JP4438074B2 - Cold-rolled steel sheet for automatic transmission member and manufacturing method thereof - Google Patents

Description

  The present invention relates to a cold-rolled steel sheet and a manufacturing method that are suitably used as a separate plate, a friction plate, a backing plate, and the like, which are constituent members of an automatic transmission of an automobile.

  Components such as separate plates, friction plates, and backing plates (hereinafter referred to as “AT plates”) that make up automatic transmissions (abbreviated as “AT”) for automobiles are formed by press-punching a steel plate into an approximately circular shape, and friction. The plate and the separate plate are alternately overlapped with each other via a sheet-like friction material (friction paper), and a torque transmission mechanism is configured by assembling a backing plate or the like thereon.

Steel plates for AT plates require a certain level of wear resistance and a smooth surface for press molding, and are required to satisfy hardness (Hv): 230 or more and surface roughness Ra: 0.4 μm or less. As a material for the AT plate, a cold-rolled steel plate made of mechanical structural steel (typically S35C) described in JIS G3311 has been used. The manufacturing process is as follows.
“Steel making → continuous casting → hot rolling → pickling → annealing → cold rolling → temper rolling → refining”
In this manufacturing process, in order to satisfy the hardness and surface roughness (Hv ≧ 230, Ra ≦ 0.4 μm) required for the AT plate, the rolling reduction in cold rolling requires 50% or more. “Annealing” is performed prior to cold rolling because steel sheets that are hot-rolled are hard, so it is difficult to ensure stable operation of cold-rolling (rolling ratio ≧ 50%), and the hot-rolled steel sheet is coarse. This is because if the pearlite structure is carried over to the cold-rolled steel sheet, the press punching property is poor, and the punched surface of the product AT plate is likely to cause mussels and roughness. The annealing treatment (softening of hot-rolled steel sheet and carbide spheroidization treatment) for avoiding such problems is performed as batch-type tight coil annealing (TCA).

In addition, in a wet clutch plate assembly process of a transmission using an AT plate obtained by press punching a cold-rolled steel plate, the friction plate is overlapped with a separate plate after the friction paper is bonded to the plate surface. The friction paper is obtained by impregnating a thermosetting resin into a punched-out product of a paper made from a fiber base material (natural pulp, heat-resistant organic synthetic fiber, etc.). Adhesion of the friction paper to the friction plate is performed by applying a resin adhesive (for example, phenol-based resin) to the plate surface, overlaying the friction paper on the plate, and applying heat and pressure with a hot plate or the like.
Several proposals have been made for improvement of the cold rolled steel sheet for AT plate.
JP 2001-040448 A JP 2001-073073 A JP 2004-292939 A

  In the conventional cold rolled steel sheet manufacturing process for AT plates using S35C and other mechanical structural steels (JIS G3311), annealing before cold rolling is essential, and the treatment is performed in a batch process for a long time (equal level). Heat (approximately 10 hours), which is a major factor in increasing costs.

  The flatness of the AT plate is an important characteristic for the torque transmission function, and the flatness is required to be 0.15 mm or less immediately after the press punching. However, with the recent increase in the displacement and weight of automobiles, the diameter of the AT plate and the width of the punching bar have been reduced, and the shape of the AT plate tends to be complicated. Along with this, the tendency of distortion (deformation) of the plate surface of the AT plate obtained by press punching becomes remarkable, making it difficult to ensure the required flatness.

  Further, depending on the use of the AT plate, there may be a case where the wear resistance is particularly required for only a part of the outer peripheral portion of the plate. In such applications, after cold-rolled steel sheet is punched into a predetermined shape, it is necessary to harden only the necessary parts by laser quenching or induction quenching and adjust to the required hardness, which is better hardenability Is required.

  Furthermore, in order to configure a wet clutch plate by combining the friction plate (friction paper adhesion to the plate surface) with a separate plate to ensure a stable function, sufficient adhesion between the friction plate and the friction paper (applied to the friction plate) Required for the resin adhesive layer). However, since the steel sheet substrate generally has poor affinity with organic polymer resins, the surface of the steel sheet is roughened as a pretreatment to improve the adhesion, and the peeling resistance of the resin adhesive (friction) as an anchor effect due to fine unevenness. The adhesive strength of the paper is increased. As the surface roughening treatment, chemical methods including film formation by chemical conversion treatment, etching treatment with acid solution and rust prevention treatment are performed, but the treatment process is cumbersome and the cost burden required for waste liquid treatment Have problems such as large.

  The above-mentioned patent document discloses omission of annealing, improvement of hardenability, etc., but it can sufficiently meet these various requirements including problems such as flatness of the AT plate and resin adhesion. I can't say that. The present invention eliminates the annealing process before cold rolling, which is essential in the manufacturing process of the conventional cold-rolled steel sheet, and greatly reduces the manufacturing cost, while having a resistance equal to or higher than that of the conventional material (S35C material). In addition to ensuring wearability and punching workability, and ensuring stable flatness after press punching, it also has good hardenability to effectively achieve partial quenching strengthening. It is an object of the present invention to provide a cold-rolled steel sheet for an AT plate that improves the adhesiveness (adhesion) to a resin necessary for assembly and simplifies the surface roughening process and reduces costs.

