WO2009107856A1

WO2009107856A1 - Cold-rolled steel sheet and process for production thereof

Info

Publication number: WO2009107856A1
Application number: PCT/JP2009/054102
Authority: WO
Inventors: 妻鹿哲也; 中村展之; 小林崇; 長滝康伸; 壁谷隆昌
Original assignee: Ｊｆｅスチール株式会社
Priority date: 2008-02-29
Filing date: 2009-02-26
Publication date: 2009-09-03
Also published as: CN101960036B; TWI395822B; JP2009228128A; CN101960036A; KR20130032393A; TW200946696A; KR20100102739A; JP5320990B2; US20110048588A1; MX2010009448A

Abstract

A cold-rolled steel sheet which has high hardness and exhibits excellent edge properties in blanking and excellent flatness even at enhanced temperatures and which is suitable for use in a clutch plate or ring, a clutch disc, or the like. A cold-rolled steel sheet which has both a composition containing by mass C: 0.01 to 0.15%, Si: 0.03% or less, Mn: 0.10 to 0.70%, P: 0.025% or less, S: 0.025% or less, Al: 0.01 to 0.05% and N: 0.008% or less and satisfying the relationship: (C%) + 0.15×(Mn%) + 0.85×(P%) > 0.21 with the balance consisting of Fe and unavoidable impurities, and a partially recrystallized structure having a mean ferrite grain diameter of 2 to 10μm and a degree of unrecrystallization of 25 to 90% and which exhibits Rockwell hardness (HRB) of 83 or above by virtue of the composition and the structure.

Description

Technical field

The present invention relates to a cold rolled copper plate excellent in strength, punching workability, and heat deformation resistance, which is suitable for use in a clutch plate, a sink port nizer ring, a clutch disk, and the like, which are mechanical parts for automobile transmissions, and a method for producing the same. It is about. Background art

Automobile transmissions are composed of clutch plates, synchronizer rings, clutch discs, etc., and transmit driving force and absorb heat generated by friction. Such parts are manufactured by punching steel plates into a ring. The transmission has a structure that transmits torque by stacking many such ring-shaped plates, and its functions require wear resistance and flatness of the plates. Therefore, the required properties of the steel sheet, which is the raw material, are required to be excellent in hardness, properties during punching (perforated surface properties such as flatness and burrs), and small deformation during heating, that is, excellent heat resistance.

Conventionally, as a material for clutch plates of automatic transmissions (hereinafter referred to as AT), S 3 5 C cold-rolled steel sheets are mainly used among machine structural steels specified in JISG 3 3 1 1. It was. This S 3 5 C cold-rolled steel sheet is manufactured in the process of “slab → hot rolling → pickling → annealing → cold rolling”. S 3 5 C cold-rolled steel sheet contains a lot of C (about 0.35% by mass), so the hot-rolled copper sheet has high hardness, so it aims to spheroidize and soften the carbide before cold rolling. Therefore, annealing for a long time of several hours or more is essential. Therefore, it is very disadvantageous in terms of cost for automobile parts that require low prices.

Patent Document 1 discloses a technique that omits annealing of a hot-rolled steel sheet before cold rolling. In other words, a hot-rolled steel sheet with a softness with C of 0.25 mass% or less, Cold rolled steel sheets for AT clutch plates have been proposed that have the desired hardness and surface roughness and are excellent in wear resistance and punchability by cold rolling. However, due to the residual stress during cold rolling, the properties of the punched end face of the copper plate deteriorate significantly during the punching process, and when the temperature rises, thermal distortion occurs and the flatness of the ring-shaped product There was a problem that the remarkably decreased.

In Patent Document 2, as a technique for improving the residual stress after cold rolling described above, a steel sheet after cold rolling is further used with a large roll having a roll diameter of 300 mm or more and a reduction ratio of about 1%. A cold-rolled copper sheet for AT clutch plates has been proposed in which residual stress is reduced by rolling down. In this method, the difference in strain introduced between the front and back surfaces of the steel sheet is reduced, which improves the properties of the punched end face during press punching, but does not release the residual stress inside the copper plate. Deformation due to thermal strain was inevitable when the temperature rose, and the flatness of the ring-shaped product was remarkably lowered.

