JP6156459B2 - Method for forging steel material and method for producing steel material using the forging method - Google Patents

Description

  The present invention relates to a method for forging a steel material, in particular, a thick-walled steel material. In particular, the present invention is intended to improve the porosity crimping ability of the steel material and to further improve the finished shape advantageously.

Generally, thick steel plates are manufactured by rolling continuous cast slabs. In the as-cast slab, a large amount of voids (porosity) generated at the time of solidification shrinkage remain in the central part of the thickness where solidification is slow. Further, since solidification of the slab also proceeds from the width end face, there is little remaining void in the vicinity of the width end portion that solidifies at an early stage, and remains in other portions. Therefore, when the width / thickness ratio is increased, voids remain in a wide region in the width direction where there is no influence of solidification from the width end face. Such voids usually disappear in the subsequent hot rolling process, resulting in a product thick steel plate without internal defects.
In order to eliminate the gap (closed-crimping), it is effective to increase the processing amount (rolling rate) in the thickness direction. However, the product plate thickness that can be manufactured from a slab having a predetermined thickness is limited.

  For example, in Patent Document 1, forging in which a slab is processed in the plate thickness direction with a flat anvil prior to rolling is used in combination, and a range of rolling reduction in the forging process and rolling reduction in the plate rolling is determined. In addition, a method of manufacturing an extra heavy steel sheet with a total rolling reduction of 30% to 70% has been proposed.

  Patent Document 2 proposes a method for producing an extra heavy steel plate with a total rolling reduction of 20 to 60% in a thick plate rolling by reducing the width by 150 mm or more in the slab forging step. Yes.

  Further, in Patent Document 3, the slab width is reduced by 300 mm or more by reduction in the width direction, and the contact length of the lower anvil with respect to the continuous cast slab is set to be 3 times or more of the contact length of the lower anvil. There has been proposed a method of manufacturing an extra heavy steel plate using an anvil under a processing condition in which the total rolling reduction is in the range of 16% or more and 20% or less.

  However, in products that require mechanical properties at the center of the plate thickness, the elongation may not meet the specifications even after passing the ultrasonic flaw detection test. It is done. When such a fracture surface of the steel material is observed, a minute gap of about 0.1 to 0.2 mm smaller than the detection sensitivity of the ultrasonic flaw detection test remains, and the methods of Patent Documents 1 to 3 are sufficient. It was difficult to say that void elimination performance was obtained.

Further, Patent Document 4 discloses an upper anvil having a width 0.4 to 0.7 times the material width and an axial length 0.3 to 0.5 times the material height, The central part of a large steel ingot, in which a gap is likely to remain, using a lower anvil having a width of 1 to 1.5 times the width and an axial length of 1 to 1.5 times the material length There has been proposed a hot forging method that applies a sufficient rolling force to effectively eliminate defects.
At this time, the axial length is determined based on the material height of the upper anvil and the axial length of the lower anvil based on the material length, and the mutual relationship is not clear.
In particular, when the width / thickness ratio is large, there is a gap near the center of the thickness in a wide area in the width direction, so that the gap disappears completely even if local reduction is applied to the center in the width direction. I can't.

  In this regard, in Patent Document 5, in the forging method using an asymmetrical anvil similar to that in Patent Document 3, by making one anvil length more than twice the other, a larger hole of φ25.4 mm is 20 A method of closing under% pressure has been proposed.

  Patent Document 6 discloses that in the FM (Free from Mannesmann effect) forging method using an asymmetric anvil, the FM forging is performed twice, and the boundary of the feed allowance of the first FM forging in the second FM forging. There has been proposed a method in which a void portion remaining in the first FM forging is eliminated by a second forging by forging the portion. According to this method, it is reported that excellent void disappearance performance is obtained in which no harmful center unbonding is observed even in the macro test or the center micro polishing microscope observation, not to mention the ultrasonic flaw detection test.

