JP2002060849A - Manufacturing method of high carbon steel sheet with excellent workability - Google Patents

Abstract

(57) [Abstract] [Problem] It has excellent workability, good hardenability,
To provide a steel sheet having good dimensional accuracy by quenching and tempering. SOLUTION: In mass%, C: 0.15 to 0.45%,
Si: 0.25% or less, Mn: 0.3% or less, Cr:
0.5% or less, Ti: 0.01 to 0.06%, B: 0.
0003-0.005%, the balance of steel substantially consisting of Fe is hot-rolled and annealed at a temperature not higher than the Ac ₁ point. Alternatively, hot rolling and cold rolling are performed, and annealing is performed at a temperature equal to or lower than Ac ₁ point. Thereby, a high carbon steel sheet having excellent workability is obtained.

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 having excellent workability used for clutch parts, chain parts, automobile parts and the like.

[0002]

2. Description of the Related Art A high carbon thin steel sheet is usually formed into a predetermined shape by machining such as cutting, punching, bending, and drawing, and then subjected to heat treatment such as quenching and tempering to adjust to a required strength. After quality, it is often applied to the intended use.
Therefore, at the steel plate stage, it is important that it is soft and has excellent workability. Since the high-carbon steel sheet is premised on obtaining high-strength mechanical properties by heat treatment, it contains a large amount of C and contains a lot of alloying elements, so that it is inevitable that workability is inferior.

[0003] However, if it is possible to form a complex shape by press working, it is possible to reduce the manufacturing cost far more than forming by cutting or welding, and the demand for workability of a high carbon thin steel sheet is increasing more and more. There is a tendency. at the same time,
In automotive products, individual parts have been reduced in size due to demands for weight reduction and the like. The dimensional accuracy required for miniaturization of parts has naturally become stricter, and the requirements for dimensional changes due to quenching and tempering heat treatment have become stricter along with processing accuracy.

[0004] For example, a drive plate incorporated in an automatic transmission of an automobile has conventionally been S-type.
The SC material such as 45C was cut, quenched, and tempered. The gear portion was manufactured by welding and shrink fitting to a plate made of ordinary steel or the like. However, from the viewpoint of reducing the weight of automobiles and reducing costs by omitting steps, it has been studied to integrally form the plate and the gear portion. As one of the integral forming methods, there is a method in which a steel plate is pressed and then the gear portion is rolled. Also, the arm pole incorporated in the recliner sheet has a part in which the gear is formed by fine blanking on the inside with half-blanking. These also tend to reduce the size of the gear module due to the demand for weight reduction and miniaturization.
Cannot obtain sufficient workability. In addition, the strength is secured by heat treatment of quenching and tempering, but in this case, the dimensional accuracy due to the heat treatment is strictly required due to the internal gear teeth. This requirement becomes increasingly severe as modules become smaller.

[0005] Japanese Unexamined Patent Publication Nos. Hei 8-3687 and Hei 1 disclose methods for improving workability and hardenability.
There is Japanese Patent Application Laid-Open No. 0-259449.

JP-A-8-3687 discloses a technique for adjusting the particle size and amount of spheroidized annealed carbide. However, the steel sheet manufactured by this technique has insufficient workability for the above-mentioned required applications, and there is no disclosure of any technique for improving the dimensional accuracy by quenching and tempering.

[0007] Japanese Patent Application Laid-Open No. Hei 10-259647 discloses that the hardenability is 10 <30C + 5Mn + 6Cr + 300B.
Is disclosed to adjust the workability to a component satisfying 5> 10C + Mn + 150S. The steel plate manufactured according to this description is used as a steel plate for a drive plate by roll forming. However, the steel sheet manufactured by this technique also has insufficient workability for severe roll formability, and there is no disclosure of a technique relating to dimensional accuracy by heat treatment.

[0008] Spheroidizing annealing is essential in order to improve the workability of a high carbon steel sheet. When performing spheroidizing annealing in the form of a coil, it is usual to perform annealing for a long time under the temperature of Ac _1. However, if conventional steel is used in this method, it is necessary to perform annealing for a long time, and variations in the material inside the coil may occur. There is a disadvantage that it becomes larger.

