JPH04288911A - Endless hot finish rolling method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an endless hot finish rolling method, and in particular, to speed up and simplify the pre-joining work of leading and trailing steel billets before finish rolling, and to improve joining efficiency in subsequent rolling. This is what we are trying to achieve.

0002

[Prior Art] Conventionally, when hot rolling steel billets, the steel billets extracted from the heating furnace were rolled one by one, which caused various troubles as described below, especially in the finish rolling process. . a) Poor engagement of the tip of the steel piece. b) Squeezing the rear end of the billet. c) Trouble running on the runout table at the tip of the steel billet. d) Dimensional defects at the front and rear ends of the steel billet. As a solution to the above problem, in the inlet conveyance line of the hot finish rolling mill, the trailing end of the leading steel billet and the tip end of the trailing steel billet are sequentially joined and then subjected to finish rolling. Rolling has been proposed, and in conjunction with this, various methods have been developed for joining steel billets.

For example, JP-A No. 60-244401 discloses an induction heating pressure welding method using a so-called solenoid coil, and JP-A No. 61-159285 discloses an energization heat-pressure welding method using an electrode roll. Each is disclosed. Furthermore, JP-A No. 61-144203 discloses that after abutting the rear end of the leading steel piece and the leading end of the trailing steel piece, and pre-joining at least both end regions in the width direction at this abutting part, the reduction is made by 20% or more. A joining method is disclosed which consists of rolling down at a constant rate.

However, in both the methods disclosed in JP-A-60-244401 and JP-A-61-159285, the entire rear end face of the leading steel piece and the entire front end face of the trailing steel piece are used as joint surfaces, and the heating Since the bonding surface is spread over the entire joint surface, there are problems as described below. 1) Requires a large amount of electricity for heating. 2) The heating time required to reach the desired bonding temperature is long. 3) For this reason, when heating with the heating equipment stopped, a long loop is required, while when heating is performed between runs, a long distance between runs is required and the length of the equipment becomes long. Furthermore, the method disclosed in Japanese Patent Application Laid-open No. 144203/1983 is as follows:
It takes a long time to obtain a pre-bonded part with sufficient bonding strength, and in addition to still having problems 3), there is also the problem of 4) complicated joining work.

[0005] In this regard, the inventors have previously attempted to solve the above problem by bringing the rear end of the leading steel piece into contact with the leading end of the trailing steel piece at least at both ends in the width direction of each steel piece. At the same time, a gap is provided between them, and the contact area is locally heated and pressed. did. The development of the above bonding method has made it possible to perform bonding operations more quickly and easily than in the past.

[0006]

[Problems to be Solved by the Invention] However, in the above method, since there is an unjoined area between the pre-joined parts, it is preferable to join this unjoined area in the subsequent finish rolling. When performing tension control rolling for the purpose of width control, it is desirable to complete the joining in the previous pass, preferably the first pass, but depending on the size of the gap, the joining may not be completed in the previous pass. In some cases, it was difficult to obtain sufficient bonding strength.

[0007] The present invention advantageously satisfies the above-mentioned requirements, and an object of the present invention is to propose a method for joining steel billets that can be joined over the entire width direction of the steel sheets in the first pass of finish rolling.

[0008]

[Means for Solving the Problems] That is, in the present invention, on the entry side of a hot finishing rolling mill, the rear end of the leading steel piece and the leading end of the trailing steel piece are butted against each other, sequentially joined, and then continuously connected. In endless rolling for finish rolling, at least a part of the butt area including both widthwise ends of each steel billet shall be pre-joined with a gap between them, and in this case, each steel slab shall be pre-joined with a gap between them. The longitudinal gap G between the bonding regions is determined by the following formula: G≦H×(1-r)×{(1+k)×r-k}, where H
This is an endless hot finish rolling method that satisfies the following relationship: : plate thickness at the entrance of the finish rolling machine r: cumulative rolling reduction ratio in the previous stage of finish rolling k: a constant determined according to the rolling conditions.

In the present invention, in the above formula, the plate thickness H at the entrance of the finish rolling machine is 20 to 50 mm, the cumulative reduction ratio r in the previous stage of finish rolling is 0.20 to 0.60, and the constant k is 0.15 to 50 mm. It is preferable to set it to about 0.35.

0010

[Operation] Hereinafter, the mechanism of rolling joining in this invention will be explained based on the drawings. 1) The gap G expands to G x (H/h) (where H is the entrance side sheet thickness and h is the exit side sheet thickness) as the sheet thickness decreases in the roll bite (effect of widening the gap. (see 1). 2) On the other hand, at the tip of the leading billet and the tip of the trailing billet, the length ΔH/2 (here ΔH is A metal flow corresponding to the amount of reduction = H - h is generated (effect of narrowing the gap, see Fig. 2). 3) In the first pass of finish rolling, deformation within the roll bite is thought to occur over the entire contact arc length;
The difference between 1) and 2) determines the gap shape on the exit side of the roll bite (see Fig. 3). That is, a) G×(H/h)−(ΔH/2)×2>0…
If (1), a gap remains and no bonding occurs (FIG. 3a). b) G×(H/h)−(ΔH/2)×2≦0…
If (2), the gap is filled and the bond is established (FIG. 3b). 4) In order to obtain good joint strength, it is not enough to simply fill the gap; it is necessary to shear deformation in the longitudinal direction. Here, if the amount of shear deformation is Y, then Y = (ΔH/2) x 2-G x (H/h)
...(3) holds true.