Japanese Patent Laid-Open No. 7-232201 JP-A-10-263614 JP 2006-263730 A JP-A-6-277783 JP-A-54-139860 JP 2001-71082 A

Okumura et al., Iron and Steel Vol. 66, no. 2, pp203 ~

  In patent document 5, the closing characteristic of the space | gap of the shape which closed the both ends of the penetrated hole with welding is evaluated. However, for example, in the example of Patent Document 6, even if the lower anvil size is twice that of the upper anvil, it can be assumed that an ultrasonic defect was seen in one forging, so that it can be estimated that It is difficult to say that it has sufficient closing ability for the existing voids. In general, there is a report (for example, Non-Patent Document 1) that the penetrated void is easier to close than the spherical void, and at least in Patent Literature 5, the void does not penetrate as seen in a continuous cast slab. The ability to close is not clear.

  Patent Document 6 is a method of shifting the reduction position between the first time and the second time. However, since there is axial extension due to the first reduction, the second feeding allowance is larger than the first feeding allowance. Since the elongation at this time changes variously depending on the rolling reduction ratio and the friction coefficient with the anvil, the feeding allowance for the second rolling reduction is not constant. In particular, the example of Patent Document 6 discloses a case where the forging ratio is 2.4 (the cross-section reduction rate is 58%) and the reduction is large, and the second feeding allowance is about twice the first. With wide slab material, it may exceed the load limit of the equipment load, so it may not be applicable.

  In general, since the width of the slab and the width of the final product are different, at the time of forging, first the width direction is reduced to adjust the width size, and then the thickness direction is reduced. In such forging, if the rolling in the width direction is performed using an asymmetrical anvil, that is, the rolling is performed in a state where the contact lengths and contact positions of the upper and lower anvils are different, the deformation becomes asymmetrical in the vertical direction and a width warpage occurs.

After the forging process as described above, if a reduction in the thickness direction is performed in a state where the width warpage has occurred, further shape defects are induced. In addition, if hot rolling is performed with the width warpage remaining, there is a concern that a threading defect such as meandering may occur, so that a step of cutting into a shape having no width warpage occurs after forging, resulting in a decrease in yield.
Normally, the length of anvil is very short compared to the length of the slab, so it is extremely difficult to correct the width warp during forging, and even if it can be corrected, the forging efficiency is greatly increased in that case. To drop.

  The present invention advantageously solves the above problem, and a first object is to reduce the ultrasonic wave in the thickness direction reduction (thickening treatment) of a steel material using asymmetric flat metal lays having different lengths of upper and lower metal lays. Needless to say, a flaw detection test is to provide a method for forging a steel material having excellent void disappearance performance in which an uncompressed void is not observed even in a macro test or central micro polishing microscope observation.

Further, the second object of the present invention is to effectively generate the width warp during the width direction reduction even when the width direction reduction and the thickness direction reduction of the steel material are continuously performed using an asymmetric flat metal laying. It is to provide a method for forging a steel material that can be suppressed to an excellent finished shape.
Furthermore, the third object of the present invention is to provide a steel material obtained by the forging method described above.

  In order to solve the above problems, the inventors focused on the deformation behavior of steel during thickness direction reduction (thickening treatment) using an asymmetric flat metal slab, and further in the width direction reduction, and bonded with porosity. Furthermore, as a result of intensive studies to prevent width warpage, the following knowledge was obtained.

When using asymmetric flat metal laying down in the thickness direction of the steel material, that is, when performing a thickness reduction process, the processing surface side pressed with a flat metal slab with a short length and the processing surface side pressed with a long flat chin Then, it turned out that the distortion | strain introduction form with respect to the steel material which is a workpiece is different, and cannot necessarily introduce | transduce distortion appropriately into the inside of steel material.
Therefore, as a result of various investigations on methods that can effectively introduce strain into the steel material, the end position of the pair of upper and lower flat metal mats when performing the reduction in the thickness direction is reduced at least on the unforged side. It was found that the intended purpose was achieved by shifting by a predetermined distance according to the previous plate thickness.

