JPH08300002A - Continuous hot rolling method - Google Patents

Abstract

(57) [Abstract] According to the present invention, since there is no blowhole at the butt joint between the rear end of the preceding steel and the front end of the following steel, the strength is stable and stable. Continuous hot finish rolling can be carried out. [Structure] In a method of sequentially joining a plurality of long steel materials for hot rolling and continuously hot rolling, a rear end of a preceding steel material and a front end of a following steel material are butted, and the butted portion is
While supplying an iron alloy wire filler containing any one of l, Ti and Si, or two or more of them, when melting and joining them with a laser while joining, the wire filler is under a condition within a specific range. After supplying and joining with
A continuous hot rolling method characterized by hot rolling.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous hot rolling method for steel products.

[0002]

2. Description of the Related Art In the hot rolling of steel products, scratches and shape defects due to no tension, especially in the so-called unsteady parts of the front and tail parts of steel products, strip width / thickness defects due to threading speed, temperature defects due to acceleration and surface quality In order to reduce the order yield deterioration caused by defects, etc., and to reduce defective part removal work and smoothing plate work, etc., in recent years, a plurality of long steel strips for hot rolling have been sequentially joined at a predetermined speed. The so-called continuous hot rolling method, in which the rolling treatment is carried out in the above, has been attempted.

In this continuous hot rolling method, a steel material which has been subjected to rough hot rolling and is supplied to a continuous hot rolling mill, or a long steel material for hot rolling such as high temperature thin-wall continuous casting slab (flat or coiled) In advance, the front and rear ends are cut with a flying crop shear, and the whole or part of the rear end cutting surface and the front end cutting surface between the steel materials are welded and joined together, and a large number of long steel materials for hot rolling are manufactured. Are sequentially rolled with the same rolling schedule or while a plurality of schedules are continuously changed by relaying, hot rolling is performed, rolling is divided and cut, and a plurality of winding machines alternately wind. As the welding means, butt electric welding, pressure bonding, laser welding, and the like have been studied, but laser welding is advantageous from the viewpoints of speed, joint strength, and quality of joints.

[0004]

When joining the rear end cutting surface and the front end cutting surface between steel materials by laser welding, the scale formed by the oxide formed on the surface of the steel material and the surrounding air are melted by the laser. It mixes with the pool and reacts with the carbon of the steel material to generate CO gas. This tendency is more pronounced in hot than in cold. Since this CO gas is generated not only from the surface of the molten portion but also from the inside, it remains as a blow hole due to foaming, and there is a risk that the steel material will be cut during rolling in order to reduce the bonding strength between the steel materials.

[0005]

The present invention provides an excellent means for solving the above problems, and is characterized in that a plurality of long steel strips for hot rolling are sequentially joined, In a method of continuously hot rolling, a trailing end of a preceding steel material and a leading end of a following steel material are butted, and the butted portion contains any one of Al, Ti, and Si, or an iron alloy wire filler containing two or more of them. While supplying the above, when they are melted while running with a laser and joined, the wire filler is supplied and joined under the condition of the following formula, and then hot rolling is performed. is there. 0.04 wt% ≦ K ≦ 2.4 wt% Deoxidizable amount K = A × C + B × D where A: calculated based on the Al, Ti, Si content of the wire filler and its deoxidizing efficiency. Deoxidizable amount (A =
0.89 [% Al] +1.14 [% Si] +0.668
[% Ti]) B: Deoxidizable amount calculated based on the content ratios of Al, Ti, and Si in the abutted portion of the steel material and the deoxidizing efficiency (B =
0.89 [% Al] +1.14 [% Si] +0.668
[% Ti]) C: Ratio of wire filler addition weight to weld fusion zone weight D: Ratio of steel material fusion weight to weld fusion zone weight

[0006]

The operation of the present invention will be described with reference to FIGS. FIG. 1A shows a comparative example 2 in which the K value is 0.042% by weight.
In (described later), the base material 1A at the rear end portion of the preceding steel material, a part of the base material 1B at the front end portion of the following steel material, and the wire filler 5
FIG. 3 is a side cross-sectional view in which the molten metal melts to form the beats 2 and the blowholes 3 having a nest shape are generated therein. Further, FIG. 6B is a side sectional view showing a sound joint in which no blowhole was generated in the beat 2 in Example 4 (described later) in which the K value was 0.062% by weight. Is.

FIG. 2 shows the relationship between the deoxidizable amount K defined above and the ratio (σ) of the tensile strength of the joint to the tensile strength of the base metal. When K <0.05% by weight, the inside of the joint is shown. To
Although blowholes are generated and the strength is reduced, K ≧ 0.
It is clear that when the content is 05% by weight, the strength equivalent to that of the base material can be secured.

FIG. 3 shows the equipment structure of laser welding, in which a laser welding machine 10 is provided in the center, and a laser beam 20 is applied to the abutting portion 40 between the trailing end portion of the preceding steel material 1A and the leading end portion of the following steel material 1B. The plasma 30 is applied and the molten bead 70 is formed. The steel material is welded by traveling from right to left in FIG. In conjunction with this laser feed rate, the wire filler 50 is continuously added to the high temperature part from the wire filler feeder 60 so that the K value becomes 0.045% by weight or more. The wire filler 50 is heated by the laser beam 20 and supplied to the welded portion in a molten state.

