 0.0045 PQ 0.0042 0.0048 0.0013 0.0017 0.0022 0.029 0.022 0.028 0.019 0.033 0.048 0.048 0.076 0.056 0.034 00 0.0025 0.0046 0.0028 0.0018 0.002 Oh 0.029 0.023 0.022 0.008 0.006 1 0.87 00 1 < 1 i 1.28 0.23 0.21 0.77 0.13 0.08 〇. 0.44 0.22 0.24 0.29 0.35 Ο v〇卜00 OS 1362424

Remarks Invention Steel Invention Steel Invention Steel Invention Steel Invention Steel Invention Steel Invention Steel Invention Steel Invention Steel Acl rc) Inch 1 ·Ή CN * 〇\ 1 _ F: K value (Κ, value) (3.06) (2.84) (2.69) (2.89) (2.37) (2.08) 2.15 (2.56) (3.13) Composition (%) 0.005 0.015 cS 0.012 0.008 0.11 0.023 0.016 > 0.04 0.025 0.011 0.035 〇0.12 0.011 0.125 0.08 0.021 0.025 0.024 Η 〇0.23 0.02 0.015 0.73 0.035 0.12 0.06 0.12 0.014 0.023 0.45 0.34 0.12 0.22 0.0039 0.0022 0.0037 0.0018 0.0015 0.0024 0.0033 0.0025 0.0024 0Q 0.0016 0.0027 0.0037 0.0051 0.0044 0.0023 0.0036 0.0029 0.0026 0.041 0.015 0.06 0.01 0.01 0.023 0.022 0.024 0.029 0.029 0.041 0.09 0.09 0.017 0.047 0.036 0.028 0.042 00 0.0034 0.0029 0.0043 0.0038 0.0029 0.0039 0.0022 0.0027 0.0015 PLh 0.012 0.013 0.026 0.029 0.037 0.026 0.014 0.027 0.019 1 1.47 1.82 1.56 0.94 0.87 0.87 1.38 1.28 1.34 0.23 0.35 0.18 0.15 0.21 0.24 0.15 0.35 0.34 Ο 0.44 0.28 0. 33 0.23 0.34 0.28 0.23 0.29 0.35 〇2: CN in (N (N 00 (Ν 33 1362424 [9<] Remarks Comparative Example Comparative Example 1 Comparative Example Comparative Example Comparative Example Comparative Example Comparative Example Comparative Example Acl (°C) ΓΊ CN (N CN Bu 1 _ (N ^ " 4 (N 737 712 Bu Bu K value (Κ, value) Π.54) (1.77) (1.70) (1.92) (3.09) (3.60) (3.68) (2.22) Composition (%) > X) 0.015 0.013 0.015 〇0.04 0.04 0.02 0.02 0.033 0.02 0.014 0.014 0.25 0.014 0.014 CN 〇0.23 0.09 0.09 0.45 0.23 0.09 0.21 0.0029 0.0032 0.0026 0.0035 0.0034 0.0033 0.0037 0.0035 DQ 0.0022 0.0029 0.0022 0.0033 0.0025 0.0039 0.0018 0.0003 0.015 0.021 0.018 0.017 0.015 0.028 0.041 0.022 0.033 0.043 0.042 0.029 0.033 0.037 0.028 0.035 (/) 0.0045 0.0033 0.0023 0.0034 0.0045 0.0057 0.0033 0.0034 〇, 0.025 0.024 0.022 0.019 0.025 0.024 0.019 0.025 1 0.59 0.64 0.52 0.47 1.25 2.31 2.13 1.23 π 0.09 0.07 0.05 0.83 0.35 0.19 0.21 U 0.23 0.28 0.35 0.43 0.24 0.29 0 .44 0.22 Ο 〇 m P! ro m Ό cn

34 1362424

The present invention is a comparative example of the present invention. Comparative Example of Comparative Example of the Invention Comparative Example of the Invention The present invention is a carburizing and igniting material of the present invention 埏遽遽遽Q. Γ 00 00 r·» O ο rn r*i v&gt ; od Vi 〇«λ ο «Λ Ο •Λ 守 · rn rn Product board characteristics Crack generation during tooth profile processing ' ' ' • ' ' • • • Product hardness (HRB) f: oo VO SI SI ΙΛ fN Products (ppm) up to the plate surface ΐόΟμιη ίο 00 in ?l Os m §1 Ό ΓΟ II • Λ mr〇 annealing (3rd time) Cooling rate at the time of annealing above Acl • Quick fire • I 400°C or more (C) • Point E at 400 °C (C) 1 1 Cold rolling. Annealing step cooling, 1 I annealing (2nd) Cooling rate rc/hr l 1 annealing condition i °r IxlOh 1 I Dew point above 400 °C ΓΟ in tT) 1 I Defects at 400 °C (C) *r> r^i 1 • Gas r 1 I _〇< CQ U CQ tN < f^l CQ ro υ m < m CD V» Cold rolling and annealing step | Annealing (first time) Cooling rate at the time of annealing above Acl ' ' < Μ °c X36h ^7ϋ(Γ j °C ! x36h ^7〇r °c x24h 710 °c x36h 710 °c x36h ^rw °c x48h ^7ΠΓ °c x48h IMf 710 °C x48h 710 ' °C x48h °c x36h ^70 (Γ °C x36h 400 °C or more pain points; (C) os in vp ? νΊ «n vp 400 °C until the pain point (C) o rn rn O «Λ 2| o rn rn wi f ο o • 7 ill il il ®i| Argon 95%+ Nitrogen 5% Hydrogen 95%f Nitrogen 50/〇Cool, • • • • • Hot rolling conditions | ISe S Ό s Ό § O s O 2 〇s 1 O g tn ο S 〇8 O oo g v> Cooling rate (C/s) up to the cooling rate (C/S) Wi s S s 〇>r> o ο 〇in m 650 〇C