Patent Document 3 proposes a steel plate for an AT clutch plate that has been subjected to steel plate surface roughness adjustment processing such as pickling to optimize the surface roughness and is excellent in adhesion to a friction material. After hot rolling and pickling, this sheet is preferably annealed at 500 to 800¾ for 3 hours or more to spheroidize the carbide, and then after temper rolling or cold rolling at a rolling reduction of 1% or more, the surface roughness of the steel sheet Although the adjustment process is performed, the remarkable decrease in the flatness of the ring-shaped product due to the residual stress after cold rolling has not been solved as in Patent Document 1 and Patent Document 2.

Patent Document 1: JP 2003-277883 A

Patent Document 2: JP 2005-200712 A

Patent Document 3: Japanese Patent Laid-Open No. 2004-107722 Disclosure of Invention

The present invention advantageously solves the above-mentioned problems, has high hardness suitable for use in clutch plates, rings, clutch disks, etc., and also has end face properties during punching and flatness when temperature rises. The object is to provide an excellent cold-rolled steel sheet together with its advantageous manufacturing method. Hereinafter, the elucidation process of the present invention will be described.

In order to eliminate the negative effects caused by the residual strain of conventional steel plates for clutch plates, instead of using cold-rolled steel as a raw material as in the past, annealing is performed after cold rolling to reduce residual strain. An open cold-rolled annealed plate may be used as the material. However, when it is completely recrystallized by annealing, the required hardness cannot be obtained.

Therefore, the inventors have intensively studied to solve this problem, and as a result, the steel structure does not become a complete recrystallized structure by annealing after cold rolling, but a part of the unrecrystallized structure remains. In addition to ensuring a desired hardness by using a partially recrystallized structure, problems caused by residual strain, that is, deterioration of end face properties during punching and deterioration of flatness due to thermal strain during temperature rise The knowledge that it is reduced is obtained.

In other words, when the recrystallized structure and the non-recrystallized structure coexist, no rolling strain remains in the recrystallized structure. Therefore, the end surface properties deteriorate during punching and the flatness deteriorates when the temperature rises. In addition, since the rolling strain remains in the non-recrystallized structure, it was investigated that this partial residual strain and the refinement of the recrystallized grains together ensure the necessary hardness. It is.

It was also found that the hardness of the steel sheet is greatly influenced by C, Mn and P in the steel components, and that the required strength can be obtained stably by adding appropriate amounts of these.

The present invention was developed after various studies based on the above findings.

The gist of the present invention is as follows.

1. In mass%,

C: 0.01 to 0.15%,

Si: 0.03% or less,

Mn: 0.10-10.70%,

P: 0.025% or less,

S: 0.025% or less,

A1: 0.01-0.05% and

N: 0.008% or less And these components are represented by the following formula (1)

(C%) + 0.15 X (Mn%) + 0.85 X (P%) ≥ 0.21

However, (M%) indicates the content (mass%) of element M

The balance is the composition of Fe and inevitable impurities, the ferrite average grain size is 2-10 / m, and the unrecrystallized rate is 25% or more and 90% or less. A cold-rolled copper sheet characterized by a Rockwell hardness of at least 83 HRB.

2. Mass%

C: 0.01-0.15%,

Si: 0.03% or less,

Mn: 0.10 to 0.70%,

P: 0.025% or less,

S: 0.025% or less,

A1: 0.01-0.05% and

N: 0.008% or less

And these components are represented by the following formula (1).

(C%) + 0.15X (Mn%) + 0.85X (P%) ≥0.21 (1)

However, (M%) indicates the content (mass%) of element M

Satisfies the relationship, the slab balance consisting Fe and inevitable impurities, finishing temperature: hot rolling at Ar ₃ transformation point or more,卷取temperature taken plated at a temperature of at 580-750, followed A method for producing a cold-rolled steel sheet, characterized by cold rolling at a reduction ratio of 65% or more after pickling and then annealing at a temperature of 680 or less by continuous annealing. Brief Description of Drawings

Figure 1 is a graph showing the relationship between C * = (C%) + 0.15X (Μη%) + 0 · 85Χ (P%) and hardness (HRB). BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be specifically described.

First, the reason why the structure of the copper plate is limited as described above in the present invention will be described.

