JPH0710427B2 - Continuous forging method of slab in continuous casting - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a continuous forging method for a slab in continuous casting, and in particular, an internal quality at a stage before a solidification completion point of a slab obtained in continuous casting. It is intended to simply and effectively carry out the forging process effective for improving the above.

(Prior art) Center segregation of continuous cast pieces of steel appears as positive segregation due to the concentration of molten steel components such as C, S, and P in the center of thickness of the final solidification zone of the cast pieces. In particular, it causes deterioration of mechanical properties in the plate thickness direction in thick plate products and causes lamination,
This is one of the quality defects that cannot be avoided in the conventional casting method.

In the case of continuous casting, in the case of continuous casting, the center segregation that causes such an adverse effect is caused by the solidification shrinkage of the solidification tip and the vacuum suction force of the void created by the bulging of the solidification shell, etc. It is considered that, as a result of the molten steel component being sucked in, positive segregation remains in the center of the cross section of the cast slab.

As a measure for preventing such center segregation, for example, electromagnetic stirring in the secondary cooling zone has been tried, but it has not yet been reduced to semi-micro segregation, and its effect is not sufficient.

In addition, an in-line reduction method (iron and steel 60th year (197
4) No. 7, pp. 875-884) was also tried, but if the reduction in the slab region where the unsolidified layer is large is insufficient, cracking occurs at the solidification interface, and conversely if the reduction is too sufficient. There is a problem that strong negative segregation occurs in the thickness center of the cast slab.

With respect to this point, in JP-A-49-12738, there is a method in which light rolling is performed by a pair of rolls near the solidification front end of a slab and the solidification shrinkage amount of the portion is compensated by the rolling reduction.
In the 54623 publication, a method of greatly reducing the vicinity of the solidification completion point of the cast piece by using a forging die, further, in JP-A-60-148651, electromagnetic stirring is performed upstream from the solidification completion point of the cast piece. The continuous casting means of a method of applying ultrasonic waves and performing forging processing near the solidification completion point of the cast piece has been proposed, respectively.

However, in the case of light rolling with rolls, even if a few mm of rolling is performed with multiple pairs of rolls, it is not possible to sufficiently prevent solidification shrinkage and bulging that occur between roll pitches, and the rolling position is appropriate. If it is not, there is a disadvantage that the center segregation deteriorates.

Also, in the case of using a forging die to largely reduce the vicinity of the solidification completion point of the slab, the solidification interface is less prone to cracking as compared to the large reduction by the roll such as the in-line reduction method, and the negative segregation and even the semi-macro segregation are improved. However, if the reduction is still insufficient in the slab area where the unsolidified layer is large, cracks will occur at the solidification interface, and if the reduction is too large, the center of the slab will develop. Since there is a disadvantage that strong negative segregation occurs and the effect cannot be obtained even when a small area of the unsolidified layer is pressed, the present situation is that an optimum rolling condition is being sought.

In addition, in the means that combines electromagnetic stirring and forging pressure processing or ultrasonic waves and forging pressure processing, the equiaxed crystal ratio, which is advantageous for reducing negative segregation, can be increased, but simply increasing the equiaxed crystal ratio does not cause solidification. It was extremely difficult to avoid the formation of negative segregation under a wide range of conditions such as thickness, casting speed, and molten steel heating degree.

In this regard, the present inventors have previously disclosed in JP-A-63-183765 a method for continuously forging a slab in continuous casting that advantageously solves the above problems.

According to the above method, it is possible to effectively avoid the occurrence of internal cracking and negative segregation and obtain a sound product.

However, the above method has a problem in that it is complicated to determine the forging pressure position.

(Problems to be Solved by the Invention) The present invention advantageously solves the above problems, and a new continuous forging pressure capable of quickly determining the forging pressure position and the forging pressure time and performing an appropriate forging pressure more easily. The purpose is to propose a method.

(Means for Solving the Problems) That is, in the present invention, when continuously performing forging processing on a cast piece after continuous casting, the inside of the cast piece is a stage before completion of solidification, and the cast piece thickness is D
The ratio d / D of unsolidified thickness d (mm) to (mm) is 0.02 to 0.4
At the position where 0 is satisfied, the following formula, δ / d ≧ 0.5, where δ: The rolling amount of the slab in continuous casting in the continuous casting, which is the rolling reduction (mm) Invention).

Further, according to the present invention, when the forging process is continuously performed on the cast product after the continuous casting, the arrival time t (mi of the cast product from the meniscus to the forging position is reached.
n) or the distance L (mm) from the meniscus to the forging position
Respectively, at the positions satisfying the following formulas (1) or (2), the following formula, δ / d ≧ 0.5, where δ: rolling that satisfies the total rolling reduction amount (mm) by forging It is a continuous forging method of a slab in casting (2nd invention).

Note 0.09 (D / k) ² ≤ t ≤ 0.24 (D / k) ² … (1) 0.09vc (D / k) ² ≤ L ≤ 0.24 vc (D / k) ² … (2) where D: casting One-sided thickness (mm) vc: Casting speed (m / min) (working) Hereinafter, the present invention will be specifically described with reference to the drawings. FIG. 1 schematically shows an example of a continuous casting machine equipped with a continuous forging device. In the figure, numeral 1 is a cast piece, 1a is a solidified shell, 1b is a non-solidified portion, 2 is a guide roll, 3 is an electromagnetic stirrer. Reference numeral 4 is a forging die for pressing down the slab, 5 is a reduction cylinder for driving the forging die 4, 6 is a pinch roll, and 7 is a casting mold for continuous casting.