The cold-rolled steel sheet for AT plates according to the present invention and the manufacturing method thereof are as follows.
(1) By mass%, C: 0.15-0.25%, Si: 0.25% or less, Mn: 0.3-0.9%, P: 0.03% or less, S: 0.015 % Or less, Al: 0.01 to 0.08%, N: 0.008% or less, Cr: 0.05 to 0.5%, Ti: 0.01 to 0.05%, B: 0.002 0.005%, the steel slab and the balance Fe and inevitable impurities was hot-rolled, Ri Na and cold rolling at a reduction ratio of 30% or more without annealing the hot rolled steel sheet, one surface of the steel sheet A cold-rolled steel sheet for an automatic transmission member having a tensile residual stress σ _T and the other surface having a compressive residual stress σ _C (Claim 1).

(2) The Cr amount of the cold rolled steel sheet for AT plate of item 1 is adjusted to 0.05 to 0.3% as desired (claim 2).
(3) The rolling reduction in the cold rolling of the cold rolled steel sheet for AT plate according to the above 1 or 2 is adjusted to a range of 30 to 50% as desired (Claim 3).

(4 ) The difference (σ _T −σ _C ) between the tensile residual stress (σ _T ) and the compressive residual stress (σ _C ) in the cold rolled steel sheet for AT plates of items 1 to 3 is 600 N / mm ² or less. ( Claim 4 ).

(5 ) The steel slab is hot-rolled at a hot rolling finish temperature: Ar ₃ transformation point or higher, a coiling temperature: 500-600 ° C., cold-rolled without annealing, and temper-rolled the cold-rolled steel sheet. After that, the automatic transmission according to any one of the above items 1 to 4 , wherein a leveler process is performed to provide a tensile residual stress on one surface of the steel sheet and a compressive residual stress on the other surface. A method for producing a cold-rolled steel sheet for members ( claim 5 ).

The steel composition of the cold-rolled steel sheet of the present invention has a lower C composition than the conventional material (S35C carbon steel), and as a C amount limiting effect, the amount of pearlite in the hot-rolled steel sheet is small and the hot-rolled steel sheet is softened. Further, it is possible to omit the annealing treatment for the purpose of softening the hot-rolled steel sheet and spheroidizing the carbide (Fe ₃ C) before cold rolling.

In addition to the above-mentioned regulation of the amount of C, the control of the steel structure by the combined addition of Cr and Ti and B and the accompanying material improvement effect are the most characteristic features of the present invention.
By adding Ti, fine precipitates (size: about 500 to 3000 mm) such as TiC and Ti (C, N) are formed in the steel, and the ferrite structure of the hot rolled steel sheet is remarkably refined. In a hot-rolled steel sheet, carbide preferentially precipitates at the ferrite grain boundaries, so that the carbide is uniformly and finely dispersed in the steel as an effect of refinement, and a structure advantageous in wear resistance is formed. Further, the coexistence of B and Ti increases the amount of dissolved B in the steel. This is because TiN is easier to produce than BN and the BN production reaction is suppressed. In addition to enhancing the hardenability of the steel sheet, the solid solution B has an effect of strengthening the grain boundaries and an effect of refining the ferrite structure of the hot-rolled steel sheet, thereby strengthening the matrix and further improving the wear resistance. Due to these effects, the required properties (Hv ≧ 230, Ra 0.4 μm or less) such as wear resistance comparable to conventional materials (S35C material) and beautiful punched surface properties, etc., are secured as cold rolled steel plates for AT plates.

Since Cr has a function of strengthening the matrix of the hot-rolled steel sheet, it is possible to set a reduction rate (cold rolling rate) in cold rolling lower than when Cr is not contained. In the conventional production of cold-rolled steel sheets for AT plates (using carbon steel such as S35C), a high cold rolling rate of about 50% or more is required to satisfy the required hardness (Hv: 230 or more). In the invention, due to the above effect (Cr matrix strengthening function), it is possible to satisfy the required hardness at a cold rolling rate of 30% or more. By reducing the cold rolling rate, it is possible to reduce the compressive residual stress generated in the center of the plate thickness. As a reduction effect of this compressive residual stress, the occurrence of deformation in press punching is mitigated, and the flatness of the AT plate is reduced. Ensuring is easy.
Cr also dissolves in the steel to enhance the hardenability of the cold-rolled steel sheet, and makes it possible to enhance the quenching of the required region such as the outer periphery of the plate by laser quenching, induction quenching or the like.