Average ferrite particle diameter: 2 to 10 / z m

In order to ensure sufficient hardness, it is necessary that the average ferrite grain size is in an appropriate range. If the average ferrite grain size exceeds 10 / z m, the desired hardness cannot be obtained. On the other hand, if it is less than 2 / z m, the hardness is excessively increased and the press punchability is reduced. The preferred ferrite average particle size is in the range of 4-8 / zm. ,,

In the present invention, the average ferrite grain size is obtained in accordance with the cutting method described in JIS G 0551 (Appendix) by observing the thickness cross section in the rolling direction of the copper plate.

Non-recrystallization rate: 25% or more and 90% or less

The greatest feature of the cold-rolled steel sheet of the present invention is that it has a partially recrystallized structure composed of an unrecrystallized structure and a recrystallized structure. In order to ensure the hardness of the steel sheet, it is necessary to contain a certain amount of non-recrystallized grains in which the rolling strain applied to the steel sheet during cold rolling remains. In order to improve punching processability and heat deformation resistance, it is necessary to contain a certain amount of recrystallized structure. In other words, the ratio of the unrecrystallized structure to the recrystallized structure is important in order to combine high hardness, punching workability, and heat distortion resistance.

Here, in order to obtain a desired hardness due to the effect of rolling strain, the non-recrystallization rate must be 25% or more. However, when the non-recrystallization rate exceeds 90%, the recrystallized grains are remarkably reduced, punching workability is deteriorated, and the residual stress is excessively increased to deteriorate the flatness. 90% or less. More preferably, it is in the range of 40% to 80%. The non-recrystallization rate can be determined by observing the thickness cross section in the rolling direction of the steel sheet, obtaining the ratio (area ratio) of the non-recrystallized structure in the entire structure, and setting this as the non-recrystallized ratio. .

Next, the reason why the component composition of the steel sheet is limited as described above in the present invention will be described. Unless otherwise specified, the “%” label for ingredients means mass%.

C: 0.01 to 0.15%

C is an important element from the viewpoint of the hardness and wear resistance of cold-rolled steel sheets, and both hardness and wear resistance increase as the C content increases. Therefore, the desired hardness and wear resistance can be obtained. Therefore, the amount of C should be 0.01% or more. On the other hand, when the C content exceeds 0.15%, the punching workability deteriorates. In addition, the deformation strain difference between the front and back during punching increases, and the deformation due to thermal strain increases as the temperature rises, so the flatness of the punched material deteriorates. Therefore, the amount of C is limited to the range of 0.01 to 0.15%. A preferable amount of C is in the range of 0.05 to 0.15%, and more preferably in the range of 0.10 to 0.15%.

Si: 0.03% or less

If the amount of Si exceeds 0.03%, defects due to scale are likely to occur on the surface of the hot-rolled copper sheet, and it is difficult to completely remove the scale even after pickling after hot rolling. Become. For this reason, defects due to scale are likely to occur on the surface of the hot-rolled copper sheet, deteriorating the surface condition of the steel sheet, and as a result, adversely affecting the surface properties of the annealed steel sheet after cold rolling. Therefore, the Si amount is limited to 0.03% or less. Preferably, it is 0.02% or less, and may be 0%. In the current refinement technology, the lower limit of the Si content is about 0.005% without a significant increase in steelmaking costs.

Mn: 0.10-10.70%

Mn is an element that has the effect of fixing S as an impurity in steel as precipitates (MnS) and reducing the adverse effects caused by S. In order to obtain this effect, the Mn content must be 0.10% or more. On the other hand, if the amount of Mn exceeds 0.70%, the hardness of the steel sheet excessively increases and the punching processability is lowered. This is because Mn strengthens the steel by solid solution strengthening. Also, if the Mn content exceeds 0.70%, defects due to scale are likely to occur on the surface of the hot-rolled steel sheet, and even if pickling is performed after hot rolling, the scale can be completely removed. It becomes difficult. As a result, the surface properties of the annealed steel sheet after cold rolling are also adversely affected, and the desired surface roughness cannot be obtained. Therefore, the amount of Mn was limited to the range of 0.10 to 0.70%. The Mn content is preferably 0.50% or less, and a more preferable Mn content is in the range of 0.20 to 0.50%.

P: 0.025% or less

P is an element that strengthens steel by solid solution strengthening. However, if the P content exceeds 0.025%, it may cause slab cracking and surface defects on the steel sheet. In addition, the hardness of the steel is significantly increased, and punching workability deteriorates. Therefore, the P content is limited to 0.025% or less. The preferred amount of P is 0.023% or less. When the amount of P is less than 0.01%, the effect on strengthening is poor, so 0.01% or more is preferable.

