JP2001073077A - High carbon steel sheet for working small in plane anisotropy and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a high carbon cold rolled steel sheet small in plane anisotropy to tensile characteristics and to provide a method for producing it. SOLUTION: At the time of producing a high carbon steel sheet having a componential system prescribed by JIS G 4501 (carbon steel for machine structures), JIS G (carbon tool steel) and JIS G 4802 (cold rolled steel strips for springs) by rolling and cold rolling, the steel sheet after hot finish rolling is coiled at 500 to 650 deg.C, next the steel sheet after the coiling is subjected to descaling, is thereafter subjected to primary annealing at 630 to 700 deg.C for >=20 hr, is subjected to cold rolling at a draft of >=50% and is subsequently subjected to secondary annealing at 600 to 710 deg.C. In this way, a high carbon steel sheet for working in which the plane anisotropy index Δr of the r value is >-0.15 to <0.15 can be obtd., where Δr denotes the value prescribed by Δr=(r0+r90-2×r45)/4. Moreover, r0, r45 and r90 respectively denote the r value in the 0 deg. direction (L direction), 45 deg. direction (S direction) and 90 deg. direction (C direction) to the rolling direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high carbon steel sheet for processing having small in-plane anisotropy in tensile properties and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, high carbon steel sheets have been used for parts for machine structures such as washers and chain parts. However, high-carbon cold-rolled steel sheets are generally harder than low-carbon steels and therefore have poor formability. In addition, due to hot rolling, annealing and cold rolling, in-plane anisotropy of mechanical properties is caused. Therefore, it has been difficult to apply the present invention to gear parts that are conventionally manufactured by casting and forging and require high dimensional accuracy. Therefore, it has been a major problem to reduce in-plane anisotropy of mechanical properties for molding.

Therefore, the following techniques have been proposed for high carbon steel sheets. (1) Materials and processes, Vol. 1 (1988), p.
1729 (hereinafter referred to as "prior art 1") Generally, a steel sheet containing carbon at a high concentration of 0.65% and exhibiting a ferrite / cementite structure (S65C)
Has lower formability and greater in-plane anisotropy than low carbon steel sheets. According to this document, after hot rolling, cold rolling (cold rolling rate of 50%) and batch annealing at 650 ° C. for 24 hours are performed, and secondary cold rolling (cold rolling rate of 65%) and 680
It is described that a high-carbon cold-rolled steel sheet having excellent workability is produced by performing batch annealing at 24 ° C. for 24 hours. In addition, for the purpose of graphitizing cementite, the chemical composition in S65C was adjusted, and after hot rolling, cold rolling (cold rolling reduction of 50%) and batch annealing at 650 ° C. for 24 hours were performed. By performing cold rolling (cold rolling rate of 65%) and secondary batch annealing at 680 ° C. for 24 hours, the tensile strength decreases, the r value and elongation improve, and r
A method for producing a high-carbon cold-rolled steel sheet having an in-plane anisotropy of a value equivalent to that of a low-carbon steel sheet is also shown.

(2) Japanese Patent Application Laid-Open No. Hei 10-152775 (hereinafter referred to as "prior art 2") According to this publication, the cause of the anisotropy of the mechanical properties of a high carbon steel sheet is that the sulfide based material which is elongated in the rolling direction is elongated. It is assumed that nonmetallic inclusions are present, and C, Si, Mn, P, Cr, Ni, M
In addition to regulating o, V, Ti, and Al, the S content is reduced to 0.002% or less by weight, the average length of the inclusions in the rolling direction is 6 μm or less, and the length in the rolling direction is 4 μm.
When the number of the following inclusions is 80% or more of the total number of inclusions, the ratio of the mechanical property in the rolling direction to the mechanical property in the direction perpendicular to the rolling direction is 0.9 for the impact value and the total elongation. It is described that a high carbon steel sheet with reduced in-plane anisotropy so as to fall within the range of 1.0 to 1.0 is produced.

(3) JP-A-6-271935 (hereinafter referred to as prior art 3) This publication discloses C, Si, Mn, Cr, Mo, Ni,
When hot rolling a high carbon steel sheet in which B and Al are specified, the hot finishing temperature is set to an Ar ₃ transformation point or higher, and cooling from the end of hot rolling to winding is performed at 30 ° C./sec or higher, and 550 to 550 ° C.
After winding in a temperature range of 700 ° C, descaling, annealing at a temperature of 600 to 680 ° C, cold rolling at a reduction of 40% or more, and further annealing at a temperature of 600 to 680 ° C, It is described that by adjusting the pressure, a high-carbon cold-rolled steel sheet having a small dimensional change during heat treatment such as quenching or tempering is produced.

[0006] However, the above-mentioned conventional technology has the following problems. That is, in the prior art 1, for S65C having a ferrite / cementite structure, the average value of the r value is as high as about 1.3, but the 0 ° direction (L direction) and the 45 ° direction (S direction) with respect to the rolling direction. From the r values r0, r45, and r90 in the respective directions of the 90 ° direction (C direction), Δr = (r0 +
r90-2 × r45) / 4 plane anisotropy index Δr of defined as r value is -0.47, and the the maximum disparity of r value delta _max is 1.17, The in-plane anisotropy of the r value is very large. Further, since the cold rolling-annealing process is performed twice, there is a problem that the manufacturing cost is increased. On the other hand, for the graphitized high-carbon steel sheet, the r value is further improved, and Δr is 0.34 and _Δmax is 0.85, both of which are small, but the in-plane anisotropy of the r value still remains. large.

Further, the prior art 2 only considers the in-plane anisotropy with respect to the impact value and the total elongation. Sex is not considered.

Further, in Prior Art 3, there is described a method for producing a high carbon steel sheet having a small dimensional change during heat treatment such as quenching and tempering, but no consideration is given to in-plane anisotropy with respect to formability.

In recent years, users of high-carbon steel sheets have been studying simplification of the forming process in order to reduce costs. In addition to the low in-plane anisotropy of the moldability, there is a strong demand for excellent moldability capable of molding a complicated shape in a small number of steps.

[0010] Techniques for improving the formability of high carbon steel sheets
The following techniques have been proposed as techniques. (4) JP-A-5-9588 (hereinafter referred to as prior art 4)
In this publication, the steel strip after hot rolling is kept at 10 ° C / sec or more.
At a cooling rate of 20 to 500 ° C.,
After 500 ℃ or more (Ac₁(Transformation point + 30 ℃)
Reheat, wind at that temperature, and after cold rolling 65
0 ° C or more (Ac ₁(Transformation point + 30 ° C) for 1 hour
Heat treatment promotes cementite spheroidization
To improve the formability by softening and increasing ductility.
It is listed.

However, the present inventors examined the ductility of a high carbon steel sheet using a method similar to the method described in the above-mentioned prior art 4, and found that a material equivalent to S35C had an elongation of at most about 35%. A high carbon steel sheet having excellent ductility enough to respond to simplification of the forming process by the user has not always been obtained.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a high carbon steel sheet for processing having a small in-plane anisotropy with respect to tensile properties and a method for producing the same. I do. Still another object of the present invention is to provide a method for producing a high carbon steel sheet for processing which has excellent ductility in addition to low in-plane anisotropy.

