JP6156320B2 - Steel forging method - Google Patents

Description

  The present invention relates to a method for forging a steel material, particularly a thick-walled steel material, and particularly intends to improve the porosity crimping ability of the steel material.

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. 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.

  In this regard, in Patent Document 4, in the forging method using an asymmetrical anvil similar to that of Patent Document 3, by making one anvil length more than twice the other, a larger hole with a diameter of 25.4 mm is 20 Proposes a method of closing under a pressure of 50%.

  Further, in Patent Document 5, in the FM (Free from Mannesmann effect) forging method using an asymmetrical 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-54-139860 JP 2001-71082 A

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

  In patent document 4, 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 5, even if the size of the lower anvil is twice that of the upper anvil, it can be estimated that an ultrasonic defect was observed 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 4, the void does not penetrate as seen in a continuous cast slab. The ability to close is not clear.

  In Patent Document 5, the reduction position is shifted 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 5 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 feed 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.

The present invention advantageously solves the above problem, and 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, it goes without saying that an ultrasonic flaw detection test is performed. Furthermore, an object of the present invention is to provide a method for forging a steel material having excellent void disappearance performance in which no uncompressed voids are observed even in macro test or central micro polishing microscope observation.
Moreover, an object of this invention is to provide the steel materials obtained by said forging method.

  Now, in order to solve the above problems, the inventors have paid attention to the deformation behavior of the steel material in the thickness direction reduction (thickening treatment) using an asymmetric flat metal stake, and are eager to effectively bond the porosity. As a result of the examination, the following knowledge was obtained.

When the thickness reduction process is performed using an asymmetric flat metal mat, the processed surface side pressed by a short flat metal mat and the processed surface side pressed by a long flat metal mat are workpieces. It was found that the introduction of strain into the steel was different.
That is, on the processed surface side pressed by a long flat metal lay, distortion is introduced almost uniformly from the processed surface toward the center, whereas the processed surface pressed by a short flat metal lay On the side, it became clear that a region where distortion is not introduced remains in the central region of the processed surface and the central portion in the thickness direction.

Therefore, the steel materials having different strain introduction forms on both the machined surfaces as described above are reversed, and the surface side where the strain is not introduced in the central region of the machined surface is brought into contact with the flat metal lay having a long length. When the thickness reduction treatment was performed again, it was found that distortion was effectively introduced into the central portion in the thickness direction, not to mention both the machined surfaces of the steel material, and as a result, porosity could be crimped.
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. Steel material is subjected to thickness reduction treatment by pass operation that alternately repeats reduction from two directions using a pair of flat anvils with different lengths of upper and lower anvils and feed operation in the same axial direction. A forging method of
The steel material thinning process by the above pass operation is divided into n times (where n is an integer of 2 or more), and i is an integer of 2 to n. A method for forging a steel material, wherein the steel material is inverted by a first thickness reduction process, and the processed surface of the steel material contacting the upper and lower flat metal lays is reversed between the (i-1) th and i-th times.

2. Regarding the feeding operation of the steel material in the same axial direction, the feed boundary portion in the i-1th thickness reduction process is the predetermined position ± (feed amount / 6) of the flat anvil having the shorter length in the ith thickness reduction treatment. 2. The method for forging a steel material according to 1 above, wherein the steel material is forged.

3. 3. The method for forging a steel material according to 1 or 2 above, wherein the end positions of the pair of upper and lower flat metal lays are separated by (thickness H before rolling of the steel material) / 2 or more on the unforged side.

4). The end positions of the pair of upper and lower flat metal lays are separated by (thickness H before rolling of steel material) / 2 or more on both sides of the unforged side and the already forged side. Steel forging method.

5. A steel material manufactured by the forging method according to any one of 1 to 4 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 also does not leave voids of about 0.2 mm that adversely affect the mechanical properties of the material.

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. 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 showing a measurement position of distortion. It is the figure which compared and showed the difference in the introduction | transduction form of the distortion in steel materials, when performing thickness direction rolling of 1 time and 2 times of thickness direction rolling down including reversal of steel materials. 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 range which the deformation | transformation produced in the thickness direction, and the edge part position shift | offset | difference of a flat anvil in the center part of a shorter flat anvil.

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.