of the coiling o 〇〇r· » IT) ΓΛ tr> oo in <NS s 诌6 s oo g OO 1 os 〇o 冢s 00 o 冢s 00 oo ο 00 00 S oo 8 oo Hold time (minutes) IT) cn oso ο oo Heating Warm Attack CC) § § General § § so <N <N o ΓΝ § § § § < my CQ <N ym < ω CQ Ui 35 1362424 [00<> Remarks Comparative Example of the Invention Comparative Example of the Invention Comparative Example of the Invention Comparative Example _ Comparative Example Comparative Example 1 Carburizing and quenching material 1 of the present invention埯v? Cup (5* rn rn cn γί CO rn rn rn Γ*Ί 0.45 0.45 | Product board characteristics I i tooth shape addition! Working time crack production | Raw condition 垂 • 1 1 1 垂 1 Cracking t 1 1 1 Product hardness (HRB) jri P SI |N Product board surface ΙΟΟμιη Island Nfi- (ppm) Μ II v〇Ό ν〇ν〇Os OO 31 On (N Division §1 OO l〇 cold rolling and annealing step | Annealing (3rd time) 3 y life may be $ · Μ岔 every 1 快火 1 • e point above 400eC; ro 1 400°C island 筠 point CC) • Μ 1 | g 1 annealing (2nd time ) Cooling rate of Acl above annealing 1 Annealing conditions 700eC x36h 700°C x36h 690〇C x24h 1 Defects above 400°C CC) • Defects up to 400°C rc) O o • Environment 100% 100% t ¥ • Z CO Ό < mm 00 § b; Q 〇\ 10A o 1 Cold rolling and annealing step 1 Annealing (third time) Cooling rate of Acl above fast fire < 1 1 1 t 1 t 690 °C X36h 690〇C x48h 700°C x36h 700°C x36h 690°C x24h 690〇C x48h 710°C x36h 735°C x!2h 690〇C x48h 690eC x36h 710°C x36h 710°C x48h 4〇trc CC) ο S5 o 泞oo •λ oo $ oo $ v> to 400°C 止 o rn or^l •λ <N \n rn o *〇irj rn o in 7 τ| 100% Ost^ a 100% 100% 100% hydrogen! 100% 100% 100% On Temple Hydrogen 95%+ Nitrogen 5% A 100% Cold Rolling (%) ' ' • • ' 1 • 1 • • I Hot Rolling Condition I Temperature (X) • η • rj S s〇 Ό SO os V» o 3 〇3 ο s »r> *n Cooling speed to 0C/S) s in «i-1 Vi ss WJ «η s 65〇t A cooling rate rc/s m •Tt 〇〇〇s v> fO S 〇o Finish temperature (X) g 00 g 00 〇〇〇s 00 o S3 s OO s 00 Ο 〇o 芟 Guaranteed time R3 (fine ossos § s heating temperature CC) i § § § i S fN § § <N s <N 8 (Ν ooav〇< CO CO 00 CQ 〇\ g I0A o 36 1362424 [6崦] a § N55i M551 i4*- s? 埯埯准埯准埯 i ss S3 s so § es § S3 S5 9Ό 3 ss -·0 S3 ~=3 broken - this you i宕~'

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The present invention is a comparative example of the present invention. Comparative Example of the Invention The present invention is a comparative example of the present invention. The present invention is a comparative example of a carburizing and fire-fighting material. The presence or absence of a normal layer of a cup is m 5 0.48 0.46 rn ΓΊ rn π Rn ΓΊ 0.45 0.45 0.45 Product board characteristics 1 Crack generation during tooth processing • • • • • ' • ' 1 ' • 1 • • Product hardness (HRB) F: ο P fN rn F: Surface of the product board ΙΟΟμηι Νϋ (ppm) 00 «Λ 51 ir> ν〇oo Ov •o <N 〇\ m Ό Ξ| Cold rolling and annealing step I 1 Annealing (3rd time) | Cooling rate of 1 l° above Acl c/li r 1 . Xunhuo 1 wc xI2h 1 1 ® ot x! 2h 400. . The above points CC) • ' * / 1 $ 400 ° C until the point of CO • r ^ it 1 o gas environment ' m / 〇 t 1 A cold rolling rate (%) • t | annealing (2nd time) Cooling rate of Acl above annealing 1 ' • 1 2°C/hr Annealing condition 1 73CfC m\ ' 1 TOCfC we >ββΊ we x3fli we >Qh gl 72fC xI2h me Defect point above 400°C rc) 1 1 1 〇! 400^: i up to: 1 point 1 CC) 1 1 1 o vl rn s 2| o ο «1 body ring 堍 1 1 t *^1 AA hydrogen lOCP/om/„ arsenic lock cold rolling rate (%) ' V» 1 1 so 〇ms〇< CD Ρ» u Q CQ oo CQ 〇\ 20A 20Β Cold rolling and annealing step | Annealing (third time) 2 3S section C ·Μ containing 彔' ' 1 1 1 1 1 1 1 ' 2°C/hr • Annealing condition lore χ48ι Tire Xl2h me gf ®cfc m\ «ere If 71CTC K39i 73CTC xlCh Jump x!2h xefe χ12ι 400X Above dew point (°C) ? ? v>V"i in *n κη oo ;no 400Ϊ; 芘 point CO W~) f*p ο rp η, $ $ o rn o rji o ο (10) Environment «ί| «:! A Cold rolling rate (%) ' 1 • s • ' ' so • Hot rolling condition I Temperature 0C) «ο ο V» o ir> o § ov~> 〇V» o VJ o ir> § V» § Vi Let S reach the cooling rate rc/s) ss ir> S o 〇〇o O 650X: Cooling rate of island stop Ct/s) CN 兖o 〇〇tr>r〇v> ro finish temperature ( t) 00 s oo s oo s oo o Ό 00 o 芸s 00 g oo g oo g oo g OO OO 沄oo 沄oo Hold time (butterfly oosgsooooos S heating temperature (X) ggsggsg § oo S < mu Q ffi 00 ffl On 20A 20B 38 1362424 11<]