The wire filler metal 50 supplied to the weld 70 is a molten work material which is a component of molten beet,
Melts into a scale mixture. As a result, the oxidizing power of the metal element hinders the reaction between carbon and oxygen in the scale, which is the main cause of blowholes, and the generation of CO gas is eliminated. As a component of the wire filler metal, it is essential to have an oxide that is not vaporized, and a metal that is highly reactive with oxygen is suitable. As an example of this, Al, T
Iron alloys containing i and Si are excellent, and the reason why the iron alloy is used is to secure the strength between steel materials as much as steel materials.

By adding a wire filler,
The reason that the deoxidizable amount K exceeds 0.045% by weight is that if it is less than this, sufficient oxidizing power cannot be obtained, blowholes are generated, and the tensile strength of the welded portion is reduced.
Further, the upper limit is set to less than 2.4% by weight because if it exceeds this, one or more of Al, Ti, and Si in the iron alloy are contained, and the total proportion exceeds 80%. ,
This is because the tensile strength is lower than that of iron and breakage occurs during rolling in the subsequent process. Furthermore, as a merit of adding the wire filler, there is a point that even if there is a gap due to unevenness of the groove portion, by filling the portion with metal, stable welding can be performed.

[0011]

[Examples] Examples of the present invention will be described below. This is an example in which a 7-stand continuous hot finish rolling mill is used for hot rolling. It was carried out in the region. Tables 1 to 4 show the compositions, dimensions, joining conditions, and joining results of the welded steel materials. In addition to Examples 1 to 8, as comparative examples, those with an upper limit of K value and those with a lower limit of K value are also listed in the table. did.

Examples 1 to 8 are made by joining various steel materials, and all have K values of 0.051 to 1.709% by weight.
Since it is within the range of 0.8 to 1.0 of the allowable range, no blowholes are generated in the joint, and the tensile strength ratio of the joint to the tensile strength of the preceding and following steel materials does not deteriorate. Was ensured and there was no breakage of the joint during continuous hot rolling.

On the other hand, in Comparative Example 1, since the K value exceeded the upper limit, the material of the joint was deteriorated and the tensile strength was lowered, and the central portion of the joint was largely ruptured after continuous hot finish rolling. Met. Further, in Comparative Example 2, since the K value was less than the lower limit, blowholes were generated in the joint, so the tensile strength here was greatly reduced, and 4 stund and 5 during continuous hot finish rolling.
It broke between the stands and the continuous rolling was stopped.

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

[Table 3]

[0017]

[Table 4]

[0018]

According to the present invention, stable continuous hot finish rolling can be carried out without lowering the strength of the joint portion due to the blowhole.

[Brief description of drawings]

FIG. 1A is a diagram showing a blowhole generation state in a welded portion when a deoxidizable amount K <0.05% by weight. (B)
FIG. 4 is a diagram showing a state where blowholes are not generated in a welded portion when the deoxidizable amount K ≧ 0.05% by weight.

FIG. 2 is a graph showing the ratio of the deoxidizable amount K and the tensile strength of the joint to the tensile strength of the base metal (leading / trailing steel).

FIG. 3 is a diagram showing an equipment configuration around laser welding.

[Explanation of symbols] 1 base material (steel material) 1A leading steel material 1B trailing steel material 2 bead 3 blowhole 10 laser welding machine 20 laser beam 30 plasma 40 butt section 50 wire filler 60 wire filler feeding machine 70 welding bead (molten state)

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[Procedure amendment]

[Submission date] February 28, 1996

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0015

[Correction method] Change

[Correction content]

[0015]

[Table 2]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

[0016]

[Table 3]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuhiro Minanda 5-10-1, Fuchinobe, Sagamihara-shi, Kanagawa Electronics Research Institute, Nippon Steel Corporation (72) Inventor Masahiro Ohara 20-1, Shintomi, Futtsu, Chiba Shin Nippon Steel Co., Ltd. Corporate Technology Development Division (72) Inventor Daiki Kato 1 Nishinosu, Oita-shi, Oita Prefecture New Nippon Steel Co., Ltd. Oita Steel Co., Ltd.

Claims (1)

[Claims] 1. A method of successively joining a plurality of long steel materials for hot rolling and continuously hot rolling, wherein the rear end of the preceding steel material and the front end of the following steel material are butted, and the butted portion is made of Al, While supplying an iron alloy wire filler containing any one or more of Ti and Si, when melting and joining them with a laser while joining, supply the wire filler under the condition of the following formula. A continuous hot rolling method characterized by hot rolling after joining. 0.04 wt% ≦ K ≦ 2.4 wt% Deoxidizable amount K = A × C + B × D where A: calculated based on the Al, Ti, Si content of the wire filler and its deoxidizing efficiency. Deoxidizable amount (A =
0.89 [% Al] +1.14 [% Si] +0.668
[% Ti]) B: Deoxidizable amount calculated based on the content ratios of Al, Ti, and Si in the abutted portion of the steel material and the deoxidizing efficiency (B =
0.89 [% Al] +1.14 [% Si] +0.668
[% Ti]) C: Ratio of wire filler addition weight to weld fusion zone weight D: Ratio of steel material fusion weight to weld fusion zone weight