Next, FIG. 2A shows the result of examining the state of strain introduced into the steel material when the thickness direction reduction is performed using the flat asymmetrical metal floor as described above. Here, the region to be processed after feeding is a portion surrounded by a black frame (hereinafter referred to as a processing region). FIG. 2B shows, for reference, the state of strain introduction when a pair of flat anvils having the same length of the upper and lower anvils is used.
In both cases of FIGS. 2A and 2B, there is a portion where distortion is not introduced on the anvil contact surface.
In addition, as shown in FIG. 2 (a), when an asymmetrical flat metal is used, the strain introduction form is different on the upper and lower surfaces of the steel material, and in the processing region on the side pressed by the long flat metal, Except for a small portion at the center of the anvil contact surface, strain is introduced almost throughout the area. On the other hand, in the processing region on the side pressed by the flat metal stake having a short length, the anvil contact surface has a small distortion portion.
Next, when looking at the central portion in the thickness direction, the distortion is reduced at the end of the processing region.
That is, in the central portion of the thickness, a moderate pressure is applied in the central region in the length direction of the flat metal lay to introduce strain, but sufficient pressure is not applied on both sides and the amount of strain introduced is small.
For this reason, even when using an asymmetric flat anvil, there is a concern that the pressure bonding capacity of the porosity will be insufficient at the central portion in the thickness direction at the boundary of the processing region boundary part, where the distortion is small, and the length is short. There is.

Therefore, in the present invention, the reduction in the thickness direction by the above-described asymmetric flat metal laying is performed twice or more, that is, the thickness reduction process is performed n times (n is an integer of 2 or more), and i is 2 to n. In this case, the steel material is inverted in the (i-1) th and ith thickness reduction processes, and the processed surface of the steel material in contact with the upper and lower flat metal lays is reversed between the (i-1) th time and the ith time.
By two or more reductions performed by reversing the steel material, the form of strain introduction to the steel material is equalized on the upper and lower processed surfaces and the center of thickness, thereby achieving effective porosity crimping.

Further, upon the i-th reduction, the feeding boundary portion in the i-1th thickness reduction process is positioned in the vicinity of the central portion of the length that contacts the shorter flat metal mat in the i-th thickness reduction process. It is preferable, and as a result, sufficient strain is introduced into both sides in the length direction of the flat anvil at the central portion of the thickness where sufficient strain is not necessarily introduced in the (i-1) th reduction. The strain is introduced more uniformly in the center of the thickness, and as a result, the porosity can be more effectively crimped.
Here, as shown in FIG. 2 (a), a large strain equivalent to or more than the rolling reduction is applied at the center in the thickness direction because the feed amount in the central area in the longitudinal direction of the flat metal mat, particularly in the central area in the longitudinal direction of the flat metal mat. The feed boundary in the (i-1) th thinning process is set so that this portion is included in the feed boundary area. It is desirable that the position is within a range of a predetermined position ± (feed amount / 6).
Note that the number of times of the thinning process may be two or more, but if the number is too large, the productivity is lowered, so the upper limit is preferably about six times. In addition, 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.
Further, the feed amount is usually about 100 to 800 mm.
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.

  Next, when the thickness direction reduction of the steel material is performed once as in the past, and when the thickness direction reduction is divided into two times and the steel material is reversed between the first time and the second time. The difference in the state of strain introduction into steel was investigated.

The experiment was performed as follows.
Deformation when a slab having an initial thickness of 310 mm was reduced to 285 mm by 25 mm by one thickness direction reduction and two thickness direction reductions including reversal of the steel material was confirmed by FE analysis. The length of the flat anvil 1 is 310 mm and the length of the flat anvil 2 is 620 mm, and after the reduction, the axial position of the steel material is shifted by 310 mm. That is, the feed amount was 310 mm. Moreover, when rolling down twice, after rolling down 12.5 mm in the 1st time, the steel material was turned upside down and further rolled down 12.5 mm.
The strain distribution was measured at the center portion of the flat anvil having a shorter length, as shown by a two-dot chain line in FIG.
The obtained results are shown in FIG.
Note that the strain is expressed as a relative ratio, where 1 is the strain corresponding to the reduction amount.

In the figure, Δ represents a case where the sheet is squeezed once, and the distortion amount is relatively small on the + side (upper side in the figure) in contact with a flat metal mattress having a small length.
On the other hand, the case indicated by ● is the case where the pressing is performed in steps of 12.5 mm, and it can be seen that the upper and lower strains are almost equal.

  The reversal of the steel material can be easily performed by using a manipulator that sandwiches the end of the steel material.

