JPH078397B2 - Press die for hot rolling - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a hot rolling press die for continuously reducing the width of a hot slab.

(Prior Art) Conventionally, as a press die for hot rolling (hereinafter simply referred to as a die), an integral die using tool steel or the like is used.

In order to extend the life (usable time) of the mold, a heat-resistant material such as 13Cr was built up on the surface of the mold, or as shown in FIG. There has been proposed a method of using alternately, or a method of providing a plurality of pairs of the same mold for each process and using them alternately. (JP-A-55-866
(See Japanese Laid-Open Patent Publication No. 37) (Problems to be solved by the invention) In the width reduction step, heating and cooling of the mold are repeated, and thermal stress generated along with this causes thermal fatigue cracks on the surface of the mold. The life of the mold is governed by the time until the crack starts and the speed of crack propagation.

As described above, by overlaying the surface of the mold with a material that is unlikely to cause thermal fatigue cracks even when subjected to repeated thermal stress, or by alternately using a plurality of pairs of molds to reduce the thermal stress. The life of the mold can be extended.

However, these conventional techniques do not prevent the generation of thermal stress between the surface of the mold where heating and cooling are repeated and the rear surface of the mold that is maintained at a substantially constant temperature, so that it does not occur for a long time. When a mold is used, cracks are generated on the surface of the mold.

As shown in FIG. 7, the slab 1, which is intermittently fed in the direction of the arrow, is subjected to width reduction by opening and closing a pair of molds 3, 3 supported by a support base 2, but cracks are shown in FIG. There is a tendency to occur intensively at the corners on the slab entry side of the mold 3 surrounded by the circle as shown, and the length thereof is 60 to 70 in the thickness direction.
mm, and the opening amount reaches 1 to 2 mm (see FIG. 9), and the mold cannot be used.

The present invention solves the problems of the prior art, reduces the thermal stress on the surface of the mold without increasing the size of the device, prevents the occurrence of cracks, and reduces the progress speed thereof to shorten the life of the mold. It is intended to be a big one.

[Structure of the Invention] (Means for Solving Problems) The present invention has been made to solve the above problems, and has a parallel surface along the slab conveyance direction and an inclined surface on the entrance side. In a hot rolling press die that feeds a hot slab between a pair of dies that are opened and closed cyclically to reduce the width to a predetermined width, the die that comes into contact with the slab side face when performing the maximum amount of reduction. Is a press die for hot rolling, characterized in that slits processed at regular intervals are formed on both surfaces of the parallel surface and the entrance-side inclined surface.

(Function) The thermal stress generated in the vicinity of the mold surface is relaxed by absorbing the thermal strain caused by the thermal expansion and contraction of the mold surface by opening and closing the slits to prevent the occurrence of cracks and to prevent cracks inside the mold. Slows down the rate of progress.

(Embodiment) An embodiment of the present invention will be described with reference to FIGS.

3 is a mold made of a heat-resistant material such as cast steel and tool steel, and a parallel surface 4 parallel to the slab 1 at the center of the longitudinal direction (the traveling direction of the slab shown by the arrow), and an entrance side to the entrance side of the slab 1. Slope 5
However, on the output side of the slab 1, the output side inclined surface 6 is provided continuously to the parallel surface 4. On the parallel surface 4 and the entrance-side inclined surface 5 of the die 3, slits 7 are engraved in a lattice pattern that intersects the height direction. The slits can be formed by electric discharge machining or circular saw blade machining.

The horizontal and vertical slits may be provided in a grid pattern, but it is particularly desirable to have a grid pattern obliquely intersecting the height direction. For example, when pressure is applied in a grid pattern with slits that are parallel to the slits that are parallel to the slab longitudinal direction, in particular, the slits in the slab longitudinal direction have the following indentations (small streaky protrusions) formed by pressing down the mold. It remains under pressure and may be amplified conversely. On the contrary, in the case of the lattice shape obliquely intersecting with the height direction, the indentation generated in the first reduction is hardly amplified again because it hardly coincides with the slit in the next reduction.

Further, as shown in FIG. 4, the slit 7 is separated only from the central portion 11 of the mold 3 which is separated from the boundary portion 10 where the mold 3 is in contact with the upper end surface 8 and the lower end surface 9 of the slab 1 having the thickness S by 10 mm or more. To be installed.

If the height of the central portion 11 is H, then H ≦ S−2 × 10, and slits are formed on the surface of the die which is in contact with the upper surface 8 and the lower surface 9 of the slab 1 within 10 mm respectively. It has not been.

It was found that the following effects can be obtained by forming the slits only in the central portion of the mold 3 in this way.

The slits 7 engraved in the mold 3 are transferred to the slab surface,
Although the slab may be scratched, the slit 7 is provided only in the central portion 11 of the mold 3 as described above, and the slit 7 is provided in the range of at least 10 mm near the upper end surface 8 and the lower end surface 9 of the slab 1. By preventing the transfer, it is possible to completely remove the influence of the scratches on the slab that may occur due to the transfer of the slit 7, and moreover, the crack of the portion of the mold 3 where the slit 7 is not formed. It has been found that the occurrence of the can also be effectively prevented.

