JPH04200907A - Hot joining method for steel material - Google Patents

Abstract

PURPOSE:To reduce the opening of a joined part and to obtain a high joining strength by making edge preparation to the rear end of a preceding hot steel material and/or the front end of a succeeding hot steel material before they are superposed to heat and pressure-weld them under the reducing atmosphere. CONSTITUTION:The edge preparation is made to at least one of joined edges of the preceding and succeeding hot steel materials 1, 2. Thereafter, when the joined edges are superposed and pressure-welded, both joining edges can be joined at a draft lower than when the edge preparation is not made. Consequently, pressure welding can be executed at a small opening, and cracking and breaking are not generated at the joined part in the succeeding continuous rolling stage.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for joining hot steel materials on a rolling line with high efficiency and high quality.

(Prior Art) In the rolling process of steel factories, continuous lines are being developed with the main purpose of improving yield and productivity.

For example, 500° to 1200° has been emphasized recently.
This is a technology in which C hot steel materials (steel materials that are still hot) are joined in front of a rolling mill and then continuously rolled.

Conventionally, there has been a known technique for welding the rear end of the preceding coil and the tip of the succeeding coil before tandem mills for pickling or cold rolling, but the target of this welding method is once cooled material. Therefore, the temperature is not high during welding.

As a method for joining hot-worked steel materials, Japanese Patent Publication No. 55-22465 discloses a method of mechanically joining a preceding rolled material and a subsequent rolled material by butting them together and driving a connecting metal fitting into the side surface thereof. -39194 Publication and Special Publication No. 5
Japanese Patent No. 4-39195 proposes a method in which a preceding rolled material and a subsequent rolled material are superimposed and joined together by crimping with a press or by welding the side surfaces to plates. However, all of these methods suffer from problems such as joints breaking during rolling due to insufficient strength of the joints or loosening of the connecting fittings, making them unsuitable for continuous rolling from both safety and production efficiency points of view. Appropriate.

Furthermore, in the method of crimping with a press or joining by tack welding the sides, it is necessary to remove scale in advance by some method.

Now, there is a pressure welding method as a method for efficiently hot joining hot steel materials. In this pressure welding method, it has conventionally been thought that it is essential to remove scale from the joint surfaces in advance to clean them. However, based on the knowledge that if pressure welding is carried out in a reducing atmosphere, it is not necessary to perform descaling in advance, the applicant first developed a method for hot joining steel materials.
filed a patent application for the invention (Japanese Patent Application No. 2-268748, hereinafter referred to as the prior invention).

(Problems to be Solved by the Invention) According to the hot joining method performed in a reducing atmosphere of the prior invention, hot joining of steel materials can be performed efficiently in a labor-saving manner, and moreover, high joining strength can be achieved. can be obtained. However, the rolling reduction ratio of the joint is usually as high as 50%, and due to plastic deformation in the width direction of the hot steel material due to rolling, the side of the joint opens as shown in Figure 2 (a). (Hereafter, this phenomenon will be referred to as ``mouth opening''). FIG. 2(a) is a plan view of the joint, and FIG. 2(b) is a Δ-A sectional view of FIG. 2(a).

In FIG. 2, 1 and 2 are hot-fighting steel materials to be joined (in this case, hot-rolled steel sheets after rough rolling), and 3 and 4 are pressure rolls. While pressing the hot steel material 1.2 from above and below with the pressure roll 3.4, the pressure roll 3.4 is moved in the direction of arrow Y in Fig. 2(a) to stack the hot steel material 1.2. Join the mating parts. ``If the opening is large, the joint strength will decrease, cracks will occur in the joint during the continuous rolling process after hot joining, and in the worst case, the joint will break.

An object of the present invention is to obtain high joint strength by reducing the opening of the joint in pressure welding of hot steel materials.

(Means for Solving the Problems) The present invention provides a method of attaching the rear end of the preceding hot steel material or the leading end of the following hot steel material, or the rear end of the preceding hot steel material and the following hot steel material, before overlapping. The gist of this method is to perform beveling on both ends, then overlap the hot steel materials and hot-join them in a reducing atmosphere.

