JP4452260B2 - Method for preventing wrinkles in block rolling - Google Patents

Description

  The present invention stably performs the reverse ingot rolling of a steel ingot or continuously cast steel slab, the subsequent hot scarfing and the cutting with high pressure water in the ingot rolling process. The present invention relates to a wrinkle prevention method for reducing surface wrinkles that occur due to failure.

Conventionally, as a method for preventing wrinkles in block rolling, for example, Patent Document 1 uses a hole mold in which a material side portion in which a dogbone-shaped concave portion is formed by a large pressure is formed and a convex portion is formed in the central portion. A wrinkle prevention method is disclosed in which the concave portions are stretched toward both sides by rolling to eliminate the dogbone shape and prevent the generation of wrinkles. In Patent Document 2, a slab having a long side indentation ratio defined by a mathematical expression having a mold aspect ratio and a block reduction ratio as parameters is used to determine the short side reduction of the slab by the long side indentation ratio and rolling geometry. A lump method has been disclosed in which the number of lump rolls to be rolled is reduced based on the short side reduction ratio with the geometric shape ratio as a parameter.
JP 2000-176501 A JP 2002-267397 A

  On the other hand, according to the inventor's original investigation, the biggest cause of surface flaws occurring in the piece of rolled steel is the intermediate process of the piece rolling, removing the decarburized layer and oxide scale on the surface of the rolled material. When performing hot cutting with gas (hot scarfing), if the shape of the rolled material is unstable, the surface of the rolled material will not be evenly cut and surface flaws will occur during rolling after hot scarfing. In addition, it has been found that hot scarfing scraps (cutting scraps) remain on the surface of the rolled material, and the rolls are pressed by rolling to generate surface flaws.

  Such surface flaws caused by insufficient cutting and surface flaws caused by pressing down can not be eliminated by the split rolling methods disclosed in Patent Document 1 and Patent Document 2. In order to reduce the wrinkle defect, it is necessary to create a stable rolled material shape in the split rolling process.

  Then, the subject of this invention provides the wrinkle prevention method for reducing the surface defect which generate | occur | produces by inadequate cutting and subsequent rolling by building the stable rolled material shape in a block rolling process. That is.

  In order to solve the above problems, the present invention employs the following configuration.

  The method for preventing wrinkles in the lump rolling according to claim 1 is a method for preventing wrinkles in the lump rolling of a steel ingot or continuously cast steel material provided with a hot scarfing process, the rolling before the hot scarfing process. Bulge portions are formed on both side surfaces of the rolled material on the final pass entry side, respectively, and the radius of curvature R of this bulge portion and the distance W in the width direction from the side surface of the rolled material on the final pass entry side to the maximum protruding position of the bulge portion The ratio R / W is 0.5 or more.

  In general, the pass schedule of the ingot rolling is composed of about 10 or more passes, and a plurality of holes are respectively formed in a pair of upper and lower rolls, and the rolled material is sequentially rotated by 90 degrees every 2 passes or 4 passes. Reverse rolled and finished to a predetermined dimension. Particularly in the finishing pass (final pass), as schematically shown in FIGS. 1A and 1B, the rolled material 3 in which the bulge part B is formed by the upper and lower rolls 1 and 2 before the final pass is used. Both side surfaces (free surfaces) 3a and 3b become pressure-contact surfaces that contact the upper and lower rolls 1 and 2 in the final pass. As described above, by forming the shape of the both side surfaces (free surfaces) 3a and 3b of the rolled material 3 in the pass before the final pass so that R / W ≧ 0.5, The rolled material 3 does not fall during biting, and a rolled material having a stable shape can be built in the final pass. Thereby, the shape of the rolled material before hot scarfing can be stabilized.

  Here, the radius of curvature R of the bulge B is obtained by approximating the bulge portion B with an arc passing through the most protruding position Bmax of the bulge portion B, as schematically shown in FIG. , The radius of this approximate circle C (approximate arc).

  The wrinkle prevention method in the partial rolling according to claim 2 is a wrinkle prevention method in the partial rolling step in which the bulge shape is a single bulge or a double bulge.

  As described above, if both sides of the rolled material are formed so that the bulge shape is R / W ≧ 0.5, the finish (final) can be achieved even if the bulge shape is not only a single bulge but also a double bulge. The rolled material does not fall when the pass is bitten into the roll hole mold, and a rolled material having a stable shape can be built in the final pass.

  When the bulge part is a single bulge, the distance W in the width direction is the maximum of the bulge part B from both side surfaces 3s of the rolling material 3 on the final pass entry side (contact surface F with the roll before the final one pass). It is desirable to use the average value of the distances W1 and W2 in the width direction to the protruding position Bmax. When the bulge part B is a double bulge, the distance W in the width direction is, as shown in FIG. 2B, the rolling material 3 on the final pass entry side closer to the maximum protruding position Bmax of the bulge part. This is the distance in the width direction from the side surface 3s (contact surface F with the roll before the last one pass) to the maximum protruding position Bmax.