The present invention is a comparative example of the present invention. The present invention is based on the present invention. The present invention is the present invention. The present invention is a carburizing and rubbing material of the present invention. 埏 VO v〇VO ri rn 0.45 rn 0.45 cn rn ! 0.35 守' Products Crack occurrence condition of the sheet characteristic tooth profile processing • • iH尨• • • • • 1 • * Product hardness (HRB) Ν Ν N NS (ppm) of the surface of the product sheet ΙΟΟμιη v〇IT) ir> 3 3 ΓΜ (N v〇m cold rolling. Annealing step ία fire (3rd) 3 y minutes 刼 2 °C/lir ' • • ' • Xunhuo 1 1 73〇t xl2h 700°C x24h 700eC x24h 690〇C xl2h 1 1 'Defects above 400°C rc) « • 1 in W) Vi ir> s ν~> m 1 1 * ' Defects up to 400°C ΓΟ 1 1 t uj *7 v-> rn o ο 1 • 1 1 Steroidal environment 100% 100% 100% 100% ' • 1 Cold rolling rate (%) m »n • 1 1 Annealing (2nd time) Acl or more Cooling rate during annealing P 1 ' • • • 1 1 Annealing conditions 710°C x48h i730〇C i xlOh 700°C x!2 h 710°c x36h 7I0°C x36h 700°C x24h ' 1 ' 690〇C x!2h I Defects above 400°C (6) 1 up m V) •λ 1 1 1 1 « IT) 400°C Dew point & m <7 1 or^i 〇IT) 〇1 1 1 1 1 ο Gas environment 103⁄41⁄4 • 100% i: Hydrogen 100% Hydrogen 100% 100% 1 1 1 1 1 Hydrogen 95°Α & Nitrogen 5% cold Rolling rate (%) 〇1 1 ' ν» 〇21A 21B 21C Q Fi 22A 22B κη <N Ό fN is 00 (N On (Ν cold rolling, annealing step | annealing (third time) cooling under Acl annealing) Speed rc/hr ' • ' ' Annealing conditions 710°C x36h i730〇C xlOh 700eC x36h 700°C x36h 710°C x36h 710eC x36h 700°C x36h 710°C x24h 710°C x36h 710°C x36h 690〇C x72h 〇 〇 x x x x x ;7 o in r^i to (N 〇 gas environment 100% 100% hydrogen 100% 100% | hydrogen 100% hydrogen 100% 100% argon 100% 100% hydrogen 1 100%i hydrogen 95% + nitrogen 5% hydrogen 95 %+ Nitrogen 5% Hydrogen 95°A & Nitrogen 5% Cold Rolling Rate (%) . s • • • ' ΙΛ1 fN 1 • 1 hot rolling condition | coiling temperature rc) s 1/1 s v> s v> m v> osos O m ο s Ο % o § mm (4) oo oo oo ooo iTt VI m ο another iyj 650〇 C is the shape of m. CC/s) •rj 沄«〇sm <N Vt s Vi (N finished (°C) 〇〇\ oo 〇s § oo g oo 〇5; o 5; 〇5; 〇 S3 § oo s 00 ο oo Ο OO 〇 Keep time (divided) 沄o SS s ο ο o Heating temperature CC) ooo 1 O oo An An i 21A 21B 21C 21D 22A 22B <N in <N SO < N 00 (Ν σ\ fS 39 1362424 [(ΝΙΪ 1 aJ ^3 u Si carburizing and quenching material cup, your cup rj Γη *〇Ο irt 〇rn •λ ο vq The characteristics of the product plate over-shape processing, Health Status • ' • • MU ' P (Ν Factory SI 551 SI MM Os fO ο Cold Rolling and Annealing Procedures? «c Cooling Rate for Annealing Above Acl • • • ISX 汔X °o§ § X llie I *^1 m *r>v> in δ δ I m rn is? I , 5? initial g Ν ® far | «5Ϊ 忒 £ ' « ο ? (N ttc Acl above the cold when annealing But the speed ' < ' Μ I * X * x 1? R x Μ \〇·* l!§g 1 苟vt *n ? wall g 1 v~> o 〇!