JP5664216B2 - Method for producing high carbon hot-rolled steel sheet for cold rolling - Google Patents

Description

  The present invention relates to a method for producing a high carbon hot rolled steel sheet for cold rolling. In addition, the high carbon hot-rolled steel sheet here is a hot-rolled steel sheet containing 0.08 to 1.5% by mass of C, for example, a hot-rolled steel sheet defined by the following standards.

・ JIS G 4401 Carbon tool steel ・ JIS G 4405 Alloy tool steel ・ JIS G 4051 Carbon steel for machine structure ・ JIS G 4053 Alloy steel for machine structure ・ JIS G 4805 High carbon chromium bearing steel ・ JIS G 4801 Spring Steels ・ SAE J 403 Chemical Compositions of SAE Carbon Steels
・ SAE J 404 Chemical Compositions of SAE Alloy Steels

  Conventionally, in order to obtain a hot-rolled steel sheet (high-carbon hot-rolled steel sheet for cold rolling) that is a material of a high-carbon steel sheet that requires high sheet thickness accuracy (for example, a thickness tolerance of ± 20 μm) after cold rolling. Various technologies have been implemented.

  For example, in Patent Document 1, when annealing a hot-rolled high carbon hot-rolled steel sheet for cold rolling, the cooling rate after heating and soaking is 15 ° C./hour or less, and the de-furnace temperature is 630 ° C. or less. Annealing is performed. By this, it is going to reduce the gauge fluctuation | variation (plate thickness fluctuation | variation) resulting from the annealing nonuniformity of a hot-rolled steel plate.

  In addition, the coiling temperature in hot rolling is often increased.

JP 2002-285242 A

  In the manufacture of high carbon steel sheets, high carbon steel sheets after cold rolling (due to thickness fluctuations) due to short-term gauge fluctuations due to hardness unevenness occurring at the tip of the steel sheet about 100 m during hot rolling ( The thickness variation often occurs at the tip of the high-carbon cold-rolled steel sheet. FIG. 2 shows an example of the plate thickness variation that occurs at the tip of such a high-carbon cold-rolled steel plate. The plate thickness fluctuation width at the front end of the steel plate is very large.

  In this way, when the thickness fluctuation width of the front end portion of the steel plate becomes large and the required thickness tolerance is deviated, that portion is discarded, resulting in a decrease in yield.

  On the other hand, the technique described in Patent Document 1 is intended to reduce gauge fluctuation caused by annealing unevenness of a high carbon steel sheet after hot rolling, and the tip of the high carbon steel sheet during hot rolling. The effect is unknown in suppressing the short-period gauge fluctuations that occur in

  Moreover, raising the coiling temperature in hot rolling has the problem that grain boundary oxidation and decarburization occur in the surface layer of the high carbon steel sheet after hot rolling.

  The present invention has been made in view of the above circumstances, and manufacture of a high-carbon hot-rolled steel sheet for cold rolling that can provide a high-carbon hot-rolled steel sheet with excellent sheet thickness accuracy after cold rolling. Is to provide a method.

  In order to solve the above problems, the present invention has the following features.

  [1] In producing a high-carbon hot-rolled steel sheet for cold rolling, after cold rolling and then annealing, a light reduction with a rolling reduction of 1.0 to 5.0% is applied. Manufacturing method of high carbon hot rolled steel sheet for hot rolling.

  In the present invention, during cold rolling, fluctuations in sheet thickness caused by hardness unevenness during hot rolling are suppressed. In particular, the effect of suppressing fluctuations in sheet thickness with respect to about 100 m of the steel sheet tip portion where unevenness in hardness is likely to occur during hot rolling is remarkable.

It is an example of the thickness chart of a high carbon cold-rolled steel plate. It is a figure which shows the suppression effect of the plate | board thickness fluctuation | variation width | variety of the high carbon cold-rolled steel plate by the light pressure after annealing.

  One embodiment of the present invention will be described.

  In one embodiment of the present invention, hot rolling with a hot rolling mill, followed by annealing with an annealing furnace, followed by a rolling reduction of 1.0 to 5.5 with a light rolling cold rolling mill (for example, a skin pass mill). High carbon hot-rolled steel sheets are manufactured and shipped with a light reduction of 0%. And the customer who purchased the high carbon hot-rolled steel sheet performs cold rolling with a cold rolling mill (for example, a reverse type cold rolling mill).

  Here, FIG. 1 is for cold rolling by performing hot rolling with a hot rolling mill and then annealing with an annealing furnace, and then performing light rolling by changing the rolling reduction rate with a light rolling cold rolling mill. The thickness fluctuation range after producing high carbon hot-rolled steel sheets and cold-rolling these high-carbon hot-rolled steel sheets with a cold rolling mill is shown.

  As shown in FIG. 1, it has shown that the board | plate thickness fluctuation | variation width | variety by subsequent cold rolling is suppressed by giving the light reduction of a rolling reduction 1.0-5.0% to the steel plate after annealing. .

  In addition, as described above, it is not clear why the sheet thickness variation due to cold rolling is suppressed by applying light reduction to the steel sheet after annealing, but strain is applied by rolling under light reduction. As a result, the soft part in the steel plate is particularly greatly affected by the strain, and the unevenness of the hardness in the steel plate is reduced. As a result, the subsequent cold rolling is uniformly performed, and fluctuations in the plate thickness are suppressed. It is thought that.

  By the way, if the rolling reduction is less than 1.0%, the hardness unevenness during hot rolling is insufficiently reduced, and if the rolling reduction exceeds 5.0%, the hardness unevenness during hot rolling is caused. Since the plate thickness variation becomes large, the rolling reduction is optimally 1.0 to 5.0%.

  In this embodiment, after hot rolling with a hot rolling mill and then annealing with an annealing furnace, a rolling reduction of 1.0 to 5.0% with a light rolling cold rolling mill (for example, a skin pass mill). A high-carbon hot-rolled steel sheet is manufactured and shipped with a light reduction of, and customers who purchase the high-carbon hot-rolled steel sheet are cold-rolled by a cold rolling mill (for example, a reverse cold rolling mill). However, the customer who purchased the high-carbon hot-rolled steel sheet from the hot-rolled steel sheet manufactured and shipped by hot rolling with a hot-rolling mill and then annealing in an annealing furnace For example, a normal cold rolling may be performed after first applying a light reduction with a reduction ratio of 1.0 to 5.0% with a reverse cold rolling mill).

  After hot rolling and then annealing, a high carbon hot rolled steel sheet was produced by applying light reduction. And the high carbon hot rolled sheet steel was cold-rolled and the high carbon cold rolled sheet steel was manufactured.

  At that time, in the example of the present invention, the reduction ratio of light reduction applied after annealing was set to 1.0 to 5.0%. On the other hand, in the comparative example, the rolling reduction under light pressure applied after annealing was set to less than 1.0% or more than 5.0%.

  Table 1 shows the plate thickness fluctuation range after cold rolling. In addition, since the general thickness tolerance of a high-carbon cold-rolled steel sheet is ± 20 μm, if the thickness fluctuation width after cold rolling exceeds 40 μm, that portion is discarded.

  As shown in Table 1, in the comparative example, the thickness variation width after cold rolling exceeds 40 μm, whereas in the present invention example, the thickness variation width after cold rolling is less than 40 μm. .

  This confirmed the effectiveness of the present invention.

Claims (1)

For the production of a high carbon hot rolled steel sheet for cold rolling, after hot rolling and then annealing, a light reduction with a rolling reduction of 1.0 to 4.7 % is given. Manufacturing method of high carbon hot rolled steel sheet.

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