Here, the term "hot steel material" mainly means a hot rolled steel plate after rough rolling, but the present invention can also be applied to hot rolled steel bars, hot rolled shaped steel, and the like.

A reducing atmosphere is an atmosphere surrounded by reducing gases such as the mixed gas of A and 11□, or is created when combustible gases such as acetylene and propane gas are burned with less oxygen than the amount required for complete combustion. Refers to the atmosphere obtained when a joint is heated using a flame (referred to as a "reducing flame").

Hot joining means joining the hot steel materials described in 1 above while they are still hot, for example on a rolling line.

(Function) A major feature of the method of the present invention is that a bevel is formed on the rear end of the preceding hot steel material or the tip of the subsequent hot steel material, or on both the rear end of the preceding hot steel material and the tip of the succeeding hot steel material. After that, the preceding hot-worked steel material and the subsequent hot-worked steel material are overlapped and pressure-welded.

In Figure 1, X is the traveling direction of the hot steel material, and there is an opening at the rear end of the preceding hot steel material or the tip of the following hot steel material, or at both the rear end of the preceding hot steel material and the tip of the following hot steel material. FIG. 3 is a side view showing the pressure welding situation when the parts are overlapped after being subjected to tip processing;
(a), (1)) and (C) are the methods of the present invention.

(a) is applied to both the preceding hot steel material and the following hot steel material, (b)
In (C), beveling is performed only on the preceding hot-worked steel material H, and in (C), only the subsequent hot-worked steel material is subjected to bevel processing. (d) is a case in which both the preceding hot-worked steel material and the subsequent hot-worked steel material are not beveled. As shown in the figure, if at least one joint end of the hot-worked steel materials is beveled, then they are overlapped and pressure welded, the rolling reduction can be made smaller than when both joint ends are not beveled. Pressure welding with a small opening can be performed, and no cracks or breaks will occur in the joint during the subsequent continuous rolling process.

The thickness of the joint after pressure welding is the thickness of hot steel material 1.2 (
In this case, the rolling reduction rate is defined as follows, assuming that both are equal to t).

Reduction ratio - (T- also) / T T: Thickness of the joint before pressure welding (see Figure 3) L: Thickness of hot steel (see Figure 3) The reduction ratio of each overlap in Figure 1 is (a) 33%, (b) 43%, (C) 43%
, (d) 50%.

In order to confirm the effect of beveling, four types of overlapping were performed using hot steel materials of the same material and size, as shown in (a), (b), (C), and (d) in Figure 1. A joint 1 was made, and the thickness of the joint was reduced to 1 under the same conditions in a reducing atmosphere.
．． Pressure welding was performed using a pressure roll 3.4 until the thickness became the same as No. 2. The results are shown in FIG.

FIG. 4 shows the correlation between the rolling reduction ratio and the opening ratio.

Here, the opening rate is defined as follows.

Opening ratio - G/W G: Size of opening (see Figure 3) W: Width of hot steel material (See Figure 3) Figure 4 shows at least one of the preceding hot steel material or the following hot steel material. Pressure welding after beveling (reduction rate of 43% or less) is better than pressure welding (reduction rate of 50%) without beveling both the preceding and subsequent hot-worked steel materials. This also shows that the mouth opening rate is less than half. If continuous rolling is performed under the same conditions after pressure welding, the rolling reduction will be 50%.
Cracks occurred in the welded joints where the rolling reduction was 43% or less, and no cracks occurred in the welded joints where the rolling reduction was 43% or less. This shows that pressure welding with a rolling reduction of 43% or less provides a higher bonding strength than pressure welding with a rolling reduction of 50%. Therefore, it can be seen that in order to prevent cracks from occurring in the joint during the continuous rolling process, it is necessary to lower the rolling reduction rate and reduce the opening in the pressure welding process in the previous process.