S: 0.025% or less

S is an element present as an impurity in steel. In particular, when S exceeds 0.025%, coarse inclusions are formed, starting from this, causing work cracks, leading to a significant decrease in punching workability. S also affects the scale peelability of hot-rolled steel sheets. If the amount of S exceeds 0.025%, the surface properties after pickling deteriorate, and as a result, the steel sheet after cold rolling is annealed. The surface roughness is also roughened. Therefore, the S content is limited to 0.025% or less. Preferably, it is 0.020% or less.

A1: 0.01-0.05%

A1 is an element to be included for deoxidation of steel. If the amount of A1 is less than 0.01%, a sufficient deoxidation effect cannot be obtained. On the other hand, even if the amount of A1 exceeds 0.05%, the deoxidation effect is saturated. Therefore, the amount of A1 was limited to a range of 0.01 to 0.05%. A preferable amount of A1 is in the range of 0.03 to 0.05%. N: 0.008% or less

N is an element present in copper as an impurity. If the amount of N exceeds 0.008%, the steel sheet is excessively hardened and the punching workability is lowered. Therefore, the N content is limited to 0.008% or less. Preferably, it is 0.005% or less.

As described above, the essential components have been described. However, in the present invention, it is not sufficient that each component satisfies the above-described composition range. In particular, for (:, Mn, and P, it is necessary to satisfy the following formula (1): C * = (C%) + 0.15X (Mn%) + 0.85X (P%) ≥0.21 · · · · (1)

In the present invention, elements that greatly affect the hardness of the copper plate are C, Mn, and P, and this C * is an index of hardness in the steel plate of the present invention. The reason for limiting C * will be described with reference to FIG. 1 created based on Example 1 described later. There is a proportional relationship between C * and hardness (HRB) as shown in Fig. 1. When the value of C * is 0.21 or more, the desired hardness is 83 HRB or more. Therefore, in the present invention, the condition of the above formula (1) is satisfied for C *. In the steel sheet of the present invention, the components other than the above are Fe and inevitable impurities. However, as long as the effects of the present invention are not impaired, the inclusion of components other than those described above is not rejected. Next, the reason why the hardness and surface roughness of the steel sheet are limited as described above in the present invention will be described.

Hardness (HRB): 83 or more

Transmission has a structure that transmits torque by stacking a number of steel plates punched into a ring. Accordingly, the steel sheet used is required to have wear resistance, and a hardness (HRB) that can ensure the wear resistance: 83 or more is required. When the hardness is less than 83 HRB, a decrease in wear resistance becomes a problem, so it is necessary to set it to 83 HRB or more. If the hardness exceeds 95 HRB, defects in the punching shape and cracks and cracks occur in the steel plate during punching.

In order to improve the wear resistance, it is preferable that the surface roughness is small. In the steel sheet of the present invention, it is preferable that the surface roughness is 0.3 / xm or less in terms of arithmetic average roughness Ra. The lower limit of the surface roughness that can be achieved without significantly increasing the manufacturing cost is about 0.1 l jt m at the current technical level.

Next, the manufacturing method of the cold rolled steel sheet of this invention is demonstrated.

The slab with the above composition is hot-rolled at a finishing temperature of Ar ₃ transformation point or higher, the cutting temperature is 580 to 750 ° C, and the hot-rolled steel sheet is pickled and then reduced. Rate: After cold rolling at 65% or more, annealing is performed at a temperature of 680¾ or less in a continuous annealing furnace.

There are no particular restrictions on the method of manufacturing the slab, and any conventional method may be followed. From the viewpoint of production efficiency and slab quality, slab melting and forging are preferably performed using a converter and a continuous forging machine.