Now, in order to obtain the optimum condition when the cast piece 1 obtained by continuous casting is pressed by the forging die 4 using the continuous casting machine shown in FIG. Experiments were carried out by varying the unsolidified thickness (d) and the amount of reduction (δ) at the center of the piece.

As a result, the ratio d / D of the unsolidified thickness d to the slab thickness D is
At the position where 0.02 to 0.40 is satisfied, the following formula, δ / d ≧ 0.5, where δ: Rolling that satisfies the total rolling reduction amount (mm) by forging is extremely effective in achieving the intended purpose. I got the knowledge that.

That is, in the case of a slab of width (l): 340 mm, thickness (D): 270 mm, when d: 8-90 mm, therefore d / D = 0.03-0.33, and l: 560 mm, D: 400 mm For cast, d: 1
When 0 to 150 mm, and therefore d / D = 0.025 to 0.38, good results were obtained when the amount of reduction satisfied δ / d ≧ 0.5.

From the above results, the unsolidified thickness d is measured by a solidification measuring instrument such as electromagnetic ultrasonic wave, and the time point when the measured relationship between d and D satisfies the above range is obtained.
The proper forging position can be obtained.

However, the above method still requires the operation of measuring the unsolidified thickness d.

Therefore, in the present invention, the following method was considered as a simpler method for detecting the forging pressure position.

Basically, δ / d ≧ 0.5, d / D = 0.02 to 0.40.

here However, s: Solidification thickness (mm) t: Arrival time of the slab from the meniscus to the forging position (mi
n) ∴t = {(D−d) / 2k} ² (3) Substituting d = (0.02 to 0.40) D of the basic equation into the equation (3), t = {(0.98 to 0.60) D / 2k} ² = (0.24 to 0.09) (D / k) ² ∴0.09 (D / k) ² ≤ t ≤ 0.24 (D / k) ² … (1) L = t / vc… (4) However, L: From the meniscus Distance to forging pressure position (mm) vc: Casting speed (m / min), so by substituting equation (4) into equation (1), the following equation 0.09vc (D / k) ² ≤L≤0.24vc ( D / k) ² (2) is obtained.

Although the value of the solidification coefficient k is somewhat different depending on the steel type, cooling conditions, etc., the actual solidification shell thickness is verified by actual measurement. And

(Example) Example 1 Using the continuous casting machine shown in FIG. 1, C: 0.25%, Si: 0.2
5%, Mn: 1.35%, P: 0.02%, S: 0.01%, Cr: 0.04%, Ni:
While casting a slab having a composition of 0.02% and a thickness D of 270 mm and a width of l: 340 mm, continuous forging processing was performed under the following conditions with a forging die provided downstream of the casting machine.

Experimental conditions ・ Casting speed vc: 0.9 (m / min) ・ Arrival time t: 23.3 (min) (d = 40mm at this time, therefore d
/D=0.148, 9.7min ≦ t ≦ 25.9min) ・ Rolling amount δ: 70 (mm) (hence δ / d = 1.75) When forging is carried out under the above conditions, there is no internal cracking or center segregation. A sound slab was obtained.

Example 2 Using the continuous casting machine also shown in FIG. 1, C: 0.53%,
Si: 0.20%, Mn: 0.70%, P: 0.02%, S: 0.015%, Cr: 0.10
While casting a slab having a thickness D: 400 mm and a width l: 560 mm having a composition of 10%, a forging die provided downstream of the casting machine was subjected to continuous forging under the following conditions.

Experimental conditions-Casting speed vc: 0.45 (m / min) ・ Distance L: 22 (m) (At this time d = 70mm, therefore d / D = 0.175, 9.2m ≦ L
≦ 24.6m) ・ Rolling down δ100 (mm) (hence δ / d = 1.4) When forging was carried out under the above conditions, a sound cast piece without internal cracks or center segregation was obtained as in Example 1. Was given.

(Effect of the invention) Thus, according to the present invention, in the continuous forging processing of the slab in the continuous casting, the forging pressure position is simply determined, and a sound product without internal cracking or negative segregation due to the forging processing is obtained. Can be easily obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a continuous casting machine equipped with a forging device. 1 ... Slab, 1a ... Solidified shell 1b ... Unsolidified part, 2 ... Guide roll 3 ... Electromagnetic stirrer, 4 ... Forging die 5 ... Reduction cylinder, 6 ... Pinch roll 7 ... Mold for continuous casting

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-2-15857 (JP, A) JP-A-2-224856 (JP, A) JP-A-63-230262 (JP, A) JP-A-63- 183765 (JP, A)

Claims (2)

[Claims] 1. When continuously performing forging processing on a cast piece after continuous casting, the cast piece thickness D is a stage before the solidification of the inside of the cast piece is completed.
The ratio d / D of unsolidified thickness d (mm) to (mm) is 0.02 to 0.4
At a position satisfying 0, the following equation, δ / d ≧ 0.5, where δ: reduction is performed so as to satisfy a total reduction amount (mm) by forging, and a continuous forging method for a slab in continuous casting is characterized. 2. When the forging is continuously applied to the slab after the continuous casting, the slab's arrival time t (mi) from the meniscus to the forging pressure position is reached.
n) or the distance L (mm) from the meniscus to the forging position
Respectively, at a position satisfying the following formula (1) or (2), the following formula, δ / d ≧ 0.5, where δ: rolling is performed to satisfy the total rolling reduction amount (mm) by forging. Continuous forging method for slabs in continuous casting. Note 0.09 (D / k) ² ≤ t ≤ 0.24 (D / k) ² … (1) 0.09vc (D / k) ² ≤ L ≤ 0.24 vc (D / k) ² … (2) where D: casting One-sided thickness (mm) vc: Casting speed (m / min)