JPH07290102A - Method and apparatus for slabbing a slab with circular cross section - Google Patents

Abstract

(57) [Summary] [Structure] When a slab with a circular cross section is slab-rolled into a bloom with a substantially square cross section, it is first rolled into an oval shape with a flat caliber, and then the entire surface is constrained with a decagonal section caliber. Rolling is performed to obtain a rolled material having a dodecagonal cross section, and thereafter, rolling with a flat caliber and rolling with a box caliber are performed to obtain a product having a substantially square cross section. [Effect] There is no concern that internal cracks will occur at the corners of the rolled material, and pressure bonding of the slab center cavity can be reliably performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to slab rolling of a slab obtained by continuous casting of metal, especially steel, and more particularly to a method and apparatus for obtaining a bloom having a substantially square cross section from a slab having a circular cross section. .

[0002]

2. Description of the Related Art When vertical continuous casting has been industrialized and the slab of the slab is subjected to slabbing, the following problems have become apparent. That is, vertical continuous casting often gives a slab with a circular cross-section having a diameter of about 350 to 400 mm, so that it was conventionally rolled with a combination of flat caliber and box caliber of rolling rolls. Then, there are many misrolls due to rollover of the material to be rolled,
This is because the cavity at the center of the slab often remains uncompressed even after rolling, and in the case of a fragile material, internal cracks easily occur near the ridge of the rolled material.

The applicant has conducted research aiming at solving these problems, has established a technique for slabbing that is free from the risk of misrolling due to rollover, and has good squeezing of the cavity at the center of the slab, and has already disclosed it. (JP-A-5-317901).
The technique is characterized in that a slab having a circular cross section is passed through a rolling roll having a rhombic caliber and subjected to four-face restraint rolling to form a rhombic cross section with rounded corners.

However, even with this technique, the problem of internal cracking is not improved, and crack-prone steel types such as δ-
It was experienced that when austenitic stainless steel slab containing ferrite was slab-rolled, when the bloom was ground, chipping occurred at the corners due to internal cracking.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to obtain a bloom having a substantially square cross-section from a slab having a circular cross-section obtained by continuous casting of steel. It is an object of the present invention to provide a rolling method and a rolling apparatus in which the possibility of cracking is reduced to substantially zero even if the above method is used.

[0006]

The method for slabbing a slab having a circular cross section according to the present invention is characterized in that rolling is carried out as shown in FIG. 2 with the following pass schedule: 1) 4) A path with an oval cross section through a flat caliber, 2) A path with a dodecagonal cross section that is subjected to full-face restraint rolling through a caliber with a 10-sided cross section, 3) A path with a substantially rectangular cross-section through a flat caliber or a box caliber, and 4 ) A path with an almost square cross section through the Box Caliber.

An apparatus for carrying out the above method, that is, an apparatus for slab-rolling a slab having a circular cross section according to the present invention is characterized by having a rolling roll having the following caliber as shown in FIG. : I) Flat caliber, II) Two rising sides (1) shown in FIG. 6, a top side (3) parallel to the roll axis, and two inclined middle sides (which connect the rising side and the top side). Caliber with a decagonal cross section having 2), as well as III) Box caliber.

[0008]

In the conventional slab rolling, a slab with a circular cross section is first rolled with a flat caliber roll into an oval cross section and then rolled with a box caliber roll having a hexagonal cross section as shown in FIG. This was done in the order of forming a substantially rectangular section and shaping it into a square section with a flat caliber and / or a box caliber.

The reason why internal cracks occur at the corners of the product bloom in the case of the slabbing is considered that the corners are not sufficiently tempered.
The inventors analyzed the relationship between the caliber shape during rolling and the stress in a slab having a circular cross section, and found that tensile stress, not compression, acts depending on the location. Even if the tensile stress is not reached,
It seems that internal cracking cannot be prevented. This pattern is as shown in Fig. 4, and the oval rolled material does not have to be tempered because it only contacts the roll at the part with the thick outline, and the corner part represented by the thin line does not contact the roll. I understand.

The four-face restraint rolling using the diamond-shaped caliber rolls disclosed by the applicant gives a rolled material having a square cross-section with rounded corners immediately from the circular cross-section. The rollover problem due to the roundness of the bottom, which is inevitable when the is rotated 90 °, is eliminated. However, it was found that the stress during rolling in the cross section of the slab is often disadvantageous.

Therefore, in the present invention, the caliber having the above-described decagonal cross section is employed so that the corner portion of the oval rolled material can be sufficiently worked. This pattern is as shown in FIG. In this figure, unlike FIG. 4, there is contact with the roll as indicated by the thick line over most of the periphery of the material, ensuring training.