[0013]

Means for Solving the Problems The present inventors have adopted JIS.
G 4051 (Carbon steel for machine structure), JIS G 44
No. 01 (carbon tool steel) and high carbon cold rolled steel sheet having a component system with a C content of 0.2% or more specified in JIS G 4802 (cold rolled steel strip for spring), the in-plane difference in tensile properties. As a result of repeated examinations on the conditions under which the ductility or good ductility is improved, it is effective to properly control the winding temperature, primary annealing temperature, cold rolling reduction, and secondary annealing temperature after hot rolling. Was found.

After the hot rough rolling, the rough bar or the rolled material is induction-heated at a temperature not lower than the Ar ₃ transformation point, and then the winding temperature, the primary annealing temperature, the cold rolling reduction, and the secondary rolling temperature after the hot rolling are performed. It has been found that by appropriately controlling the annealing temperature, a high-carbon steel sheet having a uniform structure in the sheet thickness direction and a smaller anisotropy in tensile properties can be obtained.

Furthermore, by appropriately controlling the cooling conditions after finish rolling and winding up, the winding temperature, the primary annealing temperature, the cold rolling reduction and the secondary annealing temperature, the anisotropy with respect to the tensile properties is extremely small. In addition, it has been found that a high carbon steel sheet having excellent ductility can be obtained.

The high carbon steel sheet obtained as described above is
Δr is more than −0.15 to less than 0.15, and further, Δ of the r value
It was confirmed that _max had an extremely small value of less than 0.2.

The present invention has been made based on the above findings, and the first invention is based on JIS G4051 (carbon steel for machine structure), JIS G 4401 (carbon tool steel),
A high-carbon steel sheet having a component system defined by JIS G4802 (cold rolled steel strip for spring), wherein an in-plane anisotropy index Δr of r value is more than −0.15 to less than 0.15. A high carbon steel sheet for processing having a small in-plane anisotropy is provided. Here, Δr is Δr = (r0 + r90−2 ×
r45) / 4. Where r0,
r45 and r90 are 0 ° direction (L direction), 45 ° direction (S direction), and 90 ° direction (C direction) with respect to the rolling direction, respectively.
Direction).

[0018] The second invention is a heat treatment having a component system specified by JIS G 4051 (carbon steel for machine structure), JIS G 4401 (carbon tool steel), and JIS G 4802 (cold rolled steel strip for spring). 50 steel sheets after finish rolling
After winding at 0 to 650 ° C., and then descaling the wound steel sheet, primary annealing is performed at 630 to 700 ° C. for 20 hours or more, and cold rolling is performed at a rolling reduction of 50% or more.
Provided is a method for producing a high carbon steel sheet for processing having small in-plane anisotropy, which comprises performing secondary annealing at 00 to 710 ° C.

The third invention is a high-pressure steel having a component system defined by JIS G 4051 (carbon steel for machine structural use), JIS G 4401 (carbon tool steel), and JIS G 4802 (cold rolled steel strip for spring). Provided is a high carbon steel for processing, which is a carbon steel sheet and has a small in-plane anisotropy, wherein _{Δmax of} r value is less than 0.2. Where Δ
_max is 0 ° direction (L direction) with respect to the rolling direction, 45
The maximum disparity between the values in the ° direction (S direction) and in the 90 ° direction (C direction) is shown.

The fourth invention provides a heat treatment having a component system defined by JIS G 4051 (carbon steel for mechanical structure), JIS G 4401 (carbon tool steel), and JIS G 4802 (cold rolled steel strip for spring). 50 steel sheets after finish rolling
After winding at 0 to 650 ° C., and then descaling the steel sheet after the winding, primary annealing is performed at 630 to 700 ° C. for 20 hours or more, cold-rolled at a reduction of 50% or more, and then (1) The present invention provides a method for producing a high carbon steel sheet for processing having a small in-plane anisotropy, wherein the secondary annealing is performed at a temperature satisfying the expression (2). 960−0.5 × T ₁ ≦ T ₂ ≦ 1153-0.72 × T ₁ (1) where T ₁ : primary annealing temperature (° C.), T ₂ : secondary annealing temperature (° C.)

The fifth invention is based on JIS G 4051 (carbon steel for machine structure), JIS G 4401 (carbon tool steel), and JIS G 4802 (cold rolled steel strip for spring).
The casting slab having the component system defined in the above is continuously cast or heated to a predetermined temperature after cooling, and then roughly rolled by a rough rolling mill to form a rough bar, and subsequently finished by a continuous hot finishing rolling mill. When rolling, between the entrance of the finishing mill or between the stands of the finishing mill,
The rough bar or the rolled material is induction-heated to a temperature not lower than the Ar ₃ transformation point, and the steel plate after hot finish rolling is heated to 500 to 650 ° C.
After the coiled steel sheet is descaled, the steel sheet is subjected to primary annealing at 630 to 700 ° C. for 20 hours or more, and then the annealed steel sheet is cold-rolled at a rolling reduction of 50% or more. A method for producing a high carbon steel sheet for processing having small in-plane anisotropy, characterized by performing secondary annealing at a temperature satisfying the following expression (2). 950−0.49 × T ₁ ≦ T ₂ ≦ 1160−0.72 × T ₁ (2) where T ₁ : primary annealing temperature (° C.), T ₂ : secondary annealing temperature (° C.)

The sixth invention is a steel having a component system defined by JIS G 4051 (carbon steel for machine structure), JIS G 4401 (carbon tool steel), and JIS G 4802 (cold rolled steel strip for spring). Ar ₃ in the hot rolling process
Rolled at a finishing temperature of the transformation point or higher, the finish-rolled steel sheet is cooled to Ar ₃ -100 ° C. at a cooling rate of 7 ° C./s or more, and the cooled steel sheet is cooled in a temperature range of 560 to 640 ° C.
Hold for 10 seconds and then finish the steel plate after hot finish rolling
After winding at ６630 ° C. and then descaling the steel sheet after winding, the steel sheet is subjected to primary annealing at 640 to 700 ° C. for 20 hours or more, and then the annealed steel sheet is cold-rolled at a rolling reduction of 50% or more, Thereafter, there is provided a method for producing a high carbon steel sheet for processing having excellent in ductility and small in-plane anisotropy, characterized by performing secondary annealing at a temperature satisfying the following expression (3). 1015−0.58 × T ₁ ≦ T ₂ ≦ 1230−0.83 × T ₁ (3) where T ₁ : primary annealing temperature (° C.), T ₂ : secondary annealing temperature (° C.)

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described specifically. First, the first high carbon steel sheet of the present invention will be described. The first high-carbon steel sheet has a C content of 0.2 defined in JIS G 4051 (carbon steel for machine structure), JIS G 4401 (carbon tool steel), and JIS G 4802 (cold rolled steel strip for spring). % Or more, and the in-plane anisotropy index Δr of the r value is −0.15.
Ultra-less than 0.15. Where Δr is Δr = (r
0 + r90−2 × r45) / 4. Here, r0, r45, and r90 indicate r values in the 0 ° direction (L direction), the 45 ° direction (S direction), and the 90 ° direction (C direction) with respect to the rolling direction, respectively.

As described above, Δr is more than -0.15 to 0.15.
By making it extremely small, that is, less than the above, it becomes possible to apply to gear parts which are conventionally manufactured by forging and casting and which require high dimensional accuracy.

