JP6233073B2 - Reproduction method of continuous casting roll with slit - Google Patents

Description

  The present invention relates to a method for regenerating a continuous casting roll with a slit used in a continuous casting facility for molten steel.

  In continuous casting equipment for molten steel, a large number of continuous casting rolls are used to draw out hot slab solidified by a mold. Since these continuous casting rolls rotate at a low speed, the surface in contact with the slab becomes high temperature, but the opposite surface of the slab is repeatedly cooled and cooled. For this reason, the surface may buckle or crack due to repeated thermal expansion and contraction, and the service life is short.

  Therefore, as shown in Patent Document 1, a continuous casting roll with slits in which a large number of slits extending in the circumferential direction are opened on the outer peripheral surface has been developed. This continuous casting roll with slits is formed by forming slits with a width of about 0.3 to 1 mm on the outer peripheral surface of the roll by electrolytic processing. These slits alleviate the thermal stress on the roll surface and greatly increase the service life. Has succeeded in stretching.

  However, when used over a long period of time, it is inevitable that the outer peripheral surface of the roll gradually wears like a normal roll having no slit formed on the outer peripheral surface. As a regeneration method in this case, overlay welding is generally performed on the worn outer peripheral surface. However, in the case of a continuous casting roll with slits, the pitch in the axial direction between the slits is 10 to 20 mm. Therefore, it takes a lot of work and time to perform overlay welding on such a narrow portion. There was a problem. In addition, since the slit was reworked in the build-up welded portion so that the opening of the slit was not blocked by the build-up welding, the regenerating operation was a high-cost work requiring a considerable number of man-hours.

JP 2004-195517 A

  Accordingly, an object of the present invention is to solve the above-described conventional problems and to provide a method capable of quickly and inexpensively regenerating a continuous casting roll with a slit whose outer peripheral surface is worn.

The present invention made to solve the above-described problems is that when a continuous casting roll with slits having a large number of slits extending in the circumferential direction opened on the outer peripheral surface is worn, the slit openings are formed on the outer peripheral surface that has been worn. by performing wide overlay welding was controlled according to heat input overlay welding to the remaining thickness so as to cover, to generate a crack along the slit in the overlay weld part welded to the overlay weld part The generated crack is made to function as an opening of the slit without reworking the slit.

As described in claim 2, it is preferable to perform overlay welding using a martensitic stainless material having a hardness exceeding the base metal hardness. Further, as in claim 3 , cracks can be generated intermittently in the circumferential direction. Incidentally, as claimed in claim 4, wherein the slits are those having a depth of 10 to 30 mm, the axial pitch of 10 to 20 mm.

According to the present invention, wide welding is performed by controlling the heat input of overlay welding according to the remaining thickness so as to block the opening of the slit on the worn outer peripheral surface. A crack is generated along the slit. For this reason, it is not necessary to perform overlay welding only on the narrow part between slits as in the past, or to rework the slit in the overlay welding part, and with slits much more quickly and at a lower cost than before. The continuous casting roll can be regenerated.

In the present invention, it is possible to generate a preferable crack after welding by controlling the heat input amount of overlay welding according to the remaining thickness. Further, as described in claim 2 , overlay welding is performed using a martensitic stainless material having a hardness exceeding the hardness of the outer peripheral surface, thereby improving the material strength of the repaired surface and enhancing the life extension effect. be able to.

It is explanatory drawing of the roll for continuous casting with a slit. It is an expanded sectional view of the principal part. It is a sectional view of the graph and welding part which show welding conditions.

Hereinafter, preferred embodiments of the present invention will be described.
FIG. 1 is an explanatory view of a continuous casting roll with slits. As shown in the drawing, a large number of slits 1 extending in the circumferential direction are formed on the outer peripheral surface of the continuous casting roll with slits by electrolytic processing. The width of the slit 1 is about 0.3 to 1 mm, the depth from the surface of the base material 2 is 10 to 30 mm, and the pitch of the slit 1 is 10 to 20 mm. It is preferable to form a cavity 3 having a circular cross section as shown in the bottom of the slit 1 to reduce stress concentration. The base material 2 is generally stainless steel having excellent high temperature strength.

  Such a continuous casting roll with slits has a service life much longer than that of a conventional product without slits because the thermal stress is relieved by the slits 1 so that the surface does not buckle or crack. However, it is inevitable that the outer peripheral surface is worn away by long-term use. The worn continuous casting roll with slit is removed and sent to a repair shop.

  At the repair shop, the worn outer peripheral surface of the continuous casting roll with slits is set on a large lathe, surface cutting is performed with a cutting tool to eliminate irregularities on the outer peripheral surface other than the slits, and the slits as shown in FIG. The overlaying material 4 having a wide width is welded so as to close the opening of 1. In the present invention, the material of the build-up material 4 is not particularly limited. However, in order to reduce the wear amount of the build-up weld part of the continuous casting roll with slits by increasing the hardness of the build-up weld part. As the cladding material 4, it is preferable to use a martensitic stainless steel material. Moreover, if a martensitic stainless steel material is used for the build-up material 4, even if the outer periphery of a base material is a stainless steel material, it is possible to make build-up welding part hardness higher than base material part hardness. Further, when the outer periphery of the base material is a stainless steel material that is not martensitic (for example, precipitation hardening type stainless steel material), the build-up weld hardness can be made sufficiently harder than the base material hardness. In order to select a martensitic stainless steel material as a build-up material, it is preferable that the high-temperature hardness at 500 ° C. is 120 Hv or more in order to reduce the high-temperature wear of the build-up weld of the continuous casting roll with slits.