Furthermore, as an effect of adding Cr, the adhesiveness (peeling resistance) of the resin adhesive to the steel sheet surface is enhanced. This effect of improving adhesiveness can be obtained by treating (pickling) the surface of the steel sheet with an acid solution (such as a hydrochloric acid solution whose concentration is adjusted). Thereby, compared with the complicated roughening process which consists of combinations, such as the conventional chemical conversion treatment and a pickling process, a process is simplified and a cost burden is reduced greatly. In general, a carbon steel sheet is poor in the effect of improving the adhesiveness of the resin even if it is pickled (roughening by etching), but the effect of improving the adhesiveness in the steel sheet of the present invention is good. This is presumed that, in the pickling treatment, a chromium compound (hydroxide, etc.) having high affinity with the resin is formed on the surface together with the roughening, and the bond with the resin adhesive is strengthened. The

  In addition, applying a leveler process to the cold-rolled steel sheet before press punching to adjust the residual stress distribution in the thickness direction of the steel sheet as described above is remarkable in improving the flatness of the AT plate. This is considered to be due to the fact that the width of the stress distribution of the press punched molded product (AT plate) becomes smaller as an offset effect between the residual stress distribution adjusted by the leveler processing and the stress generated during press punching (described later). . According to the present invention, as the effect of superimposing the reduction of the cold rolling rate by the addition of Cr (reducing and reducing the residual stress of the cold rolled steel sheet) and the residual stress adjustment by the leveler processing, the large diameter size, the narrow width size of the crosspiece, etc. It is possible to easily guarantee the flatness standard (≦ 0.15 mm) even in an AT plate having a shape that easily causes distortion.

The reasons for limiting the steel composition of the present invention are as follows. All element contents are mass%.
C: 0.15-0.25%
From the point of increasing the hardness and wear resistance of the cold-rolled steel sheet, the higher the amount of C, the more advantageous. However, if it exceeds 0.25%, the annealing for softening and softening the carbide of the hot-rolled steel sheet is omitted. I can't do that. On the other hand, if the amount of C is too low, it becomes difficult to ensure the same wear resistance as that of S35C, which is a conventional material.

Si: 0.25% or less Si is added as a deoxidizing element in the steel melting process. For this purpose, it is sufficient to add up to 0.25%. Moreover, addition exceeding it causes the surface defect by the pickling processability of a hot-rolled steel sheet and the scale residue after pickling, and reduces the surface quality as an AT plate, so this is the upper limit.

Mn: 0.3 to 0.9%
Mn is added to prevent hot brittleness of the steel and strengthen the matrix. If less than 0.3%, the effect is small, the strength of the matrix is insufficient, and the wear resistance is low. The effect is increased by increasing the amount, but if it exceeds 0.9%, it becomes excessively hard and the workability is impaired.

P: 0.03% or less P is an impure component, and if present in a large amount in steel, it causes a decrease in grain boundary strength, causes dents caused by slab cracking, and impairs the surface quality of the AT plate. . If it is 0.03% or less, there is no substantial adverse effect, so this is the upper limit.

S: 0.015% or less S has the effect of suppressing hot brittleness by forming MnS, but if it is too much, it may cause work cracks starting from MnS, and AT plates may cause deterioration of surface properties in stamping. Invite. In addition, wear starting from MnS tends to occur and wear resistance is reduced. If it is 0.015% or less, the actual damage is avoided, so this is the upper limit.

Al: 0.01 to 0.08%
Al is added as a deoxidizer in the steel melting process. It also has the effect of fixing N in the steel as AlN. If it is less than 0.01%, the deoxidation action is insufficient. On the other hand, if it exceeds 0.08%, the cleanliness of the steel is impaired, surface flaws occur, and the surface quality of the steel sheet is deteriorated.

N: 0.008% or less N is an element inevitably mixed. If the content is increased, the amount of nitride (AlN, TiN, etc.) produced increases, leading to excessive hardening, so 0.008% or less is required.

Cr: 0.05-0.5%
Cr dissolves in the steel and partly forms carbides (precipitated particles) to act as solid solution strengthening and precipitation strengthening. With this matrix strengthening function, it is possible to set the reduction ratio (cold rolling ratio) in cold rolling required to ensure the hardness (Hv ≧ 230) required for the AT plate to be low. Lowering the cold rolling rate is effective in reducing the compressive residual stress generated in the center of the thickness of the cold rolled steel sheet and improving the flatness of the AT plate after press punching.
Moreover, hardenability is improved as a solid solution effect of Cr, and wear resistance is increased as a carbide precipitation effect. Even when required high wear resistance is required only for the required parts such as the outer periphery of the AT plate due to improved hardenability, selective quenching strengthening by laser quenching, induction quenching, etc. (so-called local quenching) Thus, the hardness can be adjusted effectively.
Furthermore, Cr increases the affinity for the resin adhesive on the plate surface, and is effective in improving the adhesiveness (peeling resistance) of the adhesive layer necessary for assembly of the clutch plate.
In order to acquire the said effect, 0.05% or more of containing is required. The effect is increased by increasing the amount, but an excessive increase is accompanied by a decrease in workability, impact properties, fatigue properties, etc., and should not exceed 0.5%. Preferably it is 0.3% or less, More preferably, it is 0.2% or less.

