JP2007330984A - Method of hot-rolling steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method by which a billet excellent in the quality is obtained economically by heating the steel up to a required temperature while preventing generation of a scale having strong adhesiveness on the surface part when the steel is rough-rolled. <P>SOLUTION: In a method of hot-rolling the steel by which the steel is rough-rolled after heating with a heating furnace and removing the scale on the surface part, the steel is heated up to a temperature lower than the required temperature with the heating furnace and the scale in the surface part is removed after heating the steel to the required temperature by induction heating or the rough-rolling is performed by heating the steel up to the required temperature by induction heating after removing the scale on the surface part. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for hot rolling a steel material, and more particularly to a method for roughly rolling a steel material hot.

  Conventionally, when steel material is roughly rolled hot, the steel material is heated to a required temperature in a heating furnace, and after removing the scale generated on the surface portion of the heated steel material, rough rolling is performed. (For example, refer to Patent Documents 1 to 5). The steel material to be subjected to hot rough rolling is required to have a predetermined temperature depending on the type and shape of the steel material, and further the rough rolling conditions, and the temperature of the steel material is extracted from the heating furnace. Therefore, the steel material is heated to a higher temperature, that is, the required temperature in the heating furnace, and the required temperature in the heating furnace. A scale is generated on the surface portion of the steel material heated to the above, but when the steel material is roughly rolled with the scale attached, the resulting steel slab is inferior in quality due to wrinkles due to the scale, for example, wrinkle wrinkles. Therefore, the steel material heated to the required temperature in the heating furnace as described above is roughly rolled after removing the scale from the surface portion.

However, in the conventional method described above, a scale having strong adhesion may be generated on the surface portion of the steel material extracted from the heating furnace, and if such scale is to be removed, it is necessary to perform a strong removal operation. For example, when a high-pressure water descaler is used for the work, there is a problem that it is not economical because the pressure of the water to be injected needs to be remarkably increased. In particular, the problem is great when scale removal or rough rolling on the downstream side is stopped for some reason, and the steel material stays in the heating furnace. When the steel material stays in a high-temperature heating furnace for heating it to the required temperature for a long time, a scale with high adhesion that penetrates deeper into its surface is generated, and this scale is strongly removed. However, it cannot be removed sufficiently, so that it is eventually brought into rough rolling, and the resulting steel slab becomes inferior in quality.
JP-A-5-277543 JP-A-6-114432 JP-A-8-206723 JP-A-10-244312 JP 2003-94152 A

  The problem to be solved by the present invention is that when the steel material is roughly rolled hot, the steel material is heated to a required temperature while preventing the formation of a highly adherent scale on the surface portion, and the quality is excellent. It is in providing a method by which the slab can be obtained economically.

  The present invention for solving the above problems is a method of hot rolling a steel material in which the steel material is heated in a heating furnace, the scale of the surface portion is removed, and rough rolling is performed, and the steel material is lowered to a temperature lower than the required temperature in the heating furnace. The present invention relates to a hot rolling method for a steel material, characterized in that after heating and further induction heating to a required temperature, scale on the surface portion is removed and rough rolling is performed. Further, the present invention provides a method for hot rolling a steel material in which the steel material is heated in a heating furnace, the scale of the surface portion is removed, and the rough rolling is performed. The method according to the present invention relates to a hot rolling method for a steel material, characterized in that after the scale is removed and further subjected to induction heating to a required temperature, rough rolling is performed.

  Also in the hot rolling method for steel materials according to the present invention (hereinafter simply referred to as the method of the present invention), the steel materials are heated in a heating furnace, and after removing scales generated on the surface portion of the heated steel materials, rough rolling is performed. In the method of the present invention, the type of the target steel material is not particularly limited, but the effect is exerted on structural alloy steels such as tough steel and case-hardened steel, which easily generate a scale having high adhesion on the surface portion by heating. Is expensive. Also, the type of heating furnace to be used is not particularly limited, but a burner type or electric resistance type heating furnace which tends to stay for a long time under the high temperature in the furnace when removal of scale or rough rolling on the downstream side is stopped for some reason. Is highly effective. Further, the type of the apparatus used for removing the scale is not particularly limited, but it is preferable to use a high-pressure water descaling apparatus that does not add extra wrinkles to the steel material.

  In the method of the present invention, the steel material is not heated to a required temperature in a heating furnace, but is heated to a temperature lower than the required temperature. Here, as described above, the required temperature is lowered to a predetermined temperature required for the steel material when the steel material is roughly rolled hot, until the steel material is extracted from the heating furnace and subjected to the rough rolling. It means a temperature that anticipates the temperature, and usually the expected temperature is in the range of 100-300 ° C. In the method of the present invention, since the steel material is heated to a temperature lower than the required temperature in the heating furnace, it is possible to suppress the formation of scale on the surface portion of the steel material at the stage of the heating furnace, and for some reason, Even if the steel material is stagnant, it is possible to prevent the formation of a scale having strong adhesion on the surface portion of the steel material.

  In the method of the present invention, as described above, the steel material is heated to a temperature lower than the required temperature in a heating furnace, and further heated by induction to the required temperature, and then the scale of the surface portion is removed and rough rolled, or As described above, the steel material is heated to a temperature lower than the required temperature in a heating furnace, the scale of the surface portion is removed, and further, induction heating is performed to the required temperature, followed by rough rolling. Since the steel material is heated to a temperature lower than the required temperature in a heating furnace, the temperature is insufficient when the steel material is roughly rolled after removing the scale of the surface portion. Therefore, in the method of the present invention, the steel material is induction-heated before or after the surface scale is removed to compensate for the insufficient temperature. In the method of the present invention, in order to compensate for the shortage of temperature by induction heating, in other words, the shortage of temperature can be compensated for in a short time compared to heating in a heating furnace such as a burner type or an electric resistance type, A scale having strong adhesion is not generated on the surface portion of the steel material at the induction heating stage.