In hot rolling, the finishing temperature needs to be higher than the Ar ₃ transformation point in view of the quality of hot-rolled steel sheet and the efficiency of hot rolling. When the finishing temperature is lower than the Ar ₃ transformation point, the ferrite transformation in the hot-rolled steel sheet is promoted, and coarse grains are formed on the surface layer, resulting in a problem that the hardness is lowered. Subsequent scraping requires the scraping temperature to be in the range of 580 to 750¾. When the temperature is less than 580 ° C, the crystal grains become excessively fine and the hot-rolled steel sheet becomes hard due to cooling strain, resulting in cooling. Impairs hot rolling property. On the other hand, when the coiling temperature exceeds 750, the average particle size of the fly is coarsened after winding, and the surface properties are degraded due to excessive acceleration of scale formation on the surface of the steel sheet, and the surface roughness is significantly degraded. To do. A preferred scraping temperature is in the range of 600-720 ° C. The Ar ₃ transformation point can be obtained by thermal expansion measurement using a differential thermal dilatometer or the like. The hot-rolled copper sheet is pickled according to a conventional method, removed from the scale of the steel sheet surface, and then subjected to cold rolling. The rolling reduction of cold rolling needs to be 65% or more. This is necessary in order to reduce the surface roughness as well as to increase the hardness by making the ferrite grains fine in the annealing performed after cold rolling. On the other hand, the upper limit of the rolling reduction is not particularly limited. However, when cold rolling is performed at a high rolling reduction exceeding 85%, the shape of the steel sheet after rolling is reduced, the thickness accuracy is lowered, and cold rolling is performed. There is a concern that productivity will decrease due to excessive rolling load on the mill. Therefore, the rolling reduction is preferably 85% or less.

Cold-rolled steel sheets are annealed in a continuous annealing furnace. In the present invention, it is particularly important to perform annealing at a temperature lower than the recrystallization completion temperature after cold rolling. When the annealing temperature exceeds the recrystallization completion temperature, the yarn after annealing! ; Almost 100% of the weave becomes a recrystallized structure, so the rolling strain introduced during cold rolling disappears. Therefore, the desired high hardness cannot be obtained. Therefore, by setting the annealing temperature below the recrystallization completion temperature, a partially recrystallized structure in which unrecrystallized grains and recrystallized grains are mixed can be obtained.

In the method of the present invention, the ratio of the unrecrystallized ratio is determined by the annealing temperature, and the unrecrystallized ratio can be 25% or more by setting the annealing temperature to 680 or less. The lower limit of the annealing temperature is not particularly limited, but is preferably 500 ° C. or more from the viewpoint of the temperature and atmosphere controllability and productivity of the continuous furnace. The cooling rate after annealing is not particularly limited, but is preferably about 5 to 25 ° C / s. Furthermore, during this cooling process, the heat treatment is performed in the temperature range of 320 to 420. This means that the shape stability of the steel sheet and the surface roughness adjustment during temper rolling when temper rolling is applied. Is advantageous. -The unrecrystallized rate can be adjusted as appropriate according to the annealing temperature. The relationship between the unrecrystallized rate and the annealing temperature is, for example, the apparent unrecrystallized rate determined as follows and the unrecrystallized rate. A relationship with the annealing temperature for obtaining the above is obtained in advance, and based on this relationship, the annealing temperature for obtaining a desired non-recrystallization rate may be adjusted.

(Apparent unrecrystallization rate) = (HRB (P) _HRB (S)) / (HRB (H) -HRB (S)) X 100 (%) However,

-HRB (P): Rockwell hardness of copper sheet annealed at a specified temperature (B scale)

-HRB (S): Rockwell hardness (B scale) of steel sheet annealed at a temperature at which it completely recrystallizes.

-HRB (H): Rockwell hardness of steel sheet annealed at a temperature at which no recrystallization occurs (B scale)

In determining the apparent non-recrystallization ratio, the hardness of the steel sheet that has been cold-rolled and water-quenched after the cold-rolled steel sheet is measured in order to exclude hardness fluctuations due to the cooling conditions after annealing. Is preferred.

In addition, the relationship between the apparent non-recrystallization rate and the steel plate hardness obtained as described above is obtained in advance, and based on this relationship, the apparent non-recrystallization rate is obtained from the hardness of the steel plate after annealing. It is also possible to estimate the unrecrystallization rate of the copper plate.

The cold-rolled steel sheet after annealing may be lightly rolled by temper rolling. This is to adjust the surface roughness and further improve the hardness. For example, in order to obtain a preferable surface roughness of Ra≤0.3 m, the rolling rate is preferably 2% or more in terms of elongation. The upper limit of the rolling rate is not particularly limited, but if the rolling rate is excessively high, the shape of the copper plate varies. Considering the ability of a rolling mill for temper rolling, the rolling rate is preferably 5% or less in terms of elongation.

