JP6156321B2 - Hot forging method of slab - Google Patents

Description

  The present invention relates to a slab forging method, and in particular, when a slab having a large slab width / thickness ratio is forged, an excellent porosity pressing capability is achieved.

  In general, a thick steel plate is manufactured by using a slab manufactured by continuous casting or a slab obtained by performing ingot rolling of a mold casting as a raw material, and pressing them hot. When these manufacturing methods are compared, continuous casting is more dominant in terms of manufacturing cost and manufacturing efficiency, and is therefore a mainstream manufacturing method.

However, in any slab manufacturing method, void defects called porosity are generated at the final solidification position during casting due to volume shrinkage during solidification of the molten steel. Since this porosity occurs particularly in the center portion of the plate thickness, in the processing by rolling in which stress and strain are not easily applied to the center portion of the plate thickness, poor pressure bonding of the porosity often becomes a problem.
Therefore, as a method for pressure bonding the porosity, a method for improving the internal quality by hot forging with a large stress or strain applied to the center portion of the plate thickness has been developed (for example, Patent Documents 1 to 3).

JP 2002-194431 A JP-A-54-139860 JP-A-6-277783

  However, since solidification of the slab proceeds from the surface of the slab toward the center, as a feature of the continuous cast slab, solidification from the surface of the slab during casting, solidification from the back surface, There exists a triple point of coagulation in which the final coagulation position of the coagulation progress is consistent. This solidification triple point is a location where porosity compression defects are particularly problematic because there are a lot of coarser porosities than other places.

  Patent Document 1 is a forging method using a vertically symmetric anvil, and Patent Documents 2 to 3 are forging methods using a vertically asymmetric anvil having a porosity crimping capability that is even better than that of a vertically symmetric anvil. Then, even if the porosity crimping capability was secured, the crimping capability was insufficient for the coarse porosity existing at the solidification triple point near the width end of the slab.

  The present invention advantageously solves the above-described problem, and when the slab is reduced in the width direction, the thickness of the slab width end portion is uniformly thickened to uniformly bond the porosity over the entire length of the slab. The purpose is to propose a slab forging method.

Now, in order to solve the above-mentioned problems, the inventors have conducted intensive studies on thickening in the vicinity of the end portion of the slab width during the width direction reduction, and as a result, have obtained the following knowledge.
When the slab is rolled down in the width direction using an asymmetrical anvil with different vertical widths, the surface pressure of the anvil is shorter on the short side, so as shown in FIG. Thickening occurs. By performing the width direction reduction by such an anvil on the short side from both sides of the slab width end portion, the vicinity of both width end portions of the slab can be thickened. In order to perform the reduction on the short side from both side surfaces of the slab width end, the slab may be reversed.
Therefore, if the reduction in the thickness direction is performed after such a reduction in the width direction, a large reduction corresponding to the thickening can be applied, so that it is possible to press the coarse porosity present in the solidification triple point.
In FIG. 1, reference numeral 1 is an upper anvil (short-side anvil), 2 is a lower anvil (long-side anvil), 3 is a slab, and 4 is a thickening portion.

By the way, as shown in FIG. 2, it became clear that the thickening at the time of the width direction reduction becomes maximum at the end of the anvil contact region and minimum at the center of the anvil contact region.
Normally, the width of the anvil is short relative to the length of the slab, so when performing the widthwise reduction over the entire length of the slab, it is necessary to perform the widthwise reduction in several times. There will be a place where the center is crushed, that is, a place where the amount of thickening is small.

Therefore, the inventors have solved the above-mentioned problem, and as a result of repeated studies to ensure the porosity crimping effect due to thickening over the entire length of the slab, the arrangement of the anvil on the short side and the long side is the same condition. The inventors came up with a method in which the reduction in the width direction of the slab was divided at least twice and the reduction phase was shifted between the first time and the second time.
That is, according to the inventor's investigation, as shown in FIG. 3, the center of the anvil contact length (B) at the first slab feed allowance boundary and the second reduction is based on the reduction position of the short side anvil. It has been found that good porosity crimping capability can be ensured if the width reduction is performed so that the deviation (ΔL) from the above satisfies the relationship ΔL ≦ 0.20B. As this ΔL, the maximum value in the full-width direction reduction path is used.