It was also found that the cause of the width warpage when the slab was reduced in the width direction was asymmetrical vertical deformation due to the displacement of the down-sliding position of the upper and lower flat metal mats or the difference in the contact length of the upper and lower flat metal mates.
Therefore, when the displacement of the end position of the upper and lower flat anvils (slab longitudinal center side) is controlled below a certain value with respect to the contact length of the shorter flat anvil, the vertical asymmetry It has been found that deformation is suppressed and width warpage is reduced.
The present invention was developed after further studies based on the above findings.

That is, the gist configuration of the present invention is as follows.
1. For steel materials, the thickness of the upper and lower anvils is reduced by two passes using a pair of flat anvils with the same or different lengths, and a pass operation that alternately repeats the feeding operation in the same axial direction. A method for forging a steel material, wherein the end positions of a pair of upper and lower flat metal lays are separated by (thickness H of the steel material before rolling) / 2 or more on the non-forged side.

2. The steel material is subjected to a thickness reduction process by alternately repeating a reduction from two directions using a pair of flat anvils with different lengths of upper and lower anvils and a feed operation in the same axial direction. A steel material characterized in that the end positions of a pair of upper and lower flat metal lays are separated by (thickness H of steel material before reduction) / 2 or more on both the unforged side and the already forged side. Forging method.

3. The thickness reduction process by the pass operation is divided into n times (n is an integer of 2 or more) and the thickness direction reduction is performed, and when i is an integer of 2 to n, the i-1th thickness reduction process. The forging of the steel material according to 1 or 2 above, wherein the feed boundary is positioned in a range of a predetermined position ± (feed amount / 6) of an anvil having a shorter length in the i-th thickness reduction process. Method.

4). For a steel material, using a pair of flat anvils with different lengths of upper and lower anvils, in a forging method for steel materials consisting of continuously reducing in the width direction and then in the thickness direction,
The above-mentioned reduction in the width direction is performed from the end in the longitudinal direction of the steel material. At that time, the amount of shift of the end position of the upper and lower anvils at the longitudinal center side of the steel material is ΔL, and the contact length with the steel material of the upper and lower anvils is When the shorter contact length is B, the ratio ΔL / B is width-reduced under the condition of 0.20 or less,
On the other hand, when performing thickness direction reduction, the forging method of the steel materials characterized by applying the thickness reduction process in any one of said 1-3.

5. 5. The method for forging a steel material according to any one of 1 to 4 above, wherein a width / thickness ratio of a cast slab is 3 or more

6). A steel material produced by the forging method according to any one of 1 to 5 above.

According to the present invention, it is possible to obtain a steel material in which no voids remain, in particular, which cannot be detected by ultrasonic flaw detection, but does not leave voids of about 0.2 mm that affect the mechanical properties of the material.
In addition, according to the present invention, when forging using an up-and-down asymmetric anvil with high porosity crimping capability is applied not only in thickness direction reduction but also in width direction reduction, the finished shape of the slab after forging is improved. Can do.

It is the figure which showed the reduction | decrease point in the case of performing the thickness reduction process (thickness direction reduction) of steel materials using a pair of flat anvil from which the length of an upper anvil and a lower anvil is different. When the edge position deviation ΔB _E of the flat metal is provided on the non-forged side of the steel material (a), and the edge position deviations ΔB _E and ΔB _D of the flat metal edge are provided on both the non-forged side and the already forged side of the steel material. It is the figure which showed the case (b). It is the figure which showed the relationship between the minimum distortion of the longitudinal direction in the width center of steel materials, and the thickness center part, and deviation | shift amount (DELTA) _BE , (DELTA) _BD of a flat metal edge part. It is the figure which showed the state of the distortion introduce | transduced into steel materials, when thickness direction reduction is performed using an up-down asymmetric flat metal laying. It is a figure explaining the case where edge part position shift (DELTA) _BE is provided using the symmetric flat anvil with the same length as an upper and lower anvil. It is the figure which showed the reduction | decrease point which performs the width direction reduction | decrease of a slab using the asymmetrical anvil with which the length of an upper anvil and a lower anvil is different. It is the figure which showed the evaluation point of the width curvature of a slab.