- I ®ί| phase _ s〇 «ί_ I ir> SS 〇2 沄m Ρΐ f〇VJ Ό ro Cold rolling and annealing step | 冷却 Cooling rate for annealing above Acl> • ' • 1 ' ' with 1 II χ χ °〇 gx fl II I1 ? I? s sg m v>v> in ? in uj ο ; the point of 400eC 1! cc) ο rn 〇〇w-> *7 V» «7 o rn N® N© s〇®ί | shout g Sg 1 1 ' • 1 ' • • ISS «Λ os ν〇g u-> 〇§ Vi o <rj § Cooling rate to pick up: (10) V) o 〇s S IT) V» ν> Cooling rate OC/s up to 650*C) Vi <Ν VI mso SS 揉3SS s 00 § cc 〇〇〇O so ο § o oo ο Ώ E word ο ossso to β ο <Ν o fN § § § 2 § in Ρί Ά •ο v〇Ρ; 40 In general, since the surface hardness increases, the workability deteriorates, so from the viewpoint of ensuring the processability of the product, it is desirable to use the steel sheet before the carburization treatment. The surface hardness is kept at a certain value Lower. The surface hardness HrB (b scale Rockwell hardness) of the steel sheets manufactured according to the conditions of the present invention all reached below HRJB77 'confirmed from the results of the tooth profile processing test (Table 7 to Table 12) 'If the HRB is below 77, no crack. Namely, it is possible to discriminate the steel sheet according to the present invention, which is excellent in workability. In addition, the results shown in Tables 7 to 12 can be recognized green. The steel sheets obtained by the present invention exhibit sufficient performance even at a low carbon potential (Cp$〇6), and are excellent in not only excellent in permeability but also in processability. . From the results of the evaluation on the quenching property of the infiltrated carbon, it was confirmed that all of the steel sheets manufactured in accordance with the conditions of the present invention had no abnormal layer. That is, it was confirmed that the steel sheet according to the present invention is excellent in carburization and quenchability. INDUSTRIAL APPLICABILITY As described above, according to the present invention, it is possible to obtain a steel material which is excellent in workability and which can secure the surface layer hardenability at the time of the smear and a method for producing the same. Since the steel is widely used not only in automobile parts and various industrial machinery parts, but also in tools and tools, it is widely used in the industry as a whole, and the industrial value is self-evident. [Simplified description of the drawing] [Fig. 1] A schematic diagram showing the relationship between the value of K or K generated by the abnormal layer during carburizing and quenching and the average amount of N in the surface layer. [Fig. 2] Schematic diagram of the relationship between the crack at the tooth portion and the hardness of the blank during the tooth profile processing. 1362424 [Fig. 3] A flow chart for explaining the manufacturing method. [Main component symbol description] (none)

42

Claims (1)

1362424 VII. Patent application scope: 1. A carbon steel plate which is carburized under a carburizing gas environment with a carbon potential of 0.6 or less, and is characterized by containing the following components: C: 0.20 mass% or more and 0.45 mass% or less; Si: 0.05% by mass or more and 0.8% by mass or less; Μη: 0.85 mass% or more and 2.0% by mass or less; Ρ: 0.001% by mass or more and 0.04% by mass. /〇 below; S: 0.0001% by mass or more, 0.006 mass% or less; Α1: 0.01% by mass or more, 0.1% by mass or less; Ti: 0.005 by mass. /〇 or more, 0.3% by mass or less; B: 0.0005 mass% or more, 0.01 mass% or less; and N: 0.001 mass% or more, 0.01 mass% or less; and the remainder has Fe and unavoidable impurities, which are 3C+Mn The K value obtained by +0.5Si is 2_0 or more; the surface hardness is 77 or less in the B-scale Rockwell hardness; and the carbon steel plate having an average content of N of 100 ppm or less in the region from the surface layer to the depth of 1 〇〇μηι. 