The slit 7 can be provided over the entire lengths l ₁ and l ₂ of the entrance side inclined surface 5 and the parallel surface 4, but the length given by the following formula close to the boundary line 12 between the entrance side inclined surface 5 and the parallel surface 4 It is sufficient to provide it in the range of X and Y, and a great effect can be obtained.
In Fig. 1, θ: Angle formed by the parallel part of the mold and the inclined part on the inlet side ΔWmax: Maximum width reduction amount (both sides) performed by this mold (mm) δ: Amplitude of the mold (opening / closing stroke of the mold) Α): Slit longitudinal slit processing range (about 50 mm) β: Slab width slit processing range (about 20 mm)

The slab is fed between the molds in the mold opening process, and is width-reduced by the mold entrance side inclined surface 5 and the parallel surface 4 in the next closing process. In this case, the minimum distance between the left and right dies corresponds to the slab width after width reduction.

Here, the length in the slab width direction of the slit processing range on the entrance-side inclined surface 5 of the mold is Therefore, the length X along the entrance-side inclined surface 5 is Becomes

On the other hand, the maximum amount L of advance of one slab is Therefore, the length Y of the slit processing range on the parallel surface 4 is Becomes

On the other hand, if the mold is not provided with slits, the mold surface will be heated,
Due to thermal stress caused by repeated cooling, a minute crack is first generated, and this crack is enhanced as the use time is increased.
If the crack propagates to some extent, it reaches a depth beyond thermal stress, and then the growth slows down. However, the cracks in this case occur irregularly, and the growth in the depth direction is also irregular. If this happens, there will be a series of defects, and the product will become unusable early.

When the slit is formed, first, the thermal stress on the die surface is absorbed by the slit. That is, the cracks do not occur in this state only by being affected by the thermal stress in each small section of the grid-like slits. Further, since the slits are regularly formed, the conditions of each grid-like section are uniform, and the bottoms of the adjacent slits are not broken and not cut off.

Even if a crack starts from the slit bottom, the effect of thermal stress is small, and the growth rate after that is very slow.Because the regularly provided slit bottom is the starting point, Even if it grows irregularly in the depth direction, it takes a considerable amount of time to reach the end.

Fig. 5 is shown in Fig. 4.47 on page 168 of "Mechanism of Fracture and Material Strength 2" by Makoto Ishikawa, published by Baifukan on June 30, 1976, in "Analysis of Cracks and Stress Intensity Factor". It is a thing.

The above formula relates to a semi-infinite plate, which does not match the actual mold, but is applied to investigate the crack growth. The smaller FI is, the more effective it is in suppressing crack growth, but for that purpose, a / w must be large. In other words, it is sufficient to make a large and W small, but it is obvious that the mechanical strength is lowered if a / W is made large. After examining these points, a / W
It was found that 1, W = 10 mm is preferable.

By setting W = 10 mm, the propagation speed from the tip of the slit can be set to about 10 ^-4, and the expansion propagation speed at which cracks develop from the bottom of the slit is small enough not to actually damage the die life. I found that I could do it.

In addition, the step shape of the slit has an opening amount b (see FIG. 2) of 0.
It is desirable to have a V-shape of about 2 to 0.5 mm, but it is also possible to give the bottom of the slit a radius.

(Effect of the invention) As described above, according to the hot-rolling press die of the present invention, by subjecting the surface of the metal to slitting and making the cross section uneven, thermal stress is relieved and cracks Occurrence can be controlled.

Even if a crack occurs, the crack stops growing in the region where the stress is reduced and does not develop into a chip.

Further, heat input to and heat removal from the mold are performed from the mold surface.

Therefore, the temperature change of the surface layer of the mold is the same as before, but the thermal stress balances independently in the part (section) surrounded by the slit (not affected by the adjacent section), so it is alleviated by the slit. Drastically reduced.
Therefore, no cracks occur in the compartment. as a result,
The life of the mold (usable time) can be greatly extended.

[Brief description of drawings]

FIG. 1 is a perspective view of an embodiment of a hot rolling press die according to the present invention, FIG. 2 is a die thickness direction, and FIG. 3 is a die height direction orthogonal to a slit. 4 is an explanatory sectional view showing the positional relationship between the mold and the slab, and FIG. 5 is a constant for determining the depth of the slit provided in the mold and the expansion propagation speed of the slit. FIG. 6 is a perspective view of a conventional mold, FIG. 7 is a perspective view showing how to use the conventional mold, and FIG. 8 is a crack generation situation in the conventional mold. The perspective view shown in FIG. 9 is a cross-sectional explanatory view of the circular portion. Here, 1 is a slab, 2 is a support base, 3 is a mold, 4 is a parallel surface, 5 is an entrance side inclined surface, 6 is an exit side inclined surface, 7 is a slit,
8 is the upper surface of the slab, 9 is the lower surface of the slab, 10 is the boundary,
Reference numeral 11 indicates a central portion of the mold, and 12 indicates a boundary line.

Claims (3)

[Claims] 1. A hot slab having a parallel surface along the slab conveying direction and an inclined surface on the entrance side thereof, and feeding the hot slab between a pair of dies that are opened and closed periodically to reduce the width to a predetermined width. In the rolling press die, the slits machined at regular intervals were formed on both the parallel surface of the die and the inclining side of the die that contact the slab side face when the maximum amount of reduction was performed. A hot rolling press die characterized by. 2. The press die for hot rolling according to claim 1, wherein the slits are provided in a lattice shape obliquely intersecting the height direction of the slab. 3. The slit according to claim 1 or 2, wherein the slit is provided only in the central portion of the mold which is separated from the boundary of the mold in contact with the upper and lower end surfaces of the slab by 10 mm or more. Press die for hot rolling.