Hereinafter, the present invention will be specifically described with reference to the drawings.
A reduction procedure in the case of performing a steel thickness reduction process (thickness reduction) using a pair of flat anvils having different upper and lower anvil lengths will be described with reference to FIGS. In the figure, reference numeral 1 is an upper anvil, and 2 is a lower anvil. In this example, the upper anvil 1 constitutes a short flat anvil and the lower anvil 2 constitutes a long anvil. 3 is a steel material (slab).

FIG. 1 (a) shows a state in which asymmetric flat metal mats 1 and 2 are in contact with the upper and lower surfaces of the steel material 3. Thus, the thickness direction reduction of the steel material is performed from the end of the steel material 3.
FIG. 1 (b) shows a state where the reduction is actually applied from two directions by the flat metal mat pairs 1 and 2 described above.
After the end pressure reduction is completed, after the gap between the flat metal mats 1 and 2 is returned to the initial state, the steel material 3 is fed in the same axial direction by a predetermined length, and asymmetrically formed on the upper and lower surfaces of the steel material 3 again. The flat metal mats 1 and 2 are brought into contact. FIG. 1C shows this state.
Then, as in the case shown in FIG. 1 (b), the steel material is pressed down from two directions by the flat metal mat pairs 1 and 2. FIG. 1D shows this state.
As described above, the thickness direction reduction of the steel material is performed by a pass operation that alternately repeats the reduction from the two directions using the flat metal laying and the feeding operation in the same axial direction sequentially from the end of the steel material.

Now, in the present invention, in the thickness reduction process as described above, as shown in FIG. 2A, the end positions of the pair of upper and lower flat metal mats are not matched on the non-forged side of the steel material. _As shown by _E , an appropriate amount of deviation is provided.
Further, as shown in FIG. 2 (b), not only providing the .DELTA.B _E shifted to non-forged side of the steel, be provided with a displacement indicated with .DELTA.B _D also already forging side, it is more advantageous.

Hereinafter, the result of investigating the deformation inside the steel material by the FE analysis when the contact length between the flat metal plate and the upper and lower flat metal plates is different will be described.
The slab of initial thickness 310 mm, the length of the flat anvil 1 is 310 mm, the length of the flat anvil 2 and its end position are changed variously, and after forging 25 mm at a feed amount of 310 mm, the width center, thickness and the minimum distortion in the longitudinal direction at the central portion, of the flat anvil end deviation amount .DELTA.B _E, the results of examining the relationship between .DELTA.B _D, shown in FIG. For reference, FIG. 3 also shows the results of an investigation for the case where an end position shift is provided only on the forged side (ΔB _E = 0).

As shown in FIG. 3, for any case of non-forged side only when it is providing the end position deviation .DELTA.B _E and untreated forging side and already forging side of both the end position deviation .DELTA.B _E, the .DELTA.B _D provided However, by setting ΔB _E and ΔB _D to 0.50 or more in the ratio to the thickness H of the steel material before rolling, the minimum strain in the longitudinal direction at the width center and the thickness center portion could be increased. It was also confirmed that this effect was even greater when the end position displacement was provided on both the unforged side and the already forged side.
In the case where the end position shift is provided only on the already forged side, the minimum strain could not be increased regardless of the shift amount.

  Therefore, in the present invention, the end positions of the upper and lower flat anvils are shifted at least on the non-forged side, and the shift amount is set to be 0.5 times or more the steel material thickness before rolling. The upper limit of the amount of deviation is not particularly limited, but if the amount of deviation is too large, the anvil becomes larger and its manufacturing cost increases, and a dedicated device may be required for replacement work. In addition, in the forging method of reducing the width direction by reducing the shift amount of the end position of the anvil and then reducing the thickness direction, it is necessary to move the position of the anvil greatly in order to ensure the shift amount, Since adverse effects such as the time required for the setting occur, it is practical to set the upper limit of the deviation amount to about 1.0 times the steel thickness.