Ti: 0.01 to 0.05%
Ti generally has the effect of forming TiS to avoid hot brittleness. Furthermore, as described above, Ti forms fine precipitates such as TiC and Ti (C, N) in steel to refine the ferrite structure of hot-rolled steel sheets, and as a result, carbide is uniformly and finely dispersed, resulting in wear resistance. Sexuality is enhanced. In order to secure this effect, addition of 0.01% or more is required. On the other hand, if added in a large amount, excessive hardening is caused by excessive formation of fine precipitates, so 0.05% is made the upper limit.

B: 0.002 to 0.005%
Most of B forms solid solution B as described above, and strengthens the matrix by improving the hardenability by solid solution B, strengthening the grain boundary and refining the ferrite structure, thereby improving the wear resistance. Has the effect of increasing. To obtain this effect, at least 0.002% of addition is necessary. However, if it exceeds 0.005%, the ferrite structure becomes hardened due to excessive grain refinement, so this is the upper limit.

  Ni, Cu and the like are inevitably mixed in a normal melting process, but if they are in the range of 0.03% or less, there is no actual harm and mixing is allowed.

Next, the manufacturing process of the AT plate of the present invention will be described.
[Smelting and casting of steel]
First, steel melted to a predetermined chemical composition in a steelmaking furnace is made into a slab by ingot-making, ingot rolling, or by continuous casting, and after surface treatment of the slab is appropriately performed, it is hot-rolled. In the case of continuous casting, the hot slab (slab) may be inserted into a heating furnace as it is and rolled hot.

[Hot rolling]
Hot rolling is performed according to a conventional method, and the hot rolling finishing temperature is adjusted to be just above the Ar ₃ transformation point from the viewpoint of the quality of the hot rolled steel sheet and the hot rolling efficiency. The winding is preferably performed in a temperature range of 500 to 600 ° C. Low temperature winding below 500 ° C causes the crystal grain size to become excessively fine and hardens the hot-rolled steel sheet. On the other hand, high temperature winding above 600 ° C tends to agglomerate carbides and provide high wear resistance. This is because it is difficult to ensure uniform dispersion of the necessary carbides and the ferrite structure becomes coarse. Preferably it is 500-550 degreeC.

  The above hot-rolled steel sheet has been refined to a grain size of 5-15 μm (substantially not exceeding 10 μm) (JIS G0552 “Appendix 2 (normative) Judgment method by crossing line segment (grain size)”) Requires ferrite structure. A fine ferrite structure of less than 5 μm causes excessive hardening of the steel, while a coarse structure exceeding 15 μm causes problems such as insufficient wear resistance. This crystal grain size (5 to 15 μm) is stably ensured by the hot rolling conditions as an effect of the steel composition containing both the regulation of the C amount and a fixed amount of Ti and B. This refined ferrite structure ensures that the carbides in the steel in the final product (cold-rolled steel sheet) are more uniformly and finely dispersed, ensuring improved wear resistance and improved properties of the stamped end face. It becomes possible to do.

[Cold rolling]
The hot-rolled steel sheet is subjected to cold rolling after the surface scale is removed by pickling treatment. The rolling reduction in cold rolling is set to 30% or more. This is to ensure the necessary hardness and surface roughness (Hv ≧ 230, Ra ≦ 0.4 μm) as a cold rolled steel sheet for AT plates.
The hardness increases as the rolling reduction increases, but the compressive residual stress generated at the center of the plate thickness increases accordingly, which adversely affects the flatness of the AT plate after press punching. In particular, when the stamping of an AT plate having a large diameter and a narrow width of a crosspiece is performed, the influence becomes large. For this reason, it is desirable to limit to 50% or less. When performing leveler processing for residual stress control after cold rolling, a slightly higher rolling reduction is allowed, but in this case, it is advantageous from the viewpoint of operational stability to limit to about 60%. It is.
In addition, the surface roughness management of a roll is suitably implemented so that the required surface roughness may be ensured by the cold rolling of the rolling reduction of 30% or more for the rolling roll used for cold rolling.

  If desired, the cold rolling is performed in two stages of pre-rolling before pickling and finish rolling after processing. As a scale crushing effect by pre-rolling (before pickling treatment), the descaling property is greatly improved, and the pickling treatment time can be greatly shortened and the cost can be reduced. In this case, pre-rolling (before pickling treatment) and finish rolling (after pickling treatment) do not have to be continued, but a pre-rolling machine is provided on the entry side of the pickling tank and a finish rolling mill is provided on the exit side. It is advantageous from the standpoint of production efficiency to install and have a continuous configuration of pre-rolling-pickling treatment-finish rolling.