In producing such a first high carbon steel sheet, the steel sheet having the above-mentioned component system after hot finish rolling is wound at 500 to 650 ° C., and then the steel sheet after winding is descaled. Primary annealing at 630 to 700 ° C for 20 hours or more, cold rolling at a reduction of 50% or more, and then secondary annealing at 600 to 710 ° C. Hereinafter, the reason for limitation will be described.

(1) Hot-rolling winding temperature: 500 to 650 ° C. If the winding temperature is lower than 500 ° C., the pearlite structure becomes extremely fine, so that the carbide becomes extremely fine in the primary annealing, and the grains in the secondary annealing Since the texture that suppresses the growth property and reduces the in-plane anisotropy of the r value is not formed, 5
00 ° C was the lower limit. On the other hand, if the temperature is too high, coarse pearlite is generated, and lamellar carbide remains after the secondary annealing, and the workability is reduced.
The upper limit was 0 ° C.

(2) Primary annealing conditions: 630-700 ° C.
For the hot rolled sheet after winding for 20 hours or more, primary annealing is performed for the purpose of spheroidizing the carbide after descaling such as pickling. When the primary annealing temperature is higher than 700 ° C., recrystallization and grain growth occur remarkably, and the r value in the S direction becomes smaller than the average value of the r values in the L and C directions. Therefore, the upper limit was set at 700 ° C. On the other hand, if the primary annealing temperature is less than 630 ° C., it becomes difficult to make the carbide spheroidized, and lamellar carbide remains after the secondary annealing,
630 ° C. was made the lower limit because the workability was reduced. In addition,
The annealing time was set to 20 hours or more to promote spheroidization.

(3) Cold rolling reduction: 50% or more As the cold rolling reduction increases, a texture in which the in-plane anisotropy of the r value decreases is formed. In order to make it smaller, a cold rolling reduction of at least 50% or more is required. The upper limit is not particularly limited, but at a high cold rolling reduction of more than 80%, the sheet passing property is remarkably reduced, so that it is preferably 80% or less.

(4) Secondary annealing condition: 600 to 710 ° C. The cold rolled sheet is subjected to secondary annealing for recrystallization. When the secondary annealing temperature is higher than 710 ° C, recrystallization,
Grain growth occurs remarkably, the r value in the C direction becomes significantly larger than the r values in the L and S directions, and the anisotropy of the r value increases. On the other hand, if the secondary annealing temperature is lower than 600 ° C., unrecrystallized portions remain and workability deteriorates. The annealing may be either continuous annealing or box annealing.

Next, the second high carbon steel sheet of the present invention will be described. The second high carbon steel sheet is JIS G 4051
(Carbon steel for machine structural use), high carbon steel sheet with a C content of 0.2% or more specified by JIS G 4401 (carbon tool steel) and JIS G 4802 (cold rolled steel strip for spring) Therefore, the _{Δmax of} the r value is less than 0.2. However, delta _max is to the rolling direction, 0 ° direction (L direction), 45 ° direction (S direction), shows a maximum difference of 90 ° direction (C direction).

As described above, by making the r value Δ _max extremely small, less than 0.2, it is possible to apply the present invention to gear parts that are conventionally manufactured by forging or casting and that require extremely high dimensional accuracy. .

In manufacturing such a second high carbon steel sheet, the following first, second and third methods can be applied.

First, the first method will be described. First
In the method of the above, the steel plate after hot finish rolling having the above-mentioned component system is wound at 500 to 650 ° C, and then the steel sheet after winding is descaled, and then at 630 to 700 ° C for 20 hours.
The above primary annealing is performed, cold rolling is performed at a rolling reduction of 50% or more, and then secondary annealing is performed at a temperature satisfying the following expression (1). 960−0.5 × T ₁ ≦ T ₂ ≦ 1153-0.72 × T ₁ (1) (However, T ₁ : primary annealing temperature (° C.), T ₂ : secondary annealing temperature; the same applies hereinafter) The reason for limitation will be described.

(1) Hot Rolling Winding Temperature: 500 to 650 ° C. As in the first method for producing a high carbon steel sheet, when the winding temperature is lower than 500 ° C., the in-plane anisotropy of the r value decreases. Since no texture was formed, the lower limit was set at 500 ° C. On the other hand, if the temperature exceeds 650 ° C., the workability is reduced.
The upper limit was 650 ° C.

(2) Primary annealing conditions: 630-700 ° C.
The primary rolled steel sheet after winding is subjected to primary annealing for the purpose of spheroidizing carbides after descaling such as pickling, but the primary annealing is performed in the same manner as in the first method for producing a high carbon steel sheet. Temperature 70
If the temperature is higher than 0 ° C., the anisotropy of the so-called V-type r-value increases. On the other hand, if the temporary annealing temperature is lower than 630 ° C., the workability deteriorates. The annealing time was set to 20 hours or more to promote spheroidization.

(3) Cold rolling ratio: 50% or more As in the first method for producing a high carbon steel sheet, the r value is made 50% or more in order to sufficiently reduce the in-plane anisotropy of the r value. The upper limit is not particularly limited. However, as in the case of the first method for manufacturing a high carbon steel sheet, from the viewpoint of maintaining good sheet passability, the upper limit is 80.
% Is preferable.

(4) Secondary annealing conditions: 960-0.5 × T₁≤T₂≦ 1153-0.72 × T
₁  The secondary annealing condition is to reduce the in-plane anisotropy of the r value.
It is an essential condition that should be properly controlled for the primary annealing temperature.
You. Therefore, the primary annealing conditions and secondary annealing
The effect of the blunt condition was investigated. About the survey results
This will be described below.

In mass%, C: 0.34%, Si: 0.1
9%, Mn: 0.73%, P: 0.012%, S: 0.
After melting steel of 001% and Al: 0.021%, hot-rolling is performed at a finishing temperature of 850 ° C. and a winding temperature of 580 ° C., and after pickling, primary annealing is performed at 630 to 700 ° C. for 40 hours. The rolling reduction was set to 60%, and the secondary annealing was performed at 610 to 710.
The in-plane anisotropy of the steel sheet subjected to 40 ° C. for 40 hours was examined by a tensile test. The result is shown in FIG. FIG. 1 shows the primary annealing temperature T ₁ and the secondary annealing temperature T regarding the in-plane anisotropy of the r value.
Is a diagram showing the relationship of _two. As shown in FIG. 1, the secondary annealing temperature T ₂ is (960−0.5 × T ₁ ) or more and (1153-
It became clear that Δr _max was less than 0.2 in the range of 0.72 × T ₁ ) or less, and in-plane anisotropy was reduced. Therefore, the secondary annealing temperature _{T 2} 960-0.5 ×
T ₁ ≦ T ₂ ≦ 1153-0.72 × T ₁
Note that Δr _max indicates the maximum difference between r values in the L, S, and C directions. Annealing may be either continuous annealing or box annealing.