By the way, when the thickness of the steel material is reduced to a predetermined thickness, the thickness reduction process is not necessarily performed only once in the thickness direction, but the thickness is reduced to a predetermined thickness by performing the thickness direction reduction a plurality of times. It is possible to do. Note that a process of reducing the thickness to a predetermined thickness by combining a plurality of times of reduction in the feeding direction is referred to as one thickness reduction process.
In this case, the thickness reduction process is divided into n times (n is an integer of 2 or more), and when i is an integer of 1 to n, the feed in the i-1th thickness reduction process is performed. It is advantageous that the boundary portion is positioned within a range of a predetermined position ± (feed amount / 6) of the flat metal plate having a shorter length during the i-th thickness reduction process. The reason is as follows.
The feed boundary here is a position where the thickness is reduced at the end (unforged side) of the flat portion of the flat metal stake having a shorter length in the i-1th thickness reduction process. The predetermined position of the anvil is a position of the feed amount / 2 from the end (unforged side) of the flat portion of the flat anvil having a shorter length.

First, FIG. 4 shows the result of examining the state of strain introduced into the steel material when the thickness direction reduction is performed using an asymmetrical flat metal floor. Here, the region to which the processing is given after feeding is a portion surrounded by a black frame (hereinafter referred to as a processing region).
As shown in FIG. 4, when looking at the central portion in the thickness direction, the distortion is reduced at the end of the processed region.
That is, in the central part in the thickness direction, a moderate pressure is applied in the central area in the length direction of the flat metal mat, and distortion is introduced, but sufficient pressure is not applied on both sides and the amount of distortion introduced is small.
Therefore, the strain introduced into the steel material becomes more uniform in the longitudinal direction of the steel material by giving a large strain at the i-th time to a portion where the strain is small at the i-1th thickness direction pressure reduction. At this time, as shown in FIG. 4, a large strain equal to or greater than the rolling reduction is applied at the central portion in the thickness direction because the feed amount in the central region in the longitudinal direction of the flat metal mat, particularly in the central region in the longitudinal direction of the flat metal mat. The feed boundary in the (i-1) th thinning process is set to a predetermined length of the flat metal mat with a shorter length during the i-th thinning process so that this portion is included in the feed boundary area. It is desirable that the position is within a range of position ± (feed amount / 6).
The feed amount is normally set to 1/2 or more of the plate thickness before thickness reduction in which distortion corresponding to the rolling reduction is applied to the central portion in the thickness direction. Further, when the feed amount is increased, the number of processes for reducing the total length is reduced, so that the productivity is improved, but the load is increased. For this reason, the feed amount is increased as much as possible within the equipment allowable load.
Moreover, the number of times of the thickness reduction treatment can be set to 2 times or more, but if the number is too large, the productivity is lowered, and therefore the upper limit is preferably about 6 times. Further, from the viewpoint of further homogenizing the strain introduction mode at the thickness center portion of the steel material, it is preferable that the number of times is even.

While there has been described the case of using the asymmetric flat anvil as a vertical flat anvils, if only the non-forging side providing the end position deviation .DELTA.B _E, as shown in FIG. 5, is equal both the upper and lower anvil length symmetry It is also possible to use a flat anvil.

Next, with reference to FIG. 6, the case where the width reduction of steel materials is performed using the asymmetric flat anvil in which the length of an upper anvil and a lower anvil is different is demonstrated. In this example, the upper anvil 1 has a shorter flat anvil and the lower anvil 2 has a longer flat anvil. In the figure, l ₁ indicates the width of the flat anvil 1 and l ₂ indicates the length of the flat anvil 2. B ₁ represents the contact length of the flat metal lay 1 with respect to the steel material, and B ₂ represents the contact length of the flat metal lay 2 with respect to the steel material. Thus, in this example, it refers to B ₁ and the contact length B of the shorter length of contact between the steel material of the upper and lower anvil. Furthermore, ΔL indicates the amount of deviation of the end positions of the upper and lower anvils on the steel material longitudinal center side.