  The rolling reduction of the pre-rolling (before pickling treatment) in the two-stage rolling needs to be 25% or less. This is because if pre-rolling is performed at a high rolling reduction exceeding this range, wrinkles due to the pressing of the scale onto the steel sheet surface may occur, and the surface quality may be impaired. Preferably it is 10 to 20%. The reduction ratio in finish rolling (after pickling treatment) is set so that the total reduction ratio (= pre-rolling reduction ratio + finishing rolling reduction ratio) is 30% or more. The total reduction ratio is adjusted in this way, as in the case described above (cold rolling is carried out in one stage after pickling), as required characteristics (hardness: Hv ≧ 230, surface roughness) as an AT plate. Sa: Ra ≦ 0.4 μm).

[Temper rolling]
Temper rolling is performed to correct the shape of the cold-rolled steel sheet and relieve residual stress. The elongation is preferably adjusted to 1% or less. The shape correction effect by temper rolling is almost saturated at an elongation of 1%, and a higher elongation exceeding that only hardens the steel sheet unnecessarily. In the temper rolling, it is preferable to apply a large-diameter roll of 300 mm or more as a work roll from the viewpoint of the stress relaxation effect.

[Preparation]
In the present invention, (feature dimensions such as thickness and strip width, surface flaws, or the like) inspections conducted usually finishing line process other, for the purpose of improving the flatness of the flop-less punching the molded article (AT plate), cold Leveler processing for adjusting the residual stress in the thickness direction of the rolled steel sheet is performed.
The cold-rolled steel sheet has a stress distribution in which the central portion in the thickness direction is compressive residual stress and the surface layer is tensile residual stress. This is because, in the cold rolling process, the central portion in the plate thickness direction of the steel sheet tends to cause plastic deformation larger than the surface layer, and the surface layer attempts to constrain the plastic deformation. The inventors adjusted the stress distribution of the cold-rolled steel sheet by leveler processing, and conducted a detailed investigation on the relationship between the residual stress distribution in the thickness direction and the flatness of the AT plate obtained by press punching. As a result, as shown in FIG. 5, the leveler is previously set so that one side of the steel plate (the “front side” in the figure) has a compressive residual stress and the other side (the “back side”) has a tensile residual stress. The surface after compression is punched with the surface on the compressive stress side as the upper surface (sagging side) and the surface on the tensile stress side as the lower surface (burr surface), resulting in good flatness after press punching. I got the knowledge that I can do it.

In the leveler processing, for example, a leveler (roller leveler) composed of a plurality of rollers (5) arranged up and down as shown in FIG. 8 is used, and the residual stress is controlled on each of the inlet side and the outlet side. This is done by adjusting the amount of intermesh and passing through. The effect of improving the flatness by the leveler processing is that the difference Δσ (= σ _T −σ _C ) between the compressive stress σ _C (negative sign) of one surface and the tensile stress σ _T (positive sign) of the other surface is Remarkably expressed by adjusting the stress to 600 N / mm ² or less.

  The mechanism of flatness improvement by leveler processing is not necessarily clear, but is presumed as follows. In the press punching process, as shown in Fig. 6 (Fig. 1: Plan view, Fig. 2: XX arrow cross section), the corner portion a on the upper surface (sagging surface side) of the AT plate (3), which is a punched molded product Tensile stress is generated at the corners, and compressive stress is generated at the corner portion b of the lower surface (burr surface side) fixed by the mold (4). Therefore, if the stamping is performed in such a direction that the surface of the tensile residual stress of the steel sheet stress-adjusted by leveler processing is the burial surface and the surface of the compressive residual stress is the sagging surface, the residual stress distribution of the steel plate and the stress generated during the press punching are obtained. The stress distribution of the molded product (3) is offset and becomes a flattened pattern with a small width, as schematically shown in FIG. As an effect of improving the stress distribution, it is possible to easily satisfy the flatness standard (flatness ≦ 0.15 mm) even when the AT plate has a large diameter and the crosspiece has a narrow width.

  The annular AT plate obtained as a press-punched molded product does not require heat treatment for tempering and can be used as it is (as a hard-drawn material). In addition, when selective quenching strengthening of a specified region such as the outer peripheral portion of the plate is required, the hardness adjustment can be effectively achieved by laser quenching, induction quenching, or the like.