Japanese Patent Application Laid-Open No. H10-25157 discloses a technique for solving this problem. The spheroidizing annealing of this technique is performed in a hydrogen atmosphere in an Ac ₁ point to (Ac ₁ point + 3
0 ° C) in a temperature range of 1 to 10 hours,
It is characterized in that it is gradually cooled to a temperature lower than (Ar ₁ point-50 ° C.) at a cooling rate of 20 ° C./h. In the technique of this publication, workability is evaluated based on the total elongation of a tensile test. However, the workability of a high carbon steel sheet is not evaluated solely by total elongation, but rather is often correlated with other properties, for example, local elongation. Regardless, there are many applications in which workability is inferior to conventional materials. Also, this publication is hardened,
There is no disclosure of technology regarding dimensional accuracy during tempering and tool life during fine blanking.

[0010] Therefore, it is desired to provide a steel sheet having good workability, quenching strength, and dimensional accuracy at a low cost.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide a steel sheet which has the problems of the prior art, such as extremely excellent workability, good hardenability, and good dimensional accuracy by quenching and tempering.

[0012]

Means for Solving the Problems As a result of intensive studies on the above-mentioned problems of the prior art, it has been necessary to add Mn of more than 0.30% in order to secure hardenability.
When i and B are added, even if the Mn content is 0.30% or less, sufficient hardenability can be ensured, and not only the dimensional change during quenching is reduced, but also the workability is dramatically improved, and spheroidization is achieved. It has been found that annealing can be completed in a short time and the problems of the prior art such as long annealing time can be solved.

The present invention has been completed on the basis of this finding, and the gist of the present invention is as follows: C: 0.15 to 0.45
%, Si: 0.25% or less, Mn: 0.3% or less, C
r: 0.5% or less, Ti: 0.01 to 0.06%, B:
0.0003 to 0.005%, the remainder substantially consisting of Fe is hot-rolled, annealed at a temperature of ₁ point or less, or a cold-rolled hot-rolled steel sheet, and then cooled to a temperature of ₁ point or less. The present invention is directed to a method for producing a high carbon steel sheet having excellent workability, characterized by annealing at a low temperature.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

C is an element necessary for securing strength after heat treatment such as quenching and tempering of a product. However, when the amount of C added is large, workability is deteriorated. For this reason, the upper limit of the C content was specified to be 0.45%. On the other hand, when the amount of C decreases, the strength after quenching does not increase, so the lower limit was specified to be 0.15%.

[0016] Si is an element used as a deoxidizing agent when smelting steel. However, if the addition amount is large, the workability is deteriorated. The lower limit does not need to be particularly defined. However, even if the Si content is reduced to 0.005% or less, the effect of improving the workability is saturated, and the refining cost also increases. Is preferred.

Mn is one of the important constituent elements of the present invention. When the Mn content is 0.3% or less, the workability is dramatically improved, and at the same time, the spheroidizing speed of carbides is rapidly increased during spheroidizing annealing, so that the annealing temperature can be lowered and the annealing time can be shortened, so that the production cost can be reduced. Can also be lower. Also, the dimensional change due to quenching and tempering is reduced. For these reasons, the upper limit of the amount of Mn was specified to 0.3%. The preferred range is 0.2% or less for the same reason. On the other hand, Mn is an element necessary for fixing S causing hot embrittlement as MnS. For this reason, it is preferable to add the Mn amount to 0.05% or more. The reason why the workability is drastically improved by reducing the Mn content to 0.3% or less is not clear, but the present inventors have found that the transformation behavior after hot rolling, the spheroidization behavior of carbide, the cold rolling / annealing. It is thought that this affects the ferrite grain size and carbide size distribution in relation to the recrystallization behavior at the time.

[0018] Cr is well known as an element for improving hardenability. On the other hand, when the addition amount is large, the spheroidization of the carbide is delayed, and the workability of the steel sheet is deteriorated. Therefore, C
The upper limit of the amount of r was specified to 0.5%.

Ti combines with N to form TiN, which is effective in refining γ grains during quenching, and increases the ratio of B which contributes to the improvement of quenchability by being combined with B to increase the quenchability. Enhance. Therefore, it is necessary to add 0.01% or more. On the other hand, when the addition amount increases, the steel sheet is hardened,
In order to deteriorate the workability, it is necessary to add 0.06% or less, but it is preferable to add 0.03% or less.

It is well known that B is an element that segregates at the grain boundary during quenching and lowers the grain boundary energy, thereby improving the quenchability even when added in a small amount. The addition amount effective for hardenability is 0.0003% or more. On the other hand, if the addition amount exceeds 0.005%, the toughness after the heat treatment is adversely deteriorated. For this reason, the upper limit was specified at 0.005%.

P is an impurity element which hardens the steel sheet and deteriorates the toughness after the heat treatment.
It is desirable to keep it below.