  In the present invention, it is necessary to appropriately set the welding conditions in order to generate cracks along the slits in the welded welded portion. FIG. 3 summarizes the relationship between the remaining thickness (mm) and the heat input during welding (J / mm). Here, as shown in FIG. 3, the remaining thickness is a slit remaining depth on the outer periphery of the roll before overlay welding in the present invention. The remaining thickness may be the slit remaining depth on the outer periphery of the roll after setting the outer peripheral surface of the roll on a large lathe and performing surface cutting with a cutting tool to eliminate irregularities on the outer peripheral surface other than the slit.

  Although a large amount of heat input is required as the remaining thickness increases, if the amount of heat input is larger than the region shown as the optimum condition in FIG. 3, the build-up material 4 is excessively melted and reaches the inside of the slit 1. I get into it. In this state, the original function of the slit 1 is impaired, which is not preferable. Conversely, when the amount of heat input is less than the region indicated as the optimum condition, the build-up material 4 is insufficiently melted and the joining with the base material 2 becomes insufficient, so that the build-up weld is along the slit. Cracks cannot be formed.

  If the wide cladding material 4 is welded so as to close the opening of the slit 1 under the optimum conditions described above, the thermal stress due to solidification cracking during cooling after welding or the thermal history applied to the roll during subsequent use The inventors consider that a crack along the circumferential slit 1 can be generated in the overlay welded part. This crack naturally occurs starting from the slit 1. In many cases, the width of the crack is ½ or less of the width of the slit 1. However, if the width of the crack is too narrow, buckling may occur due to thermal expansion at the time of contact with the slab, and therefore it is preferably 0.15 mm or more.

  Note that the cracks are intermittently generated in the circumferential direction along the slit 1 and do not need to be continuous over the entire circumference. This is because the role of the slit 1 is to relieve the thermal stress in the axial direction and is independent of the stress in the circumferential direction.

  In this way, the continuous casting roll with a slit in which a crack is generated in the build-up weld along the slit 1 is continued as it is without re-working the slit 1 in the build-up weld as in the prior art. The cracks set in the casting machine are caused to function as the openings of the slits 1. For this reason, the efficiency of the regenerating work is dramatically improved as compared with the conventional one, and the thermal stress relaxation ability of the slit 1 is not impaired.

  The continuous casting roll with slits removed from the continuous casting machine of the steel factory was regenerated by the method of the present invention. This roll is made of a precipitation hardening type stainless steel material, and slits having a width of 0.4 mm and a depth of 20 mm are electrolytically processed at a pitch of 15 mm on the outer peripheral surface thereof.

  The surface layer of the worn outer peripheral surface is shaved with a lathe, and the entire outer peripheral surface excluding the slits is shaped so that it has a cylindrical shape with no irregularities. Overlay welding was performed using a welding machine. The remaining thickness was 4.5 mm, and the heat input amount of the submerged arc welding was 3960 J / mm. The welding speed was 250 mm / min, the current was 750 A, the voltage was 22 V, and the cooling was air cooling.

  During the cooling process after welding, cracks occurred intermittently in the circumferential direction along the slit in the overlay weld. The crack width was 0.2 to 0.4 mm, and it was possible to function as an opening of the slit as it was. Therefore, it was not necessary to rework the slit in the overlay weld.

  The continuous casting roll with slits regenerated in this way was used as it was set in a continuous casting machine, but the service life estimated from the amount of wear until the present after resuming use is 5 to 6 years. This is equivalent to or longer than the service life of 5 years. In addition, the time required for the reproduction process is 1/10 or less of the conventional method, and the time can be greatly shortened.

  As is clear from this embodiment, the present invention performs a wide overlay welding so as to block the opening of the slit and generates a crack along the slit in the welded overlay weld. Based on the original idea, it has succeeded in regenerating a worn continuous casting roll with slits quickly and inexpensively, and its practical effect including the economic effect is extremely large.

1 Slit 2 Base Material 3 Cavity 4 Overlaying Material

Claims (4)

When the continuous casting roll with slits with many slits extending in the circumferential direction opened on the outer peripheral surface , depending on the remaining thickness, the amount of heat input of overlay welding is closed so that the worn outer peripheral surface closes the slit opening. controlled Te by performing wide overlay welding, to generate a crack along the slit in the overlay weld part welded without reworking a slit in the overlay weld part, cracked slits generated A method for regenerating a continuous casting roll with a slit, which functions as an opening. The method for regenerating a continuous casting roll with slits according to claim 1, wherein overlay welding is performed using a martensitic stainless material having a hardness exceeding the base metal hardness . The method for regenerating a continuous casting roll with slits according to claim 1, wherein cracks are intermittently generated in the circumferential direction . The said slit has a depth of 10-30 mm, The axial direction pitch is 10-20 mm, The reproduction | regenerating method of the roll for continuous casting with a slit of Claim 1 characterized by the above-mentioned.