In assembling the clutch plate constituting the automatic transmission, the friction plate is coated with a resin adhesive before being combined with the separate plate, and the friction paper is bonded through the adhesive layer. The outline of the process is as follows.
`` Degreasing and cleaning of plate surface → roughening treatment → application of adhesive → drying of adhesive layer (solvent volatilization) → adhesion of friction paper ''
During the above steps, the roughening treatment before applying the adhesive is a treatment for increasing the adhesion of the adhesive layer to the plate surface as described above. In the case of using the friction plate made of the cold-rolled steel sheet of the present invention, the roughening treatment is performed by pickling treatment (acid pickling) using an acid solution (for example, 20% hydrochloric acid aqueous solution, solution temperature 60 ° C.) whose concentration is adjusted. Liquid dipping → washing → drying) This pickling treatment provides good adhesion (peeling resistance) of the resin adhesive layer. Although the details of the mechanism have not been fully elucidated, in addition to the effect of roughening the plate (formation of fine pits by the etching action of the acid solution) as described above, the plate surface has good affinity with the resin This is thought to be due to the formation of chromium compounds. After the pickling treatment, the adhesive is applied and dried (solvent volatilization), followed by heat-pressure bonding of the friction paper using a hot plate or the like.

[1] Manufacture of test steel sheet The molten steel, which has been melted and adjusted by a converter and degassing equipment, is subjected to continuous casting to form a slab (200 mm thick), and the following process A (annealing omitted) or process B A cold-rolled steel sheet for AT plates is obtained by (annealing).
A: Hot rolling → Pickling → Cold rolling (1 or 2 rolling) → Temper rolling → Refinement (inspection)
B: Hot Rolling → Pickling → Annealing → Cold Rolling (Single Roll) → Temper Rolling → Refinement (Inspection)

(1) Steel composition See Table 1. Nos. 1 to 6 are invention examples, Nos. 11 to 17 are comparative examples in which the content of any element of C, Cr, Ti, and B (underlined) is not within the scope of the present invention, No. 21 -24 is a conventional material (S35C equivalent material).

(2) Hot rolling
(2.1) No.1-6
Heating temperature: 1230 ° C, Hot rolling finishing temperature: 860 ° C, Winding temperature: 540 ° C
Thickness of hot-rolled sheet: 2.8-4.0mm
(2.2) No.11 ~ 17
Heating temperature: 1230 ° C, Hot rolling finishing temperature: 860 ° C, Winding temperature: 540 ° C
Thickness of hot-rolled sheet: 3.3-5.1mm
(2.3) No.21 ~ 24
Heating temperature: 1230 ° C, Hot rolling finishing temperature: 850 ° C, Winding temperature: 600 ° C
Thickness of hot-rolled sheet: 4.0mm

(3) Annealing treatment
Conducted in No. 21-24 (S35C material) (No. 1-6 and No. 11-17 are not annealed).
Annealing method: Tight coil annealing (TCA)
Processing temperature: 700 ° C
Processing time: 10 hours

(4) Cold rolling
(4.1) No.1 ~ 6
Reduction ratio (total reduction ratio in the case of two-stage rolling): 35 to 55%
Product steel plate thickness: 1.8mm
(4.2) No.11-17
Reduction ratio (total reduction ratio in the case of two-stage rolling): 45 to 65%
Product steel plate thickness: 1.8mm
(4.3) No.21-24
Reduction ratio: 55%
Product steel plate thickness: 1.8mm
(5) Temper rolling Temper rolling ratio (elongation): 0.8%
Roll diameter: 350mm

[2] Evaluation test of various properties The above-described cold-rolled steel sheet was subjected to observation of the metal structure and the following test.
(1) Wear resistance test Using Ogoshi type rapid wear tester (see Fig. 1).
After the test under the following conditions, the width (b ₀ ) of the wear scar is measured, and the wear amount A (mm ³ ) is calculated from the volume of the worn portion. The wear resistance was evaluated by the specific wear amount [= A / (P × L) (mm ³ / kg · m)].
Test environment: Room temperature (14 ℃), in the air Rotating disc: SK5 / 400Hv (tempered by quenching and tempering)
Disc radius (r) 30mm, Disc thickness (B) 3.0mm
Wear distance (L): 200m
Load (P): 61.7N
Wear speed (V): 4m / sec

(2) Press punching test A separate plate was press punched, and the punching end face property was evaluated.
(2.1) Punching conditions Press machine: 200-ton mechanical press Stroke length: 250mm
Number of strokes: 25spm
Clearance: 10% (plate thickness 1.8mm)
Punching dimensions: Inner diameter 105 mm x Outer diameter 127 mm

(2.2) Evaluation of punched end surface properties Observation method: Judged by scanning electron microscope (magnification × 20) Observation cross section: Longitudinal cross section of steel sheet Evaluation criteria: Yes ... Beautiful punched end surface (no burrs or cracks)
× ... Muscle / crack (1 or more) is found on the punched end face