By performing the slab reduction in the width direction under the above conditions, the vicinity of the slab width end portion on the short anvil reduction side can be uniformly thickened, and the porosity crimping ability can be improved.
Therefore, in order to cause the same thickening in the vicinity of both ends in the width direction of the slab, the slab pressure in the width direction is divided into two stages in which the slab is reversed between the first stage and the second stage, and At each stage, at least two reductions are performed, and when the slab is reduced in the width direction at each stage, the reduction position at the short side of the anvil is the boundary between the slab feed allowance at the first slab reduction and the next reduction. The rolling phase may be shifted so that the deviation (ΔL) from the center of the anvil contact length (B) satisfies ΔL ≦ 0.20B.

In addition, since the thickening at the time of the width direction reduction increases with the amount of the width direction reduction, in order to secure the coarse porosity crimping ability of the solidification triple point, the respective reduction ratios of the width direction reductions shifted from each other by 4 are set. It has also been found that it is necessary to make it at least%.
In addition, the number of times of the width direction rolling under the same arrangement of the anvil on the short side and the long side is not limited to two times, and if the mutual rolling phase is appropriately shifted, it is more than that number. It was also confirmed that it was good.

Furthermore, in the reduction in the thickness direction after the reduction in the slab width direction as described above, it has also been found that the total reduction ratio is required to ensure good porosity crimping ability to be 10% or more. It was.
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. In a slab forging method consisting of continuously rolling down in the width direction and then in the thickness direction, using an asymmetrical anvil on the slab produced by continuous casting,
The slab pressure reduction in the width direction is performed in two stages in which the slab is reversed between the first stage and the second stage, and at least twice in each stage, and the slab pressure reduction in the width direction in each stage. In this case, the reduction position of the anvil on the short side is such that the deviation (ΔL) between the slab feed allowance boundary at the first slab reduction and the center of the anvil contact length (B) at the next reduction is ΔL ≦ 0.20B. In order to satisfy
Each slab forging method characterized by making each rolling reduction in the width direction slab pressure 4% or more and making the total rolling reduction in the thickness direction slab pressure 10% or more.

2. 2. The slab forging method according to 1 above, wherein a width / thickness ratio of the slab is 2.0 or more.

  According to the present invention, even when producing a very thick steel plate having a finished plate thickness exceeding 100 mm, it is possible to secure a good porosity crimping ability over the entire surface of the slab and to stably obtain a very thick steel plate having excellent internal properties. It is extremely useful in industry.

It is the figure which showed the state in which the thickening part produced in the slab width end part vicinity of the short anvil pressure reduction side, when performing the width direction reduction of a slab using an up-down asymmetrical anvil. It is the figure which showed the state where the thickening part produced in the slab width edge part vicinity becomes the maximum in the edge part of an anvil contact area, and becomes the minimum in the center part of an anvil contact area. It is a figure explaining the shift | offset | difference ((DELTA) L) with the center of the anvil contact length (B) at the time of the 2nd reduction of a slab feed allowance.

Hereinafter, the reason for limitation of each component in the present invention will be described.
・ Inverting the slab between the first and second stages When using an asymmetrical anvil to reduce the width of the slab in the width direction, thickening occurs near the end of the slab width only on the short anvil downside. In order to thicken the vicinity of both width end portions of the slab, it is necessary to perform slab width reduction in two stages, the first stage and the second stage, and to reverse the slab during this period.

The relationship of ΔL ≦ 0.20B regarding the deviation (ΔL) between the short slab feed allowance boundary at the time of the first slab width direction reduction and the center of the anvil contact length (B) at the next slab width direction reduction. In the width direction reduction using an up-down asymmetrical anvil, the surface pressure of the short side anvil increases, so thickening during the slab width direction reduction mainly occurs on the short side. For this reason, the reduction standard is the short side.
When ΔL becomes larger than 0.20B, a portion where the thickening amount is still small is generated at the center portion of the anvil contact region, and due to the influence, a region where the porosity crimping capability is partially insufficient is generated. Therefore, ΔL ≦ 0.20B. Preferably ΔL ≦ 0.15B.

-Each rolling reduction ratio in the width direction with the phase shifted is 4% or more If the width direction rolling amount is less than 4%, the thickening amount in the vicinity of the width end cannot be increased sufficiently, and the solidification triple point Porosity crimping ability may be insufficient. Therefore, each rolling reduction in the width direction with the phase shifted is set to 4% or more.

-The total reduction ratio in the thickness direction reduction of the slab is 10% or more. If the total reduction ratio in the thickness direction reduction after the reduction in the width direction of the slab is less than 10%, it is difficult to exhibit sufficient porosity pressing capability. Therefore, the total reduction ratio in the thickness direction is 10% or more. This total rolling reduction is a rolling reduction based on the initial slab thickness that does not take into account the amount of thickening after rolling in the width direction.