  According to the method of the present invention, when the steel material is roughly rolled hot, the steel material is not heated to the required temperature in the heating furnace, but the steel material is heated to a temperature lower than the required temperature in the heating furnace, and the insufficient temperature. In order to compensate for this by induction heating, even if for some reason the scale removal or rough rolling downstream of the heating furnace stops and the steel material stays in the heating furnace for a long time, it adheres to the surface of the steel material. Can be prevented, and as a result, an excellent quality slab can be obtained economically.

  FIG. 1 is a system diagram showing an implementation state of the method of the present invention. An induction heating device 21 is connected to the downstream side of the heating furnace 11, a scale removing device 31 is connected to the downstream side of the induction heating device 21, and a rough rolling mill row 41 is connected to the downstream side of the scale removing device 31. Has been. In the case of FIG. 1, a burner type heating furnace using a burner as a heat source is used as the heating furnace 11, and a high-pressure water descaler is used as the scale removing device 31. In the case of FIG. 1, the steel material is heated to a temperature lower than the required temperature in the heating furnace 11, further heated to the required temperature with the induction heating device 21, and then the scale on the surface portion is removed with the scale removing device 31, followed by rough rolling. Rough rolling is performed in the machine row 41.

  FIG. 2 is a system diagram showing another state of implementation of the method of the present invention. A scale removing device 32 is connected to the downstream side of the heating furnace 12, an induction heating device 22 is connected to the downstream side of the scale removing device 32, and a rough rolling mill row 42 is connected to the downstream side of the induction heating device 22. Has been. Also in the case of FIG. 2, a burner type heating furnace using a burner as a heat source is used as the heating furnace 12, and a high-pressure water descaler is used as the scale removing device 32. In the case of FIG. 2, the steel material is heated to a temperature lower than the required temperature in the heating furnace 12, the scale on the surface is removed by the scale removing device 32, and further heated to the required temperature by the induction heating device 22. Rough rolling is performed in the machine row 42.

  According to the implementation state described above with reference to FIG. 1, the steel material was hot-rolled as follows (Example 1). Case-hardened steel (SNCM220) having a cross section of 155 mm × 155 mm and a length of 11.2 m was supplied to the heating furnace 11 and extracted at 900 ° C. The residence time in the furnace until extraction was 2 hours. Next, this steel material was supplied to the induction heating device 21 and heated to 1100 ° C. And this steel material was used for the scale removal apparatus 31, and the scale of the surface part was removed. Finally, the steel material having a temperature of 900 ° C. was subjected to rough rolling by using a rough rolling machine row 41 to finally form a round bar having a diameter of 48 mm. The round bar thus hot-rolled had slight wrinkles of about 0.03 mm in depth in the longitudinal direction.

  According to the implementation state described above with reference to FIG. 2, the steel material was hot-rolled as follows (Example 2). The same case-hardened steel as in Example 1 was subjected to the heating furnace 12 and extracted at 900 ° C. The residence time in the furnace until extraction was 2 hours. Next, the steel material was subjected to a scale removing device 32 to remove scale on the surface portion. And this steel material was used for the induction heating apparatus 22, and was heated at 1000 degreeC. Finally, the steel material having a temperature of 900 ° C. was subjected to rough rolling by using a rough rolling machine row 42 to finally form a round bar having a diameter of 48 mm. The round bar thus hot-rolled had slight wrinkles of about 0.03 mm in depth in the longitudinal direction.

  The steel material was hot-rolled as follows (Comparative Example 1). The same case-hardened steel as in Example 1 was subjected to the heating furnace 11 and extracted at 1100 ° C. The residence time in the furnace until extraction was 2 hours. And this steel material was used for the scale removal apparatus 31 without induction heating, and the scale of the surface part was removed. Finally, the steel material having a temperature of 900 ° C. was subjected to rough rolling by using a rough rolling machine row 41 to finally form a round bar having a diameter of 48 mm. In this way, a large number of severe wrinkles having a depth of about 0.15 mm were formed in the longitudinal direction on the hot rolled round bar.

The system diagram which shows the implementation state of the method of this invention. The system diagram which shows the other implementation state of the method of this invention.

Explanation of symbols

11,12 Heating furnace 21,22 Induction heating device 31,32 Scale removal device 41,42 Rough rolling mill row

Claims (5)

  In a hot rolling method for steel that is roughly rolled by removing the scale of the surface portion by heating the steel in a heating furnace, the steel is heated to a temperature lower than the required temperature in the heating furnace, and further heated by induction to the required temperature. Then, the scale of the surface part is removed, and the hot rolling method of steel materials characterized by carrying out rough rolling.   In a hot rolling method for steel that is rough rolled by heating the steel in a heating furnace to remove the scale on the surface, the steel is heated to a temperature lower than the required temperature in the heating furnace to remove the scale on the surface. A method of hot rolling a steel material, further comprising: induction heating to a required temperature and then rough rolling.   The method of hot rolling steel according to claim 1 or 2, wherein the heating furnace is a burner type or electric resistance type heating furnace.   The hot rolling method of steel materials as described in any one of Claims 1-3 which removes the scale of a surface part with a high pressure water descaling apparatus. The method of hot rolling steel according to any one of claims 1 to 4, wherein the steel is heated to a temperature lower by 100 to 300 ° C than the required temperature in a heating furnace.

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