Next, the second method will be described. Second
In the method, the casting slab having the above-mentioned component system is continuously cast, or after cooling to a predetermined temperature after cooling, rough-rolled by a rough rolling mill to form a coarse bar, and subsequently,
When finishing rolling by a continuous hot finishing rolling mill,
The rough bar or the rolled material is induction-heated to a temperature equal to or higher than the Ar ₃ transformation point on the entrance side of the finish rolling mill or between stands of the finish rolling mill, and the steel plate after hot finish rolling is 500 to
After winding at a temperature of 650 ° C., and then descaling the wound steel sheet, primary annealing is performed at 630 to 700 ° C. for 20 hours or more, and then the annealed steel sheet is cold-rolled at a rolling reduction of 50% or more. Then, secondary annealing is performed at a temperature satisfying the following expression (2). 950−0.49 × T ₁ ≦ T ₂ ≦ 1160−0.72 × T ₁ (2) Thereby, the structure in the plate thickness direction is uniform, and the in-plane anisotropy of the tensile properties is reduced by the first method. A smaller high carbon steel sheet can be obtained. Hereinafter, the reason for limitation will be described.

(1) Induction Heating The induction heating treatment is to make the γ grain size and the structure during hot rolling uniform in the thickness direction, to make the structure of the steel sheet after winding uniform, and to perform the tensile treatment after the secondary annealing. A texture in which in-plane anisotropy with respect to characteristics is reduced is uniformly formed in the thickness direction. Specifically, after rough rolling, when finishing rolling by a continuous hot finish rolling mill, before finishing rolling, for the rough bar at the entrance side of the finishing rolling mill, or during finishing rolling between the stands of the finishing rolling mill. The rolled material is subjected to at least one induction heating at a temperature equal to or higher than the Ar ₃ transformation point. The reason for setting the heating temperature to the Ar ₃ transformation point or higher is to make the γ particle size and the structure uniform. The heating time is desirably at least 3 seconds or more. Note that the heat treatment also includes raising and lowering the temperature.

(2) Hot-rolling winding temperature: 500 to 650 ° C. Similar to the method for producing the first high-carbon steel sheet, when the winding temperature is lower than 500 ° C., an aggregate having a small in-plane anisotropy of the r value. Since the structure is not formed and the workability is lowered when the temperature exceeds 650 ° C, the winding temperature is set in the range of 500 to 650 ° C.

(3) Primary annealing conditions: 630-700 ° C.
For the hot rolled sheet after descaling for at least 20 hours, primary annealing is performed for the purpose of spheroidizing carbides. When the primary annealing temperature becomes higher than 700 ° C., as in the method for producing the first high carbon steel sheet. Since the anisotropy of the so-called V-type r-value increases, while the workability decreases when the temperature is lower than 630 ° C, the primary annealing temperature is set to 630 to 700 ° C, and the annealing time is set to 20 hours from the viewpoint of promoting spheroidization. Above.

(4) Cold rolling reduction: 50% or more As in the method for producing the first high carbon steel sheet, the cold rolling reduction is 50% in order to sufficiently reduce the in-plane anisotropy of the r value.
Above. Further, as in the method for producing the first high-carbon steel sheet, the content is preferably 80% or less from the viewpoint of maintaining good sheet passability.

(5) Secondary annealing conditions: 950-0.49 × T₁≤T₂≦ 1160−0.72 ×
T₁  As in the first method, the secondary annealing conditions are based on the in-plane difference in r value.
Appropriate control of primary annealing temperature to reduce anisotropy
This is a mandatory requirement to be controlled. Therefore, the effect on in-plane anisotropy
The effects of primary annealing conditions and secondary annealing conditions were investigated.
The results of the survey are described below.

By weight%, C: 0.35%, Si: 0.1
8%, Mn: 0.72%, P: 0.011%, S: 0.
After melting 001%, Al: 0.022% steel, slab
Prior to finish rolling, the coarse bar is heated at 1010 ° C for 1
5 seconds heat treatment, finish rolling at 850 ° C finishing temperature
After finish rolling, take up at 580 ° C take-up temperature and pickle
After that, primary annealing is performed at 630 to 700 ° C. for 40 hours,
The rolling reduction was set to 60%, and the secondary annealing was performed at 610 to 710.
Temperature of steel plate for 40 hrs.
In-plane anisotropy of the steel sheet, and the surface and thickness of the steel sheet by X-ray diffraction
About the plane parallel to the rolling surface at each position of 1/4,
To investigate the integrated reflection intensity. Table 1 shows the plate of integrated reflection intensity.
The measurement results in the thickness direction are shown. Induction heating of coarse bar
As a result, the maximum disparity of the (222) integrated reflection intensity is reduced.
That is, the structure is formed to be uniform in the thickness direction. Figure
2 is the value of r when the coarse bar is induction-heated according to the present method.
Primary annealing temperature T for in-plane anisotropy₁And secondary annealing temperature T
₂Shows the relationship. Do not conduct induction heating according to the first method.
In this case, as shown in FIG. 1, the secondary annealing temperature is (960-
0.5 × T₁) Or more and (1153-0.72 ×
T₁) In the following range, Δr _maxIs less than 0.2
However, by performing induction heating of the coarse bar, the secondary annealing temperature
T₂Is (950−0.49 × T₁) Or more and (116)
0-0.72 × T₁) While spreading to the following range, Δ
r_maxDecreases from less than 0.2 to less than 0.15, more
Clearly smaller in-plane anisotropy over a wide range
became. Therefore, in the second method, the secondary annealing temperature T₂To
950-0.49 x T₁≤T₂≦ 1160−0.72 ×
T₁And a wider range than the first method. What
The above Δr_maxIs the maximum case of the r value in the L, S, and C directions.
Show the difference. Annealing is either continuous annealing or box annealing.
May be.

[0046]

[Table 1]

Next, the third method will be described. Third
In the method, Ar ₃ -100 steels were rolled at Ar ₃ transformation point or more finishing temperature at hot rolling step, a finish rolled steel plate at 7 ° C. / s or more cooling rate with the component
C., the cooled steel sheet is kept in a temperature range of 560 to 640 ° C. for 2 to 10 seconds, and then the steel sheet after hot finish rolling is wound at 500 to 630 ° C., and then the steel sheet after winding is wound. After descaling, the steel sheet is subjected to primary annealing at 640 to 700 ° C. for 20 hours or more, and then the annealed steel sheet is cold-rolled at a reduction ratio of 50% or more, and then subjected to secondary annealing at a temperature satisfying the following equation (3). Anneal. 1015−0.58 × T ₁ ≦ T ₂ ≦ 1230−0.83 × T ₁ (3) Due to this, not only the in-plane anisotropy with respect to the tensile properties is extremely small, but also the ductility is excellent. High carbon steel sheet can be obtained. Hereinafter, the reason for limitation will be described.

(1) Hot rolling finish temperature: Ar ₃ transformation point or more In hot rolling, when α-region rolling is performed below the Ar ₃ transformation point, a non-uniform pearlite structure is formed in the sheet thickness direction. Even after the rolling and annealing steps, the structure is not uniform, and the ductility is reduced. Therefore, the finishing temperature is set to the Ar ₃ transformation point or higher.