・ At least two reductions in the width direction of the first and second slabs across the inversion of the slab, respectively, as shown in FIG. When the slab is rolled down in the width direction, thickening occurs only in the vicinity of the end of the slab width on the short anvil side. I can't.
In this respect, in order to thicken the vicinity of both width end portions of the slab, the following may be performed.
That is, after the slab is reduced in the width direction at least twice as described above, the slab is reversed, and similarly, the reduction phase is set so that the reduction position on the anvil on the short side satisfies ΔL ≦ 0.20B. Further, the width direction reduction is further performed at least twice under the condition of shifting.

As described above, after performing the widthwise reduction twice, the slab is reversed, and then the widthwise reduction is performed twice in the same manner, so that the vicinity of both width ends of the slab can be thickened. Therefore, the subsequent pressure reduction in the thickness direction enables the pressure bonding of the porosity over the entire surface of the slab.
In addition, the width direction reduction according to the present invention is not limited to the above-described two-time reduction-slab reversal-two-time reduction. If the respective reduction phases are appropriately adjusted, the reduction is performed three times or more. In addition, if necessary, such a series of operations may be repeated.

  The present invention is particularly suitable when applied to a slab having a width / thickness ratio of 2.0 or more, for which it has been difficult to obtain sufficient porosity pressing capability.

Since the present invention is not affected by the chemical composition of the slab to be pressed, it can be applied to a slab having any chemical composition.
The slab can be easily reversed by using a manipulator that sandwiches the longitudinal end of the slab.

  Cast pieces having a thickness of 310 mm, a width of 2400 mm, and a length of 3000 to 4300 mm were prepared for the general structural 400 MPa class steel, the general structural 490 MPa class steel, and the tempered 780 MPa class steel manufactured by continuous casting. After heating these to 1200-1250 degreeC with a heating furnace, after performing the width direction reduction of a slab with a 6000-ton forging press, the hot forging of performing thickness direction reduction was performed.

  Table 1 shows the results of an investigation of the rolling conditions in hot forging and the internal properties of the slab after forging by an ultrasonic flaw detection test. The ultrasonic flaw detection test and the pass / fail judgment were performed according to JIS G 0801, and the case of passing was indicated by ◯ and the case of failure was indicated by ×. The anvil used was an asymmetrical shape. Each reduction ratio in the width direction with the phase shifted is the minimum value of all the paths that have been shifted with the short side anvil with the phase shifted.

No. The invention examples 1, 2, 3, 5, 8, 12, 13, 14, and 17 all have excellent porosity crimping ability due to the thickening effect during the slab width reduction and the subsequent thickness reduction effect. Had.
In contrast, no. In Comparative Examples 7 and 11, the phase shift at the time of the slab reduction in the width direction was inappropriate, and therefore porosity remained at a location where the thickening amount was small at the center of the anvil contact area.
No. In Comparative Examples 10 and 18, since the rolling reduction in the slab width direction was insufficient, a sufficient amount of thickening could not be obtained, and the porosity pressing capability was insufficient.
No. In Comparative Examples 4 and 15, the total pressure reduction rate in the slab thickness direction was insufficient, so that the porosity crimping capability was insufficient.
Furthermore, no. In the comparative examples of 6, 9 and 16, only the width one side end was shifted in the width direction by shifting the phase with the short side anvil, so that the thickening effect was not obtained at the other width end portion, and the porosity remained. did.

1 Upper anvil 2 Lower anvil 3 Slab 4 Thickening part

Claims (2)

In the hot forging method of a slab consisting of continuously rolling down in the width direction and then in the thickness direction, using an asymmetrical anvil for a slab produced by continuous casting,
The slab pressure reduction in the width direction is performed in two stages in which the slab is reversed between the first stage and the second stage, and at least twice in each stage, and the slab pressure reduction in the width direction in each stage. when the anvil its width is 400~1200mm as anvil of the short side, also using the anvil width of 800~1500mm as anvil long side, pressing position in anvil of the short side, the first slab While shifting the rolling phase so that the deviation (ΔL) between the slab feed allowance boundary at the time of rolling down and the center of the anvil contact length (B) at the next rolling down satisfies ΔL ≦ 0.20B,
A method for hot forging a slab , characterized in that each rolling reduction under the slab pressure in the width direction is 4% or more, and the total rolling reduction under the slab pressure in the thickness direction is 10% or more. The slab hot forging method according to claim 1, wherein a width / thickness ratio of the slab is 2.0 or more.

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