Suitable reduction ratios in each pass of the slabbing method of the present invention are 1) 5 to 20% and 2) 15 to, respectively.
25%, 3) 20-35% and 4) 20-40%.

The caliber shape of the rolling roll having the caliber having a decagonal section, which characterizes the slabbing mill of the present invention, is preferably defined as follows.
That is, in FIG. 6, a) the inclination α with respect to the axis (X) of the two rising sides (1) is in the range of 76 to 81 °, and b) with respect to the axes (X) of the two middle sides (2). Slope β is 40
And the ratio l / L of the length l of the top side (3) to the length L of the caliber opening is in the range of 50 to 70%.

[0014]

EXAMPLE A cast roll of austenitic stainless steel having a diameter of 350 mm was slab-rolled with a rolling roll having a caliber having the profile shown in FIG.

The caliber shape of roll II is shown in FIG. 6, where α = 11 °, β = 45 °, l = mm, L = mm (thus 1 / L = 60%).
The rolled austenitic stainless steel has the following alloy composition (% by weight, the balance being substantially Fe), and contains C Si Mn Cu Cu Ni Cr N 0.022 0.30 1.85 2.20 9.37 18.41 0.02 δ-ferrite at a depth of 50 mm from the surface layer. About 8
%contains.

Correspondence between pass order and caliber, and material size and reduction amount are as follows: pass caliber material dimension (mm) reduction amount (mm) 0 350 φ 1 I 280 × 370 90 ° rotation 70 2 II 300 × 300 90 ° rotation 70 3 I 220 × 320 90 ° rotation 80 4 III 240 × 240 After removing visible scratches on the rolled product by grinding, visually check the corners and check that the length is 0.3 mm or more. A product in which internal cracks were found was regarded as a defective product. The defect rate, which reached 4 to 8% when the conventional rolling roll shown in FIG. 3 was used, became substantially zero when the present invention was used.

[0017]

According to the present invention, when a slab having a circular cross section is slab-rolled into a bloom having a square cross section, it is possible to obtain perfect adhesion of the center cavity of the slab.
It is possible to obtain a rolled material with almost no internal cracks that tend to occur at the corners when rolling a material having high cracking sensitivity. The present invention is particularly significant when applied to austenitic stainless steel containing δ-ferrite.

[Brief description of drawings]

FIG. 1 is a partial sectional view showing a caliber shape of a series of rolling rolls used in a slabbing mill of the present invention.

FIG. 2 is a diagram showing a change in cross-sectional shape of a rolled material when slab rolling of a slab is performed using the rolling roll of FIG.

FIG. 3 is a view corresponding to a part of FIG. 1, showing a caliber shape of a part of a rolling roll used in a conventional slab mill.

FIG. 4 is a view showing a state of contact between a rolled material and a roll when slab rolling of a slab is performed using the rolling roll of FIG.

FIG. 5 is a view similar to FIG. 4, showing a state of contact between a rolled material and a roll when the slab is slab-rolled using the rolling roll II of FIG. 1.

FIG. 6 is a view showing the caliber shape of the rolling roll II of FIG. 1.

[Explanation of symbols]

 I Flat caliber II 10-section cross-section caliber III Box caliber 1 Rising edge 2 Middle edge 3 Top edge

Claims (4)

[Claims] 1. A method for slabbing a slab having a circular cross section, characterized in that rolling is carried out according to the following pass schedule: 1) pass for making an oval cross section through a flat caliber, 2) decagonal cross section Fully constrained rolling through the caliber to produce a dodecagonal cross section, 3) a pass with a nearly rectangular cross section through a flat caliber or box caliber, and 4) a pass with a substantially square cross section through a box caliber. 2. The reduction amount in each pass of claim 1 is 1) 5 to 20%, 2) 15 to 25%, and 3) 20 respectively.
2. The method of claim 1 which is performed in the range of .about.35% and 20-40%. 3. An apparatus for slabbing a slab having a circular cross section, comprising a rolling roll having the following caliber: I) flat caliber, II) two rising sides, and a roll axis 1 with parallel tops and two inclined midsides connecting the rising and top edges
Caliber with zero cross section, and III) Box caliber. 4. The apparatus according to claim 3, wherein the rolling roll having a caliber having a decagonal cross section has a caliber shape defined by the following: a) The inclination α of the two rising sides with respect to the axis is 76 to 81 °.
B) the inclination β of the two middle sides with respect to the axis is in the range of 40 to 50 °, and c) the ratio l / L of the length l of the top side to the length L of the caliber opening is 50 to 50. It is in the range of 70%.