(2) Transformation point of Ar ₃ after hot rolling—100 ° C.
Cooling rate up to: 7 ° C./sec or more The steel sheet after hot rolling is suppressed in the subsequent spheroidizing annealing (primary annealing) to suppress the formation of polygonal ferrite in order to form a microstructure favorable for ductility, and to form a uniform steel sheet. It is necessary to have perlite. For that purpose, the pearlite transformation may be completed in a short time while maintaining the temperature in the temperature range near the nose of the pearlite transformation. However, A after hot rolling
r ₃ If the cooling rate until transformation point -100 ° C. of less than 7 ° C. / sec, pro-eutectoid polygonal ferrite during cooling is produced, hot-rolled steel sheet structure becomes a mixed structure of polygonal ferrite + pearlite, secondary annealing After that, a mixed grain structure having a non-uniform ferrite grain size is obtained, resulting in a decrease in ductility. Therefore, after hot rolling, the cooling rate from the Ar ₃ transformation point to −100 ° C. is set to 7 ° C.
/ Sec or more.

(3) Cooling holding temperature and holding time: 56
0 to 640 ° C., 2 seconds to 10 seconds If the holding temperature after cooling is lower than 560 ° C., polygonal ferrite is not generated, but the pearlite colony size becomes small and the curl at the colony boundary during spheroidizing annealing is reduced. The tool becomes extremely coarse and ductility decreases. on the other hand,
When the temperature exceeds 640 ° C., polygonal ferrite is partially generated, and pearlite is coarsened, and ductility is reduced. If the holding time is less than 2 seconds, the pearlite transformation does not end, and if it exceeds 10 seconds, the pearlite becomes coarse and uniform pearlite cannot be obtained. Therefore, the cooling holding temperature is set to 560 to 640 ° C., and the holding time is set to 2 seconds to 10 seconds.

The holding in the temperature range of 560 to 640 ° C. does not necessarily have to be performed at a constant temperature in this temperature range.
It only has to be held for 0 seconds. Actually, in order to keep the temperature in this temperature range for a short time, for example, cooling by watering after hot rolling may be stopped for a short time in this temperature range, or the temperature may be controlled by reducing the amount of water.

(4) Hot-rolling winding temperature: 500 to 630 ° C. Similar to the method for producing the first high-carbon steel sheet, when the winding temperature is lower than 500 ° C., a set having small in-plane anisotropy of r value is obtained. Since the structure is not formed and the workability is lowered when the temperature exceeds 650 ° C, the winding temperature is set in the range of 500 to 650 ° C.

(5) Primary annealing conditions: 640 to 700 ° C.
For the hot rolled sheet after descaling for at least 20 hours, primary annealing is performed for the purpose of spheroidizing carbides. When the primary annealing temperature becomes higher than 700 ° C., as in the method for producing the first high carbon steel sheet. The so-called V-type r-value anisotropy increases. On the other hand, when the temperature is lower than 640 ° C., the spheroidization of the carbide becomes insufficient,
Part of the structure after the secondary annealing becomes mixed grains, and the ductility decreases.
Therefore, the primary annealing temperature is set to 640 to 700 ° C.
Further, similarly to the method of manufacturing the first high carbon steel sheet, the annealing time is set to 20 hours or more from the viewpoint of promoting spheroidization.

(6) Cold rolling reduction: 50% or more Like the first method for producing a high carbon steel sheet, the cold rolling reduction is 50% in order to sufficiently reduce the in-plane anisotropy of the r value.
Above. Further, as in the method for producing the first high-carbon steel sheet, the content is preferably 80% or less from the viewpoint of maintaining good sheet passability.

(7) Secondary annealing conditions: 1015−0.58 × T₁≤T₂≤1230-0.83
× T₁  As in the first method, the secondary annealing conditions are based on the in-plane difference in r value.
Appropriate control of primary annealing temperature to reduce anisotropy
This is a mandatory requirement to be controlled. Therefore, the effect on in-plane anisotropy
The effects of primary annealing conditions and secondary annealing conditions were investigated.
The results of the survey are described below.

By mass%, C: 0.34%, Si: 0.1
9%, Mn: 0.73%, P: 0.012%, S: 0.
After melting 001%, Al: 0.021% steel, 850 ° C
Finish rolling at a finishing temperature of 3 ° C. After finishing rolling, the cooling rate is 7 ° C.
/ Sec or more for Ar₃Transformation point-Cool down to -100 ° C and cool
After the rejection, it is kept in the temperature range of 560 to 640 ° C. for 2 to 10 seconds,
After winding at a winding temperature of 580 ° C. and pickling, primary annealing is performed at 64 ° C.
Performed at 0 to 700 ° C for 40 hours, and the rolling reduction of cold rolling was 60
%, And the secondary annealing was performed at 610 to 710 ° C. for 40 hours.
The in-plane anisotropy of the steel sheet was examined by a tensile test. So
FIG. 3 shows the results. FIG. 3 shows the in-plane anisotropy of the r value.
Primary annealing temperature T₁And secondary annealing temperature T₂Shows the relationship. Figure
As shown in FIG. 3, the secondary annealing temperature T₂Is (1015-0.
58 × T ₁) Or more, (1230−0.83 × T)₁)Less than
Δr_maxIs less than 0.2 and in-plane anisotropy
Was found to be smaller. Therefore, secondary
Annealing temperature T₂Is 1015−0.58 × T₁≤T₂≦ 1
230-0.83 × T₁Range. The above Δr
_maxIndicates the maximum difference between r values in the L, S, and C directions. Ma
The annealing may be either continuous annealing or box annealing.

In the present invention, when a steel sheet is manufactured, the method of rolling after heating the slab is a method of performing a short-time heat treatment after continuous casting, or immediately omitting this heating step. Any method of rolling may be employed, but a method of reheating the slab without cooling it to room temperature is particularly preferable from the viewpoint of energy saving. During hot rolling, there is no problem even if heating is performed by a bar heater or the like for the purpose of soaking. The heating by the bar heater can be effectively used for a continuous hot rolling process using a coil box or the like. In this case, the heating of the rough rolling bar may be performed before and after the coil box, during or after the rough rolling mill, in addition to the above. Even if the rough rolling bar is heated before and after the welding machine after the coil box, the effect of the present invention is sufficiently exhibited. Further, in order to improve the slidability of the surface of the steel sheet manufactured in this manner, a phosphate treatment may be performed after zinc plating. Galvanization can be performed by an electrogalvanizing method, a hot-dip galvanizing method, or the like.

[0058]

EXAMPLES Specific examples of the present invention will be described below in comparison with comparative examples. (Embodiment 1) In this embodiment, an example of a method of manufacturing a first high carbon steel sheet will be described. S35 of JIS G4051
C equivalent component system (by mass, C: 0.35%, Si: 0.
20%, Mn: 0.76%, P: 0.016%, S:
(0.003%, Al: 0.026%) was manufactured by continuous casting, and this slab was heated to 1100 ° C., hot-rolled, cooled, wound up under the conditions shown in Table 2, and subjected to primary annealing. , Cold rolling, and secondary annealing are sequentially performed.
%, And a 1.0 mm-thick steel sheet was produced. The sample No. I is a conventional material.

[0059]

[Table 2]

With respect to these samples, 0
° direction (L direction), 45 ° direction (S direction), 90 ° (C
JIS No. 5 test piece was taken along the
A tensile test was performed at 0 mm / min, tensile properties in each direction were measured, and in-plane anisotropy was evaluated. Table 3 shows the results. Incidentally, the yield strength in Table 3, the tensile strength and delta _max described in the respective columns of all elongation, L of each of the tensile characteristic value, S, indicates the maximum disparity in the C direction. Also,
Δr described in the column of r value in Table 3 means Δr = (r0 +
r90−2 × r45) / 4.
Here, r0, r45, and r90 indicate r values in the 0 ° direction (L direction), the 45 ° direction (S direction), and the 90 ° direction (C direction) with respect to the rolling direction, respectively.