2. The steel sheet according to the first aspect of the patent application, further comprising one or more of the following components: Nb: 0.01% by mass or more, 0.5% by mass or less; V: 0.01% by mass or more, 0.5% by mass or less Ta: 0.01% by mass or more and 0.5% by mass or less; W: 0.01% by mass or more, 0.5% by mass or less; Sn: 0.003% by mass or more, 0.03% by mass or less; 43 1362424 Sb: 0.003% by mass or more, 0.03 by mass % or less; and As: 0.003 mass% or more and 0.03 mass% or less. 3. A method of producing a carbon steel sheet according to claim 1 or 2, characterized in that it comprises: a heating step of heating the steel slab at 1200 ° C or lower; and a temperature of 800 ° C or higher and 940 ° C or lower Hot rolling the steel slab at a rolling temperature to obtain a hot rolling step of the steel sheet; Cooling the steel sheet at a cooling rate of 20 ° C /sec or more until the steel sheet reaches a first cooling step of 650 ° C or lower; and then cooling the steel sheet at a cooling rate of 20 ° C / sec or less in the first cooling step a second cooling step; a winding step of winding the steel sheet at 650 ° C or lower and 400 ° C or higher; Acid pickling step of pickling the steel sheet; and 660 ° in a gas atmosphere having a dew point of -20 ° C or lower at a hydrogen content of 95% or more and 400 ° C or a dew point of -40 ° C or lower at 400 ° C or higher; The first annealing step of annealing the steel sheet for 10 hours or more at a temperature of C or more. 4. The method for producing a carbon steel sheet according to claim 3, wherein the first annealing step is such that the gas atmosphere is 95% or more of hydrogen and the annealing temperature is in the range of Acl to Acl + 50 ° C, and The cooling rate after annealing to Acl-30 ° C was set to 5 ° C / hour or less. 5. The method for producing a carbon steel sheet according to claim 4, further comprising: after the pickling step, cold rolling the first cold rolling of the steel sheet at a rate of 5% or more and less than 60% of the rolling length of 44 1362424 step. 6. The method for producing a carbon steel sheet according to claim 5, further comprising: a second cold rolling step of cold rolling the steel sheet at a rolling ratio of 5% or more and 60% or less after the first annealing step And after the second cold rolling step, in a gas atmosphere in which the dew point of hydrogen of 95% or more and 400 ° C is -20 ° C or less, and the dew point of 400 ° C or more is -40 ° C or less, at 660 The second annealing step of annealing the steel sheet at a temperature of ° C or higher. 7. The method for producing a carbon steel sheet according to claim 6, wherein the second annealing step is performed by annealing the gas atmosphere to a hydrogen content of 95% or more and annealing at a temperature of Acl to Acl + 50 ° C, and The cooling rate after annealing to Acl-30 ° C was set to 5 ° C / hour or less. 8. The method for producing a carbon steel sheet according to claim 7, further comprising: a third cold rolling step of cold rolling the steel sheet at a rolling ratio of 5% or more and 60% or less after the second annealing step; After the third cold rolling step, the dew point of hydrogen at 95% or more to 400 ° C is -20 ° C or lower, and the dew point of 400 ° C or higher is -40 ° C or lower, at 660 °. The third annealing step of annealing the steel sheet at a temperature higher than C. 9. The method of producing a carbon steel sheet according to item 8 of the patent application, wherein the third annealing step is such that the gaseous environment is hydrogen 95°/. The above annealing is performed at an annealing temperature in the range of Acl to Acl + 50 ° C, and the cooling rate after annealing to 45 1362424 Acl -30 ° C is set to 5 ° C / hour or less ίο. The method for producing a carbon steel sheet of the sixth aspect includes: further, after the second annealing step, the third cold rolling step of cold rolling the steel sheet at a rolling ratio of 5% or more and 6% or less; and After the cold rolling step, the dew point of hydrogen at 95% or more i to 4 Torr is -20 ° C or lower, and the dew point at 400 ° C or higher is j. 