Example

Example 1

Slabs with the composition shown in Table 1 were heated to 1200T, then hot-rolled with a finishing temperature equal to or higher than the Ar ₃ transformation point, then cooled on a run-out table and scraped at 600 to obtain hot rolled steel sheets. The plate thickness was 5 mm. Next, after removing the scale by pickling, it is cooled at a reduction ratio of 70%. Cold rolled to a cold rolled steel sheet with a thickness of 1.5 mm. The cold-rolled steel sheet was degreased and then annealed at 650 ° C by continuous annealing. The annealing time was 1 minute. After annealing, the copper plate was cooled at a rate of 10 / s, then kept at 320 to 420 for 2.5 minutes, and then cooled to room temperature. Furthermore, in the temper rolling line, rolling was performed under a light reduction at a rolling rate (elongation rate) of 3.0%.

Table 1 shows the results of examining the ferrite average grain size, non-recrystallization ratio, surface roughness, hardness, punching workability, and heat deformation resistance of the steel sheet thus obtained.

Each survey item was measured by the following method.

Ferrite average particle size

After cutting and grinding a specimen (sheet thickness section in the rolling direction) from a steel plate, the ferrite grain boundaries were revealed, and photographed by observing with an electron microscope at a magnification of 800 times, JIS G 0551 (Appendix) It was determined according to the ferrite grain size test method (JIS G 0552 (1998)) for steel by the described cutting method.

Unrecrystallized rate

As in the case of obtaining the average ferrite grain size, the non-recrystallized ratio was obtained by observing the sheet thickness cross section in the rolling direction at a magnification of 800 times to obtain the area ratio of the non-recrystallized structure, which was defined as the non-recrystallized ratio.

Surface roughness

In accordance with the measurement method stipulated in JIS B0601, arithmetic average roughness Ra was obtained.

Hardness (HRB)

A sample having a size of 20 X 60 imn was cut out from the steel sheet and measured according to the Rockwell hardness test method specified in JIS Z 2245. The measurement was performed at 10 points on the B scale, and the average value was taken as the hardness.

(HRB).

Punching workability

With a press punching machine, punching dimensions: inner diameter 140 mm x outer diameter 160 strokes, clearance: ring-shaped specimens punched at 10% of the plate thickness (plate thickness: 1.5 mm), The punched end face was observed with an optical microscope with a magnification of 10 to 20 times and evaluated according to the following criteria: • Good (O): No cracks or voids were found on the punched end face, and burrs and extreme sagging were observed. There is no occurrence. • Defect (X): Cracks or voids are found on the punched end face, or Paris has occurred.

Heat-resistant deformation

The same ring-shaped test piece that was evaluated for punching workability was heated at 300 for 30 minutes and then evaluated by the amount of warpage of the test piece when air-cooled to room temperature. A warp amount of 0.1 or less is good.

The amount of warpage was measured as follows. Heat and air-cooled test material is polished on both sides with # 800 or more emery single abrasive paper, then placed on a surface plate and measured using a contact-type height gauge to measure the height of 10 points in the circumferential direction. The difference from the plate thickness at the same location measured with a meter was determined, and the maximum value was taken as the amount of warpage.

table 1

Note) Underline indicates outside the proper range.

As shown in Table 1, all of the inventive steels have the desired ferrite average grain size, unrecrystallized ratio, and surface roughness, and are confirmed to be excellent in hardness (HRB), punching workability and heat distortion resistance. It was.

Example 2

A slab having the composition shown in Table 2 was heated to 1250 ° C, hot-rolled at the finishing temperature shown in Table 3, cooled on a run-out table, and scraped at 650. The thickness of the hot-rolled steel sheet was 3-10 mm. Next, the scale was removed by pickling, and then cold-rolled at a reduction ratio in the range of 50 to 80% to obtain a cold rolled steel sheet having a thickness of 1.5 thighs. After degreasing the cold-rolled steel sheet, it was annealed in a continuous annealing furnace. The annealing temperature was set at various temperatures below 680, and the annealing time was 1 minute. After annealing, the copper plate was cooled at a rate of 10 / s, then kept at a temperature range of 320 to 420 ° C for 2.5 minutes, and then cooled to room temperature. Furthermore, in the temper rolling line, the rolling rate (stretching rate) is in the range of 0 to 3.5%.

Rolled with light reduction.

The Ar ₃ transformation point shown in Table 2 is the differential thermal dilatometer for specimens taken from each copper slab, heated at 1250 for 30 minutes and then cooled at a cooling rate of 1 ° C / second. Measured with

Table 3 shows the results of examining the average grain size, non-recrystallization ratio, surface roughness, hardness (HRB), punching workability and heat distortion resistance of the steel plates obtained by strengthening.