[0061]

[Table 3]

As shown in Table 3, No. 1 of the present invention example. A
-No. C is, delta _max of yield strength and tensile strength 1
0MPa below, the elongation of the delta _max 1.5% or less, [Delta] r of the r value is less than -0.15 ultra 0.15, anisotropy of tensile properties in the plane is small is confirmed.

On the other hand, in the comparative example, Δr was large, and it was confirmed that the in-plane anisotropy was poor. For example, when the winding temperature is low (No. D), the elongation Δ
_{When the maximum} annealing is 2.0% and the r value Δr is 0.18, and when the temporary annealing temperature is high (No. E), the r value Δr is 0.1%.
20 when the cold rolling reduction is as low as 40% (No.
In F), _Δmax of the yield strength is 14, and Δ of the tensile strength is
_{When the max} is 16 and the r-value Δr is as large as 0.19, respectively, and when the secondary annealing temperature is high (No. G), the r-value Δr is as large as 0.23 and the secondary annealing temperature is low. In (No. H), the r value Δr was as large as −0.29, and in each case, the in-plane anisotropy was large. In addition, the conventional materials No. I also had a high r value, Δr, of 0.18 and a large in-plane anisotropy. (Embodiment 2) In this embodiment, an example of a first method for producing a second high carbon steel sheet will be described. A component system equivalent to S35C of JIS G4051 (by mass, C: 0.34%, S
i: 0.19%, Mn: 0.73%, P: 0.012
%, S: 0.001%, Al: 0.021%) was manufactured by continuous casting, and this slab was heated to 1100 ° C., hot-rolled, cooled, and then rolled under the conditions shown in Table 4. , Primary annealing, cold rolling, and secondary annealing are sequentially performed, and then, a temper rolling of 1.5% is performed to obtain a sheet having a thickness of 2.5 mm.
Six types of steel sheets were produced. The sample No. 16
Is a conventional material.

[0064]

[Table 4]

With respect to these samples, 0
° direction (L direction), 45 ° direction (S direction), 90 ° (C
JIS No. 5 test piece was taken along the
A tensile test was performed at 0 mm / min, tensile properties in each direction were measured, and in-plane anisotropy was evaluated. Table 5 shows the results. Incidentally, the yield strength in Table 5, tensile strength, total elongation, and the delta _max described in the respective columns of r values, L of each of the tensile characteristic value, S, indicates the maximum disparity in the C direction.

[0066]

[Table 5]

As shown in Table 5, No. 1 of the present invention was used. 1
-No. 7, Δ _max of the yield strength and tensile strength 1
0MPa below, the elongation of the delta _max 1.5% or less, delta _{m ax} of r value is less than 0.2, the anisotropy of the tensile properties in the plane is very small is confirmed.

On the other hand, in the comparative example, _Δmax was increased in any of the tensile properties, and it was confirmed that the in-plane anisotropy was poor. For example, if the primary annealing temperature is high (No.11), the delta _max is 0.30, and the r value, when the cold rolling reduction is 30% and lower (No.13) is the yield strength, tensile strength and Δ _{max of} r value is 1
8, 13, and 0.59, which were all large in-plane anisotropy. In addition, the conventional materials No. Sample _No. 16 also had a high r value _Δmax of 0.42 and large in-plane anisotropy.

(Embodiment 3) This embodiment also shows an example of the first method for producing the second high carbon steel sheet. JIS G
4802 S65C-CSP equivalent component system (by mass
C: 0.64%, Si: 0.20%, Mn: 0.75
%, P: 0.010%, S: 0.003%, Al: 0.
Slab is manufactured by continuous casting, and the slab is heated to 1100 ° C., hot-rolled, cooled, and then wound under the conditions shown in Table 6, and subjected to primary annealing, cold rolling, and secondary annealing. This was performed sequentially to produce 16 types of steel plates having a thickness of 2.5 mm. The sample No. 32 is a conventional material.

[0070]

[Table 6]

With respect to these samples, 0
° direction (L direction), 45 ° direction (S direction), 90 ° (C
JIS No. 5 test piece was taken along the
A tensile test was performed at 0 mm / min, tensile properties in each direction were measured, and in-plane anisotropy was evaluated. Table 7 shows the results.
Shown in In Table 7, the yield strength, tensile strength, total elongation,
And the the delta _max described in the columns of r values, L of each of the tensile characteristic value, S, indicates the maximum disparity in the C direction.

[0072]

[Table 7]

As shown in Table 7, No. 1 of the present invention was used. 1
7-No. 23, the yield strength and tensile strength Δ _max
Is 20 MPa or less, the elongation _Δmax is 2.0% or less, r
The value _Δmax was less than 0.2, and it was confirmed that the in-plane anisotropy of tensile properties was extremely small.

On the other hand, in the comparative example, _Δmax was increased in any of the tensile properties, and it was confirmed that the in-plane anisotropy was poor. For example, if the primary annealing temperature is high (No.27), the delta _max is 0.31 in r value, when the cold rolling reduction is 30% and lower (No.29) is the yield strength, tensile strength and Δ _{max of} r value is 2
2, 15 and 0.32, all of which had large in-plane anisotropy. In addition, the conventional materials No. Sample No. 32 also had a high r value _Δmax of 0.44 and large in-plane anisotropy.

(Embodiment 4) In this embodiment, an example of a second method for producing a second high carbon steel sheet will be described. JIS
G4051 component system equivalent to S35C (by mass, C: 0.
35%, Si: 0.18%, Mn: 0.72%, P:
0.011%, S: 0.001%, Al: 0.022
%) Of the slab is manufactured by continuous casting, and
After heating to 100 ° C., hot rolling, primary annealing, cold rolling, and secondary annealing are sequentially performed under the conditions shown in Table 8;
By performing temper rolling of 5%, 23 types of steel plates having a thickness of 2.5 mm were produced. The sample No. 55 is a conventional material.

[0076]

[Table 8]

With respect to these samples, the in-plane anisotropy was examined by a tensile test, and the uniformity of the structure in the thickness direction was examined by X-ray diffraction. In the tensile test, JIS No. 5 test pieces were sampled along the 0 ° direction (L direction), 45 ° direction (S direction), and 90 ° (C direction) with respect to the rolling direction, and the tensile speed was 10 mm / mi.
n, a tensile test was performed, and tensile properties in each direction were measured. Table 9 shows the results. Incidentally, the yield strength in Table 9, tensile strength, total elongation, and the delta _max described in the respective columns of r values, L of each of the tensile characteristic value, S, indicates the maximum disparity in the C direction. Table 9 shows, regarding the uniformity of the structure in the thickness direction, the steel sheet surface, the thickness 1/4, and the thickness 1/2.
The results obtained by examining the integrated reflection intensity of the surface parallel to the rolling surface at each position are also shown.

[0078]

[Table 9]

As shown in Table 9, No. 1 of the present invention was used. Three
3-No. 46, the yield strength and tensile strength Δ _max
There 10MPa or less, Δ _max of growth of 1.5% or less, r
The value _Δmax was less than 0.2, and it was confirmed that the in-plane anisotropy of tensile properties was extremely small. Furthermore, it was confirmed that the method of performing induction heating before rough rolling is more preferable from the viewpoint of not only reducing the in-plane anisotropy of the tensile properties but also improving the uniformity of the structure in the thickness direction.