'In the gas environment below 4°°C, the third annealing step of annealing the former steel plate at a temperature of TC or higher. The manufacturing method of the carbon steel plate according to item 10 of the patent application ^' 3 The annealing step is such that the gas atmosphere is 95% or more of hydrogen and the annealing is performed in the range of -C, and the cooling rate until A c 1 - 30 ° C is set to 5/hour or less. Article 4 of the production of carbon steel plate moxibustion' further After the first annealing step, the second cold rolling step of cold rolling the steel sheet at a rolling ratio of 5% or more and ± ^ 6 % by weight is as follows: , the road point to the end of the 400' is less than _20 °c, the dew point of 4 〇〇t or more, and the 4 〇 chaotic environment, the second part of the former fire at a temperature of 660 ° C or higher Annealing step. For example, the manufacturing method of the carbon steel plate according to Item 12 of the patent scope, wherein the second annealing step is to make the gas bribe a hydrogen (10) or more and anneal in the range of the annealing temperature in the range of Acl~Ael+thief, and after annealing = 46 13. 1362424 The cooling rate up to 30 °C / hour is set at Acl-30 °C. 14. The method of producing a carbon steel sheet according to claim 13, further comprising: 5°/ after the second annealing step. The third cold rolling step of cold rolling the steel sheet at a rolling ratio of 60% or less; and the dew point of hydrogen at 95% or more to 400 ° C after the third cold rolling step is -20 ° C or lower. The third annealing step of annealing the steel sheet at a temperature of 660 ° C or higher in a gas atmosphere having a dew point of 400 ° C or higher and a temperature of -40 ° C or lower. 15. The method for producing a carbon steel sheet according to claim 14, wherein the third annealing step is performed by annealing the gas atmosphere to a hydrogen content of 95% or more and annealing at a temperature of Acl to Acl + 50 ° C, and The cooling rate after annealing to Acl-30 ° C was set to 5 ° C / hour or less. 16. The method for producing a carbon steel sheet according to claim 12, further comprising: a third cold rolling step of cold rolling the steel sheet at a rolling ratio of 5% or more and 60% or less after the second annealing step After the third cold rolling step, the dew point of hydrogen at 95% or more to 400 ° C is -20 ° C or lower, and the dew point of 400 ° C or higher is -40 ° C or lower, at 660 ° The third annealing step of annealing the steel sheet at a temperature higher than C. The method for producing a carbon steel sheet according to claim 16, wherein the third annealing step is performed by annealing the gas atmosphere to a hydrogen content of 95% or more and annealing at a temperature of from Acl to Acl + 50 °C. The cooling rate from 47 1362424 to Acl-30 °C after annealing was set to 5 ° C / hour or less. 18. The method for producing a carbon steel sheet according to claim 3, further comprising: after the pickling step, cold rolling the first cold rolling step of the steel sheet at a rolling ratio of 5% or more and 60% or less. 19. The method for producing a carbon steel sheet according to claim 18, further comprising: step of cold rolling the second cold milk of the steel sheet at a rolling ratio of 5% or more and 60% or less after the first annealing step And after the second cold rolling step, in a gas atmosphere in which the dew point of hydrogen of 95% or more and 400 ° C is -20 ° C or less, and the dew point of 400 ° C or more is -40 ° C or less, at 660 The second annealing step of annealing the steel sheet at a temperature of ° C or higher. 