JP2007090360A - Method and apparatus for dispersing residual stress after straightening with leveler - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cold-rolled steel sheet, wherein the residual stress which is a primary factor for causing deformation accompanying with thermal strain is reduced as much as possible when heating and holding a punched material. <P>SOLUTION: After straightening the cold-rolled steel sheet which is paid off from a pay-off reel 1 with a leveler 2, light reduction rolling 5 is applied to the steel sheet at the draft of 0.2-1.0 and offered to a punching work 3. Then, the residual stress generated at the straightening with the leveler is removed by performing light reduction rolling after the straightening with the leveler and, after that, even when the steel sheet is heated to and held at a certain degree of temperature, the deformation with the thermal strain owing to the release of the residual stress does not occur. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention, for example, in a cold-rolled steel sheet for an AT plate or the like that is suitably used as a separation plate, friction plate, backing plate, etc., which is a component of an automatic transmission of an automobile, The present invention relates to a reduction method and apparatus.

  Separate plate (also called driven plate or mating plate), friction plate (also called drive plate, core-plate or disk), backing plate (retaining plate, reaction) constituting the automatic transmission (AT) of an automobile A member (hereinafter also referred to as “AT plate”) such as a plate or an end plate is a molded product obtained by press punching a steel plate into a substantially annular shape. The separate plate and the friction plate are members that are alternately arranged via a friction material, and a backing plate or the like is assembled thereto to constitute a torque transmission mechanism.

  Conventionally, as such a material for an AT plate, a steel for machine structure defined in JIS G3311, mainly a cold rolled steel sheet such as medium carbon steel, is used. And the cold rolled steel sheet for AT plates is manufactured in the process of "steel making-> continuous casting-> hot rolling-> pickling-> annealing-> cold rolling-> defatting-> refinement". And after punching this cold-rolled steel plate into a desired shape, the adhesive is applied, and the plate material on which the friction material is affixed is combined to manufacture an actual automatic transmission.

  When there is a step of performing a heat treatment during manufacture or when the temperature becomes high due to the environmental temperature during actual vehicle travel, the residual stress generated during cold rolling is released, and the plate material is deformed due to thermal distortion. In order to prevent the deformation caused by this thermal strain, in some cases, the plate material after punching is subjected to a press tempering treatment that heats and holds the plate at a high temperature to remove residual stress. Performing flattening. For this reason, when it was going to suppress the deformation | transformation accompanying heat distortion, the cost might be increased on the contrary.

It is necessary to reduce the residual stress of the cold-rolled steel sheet in order to prevent the plate material from being deformed due to thermal strain even when exposed to high temperatures. A method of mechanically reducing the residual stress of a cold-rolled steel sheet without performing heat treatment for removing stress has been proposed in Patent Document 1, Patent Document 2, and the like.
However, in the cold rolled steel sheet for AT plate as the object of the present invention, the plate thickness is as thick as 0.7 to 3 mm, and it is necessary to give an excessive tensile force in order to give a simple tensile deformation. The residual stress reduction proposed in the patent literature is not a realistic method.
Therefore, the applicant reduced the residual stress as much as possible by subjecting the cold-rolled steel sheet to light rolling at a rolling reduction of 0.2 to 1.0% using a roll having an outer diameter of 300 mm or more. A method to do this was proposed in Patent Document 3.
JP-A-1-99721 JP-A-63-273518 JP 2005-199316 A

By the way, when a coiled cold-rolled steel sheet slit to a predetermined width is paid out from a payoff reel and then punched into a desired shape such as an AT plate, punching is performed after a roller leveler is applied to correct curling habits. Processing is in progress. For example, in the case of a material having a Bauschinger effect such as a cold-rolled finish material of S35C, residual stress increases when correction is performed using a roller leveler. Even if the residual stress is reduced by applying the method proposed in Patent Document 3 to the cold-rolled steel sheet having such a Bauschinger effect, the residual stress increases when the leveler correction is performed at the previous stage of the punching process, Deformation occurs in the AT plate actually used.
The present invention has been devised to solve such problems, and a method for dispersing residual stress introduced by leveler correction of a cold-rolled steel sheet that is paid out from a payoff reel and subjected to punching. And an apparatus.

In order to achieve the object, the residual stress dispersion method after leveler correction of the present invention is applied to a cold-rolled steel sheet having a Bauschinger effect that is paid out from a payoff reel and subjected to punching after leveler correction. Light rolling is performed at a rolling reduction of 0.2 to 1.0%.
Moreover, the residual stress dispersion apparatus after leveler correction according to the present invention is an apparatus in which a roller leveler is disposed between a payoff reel and a press apparatus, and a light reduction rolling mill is further disposed between the roller leveler and the press apparatus. Features.