S is an element that causes hot embrittlement, and at the same time, is an impurity element that becomes an inclusion in the steel as MnS and TiS and deteriorates the workability of the steel sheet. Since the refining cost increases to reduce the S content, the present invention requires 0.001 to 0.008.
%.

When Al is used as a deoxidizer during steelmaking, it has a role of fixing N in steel as AlN.
As the amount of addition increases, it causes surface defects.
When the amount of addition is low, inclusions increase in the oxide system and workability is deteriorated. Therefore, the content may be included in the range of 0.01 to 0.06%.

N is one of the elements that are inevitably mixed. However, if the amount of N is increased, it is combined with B and the amount of B effectively acting on hardenability is reduced. However, since the refining cost becomes high to reduce the N content to 0.0025% or less, the present invention requires 0.0025%.
It is preferable to carry out in the range of -0.006%.

Such steel is melted in a usual converter or electric furnace, and if necessary, subjected to vacuum degassing. The molten steel is made into a slab by continuous casting or the like, and hot-rolled to produce a hot-rolled coil. Although the present invention is not particularly affected by hot rolling conditions, the hot rolling finish temperature is preferably performed just above the Ar ₃ point. This is because if the hot rolling finish temperature is too high,
It becomes a structure in which pearlite and ferrite are dispersed in layers,
This is because the unevenness of the structure cannot be eliminated even by annealing, and the workability of the high carbon steel sheet is impaired. On the other hand, if the hot-rolling finishing temperature is lower than the Ar ₃ point, the shape of the steel sheet deteriorates, and stable hot-rolling becomes difficult, and at the same time, the cooling after hot-rolling becomes non-uniform and the material variability becomes large, which is not preferable.

Since the characteristics of the present invention do not depend on the coiling temperature of hot rolling, there is no need to specify it. In the present invention, 5
It is mainly performed in the range of 50 to 650 ° C.

The hot-rolled coil is descaled by a method such as pickling.
Is annealed. This annealing is Ac₁Perform at a temperature below the point
There is a need. Ac₁Annealing at a temperature above the
Or coarse carbides are formed.
At the same time as the processability of
Shortening tool life during ranking molding. Conventionally, Ac ₁
Annealing below the point required a long time for carbide spheroidization
However, in the steel of the present invention, carbide spheroidization is extremely fast,
, The annealing time does not need to be increased.

In the case where the thickness accuracy, surface texture, and workability are required, the descaled hot-rolled coil or the spheroidized coil is annealed after cold rolling. The cold rolling reduction in this case is not particularly specified as long as it is within a range in which the required sheet thickness and sufficient shape control can be performed.
%. Annealing after cold rolling also needs to be performed at a temperature of not more than Ac ₁ point.

The annealed coil is temper-rolled if necessary, and is supplied to a product.

[0030]

EXAMPLES Steel having the composition shown in Table 1 was melted in a converter, a continuous cast slab was produced, and hot-rolled coils having a thickness of 5.0 mm and 7.0 mm were formed by hot rolling under the conditions shown in Table 2. Manufactured by. After pickling the coil, the 5.0 mm thick coil was annealed as it was, and the 7.0 mm thick coil was cold rolled to 5.0 mm thickness and then annealed under the conditions shown in Table 2. After each of the annealing coils was subjected to temper rolling of 1.0%, an arm pole of an internal tooth type sheet recliner module: 0.3 was manufactured by fine blanking. Cracks in the appearance of the formed arm poles, visual observation of the presence or absence of cracks, and observing the cross section of the tooth tip with the highest degree of processing with an optical microscope, observing the appearance and optical microscopy without micro cracks, ○, Cracks were not observed in the external appearance observation, but those in which microcracks were observed in optical microscopic observation were evaluated as “△”, and those in which cracks were observed in external appearance observation were evaluated as “x”. Also,
The number of molded articles that can be continuously molded with one tool and obtain a good product shape was investigated. 860 ° C x 5
A heat treatment of quenching by heating for 0 min and a tempering of 400 ° C. × 50 min were performed, and the hardness after the heat treatment and the product dimensional change before and after the heat treatment were measured. In the case where the appearance crack was observed in the fine blanking process, the quenching and tempering heat treatments were not performed. Table 2 shows the obtained scores of moldability, tool life, hardness, and dimensional change.