  In the present invention, the shape of the bulge portion on the side surface of the rolled material, which is subjected to reduction in the final pass before hot scarfing in the block rolling process and rolled in the pass before the final pass (roll hole mold), is as described above. Furthermore, the ratio R / W between the radius of curvature R of the bulge part and the distance W in the width direction from the side surface of the rolled material on the final pass entry side to the maximum protruding position Bmax of the bulge part is set to 0.5 or more. The rolled material does not fall when it is bitten into the roll hole mold in the final pass, and a rolled material having a stable shape can be built in the final pass. As a result, the shape of the rolled material before hot scarfing can be stabilized, and it is possible to prevent surface defects that occur in inadequate cutting in the batch rolling or subsequent rolling after the hot cutting.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 3 to 6.

  In the batch rolling process, a material such as a continuous cast steel slab heated and soaked in a soaking furnace is usually a plurality of box holes in a roll of a double reversible split mill shown in FIG. With the upper and lower rolls 1 and 2 having the molds 1a to 1d, 2a to 2d and the flat roll portions 1e and 2e, the lift amount (roll gap) is changed and the roll is turned 90 degrees every 2 or 4 passes. While being subjected to repeated reductions, the cross-sectional area is successively reduced to create vertical and horizontal dimensions, and rolled to the required dimensions before hot scarfing in the final (finishing) pass. FIG. 4A shows the cross-sectional shape of the rolled material 3 after rolling in the box hole molds 1a and 2a before the final pass, and FIG. 4B shows the lift amount (roll gap) of the upper roll 1. The cross-sectional shapes of the rolled material 3 before and after rolling at the flat roll portions 1e and 2e in the final pass, and after rolling are shown respectively, in which m) is increased from the pass before the final pass. In FIG. 4 (a), the bulge part B of the rolled material 3 is a single bulge, and the bulge part is adjusted by adjusting the roll gap of each pass of the block rolling, in particular, the roll gap of the subsequent pass close to the finishing pass. The ratio R / W of the radius of curvature R of B and the distance W in the width direction is formed to be 0.5 or more. Here, the curvature radius R of the bulge B is the approximate circle when the bulge portion B is approximated by an arc passing through the most projecting position Bmax of the bulge portion B as described with reference to FIG. This approximate circle is the radius of a circle (arc) of the maximum (minimum curvature) that can be approximated, as shown in FIG. Further, the distance W in the width direction is the maximum from the contact surface F (the side surface 3s of the rolled material 3 on the final pass entry side (see FIG. 4B)) with the hole-shaped groove bottoms G1 and G2 before the final pass. It is the distance to the protruding position Bmax, and it is desirable to use the average value of both distances W1 and W2 as described above.

  As described above, the ratio R / W related to the shape of the bulge portion B on the side surface of the rolled material 3 rolled in the pass before the final pass shown in FIG. 4 (b), the contact area between the rolled material 3 and the flat rolls 1e and 2e is increased immediately after the final pass is engaged with the flat rolls 1e and 2e. As a result, the rolled material 3 does not fall down, and the rolled material 3 having a stable shape can be built in the final pass, and the shape of the rolled material 3 before hot scarfing can be stabilized.

  Using the 610 mm square steel slabs of S45C continuously cast as an object, using the finite element method general-purpose program, the upper and lower rolls 1 of the double reversible block mill shown in FIG. In each of the two hole types, the first pass entry side temperature is 900-1200 ° C, the finished steel slab dimensions are 300 mm x 400 mm, and the deformation simulation of 13-roll split rolling in total is performed with the basic pass schedule shown in Fig. 5 did. At that time, by adjusting the amount of rolling reduction in each pass hole type from No.1 to No.11 pass, the hole exit side (final pass (No. The ratio R / W related to the bulge part B on the 13th pass) was changed over a wide range. Using this deformation simulation result, the block rolling conditions were determined, and an actual machine experiment was conducted. As a result of actual machine tests, the same rolling conditions as the shape of the rolled material (R / W) on the hole exit side (final pass (No. 13 pass) entry side) before the final pass (No. 12 pass) The shape almost coincides with the deformation simulation shape, and the results shown in Table 1 were obtained. The upper R / W in Table 1 is a measured value of the actual rolled material on the exit side of the hole mold before the final pass, and this measured value is obtained by image analysis of a cross-sectional photograph of the end surface of the actual rolled material. It is a thing. From Table 1, when the R / W is 0.5 or more, the rolled material does not collapse due to biting into the final pass (No. 13 pass), and the rolled material on the exit side of the same pass (No. 13 pass) The cross-sectional shape was stable and good. On the other hand, when the R / W is 0.1 or 0.3, the rolled material falls due to biting into the final pass (No. 13 pass), and the exit side of the same pass (No. 13 pass) The cross-sectional shape of the rolled material was also unstable and poor.