According to the present invention, the residual stress generated at the time of leveler correction is dispersed by subjecting the cold-rolled steel sheet having a Bausinger effect, which has been paid out from the payoff reel and leveled, to light rolling. For this reason, products made of cold-rolled steel sheets that have the Bausinger effect and punched into a predetermined shape are restrained from being deformed due to thermal strain due to the release of residual stress even if heated and maintained at a certain temperature. The
Therefore, the cold-rolled steel sheet in which the residual stress is dispersed according to the present invention can be used as it is as an AT plate material without being subjected to heat treatment for tempering after being punched into a predetermined shape. Even if heated and maintained at a certain temperature, an AT plate with little thermal deformation can be obtained.

The present inventors, for example, the deformation due to the thermal strain generated in the plate material when the AT plate material manufactured by punching the cold rolled steel plate is heated to a high temperature, the residual stress remaining in the material cold rolled steel plate It was confirmed that this was the case, and a method for removing this residual stress by a mechanically simple means was studied.
As a result, the residual stress remaining in the material cold-rolled steel sheet having the Bauschinger effect was introduced at the time of leveler correction, and was dispersed by subsequent light rolling, and the cold-rolled steel sheet in which the residual stress was dispersed It was confirmed that when the punching process was performed using as a raw material, the processed product was not deformed due to thermal strain even when heated to a high temperature.

Since the residual stress introduced at the time of cold rolling can be canceled by performing light rolling using the large-diameter roll proposed in Patent Document 3, the residual stress remaining in the material cold-rolled steel sheet for punching Most of these are introduced at the time of leveler correction, which is paid out from the payoff reel and is applied at the stage prior to punching. A material having a Bausinger effect, that is, a cold-rolled steel sheet having a higher C content, has a larger residual stress introduced during leveler correction, which greatly affects the shape accuracy of the punched product thereafter.
Therefore, the present invention examines a technique for reducing and dispersing residual stress introduced during leveler correction.

  Normally, as shown in FIG. 1, the product 4 is manufactured by being punched out by a press device 3 after being paid out from a payoff reel 1 and corrected by a roller leveler 2. At this time, if leveling correction is applied to a cold-rolled steel sheet having a Bauschinger effect, repeated bending and unbending deformation is performed by a staggered roll, that is, tension and compression are applied to the front surface, and compression and tension are applied to the back surface. Are repeatedly applied alternately. Examining the stress distribution when bending / unbending deformation is applied to the plate, during bending deformation, tensile stress is applied to the outside of the bend and compression stress is applied to the inside of the bend, yielding on the surface layer side of the plate and causing plastic deformation. .

At that time, the material with the Bauschinger effect yields with a stress smaller than the stress in the tensile direction on the compression side, so that the neutral surface of the bend shifts to the outside of the bend, thereby balancing the tensile and compressive stresses. (See FIG. 2 (a)). Therefore, a compressive stress is generated at the central portion of the plate thickness, and a compressive stress remains in the central portion of the plate thickness at the time of bending / unbending deformation (see FIG. 2B).
By repeating such bending and unbending deformations, the compressive residual stress at the central portion of the plate thickness is accumulated and increased, and the tensile residual stress is increased on the front and back surfaces (see FIG. 2D). ).
FIG. 3 schematically shows the residual stress distribution of the cold-rolled steel sheet after leveler correction in order to refer to the effect of the light reduction rolling described later.

Therefore, in the present invention, as shown in FIG. 4, an apparatus having a light reduction mill 5 between the roller leveler 2 and the press apparatus 3 is used, and the reduction ratio is 0.2 to 1.0% after leveler correction. It was adopted to apply light rolling under.
The reason (mechanism) that the residual stress introduced at the time of leveler correction is dispersed by light rolling after leveler correction is estimated as follows.

In normal rolling, when plastic deformation is attempted to be extended over the entire plate thickness, the plate thickness center portion tends to cause greater plastic deformation than the plate thickness surface layer portion. And since a plate | board thickness center part is restrained by a surface layer part, as a result, a compressive stress is created in a center part and a tensile stress is created in a surface layer part.
However, when the rolling reduction is reduced, the surface layer portion of the plate thickness tends to be stretched, but the central portion of the plate thickness is not plastically deformed, so the surface layer side is constrained by the central portion of the plate thickness, pulled to the central portion, Create compressive stress.
Therefore, the residual stress introduced at the time of leveler correction is reduced by canceling the residual stress by performing rolling under light rolling because the surface layer is tensile and the central portion of the plate thickness is compressed. As schematically shown in FIG. 5, the residual stress distribution of the cold-rolled steel sheet after leveler correction is significantly smaller than that in FIG.