Now, in the case shown in FIG. 6, when the reduction in the width direction is performed from the end in the longitudinal direction of the steel material, the shift amount ΔL of the end position (the slab longitudinal center side) of the upper and lower flat metal mats is gradually reduced. As a result, by reducing this ΔL, specifically, ΔL is 0.20 or less with respect to the contact length B (B _{1 in} this example) of the upper and lower flat anvils with the shorter contact length to the steel material. In this case, it was found that the vertical asymmetric deformation is effectively suppressed and the width warpage is reduced. A more preferable range of ΔL is 0.10 or less with respect to the contact length B of the shorter contact length. ΔL may be zero.
FIG. 6 shows the case where B ₁ is smaller than B _2. Similarly, when B ₁ is larger than B ₂ , ΔL is the contact length of the upper and lower flat anvil with the shorter contact length to the steel material. The width warpage is reduced by setting it to 0.20 or less, preferably 0.10 or less with respect to B (B ₂ ).

At this time, the contact length B ₁ of the flat metal mat ₁ having the shorter contact length is preferably set to (0.60 to 1.00) times the length l ₁ of the flat metal mat _1. found. This is because if B ₁ is less than 0.60 times l _1, the number of buses increases and the forging efficiency decreases. A more preferred B ₁ / l ₁ ratio is in the range of 0.80 to 0.95.

  As described above, even if the lengths of the upper and lower anvils are different, and even if the center positions of the upper and lower anvils are shifted, the reduction in the width direction against the slab is preferably performed under an appropriate contact length, and By controlling the amount of deviation of the end position of the upper and lower anvils (slab longitudinal center side) within a predetermined range, the deformation position by the upper and lower anvils is equivalent to the surface pressure, effectively reducing the width warpage during the reduction. It was discovered that it can be suppressed.

  The vicinity of the width end where there are few voids remaining in the raw slab is only about ½ of the thickness in the width direction, and therefore there are many voids remaining in the center area of the “width-thickness” in the width direction. It has been known. In other words, when the width / thickness ratio of the material slab is 3 or more, voids remain over a wide region of 2/3 or more of the width, the width to which the reduction is applied becomes wider, and the contact area with the anvil increases. This leads to an increase in forging load. For this reason, it is preferable to apply this invention which can reduce the contact length of a feed direction.

In addition, in order to adjust the deviation | shift amount of the edge part position of an up-and-down anvil, the method of sliding an up-and-down each anvil position is mentioned.
Further, the present invention is not affected by the component composition of the slab to be pressed, and thus can be applied to a slab having any component composition.

Example 1
Cast pieces having a thickness of 310 mm, a width of 1800 mm, and a length of 3500 mm were prepared for general structural 400 MPa grade steel, general structural 490 MPa grade steel, tempered 780 MPa grade steel, carbon steel S35C and SUS304 steel, respectively. These were reheated to 1250 ° C. in a heating furnace, and then the whole width was sequentially reduced from the end portion in the longitudinal direction at a time in the thickness direction, and finished in one reduction to a thickness of 280 mm. In addition, some slabs were reheated to 1250 ° C. in a heating furnace, and then the entire width was reduced to 295 mm in the thickness direction at a time while feeding 270 mm in the longitudinal direction from the end. Subsequently, the pressed slab was reversed so that the surface in contact with the flat metal lay was reversed, and the second squeezing was performed up to a thickness of 280 mm while feeding 290 mm in the longitudinal direction. At this time, the slab longitudinal direction of the flat anvil was provided with relief of R80 mm on both sides, and the end position was adjusted by moving the position of the lower anvil with a long length in the longitudinal direction. In addition, when the reduction is performed twice, the position of the upper flat anvil having a short length is moved in the longitudinal direction in the second reduction, so that the feeding boundary portion of the first reduction becomes the length of the upper flat anvil. It adjusted so that it might become within 40 mm from the predetermined position of a horizontal direction.

When a sample with a thickness center of ± 10 mm and a length center of ± 250 mm is taken from the center of the width of the steel material thus obtained, and the presence or absence of porosity is first observed with a 20 × projector, and porosity is observed The size was confirmed by enlarging 100 times, and the number of porosity of 0.1 mm or more was investigated over the longitudinal direction.
The forging conditions and the investigation results of porosity are shown in Tables 1-1 and 1-2. The flat metal lay length is the total length of the flat portion and the relief R portion. Moreover, the numbers 01-12 are attached | subjected to the forging conditions for every steel types AE.