20. The method for producing a carbon steel sheet according to claim 19, wherein the second annealing step is performed by annealing the gas atmosphere to a hydrogen content of 95% or more and annealing at a temperature of Acl to Acl + 50 ° C, and The cooling rate after annealing to Acl-30 ° C was set to 5 ° C ^ 2 or less. 21. The method for producing a carbon steel sheet according to claim 20, further comprising: a third cold rolling step of cold rolling the steel sheet at a rolling ratio of 5% or more and 60% or less after the second annealing step And after the third cold rolling step, in a gas atmosphere in which the dew point of hydrogen of 95% or more and 400 ° C is -20 ° C or less, and the dew point of 400 ° C or more is -40 ° C or less, The steel sheet was subjected to a third annealing step of annealing at 48 1362424 at a temperature of 660 ° C or higher. 22. The method for producing a carbon steel sheet according to claim 21, wherein the third annealing step is performed by annealing the gas atmosphere to a hydrogen content of 95% or more and annealing at a temperature of Acl to Acl + 50 ° C, and The cooling rate after annealing to Acl-30 ° C was set to 5 ° C / hour or less. 23. The method for producing a carbon steel sheet according to claim 19, further comprising: a third cold rolling step of cold rolling the steel sheet at a rolling ratio of 5% or more and 60% or less after the second annealing step And after the third cold rolling step, in a gas atmosphere having a dew point of -20 ° C or lower at a hydrogen content of 95% or more and 400 ° C or a dew point of -40 ° C or lower at 400 ° C or higher, at 660 The third annealing step of annealing the steel sheet at a temperature of ° C or higher. 24. The method for producing a carbon steel sheet according to claim 23, wherein the third annealing step is performed by annealing the gas atmosphere to a hydrogen content of 95% or more and annealing at a temperature of Acl to Acl + 50 ° C, and The cooling rate after annealing to Acl-30 ° C was set to 5 ° C / hour or less. 25. The method for producing a carbon steel sheet according to claim 3, further comprising: a second cold rolling step of cold rolling the steel sheet at a rolling ratio of 5% or more and 60% or less after the first annealing step And after the second cold rolling step, in a gas atmosphere in which the dew point of hydrogen of 95% or more and 400 ° C is -20 ° C or less, and the dew point of 400 ° C or more is -40 ° C or less, at 660 The second steel sheet is subjected to a second annealing step of retreating the flame of 49 1362424 at a temperature above °C. 26. The method for producing a carbon steel sheet according to claim 25, wherein the second annealing step is performed by annealing the gas atmosphere to a hydrogen content of 95% or more and annealing at a temperature of Acl to Acl + 50 ° C, and The cooling rate up to Ac 1 -30 ° C after annealing was set to 5 ° C /hr or less. 27. The method for producing a carbon steel sheet according to claim 26, further comprising: cold rolling the third cold rolling of the steel sheet at a rolling ratio of 5% or more and 60% or less after the second annealing step; And after the third cold rolling step, in a gas atmosphere in which the dew point of hydrogen of 95% or more and 400 ° C is -20 ° C or less, and the dew point of 400 ° C or more is -40 ° C or less, The third annealing step of annealing the steel sheet at a temperature of 660 ° C or higher. 