According to the research conducted by the inventors, in order to obtain the necessary bonding strength (1/3 or more of the base material strength is sufficient), Y≧k×h.
... (4) Here, it was found that k is a constant determined depending on the rolling conditions. FIG. 4 shows the results of an investigation on the relationship between the shear deformation amount Y and the bonding strength in terms of the relationship between the shear deformation amount ratio k and the bonding strength ratio. As is clear from the figure, in order to obtain a joint strength that is 1/3 or more of the base metal strength, the shear deformation ratio k must be at least 0.1.
5. It can be seen that it is sufficient to set the value to about 0.25 on average. Here, if the shear deformation amount ratio k is too small, sufficient bonding strength cannot be obtained, while if it is too large, there is no problem in terms of bonding strength, but it is disadvantageous in terms of allowable gap amount, so k is 0.15 to 0. It is preferable to set it to about .35. Note that when the constant k is set to a general value of 0.25, when G=0, Y=ΔH≧0.25×h, which is equivalent to the case where the rolling ratio≧0.20.

5) Rearranging equations (3) and (4), (ΔH/2)×2−G×(H/h)≧k×
h... (5) ∴G≦H×(1-r)
×{(1+k)×r−k} … (6) Here, r is the rolling reduction ratio (=ΔH/H) Therefore, if the gap shape is set so that the above equation (6) is established, the first pass of finish rolling This means that good bonding strength can be obtained. Note that if it is desired to complete the joining in the first pass of finish rolling, various conditions may be set so that the rolling conditions of the first pass satisfy the relationship expressed by equation (6) above.

The entrance plate thickness H is preferably about 20 to 50 mm based on the cutting ability of the end of the steel piece by the crop shear and the rolling ability of the finishing mill. Also, when the reduction ratio r is less than 0.20, the gap amount is 0.
However, if it is not bonded and the other side exceeds 0.60, the effect of widening the gap will be overwhelming and it will not be efficient, so 0.20 to 0.60
It is preferable to set it as approximately. Furthermore, regarding the shear deformation ratio k, if k is too small, sufficient bonding strength will not be obtained, while if it is too large, there will be no problem in terms of bonding strength, but it will be disadvantageous in terms of allowable gap amount, so 0.25~ 0.3
It is preferable to set it to about 5.

FIG. 5 shows the relationship between the preferred gap amount and the rolling reduction ratio when the shear deformation ratio k is 0.25 and the plate thicknesses are 20, 30, 40 and 50 mm, respectively. In the figure, the area surrounded by diagonal lines is the area where a good bonding state can be obtained.

Next, FIG. 6 schematically shows a preferred finishing rolling line according to the present invention. In the figure, numbers 1-a and 1-b are a leading steel piece and a trailing steel piece, respectively, 2 is a coil box, 3-a, 3-b and 3-c are pinch rolls, 4 is a leveler, 5 is a cutting device, And 6 is a joining device. The figure shows an example in which the welding device 6 performs the heating and welding process in synchronization with the running of the steel billet 1, so-called "intertravel". In this case, the looper indicated by the broken line 7 will be used. Further, 8 is an FSB (descaler), and 9 is the first stand of the finishing rolling mill.

[0016] In the present invention, first, at least a part of the butt region including both ends in the width direction of each steel piece is
They are pre-bonded with a gap between them. This pre-joining method is not particularly limited, but for example, as shown in FIG. The method of joining by pressing is particularly advantageous in terms of shortening the joining time. In Figure 7, (a) shows the case where the rear and tip parts are cut in a concave shape with the same curvature, (b) shows the case where both the back and the tip part are concave but have different curvatures, and (c) shows that one is cut straight. , when only the other side is concave, (d) is one side convex,
This is a case where the other side is concave and the concave curvature is somewhat larger than the convex curvature. In all of the above examples, only both ends of the steel slab in the width direction are brought into contact, and a gap is provided in the central region. As shown in f), contact can be made at three points at both ends and the center, with a gap between them, or, although not shown, contact can be made at four or more points with a gap between them. It can also be a shape.

[0017] Also, as a method for cutting the leading end of each leading and trailing steel piece, any of the conventionally known methods such as shearing, gas cutting, and laser cutting are suitable, but a drum shear with two curved blades is suitable. Particularly advantageous is cutting using a .

Furthermore, the heating means is not particularly limited, and any of gas burners, electrical heating, induction heating, etc. can be used, but among these, a so-called transformer that applies an alternating magnetic field to the steel billet by penetrating it in the thickness direction is used. Induction heating by the bath method (see Japanese Patent Application No. 203991/1999) is particularly advantageously suitable.