  Next, the 610 mm square S45C steel slab used in the deformation simulation is shown in FIG. 5 with the hole types of the upper and lower rolls 1 and 2 of the actual double-reversible-type block mill. Using the same basic pass schedule as in the simulation, first, the shape of the rolled material on the exit side of the last die (No. 12 pass) and the exit side of the final pass (No. 13 pass) is first grasped by deformation simulation. In particular, after adjusting and setting the roll gap of the No. 8 to No. 11 pass so that the protruding amount of the bulge part on the side of the rolled material on the exit side of the No. 12 pass becomes small, a total of 13 passes Rolling was performed to finish a 300 mm × 400 mm square steel piece. And about 2% hot scarfing was implemented to the rolling material after the last pass. The shape ratio R / W of the bulge part B on the hole exit side (final pass (No. 13 pass) entry side) before the final pass (No. 12 pass) in the above-mentioned block rolling (see FIG. 4A) ) Is 4.1, satisfies the requirement of shape ratio R / W ≧ 0.5 or more, and the rolled material does not fall down due to biting into the final pass (No. 13 pass). .13 pass) The cross-sectional shape of the rolled material on the exit side was also stable and good. In addition, after carrying out hot scarfing, in the subsequent double-side reversible rolling mill installed downstream of the hot scarfing machine, any pass hole type does not cause a fall due to biting, Rolling to 250 mm square bloom was performed. Because the shape of the rolled material on the exit side of the final pass (No. 13 pass) before hot scarfing is stable, the surface of the rolled material (surface layer) is uniformly welded and the hot scarfing noro ) Was not observed. In addition, surface flaws that were clearly considered as lack of cutting with decarburized layers and oxide scale were not recognized, and the effect of the method of preventing surface flaws by performing cutting with a stable shape was confirmed.

  FIG. 6A shows a case where the bulge portion B formed on the side surfaces 3a and 3b of the rolled material 3 on the pass exit side before the last pass before the hot scarfing is a double bulge, FIG. 6 (b) shows that the rolled material 3 has the lift amount (roll gap m) of the upper roll 1 increased from the pass before the final pass, before rolling at the flat roll portions 1e and 2e in the final pass (biting). ) And the cross-sectional shape after rolling. In the case of the double bulge, the definition of the radius of curvature R of the bulge parts B1 and B2 is the same as in the case of the single bulge, but the distance W in the width direction is the maximum protruding positions B1max and B2max of the bulge parts B1 and B2. Contact surface F with hole groove bottoms G1 and G2 that are closer to maximum projecting positions B1max and B2max, respectively, before the final pass (side surface 3s of rolling material 3 on the final pass entry side (see FIG. 2B)) To the maximum protruding positions B1max and B2max. The distance K between the maximum protrusion positions B1max and B2max of the double bulge does not need to be specified in the present invention. By forming the ratio R / W to be 0.5 or more, the distance K shown in FIG. As shown, since the contact area between the rolled material 3 and the flat roll portions 1e, 2e is increased immediately after biting into the flat roll portions 1e, 2e in the final pass, The rolled material 3 having a stable shape can be formed in the final pass without falling down, and the occurrence of surface defects such as folding folds between the bulge portions B1 and B2 is prevented.

(A) It is explanatory drawing which shows typically the rolling-material cross-sectional shape in the pass before the last 1 pass of a block rolling. (B) It is explanatory drawing which shows typically the cross-sectional shape of the rolling material before and behind rolling in the final pass of a block rolling. (A) It is explanatory drawing which shows typically the definition of the shape ratio R / W of the bulge part of the rolling material of Fig.1 (a) (in the case of a single bulge). (B) Same as above (in case of double bulge). It is explanatory drawing which shows typically an example of the roll of a block mill. (A) It is explanatory drawing of the rolling-material cross-sectional shape in the pass before the last 1 pass of a block rolling (in the case of a single bulge). (B) It is explanatory drawing of the cross-sectional shape of the rolling material before and behind rolling in the final pass of a block rolling (in the case of a single bulge). It is explanatory drawing which shows an example of the pass schedule in partial rolling. (A) It is explanatory drawing of the rolling-material cross-sectional shape in the pass before the last 1 pass of a block rolling (in the case of a double bulge). (B) It is explanatory drawing of the cross-sectional shape of the rolling material before and behind rolling in the final pass of a block rolling (in the case of a double bulge).

Explanation of symbols

1: Upper roll 1a-1c: Roll hole type 2: Lower roll 2a-2c: Roll hole type 3: Rolled material 3a, 3b, 3s: Rolled material side surface B, B1, B2: Bulge part Bmax, B1max, B2max: Bulge Part maximum projecting position C, C1, C2: approximate circle F: contact surface G1, G2: hole-type groove bottom P: rolling direction

Claims (2)

  A method for preventing flaws in a lump rolling of a steel ingot or a continuously cast steel material provided with a hot scarfing process, wherein bulge portions are respectively formed on both side surfaces of a rolled material on a rolling final pass entrance before the hot scarfing process. The ratio R / W between the radius of curvature R of the bulge part and the distance W in the width direction from the side surface of the rolled material on the final pass entry side to the maximum protruding position of the bulge part is 0.5 or more. A method for preventing wrinkles in ingot rolling.   The method for preventing wrinkles in ingot rolling according to claim 1, wherein the bulge shape is a single bulge or a double bulge.

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