[0031]

[Table 1]

[0032]

[Table 2]

A-1, B-1, C-1, D-1, E-
1, F-1 is an example in the range of the present invention manufactured by hot rolling-annealing-temper rolling. In each case, the moldability of fine blanking is good, the tool life is long, the hardness after quenching and tempering heat treatment is high, and the dimensional change due to heat treatment is small. G-1 is an example in which the amounts of Ti and B are out of range, and M-1 is an example in which the amount of C is out of the range of the present invention. Although this steel sheet has excellent fine blanking properties, it has low hardness after heat treatment and has insufficient hardenability.

H-1 and I-1 are examples in which the amount of Mn is out of the range of the present invention. A steel sheet having an Mn content outside the range of the present invention has poor formability at the time of fine blanking or has a short tool life. In addition, the dimensional change due to heat treatment is large, making it unsuitable for products requiring precise dimensional accuracy. J-1 has a Cr content,
K-1 is an example in which the amount of Si is L and L-1 is an example in which the amount of C is out of the range of the present invention.

A-2, B-2, C-2 and E-2 are hot rolled.
It is an Example within the scope of the present invention manufactured by cold rolling-annealing-temper rolling. All steel sheets have good fine blanking formability, long tool life, small dimensional changes due to quenching and tempering, high quenching hardness, and have both excellent quenchability and fine blanking properties. F-2 is an example within the scope of the present invention manufactured by hot rolling, pickling, annealing (710 ° C. × 16 hours), cold rolling, annealing (690 ° C. × 16 hours), and temper rolling. It can be seen that this steel sheet also has excellent fine blanking properties and excellent quenching properties. G-2 to M-2 are examples in which steel components produced by hot rolling, pickling, annealing, and temper rolling are outside the scope of the present invention. T
G-2 in which i and B contents are out of the range of the present invention has hardenability of
H-2 and I-2 whose amounts are out of the range of the present invention are inferior in the fine blanking property and hardenability to the examples within the range of the present invention. J-2 with a Cr content not less than the range of the present invention, K-2 with a Si content not less than the range of the present invention, L-2 with a C content not less than the range of the present invention have a short tool life at the time of fine blanking or a heat treatment at the time of heat treatment. Fine blanking property and hardenability are not compatible with each other due to large dimensional change. M whose C amount is below the range of the present invention.
-2 is unsatisfactory in hardness after quenching.

A-3 is an example in which the annealing is performed at a temperature equal to or higher than the Ac ₁ point although the composition is within the scope of the present invention.
This steel sheet has good hardness and dimensional change after heat treatment, but has microcracks during fine blanking, and has a short tool life and poor fine blanking properties.

[0037]

As described above in detail, the present invention can provide a steel sheet having both good fine blanking properties and hardenability. Also, as in the conventional case, annealing-cold rolling-
Without adopting a manufacturing process such as annealing, even a steel sheet obtained by directly annealing a hot-rolled sheet has fine blanking properties and hardenability more than conventional materials. This is an industrially useful invention because a steel sheet can be provided at a low cost.

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Shiro Sanagi 1-1 Futaba-cho, Tobata-ku, Kitakyushu Nippon Steel Corporation Yawata Works F-term (reference) 4K037 EA01 EA02 EA06 EA11 EA15 EA18 EA23 EA25 EA27 EA31 FC03 FC07 FE02 FF01 FF02 FG01 FH03 FJ04 FJ05

Claims (3)

[Claims] 1. A mass% of C: 0.15 to 0.45%,
Si: 0.25% or less, Mn: 0.3% or less, Cr:
0.5% or less, Ti: 0.01 to 0.06%, B: 0.
A method for producing a high-carbon steel sheet having excellent workability, characterized by hot rolling steel having a ratio of 0003 to 0.005%, with the balance being substantially Fe, and annealing at a temperature of ₁ point or less. 2. C: 0.15 to 0.45% by mass%
Si: 0.25% or less, Mn: 0.3% or less, Cr:
0.5% or less, Ti: 0.01 to 0.06%, B: 0.
Production of high-carbon steel sheets with excellent workability, characterized in that steel comprising 0003 to 0.005%, with the balance being substantially Fe, is hot-rolled and cold-rolled and then annealed at a temperature of ₁ point or less. Method. 3. C: 0.15 to 0.45% by mass%
Si: 0.25% or less, Mn: 0.3% or less, Cr:
0.5% or less, Ti: 0.01 to 0.06%, B: 0.
0003 to 0.005%, with the balance substantially consisting of Fe, hot-rolled, annealed at a temperature of ₁ point or less, cold-rolled, and annealed at a temperature of ₁ point or less. Of high carbon steel sheet with excellent heat resistance.