Next, the heating and pressing treatments will be explained.
The heating and pressing treatments include a) a method of stopping heating when the temperature of the part to be joined reaches the target temperature and then pressing; b) a method of heating once the temperature of the part to be joined reaches the welding temperature. (However, the melting temperature of the steel slabs is not exceeded) and the pressing is started; c) The steel slabs are pressed together from the beginning and the contact area is also heated at the same time; d) Until the specified joint thickness is reached. Any method such as pressing and then heating may be used, but method c) is particularly effective. This is because, before hot finish rolling, the steel slabs are still at a high temperature of about 1,000 to 1,100°C, so even just pressing will progress the joining of the steel slabs to some extent. This is because if heating is performed while performing this, the bonding will be effectively promoted, and it can be expected that the bonding time and the amount of power input required for heating will be reduced.

The temperature at which bonding progresses well is 125
The temperature is 0℃ or higher, but if the heating temperature is too high, the ends of the steel piece may melt, so even if heating is
The temperature is preferably 450°C or lower. Further, it is preferable that the pre-joining allowance is at least 0.1 times the width of the steel piece at least in both end regions, and 0.2 times or more in total. This is because if the total joining allowance is less than 0.2 times the width of the steel plate,
This is because there is a risk that the first and second billets will separate and break during the subsequent finish rolling.

[0021]

[Example] Steel slabs were joined in the following manner on the conveyance line on the entry side of a finishing rolling mill (7 tandem mill) shown in Fig. 6. The steel pieces used in the experiment had a thickness of 30 mm and a width of 1000 m for both the leading and trailing seat bars.
The cutting device used was a drum shear with two curved blades.

Next, the rear end of the leading seat bar and the tip of the trailing seat bar are each cut into an arc shape by a drum shear, and then both ends of the rear end of the leading seat bar and the tip of the trailing seat bar are cut into arc shapes. After the areas were butted together in contact, a pre-bonding process was performed under the following conditions. a. Alternating magnetic field (C-type magnetic pole) Input power: 2000 k
W frequency: 500 Hz b. Heating temperature: 1400℃ (Initial temperature: 1000℃)c
．． Pre-joining length: 100mm on one side d. Pre-joining form: Heating starts at the same time as pressing e. Center gap amount after pre-joining: 4.12 mmf. Constant k in equation (6) = 0.25

After pre-joining both ends under the above conditions, the rolling reduction rate in the first pass of finish rolling was:
When 40% rolling was applied, when the gap amount was 4 mm, it was possible to join completely, but when the gap amount was 12 mm.
In this case, complete bonding was not possible and an unbonded portion remained. In addition, the relationship of the above-mentioned formula (6) when the rolling reduction rate is 40% is as follows. G≦30×(1-0.40)×(1.25×0.4
0-0.25) = 4.5

[0024]

Thus, according to the present invention, even in the case of partial joining with a gap in the joining area, the gap can be completely joined in the first pass of the subsequent finish rolling, so that hot Finish rolling can be continued stably.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the gap widening effect accompanying rolling.

FIG. 2 is a schematic diagram showing the narrowing effect of the gap due to rolling.

FIG. 3 is a schematic diagram showing conditions for joining and non-joining of gap portions due to rolling.

FIG. 4 is a graph showing the influence of the shear deformation amount Y on the bonding strength in terms of the relationship between the shear deformation amount ratio k and the bonding strength ratio.

FIG. 5 is a graph showing the relationship between the rolling reduction and the gap amount for obtaining a good bonding state, using the plate thickness as a parameter.

FIG. 6 is a schematic diagram of a preferred finishing rolling line according to the present invention.

FIG. 7 is a diagram showing preferred end shapes of a leading steel piece and a trailing steel piece according to the present invention.

[Explanation of symbols]

1-a Preceding steel piece 1-b Trailing steel piece 2 Coil box 3-a Pinch roll 3-b Pinch roll 3-c Pinch roll 4 Leveler 5 Cutting device 6　Joining equipment 7 Lupa 8 FSB 9 First stand of finishing rolling mill

Claims (2)

[Claims] Claim 1: In endless rolling in which the trailing end of the leading steel piece and the leading end of the trailing steel piece are butted against each other on the entry side of a hot finish rolling mill and sequentially joined, and then subjected to continuous finish rolling, At least a part of the butt region including both ends in the width direction of each steel slab shall be pre-joined with a gap between them, and in this case, the gap G in the longitudinal direction between each joint region at the end of pre-joining shall be is the following formula G
≦H×(1-r)×{(1+k)×r-k}where H:
An endless hot finish rolling method, characterized in that the following relationship is satisfied: plate thickness r at the entrance of the finish rolling machine: cumulative reduction ratio k at the front stage of finish rolling k: a constant determined according to rolling conditions. 2. In claim 1, the plate thickness H at the entrance of the finish rolling machine is 20 to 50 mm, the cumulative reduction ratio r in the previous stage of finish rolling is 0.20 to 0.60, and the constant k is 0.15.
~0.35 endless hot finish rolling method.