On the other hand, in the comparative example, _Δmax was increased in any of the tensile properties, and it was confirmed that the in-plane anisotropy was poor. For example, if the primary annealing temperature is high (No.50), the delta _max 0.28 next to the r value, when the cold rolling reduction is 30% and lower (No.52) is the yield strength, tensile strength and Δ _{max of} r value is 1
6, 11, and 0.34, all of which had large in-plane anisotropy. In addition, the conventional materials No. 55 also, delta _max of r value was as high as 0.40, in-plane anisotropy is large.

(Embodiment 5) This embodiment also shows an example of a second method for producing a second high carbon steel sheet. JIS G
4802 S65C-CSP equivalent component system (by mass
C: 0.64%, Si: 0.20%, Mn: 0.75
%, P: 0.010%, S: 0.003%, Al: 0.
(019%) by continuous casting, and after heating this slab to 1100 ° C., hot rolling, cooling, winding, primary annealing, cold rolling, and secondary annealing are sequentially performed under the conditions shown in Table 10. And 23 types of steel plates having a thickness of 2.5 mm. The sample No. 78 is a conventional material.

[0082]

[Table 10]

For these samples, the in-plane anisotropy was examined by a tensile test, and the uniformity of the structure in the thickness direction was examined by X-ray diffraction. In the tensile test, JIS No. 5 test pieces were sampled along the 0 ° direction (L direction), 45 ° direction (S direction), and 90 ° (C direction) with respect to the rolling direction, and the tensile speed was 10 mm / mi.
n, a tensile test was performed, and tensile properties in each direction were measured. Table 11 shows the results. Note that Δ _max described in each column of the yield strength, tensile strength, total elongation, and r value in Table 11 was used.
Indicates the maximum difference between the tensile property values in the L, S, and C directions. Table 11 shows the uniformity of the structure in the sheet thickness direction with respect to the steel sheet surface, the sheet thickness １ ／, and the sheet thickness 1.
The results obtained by examining the integrated reflection intensity of the plane parallel to the rolling plane at each position of / 2 are also shown.

[0084]

[Table 11]

As shown in Table 11, No. 1 of the present invention example.
56-No. 69 is Δ of yield strength and tensile strength
_max is 20MPa or less, the elongation of the delta _max 1.5% or less, delta _max of r value is less than 0.2, the anisotropy of the tensile properties in the plane is very small is confirmed. Furthermore, it was confirmed that the method of performing induction heating before the rough rolling is more preferable from the viewpoint of not only reducing the in-plane anisotropy of the tensile properties but also improving the uniformity of the structure in the thickness direction.

On the other hand, in the comparative example, _Δmax was increased in any of the tensile properties, and it was confirmed that the in-plane anisotropy was poor. For example, if the primary annealing temperature is high (No.73), the delta _max is 0.34 in r value, when the cold rolling reduction is 30% and lower (No.75) is the yield strength, tensile strength and Δ _{max of} r value is 1
9, 13, and 0.41 and all had large in-plane anisotropy. In addition, the conventional materials No. Sample _No. 78 also had a high r-value _Δmax of 0.42 and large in-plane anisotropy.

(Embodiment 6) In this embodiment, an example of a third method for producing a second high carbon steel sheet will be described. JIS
G4051 component system equivalent to S35C (by mass, C: 0.
34%, Si: 0.19%, Mn: 0.73%, P:
0.012%, S: 0.001%, Al: 0.021
%) Of the slab is manufactured by continuous casting, and
After heating to 100 ° C. and hot rolling, finish rolling, cooling, winding, primary annealing, cold rolling, and secondary annealing are sequentially performed under the conditions shown in Table 12, followed by 1.5% temper rolling. To produce 22 types of steel plates having a thickness of 2.5 mm. The sample No. 100 is a conventional material.

[0088]

[Table 12]

For these samples, 0
° direction (L direction), 45 ° direction (S direction), 90 ° (C
JIS No. 5 test piece was taken along the
A tensile test was performed at 0 mm / min, tensile properties in each direction were measured, and in-plane anisotropy was evaluated. Table 1 shows the results.
3 is shown. Incidentally, the yield strength in Table 13, the tensile strength, total elongation, and the delta _max described in the respective columns of r values, L of each of the tensile characteristic value, S, indicates the maximum disparity in the C direction.

[0090]

[Table 13]

As shown in Table 13, No. 1 of the present invention example.
79-No. 92 is the Δ of the yield strength and the tensile strength.
_max is 10MPa or less, the elongation of the delta _max 1.5% or less, delta _max of r value is less than 0.2, the anisotropy of the tensile properties in the plane is very small is confirmed. Further, the finish-rolled steel sheet is cooled at a cooling rate of 7 ° C./s or more to A
r ₃ −100 ° C. and the cooled steel sheet
Holding at a temperature range of ６640 ° C. for 2 to 10 seconds, and then winding the steel plate after hot finish rolling at 500〜630 ° C.,
From the viewpoint of improvement of ductility, it was confirmed that it was more preferable.

On the other hand, in the comparative example, it was confirmed that the ductility was low, or _Δmax was large in any of the tensile properties, and the in-plane anisotropy was poor. For example, if the primary annealing temperature is high (No.96) is, delta _max is 0.37 in r value, the cold rolling reduction is 40%
When the lower case (No.99), yield strength, tensile strength and delta _max is respectively 14, 18 and 0.3 for r value
In each case, the in-plane anisotropy was large. In addition, the conventional materials No. 100 also extends is approximately 36%, delta _max of r value was as high as 0.42, in-plane anisotropy is large. Thus, it was confirmed that the inventive examples exhibited higher elongation and reduced anisotropy in tensile properties as compared with comparative examples having the same component system and plate thickness.

(Embodiment 7) This embodiment also shows an example of the third method for producing the second high carbon steel sheet. JIS G
4802 S65C-CSP equivalent component system (by mass
C: 0.64%, Si: 0.20%, Mn: 0.75
%, P: 0.010%, S: 0.003%, Al: 0.
Slab is manufactured by continuous casting, and the slab is heated to 1100 ° C. and hot-rolled. Then, under the conditions shown in Table 14, finish rolling, cooling, winding, primary annealing, cold rolling, and secondary rolling are performed. Annealing was sequentially performed to produce 22 types of steel plates having a thickness of 2.5 mm. At this time, the cooling rate after hot rolling was changed by adjusting the amount of water and the water pressure on the line-out table. The sample No. 122 is a conventional material.

[0094]

[Table 14]

For these samples, 0 to the rolling direction
° direction (L direction), 45 ° direction (S direction), 90 ° (C
JIS No. 5 test piece was taken along the
A tensile test was performed at 0 mm / min, tensile properties in each direction were measured, and in-plane anisotropy was evaluated. Table 1 shows the results.
It is shown in FIG. Incidentally, the yield strength in Table 15, the tensile strength, total elongation, and the delta _max described in the respective columns of r values, L of each of the tensile characteristic value, S, indicates the maximum disparity in the C direction.