(3) Residual stress control by leveler processing and flatness test The cold rolled steel sheet of Invention Example No. 2 was used as a work material, and the test was performed under the following conditions.
(3.1) Leveler processing conditions and measurement of residual stress As shown in FIG. 8, the leveler has a roll configuration arranged in the upper three stages and the lower two stages (roll diameter d: both 90 mm, distance between roll centers s: 105 mm). use. Residual stress distribution was controlled by setting the entrance side mesh and the exit side mesh of the leveler to various values and passing the steel plate (in the direction of the arrow).
After leveler processing, a strip-shaped test specimen was cut out, etched with a ferric chloride solution from the surface layer on one side, and the change in curvature (change in curvature) before and after etching was measured to determine the residual stress (reference) : Published by Shigeru Yoneya, “Generation and Countermeasures for Residual Stress, Yokendo”)

(3.2) Measurement of flatness
After leveler processing, place the separate plate obtained by stamping on the platen, measure the circumferential height distribution of the separate plate with a laser displacement meter, and define the difference between the maximum and minimum height as flatness. did. The flatness immediately after the separation plate was punched was evaluated as follows according to the flatness standard of the AT plate (0.15 mm or less).
○: Flatness ≦ 0.15 mm
X: Flatness> 0.15 mm

[3] Results
(1) Metallographic structure Figures 2, 3 and 4 show Invention Example No. 2, Comparative Example No. 17 (Ti, B not added, Cr content insufficient , annealing omitted) and Comparative Example No. 21 (S35C equivalent material) ) Shows each organization. Comparative Example No. 17 exhibits a rough pearlite structure, while Inventive Example No. 2 has the carbides uniformly and finely dispersed despite the omission of annealing, and Comparative Example No. 21 (S35C Equivalent material) was observed to have a finely divided fine homogeneous structure equivalent to the annealed material.

(2) Mechanical properties and press punchability Table 2 shows the ferrite grain size (μm) of hot-rolled steel sheet, hardness (Hv) of product cold-rolled steel sheet (load: 98N), and surface roughness (Ra). The measurement results and the test results are shown together with the manufacturing conditions.
Invention examples (No. 1 to 6) have wear resistance equivalent to or higher than that of S35C (No. 21 to 24), which is a conventional material, and have the hardness and surface required as a cold-rolled steel sheet for AT plates. Roughness specifications (Hv ≧ 230, Ra ≦ 0.4μm) are fully satisfied. The press punching property is also good, and it has the same beautiful punching surface property as the conventional material (S35C).
In addition, it was observed that the invention examples (No. 1 to 6) can effectively achieve partial quenching strengthening according to the Cr content in a separate hardenability evaluation test (laser quenching of the outer periphery of the plate). It was. These properties are based on the chemical composition of the steel described above and the fine, fine and fine structure.

  On the other hand, in Comparative Examples No. 11 to No. 17, No. 11 (insufficient amount of C) is below the lower specification limit of hardness, and the wear resistance is significantly lower than that of the conventional material (S35C). No. 12 (excess amount of C) has good wear resistance, but is too hard and has poor punched surface properties. No. 13 (Ti deficiency), No. 14 (B deficiency), No. 17 (Ti, B, Cr deficiency) are inferior in wear resistance compared to the conventional material (S35C) and hardenability evaluation test (as described above) It was recognized that the results of the same) did not reach the invention examples (Nos. 1 to 6). No.16 (Cr excess) increased in hardness unnecessarily and was found to be inferior in press punchability.

(3) Flatness of AT plate (separate plate immediately after press punching) Table 3 shows the residual stress control by leveler processing and the measurement and evaluation results of the flatness of the press punched molded product (AT plate). : Cold rolled steel sheet of Invention Example No. 2).
As an indication of the front and back surfaces of the steel sheet, one surface is tentatively referred to as the “back surface” and the other surface is referred to as the “front surface”. The cold-rolled steel sheets used in No. 101 to 103 and No. 201 and No. 202 are subjected to leveler processing, the back surface is the tensile residual stress σ _T , the front surface is the compressive residual stress σ _C , and the stress difference Δσ It is a steel plate that has been stress adjusted so that (= σ _T −σ _C ) is 600 N / mm ² or less.
On the other hand, the cold-rolled steel sheets used in No. 301 and No. 302 have been subjected to leveler processing, but they are steel sheets with insufficient stress control effect (compressive residual stress on both front and back surfaces). The cold-rolled steel sheet used in No. 402 is a steel sheet that omits leveler processing (both front and back surfaces have tensile residual stress).

Nos. 101 to 103 (invention examples) were stamped with the front side (compression residual stress surface) of the steel sheet adjusted with the leveler as the residual stress and the back side (tensile residual stress surface) as the fray side. Thus, as an effect of offsetting the residual stress at the time of pressing, the obtained AT plate has a good flatness that sufficiently satisfies the flatness standard (0.15 mm or less).
On the other hand, No. 201 and No. 202 use cold-rolled steel sheets with the same stress adjustment as No. 101 to 103 above, but on the contrary to No. 101 to 103, the front surface (compressed residual stress) Since the surface is pressed with the fray side and the back surface (the surface of the tensile residual stress) is the punch side, there is no canceling effect of the residual stress, and the obtained AT plate is inferior in flatness. No. 301 and No. 302 have insufficient effect of adjusting the stress of the steel plate by the leveler, and No. 401 and No. 402 have omitted the leveler processing of the steel plate. It is inferior in flatness.