28. The method for producing a carbon steel sheet according to claim 27, wherein the third annealing step is performed by annealing the gas atmosphere to a hydrogen content of 95% or more and annealing at a temperature of Acl to Acl + 50 ° C, and The cooling rate up to ACl-30 °C after annealing was set to 5 ° C / hour or less. 29. The method for producing a carbon steel sheet according to claim 25, further comprising: a third cold rolling step of cold rolling the steel sheet at a rolling ratio of 5% or more and 60% or less after the second annealing step And after the third cold rolling step, in a gas atmosphere in which the dew point of hydrogen of 95% or more and 400 ° C is -20 ° C or less, and the dew point of 400 ° C or more is -40 ° C or less, The steel sheet was subjected to a third annealing step of annealing at 50 1362424 at a temperature of 660 ° C or higher. 30. The method for producing a carbon steel sheet according to claim 29, wherein the third annealing step is performed by annealing the gas atmosphere to a hydrogen content of 95% or more and annealing at a temperature of Acl to Acl + 50 ° C, and The cooling rate after annealing to Acl-30 ° C was set to 5 ° C / hour or less. 31. A carbon steel sheet which is carburized in a carburizing gas atmosphere having a carbon potential of 0.6 or less, and is characterized by containing the following components: C: 0.20% by mass or more and 0.45 mass% or less; Si: 0.05% by mass or more and 0.8% by mass or less; Μη: 0.85 mass% or more and 2.0% by mass or less; Ρ: 0.001% by mass or more, 0.04 mass%/〇 or less; S: 0.0001% by mass or more, 0.006 mass% or less; Α1 : 0_01% by mass or more, 0.1% by mass or less; Ti: 0.005 mass% or more, 0.3 mass% or less; 8: 0.000 mass% or more, 0.01 mass% or less; and N: 0.001 mass% or more, 0.01 mass% or less; and further one or more of the following Component: Cr: 0.01% by mass or more, 2.0% by mass or less; Ni: 0.01% by mass or more, 1.0% by mass or less; Cu: 0.005% by mass or more, 0.5% by mass or less; and Mo: 0.01% by mass or more, 1.0 mass% % or less; the remaining part has Fe and unavoidable impurities; K' value obtained by 3C+Mn+0.5Si+Cr+Ni+Mo+Cu is 2.0 or more; 51 1362424 Surface hardness is B scale Rockwell hardness 77 Hereinafter, the average content of N in the region from the surface layer to the depth ΙΟΟμηη is 100 ppm or less. 32. The carbon steel sheet according to claim 31, further comprising one or more of the following components: Nb: 0.01% by mass or more and 0.5% by mass or less; V: 0.01% by mass or more and 0.5% by mass or less ; Ta : 0.01% by mass or more, 0.5% by mass or less; W: 0.01% by mass or more and 0.5% by mass or less; Sn: 0.003 mass% or more and 0.03 mass% or less; Sb: 0.003 mass% or more, 0.03 mass%/〇 or less; and As: 0.003 mass% or more and 0.03 mass% or less . 33. A method of producing a carbon steel sheet according to claim 31 or 32, characterized in that it comprises: a heating step of heating the steel slab below 1200 ° C; Hot rolling the steel slab at a finishing temperature of 800 ° C or higher and 940 ° C or lower to obtain a hot rolling step of the steel sheet; cooling the steel sheet at a cooling rate of 20 ° C /sec or more until the steel sheet reaches 650 ° C or lower a first cooling step; the second cooling step of cooling the steel sheet at a cooling rate of 20 ° C /sec or less; and a winding step of winding the steel sheet at 650 ° C or lower and 400 ° C or higher; Pickling the pickling step of the aforementioned steel sheet; and 52 1362424 The steel sheet is annealed at a temperature of 660 ° C or higher in a gas atmosphere having a dew point of -20 ° C or lower and a dew point of 400 ° C or higher at a temperature of 95% or more and 400 ° C or less. The first annealing step of more than one hour. 53