Next, the FE analysis was performed about the influence of the difference of the edge part position of two flat anvils.
In FIG. 5, the definition of the shift | offset | difference amount of the anvil edge part position in the contact area of the up-and-down flat anvil with respect to steel materials is shown.
FIG. 5A shows a case where the position of the end portion of the flat anvil is shifted on the non-forged side of the steel material, and the shift amount is indicated by ΔB _E.
5 (b) is a case where shifting the edge position of the flat anvil on opposite sides of the non-forged side and already forging side of steel, showing the amount of displacement existing forging side of the case in .DELTA.B _D.

FIG. 6 summarizes the results of examining the relationship between the range of deformation in the thickness direction and the shift amount of the end position of the anvil at the center of the flat anvil with a shorter length. Here, a range in which a strain of 50% or more of the strain corresponding to the amount of reduction was generated was defined as a range in which the deformation occurred. Also, shift amounts .DELTA.B _E and .DELTA.B _D end positions of the flat anvil was expressed as a ratio to the thickness H of the front pressure of the steel.

  As shown in the figure, the range in which deformation occurs in the thickness direction increases by shifting the end positions of the upper and lower flat anvils. And the increase amount of this deformation range is larger in the second reduction including the reversal of the steel material than in the case where the reduction is performed once. In addition, the effect is greater when both the unforged side and the already forged side are shifted than when only the unforged side is shifted. Furthermore, regarding the deviation amount ΔB, by setting ΔB / H to 0.50 or more, a very good result can be obtained. Here, the thickness H of the steel material in the second reduction in the second method is the thickness of the steel material after the first reduction.

In addition, in order to adjust the deviation | shift amount of the edge part position of an up-and-down flat 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
A slab having a thickness of 310 mm, a width of 1800 mm, and a length of 3500 mm of general structural 400 MPa class steel manufactured by continuous casting was prepared. These 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 300 mm from the end portion in the longitudinal direction. Subsequently, the slab was reversed to reverse the surface in contact with the flat metal lay, and the second reduction was performed up to a thickness of 280 mm while feeding 315 mm in the longitudinal direction. At this time, the slab longitudinal direction of the flat metal lay was provided with a relief of R80 mm on both sides, and the end position was adjusted by moving the position of the lower flat metal lay having a long length in the longitudinal direction. No. In 14 and 15, by moving the position of the upper flat anvil with a short length in the longitudinal direction in the second reduction, the feeding boundary portion of the first reduction is moved from a predetermined position in the length direction of the upper flat anvil. Adjustments were made to be within 30 mm.

When a sample of the total thickness is collected from the center of the width of the steel material thus obtained within the range of the length center ± 250 mm, the position of the porosity is first observed with a 20 × projector, and the 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.
Table 1 shows the forging conditions and the survey results of porosity. The flat metal lay length is the total length of the flat portion and the relief R portion.

As shown in the table, No. 1 satisfying the requirements of the present invention. Under the conditions of 1 to 6, 13, 14, and 15, only a porosity of 0.5 mm or less remains. Furthermore, the distance between the edge portions of the unforged side is 0.5 or more in ΔB / H. In 2, 3, 5 and 6, no porosity of 0.2 to 0.5 mm remained. In particular, no. 5 and 6 indicate that the porosity is not excellent at all and is particularly excellent.
On the other hand, No. in which the contact surface with the flat anvil was the same without reversing the steel material. In 7-12, more porosity remained. Although the lengths of the top and bottom flat bars are different, the difference in end position is small. In 7, 10, the porosity of more than 0.5 mm detected by ultrasonic flaw detection remained.

1 Upper anvil 2 Lower anvil 3 Slab

Claims (4)

Steel material is subjected to thickness reduction treatment by pass operation that alternately repeats reduction from two directions using a pair of flat anvils with different lengths of upper and lower anvils and feed operation in the same axial direction. A forging method of
The steel material thinning process by the above pass operation is divided into n times (where n is an integer of 2 or more), and i is an integer of 2 to n. A method for forging a steel material, wherein the steel material is inverted by a first thickness reduction process, and the processed surface of the steel material contacting the upper and lower flat metal lays is reversed between the (i-1) th and i-th times.   Regarding the feeding operation of the steel material in the same axial direction, the feed boundary portion in the i-1th thickness reduction process is the predetermined position ± (feed amount / 6) of the flat anvil having the shorter length in the ith thickness reduction treatment. The steel forging method according to claim 1, wherein the steel material is forged.   The method for forging a steel material according to claim 1 or 2, characterized in that the end positions of the pair of upper and lower flat metal lays are separated by (thickness H before rolling of the steel material) / 2 or more on the unforged side.   The end positions of the pair of upper and lower flat metal lays are separated by (thickness H before rolling of steel material) / 2 or more on both sides of the unforged side and the already forged side. Steel forging method.