Table 2 (mass%)

Note) Underline indicates outside the proper range.

Table 3

Note) Underline indicates outside the proper range.

As shown in Table 3, in the copper types A, I and J, which are invention steels, the finishing temperature during hot rolling, the rolling reduction during cold rolling, the annealing temperature, and the rolling rate during temper rolling (elongation rate) When all of the above are within the proper range, the desired average ferrite particle size, unrecrystallized ratio and surface roughness can be obtained, and excellent hardness (HRB), punching workability and heat distortion resistance can be obtained. It could be confirmed.

On the other hand, for steel types B to H, which are comparative copper, even if the finishing temperature during hot rolling, the rolling reduction during cold rolling, and the annealing temperature are all within the appropriate ranges, Either the unrecrystallized rate or the surface roughness was outside the proper range, and as a result, the hardness (HRB), punching workability and heat distortion resistance as good as expected in the present invention were not obtained.

For Examples 1 and 2, the apparent non-recrystallized rate was determined as follows, but a result equivalent to the apparent non-recrystallized rate determined as described above was obtained.

(Apparent unrecrystallization rate) = ((HRB (P))-(HRB (S)) ') / ((HRB (H)) — (HRB (S)),) X 100 (%)

,,

However,

(HRB (P)) ': Rockwell hardness of steel sheet with partially recrystallized structure (B scale) (HRB (S))': Rockwell hardness of steel sheet with completely recrystallized structure (B scale) Le)

(HRB (H)) ': Rockwell hardness (B scale) of a steel plate that does not contain any recrystallized structure. (HRB (S))' and (HRB (H)) 'are obtained as follows. It was. The pre-annealed cold-rolled steel sheet was heated at 580 and 780 for 100 seconds or less, then water-quenched, and the hardness (HRB) measurement and microstructure observation were performed on each sample. The sample with a heating temperature of 580 was confirmed to contain no recrystallized structure, and the hardness (HRB) was measured to give (HRB (H)) '. On the other hand, for the sample with a heating temperature of 780 ° C, the hardness (HR B) was measured after confirming that it had a completely recrystallized structure, and was set as (HRB (S)) '. Industrial applicability In accordance with the present invention, by adjusting the copper component, and by making the steel structure a partially recrystallized structure, it is suitable for use in components of automobile transmissions such as clutch plates, with high strength (high hardness). A cold-rolled sheet having excellent punchability and heat distortion resistance can be obtained. According to the present invention, annealing after cold rolling can be performed in a short time of less than 1 hour, and can be performed in a continuous annealing furnace with extremely high production efficiency. It can be manufactured without incurring uplift, and is therefore suitable for use in auto parts with severe price competition.

Claims

The scope of the claims

1. By mass%

C: 0.01-0.15%,

Si: 0.03% or less,

Mn: 0.10 ~ 0.70%,

P: 0.025% or less,

S: 0.025% or less,

A1; 0.01-0.05% and

N: 0.008% or less

And these components are represented by the following formula (1)

(C%) + 0.15X (Mn%) +0.85 X (P%) ≥0.21 (1)

However, (M%) indicates the content (mass%) of element M

The balance is composed of Fe and inevitable impurities, the ferrite average grain size is 2 to 10 / m, and the non-recrystallization rate is 25% or more and 90% or less. Cold-rolled steel sheet, characterized in that its mouth has a mouth-well hardness of 83 or more in HRB.

2. Mass%

C: 0.01-0.15%,

Si: 0.03% or less,

Mn: 0.10-70%,

P: 0.025% or less,

S: 0.025% or less,

A1: 0.01-0.05% and

N: 0.008% or less

And these components are represented by the following formula (1)

(C%) + 0.15X (Mn%) +0.85 X (P%) ≥0.21

However, ', (M%) indicates the content (mass%) of element M

The remaining slab is composed of Fe and unavoidable impurities in the balance. Finishing temperature: Hot-rolled at the Ar ₃ transformation point or higher, Cutting temperature: Scraped at a temperature of 580-750, Just After pickling, cold-roll at a reduction ratio of 65% or more, and then anneal at a temperature of 680 ° C or lower by continuous annealing.

A method for producing a cold-rolled steel sheet.