[0096]

[Table 15]

As shown in Table 15, no.
101-No. 114 is the Δ of the yield strength and the tensile strength.
_max is 20MPa or less, the elongation of the delta _max 2.0% or less, delta _max of r value is less than 0.2, the anisotropy of the tensile properties in the plane is very small is confirmed. Further, the finish-rolled steel sheet is cooled at a cooling rate of 7 ° C./s or more to A
r ₃ −100 ° C. and the cooled steel sheet
Holding at a temperature range of ６640 ° C. for 2 to 10 seconds, and then winding the steel plate after hot finish rolling at 500〜630 ° C.,
From the viewpoint of improvement of ductility, it was confirmed that it was more preferable.

On the other hand, in the comparative example, _Δmax was increased in any of the tensile properties, and it was confirmed that the in-plane anisotropy was poor. For example, if the primary annealing temperature is high (No.118), the delta _max 0.44 next to the r value, when the cold rolling reduction is 40% and less (No.121) is
Yield strength, delta _max tensile strength and r values respectively 1
8, 18, and 0.32, all of which had large in-plane anisotropy. In addition, the conventional materials No. 122 is also r
The value _Δmax was as high as 0.44, and the in-plane anisotropy was large.

[0099]

As described above, according to the present invention,
A high carbon steel sheet for processing having small in-plane anisotropy of tensile properties can be obtained. In addition, a high carbon steel sheet for processing excellent in ductility in addition to low in-plane anisotropy of tensile properties can be obtained. Therefore, the high-carbon steel sheet obtained by the present invention can be manufactured by integrally forming a steel sheet by providing the gear part or the like to a gear part or the like that requires high dimensional accuracy. It can be manufactured at a lower cost than in the case of When induction hardening is performed on the teeth of the gear, the distance between the high-frequency coil and the circumferential portion is kept constant, so that the characteristics of the teeth can be homogenized in the circumferential direction.

[Brief description of the drawings]

FIG. 1 is a view showing the influence of a primary annealing temperature and a secondary annealing temperature on an in-plane anisotropy of an r value in a first method for producing a second high carbon steel sheet of the present invention.

FIG. 2 is a view showing the influence of the primary annealing temperature and the secondary annealing temperature on the in-plane anisotropy of the r value in the second method of manufacturing the second high carbon steel sheet of the present invention.

FIG. 3 is a view showing a relationship between a primary annealing temperature and a secondary annealing temperature affecting an in-plane anisotropy of an r value in a third method of manufacturing a second high carbon steel sheet according to the present invention.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Noboru Shioya 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Inside Nihon Kokan Co., Ltd. (72) Inventor Yasuyuki Takada 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Katsutoshi Ito 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Yoshihiro Hosoya 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan 4K037 EA06 FC07 FE01 FE02 FE03 FF02 FG03 FJ04 FJ05

Claims (6)

[Claims] 1. JIS G 4051 (carbon steel for machine structure), JIS G4401 (carbon tool steel), JIS
A high-carbon steel sheet having a component system defined by G4802 (cold rolled steel strip for spring), wherein the in-plane anisotropy index Δr of the r value is more than −0.15 to less than 0.15. A high carbon steel sheet for processing with small in-plane anisotropy characterized by the following characteristics. However,
Δr indicates a value defined by Δr = (r0 + r90−2 × r45) / 4. Where r0, r45, r90
Are 0 ° direction (L direction) with respect to the rolling direction, respectively.
The r values in the 45 ° direction (S direction) and the 90 ° direction (C direction) are shown. 2. JIS G 4051 (carbon steel for machine structure), JIS G4401 (carbon tool steel), JIS
G-4802 (cold-rolled steel strip for springs).
After descaling the rolled steel sheet, 630 to 7
High carbon steel sheet for working with small in-plane anisotropy characterized by subjecting to primary annealing at 00 ° C for 20 hours or more, cold rolling at a reduction of 50% or more, and then secondary annealing at 600 to 710 ° C. Manufacturing method. 3. JIS G 4051 (carbon steel for machine structure), JIS G4401 (carbon tool steel), JIS
G 4802 A high carbon steel sheet having a component system defined by (cold spring rolled steel strip), small planar anisotropy, wherein the delta _max of r value is less than 0.2 High carbon steel sheet for processing. However, Δ _max is 0 ° (L direction), 45 ° direction (S direction), 90 ° with respect to the rolling direction.
Indicates the maximum disparity in the value in the ° direction (C direction). 4. JIS G 4051 (carbon steel for machine structure), JIS G4401 (carbon tool steel), JIS
G-4802 (cold-rolled steel strip for springs).
After descaling the rolled steel sheet, 630 to 7
Primary annealing at 00 ° C. for 20 hours or more, cold rolling at a rolling reduction of 50% or more, and then secondary annealing at a temperature satisfying the following formula (1): Manufacturing method of small high carbon steel sheet for processing. 960−0.5 × T ₁ ≦ T ₂ ≦ 1153-0.72 × T ₁ (1) where T ₁ : primary annealing temperature (° C.), T ₂ : secondary annealing temperature (° C.) 5. JIS G 4051 (carbon steel for machine structure), JIS G4401 (carbon tool steel), JIS
A casting slab having a component system defined by G 4802 (cold rolled steel strip for spring) is continuously cast or heated to a predetermined temperature after cooling, and then roughly rolled by a rough rolling mill to form a rough bar, Subsequently, when finish rolling is performed by a continuous hot finishing rolling mill, the rough bar or the rolled material is Ar at the entrance side of the finishing rolling mill or between stands of the finishing rolling mill.
Induction heating to a temperature of ₃ transformation point or more, winding of the steel plate after hot finish rolling at a temperature of 500 to 650 ° C., and then descaling the wound steel plate, and then 630 to 7
Primary annealing at 00 ° C. for 20 hours or more, then cold rolling the annealed steel sheet at a rolling reduction of 50% or more, and then secondary annealing at a temperature satisfying the following equation (2). Manufacturing method of high carbon steel sheet for processing with small in-plane anisotropy. 950−0.49 × T ₁ ≦ T ₂ ≦ 1160−0.72 × T ₁ (2) where T ₁ : primary annealing temperature (° C.), T ₂ : secondary annealing temperature (° C.) 6. JIS G 4051 (carbon steel for machine structure), JIS G4401 (carbon tool steel), JIS
G 4802 (cold rolled steel strip for springs) is rolled at a finishing temperature of not less than the Ar ₃ transformation point in a hot rolling step at a finishing temperature of not less than 7 ° C./s. At a cooling rate of Ar ₃ -100 ° C., keeping the cooled steel sheet in a temperature range of 560 to 640 ° C. for 2 to 10 seconds, and then winding the steel sheet after hot finish rolling at 500 to 630 ° C. Then, after descaling the wound steel sheet, 640 to 7
Primary annealing is performed at 00 ° C. for 20 hours or more, and then the annealed steel sheet is cold-rolled at a rolling reduction of 50% or more, and then subjected to secondary annealing at a temperature satisfying the following expression (3). A method for producing a high carbon steel sheet for processing having excellent ductility and small in-plane anisotropy. 1015−0.58 × T ₁ ≦ T ₂ ≦ 1230−0.83 × T ₁ (3) where T ₁ : primary annealing temperature (° C.), T ₂ : secondary annealing temperature (° C.)