As shown in the table, the porosity of 0.2 to 0.5 mm does not remain under the conditions of 03, 04, 09, 10, 11, and 12 that satisfy the requirements of the present invention, and particularly the end portions on both sides. It can be seen that 09, 10, and 12 in which the positions are shifted are particularly excellent with no porosity remaining. In condition 03, the length of the lower anvil was 1.6 times and less than twice the length of the upper anvil, but a sufficient porosity pressing effect was obtained.
On the other hand, although the lengths of the upper and lower anvils are different, in the case of 02,08 where the shift of the end position is not sufficient, although there is no porosity of 0.5 mm or more detected by ultrasonic flaw detection, 0.2-0 A porosity of 5 mm remained. In addition, in 05,06,07 in which the position of the end of the anvil on the unforged side is the same position, a porosity of 0.5 mm or more remains, for example, the length of the anvil is doubled as in 07 However, it turns out that it is insufficient.

Example 2
Table 2 shows the results of the investigation on the amount of warpage of the slab after the reduction when the slab is reduced in the width direction under various conditions shown in Table 2.
As shown in FIG. 7, the slab width warpage amount is L as the length of the slab after the reduction in the width direction, and the maximum value from the line connecting both width ends of the slab to the inside of the warp. When it was set as ΔW _max , it was assumed that ΔW _max / L × 100 (%) was evaluated, and a case where this value was 0.8% or less was regarded as acceptable.

As shown in the table, No. 1 was subjected to width direction rolling under the conditions according to the present invention. In all of Nos. 1 to 7, the amount of displacement of the end portion of the upper and lower anvils at the longitudinal center side of the slab was sufficiently small with respect to the anvil contact length, so that the amount of width warp produced was small.
On the other hand, No. 1 in which the width direction reduction was performed under conditions deviating from the present invention. In Nos. 8 to 13, since the shift amount of the end position on the slab longitudinal center side of the upper and lower anvils is large, as a result of the asymmetrical deformation in the vertical direction, the width warpage is large.

1 Upper anvil 2 Lower anvil 3 Slab

Claims (6)

  For steel materials, the thickness of the upper and lower anvils is reduced by two passes using a pair of flat anvils with the same or different lengths, and a pass operation that alternately repeats the feeding operation in the same axial direction. A method for forging a steel material, wherein the end positions of a pair of upper and lower flat metal lays are separated by (thickness H of the steel material before rolling) / 2 or more on the non-forged side.   The steel material is subjected to a thickness reduction process by alternately repeating a reduction from two directions using a pair of flat anvils with different lengths of upper and lower anvils and a feed operation in the same axial direction. A steel material characterized in that the end positions of a pair of upper and lower flat metal lays are separated by (thickness H of steel material before reduction) / 2 or more on both the unforged side and the already forged side. Forging method.   The thickness reduction process by the pass operation is divided into n times (n is an integer of 2 or more) and the thickness direction reduction is performed, and when i is an integer of 2 to n, the i-1th thickness reduction process. The feed boundary portion is positioned in a range of a predetermined position ± (feed amount / 6) of an anvil having a shorter length in the i-th thickness reduction process. The steel material according to claim 1 or 2, Forging method. For a steel material, using a pair of flat anvils with different lengths of upper and lower anvils, in a forging method for steel materials consisting of continuously reducing in the width direction and then in the thickness direction,
The above-mentioned reduction in the width direction is performed from the end in the longitudinal direction of the steel material. At that time, the amount of shift of the end position of the upper and lower anvils at the longitudinal center side of the steel material is ΔL, and the contact length with the steel material of the upper and lower anvils is When the shorter contact length is B, the ratio ΔL / B is width-reduced under the condition of 0.20 or less,
On the other hand, when performing thickness direction reduction, the forging method of the steel materials characterized by applying the thickness reduction process in any one of Claims 1-3.   The method for forging a steel material according to any one of claims 1 to 4, wherein a width / thickness ratio of a cast slab is 3 or more. Method for producing a steel material, characterized in that the production of steel by forging method of the steel according to any one of claims 1 to 5.