According to the present invention, in the manufacturing process of cold-rolled steel sheets used for AT plates (separate plates, friction plates, backing plates, etc.) of automobiles, etc., the conventional manufacturing process omits the annealing process, which has been indispensable. A cold-rolled steel sheet having wear resistance equal to or better than that of the material and sufficiently satisfying the required characteristics of the AT plate can be obtained. The AT plate of this cold-rolled steel sheet does not require heat treatment for tempering and can be used as it is (as a hard-drawn material). As these effects, the AT plate can be provided at a lower cost.
In connection with recent movements of automobiles, such as higher displacement and lighter weight, the AT plate has become larger in diameter and the width of the pulling bar has become narrower, and it has become difficult to ensure flatness as the shape changes. However, according to the present invention, it is possible to sufficiently cope with such a shape change and to ensure good flatness that sufficiently satisfies the flatness standard of the AT plate.
In addition, even when it is required to partially harden the outer periphery of the AT plate, it is possible to effectively achieve quenching strengthening and hardness adjustment of a required part by laser hardening or induction hardening. This increases the usefulness of the AT plate.

  Furthermore, the adhesion of the friction plate (friction paper to which the friction paper is required) to the clutch plate to the resin should be ensured by a simple treatment process such as pickling (soaking of the plate with acid solution, washing with water, and drying). Can do. This simplifies the friction paper bonding process, reduces the cost required to assemble the clutch plate, and improves the stability and durability of the clutch function due to the good adhesion of the friction paper. It is done. The cold-rolled steel sheet of the present invention is used as a material in various fields where wear resistance, press punchability, partial hardenability, adhesion with a resin film, etc. are required in addition to the use of AT plates. It contributes to quality stability and cost reduction.

It is explanatory drawing which shows the test point of abrasion resistance evaluation in the Example column. FIG. 2 is a drawing-substituting micrograph (magnification × 400) showing a metal structure of a test material (No. 2 cold-rolled steel sheet) in an example column. FIG. 3 is a drawing-substituting micrograph (magnification × 400) showing a metal structure of a test material (No. 17 cold-rolled steel sheet) in an example column. FIG. 3 is a drawing-substituting micrograph (magnification × 400) showing a metal structure of a test material (No. 21 cold-rolled steel sheet) in an example column.

It is explanatory drawing which shows typically the stress distribution of the cold rolled steel sheet in which the residual stress distribution was adjusted by the leveler process. It is explanatory drawing which shows typically the shape of a press stamping molded product, and the stress generation condition (1 figure: top view, 2 figures: XX arrow sectional drawing). It is a figure which shows typically the residual stress distribution of the press punching molded article using the cold-rolled steel plate which stress was adjusted by the leveler process. It is explanatory drawing which shows typically the leveler structure for adjusting the residual stress of the steel plate used in the Example column.

Explanation of symbols

1: Test material 2: Rotating disk (mating material)
3: Punched molded product (AT plate)
4: Mold 5: Roller

Claims (5)

In mass%, C: 0.15-0.25%, Si: 0.25% or less, Mn: 0.3-0.9%, P: 0.03% or less, S: 0.015% or less, Al: 0.01-0.08%, N: 0.008% or less, Cr: 0.05-0.5%, Ti: 0.01-0.05%, B: 0.002-0.005 %, the balance being hot rolled steel slab consisting of Fe and unavoidable impurities, hot-rolled steel sheet, Ri Na and cold rolling at a reduction ratio of 30% or more without annealing treatment, one surface of the steel sheet tensile A cold-rolled steel sheet for an automatic transmission member having a residual stress σ _T and the other surface having a compressive residual stress σ _C.   The cold-rolled steel sheet for automatic transmission members according to claim 1, wherein Cr: 0.05 to 0.3%.   The cold-rolled steel sheet for automatic transmission members according to claim 1 or 2, wherein the rolling reduction in cold rolling is 30 to 50%. 4. The cold rolling for an automatic transmission member according to claim 1 , wherein a difference (σ _T −σ _C ) between the tensile residual stress σ _T and the compressive residual stress σ _C is 600 N / mm ² or less. steel sheet. A steel slab is hot-rolled at a hot rolling finish temperature: Ar ₃ transformation point or higher and a coiling temperature: 500 to 600 ° C., and cold-rolled at a predetermined reduction rate without annealing, and the cold-rolled steel sheet is prepared. The steel sheet according to any one of claims 1 to 4 , wherein the steel sheet is subjected to leveling after the material is rolled, thereby giving a tensile residual stress on one surface of the steel sheet and a compressive residual stress on the other surface. Manufacturing method for cold-rolled steel sheets for automatic transmission members.