Next, the conditions of light reduction rolling will be described.
If the rolling reduction of the light rolling is over 1.0%, not only the surface layer portion but also the vicinity of the center portion of the plate thickness is stretched and undergoes plastic deformation, so that the residual stress cannot be dispersed. Conversely, if the rolling reduction is less than 0.2%, the build-up of residual stress by light rolling is reduced, and the residual stress introduced by the leveler cannot be dispersed. Therefore, it is necessary to employ 0.2 to 1.0% as the rolling rate of the light rolling.

A 0.35 mass% carbon steel cold-rolled coil with a plate thickness of 1.0 mm and a plate width of 200 mm is discharged from the payoff reel and then has a roll diameter of 70 mm and a roll pitch of 73 mm. The number of upper rolls is 8 and the number of lower rolls is 8 The roller leveler was used to correct curly wrinkles with an indentation amount of 4.2 mm on the entry side intermesh and an indentation amount (opening amount) of 1.6 mm on the exit side mesh.
The residual stress before correction by the roller leveler is 60N / mm ² compressive stress at the center of the plate thickness and 60N / mm ² of tensile stress at the surface layer, and the difference in residual stress between the center of the plate thickness and the surface layer. Was 120 N / mm ² . The residual stress after applying the roller leveler is a compressive stress of 150 N / mm ^{2 at} the center of the plate thickness and a tensile stress of 110 N / mm ^{2 at} the surface layer, and the difference between the residual stress at the center of the plate thickness and the surface layer is 260 N / mm ^2. It had increased to.

The steel sheet after the roller leveler was subjected to light rolling with different rolling reductions under various conditions as shown in Table 1 using a roll having an outer diameter of 200 mm.
The cold-rolled steel sheet produced under each condition was immediately punched out as it was as a ring-shaped AT plate having an outer diameter of 180 mm. The flatness defined by the difference between the maximum height and the minimum height of the AT plate at this time was 0.15 mm.
Thereafter, each AT plate was held at 300 ° C. for 10 minutes. Thermal deformation was evaluated based on the degree of deformation after holding. The case where there was almost no thermal deformation and the flatness defined by the difference between the maximum height and the minimum height of the AT plate was 0.2 mm or less was rated as ◯. When the thermal deformation was large and the flatness exceeded 0.2 mm, it was rated as x because it deviated from the AT plate standard.
Table 1 shows the relationship between the light reduction conditions, the residual stress of each cold-rolled steel sheet obtained, and the thermal deformation after punching into the AT plate.

In Table 1, No. 1-3 are examples of the present invention. Since the residual stress of the steel sheet is small, thermal deformation is small and flatness is excellent even if heat treatment is performed after punching into the AT plate.
On the other hand, No. which is a comparative example. No. 4 is used as an AT plate material as it is without being subjected to light reduction rolling after the roller leveler. The residual stress after the roller leveler is high and the thermal deformation is large.

  Comparative Example No. No. 5, although light rolling is performed after the roller leveler, since the rolling reduction is too small, the residual stress after the roller leveler can hardly be reduced, and the thermal deformation of the AT plate is large. Further, Comparative Example No. No. 6 is rolling at a rolling reduction of more than 1% after the roller leveler, so the rolling reduction is too large, and the amount of reduction in residual stress generated by the roller leveler is small, and thermal deformation of the AT plate It is getting bigger.

The figure explaining the conventional device arrangement at the time of punching the cold-rolled steel sheet paid out from the payoff reel The figure which illustrates typically the situation where stress distribution is generated when bending and unbending deformation is given to the material which has the Bauschinger effect. Diagram showing residual stress distribution of cold-rolled steel sheet after leveler correction The figure explaining the apparatus arrangement | positioning of this invention at the time of punching the cold-rolled steel plate paid out from the payoff reel The figure which shows roughly the magnitude | size of the residual stress distribution of the steel plate after light-rolling after leveler correction in comparison with FIG.

Claims (2)

  Cold-rolled steel sheet with a Bausinger effect that is paid out from the payoff reel and used for punching after leveler correction is subjected to light reduction rolling at a reduction rate of 0.2 to 1.0% after leveler correction. The residual stress distribution method after leveler correction.   An apparatus in which a roller leveler is disposed between a payoff reel and a press apparatus, wherein a light rolling mill is further disposed between the roller leveler and the press apparatus.

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