Next, we will check the effect when the rolling ratio is constant and the overlapping ratio is changed.

Here, the overlapping rate is defined as follows.

Overlap ratio = L, /l L: Overlap allowance (see Figure 3) (,: Thickness of hot steel material (see Figure 3) FIG.

(a), (b), and (C) in Fig. 5 are grooves with a constant rolling reduction of 33% and an overlapping ratio of 0.5.1.0.1.5. It is changing. The shape of the groove is changed in order to change only the overlapping ratio while keeping the rolling reduction constant. Fifth
Figures (d), (e), and (f) are those without beveling, with a constant rolling reduction of 50% and an overlapping ratio of 0.5.1. , O,1,5.

For the hot-worked steel materials shown in (a) to (f) in Figure 5, the thickness of the joint under the same conditions of reducing atmosphere is hot-worked steel + 41.2.
Pressure welding was carried out using a pressure roll 3.4 until the thickness became the same as that of . The results are shown in FIG.

FIG. 6 shows the correlation between the overlapping ratio and the opening ratio when the rolling reduction ratio is constant. Regardless of the presence or absence of bevel processing, if the overlapping ratio decreases, the opening ratio will become smaller, but in pressure welding (reduction ratio 50%) with no beveling performed on both sides, the overlapping ratio will be reduced to 0.5. However, both were pressure welded (reduction rate 33%) after beveling,
It can be seen from FIG. 6 that the opening ratio is larger than that in which the overlapping ratio is 1.5. After pressure welding, if continuous rolling is carried out under the same conditions, if the rolling reduction is 50%, cracks will not occur in the joint if the overlap ratio is 0.5, but if the overlap ratio is 1.0 or more, cracks will not occur in the joint. In some cases, cracks occur in the joint, and when the reduction rate is 33%, the overlap rate is reduced to 0.
．． No cracks occurred in the joints in all cases where the test was rated from 5 to 1.5. From this, in order to prevent cracks from occurring at the joint during continuous rolling, the opening ratio should be 0.1 to 1.
It can be said that there is a difference between 0.2 and 0.2.

In addition, in pressure welding where the overlap ratio is less than 0.1, the joint area is too small regardless of the presence or absence of beveling, and the joint strength itself (joint strength) is insufficient, so the overlap ratio is set to 3.0 or more. In pressure welding, the joint strength is basically high because the overlapping part is large, but the amount of plastic deformation increases, so the opening becomes thick (this means that even if both sides are beveled and the rolling reduction rate is lowered, the joint strength will be higher). It has been found from another test that cracks occur.Also, in actual pressure welding on a rolling line, it is difficult to reduce the overlap ratio to less than 1.0, and taking the above findings into consideration, It is appropriate that the matching ratio be 1.0 or more and less than 3.0.

When increasing the overlapping ratio, (a) and (
As shown in b) and (C), it is necessary to change the shape of the groove in order to keep the rolling reduction constant.

The method of the present invention is based on pressure welding in a reducing atmosphere without performing descaling in advance, as in the prior invention described above. For example, if the beveling process is performed using the gas scarfing method, oxide scale will be generated on the joint surface, but it is not necessary to remove this prior to pressure welding. However, it is desirable to remove extremely thick scales in advance. If the beveling is done by mechanical cutting, the scale on the joint surface will inevitably be removed, so pressure welding can naturally be carried out as is. In carrying out the method of the present invention, if there is a bend in the edge of the hot steel material, it will take a lot of time for beveling, overlapping, and pressure welding, and the accuracy of these operations will be insufficient, making it difficult to proceed to the next step. During continuous rolling, cracks may occur in the joints, or the joints may shift in the width direction or longitudinal direction, making it impossible to perform good continuous rolling. It is preferable to process it.

(Example) A steel plate having a thickness of 15 mm, a width of 300 mm, a length of 1000 mm, and a steel type SPC, C was heated to 1150°C in a heating furnace.

After extraction from the heating furnace, it was transported to a rolling line consisting of a gas scarfer-1 direct-fired reduction burner, a pressure roller, and a rolling mill.

As for the groove processing, which is not shown in FIG. 7 (side view), the groove shape was formed by gas scarfing using 02 gas.

The groove length (K) is 1 when the overlap ratio is 1 or less.
．． 5mm, 22.5mm when the overlap ratio is 1.5
And so. (a) shows the groove of the preceding hot-worked steel plate, and (b) shows the groove of the subsequent hot-worked steel plate. After beveling, the material was sent as is (without descaling) to a direct reduction burner.

The reducing atmosphere was created by generating a reducing flame of C gas (coke oven waste gas) using a direct reducing burner, and heating the joint for 3 seconds by blowing this reducing flame onto the joint.

The heating temperature was 1200°C.

In the hot bonding, the ends of the hot steel plates were overlapped and pressed together with a pressure roll until the thickness of the overlapped joint became 15 mm, which was the same as the plate thickness. The pressure roll diameter was φ650 mm, and the pressing speed was 300 mm and 7 seconds. The state of overlapping during pressure welding is shown in (a), (b), (C), (d) and (e) of Figure 8, and the overlapping ratio and reduction ratio at that time are shown in Table 1. .

After pressure welding, the plate thickness is 3.0mm using a rolling mill (rolling ratio: 80%)
Continuous rolling was carried out until the bond was reached, and the presence or absence of cracks, deviations, or breaks in the joints was examined to determine whether continuous rolling was possible.

The results are also listed in Table 1. No. 1 to 4 in Table 1
No. 5 is an example of the present invention, and No. 5 is a comparative example without beveling.

As shown in Table 1, if the edges of the steel sheet are beveled and then hot bonded, good rolling can be achieved without any trouble during continuous rolling.

Table 1 *l) See Figure 7 for the overlapping state.

*2) Test No. 5 is a comparative example without beveling.

(Effects of the Invention) According to the method of the present invention, it is possible not only to efficiently join hot-worked steel materials without necessarily requiring descaling in advance of the joint part, but also to achieve extremely strong joints by performing the above-mentioned beveling process. (seam) can be obtained. The hot steel material joined in this way can be safely and reliably continuously rolled in the next step.

[Brief explanation of the drawing]

In Fig. 1, (a), (b), and (C) are side views showing the situation in which the front and rear ends of hot-worked steel materials are beveled and pressed together, and (d) is a side view showing the situation in which the front and rear ends of the hot steel materials are overlapped and pressure-welded. FIG. 3 is a side view showing a situation in which they are overlapped and pressed together without being applied. FIG. 2 is a diagram explaining that an opening occurs on the side surface of the joint due to pressure welding, (a) is a plan view, and (b) is an A
-A sectional view. FIG. 3 is a diagram illustrating symbols used in defining the rolling reduction ratio, opening ratio, and overlapping ratio. FIG. 4 is a diagram illustrating the correlation between the rolling reduction rate and the opening rate. FIG. 5 is a side view showing a situation in which pressure is applied by keeping the reduction rate constant and changing the overlapping rate; (d), (
e) and (f) are not beveled. FIG. 6 is a diagram illustrating the correlation between the overlapping ratio and the opening ratio. FIG. 7 is a diagram showing dimensions and shapes of beveling in an embodiment of the method of the present invention, and the units of dimensions are mm. FIG. 8 shows the overlapping state during pressure welding in an embodiment of the method of the present invention, and shows (a), (b), (C) and (d)
) is the method of the present invention, (e) is the method carried out for comparison, and the unit of dimension is mm. In the figure, 1 is a preceding hot steel material, 2 is a subsequent hot steel material, 3 is an upper pressure roll, and 4 is a lower pressure roll.

Claims (1)

[Claims] Before stacking, the trailing edge of the preceding hot steel material and/or the leading edge of the subsequent hot steel material is beveled, and then the preceding hot steel material and the subsequent hot steel material are overlapped and heated in a reducing atmosphere. A hot joining method for pressure welding steel materials.